In most petrochemical complexes and oil refineries the wastewater contains the aromatic compounds among which Benzene, Toluene, Ethyl Benzene and Xylene (BTEX) have harmful effects on environment and human health. The present work mainly deals with the UV-based advanced oxidation processes (AOPs), UV/H2O2 were tested in batch reactor systems to evaluate the removal efficiencies and optimal conditions for the photodegradation of BTEX in order to wastewater treatment. The efficiency of this method was analyzed by evaluating the Chemical Oxygen Demand (COD) as a pollution criterion through the COD reactor. The influence of the basic operational parameters such as initial concentration of H2O2, pH, Temperature, irradiation time and UV amount on the photo degradation of BTEX were also studied. The oxidation rate of BTEX and respectively the reduction rate of COD were low when the oxidation was carried out in the absence of H2O2 or UV light. The addition of proper amount of hydrogen peroxide improved the degradation, while the excess hydrogen peroxide could quench the formation of hydroxyl radicals (•OH). The optimal conditions of suspended slurry with 1.11(g/l) initial concentration of H2O2 and pH value of 3.1 were obtained under three UV lights illumination (6 W). Under the optimal conditions, COD reduction during the initial period of 180 min in UV/H2O2 systems reached about 90%.

1. 0
In the name of God
School of Engineering
Department of Chemical and Petroleum Engineering
Shiraz University, Shiraz, Iran
Vahidreza Bitarafhaghighi (Student ID: 863049)
Bachelor project report title:
COD reduction of aromatic polluted waste water by
Advanced Oxidation Process (UV/H2O2)
Supervisor:
Dr. Darioush Mowla, Professor in Chemical Engineering
Fall 2011

2. 1
Table of Contents
Item Page No.
Abstract 2
1. Introduction 2
2. Experimental 5
2.1. Chemicals 5
2.2. Batch reactor and reaction procedures 5
2.3. Sample analysis 6
3. Results and Discussion 6
3.1. Effects of H2O2 dosages at different pHs 6
3.2. Effects of temperature 8
3.3. Effects of UV light 8
3.4. Combination of UV light and H2O2 9
4. Conclusion 10
5. References 11

3. 2
Abstract
In most petrochemical complexes and oil refineries the wastewater contains the aromatic
compounds among which Benzene, Toluene, Ethyl Benzene and Xylene (BTEX) have harmful
effects on environment and human health. The present work mainly deals with the UV-based
advanced oxidation processes (AOPs), UV/H2O2 were tested in batch reactor systems to
evaluate the removal efficiencies and optimal conditions for the photodegradation of BTEX in
order to wastewater treatment. The efficiency of this method was analyzed by evaluating the
Chemical Oxygen Demand (COD) as a pollution criterion through the COD reactor. The
influence of the basic operational parameters such as initial concentration of H2O2, pH,
Temperature, irradiation time and UV amount on the photo degradation of BTEX were also
studied. The oxidation rate of BTEX and respectively the reduction rate of COD were low
when the oxidation was carried out in the absence of H2O2 or UV light. The addition of proper
amount of hydrogen peroxide improved the degradation, while the excess hydrogen peroxide
could quench the formation of hydroxyl radicals (•OH). The optimal conditions of suspended
slurry with 1.11(g/l) initial concentration of H2O2 and pH value of 3.1 were obtained under
three UV lights illumination (6 W). Under the optimal conditions, COD reduction during the
initial period of 180 min in UV/H2O2 systems reached about 90%.
1. Introduction
The importance of oil in the world economy is well known in recent years. However,
because of the composition of its residues and of the oil itself, which contains mainly aromatic
and aliphatic compounds (Mariano, 2005), the environmental question that surrounds its
production must always be well assessed. The aromatic fraction is more toxic than that of the
aliphatic fraction. Aromatic compounds, including benzene, toluene, ethyl benzene and xylene
isomers (the so-called BTEX) are known to be more recalcitrant.
There are conventional techniques applied in the treatment of wastewaters such as
physical, chemical and mechanical, generally associated with biological treatment. The
conventional treatments include centrifugation, gravitational separation, filtration, application
of coagulants, flotation, and adsorption with activated coal, among others (Yavuz and Koparal,
2006; Saien and Nejati, 2007). These conventional techniques superintend to remove free and
emulsioned oil and solids in suspension from the wastewater. They also reduce BOD when

