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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

AN OVERVIEW OF THE INTEGRATION OF ADVANCED OXIDATION

TECHNOLOGIES AND OTHER PROCESSES FOR WATER AND
WASTEWATER TREATMENT

Masroor Mohajerani mmohajer@ryerson.ca

Department of Chemical Engineering

Ryerson University

350 Victoria Street, Toronto, Ontario, Canada M5B 2K3

Mehrab Mehrvar mmehrvar@ryerson.ca

Department of Chemical Engineering

Ryerson University

350 Victoria Street, Toronto, Ontario, Canada M5B 2K3

Farhad Ein-Mozaffari fmozaffa@ryerson.ca

Department of Chemical Engineering

Ryerson University

350 Victoria Street, Toronto, Ontario, Canada M5B 2K3

ABSTRACT

Integration of advanced oxidation technologies and other traditional wastewater

treatment processes has been proven to be more effective for treating polluted sources
of drinking water and industrial wastewater economically. The way of selecting the
methods depends on the characteristics of the waste stream, environmental regulations,
and cost. Reviewing the experimental works on this area and discussing their
effectiveness as well as modeling would be helpful for deciding whether the integrated
processes is effective to fulfill the annually restricted legislations with lower investment.
Therefore, optimization of each process should be done based on different aspects
such as operation time, operating cost, and energy consumption. In this review, recent
achievements, developments and trends (2003-2009) on the integration of advanced
oxidation technologies and other remediation methods have been studied.
Keywords: Advanced oxidation technologies, Biological processes, Physical methods, Integration of Processes,

Optimization

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

1. INTRODUCTION
In recent decades, very severe regulations have forced researchers to develop and evolve novel
technologies to accomplish higher mineralization rate with lower amount of detectable contaminants.
Different physical, chemical, and biological treatment processes have been employed to treat various
municipal and industrial wastewaters such as chemical [1-2], biological, food [3], pharmaceutical [4-5],
pulp and paper [6], dye processing and textile [7-10], and landfill leachate [11] effluents. These processes
are also being used for oxidizing, removing, and mineralizing various surface and ground waters. The
waste streams contain a wide range of compounds with different concentrations. Based on the
concentrations and the type of contaminants exist in the wastewater, various treatment methods have
been developed to release an environmentally friendly effluent. Pollutants can be classified in several
categories. Decision making can be based on whether the chemicals are organic or inorganic and they
can be branched out based on chemical structure, solubility, biodegradability, volatility, toxicity, polarity,
oxidation potential, adsorbability, electrical charge, and the nature of daughter compounds. Studies on
the wastewater treatment area have been conducted in two main groups: treatment of single and multi-
component solutions. Although results obtained by single component solutions are more helpful for
predicting the behavior of such solutions, wastewater streams containing a single compound are very rare
and the results cannot be applicable to actual wastes. On the other hand, studies on multi-component
solutions are useful to employ for real wastewater streams in larger scale. In investigating multi-
component systems, some problems such as daughter compounds’ formation during oxidization, inter-
reaction between existing compounds besides difficulty of modeling and simulation of such systems make
experimentation very complicated.

Some researchers prefer to study the actual effluent from various industries but others prefer to
investigate synthetic wastewater behavior. Both have their own advantages and drawbacks. Synthetic
wastewater is helpful in a way one can measure intermediates during the degradation and mineralization.
Moreover, these kinds of experiments can be extended for a range of different concentrations for each
compound. On the other hand, actual waste solution from a specific source is beneficial to solve the
problem of a real case. As explained earlier, choosing the best method of remediation depends on the
characteristics and concentrations of different compounds in a wastewater. For example, physical
treatment processes are very effective to separate volatile organic compounds (VOCs) using a gas
stripper column. For real effluents, sometimes employing different techniques is more beneficial to
separate, degrade, and mineralize various components of different behavior. In the case of municipal and
industrial wastewater treatment plant, different processes such as physical, chemical, and biological are
being used to increase the efficiency. Deciding about the selection of treatment methods is also
influenced by the intermediates produced during oxidization (the product of previous process). The entity
of the chemicals after each chemical processes are normally changed due to chemical reactions
occurred. Therefore, the selection, design, and operation of such processes and their post-treatment
methods should be carefully carried out. The responsibility of chemical treatment techniques has the
governing role in facilitating the remediation. Chemical processes can change the characteristics of
chemicals such as toxicity and biodegradability. Therefore, suitable techniques should be opted for further
cleaning of the new product.

Among chemical technologies, a novel method that has been growing in recent decades is the advanced
oxidation processes (AOPs) which are very potent in oxidization, decolorization, mineralization, and
degradation of organic pollutants. Due to high oxidation rate of the chemical reactions caused by AOPs,
the behavior of chemicals is significantly changed after the treatment. The degradation makes organic
chemicals smaller and biodegradable. AOPs for wastewater treatment are not an economical process due
to their high operating cost, thus; it is suggested to integrate these technologies with other post-treatment
methods such as biological processes. The integration of advanced oxidation technologies and biological
processes has been reviewed by Scott and Ollis (1995) [12], Tabrizi and Mehrvar (2004) [13], and
Mantzavinos and Psillakis (2004) [14]. The aim of this study is to review and analyze recent studies on

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

the integration of AOPs and other conventional techniques for the treatment of water and wastewater
during the period of 2003 to 2009.

2. ADVANCED OXIDATION PROCESSES

In the past two decades, advanced oxidation processes (AOPs) have been proven to be powerful and
efficient treatment methods for degrading recalcitrant materials or mineralizing stable, inhibitory, or toxic
contaminants [15]. These technologies could be applied for contaminated groundwater, surface water,
and wastewaters containing recalcitrant, inhibitory, and toxic compounds with low biodegradability as well
as for the purification and disinfection of drinking water. Advanced oxidation processes are those groups
.
of technologies that lead to hydroxyl radical ( OH) generation as the primary oxidant (second highest
powerful oxidant after the fluorine). These radicals are produced by means of oxidizing agent such as
H2O2 and O3, ultraviolet irradiation, ultrasound, and homogeneous or heterogeneous catalysts.
Investigators are trying to find better methods for OH production. Hydroxyl radicals are non-selective in
.

nature and they can react without any other additives with a wide range of contaminants whose rate
6 9 -1 -1
constants are usually in the order of 10 to 10 mol.L .s [16-17]. These hydroxyl radicals attack organic
molecules by either abstracting a hydrogen atom or adding hydrogen atom to the double bonds. It makes
new oxidized intermediates with lower molecular weight or carbon dioxide and water in case of complete
mineralization. A full understanding of the kinetics and mechanisms of all the chemical and photochemical
reactions involved under the condition of use are necessary, by which, based on the well understood
mechanisms, optimal conditions could be obtained.

