TERTIARY TREATMENT OF PALM OIL MILL EFFLUENT (POME)
USING HYDROGEN PEROXIDE PHOTOLYSIS METHOD
SHAKILA BINTI ABDULLAH
A project report submitted in partial fulfilment of the requirements for the award of
the degree of Master of Engineering (Civil – Environmental Management)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
NOVEMBER 2008
iii
ACKNOWLEDGEMENT
First and foremost, praise to Allah, the most Graceful and Merciful for His
bless for giving me an excellent health to ensure best performance during completing
my work especially on this report. He also has given me such a big patience to cope
with my works and finally completed this report in a given time.
I would like to express our sincere and gratitude and appreciation to my
supervisor Dr. Azmi Aris for his valuables ideas, concern, help, dedication,
suggestion, guidance, and especially his support either moral or physical to help me
in completing this report. All of his effort and willingness had managed me to give
the very best in this report.
Special appreciation to my father Abdullah Ibrahim, my lovely mother,
Hasnah Mohd Yatim who sacrificed much for this current effort.
Special thanks to all the lab assistants, including Pn. Ros, En. Yusuf, En.
Suhaimi and En. Ramlee for helping me in collection of samples, giving me
guideline on how to operate the instrument and given me information to complete
this report. Last but not least, biggest complement goes to my entire friend for their
direct and indirect help, support and understanding throughout the work.
IV
ABSTARCT
Palm oil mill effluent (POME) is in the fonn of highly concentrated dark
brown colloidal suspension. Despite of being treated using biological treatment, the
wastewater is still coloured and indicates the remaining of significant concentrations
of organics in the effluent discharge. Hence, tertiary treatment is required to further
improve the quality of the effluent. Hydrogen peroxide photolysis (UVIH202) is one
of the advanced oxidation process (AOP) that can be an option to treat the
biologically treated POME (BT-POME). Experiments were conducted to investigate
the removal of colour and COD in order to assess the effectiveness and feasibility of
(UVIH20 2) catalytic system for tertiary treatment of POME. The operating
parameters such as hydrogen peroxide dosage, pH value and initial BT-POME
concentrations were evaluated. The removal process could be fitted by the zeroth
orger for COD and second order kinetics for colour. The efficiency of colour and
COD removal ranged from 7.3%-61.3% and 7.4%-61.1% respectively. Examination
of the effect showed the maximum removal could be achieved under optimal
conditions of H202 dosage of 250 mgIL and pH of 7.5. In general, the three factors
mentioned earlier affect the perfonnance of the process and discussed in the report.
Further study is needed to improve the perfonnance of UVIH202 process in treating
BT-POME.
v
ABSTRAK
Air sisa berwama daripada kilang kelapa sawit ialah dalam bentuk bahan lekit
berwama coklat gelap. Walaupun telah dirawat secara biologi, air sisa kelapa sawit
masih mengandungi wama dan bahan organik yang tinggi. Oleh itu, rawatan tahap
ketiga diperlukan untuk meningkatkan mutu eftluen. 'Hydrogen peroxide photolysis'
adalah satu dari proses oksida lanjutan yang boleh menjadi pilihan untuk merawat air
sisa berwama daripada kilang kelapa sawit. Ujian telah dijalankan untuk mengkaji
penyingkiran wama dan COD dengan tujuan menilai
keberkesanan dan
keboleWaksanaan proses'UV/H202'. Faktor dos hydrogen peroksida, nilai pH dan
kepekatan awal air sisa ke atas keberkesanan proses olahan dinilai. Proses
pengurangan boleh dikategorikan sebagai 'zeroth order' untuk COD dan 'second
order' untuk wama. Berdasarkan ketiga-tiga faktor yang telah dinilai, pengurangan
wama adalah dalam 7.3% - 61.3% dan COD 7.4% - 61.1%. Penyingkiran terbaik
dapat dicapai berdasarkan tahap optimum sebanyak 250 mg/L untuk dos hydrogen
peroksida dan pH 7.5. Secara umumnya ketiga-tiga faktor mempengaruhi
keberkesanan proses 'UV/H202'. Pengaruh ini telah diperjelaskan di dalam laporan
ini. Daripada keputusan ujikaji ini boleh disimpulkan bahawa proses 'UV/H202'
memerlukan kajian selanjutnya supaya kegunaannya dapat diaplikasikan dalam
rawatan air sisa kelapa sawit.
vi
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
ACKNOWLEDGEMENT
iii
ABSTRACT
iv
ABSTRAK
v
TABLE OF CONTENT
vi
LIST OF ABBREVIATIONS/ SYMBOLS/ TERMS
ix
LIST OF TABLES
xii
LIST OF FIGURES
xiv
LIST OF APPENDICES
xvi
INTRODUCTION
1.1
Background
1
1.2
Aim of Study
2
1.3
Objectives of Study
3
1.4
Scope of Study
3
1.5
Problems Statement
3
vii
2
LITERATURE REVIEW
2.1
Palm Oil Mill Effluent
2.1.1
Sterilization
6
2.1.2
Clarification
6
2.1.3
Nut Cracking
7
2.2
Characteristic of Palm Oil Mill Effluent
7
2.3
Palm Oil Mill Effluent Treatment
8
2.3.1
Aerobic and Anaerobic Digestion
9
2.3.2
Membrane Treatment
10
2.4
Advanced Oxidation Process
14
2.5
Hydrogen Peroxide Photolysis
16
2.5.1
3
5
Application of UV/H2O2 System
22
METHODOLOGY
3.1
Materials
26
3.2
Analytical Method
26
3.2.1
Colour – ADMI Weighted Ordinate Method
28
3.2.2
Chemical Oxygen Demand – Reactor
29
Digestion Method
3.2.3
Suspended Solid – Standard Method
29
(APHA, 2005)
3.2.4
3.2.5
Ammoniacal Nitrogen – Nessler Method
30
Biochemical Oxygen Demand – Standard
31
Method (APHA, 2005)
3.3
Experimental Procedures
32
viii
4
5
RESULTS AND DISCUSSIONS
4.1
Introduction
35
4.2
Wastewater Characteristics
35
4.3
Effect of H2O2 Dosage
37
4.4
Effect of pH
43
4.5
Effect of Initial BT-POME Concentration
48
CONCLUSIONS AND RECOMMENDATIONS
5.1
Conclusions
55
5.2
Recommendations
56
REFERENCES
58
APPENDIXES
63
ix
LIST OF ABBREVIATIONS/ SYMBOLS/ TERMS
Ao
-
Initial absorbance
A
-
Final absorbance
AAN
-
Artificial neutral network
AOP
-
Advance oxidation process
BOD
-
Biochemical oxygen demand
BPA
-
Bisphenol A
BT-POME
-
Biological treated POME
Co
-
Initial concentration
Ct
-
Concentration at time
CO2
-
Carbon dioxide
COD
-
Chemical oxygen demand
CH4
-
Methane gas
DCA
-
Dichloroacetic acid
DOC
-
Dissolved organic carbon
x
DOE
-
EFB
Department of Environment
Empty fruit bunch
Fe2+/H2O2
-
Ferrous oxide
FFB
-
Fresh fruit bunch
GC-MS
-
Gas chromatography-mass spectroscopy
H2O
-
Water
H2O2
-
Hydrogen peroxide
HO●
-
Hydroxyl radicals
HO2●
-
Hydroperoxyl radicals
HO2-
-
Hydroperoxide anion
H2SO4
-
Sulphuric acid
HRT
-
Hydraulic retention time
k
-
Rate constant
LW
-
Low pressure
MABR
-
Modified anaerobic baffled bioreactor
MC-RR
-
Microcystin -RR
NaOH
-
Sodium hydroxide
NH3-N
O2
Ammoniacal nitrogen
-
Oxygen
xi
OH-
-
Hydroxyl anion
POME
-
Palm oil mill effluent
PPNJ
-
Pertubuhan Peladang Negeri Johor
RBC
-
Rotating biological contactor
RO
-
Reverse osmosis
SBR
-
Sequencing batch reactor
SS
-
Suspended solids
t
-
Irradiation time
TDS
-
Total dissolved solid
TKN
-
Total khejadl nitrogen
TOC
-
Total organic carbon
TSS
-
Total suspended solids
UASFF
-
Up-flow anaerobic sludge blanket fixed film
UV
-
Ultraviolet
UV/H2O2
-
Hydrogen peroxide photolysis
UV/O3
Ozone photolysis
UV/TiO2
-
Titanium dioxide photolysis
VTG
-
Vivo vitellogenin
YES
-
Yeast estrogen screen
xii
LIST OF TABLE
TABLE NO.
2.1
TITLE
Environmental regulations for watercourse discharge for
PAGE
8
POME
2.2
Efficiency comparison between POME treatment
12
technologies
2.3
The oxidation potential of several oxidants
15
2.4
Comparative cost of some AOPs
16
3.1
List of analytical methods and instrumentations for
27
experimental work
3.2
Value of initial colour and COD removal
34
4.1
Characteristics of BT-POME
36
4.2
Value of percentage colour removal at different H2O2
37
dosage
4.3
Value of percentage COD removal at different H2O2
38
dosage
4.4
Value of percentage colour removal at different pH
43
xiii
4.5
Value of percentage COD removal at different pH
44
4.6
Value of percentage colour removal at different initial
concentration
48
4.7
Value of percentage COD removal at different initial
concentration
49
xiv
LIST OF FIGURES
FIGURES NO.
