LEACHATE TREATMENT USING SUBSURFACE FLOW AND FREE
WATER SURFACE CONSTRUCTED WETLAND SYSTEMS
AIN NIHLA BINTI KAMARUDZAMAN
A project report submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Engineering (Civil – Wastewater)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
NOVEMBER 2006
iii
This work is dedicated to my beloved family members, especially to abah
(Kamarudzaman Hj. Abd. Rahim), mak ( Saodah Hj. Abd. Karim), my bothers and
sisters (Mohd. Suffian, Ainul Zakiah, Ahmad Zaki, Kamaliah and Atiqah).
Thanks for all your love and support!
iv
ACKNOWLEDGEMENT
In the name of Allah, the Most Gracious, the Most Graceful. With His
blessing and permission, finally this Master’s project report has been accomplished
successfully in the given time frame.
First of all, I would like to extend my gratitude to everyone who has been
helping me directly or indirectly from the beginning until the final stage in this
project. All the help and cooperation from various parties had been a motivation
factor for me to complete this project. I would like to express my utmost gratitude
and appreciation to the thesis supervisor Dr. Johan Sohaili for his cooperation,
guidance, facilitation and advice for me to finish this project.
All staff in the Environmental Engineering Laboratory, Faculty of Civil
Engineering UTM, who has been helping me in providing the equipments for data
collection in this project, to all of you I extend my gratitude. Thank you for your
cooperation and assistance. Not to forget, thank you very much to my fellow friends
Siti Kamariah, Shila and Kak Ida who have been helping me during the data
collection process and provided support to the completion of the project.
Finally, to my parents, my siblings and others that are involves I would like
to express my greatest appreciation for the support and encouragement. May all the
good deeds that were done will be blessed by Allah. Wassalam.
v
ABSTRACT
The sanitary landfill plays a most important role in the framework of solid
waste disposal. Discharge of leachate into the environment constitutes the major
environmental concern associated with sanitary landfill and need to prevent. Based
on previous study, constructed wetland system has high efficiency in treating landfill
leachate with low operating and maintenance cost. A combination system utilizing a
subsurface flow (SSF) wetland followed by a free water surface (FWS) wetland was
studied to treat landfill leachate. In this study, Limnocharis flava and Eichhornia
crassipes were used as aquatic plants in wetland system. SSF and FWS constructed
wetland systems were arranged in series and operated for around 3 weeks with
hydraulic loading rate (HLR) (0.13 m/cycle/day). Two lab scale systems of
constructed wetlands were used in the experiments. Performance of SSF-FWS
constructed wetland was evaluated with comparison to a Control system (unplanted).
The result demonstrated that a combination system utilizing a SSF-FWS constructed
wetland systems have shown higher performance in treating leachate landfill. The
result demonstrated that the removal efficiency of pollutants in leachate using
Limnocharis flava and Eichhornia crassipes in SSF-FWS constructed wetlands were
NH4-N (93.1%), NO3-N (96.4%), PO43- (95.9%), Fe (99.5%) and Mn (97.7%).
Removal efficiency of SS and turbidity were achieved 87.3% and 99.6%,
respectively. Limnocharis flava had higher capacity to accumulate heavy metals (Fe
and Mn) in leachate constituents compared than Eichhornia crassipes. From the
study, it shows that Fe and Mn uptake is more significant in roots compare to leaves.
This study concludes that SSF-FWS constructed wetlands can increase the
performance of nutrient and heavy metal removal and also enhance leachate water
quality.
vi
ABSTRAK
Tapak pelupusan sampah memainkan peranan penting dalam rangka kerja
pelupusan sisa pepejal. Pelepasan air larut lesap ke alam sekitar menimbulkan
kebimbangan yang tinggi terhadap alam sekitar berkaitan dengan tapak pelupusan
sampah dan keadaan ini perlu dielakkan. Berdasarkan kajian yang dijalankan
sebelum ini, sistem tanah bencah yang dirangka menunjukkan tahap efisyen yang
tinggi dalam mengolah air larut lesap dengan kos operasi dan penyelenggaraan yang
murah. Gabungan sistem menggunakan tanah bencah buatan aliran subpermukaan
(SSF) dan diikuti dengan tanah bencah buatan aliran permukaan bebas (FWS) telah
dikaji untuk mengolah air larut lesap. Dalam kajian ini, Limnocharis flava dan
Eichhornia crassipes telah digunakan sebagai tumbuhan akuatik dalam sistem tanah
bencah. Sistem tanah bencah buatan SSF dan FWS disusun secara bersiri dan
beroperasi dalam jangka masa 3 minggu dengan kadar masukan hidraulik (0.13
m/kitaran/hari). Dua sistem tanah bencah buatan berskala makmal telah digunakan
di dalam kajian ini. Prestasi sistem tanah bencah buatan SSF-FWS ini telah dinilai
dan diperbandingkan dengan sistem kawalan iaitu tanpa tumbuhan. Keputusan yang
diperolehi menunjukkan bahawa gabungan sistem tanah bencah buatan SSF dan
FWS menunjukkan prestasi yang lebih baik dalam mengolah air larut lesap.
Keputusan menunjukkan bahawa kadar penyingkiran bahan pencemar dalam air larut
lesap menggunakan Limnocharis flava dan Eichhornia crassipes dalam sistem tanah
bencah buatan SSF-FWS adalah NH4-N (93.1%), NO3-N (96.4%), PO43- (95.9%), Fe
(99.5%) and Mn (97.7%). Tahap penyingkiran yang efisien bagi SS dan kekeruhan
pula dicapai sebanyak 87.3% dan 99.6%. Limnocharis flava mempunyai kapasiti
yang lebih tinggi untuk mengumpul logam berat (Fe and Mn) dalam juzuk air larut
lesap jika dibandingkan dengan Eichhornia crassipes. Daripada kajian yang
dijalankan, ia menunjukkan bahawa pengambilan Fe and Mn adalah lebih ketara di
akar berbanding dengan daun. Kajian ini dapat memberi kesimpulan bahawa sistem
tanah bencah buatan SSF-FWS boleh meningkatkan prestasi penyingkiran
kandungan nutrien and logam berat dan juga meningkatkan kualiti dalam air larut
lesap.
vii
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xi
LIST OF SYMBOLS AND ABREVIATIONS
xv
LIST OF APPENDICES
xvii
INTRODUCTION
1
1.1
Introduction
1
1.2
Problem Statement
3
1.3
Objective of the Study
5
1.4
Scope of the Study
5
1.5
Important of the Study
6
LITERATURE REVIEW
7
2.1
Introduction
7
2.2
An Overview of Leachate
8
2.2.1
Leachate Generation
8
2.2.2
Leachate Characterization
10
viii
2.2.3
2.3
Leachate Composition
13
Treatment of Leachate
16
2.3.1
Biological Treatment of Leachate
16
2.3.2
Physical-Chemical Treatment of
Leachate
18
2.4
Problem in Leachate Treatment
27
2.5
Wetland
28
2.6
Constructed Wetland
29
2.7
Types of Constructed Wetland
30
2.7.1
Free Water Surface Wetlands
31
2.7.2
Subsurface Flow Wetlands
34
2.7.3
Combine FWS-SSF Constructed
Wetland System in Wastewater
Treatment
2.8
Pollutants Removal Process Mechanisms
40
2.9
Wetland Plant
45
2.10
Role of Wetland Vegetation
47
2.11
Application of Constructed Wetlands in
2.12
3
37
Treating Landfill Leachate
49
Conclusion
57
METHODOLOGY
59
3.1
Introduction
59
3.2
Research Design and Operational Framework
59
3.3
Leachate Sample Collection and Preparation
61
3.4
Experiment Set up
61
3.5
Plants
64
3.6
Media
67
3.7
Sampling and Analysis
67
3.8
Analysis Procedure
67
3.8.1
3.9
Analysis of Heavy Metals in Plant
Tissues
68
Performance Evaluation
69
ix
4
5
RESULTS AND DISCUSSIONS
70
4.1
Introduction
70
4.2
Basic Characteristics of the Landfill Leachate
71
4.3
Nutrients Removal
71
4.3.1
Ammonia Nitrogen
71
4.3.2
Nitrate Nitrogen
75
4.3.3
Orthophosphate
78
4.4
Suspended Solid Removal
81
4.5
Turbidity
84
4.6
Heavy Metals Removal
87
4.6.1
Ferum
87
4.6.2
Manganese
90
4.7
Heavy Metal in Plant’s Tissues
93
4.8
Comparison with Other Researchers
96
4.9
Conclusion
98
CONCLUSIONS
100
5.1
Conclusion
100
5.2
Recommendations
101
REFERENCE
102
APPENDICES
113
x
LIST OF TABLES
TABLE NO.
TITLE
PAGE
2.1
Data on the composition of leachate from landfill
14
2.2
Leachate sampling parameters
15
2.3
Physical, chemical and biological treatment processes
applicable to process trains for leachate treatment
2.4
Summary of biological and physical-chemical
treatment processes applied to leachate treatment
2.5
24
Advantages and disadvantages of Free Water Surface
Flow wetlands
2.6
21
32
Advantages and disadvantages of Subsurface Flow
wetlands
35
2.7
Overview of pollutant removal process
41
2.8
Roles of macrophytes in constructed wetlands
48
2.9
Wastewater pollutants removal in constructed
wetland
51
2.10
Leachate pollutants removal in constructed wetland
54
3.1
Summary of experimental design
64
3.2
The parameter observed in leachate analysis
68
4.1
Influent characteristics of the Pasir Gudang leachate
71
4.2
Comparison of different models of constructed
wetlands for landfill leachate treatment
97
xi
LIST OF FIGURES
FIGURE NO.
TITLE
2.1
How leachate is generated
2.2
Factors influencing gas and leachate composition in
PAGE
9
landfills
10
2.3
Wetland design categories
31
2.4
Types of Free Water Surface (FWS) treatment
wetlands
2.5
Typical arrangement of horizontal subsurface flow
constructed wetland system
2.6
37
Plan view of constructed wetland at Munroe Country
wastewater treatment , New York
2.8
36
Typical arrangement of vertical subsurface flow
constructed wetland system
2.7
33
38
Layout of the pilot-scale FW-SSF series constructed
wetlands system for treating fishpond water. (A)
Sampling location for the influent; (B) sampling
location for the FWS effluent; (C) sampling location
for the SSF effluent
2.9
Schematic diagram of the recirculating aquaculture
system
2.10
2.11
39
40
Major pollutants uptake and release pathway in
wetland system
41
Nitrogen transformation in wetland system
43
xii
2.12
Summary of the major physical, chemical and
biological processes controlling contaminant removal
in wetlands
45
2.13
Types of wetland plants
46
3.1
Frameworks and experimental design
60
3.2
Schematic diagram of SSF-FWS constructed wetland
used in experiment. (1) Storage tank; (2) Media
without plant; (3) water tank without plant; (4) SSF
tank with Limnocharis flava (5) FWS tank with
Eichhornia crassipes; (6) Settling tank; and (A)
Sampling location for the influent; (B) sampling
location for the SSF effluent; (C) sampling location
for the FWS effluent.
3.3
Arrangement of SSF-FWS constructed wetland
systems
3.4
62
63
Two-stage lab-scaled system comprised of a SSF and
FWS constructed wetland located outside of the
building in an open area
64
3.5
Short description of Limnocharis. flava
65
3.6
Short description of Eichhornia crassipes
66
3.7
Plants digestion for root and leaves
69
4.1
NH4-N concentration profile in Control and Planted
system through SSF constructed wetland within 18
days of treatment
4.2
72
NH4-N concentration in profile in Control and
Planted system through FWS constructed wetland
within 18 days of treatment
4.3
72
Comparison of NH4-N concentration (C/CO) for
overall performance in Control and Planted system
through SSF-FWS constructed wetland
4.4
73
NO3-N concentration profile in Control and Planted
system through SSF constructed wetland within 18
days of treatment
76
xiii
4.5
NO3-N concentration profile in Control and Planted
system through FWS constructed wetland within 18
days of treatment
4.6
76
Comparison of NO3-N concentration (C/CO) for
overall performance in Control and Planted system
through SSF-FWS constructed wetland
4.7
77
PO43- concentration profile in Control and Planted
system through SSF constructed wetland within 18
days of treatment
4.8
79
PO43- concentration profile in Control and Planted
system through FWS constructed wetland within 18
days of treatment
4.9
79
Comparison of PO43- concentration (C/CO) for
overall performance in Control and Planted system
through SSF-FWS constructed wetland
4.10
80
SS concentration profile in Control and Planted
system through SSF constructed wetland within 18
days of treatment
4.11
82
SS concentration in profile in Control and Planted
system through FWS constructed wetland within 18
days of treatment
4.12
82
Comparison of SS concentration (C/CO) for overall
performance in Control and Planted system through
SSF-FWS constructed wetland system
4.13
83
Turbidity measure in Control and Planted system
through SSF constructed wetland within 18 days of
treatment
4.14
85
Turbidity measure in Control and Planted system
through FWS constructed wetland within 18 days of
treatment
4.15
85
Comparison of turbidity value (C/CO) for overall
performance in Control and Planted system through
SSF-FWS wetland
86
xiv
4.16
Fe concentration profile in Control and Planted
system through SSF constructed wetland within 18
days of treatment
4.17
88
Fe concentration profile in Control and Planted
system through FWS constructed wetland within 18
days of treatment
4.18
88
Comparison of Fe concentration (C/CO) for overall
performance in Control and Planted system through
SSF-FWS wetland
4.19
89
Mn concentration profile in Control and Planted
system through SSF constructed wetland within 18
days of treatment
4.20
91
Mn concentration profile in Control and Planted
system through FWS constructed wetland within 18
days of treatment
4.21
91
Comparison of Mn concentration (C/CO) for overall
performance in Control and Planted system through
SSF-FWS wetland
4.22
92
Heavy metal (Fe) accumulation by Limnocharis flava
and Eichhornia crassipes in SSF-FWS wetland
systems
4.23
94
Heavy metal (Mn) accumulation by Limnocharis
flava and Eichhornia crassipes in SSF-FWS wetland
systems
95
xv
LIST OF SYMBOLS AND ABREVIATIONS
BOD
-
Biochemical Oxygen Demand
cm/day
-
Centimeter per day
CAP
-
Consumers Association of Penang
Ca2-
-
Calcium
CaCO3
-
Calcium carbonate
C/CO
-
Present concentration over initial concentration
Cl
-
Clorine
Cl2
-
Chlorine gas
Cd
-
Cadmium
Cr
-
Chromium
COD
-
Chemical Oxygen Demand
CWs
-
Constructed wetland
Fe
-
Ferum
FWS
-
Free Water Surface
HCO3-
-
Bicarbonate
HF-SSF
-
Horizontal Subsurface Flow
HLR
-
Hydraulic Loading Rate
HRT
-
Hydraulic Retention Time
IUCN
-
International Union for the Conservation of Nature
kg
-
Kilogram
kg/m3
-
Kilogram per meter cube
m
-
Meter
mm
-
Millimeter
m/day
-
Meter per day
mg/g
-
Milligram per gram
xvi
mg/L
-
Milligram per liter
mL/s
-
Milliliter per second
Mg2+
-
Magnesium
MLVSS
-
Mix liquor Volatile Suspended Solid
Mn
-
Manganese
N2
-
Nitrogen gas
N2O
-
Nitrogen Oxides
NH4+
-
Ammonia
NH4-N
-
Ammonia Nitrogen
NO2-
-
Nitrite
-
-
Nitrate
NO2 -N
-
Nitrite Nitrogen
NO3 -N
-
Nitrate Nitrogen
P
-
Phosphorus
PO43-
-
Orthophosphate
SO4-
-
Sulfate
SSF
-
Subsurface Flow
SSF-FWS
-
Combine Subsurface Flow and Free Water Surface System
SS
-
Suspended Solid
TIN
-
Total Inorganic Carbon
TKN
-
Total Kjeldahl Nitrogen
TN
-
Total Nitrogen
TP
-
Total Phosphorus
TOC
-
Total Organic Carbon
TSS
-
Total Suspended Solid
VF
-
Vertical Flow
VF-SSF
-
Vertical Subsurface Flow
VFA
-
Volatile Fatty Acid
VOC
-
Volatile Organic Carbon
RBC
-
Rotating Biological Reactor
Zn
-
Zinc
µg/g
-
Microgram per gram
%
-
Percent
˚C
-
Degrees Celsius
NO3
xvii
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
Raw Data
113
B
Varian Analysis Calculation (ANOVA)
117
C
Lab Apparatus and Equipments
124
CHAPTER 1
INTRODUCTION
1.1
Introduction
Solid waste disposal creates a problem primarily in highly populated areas.
In general, the more concentrated the population, the greater the problem becomes,
although some very populated areas have developed creative solutions to minimize
the problem. Various estimates have been made of the quantity of solid waste
generated and collected per person per day. Malaysia, like most of the developing
countries, is facing an increase of the generation of waste and accompanying
problems with the disposal of this waste. Municipal, industrial, agricultural, and
urban activities produce huge amounts of wastes which require permanent disposal.
Overall, the local communities generate 16,000 tonnes of domestic waste per day and
the amounts per capita vary from 0.45 to 1.44 kg per day depending on the economic
status of the areas concerned. On average, waste generation in Malaysia is about 1
kg per capita per day (Lina, 2004).
There are different alternatives to reduce, treat and dispose the solid wastes.
In many developing countries including Malaysia, sanitary landfills have been the
most popular method of municipal solid waste disposal. There are 230 official
dumping sites in Malaysia, the majority of which are crude landfills, with only 10%
providing leachate treatment ponds and gas ventilation systems and with most having
2
no control mechanisms and supervision (Zaman, 1992). However, the amount of
waste produced rapidly increases; space for permanent disposal becomes crucial.
Since the production of solid waste is increasing much more rapidly than it degrades,
land space for disposal has become more difficult and expensive to attain.
Incineration of solid waste can be used but this is expensive and the emissions are of
health concern. This is why landfills remain the major solid waste disposal option
for most countries.
In conjunction with the increasing number of sanitary landfills, leachate
treatment has become a major environmental issue, especially with regulatory
agencies and environmentalists. The treatment of landfill leachates is of concern
because they have the potential to degrade the environment.
Leachates are a
potential hazardous waste from landfill sites. Malaysian solid wastes contain very
high organic waste and consequently high moisture content and bulk density of
above 200 kg/m3. A recent study conducted in Kuala Lumpur has revealed that the
amount of organic wastes for residential area range from 62 to 72% (CAP, 2001).
Therefore, leachate production may arise because most of solid wastes contain high
moisture content and organic matter.
Most organic matter contained in the solid wastes is biodegradable and can be
broken down into simpler compounds by anaerobic and aerobic microorganisms,
leading to the formation of gas and leachate. Leachate is defined as liquid that has
percolated through solid waste and has extracted dissolved or suspended materials
from it. It arises from the biochemical and physical breakdown of waste (Lu et al.,
1985). Landfill leachate characteristics vary depending on the operation type of the
landfill and the age of the landfill. Leachate initially is a high-strength wastewater,
contains high concentration of organic matter, inorganic matter and heavy metal
(Qasim and Chiang, 1994). The main environmental aspects of leachate are the
impacts on surface water quality and groundwater quality, because leachate may
migrate from the refuse and contaminate the surface waters and groundwater. If not
dealt properly its can affecting aquatic ecosystems, human health problems and
effect the environment. It is important that leachates are treated and contained to
prevent these occurrences.
3
Therefore, the treatment of leachates by natural systems seems to be
environmentally sustainable for treatment of many constituents.
Constructed
wetlands have proven very effective technology for the treatment of variety of
wastewaters. Constructed wetlands are increasingly being employed to treat landfill
leachate, and the use of natural systems in waste management seems to be gaining in
popularity as a result of their sustainability and cost savings. Wetland has been
shown to improve leachate quality through processes that include microbial mediated
transformations, biotic uptake of organic chemicals and nutrients, precipitation,
complexation and adsorption reactions (Kadlec and Knight, 1996; Brix, 1997;
Mutamoottil et al., 1999).
A thorough understanding of these mechanisms is
required before a constructed wetland system can be developed that can provide
successful, long-term treatment of landfill leachate on a large scale.
The environmental benefit treatment of leachate in a constructed wetland
include; decreased energy consumption by using natural processes rather than
conventional, electrically driven wastewater-treatment processes; efficiently removed
many pollutants from wastewater and also enhance the environment by providing a
habitat for vegetation, fish and other wildlife (Jin et al., 2003). Studies of the longterm use of wetlands for leachate treatment have demonstrated significant economic
advantages, mainly through lowered construction, transportation and operation costs
(Kadley and Knight, 1996).
1.2
Problem Statement
Landfill leachate with its variable and complex characteristics poses a well
established threat to the environment. Leachate is often quite varies in water quality
but generally has very high concentrations of Chemical Oxygen Demand (COD),
Biochemical Oxygen Demand (BOD), and ammonia content, with high COD and
BOD ratio and the presence of heavy metals ions present unique difficulties
treatment of landfill leachate (Aeslina, 2004).
Landfill leachates will cause
environmental problems if it is not properly handled. Increase in landfill leachate
creates challenges for those seeking cost effective treatment methods to process this
4
wastewater. Enhancement of the environmental quality through the minimization of
the leachate problem should therefore be the major objective of good landfill
management. The need to control and manage landfill leachate has resulted in
various treatment alternatives which include both biological and physical-chemical
processes (Ho et al., 1974; Lu et al., 1984; Qasim and Chiang, 1994).
Usually several physical-chemical wastewater treatment technologies are
used to treat the leachate. These physical-chemical approaches to leachate treatment
are undesirable since the costs of operation and maintenance are high, and labors and
services are required even after landfill site closure. Some of these processes even
require extensive pretreatment process (Britz, 1995).
However, these types of
treatment systems were hardly comply with the Environmental Quality Act, 1974.
For a small community with limited funds for expanding or updating
wastewater treatment plants, constructed wetlands are an attractive option. Rural
municipalities have access to adequate inexpensive land, and wetlands blend into a
natural landscape setting. Once the wetlands are designed and constructed, annual
maintenance costs are low. Municipalities in general have small budgets and they
normally face a lack of adequately trained staff.
Investment into sustainable
reclamation of landfill sites could be more favourable and justifiable from an
economic, environmental and also human-resources point of view.
In addition,
wetlands add aesthetic value, and provide wildlife habitat and recreation
opportunities (Renee, 2001).
Therefore, constructed wetland was developed as an alternative method to
treat leachate since constructed wetland has low cost of construction and
maintenance. Constructed wetlands have great potential as a clean-up technology for
a variety of wastewaters. Constructed wetlands have proven to be a very effective
method for the treatment of municipal wastewater.
For example, agricultural
wastewater, industrial wastewater, storm water runoff, landfill leachate and airport
runoff are all good candidates for remediation using constructed wetlands (Renee,
2001; Lin et al., 2005).
The treatment of landfill leachate is one particular
application for which constructed wetlands have been used widely (Crites, 2005). In
numerous studies, wetland systems have shown great potential in removal of heavy
5
metals in landfill leachate (Lu et al., 1984; Qasim and Chiang, 1994; Renee et al.,
2001; Nancy, 2004). Due to its high rate of the biological activities, the wetland can
transform common pollutants into harmless byproducts and essential nutrients
(Kadlec and Knight, 1996).