The most eye-catching drawback of advanced oxidation technologies is their operating cost compared to
other conventional physicochemical or biological treatments. Therefore, AOPs cannot achieve complete
mineralization due to this restriction. One of the most reasonable solutions to this problem is coupling
AOPs with other treatment methods. Advanced oxidation processes often are employed as a pre-
treatment method in an integrated system. AOPs are also able to enhance the biodegradability of
contaminants through converting recalcitrant contaminants into smaller and consequently more
biodegradable intermediates. This integration is justified commercially when intermediates are easily
degradable in the next process. There are some review papers on the integration of chemical and
biological treatment processes [12-13, 17]. In this study, recent achievements and developments on the
integrations of AOPs and other treatment methods during the period of 2003-2009 are provided. Table 1
shows the main results along with the operating conditions obtained by the recent studies. The selection
of the method, the equipment, the operating conditions, and the sequence of the processes are better
obtainable based on the recent achievements.

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

Table 1: Summary of recent studies on the Integration of AOPs with other processes for water and wastewater treatment

Target System and Method Efficiency References

Compound(s)

Surfactant effluent Initial COD: 1500 and 490 mgL-1, Lab 40 min for Fenton process and 2 h for biological 18
containing scale Fenton process effluent treatment were sufficient to reduce the effluent
abundant sulfate concentrations were 230 and 23 mg concentration up to less than 100 and 5 mgL-1 for
ions L-1 after 40 min. In pilot scale Fenton COD and LAS concentration. The effect of ferrous
followed by immobilized biomass ions is more important than that of H2O2. Sufficient
reactor was employed. dosage of Fe+2 was 600 mgL-1 for an efficient
treatment. Increasing the H2O2 leads to higher
biodegradability.

Pulp and paper 2 different samples with 2500 and The removal efficient of secondary wastewater was 19
3520 mgL-1 COD, were treated by arranging: Fenton > H2O2/O3 > Ozonation > catalytic
some chemicals (alum, lime and ozonation with metal oxides. In ozonation: for higher
polyelecetrolyte) up to 1900 mgL-1, COD, 60% COD reduction was observed after 1 h. No
Followed by activated sludge process further degradation was found after 2 h. For lower
up to 260-400 mgL-1, then secondary COD in less than 30 min, 200 mgL-1 effluent was
wastewater was treated by different obtained. Fenton process showed 88% and 50% COD
methods such as ozonation, catalytic reduction for secondary and raw wastewater.
ozonation, H2O2/O3, and Fenton. Optimum chemicals concentration ratios were 0.5
mol/1 mol Fe+2/H2O2 and 2 mol/1 mol H2O2/COD.

Landfill leachate Wastewater pretreated by sequence After 2h pretreatment with activated sludge, ozone 20
batch reactor was used for additional and pH adjusted ozone showed the highest
advanced oxidation such as O3, biodegradability. The most efficient method was
O3/pH adjustment (pH 9), H2O2, observed in combination of O3/H2O2 and biological
O3/H2O2 and performic acid treatment as pre- and post-treatment. Performic acid
did not show any TOC reduction.

2,4,5- 122 ml bench scale photocatalytic UV photocatalysis alone did not show any degradation 21
trichlorophenol circulating-bed biofilm reactor up to 96 h, After the addition of carriers with biofilm,
(PCBBR), high intensity UV lamp and biodegradation of acetate was started quickly up to
Degussa P25 TiO2 were used for 200h and then smooth acetate concentration was
irradiation source and photocatalyst, observed.

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

respectively

Hydroxyl-benzene Photo-Fenton process in a 8 L 6-lamp Photolysis (with H2O2 and without Fe+3) showed 57% 22
CPC solar continuous photoreactor and 65% TOC reduction before and after SFF. Fe+3
for treating raw river water and concentration even as low as 1 mgL-1 depicted
pretreated with slow sand filtration treatment improvement drastically. The presence of
river water H2O2 under sunlight resulted in 50% mineralization.

Cibacron Red FN- A two stage aerobic-anaerobic Aerobic treatment showed less than 9% 23
R method followed by photo-Fenton and biodegradation after 28 days. The photo-Fenton
ozonation processes was employed. process conducted with different ratios of Fe+3/H2O2,
The initial concentration of 10/250, 20/500, and 100/2500 mgl-1/mgl-1. DOC
wastewater samples were 250, 1250, reduction was increased with increasing of Fe+3 and
3135 mgL-1. H2O2. After 30 min, DOC was reached a plateau and
no further DOC removal was observed. Ozonation
was carried out with different pH (3, 7, 10, and 10.5).
pH 10.5 showed the best results (83% mineralization
in 150 min). Neutral and acidic ozonation showed 48%
degradation.

Phenol Hydrodynamic cavitation combined Results showed that both hydrodynamic cavitation and 24
with advanced Fenton was employed advanced Fenton have greater efficiency for lower
for treating phenolic wastewater (2.5 phenol concentration. Continuous leaching resulted in
mM).Hydrodynamic cavitation was higher concentration of iron ions with longer residence
generated by a liquid whistle reactor time. Increasing H2O2 dose in the range of 500-2000
(LWR). mg/L led to greater TOC removal. In hydrodynamic
cavitation, applied pressure had positive effect on
TOC reduction. The closer distance between orifice
and catalyst bed also performed better TOC removal.

Nonylphenol (NP) Sonochemical reactor equipped with US-Fenton process showed better degradation rate in 25
300kHz ultrasound transducer and case of lower initial contaminant concentration. Lowest
cooling system, combined with initial concentration performed the complete
biosoprtion of fungal cultures was mineralization. On the other hand, US only and Fenton
used for treating different only were ineffective after 1-2 h. Biosorption showed

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

concentrations (100, 500, and 1000 around 39 and 60% removal after 4 and 7 days. Initial
ppm) of polluted water. concentration did not affect the removal percentage. In
combined method 74 and 88% NP removal were
observed after 1h US/Fenton and subsequent 4 and 7
days biosorption, respectively.