TITLE
PAGE
2.1
Reaction pathways for UV/H2O2 system
17
2.2
Schematic representation of photo-assisted Fenton and
19
the H2O2 photolysis processes
3.1
Analytical Instrument used (a) pH meter (b)
28
DR5000U (c) SS apparatus
3.2
Low pressure UV lamp of 15W
32
3.3
Set up instrument (a) Beaker 2L (b) Experimental set-
33
up
3.4
BT-POME at different dilution factors (a) no dilution
34
(b) 25%, 50%, 75% and 90% dilution
4.1
Profile of colour and at different H2O2 dosage
38
4.2
Profile of COD at different H2O2 dosage
39
4.3
Removal percentage of colour and COD at different
39
H2O2 dosage
4.4
Rate constant of colour at different H2O2 dosing
41
xv
4.5
Rate constant of COD at different H2O2 dosing
41
4.6
Residual of (a) colour and at different H2O2 dosage
42
4.7
Profile of colour at different pH
44
4.8
Profile of COD at different pH
45
4.9
Removal percentage of colour and COD at different pH
45
4.10
Rate constant of colour at different pH
46
4.11
Rate constant of COD at different pH
46
4.12
Residual of colour at different pH
47
4.13
Profile of colour at different initial concentration
49
4.14
Profile of COD at different initial concentration
50
4.15
Removal of colour at different initial concentration
50
4.16
Removal of COD at different initial concentration
51
4.17
Rate constant of colour at different initial concentration
52
4.18
Rate constant of COD at different initial concentration
52
4.19
Residual colour at different initial concentration
53
xvi
LIST OF APPENDIXES
APPENDIX
TITLE
PAGE
NO.
A
Stock Solution Calculation
63
CHAPTER 1
INTRODUCTION
1.1
Background
The Malaysian oil palm industry has recorded an impressive performance as
one of the largest producer and exporter of palm oil in the world (Ahmad et al.,
2003). Recently, the production of crude palm oil for 2006 stood at 15.9 million
tones in 2006 from 15.0 million tons the previous year and exports increased by 2.36
million tons (MPOB, 2007).
However, the palm oil industries also cause some environmental concerns. The
industry generates the most biomass from the oil extraction process such as
mesocrap, fiber, shell, empty fruit bunch (EFB) and palm oil mill effluent (POME).
It is estimated that more than 50 million tones of biomass was generated from the
palm oil industry in the year 2005 (Yacob et al., 2006). The wet process of palm oil
milling consumes a large amount of process water. The final POME is generated
from hydrocyclone washing and cleaning up processes in the mill (Hassan et al.,
2004). Zinatizadeh et al. (2006) reported, during palm oil mill extraction, about 1.5
tonnes of palm oil mill effluent is produced per tonne of fresh fruit brunch (FFB)
processed by the mill. Wu et al. (2007) estimated that for 1 tonne of crude palm oil
2
produced 5 to 7.5 tonnes water are required and more than 50% of the water will end
up as effluent.
Several innovative treatment technologies have been explored and applied by
palm oil mill to treat POME. Biological approach is the most popular treatment
method to treat the effluent as POME has high organic and mineral content which
can be broken down by microorganisms. Currently, the majority of palm oil mills
have adopted conventional biological treatments of anaerobic or facultative digestion
which need large treatment area, long treatment periods and high cost for
maintenance. However, not all of the palm oil mill is satisfying the Malaysian
Department of Environment (DOE) requirements. In order to regulate the discharge
of effluent from the crude palm oil industry as well as to exercise other
environmental control under the Environmental Quality (Prescribed Premises)
(Crude Palm Oil) Order, 1977 and the Environment Quality (Prescribed Premises)
(Crude Palm Oil) Regulations, 1977 were promulgated under the Environmental
Quality Act, 1974 (DOE, 1999 and Ahmad et al., 2003).
1.2
Aim of Study
The aim of the study is to develop an effective tertiary process in treating
biological treated palm oil mill effluent (BT-POME).
3
1.3
Objectives of Study
The objectives of this study were:
1. To evaluate the feasibility of hydrogen peroxide photolysis (UV/H2O2)
method in removal of organics and colour from biologically treated
POME
2. To determine the effect of the H2O2 dosing, pH and initial BT-POME
concentration on the effectiveness of the process.
1.4
Scope of Study
This study consists of a series of lab scale experiment which utilize hydrogen
peroxide photolysis (UV/H2O2) method in treating biologically treated POME. The
biologically treated POME was obtained from a nearby palm oil mill. The efficiency
of the system was assessed based on colour and COD removal.
1.5
Problems Statement
The biological treatment employed by the palm oil mill industry currently is
able to meet the standard discharge limit by the Malaysian Department of the
Environment. However, despite of being treated the wastewater is still coloured and
contains high biochemical oxygen demand (BOD), chemical oxygen demand (COD),
oil and grease, total solids as well as suspended solids and it can certainly cause
4
considerable environmental problems (Wu et al., 2007). Hence, tertiary treat is
required to further improve the quality of the effluent. Hydrogen peroxide photolysis
(UV/H2O2) is one of the advanced oxidation processes (AOPs) that can be an option
to treat the biologically treated POME (BT-POME). These studies explore the
feasibility of UV/H2O2 process in polishing the treated POME.
CHAPTER 2
LITERATURE REVIEW
2.1
Palm Oil Mill Effluent
Palm oil mill effluent is thick brownish colloidal suspension which is not
toxic but has unpleasant odour (Ahmad et al., 2003). Palm oil mill effluent originates
from three main processes in crude oil production, which are sterilization,
clarification and nut cracking processes. The clarification sludge contains the highest
level of solid residue and unrecovered oil and grease as compared to the sterilizer
and hydrocyclone effluents. Both sterilizer and clarification effluent consist of a
significant value of organic content in terms of BOD and COD (Hassan et al., 2004).
6
2.1.1
Sterilization
The objectives of the FFB sterilization are to remove external impurities,
soften and loosen the fruitless from the bunches, detach the kernels from the shell
and most importantly is to deactivate the enzymes responsible for the buildup of free
fatty acids to ensure the quality and the productivity of palm oil mill. The FFB must
be processed within 24 hours of harvesting. Thus, most of the palm oil mills are
located in close proximity to the oil palm plantation. During, sterilization, the FFB is
subjected to three cycles of pressure for a total holding time of 90 minutes. The
sterilization process acts as the first contributor to the accumulation of POME in the
form of sterilizer condensate.
2.1.2
Clarification
The extracted oil is clarified and purified to produce crude palm oil. Dirt and
other impurities are removed from the oil by centrifugation. Before the crude palm
oil is transferred to the storage tank, it is subjected to high temperatures to reduce the
moisture content in the crude palm oil. This is to control the rate of oil deterioration
during storage prior to processing at the palm oil refinery. The sludge, which is the
by product of clarification and purification procedures, is the main source of POME
in terms of pollution strength and quantity.
7
2.1.3
Nut Cracking
The nuts from the digestion and pressing processes are polished before being
sent to the nut-cracking machine or ripple mill. The cracked mixture of kernels and
shell is then separated in a winnowing column using upwards suction (hydrocyclone)
and a clay bath. The third source of POME is the washing water of the hydrocyclone.
The kernel produced is then stored before being transferred to palm kernel mill for
oil extraction. Shell wastes will join the fiber at the boiler for steam and power
generation.
2.2
Characteristics of Palm Oil Mill Effluent
The raw or partially treated POME has an extremely high content of
degradable organic matter, which is due in part to the presence of unrecovered palm
oil. It consist of 95-96% water, 0.6-0.7% oil and 4-5% total solids, 2-4% suspended
solids and extremely high content of degradable organic matter originating from the
mixture of a sterilizer condensate, separator sludge and hydrocyclone wastewater
(Ma, 2000; Ahmad et al., 2003 and Mohammad et al., 2007). This highly polluting
wastewater can therefore cause severe pollution of water ways due to oxygen
depletion and other related effects.
The oil droplets of POME can be found in two phases. They either suspend in
the supernatant or float on the upper layer of the suspension. The residue oil droplets
in POME were solvent extractable (Ahmad et al., 2005). The effluent is also
characterized by high temperature of approximately 80-90oC and acidic (pH 3.8 to
4.5). The characteristics of POME are highly dependent on the operation and quality
control of individual mill (Basiron et al., 1995). The typical characteristics of POME
and standard discharge limit set by Malaysian Department of Environment (DOE)
are given in Table 2.1
8
Table 2.1: Characteristics of POME and its respective standard discharge limit by the
Malaysian Department of the Environment (Hassan et al., 2004).
Parameter
Range, mg/L
Standard limit, mg/L
3.4 – 5.2
5-9
150 – 18,000
50
BOD
10,250 – 43,750
100
COD
15,000 – 100,000
-
Total solids
11,500 – 78,000
-
5000 – 54,000
400
180 – 1400
150
4 – 80
-
pH
Oil and grease
Suspended solids
Total nitrogen
Ammoniacal Nitrogen
The extract of the oil droplets consist of 84 wt % neutral lipids and 16 wt% of
complete lipids (6 wt % glygolipids and 10 wt % phospholipids). The neutral lipids
consist of 74.7% triglycerides, 8% diglycerides, 0.5% monoglycerides and 0.8% free
fatty acids. POME also contributes a high concentration of surface active compounds
like phospholipids (10 wt %) and glycolipids (6 wt %) (Ahmad et al., 2005).
2.3
Palm Oil Mill Effluent Treatment
Treatability of POME had been examined by a wide range of technologies
and approaches. Owing to its properties, POME can be easily treated using a
biological approach. With high organic and mineral content, POME is a suitable
environment in which microorganism can thrive. The various effluent treatment
schemes which are currently used by the Malaysian palm oil industry include
9
anaerobic/facultative ponds and physico-chemical and biological treatment
(Vijayaraghavan et al., 2007).
2.3.1 Aerobic and Anaerobic Digestion
Conventional biological treatment of anaerobic or aerobic digestion is the
commonly applied method for treatment of different type of wastewater. For a highly
organic content of POME, anaerobic process is the most suitable approach for its
treatment. The up-flow anaerobic sludge blanket fixed film bioreactor (UASFF) has
been shown to be highly efficient in the treatment of POME achieving 92% and 97%
COD removals at low hydraulic retention time (HRT) of 3.5 and 3 day, respectively
(Zinatizadeh et al., 2006).