In this research, a combination system utilizing a
subsurface flow (SSF) wetland followed by a free water surface (FWS) wetland was
studied to treat landfill leachates.
1.3
Objective of the Study
The objectives of the study are:
(i)
To investigate the performance of the SSF-FWS constructed wetland
system in treating landfill leachate.
(ii)
To examine the effect of the SSF-FWS constructed wetland system on
leachate quality for Suspended solid (SS), Turbidity, Ammonia
Nitrogen (NH4-N), Nitrate Nitrogen (NO3–N), Orthophosphate
(PO43-) and heavy metal (Ferum (Fe) and Manganese (Mn)) removal.
(iii)
To examine the amount of heavy metal taken off by roots and leaves
of the wetland plants for SSF and FWS constructed wetland system.
1.4
Scope of the Study
The scope of study includes set-up a two-stage lab-scaled system comprised
of a SSF and FWS constructed wetland to treat landfill leachate. The leachates were
collected from Pasir Gudang Municipal Landfill, Pasir Gudang, Johor and initial
water quality of the leachates were analysed. The efficiency of leachate treatment
was evaluated in terms of water quality parameters SS, turbidity, NH4-N, NO3-N,
PO43- and heavy metal (Fe and Mn) analysis. The experiment was carried out for
6
duration of 18 days. The amount of heavy metal (Fe and Mn) uptake by plants was
determined by analysis the heavy metal concentration in plant leaves and roots. The
vegetation species used are Limnocharis flava for SSF and Eichhornia crassipes for
FWS constructed wetland.
The experiment was carried out at Environmental
Engineering Laboratory, Faculty of Civil Engineering, Universiti Teknologi
Malaysia
1.5
Importance of the Study
The use of constructed wetlands to treat water pollution is relatively new
development in Malaysia. The recently completed Putrajaya Constructed Wetland
and Lake system, which is designed to treat stormwater runoff. The abundance of
wetland plant species and good conditions for plant growth in Malaysia provided an
ideas environment for introducing constructed wetlands for the treatment of leachate.
The potential to expand the use of constructed wetlands to the treatment of leachates
beyond the more general treatment of wastewaters is relevant in today’s context. It
also an environmental friendly approach to remove pollutants from leachate. Many
studies have been conducted for leachate treatment in wastewater treatment using
single type of constructed wetlands, whether SSF or FWS system. Nevertheless, the
study of combine system of constructed wetland (SSF-FWS) for leachate treatment
has not been investigated in Malaysia.
Therefore, in this research, a combination system utilizing a SSF wetland
followed by a FWS wetland were studied to treat landfill leachates and by
incorporating local component and expertise. In term of removal efficiency, the
percentage of removal under SSF-FWS constructed wetland systems should be much
better to enhance leachate quality compare than one-single type constructed wetland
system. Beside that, the performance of SSF-FWS constructed wetland system hope
strongly supports the use of wetlands as efficient, low cost alternatives to
conventional treatment of landfill leachate.
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction
The major environmental concern associated with landfills is related to
discharge of leachate into environment and the current landfill technology is
primarily determined by the need to prevent and control leachate problems. Health
problems and environmental pollution are often related to inadequate landfill
leachate treatment.
Proper collection, treatment and disposal of leachate are
necessary to promote better environment and healthful condition.
The use of constructed wetlands has considerable promise for the control of a
large number of landfill leachate problems. Therefore, in order to develop a landfill
leachate treatment by using constructed wetland system effectively, it is important to
understand what factors those contribute the leachate generation, composition, and
problem in leachate treatment. A brief discussion of constructed wetland system in
term of definitions, types, role of wetland vegetation and mechanisms involved in
wastewater treatment also included in this chapter. In addition, the specific influent
wastewater must be characterized more fully, and a more fundamental understanding
of the transport and fate processes must be developed. Therefore, information on the
effects of constructed wetlands on leachate quality improvement has been collected
from many operational constructed wetland treatment systems.
8
2.2
An Overview of Leachate
Leachate is defined as the liquid produced when water percolates through any
permeable material in the landfill cell. It can contain either dissolved or suspended
material, or usually both (Tchobanoglous et al., 1993). Leachate also is defined as a
liquid waste produced at every landfill site from liquid-waste disposal, waste
moisture content and precipitation (Tjasa et al., 2004). Leachate poses a number of
environmental problems. This is due primarily to the extreme variability of sources
of this material, and, therefore, the heterogeneity of its composition.
The production of leachate from municipal sanitary landfill is an important
environmental problem. The leachate may migrate from the refuse and contaminate
the surface water and groundwater (Paredes, 2003). To minimize leachate
production, the factors that contribute to leachate generation need to be taken into
consideration. Similarly, composition of the leachate is important to determine its
potential effect on the quality of nearby surface and groundwater (Qasim and Chiang,
1994). Many factors interact to produce variable quantity and quality of leachate
from landfills.
2.2.1
Leachate Generation
The generation of leachate from landfill depends on many factors including
availability of water, landfill surface condition, refuse condition, climatic condition
on the site, underlying of soil condition, operating procedures and the physical
phenomena of wastes (Paredes, 2003). Leckie et al. (1979) reported some of the
most relevant factors that influent leachate generation. These factors are; annual
precipitation, runoff, infiltration, evaporation, transpiration, freezing, mean ambient
temperature, waste composition, waste density, initial moisture content and depth of
the landfill. In most landfill, leachate is a liquid that has enter the landfill from
external sources, such as surface drainage, rainfall, groundwater and water from
underground springs and the liquid produced from the decomposition of the wastes
(Tchobanoglous et al., 1993). Rainfall is the main contributor to generation of
9
leachate. Leachate formation is the result of the removal of soluble compounds by
the non-uniform and intermittent percolation of water through the refuse mass. The
precipitation percolates through the waste and gains dissolved and suspended
components from the biodegrading waste through several physical and chemical
reactions (Qasim and Chiang, 1994; Matthew, 2001).
The sources of percolating water are primarily the precipitation, irrigation,
and runoff which cause infiltration through the landfill cover, ground water intrusion,
and to a lesser extent, the initial refuse moisture content (El-Fadel et al., 1997).
Liquid fractions in the waste will also add to the leachate as well as moisture in the
cover material. Moisture can be removed from the landfill by water consumed in the
formation of landfill gas, water vapor removed in the landfill gas, and leachate
leaking through the liner (Tchobanoglous et al., 1993).
The major land surface conditions affecting surface runoff include surface
topography (size, shape, slope and elevation), cover material, vegetation, soil
permeability and soil moisture (Lu et al., 1985). Surface topography controls the
flow at the surface. Meanwhile, in a not vegetation-covered landfill, the amount of
infiltration of water through the refuse increased due to lower water evaporation by
vegetation (Qasim and Chiang, 1994).
Refuse decomposition due to microbial
activity may also contribute to leachate formation but in smaller amounts (El-Fadel
et al., 1997). Figure 2.1 was shown how leachate is generated.
Precipitation
Evapotranspiration
Surface
Runoff
Percolation
Into Waste
Leachate
Figure 2.1 : How leachate is generated (Bagghi, 1994)
10
2.2.2
Leachate Characterization
When water percolates through solid wastes that are undergoing
decomposition, both biological materials and chemical constituents are leached into
solution (Tchobanoglous et al., 1993). Chian and DeWalle (1976); Chian (1977) and
Lu et al. (1985) indicate that leachate quality was highly variable. It contains larger
pollutant loads than raw sewage or many industrial wastes.
The main factors
influencing characteristics and flow of landfill leachates depend of the composition
of solid waste composition, type and depth of solid waste, age of landfill, pH,
operational procedures, and co-disposal of industrial wastes (Christensen et al., 1992;
Qasim and Chiang, 1994; Paredes, 2003). The effects of some of these variables
upon leachate quality are presented below in Figure 2.2.
Refuse
composition
Nutrient
Microbes
Industrial waste
co-disposal
Gas and leachate
Generation in Landfill
Precipitation
Water intrusion
Temperature
pH
Oxygen
Air intrusion
Figure 2.2 : Factors influencing gas and leachate composition in landfills
(Paredes, 2003)
(a)
Solid Waste Composition
The nature of the waste organic fraction influences considerably the
degradation of waste in the landfill and also the quality of the leachate produced. In
particular, the presence of substances which are toxic to bacterial flora may slow
down or inhabit biological degradation processes with consequences for the leachate
(Christensen et al., 1992). The inorganic content of the leachate depends on the
11
contact between waste and leaching water as well as on pH and the chemical balance
at the solid-liquid interface. In particular, the majority of metals are released from
the waste mass under acid conditions (Qasim and Chiang, 1994).
(b)
Processed Refuse
Leachate characteristics from shredded or baled refuse fills also differ greatly.
Fungaroli and Steiner (1979); Kemper and Smith (1981) and Lu et al. (1984)
conducted experiments with processed landfills i.e. shredded and baled. The results
clearly indicated that leachates from shredded fills have significantly higher
concentrations of pollutants than those from unshredded refuse. Christensen et al.
(1992) reported, attainment of field capacity is also delayed, but the rate of pollutant
removal, solid waste decomposition rate, and the cumulative mass of pollutants
released per unit volume of leachate is significantly increased when compared with
unshredded fills.
Baling, however has shown opposite results on leachate generation and
quality. Baling results in a large volume of dilute leachate with a longer period of
stabilization than required for unbaled refuse. Lu et al. (1984) reported that once the
field capacity of shredded and baled refuse is reached, in the long run, the cumulative
mass of pollutant removal per kg of solid waste will be the same regardless of waste
processing.
(c)
Depth of Refuse
One of the earlier studies performed by Qasim and Burchinal (1970) reported
that substantially greater concentrations of constituents are obtained in leachates
from deeper fills under similar conditions of precipitation and percolation. Deeper
fills, however, require more water to reach saturation, require longer time for
decomposition, and distribute the bulk of extracted material over a longer period of
time. Water entering from surface of the landfill and traveling down through the
refuse will successively come in contact with solid waste, and the polluting
chemicals will successively transfer to the percolating water (Qasim and Chiang,
12
1994). Deep fills offer greater contact time and longer travel distance, thus higher
concentrations will result.
(d)
Age of Landfill
Variations in leachate composition and in quantity of pollutants removed
from waste are often attributed to landfill age, defined as time measured from the
deposition of waste or time measured from the first appearance of leachate. Landfill
age obviously plays an important role in the determination of leachate characteristics
governed by the type of waste stabilization processes. It should be underlined that
variations in composition of leachate do not depend exclusively on landfill age but
on the degree of waste stabilization and volume of water which infiltrates into the
landfill. The pollutant load in leachate generally reaches maximum values during the
first years of operation of a landfill (2-3 years) and then gradually decreases over
following years. This trend is generally applicable to organic components, main
indicators of organic pollution i.e. COD, BOD, total organic carbon (TOC),
microbiological population and to main inorganic ions i.e. heavy metals, chlorine
(Cl) and sulphate (SO4) (Christensen et al., 1992).
(f)
pH
pH influences chemical processes which are the basis of mass transfer in the
waste leachate system, such as precipitation, dissolution, redox and sorption
reactions. It will also affect the speciation of most of the constituents in the system.
Generally, acid conditions, which are characteristic of the initial phase of anaerobic
degradation of waste, increase solubilization of chemical constituents (oxides,
hydroxides and carbonated species), and decrease the sorptive capacity of waste
(Christensen et al., 1992).
(g)
Co-disposal of Industrial Wastes
The co-disposal of industrial waste in the landfill may provide adverse effect
on leachate. Industrial waste varies greatly in content, physical characteristics and
the potential for environmental degradation (Lu et al., 1985). Addition of industrial
13
waste may result in occurrence of various toxic elements in leachate in excess of that
initial content of municipal refuse leachate (Qasim and Chiang, 1994). Evidence
suggests that the addition of industrial sludge which is high in trace metals and heavy
metals will result in elevated metal concentrations in leachate.
(h)
Precipitation Water Intrusion
The leachate generation induced by precipitation, it is also produced as a
result of biochemical processes that convert solid materials to liquid forms. The
leachate generated by biochemical processes is characterized by high concentrations
of organic and inorganic constituents. The leachate is diluted by water percolating,
that also it can aid in the formation of new leachate (Paredes, 2003).
2.2.3
Leachate Composition
Leachate is most commonly encountered in connection with landfills where it
is produced as a result of rain percolating through the waste and reacting with the
chemicals and other materials in the waste (Lu et al., 1985; Tchobanoglous et al.,
1993; Paredes, 2003). Landfill leachate initially is a high-strength wastewater,
characterized by low pH, high BOD, COD, and by the presence of toxic chemicals
(Lu et al., 1985; Qasim and Chiang, 1994). In addition, the leachate quality is
variable from landfill to landfill, and over time as a particular landfill ages (Leckie et
al., 1979; Qasim and Chiang, 1994).
Qasim and Burchinal (1970) indicated from their lysimeter tests that leachate
was high in dissolved solids and found BOD concentrations 40 to 85 times higher in
leachate than in most raw domestic sewage sludge.
Leachate contained larger
pollutant loads than raw sewage or industrial waste; concentrations of heavy metals
were higher than the applicable drinking water (Lu et al., 1985). Note that the
chemical composition of leachate will vary greatly depending on the age of landfill
and the events proceeding the time of sampling. For example, if a leachate sample is
collected during the acid phase of decomposition, the pH value will be low and the
14
concentration of BOD, TOC, COD, nutrients and heavy metals will be high
(Tchobanoglous et al., 1993). If, on the other hand, a leachate sample is collected
during methane fermentation phase, the pH will be in range from 6.5 to 7.5, and the
BOD, TOC, COD and nutrients concentration values will be significantly lower.
Similarly, the concentrations of heavy metals will be lower because most metals are
less soluble at neutral pH values (Tchobanoglous et al., 1993).
The biodegradability of the leachate will vary with time. Changes in the
biodegradability of the leachate can be monitored by checking the BOD/COD ratio.
Initially, the ratios will be in the range of 0.5 or greater (Tchobanoglous et al., 1993).
Ratios in the range of 0.4 to 0.6 are taken as an indication that organic matter in the
leachate is readily biodegradable (Tchobanoglous et al., 1993). The characterization
of the leachate is based mainly on an analysis of conventional physical-chemical
parameters used in wastewater quality analysis. Representative data on the chemical
characteristics of leachate are reported in Table 2.1.
Table 2.1 : Data on the composition of leachate from landfill (Tchobanoglous et
al., 1993)
Value, mg/L
Constituent
BOD5 (5-day biochemical oxygen demand)
TOC (total organic carbon)
COD (chemical oxygen demand)
Total suspended solids
Organic nitrogen
Ammonia nitrogen
Nitrate
Total phosphorus
Orthophosphorus
Alkalinity as CaCO3
pH
Total hardness as CaCO3
Calcium
Magnesium
Potassium
Sodium
Chloride
Sulfate
Total iron
Range
Typical
2000-30,000
1500-20,000
3000-45,000
200-1000
10-600
10-800
5-40
1-70
1-50
1000-10,000
5.3-8.5
300-10,000
200-3000
50-1500
200-2000
200-2000
100-3000
100-1500
50-600
10,000
6,000
18,000
500
200
200
25
30
20
3,000
6
3,500
1,000
250
300
500
500
300
60
15
Table 2.2 : Leachate sampling parameters (Tchobanoglous et al., 1993)
Physical
Organic
constituents
Inorganic
constituents
Biological
Appearance
Organic chemicals
Suspended solids
(SS), total dissolved
solids (TDS)
Biochemical oxygen
demand (BOD)
pH
Phenols
Volatile suspended
solids (VSS), volatile
dissolved solids
(VDS)
Coliform bacteria
(total; fecal; fecal
streptocooci)
Oxidation-reduction
potential
Chemical oxygen
demand (COD)
Chloride
Standard plate count
Conductivity
Total organic carbon
(TOC)
Sulfate
Color
Volatile acids
Phosphate
Turbidity
Tannins, lignins
Alkalinity and
acidity
Temperature
Organic-N
Nitrate Nitrogen
Odor
Ether soluble (oil
and grease)
Methylene blue
active substances
(MBAS)
Nitrite Nitrogen
Organic functional
groups as required
Sodium
Chlorinated
hydrocarbons
Potassium
Ammonia Nitrogen
Calcium
Magnesium
Hardness
Heavy metals (Pb,
Cu, Ni, Cr, Zn, Cd,
Fe, Mn, Hg, Ba, Ag)
Arsenic , Cyanide
Fluoride,
Selenium.
16
2.3
Treatment of Leachate
Numerous treatability studies have been conducted with landfill leachate over
the past three decades (Ho et al. 1974; Pohland 1975; Chian and DeWalle,1976; Palit
and Qasim,1977; Uloth and Mavinec, 1977; Christensen et al., 1992 and Qasim and
Chiang, 1994). Early studies utilized bench scale and pilot plant setup. Many
treatment processes were tested and operational ranges and performance levels were
established. The applicable methods of leachate treatment are biological, physical,
chemical, and a combination of these processes.
2.3.1 Biological Treatment of Leachate
Leachate treatment might be a very complex process if low discharge values
have to be obtained.
Using only the biological process the organic-degradable
components can be reduced to very low values and almost complete nitrification and
denitrification can be achieved (Christensen et al., 1992). Biological processes are in
most cases less expensive than chemical-physical processes. Biological treatment
processes involve placing a waste stream in contact with mixed culture of
microorganism.
The microorganisms consume the organic matter in the waste
stream. The process must provide optimum environmental conditions for enhanced
degradation of organic wastes (Qasim and Chiang, 1994).
The methods for
optimizing the biological degradation include controlling the dissolved oxygen level,
adding nutrients, increasing the concentration of microorganisms and maintaining
many environmental factors such as pH, temperature and mixing (Qasim and Chiang,
1994).
Biologically treated leachate still has relatively high concentrations of COD
and chlorinated hydrocarbons that can be further reduced by other methods. A basic
problem in biological treatment is that the leachate metals and other contaminants
may exert toxic effects on the biological treatment culture (Lu et al., 1985).
Biological systems can be distinguished in anaerobic and aerobic treatment processes
that are realized by mean of different techniques. In aerobic biological treatment
17
processes, the organics are decomposed to carbon dioxide and water. Oxygen is
essential for decomposition of organic matter. In anaerobic treatment processes,
organics are decomposed in the absence of free oxygen.
Methane and carbon
dioxide are the major end products (Qasim and Chiang, 1994). Some of the major
biological treatment processes demonstrated is described below.
(a)
Activated Sludge
Activated sludge process successfully treated the leachate in most case. The
following generalizations can be made in treating leachate by activated sludge
process (Chian and DeWalle, 1976; Palit and Qasim, 1977; Uloth and Mavinec,
1977; and Christensen et al., 1992): (1) BOD and COD removal, 90-99%,; (2) Metal
removal, 80-99% and Operational range (MLVSS concentration of 5000-10,000
mg/L, food to microorganisms ratio 0.02-0.06 per day, hydraulic retention time 1-10
days and solids retention time 15-60 days). The operational parameters clearly
indicate that large amounts of organic matter in leachate were not readily oxidized,
and required extensive biological activity for stabilization.
(b)
Stabilization Pond and Aerated Lagoon
Stabilization ponds and aerated lagoons have been effectively used for
treatment and polishing of municipal wastewater. For pretreatment of leachate, they
offer a relatively economical method, prior to disposal into municipal sewers or
recycling into landfills. Early studies were conducted to evaluate the performance of
aerobic and anaerobic ponds, and aerated lagoons for treatment of raw leachate, and
also to evaluate their performance in conjunction with other treatment processes
(Qasim and Chiang, 1994). Chian and DeWalle (1977) have reported that in treating
raw leachate by aerated lagoon, a COD removal was 22-99%.
The range of
BOD/COD, and BOD/TOC ratios fed to aerated lagoon varied from 0.03 to 0.08, and
1.56 to 3.45 respectively. It is clearly noted that COD removal decreases for lower
ratios. Chian and DeWalle (1977) treated high strength leachate in laboratory scale
aerated lagoons. Nutrient addition was necessary. Removal efficiencies achieved
were; 97% organics, over 99% iron, zinc, and calcium, and 76% magnesium. Vyda
and Grimm (1977) studied the combination of aerated lagoon and polishing pond
18
each had a 10 days aeration period. The combination provided an effective leachate
treatment system.
(c)
Anaerobic Treatment Processes
Anaerobic processes have also been used for treatment of landfill leachates.
The process offers several benefits over aerobic processes. Among these are (1)
sludge production is significantly reduced, (2) stabilization of organics is lower, and
(3) recovery of methane may provide energy. Many researchers demonstrated BOD
removal in the range of 90-99% (Boyle and Ham, 1974; Pohland, 1975; and Chian
and DeWalle, 1977). In these studies the average BOD/COD and TOD/TOC ratios
were 0.68 and 2.86 respectively. Christensen et al. (1992) treated high strength
leachate (BOD 38,500 mg/L and COD 60,000 mg/L) from existing landfill using
upflow fixed film reactor, and found 95% BOD and TSS removal.
2.3.2
Physical-Chemical Treatment of Leachate
Various physical-chemical treatment processes have been applied to leachate
treatment. Physical or chemical treatment processes may be particularly useful in
treating leachates from older landfills whose organic content is negligible, or as a
polishing step for leachates previously treated by biological methods (Lu et al.,
1985). Some of the major physical-chemical treatment processes demonstrated is
described below:
(a)
Precipitation and Coagulation
Chemical precipitation and coagulation experiences have been fairly
successful in removing iron, color and suspended solids in leachates. Thornton and
Blanc (1973) and Ho et al. (1974) have demonstrated that precipitation with lime is
effective in the removal of iron and other multivalent ions, color, suspended solids
and COD.
BOD concentrations, however, are apparently unaffected.
Iron
precipitation by lime is particularly pronounced, as nearly 100 percent removal is
19
consistently reported at lime concentrations over 300 mg/L. Precipitation by sodium
sulfide is reported by Ho et al. (1974). Iron removal occurred only at a very high
chemical dose (1000 mg/L), and its effects on other constituents were negligible.
Sulfides are apparently not as promising for leachate cation removal as lime.
Coagulation is able to reduce colloidal suspension which is partially responsible for
turbidity and color. Also, dissolved organic substances, principally those with higher
dimension are involved in flocculation process, because they are adsorbed in the
flocs and successively removed through gravity settling (Christensen et al., 1992).
More favourable results were obtained for suspended solids and color removal
(Thornton and Blanc, 1973 and Ho et al., 1974). A removal efficiency of 75% for
suspended solid and 50-70% for certain heavy metals was obtained with high
coagulant dosage.
(b)
Carbon Adsorption
The removal of leachate organics by carbon adsorption was studies by
Pohland (1975), for leachates previously treated by ion exchange.
Through
moderately successful, activated carbon was found to release solids which adversely
affected the total solids concentration of the leachate. Pohland (1975) suggested that
if leachate were to be treated with both carbon and mixed resins, the carbon
treatment should precede the mixed resins. Activated carbon column tests performed
by Ho et al. (1974) demonstrated complete color and odor removals at a detention
time of 20 minutes, along with 55% COD removal.
