EFFECT OF TEMPERATURE ON SUBMERGED MEMBRANE ACTIVATED
SLUDGE REACTOR
SABARIAH BINTI ABDUL RAHMAN
A project report submitted in partial fulfillment of the
requirement for the award of the degree of
Master of Engineering (Civil – Environmental Management)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
NOVEMBER, 2009
iii
“TO MY LOVES FAMILY…..”
AYAH, MAMA, SHAHRIL, SYAFIQ, SAIFUDIN AIMAN
THANKS FOR YOUR SUPPORT,
TO MY LOVES ONE, THANKS FOR YOUR LOVE, CARE AND
ENCOURAGEMENT….
ALL FRIENDS…..
THANK YOU FOR EVERYTHING…..
OUR LOVES NEVER ENDS
iv
ACKNOWLEDGEMENT
Thanks to Allah S.W.T. the Exalted, the Most Merciful, for giving me the
stregnth and presistence to keep going with this research even during the most
difficult moments. May ALLAH S.W.T. accept this work and count it as a good
deed.
In preparing this project report, I was in contact with many people,
researchers, academicians and practitioners. They have contributed towards my
understanding and thoughts. In particular, I wish to express my sincere appreciation
to my main project report supervisors, Dr C. Shreesivadasan and Dr Muhamad Ali
bin Muhammad Yuzir for encouragement, guidance, critics and friendship. Without
their continued support and interest, this project report would not have been the same
as presented here.
I am also indebted to Environmental Lab,Faculty of Civil Engineering,
Universiti Teknologi Malaysia (UTM) International Campus for provide facilities for
my master project. A special thanks goes to En Azmi Abu Bakar, senior technicians
of his willingness to spend his valuable time , continued support and interest in
helpinh my laboratory work there.
My fellow postgraduate students should also be recognized for their support.
My sincere appreciation also extends to all my colleagues and others who have
provided assistance at various occasions. Their views and tips are useful indeed.
Unfortunately, it is not possible to list all of them in this limited space. I am grateful
to all my family members.
v
ABSTRACT
This study investigates the performance of Submerged Membrane Activated Sludge
Reactor on treating synthetic wastewater and also the effects of varying temperature
of a laboratory scale Submerged Membrane Activated Sludge reactor. Laboratory
bench-scale continuous reactors, fed with synthetic wastewater were used.
The
operational volume of the reactor was 20 litres and included a membrane. The
membrane was made from a polymer material (HDPE) with a thickness of 3.5 mm.
The membrane, whose pore size ranged between 0.1 – 1mm, played the role of a
secondary clarifier. Effects of temperatures of 27, 32, 37, 42, and 47°C were studied.
Studies on the effects of temperatures were carried out as the pH was maintained in
the range of 6.5 to 8.00 by adjustment of the feed pH with NaOH. Nutrients levels
were maintained in the ratio of COD: N: P at 100:5:1. The biomass was considered
to be acclimatized when MLSS concentration maintained constant levels (3000 ±
2000 mg/L). The reactor was aerated continuously with an aquarium air stone with
compressed air supplied at approximately 3 L/min to maintain dissolved oxygen
(DO) concentration of 1.5 to 3.0 mg/L. Results indicated that as the operating
temperatures of the reactors were increased, the percent removal of the soluble
chemical oxygen demand (COD) also increased. The highest percent removal of
soluble COD was obtained at 47 ºC (90.45%) while the lowest percent removal of
soluble COD was obtained at 32 ºC (24.27%). The higher concentration of MLSS
was obtained at 42 ºC (80 mg/L) while the lowest concentration was obtained at 10
mg/L at the same temperature (42 ºC). The patterns of the MLSS concentration for
the temperature of 27 ºC, 32 ºC, 37 ºC, 42 ºC, and 47 ºC was increased and decreased
gradually. The greatest concentration of MLVSS was achieved at 47 ºC and 32 ºC
(80 mg/L) while the lowest was attain at 42 ºC which is 10 mg/L. On the other
hand, increases the temperature affected the DO concentrations. The highest and
lowest DO concentration was obtained at 27 ºC which is 5.1 mg/L and 1.7 mg/L.
vi
ABSTRAK
Kajian ini dijalankan bagi mengkaji keupayaan Reaktor Penenggelaman Membran
Enapcemar Teraktif di dalam merawat air sisa sintetik dan juga mengkaji kesan ke
atas pelbagai suhu terhadap reaktor tersebut.
Reaktor berskala makmal yang
beroperasi secara berterusan ini telah menggunakan air sisa sintetik sebagai larutan
penyuapan. Isipadu opearasi bekerja bagi reaktor tersebut termasuk membran adalah
20 liter.
Membran yang digunakan diperbuat daripada bahan polimer (HDPE)
dengan ketebalan 3.5mm. Membran tersebut mempunyai saiz liang berjulat 0.1 –
1mm, bertindak sebagai klarifier sekunder. Kesan ke atas suhu 27 ºC, 32 ºC, 37 ºC,
42 ºC dan 47 ºC telah dikaji. Kajian terhadap kesan suhu dijalankan dengan pH
ditetapkan di dalam julat 6.5 – 8.0 dengan menukarkan pH larutan penyuapan dengan
penambahan NaOH. Kadar nutrisi ditetapkan di dalam nisbah COD : N : P (100: 5:
1).
Kandungan berat biologi dianggap sesuai dengan iklim sekitaran apabila
kandungan MLSS berada pada (3000 ± 2000 mg/L).
Reaktor tersebut telah
diudarakan secara berterusan dengan menggunakan batu udara akuarium yang
membekalkan udara pada anggaran 3 L/min bagi mengekalkan kandungan oksigen
terlarut (DO) pada 1.5 – 3.0 mg/L. Berdasarkan keputusan yang diperoleh, apabila
suhu operasi reaktor dinaikkan, peratus penyingkiran permintaan oksigen kimia
(COD) hancur tertinggi dicatatkan pada suhu 47 ºC (90.45%) manakala yang
terendah dicatatkan pada 32 ºC (24.27%).
Kandungan MLSS yang tertinggi
dicatatkan pada suhu 32 ºC (80mg/L) manakala yang terendah pada suhu yang sama
iaitu 10 mg/L. Corak kandungan MLSS bagi kajian terhadap suhu 27 ºC – 47 ºC
adalah menaik dan menurun dengan perlahan. Kandungan MLVSS yang paling
tinggi dicapai pada 47 ºC dan 32 ºC (80 mg/L) manakala yang terendah pada 42 ºC
(10mg/L). Selain itu, peningkatan suhu turut mempengaruhi kandungan oksigen
terlarut (DO). DO yang tertinggi dan terendah dicapai pada suhu 27 ºC iaitu 5.1
mg/L dan 1.7 mg/L.
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
xii
LIST OF FIGURES
xiii
LIST OF ABBREVIATIONS
xv
LIST OF APPENDICES
xvi
INTRODUCTION
1
1.1
Introduction
1
1.2
Problem Statement
3
1.3
Aim and Objectives
5
1.4
Scope and Limitation
5
1.5
Importance of the Study
6
LITAERAURE REVIEW
7
2.1
Biological Treatment
7
2.2
Aerobic Treatment Process
8
viii
2.3
Principal Application of Aerobic Biological
9
Process
2.3.1 Removal of Biodegradable Dissolved
10
and Colloidal Organic Matter
2.3.2 Nitrification
11
2.3.3 Denitrification
12
2.3.4 Phosphorus Removal
13
Classification of Aerobic Biological Process
13
2.4.1 Attached Growth System
14
2.4.2 Suspended Growth System
14
2.5
Microbial Process In Aerobic Treatment
15
2.6
Factors Affecting Aerobic Process
16
2.6.1 Dissolved Oxygen
17
2.6.2 Food over Mass Ratio
18
2.6.3 Solids Retention Time (SRT)
19
2.6.4 Organic Loading
20
2.6.5 pH
21
2.6.6 Temperature
21
2.6.7 Nutrients
22
Advantages and Disadvantages of Aerobic
22
2.4
2.7
Process
2.8
Activated Sludge
23
2.8.1 Characteristics of Conventional
24
Activated Sludge System
2.8.2 Activated Sludge Process Design
26
Requirements
2.8.3
Process Analysis and Control of
27
Activated Sludge Process
2.8.3.1Selection of Reactor Type
27
2.8.3.2Kinetic Relationships
28
2.8.3.3Solids Retention Time and
29
Loading Criteria
2.8.3.4Sludge Production
30
ix
2.8.3.5Nutrients and Other
30
Chemicals Requirements
2.8.4 Issues on Design, Operation and
31
Maintenance of Conventional
Activated Sludge System
2.8.4.1Sludge Bulking
31
2.8.4.2Rising Sludge
34
2.8.4.3Processing Time
35
2.8.4.4Large Area Requirements and
35
High Energy Cost
2.9
2.10
Sequencing Batch Reactors
36
Membrane Bioreactors
38
2.10.1 Classification of MBRs
41
2.10.2 External Loop (Side- stream) Cross-
42
flow Membrane MBR
2.11
2.12
3
2.10.3 Submerged Membrane
43
Effect of Temperature
44
Summary of Literature Review
47
RESEARCH METHODOLOGY
49
3.1
Introduction
49
3.2
Study Outline
50
3.3
Design of Submerged Membrane Activated
52
Sludge reactor
3.4
Operational Method of Submerged
54
Membrane Activated Sludge Reactor
3.4.1 Organic Loading Rate
54
3.4.2 Feed and Nutrients
55
3.5
Seed Sludge
56
3.6
Design of Experiments
58
3.7
Sampling and Analysis
58
3.7.1 COD Measurements
59
x
3.7.2 Total Suspended Solids (TSS or
61
MLSS) Measurements
3.7.3 Volatile Suspended Solids (VSS or
63
MLVSS)
3.8
4
On-line measurements
64
3.8.1 pH
64
3.8.2 Dissolved Oxygen (DO)
65
RESULTS ANALYSIS AND DISCUSSIONS
66
4.1
Introduction
66
4.2
Research Data Methodology
67
4.3
Feed and Nutrients Characterization
67
(Synthetic Wastewater)
4.4
Seed Sludge
67
4.5
Submerged Membrane Activated Sludge
68
Reactor Start-Up
4.6
Effect of Temperature on COD Removal
69
4.7
Effect of Temperature on pH profile
71
4.8
Effect of Temperature on Dissolved Oxygen
72
(DO) profile
4.9
Solids Washout
73
4.9.1 Effect of Temperature on Mixed
73
Liquor Suspended Solids (MLSS)
4.9.2 Effect of Temperature on Mixed
74
Liquor Volatile Suspended Solids
(MLVSS)
4.10
Effect of Temperature on Specific
Degradation Rate
75
xi
5
CONCLUSIONS AND RECOMMEMDATIONS
78
5.1
Introduction
78
5.2
Conclusions
78
5.3
Recommendations
80
REFERENCES
83
APPENDICES
89
xii
LIST OF TABLES
TABLES NO.
TITLE
PAGE
2.1
Important kinetics relationships factors
29
2.2
Factors that affect sludge bulking
33
2.3
Description of operational steps for the
37
Sequencing Batch Reactors (SBR)
2.4
Examples of MBR Applications to different
41
types of wastewaters
3.1
Chemical composition of the synthetic
55
wastewater.
32
Operating condition of the reactor.
58
3.3
Monitoring schedule for chemical analysis.
59
4.1
Characteristics of raw synthetic wastewater.
67
4.2
Characteristics of seeding sludge.
68
5.1
Problems occur during the reactor start-up
80
and operational difficulties of the reactor
during this study.
xiii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
Aerobic systems.
9
2.2
Typical activated sludge systems.
25
2.3
Typical SBR operations for one cycle
38
2.4
Typical MBR systems.
39
2.5
Replaced units in a wastewater treatment
40
plant with the use of MBR
2.6
External Loop Crossflow and submerged
42
systems
2.7
Two different set-ups for submerged
44
membranes.
3.1
Outline of the study
51
3.2
Submerged Membrane Activated Sludge
52
reactor.
3.3
Laboratory – scale Submerged Membrane
53
Activated Sludge reactor.
3.4
Chemicals used for the synthetic wastewater.
56
3.5
Wastewater treatment plant at Glaxo Smith
57
Kline (GSK) company.
3.6
Sludge collected at Glaxo Smith Kline
57
(GSK) company.
3.7
The HACH COD reactor used for COD
61
measurements.
3.8
Oven used for Total Suspended Solids (TSS
62
or MLSS) measurements.
3.9
Vacuum pump used for Total Suspended
62
xiv
Solids (TSS or MLSS) measurements.
3.10
Wise Therm Muffle Furnace used for the
63
volatile suspended solids measurements.
3.11
pH probe use for the pH measurements.
64
3.12
DO probe use for the DO measurements.
65
4.1
The effect of the temperature on soluble
70
COD removal of the Submerged Membrane
Activated Sludge reactor.
4.2
Effect of Temperature on the profile of pH.
71
4.3
Effect of Temperature on the profile of
72
Dissolved Oxygen (DO).
4.4
Effect of Temperature on Mixed Liquor
74
Suspended Solids (MLSS).
4.5
Effect of Temperature on Mixed Liquor
75
Volatile Suspended Solids (MLVSS).
4.6
Effect of the temperature on specific
degradation rate.
77
xv
LIST OF ABREVATIONS
ºC
Degree celcius
DO
Dissolved Oxygen
COD
Chemical Oxygen Demand
BOD
Biological Oxygen Demand
MLSS
Mixed Liquor Suspended Solids
MLVS
Mixed Liquor Volatile Suspended Solids
SS
Suspended Solids
VSS
Volatile Suspended Solids
HDPE
High Density Polyvinyl Ethylene
mg/L
Milligram per litre
g/L
Gram per litre
UTM
Universiti Teknologi Malaysia
m
metre
cm
centimetre
mm
milimetre
xvi
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
LABORATORY DATA
89
B
DETERMINATION OF CHEMICAL OXYGEN
95
DEMAND (COD)
CHAPTER 1
INTRODUCTION
1.1
Introduction
The expand number of industrial sector in Malaysia have increased the
production of products such as plastics, metals and chemicals in order to fulfil the
living needs of human and increased national economics. Through the increases of
industrial sector in Malaysia, the manufacturing produce millions tans of industrial
waste which will arise the environmental quality issues, safety and health concerns in
the wastewater management, which will develop seriously and should be aware.
Effective and quick measurements should be done in order to minimize serious
problems that may arise such as the increase treatment costs of drinking and clean
water supply, public health and safety and also declining on health and environment
standards.