Biological treatment using attached growth on a rotating biological contractor
(RBC) was used for the wastewater from palm oil mill industries which contain high
strength of organic compounds with COD of about 16000 mg/L. An acclimated
Saccharomyces cerevisiae with POME was used as the initial biomass for the
attached growth on bio-discs. After 5-days 91% BOD removal was achieved in a
batch experiment while 88% removal of COD was obtained with 55 hour of HRT
(Najafpour et al., 2005).
Oswal et al. (2002) studied on the treatment of POME using tropical marine
yeast in a lagoon. Palm oil mill effluent from a factory in India consist of about
25000 mg/L COD, 11000 mg/L BOD, 65 mg/L total dissolved solids and 9000 mg/L
of chloroform soluble material was treated. Treatment of this effluent using Yarrowia
lypolytica NCIM 3589, marine hydrocarbon-degrading yeast isolated from Mumbai
gave a COD reduction about 95% with a retention time two days. Treatment with a
chemical coagulant further reduced the COD and a consortium developed from
garden soil clarified the effluent and adjusted the pH to between 6 and 7. The
10
complete treatment reduced the COD content to 1500 mg/L which is a 99% reduction
from the original.
Biodegradation of POME under anaerobic conditions to environmentally
acceptable product was carried out by Ugoji (1997). Efficiency of COD and BOD
removal of the operation was investigated. Experiment were carried out in three
stages were a single stage anaerobic ponding system, second stage was a single stage
anaerobic tank digester with a certain degree of mixing and third stage was recycled
spent POME sludge in a single stage anaerobic tank. Results show the efficiency
obtained from three set up were 96.91%, 96.50% and 94.50% respectively after 10
days of retention time. The mean production values obtained after digestion for the
mode of digestion recommended for their local populace gave 2.4 cm3 per m3 of
digester vol/day and 1900 mg/L of discharged solid.
A modified anaerobic baffled bioreactor (MABR) studied by Faisal et al.
(2001) under steady-state conditions for treating palm oil mill wastewater. Methane
gas (CH4) production was in the range of 0.32–0.42l-CH4 (g-COD)−1 removal, which
corresponded to the methane content of 67.3–71.2% within the range of examined
HRT of 3–10 days. The results showed removal ranges of COD and grease/oil were
from 87.4 to 95.3% and from 44.1 to 91.3%, respectively. The total volatile fatty acid
production was 1450 mg/L at HRT of 3 days and gradually decreased to 608 mg /L
at HRT of 10 days
2.3.2 Membrane Treatment
Ahmad et al. (2003) reported that two stages of treatment have been
conducted whereby coagulation, sedimentation and adsorption play their roles at the
first stage as a membrane treatment process. Ultrafiltration (UF) and reverse osmosis
11
(RO) membranes were combined for the membrane separation treatment. Results
from the total treatment system show a reduction in turbidity, COD and BOD up to
100%, 98.8% and 99.4%, respectively, with a final pH of 7. Thus, the results show
that this treatment system has a high potential for producing boiler feed water that
can be recycled back to the plant.
Nik Sulaiman et al (2007) study on the potential use of membrane technology
to treat POME from the final discharged pond. The membrane study essentially used
hollow fiber membrane of MWCO ranging from 30,000 to 100,000. The results
showed that the hollow fiber membrane with MWCO 100,000 gave higher fluxes
compared to the MWCO 30,000. The quality of permeate achieving from the
membrane with MWCO 30,000 gave reduction in COD, SS, TKN and NH3-N of
97.66%, 98%, 53.85% and 61.91% respectively. However colour removal may
require further treatment.
Wu et al. (2007) study indicated that the applied pressure imposed a direct
effect on fouling; permeate flux, protein and carbohydrate recovery as well as
wastewater treatment. In total, the permeate flux decreased with filtration time until
it reached steady-state values. Beyond a certain applied pressure between 0.6 and 0.8
MPa, the increase in permeate flux with pressure was negligible and insignificance.
The highest applied pressure (0.8MPa) encouraged the formation of fouling up to
85.8% but at the same time enabled the recovery of protein and carbohydrate up to
61.4% and 76.4%, respectively. The highest reduction of TSS, turbidity, TDS and
COD also occurred at 0.8 MPa up to 97.7%, 88.5%, 6.5% and 57.0%. Comparison
between POME treatment technologies is shown in Table 2.2 and 2.3.
12
Table 2.2: Efficiency comparison between POME treatment technologies
Method
Influent
Efficiency
References
92 -97% COD
Zinatizadeh et
CODo = N.A
removal
al, 2006
HRT = 17 days
> 95% COD
Yacob et al,
CODo = N.A
removal
2005
Rotating biological
HRT = 55 hours
88% COD
Najafpour
contractor (RBC)
CODo = 16000mg/L
removal
al, 2005
Tropical marine yeast
RT = 2 days
95% COD
Oswal et al,
CODo = N.A
removal
2002
HRT = 3 – 10 days
7.3%-
0.32 – 0.421
COD removal
methane g(COD)-1
72.1%-95.9%
High rate upflow anaerobic HRT = 3-4 days
sludge fixed film
bioreactor
Anaerobic digestor
Anaerobic baffled reactor
et
95.3% Faisal et al,
2001
TOC removal
44.2%- 91.3%
oil & grease
removal
Ultrafiltration membrane
Pressure = 0.8 MPa
TSS = 97.7%
Turbidity
Wu
et
al,
= 2007
88.5%
COD = 57.0%
Synthetic polyelectrolytes
Dosage = 32 mg/L
Turbidity
pH = 3
98%
= Arrifin et al.
SS removal =
98.7%
COD removal
= 54%
2005
13
Table 2.3: Efficiency comparison between POME treatment technologies (continue)
Method
Membrane treatment
Influent
Efficiency
Turbidity = 10563
100% (turbidity Ahmad et al,
NTU
F=
CODo = 26107
98.8% (CODF=
mg/L
314 mg/L)
BODo
=
Fiber
0.81 NTU)
2003
15800 99.4% (BODF=
mg/L
Membrane technology
References
91mg/L)
membrane 97.66%
COD Nik Sulaiman
et al, 2007
MWCO range from removal
30,000 to 100,000
98%
SS
removal
53.85%
TKN
removal
61.91%
AN
removal
Coagulation-flocculation
Dosage = 3469 and
17.927 mg/L to Bhatia et al,
6736 mg/L
181mg/L
pH = 5
reduced
Time = 114 min
87%
SS 2007
recovery
sludge
Anaerobic treatment
RT = 10 days
Stage
1
= Ugoji, 1997
2
=
Discharge solid = 96.91%
1900 mg/L
removal
Stage
96.5% removal
Stage
3
=
94.5% removal
14
2.4
Advanced Oxidation Processes
Advanced Oxidation processes have been widely accepted in wastewater
treatment. They offer a promising technology for complete removal of organics
owing to its great efficiency in mineralization (Kavitha and Palanivelu, 2004). The
early stage of AOP development is mainly to overcome the problems in conventional
phase separation techniques, such as adsorption processes and stripping technologies.
The conventional technologies only transfer the pollutants to another phase leaving
the consequent problem of disposing, whereas AOPs are well known for their
capacity for oxidizing and mineralizing almost any recalcitrant organic compound
(Gernjak et al., 2006)
Advanced oxidation processes are defined as the oxidation processes that
involve the generation of the highly reactive hydroxyl radicals (HO●).
These
processes employ chemical, photochemical, sonochemical or radiolytic techniques to
bring about chemical degradation of pollutants (Al-Tawabini, 2003).
Hydroxyl radical is one of the most important oxidants found in air, water
and biological systems. It has a very high oxidation potential (2.8 V) compared to
other oxidant as shown in Table 2.3. The hydroxyl radicals can mineralize the
organic compounds into carbon dioxide (CO2), water (H2O) and inorganic ions or at
least transform the compound into less harmful and biodegradable ones.
The
reaction occurs rapidly and unselectively attack organic pollutants and degrades them
in aqueous medium (Perez, 2006). The most common chemical reaction mechanisms
of the HO● in water consist of addition, hydrogen abstraction and radical interaction.
However, only the first two mechanisms are the ones involved in AOPs.
For
addition mechanisms, HO● adds to a saturated compound, aliphatic or aromatic to
form a free radical product. In the hydrogen abstraction mechanism the HO● can
abstract a hydrogen atom to form organic free radical and water as with alkenes and
alcohols (Al-Tawabini, 2002).
15
The most widely used AOP systems include UV/H2O2, UV/O3, UV/H2O2/O3,
Fe2+/H2O2 and UV/TiO2. The processes can also be categorized into homogeneous
and heterogeneous process depending on the physical state of the catalyst. Examples
of heterogeneous catalytic oxidations are UV/TiO2 and UV/O3, while the
homogeneous processes include UV/H2O2 and Fe2+/H2O2.
The homogeneous
processes possess low mass transfer resistance between the phases and therefore
favour faster degradation of pollutants (Kavitha and Palanivelu, 2003). The methods
based on H2O2 to promote the formation of the HO● are the most promising
approaches, since these methods do not involve the use of dangerous chemicals and
simple operation (Christine et al., 2004)
Table 2.3: The oxidation potential of several oxidants (Al-Tawabini, 2002).
Oxidant
Oxidation Potential, V
Fluorine
3.0
Hydroxyl radical
2.8
Ozone
2.1
Hydrogen peroxide
1.8
Potassium permanganate
1.7
Chlorine dioxide
1.5
Chlorine
1.4
The main weakness of AOPs is being too high cost for practical applications
according to their requirement of large amounts of energy and chemical to be spent.