(c)
Chemical Oxidation
A typical problem for physico-chemical processes is the production of
residues with concentrated pollutants.
However, processes aimed at completely
destroying pollutants, such as chemical oxidation may provide a final solution to the
problem. Chemical oxidation was shown to be reasonable effective in removal of
COD, iron and color (Ho et al., 1974), though only at high concentrations of the
oxidizing agent.
Oxidizing agents included chlorine, calcium hypochlorite,
potassium permanganate and ozone.
Most of these compounds have both a
significant bacterial disinfection and oxidation capacity. They are less frequently
20
used for organic compound oxidation, principally for economic reasons due to the
high dosage required. However, since leachate is a wastewater often with a low flow
rate, chemical oxidation for refractory organic compounds removal has been
proposed (Christensen et al., 1992).
Early studies by Ho et al. (1974), examined the most favourable results were
obtained with calcium hydrochlorite, but the COD removal efficiency was less than
50%.
Moreover, all oxidants required high dosage which consequently caused
numerous problems, such as increases in chlorine and hardness when using,
respectively chlorine gas (Cl2). With regard to the utilization of ozone, no residual
compound problem was observed, but it was not possible to obtain more than 50%
COD removal (Chian and DeWalle, 1976).
(d)
Reverse Osmosis
Of all the physical-chemical processes evaluated for leachate treatment,
reverse osmosis was found most effective for removal of COD. Chian and DeWalle
(1977) reported between 56-70% removals of TOC with the conventional cellulose
acetate membrane, while the removal increased to 88% with the polyethyleamine
membranes. Since low rejection of undisassociated fatty acids by membranes was
responsible for the leakage of TOC into the permeate, the performance of the
membrane process was improved to 94% when the pH of the leachate was increased
from 5.5 to 8.0 (Chian and Fang, 1973).
In addition to efficient TOC removal, total dissolved solids removal was as
high as 99%.
In most studies, severe membrane fouling was experienced, and
biological pretreatment of leachate prior to membrane processes was necessary. Lu
et al. (1984) suggested that reverse osmosis is perhaps most effective as a post
biological treatment step for removal of residual COD and dissolved solids. Chian
and DeWalle (1977) also noted that membranes are sensitive to pH. Table 2.3 and
Table 2.4 showed the summary of biological and physical-chemical treatment
processes applied to leachate treatment.
21
Table 2.3 : Physical, chemical and biological treatment processes applicable to
process trains for leachate treatment (Qasim and Chiang, 1994)
Process
Physical Processes
Equalization
Description
Flow and mass loadings are equalized by means of utilizing inline or off-line equalization chambers.
Screening
Suspended and floating debris are removed. Removal is by
straining action.
Flocculation
Fine particles are aggregated. Gentle stirring is utilized.
Sedimentation
Settleable solids and floc are removed by gravity.
Flotation
Solids are floated by fine air bubbles and skimmed from the
surface. Dissolved air flotation (DAF) is commonly used.
Air Stripping
Air and liquid are contacted in countercurrent flow in a stripping
tower. Ammonia, other gases and volatile organics are removed.
Filtration
Suspended solids and turbidity are removed in a filter bed or
micro screen.
Membrane Processes
These are demineralization processes. Dissolved solids are
removed by membrane separation. Ultrafiltration, reverse
osmosis and electrodialysis are the most common systems.
Natural Evaporation
The waste is impounded in basins that have an impervious liner.
Liquid is evaporated. The rate of evaporation depends upon
temperature, wind velocity, humidity, and natural precipitation.
Chemical Processes
Coagulation
Colloidal particles are destabilized by rapid dispersion of
chemicals. Organics, suspended solids, phosphorus, some
metals, and turbidity are removed. Alum, iron salts and polymers
are commonly used coagulation chemicals.
Precipitation
Solubility is reduced by chemical reaction. Hardness,
phosphorus, and many heavy metals are removed.
Gas Transfer
Gases are added or removed by mixing, air diffusion and change
in pressure.
Chemical Oxidation
Oxidizing chemicals such as chlorine, ozone, potassium
permanganate, hydrogen peroxide and oxygen are used to oxidize
organics, hydrogen sulfide, ferrous, and other metal ions.
Ammonia and cyanide are oxidized by strong oxidizing
chemicals.
Chemical Reduction
Many metals are removed. Common reducing chemicals are
sulfur dioxide, sodium bisulfite and ferrous sulfate.
22
Table 2.3 (Continued)
Process
Description
Disinfection
Destruction of pathogens is achieved by using oxidizing
chemicals or ultraviolet light.
Ion Exchange
Removal of inorganic species is achieved from liquid. Ammonia
is selectively removed by clinoptilite resin. This process is used
for mineralization.
Carbon Adsorption
Used for reduction of residual BOD, COD, toxic and refractory
organics. Some heavy metals are also removed. Carbon is used
in powdered form or in a granular bed.
Biological Processes
Aerobic
Microorganisms are cultivated in the presence of molecule
oxygen. Solids are recirculated. The end product is carbon
dioxide.
Suspended Growth
The wastewater containing BOD, solids, and nutrients are mixed
with a large population of active microorganisms suspended in an
aeration basin.
Activated Sludge
In the activated sludge process the food and sludge
microorganisms are aerated. The microorganisms are settled and
recirculated. Common process modifications are conventional,
completely mixed, pure oxygen, extended aeration and contact
stabilization.
Nitrification
Ammonia nitrogen is oxidized to nitrate. BOD removal can also
be achieved in a single aeration basin, or in a separate basin.
Aerated Lagoon
Large aeration basins with several days of detention period are
used.
Sequencing
Batch Reactor
(SBR)
A SBR is a fill-and-draw activated sludge treatment systems.
Food and microorganisms contact, organics stabilization,
sedimentation and discharge of clarified effluent occur in a single
basin.
Attached Growth
Trickling Filters
Rotating
Biological
Contactor
(RBC)
Anaerobic
The population of active microorganisms is supported over solid
media. The solid media may be of rocks or synthetic material.
Water is applied over a bed of rocks or synthetic media.
Trickling filters are slow rate, high rate, and two stage filters.
Aeration is by natural draft or forced draft.
Consists of a series of closely spaced circular contactor disks of
synthetic material. The disks are partly submerged in the
wastewater.
The microorganisms are cultivated in the absence of oxygen. The
complex organics are solubilized and stabilized. Carbon dioxide,
methane and other organic compounds are the end products.
23
Table 2.3 (Continued)
Process
Suspended Growth
Description
The waste is mixed with biological solids in a digester, and the
contents are commonly stirred, and heated to an optimum
temperature.
Conventional
High organic strength waste or sludge is stabilized in a digester.
The digesters are standard rate, high rate, one-stage, or two stages.
Denitrification
Nitrite and nitrate are reduced to gaseous nitrogen in an anaerobic
environment. A suitable organic carbon source (acetic acid,
methanol, sugar etc.) is required.
Combine
Anoxic,
Anaerobic and
Aerobic System
Nitrogen and phosphorus are removed along with BOD in an
anoxic, anaerobic and aerobic treatment system. Nitrate is
converted to gaseous nitrogen in the anoxic reactor. Phosphorus is
released in anoxic and anaerobic reactors. Uptake of released
phosphorus, BOD stabilization, and nitrification of ammonia
occurs in the aerobic reactor.
Attached Growth
The microbiological film is supported over a solid media. The
organic matter is stabilized as the waste comes in contact with the
attached growth.
Anaerobic
Filter
The reactor is filled with the solid media, and the waste flows
upward.
Expended Bed
or Fluidized
Bed
The reactor is filled with media such as sand, coal and gravel. The
influent and recycled effluents are pumped from the bottom. The
bed is kept in an expanded condition.
Combined
Suspended and
Attached growth
The attached and suspended microbiological growth in an
anaerobic environment consumes the organic matter.
Aerobic-anaerobic
Stabilization Ponds
Stabilization ponds are earthen basins with impervious liner. The
basins may be aerobic, facultative, or anaerobic depending upon
the depth and strength of waste. Source of oxygen is natural
aeration.
Land Treatment
The waste is applied over land to utilize plants, soil matrix and
natural phenomena to treat waste by a combination of physical,
chemical and biological means. The methods of land application
are slow-rate irrigation, rapid infiltration-percolation, and overland flow.
24
Table 2.4 : Summary of biological and physical-chemical treatment processes applied to leachate treatment
Type of Treatment
Results
References
Activated Sludge
The removal efficiency for BOD and COD removal was 90-99%, metal removal
80-99% and operational range (MLVSS concentration of 5000-10,000 mg/L,
food to microorganisms ratio 0.02-0.06 per day, hydraulic retention time 1-10
days and solids retention time 15-60 days). The operational parameters clearly
indicate that large amounts of organic matter in leachate were not readily
oxidized and required extensive biological activity for stabilization.
Chian and DeWalle (1976); Palit
and Qasim (1977); Uloth and
Mavinec (1977); and Christensen
et al. (1992)
Aerobic/Anaerobic Activated
Sludge (A/A Process)
The A/A process removed up to 70% of the nitrogen contained in leachate,
compared to 20% nitrogen removal by a conventional activated sludge system,
when the leachate BOD5:TKN ratios exceeded 10. The A/A process achieved
greater nitrification removals than aerobic system with no loss in BOD removal
efficiency, while using 50% less aeration energy than the fully aerobic system.
Manganese removal was greater than 50% with effluent concentrations of 4-5
mg/L.
Christensen et al. (1992)
Aerated Lagoon
The COD removal was achieved 22-99% have reported by using aerated lagoon.
The range of BOD/COD, and TOD/TOC ratios fed to aerated lagoon varied from
0.03 to 0.08, and 1.56 to 3.45 respectively. It is clearly noted that COD removal
decreases for lower ratios. Removal efficiencies achieved were: 97% organics,
over 99% irons, zinc, and calcium, and 76% magnesium.
Chian and DeWalle (1977)
Rotating Biological Reactor
(RBC)
This report was investigated the comparative performance of activated sludge
and RBC in treating leachate from existing landfill. Bench scale and pilot plant
studies indicated that BOD5 removal rates in RBC were 95-97%, and soluble
COD removal rates were 80-90%. The RBC unit after an aeration basin
provided additional removal and nitrification was 98-99%.
Lugowski et al. (1989)
Biological Process
25
Table 2.4 (Continued)
Type of Treatment
Results
References
This report investigated the use of subsurface flow rock-reed filters for treatment
of leachate from a solid waste landfill. The results showed BOD removal 7694% with greatest removal occurring in gravel mini beds. Removals of heavy
metals, nitrogen and phosphorus also high.
Sanford et al.. (1990)
Precipitation and Coagulation
These researchers demonstrated that BOD and COD removal by lime
precipitation is small, but removal of color, iron and other multivalent cations
was excellent at higher lime doses (300-400 mg/L). Coagulation with alum and
ferric chloride was also not very effective in removing BOD and COD. High
chemical doses were needed and the process was sensitive to pH. Also
production of large quantities of sludge was reported.
Thornton and Blanc (1973) and
Ho et al. (1974)
Ion Exchange
This researcher utilized combination of cation and anion exchange resins to
improve the quality of biologically treated leachate. The process was effective
in removing dissolved salt, and nutrients. Very little removal of residual
organics was reported. However, the use of mixed resins was considered a
promising approach for the removal of the non-organic fraction of leachate.
Pohland (1975)
Carbon Adsorption
These researchers reported that leachate having COD/TOC ratio of 2.9, showed
an initial TOC removal of 70%, which decreased to 13% after 140 bed volumes.
These clearly indicate that treatment of leachate by activated carbon is not
feasible due to the large quantities of activated carbon required. However, also
reported up to 70% COD removal by activated carbon with stabilized leachate
having a BOD/COD ratio of less than 0.1.
Chian and DeWalle (1977)
Fixed Film Reactor
Physical-chemical process
26
Table 2.4 (Continued)
Type of Treatment
Results
References
Chemical Oxidation
Chian and DeWalle suggested that calcium hypochlorite produced the best
results as chemical oxidant, especially in removing COD, iron and color in
leachate treatment. But, the COD removal efficiency was less than 50%.
Chian and DeWalle (1977) and
Ho et al. (1974)
Reverse Osmosis
This study reported between 56-70% removals of TOC with the conventional
cellulose acetate membrane, while the removal increased to 88% with the
polyethyleamine membranes. However, this study showed high COD removal
(more than 80%), although some operating problems, such as membrane fouling
were observed.
Chian and DeWalle (1976)
27
2.4
Problem in Leachate Treatment
There are various options to treat landfill leachates. The identification of the
preferred option in specific circumstances is a function of the costs, both operating
and capital, and the limitation impose on the quality and quantity of discharge.
Selection and design of a leachate treatment process is not simple. Important factors
that govern the selection and design of treatment facilities include leachate
characteristics, effluent discharge alternatives, technological alternatives, costs and
permit requirements (Qasim and Chiang, 1994). Specific problems inherent with
treatment of landfill leachate are:
(i)
The high strength of waste and magnitude of pollution potential
dictates the selection and use of reliable treatment processes;
(ii)
The changes encountered from landfill to landfill are such that waste
treatment techniques applicable at one site may not be directly
transferable to other locations. It may be necessary that each instance
be separately engineered for proper treatment;
(iii)
The source of leachate is primarily percolating water that may be
seasonal depending on hydrologic and climatic factors;
(iv)
The chemical nature of the solid wastes accepted at a landfill has a
marked effect on the composition of the leachate; and
(v)
The fluctuations in the leachate quantity and quality, which occur over
both short and long time intervals, must be considered in the treatment
plant design. The process designed to efficiently treat the leachates
from a young landfill should be modified in the future to treat the
leachate adequately as the landfill ages, or effluent standards change.
28
2.5
Wetland
A wetland can be many things to many people.
Generally, the word
“wetland” conjures an image of a river or pond surrounded by cattails, alive with
ducks, fish, frogs and the like paddling about. Identification and delineation of
wetlands has become an important topic. This is partly due to the variety of groups
that have interest in wetlands (Navid, 1989).
Wetlands are defined by The International Union for the Conservation of
Nature and Natural Resources (IUCN) at the Convention on Wetlands of
International importance especially as Waterfowl Habitat, better known as the
Ramsar Convention adopted the following definition of wetlands (Navid, 1989;
Finlayson and Moser, 1991):
"Areas of marsh, fen, peat land or water, whether natural or artificial,
permanent or temporary, with water that is static or flowing, fresh, brackish, or salt
including areas of marine water, the depth of which at low tide does not exceed six
meters" and also defined as "Land inundated with permanent or temporary water that
is usually slow moving or stationary, shallow, either fresh, brackish or saline, where
the inundation determines the type and productivity of soils and the plant and animal
communities".
Both natural and constructed wetlands have been used as wastewater
treatment system; it is found that both systems may act as efficient water purification
systems and nutrient sinks (Brix, 1997). Natural wetlands are characterized by
extreme variability in functional components, making it virtually impossible to
predict responses to wastewater application and to translate results from one
geographical area to another. Although significant improvement in the quality of the
wastewater is generally observed as a result of flow through natural wetlands, the
extent of their treatment capability is largely unknown.
The performance may
change over time as a consequence of changes in species composition and
accumulation of pollutants in the wetlands (Aeslina, 2004). Therefore, the treatment
capacity of natural wetlands is unpredictable, and design criteria for constructed
wetlands cannot be extracted from results obtained in natural wetlands.
29
2.6
Constructed Wetland
Constructed wetlands represent an emerging ecotechnological treatment
system, which are designed to overcome the disadvantages of natural wetlands.
Constructed wetland treatment systems are human-made, engineered wetland areas
specifically designed for water quality improvement by optimizing physical,
chemical and biological processes that occur in natural aquatic wetland ecosystems.
Constructed wetlands have been demonstrated to immobilize and remove metals
contained in wastewater very effectively (Kadlec and Knight, 1996; Lytle et al.,
1998; Polonsky and Clements, 1999; Zhu et al., 1999; Vesk et al., 1999).
According to Hammer and Bastian (1989), a constructed wetland is a
“designed and man-made complex of saturated substrates, emergent and submergent
vegetation, animal life, and water that simulates natural wetlands for human use and
benefits”. A constructed wetland is an ecological system that combines physical,
chemical and biological treatment mechanisms in removing pollutants from
wastewater as it flows throught the wetland.
The use of constructed wetlands has several advantages over conventional
wastewater treatment methods.
The initial cost of constructed wetlands is
considerably lower than conventional treatments in treating wastewater discharged
from municipal, agriculture and industrial sources (Kadlec and Knight, 1996).
Annual cost of operation is also considerably less due to its relatively simple design.
While constructed wetlands efficiently remove many pollutants from wastewater
streams, constructed wetlands also enhance the environment by providing a habitat
for vegetation, fish, birds, and other wildlife (Mashhor et al., 2002; Jin et al., 2003).
Among the aquatic treatment systems, constructed wetlands have a greater
potential because they can tolerate higher organic loading rate and shorter hydraulic
retention time. Consequently, land requirement for construction wetland is less than
that for other aquatic treatment systems.
In addition, these systems have the
capability of treating more than one type of pollutants simultaneously to some
satisfactory levels. This can rarely be achieved by other treatment systems (Mashhor
et al., 2002).
30
Constructed wetland system are designed, built and operated to emulate the
functions of natural wetlands especially marshes in the treatment of wastewater and
urban runoff water. According to Brix (1994), constructed wetlands are suitable for
wastewater treatment especially for post treatment, because the wetland vegetation
and organisms can adapt to the wastewater inflow and utilize the various organic and
inorganic pollutants during the metabolic and other life processes.
Constructed wetland are designed to maximize the physical, chemical and
biological abilities of natural wetlands to reduce BOD, total suspended solid (TSS),
total nitrogen (TN), phosphorus, and pathogens as wastewater flows slowly through
the vegetated subsurface (Masud et al., 2004). Precipitation and uptake of metals are
also possible along with biodegradation and bioaccumulation. The mechanisms of
pollutant removal in wetlands include both aerobic and anaerobic microbiological
conversions, sorption, sedimentation, volatilization and chemical transformations
(Nancy, 2004; Masud et al., 2004).
2.7
Types of Constructed Wetland
There are several types of constructed wetlands and the main are classified as
either FWS systems or SSF systems. Any wetland, in which the surface of the water
flowing through the system is exposed to the atmosphere, is classified as an FWS
system (Lim, 2002; Lee, 2004).
It has a natural or constructed clay layer or
impervious liner made of geotechnical material as bottom to prevent seepage. Above
the layer is the soil or other suitable medium to support the growth of emergent
plants (Lim, 2002; Lee, 2004).
In SSF systems water is designed to flow through a granular media, without
coming into contact with the atmosphere.
It is basically consists the same
components as the FWS systems but the water level is maintained below the top of
media and the media supporting plant growth normally consist of gravel to ensure
better bed porosity (Lim, 2002; Lee, 2004; Paquiz, 2004).
Free water surface
wetlands can be sub-classified according to their dominant type of vegetation;
31
emergent macrophyte, free floating macrophyte, or submerged macrophyte (Le,
2003).
Subsurface flow wetlands (which by definition must be planted with
emergent macrophytes) can best be sub-classified according to their flow patterns:
Horizontal flow or Vertical flow. A classification system is shown in Figure 2.3.
Free Water Surface (FWS)
Subsurface Flow (SSF)
Emergent Macrophyte based
Horizontal
Free Floating Macrophyte based
Vertical
Submerged Macrophyte based
Figure 2.3 : Wetland design categories (Le, 2003)
2.7.1
Free Water Surface Wetlands
Based on the ecological engineering of natural wetlands, the constructed free
water surface (FWS) wetlands were build for wastewater treatment purposes mainly
(Mashhor et al., 2002; Le, 2003). FWS wetlands consist of a shallow basin, soil or
other medium to support the roots of vegetation and a water control structure that
maintains a shallow depth of water. The water surface is above the substrate. FWS
wetlands look much like natural marshes and can provide wildlife habitat and
aesthetic benefits as well as water treatment (Mashhor et al., 2002; Le, 2003). In
FWS wetlands, the near surface layer is aerobic while the deeper waters and
substrate are usually anaerobic. Stormwater wetlands and wetlands built to treat
mine drainage and agricultural runoff are usually FWS wetlands.
Emergent macrophytes based wetlands are the most common type of FWS.
They consist of a series of channels or basins which are lined with an impermeable
material (such as clay) in order to limit infiltration. A layer of soil is provided on top
of the impervious material in which emergent macrophytes are planted.
The
macrophytes supply oxygen to the sludge zone through their roots, thereby
32
promoting aerobic digestion of the pollutants by microorganisms. Macrophytes also
act as physical supports for microorganisms that help remove pollutants (Le, 2003).
As the name implies, free floating macrophytes based wetlands make use of floating
plants, such as duckweed and water hyacinth, to remove nutrients and control algae
in wastewater. A floating barrier grid is used to support the growth of floating
macrophytes and to reduce wind effects, which would otherwise cause the plants to
drift. It has been claimed that the floating plant mat blocks out sunlight, thereby
preventing photosynthesis and inhibiting algae growth (Lemna Corporation, 1994).
The plant mat and barrier grid reduce turbulence, allowing suspended solids to settle
out more readily.
The advantages of FWS wetlands are that their capital and operating costs are
low, and their construction, operation, and maintenance are straight forward. The
main disadvantage of FWS systems is that they generally require a larger land area
and other systems (Le, 2003; Galbrand, 2003; Aeslina, 2004). Table 2.5 showed the
advantages and disadvantage of Free Water Surface Flow Wetlands. And, Figure 2.4
shows the different types of FWS wetlands.
Table 2.5 : Advantages and disadvantages of Free Water Surface Flow wetlands
(Nancy, 2004)
Advantages
Disadvantages
Less expensive to construct (on a cost per
acre basis) and operate and simpler to design
than SSF wetlands and conventional
treatment methods.
Lower rates of contaminant removal per unit
of land than SSF wetlands, thus they require
more land to achieve a particular level of
treatment than SSF wetlands
Can be used for higher suspended solids
wastewaters
Requires more land than conventional
treatment methods.
Offer greater flow control than SSF
wetlands.
Risk of ecological or human exposure to
surface-flowing wastewater.
Offer more diverse wildlife habitat
May be slower to provide treatment than
conventional treatment.
Provides habitat for plants and wildlife
Odors and insects may be a problem due to
free water surface.
33
Inlet pipe
Outlet weir/pipe
Low-permeability soil
(a) FWS wetland with emergent macrophytes
Inlet pipe
Outlet weir/pipe
Lined basin
(b) FWS wetland with floating plants
Inlet pipe
Outlet weir/pipe
Low-permeability soil
(c) FWS wetland with submerged macrophytes
Figure 2.4 : Types of Free Water Surface (FWS) treatment wetlands (Brix,
1993)
34
2.7.2
Subsurface Flow Wetlands
The Subsurface Flow (SSF) wetland basically consists of the same
components as the FWS systems, but the wastewater is confined to the substratum
(Freeman, 1993). The SSF wetlands are designed as a basin or channel with a
boundary to prevent seepage and a suitable depth bed of porous media that support
the emergent plants (Le, 2003). The wastewater will flow in a high level site of the
wetland and then flow through the porous media of sand soil and plant rhizosphere
(Le, 2003).