Methomyl, 50 mgL-1 concentration of each 90% DOC removal was observed in 1197 and 512 min 26
Dimethoate, compound was used to be treated in in case of case of TiO2 photocatalysis and photo-
Oxamyl, combined AOP/biological method. Fenton. Shorter irradiation time with two different iron
Cymoxanil, AOPs were TiO2 photocatalysis and concentrations (20 and 55 mgL-1) resulted in 50 and
Pyrimethanil photo-Fenton. 35 L solar pilot plant 72% DOC reduction. Photo-Fenton process showed
equipped with 3 CPCs for TiO2 greater pesticide degradation (more than twice) than
photocatalysis and 75 L solar pilot the TiO2 photocatalysis. Pretreatment by photo-Fenton
plant using 4 CPCs were employed process decreased toxicity from 90 to 47%.
for AOP stage. A 35 L aerobic Biodegradability tests showed 70% biodegradability is
immobilized biomass reactor (IBR) obtained after 12 days. Combined batch method
was used for biological treatment. showed 85% efficiency (23% AOP, 62% biological
treatment). Combined batch AOP and continuous
biological treatment showed more than 90% removal.

Procion blue A 130 ml plate and frame Photo-electrochemical and photocatalytic 27-28
electrochemical flow cell and electrochemical methods showed 98% dye
immobilized photocatalytic UV reactor degradation within 7 h. After 4 h different combined
were employed for degradation of 50 method showed more than 90% color removal. COD
mg/L procion blue solution removal was proportional to applied current. The
optimum TiO2 concentration was 40 mgL-1. Acidic
condition performed greater degradation.

Reactive black 5 Fenton processes followed by aerobic pH 3 showed the highest decolorization for all dyes 29
(RB5), Reactive biological treatment (sequential batch (more than 99%), Decolorization was increased at
blue 13 (RB13), reactors) were used for 50 mg/L dye higher H2O2 concentration up to an optimal dose(50
Acid orange 7 solution. Different factors such as pH, mgL-1). optimal Fe+2 dose was found to be 15 mgL-1.
(AO7) H2O2 and Fe+2 were optimized. 82, 89, and 84% COD removal was observed for RB5,
RB13, and AO7, respectively.

Pharmaceutical The combination of solar AOP Industrial effluent containing α-methylphenylglycine 30

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

factory effluent followed by biological treatment. Four (MPG) treated using a pilot plant. Fenton (Fe+2 = 20
CPC with 1.04 m2 with 50 mm mgL-1) process showed complete degradation and
diameter absorber tubes. Initial TOC 70% TOC reduction in less than 1 h with seawater, but
was 500 mgL-1. Iron concentration in case of distilled water, the degradation rate was 3
was 20 mgL-1. times greater. 60 mM of H2O2 is required to degrade
MPG. For complete MPG degradation, 30-35 mM
H2O2 is required and also for cost minimization, the
H2O2 concentration should be kept around 150 mgL-1.
Batch mode treatment in immobilized biomass reactor
(IBR) showed 80% TOC reduction for pre-treated
water after 4-5 days. 150 min illumination is required
to reach the biodegradability threshold. In industrial
scale, 100 m2 CPC collectors are sufficient to treat 3
m3/day wastewater.

Textile surfactant UV/H2O2 using 40 W low pressure pH did not show significant influence on the AOP 31-32
formulation mercury vapor lamp carried out with mechanism but the pH was decreased until neutral
different pH (from 5 to 12) and H2O2 condition due to formation of the acids during
dose from 10-100 mM for treating degradation. The optimal H2O2 dose was found to be
textile surfactant formulation with an 917 mgL-1. Biodegradable COD was increased from 4
initial 1000 mgL-1 COD. to 14-15% when the UV/H2O2 (60 mM H2O2 and 60-90
min illumination time) was used as a pretreatment.
Rapidly hydrolysable COD significantly increased
during photochemical treatment but against results
were found for slowly hydrolysable COD.

Distillery The distillery spent wash was pre- Ultrasonic (US) pretreatment did not show significant 33-34
wastewater treated by thermal and sonication COD (13% after 48 h), decolorization, and TOC
(ultrasonic bath) and ozonation (flow reduction but converted complex organic compounds
rate: 260 l/h) processes sent to into smaller ones. Ozonation was effective on the
biological treatment process. decolorization and COD reduction (45.6%) and the pH
was decreased 0.1-0.2 units every 2 min. Oxidizing
and mineralization rate was enhanced with an
increase of ozone flow rate. Ozonation pretreatment
resulted in greater biodegradability enhancement than
US.

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

Diuron and 42 mgL-1 Diuron and 75 mgL-1 Linuron TOC reduction was significantly enhanced by an 35-36
Linuron was chosen for the photo-Fenton and increase of Fe+2 and H2O2 doses. Inorganic acids such
biological treatment. Different doses as acetic acid, oxalic acid, and formic acid were
of H2O2 (97.1, 143, and 202 mgL-1) produced, reached a maximum and then degraded
and Fe+2 (9.25, 13.3, and 15.9 mgL-1 ) during photo-Fenton process, higher dose of H2O2 and
were used for photo-Fenton process. Fe+2 resulted in greater production and degradation
rate.

Natural water Enhanced coagulation (using alum Ferric chloride coagulation showed better coagulation 37-38
systems and ferric chloride) and photocatalytic compared with alum.
oxidation (UV/TiO2) were employed to
treat three different natural water
samples.

Reactive black 5 Fenton process in 800 ml cylindrical Decolorization rate was significantly decreased with 39
(RB5) glass reactor was combined with an increase of RB5 concentration so that after 60 min,
yeast as a post treatment was 98 and 62.6% decolorization was observed for 100
employed to degrade 100-200-300- and 500 mgL-1 samples. For solution concentration
500 mgL-1 RB5. The Fe+2/H2O2 ratio greater than 200 mg-1 incomplete decolorization was
was 10. observed. The reaction rate constant for 100 mgL-1
solution was 10 times greater than that of 500 mgL-1
but the half-life was 0.01 of the latter solution.
Decolorization under yeast experiment was not able to
completely decolorize concentration greater than 200
mgL-1. The impact of initial concentration in biological
treatment was lower. The combined method showed
complete decolorization of 500 mgL-1 solution.