The production of industrial solid waste increase tremendously every year.
Approximately around 10, 000 of new organic material concentrations were added in
the industrial waste each year (Metcalf and Eddy, 2004). The new organic materials
concentrations were mainly consists complex materials which require high treatment
cost that will be treated in conventional systems.
According to Environmental Quality Report 2004, in Malaysia approximately
an average of 431,000 tan metric a year of industrial waste mainly from textile and
chemical industries, pharmaceutical wastes, agricultural and domestic waste are
2
produced. The effluent from industrial waste was highly in toxic, danger to public
health and seriously affects the environment conditions. Normally, the industrial
factory did not apply the suitable and standardize treatment required by the authority
and ignore the standard or law that being permitted.
Aerobic treatment systems include the activated sludge process, extended
aeration activated sludge process, activated sludge with granular activated carbon, or
natural or genetically engineered microorganisms and aerobic fixed growth system
such as trickling filters and rotating biological contactors.
Among the aerobic
processes, the trickling filter and the activated sludge processes have been used to
treat industrial and domestic wastewater. In the past few years the treatment of
wastewater by a modified activated sludge process, the sequencing batch reactor
(SBR) has gained recognition. The SBR system do receive worldwide attention and
several thousands SBR facilities have been designed, built and put into operation
(Wilderer et al., 2000, Hastings et al., 2007). Most sewage treatment facilities are
still based on continuously operated activated sludge processes. Aerobic systems
have many advantages such as relatively easy operation, lower equipment cost,
produce a better quality supernatant lower nitrates and phosphorus concentrations,
thereby protecting the liquid side upstream and can achieve comparable volatile
solids reduction with shorter retention periods, less hazardous cleaning and repairing
tasks (Metcalf and Eddy, 2004).
In this study, the efficiency of a submerged membrane activated sludge
reactor in treating synthetic wastewater which was similar to industrial wastewater
was being studied in order to determine the efficiency of the reactor as an effective
alternative technique in treating industrial wastewater. Furthermore, this study also
analyzes the effect of varying temperature of a laboratory scale aerobic digester on
process performance.
3
1.2
Problem Statement
Industry is a huge source of water pollution, it produces pollutants that are
extremely harmful to people and the environment. Many industrial facilities use
freshwater to carry away waste from the plant and into rivers, lakes and oceans.
Pollutants from industrial sources include asbestos, lead, mercury, nitrates,
phosphates, sulphur, oils and petrochemicals.
Increasing population, rapid urbanization and rapid intensifying human
activities have exerted immense pressures on water quality. Whenever human and
industrial wastes are not properly managed, surface waters and ground waters
become the sink for receiving such waste.
When effluents from industries are
discharged into river channels, the river water will be polluted due to the increase
concentration of dissolved solids, toxic chemicals, BOD loadings, heavy metals and
other pollutants. Other than that, pesticides and herbicides from agricultural areas
add to the increasingly polluted water sources.
According to the Environmental Quality Report (EQR) 2006, 16 rivers in
Malaysia are polluted and 33 rivers are slightly polluted. Sources of the pollutions
are from domestic waste and industrial waste which was mainly from agriculture and
also factory sector. On the other hand, effective and suitable wastewater treatment
systems that are economically and reducing cost were complicated and difficult to
select which required fundamental knowledge about the critical role and operation of
the wastewater treatment system.
The activated sludge process is the most commonly used treatment system for
industrial and municipal wastewater. The activated sludge process consists at least
one aeration tank (aeration period) and one sedimentation tank (settling period)
(Gerardi, 2002).
The activated sludge process is capable of performing four critical wastewater
treatment functions which are: the degradation or oxidation of carbonaceous waste,
4
the degradation or oxidation of nitrogenous wastes, the removal of fine materials and
the removal of heavy metals.
The objective of the activated sludge process in
treating industrial wastewater is to remove soluble and insoluble organics and to
convert this material into a flocculent microbial suspension that settles well in
conventional gravity clarifiers (Arthur, 2002). Several modifications of activated
sludge process have been developed to accommodate specific wastewater
characteristics and operational needs.
The activity and the physical properties of the microbial community within a
system will determine the efficiency of treatment in terms of substrate utilisation,
floc formation and efficient separation of the solids (specifically in gravity
separators) from the treated supernatant. In order to achieve these objectives, the
environmental and operational parameters that need to be controlled are dissolved
oxygen, F/M ratio, solids retention time (SRT), organic loading, pH, temperature and
nutrients.
Therefore, operational condition in the aerobic reactor must be
periodically monitored and maintained within optimum ranges.
Temperature affects all biological reactions. The magnitude of the effect is
related to the characteristics of the wastewater organics and their physical state.
Previous study from Henze et. al., (2001). shows that the activity of the biomass
increases with the increasing in temperatures which results in low the solubility of
the oxygen. Experimental work has also demonstrated that widely varying mixed
liquor temperatures (25 C to 5 - 8 C) during treatment can yield an increase in
suspended solids in the treated effluent (Eckenfelder and Musterman, 2001). There
have been some efforts to operate the activated sludge process in the thermophilic
range (45 to 55 ºC) when the influent wastewater temperature is already in this range
and the BOD is high (2500 to 3000mg/L). Under these operating conditions, the
sludge generated was frequently difficult to separate, the mixed liquor was dispersed,
and effluent solids concentrations were high (Grau and Eckenfelder, 2001). The
activated sludge process can adapt to a wide range of temperatures but will become
unstable with a sudden temperature change resulting in floc dispersion and increase
in effluent suspended solids (Eckenfelder, 2001).
5
Therefore in this study, the effectiveness of the Submerged Membrane
Activated Sludge Reactor in treating synthetic wastewater which is similar to
industrial wastewater will be investigate as one of other effective alternative
treatment in order to produce treated wastewater that are safe and clean to be
disposed and used.
1.3
Aim and Objectives
The aim of this research is to evaluate the effect of temperature in aerobic
reactor by using Submerged Membrane Activated Sludge Reactor. To achieve this
aim, the following objectives are as follows:
a)
To investigate the performance of Submerged Membrane Activated
Sludge Reactor on treating synthetic wastewater,
b)
To investigate the effect of varying temperature of laboratory scale
aerobic reactor on treating synthetic wastewater
This study does not aim to develop or optimise a system and does not provide
detailed design criteria. However more importantly, it explores the potential of
aerobic treatment under strictly controlled extreme operating conditions.
1.4
Scope and Limitation
Scope of this research is based on the treatment of synthetic wastewater by
using Submerged Membrane Activated Sludge Reactor in order to investigate the
performance of this reactor. This research will be focused on the treatment of
synthetic wastewater that has been prepared with glucose as the main component.
6
Sludge that is used for microb growth was collected from Glaxo Smith Kline (GSK)
company, near Ulu Klang, Selangor.
In this research, the sludge sample and the synthetic wastewater will be
examined by performing lab work analyse at Environmetal Engineering Lab,
Universiti Teknologi Malaysia (UTM) International Campus. The parameter that are
being tested in order to identify the synthetic wastewater characteristics effluent are
Chemical Oxygen Demand (COD), Mixed Liquor Suspended Solids (MLSS), Mixed
Liquor Volatile Suspended Solids (MLVSS), pH and Dissolved Oxygen (DO).
This study determined the effect of temperature on the performance of the
Submerged Membrane Activated Sludge Reactor on treating synthetic wastewater.
In this study, different range of temperature will be used in order to determine the
effectiveness of this aerobic reactor. Temperature factors are important in affecting
the process performance of the aerobic reactor and have to be considered. This is
important to ensure that the effluent that will produce from treatment are followed
the allowable standard required.
1.5
Importance of the Study
The research is important to ascertain the effectiveness of Submerged
Membrane Activated Sludge Reactor in treating wastewater. In order to investigate
the effect of temperature on the performance of Submerged Membrane Activated
Sludge Reactor, the optimization and the appropriate temperature that will affect the
aerobic reactor on process performance and for the most efficient in the aerobic
reactor will be recognized. Other than that, the efficiency of this aerobic reactor will
be determined. The exact water parameter of the effluent is important to make sure
such as the COD values, which are important in order to characterize the organic
strength of wastewater.
CHAPTER 2
LITERATURE REVIEW
2.1
Biological Treatment
In the early 1900s, the primary purpose of biological wastewater treatment
has been used to remove organic constituents and compounds to prevent excessive
DO depletion in receiving waters from municipal or industrial point discharges, to
remove colloidal and suspended solids to avoid the accumulation of solids and the
creation of nuisance conditions in receiving waters and also to reduce the
concentration of pathogenic organisms released to receiving waters (Metcalf and
Eddy, 2004).
Generally, biological treatment is used to treat liquid waste, where this system
is one of secondary wastewater treatment systems. Biological treatment is a system
that eliminates suspended solids and also soluble organic load from wastewater by
the use of populations of microorganisms. The microorganisms used in the treatment
systems play role to dispose organic matter and also acted to stabilize the wastewater.
There are three process in the biological treatment systems which are aerobic
treatment (need oxygen), anaerobic treatment (without oxygen), and facultative
treatment where the treatment can operates with and without oxygen.
8
In treating wastewater, biological treatment process can be classified to
aerobic or anaerobic treatment.
If the microorganisms in the wastewater in a
suspended conditions during the biological treatment, hence that operation is describe
as suspended growth systems while when the microorganisms are attached to a
surface during growth, hence that process is describe as attached growth systems.
In this study, the efficiency of a submerged membrane activated sludge
reactor (aerobic systems) in treating synthetic wastewater which was similar to
industrial wastewater was being studied. Other than that, this study will determine
the efficiency of the aerobic reactor as an effective alternative technique in treating
industrial wastewater. This study also analyzes the effect of varying temperature of a
laboratory aerobic digester on process performance.
2.2
Aerobic Treatment Process
Aerobic treatment is a biological treatment process. The principal of aerobic
treatment is the use of free or dissolved oxygen by microorganisms (aerobes) in the
degradation of organic wastes. Since oxygen is available to working aerobes as an
electron acceptors, the biodegradation process can be significantly accelerated,
leading to increased throughput capacity of treatment system (Metcalf and Eddy,
2004).
In aerobic treatment process, oxygen was the important element in the
biodegradation process of the wastewater by the microorganism other than the needs
of other nutrients such as nitrogen and phosphorus. Without oxygen, the growth rate
of the microorganism will decelerate where these organic material will not able to
survive and will influence the required wastewater treatment needs. Some examples
of the typical aerobic treatment process are activated sludge process, lagoon, and
biological filter.
9
The principal applications of aerobic processes are the removal of
biodegradable dissolved and colloidal organic matter, nitrification, denitrification,
phosphorus removal and waste stabilization. Figure 2.1 shows the typical aerobic
systems.
Based on growth of microorganisms, aerobic process can be classified into
two, which are:
1. Suspended growth - activated sludge, aerated lagoon, sequencing batch
reactors (SBR)
2. Fixed film growth/attached growth
-
trickling filter, rotating biological
contactor (RBC)
Figure 2.1
2.3
Aerobic systems.
Principal Application of Aerobic Biological Process
Both aerobic suspended growth and attached growth require sufficient contact
time between the wastewater and heterotrophic microorganisms, and sufficient
10
nutrients and oxygen. During the initial biological uptake of the organic material,
more than half of it is oxidized and the remainder is assimilated as new biomass,
which may be further oxidized by endogenous respiration (Henze et al., 2001).
For both suspended and attached growth process, the excess biomass
produced each day is removed and processed to maintain proper operation and
performance. The principal applications of the aerobic biological process are the
removal of biodegradable dissolved and colloidal organic matter, nitrification,
denitrification, phosphorus removal and waste stabilization.
2.3.1 Removal of Biodegradable Dissolved and Colloidal Organic Matter
Most of the organic compounds in domestic wastewater and some in
industrial wastewater are of natural origin and can be degraded by common bacteria
in aerobic or anaerobic processes. Unfortunately, some of the organics (synthetic
organics chemicals) compounds pose unique problems in wastewater treatment. It is
due to their resistance to biodegradation and potential toxicity to the environment and
human health.
Organic compounds that are difficult to treat in conventional
biological treatment process are termed as refractory.
With a few exceptions most organic compounds can be biodegraded
eventually, but in some cases the rates may be slow, unique environmental conditions
may be required, such as temperature and pH. There are three principal types of
degradation pathways that have been observed which are, the compound serves as a
growth substrate, the organic compound provides an electron acceptors and also the
organic compound degraded by metabolic degradation.
11
2.3.2 Nitrification
Nitrification process can be described as the two-step biological process in
which ammonia (NH4-N) is oxidized to nitrite (NO2-N) and nitrite is oxidized to
nitrate (NO3-N). The need for nitrification process in wastewater treatment process
arises from water quality concerns over the factors of the effect of ammonia on
receiving water with respect to DO concentrations and fish toxicity, the need to
provide nitrogen removal to control eutrophication and the need to provide nitrogen
control for water-reuse applications including groundwater recharge.
In BOD removal, nitrification can be accomplished in both of the suspended
growth and attached growth biological process. For suspended growth processes, a
more common approach is to achieve nitrification along with BOD removal in the
same single-sludge process which consists of an aeration tank, clarifier, and sludge
recycle system. In cases where there is a significant potential for toxic and inhibitory
substances in the wastewater, a two-sludge suspended growth system may be
considered. The two-sludge system consists of two aeration tanks and two clarifiers
in series with the first aeration tank/clarifier unit operated at a short SRT for BOD
removal (Metcalf and Eddy, 2004).
While in attached growth systems used for nitrification, most of the BOD
must be removed before nitrifying organisms can be established. The heterotrophic
bacteria have a higher biomass yield and thus can dominate the surface area of fixedfilm systems over nitrifying bacteria. Nitrification is accomplished in an attached
growth reactor after BOD removal or in a separate attached growth system designed
specifically for nitrification (Metcalf and Eddy, 2004).
Nitrification is affected by a number of environmental factors including pH,
toxicity, metals and un-ionized ammonia. Nitrification process is sensitive to the pH.
In nitrification process, the pH rates decline significantly at pH values below 6.8
(EPA, 1999). Optimal nitrification rates occur at pH values in the range of 7.5 to 8.0.
Nitrifying organisms are also sensitive to a wide range of organic and inorganic
12
compounds and at concentrations well below those concentrations that would affect
aerobic heterotrophic organisms. While for metals as described by Skinner and
Walker (2000) have shown complete inhibition of ammonia oxidation at 0.25 mg/L
nickel, 0.25 mg/L chromium and 0.10 mg/L copper. Nitrification also inhibited by
un-ionized ammonia, and un-ionized nitrous acid. The inhibition affects are the
dependent on the total nitrogen species concentration, temperature and pH.