Subsurface flow type wetlands make use of the same removal mechanisms as
FWS wetlands; sedimentation, filtration and microbiological degradation. When the
wastewater flows through the media, it is being purified through contact with the
surface of the media and the root zone of the plants (Lim and Polparasert, 1996).
However, since the wastewater flow is below the surface, it is in continuous contact
with the filter media, which in turn provides more surface area for bacterial growth,
therefore allowing for higher organic loading rates (Le, 2003). The media supporting
plant growth normally consist of soil, sand, gravels and rocks in that order
downwards to provide better bed porosity (Mashhor et al., 2002).
The SSF wetland types have several advantages if compared with the FWS
wetland types. It is found that in the constructed SSF wetland, the available of
wastewater treatment is better than the constructed FWS one. SSF are more effective
than FWS system at removing pollutants at high application rate (Aeslina, 2004).
Wastewater flowing subsurface media may also avoid of the little risk of heavy
odors, dark-color exposure and insect vectors effects (Kowalk, 2002). The area
application for SSF wetland can be smaller than a FWS system with the same
wastewater withdrawing conditions (Le, 2003; Galbrand, 2003).
The disadvantages of SSF wetlands are that they are more expensive to
construct, on a unit basis than FWS wetlands. Because of cost, SSF wetlands are
often used for small flows. SSF wetlands may be more difficult to regulate than
FWS wetlands, and maintenance and repair costs are generally higher than for FWS
wetlands. A number of systems have had problems with clogging and unintended
35
surface flows (Galbrand, 2003; Nancy, 2004). Table 2.6 shows the advantages and
disadvantages of SSF Wetlands.
Table 2.6 : Advantages and disadvantages of Subsurface Flow wetlands (Nancy,
2004)
Advantages
Disadvantages
Higher rates of contaminant removal per unit of
land than FWS wetlands, thus they require less
land to achieve a particular level of treatment
than FWS wetlands.
Requires more land than conventional
treatment methods.
Lower total lifetime costs and capital costs than
conventional treatment systems.
May be slower to provide treatment than
conventional treatment
Minimal ecological risk due to absence of an
exposure pathway.
Waters containing high suspended solids
may cause plugging
More accessible for maintenance because there is
no standing water.
More expensive to construct than SF
wetlands on a cost per acre basis.
Odors and insects not a problem because the
water level is below the media surface.
There are two types of constructed SSF wetlands, which are horizontal flow
systems and vertical flow systems (Liu, 2002; Mashhor et al., 2002). As their names,
this classification is based on the flow direction to the soil and gravel layers. This
technology is generally limited to systems with low flow rates and can be used with
less than secondary pretreatment (Kadlec, 1999).
(a)
Horizontal Flow System
In Horizontal Subsurface Flow (HF-SSF) wetlands, the medium is kept
saturated under a continuous wastewater flow. Wastewater is fed in at the inlet and
flows slowly through the porous medium under the surface of the outlet zone, where
it is collected and discharged at the outlet. During this passage, the wastewater will
into contact with a network of aerobic, anoxic and anaerobic zones. The aerobic
zones occur around roots and rhizomes that leak oxygen into the substrate. When the
36
wastewater passes through the rhizosphere, the wastewater is cleaned by
microbiological degradation and by physical and chemical process (Cooper et al.,
1996). Oxygen is then transferred from the atmosphere into the wetland through the
emergent plants (Galbrand, 2003). Figure 2.5 shows a typical arrangement for the
constructed wetland with HF-SSF.
Figure 2.5 : Typical arrangement of horizontal subsurface flow constructed
wetland system (Le, 2003)
(b)
Vertical Flow System
Vertical Subsurface Flow (VF-SSF) wetlands are operated as a batch process
rather than in continuous flow mode. Wastewater is dosed at timed intervals so that
the filter is allowed to drain. Consequently, the system is not always saturated and
oxygen is more easily transferred from the atmosphere through diffusion. Therefore,
this system tends to be less anoxic compared to horizontal flow system and it is
suitable for treatment of wastewater that has a relatively high oxygen demand (Liu,
2002). In general, vertical flow SSF wetlands are less common and not as well
documented as horizontal flow systems.
VF-SSF treatment wetlands are frequently planted with common reed. Other
emergent wetlands plants such as cattails or bulrush can also be used. They are
composed of a flat bed of gravel topped with sand. The liquid or wastewater then
gradually drains vertically down through the bed and is collected by a drainage
37
network at the base. The bed drains completely free, allowing air to refill the bed.
The next dose of liquid traps this air and this together with aeration caused by the
rapid dosing on the bed leads to good oxygen transfer and hence the ability to
decompose BOD and to nitrify ammonia nitrogen (Cooper et al., 1996). Figure 2.6
shows a typical arrangement for the constructed wetlands with a VF-SSF.
Figure 2.6 : Typical arrangement of vertical subsurface flow constructed
wetland system (Cooper et al., 1996)
2.7.3 Combine FWS-SSF Constructed Wetland System in Wastewater
Treatment
Integrated constructed wetland comprised of a FWS-SSF systems have
introduced as alternative to enhance the potential of constructed wetland in
wastewater treatment. Several researchers were involved in this treatment system
(Eckhardt et al., 1999; Lin et al. 2002, 2005) In the paper by Eckhardt et al. (1999),
results of dual system involving a FWS-SSF constructed wetland to treat landfill
leachate in Munroe Country, New York are presented. Both contained Phragmites
australis reeds and were designed for leachate application at a rate of 1.8 m3/day.
The FWS wetland provided an effective pretreatment site for certain constituents,
while the SSF wetland functioned as an environment for plant uptake, microbial
38
activity and geochemical processes, all of which assisted in contaminant removal. In
this study, the data demonstrated that removal rates for 14 constituents ranged from
49% to 100%. The removal efficiencies exceeded 90% for most metals species, total
phosphorus, ammonium, BOD and volatile organic compound (VOC). Removal
rates were lowest for the major inorganic ions and barium. The results indicate the
(1) total iron removal was 98%, and load reduction for most metals species was
facilitated by oxygen from rainfall, aeration, plant input, especially in the SSF bed;
(2) nitrogen removal (mostly as ammonium) was 91%; and (3) total phosphorus
removal was 99% and was mainly through plant uptake and concentration in plant
tissues, especially the rhizomes. Figure 2.7 shows the plan view of constructed
wetland at Munroe Country wastewater treatment.
Figure 2.7 : Plan view of constructed wetland at Munroe Country wastewater
treatment , New York (Eckhardt et al., 1999)
Lin et al. (2002) were developed a pilot-scale wastewater treatment system
consisting of FWS and SSF constructed wetlands to evaluate the performance of
nutrient removal from aquaculture wastewater under various hydraulic loading rate
(HLR) of 1.8 to 13.5 cm/day.
By observation the performance transitions and
growth of wetland plants, the result demonstrated that FWS and SSF constructed
wetlands showed quick start-up behaviors for treating aquaculture wastewater, with
the SSF wetland achieving stable performance more rapidly than the FWS wetland.
39
The result showed that nitrogen removals were excellent, with efficiencies of
86% to 98% for ammonia nitrogen (NH4-N) and 95% to 98% for total inorganic
nitrogen (TIN). Phosphorus removal of 32% to 71% occurred, with the efficiencies
being inversely related to hydraulic loading. The study was concluded that the FWS
wetland removed most inorganic nitrogen, whereas the SSF wetland removed
phosphate at a rate equal to or even greater than the FWS. Figure 2.8 shows the
pilot-scale system consisted of a FWS and a SSF constructed wetlands arranged in
series.
Earthen fishpond
A
Effluent
to fish
B
FWS wetland
Influent
from
fishpond Perforated distribution pipeTrough-shaped colletor
SSF wetland
C
Perforated collection pipe
Figure 2.8 : Layout of the pilot-scale FWS-SSF series constructed wetlands
system for treating fishpond water. (A) Sampling location for the influent; (B)
sampling location for the FWS effluent; (C) sampling location for the SSF
effluent (Lin et al., 2002)
Beside, a study conducted by Lin et al. (2005) were investigated the
performance of the treatment wetlands for controlling water quality. The results
showed that the FWS-SSF constructed wetlands effectively removed BOD5 (3754%), SS (55-66%) and NO2-N (83-94%), total ammonia (64-66%) from
recirculating water under high hydraulic loading rate, HLR in range 1.57 to 1.95
m/day. However, NO3-N was removed poorly as the nitrate level increased from
influent to effluent. The high HLR applied in this study affected the performance of
pollutants removal. The study also showed that high HLR diminished the contact
time for nitrate and denitrifying bacteria, thus decreasing the performance of wetland
40
for denitrification.
Figure 2.9 shows a schematic diagram of the recirculating
aquaculture system.
SF wetland
Compressor
FWS wetland
Culture Tank
Sump
Settling cell
Recirculation Water
Indoor
Outdoor
Figure 2.9 : Schematic diagram of the recirculating aquaculture system (Lin et
al., 2005)
2.8
Pollutants Removal Process Mechanisms
Constructed wetlands consist of channels and basins in which aquatic plants
are planted. Wastewater is discharged into the wetland system by either pumping or
gravity. Several physical, chemical and biological processes take place in a wetland
system.
On average, wetlands are capable of providing removal rates ranging
anywhere from 60% to over 95% for many pollutants (Mashhor et al., 2002). There
are six major biological reactions of interest in the performance of constructed
wetlands; photosynthesis, respiration, fermentation, nitrification, denitrification and
microbiological phosphorus removal (Hammer, 1990; Mashhor et al., 2002; Nancy,
2004).
The principal pollutant removal mechanisms operative in wetland systems are
includes sedimentation, chemical precipitation and adsorption, microbial metabolic
activity and plant uptake. Chemical reactions between certain substances, especially
41
metals, can lead to their precipitation from the water column as insoluble
compounds. The following Table 2.7 provides an overview of pollutant removal
mechanisms. And, Figure 2.10 shows mechanisms treating inorganic compounds in
wetland treatment systems.
Table 2.7 : Overview of pollutant removal process (Watson et al., 1989)
Pollutant
Removal Process
Organic Material
(measured as BOD)
biological degradation, sedimentation, microbial uptake
Organic Contaminants
(e.g. pesticides)
adsorption, volatilization, photolysis, biotic or abiotic
degradation
Suspended solids
sedimentation, filtration
Nitrogen
sedimentation, nitrification/denitrification, microbial
uptake, plant uptake, volatilization
Phosphorus
sedimentation, filtration, adsorption, plant & microbial
uptake
Heavy metals
sedimentation, adsorption, plant uptake
Figure 2.10 : Major pollutants uptake and release pathway in wetland system
(Nancy, 2004)
42
(a)
Suspended Solids Removal
Most of the solids are removed through sedimentation and filtration, as
vegetation obstructs the flow and reduces velocities. Settleable solids are removed
easily by sedimentation since wetland systems generally have long hydraulic
retention times (Lim, 2002).
Non-settling or colloidal solids are removed by
processes which include; straining (sand media), adsorption on plants and wetland
media and biodegradation.
The types of removal mechanism at work are very
dependent on the size and nature of solids present in the wastewater and the types of
filter media used (Lim, 2002). In all cases, wetland vegetation has a negligible role
to play. In most applications, a sedimentation pond is added upstream of the wetland
cells to promote the removal of larger sediment particles and minimize the chance of
clogging the wetland cells. These processes remove a significant portion of the
BOD, nutrients (mostly nitrogen and phosphorus) and pathogens (Watson et al.,
1989; Lim, 2002).
(b)
Biochemical Oxygen Demand Removal
Microbial degradation plays a dominant role in the removal of soluble or
colloidal biodegradable organic matter (BOD) in wastewater (Lim et al., 2001).
Both the FWS and SSF system essentially function as attached growth biological
reactors. The remaining soluble organic material, left over after sedimentation, is
aerobically degraded by the bacterial biofilm that is attached to the plants. In the
wetland the aquatic plants supply oxygen to the wetland floor through their roots,
thereby promoting the aerobic digestion of organic material (Lim, 2002). Some
anaerobic degradation of organic material also occurs in the bottom sediments.
Various processes occur within the water column, on the plants, in the
wetland substrate and in concentrated areas of microbial activity known as biofilms.
Biofilms are formed as bacteria and microorganisms attach themselves to the plant
stems, the plant roots and the substrate matrix to form a biological filter from the
water surface to the wetland floor. As water passes through the thick growth of
plants, it is exposed to this living biofilm, which provides a treatment process similar
to that found in conventional treatment plants (Watson et al., 1989).
43
(c)
Nitrogen Removal
Nitrogen (N) can exist in various forms, namely ammoniacal nitrogen (NH3
and NH4+), organic nitrogen and oxidized nitrogen (NO2- and NO3-). There are
several possible mechanisms for nitrogen removal such as plant uptake, nitrification,
denitrification, soil adsorption and volatilization (Watson et al., 1989; Lim et al.,
2002 and Paredes, 2003). It is clear that the main role for nitrogen removal is played
not by plants but microorganisms. Wetlands promote the process of nitrification or
denitrification which removes nitrogen from the water.
Organic Nitrogen is mineralized to NH4+-N in both oxidized and reduced soil
layers. The oxidized layer and the submerged portions of plants are important sites
for nitrification in which NH4+ is converted to NO2--N by Nitrosomonas and
eventually to NO3--N by Nitrobacter bacteria.
Figure 2.11 depicts nitrogen
transformation in wetland system. At higher pH, some NH4+ exists in the form of
NH3 and it lost to the atmosphere by the volatilization process.
NH3
Atmosphere
Water
N2, N2O
Volatilization
Influent
NH4+-N
Aerobic sediment
(Oxidized
Org.N
zone)
(a)
NH4+-N
(b)
Nitrification
NO2--N
NO3--N
(a)
NH4+-N
Plant uptake
Sorption
Plant
Plant uptake
(b)
Anaerobic sediment
(reduced zone)
Effluent
uptake
Plant uptake
Sedimentation
Org.N
Nitrification
NO2--N
NO3--N
-
NO3 -N
Microbial
assimilation
Cation exchange
complex
Leaching
Denitrification
N2
N2O
Note:
(a) Decomposition or Ammonification
(b) Microbial uptake
Figure 2.11 : Nitrogen transformation in wetland system (Lim and Polpraset,
1996)
44
Nitrate nitrogen (NO3--N) in the reduced zone is removed through
denitrification, leaching and some plant uptake. It is however replenished by NO3from the oxidized zone by diffusion. At the root soil interface, atmospheric oxygen
diffuses into the rhizosphere through the leaves, stems, rhizomes and roots of the
wetland plants thus creating an aerobic layer similar to that existed at the media
water or media air interface. Nitrification takes place in the aerobic rhizosphere
where NH4+ is oxidized to NO3- which is either taken up by the plants or diffuses into
the reduced zone where it is converted to N2 and N2O by the denitrification process
(Lim, 2002). This reaction is catalyzed by the denitrifying bacteria Pseudomonas
spp. and other bacterias (Mashhor et al., 2002).
(d)
Phosphorus Removal
Many treatment wetlands have been shown to be successful at retaining
phosphorus (Kadlec and Knight, 1996; Reddy et al., 1983). Phosphorus removal in
wetlands is based mainly on the phosphorus cycle and can involve a number of
processes such as adsorption onto soil and organic matter, filtration, sedimentation,
assimilation or plant uptake, complexation or precipitation reactions with calcium,
Ca2-, magnesium, Mg2+, Fe3+ and Mn2+ (Renee, 2001; Fraser et al., 2004; Huett et al.,
2005). Plant uptake may be significant in systems where the area specific loading
rate is low.
Therefore, phosphorus removal in wetlands is less effective than
nitrogen. Phosphorus removal in many wetlands and aquatic plant systems is not
very effective because of the limited contact opportunities between the wastewater
and the soil (Aeslina, 2004). Adsorption and precipitation are the major removal
pathways when the hydraulic retention times are longer and finer-textured soils are
being used. Adsorbed phosphorus can be held tightly and is generally resistant to
leaching (Lim, 2002).
(e)
Heavy metal Removal
Heavy metals are common environmental pollutants. Metal contamination of
soils and waters has a severe impact on the environment and human health. Kadlec
and Knight (1996) report the removal of several metals in treatment wetlands,
including aluminium, arsenic, cadmium, copper, iron, manganese, mercury, nickel,
45
silver and zinc.
Metals are removed in treatment wetlands by three major
mechanisms (Kadlec and Knight, 1996); binding to soils, sediments, particulates, and
soluble organics by cation exchange and chelation; precipitation as insoluble salts,
principally sulfides and oxyhydroxides and uptake by plants, including algae and by
bacteria.
Removals of heavy metal occur mainly through adsorption and
precipitation and to a minor extent through plant uptake for some metals. Metals are
retained in the soil profile or the sediments or substratum. Metals can precipitate out
as sulfides and carbonates, or get taken up by plants (Renee, 2001). Figure 2.12
shows the summary the major physical, chemical and biological processes
controlling contaminant removal in wetlands.
Figure 2.12 : Summary of the major physical, chemical and biological processes
controlling contaminant removal in wetlands (Lim, 2002)
2.9
Wetland Plant
In selecting plants for use in a constructed wetland it is necessary to consider
the factors that affect their natural distribution both overall within the state and
locally, as these will have a major impact on the success of the plants that are used
for wetland planting. Wetland vascular plants are generally categorized based on
46
their growth form. Types of wetland plants can be classified into three broad types
as shown in Figure 2.13. These broad types are; floating, submerged and emergent
plants (Mashhor et al., 2002).
Figure 2.13 : Types of wetland plants (Mashhor et al., 2002)
The floating plants that are free floating and not attached to any substrate. A
widespread family of free-floating plants is the Lemnaceae, which includes the
genera Lemna (duckweed), Wolffiella and Wolffia (water meal). Also included in the
floating plants are larger species, such as Eichhornia crassipes (water hyacinth) and
Pistia stratiotes (water lettuce) (Cronk and Fennessy, 2001). Both have extensive
branching roots that hang down into the water column. Besides the roots role in
absorbing nutrients, they also serve as a weight that helps stabilize the plant on the
water.
The submerged plans that are attached to the substrate or free floating but
whose leaves and stems are permanently submerged.
It includes plants whose
flowers may be emergent. In submerged species, all photosynthetic tissues are
normally underwater. Examples of submerged species include Hydrilla verticillata
(hydrilla) and Ceratophyllum demursum (coontail) (Cronk and Fennessy, 2001).
Submerged plants take up dissolved oxygen and carbon dioxide from water column
and many are able to use dissolved bicarbonate (HCO3-) in photosynthesis as well.
Rooted submerged species acquire the majority of their nutrients from the sediment,
although some nutrients, particularly micronutrients, may be absorbed from the water
column (Cronk and Fennessy, 2001).
47
The emergent plants, those rooted in the soil and emerge the water surface
have a higher potential in wastewater treatment because they can serve as microbial
habitat and as a filtering media (Mashhor et al., 2002). An example of emergent
plants includes Scirpus longii (bulrush), Typha latifolia (cattail) and Pragmites
communis (reeds) (Kadlec, 1999). Recent research in use of constructed wetlands
that water hyacinth (Eichhornia crassipes) is also useful for metals uptake. Study by
Thien (2005), water hyacinth had higher capacity to accumulate heavy metals in
roots than leaves.
2.10
Role of Wetland Vegetation
Plants are an integral part of the effluent treatment processes in constructed
wetlands (Brix, 1997). The plant transfer oxygen through their root and rhizome
systems to the bottom of treatment basins and providing a medium beneath the water
surface for attachment of microorganisms that perform most of biological treatment
(Mashhor et al., 2002).
Several processes are envisioned as being effective in
pollutant reduction; phytoextraction, phytostabilization, transpiration stripping, and
rhizofiltration (Kadlec, 1999). In particular, for leachate context, vegetation fosters
and provide several storage and reduction mechanisms.
Phytoextraction refers to plant uptake of toxicants, which is known to occur
and has been studies in the storm water and mine water wetland context (Kadlec,
1999). However, in many cases the contaminant is selectively bound up in below
ground tissues, roots and rhizomes, and is not readily harvested. For example, metals
are taken up by plants, and in many cases stored preferentially in the roots and
rhizomes (Sinicrope et al., 1992).
Phytostabilization refers to the use of plants as a physical means of holding
soils and treated matrices in place. This process is also one of the chief
underpinnings of treatment wetlands, as it relates to sediment trapping and erosion
prevention in those systems (Kadlec, 1999). Wetland plants possess the ability to
transfer significant quantities of gases to and from their root zone and the atmosphere
48
(Brix, 1997). Rhizofiltration refers to a set of processes that occur in the root zone,
resulting in the transformation and immobilization of some contaminants.
The macrophytes growing in constructed wetlands have several properties in
relation to the treatment processes that make them an essential component of the
design. The most important effects of macrophytes in relation to the wastewater
treatment processes are the physical effects that the plant tissues give rise to (such as
erosion control, filtration effect and the provision of surface area for attached micro
organisms). The metabolism of the macrophytes (such as plant uptake and oxygen
release) affects the treatment processes to different extents depending on design. The
macrophytes have other site specific valuable function, such as providing a suitable
habitat for wildlife and giving systems an aesthetic appearance. The major roles of
macrophytes in constructed wetlands are summarized in Table 2.8.
Table 2.8 : Roles of macrophytes in constructed wetlands (Mashhor et al., 2002)
Macrophyte Property
Role in treatment process
Aerial plant tissue
Light attenuation: reduce growth of phytoplankton
Reduce wind velocity: reduces risk of resuspension
Aesthetically pleasing appearance of system
Storage of nutrients
Plant tissue in water
Filtering effect: filter out large debris
Reduce current velocity: increases rate of sedimentation,
Reduces risk of resuspension
Provide surface area for attached biofilms
Excretion of photosynthetic oxygen: increases aerobic degradation
Uptake of nutrients
Roots and rhizomes in
the sediment
Provide surface for attached bacteria and micro-organisms
Stabilizing the sediment surface: less erosion
Prevents the medium from clogging
Release of oxygen increase degradation and nitrification
Uptake of nutrients
Release of antibiotics
49
2.11
Application of Constructed Wetlands in Treating Landfill Leachate
Leachate composition depends on the type and quantity of materials placed in
the landfill and on the time since placement (Crites, 2005). Thus, characterization of
the leachate is essential for proper wetland design because it can contain high
concentrations of BOD, ammonia, metals, high or low pH, and possibly priority
pollutants of concern. In addition, the nutrient balance in the leachate may be
inadequate to support vigorous plant growth in the wetland and supplemental
potassium, phosphorus, and other micronutrients may be necessary (Crites, 2005).
Many researchers are involved in treating landfill leachate using constructed
wetland. A study by Rafidah (2003) reported that the pollutants removal efficiency
for S. sumantrensis was BOD (94%), COD (92%), Fe (89%), Zn (90%), Mn (89%)
compared to S.mucronatus that removed BOD (98%), COD (95%), Fe (95%), Zn
(90%), Mn (91%) by using FWS constructed wetland system. In this study, the
author was remarked that the removal rate for nutrient and heavy metal depends
directly with time. The more the contact time between leachate and vegetation in the
wetland system, was better the removal rate.