Natural organic Combined UV/H2O2 (equipped with Disinfection by product formation potential (DBP-FP) 40
matter (NOM) LP lamp) and biological activated was effectively removed during UV/H2O2 at higher UV
carbon (BAC) in a 2 cm diameter fluency, but AOP-BAC showed significant organic
column used for degradation of NOM. carbon content reduction. During AOP the
concentration of dichloroacetic acid (DCAA) increased

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

due to formation of some intermediates such as

aldehydes but in subsequent BAC, DCAA
concentration was significantly decreased.
Trihalomathane formation potential (THM-FP) and
trichloroacetic acid formation potential (TCAA-FP) also
showed no change or slight reduction in AOP, and
great removal was observed during integrated AOP-
BAC.

Resin acids Different AOPs such as ozonation, The highest COD reduction was observed under 41
(abietic acid, O3/UV, O3/UV/H2O2 in a 1.5 L O3/UV/H2O2 @ T=800C. Higher temperature resulted
dehydroabietic photoreactor combined with activated in lower required ozone for degradation.
acid, isopimaric sludge were used. Dehydroabietic acid showed greater resistance to be
acid) oxidized by ozone. Biological post-treatment indicated
that the biodegradability of resin acids was decreased
during AOP because of the production of more
resistant byproducts.

Reactive red 195A Combined UV/H2O2 and moving bed The optimization was carried using Box-Wilson 42
(RR195A) biological reactor was used for statistical design method. The greatest impact was
treatment the experimental design observed by recirculation ratio. In addition, higher
was based on H2O2dose, radiation irradiation time and H2O2 dose were effective for better
time and circulation ratio (0 to 600%). decolorization.

Tetrahydrofuran Biodegradability of the compounds UV/H2O2 showed greater efficiency for increasing 43
(THF), 1,4- individually and mixed was analyzed biodegradability and destruction than UV/O3 for
dioxane, pyridine after UV/H2O2 and UV/O3 treating THF solution. For dioxane solution UV/H2O2
degraded all the contaminants within 60 min but did
not show biodegradability improvement. No
biodegradability enhancement was observed during
UV/O3 and UV/H2O2 of pyridine. UV/O3 slightly
improved the biodegradability of the mixture.

Deltamethrin, 100 mgL-1 of three pesticides with Over 80 and 92% degradation observed under O3 and 44
lambda- 6500, 6300, 6500 mgL-1 COD were O3/UV, respectively. Higher pH showed positive effect
cyhalothrin, selected for O3 and O3/UV on the degradation and COD reduction. In combined

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

triadimenol degradation alone and combined with process, O3/UV pre-treated solution showed higher
biological treatment. degradation rate as compared to O3 pretreated,
aerated, and raw solutions. Temperature was effective
for enhancing the biodegradation.

Pulp and paper Combined AOP (photocatalysis or Suspended photocatalysis showed a better 45
effluent ozonation) and biological process was decolorization for Kraft E1 with respect to ozonation
assisted for treating Kraft E1and (54 versus 27%). On the other hand, decolorization of
black liquor effluent. TOC of these black liquor effluent was more desirable with
effluents were 934 and 128750 mgL-1. ozonation (14 versus 5%) due to the darkness of the
solution. Photocatalysis showed 45% improvement for
mineralization of Kraft E1, but ozonation enhanced
37% mineralization in combined method.

Green table olive Lab scale and pilot scale of biological Inoculums’ size performed positive effect on COD 46
processing treatment followed by electrochemical removal so that 104 and 106 conidialml-1 showed 71.5
wastewater reactor in the presence and absence and 85.5% COD reduction. pH decreased faster for
of H2O2 was studied. the high inoculum concentration. Most of the
contaminants were degraded completely during
biological treatment. Pre-treated solution was sent to
electrolytic reactor with various H2O2dose (0, 2.5, and
5 v%). Results showed that the degradation was
increased in the presence of H2O2. In pilot plant, 98%
COD reduction was obtained during combined
processes.

Dissolved organic Single stage and multistage AOP-biological showed better mineralization rather 47
matter (DOM) in ozonation-biological and AOP- than ozonation-biological. Further mineralization was
drinking water biological treatment were used for achieved in multi-stage process, because in each
oxidizing DOC of the reservoir water biological stage, BDOC portion of the effluent was
and secondary effluent of the removed because this fraction can act as radical
municipal wastewater when the DOC scavenger. Single stage and Multistage ozonation-
concentration was 20 mgL-1. biological did not perform significant oxidization for
residence time greater than 15 min.

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

4-chlorophenol (4- Photo-Fenton in 2.2 L reactor H2O2 showed higher influence on the degradation rate 48
CP) followed by sequencing batch biofilter rather than Fe+2 and temperature. Moreover, higher
reactor (SBBR) was used for treating H2O2 dose improved the biodegradability of the
200 ppm of 4-CP solution.

Cibacron brilliant Combined photocatalysis (1 mgL-1 Higher decolorization rate was observed under 9-10
yellow 3G-P TiO2) and aerobic biological (activated aerobic treatment of partially photocatalytically pre-
sludge) treatment was used for 100 treated solution. Acclimated sludge also increased the
mgL-1 of the target. oxygen uptake rate of the solution.

Winery Solar homogeneous and Unlike the heterogeneous photo-Fenton, 49

wastewater heterogeneous photo-Fenton process Homogeneous method required additional H2O2 during
was employed in the presence of 10 the experiments. Homogeneous performed higher
mLL-1 H2O2 for treating winery degradation rate and TOC reduction rather than
wastewater (COD= 3300 and TOC = heterogeneous photo-Fenton. The heterogeneous
969 mgCL-1) Fenton method was advantageous because further
precipitation was not necessary.

Cellulose effluent The effluent from the acid stages of Activated sludge increased the wastewater color but it 50
the bleaching process of Eucalyptus was very effective for COD and BOD reduction. UV
urograndis wood was examined by radiation was helpful for decolorization and it showed
activated sludge followed by UV lower ability for COD and BOD removal. The
radiation (200 ml batch reactor) combined system did not show any improvement for
further BOD and COD reduction.

Mixed industrial Pathogen removal and re-growth of Increasing the ozonation time did not improve the 51
wastewater an UASB effluent was studied with pathogen removal. 350 mgL-1 H2O2, 15 V% PAA, and
ozonation, UV, UV/H2O2 , peracetic 120 sec UV radiation was effective for above 99%
acid (PAA) pathogen inactivation. In higher temperature (350C)
pathogen re-growth was higher.