Thus, application of solar energy gives potential low cost of AOPs to help reducing
energy consumption required for generating UV radiation (Gernjak et al., 2002).
Table 2.4 show the comparative cost of some AOPs (Munter, 2001). Another
alternative for cost reduction is AOPs can be utilized to integrate the biological
treatments by an oxidative degradation of toxic or refractory substances entering or
leaving the biological stage. Therefore, the amount of energy and chemical can be
reduced (Muruganandham et al., 2005).
16
Table 2.4: The comparative cost of some AOPs (Munter, 2001)
Parameter
UV/O3
O3/H2O2
UV/H2O2
Photocatalytic oxidation
2.5
Cost of oxidant
High
High
Medium
Very low
Cost of UV
Medium
0
High
Medium to High
Hydrogen Peroxide Photolysis
The hydrogen peroxide photolysis (UV/H2O2) has been applied to remove a
wide range of toxic hazardous substances from groundwater, drinking water,
municipal and industrial wastewater. After Koubek at the US Naval Academy was
awarded a patent for his work on “oxidation of refractory organic in aqueous waste
stream by H2O2 and UV light” the first commercial application of UV/H2O2
processes has been successfully applied for groundwater remediation and wastewater
treatment (Tang, 2004).
The hydrogen peroxide photolysis is a simple and homogenous process. The
process is general demands the generation of HO● in solution in the presence of H2O2
and UV light. Hydrogen peroxide photolysis process may degrade organic
contaminants either directly by photolysis or indirectly by HO●. UV light without
H2O2 is not very effective for the degradation of organics. When UV light and H2O2
are combined, the overall oxidative reaction potential is greatly enhanced even under
ambient temperature and pressure. The efficiency of direct photolysis depends on
UV absorbance by substrate, quantum yield of photolysis, presence of other
competitive UV absorbents and intensity of UV sources (Tang, 2004).
17
The UV/H2O2 technologies have been applied for the remediation of
contaminated groundwater and some specialized chemical waste treatment. It can be
used to treat 64 different organic compounds and can be used for the removal of
BOD, COD colour and TOC (Tang 2004).
The main advantages of UV/H2O2
method are high rates of pollutant oxidation, large range of applicability regardless
the water quality and convenient dimensions of the required equipment (Zalazar, et
al, 2007).
Figure 2.1: Reaction pathways for UV/H2O2 system (Tang, 2004)
The basic mechanism of the photolysis reaction is shown in Equation 2.1. For
1 mole of H2O2 irradiated two moles of HO● are produced. Figure 2.1 as shown
above illustrates the chemical pathways of UV/H2O2 system. The other possible
chain reactions during UV/H2O2 are stated in Equation 2.2 to 2.11.
H2O2 + hv
→
2OH
(2.1)
H2O2 + HO• → HO2• + H2O
(2.2)
HO2• + HO• → H2O + O2
(2.3)
2HO• → H2O2
(2.4)
18
HO2- + HO•
→ HO2• + OH
(2.5)
The mechanism of UV/H2O2 decomposition in water involved the following
equations:
HO + H2O2 → HO2 + H2O
(2.6)
-
(2.7)
HO + HO2 →
HO2 + OH
2HO →
H2O + ½ O2
(2.8)
2 H2O2 →
H2O + O2
(2.9)
In the UV/H2O2 process, radiation having wavelength shorter than 300nm
transform H2O2 into HO● but every often radiation of these wavelength acts directly
and simultaneously on the organic compound (Alfano et al, 2001). If the photon
wavelength is greater than 254 nm, HO● are largely responsible for initiating
oxidation reactions. The HO● are short-lived extremely potent oxidizing agent
capable of oxidizing organic compounds primarily by either hydroxylation or
hydrogen abstraction (Tang, 2004). These reactions generate organic radicals, which
continuously react with OH to produce the final products such as CO2, H2O and
inorganic salts (Alfano et al, 2001). As depicted in Figure 2.2, this reaction closes a
cycle that maintains a continuous generation of HO● as long as the H2O2 remains in
solution.
19
Figure 2.2: Schematic representation of the photo-assisted Fenton and the H2O2
photolysis processes (Palomar, M., 2005).
Bertelli et al. (2006) reported that UV/ H2O2 at 254 nm are more effective for
highest degradation and mineralization efficiencies. According to Goslan et al.
(2006) H2O2 treatment combined with UV light increased the reduction of UV 254
considerably compared to UV light alone and resulted in removal of dissolved
organic carbon (DOC). Poulopoulos et al. (2006) studies, evaluated that combination
of UV light and H2O2 enhanced considerably the efficiency of phenol destruction
compared to direct photolysis and oxidation by H2O2.
When photon wavelength is shorter than 242 nm, photolysis of water generally
occurs:
H2O2 + hv
→
HO + H
(2.10)
20
Under even shorter wavelength, H2O2 may form a HO● by emitting an
electron. However, considering that conventionally mercury lamps are not capable of
emitting such low lengths, it is unlikely that this reaction pathways bears significance
in the overall oxidation process sequence.
2H2O2 + hv
→
e- + HO + H3O+
(2.11)
The efficiency of UV/H2O2 is due to the generation of 2 mol of hydroxyl
radicals/mol of hydrogen peroxide photolyzed (Mazellier et al, 2004). Generated at
high local concentrations, HO● may dimerize to H2O2 by Equation 2.4. Under
conditions of excess H2O2, HO● will also produces hydroperoxyl radicals (HO2●) as
shown in Equation 2.2, which are much less reactive and do not contribute to the
oxidative degradation of organic substrates. The concentration of HO2● is controlled
by pH of the reaction system, in which turn determines the efficiency of superoxide
dismutation.
Concentration of organic substrate directly influences the required H2O2
dosage. When H2O2 is below the optimum dose, increasing H2O2 dose will improve
the oxidation. If the H2O2 dose is higher than the optimum, the overdosed H2O2 may
act as a HO● scavenger resulting in lower oxidation efficiency. The concentration of
target contaminants decreased with increasing H2O2 but then stabilized for H2O2
beyond optimal dosage. At high concentration excess peroxide can react with HO● to
form H2O and O2. It is implies that an optimal dosage of the chemical oxidant H2O2
can provide maximum removal of the contaminant per unit of H2O2 (Tang, 2004).
Hydrogen peroxide dosage can be rate limiting if applied in very low
concentrations. On the other hand, very high concentrations of H2O2 can compete
successfully with contaminants for HO● generated by Equation 2.6 (Alvarez et al.,
2007). However, the excessive dosage also may inhibit the reaction, possibly due to
the scavenging effect of H2O2 producing HO2●, which are less reactive species than
21
HO●, or through recombination of HO● reproducing H2O2 resulting in lower
oxidation efficiency (Ooi, 2006).
According to Joo An (2002) a number of organic and inorganic compounds
are reported to inhibit the photochemical decomposition of H2O2 solutions. Mathews
and Curtis investigated the effect of six substances on the photolysis of H2O2,
including acetanilide, sulfuric acid, sodium chloride, and sodium hydroxide, calcium
hydroxide, and barium hydroxide. They showed that all the six compounds they
studied acted as inhibitors for photochemical reaction. Anderson and Taylor (1925)
reported 25 inhibitors for H2O2 photolysis, including acids, ethers, amides, alcohols,
ketones, benzene and alkaloids.
The decay of herbicide 2,4-dichlorophenoxy acetic acid (2,4-D) is strongly
dependent on pH attribute to Chu et al (2001). It was interesting to find that the
highest decay rates were observed at acid pH and were followed by basic pH, the
lowest decay rates were observed at neutral pH owing to the property change of
reactant and the shiffing of dominant mechanisms among photolysis and chemical
oxidations. Qioa et al.(2005) reported the degradation rate of microcystin-RR (MCRR) increasing with increasing pH. However, the degradation rate of MC-RR was
reduced when pH values was much higher. They concluded that the degradation rate
of MC-RR increased with increasing pH within lower pH range, and decreased with
increasing pH values within higher pH range.
The time evolution of dichloroacetic acid (DCA) degradation under various
UV incident radiation rates for the initial DCA concentration of 60 ppm were
carefully tested by Zalazar et al. (2007) with three different irradiation conditions.
They observed the 40W lamp (Gw = 3.0 x 10-8 Einstein cm-2 s-1) at the reaction time
of 530 s, a DCA conversion of 82% was achieved, while the conversions for the 15W
(Gw = 9.9 x 10-9 Einstein cm-2 s-1) and 40W with filter (Gw = 4.8 x 10-9 Einstein cm-2
s-1) lamp were 39% and 23% was achieved respectively. It is noticed that is not a
direct indication of the reaction rate dependence with the involved radiation energy
22
because from the kinetic point of view the required property was the average value of
the local volumetric rate of photon absorption by the H2O2.
Qiao et al, (2005) evaluated the effect of UV light intensity on MC-RR
degradation by UV/H2O2 process under four levels of UV light intensity equaling to
7.32, 3.66, 1.46 mW/cm2 and dark reaction respectively. The results show increasing
in UV light intensity significantly improved the degradation rate of MC-RR
compared with the dark reaction. MC-RR was found to be refractory to oxidize with
H2O2 applied alone. The amount of HO● formed from the decomposition of H2O2
was increased and the UV photolysis action was also enhanced with increasing UV
light intensity. Hence, it was quite evident that the combination of these two impacts
contributed available to get higher degradation rate of MC-RR. However, the UV
light intensity was not directly proportional to the degradation rate of MC-RR. From
the economic point of view, the UV light intensity 3.66 mW/cm2 was enough for the
MC-RR degradation in the present experiments.