El-Gendy (2003) reported on landfill leachate treatment by a FWS
constructed wetland with water hyacinth (E.crassipes) and salvinia. From this study,
the removal efficiency of pollutants in leachate using water hyacinth was more 80%
in TKN (91%), total ammonia (100%), total reactive phosphorus (97%) and total iron
(84%). Salvinia plants died after the first day of experiments.
Ammonia was
removed completely from the system incorporating water hyacinth after 21 days of
experiment. Water hyacinth therefore out performed salvinia in leachate treatment.
A study by Lee (2004) was reported that horizontal SSF constructed wetland
with T.angustifolia has high performance in treating ammonical nitrogen with 80%
removal efficiency compare to phosphorus with about 65% removal. The plant
uptake of Chromium, Cr and cadmium, Cd was 91.7% and 81.8% respectively with
more than 80% Cd retained in plant leaves. Vegetation played an important role in
nutrient removal. Beside that, Lee (2004) also concluded that the nutrient removal
50
efficiency could be affected by process variables such as HLR, HRT and mass
loading rate.
Recently, study by Thien (2005) clearly demonstrates the FWS constructed
wetland system was proven effective in pollutants removal in leachate treatment. In
her study, she was mentioned that wetland of 100% and 50% leachate concentration
showed high removal efficiency for BOD, NO3-N, Fe and Mn compared to 25%
leachate concentration wetland. In FWS constructed wetland with 100% leachate
concentration, the removal efficiency of BOD (74.07%) and Fe (100%) respectively.
While, in FWS constructed wetland with 50% leachate concentration, the removal
efficiency of NO3-N and Mn were 64.51% and 53.13% respectively. Beside, the
study showed Eichhornia crassipes had higher capacity to accumulate heavy metals
in roots than leaves. Table 2.9 and Table 2.10 showed the summary of wastewater
pollutants removal in constructed wetland and leachate pollutants removal in
constructed wetland, respectively.
51
Table 2.9 : Wastewater pollutants removal in constructed wetland
System Type
Constructed wetlands
systems under different
seasons.
Horizontal sub-surface flow
(HFCWs) and hybrid
constructed
wetlands systems
FWS and SSF constructed
wetlands under under high
HLR in range 1.57 to 1.95
m/day.
Type of Influent
Finding
References
Domestic wastewater
Comparisonof mean inlet and outlet concentrations showed that the
constructed wetland system could effectively reduce the output of SS
(71.8%), BOD5 (70.4%), COD (62.2%), total coliform (99.7%) and
fecal coliform (99.6%). However, the percent reduction of ammonia
nitrogen was relatively low (40.6%), and total phosphorus showed the
least efficient reduction (29.6%). BOD5 and COD removal was more
efficient in spring and summer than in autumn and winter whereas
ammonia nitrogen and total phosphorus removal was more efficient in
summer and autumn than in spring and winter.
Song et al. (2006)
Municipal sewage
HFCWs provide high removal of organics and suspended solids but
removal of nutrients is low. Removal of nitrogen is limited by
anoxic/anaerobic conditions in filtration beds which do not allow for
ammonia nitrification. Phosphorus removal is restricted
by the use of filter materials (pea gravel, crushed rock) with low
sorption capacity. However, hybrid systems are comprised most
frequently of vertical flow (VF) and HF systems arranged in a staged
manner. HF systems cannot provide nitrification because
of their limited oxygen transfer capacity. VF systems, on the other
hand, do provide a good conditions for nitrification but no
denitrification occurs in these systems.
Vymazal (2005)
Shrimp aquaculture
wastewater
The results showed that the FWS-SSF constructed wetlands effectively Lin et al. (2005)
removed BOD5 (37-54%), SS (55-66%) and NO2-N (83-94%), total
ammonia (64-66%) under high HLR. The high HLR affected the
performance of pollutants removal. The study also showed that high
HLR diminished the contact time for nitrate and denitrifying bacteria,
thus decreasing the performance of wetland for denitrification.
52
Table 2.9 (Continued)
System Type
Type of Influent
Finding
References
Two combined systems
composed of a vertical flow
bed planted with
Phragmites and a
horizontal flow bed planted
with Typha.
Domestic Wastewater
he system shows a good performance in the bacterial removal (90%) as
well for planted and unplanted system. Nitrogen removal in planted
system was greater than in unplanted one especially for nitrogen
Kjeldahl (27 and 5%) and nitrogen ammonia (19 and 6%). Whereas,
removal of nitrate-nitrite in planted system is less than in unplanted one
(4 and 13%).
Keffala and Ghrabi
(2005)
constructed wetlands with
Cyperus papyrus (papyrus)
and Miscanthidium
violaceum (K.Schum.) in
tropical climate
Domestic sewage
wastewater
Papyrus root structures provided more microbial attachment sites,
sufficient wastewater residence time, trapping and settlement
of suspended particles, surface area for pollutant adsorption, uptake,
assimilation in plant tissues and oxygen for organic and inorganic
matter oxidation in the rhizosphere, accounting for its high treatment
efficiency. Papyrus showed higher ammonium-nitrogen and total
reactive phosphorus (TRP) removal (75.3% and 83.2%) than
Miscanthidium (61.5% and 48.4%). Plant uptake and storage was the
major factor responsible for N and P
removal in treatment
Kyambadde et al.
(2004)
Small-scale wetland
mesocosms (400L each)
containing two treatment
designs (a mixture of
Typha, Scirpus, and Juncus
species;
Domestic wastewater
Significant differences between influent and effluent water quality for
the vegetated wetlands (p>05) were observed in TSS, BOD and TKN.
Increased DO and reduction in fecal coliform, enterococcus,
Salmonella, Shigella, Yersinia, and coliphage populations also were
observed in vegetated wetlands. Greatest microbial reductions were
observed in the planted mesocosms compared to those lacking
vegetation.
Hencha et al. (2003)
53
Table 2.9 (Continued)
System Type
Type of Influent
Finding
References
Cameron et al. (2003)
FWS with Typha latifolia
and Scirpus acutis
Municipal sewage
lagoon
The FWS cells achieved removals as follows: BOD (34%),
ammonia and ammonium (52%), TKN (37%), TSS (93%),
TP (90%), ortho-P04 (82%) and E. coli (58%). The vegetated filter
strip treating the effluents from the wetland cells achieved removals
as follows: biochemical oxygen demand (18%), ammonia and
ammonium (28%), TKN (11%), TSS (22%), TP (5%) and F. coli
(22%). It may therefore serve as an additional treatment stage
further.
Horizontal SSF with
Phragmites australis
Domestic Sewage
Mantovi et al. (2003)
Removal of suspended solids and organic load was above 90%,
while those of the nutrients N and P were about 50% and 60%,
respectively. Nitrogen removal is usually not very efficient in
horizontal SSF wetlands, due to insufficient oxygen supply. The role
of plants in the CWs is limited but essential. Absorption by plants
was not the main route through which the contaminants were
removed or transformed, but certainly the presence of plants was
fundamental for establishing a heterogeneous environment.
FWS and SSF constructed
wetlands under various
HLR (1.8 to 13.5 cm/day)
Fishpond water (shrimp
aquaculture
wastewater)
The result showed that nitrogen removals were excellent, with
efficiencies of 86% to 98% for ammonia nitrogen (NH4-N) and 95%
to 98% for total inorganic nitrogen (TIN). Phosphorus removal of
32% to 71% occurred, with the efficiencies being inversely related
to hydraulic loading. The study was concluded that the FWS
wetland removed most inorganic nitrogen, whereas the SSF wetland
removed phosphate at a rate equal to or even greater than the FWS.
Lin et al., (2002)
54
Table 2.10 : Leachate pollutants removal in constructed wetland
System Type
Type of Influent
Findings
References
FWS constructed wetland
with magnetic field and
Eichhornia crassipes.
Treated leachate
The results showed continuous circulation magnetic field with wetland
(CRM-W) systems can reduce up to 60% of ammonia nitrogen removal,
68.7 % of ferum and 60% of manganese after 6 hours of treatment.
Wetland was able to remove 99% of nitrate nitrogen, 96% of ammonia
nitrogen and 83% of BOD after end of experiment.
Noor Ida Amalina
(2006)
Horizontal SSF constructed
wetland with Typha
angustifolio
Treated leachate
The study was conducted to determine removal of nutrient treated by SSF
with different concentration, HRT and sand ratios. Removal efficiency of
AN and nitrate by Typha angustifolio ranges from 42.6-88.9%. Removal
of BOD and COD by horizontal SSF constructed wetland ranges from
62.6-72.8% and 64.5-85.7%, respectively. The HRT was found to affect
the results, about 10-30% of differences in removal efficiency for longer
HRT compare to shorter HRT.
Chew (2006)
Constructed wetland with
floating plant (E.crassipes)
Treated leachate
This study demonstrates the FWS constructed wetland system with 100%
and 50% leachate concentration showed high removal efficiency for BOD,
NO3-N, Fe and Mn compared to 25% leachate concentration wetland. In
FWS constructed wetland with 100% leachate concentration, the removal
efficiency of BOD (74.07%) and Fe (100%) respectively. While, in FWS
constructed wetland with 50% leachate concentration, the removal
efficiency of NO3-N and Mn were 64.51% and 53.13% respectively. The
study showed E.crassipes had higher capacity to accumulate heavy metals
in roots than leaves.
Thien (2005)
FWS with Typha latifolia,
Phragmites australis and
Elodea canadensis
Leachate
Submerged plant E.canadensis had a greater capacity for denitrification,
because it offered higher carbon availability or other species-specific
advantages, such as suitable attachment surfaces. The potential
denitrification rates were more than three times higher in the cores
containing E. canadensis than in the cores with T.latifolia and P.australis
Bastviken et al.
(2005)
55
Table 2.10 (Continued)
System Type
Type of Influent
Findings
References
Horizontal SSF constructed
wetland with T.angustifolia
Treated leachate
A study was reported that horizontal SSF constructed wetland with
T.angustifolia has high performance in treating AN with 80% removal
efficiency compare to phosphorus with about 65% removal. The plant
uptake of Chromium, Cr and cadmium, Cd was 91.7% and 81.8%
respectively with more than 80% Cd retained in plant leaves. Vegetation
played an important role in nutrient removal. Beside that, Lee (2004)
also concluded that the nutrient removal efficiency could be affected by
process variables such as HLR, HRT and mass loading rate.
Lee (2004)
FWS constructed wetland
with water hyacinth
(E.crassipes) and salvinia.
Landfill leachate
This study reported on landfill leachate treatment by a FWS constructed
wetland with water hyacinth (E.crassipes ) and salvinia. From this study,
the removal efficiency of pollutants in leachate using water hyacinth was
more 80% in TKN (91%), total ammonia (100%), total reactive
phosphorus (97%) and total iron (84%). Salvinia plants died after the
first day of experiments. Ammonia was removed completely from the
system incorporating water hyacinth after 21 days of experiment. Water
hyacinth therefore out performed salvinia in leachate treatment.
El-Gendy (2003)
FWS constructed wetland
with S. sumantrensis
Landfill leachate
A study reported that the pollutants removal efficiency for S.
sumantrensis was BOD (94%), COD (92%), Fe (89%), Zn (90%), Mn
(89%) compared to S.mucronatus that removed BOD5 (98%), COD
(95%), Fe (95%), Zn (90%), Mn (91%) by using FWS constructed
wetland system. In this study, the author was remarked that the removal
rate for nutrient and heavy metal depends directly with time. The more
the contact time between leachate and vegetation in the wetland system,
was better the removal rate.
Rafidah (2003)
56
Table 2.10 (Continued)
System Type
Type of Influent
Findings
References
Dual system (FWS-SSF)
constructed wetland with
Phragmites australis reeds.
Municipal landfill
leachate
The data demonstrated that removal rates for 14 constituents ranged from
49% to 100%. The removal efficiencies exceeded 90% for most metals
species, total phosphorus, ammonium, BOD and volatile organic
compound (VOCs). Removal rates were lowest for the major inorganic
ions and barium. The results indicate the (1) total iron removal was 98%
(2) nitrogen removal (mostly as ammonium) was 91%; and (3) total
phosphorus removal was 99% and was mainly through plant uptake and
concentration in plant tissues, especially the rhizomes.
Eckhardt et al. (1999)
SF with Scleria
sumantrensis Retz. and
Scirpus mucronatus
Treated leachate
S.mucronatus accumulated more Zn, Mn, and Fe in the roots than
S.sumantrensis Retz. S.mucronatus had higher metal absorption compared
to S.sumantrensis Retz.. The heavy metal concentration was higher in the
root zones compared to the stem zones for Fe, Zn and Mn. The high
accumulation of heavy metal in S.mucronatus was due to the plant that
had many shorter roots that were able to create aeration zones for heavy
metal uptake.
Krishnan (2002)
Pre-treatment using FWS
constructed wetland
Municipal landfill
leachate
The treatment wetland consists of a primary treatment lagoon and ten
FWS wetlands cells. Chemical and biological data indicated that the
wetland treatment system has provided a high level of landfill treatment.
For example, BOD was reduced by an average of 96%, while TSS, iron
and TKN concentration were decreased by more than 95%, on average.
The FWS constructed wetland has proved to be sustainability means for
removal metals from leachate during an operational period over 5 years.
Debusk, W.F. (1999)
57
2.12
Conclusion
Leachates from landfill vary in their hazardous characteristics and include
numerous pollutants and phenolics. Leachates are well known as a particular sort of
problematic wastewater both from the viewpoint of eco-toxicity and the treatment
technique. Methods developed for treatment of landfill leachates can be classified as
physical, chemical and biological, which are usually, used as a combination in order
to improve the treatment efficiency. The treatment of leachates by natural systems
seems to be environmentally sustainable for the treatment of many constituents. The
high productivity and nutrient removal capability of wetlands has created substantial
interest in their potential use for improving leachate water quality. It is probable that
they would be part of an integrated natural system, comprised of aquatic and
terrestrial components together with wetlands. Constructed wetlands can be built
with a much greater degree of control, thus allowing the establishment of
experimental treatment facilities with well-defined composition of substrate, type of
vegetation and flow pattern (Moshiri, 1993).
Constructed wetlands for leachate treatment have several advantages
compared to conventional secondary and advanced leachate treatment systems.
Some of these advantages are; low cost of construction and maintenance; low energy
requirements; being a “low technology” system, they can established and run by
relatively untrained personnel; and the systems are usually more flexible and less
susceptible to variations in loading rate than conventional treatment systems
(Moshiri, 1993). A constructed wetland was an ecological system that combines
physical, chemical and biological treatment mechanisms in removing pollutants from
leachate wastewater as it flows through the wetland (Kadlec and Knight, 1996; Lim,
2002). These systems effectively reduce total suspended solids, BOD, nitrogen
(ammonia and total nitrogen), phosphorus (P) and fecal coliform (Neralla et al.,
2000).
However, the major disadvantages of constructed wetland treatment systems
are the increased land area required, compared to conventional systems and the
possible decreased performance during winter in temperate regions (Moshiri, 1993).
But, the use of constructed wetlands has considerable promise for the control of a
58
large number of organic compounds, which are the subject of landfill leachate
regulation. Therefore, the disposal of wastewater especially landfill leachate into
constructed wetlands is an especially attractive alternative to conventional
wastewater treatment technologies for small to medium sized communities, in
sparsely populated areas and in developing countries.
Treatment wetlands are either natural or constructed wetlands almost
completely covered with emerging macrophytes or they are being managed as water
quality improving systems. Several studies also have shown the important role
played by macrophytes in constructed wetlands (Brix, 1997). Macrophytes enriched
their substrate with oxygen and reduce filter erosion. In this study, Limnocharis
flava and Eichhornia crassipes were used as aquatic plants. These plants were
selected as the wetland plants because of their local availability (available at nearest
study area), easy to control and maintain, and have capability to survive with
leachate constituents. The functions and ability of these plants were proved, as it is
one of the plants used in Putrajaya wetlands. Its ecological function is to reduce
suspended solids and chemical pollution; biodegradable organic pollutants in water
which is in need in leachate treatment.
The increasing application of treatment wetlands coupled with increasingly
strict water quality standards has been an incentive for the development of better
design tools. This study reviews the application of constructed wetland on leachate
treatment using combined SSF and FWS constructed wetland system and planted
with Limnocharis flava and Eichhornia crassipes. The focus of this study is on the
removal efficiency of constructed wetlands as well as standard water variables such
as SS, turbidity, nutrients and heavy metals.
CHAPTER 3
METHODOLOGY
3.1
Introduction
This chapter describes several research design, operational framework,
method and experimental procedure used in this study. The activity such as in
engineering approach (basic knowledge and understanding activities, design
parameters or verification, and process design and set-up the configuration) and
mathematical analysis are the main approach to be involved simultaneously.
3.2
Research Design and Operational Framework
The research methodology was divided into 6 phases as shown in Figure 3.1.
This study was focussed on the ability of SSF-FWS constructed wetland systems in
removing nutrients and heavy metals in leachate. Control was set up which was the
constructed wetland. The control system is important to carry out to compare the
effectiveness between constructed wetland with plants and without plants.
The
wetlands systems are constructed using fiber glass tank. The experiments were
carried out at Environmental Engineering Laboratory, Faculty of Civil Engineering,
Universiti Teknologi Malaysia.
60
Phase 1: Literature Review
ƒ
ƒ
ƒ
ƒ
Determine objectives and scope of
study
Theoretical approach and literatures
Types of constructed wetland
Wetland plants
Phase 2: Process Design and Set up the
Experiment
ƒ
Set up of experimental scale SSF-FWS
constructed wetland systems
Phase 3: Experimental Works
Control System
Planted System
Without plant
ƒ
HLR = 0.13 m/cycle/day
ƒ
Leachate (50% concentration)
Constructed wetland (Planted)
ƒ
HLR = 0.13 m/cycle/day
ƒ
Leachate (50% concentration)
Phase 4: Sampling and Preservation
Phase 5: Data analysis
ƒ
ƒ
Based on the parameter observed in the
experiment
Removal efficiency of pollutants
Phase 6: Recommendation and Conclusion
Figure 3.1 : Frameworks and experimental design
61
3.3
Leachate Sample Collection and Preparation
Before any experiment can be run in the constructed wetlands, leachate
sample need to be collected. For this study, raw leachate (without treatment) sample
was taken from Pasir Gudang Sanitary Landfill.
Some equipment needs to be
prepared and 4 containers (750 liter) of leachates were collected in every collection
trips. Once the leachate sample arrives at the laboratory, the leachate was stored at
4°C to minimize any further change that might occur in its physiochemical and
biological properties until the experiments analyses were carried out within a week.
Before run the experiments, the characterizations of the raw leachate samples in this
study were analysed.
3.4
Experiment Set up
The experiments were conducted using two lab-scale constructed wetland
systems. Planted system was set-up a two-stage lab-scaled system comprised of a
SSF and FWS constructed wetland plants, while the Control system is without plants.
The equipment consists of 4 tanks which are storage tank, SSF tank, FWS tank and
settling tank. Each tank was fabricated in trapezoidal shape with dimension of 0.23
m width, 0.43 m length and 0.3 m depth.
SSF and FWS constructed wetland systems were arranged in series and
operated for around 3 weeks (18 days). Before leachate sample were poured in
storage tanks, the sample was diluted to the concentration of 50% leachate and 50%
tap water. After that, diluted leachate was poured into storage tank of about 18 liter
before flow into the SSF tank. The plastic valve installed at storage tank was
adjusted to control the flow rate of the leachate and to make sure the entire tank were
fed with leachate effluent at a constant flow rate which is designed accordingly the
HLR (0.13 m/cycle/day) and to obtain a hydraulic retention time (HRT) of 7 hours
per cycle for SSF tank and 10 hours per cycle for FWS tank. The daily HLR was
adjusted and checked manually using a measuring cylinder and a stopwatch to obtain
and maintain a continuous flow rate. The HRT of each bed was regulated throughout
62
the time that the valves remained opened during irrigation. Leachate wastewater was
continuously daily return feed (around 3 weeks) into the SSF wetland directly from
the storage tank and then passed through the FWS wetland and settling tank via
gravity flow. The elevation level of the SSF wetland was higher than the FWS
wetland, to allow gravity flow. The schematic plans of laboratory equipments for
SSF and FWS constructed wetland are shown in the Figure 3.2.
Control
Planted
1
1
A
A
2
4
Daily
Return
Daily
Return
B
B
3
5
C
C
6
6
Figure 3.2 : Schematic diagram of SSF-FWS constructed wetland used in
experiment. (1) Storage tank; (2) Media without plant; (3) water tank without
plant; (4) SSF tank with Limnocharis flava (5) FWS tank with Eichhornia
crassipes; (6) Settling tank; and (A) Sampling location for the influent; (B)
sampling location for the SSF effluent; (C) sampling location for the FWS
effluent.
63
Control
Planted
STORAGE TANK
SSF
B
Limnocharis
flava
SSF
B
FWS
C
SETTLING
TANK
Eichhornia
crassipes
FWS
C
SETTLING
TANK
Figure 3.3 : Arrangement of SSF-FWS constructed wetland systems
Figure 3.3 shows the leachate was treated in SSF-FWS constructed wetland
systems. Sampling ports were set up at the inlet and outlet of the SSF wetland and at
the outlet of the FWS wetland as illustrated above in Figure 3.3. The SSF and FWS
tanks were contained with the same quantity of leachates and the experiments were
conducted under natural environmental conditions which were exposed to sunlight as
shown in Figure 3.4. Detail of experimental design in this study is summarized in
Table 3.1.
64
Table 3.1 Summary of experimental design
System : 50% Leachate + 50% Tap water
Type of flow
Q
(m3/day)
HLR
(m/day)
HRT
(hours)
Duration
Type of
plants
Continues flow
(SSF constructed
wetland system)
0.014
(per cycle)
0.13
(per cycle)
7
(per cycle)
18 days
Limnocharis
flava
Continues flow
(FWS constructed
wetland system)
0.014
(per cycle)
0.13
(per cycle)
10
(per cycle)
18 days
Eichhornia
crassipes
Figure 3.4 : Two-stage lab-scaled system comprised of a SSF and FWS
constructed wetland located outside of the building in an open area
3.5
Plants
In this study, yellow bur-head (Limnocharis flava) and water hyacinth
(Eichhornia crassipes) were used as aquatic plants. The SSF wetland was planted
with Limnocharis flava.
And, the FWS wetland was planted with floating
Eichhornia crassipes plants. SSF wetlands are planted by hand. The planting
65
densities were 10 plants of Limnocharis flava for the SSF tank and 7 plants of
Eichhornia crassipes for the FWS tank. These plants were selected as the wetland
plants because of their local availability (available at nearest study area), easy to
control and maintain, and have capability to survive with leachate constituents. A
short description about Limnocharis flava and Eichhornia crassipes are shown in
Figure 3.5 and Figure 3.6.
Scientific Name : Limnocharis flava
Local names
: Yellow bur-head (English), Yellow sawah lettuce, Sawah
flowering rush, Paku rawan (Malay)
Family
: Limnocharitaceae
Synonyms
: Limnocharis emarginata, Alisma flava, Damasonium flavum
Limnocharis laforesti, and Limnocharis plumieri .