2.3.3 Denitrification
The denitrification process is the biological reduction of nitrate to nitric
oxide, and nitrogen gas. Biological denitrification is an integral part of biological
nitrogen removal, which involves both nitrification and denitrification (Metcalf and
Eddy, 2004). The biological nitrogen removal is generally more cost effective and
used more often if compared to alternatives of ammonia stripping, breakpoint
chlorination, and ion exchange.
Biological nitrogen removal is used in wastewater treatment where there are
concerns for eutrophication and also when groundwater must be protected against
elevated NO3-N concentrations. It is when the wastewater treatment plant effluent is
used for groundwater recharge and other reclaimed water application.
Denitrification is affected by a pH factors. It occurs when the alkalinity is
produced in denitrification reactions and the pH is generally elevated. There has
been less concern about pH influences in denitrifaction rates. There has been no
significant effect on the denitrification rate for pH between 7.0 and 8.0.
13
2.3.4 Phosphorus Removal
Phosphorus removal is generally performed to control eutrophication because
phosphorus is the limiting nutrient in most of freshwater system. Chemical treatment
using alum or iron salts is the most commonly used technology for phosphorus
removal. But since the early 1980s, success in full-scale plant biological phosphorus
removal has encouraged the further used practice.
The principal advantages of
biological phosphorus removal are can reduced chemical costs and less sludge
production as compared to chemical precipitation (Metcalf and Eddy, 2004).
Phosphorus removal in biological systems is based on the following
observations (Sedlak, 1999):
1.
Numerous bacteria are capable of storing excess amounts of
phosphorus as polyphosphates in their cells
2.
Under anaerobic conditions, PAOs will assimilate fermentataion
products (volatile fatty acids; VFAs) into storage products within the
cells with the concomitant release of phosphorus from stored
polyphosphates.
3.
Under aerobic conditions, energy is produced by the oxidation of
storage products and polyphosphates storage within the cell increases.
The system performance is not affected by DO as long as the aerobic zone
DO concentration is above 1.0 mg/L. At pH values below 6.5, phosphorus removal
efficiency is greatly reduced (Sedlak, 1999):
2.4 Classification of Aerobic Biological Process
Biological treatment system is a practice to treat wastewater by the utilization
of microorganisms by biodegradation process and also to decompose nutrients
14
contents in the wastewater. Nowadays, the biological treatment process usually used
in treating domestic wastewater rather than treating by the used of chemicals because
natural friendly. Frequently, biological treatment is used as secondary treatment and
tertiary treatment in treating wastewater.
The biological wastewater treatment can be classified into 2 systems which
are Attached Growth System and Suspended Growth System. Both of these systems
are classified under aerobic treatment which by the use of oxygen during nutrient
utilization process as operational theory.
2.4.1 Attached Growth System
The attached growth system is the biological treatment which used a medium
such as rock, plastic, or other material for the growth of microorganism or bacteria.
In this system, sludge will be provided for growth of the microorganism.
The
microbe will attach to the provided medium. The biodegradation process will occur
during the flow of the wastewater via the biological medium.
Examples of the attached growth system are the trickling filters, rotating
biological contactors and combined attached and suspended growth processes.
Attached growth processes can be grouped into three general classes which are
nonsubmerged attached growth processes, suspended growth process with fixed-film
packing and submerged attached growth aerobic process.
2.4.2 Suspended Growth System
The theory of the suspended growth systems are when the microorganism or
bacteria are allowed to suspend in the treated wastewater for the microbe growth.
The microorganism or bacteria will utilize the wastewater as a growth medium and to
15
perform biodegradation process for treating wastewater. These suspended growth
systems required oxygen for the utilization and biodegradation process. Examples of
the suspended growth system as the operational theory are the oxidation pond,
activated sludge process and sequencing batch reactors (SBR).
2.5 Microbial Process In Aerobic Treatment
Microorganisms found in aerobic suspended and attached growth treatment
process are used for the removal of organic material. Aerobic heterotrophic bacteria
found in aerobic process are able to produce extracellular biopolymers that result in
the formation of biofilms for attached growth process that can be separated from the
treated liquid by gravity settling with relatively low concentrations of free bacteria
and suspended solid (Metcalf and Eddy, 2004).
Protozoa also play an important role in aerobic process. By consuming free
bacteria and colloidal particulates, protozoa aid effluent clarification. The aerobic
attached growth process are depending on the biofilm thickness, and generally have a
much more complex microbial ecology than activated sludge with films containing
bacteria, fungi, protozoan, rotifiers, and possibly annelid worms, flatworms, and
nematods (WEF, 2000).
Depending on process loadings and environmental conditions, a number of
nuisance organisms can also develop in the activated sludge process. The principal
problems caused by nuisance organisms are known as bulking sludge. This problem
occurs when the biological floc has poor settling characteristics. In extreme, bulking
sludge can result in high effluent suspended solids concentrations and poor treatment
performance (Metcalf and Eddy, 2004).
16
The conversion of organic matter is carried out by mixed bacterial cultures in
general accordance with the stoichiometry of:
1.
Oxidation and synthesis
COHNS + O2 + nutrients
bacteria
CO2 + NH3 + C5H7NO2 + other end products
Organic
(2.1)
New cells
matter
2.
Endogenous respiration
bacteria
C5H7NO2 + 5O2
5CO2 + 2H2O + NH3 + energy
(2.2)
cells
In equation (2.2), COHNS is used to represent the organic matter in
wastewater, which serves as the electron donor while the oxygen serves as the
electron acceptor. Although the endogenous respiration reaction, (equation (2.2)), is
shown as resulting in relatively simple end products and energy, stable organic end
products are also formed.
2.6 Factors Affecting Aerobic Process
The activity and the physical properties of the microbial community within a
system determine the efficiency of treatment in terms of substrate utilisation, floc
formation and efficient separation of the solids (specifically in gravity separators)
from the treated supernatant. In order to achieve these objectives, the environmental
and operational parameters need to be controlled are dissolved oxygen, F/M ratio,
solids retention time (SRT), organic loading, pH, temperature and nutrients.
Therefore, operational condition in the aerobic reactor must be periodically
monitored and maintained within optimum ranges.
17
2.6.1 Dissolved Oxygen
As the oxygen is low solubility in water, the oxygen transfer is often the
limiting process in achieving effective wastewater treatment objectives.
This
capacity is also influenced by environmental factors such as temperature, pressure
and salinity.
Oxygen is the key element in controlling the wastewater quality. Though the
oxygen has low solubility in wastewater, the DO concentration is significant for the
aquatic life and the microbe (Ali et al., 1999; Nafryzal Carlo, 2000). For the aquatic
life, the DO is used for the metabolism cell growth process for life in the water.
Therefore, oxygen is required for the respiration process of the aerobic
microorganism. The oxygen concentration will reduced as the temperature of the
wastewater are high, especially the wastewater come from the industrial factory.
With the DO concentrations, this will help to prevent the odour problem and the flora
and fauna.
Murat (2002) stated that, a minimum concentration of dissolved oxygen is
required by aerobic Heterotrophic bacteria to metabolise organic matter, and its
availability determines whether biological changes are carried out in an aerobic or
anaerobic environment, or whether only partial oxidation is accomplished.
The
occurrence of the nitrification also adds up to the oxygen demand of the system.
Better settling qualities were reported by Wilen and Balmer (1999) for the
DO concentrations (2.0 mg/l – 5.0 mg/l) in the aerobic reactor basins. The typical
range for the DO concentrations in activated sludge process was 1.5 to 3.0 mg/L
(Gray, 2004).
18
2.6.2 Food over Mass Ratio
The food over mass ratio (F/M ratio) is a process commonly used to
characterize process designs and operating conditions (Metcalf and Eddy, 2004).
This parameter represents the organic loading to the system and is expressed as the
ratio of COD or BOD (kg/day) for a given mass of biomass in the reactor (kg
MLVSS). The Food to Micro-organism ratio controls the rate of biological oxidation
as well as the mass of organisms present by maintaining microbial growth in the log,
declining or endogenous phase (Gray, 1989).
As stated by Gray (1989), high F/M ratios indicate high amounts of food
source available for the micro-organisms, with growth at the log growth phase. It has
been found that under these conditions, micro-organisms don’t form flocs but
generally disperse and do not readily settle. As food is in excess at high F/M ratios,
not all the organics are utilised and part of them passes on to the effluent.
During low F/M conditions, organisms are exposed to a food-limited
environment and micro-organisms function in the endogenous respiration phase, with
cell lysis and resynthesis taking place. During these conditions, there is almost
complete oxidation of the organics with low concentrations in the effluent (Metcalf
and Eddy, 2004).
Typical values for the BOD F/M ratio reported by Henze et al., (2004) are
vary from 0.04g substrate/g biomass.d for extended aeration process to 1.0g/g.d for
high rate process. The BOD F/M ratio is usually evaluated for systems that were
designed based on the SRT value to provide a reference point to activated sludge
design and operating performance.
19
2.6.3 Solids Retention Time (SRT)
The mean solids retention time (SRT), is the ratio of the micro-organisms in
the reactor to the sludge produced or wasted. It is a function of the F/M ratio and
shows the operating state of the systems in terms of organic loading and mass
loading per unit of biomass.
The SRT in effect, characterize the average period of time during which the
sludge has remained in the system. SRT is the most critical parameter for activated
sludge design as SRT affects the treatment process performance, aeration tank
volume, sludge production, and oxygen requirements. SRT values may range from 3
to 5 days for BOD removal which depends on the mixed-liquor temperature. At 18
to 25 ºC, the SRT value are near to 3 days which is the desired value where at that
time range, only the BOD removal is required and to discourage nitrification and also
eliminate the associated oxygen demand.
In order to limit nitrification, some
activated sludge plants have been operated at SRT values of 1 days or less. While at
10 ºC, the SRT values f 5 to 6 days are common for the BOD removal only (Metcalf
and Eddy, 2004).
Temperature is an important environmental condition that affects the
treatment performances. It is because changes in the wastewater temperature can
affect the biological rate.
Temperature is particularly important in nitrification
design process as the expected mixed-liquor temperature will affect the design SRT.
The precipitation affects and the groundwater infiltration are the local factors that can
influence both flow rates and constituents concentrations. If the high flow rate
occurred, these can cause the washout of solids in biological reactors (Metcalf and
Eddy, 2004).
Since nitrification process is temperature-dependent, the design SRT for
nitrification must be selected with caution as variable nitrification growth rates have
been observed at different sites, presumably due to the presence of inhibitory
substances (Barker and Dold, 1997; Fillos et al., 2000).
20
At higher F/M ratios, biomass activity increases due to the increase in
available substrate. This increase in biomass requires more continuous wasting of
the sludge to maintain a given MLSS within the reactor, and thus a reduction in the
SRT of the system (Murat, 2002).
2.6.4 Organic Loading
This parameter is expressed as kg of COD or BOD per unit volume of reactor
per unit time. It determines the organic load into the system. Low organic loadings
result in less food availability for the micro-organisms (hence a low F/M), and this
reduces the need for more efficient and vigorous oxygen transfer. On the other hand,
at high organic loading rates unless the biomass concentrations are kept high (e.g MBRs- Membrane Bioreactors) oxygen transfer limitations may occur due to high
F/M ratios.
The organic loading rate should be determined in order to get daily flow rate
and the concentration measurement that will be prepared. The organic loading rate
can be calculated using the following formula.
Organic Loading Rate 
OLR
=
kg COD * Vin
m3.dVtotal
organic loading rate (kg/m3.d)
COD =
COD value for the synthetic wastewater before treatment
Vin
=
volume of the synthetic wastewater (L)
Vtotal
=
reactor volume (L)
(2.3)
21
2.6.5
pH
This parameter will dictate the speed of biochemical reactions within
biological treatment processes by controlling the rate of enzyme production and
activity. Optimum pH levels for heterotrophic bacteria fall within a narrow range
between 6 and 8. For the autotrophic bacteria (Nitrifiers) this range is also acceptable
and it is also known that their activity rises up to pH 8.4 (Metcalf Eddy, 2004).
pH is known as the hydrogen-ion concentrations which is an important
quality parameter of both natural waters and wastewaters. The concentration range
suitable for the existence of most biological life is quite narrow and critical (typically
from 6 to 9). Wastewater with an extreme concentration of the hydrogen ion is
difficult to treat by biological means. Other than that, if the concentration is not
altered before discharge, the wastewater may influence may alter the concentration in
the natural wastewater.
For treated effluent discharged to the environment, the
allowable pH was usually varies from 6.5 to 8.5 (Henze et. al., 1999).
2.6.6
Temperature
Temperature conditions in the reactor have a direct effect upon the biological
treatment processes primarily by influencing the metabolic activities of the microorganisms and effecting on the gas transfer rates within the system.
Previous work shows that the activity of the biomass increases with the rising
reactor temperatures (Henze et. al., 2001). However the solubility of the oxygen
reduces at the same time. Experimental work has also demonstrated that widely
varying mixed liquor temperatures (25 C to 5 - 8 C) during treatment can yield an
increase in suspended solids in the treated effluent. (Ekenfelder and Musterman,
2001).
Therefore, in this study, it was aimed to analyze the effect of varying
temperature of a laboratory aerobic reactor on process performance.
22
2.6.7
Nutrients
Most domestic wastewaters contain adequate amounts of macro-nutrients for
cell utilisation. However, many industrial wastewater streams lack these nutrients
and require addition of appropriate amounts of nitrogen and phosphorus. In an
aerobic treatment process, nutrients levels were maintained in the ratio of COD: N: P
at 100:5:1 (Metcalf and Eddy, 2004).
Nutrients level must be available in adequate amounts if the biological
treatment system needs to be in a good and properly treatment function. Nutrientdeficient conditions can contribute to filamentous growth within the mixed liquor and
a reduction in the carbon removal rates. This occurs due to the “growth advantage”
that filamentous organisms have under these conditions over floc forming organisms.
Deficient conditions also may result in reduced microbial growth and partial
conversion of the organics in the wastewater stream (Murat, 2002).
2.7
Advantages and Disadvantages of Aerobic Process
Aerobic treatment has many advantages and also disadvantages.
The
advantages which are can produce a minimum odor when the aerobic system is
properly loaded and maintained, the removals of biochemical are large hence provide
good effluent quality. Other than that, the aerobic treatments are high rate treatment
that allowed smaller scale systems which is less land required. The final discharge
also may contain dissolved oxygen (DO) which can reduces the immediate oxygen
demand on receiving waters and lastly, the aerobic treatment also eliminates many
pathogens that presents in agricultural waste.