2.5.1 Applications of Hydrogen Peroxide Photolysis System
The possibility of applying UV light in UV/H2O2 process has paved a new
way for industrial wastewater treatment. As described earlier, UV/H2O2 system is the
generation of HO● in solution in the presence of H2O2 and UV light. Of particular
importance is the fact that many techniques required consumption of high energy
photon generates by UV light, being costly for practical applications. The
involvement of UV light in the removal of contaminants from industrial wastewater
gives great advantage for real applications. Application of UV/H2O2 system with
POME is currently has not been documented.
23
Qiao et al. (2005) investigate the degradation of microcystin-RR in order to
assess the effectiveness and feasibility of the combined UV/H2O2 catalytic system for
purification of water polluted by microcystins. The operating parameters such as
hydrogen peroxide dosage, pH value, UV light intensity, initial concentration of
microcystin-RR and reaction time were evaluated. The degradation process could be
fitted by both of the pseudo first-order and second-order kinetics. The combined
UV/H2O2 system could significantly enhance the degradation efficiency due to the
synergetic effect between UV radiation and hydrogen peroxide oxidation. The
observed rate constants decreased and the corresponding half-lives prolonged as the
concentrations of microcystin-RR increased. MC-RR degradation efficiency could
reach 94.83% under the optimal conditions of MC-RR 0.72 mg/L, H2O2 dosage 1.0
mmol/L, reaction temperature 24.5 to 26.5 oC, pH of 6.8, UV light intensity of 3.66
mW/cm2 and reaction time of 60 min. The combined UV/H2O2 process provides an
effective technology for the removal of microcystins from drinking water supplies
The potential of purifying phenol aqueous solutions (0.0006–0.0064 M) using
ultraviolet (UV) radiation and hydrogen peroxide (H2O2; 0.005–0.073 M) was
investigated by Poulopoulos et al. (2006). Although the direct photolysis of phenol
and its oxidation by hydrogen peroxide (without ultraviolet light) were insignificant,
the combination of UV and H2O2 was extremely effective on phenol degradation.
However, the chemical oxygen demand was on no occasion entirely eliminated,
indicating the resistance of the intermediate products formed to the photo-oxidation.
Increasing the initial concentration of phenol had resulted in lower phenol
conversions, whereas the increase in hydrogen peroxide initial concentration
enhanced significantly the degradation of phenol. In contrast, COD removal was less
sensitive to these changes.
Salari et al. (2005) evaluated the influence of the basic operational parameters
such as initial concentration of H2O2 and irradiation time on the photodegradation of
methyl tert-butyl ether (MTBE). They observed oxidation rate of MTBE was low
when the photolysis was carried out in the absence of H2O2 and it was negligible in
the absence of UV light. The addition of proper amount of hydrogen peroxide
24
improved the degradation, while the excess hydrogen peroxide could quench the
formation of HO●. The semi-log plot of MTBE concentration versus time was linear,
suggesting a first order reaction. Therefore, the treatment efficiency was evaluated by
figure-of-merit electrical energy per order (EEo). The results showed that MTBE
could be treated easily and effectively with the UV/H2O2 process with EEo value 80
kWh/m3/order. The proposed model based on artificial neural network (ANN) could
predict the MTBE concentration during irradiation time in optimized conditions. A
comparison between the predicted results of the designed ANN model and
experimental data was also conducted.
In this study Chen et al. (2007) investigated the use of direct photolysis with
low-pressure (LP) Hg UV lamps and UV/H2O2 for the degradation of a prototypic
endocrine disrupter, bisphenol A (BPA) in laboratory. Removal rates of BPA and
formation of degradation products were determined by high performance liquid
chromatography (HPLC) analysis. Changes in estrogenic activity were evaluated
using both in vitro yeast estrogen screen (YES) and in vivo vitellogenin (VTG)
assays with Japanese medaka fish (Oryzias latipes). The results demonstrate that UV
alone did not effectively degrade BPA. However, UV in combination with H2O2
significantly removed BPA parent compound and aqueous estrogenic activity in vitro
and in vivo. Removal rates of in vivo estrogenic activity were significantly lower
than those observed in vitro, demonstrating differential sensitivities of these
bioassays and that certain UV/AOP metabolites may retain estrogenic activity.
Furthermore, the UV/H2O2 AOP was effective for reducing larval lethality in treated
BPA solutions, suggesting BPA degradation occurred and that the degradation
process did not result in the production of acutely toxic intermediates.
Siedlecka et al. (2006) reported the degradation of mechanically pretreated
oily wastewater by H2O2 in the presence and absence of UV irradiation. The effect of
chemical oxidation on wastewater biodegradability was also examined. The
exclusive use of H2O2 photolyzed by daylight result in quite efficient degradation
rates for the low peroxide concentration used. Higher H2O2 concentrations inhibit
degradation of organic contaminants in the wastewater. The degradation rates of all
25
contaminants were relatively high with an advanced oxidation system (UV/H2O2) but
degradation efficiencies were not distinguishable different when 20 or 45 minutes of
UV radiation used. The excess of H2O2 used in the process can inhibit phenolic
degradation and may lead to the formation of a new phenolic fraction. The
biodegradability of oily port wastewater did not increased significantly following the
application of the AOPs.
Paracetamol oxidation from aqueous solutions studied by Andreozzi et al.
(2003) of ozonation and H2O2 photolysis. Both oxidative systems are able to destroy
the aromatic ring of the substrate with a partial conversion of the initial carbon
content into carbon dioxide. For the adopted experimental conditions mineralization
degrees up to 30% and 40% are observed with ozonation and H2O2 photolysis,
respectively. Main reaction intermediates and products are identified for both
systems by HPLC and gas chromatography- mass spectroscopy (GC–MS) analyses
and a kinetic characterization is achieved.
CHAPTER 3
METHODOLOGY
3.1
Materials
Chemicals used in this study were analytical hydrogen peroxide (35%w/w),
reagent grade sulphuric acid (H2SO4) and sodium hydroxide (NaOH) for pH
adjusment. All chemicals were used as received and distilled water was used in the
synthesis and preparation of solution. Hydrogen peroxide stock solution was stored
in light resistant Pyrex bottles and refrigerated. Palm oil mill effluent was obtained
from palm oil mill owned by Pertubuhan Peladang Negeri Johor (PPNJ) in Kahang,
Johor. Palm oil mill effluent was collected from the final clarifier after sequencing
batch reactor (SBR) treatment.
3.2
Analytical Method
The characteristics of the BT-POME were analyzed for colour, COD, BOD,
pH, suspended solid (SS) and ammoniacal nitrogen (NH3-N), while the efficiency of
27
UV/H2O2 process was assessed based on COD and colour. Colour was measured by
Hach DR5000U spectrophotometer based on ADMI Weight Ordinate Method.
Chemical oxygen demand measurement was measured by Hach DR5000U
spectrophotometer based on Reactor Digestion Method. Biochemical oxygen demand
and SS were analyzed based on Standard Method, (APHA 2005). The pH was
analyzed using pH meter (Multiparameter analyser consort C535) and NH3-N was
measured by Hach DR5000U spectrophotometer based on Nessler Method. The list
of the analytical methods and instrumentations that were used in the experimental
work are presented in Table 3.1.
Table 3.1: List of analytical methods and instrumentations for experimental work.
Parameter
Analytical method and Instrument
Colour
Hach DR5000U spectrophotometer (ADMI Weight
Ordinated Method)
COD
Hach DR5000U spectrophotometer (Reactor Digestion
Method)
Suspended Solid (SS)
Ammoniacal
Standard Method APHA (2005)
Nitrogen Hach DR5000U spectrophotometer (Nessler Method)
(NH3-N)
BOD
Standard Method APHA (2005)
pH
pH meter (Multiparameter analyser consort C535)
28
(a)
(b)
(c)
Figure 3.1: Analytical instruments used (a) pH meter (Multiparameter Analyser
Consort C535) (b) DR 5000U Spectrophotometer (c) suspended solids apparatus
3.2.1
Colour – ADMI Weighted Ordinate Method
Colour detection with Hach Spectrophotometer DR5000U was carried out
according to procedure Method 10048 – ADMI Weighted Ordinate Method provided
by HACH (2005). A sample was filled with 10 mL of distilled water as blank, and
another was filled with 10 mL of pH adjusted POME. The stored Hach program ‘126
Color, ADMI’ was recalled for the colour test. The blank sample cell was placed in
the cell holder with the light shield closed and set as zero. Then, the pH adjusted
POME cell was placed in the cell holder with the reading of colour in ADMI unit
displayed on the screen. The percentage colour removal of parameters in POME was
calculated based on following equation:
% R = [(Co – Ct) / Co] x 100
Where, % R = percentage removal
Co = initial colour of POME (ADMI)
Ct = colour of POME measured at time of t (ADMI)
(3.1)
29
3.2.2
Chemical Oxygen Demand – Reactor Digestion Method
Measurement of COD with Spectrophotometer DR5000U were carried out
according to procedure Method 8000-Reactor Digestion Method provided by Hach.