4. 3
associated with biological treatment. However, when the wastewater contains highly toxic
recalcitrant compounds, such as the aromatic fraction from the dissolved organic compounds,
applying the biological process is insufficient. As a result, more advanced techniques must be
used to degrade these compounds (Yavuz and Koparal, 2006; Saien and Nejati, 2007).
advanced oxidation process (AOP) is one of the processes for treating water containing
toxic organic pollutants that has been increasingly used in recent years, a powerful tool applied
to degrade these pollutants (Perez-Moya et al., 2007 ; Duran et al., 2008 ).
Advanced oxidation processes (AOP) are technologies based on the generation of the
hydroxyl radicals, which are highly reactive species used in quick and non-selective oxidative
degradation procedures for organic compounds dissolved or dispersed in aquatic media. These
processes are auspicious substitutes for decontamination of media containing dissolved
recalcitrant organic substances, which would not be efficiently removed by customary methods.
AOP is a suitable treatment of wastewater which uses expensive reactants such as H2O2,
and/or O3 and therefore its application should not be replaced, whenever possible, by the more
economic treatments such as the biological degradation. The potentialities offered by AOP can
be exploited to integrate biological treatments by an oxidative degradation of toxic or refractory
substances entering or leaving the biological stage.
Another aspect concerning the application of AOP is the polluting load of wastes
normally expressed as COD. Only wastes with relatively small COD contents (5.0 g/l) can be
suitably treated by means of these techniques since higher COD contents would require the
consumption of too large amounts of expensive reactants. Wastes with more massive pollutants
contents can be more conveniently treated by means of wet oxidation or incineration (V.S.
Mishra et al., 1995)
As an alternative, biological and chemical methods can be employed. Biological
oxidation for cleaning hydrocarbon-contaminated sites has increasing attracted interest in
recent years as a cost-effective remediation technology. The synthetic additive MTBE is
particularly recalcitrant to biodegradation, because it contains an ether bond and a tertiary
carbon, leading to a low biodegradation rate. Nonetheless, a vast range of microbial species
have been exhibited to be able to metabolize MTBE, mostly in aerobic conditions (Deeb et al.,
2000) and field-scale bioremediation studies have already given accurate results [Salanitro et
al., 2000 ; Estcp – Envirogen Inc. (2003)]. However, long degradation times, usually lasting

5. 4
several months, are required for a significant MTBE decrease (Aglietto et al., 2003)Chemical
remediation methods, instead, are known to be much faster in removing organic contaminants.
Among them advanced oxidation processes (AOPs) such as UV/ H2O2, ozone, ozone/ H2O2,
Fenton and UV/TiO2 are known to be effective in removing several compounds contained in
gasoline, such as MTBE and aromatic hydrocarbons (Baus et al., 2005 ; Mitani et al., 2002 ;
Burbano et al., 2005). However, data concerning the comparison of the effectiveness of UV
based AOPs on real polluted groundwater are scarce. In fact, the chemical composition of
polluted groundwater, in terms of the concentration of metals, inorganic species, pH and
organic substances, can dramatically affect the efficiency of the process with respect to the
treatment carried out with synthetic solutions.
Based on the literature information, pesticide degradation has been accomplished by
different photochemical processes including those using artificial light source (Wan et al.,
1994). It was shown that such degradation process requires long treatment periods and rarely
achieves complete degradation of the pesticides (Chiron et al., 2000). Accordingly, the
degradation power of photochemical oxidation process could be improved using an additional
homogenous or heterogeneous oxidant (Legrini et al., 1993). Homogenous systems utilize
H2O2, O3 (Hoign´e and Bader, 1976), or combination of O3/ H2O2, H2O2/UV and O3/UV/Fe+2
(Abe and Tanaka, 1999), Fe+3
/UV, Fe+2
/ H2O2 (Zepp et al., 1992; Ruppert et al., 1993), Fe+3
/
H2O2 (Rivas et al., 2002) as oxidants whereas heterogeneous systems use semiconductor
slurries of TiO2/UV or ZnO/UV for catalysis (Chiron et al., 2000). In all the previous
investigations, it was reported that the AOPs were able to degrade different types of pesticides
as well as different inhibitory organic compounds. However, two major drawbacks are
associated with the use of AOPs: their operational cost is relatively high compared to that of
biological treatment processes and the COD load caused by the produced biodegradable
intermediates are still above the regulation standards of many countries like Jordan (Al-
Momani, 2003; Lafi, 2006). Consequently, AOPs could be combined with biological treatment
process in order to overtake the previous drawbacks. The AOPs can be used as a pretreatment
step for converting pollutants such as pesticides or any inhibitory compounds to more readily
biodegradable intermediates or to the point where the inhibition effect of these compounds is
not significant. Then, this step will be followed by a biological treatment step for bulk COD