The main disadvantage of aerobic treatment is the energy cost of aeration at
an adequate rate to maintain the dissolved oxygen levels needed to maintain aerobic
conditions in the treated wastewater for aerobic growth. In addition, some organics
cannot be efficiently decomposed aerobically.
These biologically non-reactive
23
components mainly composed of insoluble materials can account for up to 70% of
the chemical oxygen demand (COD).
Another issue may rest with the fast
production of biomass (sludge build-up) due to active aerobic growth powered by a
sufficient oxygen supply by aeration, potentially leading to reduction in storage
capacity of lagoons and/or ponds.
2.8
Activated Sludge
The activated sludge process is the most commonly used treatment system for
industrial and municipal wastewater. The activated sludge process consists at least
one aeration tank (aeration period) and one sedimentation tank (settling period)
which also known as sedimentation tank. The aeration tank is a biological reactor or
amplifier in which wastes are converted through the activity of microscopic
organisms, to less polluting wastes or none polluting wastes and more solids, which
were mostly bacteria cells. The secondary clarifier is a quiescent that permits the
separation of solids from water and also removes floating foam and scum produced
in and discharged from aeration tank while the primary clarifier permits the
separation and removal of floatable materials and settleable solids (Gerardi, 2002).
The activated sludge process is capable of performing four critical wastewater
treatment functions which are 1) the degradation or oxidation of carbonaceous waste,
2) the degradation or oxidation of nitrogenous wastes, 3) the removal of fine
materials and 4) the removal of heavy metals. The objective of the activated sludge
process in treating industrial wastewater is to remove soluble and insoluble organics
and to convert this material into a flocculent microbial suspension that settles well in
conventional gravity clarifiers (Arthur, 2002). A number of modifications of the
activated sludge process have been developed to accommodate specific wastewater
characteristics and operational needs.
The activated sludge process is a rather unique biotechnological process and
not having many similarities with the other processes utilized in practice and
24
frequently called fermentations. Typical features of the activated sludge process are
(Eckenfelder et al., 2004):
1. Multifarious substrate in terms of chemical composition and variety of
particle size
2. Multispecies biological culture, desirably growing in aggregates (flocs)
3. Widely fluctuating flows, temperatures, and changes in the influent
wastewater concentration and composition
4. Ability to metabolize a vast number of organic compounds and to
oxidize/reduce/ polymerize (compounds containing nitrogen, phosphorus,
sulphur, and others)
5. A variety of reactor configurations used (completely stirred tanks, plug-flow,
sequencing batch, oxic, anoxic, anaerobic selectors and others)
The core of the activated sludge process is the aeration basin where the
conversion of the organic compounds to less harmful end products takes place in the
presence of a diverse microbial consortium. The effective conversion of the
pollutants requires certain operating conditions and reactor environments (e.g.
Mixing, Dissolved Oxygen, pH etc.) depending on the nature of the targeted organic
compound (e.g. Carbon Removal, Nitrification) and the mass loading (OLR Organic
loading rate) of the same species..
2.8.1 Characteristics of Conventional Activated Sludge System
In an activated sludge process, the microorganisms are used to feed on organic
contaminants and can produce a high-quality of effluent. The basic principle behind
the activated sludge process is the microorganisms grow and form particles that
clump together. These particles (flocs) are allowed to settle to the bottom of the tank,
25
leaving a relatively clear liquid free of organic material and suspended solids
(Metcalf and Eddy, 2004).
As stated by Metcalf and Eddy (2004), the basic activated sludge treatment
process is illustrated in Figure 2.2. From the figure, the activated sludge process is
consists of 3 basic components which are a reactor in which the microorganisms
responsible for treatment are kept in suspension and aerated, liquid separation usually
in a sedimentation tank and lastly a recycle system for returning solids removed from
the liquid-solids separation unit back to the reactor.
Figure 2.2
Typical activated sludge systems.
26
In the activated sludge process, screened wastewaters is mixed with varying
amounts of recycled liquid containing a high proportion of organisms taken from a
secondary clarifying tank, and develop into mixed liquor. This mixture is stirred and
injected with large quantities of air, in order to provide oxygen and keep solids in
suspension. After a period of time, mixed liquor flows to a clarifier and allowed to
settle. A portion of bacteria is removed when settles and the partially of its cleaned
water flows for the further treatment. The resulting settled solids which are the
activated sludge are returned to the first tank to begin the process again.
The activated sludge process is applied widely by large cities and
communities where large volumes of wastewater must be highly treated. The used of
activated sludge practiced are good options for small communities and also cluster
situations.
2.8.2 Activated Sludge Process Design Requirements
As described by Metcalf and Eddy (2004), there are several important
considerations in design activated sludge process. The activated sludge process
design requirements are:
1. The aeration basin volume
2. The amount of sludge production
3. The amount of oxygen needed
4. Effluent concentration of important parameters such as heavy metals,
chemical oxygen demand (COD) and total suspended solids and volatile
suspended solids.
To design the activated sludge treatment process properly, characterization of
the wastewater is the most critical and important step in the activated sludge process
27
design requirements.
For biological nutrient-removal processes, wastewater
characterization is critical part in predicting the process performance.
The
wastewater characterization is also an important element in evaluated the existing
facilities for optimizing performance and available treatment capacity. Other than
that, the flow characterization is also important which include the diurnal, seasonal
and wet-weather flow variations. Without complete and comprehensive wastewater
characterization, the facilities may become overdesign or under design and results to
inadequate and inefficient treatment process requirements.
The wastewater characteristics are importance in the design of the activated
sludge process. The wastewater characteristics can be grouped into carbonaceous
substrates, nitrogenous compounds, phosphorus compounds, total and volatile
suspended solids (TSS and VSS) and alkalinity (Yong, 2008)
2.8.3 Process Analysis and Control of Activated Sludge Process
As described by Eckenfelder et al., (2004), in the design of the activated
sludge process, consideration must be given into the following factors which are the
selection of the reactor type, applicable kinetic relationships, solids retention time
and loading criteria to be used, sludge production, oxygen requirements, nutrient
requirements, other chemical requirements, settling characteristics of biosolids, use
of selectors, effluent characteristics.
2.8.3.1 Selection of Reactor Type
Important factors that must be considered in the selection of reactor types for
the activated sludge process include the effects of reaction kinetics, oxygen transfer
requirements, and nature of the wastewater, local environmental conditions, presence
28
of toxic or inhibitory substances in the influent wastewater, costs and also the
expansion to meet future treatment needs (Metcalf and Eddy, 2004).
2.8.3.2 Kinetic Relationships
The kinetic relationship is used to determine the biomass growth and
substrate utilization and also define the process performance. Important kinetics
relationships factors are the effect of reaction kinetics, oxygen transfer requirements,
nature of wastewater, local environmental conditions, toxic or inhibitory substances,
costs and the effluent characteristics.
The detail of the important kinetics
relationships factors are illustrated in Table 2.1.
29
Table 2.1
Important kinetics relationships factors (adapted from Metcalf and
Eddy, 2004).
FACTOR
Effect of reaction
kinetics
-
Oxygen transfer
requirements
-
Nature of wastewater
-
Local environmental
conditions
Toxic or inhibitory
substances
-
-
Costs
-
Effluent characteristics
-
DESCRIPTION
Two types of reactor commonly used are complete-mix
and plug-flow reactor
The hydraulic detention time of the complete-mix and
plug-flow reactor are about to same
It is because the designs BOD removals are generally
governed by sufficient SRT to assure good settling
properties and longer duration is needed for BOD
removal.
Most of the past oxygen transfer limitations have been
overcome by better selection of process operational
parameters and improvements in the design and
application of aeration equipment
Includes the overall characteristics as affected by
contributions such as domestic wastewater and
industrial discharge
Alkalinity and pH are important for the nitrification
process
pH adjustment may be required because low pH inhibit
the growth of nitrifying organism
Industrial discharge may also affect the pH by lowalkalinity wastewaters
Temperature affects the treatment performance because
change in the wastewater temperature affects the
biological reaction rate
Temperature is important in nitrification design
For municipal wastewater treatment systems with large
number of industrial connections, the potential of
receiving inhibitory substances that can affect
nitrification are high
Construction and operational cost are the important
considerations in selecting the type and size of the
activated sludge reactor
Potential future treatment needs can have an impact on
present process selection
2.8.3.3 Solids Retention Time and Loading Criteria
The common parameters that are differentiating for the designs and operating
of the activated sludge reactor are solids retention time (SRT) and the food to
biomass ratio (F/M) and the volumetric organic loading rate. The SRT is the basic
30
design and operating parameter while the F/M ratio and volumetric loading rate
provides the useful values that are useful in comparing the historical and typical
observed operating conditions data.
2.8.3.4 Sludge Production
The design of the sludge handling and disposal/reuse facility depends on the
prediction of the sludge production for the activated sludge process. The sludge
handling facilities will affect the treatment process performance. The sludge will
accumulate in the activated sludge process if it cannot be processed fast enough by
an undersized sludge handling facilities.
Two methods are used to determine sludge production. The first methods are
based on an estimate of an observed sludge production yield from published data
from similar facilities. The second method is based on the actual activated sludge
process design. It is when the characterization is done and the various sources of
sludge production are in considerations (Eckenfelder et al., 2004).
2.8.3.5 Nutrients and Other Chemicals Requirements
Nutrients levels which are the nitrogen and phosphorus levels must be
available in adequate amounts if the biological systems need to be function properly.
If the amount of nutrient are fail to be accomplish, it will affect the process
performance of the activated sludge reactor and also the sludge bulking problems can
occur. Therefore sufficient amount of nutrients should be provided and the study on
the nitrogen and phosphorus optimum concentrations in the wastewater should be
done.
31
Alkalinity is the major chemical requirements needed for nitrification. The
amount of alkalinity must be available to maintain the pH in the neutral range
2.8.4 Issues on Design, Operation and Maintenance of Conventional Activated
Sludge System
In the wastewater treatment system using activated sludge process, there are
several and common problems encountered. Most of the common problems and
issues that usually encountered in activated sludge process are sludge bulking and
foaming, rising sludge, long processing time, occupy substantial land areas and the
system is high cost. Following sub-section are discussing more detailed on this
issues.
2.8.4.1 Sludge Bulking
Sludge bulking and foaming are common and serious problems in activated
sludge operation. The Sludge bulking and foaming are the most problems affecting
the activated sludge plants at one time or other. Most of the effluent non-compliance
problems are the caused by filamentous bulking.
The bulking sludge problems occur when the MLSS have a poor settling
characteristics develop and defines as a condition in the activated sludge clarifier
caused high effluent suspended solids and poor treatment performance. In a bulking
sludge condition, the MLSS floc does not compact or settle well and floc particles are
discharged in the clarifier effluent. In extreme bulking sludge conditions, the sludge
blanket cannot be contained and large quantities of MLSS are carried into the system
effluent and potentially resulting in violation of permit requirements, inadequate
disinfection, and clogging of effluent filters (Metcalf and Eddy, 2004).
32
There are two principal of sludge bulking problems.
The first type is
filamentous bulking that caused by the growth of filamentous organisms or
organisms that can grow in a filamentous form under adverse condition. The second
types of bulking problems are the viscous bulking which caused by an excessive
amount of extracellular biopolymer, which produces sludge with a slimy, jellylike
consistency (Wanner, 1994).
A bulking sludge also defined as one that settles and compacts slowly. An
operational definition often used is, a sludge with a sludge volume index (SVI) of >
150 mL/g. However, each plant has a specific SVI value where sludge builds up in
the final clarifier and is lost to the final effluent. It can vary from a SVI <100 mL/g
to > 300mL/g, depending on the size performance of the final clarifiers and hydraulic
considerations (Richard, 2003). Thus, a bulking sludge may or not lead to a bulking
problem. It depends on the specific treatment plants ability to contain the sludge
within the clarifier.
A bulking sludge can result in the loss of sludge inventory to the effluent. Thus,
can causing environmental damage and effluent violations. In severe cases, loss of
the sludge inventory can lead to a loss of the plants treatment capacity and failed the
operational process. Furthermore, the excess solids present during bulking leads to
excessive return sludge recycle rates and problems in waste activated disposal. Many
problems in waste sludge thickening are sludge or filamentous bulking problems
(Crocetti, 2008)
Sludge bulking and foaming also have wider implications rather than difficult
the secondary settling. The sludge bulking and foaming also can results on the low
setleability in poor effluent quality due to a high solids carry-over from the secondary
settlers. The high effluents solids can be described as to incomplete settling process
as well as anoxic conditions develop in the settler due to sludge accumulation.
Denitrification occurs and the resulting nitrogen bubbles will cause the sludge
particles to float. The poorly compacted sludge results in excessive waste sludge
volumes usually with poor thickening properties with respect to gravity settling and
33
dissolved air flotation (Bratby, 1977) and poor dewaterability in centrifuges and belt
press (Osborn et al., 1986).
Many types of filamentous bacteria exist, and have been developed for the
identification and classification of filamentous bacteria found commonly in activated
sludge systems (Eikelboom, 2000). Sludge bulking can be caused by a variety of
factors including wastewater characteristics, design limitations, and operational
issues.
Individual items that are associated with each of these categories are
identified in Table 2.2.
Table 2.2
Factors that affect sludge bulking (adapted from Metcalf and Eddy,
2004).
FACTOR
\Wastewater characteristics
DESCRIPTIONS
Variations of flow rate
Variations in compositions
Design limitations

pH

Temperature

Septicity

Nutrient content

Nature of waste components
Limited air supply
Poor mixing
Short circuiting (aeration tank and clarifiers)
Clarifier design (sludge collection and removal)
Limited return sludge pumping capacity
Operational issues
Low dissolved oxygen
Insufficient nutrients
Low F/M
Insufficient soluble BOD
34
2.8.4.2 Rising Sludge
Pastor et al., (2008) described that the sludge rising problems is only seen in the
final settling tank and has definite operational causes and it can be corrected through
an understanding of the system and defined management practices. The biological
oxidation of a wastewater is a two-phase reaction where the organic carbon oxidation
occurs first and followed by the biological oxidation of ammonia or nitrification.
Generally, sludge that has good settling characteristics will be observed to rise
or float to the surface after a relatively short settling period. The most common
cause of this problem is denitrification. Denitrification occurs in the sludge layer in
the secondary clarifier when conditions become anaerobic or nearly anaerobic. As
the nitrogen gas accumulates, the sludge mass becomes buoyant and rises or floats to
the surface (Pitt and Jenkins, 1990). Rising sludge can be easily differentiated from a
bulking sludge by noting the presence of small gas bubbles attached to the floating
solids and by microscopic examination.