Semiconductor Combined physical (fixed bed air Air stripper was used to recover isopropyl alcohol 52
wastewater stripping column), chemical (Fenton (IRA). IPA recovery was enhanced by increasing air

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

process), and biological (sequencing flow rate, temperature and separation time. Fenton
batch reactor (SBR)) was employed was very effective at pH between 2 and 5. Lower
for treating a semiconductor FeSO4 dose (lower than 5 mgL-1) showed greatest
wastewater and recover isopropyl COD reduction. The removal rate was also increased
alcohol. under higher H2O2 flow rate up to 1 ml/min.
Temperature was also beneficial for better Fenton
efficiency. SBR with 12 cycles performed well to
reduce COD from 600 to 100 mgL-1.

2,4-dichlorophenol 100 ppm 2,4-DCP was treated in Ozonation improved the biodegradability of the 53
(2,4-DCP) combined ozonation and biological solution from 0 to 0.25 and 0.48 for BOD5/COD and
treatment (activated sludge and BOD21/COD. Activated sludge (non-acclimated with
acclimated biomass with phenol) phenol) showed better removal rate than that of
acclimated to phenol.

Linear 76.6 L Pilot plant cylindrical Biodegradability was increased during LAS 54
alkylbenzene photoreactor (UV/H2O2) for 12, 25, 50, photocatalysis especially for lower concentration of
sulfonate (LAS) 100 mgL-1 LAS LAS. Over 90% of LAS was removed and
biodegradability increased up to 0.4 during 90 min.
Solution BOD was increased with photocatalysis
residence time.

Methyl tert-butyl 3 L batch glass photoreactor Over 90% MTBE removal achieved by UV/H2O2 within 55
ether (MTBE) equipped with 2 different UV lamps 1 h. Optimal H2O2 dose was 14 times greater than
with wavelengths 365 and 254 nm MTBE dose. UV-254 was more effective than UV-365
employed for UV/H2O2 and UV/TiO2 for both UV/H2O2 and UV/TiO2 in degrading MTBE.
followed by biodegradation using SBR UV/H2O2 and UV/TiO2 were not effective for enhancing
the biodegradability of solution.

Wool scouring Flocculation followed by aerobic BOD5 was increased during UV/H2O2 from <10 to 86 56
effluent biological treatment is being used to mgL-1. COD and TOC were removed by 75 and 85%,
treat and UV/H2O2 was used as a respectively. Decolorization was complete in less than
post-treatment process. Biological 30 min. pH variation was ineffective on COD and TOC
treatment was also used as a post- reduction. Higher COD removal was achieved in
treatment process. integrated AOP and Biological post-treatment.

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Oily wastewater UV/H2O2 followed by biological Biodegradation alone showed 60% COD reduction. 57
from the lubricant (Pseudomonas putida DSM 437) Fe+3/UV/H2O2 improved COD reduction rather than
unit treatment used to treat oily UV/H2O2 from 5 to 30% within 10 min. Integrated
wastewater containing ethylene photolysis and biological showed greater organics
glycol, phenol, p-cresol, o-cresol. removal relative to direct biodegradation. For example
Direct biological results were ethylene glycol was 100% removed from the solution.
compared to integrated system COD removal was increased from 60 to 72% by
integrated process.

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3. PHYSICAL PROCESSES
Physical processes are widely used in the water and wastewater treatment plants. These physical
techniques are based on the separation of one or more compounds from the waste stream. Because of
the separation, the pollutant is transferred from one phase to another. Therefore, further treatment is
required for the degradation of the contaminants in the second phase. Physical methods are employed
mainly to separate large settleable and floating matter, clarify turbid solutions, recover and recycle
valuable substances utilized in the main processes and separating inorganic materials. The conventional
and advanced physical techniques include filtration, adsorption, gas stripping, and others. Physical
treatment methods can be used before or after the advanced oxidation processes depending on the
influent nature and its concentration as well as the AOPs operation conditions. Using physical techniques
in wastewater treatment before and after the AOPs can be selected based on the consideration of various
aspects of applications provided as follow: It is believed that the insoluble compounds and solid matter
should be removed before any chemical or biochemical treatment because these materials may damage
the equipment, increase the size of the equipment, results in a greater cost, and reduce the process
efficiency.

For AOPs utilizing an irradiation source such as UV lamps (UV/H2O2, UV/O3, UV/TiO2, photo-Fenton and
others), turbid solutions reduce the efficiency of the system. Turbidity decreases the local volumetric rate
of energy absorption (LVREA) in the photoreactor, thus, the attenuation coefficient inside the reactor
increases and it leads to smaller photochemically effective radiation field. Therefore, it is required to
reduce the turbidity of the solutions by means of physical methods. The presence of some compounds in
the solution that can adsorb on the surface of the catalyst results in deactivation of the catalyst due to the
occupation of active sites. The lower amount of valent sites decreases the mass transfer between the
catalyst and the species exist in the reactor, therefore, it reduces the number of hydroxyl radicals
generated in the system. Some substances can also increase the agglomeration and aggregation of the
catalyst powders in the system and reduce the mass transfer rate and system efficiency.

Free radical scavengers such as carbonate and bicarbonate ions reduce the number of hydroxyl radicals
and system efficiency. Furthermore, these ions increase the attenuation coefficient and reduce the
irradiation field. Physical and chemical methods can be employed for reducing such ions. Inorganic
compounds such as heavy metals along with some chemicals may be detrimental to the AOPs and other
subsequent processes. Therefore, they should be removed before AOPs. These substances are
generally removed by adsorption, biosorption, and partition [58] methods such as granular activated
carbon (GAC) column [59], biological activated carbon (BAC) column [60], unmodified clays (kaolinite and
smectite) organoclays modified with short and long chain organic cations [61], or natural and modified
zeolite [62].

It is beneficial to remove some compounds that have relatively lower oxidation potential than other
compounds in the wastewater solutions by low cost physical methods. The separation of such
compounds can help to keep the concentration of hydroxyl radicals high enough. The separation of
volatile organic compounds is also helpful before ultrasonic AOPs. The oxidation of volatile organic
compounds by acoustic cavitation is usually conducted by combustive reactions due to their extremely
high temperature and pressure. If these compounds are removed before advanced oxidation processes, a
lower power and ultrasonic intensity are required to oxidize the wastewater.