6. 5
removal by converting the resulting intermediates to biomass, biogas, CO2, HCl and water
(Parra et al., 2000; Mantzavinos and Kalogerakis, 2005).
In this study, photodegradation of aromatic compounds in wastewaters is well assessed
by evaluating the effects of H2O2 along with UV lamps in a batch reactor. The experiment is
done separately using H2O2, UV light and UV/H2O2 together. The efficiency of the method is
checked by providing different number of UV lamps and different process conditions such as
pH, temperature, and initial concentration of H2O2. Comparing the obtained results showed that
the maximum COD reduction has reached about 90% at optimal conditions.
2. Experimental
2.1. Chemicals
Benzene, Toluene, Ethyl Benzene, Xylene (99.9%, Merck, Germany), K2Cr2O4,
H2SO4, HgSO4 and Ag2SO4 (Extra Pure, Merck, Germany) were all analytical reagent grade.
Each compound was obtained in the highest purity that was commercially available. A stock
solution of 0.2 ml BTEX was prepared in aqueous solution and stored at 5 ◦C.
For the COD tests, synthetic solutions are required which are:
a- Digestion solution high range: 500 ml distilled water was added to 10.216 g K2Cr2O7,
primary standard grade, previously dried at 150 ◦C for 2h, 167 ml H2SO4, and 33.3 g
HgSO4.Dissolve, cool and diluted to 1000 ml.
b- Sulfuric acid reagent: Ag2SO4, in reagent or technical grade, crystal or powder was added to
H2SO4 at the rate of 5.5 g Ag2SO4/ kg H2SO4. It let stand 1 to 2 day to dissolve and then mixed.
2.2. Batch reactor and reaction procedures
For the first part of the experiment, predetermined amount of H2O2 was used in the
batch reactor in different range of pHs. H2SO4 0.1 N and NaOH 0.1N were used to set the pH.
In second part, an ultraviolet lamp (6W power) was attached into the quartz glass tube in the
center of the reactor and two other lamps were attached outside of the reactor. An 800-ml
BTEX solution (adjusted to the desirable pH) was carefully introduced into the Plexiglas tube
with the predetermined amount of H2O2. Control reactors with UV only were also included.
The reactor was tightly closed and the reaction solutions were stirred to ensure complete
mixing. The ultraviolet lamps were then turned on to start the reaction. Temporal samples were

7. 6
typically taken after 30, 60, 90, 120, 150, and 180 min of the reaction time from the sampling
port at the top of the reactor.
2.3. Sample analysis
For COD analysis, a 20-ml sample was collected from the UV/ H2O2 system and then
sample was made according to the following table.
Table. 1. Sample and Reagent Quantities for Digestion Vessels
Digestion Vessel
(culture tubes)
Sample
ml
Digestion Solution
ml
Sulfuric Acid
Reagent
ml
Total Final
Volume
ml
16*100 mm 2.5 1.5 3.5 7.5
When the samples were made with the information above in the sealed vials, and after
about 10 minutes to reach equilibrium , the vials were put in the COD reactor (Digital Reactor
Block 200) and kept there for 2 h in 150 ◦C. After this process the vials were cooled for 30 min
and put in the COD meter one by one.
3. Results and Discussion
3.1. Effects of H2O2 dosages at different pHs
Fig.1 shows the temporal changes in COD reduction efficiency in a batch reactor
containing 0.2 ml BTEX and H2O2 at various initial concentrations ([H2O2]0 = 0.2775, 0.555,
0.8329, 1.11, 1.9425 g/l).
H2O2(g/l)
0.0 0.5 1.0 1.5 2.0 2.5
COD(mg/l)
250
300
350
400
450
500
550
600
pH=3.1
pH=5.7
pH=7.2
pH=9.3
pH=11.6
Fig.1. COD reduction versus H2O2 conc. in different pHs