This problem can be overcome by
increasing the removal rate of the sludge from sludge colleting mechanism, by
regulation of the flows (loading) and monitoring of the dissolved oxygen levels in the
final settling tank.
Rising sludge problems can be overcome by increasing the return activated
sludge withdrawal rate from the clarifier to reduce the detention time of the sludge in
the clarifier and also decreasing the rate of flow of aeration liquor into the offending
clarifier if the sludge depth cannot be reduced by increasing the return activated
sludge withdrawal rate. Other than that, the rising sludge problems also can be
overcome by increasing the speed of the sludge-collecting mechanisms in the settling
tanks and also decreasing the SRT to bring the activated sludge out of nitrification.
35
2.8.4.3 Processing Time
Typically, the conventional activated sludge system took a long time to treat a
large volume of wastewater, especially in the big cities. As example described by
Marilyn (2003), the normal processing time for an extended aeration (systems that
are based on the activated sludge technology) is 24 hours to turn out effluent from a
high quality wastewater system that can be put back into the ground which is after
chlorination.
The relatively poor settling characteristics of conventional activated sludge floc
also lead to the system facing with time consuming problems of biomass and effluent
separation in secondary clarifier, which took more than hour (Hastings et al., 2007).
Therefore, a system with short processing time and produce efficient and affective
treatment process is required to improve the old technology.
2.8.4.4 Large Area Requirements and High Energy Cost
The activated sludge plants required large land areas and expensive in costs
terms. It is because, the activated sludge process required a large and costly settling
tanks and aeration basins to settle out and digest biosolids in the waste stream as well
as the introduction of bacteria, chemicals, or membranes in order to treta the sewage
and industrial waste and remove the amount of leftover sludge (Metcalf and Eddy,
2004).
Other than that, high energy cost are required in the operations of the activated
sludge process due to the pumping of oxygen into aeration tanks and also to the
operating moving screens or filters.
The activated sludge process also produce
significant amounts of sludge which must be further treated and disposed at the
excessive cost.
36
More importantly, as stated by Badreddine (2008), the local odour emission
regulations require that no gas or odour emissions may be released within 100 metres
of residential areas.
Therefore, the activated sludge system needs addition
equipments or other solutions, to overcome and control the odour problems. This
may lead to the increase of the equipments cost, maintenance and labour will become
expensive and also will consume a large amount of space and energy.
Therefore, nowadays more researchers were looking for new alternatives
technology for improving wastewater treatment systems in which was cost effective,
less energy requirements, reduced the processing time, less land area are required,
enhanced odour control and also can adopt at many changes and conditions of the
wastewater and also changes in the environmental factors such as temperature and
pH. Therefore, in this study, the efficiency of a submerged membrane activated
sludge reactor in treating synthetic wastewater which was similar to industrial
wastewater was being studied in order to determine the efficiency of the reactor as an
effective alternative technique in treating industrial wastewater. This study also
analyzes the effect of varying temperature of a laboratory aerobic digester on process
performance.
During the last decades, different compact treatment systems are developed
based on the activated sludge systems process such as sequencing batch reactors and
membrane bioreactors.
2.9
Sequencing Batch Reactors
The sequencing batch reactor (SBR) is a process that utilizes a fill-and-draw
activated sludge system. The fill-and-draw is a complete mixing process during the
batch reaction step (after filling) and where the subsequent steps of aeration and
clarification occur in the same tank. The processes of equalization, aeration, and
clarification are all achieved in the same tank, unlike a conventional activated sludge
37
system where the same processes are accomplished in separate tanks (Morgenroth et
al., 2000).
Wastewater is added to the tank and treated to remove undesirable components
and then is discharged. SBR systems consist of five common steps carried out in
sequence as follows: (1) fill, (2) react (aeration), (3) settle (sedimentation /
clarification), (4) draw (the effluent is decanted), and (5) idle.
Sludge wasting
usually occurs during the settling phase. The SBR act as an equalization basin when
filling with the wastewater and enabling the system to tolerate peak flows or loads
(Guo et al., 2007). Table 2.3 illustrates the description of operational steps for the
SBR.
Table 2.3
Description of operational steps for the Sequencing Batch
Reactors (SBR) (adapted from Metcalf and Eddy, 2004).
OPERATIONAL
STEP
Fill
DESCRIPTION
-
React
-
Settle
-
Decant
-
Idle
-
-
Volume and substrates are added to the reactor
The fill process typically allows the liquid level in the
reactor to rise from 75% of capacity to 100%
When two tanks are used, the fill process may be mixed
and aerated to promote biological reactions with the
influent wastewater
The biomass consumes the substrate under controlled
environmental conditions
Solids are allowed to separate from the liquid under
quiescent condition
Resulting in a clarified supernatant that can be
discharged as effluent
Clarified effluent is removed during the decant period
Many types of decanting mechanisms can be used
(floating or adjustable weirs)
Used in a multitank system to provide time for one
reactor to complete its fill phase before switching to
another unit.
Idle is not necessary phase, it is sometimes omitted
After passing through a screen to remove grit, the effluent enters a partially
filled reactor. Once the reactor is full, it performs like a conventional activated
sludge system without a continuous influent of effluent flow. Aeration and mixing
are discontinued after the biological reactions are complete and the solids are allowed
38
to settle, and the treated effluent (supernatant) is removed.
Excess solids are
removed at any time during the cycle. Figure 2.3 shows the typical SBR operation
for one cycle.
Figure 2.3
Typical SBR operations for one cycle
SBR are typically used where flow rates are five million gallons per day or
less. The SBR systems required small land area and useful in areas where available
land is limited. Furthermore, it is easy to modify cycles within the system for
nutrient removal if required and necessary. The SBRs systems are also cost effective
if filtration process is required. SBRs also offer potential capital cost savings by
eliminating the need for clarifiers (Wang et al., 2006).
Other than that, SBRs requires a complicated level of maintenance due to
timing units and controls.
Depending upon downstream processes, it may be
necessary to equalize effluent after leaving the SBR (Nor Anuar, 2008).
2.10
Membrane Bioreactors
A membrane biological reactor (MBRs) is consisting of a biological reactor
(bioreactor) with suspended biomass and solids separations by microfiltration
membranes. The MBR are based on a combination of activated sludge processes and
membrane filtration in one treatment steps.
An ultrafiltration or microfiltration
39
membranes separates the activated sludge from the effluent. The membrane can be
applied within the bioreactor or externally through recirculation. Since external
settlers, or any other post treatment step, become superfluous by using a membrane
for the suspended solids and effluent separation, the required space for an installation
is small and sludge concentration in the aeration tanks can be two or three times
higher than in conventional systems (Nor Anuar, 2008). Furthermore, the effluent
quality is significantly better as all suspended and colloidal material as micro
contaminants, bacteria and viruses is removed (Ujang and Anderson, 2000; Trussell
et al., 2005).
Membrane biological reactors have been used for treatment of both municipal
and industrial wastewater (Brindle and Stephenson, 1996; Van Dijk and Roncken,
1997; Trussell et al., 2000). Biological processes in a MBR are often comparable
and beter than conventional activated sludge systems.
It is because, the MBR
systems can produce long sludge ages, N-removal is more efficient because the slow
growing autotraph are kept efficiency in the systems. Other than that, denutrification
can occur by introducing anoxic tanks or intermitted aeration (Drews et al., 2005;
Gander et al., 2000). Figure 2.4 shows the typical MBR systems.
Figure 2.4
Typical MBR systems.
As stated by Ujang et al., (2007), despite the excellent effluent quality, the
breakthrough of the MBR technology is sill lacking. This is mainly due to the cost
40
involved with membrane modules.
Furthermore, the present generation of
membranes show low permeability due to fouling, operation of membranes are still
relatively expensive (Brouwer et al., 2005).
MBRs substitute the secondary settling tanks with membrane separation
units. Their effectiveness in terms of reduction in foot print and replacing process
units can be observed on Figure 2.5 (Gunder and Krauth, 1998). In addition to being
very compact, the MBR systems are very robust to shock loads and several other
environmental and operational factors which can interfere with the biological
conversion processes and the separation efficiency.
In previous studies on MBRs, organic loading rates ranging from <1
kgCOD/m3/day to 3.2 kgCOD/m3/day was experienced with removal efficiencies
more than 95% (Ueda and Hata, 1999; Buisson et. al., 1998; Rosenberger et. al.,
1999; Bouhabila et al., 1998). Table 2.4 represents some MBRs applications to
industrial wastewaters.
Figure 2.5
Replaced units in a wastewater treatment plant with the use of MBR
(Adapted from Gunder and Krauth, 1998).
41
Table 2.4
Examples of MBR Applications to different types of wastewaters
(adapted from Murat, 2002).
Industry
Chemical
Influent
Effluent COD OLR
Reference
COD mg/L
mg/L
(kgCODm3/day)
10000
<400
3
Industry
Landfill
and
Roncken, 1997
4000
<400
0.7
Leachate
Food
Dijk
Dijk
and
Roncken, 1997
42660
70.8
up to 10.3
Processing
Krauth
and
Staab, 1993
Municipal
457
16
2.3
Tannery
2614
119
approx. 1
Brewery
68000
1350
16
Cote et al., 1998
Krauth, 1996
Kempen et al.,
1997
Oily wastes
29400
<2720
0.7
Zaloum et al.
1994
2.10.1 Classification of MBRs
There are mainly two types of membrane bioreactors in terms of the location
of the membrane unit and the flow through the membrane surface. These are cross
flow filtration and the submerged membrane filtration (Figure 2.6). Both systems
can accommodate MF and UF membranes to serve the needs of the required effluent
characteristics.
However, the common pore size is generally in the range of
microfiltration (0.1-0.4μm). During operation, it is also known that the membrane
effective pore size reduces due to concentration polarization and cake formation on
the membrane surface. This leads to an ultra-filtration effect.
42
Figure 2.6
External Loop Crossflow and submerged systems (adapted from Cote
et. al., 1998)
2.10.2 External Loop (Side- stream) Cross-flow Membrane MBR
The Cross-flow Membrane MBR also called as external separation loop
membranes. The membrane unit is outside the bioreactor and reactor content is
circulated with pumps through the membrane unit back into the reactor. It is also
known that sparging air into the membrane unit also improves the flux by reducing
the cake formation. Such systems do not need high crosflow velocities and energy
savings can be achieved during operation. On the other hand in terms of access to
the membrane modules this type of configuration is superior to the submerged
applications. The membrane units can be individually isolated and replaced without
interrupting the operation of the plant (Murat, 2002).
Because of the biomass characteristics tubular modules are the widely used
configuration for external loop systems. There are also modules with plate and frame
or large hollow fibres.
43
2.10.3 Submerged Membrane
The Submerged Membrane type of configuration seems to be the future for
MBRs. At the moment many MBR plants are equipped and operated with immersed
membranes (eg Zenon (Cote et. al., 2000), Kubota (Churchouse, 1998)) that require
low pressures as low as 5psi for permeated production.
Main feature of this configuration is the submerged membrane elements
located in the activated sludge tank. The aeration provided at the bottom of the
membrane modules provides the continuous cleaning of the membranes by reducing
the concentration polarisation layer. These membrane units can also be mounted in a
different compartment to provide ease of handling and cleaning. Currently two types
of membrane modules are used inside bioreactors, plate frame panels and hollow
fibre modules (cassettes).
The cross-flow on the membrane surface to reduce the concentration
polarisation and the cake formation are provided via the aeration device placed below
the membrane elements.
Aeration is usually coarse bubble aeration.
During
operation uprising air liquid mixture generates a cross flow and turbulence on the
surface of the membrane, reducing the filter cake formation and decay of the flux.
The aeration also provides all or part of the oxygen that is required by the biological
system for the conversion of the organics (Murat, 2002).
Permeate is produced via a suction pump that provides the transmembrane
pressure (≤5psi by Milleniumpore- Wilkes, 1999). Diagrams in Figure 2.7 show the
two different set-ups for submerged membranes.
44
Figure 2.7
2.11
Two different set-ups for submerged membranes.
Effect of Temperature
Temperature affects all biological reactions. The magnitude of the effect is
related to the characteristics of the wastewaters organics and their physical state
(suspended, colloidal, or soluble).
The aerobic process is generally used at smaller wastewater treatment plant
and mostly at ambient temperature rates. The degradation rate is even smaller, about
30 – 40 %. at 50 days retention time (Borchardt et al., 1981; Aasheim, 1985; EPA,
1990). The aerobic digestion of biological sludge is a continuation of the activated
sludge process under endogenous conditions (Rös et al., 1993)
The operating temperature of the aerobic systems is the main parameter in
this study. Because the aerobic digestion system is a biological process, the effects
of temperature can be estimated by the following equation (Larry, 1980: Borchardt et
al., 1981; Aasheim et al., 1985; Metcalf and Eddy, 2004).
KT = K20 X Ө(T-20)
(2.4)
45
reaction rate coefficients at temperatures of T and 20 ºC, respectively, d -1
KT, K20
=
T
= mixed liquor temperature, ºC
Ө
= empirical temperature correction coefficient, dimensionless
The rate of biological processes generally increases with temperature.
Hartman (1979) found a maximum volatile solids destruction rate at 30 ºC with a
reduction in rate at higher temperature.
It should be noted that a significant difference in the effect of temperature and
substrate removal has been found for municipal wastewater as compared to industrial
wastewater. This is because, a primary substrate removal mechanism for municipal
wastewater is the biological entrapment of suspended and colloidal organics (a
physical phenomenon that is insensitive to temperature) (Eckenfelder, 2001).
In countries that have season changes, the magnitude of the temperature effect
on removal of specific compounds creates operating problems when low effluent
values are required on a year-round basis. In many cases, permit values are readily
achievable during summer operation but difficult or impossible to achieve during
winter operation.
In addition to the temperature affect on the biological reaction rate, two other
temperatures related phenomena must be take considerations. As the mixed liquor
temperature decreases, from approximately 25 ºC towards 5 to 8 ºC, there may be an
increase in effluent suspended solids. These suspended solids are typically nonsettleable, dispersed in nature, and are not removed by conventional clarification
processes.
There have been some efforts to operate the activated sludge process in the
thermophilic range (45 ºC to 55 ºC) when the influent wastewater temperature is
already in this range and the BOD is high (2500 – 3000 mg/L).