As mentioned earlier, AOPs change the characteristics and entity of the chemicals during the process,
therefore, sometimes it is beneficial to use physical post-treatment. For example, the effluent of the AOPs
may be adsorbed better by GAC. The most important issues in designing integrated processes such as
fixed and operating costs should not be disregarded in order to achieve the desirable concentration limit
of compounds.

4. BIOLOGICAL TREATMENT
Biological treatment methods are very common in wastewater treatment plants. These processes are
useful for treating biodegradable waste streams. The use of biological treatment is attractive due to its low

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operating cost but the residence time is very high relative to that of other processes. On the other hand,
the removal rate of advanced oxidation processes is relatively high while the operating cost is relatively
expensive due to the use of reagents and irradiation sources. Capital and operating costs of biological
treatment methods are 5-20 and 3-10 times cheaper than those of chemical methods, respectively [56-
63]. Based on the cheaper construction and their operating cost, it is desirable to maximize the residence
time and the removal rates of contaminants in biological processes. Biological treatment techniques are
classified into two main groups: aerobic and anaerobic. Aerobic processes could be carried out by
suspended (activated sludge), attached (biofilm reactor, trickling filter, and rotating disk contactor) or
combined (moving bed biofilm reactor) depending on the operating conditions and wastewater
characteristics. Wastewater can also be treated by anaerobic processes such as up-flow anaerobic
sludge blanket (UASB), anaerobic fluidized bed reactor (AFBR), expanded granular sludge bed (EGSB),
and anaerobic baffled reactor (ABR). Anaerobic techniques are usually employed for treating a
concentrated municipal and industrial wastewater.

Depending on the type of wastewater, the nature of compounds and their concentrations, the integration
of AOPs and biological processes could be designed in different configurations as follows: Wastewater
solutions containing compounds which are toxic and inhibitory to biomass are necessary to be pre-treated
by advanced oxidation processes. The AOPs reduce the toxicity of the wastewater. AOPs are also
beneficial to pre-treat the wastewater containing bio-recalcitrant substances. This kind of wastewater is
not biodegradable enough to be treated by biological processes. If the ratio of the BOD/COD of a
wastewater is lower than 0.4, it is categorized as non-biodegradable or low in biodegradability [10,13].
Most AOPs enhance the biodegradability of the wastewater usually by decreasing the COD load. A class
of waste solutions and wastewater streams is categorized as a biodegradable wastes with small amounts
of recalcitrant compounds. This group contains a wide range of domestic and industrial effluents because
none of the effluents after preliminary physical treatment is totally biodegradable. For this type of
wastewater, AOPs could be applied as a pre-treatment or post-treatment stage depending on the
concentrations of the compounds.

A wastewater with high COD or TOC is usually treated in an anaerobic process for decreasing the organic
load of the effluent. AOPs are useful to be employed as a post-treatment of anaerobically treated effluent
to further destroy the residual compounds dissolved in the wastewater. For a wastewater with a high
organic loading that is not highly biodegradable, it is useful to apply integrated processes such as
anaerobic process, AOP, and another aerobic process in sequence. In the first stage (anaerobic
process), a large portion of COD is removed from the effluent. Then in AOP, non-biodegradable residuals
are decomposed to smaller and more biodegradable molecules which are suitable for aerobic treatment in
the final stage. The effluents with high biodegradable organic loading could be treated by integrated
anaerobic-aerobic-AOP processes. The first two stages are employed to reduce the COD, BOD, and TOC
and further polishing. Using the last stage is also effective for post-treatment of residuals. Multi-stage
integrated AOP-biological treatment is also advantageous for a class of wastewater solutions (bio-
recalcitrant and inhibitory streams) for decreasing operating cost of the treatment but it requires a
relatively higher capital cost. Instead of using multi-stage integrated AOP-biological systems, recycling is
another alternative for higher removal rate of contaminants. Recycling is helpful to keep the fixed cost
lower than that of multi-stage processes. The circulation ratio is an important factor to determine the
efficiency of the integrated AOP-biological method. The optimization of circulation ratio is beneficial to
maximize the system efficiency and minimize the operating cost.

5. BIODEGRADABILITY
In the integration of advanced oxidation technologies and biological processes, the main responsibility of
advanced oxidation processes is to enhance the biodegradability of the wastewater not the complete
oxidation, mineralization, and COD or TOC reduction because COD and TOC can be reduced during low
cost biological method. Therefore, it is desirable to increase the biodegradability of wastewater in the
AOP stage as much as possible. The biodegradability of a solution can be evaluated as follows:

- BOD enhancement

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- BOD/COD enhancement

- BOD/TOC enhancement

Most of studies have emphasized on the enhancement of BOD/COD relative to the others. It is important
to note that sometimes BOD/COD enhancement is due to only COD reduction and it may not result in a
higher biodegradability. Although the COD of the solution is decreased, AOP may decompose the
complex and toxic compounds and produce a relatively more toxic daughter compounds with lower BOD
than that of the parent compounds. Therefore, the biodegradability is increased in the case of both COD
or TOC reduction and BOD enhancement.

6. INTEGRATION OR COMBINATION?
In recent years, different studies have tried to increase the efficiency of AOPs by using various methods
such as integrated (sequential) and combined (simultaneous) processes. As explained earlier, the main
purpose of integrating different treatment methods is to enhance the process efficiency as well as to
reduce the operating cost. On the other hand, a combined process is used for intensification of the
process. Neelavannan et al. (2007) [27-28] showed that combined photocatalytic and electrochemical
processes performed a better procion blue dye degradation rate as compared to that of integrated
processes. The main parameter in combined processes to evaluate the effectiveness of the system is the
synergetic effect. Synergetic effect is a parameter that shows the enhancement of organic compounds’
degradation under combined method relative to the linear combination (sequential) method. The
synergetic effect could be estimated as follow [17]:

Combined reaction rate constant

Synergetic effect = (1)
Linear summation of individual methods rate constant

The existence of two or more advanced oxidation processes often results in a greater degradation rate
due to several factors that are explained in details in the next sections. The design, construction,
operation, and maintenance of combined (simultaneous) advanced oxidation processes is more difficult
than those of the individual methods, but by combining various technologies, lower capital and operating
costs are achievable. It is obvious that the purpose of combination of advanced oxidation processes is to
enhance the degradation rate that is not achievable by a single process alone under the same condition.
Several factors are required to be considered simultaneously in combined advanced oxidation
technologies. These factors are as follows:

Method: The strength of different combined methods is useful to decide whether this hybrid system is
beneficial. For those methods employed to degrade organic compounds or to enhance the
biodegradability, the combined method which has the greatest removal rate would be the best choice. On
the other hand, if the goal of the treatment is mineralization, it is better to select the combined system that
has the highest TOC reduction rate.