8. 7
As shown in fig. 1 in all used pHs, the removal efficiency of COD increased with
increasing H2O2 concentrations from 0.2775 to 1.11g/l. Further increase in H2O2 to 1.9425 g/l,
however, reduced both the rate and extent of COD removal. The reactions describing UV/ H2O2
process are presented below (Buxton et al., 1988):
H2O2+hν→2HO•
(1)
H2O2+HO•
→ΗΟ2
•
+Η2Ο (2)
H2O2+ΗΟ2
•
→HO•
+Η2Ο+Ο2 (3)
2HO•
→H2O2 (4)
2ΗΟ2
•
→H2O2+Ο2 (5)
HO•
+ΗΟ2
•
→H2O (6)
In the aforementioned equations, Eq. 1 is the rate limiting reaction because the rates of
the other reactions are much higher than that of Eq. 1. Theoretically in UV/ H2O2 process, the
higher initial hydrogen peroxide concentration produces higher hydroxyl radical concentration
(Eq. 1), which decomposes more target compound. However, an optimal hydrogen peroxide
concentration exists because overdosing of hydrogen peroxide would lead to reaction with
hydroxyl radical and formation of HO2
•
(Eq. 2). Finally, fig.1 reveals that the optimal hydrogen
peroxide concentration is 1.11 g/l.
According to fig.1 the rate of COD reduction affects by changing the pH in different
ranges. After evaluating the optimum hydrogen peroxide concentration, the effects of various
pHs on the process is assessed.
In this system COD reduction was at the highest level at acidic pH and decreased when
pH was increased. The maximum COD reduction occurs at the acidic pH around 3.1. One
major factor responsible for the decreased BTEX removal is due to the instability of H2O2 at a
high pH since H2O2 decompose rapidly at an alkaline condition. A contributing factor for the
reduced BTEX photodegradation is resulted from the scavenging of •
OH by HCO3 −
and CO32−
that could be formed from CO2 as the mineralization product of BTEX. At an alkaline pH, CO2
(aq) is present predominantly in HCO3
−
(pH>pKa1 = 6.35) or CO32−
(pH>pKa2 = 10.33) (Hu et
al., 2008).

9. 8
3.2. Effects of temperature
The effects of temperature are also discussed in the obtained optimal conditions ([H2O2]
=1.11g/l and pH=3.1). Fig.2 shows that the efficiency of BTEX removal increases by
increasing the temperature. This proves the fact that, increasing the temperature would
increases the production rate of hydroxyl radicals that results in more COD reduction.
However, providing the optimal thermal condition demands a certain level of energy and cost
which may not be practical at industrial scales.
Time(min)
0 20 40 60 80 100 120 140 160 180 200
COD(mg/l)
100
200
300
400
500
600
T=27 c
T=40 c
T=55 c
T=68 c
T=86 c
Fig.2. COD reduction versus temperature in optimal condition at various temperature (pH=3.11, [H2O2]
=1.11 g/l)
3.3. Effects of UV light
The effects of UV lights on the removal efficiency of COD are shown in fig.3. It is
very clear that BTEX photodegradation was much more effective when the number of UV
lights increased.

10. 9
Time(min)
0 20 40 60 80 100 120 140 160 180 200
COD(mg/l)
350
400
450
500
550
600
1UV light
2UV light
3UV light
Fig.3. COD reduction for different number of UV lights in optimal condition (pH=3.11)
As shown in fig.3 the reduction efficiency of COD increases by adding the number of
lights which is because of increasing the irradiation amount. Increasing the irradiation amount
help the improvement of mineralization reaction of aromatic compounds. It should be
considered that, this method does not have high efficiency alone.
3.4. Combination of UV light and H2O2
This process includes H2O2 injection and mixing followed by a reactor that is equipped
with UV lights. During this process, ultraviolet radiation is used to cleave the O-O bond in
hydrogen peroxide and generate the hydroxyl radical. The reactions describing UV/ H2O2
process are presented in equations (1) to (6).
Fig.4 depicts the results obtained by this combined method at optimal conditions
([H2O2]0=1.11g/l and pH=3.1).

11. 10
Time(min)
0 20 40 60 80 100 120 140 160 180 200
COD(mg/l)
0
100
200
300
400
500
600
UV(1 light)/H2O2
UV(2light)/H2O2
UV(3light)/H2O2
Fig.4. COD reduction for UV/H2O2 system in optimal condition (pH=3.11)
According to the above figure it is clear that UV/ H2O2 process is very efficient in
mineralizing oily organic pollutants. Applying UV/ H2O2 along with other optimal conditions
resulted in about 90% COD reduction. The high efficiency of this method in comparison with
using H2O2 and UV alone can be described by the fact that irradiation of UV on H2O2 produces
more hydrocele radicals, and therfore the remediation rate of COD increases.
4. Conclusion
The treatment of oily wastewater is investigated in a synthetic solution by using the
method of advanced oxidation process (UV/H2O2). This study demonstrates that UV/ H2O2
system readily degraded BTEX in the test concentration of 0.2 ml. The optimal conditions for
COD reduction was found to be acidic (pH 3.1), and 1.11g/l H2O2 under three UV lights. COD
reduction efficiency increased by raising doses of H2O2 (0.2775–1.11 g/l). Very alkaline pH
and high doses of H2O2 (1.9425g/l) had adverse results and reduced BTEX photodegradation.
The COD reduction efficiency for UV light was about 20%, for H2O2 was about 50% and for
the combination UV/ H2O2 it raised to about 90%. The thermal condition was also investigated
and the results showed that the COD rate of reduction increased by raising the temperature, but
it may not be applicable to work at high temperature.

12. 11
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