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M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 120
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
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 121
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
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 122
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
H
2
O
2
and O
3
, 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
constants are usually in the order of 10
6
to 10
9
mol.L
-1
.s
-1
[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.
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 123
Table 1: Summary of recent studies on the Integration of AOPs with other processes for water and wastewater treatment
Target
Compound(s)
System and Method Efficiency References
Surfactant effluent
containing
abundant sulfate
ions
Initial COD: 1500 and 490 mgL
-1
, Lab
scale Fenton process effluent
concentrations were 230 and 23 mg
L
-1
after 40 min. In pilot scale Fenton
followed by immobilized biomass
reactor was employed.
40 min for Fenton process and 2 h for biological
treatment were sufficient to reduce the effluent
concentration up to less than 100 and 5 mgL
-1
for
COD and LAS concentration. The effect of ferrous
ions is more important than that of H
2
O
2
. Sufficient
dosage of Fe
+2
was 600 mgL
-1
for an efficient
treatment. Increasing the H
2
O
2
leads to higher
biodegradability.
18
Pulp and paper 2 different samples with 2500 and
3520 mgL
-1
COD, were treated by
some chemicals (alum, lime and
polyelecetrolyte) up to 1900 mgL
-1
,
Followed by activated sludge process
up to 260-400 mgL
-1
, then secondary
wastewater was treated by different
methods such as ozonation, catalytic
ozonation, H
2
O
2
/O
3
, and Fenton.
The removal efficient of secondary wastewater was
arranging: Fenton > H
2
O
2
/O
3
> Ozonation > catalytic
ozonation with metal oxides. In ozonation: for higher
COD, 60% COD reduction was observed after 1 h. No
further degradation was found after 2 h. For lower
COD in less than 30 min, 200 mgL
-1
effluent was
obtained. Fenton process showed 88% and 50% COD
reduction for secondary and raw wastewater.
Optimum chemicals concentration ratios were 0.5
mol/1 mol Fe
+2
/H
2
O
2
and 2 mol/1 mol H
2
O
2
/COD.
19
Landfill leachate Wastewater pretreated by sequence
batch reactor was used for additional
advanced oxidation such as O
3
,
O
3
/pH adjustment (pH 9), H
2
O
2
,
O
3
/H
2
O
2
and performic acid
After 2h pretreatment with activated sludge, ozone
and pH adjusted ozone showed the highest
biodegradability. The most efficient method was
observed in combination of O
3
/H
2
O
2
and biological
treatment as pre- and post-treatment. Performic acid
did not show any TOC reduction.
20
2,4,5-
trichlorophenol
122 ml bench scale photocatalytic
circulating-bed biofilm reactor
(PCBBR), high intensity UV lamp and
Degussa P25 TiO
2
were used for
irradiation source and photocatalyst,
UV photocatalysis alone did not show any degradation
up to 96 h, After the addition of carriers with biofilm,
biodegradation of acetate was started quickly up to
200h and then smooth acetate concentration was
observed.
21
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 124
respectively
Hydroxyl-benzene
Photo-Fenton process in a 8 L 6-lamp
CPC solar continuous photoreactor
for treating raw river water and
pretreated with slow sand filtration
river water
Photolysis (with H
2
O
2
and without Fe
+3
) showed 57%
and 65% TOC reduction before and after SFF. Fe
+3
concentration even as low as 1 mgL
-1
depicted
treatment improvement drastically. The presence of
H
2
O
2
under sunlight resulted in 50% mineralization.
22
Cibacron Red FN-
R
A two stage aerobic-anaerobic
method followed by photo-Fenton and
ozonation processes was employed.
The initial concentration of
wastewater samples were 250, 1250,
3135 mgL
-1
.
Aerobic treatment showed less than 9%
biodegradation after 28 days. The photo-Fenton
process conducted with different ratios of Fe
+3
/H
2
O
2
,
10/250, 20/500, and 100/2500 mgl
-1
/mgl
-1
. DOC
reduction was increased with increasing of Fe
+3
and
H
2
O
2
. 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.
23
Phenol Hydrodynamic cavitation combined
with advanced Fenton was employed
for treating phenolic wastewater (2.5
mM).Hydrodynamic cavitation was
generated by a liquid whistle reactor
(LWR).
Results showed that both hydrodynamic cavitation and
advanced Fenton have greater efficiency for lower
phenol concentration. Continuous leaching resulted in
higher concentration of iron ions with longer residence
time. Increasing H
2
O
2
dose in the range of 500-2000
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.
24
Nonylphenol (NP) Sonochemical reactor equipped with
300kHz ultrasound transducer and
cooling system, combined with
biosoprtion of fungal cultures was
used for treating different
US-Fenton process showed better degradation rate in
case of lower initial contaminant concentration. Lowest
initial concentration performed the complete
mineralization. On the other hand, US only and Fenton
only were ineffective after 1-2 h. Biosorption showed
25
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 125
concentrations (100, 500, and 1000
ppm) of polluted water.
around 39 and 60% removal after 4 and 7 days. Initial
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,
Dimethoate,
Oxamyl,
Cymoxanil,
Pyrimethanil
50 mgL
-1
concentration of each
compound was used to be treated in
combined AOP/biological method.