Description
: Perennial herb to 1 m high and rooting in mud. Leaves broadovate, thick, 5–30 cm long, 4–25 cm wide, leaf stalk (petiole) 5–
75 cm long, green. Fruit compound, to 2 cm wide, each fruit
containing about 1,000 seeds. Seeds dark brown, horseshoeshaped, to 1.5 mm long with obvious ridges. Dispersal by
production of numerous seeds.
Habitat
:
Emergent, L. flava inhabits shallow swamps, ditches, pools and
wet rice fields, occurring usually in stagnant fresh water.
Figure 3.5 : Short description of Limnocharis flava (Waterhouse and Mitchell,
1998)
66
Scientific Name : Eichhornia crassipes
Local names
: Water hyacinth (English), Keladi bunting (Malay)
Family
: Pontederiaceae
Synonyms
: Eichhornia speciosa, Heteranthera formosa, Piaropus crassipes
Piaropus mesomelas and Pontederia crassipes
Description
: E. crassipes is a free-floating aquatic macrophyte growing
generally to 0.5 m in height. The individual plants consist of
several leaves in rosettes and are connected by stolons. The leaf
petiole is usually inflated, spongy, and up to 20 cm long. The
leaf blades are thickened, leathery, 2 to 15 cm long and 2 to 10
cm wide, sub orbicular, ovate or broadly elliptic with parallel
veins. Their roots are long, fibrous, branched root stocks hang
from the underside of the plant.
Habitat
:
Grow in a wide variety of aquatic habitats including lakes, ponds,
rivers, wetlands and marshes. It will grow most prolifically in
water of high nutrient content; it has been used in wastewater
treatment facilities.
Figure 3.6 : Short description of Eichhornia crassipes (Waterhouse and
Mitchell, 1998)
67
3.6
Media
In this study, the media used in the SSF constructed wetlands consists of a
layer of coarse stone with 15-20 mm diameter (2 cm), followed by a layer of fine
stone with 5-10 mm diameter (1 cm), a mixture of sand and soil with ratio (2:1)
(5 cm), a layer of soil at the surface (2 cm) and providing a porosity of 45%.
According to Pant et al. (2001), inexpensive materials such as sand for example, can
effectively removed phosphorus through sorption and their usage as root bed media
can increasing the efficiency of phosphorus removal in constructed wetland. The
gravels were cleaned first by washing with tap water before putting into the SSF tank
to free from debris which can block the flow of leachate through the media. The
water table in the bed was controlled and maintained 1 cm under the media surface
by an adjustable outflow pipe leading into a storage tank.
3.7
Sampling and Analysis
Water samples were taken two times each week for the duration of the study
from the influent and effluent of SSF wetland and at the effluent FWS wetland. Such
sampling was usually carried out at around 9 a.m. in each sampling date. After
termination of the each different concentration of leachate, the plants leaves and
roots were harvested for each constructed wetland and were analysed for heavy metal
(Fe and Mn). For roots and leaves, analysis samplings were carried out during initial
and after 3 weeks of treatment.
3.8
Analysis Procedure
All the laboratory analysis was done in Environmental Engineering
Laboratory of Faculty of Civil Engineering, UTM. The samples were analyzed for
SS, turbidity, NH4-N, NO3-N, PO43- and heavy metal (Fe and Mn). All the analytical
measurements were carried out according to DR/4000 Procedures and Standard
68
Methods (APHA, 2002). A table described the analytical method is shown in Table
3.2. Analysis procedures are described briefly as below:
Table 3.2 : The parameter observed in leachate analysis
Parameter
Method/Equipment
Method code
Source
NH4- N
Nessler Method
8038
DR/4000
NO3- N
Cadmium Reduction Method
8039
DR/4000
PO43-
Molybdovanadate Method
8114
DR/4000
Fe
FerroVer Method
8008
DR/4000
Mn
PAN Method
8149
DR/4000
Turbidity
Attenuated Radiation Method
10047
DR/4000
SS
Total Suspended Solids Dried at
APHA 2450-B
*SA
o
103-105 C
*SA = Standard Method
3.8.1
Analysis of Heavy Metals in Plant Tissues
After termination of the experiments, the plant’s leaves and roots were
harvested for each constructed wetland. Then, the leaves and the roots were washed
with tap water and distilled water. After that, the plant samples were dried in oven at
105˚C for 24 hour, and the dry weight of each component was measured. The
samples were then ground with mortar and pestle to a fine powder. And 0.5 - 3.0 g
of the ground plant sample was put inside the conical flask 250 ml and 50 ml of 2 M
hydrochloric acid was added in for plant digestion. The sample mixture was then
shaken overnight with orbital shaker. After that, the mixture was centrifuged for 20
minutes and filtered with cellulose acetate membrane 0.45 µm (Markert, 1994). The
filtrate was then analyzed for heavy metal (total iron and manganese) according to
the method mentioned above in Table 3.2. Figure 3.7 shows plant digestion for
analysis of heavy metal in plant tissues.
69
Figure 3.7 : Plants digestion for root and leaves.
3.9
Performance Evaluation
Pollutant loading rate (g/m2.day) was calculated by multiplying the hydraulic
loading rate (m/day) by the influent pollutant concentration (mg/L).
Pollutant
2
removal rate (g/m .day) was defined as hydraulic loading rate times the difference in
concentration between the influent and the effluent. The first-order plug flow kinetic
reaction was applied accordingly:
Ci
Co
=
k t)
e (-
Where,
Ci
=
effluent pollutant concentration, mg/L
Co
=
influent pollutant concentration, mg/L
k
=
first-order removal rate constant, day-1
t
=
nominal hydraulic retention time, day
(3.1)
CHAPTER 4
RESULTS AND DISCUSSIONS
4.1
Introduction
In this chapter, the results obtained from the two lab-scales of SSF-FWS
constructed wetland systems observation and experiment will be discussed in details.
The experiments were done two times and run for 18 days to get the data. The entire
results were analysed and plotted from the average data. The experiments period
were from July to end of August 2006. Water samples were taken two times each
week for the duration of the study and were analysed immediately. In this study, the
leachate analysis consists of nutrients, SS, turbidity, heavy metals removal. All data
will be carried out in graphical approach to evaluate the specific analysis processes.
Thus, an extensive discussion had been concluded in the behaviour obtained.
The analysis considers the removal efficiency and performance of the planted
and unplanted system as the control in landfill leachate treatment. Analysis of
variance (ANOVA) has been used to reveal significant differences between Control
and Planted system. Statistical significance differences were tested at p≤0.05 (95%
levels of significance). Individual system was analysed to discover the common
trends for individual wetlands. Removal efficiency from all SSF-FWS constructed
wetland was compared to evaluate overall performance trends representative of this
SSF-FWS constructed wetlands system design.
71
4.2
Basic Characteristics of the Landfill Leachate
The characterizations of the raw leachate samples in this study were analysed
before run the experiments. Basic characteristics of the influent landfill leachate
from the Pasir Gudang Landfill site are shown in Table 4.1. The inlet concentration
of NH4-N, NO3-N, PO43-, Fe, Mn, turbidity and SS were very high. All the nutrients,
SS, turbidity and heavy metals analysed are above the water quality standard. The
constituents in the leachate may vary depending on waste composition and weather.
Table 4.1 : Influent characteristics of the Pasir Gudang leachate
Parameter
Value (mg/L)
Ammonia Nitrogen (NH4-N)
84.5
Nitrate Nitrogen (NO3-N)
35.0
Orthophosphate (PO43-)
87.5
Suspended Solid (SS)
Turbidity
Ferum (Fe)
Manganese (Mn)
160
450
33.68
0.48
4.3
Nutrients Removal
Landfill leachate contained high concentration of nutrients as shown in Table
4.1.
Therefore, the performance of SSF-FWS constructed wetland system was
investigated to determine removal efficiency of nutrients from landfill leachate.
Three types of nutrients were studied in this study which was Ammonia nitrogen
(NH4-N), Nitrate nitrogen (NO3-N) and Orthophosphate (PO43-).
4.3.1
Ammonia Nitrogen
Ammonia nitrogen (NH4-N) is an undesirable constituent of many wastewater
discharges because of its toxicity to fish and considerable microbial oxygen demand
on receiving waters. NH4-N concentration is considered high in landfill leachate. In
72
this study, the system consisting of SSF-FWS constructed wetland vegetated with
Limnocharis flava and Eichhornia crassipes were effective for 18 days in reduction
high level of NH4-N. Significant reduction in concentration of NH4-N through the
SSF and FWS wetland was achieved after approximately 3 days of operation as
NH4-N Co ncentratio n (m g/L)
shown in Figure 4.1 and Figure 4.2.
100
Control
90
Planted
80
70
60
50
40
30
20
10
0
0
3
6
9
12
15
18
Time (days)
Figure 4.1 : NH4-N concentration profile in Control and Planted system through
NH4-N Concentration (mg/L)
SSF constructed wetland within 18 days of treatment
100
Control
90
Planted
80
70
60
50
40
30
20
10
0
0
3
6
9
12
15
18
Time (days )
Figure 4.2 : NH4-N concentration in profile in Control and Planted system
through FWS constructed wetland within 18 days of treatment
73
All the systems show the high reduction of NH4-N concentration as the time
increased. Concentrations of NH4-N through the SSF-FWS wetland were decreased
steadily from day 3 to day 18 of operations. Figure 4.3 illustrated that Planted
systems have the ability to removed NH4-N faster than Control system. After 18
days of treatment, the removal efficiencies for overall performance in Control and
Planted system for the SSF-FWS wetlands were achieved 78.1% and 93.1%
respectively. NH4-N removal followed the first order removal model, with rate
constants of 0.075 day-1 and 0.137 day-1 in Control and Planted systems. A higher
value of removal rate constant, k in Planted system would indicate a better NH4-N
removal mechanism compared than in Control system. The ANOVA test did reveal
a significant differences p≤0.05 between Control and Planted systems (Refer to
Appendix B). It can be concluded that NH4-N level were reduced more efficiently in
wetlands containing plants.
Control
Planted
1.00
0.80
C
= 1 . 02 e − 0 .075 t
Co
C/Co
0.60
0.40
C
= 1 . 03 e − 0 .137 t
Co
0.20
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.3: Comparison of NH4-N concentration (C/CO) for overall performance
in Control and Planted system through SSF-FWS constructed wetland
There are several mechanisms for the reduction of NH4-N, which are
volatilization, soil adsorption, plant uptake and nitrification (Watson et al., 1989;
IWA, 2000; Lim et al., 2002 and Paredes, 2003). Nitrogen transformation takes
place in the oxidized and reduced layers of media, the root-media interface and the
submerged portion of the emergent plants. At higher pH, some NH4-N which exists
74
in form of NH3 is lost to the atmosphere by the volatilization process (Lim, 2002).
NH4-N may be taken up in biota or transformed into nitrate. In addition, because of
it’s positively charge, NH4-N can be absorbed onto negatively charged soil particles
that can be deposited as sediment (Cronk and Fennessy, 2001). So, this fact was
supported the high removal efficiency in Control system. However, such removal is
not considered to be a long-term sink because the adsorbed NH4-N is released easily
when water chemistry conditions change (Kadlec and Knight, 1996).
Wetland plants will assimilate nitrogen as an important part of their
metabolism.
Limnocharis flava and Eichhornia crassipes have high nutrient
assimilative capacity and this mechanism was increased the NH4-N removal. From
the observation, the percentage of NH4-N removal in FWS wetland was higher than
in SSF wetland. This was because the floating plants tend to diffuse more oxygen
through their roots than emergent plants (Cronk and Fennessy, 2001). However,
plant uptake rates were only about one third of those reported for this species in
experimental systems where plants still in actively spreading (Tanner, 1996). This
concluded that plant uptake rates in the systems were almost moderately, but not
excessively, above normal levels likely to occur in treatment wetlands.
The major pathway for removal of ammonia nitrogen in constructed wetlands
is nitrification. Both systems had capability in NH4-N reductions as previously
shown in Figure 4.3. This was because the nitrification process was taking place
actively in both Control and Planted system. Nitrification process occurs in the
oxidized areas of substrate or water column, where NH4-N is oxidized to nitrite
nitrogen (NO2-N) by Nitrosomonas and eventually to NO3-N by Nitrobacter bacteria
(Cronk and Fennessy, 2001; Lim, 2002). Because the transformation of NH4-N
involves microbial processes, NH4-N removal is enhanced during the growing season
when high temperature stimulates microbial population growth (Cronk and Fennessy,
2001). However, nitrification processes were controlled by many factors, including
temperature, dissolved oxygen, pH, and alkalinity of the water, inorganic source,
microbial population and NH4-N concentration (Vymazal, 2005). It is clear that the
main role for NH4-N removal is played not by plants but microorganisms. The
substrate media such as gravel, soil and sand also support vegetation, provided
surface area and retain nutrient for microb.
75
However, the Planted system has greater removal efficiency compared to
Control because of the plants uptake and the root of the plants provided aerobic zone
for nitrification to be occurred (Lim and Polprasert, 1996). The plants also provided
surface areas for microbial attachment (Hammer, 1990). At the root-soil interface,
atmospheric oxygen diffuses into the rhizosphere through the leaves, stems, rhizomes
and roots of the wetland plants thus creating an aerobic layer. For these reason,
vegetated treatment wetlands are more efficient at removing ammonia than
unvegetated wetlands.
A review by Brix (1997) describes macrophytes plants encourage the
assimilation and breakdown of nutrients within a wetlands system. They have the
ability not only to bind high amounts of nutrients within their system, but also to
create an environment conducive to decreasing nutrients.
Macrophytes provide
surface area on their stems and leaves, which is necessary for microbial growth. The
roots provide a structure for microorganisms to perform the processes necessary for
transformation of nutrients. Moreover, roots not only provide a place for microbes
but also serve to decrease erosion and increase the levels of oxygen, which provides
for the oxidation of toxic substances like ammonia and nitrites.
4.3.2
Nitrate Nitrogen
In this study the system consisting of SSF-FWS constructed wetland
vegetated with Limnocharis flava and Eichhornia crassipes were effective for 18
days in reduction high level of NO3-N constituents in landfill leachate. During initial
stage, reduction of NO3-N concentration through the SSF wetland in Planted system
was negligible. NO3-N concentration in the effluent of the SSF wetland was higher
than influent concentration as shown in Figure 4.4, resulting in negative removal
efficiencies. Reduction of NO3-N concentration through the SSF wetland in Planted
system did not occur until around day 3 of operation. However, after approximately
6 days of operation SSF wetland show the improvement in NO3-N removal.
Conversely, significant reductions in concentration of NO3-N through the FWS
wetland for both systems were achieved after approximately 3 days of operation.
76
Subsequently, the FWS wetland showed consistently low nitrate concentration in its
effluent as shown in Figure 4.5. NO3-N concentration in SSF effluent was higher
than its influent due to both of systems were not stable at early stage. This is because
it begins to acclimatize with its environment (Lin et al., 2002).
45
Control
Planted
NO3-N Concentration (mg/L)
40
35
30
25
20
15
10
5
0
0
3
6
9
12
15
18
Time (days)
Figure 4.4 : NO3-N concentration profile in Control and Planted system through
NO3-N Concentration (mg/L)
SSF constructed wetland within 18 days of treatment
45
Control
40
Planted
35
30
25
20
15
10
5
0
0
3
6
9
12
15
18
Time (days)
Figure 4.5 : NO3-N concentration profile in Control and Planted system through
FWS constructed wetland within 18 days of treatment
77
Figure 4.6 shows trend of NO3-N reduction over time. After 18 days of
experiment, both systems show higher performance in NO3-N removal. From the
graph it can be seen that concentration of NO3-N through the SSF-FWS wetland in
both systems decreased steadily from day 3 to day 18 of operations. After 18 days of
treatment, the removal efficiencies for overall performance in Control and Planted
systems were 77.1% and 96.4% respectively.
As depicted in Figure 4.6, the
reductions of NO3-N in Planted systems were significantly (p≤0.05) higher than in
Control. The removal rate constant (k) for planted constructed wetland are 0.135
day-1 while for Control 0.07 day-1. This study of SSF-FWS wetlands demonstrated
that Planted system consistently exhibited greater NO3-N removal than did unplanted
Control system.
The ANOVA test did reveal a significant differences p≤0.05
between Control and Planted systems as shown in Appendix B.
Control
1.00
Planted
0.90
0.80
0.70
C
= 1 . 0 e − 0 . 07 t
Co
C/Co
0.60
0.50
0.40
C
= 1 . 05 e − 0 .135 t
Co
0.30
0.20
0.10
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.6 : Comparison of NO3-N concentration (C/CO) for overall
performance in Control and Planted system through SSF-FWS constructed
wetland
Studies have shown that NO3-N concentration levels were reduced more
efficient in wetlands containing plants. This was because NO3-N is not immobilized
by soil minerals and remains in the water column or pore water of the sediments.
Previous studies (Ingersoll and Baker, 1998; Baker, 1998) showed that NO3-N
removal in wetlands occurred through plant uptake and denitrification. However,
78
denitrification is only one mechanism for NO3-N removal in the FWS wetland. And
also, with high NO3-N loading rates typical in treatment wetlands, denitrification is
generally considered the dominant mechanism of NO3-N loss. Denitrification is
carried out by microorganisms under anaerobic i.e. anoxic conditions, with NO3-N as
the terminal electron acceptor and organic carbon as the electron donor (EPA, 1993).
That is to say, the reaction occurs in the absence of oxygen and requires an organic
carbon source.
Also, the low NO3-N levels in planted constructed wetlands can be explained
by heterotrophic competition with nitrificants for oxygen (Focht and Verstraete,
1977). Experiments with plants such as Limnocharis flava and Eichhornia crassipes
also demonstrated that NO3-N removal from sediments is enhanced in the presence
of macrophytes. Gersberg (1986) contends that the high NO3-N removal is due to a
stimulation of denitrification by the supply of organic material from the
macrophytes. In wetlands, the organic carbon was supplied mainly by the vegetation
and it was used as a carbon and energy sources for heterotrophic bacteria, such as the
denitrifying bacteria (Bastviken et al., 2005). When sufficient carbon is available for
microbial metabolisms, denitrification is enhanced (Watson et al., 1989; EPA, 1993;
Cronk and Fennessy, 2001; Lim, 2002). Decomposing wetland plants and plant root
exudates are potential sources of biodegradable organic carbon for denitrification
(EPA, 1993). This link between vegetation and carbon availability is one of the
ecologically critical features of effective treatment of high nitrogen loadings.
Consequently, NO3-N later which is either taken up by the plants or diffuses into the
reduced zone where it is converted to nitrogen gases, N2 and nitrogen oxide, N2O by
the denitrification process (Watson et al., 1989; IWA, 2000; Lim et al., 2002 and
Paredes, 2003). Both N2 and N2O are released to the atmosphere.
4.3.3 Orthophosphate
Orthophosphate (PO43-) concentration was high in the initial leachate landfill
as previously shown in Table 4.1. In this study, the system consisting of SSF-FWS
constructed wetland vegetated with Limnocharis flava and Eichhornia crassipes
79
were effective for 18 days in reduction high level of PO43-. From the observation,
PO43- concentration reduction in the SSF effluent were stable and consistently lower
than in the FWS effluent, and it followed the trend of the FWS effluent. Figure 4.7
and Figure 4.8 shows PO43- concentration in Control and Planted system through the
SSF and FWS constructed wetland. Respectively, both systems show the significant
reductions in concentration of PO43- through the SSF-FWS wetland.
Control
Planted
100
3-
PO4 Concentration (mg/L)
90
80
70
60
50
40
30
20
10
0
0
3
6
9
12
15
18
Time (days)
Figure 4.7 : PO43- concentration profile in Control and Planted system through
SSF constructed wetland within 18 days of treatment
Control
Planted
30
20
15
10
3-
PO4 Concentration (mg/L)
25
5
0
0
3
6
9
12
15
18
Time (days)
Figure 4.8 : PO43- concentration profile in Control and Planted system through
FWS constructed wetland within 18 days of treatment
80
Figure 4.9 represents overall performance of Control and Planted through
SSF-FWS constructed wetland systems in removing of PO43-. After 18 days of
operation, both systems had the capability to reduce PO43- concentration in leachate.
From the graph it can be seen that concentration of Fe decreased more rapidly after 3
days of operation and decreased steadily from day 3 to day 12 and then stay constant
after that.
The PO43- removal efficiency can be considered high for the entire
systems, more than 90%. The removal efficiencies of PO43- for overall performance
in Control and Planted system through the SSF-FWS constructed wetland systems
were achieved 92.4% (k = 0.236 day-1) and 95.9% (k = 0.337 day-1), respectively.
Based on removal rate constant, k value for Planted system was slightly higher than
Control in removing of PO43-..
From analysis ANOVA, there was significant
different (p≤0.05) between Control and Planted systems in PO43- removal as shown
in Appendix B.
Control
1.00
Planted
0.80
C/Co
0.60
C
= 0 .94 e − 0.236 t
Co
0.40
0.20
C
= 0 .97 e − 0 .337 t
Co
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.9 : Comparison of PO43- concentration (C/CO) for overall performance
in Control and Planted system through SSF-FWS constructed wetland
The PO43- removal capacity of constructed wetlands depends on the physical,
chemical and microbiological processes, which influence PO43- incorporation in both
inorganic and organic forms in wetland sediments. PO43- removal in wetlands takes
place by plant uptake, accretion of wetland soils, microbial immobilization, retention
by root bed media, and precipitation in the water column (Pant et al., 2001). PO43-
81
may be deposited onto the wetland system sediment by sedimentation or entrapped
within the emergent macrophytes stem matrix and attached onto biofilms (EPA,
1993). Sand that was used as the media is a better system to remove PO43- from
wastewater. Sand can effectively remove PO43- through sorption and its use as root
bed media could enhance the efficiency of constructed wetlands to remove PO43from effluents (Aeslina, 2004).
As suspended solid settle, the sorbed PO43- is
removed from water column.
PO43- also sorbs to oxides and hydroxyoxides of iron and aluminium and to
calcium carbonate. There is a finite supply of these minerals in the sediments, and
inorganic phosphorus must come in direct contact with the sediments before it can
retained there (Cronk and Fennessy, 2001). Under reduced conditions, PO43- is
released the reduction of ferric, Fe3+ phosphate compounds to more soluble ferrous,
Fe2+ forms. If the soil is not vegetated such as in Control system, this released PO43diffuses back to surface waters. However, when plants are present, such as in
Planted system, the wetland plants were assimilated the released PO43- and prevent
its movement out of the sediments (Cronk and Fennessy, 2001). PO43- may be
broken down to inorganic forms such as HPO42- through microbial enzyme activity.
Dissolved organic PO43- and insoluble inorganic and organic PO43- are not usually
available to plants until transformed to a soluble inorganic form. These
transformations may take place in the water column by way of suspended microbes
and in the biofilms on the emergent plant surfaces and in the sediments (EPA, 1993).
Finally, floating and emergent macrophytes, as well as algae take up varying
amounts of PO43- (Debusk, 1999).
Uptake by the macrophytes occurs in the
sediment pore water by the plant root system.