Under these
operating conditions, the sludge generated was frequently difficult to separate, the
mixed liquor was dispersed, and effluent solids concentrations were high.
46
While the activated sludge process can adapt to a wide range of temperature,
it will become unstable with a sudden temperature change. This will cause floc
dispersion and an increase in effluent suspended solids.
When the industrial
wastewater has a high soluble substrate load, this will decrease the process efficiency
at reduced mixed liquor operates temperatures and will increase the temperature
coefficient at the combined process.
Study on the effect of digestion temperature and pH on treatment efficiency
and evolution of volatile fatty acids during thermophilic aerobic digestion of model
high strength agricultural waste done by J. Obeta Ugwuany (2002) results shows that,
the efficiency of treatment increase with the temperature of digestion, dropping only
slightly as the temperature increased above 60 ºC. Furthermore, in full scale process,
the choice of digestion temperature (above 50 ºC) depends on nature of waste.
Daigger et al., (1999) described that the effect of pH levels in an aerobic
digester which was carried in 3-stage digester system. This research was study on
the effect of both high dissolved oxygen and high temperature on pH fluctuation.
The results conclude that high DO causes low pH. The high temperature also causes
high pH which at high temperature there is faster generation of ammonia from the
heterotrophic protein degradation.
Temperature effect in the performance of aerobic digesters will affect the rate
of volatile solids reduction and pathogen reduction.
The rate of volatile solids
reduction increases as the temperature increases. With all biological processes, the
higher the temperature, the higher the efficiency. Temperature less than 10 ºC (50
ºF), the process is basically ineffective.
This study was focused on pathogen
destruction and volatile solids performance of 3-stage digester systems operated at
temperature in the range of 8-31ºC (Daigger et al., 1999).
47
2.12
Summary of Literature Review
From the literature review above, it can be concluded that:
1. The activated sludge process is capable of performing four critical wastewater
treatment functions which are the degradation or oxidation of carbonaceous
waste, the degradation or oxidation of nitrogenous wastes, the removal of fine
materials and the removal of heavy metals. A number of modifications of the
activated sludge process have been developed to accommodate specific
wastewater characteristics and operational needs.
2. A membrane biological reactor (MBRs) is consisting of a biological reactor
(bioreactor) with suspended biomass and solids separations by microfiltration
membranes. The Submerged Membrane type of configuration seems to be the
future for MBRs. Main feature of this configuration is the submerged
membrane elements located in the activated sludge tank. The aeration is
provided at the bottom of the membrane modules provides the continuous
cleaning of the membranes by reducing the concentration polarisation layer.
3. The activity and the physical properties of the microbial community in
aerobic systems determine the efficiency of treatment in terms of substrate
utilisation, floc formation and efficient separation of the solids (specifically in
gravity separators) from the treated supernatant.
4. Important environmental factors affecting aerobic process are dissolved
oxygen, F/M ratio, solids retention time (SRT), organic loading, pH,
temperature and nutrients. Therefore, operational condition in the aerobic
digester must be periodically monitored and maintained within optimum
ranges.
5. Temperature affects all biological reactions. The magnitude of the effect is
related to the characteristics of the wastewater organics and their physical
state. Previous study shows that the activity of the biomass increases with the
rising reactor temperatures (Henze et. al., 2001). However the solubility of
the oxygen reduces at the same time.
Experimental work has also
48
demonstrated that widely varying mixed liquor temperatures (25 C to 5 - 8
C) during treatment can yield an increase in suspended solids in the treated
effluent. (Eckenfelder and Musterman, 2001).
6. There have been some efforts to operate the activated sludge process in the
thermophilic range (45 to 55 ºC) when the influent wastewater temperature is
already in this range and the BOD is high (2500 to 3000mg/L). Under these
operating conditions, the sludge generated was frequently difficult to
separate, the mixed liquor was dispersed, and effluent solids concentrations
were high (Grau and Eckenfelder, 2001). The activated sludge process can
adapt to a wide range of temperatures but will become unstable with a sudden
temperature change. This will causes floc dispersion and increase in effluent
suspended solids (Eckenfelder, 2001).
CHAPTER 3
RESEARCH METHODOLOGY
3.1
Introduction
This chapter describes materials and methods used by which experiments
were carried out. The Submerged Membrane Activated Sludge system configuration,
operation system of the reactor and the analysis of the samples for each parameter
will be discussed.
This chapter is divided into three main sections which is the preparation of
the experiment apparatus, experiment method used for the important parameter that
influence the treatment of the synthetic wastewater by the used of the Submerged
Membrane Activated Sludge reactor.
This chapter will also discuss the reactor feeding require and nutrients, seed
sludge, the effect of temperature, sampling analysis and on-line measurements of the
research. The laboratory analysis were conducted according to Standard Method,
APHA 1998.
50
3.2
Study Outline
Methodology flowchart is performing in order to fulfil the operation and
analysis of the study to optimize data analysis. Figure 3.1 illustrates the flowchart of
this study. The study was divided into three phases. In phase 1, reactor start-up and
acclimatization to synthetic wastewater in Submerged Membrane Activated Sludge
reactor was investigated. Phase 2 was conducted when COD removal of 50% was
achieved. The last phase (Phase 3) was carried out when COD removal of 70% was
achieved and was carried out at a temperature of ranging between 27 ºC to 47 ºC.
51
Figure 3.1
Outline of the study
52
3.3
Design of Submerged Membrane Activated Sludge reactor
The Submerged Membrane Activated Sludge reactor used in this study is
shown in Figure 3.2. The reactor was a cylindrical shape, 380 mm high and 242 mm
in diameter. The operational volume of the reactor was 20 litres because it included a
membrane 380 mm and 180 mm in diameter, and was hopper bottomed.
The
membrane was made of a polymer material (HDPE) with has a thickness of 3.5 mm.
The membrane pore size ranged between 0.1 – 1mm, played the role of a secondary
clarifier. Peristaltic pumps were used to supply the feed. Aeration was provided by
the laboratory compressed air system with a diffuser stone located in the reactor. The
DO concentration was maintain by DO metre at a minimum range of 1.5 mg/L at all
times.
Figure 3.2
Submerged Membrane Activated Sludge reactor.
53
A storage tank contained the feed which was the synthetic wastewater which
were fed at a constant rate by means of pump to the membrane aeration vessel,
contained within an outer impermeable vessel. Effluent passed through the pores of
vessel, which retained nearly all the sludge and overflowed through the outlet of
vessel into the collection tank. A diffuser stone aerator was suspended in vessel
while the air flow through the aerator was controlled by a rota meter. The schematic
diagram of the Laboratory – scale Submerged Membrane Activated Sludge reactor
used in this study is shown in Figure 3.3.
Figure 3.3
Laboratory – scale Submerged Membrane Activated Sludge reactor.
54
3.4
Operational Method of Submerged Membrane Activated Sludge Reactor
The operational method of the Submerged Membrane Activated Sludge
reactor will be divided into three main sections which are the flowrate
determinations, organic loading rate determinations, preparation of the synthetic
wastewater (feed and nutrients) and seeding process of the Submerged Membrane
Activated Sludge Reactor.
3.4.1
Organic Loading Rate
The organic loading rate should be determined in order to obtain the flowrate
and the concentrations and quantity of the synthetic wastewater that will be prepared.
As describe in Chapter 2, the organic loading rate should be determined in order to
get daily flow rate and the concentration measurement that will be prepared. The
organic loading rate can be calculated using equation (2.3).
OLR
=
(500/106) x 20
20/1000
=
0.55 kg/m3 .d
In the operational of the Submerged Membrane Activated Sludge Reactor, the
COD concentrations of the synthetic wastewater was sustain in the range of (500 ±
600 mg/L) and the COD concentration of the synthetic wastewater was assumed to
be 500 mg/L. The Vin and the Vtotal of the reactor was 20 L. From the calculation
carried out, the OLR values obtain in the reactor was 0.5 kg/m3.d and will be at a
constant value (0.5 kg/m3.d) during all the Submerged Membrane Activated Sludge
study.
55
3.4.2
Feed and Nutrients
Synthetic wastewater is a feeding solution containing chemical substances
which are being produced in order to equalize the characteristic of actual wastewater.
The composition of synthetic wastewater that being prepared contained 6 chemicals
substances which are glucose, ammonium chloride ((NH4)Cl), magnesium sulphate
(MgSO4.7H2O), calcium chloride (CaCl2.2H2O), kalium hydrogen phosphate
(K2HPO4) and kalium dehydrogen phosphate (KH2PO4). These chemical substances
will be measured accordingly to the specified mass required. The compositions of
synthetic wastewater used in this study are given in Table 3.1.
Table 3.1
Chemical composition of the synthetic wastewater.
Components
Concentrations Composition Function
(g/L)
K2HPO4
0.09
pH, source of K,P
CaCl2.2H2O
0.007
pH
KH2PO4
0.05
Source of K,P
(NH4)Cl
0.32
Source of N, S
MgSO4.7H2O
0.60
Source Mg, S
Glucose
0.50
Source of C and Energy
Distilled water
The chemical components in Table 3.1 was measured and filled in a 1000 mL
beaker. 1 litre of distilled water was added and the composition of synthetic that
being produced will being stirred. Dilution was being done by adding 3 litre distilled
water into the prepared synthetic composition.
These synthetic wastewater
compositions were prepared daily because lacked of storage area and also to avoid
bacterial grow in the feed tank.
Figure 3.4 shows the chemicals used for the
preparation of the synthetic wastewater.
56
Figure 3.4
Chemicals used for the synthetic wastewater.
Submerged membrane activated sludge reactor was operated 24 hours, which
the hydraulic retention time (HRT) was 2 days. 5 cycles is being done (temperature
27 ºC, 32 ºC, 37 ºC, 42 ºC, 47 ºC) and each temperature analysis was measured in 13
days.
3.5
Seed Sludge
The reactor was seeded with aerobic digested pharmaceutical sewage taken
from Glaxo Smith Kline (GSK), near Ulu Kelang. It was first sieved (<3 mm) to
remove unwanted debris and particles giving a final MLSS concentration of 3000 ±
2000mg/L which was 2500mg/L. The sludge was then introduced into the reactor
through the anterior inlet of the reactor tank. The remaining volume of the reactor
was filled with the feed of synthetic wastewater. The reactor was then allowed to
stabilize for 24h prior starting the experiments and was aerated continuously with an
aquarium air stone with compressed air supplied at approximately 3 L/min to
maintain dissolved oxygen concentration of 1.5 to 3.0 mg/L. Figure 3.5 shows
wastewater treatment plant Glaxo Smith Kline (GSK) company while Figure 3.6
shows the sludge collected at Glaxo Smith Kline (GSK) company.
57
Figure 3.5
Wastewater treatment plant at Glaxo Smith Kline (GSK) company.
Figure 3.6
Sludge collected at Glaxo Smith Kline (GSK) company.
58
3.6
Design of Experiments
Different temperatures, starting at 27 ºC were selected to study the effect of
temperature on the efficiency of submerged membrane activated sludge reactor.
Other temperatures studied were 32, 37, 42 and 47 ºC. Studies on the effects of
temperatures were carried out as the pH was maintained in the range of 6.5 to 8.00 by
adjustment of the feed pH with NaOH. Changes in the temperature of the control
reaction were measured at 24 hourly intervals by the use of calibrated pH probe.
Nutrients levels were maintained in the ratio of COD: N: P at 100:5:1 (Metcalf and
Eddy, 2004).
The biomass was considered to be acclimatized when MLSS
concentration maintained constant levels (3000 ± 2000 mg/L). The reactor was
aerated continuously with an aquarium air stone with compressed air supplied at
approximately 3 L/min to maintain dissolved oxygen concentration of 1.5 to 3.0
mg/L which was the typical range for activated sludge process (Gray, 2004). Table 3
2 shows the reactors operating condition of the reactor with the change of
temperature value range from 27 ºC to 47 ºC.
Table 3 2
Influent COD
Temperature (ºC)
(mg/L)
3.7
Operating condition of the reactor.
HRT
Flow Rate
Operating
(days)
(L/hr)
Days
500±600
27
2
0.42
13
500±600
32
2
0.42
15
500±600
37
2
0.42
13
500±600
42
2
0.42
13
500±600
47
2
0.42
13
Sampling and Analysis
Supernatant liquor was taken for analysis of the effluent.
Monitoring
procedure including experiment number and frequency is tabulated in Table 3.3.
Sample analyses included chemical oxygen demand (COD), pH, mixed liquor
59
suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS),
dissolved oxygen (DO), all was determined by the method described according to the
Standard Methods (APHA 1998). Detailed chemical analysis is discussed below.
Table 3.3
Monitoring schedule for chemical analysis.
PARAMETER
Flowrate
COD
TEST FREQUENCY
SAMPLING POINT
1x / week
Feed
3 x / week
Feed Tank
In Reactor
3 x / week
In reactor
3 x / week
Effluent Tank
pH
Daily
In reactor
Temperature
3 x / week
In reactor
Solids : MLSS/MLVSS
3 x / week
Effluent Tank
DO
Daily
In reactor
Feed
1x / week
Feed Tank
Effluent
1x / week
Effluent Tank
Feed
1x / week
Feed Tank
Effluent
1x / week
Effluent Tank
1x / week
Feed Tank
1x / week
Effluent Tank
Effluent
Nitrogen
Phosphate
Trace Elements Feed
Effluent
3.7.1 COD Measurements
The strength of the feed solution and the effluent organic material
concentrations were measured by conducting the COD test. The COD test involved
the oxidation of organic species in a closed controlled environment using the (Cr2O72) dichromate ion as mentioned in the standard methods (APHA, 1998).
The measurement of COD was based on the Standard Closed Reflux Method
using HACH COD reactor as described in Standards Methods (APHA, 1998). At the
60
beginning, the HACH COD reflux reactor was preheated until the temperature
attained to 150 ºC. Sample of 2 mL were added to HACH reflux tube and followed
by 2 mL of digestion solution which was the 0.075 N of potassium dichromate
solution containing mercuric sulphate. Then, 3.5 mL of concentrated sulphuric acid
containing 8.8 g/L of silver sulphate were added. The tubes were tightly sealed and
inverted three times to mix properly. The mixtures were then refluxed in the HACH
COD reactor at 150 ºC for 2 hours.
After cooling, contents in
the tube was
transferred to a 100 mL conical flask before being titrated with the fresh 0.025 N
ferrous Ammonium Sulphate (FAS) using ferroin as the indicator. Each sample was
done in duplicate and at least two blanks, using distilled water, were prepared per
each batch of samples by being treated same as the samples. The COD value was
obtained using the following formula.