AOPs were TiO
2
photocatalysis and
photo-Fenton. 35 L solar pilot plant
equipped with 3 CPCs for TiO
2
photocatalysis and 75 L solar pilot
plant using 4 CPCs were employed
for AOP stage. A 35 L aerobic
immobilized biomass reactor (IBR)
was used for biological treatment.
90% DOC removal was observed in 1197 and 512 min
in case of case of TiO
2
photocatalysis and photo-
Fenton. Shorter irradiation time with two different iron
concentrations (20 and 55 mgL
-1
) resulted in 50 and
72% DOC reduction. Photo-Fenton process showed
greater pesticide degradation (more than twice) than
the TiO
2
photocatalysis. Pretreatment by photo-Fenton
process decreased toxicity from 90 to 47%.
Biodegradability tests showed 70% biodegradability is
obtained after 12 days. Combined batch method
showed 85% efficiency (23% AOP, 62% biological
treatment). Combined batch AOP and continuous
biological treatment showed more than 90% removal.
26
Procion blue A 130 ml plate and frame
electrochemical flow cell and
immobilized photocatalytic UV reactor
were employed for degradation of 50
mg/L procion blue solution
Photo-electrochemical and photocatalytic
electrochemical methods showed 98% dye
degradation within 7 h. After 4 h different combined
method showed more than 90% color removal. COD
removal was proportional to applied current. The
optimum TiO
2
concentration was 40 mgL
-1
. Acidic
condition performed greater degradation.
27-28
Reactive black 5
(RB5), Reactive
blue 13 (RB13),
Acid orange 7
(AO7)
Fenton processes followed by aerobic
biological treatment (sequential batch
reactors) were used for 50 mg/L dye
solution. Different factors such as pH,
H
2
O
2
and Fe
+2
were optimized.
pH 3 showed the highest decolorization for all dyes
(more than 99%), Decolorization was increased at
higher H
2
O
2
concentration up to an optimal dose(50
mgL
-1
). optimal Fe
+2
dose was found to be 15 mgL
-1
.
82, 89, and 84% COD removal was observed for RB5,
RB13, and AO7, respectively.
29
Pharmaceutical The combination of solar AOP Industrial effluent containing α-methylphenylglycine 30
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 126
factory effluent followed by biological treatment. Four
CPC with 1.04 m
2
with 50 mm
diameter absorber tubes. Initial TOC
was 500 mgL
-1
. Iron concentration
was 20 mgL
-1
.
(MPG) treated using a pilot plant. Fenton (Fe
+2
= 20
mgL
-1
) process showed complete degradation and
70% TOC reduction in less than 1 h with seawater, but
in case of distilled water, the degradation rate was 3
times greater. 60 mM of H
2
O
2
is required to degrade
MPG. For complete MPG degradation, 30-35 mM
H
2
O
2
is required and also for cost minimization, the
H
2
O
2
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 m
2
CPC collectors are sufficient to treat 3
m
3
/day wastewater.
Textile surfactant
formulation
UV/H
2
O
2
using 40 W low pressure
mercury vapor lamp carried out with
different pH (from 5 to 12) and H
2
O
2
dose from 10-100 mM for treating
textile surfactant formulation with an
initial 1000 mgL
-1
COD.
pH did not show significant influence on the AOP
mechanism but the pH was decreased until neutral
condition due to formation of the acids during
degradation. The optimal H
2
O
2
dose was found to be
917 mgL
-1
. Biodegradable COD was increased from 4
to 14-15% when the UV/H
2
O
2
(60 mM H
2
O
2
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.
31-32
Distillery
wastewater
The distillery spent wash was pre-
treated by thermal and sonication
(ultrasonic bath) and ozonation (flow
rate: 260 l/h) processes sent to
biological treatment process.
Ultrasonic (US) pretreatment did not show significant
COD (13% after 48 h), decolorization, and TOC
reduction but converted complex organic compounds
into smaller ones. Ozonation was effective on the
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.
33-34
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 127
Diuron and
Linuron
42 mgL
-1
Diuron and 75 mgL
-1
Linuron
was chosen for the photo-Fenton and
biological treatment. Different doses
of H
2
O
2
(97.1, 143, and 202 mgL
-1
)
and Fe
+2
(9.25, 13.3, and 15.9 mgL
-1
)
were used for photo-Fenton process.
TOC reduction was significantly enhanced by an
increase of Fe
+2
and H
2
O
2
doses. Inorganic acids such
as acetic acid, oxalic acid, and formic acid were
produced, reached a maximum and then degraded
during photo-Fenton process, higher dose of H
2
O
2
and
Fe
+2
resulted in greater production and degradation
rate.
35-36
Natural water
systems
Enhanced coagulation (using alum
and ferric chloride) and photocatalytic
oxidation (UV/TiO
2
) were employed to
treat three different natural water
samples.