4.4
Suspended Solid Removal
Suspended solid (SS) concentration was high in the initial leachate landfill as
previously shown in Table 4.1. High SS will put a greater stress on the water body
because too much SS in water can adversely affect the light penetration and
photosynthetic activity and hence fish and other aquatic life would be intolerant
82
adaptation. As depicted in Figure 4.10 and Figure 4.11, both systems show the
concentration of SS through the SSF and FWS wetland in both systems decreased
steadily from day 3 to day 18 of operations.
Control
200
Planted
180
SS Concentration (mg/L)
160
140
120
100
80
60
40
20
0
0
3
6
9
12
15
18
Time (days)
Figure 4.10 : SS concentration profile in Control and Planted system through
SSF constructed wetland within 18 days of treatment
200
Control
Planted
180
SS Concentration (mg/L)
160
140
120
100
80
60
40
20
0
0
3
6
9
12
15
18
Time (days)
Figure 4.11 : SS concentration in profile in Control and Planted system through
FWS constructed wetland within 18 days of treatment
83
Figure 4.12 represents overall performance of Control and Planted system
through the SSF-FWS constructed wetland in removing of SS. After 18 days of
operation, both systems had the capability to reduce SS concentration in leachate.
The removal efficiencies of SS for overall performance in Control and Planted
system through SSF-FWS constructed wetland were achieved 75.9% (k = 0.076
day-1) and 87.3% (k = 0.106 day-1), respectively at the end of operations.
As
depicted in Figure 4.12, the reductions of SS in Planted systems were significantly
(p≤0.05) higher than in the Control as shown in Appendix B.
1.00
Control
Planted
0.80
C
= 1 .04 e − 0 .076 t
Co
C/Co
0.60
0.40
C
= 1 .03 e − 0 .106 t
Co
0.20
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.12 : Comparison of SS concentration (C/CO) for overall performance in
Control and Planted system through SSF-FWS constructed wetland system
The removal of SS in constructed wetlands is achieved through several
mechanisms. Settleable solids are removed easily by sedimentation since wetland
systems generally have long HRT. Nonsettling or colloidal solids are removed by
processes which include; straining of sand media, adsorption on plants and wetland
media and biodegradation.
The types of removal mechanism at work are very
dependent on the size and nature of solids present in the wastewater and the types of
filter media used (Lim, 2002). Control and Planted systems shows the significant
different in SS removal. Therefore, studies have shown that SS concentration levels
were reduced more efficient in wetlands containing plants especially in SSF-FWS
wetland.
This was because the presence of macrophytes stands reduces water
84
velocity and allows for the filtering and settling of organic particulate matter; other
suspended solids, and associated nutrients.
With decreased water velocity, the
contact time between the wastewater and the sediments and plant surface area is
increased, thus adding to the potential treatment of the waste by adsorption or
microbial processes (Carpenter and Lodge, 1986; Cronk and Fennessy, 2001).
Most of the solids are removed through sedimentation and filtration in SSF
wetland and settling process in FWS wetland, and all the processes are based on
velocities of flow (Lim, 2002). In this case, wetland plants which were planted in
both wetlands were obstructed the flow and reduces the influent velocity. Once the
velocity was reduce, sedimentation, filtration and settling processes of wetlands
effectively removed SS. This was because the influent moves slowly, SS settle out
and creating sediment at the bottom of the wetlands. Besides, sand and soil in SSF
wetland helps to settle out the solids and effluents slowly filters before the end
product is released into FWS wetland (Cronk and Fennessy, 2001; Mashhor et al.,
2002).
In Control system, SS reduction is attributed to filtering action as wastewater
passes through the bed media. SS are removed by wetlands due to the filtering
action of the bed media.
Microorganisms are removed by die-off, straining,
sedimentation, entrapment and adsorption (Metcalf and Eddy, 1991). Besides, plant
surfaces in the water column are coated with an active biofilm of periphyton. This
biofilm can adsorb colloidal and supracolloidal particles as well as absorb soluble
molecules (EPA, 1993).
4.5
Turbidity
Turbidity is a measure of the cloudiness of the water. Sediment, algae,
bacteria and zooplankton all contribute to what is technically known as the TSS that
increases the turbidity.
As turbidity increases, the degree to which sunlight
penetrates the water column declines (EPA, 1993).
In this study, the system
consisting of SSF-FWS constructed wetland vegetated with Limnocharis flava and
85
Eichhornia crassipes were effective for 18 days in reduction high level of turbidity.
As shows in Figure 4.13 and Figure 4.14 respectively, turbidity value reductions in
the FWS effluent were stable and consistently lower than in the SSF effluent.
500
Control
450
Planted
Turbidity (NTU)
400
350
300
250
200
150
100
50
0
0
3
6
9
12
15
18
Time (days)
Figure 4.13 : Turbidity measure in Control and Planted system through SSF
constructed wetland within 18 days of treatment
250
Control
Planted
Turbidity (NTU)
200
150
100
50
0
0
3
6
9
12
15
18
Time (days)
Figure 4.14 : Turbidity measure in Control and Planted system through FWS
constructed wetland within 18 days of treatment
86
From the graph it can be seen that turbidity decreased more rapidly after 3
days of operation and decreased steadily from day 3 to day 18 of operations.
Turbidity value more rapidly decreased for all the wetlands due to the sorption on the
new sand and soil media. During the next 15 days of operation, the turbidity value
decreased gradually at the outlet due to the sand and soil already saturated with
solids particles. Figure 4.15 shows the trend of turbidity reduction over time.
Control
1.00
Planted
C/Co
0.80
0.60
0.40
0.20
C
= 0 .97 e − 0 .251 t
Co
C
= 0 .98 e − 0 .306 t
Co
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.15 : Comparison of turbidity value (C/CO) for overall performance in
Control and Planted system through SSF-FWS constructed wetland system
Due to good removal efficiency of SS in both systems, reductions of turbidity
in both systems after FWS wetland is also high.
The removal efficiencies of
turbidity for overall performance in Control and Planted system through SSF-FWS
constructed wetland were achieved 98% (k = 0.251 day-1) and 99.6% (k = 0.306
day-1), respectively after 18 days of operation. As depicted above in Figure 4.15, the
reductions of turbidity in Planted systems were significantly (p≤0.05) higher than in
the Control as shown in Appendix B. However, turbidity removal rate constants for
Control and Planted system in this study were high. This result might be caused by
the high turbidity removal efficiency in both systems. After 18 days of operation,
both systems had the capability to reduce turbidity value in landfill leachate. This
was subsequently affected from the highest SS removal as shown previously in
Figure 4.12. As previously mention, SS concentration was contributed the turbidity
87
value. In this study, the reduction of SS was high and this result was influence the
removal of turbidity. That means the removal of turbidity in constructed wetlands is
achieved through several mechanisms which is similar like SS removal.
Turbidity reduction in constructed wetlands is best facilitated through the
encouragement of settling.
Densely vegetated wetland facilitate the settling of
suspended matter by obstructing water flows, stabilizing bottom sediments and
physically filtering and trapping the matter (Galbrand, 2003). Sedimentation and
filtration mechanisms of constructed wetlands effectively removed fine particle of
organic and inorganic matter, and at the same time reduced turbidity (Lin et al.,
2005). In this study, treatment wetlands that use emergent and floating plants such
as Limnocharis flava and Eichhornia crassipes, the plants act as a filter, straining
wastewater and retaining solids in their dense roots.
It’s so obvious that by
comparing Limnocharis flava and Eichhornia crassipes bed to unplanted bed,
turbidity decreased up to 6 % after 5 days of treatment. With a decreased in turbidity
came a reduction in suspended organic matter, which resulted in a decreased in BOD
(Reddy et al., 1983).
4.6
Heavy Metals Removal
Iron and manganese were present at relatively high concentrations in the
leachate, but were efficiently removed by the wetland treatment system. Probable
removal mechanisms are plant uptake and probably more importantly, precipitation
and sedimentation of Fe and Mn oxide (Debusk, 1999).
4.6.1
Ferum
Heavy metals concentrations is of great concern due to their serious effects
on food chain and furthermore on animal and human health (EPA, 1993). Ferum
(Fe) reduction during experiments for both SSF and FWS constructed wetland were
88
shown in Figure 4.16 and Figure 4.17.
Respectively, both systems show the
significant reductions in concentration of Fe through the SSF-FWS wetland. The
results also show that effluent concentration was decreasing after 18 days in all
systems.
40
Control
Planted
Fe Concentration (mg/L)
35
30
25
20
15
10
5
0
0
3
6
9
12
15
18
Time (days)
Figure 4.16 : Fe concentration profile in Control and Planted system through
SSF constructed wetland within 18 days of treatment
16
Control
Planted
Fe Concentration (mg/L)
14
12
10
8
6
4
2
0
0
3
6
9
12
15
18
Time (days)
Figure 4.17 : Fe concentration profile in Control and Planted system through
FWS constructed wetland within 18 days of treatment
89
Fe was efficiently removed in both wetlands systems as illustrated in Figure
4.18. From the graph it can be seen that concentration of Fe decreased more rapidly
after 3 days of operation and decreased steadily from day 3 to day 12 and then stay
constant after that.
The removal efficiencies of Fe for overall performance in
Control and Planted were 97.2% and 99.5%, respectively after 18 days of operation.
Fe removal followed the first order removal model, with rate constants of 0.286 day-1
and 0.43 day-1 in Control and Planted systems. In this study, Fe removal rate
constants for both Control and Planted systems were high. This result might be
caused by the high Fe removal efficiency in both systems.
In this study, the
reductions of Fe in Planted systems were slightly higher (p≤0.05) than in the Control.
Control
1.00
Planted
0.80
C/Co
0.60
0.40
C
= 0 . 97 e − 0 .286 t
Co
C
= 0 . 99 e − 0 .43 t
Co
0.20
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.18 : Comparison of Fe concentration (C/CO) for overall performance in
Control and Planted system through SSF-FWS wetland
From the results, this phenomenon might be explained. Emergent plants and
floating plants help in reducing heavy metals by retaining it either in the root or in
the leaves. Plants species have variety of capacity in accumulating and removing
heavy metals. Uptake and accumulation of elements by plants may follow two
different paths, i.e., the root system and foliar surface (Sawidis et al., 2001). The
results indicated that Limnocharis flava and Eichhornia crassipes could accumulate
significant amount of Fe concentration. Wetland plants, however, can influence
metals removal and storage indirectly through their effects on hydrology, sediment
90
chemistry and microbial activity. However, it is important to know that although
plants uptake is a direct way to remove heavy metal by vegetation, the amount of
heavy metal removed by uptake is not significant comparing to other removal
mechanisms.
It’s so obvious that by comparing Limnocharis flava and Eichhornia
crassipes bed to unplanted bed, both of Planted and Control system were achieved
high Fe removal percentage at the end of operations. The greater heavy metals
removal in the Control system maybe was due to clogging of the substrate in soil
sediment. So it can be concluded that, reduction of heavy metal concentration in the
Planted and Control system were most likely due to chemical precipitation and
sorption on sediment, and aided by the macrophytes.
Other possible removal processes include precipitation as metal hydroxides in
the aerobic zone. It is also believed that an external aerobic microzone can be
established around parts of the growing roots (Armstrong and Armstrong, 1990). As
a result, iron is precipitated. It is suggested Fe precipitated as a result of oxygen
release from the roots (Peverly et al., 1995). In this study, the reduction of nitrate
was high and this result was influence the removal of Fe. The reasons are because
some of the microorganisms involved in Fe reduction can also reduce nitrate. They
favor nitrate, so the reduction of Fe starts once nitrate has been depleted (Cronk and
Fennessy, 2001).
4.6.2
Manganese
Manganese (Mn) which is most commonly present in landfill leachate at high
concentration and present in it reduced forms (Mn2+), which is one of the heavy
metals concern in this study. In this study, the system consisting of SSF-FWS
constructed wetland vegetated with Limnocharis flava and Eichhornia crassipes
were effective for 3 weeks in reduction high level of manganese from landfill
leachate.
As depicted in Figure 4.19 and Figure 4.20, both systems show the
significant reductions in concentration of Mn through the SSF-FWS wetland. The
91
results also show that effluent concentration was decreasing after 18 days in all
reactors. From the graph it can be seen that concentration of Mn through the SSFFWS wetland in both systems decreased steadily from day 3 to day 18 of operations.
Control
0.60
Planted
Mn Concentration (mg/L)
0.50
0.40
0.30
0.20
0.10
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.19 : Mn concentration profile in Control and Planted system through
SSF constructed wetland within 18 days of treatment
Control
Planted
0.50
0.45
Mn Concentration (mg/L)
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.20 : Mn concentration profile in Control and Planted system through
FWS constructed wetland within 18 days of treatment
92
Mn was also decreasing significantly in Control and Planted systems as
shown in Figure 4.21. From the graph it can be seen that concentration of Mn
decreased more rapidly after 3 days of operation and decreased steadily from day 3
to day 12 and then stay constant after that. The removal efficiency which was more
than 90% was achieved for all the treatment systems after 18 days of treatment. It
shown the highest removal of Mn determined by Planted system (97.7%), followed
by Control (95.6%). The removal rate constant (k) for Mn is slightly higher in
Planted (k= 0.16 day-1) compared to Control system (k= 0.137 day-1). It shows that
Mn concentration is only slightly decreased in Planted system compared than in
Control system.
The ANOVA test did reveal a significant differences p≤0.05
between Control and Planted systems as shown in Appendix B.
Control
1.00
Planted
0.80
C/Co
0.60
0.40
0.20
C
= 1 .03 e − 0 .137 t
Co
C
=1 . 02 e − 0 .16 t
Co
0.00
0
3
6
9
12
15
18
Time (days)
Figure 4.21 : Comparison of Mn concentration (C/CO) for overall performance
in Control and Planted system through SSF-FWS wetland
In this study, the unplanted system also demonstrated high reduction of Mn.
This results shows that the amount of heavy metal removed by Limnocharis flava
and Eichhornia crassipes plants uptake is not significant comparing to other removal
mechanisms. The reduction of Mn in SSF wetland system maybe was due to settling
and sedimentation, uptake by algae and bacteria, precipitation as insoluble salts, and
binding to soil, sediments and particulate (Kadlec and Knight, 1996; Lim, 2002).
Sedimentation has long been recognized as the principle process in removal of heavy
93
metals from waste water in natural and constructed wetlands. It is not a simple
straightforward physical reaction. Other chemical processes like precipitation and
co-precipitation have to occur first. Precipitation and co-precipitation in the removal
of heavy metals is an important adsorptive mechanism in wetland sediments.
Meanwhile, in sediments heavy metals are adsorbed to the soil particles by either
cation exchange or chemisorptions (Sheoran and Sheoran, 2005).
However, the reduction of Mn in Control system still showed lower Mn
removal if compared with performance of Planted system. This result suggests that
macrophytes could induce higher Mn removal in wetland. It can be concluded that
wetland plants are an integral part of the Mn removal in SSF-FWS wetlands. Plants
mechanisms for metals removal in wetlands include adsorption, chemical
precipitation and plant uptake (Reed et al., 1995). Several processes are envisioned
as being effective in pollutant reduction; for example metals are taken up by plants,
and in many cases stored preferentially in the roots and rhizomes (Kadlec, 1999).
Manganese, a micronutrient is reduced from Mn4+ to Mn2+ at a redox potential. The
transformation is a microbial process. The reason is in the reduced form, Mn2+ is
slightly more available to plants than in the oxidized form Mn4+ (Cronk and
Fennessy, 2001).
4.7
Heavy Metal in Plant’s Tissues
Biological removal is perhaps the most important pathway for heavy metal
removal in the wetlands. Probably the most widely recognized biological processes
for metal removal in wetlands is plant uptake (Sheoran and Sheoran, 2005).
Therefore, analysis of the roots and leaves were done at the beginning of experiment
before the plants planted in the constructed wetland and at the end of experiment.
As the results, concentration of Fe was significantly greater in roots
compared to in leaves with the highest accumulation by Limnocharis flava in SSF
wetlands system, followed by Eichhornia crassipes in FWS wetlands, which were
209.5 μg/g dry weight, and 102.2 μg/g dry weight, respectively. While, Fe uptake in
94
the leaves of the Limnocharis flava and Eichhornia crassipes were 29 μg/g dry
weight and 58.4 μg/g dry weight, respectively. From the study, it shows that heavy
metal uptake is more significant in roots compare to leaves as illustrated in Figure
4.22. The highest total accumulation of Fe was achieved by Limnocharis flava in
SSF wetlands system which was 238.5 μg/g dry weight followed by Eichhornia
crassipes in FWS wetlands, 160.6 μg/g dry weight in roots and leaves.
500
Limnocharis
flava
Limnoclaris
flava
Fe conc. (ug/g dry weight)
450
Eichhornia
Eichhorniacrassipes
crassipes
400
350
300
250
200
150
100
50
0
Initial
Root
Final
Root
Initial Final
Leaves Leaves
Initial Final
Root Leaves
Initial Final
Leaves Leaves
Plants Tissues
Figure 4.22 : Heavy metal (Fe) accumulation by Limnocharis flava and
Eichhornia crassipes in SSF-FWS wetland systems
Figure 4.23 shows that concentration of Mn was significantly greater in root
compared to in leaves with the highest accumulation by Limnocharis flava in SSF
wetlands system, followed by Eichhornia crassipes in FWS wetlands, which were
6.52 μg/g dry weight, and 4.8 μg/g dry weight, respectively. While, Mn uptake in
the leaves of the Limnocharis flava and Eichhornia crassipes were 1.18 μg/g dry
weight and 1.48 μg/g dry weight, respectively. The highest total accumulation of Mn
was achieved by Limnocharis flava in SSF wetlands system which was 7.7 μg/g dry
weight followed by Eichhornia crassipes in FWS wetlands, 6.28 μg/g dry weight in
roots and leaves. The results proved that leaves of Limnocharis flava and Eichhornia
95
crassipes have less ability for metal accumulation than roots.
The study also
demonstrated that the uptake of Fe by plants was higher compared to Mn.
9
Limnocharis
flava
Limnoclaris
flava
Mn conc. (ug/g dary weight)
8
Eichhorniacrassipes
crassipes
Eichhornia
7
6
5
4
3
2
1
0
Initial
Root
Final
Root
Initial
Final
Leaves Leaves
Initial
Root
Final
Leaves
Initial
Final
Leaves Leaves
Plants Tissues
Figure 4.23 : Heavy metal (Mn) accumulation by Limnocharis flava and
Eichhornia crassipes in SSF-FWS wetland systems
One of the major mechanisms of heavy metal removal is due to plants uptake.
Plants have the ability to accumulate nutrient including heavy metals from soil and
wastewater (Cronk and Fennessy, 2001; Aeslina, 2004; Thien, 2005). Emergent
plants and floating plants help in reducing heavy metals by retaining it either in the
root or in the leaves. The high accumulation of heavy metal in Limnocharis flava
was due to the plant that had many shorter roots that were able to create aeration
zones for heavy metal uptake (Krishnan, 2002).
Study by Soltan and Rashed (2001) reported that Eichhornia crassipes only
effectively removes appreciable quantities of heavy metals, especially at low
concentrations, whilst it releases small quantities of heavy metals at wilting. This
fact supported low concentration of heavy metals accumulates in roots and leaves of
Eichhornia crassipes because at the end of experiments, Eichhornia crassipes cannot
survive in leachate constituents and begin to wilt. The study also observed that
96
Limnocharis flava had capability to survive with leachate constituents compared than
Eichnornia crassipes.
According to previous study, it shows that heavy metal uptake is more
significant in roots compare to the leaves (Cooly and Martin, 1979; Peverly et al.,
1995; Pant et al., 2001; Thien, 2005; Noor Ida Amalina, 2006). These roots have
been reported to be the most beneficial for phytostabilisation of the metal
contaminants. Denny (1987) and Greenway (1997) also reported that the main route
of heavy metal uptake in wetland plants was through roots in emergent and surfacefloating. Greenway and Simpson (1996); Polprasert et al. (1996); Greenway (1997);
and Scholes et al. (1998) reported that roots of the wetlands play very important role
in wastewater purification followed by stem and leaves.
A limited uptake or
translocation of metals is suggested by higher concentrations of roots than leaves.
Meanwhile, plaques of iron and manganese oxyhydroxides often form on
waterlogged roots (Vest and Allaway, 1997), and co-precipitation of other metals in
these plaques is one process to explain the elevated concentrations found in roots.
As depicted previously in Figure 4.22 and Figure 4.23, the result shows that
Mn uptake by plants was less than Fe. Recently, study by Thien (2005) and Noor Ida
Amalina (2006) also reported that the amount of Fe uptake by plants was higher
compared to Mn in plants tissues. Fe2+ was the micronutrient for plants that was
required in higher concentration than Mn2+ (Kamal et al., 2004). Additionally, plants
require a small amount of Mn, high level of Mn interfere with enzyme structure and
nutrient consumption. Actually the role and potential importance of plants uptake
and storage of heavy metals are poorly understood in wetland treatment system. The
rate of heavy metal uptake is controlled by the plants growth rate and the
accumulation of heavy metals in the plants tissues (Cronk and Fennessy, 2001).
4.8
Comparison with Other Researchers
The results of several studies on constructed wetlands of leachate treatment
are presented in Table 4.2. This table shows the comparison between this study and
97
the other researchers. It shows that leachate treatment using combine SSF-FWS
constructed wetlands (CWs) have better performance in nutrient and heavy metals
removal compare than by using one-single type of constructed wetlands system.
Table 4.2 : Comparison of different models of constructed wetlands for landfill
leachate treatment
Type of CWs
and Plants
NH4-N
(%)
NO3-N
(%)
PO43(%)
SS
(%)
Fe
(%)
Mn
(%)
UTM, Malaysia
Ain Nihla
(2006)
SSF-FWS
CWs with
L.flava and
E.crassipes
>93%
>96%
>95%
>87%
>99%
>97%
UTM, Malaysia
Noor Ida
Amalina (2006)
FWS CWs
with magnetic
field and E.
crassipes
>64%
>90%
>59%
-
>100%
>87%
UTM,Malaysia
Thien (2005)
FWS CWs
with
E.crassipes
>25%
>60%
>15%
-
>60%
>50%
UTM, Malaysia
Aeslina (2004)
Horizontal
(SSF)
Thypa
Angustifolia
Safety Flow®
>90%
>60%
>80%
-
-
-
University of
Windsor, ElGendy (2003)
FWS CWs
with
E.crassipes
and salvinia
>100%
-
>97%
-
>84%
-
UTM, Malaysia
Rafidah (2003)
Vertical (SSF)
S.Sumatrensis
And
S.Mucronatus
-
-
-
-
>95%
>91%
Norway,
Maehlum (1995)
Horizontal
(SSF)
P. Australis
And
T.Latifolia
>70%
-
>70%
-
-
-
Site and
Researchers
98
However, study by Noor Ida Amalina (2006) also show high heavy metals
removal efficiency compared to others system.
This was due to the effects of
magnetic field in treating landfill leachate. Rafidah (2003) also reported high heavy
metals (Fe and Mn) removal by using vertical (SSF) planted with S.sumatrensis and
S.mucronatus. The reason might be because the effect on using two types of plants
such as S.sumatrensis and S.mucronatus in one constructed wetland system which is
can increased the removal of heavy metals in landfill leachate. In this study, Rafidah
(2003) was also remarked that the removal rate for nutrient and heavy metal depends
directly with time. The more the contact time between leachate and vegetation in the
wetland system, was better the removal rate.