COD 
( A  B)  M  8000
mLsample
A = Volume of FAS (Ferrous Ammonium Sulphate) titrated for blank (mL);
B = Volume of FAS titrated for sample (mL);
M = Molarity of FAS
8000 = Milliequivalent weight of oxygen x 1000ml/L
This test could be applied to samples at concentrations between 40 to
400mg/L COD. On the other hand the effluent samples did not require dilution.
Figure 3.7 illustrates the HACH COD reactor used in this laboratory analysis.
61
Figure 3.7
The HACH COD reactor used for COD measurements.
3.7.2 Total Suspended Solids (TSS or MLSS) Measurements
The TSS tests were carried out following the procedures presented in Section
2540 D of Standard Methods for the Examination of Water and Wastewater (2540 DAPHA, 1998). The procedure involved the filtration of a suitable amount of the
rector mixed liquor through the prepared GF/A filter papers. The filter papers were
then dried in an oven (Figure 3.8) at 103 C to 150 ºC for 1 hour and cooled
afterwards in a desiccator. Figure 3.9 shows the vacuum pump used in the laboratory
62
analyses of the Total Suspended Solids (TSS or MLSS) measurements. Following
that, the papers with their dry content were weighed to the nearest 0.1 mg using an
analytical balance. The initial and the final balance readings were then used to
calculate the solids concentrations (mg solids/L) in the samples.
mgTotalSuspendedSolids / L 
( A  B) x1000
samplevol.mg / L

A= weight of filter + dried residue, mg
B= weight of filter, mg
Figure 3.8
Figure 3.9
Oven used for Total Suspended Solids (TSS or MLSS) measurements.
Vacuum pump used for Total Suspended Solids (TSS or MLSS)
measurements.
63
3.7.3 Volatile Suspended Solids (VSS or MLVSS)
The volatile suspended solids which are the VSS or the Mixed Liquor
Volatile Suspended Solids (MLVSS) is a useful parameter to roughly determine the
organic part of the mixed liquor in treatment processes.
For the duration of the study, in order to determine the volatile fraction of the
suspended solids concentration, an additional procedure was carried out following
the total suspended solids determinations (2540E- APHA, 1998). This additional step
included ignition of the filter papers at a temperature of 550 C and the determination
of the fixed fraction of the solids. The volatile fraction of the solids was then
calculated using the difference between the total solids and the fixed part of the
solids. Figure 3.10 shows the Wise Therm muffle furnace for the volatile suspended
solids measurements.
Figure 3.10
Wise Therm Muffle Furnace used for the volatile suspended solids
measurements.
64
3.8
On-line measurements
Dissolved oxygen (DO), pH were measured by using appropriate probes
calibrated. Probes were calibrated at pH 4.0 and 7.0 for use in analyze pH reactions.
Dissolved oxygen and pH probes were obtained from Ingold Ltd., (Switzerland),
while the temperature controller was consist the PID controller with PV and SV
display.
3.8.1 pH
The pH is a measure of the concentration of the hydrogen ions in the solution
and it is also an extremely important parameter for the operation of the treatment
processes. The microorganisms’ activity depends on the pH of the reactor. Most
organisms operate in a pH range of 6.5 to 8. Most aerobic plants operate within the
range of pH 7. Studies on the effects of temperatures were carried out as the pH was
maintained in the range of 6.5 to 8.00 by adjustment of the feed pH with NaOH.
Changes in the temperature of the control reaction were measured at 24 hourly
intervals by the use of calibrated pH probe. The pH readings from the reactor were
logged every day for the whole duration of the study. Figure 3.11 shows the pH
probe use for the pH measurements.
Figure 3.11
pH probe use for the pH measurements.
65
3.8.2 Dissolved Oxygen (DO)
The dissolved oxygen is the main component of all aerobic biological
conversion processes. Therefore it is an essential parameter and requires continuous
inspection whilst the reactions take place.
The DO level was measured using
calibrated DO meter. Throughout the study, the DO levels were measured everyday
in order to maintain dissolved oxygen concentration of 1.5 to 3.0 mg/L which was
the typical range for activated sludge process (Gray, 2004). Figure 3.12 shows the
DO probe use for the DO measurements.
Figure 3.12
DO probe use for the DO measurements.
CHAPTER 4
RESULTS ANALYSIS AND DISCUSSIONS
4.1
Introduction
This chapter will discuss on the results that were obtained from the
experiment that had been done throughout the project. This chapter will also discuss
and evaluate the data obtained before the treatment with the data before treatment of
synthetic wastewater by the use the Submerged Membrane Activated Sludge reactor.
Data obtained were tabulated in tables and shown in graphical approach for ease of
analysis.
This chapter are divided into three main sections which are the data and
results before the treatment, the data and results after the treatment process and also
the discussion of results obtained. From the data obtained from the discussion and
analysis of the results, the effect of temperature of an aerobic reactor which is by
using Submerged Membrane Activated Sludge Reactor can be evaluate.
Furthermore, the performance of Submerged Membrane Activated Sludge Reactor on
treating synthetic wastewater will be recognized. The effect of varying temperature
of a laboratory aerobic reactor, which is the Submerged Membrane Activated Sludge
Reactor on process performance, will be identified. However more importantly, this
study will explore the potential of aerobic treatment under strictly controlled extreme
operating conditions based on the results and discussion obtained.
67
4.2
Research Data Methodology
The duration and frequency of the data collected are different for each
parameter. The chemical oxygen demand (COD), suspended solids (MLSS) and
volatile suspended solids (MLVSS) will be collected once in two days while the
dissolved oxygen and pH will be measured daily.
4.3
Feed and Nutrients Characterization (Synthetic Wastewater)
The characteristics of the synthetic wastewater prepared in the laboratory
were determined.
The determined parameters include pH, biochemical oxygen
demand (BOD) (5 days), chemical oxygen demand (COD) and soluble chemical
oxygen demand (soluble COD). The results of the 4 respective parameter of the
synthetic wastewater before treatment were analyzed and presented in Table 4.1
below.
Table 4.1
Characteristics of raw synthetic wastewater.
PARAMETERS
pH
4.4
CONCENTRATION
6.5 - 7
BOD
250 – 300 mg/L
COD
500 – 600 mg/L
Soluble COD
400 – 500 mg/L
Seed Sludge
The reactor was seeded with aerobic digested pharmaceutical sewage taken
from Glaxo Smith Kline (GSK), near Ulu Kelang. It was first sieved (<3 mm) to
remove unwanted debris and particles. The characteristics of the seeding sludge
were determined.
The determined parameters include pH, biochemical oxygen
68
demand (BOD) (5 days) and chemical oxygen demand (COD). The results of the 3
respective parameter of the seeding sludge were analyzed and presented in Table 4.2
below.
Table 4.2
Characteristics of seeding sludge.
PARAMETERS
CONCENTRATION
pH
4.5
6.5 - 7
BOD
700 -800 mg/L
COD
1600 - 1800 mg/L
Submerged Membrane Activated Sludge Reactor Start-Up
During the reactor start-up period, the reactor was fed with synthetic
wastewater (500 mg/L COD and pH 7) continuously. The influents were freshly
prepared while the effluents were collected on time. The parameters such as pH and
DO in the reactor were measured daily. While the COD of effluent and influent was
measured and the MLSS and MLVSS of the effluents was measured once in two
days durations.
From the data obtained, the COD removal, MLSS removal and MLVSS
removal of the reactor could be determined. The correlation of the COD removal
with the pH profile and the DO profile within treatment period was plotted and
discussed in the next section. The MLSS and MLVSS removal within the treatment
period was also plotted and discussed.
Then, the effect of temperature on the
performance of the Submerged Membrane Activated Sludge Reactor on treating
synthetic wastewater could be defined.
Furthermore, the effect of varying
temperature of a laboratory aerobic reactor on process performances could be
identified.
69
4.6
Effect of Temperature on COD Removal
The effect of the temperature on soluble COD removal of the Submerged
Membrane Activated Sludge reactor is illustrated in Figure 4.1. The experiment was
conducted approximately 67 days. Different temperatures, starting at 27 ºC were
selected to study the effect of temperature on the efficiency of submerged membrane
activated sludge reactor. Other temperatures studied were 32, 37, 42 and 47 ºC.
From Figure 4.1, the highest percent removal of soluble COD was obtained at
27 ºC (90.45%) before increased slightly to 79.65% at the fifth day of the 32 ºC
cycle. The lowest percent removal of soluble COD was obtained at 32 ºC (24.27%).
For temperature 27 ºC, the percent removal of soluble COD was first obtained at
75.34% before declining slightly at day 5 and day 7 (66.13% and 64.17%).
However, there were no significantly differences in the percent removal of soluble
COD as the study on the effect of temperature 27 ºC continued at day 9 to day 13 of
the cycle. The percent removal of soluble COD was increased gradually after the
third cycle (day 9) of the operating cycle of Submerged Membrane Activated Sludge
reactor. It is observable that the COD removal efficiency of the reactor for 27 ºC was
76.56% in average.
From day 14 to day 29, the reactor was operated at temperature 32 ºC, while
the pH was maintained at 6.5 to 8.0. It is observable that the percent removal of the
soluble COD was at first lower (24.17%) which was the lowest COD removal of this
study and increased gradually to 79.65% and obtained at 67.38% removal for the last
cycle of the 32 ºC temperature study. The sudden decreased of the soluble COD
removal value that occurred at day 2 of the 32 ºC operations is mainly caused by the
foaming problem occurred.
This problem was prevented by the use of an
antifoaming agent (Silicone Antifoaming Agent) which did not appear to inhibit the
biomass. The average of soluble COD removal for the temperature study at 32 ºC
was achieved at 67.66% in average.
70
For temperature 37 ºC, 42 ºC and 47 ºC, there were no significant differences
on the percent of soluble COD removal. The percent removal of soluble COD was
increased slightly at 37 ºC, 42 ºC and 47 ºC. However, the COD removal efficiency
increased noticeably from 73.89% to 80.06% in average from 37 ºC to 47 ºC. The
profile on the effect of temperature on the removal of soluble COD concentrations
followed the order of temperature 32 ºC < 37ºC < 42 ºC < 27 ºC < 47 ºC (67.66% <
73.89% < 75% < 76.56% < 80.06% ). Better COD removal effectiveness was
achieved at temperature 47 ºC where the removal reaches in average 80.06%.
As reported by Metcalf and Eddy (2004), temperature conditions in the
reactor have a direct effect upon the biological treatment processes primarily by
influencing the metabolic activities of the micro-organisms. According to Daigger
(1999), higher the temperature, the efficiency of the aerobic reactor was high.
Results indicated that as the operating temperatures of the reactors were increased,
the percent removal of the soluble COD also increased.
Figure 4.1
The effect of the temperature on soluble COD removal of the
Submerged Membrane Activated Sludge reactor.
71
4.7
Effect of Temperature on pH profile
The effect of temperature on the profile of pH in the Submerged Membrane
Activated Sludge Reactor is shown in Figure 4.2. The pH was maintained in the
range of 6.5 to 8.0 by adjustment of the feed pH with NaOH. The pH was observed
everyday in order to maintain in neutral condition (pH 6.5 to 8.0).
pH will dictate the speed of biochemical reactions within biological treatment
process by controlling the rate at enzyme production and activity. Optimum pH
levels for heterotrophic bacteria fall within a narrow range between 6 and 8. Metcalf
and Eddy (2004) stated that in aerobic system the pH should be between 4.0 to 9.5
and the optimum range was between 6.5 to 75. Increases in the pH of the reactors
caused the sludge to become more compressible (F.Dilek Çetin, 2004). From the pH
data, it can be concluded that the reactor was stable during the reactor start-up and
treatment of the synthetic wastewater.
Figure 4.2
Effect of Temperature on the profile of pH.
72
4.8
Effect of Temperature on Dissolved Oxygen (DO) profile
The effect of temperature on the profile of Dissolved Oxygen (DO) in the
Submerged Membrane Activated Sludge reactor is shown in Figure 4.3. The reactor
was aerated continuously with an aquarium air stone with compressed air supplied at
approximately 3 L/min to maintain DO concentrations of 1.5 to 3.0 mg/L which is
the typical range for an activated sludge reactor (Metcalf and Eddy, 2004).
From Figure 4.3, it is observed that increased the temperature affect the DO
concentrations. The highest and lowest DO concentration was obtained at 27 ºC
which is 5.1 mg/L and 1.7 mg/L. On the other hand, low DO concentrations reduced
the filterability of sludges; and caused the formation of low compressible sludges,
and poor effluent qualities. At higher DO concentrations higher filterabilities, better
effluent qualities and more compressible sludge are resulted.
Figure 4.3
Effect of Temperature on the profile of Dissolved Oxygen (DO).
73
4.9
Solids Washout
The sludge washout from the reactor system was measure frequently during
the test period (Figure 4.4 and Figure 4.5). The effect of temperature on Mixed
Liquor Suspended Solids (MLSS) and Mixed Liquor Volatile Suspended Solids
(MLVSS) will be discuss and analyse in the next section.
4.9.1
Effect of Temperature on Mixed Liquor Suspended Solids (MLSS)
Figure 4.4 shows the results of the effect of the temperature on MLSS
concentrations. It is observable that the pattern of MLSS concentrations was slightly
different for each temperature range (27 ºC to 47 ºC).
For temperature 27 ºC, the concentrations of MLSS was increased from 20
mg/L to 50 mg/L before declining slightly to 25mg/L. For temperature 32 ºC, the
concentrations of MLSS was increased and decreased gradually for the cycle period
at 13 days. At temperature 37 ºC, the concentration of MLSS was slightly increased
from 20 mg/L to 70 mg/L before declined slightly to 30 mg/L.
The higher
concentration of MLSS was obtained at 42 ºC (80 mg/L) while the lowest
concentration was obtained at 10 mg/L at the same temperature (42 ºC). The patterns
of the MLSS concentration for the temperature of 27 ºC, 32 ºC, 37 ºC, 42 ºC, and 47
ºC was increased and decreased gradually.
Experimental work has also demonstrated that widely varying mixed liquor
temperature during treatment can yield on increase in MLSS in the treated effluent
(Ekenfelder and Mustermann, 1999). As the result, the MLSS concentration was
found to be lower, because the highest concentration of MLSS was recorded at 80
mg/L which was relatively lower as compared to the desired MLSS concentration for
Activated Sludge reactor.
Metcalf and Eddy (2004) stated a desired biomass
concentration of 3000 – 6000 mg/L MLSS for effective functioning of Activated
Sludge reactor.