COD. The Reactor was preheated to 150oC. Homogenize POME of 2.0 ml were
added to the high range COD Digestion Reagent Vial. The mixture was inverted
several times to ensure well mixing. Deionised water of 2.0 ml was added to another
high range COD digestion reagent vial to be served as blank. Both vials were cooled
to room temperature before reading. The stored Hach Program 435 COD HR was
recalled for the COD test. The blank vial is placed in the cell holder with the light
shield closed and set as zero. Then, the sample vial was placed in the cell holder with
the reading of COD in mg/L were displayed on the screen. The percentage COD
removal of parameters in POME was calculated based on following equation:
% R = [(Co – Ct) / Co] x 100
(3.2)
Where, % R = percentage removal
Co = initial COD of POME (mg/L)
Ct = COD of POME measured at time of t (mg/L)
3.2.3 Suspended Solids – Standard Method (APHA, 2005)
Suspended solids were analyzed based on Standard Method provided by
APHA (2005). A filter paper was weighted and placed on a funnel. A 100 ml of the
BT-POME was poured onto it with the vacuum pump was turned on. The apparatus
was rinsed thoroughly. After the filtration, the paper filter was dried in an oven at
105oC for at least an hour. Then, the filter paper was cooled in desiccators and
30
weighed. The drying, cooling, desiccating and weighing were repeated until constant
weight was obtained or change in weight is less than 4% or 0.5 mg. Total Suspended
solids for each sample are calculated using following equation:
Suspended Solids (mg/L) = [(A-B) / Volume sample] x 1000
(3.3)
Where,
A = Total weight of filter paper and solids (mg) after heating
B = Weight of filter paper only
3.2.4
Ammoniacal Nitrogen – Nessler Method
Measurement of NH3-N with Hach Spectrophotometer DR5000U was carried
out according to procedure Nessler Method provided by Hach. The graduated
cylinder was filled with 25 mL deionized water to be served as a blank. Homogenize
BT-POME of 8.0 mL with 17 mL deionized water was added to the graduated
cylinder. Three drops of mineral stabilizer, polyvinyl alcohol and 1 mL of nessler
reagent was added to each cylinder, stopper and the mixture was inverted several
times to ensure well mixing. The start timer was press at Hach DR5000U. The
sample cell with BT-POME and each solution was inserted in the cell holder to
replace the blank. After closing the light shield, the ammoniacal nitrogen
concentration in mg/L was display on the screen.
31
3.2.5
Biochemical Oxygen Demand (BOD)
Biological Oxygen Demand (BOD) was analysed based on Standard Method.
A clean graduated cylinder was used and the correct sample volume was poured into
BOD sample bottle. Three bottles were prepared and labelled. The sample was
placed in BOD bottle and the bottle was top up with the dilution water. Duplicate
bottle was prepared and have a same sample volume. A 3.8 cm (1.5 in) magnetic stir
bar was placed in each sample bottle. The DO in each bottle was measured. The
bottles were placed into the incubator in the dark to prevent photosynthesis from
adding oxygen to the samples and invalidating the oxygen consumption results. The
incubator was adjusted to the appropriate temperature (20oC) setting for each sample
volume. The bottles were left about 5 days. At the end of 5 days, the remaining DO
in each bottle was read again and the results were recorded. The BOD for each
sample was calculated using following equation:
BOD5 = [(DO0 – DO5) / P]
Where,
DO0 = DO value for day first
DO5 = DO value for day five
P
= Dilution factor
= Volume Sample / Total Volume
(3.4)
32
3.3
Experimental Procedures
This study composed of three stages of UV/H2O2 processes, in which
different H2O2 dosing, pH levels and initial BT-POME concentration were used. The
study was conducted in batch mode using a 2L beaker with working volume of 1L.
Mixing was achieved using magnetic stirrer and the reaction was conducted using a
low pressure UV lamp of 15W. Figure 3.2 shows the UV lamp which produced
monochromatic ultraviolet light of 254 nm. The reaction was conducted in a closed
area for safety precaution. In each experiment the lamp were turned on for 1min prior
to experiment on to stabilize the operation.
Figure 3.2: Low pressure UV lamp of 15W
The first stage was conducted at different H2O2 dosing (i.e. 25, 50, 100, 250,
500 and 1000 mg/L). The sample at t=0 were taken when the lights was off. Once the
H2O2 was added, samples were taken at different intervals (i.e. 0, 15, 30, 45, 60, 90
and 120 mins). At each time 10 mL of samples were taken out, 8 mL for colour and
2 mL for COD analyzing. The best H2O2 dosing with highest COD percentage
removal was used in the second stage of the experiment. Figure 3.3 shows the set up
of the reactor.
33
(a)
(b)
Figure 3.3: Set-up instrument (a) Beaker 2L (b) Experimental set-up
In the second stage the treatment was conducted at different pH levels (i.e. 5,
5.5, 6, 6.5, 7, 7.5, 8, 8.5 and 9). The pH of the solution was adjusted at desired level
using dilute NaOH (240 g of NaOH in 1000 mL distilled water) or H2SO4 (10 mL
H2SO4 in 20 mL distilled water). The samples were taken out at different reaction
time (i.e. 0, 30, 60 and 120 mins) and analyzed for COD and colour. The pH which
yields the highest COD was used in the third stage experiment.
In the third stage, the best H2O2 dosing and pH levels with highest percentage
COD removal were used. The procedure was repeated again with samples at different
dilution percentage (i.e. 25, 50, 75 and 90%). The different dilution resulted in
samples with different initial concentration as shown in Table 3.2. Figure 3.5 shows
the colour intensity of the samples at different dilution. The efficiency of UV/ H2O2
process was assessed again at certain interval in term of colour and COD removal.
34
25%
(a)
50%
75%
90%
90
%
(b)
Figure 3.4: BT-POME at different dilution factors (a) no dilution (b) 25%, 50%, 75%
and 90% dilution.
Table 3.2: Value of initial colour and COD removal
Dilution (%)
Initial Colour (ADMI)
Initial COD (mg/L)
0
1341
731
25
1125
600
50
700
420
75
391
251
90
163
90
CHAPTER 4
RESULTS AND DISCUSSION
4.1
Introduction
This chapter discusses the result of the experimental work. As mentioned
earlier, the study was conducted to determine the effectiveness of hydrogen peroxide
photolysis process in treating BT-POME. The effects of H2O2 dosing, pH and initial
BT-POME concentration were investigated. The COD and colour were used to
assess the performance of the process.
4.2
Wastewater Characteristics
The characteristics of BT-POME are tabulated in Table 4.1. Despite being
treated by a series of biological treatment, the wastewater is still coloured with high
concentration of organics, SS and NH3-N. The wastewater was alkaline with pH of
8.18. The COD value (921 mg/L) was appreciably low when compared to Ooi (2006)
and Kon (2007). However, the colour (1773 ADMI) was higher than Ooi (2006) but
36
slightly lower than Kon (2007) while the SS was much lower than Kon. The ratio of
BOD/COD of 0.46 indicates the biodegradability of the wastewater despite being
treated by the biological process. The characteristics of BT-POME are shown in
Table 4.1.
Biological treated POME obtained from PPNJ Kahang palm oil mill had
lower COD, colour and suspended solids, possibly due to dilution effect from
continuous rainy days prior to sample collection. The biological treatment employed
by palm oil mill currently able to meet the requirements set by the Department of
Environment of Malaysia except for BOD.
Table 4.1: Characteristics of BT-POME
Parameter
Unit
BT-POME
Ooi (2006)
Kon (2007)
Standard
limit
pH
-
8.18
-
-
5–9
COD
mg/L
921
1854
1095
-
BOD
mg/L
422
-
-
100
Colour
ADMI
1773
1138
1800
-
SS
mg/L
370
-
1830
400
NH3-N
mg/L
10.47
-
-
150
37
4.3
Effect of H2O2 Dosage
The first part of the experiment stages was to determine the effect of H2O2
dosage in the UV/H2O2 process. Investigation of H2O2 dosage was conducted at 25,
50, 100, 250, 500 and 1000 mg/L. As mentioned earlier, Figures 4.1and Table 4.2
and 4.2 and Table 4.3 show the removal profile of colour and COD.
Table 4.2: Value of percentage colour removal at different H2O2 dosage
Time
0
15
30
45
60
90
120
Removal (%)
25 mg/L
0
0.2
3.0
0.2
0.7
1.5
5.9
50 mg/L
0
2.0
0.7
0.8
1.0
1.1
1.9
100 mg/L
0
2.7
1.8
0.5
0.8
1.1
1.4
250 mg/L
0
8.5
0.9
0.2
0.3
0.6
2.0
500 mg/L
0
3.1
1.9
0.3
1.9
0.3
1.7
1000 mg/L
0
2.4
3.1
1.4
5.2
5.8
4.9
Based on Figure 4.1, it shows that the colour removal at different H2O2
dosage is not very encouraging. The reduction of colour removal remained relatively
constant over the time. Both 25 mg/L and 1000 mg/L of colour removal showed a
steady increase with 5.9% and 4.9% removal were recorded respectively. On the
other hand, colour removal at 250 mg/L increased up to 8.5% for reaction time of 15
minutes but dropped to 2% removal after 2 hours reaction.
38
9
Colour Removal (%)
8
7
25 mg/L
50 mg/L
100 mg/L
250 mg/L
500 mg/L
1000 mg/L
6
5
4
3
2
1
0
0
15
30
45
60
75
time (min)
90
105
120
135
Figure 4.1: Profile of colour and at different H2O2 dosage
Table 4.3: Value of percentage COD removal at different H2O2 dosage
Time
25 mg/L
0
2.9
1.2
1.9
19.1
0.9
15.1
0
15
30
45
60
90
120
50 mg/L
0
1.0
8.9
0.5
0.9
1.0
1.7
Removal (%)
100 mg/L 250 mg/L
0
0
3.1
3.7
0.5
1.3
11.4
3.4
11.9
0.8
6.5
26.1
0.3
12.1
500 mg/L
0
0.5
0.1
0.2
1.6
22.3
11.3
1000 mg/L
0
2.1
0.8
1.8
0.6
1.2
1.1
Figure 4.2 shows that the COD removal increases as the time of reaction
increases. COD removal in UV/H2O2 process increased from 3.7% to 26.1% at 250
mg/L and from 0.5% to 22.3% at 500 mg/L between 15 to 60 minutes reaction time.
Sharp decrease of COD removal can be observed just after 60 min reaction time with
18.2% removal at 25 mg/L of H2O2 dosage. It is important for COD removal in
UV/H2O2 process to increase significantly after longer time of reaction. Therefore,
UV/H2O2 mechanism plays a major role in removing the organic compound in BTPOME.