Residence time: The product of the synergetic effect and residence time is equal to the summation of
individual processes’ residence times.

Cost: Fixed and operating costs of hybrid methods are less than those of the summation of different
individual process. By increasing the synergetic effect, these costs can be even less. Synergetic effects of
less than one are almost always not practical due to the lower degradation rate and higher maintenance
cost. It is also not economical to combine different methods with the synergetic effect slightly greater than
one when the contribution of a method is lower in the degradation of organic compounds and synergetic
effect.

Energy: In combining different single processes, the amount of energy or power required for the
degradation should be considered. Methods employing UV, ultrasonic irradiation, ozone generation, gas
sparging, and mechanical mixing consume a higher amount of energy relative to others, but they enhance
the degradation rate.

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There are many studies in combining different AOPs such as combined photocatalysis and ultrasound
[64-71], ozonation and ultrasound [72-74], photo-Fenton processes [75-77], and combined Fenton, photo-
Fenton, and ultrasound [78-85]. Combining an advanced oxidation technology and biological process is
very rare because hydroxyl radicals’ formation during the AOPs may be inhibitory to biomass. Moreover,
the presence of H2O2 is also poisonous to microorganisms. Therefore, it is better to use the combined
system in the AOP part to enhancing the oxidation and biodegradability in less time. In studying the
behavior of the integration of combined AOPs and biological treatment processes, it is better to define a
new parameter to depict the biodegradability enhancement due to the combination of different methods.

Biodegradability enhancement by combined process

Synergetic biodegradability enhancement = (2)
Total biodegradability enhancement by individual processes

This equation shows the amount of additional BOD produced by combined process. This equation is
useful in evaluating the integrated AOP-biological process efficiency as the biodegradability enhancement
is necessary to be achieved.

7. KINETICS AND MODELING OF INTEGRATED PROCESSES

AOPs have their own kinetics and mechanisms for oxidizing organic compounds depending on irradiation
source characteristics and the type and the dose of reagents functioning in the reactor. Different studies
carried out for modeling AOPs such as UV/H2O2 [5, 86], photocatalysis [87], and Fenton [88-89]. A few
studies were carried out for modeling of integration processes [86, 90-91].

7.1 BIOLOGICAL MODELING

Usually biological reactions are modeled by Monod [90, 92-95], Haldane [90], two-step Haldane [90],
Contois [96-97], and Grau [98]. The Monod equation has been found as an acceptable and powerful
mathematical expression fitted to experimental data described as follows [90]:

COD
µ = µ max (3)
K COD + COD

where µ and µmax are the specific and maximum specific growth rates of microorganisms, KCOD is the half
saturation constant, and COD is standing for any limiting organic source (COD concentration),
respectively. In case of KCOD << COD that is applicable to no inhibition, Monod equation can be simplified
as follows [90, 94]:

1 d (VSS ) COD
µ= = µ max ≅ µ max (4)
Vss dt K COD + COD

Cell yield coefficient can be defined based on the COD consumption and volatile suspended solids
(VSS) production during aerobic biochemical degradation and it can be defined as follows [90]:

VSS − VSS 0
YVSS / COD = (5)
COD 0 −COD

where VSSo and VSS are the initial and final volatile suspended solids in the bioreactor, and CODo– COD
is the organic consumption during the biological treatment. Rivas et al., (2003) [91] also employed
Equation (5) based on the utilization of biodegradable COD fraction.

Monod expression can be employed for modeling as follows:

1 d [COD ] µ µ max [COD ]  [COD ]0 − [COD ]

− = = .  (6)
[VSS ] dt YVSS / COD K COD + [COD ]  [VSS ] − [VSS ]0 

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

d [COD ] µ max [VSS ][COD ]0 µ max [VSS ][COD ]

− = − (7)
dt K COD ([VSS ] − [VSS ]0 ) K COD ([VSS ] − [VSS ]0 )

µ max [VSS ][COD ]0 µ max [VSS ]

If A = , B = , and KCOD << [COD], after integration of the
K COD ([VSS ] − [VSS ]0 ) K COD ([VSS ] − [VSS ]0 )
equation, following equation can be achieved:

 A + B[COD ] 
ln  = Bt
 (8)
 A + B[COD ]0 

A plot of the left hand side of Equation (8) versus t should give a straight line to find the parameters of
interest.

7.2 MODELING OF ADVANCED OXIDATION TECHNOLOGIES

Modeling of the AOPs is carried out based on the summation of degradation rates in different methods
such as direct photolysis, direct ultrasonolysis, direct ozonolysis, the degradation due to hydroxyl radicals
attack, and the degradation due to the synergetic effect. A typical kinetics of US/UV/H2O2 and US/UV
reaction can be written based on the degradation rate of individual processes and the impact of the
synergetic effect as follows [73, 83, 86]:

 
dCi  ε Ci  − 2.303 L ∑ ε i Ci 
− = K pyr [Ci ] + K .OH [Ci ] + φC .I 0 . .1 − e i
 − K synergy [Ci ] (9)
dt 


∑
i
ε i Ci  




where , , , and are quantum yield, light intensity, molar absorptivity, and the compounds’
concentration. Kpyr and K.OH are the constant of pyrolytic decomposition rate of organic compounds and
the constant of the rate of reaction between organics and hydroxyl radicals, respectively. is the
synergetic effect constant representing the degradation rate enhancement due to combined treatment
methods. In the combined UV/US/H2O2 processes, organic compounds are oxidized through direct
photolysis, combustion or pyrolysis, free radical attack, and the synergetic effect predicted by combined
system. If the completely mixed solution is assumed, the degradation of contaminants is due to the
location of UV lamps, ultrasonic transducer, and the physical and geometrical characteristics of the
reactor. The location of the ultraviolet lamps and ultrasonic irradiation is also very critical for determining
the synergetic effect. The highest synergetic effect is predicted when the UV lamps bounded with
ultrasonic irradiation field. In other words, maximum local volumetric rate of energy absorption (LVREA)
and ultrasonic field overlap can produce a highest synergetic effect. Therefore, for designing an AOP
system, the location of internal equipment employing for irradiation should be carefully selected to
maximize the synergetic effect of the process.