74
Figure 4.4
4.9.2
Effect of Temperature on Mixed Liquor Suspended Solids (MLSS).
Effect of Temperature on Mixed Liquor Volatile Suspended Solids
(MLVSS)
Figure 4.5 shows the results of the effect of the temperature on MLVSS
concentrations. The highest concentration of MLVSS was obtained at 47 ºC and 32
ºC (80 mg/L) while the lowest was obtained at 42 ºC which is 10 mg/L.
For temperature 42 ºC, the MLVSS concentration was increased gradually
from 10 mg/L to 40 mg/L.
It is observed that the pattern of the MLVSS
concentrations for this study (temperature 27 ºC to 47 ºC) was increased and
decreased gradually. At temperature 32 ºC, which was the concentration of the
MLVSS was the highest, this may occur by the consequences by the foaming the
problem occurred.
As reported by Daigger (1999), temperature affects the rate of MLVSS
reduction and increases as the temperature is increased. From this study, it is showed
that the temperature did not affect the rate of MLVSS concentrations.
75
Figure 4.5
Effect of Temperature on Mixed Liquor Volatile Suspended Solids
(MLVSS).
4.10
Effect of Temperature on Specific Degradation Rate
Figure 4.6 shows the results of the effect of the temperature on specific
degradation rate. The parameters obtained in this case suggest that the specific
degradation rate predict the behaviour of the Submerged Membrane Activated
Sludge reactor in affecting the aerobic digestion of the synthetic wastewater with the
effect of temperature. From the figure, the highest specific degradation rate was
obtained at 42 ºC (40.2 g/m3.d), while the lowest specific degradation rate was
attained at temperature 32 ºC (1.55 g/m3.d) at day 16 of the laboratory analysis.
The specific degradation rate at temperature 37 ºC and 42 ºC was better than
at the other temperature (27 ºC, 32 ºC and 47 ºC). The higher specific degradation
rate indicates that the sludge was in a good condition. It was because the amount of
bacteria utilizes the organic concentrations of the synthetic wastewater was high and
the amount of bacteria was sufficient for the biological conversion of the treatment.
76
As mentioned before, the lowest specific degradation rates was obtained at
temperature 32 ºC (1.55 g/m3.d) which was at day 16 of the laboratory analysis. This
indicates that the amounts of bacteria in the sludge are not sufficient to utilize the
organic constituents in the synthetic wastewater. These maybe caused by the bacteria
community in the sludge are probably died. This will affect the treatment process
performance of the reactor.
According to Metcalf and Eddy (2004), the performance of biological
processes used for wastewater treatment depends on the dynamics of substrate
utilization and microbial growth. Effective design and operation of such systems
requires an understanding of the biological reactions occurring and an understanding
of the basic principles governing the growth of the microorganisms.
Furthermore, the need to understand all of the environmental conditions that
affect the substrate utilization and microbial growth rate cannot be overemphasized.
It is necessary to control such as the pH and nutrients in order to provide an effective
treatment performance.
The kinetics of microbial growth governs the oxidation process which is the
utilization of substrate and the production of biomass, which contributes to the total
suspended solids concentration in the biological reactor. The patterns of the effect of
temperature on the specific degradation rate for the temperature of 27 ºC, 32 ºC, 37
ºC, 42 ºC, and 47 ºC was increased and decreased gradually.
77
Figure 4.6
Effect of the temperature on specific degradation rate.
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
5.1
Introduction
In this chapter, the conclusions and summary of this study will be explained.
All the objective describes in Chapter 1 have been accomplished. According to the
discussion of the results, some conclusions can be drawn from the study.
5.2
Conclusions
The following conclusions can be drawn from the study:
1. The effect of temperature on the Submerged Membrane Activated Sludge reactor
does not really achieved as the soluble COD removal are not interrelated with the
increases of temperature (27ºC to 47ºC) although the highest soluble COD
removal in average was recorded at 47ºC (80.06%).
2. The profile on the effect of temperature on the removal of soluble COD
concentrations followed the order of temperature 32 ºC < 37ºC < 42 ºC < 27 ºC <
47 ºC (67.66% < 73.89% < 75% < 76.56% < 80.06% ).
79
3. The efficiency removal of the reactor should increased accordingly as the
temperature reactor is increased. The MLSS and MLVSS effluent concentration
also does not permit with the effect of increases the reactor temperature. The
data gathered for MLSS and MLVSS concentration from this study are relatively
lower compared to the MLSS and MLVSS concentration for effective
functioning of activated sludge reactor.
4. The examinations during the reactor operation at the effect of temperature
conditions also revealed that the dispersed growth could cause the wash out of the
species involved in the treatment process. On the other hand, the use of a
membrane in order to retain the biomass within the reactor enabled the system
preserve its integrity and reliability for the whole duration of the experimental
runs. This showed that at low and high temperature, membrane separation is the
only reliable and robust solution for biomass separation provided that the
treatment is taking place at low sludge ages and in highly turbulent conditions.
5. The highest specific degradation rate was obtained at 42 ºC (40.2 g/m3.d), while
the lowest specific degradation rate was attained at temperature 32 ºC (1.55
g/m3.d) at day 16 of the laboratory analysis. The specific degradation rate at
temperature 37 ºC and 42 ºC was better than at the other temperature (27 ºC, 32
ºC and 47 ºC). The higher specific degradation rate indicates that the sludge was
in a good condition.
Thus, it would be concluded that the objectives of the study had been
achieved. Overall, the outcomes of the study proved that there was a considerable
unexplored treatment potential in suspended growth systems (activated sludge
process) that can be utilised and enhanced for the treatment of industrial wastewaters
in various temperature ranges.
In the study of the effect of temperature on the Submerged Membrane
Activated Sludge Reactor, some operational difficulties during the reactor start-up
and operational was occurred and therefore affected the reactor performance and also
the results obtained. Table 5.1 illustrated the problems occur during the reactor startup and operational difficulties of the reactor during this study.
80
Table 5.1
Problems occur during the reactor start-up and operational difficulties
of the reactor during this study.
DAY
PROBLEMS AND OPERATIONAL DIFFICULTIES
Start-up of
Problem in pump calibration. The digital pump performance used in
the reactor
this study does not interrelated with the flowrate illustrated in the
pump. The pump performance is relatively lower than the flowarate
value shown in the pump.
Start-up of
The vessels used to cover the porous wall are having many holes.
This result the solids that have to be remain in the reactor vessel was
going out.
The porous liners are easily removable and cause the reactor to be
the reactor
overflow.
Start-up of
Membrane used in this study is not suitable and the pore size is bigger
the reactor
than the suggested value.
Start-up of
Change of new membrane with better pore size diameter ranges
the reactor
(0.1 - 1 mm diameter)
Start-up of
the reactor
Start-up
the reactor
Start-up
of The pH is in acidic which is in the range of 2 – 4. The pH in the
reactor was then being adjusted with the feed of NaOH.
of Overflow problem occurred in the reactor.
the reactor
16
5.3
Membrane Fouling problem occur
Recommendations
There are certain improvements that can be done to improve the study for
better results. The improvements and modifications can be carried out from times to
times to keep abreast of the latest technologies available. Some of the
recommendations to improve this study are as below:1. It was suggested that the pore size of the submerged membrane that used in
the reactor should be around 8 to 5μm (Chelliapan, 2006). From overall
observations, the pore sizes of the submerged membrane used are relatively
bigger and influence the overall result and analysis of this study.
As
81
mentioned previously, the membrane play role of a secondary clarifier in this
reactor.
Other than that, during the course of investigation, a problem
developed from foaming in the reactor, probably due to surfactant chemicals
in the synthetic wastewater and the sludge. Rather than that, it is difficult to
find the most suitable pore size and type of membrane to use for this study as
time constrain.
2. In order to fulfil the laboratory analyses, it was also proposed that the flow
rate of the system also need to be reduced in order to provide sufficient
contact time between the wastewater and the sludge.
3. Analysis on other parameter such as the nitrogen and phosphorus. Beside,
other parameters i.e. zinc and ferum also must be analyzed to check the
efficiency of the Submerged Membrane Activated Sludge Reactor in
removing heavy metals.
4. Investigations should be made into the treatment by using the real wastewater
in order to know the effect of temperature of the aerobic reactor.
5. The membrane flux performance and enhancement was not the main focus of
this study. However for the commercialisation of such plants of the
Submerged Membrane Activated Sludge Reactor, it is an important factor and
detailed investigations are required on it. The following study on the
membrane flux performance can involve the improvement of the crossflow
velocity across the membrane. The use of different membrane lumen sizes,
backflush and backpulsing of membranes and their effects on membrane flux
enhancement can also be covered in a future study.
6. In addition to that a further study on membranes may include the effects of
ECP (Extracellular Polymeric Substances) levels and the particle size
distribution on the membrane fouling.
7. Further study on the effect of other environmental effects such as pH, SRT,
OLR and others to the reactor process performance should be done
82
8. Another important aspect of wastewater treatment is the removal of
pathogens. In activated sludge, pathogens (viruses, bacteria, protozoa and
helminths) are incorporated in the sludge flocs and are removed with the
sludge in the sludge digestor. Because the open structure of the activated
sludge flocs, remove pathogens cab adequately from the influent. However,
the dense structure of the Submerged Membrane Activated Sludge Reactor
and their different ability of incorporating suspended solids could lead to a
different removal capacity. This should be a subject of attention especially
when it becomes to real implementations (pilot or full-scale study) in order to
guarantee the protection of public health.
83
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89
APPENDIX A
LABORATORY DATA
90
TEMPERATURE 27ºC
Date
Day
28-Jul
29-Jul
30-Jul
31-Jul
1-Aug
2-Aug
3-Aug
4-Aug
5-Aug
6-Aug
7-Aug
8-Aug
9-Aug
1
2
3
4
5
6
7
8
9
10
11
12
13
HRT
(Day)
2
2
2
2
2
2
2
2
2
2
2
2
2
Loading
Rate
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
COD
mg/d
515
Influent COD
Effluent
COD
% COD
Removal
561
515
127
75.34
561
561
190
66.13
539
561
201
64.17
597
539
123
77.18
597
597
83
86.1
597
597
57
90.45
515
pH
DO
6.88
6.72
6.69
7.17
7.07
6.7
7.67
6.97
7.29
7.08
6.7
6.5
6.98
1.8
1.7
2.5
2.3
2
2.2
3
4.7
5.1
3.8
3.1
3.2
3
MLSS
MLVSS
20
30
50
50
50
40
40
55
25
35
45
25
91
TEMPERATURE 32ºC
Date
Day
10-Aug
11-Aug
12-Aug
13-Aug
14-Aug
15-Aug
16-Aug
17-Aug
18-Aug
19-Aug
20-Aug
21-Aug
22-Aug
23-Aug
24-Aug
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
HRT
(Day)
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Loading
Rate
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
COD
mg/d
510
Influent
COD
510
Effluent
COD
% COD
Removal
511
511
387
24.27
576
576
104
79.65
580
580
123
78.65
543
543
145
75
581
581
130
76.06
564
564
159
72.63
564
564
184
67.38
pH
DO
7.62
7.44
7.71
7.17
7.25
7.77
7.3
7.2
7.14
7.37
7.37
6.87
7.74
7.65
7.09
4.3
4.1
4.2
2.7
3.4
2.7
2
2.2
4
3
3.1
3
2
2.1
2.2
MLSS
MLVSS
60
80
35
25
50
50
30
25
30
45
50
45
20
30
92
TEMPERATURE 37ºC
Date
Day
25-Aug
26-Aug
27-Aug
28-Aug
29-Aug
30-Aug
31-Aug
1-Sep
2-Sep
3-Sep
4-Sep
5-Sep
6-Sep
1
2
3
4
5
6
7
8
9
10
11
12
13
HRT
(Day)
2
2
2
2
2
2
2
2
2
2
2
2
2
Loading
Rate
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
COD mg/d
Influent COD
Effluent
COD
% COD
Removal
580
547
580
115
80.17
584
547
177
67.64
597
584
128
78.08
596
597
208
65.16
542
596
148
75.17
542
542
124
77.12
pH
DO
7.39
7.17
6.93
7.31
7.52
6.87
6.6
7.01
7.6
7.87
7.54
7.2
7.84
1.8
4.1
2.1
3
3.3
3
2.9
3
3.3
2.3
2.3
2.1
4.3
MLSS
MLVSS
15
15
70
65
30
40
35
35
35
35
40
20
93
TEMPERATURE 42ºC
Date
Day
7-Sep
8-Sep
9-Sep
10-Sep
11-Sep
12-Sep
13-Sep
14-Sep
15-Sep
16-Sep
17-Sep
18-Sep
20-Sep
1
2
3
4
5
6
7
8
9
10
11
12
13
HRT
(Day)
2
2
2
2
2
2
2
2
2
2
2
2
2
Loading
Rate
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
COD
mg/d
542
Influent
COD
Effluent
COD
% COD
Removal
542
542
124
77.12
592
542
140
74.17
592
592
92
84.46
548
592
178
69.93
589
548
142
74.09
589
175
70.28
pH
DO
7.93
7.5
6.43
7.05
7.42
7.2
7.08
7.07
7.06
7.08
7.36
7.2
7.05
3.4
4
4.5
4.3
4.3
3.1
2
2
3.52
2.98
2.3
2.4
2.3
MLSS
MLVSS
30
20
10
10
10
30
80
30
30
40
20
30
94
TEMPERATURE 47ºC
Date
Day
28-Sep
29-Sep
30-Sep
1-Oct
2-Oct
3-Oct
4-Oct
5-Oct
7-Oct
8-Oct
9-Oct
10-Oct
11-Oct
1
2
3
4
5
6
7
8
9
10
11
12
13
HRT
(Day)
2
2
2
2
2
2
2
2
2
2
2
2
2
Loading
Rate
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
0.42
COD
mg/d
589
Influent
COD
Effluent
COD
% COD
Removal
589
589
198
66.38
589
589
223
62.14
561
561
90
83.96
561
561
64
88.59
543
543
60
88.95
570
570
55
90.35
pH
DO
7.24
6.79
6.92
6.88
6.7
6.6
6.6
6.2
7.06
7.08
7.36
7.2
7.05
3.4
4
4.5
4.3
4.3
3.1
2
2
3.52
2.98
2.3
2.4
2.3
MLSS
MLVSS
40
70
30
20
40
20
50
80
30
40
20
30
95
APPENDIX B
DETERMINATION OF CHEMICAL OXCIGEN DEMAND (COD)
96
97
98
99