39
30
25 mg/L
100 mg/L
500 mg/L
COD Removal (%)
25
50 mg/L
250 mg/L
1000 mg/L
20
15
10
5
0
0
15
30
45
60
75
90
105
120
135
-5
time (min)
Figure 4.2: Profile of COD at different H2O2 dosage
45
% COD removal
% colour removal
40
Removal (%)
40.8
35.9
35
30
29.8
32.8
25
20.8
20
13.3
15
12.2
11.1
10
7.3
5
8.8
8
7.4
0
0
100
200
300
400
500
600
700
800
900
1000
H2O2 (mg/L)
Figure 4.3: Removal percentage of colour and COD at different H2O2 dosage
From Figure 4.3, the results show the colour removal ranged from 7.3% 20.8% for 2 hours reaction. The highest removal percentage took place at 1000 mg/L
and the lowest percentage was at 250 mg/L. COD removal commonly ranged from
7.4% - 40.8%. The highest removal percentages at 250 mg/L while the lowest
40
removal percentage at 1000 mg/L. Figure 4.3 illustrates the effect of H2O2 dosage on
removal of colour and COD.
Based on the calculation data, the kinetics of colour and COD removal with
respect to its change in absorption values fitted well to second order rate and zeroth
order reaction kinetics using following equation:
(1/A) = kt + (1/Ao)
(4.1)
(A) = -kt + Ao
(4.2)
where k is the rate constant, t is the irradiation time and Ao and A are the initial and
the final absorbance values of the concentration respectively.
Figure 4.4 shows the rate constant of colour at different H2O2 dosing. The
rate of removal was directly proportional to H2O2 dosing. It can be seen that the rate
relatively constant from 25 mg/L to 500 mg/L but increasing steadily at 1000 mg/L
of H2O2 dosage. Figure 4.5 depicted the rate constant of COD are decreased at 50
mg/L but is accelerated up to 250 mg/L by the addition of H2O2 dosage to the UV
treatment. However, the rate constant declined above 250 mg/L dosage.
41
5.00E-05
4.00E-05
(L.min/mg)
4.00E-05
3.00E-05
2.00E-05
1.00E-05
1.00E-05
1.00E-05
1.00E-05
0.00E+00
0
100 200 300 400 500 600 700 800 900 1000
H2O2 concentration (mg/L)
Figure 4.4: Rate constant of colour at different H2O2 dosing
80
70
60
(mg/L.min)
70
66
57
50
49
40
30
20
20
10
8
0
0
200
400
600
800
1000
1200
H2O2 concentration (m g/L)
Figure 4.5: Rate constant of COD at different H2O2 dosing
These patterns of rate constant were different between colour and COD. This
could be due to the fact that the higher H2O2 dosage, scavenging of HO● will occur.
It has been proved that the H2O2 acts as both promoter and scavenger of HO●. In the
UV/H2O2 process HO● were mainly responsible for the removal of colour and COD.
Hydrogen peroxide can produce HO●, HO● reacts with H2O2 to form HO2●. Since,
42
HO2● are less reactive than HO● increased amount of H2O2 has a diminishing return
on the reaction rate and reduce the oxidation power at a certain extent. Therefore it is
important to optimize the applied dose of H2O2 to maximize the performance of the
UV/H2O2 process and minimize the treatment cost. The performance of pH for
colour removal was shown in Figure 4.6.
R1
R1
R3
R2
R5
R4
R6
Figure 4.6: Residual of colour at different H2O2 dosage
The dosage of H2O2 had an important influence on the degradation of MCRR attribute to Qiao et al. (2005). The results show the degradation rate increased
with increasing H2O2 concentration rapidly. It is noticed that increasing H2O2
concentration for the degradation of MC-RR attributed to the amount HO● increased
from the decomposition of increasing H2O2. From the results obtained the optimal
H2O2 dosage reach at 1.0 mmol/L was enough for the MC-RR degradation in the
present experiments.
Zalazar et al. (2007) evaluated that high concentration of H2O2, the
conversion of DCA is slow as similar results observed a low concentration of H2O2,
the conversion was very high, indicating an advantageous use of reactants. The
obtained results noticed when the concentration of H2O2 is too low, since its
43
radiation absorption coefficient at the usually employed wavelengths is rather weak,
the reaction rate more specifically the initiation step of H2O2 decomposition results
slow. When the concentration of H2O2 is too high it becomes a scavenger of HO●
competing with the pollutant degradation reaction and decreasing the rate of the
latter. From the results, the optimal H2O2 dosage 60 ppm was enough for conversion
of DCA.
4.4
Effect of pH
Hydrogen peroxide photolysis process at different pH levels was carried out
in the second stage. Colour and COD removal analyzed for UV/H2O2 process with
pH levels of (i.e. 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5 and 9) with H2O2 dosage of 250 mg/L
obtained from stage 1 study. Figures 4.7 and Table 4.4 and Figure 4.8 and Table 4.5
show the removal profile of colour and COD.
Table 4.4: Value of percentage colour removal at different pH
Time
0
30
60
120
pH 5
0
5.4
2.8
2.5
pH 5.5
0
5.1
3.7
1.2
pH 6
0
9.4
6.6
2.8
Removal (%)
pH 6.5 pH 7 pH 7.5
0
0
0
7.2
6.8
2.6
6.1
3.8
5.2
3.3
6.8
13.9
pH 8
0
5.0
5.1
3.9
pH 8.5
0
7.9
1.2
3.9
pH 9
0
10.3
1.9
4.9
From Figure 4.7, it can be observed that the overall colour removal at
different pH steady decline over the time, the removal falls 0.1% to 8.4%. Obviously
pH 9 implies the sharply decreased of 8.4% removal but pH 7 turnover rose against
the pH by 13.9% removal after 2 hours reaction.
Colour Removal (%)
44
16
14
pH 5
pH 6.5
pH 8
12
pH 5.5
pH 7
pH 8.5
pH 6
pH 7.5
pH 9
10
8
6
4
2
0
0
20
40
60
80
100
120
140
time (min)
Figure 4.7: Profile of colour at different pH
Table 4.5: Value of percentage COD removal at different pH
Time
0
30
60
120
pH 5
0
10.4
6.5
12.1
pH 5.5 pH 6
0
0
11.3
23.4
13.3
3.9
7.2
1.8
Removal (%)
pH 6.5 pH 7
pH 7.5 pH 8
0
0
0
0
13.7
3.7
12.4
4.2
2.2
6.1
1.4
1.6
25.0
15.1
27.4
2.1
pH 8.5 pH 9
0
0
7.9
5.0
6.3
3.4
3.9
13.4
Figure 4.8 depicted the COD removal increasing steadily over the time. pH
6.5, 7 and 7.5 implies increase sharply of 11.3%, 11.4% and 15% removal
respectively for 2 hours reaction. A lower of COD removal and slower reaction can
be observed after 30 minutes reaction of the process at pH 6. These could be due to
the COD contribution from the organics remaining in the solution, it is possible that
the H2O2 was not completely dissociates and hence contributed to the COD value.
45
30
pH 5
pH 6.5
pH 8
COD Removal (%)
25
pH 5.5
pH 7
pH 8.5
pH 6
pH 7.5
pH 9
20
15
10
5
0
0
30
60
90
120
time (min)
Figure 4.8: Profile of COD at different pH
40
37.3
30
Removal (%)
% COD
removal
% colour
removal
36.6
35
26.3
25
28.6
27.7
23.3
20.5
20.5
20
17.8
15
10.3
10
16.5
15.7
13.2
12.5
16.3
9.7
5
7.7
0
5
5.5
6
6.5
7
7.5
8
8.5
9
pH
Figure 4.9: Removal percentage of colour and COD at different pH
The colour removal ranged from 9.7% - 20.5% for 2 hours reaction. It was
interesting to find that were observed the highest removal at pH 7.5 while the lowest
removal at pH 5.5. The COD removal ranged from 7.7% - 37.3%, it can be observed
that the highest removal percentage at pH 7.5 and the lowest percentage took place at
pH 8. Figure 4.9 illustrates the effect of pH on removal of colour and COD.
46
The experimental data for both colour and COD removal can be fitted in
second order rate and zeroth order reaction kinetics respectively. Figure 4.10
observed that the trend of colour was fluctuated; the rate constant turnover rose to pH
6 but declined at neutral pH, then increased steeply to pH 7.5 and no further
acceleration with pH increase. From Figure 4.11, it can be seen that the increase the
pH, the lower the rate constant. At neutral pH, the rate constant was higher than the
high pH.
7.00E-05
6.00E-05
6.00E-05
5.00E-05
4.00E-05
4.00E-05
4.00E-05
4.00E-05
3.00E-05
4.00E-05
3.00E-05
3.00E-05
2.00E-05
3.00E-05
1.00E-05
0.00E+00
5
5.5
6
6.5
7
7.5
8
8.5
9
pH
Figure 4.10: Rate constant of colour at different pH
120
108
91.8
100
96.3
(mg/L.min)
(L.min/mg)
5.00E-05
80
82.8
87.3
81.3
60
36.3
40
20
18.9
23.7
0
5
5.5
6
6.5
7
7.5
8
8.5
pH
Figure 4.11: Rate constant of COD at different pH
9
47
Based on the trends, it can be discussed that high removal rate observed at
low pH range, this is because H2O2 is stable in acid situation and is capable of
generating HO● are low and will slightly lower the overall removal rate. Therefore,
the overall rate constant at high pH is lower than at low pH.
As compared the results of 2, 4-D in UV/H2O2 process reported by Chu
(2001), the H2O2 is photodegradable under UV illumination. The highest decays rates
were observed at acid pH and were followed by basic pH, the lowest decay rates
were observed at neutral pH. From the results it was found that photodecay is
strongly dependent on pH where the higher the pH, the higher the H2O2 decays rates.
The performance of pH for colour removal are shown in Figure 4.12
R1
R3
R2
R5
R4
R6
Figure 4.12: Residual of colour at different pH
As similar reaction was reported by Qiao et al. (2005) it was found that the
degradation of MC-RR increased with increasing pH in the range of pH 5–8.