The experiments for the advanced oxidation processes are usually conducted by optimizing the operating
conditions and photoreactor characteristics since the efficiency of the AOPs is affected by various
variables such as the concentration of initial compounds, residence time, H2O2 dose, photocatalyst
concentration, temperature, and pH. Therefore, it is necessary to employ the optimal condition. Recently,
the experiments are conducted to analyze the effects of different parameters on the process
effectiveness. Experimental design is also useful in order to avoid one-factor-at-a-time approach, where
one variable was changed while keeping the others constant. Experimental design also helps to find the
complex interaction between independent variables. Among these interactions, synergetic effect leads to
the generation of higher hydroxyl radicals and it requires to be carefully optimized.

8. OPTIMIZATION OF THE INTEGRATED PROCESSES

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Integrated processes are optimized to enhance the mineralization efficiency. Process optimization can be
based on the residence time, the energy consumption, and the total cost. The optimization of each
parameter depends on the environmental regulation, the process location, and characteristics of
individual processes.

8.1 Residence time

The minimization of the total residence time of all processes involved in integrated system is the objective
function of the optimization. The constraints are also the limits of residence times of individual processes
including the mass balance of each component in every process. Therefore, the objective function of
integrated processes based on the total residence time is as follows [12]:

Minimize: F = θ P + θ C + θ B (10)

where θ P , θ C , and θ B (h) are physical, chemical, and biological residence times, respectively. F (h) is
the total residence time of the system. The constraints are usually defined such that θp and θb should be
positive where θ C should be greater than a value so that a reasonable biodegradability is achieved.

8.2 Fixed cost

The fixed or capital cost of AOPs is relatively higher as compared to other treatment methods. Hirvonen
et al. (1998) [99] provided the capital and operating cost of UV/H2O2 (AOPs) and activated carbon.
Estimated fixed costs of different treatment methods based on the depreciation period (40 years) are
provided as follow [99]:

Photoreactors:

85,000 + 40 ×1,500  1m 3 
FC C = ×  (11)
 VC   1000L 
(40 × 24 × 365) 
θC 
3
where FCC ($/L) is a typical UV/H2O2 fixed cost, and VC (m ) is the volume of the photoreactor. (h) is
the residence time of the wastewater in the photoreactor. The fixed cost for a UV/H2O2 process is usually
$58,000 plus the cost of UV lamp which is $15,000 per year. The maximum allowable useful life estimate
under U.S.A. income tax regulations is 40 years which can be considered as depreciation time.

Activated carbon:

58,000  1m 3 
FC P = ×   (12)
 VP   1000L 
(40 × 24 × 365) 
 θP 
3
where FCp ($/L) represents the fixed cost of a typical activated carbon column and Vp (m ) is the volume
of the column. $58,000 is the capital cost for a typical activated carbon column.

Biological reactor:

 VB 
(72 × 40 × 24 × 365)  + 368,403
θB 
FC B = (13)
V 
(40 × 24 × 365) B 
θB 

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

where FCB ($/L) shows a typical activated sludge capital cost based on the bioreactor volume (VB) and
the residence time ( θ B ). $368,403 is the capital cost for a typical biological treatment and $72 is also
3
required for the treatment of 1 m wastewater.

8.3 Maintenance and operating costs

The operating cost of different processes is necessary to be optimized. The operating cost of AOPs is
+2
also high due to the continuous addition of reagents such as H2O2 and Fe . Physical treatment methods
utilizing an adsorbent are considered to be an additional expense for regeneration. Operating and
maintenance cost of typical UV/H2O2, activated carbon, and biological processes are provided as follows
[90, 99]:

2000  1m 3 
OMCC = ×   (14)
 VC   1000L 
 (24 × 365)
 θC 
where is the operating and maintenance costs for a typical UV/H2O2 system and $2,000 is the
operating cost estimated for 40 years.

1,200 + 0.29VP  1m 3 
OMC P = × (15)
 Vp  1000 L 
 (24 × 365) 
θ 
 P

where OMCP is the maintenance and operating cost of a typical activated carbon column. $1,200 is the
3
operating and maintenance cost estimated for 40 years, and 0.29 [$/m ] is the cost for the regeneration
and reactivation of the carbon bed.

V 
4.58 × (24 × 365) B  + 36,295
 θB   1m 3 
OMC B = ×  (16)
 VB   1000 L 
 (24 × 365)  
θB 

where OMCB is the maintenance and operating cost of a typical biological treatment. $36, 295 is the
3
operating and maintenance cost predicted for 40 years plus the 4.58 [$/m ].

Above Equations (10-16) are useful for optimizing the cost of various integrated processes containing
advanced oxidation technologies.

9. CONCLUDING REMARKS
To achieve a cleaner water and healthier environment, more effective and powerful treatment methods
are required. The integration of such methods is useful in order to fulfill the environmental regulations.
Integration of physical, chemical, and biological treatment processes are useful to take advantages of the
methods and to minimize the drawback of each methods. Anaerobic degradation is very helpful for
treating high organic loading wastewater with lower energy consumption. Aerobic methods are usually
employed to polish residuals. Therefore, in some cases, more than one biological method is required for a
better treatment. Intensification of AOPs is one of the challenges of researchers in this area. Authors are
trying to develop more effective and economical ones. Combining different reagents and irradiation
sources are used to achieve higher synergetic effects for biodegradability enhancement. Modeling and
optimization of integrated systems are also valuable to be extended to similar cases that might be
practical for scale up. The effect of different parameters such as residence time, temperature, pH, the
presence of different ions and acids, reagents doses, irradiation sources, recycling ratio is better to be
embedded in the model. An optimization determines the optimal residence time, optimal size of the

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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari

equipment, optimal reagents doses, optimal operating condition such as oxygen concentration in the
bioreactor, and optimal biodegradability achieved after advanced oxidation process.

ACKNOWLEDGEMENT
The financial support of Natural Sciences and Engineering Research Council of Canada (NSERC) and
Ryerson University is greatly appreciated.

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82. R.A. Torres, F. Abdelmalek, E. Combet, C. Pétrier, and C. Pulgarin. “A comparative study of
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