Meanwhile, the treatment systems of El-Gendy (2003) showed the best
performance in removal of NH4-N and PO43- from landfill leachate which is achieved
100% and 97% respectively. El-Gendy (2003) also reported that by using two types
of plants such as E.crassipes and salvinia in FWS constructed wetland system can
enhanced the removal efficiency of nutrients from landfill leachate. So, it can be
concluded that use of multi-types of plants rather than mono-types of plants in
wetland systems also gives higher removal either in nutrient or heavy metals
removal.
4.9
Conclusion
As the conclusion, the SSF-FWS wetland system was proven effective in
pollutants removal in leachate. From the results, this study has demonstrated that
both systems (i.e. Planted and Control) of the experiments had the ability to reduce
all the parameters measured. However, the removal efficiency obtained from this
study indicated that Planted system with Limnocharis flava and Eichhornia crassipes
had the highest percentage of removal compared to unplanted Control system.
Significant differences were revealed by ANOVA between systems at p≤0.05 for
NH4-N, NO3-N, PO43-, SS, turbidity and heavy metals (Fe and Mn) removal.
Overall, Planted system had shown the best operating system for removal of
measured parameters during this study.
99
According to the study, removal efficiency of nutrients from landfill leachate
in the form of NH4-N, NO3-N and PO43- by Planted system through the SSF-FWS
constructed wetland were achieved 93.1%, 96.4% and 95.9% respectively after 18
days of operations. Removal of heavy metals by SSF-FWS constructed wetland with
Limnocharis flava and Eichhornia crassipes were achieved Fe (99.5%) and Mn
(97.7%) after end of treatment. And, also removal efficiency of SS and turbidity
were achieved 87.3% and 99.6% respectively. While, removals of nutrients by
unplanted system were achieved 78.1% of NH4-N, 77.1% of NO3-N and 92.4% of
PO43-. Removals of heavy metals by unplanted system were achieved 97.2% of Fe
and 95.6% of Mn. In unplanted Control system also shows removal 75.9% of SS and
98% of turbidity.
In this study, gravel, sand and soil that were used as the media are also an
effective combination to remove pollutants.
However, it was observed that
Limnocharis flava and Eichhornia crassipes did attribute to nutrients and heavy
metals removal. It is because macrophytes in leachate treatment play an important
role in constructed wetlands by providing microbial attachments, sufficient leachate
residence time, trapping and settlement of suspended leachate components. These
were results of resistance to hydraulic flow, surface area for pollutant adsorption,
uptake and storage in plant tissues, roots or leaves and diffusion of oxygen from
aerial parts to the rhizosphere.
The study showed Limnocharis flava and Eichhornia crassipes had higher
capacity to accumulate heavy metals (Fe and Mn) in roots compared than in leaves.
Fe uptake in the root and leaves of the Limnocharis flava were 209.5 μg/g dry weight
and 29 μg/g dry weight, and by Eichnornia crassipes were 102.2 μg/g dry weight
and 58.4 μg/g dry weight respectively. While, Mn uptake in the root and leaves of
the Limnocharis flava were 6.52 μg/g dry weight and 1.18 μg/g dry weight, and by
Eichnornia crassipes were 4.8 μg/g dry weight and 1.48 μg/g dry weight,
respectively.
CHAPTER 5
CONCLUSION
5.1
Conclusion
Constructed wetland is one of approaches that can promotes the best
achievement in nutrient and heavy metal removal and also enhance landfill leachate
water quality. In this study, a combination system utilizing a SSF-FWS constructed
wetland systems have shown higher performance in treating landfill leachate. The
results demonstrated that nutrients and heavy metals removal can be increased up to
90% by applying SSF-FWS constructed wetland systems. The performance of SSFFWS constructed wetland was evaluated with comparison to Control systems
(without plants). The SSF-FWS constructed wetland planted with Limnocharis flava
and Eichhornia crassipes shows the higher performance than unplanted constructed
wetlands for all parameters evaluated.
The results indicated that the removal efficiency of nutrients, and heavy
metals in leachate using Limnocharis flava and Eichhornia crassipes were achieved
NH4-N (93.1%), NO3-N (96.4%), PO43- (95.9%), Fe (99.5%) and Mn (97.7%) after
end of the treatment. And, also removal efficiency of SS and turbidity were achieved
87.3% and 99.56% respectively.
While, in Control system shows removal of
nutrients, SS, turbidity and heavy metals (Fe and Mn) were NH4-N (78.1%), NO3-N
(77.1%), PO43- (92.4%), SS (75.9%), turbidity (98% ), Fe (97.2%) and Mn (95.6%).
101
Control system has almost the same performance with the Planted systems in
PO43-, turbidity and heavy metals removal. Difference between the performances of
both systems was less than 5% in these parameters removal. Therefore, it can be
concluded that Limnocharis flava and Eichhornia crassipes have little enhancement
in PO43-, turbidity and heavy metals removal. The role of the plant was more
obvious in NH4-N, NO3-N and SS removal with 15%, 19% and 11% better than the
Control system, respectively.
Limnocharis flava had higher capacity to accumulate heavy metals (Fe and
Mn) in leachate constituents compared than Eichhornia crassipes.
From the
analysis, it shows that Fe and Mn uptake by Limnocharis flava and Eichhornia
crassipes is more significant in roots compare to leaves. The study also observed that
Eichhornia crassipes planted in the FWS beds were notable less vigorous and
healthy than Limnocharis flava in the SSF beds. So, it can be concluded that
Limnocharis flava had capability to survive with leachate constituents compared than
Eichhornia crassipes.
5.2
Recommendations
Recommendation will be given in order to further enhance the applicability of
the findings in this study, the soundness of which has been well demonstrated in this
study:
(i)
Further studies should vary the flow rates, HLR, retention time, type
of plants and size of constructed wetlands system in order to
determine the efficient of pollutants removal;
(ii)
Further studies are recommended to analyse accumulation of nutrients
and heavy metals in the soil sediment adjacent to the plants roots. The
measurement of soil sediment near the plants wetland will give an
indication of nutrient and heavy metals removal performance.
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APPENDIX
113
APPENDIX A
Raw Data
Table A1 : Influent characteristics of the Pasir Gudang leachate
Parameter
Value (mg/L)
Ammonia Nitrogen (NH4-N)
84.5
Nitrate Nitrogen (NO3-N)
35.0
Orthophosphate (PO43-)
87.5
Suspended Solid (SS)
Turbidity
Ferum (Fe)
Manganese (Mn)
160
450
33.68
0.48
Table A2 : Quality of leachate after 3 days of treatment
NH4-N
(mg/L)
NO3-N
(mg/L)
PO4-3
(mg/L)
Fe
(mg/L)
Mn
(mg/l)
Turbidity
SS
mg/L
Trial
1
Influent
Control
SSF effluent
Control
FWS effluent
84.5
94.7
89.9
82.4
76.1
35.0
30.0
37.0
28.0
31.0
87.5
18.2
19.5
31.6
17.0
33.68
15.1
12.5
11.2
9.1
0.48
0.42
0.43
0.35
0.32
450
250
240
200
180
160.0
156.7
130.0
140.0
128.3
Trial
2
Control
SSF effluent
Control
FWS effluent
87.8
62.5
53.2
53.0
30.0
40.0
26.0
25.0
32.0
9.0
16.5
25.5
13.5
11.6
10.1
7.4
0.39
0.41
0.32
0.29
120
118
117
105
181.7
141.7
135.0
126.7
Control
SSF effluent
Average
Control
FWS effluent
91.3
76.2
67.8
64.5
30.0
38.5
27.0
28.0
25.1
14.3
24.1
21.3
14.3
12.0
10.7
8.2
0.41
0.42
0.34
0.30
185
179
159
143
169.2
135.8
137.5
127.5
Parameter
Trial
114
APPENDIX A
Raw Data
Table A3 : Quality of leachate after 6 days of treatment
NH4-N
(mg/L)
NO3-N
(mg/L)
PO4-3
(mg/L)
Fe
(mg/L)
Mn
(mg/l)
Turbidity
SS
mg/L
Trial
1
Influent
Control
SSF effluent
Control
FWS effluent
84.5
74.6
87.9
63.6
40.1
35.0
27.0
25.0
26.0
18.0
87.5
28.4
16.4
26.2
15.8
33.68
10.1
6.9
8.9
3.8
0.48
0.31
0.25
0.27
0.21
450
174
153
125
109
160
128.3
98.3
123.3
75.0
Trial
2
Control
SSF effluent
Control
FWS effluent
52.3
39.9
54.3
32.5
25.0
22.0
24.0
14.0
19.4
17.9
19.3
16.8
8.7
6.4
6.4
4.4
0.27
0.24
0.24
0.22
106
94
99
70
135.0
110.3
115.0
98.7
Control
SSF effluent
Average
Control
FWS effluent
63.4
63.9
58.9
36.3
26.0
23.5
25.0
16.0
23.9
17.2
22.7
16.3
9.4
6.7
7.7
4.1
0.29
0.24
0.26
0.21
140
124
112
90
131.7
104.3
119.2
86.8
Parameter
Trial
Table A4 : Quality of leachate after 9 days of treatment
NH4-N
(mg/L)
NO3-N
(mg/L)
PO4-3
(mg/L)
Fe
(mg/L)
Mn
(mg/l)
Turbidity
SS
mg/L
Trial
1
Influent
Control
SSF effluent
Control
FWS effluent
84.5
58.7
18.6
48.1
12.5
35.0
23.0
16.0
19.0
15.0
87.5
22.2
14.4
19.5
8.7
33.68
6.7
1.6
5.4
0.7
0.48
0.19
0.18
0.15
0.12
450
114
75
76
50
160.0
100.7
55.0
89.3
45.7
Trial
2
Control
SSF effluent
Control
FWS effluent
49.6
37.2
45.3
35.6
22.0
12.0
19.0
10.0
18.3
15.5
17.5
14.9
4.7
1.3
3.6
0.9
0.19
0.19
0.13
0.11
74
61
69
55
98.3
80.7
87.0
78.3
Control
SSF effluent
Average
Control
FWS effluent
54.1
27.9
46.7
24.0
22.5
14.0
19.0
12.5
20.3
15.0
18.5
11.8
5.7
1.4
4.5
0.8
0.19
0.18
0.14
0.11
94
68
73
53
99.5
67.8
88.2
62.0
Parameter
Trial
115
APPENDIX A
Raw Data
Table A5 : Quality of leachate after 12 days of treatment
NH4-N
(mg/L)
NO3-N
(mg/L)
PO4-3
(mg/L)
Fe
(mg/L)
Mn
(mg/l)
Turbidity
SS
mg/L
Trial
1
Influent
Control
SSF effluent
Control
FWS effluent
84.5
38.6
8.5
35.7
5.7
35.0
17.0
2.0
15.0
6.0
87.5
9.1
13.3
8.8
10.5
33.68
4.4
0.6
2.9
0.4
0.48
0.13
0.10
0.09
0.08
450
45
28
39
25
160.0
60.3
35.7
57.0
33.3
Trial
2
Control
SSF effluent
Control
FWS effluent
39.8
31.5
36.5
28.1
21.0
9.0
18.0
5.0
16.8
14.4
16.2
14.1
2.6
0.8
2.1
0.6
0.09
0.06
0.07
0.04
52
46
47
40
70.7
69.3
68.3
66.0
Control
SSF effluent
Average
Control
FWS effluent
39.2
20.0
36.1
16.9
19.0
5.5
16.5
5.5
13.0
13.8
12.5
12.3
3.5
0.7
2.6
0.5
0.11
0.08
0.08
0.06
49
37
43
33
65.5
52.5
62.7
49.7
Parameter
Trial
Table A6 : Quality of leachate after 15 days of treatment
NH4-N
(mg/L)
NO3-N
(mg/L)
PO4-3
(mg/L)
Fe
(mg/L)
Mn
(mg/l)
Turbidity
SS
mg/L
Trial
1
Influent
Control
SSF effluent
Control
FWS effluent
84.5
23.5
2.3
21.6
1.3
35.0
12.0
5.0
10.0
3.0
87.5
8.1
7.5
7.6
5.8
33.68
1.9
0.3
1.6
0.3
0.48
0.06
0.05
0.03
0.02
450
37
20
25
11
140.0
55.0
31.7
53.7
30.3
Trial
2
Control
SSF effluent
Control
FWS effluent
34.5
24.5
28.9
20.3
15.0
6.0
13.0
4.0
14.9
13.9
14.4
13.5
0.9
0.4
0.8
0.3
0.06
0.03
0.05
0.03
36
32
34
18
49.7
30.0
45.0
28.7
Control
SSF effluent
Average
Control
FWS effluent
29.0
13.4
25.2
10.8
13.5
5.5
11.5
3.5
11.5
10.7
11.0
9.7
1.4
0.4
1.2
0.3
0.06
0.04
0.04
0.02
37
26
30
15
52.3
30.8
49.3
29.5
Parameter
Trial
116
APPENDIX A
Raw Data
Table A7 : Quality of leachate after 18 days of treatment
NH4-N
(mg/L)
NO3-N
(mg/L)
PO4-3
(mg/L)
Fe
(mg/L)
Mn
(mg/l)
Turbidity
SS
mg/L
Trial
1
Influent
Control
SSF effluent
Control
FWS effluent
84.5
18.4
1.8
14.5
0.2
35.0
9.5
2.0
7.0
1.0
87.5
5.5
4.6
2.1
1.6
33.68
1.3
0.2
1.1
0.1
0.48
0.02
0.02
0.02
0.01
450
18
7
10
1
140.0
51.0
27.0
47.3
23.7
Trial
2
Control
SSF effluent
Control
FWS effluent
25.4
14.2
22.5
11.5
12.0
3.0
9.0
1.5
13.6
9.9
11.2
5.5
1.0
0.2
0.8
0.2
0.04
0.02
0.02
0.01
15
5
8
3
35.3
20.0
29.7
17.0
Control
SSF effluent
Average
Control
FWS effluent
21.9
8.0
18.5
5.9
10.8
2.5
8.0
1.3
9.6
7.3
6.7
3.6
1.1
0.2
1.0
0.2
0.03
0.02
0.02
0.01
17
6
9
2
43.2
23.5
38.5
20.3
Parameter
Trial
117
APPENDIX B
Varian Analysis Calculation (ANOVA)
Table B1 : Varian Analysis Calculation (ANOVA) for NH4-N removal (%).
Comparison between Control system and Planted system
Day
0
3
6
9
12
15
18
Control
0
19.82
30.27
44.74
57.32
70.13
78.11
Planted
0
23.64
57.07
71.57
80.03
87.27
93.08
Anova: Two-Factor without Replication
SUMMARY
Row 1
Row 2
Row 3
Row 4
Row 5
Row 6
Count
Column 1
Column 2
2
2
2
2
2
2
Sum
43.5
87.3
116.3
137.3
157.4
171.2
6
6
300.4
412.7
Average Variance
21.7
7.3
43.7
359.2
58.2
359.9
68.7
9
78.7
146.8
85.6
112.1
50.1
68.8
515.3
648.2
ANOVA
Source of
Variation
Rows
Columns
Error
Total
SS
df
5624.9
1050.3
192.9
5
1
5
6868.04
11
MS
1124.98
1050.31
38.57
F
29.17
27.23
P-value
0.001
0.003
F crit
5.05
6.61
118
APPENDIX B
Varian Analysis Calculation (ANOVA)
Table B2 : Varian Analysis Calculation (ANOVA) for NO3-N removal (%).
Comparison between Control system and Planted system
Day
0
3
6
9
12
15
18
Control
0
22.86
28.57
45.71
52.86
67.14
77.14
Planted
0
20.00
54.29
64.29
84.29
90.00
96.43
Anova: Two-Factor without Replication
SUMMARY
Row 1
Row 2
Row 3
Row 4
Row 5
Row 6
Column 1
Column 2
Count
2
2
2
2
2
2
Sum
42.86
82.86
110
137.14
157.14
173.57
6
6
294.29
409.29
Average Variance
21.437
4.08
41.43
330.61
55
172.45
68.57
493.88
78.57
261.22
86.79
185.97
49.05
68.21
449.52
812.60
MS
1192.9
1102.08
69.23
F
17.23
15.92
ANOVA
Source of
Variation
Rows
Columns
Error
SS
5964.49
1102.08
346.13
Total
7412.71
df
5
1
5
11
P-value
0.004
0.010
F crit
5.05
6.61
119
APPENDIX B
Varian Analysis Calculation (ANOVA)
Table B3 : Varian Analysis Calculation (ANOVA) for PO4-3 removal (%).
Comparison between Control system and Planted system
Day
0
3
6
9
12
15
18
Control
0
72.51
74.01
78.86
85.71
87.43
92.40
Planted
0
75.71
81.38
86.53
85.92
88.97
95.94
Anova: Two-Factor without Replication
SUMMARY
Row 1
Row 2
Row 3
Row 4
Row 5
Row 6
Column 1
Column 2
Count
2
2
2
2
2
2
Sum
148.23
155.39
165.39
171.63
176.41
188.34
6
6
490.93
514.46
Average Variance
74.11
5.12
77.69
27.21
82.69
29.40
85.82
0.02
88.20
1.18
94.17
6.28
81.82
85.74
63.01
46.94
ANOVA
Source of
Variation
Rows
Columns
Error
Total
SS
526.66
46.14
23.07
595.87
df
5
1
5
11
MS
105.33
46.14
4.62
F
22.83
10.00
P-value
0.002
0.025
F crit
5.05
6.61
120
APPENDIX B
Varian Analysis Calculation (ANOVA)
Table B4 : Varian Analysis Calculation (ANOVA) for SS removal (%).
Comparison between Control system and Planted system
Day
0
3
6
9
12
15
18
Control
0
14.06
30.52
44.90
60.83
69.17
75.94
Planted
0
20.31
45.73
61.25
68.96
81.56
87.29
Anova: Two-Factor without Replication
SUMMARY
Row 1
Row 2
Row 3
Row 4
Row 5
Row 6
Column 1
Column 2
Count
2
2
2
2
2
2
Sum
34.38
76.25
106.15
129.79
150.73
163.23
6
6
295.42
365.10
Average Variance
17.19
19.54
38.13
115.62
53.07
133.71
64.89
33.01
75.36
76.84
81.61
64.45
49.24
60.85
570.18
613.18
MS
1175.67
404.67
7.69
F
152.7255
52.5691
ANOVA
Source of
Variation
Rows
Columns
Error
SS
5878.33
404.67
38.49
Total
6321.49
df
5
1
5
11
P-value
1.84E-05
0.001
F crit
5.050329
6.607891
121
APPENDIX B
Varian Analysis Calculation (ANOVA)
Table B5 : Varian Analysis Calculation (ANOVA) for Turbidity removal (%).
Comparison between Control system and Planted system
Day
0
3
6
9
12
15
18
Control
0
64.78
75.11
83.89
90.44
93.44
98.00
Planted
0
68.33
80.11
88.33
92.78
96.78
99.56
Anova: Two-Factor without Replication
SUMMARY
Row 1
Row 2
Row 3
Row 4
Row 5
Row 6
Count
Column 1
Column 2
2
2
2
2
2
2
Sum
133.11
155.22
172.22
183.22
190.22
197.56
6
6
505.67
525.89
Average Variance
66.56
6.32
77.61
12.5
86.11
9.88
91.61
2.72
95.11
5.56
98.78
1.21
84.28
87.65
154.96
136.36
ANOVA
Source of
Variation
Rows
Columns
Error
SS
1452.47
34.08
4.1q
Total
1490.65
df
5
1
5
11
MS
290.49
34.08
0.82
F
353.66
41.49
P-value
2.29E-06
0.001
F crit
5.050329
6.607891
APPENDIX B
Varian Analysis Calculation (ANOVA)
122
Table B6 : Varian Analysis Calculation (ANOVA) for Fe removal (%).
Comparison between Control system and Planted system
Day
0
3
6
9
12
15
18
Control
0
68.30
77.20
86.54
92.43
96.33
97.18
Planted
0
75.58
87.92
97.67
98.53
99.17
99.52
Anova: Two-Factor without Replication
SUMMARY
Row 1
Row 2
Row 3
Row 4
Row 5
Row 6
Column 1
Column 2
Count
2
2
2
2
2
2
Sum
143.88
165.11
184.20
190.96
195.50
196.70
6
6
517.98
558.39
Average Variance
71.94
26.46
82.56
57.44
92.10
61.99
95.48
18.61
97.75
4.02
98.35
2.75
86.33
93.06
132.67
92.47
ANOVA
Source of
Variation
Rows
Columns
Error
SS
1090.47
136.08
35.19
Total
1261.74
df
5
1
5
11
MS
218.09
136.08
7.04
F
P-value
F crit
30.99 0.000908 5.050329
19.33 0.007042 6.607891
123
APPENDIX B
Varian Analysis Calculation (ANOVA)
Table B7 : Varian Analysis Calculation (ANOVA) for Mn removal (%).
Comparison between Control system and Planted system
Day
0
3
6
9
12
15
18
Control
0
29.47
45.68
71.05
83.68
91.89
95.58
Planted
0
36.11
55.26
76.32
87.79
95.26
97.68
Anova: Two-Factor without Replication
SUMMARY
Row 1
Row 2
Row 3
Row 4
Row 5
Row 6
Column 1
Column 2
Count
2
2
2
2
2
2
Sum
65.58
100.95
147.37
171.47
187.16
193.26
6
6
417.37
448.42
Average Variance
32.79
21.98
50.47
45.88
73.68
13.85
85.74
8.43
93.59
5.67
96.63
2.22
69.56
74.74
710.90
598.48
ANOVA
Source of
Variation
Rows
Columns
Error
SS
6529.23
80.36
17.68
Total
6627.27
df
5
1
5
11
MS
1305.85
80.36
3.54
F
369.35
22.73
P-value
2.05E-06
0.005026
F crit
5.050329
6.607891
APPENDIX C
Lab Apparatus and Equipments
Figure C1 : Leachate pond at Pasir Gudang Sanitary Landfill
Figure C2 : Leachate was poured into container
124
APPENDIX C
Lab Apparatus and Equipments
Figure C3 : Limnocharis flava founded at Pontian Road
Figure C4 : Eichhornia crassipes founded at fish pond
125
APPENDIX C
Lab Apparatus and Equipments
Figure C5 : Limnocharis flava planted in SSF wetland tank
Figure C6 : Eichhornia crassipes planted in FWS wetland tank
126
APPENDIX C
Lab Apparatus and Equipments
127
Figure C7 : Control and Planted systems for SSF constructed wetland
Figure C8 : Control and Planted systems for FWS constructed wetland
APPENDIX C
Lab Apparatus and Equipments
128
Figure C9 : HACH DR/4000 spectrophotometer machine
Figure C10 : Glass microfibre filter disc 5.5m Whatman type GF/C (0.7 µm)
APPENDIX C
Lab Apparatus and Equipments
Figure C11 : Mettler AT261 Delta Range weighing machine
Figure C12 : Drying oven for operation at 103˚C to 105˚C
129