However, the degradation rate of MC-RR was reduced when pH value was much
higher. It is noticed that the increase of pH yielded two opposing effects: on one
hand, there was an improvement of hydroxyl radical formation through reaction 2.1
since the molar extinction coefficient of the hydroperoxide anion (HO2), the ionic
48
form of H2O2 at high pH, was higher than that of H2O2. On the other hand, the HO2
could also scavenge the HO● through the following reaction Because the reaction
rate of HO2 reacted with HO● are was faster than that of H2O2 the scavenging rate of
HO● was also increased according to reactions 2.2 and 2.5 as pH increased.
Abdullah et al. (2007) were carefully testing with other dyes; it observed that
photolytic dye decoloration appears to be more at alkaline pH and less at acidic pH.
Perhaps, the well documented pH effect on the dye degradation is dye dependent.
The result shows that slight increase in the degradation of Safranin O at pH 9. This
enhancement in dye decoloration in basic conditions is most likely due to the fact
that at alkaline pH, peroxide anions (HO2) are produced in solution by UV radiation,
which in turn can generate more HO●.
4.5
Effect of initial BT-POME concentration
The initial BT-POME concentration had an important effect on the
performance of combined UV/H2O2 system. The effect of initial BT-POME
concentration was carried out for UV/H2O2 process with initial concentration value
that mentioned in Table 3.7. The H2O2 dosage and of 250 mg/L and pH 7.5
respectively obtained from stage 1 and 2 study. Figures 4.13 and Table 4.6 and
Figure 4.14 and Table 4.7 show the removal profile colour and COD.
Table 4.6: Value of percentage colour removal at different initial concentration
Time
0
30
60
120
25%
0
4.7
8.8
7.7
Removal (%)
50%
75%
0
0
4.0
21.0
21.0
18.1
11.7
9.9
90%
0
27.0
37.0
16.0
49
From Figure 4.13, it can be seen, the colour removal rose steadily for reaction
time 60 minutes, but steadily decline after 60 minutes of the process. Initial
concentration at 391 ADMI depicted that the colour removal gradually dropped over
the time. In the same way, it can be observed both initial concentration at 163 ADMI
and 700 ADMI have been increasing drastically, it became almost 10% and 17% of
removal. This is possibly due to more dilutions are good to get better results.
40
Colour Removal (%)
35
30
25
20
15
10
5
0
0
30
1125 ADMI
60
90
time (min)
700 ADMI
391 ADMI
120
163 ADMI
Figure 4.13: Profile of colour at different initial concentration
Table 4.7: Value of percentage COD removal at different initial concentration
Time
0
30
60
120
25%
0
10.2
5.9
12.4
Removal (%)
50%
75%
0
0
7.4
24.3
3.6
21.0
18.4
28.0
90%
0
13.3
35.0
31.4
50
From Figure 4.14 depicted the overall COD removal steadily decline after 30
minutes reaction, but increase gradually after 60 minutes of the process. However,
sharply increased show at initial concentration 90 mg/L after 60 minutes reaction but
it decreased gradually after 2 hours of the process.
40
COD Removal (%)
35
30
25
20
15
10
5
0
0
30
60
90
120
time (min)
600 mg/L
420 mg/L
251 mg/L
90 mg/L
Figure 4.14: Profile of COD at different initial concentration
70
61.3
Removal (%)
60
50
41.7
40
30
22.2
33
20
10
0
0
200
400
600
800
1000
1200
Initial colour BT-POME concentration (ADMI)
Figure 4.15: Removal of colour at different initial concentration
51
70
60
Removal (%)
61.1
56.6
50
40
27
30
26
20
10
0
0
100
200
300
400
500
600
700
Initial COD BT-POME concentration (mg/L)
Figure 4.16: Removal of COD at different initial concentration
Figure 4.15 and 4.16 above illustrates the effect of initial concentration on
removal of colour and COD. The colour removal was ranged from 22.2% - 61.3% for
2 hours reaction, where the highest removal took place at initial concentration of 163
ADMI and the lowest removal at initial concentration of 1125 ADMI. The COD
removal ranged was from 26% - 61.1%, it was depicted that the highest removal
could obtained at initial concentration 90 mg/L, while the lowest removal at initial
concentration 600 mg/L.
The experimental data for both colour and COD removal can be fitted in
second order rate and zeroth order reaction kinetics respectively. From Figure 4.17, it
can be seen that the trend rate constant of colour decreased drastically with
increasing initial concentration.
52
4.00E-03
3.50E-03
3.40E-03
(L.min/mg)
3.00E-03
2.50E-03
2.00E-03
1.50E-03
1.00E-03
6.00E-04
2.00E-04
5.00E-04
0.00E+00
100
250
400
550
700
850
8.00E-05
1000 1150
1300
Initial colour BT-POME concentration (ADMI)
Figure 4.17: Rate constant of colour at different initial concentration
60
(mg/L.min)
50
50
46
40
35
30
20
19
10
0
90
190
290
390
490
590
690
Initial COD BT-POME concentration (mg/L)
Figure 4.18: Rate constant of COD at different initial concentration
Figure 4.18 depicted that the rate constant increase steadily with increasing
initial concentration. However, the rates gradually decrease at initial concentration
420 mg/L. The performance of pH for colour and COD removal are also shown in
Figures 4.19.
53
R1
R3
R2
R4
Figure 4.19: Residual colour at different initial concentration
For both reaction with respect to the experimental results indicate there
existed synergetic effect between dilution factor of BT-POME and initial
concentration in the UV/H2O2 process. Besides, dilution factor also very important in
the removal of COD and might be attributed to the presence of high concentration of
the substrate in the treatment system.
As similar observation was reported by Qiao et al. (2005), the results of these
experiments showed that the degradation rate of MC-RR decreased with increasing
initial MC-RR concentration. This could be attributed to the relative reduction of
H2O2/ MC-RR molar ratio as MC-RR concentration increased. Although the
concentration of H2O2 was relative high comparing with low initial concentration of
MC-RR, the degradation efficiency of MC-RR changed insignificantly due to the
scavenging effect of H2O2 on HO●.
At different approach by Poulopoulus (2006) lower conversions were
observed with increasing the initial concentration of phenol. Less than 16 min were
required for 100% phenol destruction when its initial concentration was 0.0006 M,
54
whereas the corresponding time for initial phenol concentration 0.0032M was 30
min. When phenol initial concentration was increased to 0.0064 M, phenol was still
detected in the solution after 120 min.
This negative impact of phenol initial concentration on the phenol
decomposition can be associated with different reaction pathways due to different
H2O2/phenol molar ratios. On the contrary, COD removal seemed to be insensitive to
phenol initial concentration. With the exception of 0.0006 M, demonstrating the
difficulty of the oxidation of the intermediate products which contained organic acids
as indicated from the drop of pH values with time. The conversion of H2O2 decreased
by increasing the initial concentration of phenol due to less fraction of light available
to UV/H2O2 process
CHAPTER 5
CONCLUSIONS
5.1
Conclusions
The followings are conclusions obtained from the study:
1) The colour and COD removal ranged from 7.3% - 61.3% and 7.4% - 61.1%
respectively.
2) It was found that UV/H2O2 process had better COD removal compare to
colour removal
3) The removal process fitted well to zeroth order for COD and second order
kinetics for colour and primarily followed a mechanism of both UV/H2O2
and hydroxyl radicals oxidation.
4) Effect of H2O2 dosage is important of removal organic compound as
contribution removal had achieved 40.8% for all experimental conditions.
Based on the H2O2 dosage; the rate constant of colour mg/L are slightly
constant but increased at increasing H2O2 dosage and COD trend are
56
fluctuated; as H2O2 dosing increase the rate constant of COD is accelerated
up but above it, the rate constant decrease.
5) Contribution effect of pH the removal had achieved at pH 7.5 with COD
removal 37.3%. The trend of COD; the increase the pH, the lower the rate
constant and colour are fluctuated; the rate constant accelerated but
decreased at neutral pH and no further acceleration at basic pH.
6) Effect of initial BT-POME concentration had achieved more than 60% for
both removals. The trend rate constant of colour decreased with increasing
initial concentration while the rate constant of COD increased with
increasing initial concentration was achieved.
5.2
Recommendations
Hydrogen peroxide photolysis system has been utilized in this study to offer a
tertiary treatment method. Following recommendations should be carried on in order
to improve the performance and usability of UV/H2O2 process.
1) BT-POME should be filtered out first before doing the experimental by using
UV/H2O2 system as it can improve the performance of UV/H2O2 system.
2) The reaction time should be increase to make sure the removal was
completely dissociated.
3) The optimum condition of pH in UV/H2O2 system should be investigated.
4) The UV light intensity should be increase in order to improve the
performance of UV/H2O2 system.
57
5) The photoreactor used should be convenient dimension that include large
volume glass tank and the whole equipment was protected from extraneous
light.
6) The working volume should be increase so that the UV lamp can irradiate all
the solution completely.
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APPENDIXES
A.
Stock Solution Calculation
Stock Solution of Hydrogen Peroxide (H2O2)
Volume of H2O2 required for concentration of 575 mg/L is shown as below:
Concentration of H2O2 (35 % w/w)
⎛
⎞⎛ 1.11 × 10 3 g H 2O2 solution ⎞
35 g H 2O2
⎟
⎟⎜
= ⎜⎜
⎟⎜
⎟
1L H 2O2 solution
⎝ 100 g H 2O2 solution ⎠⎝
⎠
= 388.5 g / L
Thus, volume of H2O2 for 500 mL POMSE
⎛ mL ⎞
⎟⎟(0.5 L )
= (575mg / L )⎜⎜
⎝ 388.5mg ⎠
= 0.74mL