Ferric chloride coagulation showed better coagulation
compared with alum.
37-38
Reactive black 5
(RB5)
Fenton process in 800 ml cylindrical
glass reactor was combined with
yeast as a post treatment was
employed to degrade 100-200-300-
500 mgL
-1
RB5. The Fe
+2
/H
2
O
2
ratio
was 10.
Decolorization rate was significantly decreased with
an increase of RB5 concentration so that after 60 min,
98 and 62.6% decolorization was observed for 100
and 500 mgL
-1
samples. For solution concentration
greater than 200 mg
-1
incomplete decolorization was
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.
39
Natural organic
matter (NOM)
Combined UV/H
2
O
2
(equipped with
LP lamp) and biological activated
carbon (BAC) in a 2 cm diameter
column used for degradation of NOM.
Disinfection by product formation potential (DBP-FP)
was effectively removed during UV/H
2
O
2
at higher UV
fluency, but AOP-BAC showed significant organic
carbon content reduction. During AOP the
concentration of dichloroacetic acid (DCAA) increased
40
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 128
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
(abietic acid,
dehydroabietic
acid, isopimaric
acid)
Different AOPs such as ozonation,
O
3
/UV, O
3
/UV/H
2
O
2
in a 1.5 L
photoreactor combined with activated
sludge were used.
The highest COD reduction was observed under
O
3
/UV/H
2
O
2
@ T=80
0
C. Higher temperature resulted
in lower required ozone for degradation.
Dehydroabietic acid showed greater resistance to be
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.
41
Reactive red 195A
(RR195A)
Combined UV/H
2
O
2
and moving bed
biological reactor was used for
treatment the experimental design
was based on H
2
O
2
dose, radiation
time and circulation ratio (0 to 600%).
The optimization was carried using Box-Wilson
statistical design method. The greatest impact was
observed by recirculation ratio. In addition, higher
irradiation time and H
2
O
2
dose were effective for better
decolorization.
42
Tetrahydrofuran
(THF), 1,4-
dioxane, pyridine
Biodegradability of the compounds
individually and mixed was analyzed
after UV/H
2
O
2
and UV/O
3
UV/H
2
O
2
showed greater efficiency for increasing
biodegradability and destruction than UV/O
3
for
treating THF solution. For dioxane solution UV/H
2
O
2
degraded all the contaminants within 60 min but did
not show biodegradability improvement. No
biodegradability enhancement was observed during
UV/O
3
and UV/H
2
O
2
of pyridine. UV/O
3
slightly
improved the biodegradability of the mixture.
43
Deltamethrin,
lambda-
cyhalothrin,
100 mgL
-1
of three pesticides with
6500, 6300, 6500 mgL
-1
COD were
selected for O
3
and O
3
/UV
Over 80 and 92% degradation observed under O
3
and
O
3
/UV, respectively. Higher pH showed positive effect
on the degradation and COD reduction. In combined
44
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 129
triadimenol degradation alone and combined with
biological treatment.
process, O
3
/UV pre-treated solution showed higher
degradation rate as compared to O
3
pretreated,
aerated, and raw solutions. Temperature was effective
for enhancing the biodegradation.
Pulp and paper
effluent
Combined AOP (photocatalysis or
ozonation) and biological process was
assisted for treating Kraft E1and
black liquor effluent. TOC of these
effluents were 934 and 128750 mgL
-1
.
Suspended photocatalysis showed a better
decolorization for Kraft E1 with respect to ozonation
(54 versus 27%). On the other hand, decolorization of
black liquor effluent was more desirable with
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.
45
Green table olive
processing
wastewater
Lab scale and pilot scale of biological
treatment followed by electrochemical
reactor in the presence and absence
of H
2
O
2
was studied.
Inoculums’ size performed positive effect on COD
removal so that 10
4
and 10
6
conidialml
-1
showed 71.5
and 85.5% COD reduction. pH decreased faster for
the high inoculum concentration. Most of the
contaminants were degraded completely during
biological treatment. Pre-treated solution was sent to
electrolytic reactor with various H
2
O
2
dose (0, 2.5, and
5 v%). Results showed that the degradation was
increased in the presence of H
2
O
2
. In pilot plant, 98%
COD reduction was obtained during combined
processes.
46
Dissolved organic
matter (DOM) in
drinking water
Single stage and multistage
ozonation-biological and AOP-
biological treatment were used for
oxidizing DOC of the reservoir water
and secondary effluent of the
municipal wastewater when the DOC
concentration was 20 mgL
-1
.
AOP-biological showed better mineralization rather
than ozonation-biological. Further mineralization was
achieved in multi-stage process, because in each
biological stage, BDOC portion of the effluent was
removed because this fraction can act as radical
scavenger. Single stage and Multistage ozonation-
biological did not perform significant oxidization for
residence time greater than 15 min.
47
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 130
4-chlorophenol (4-
CP)
Photo-Fenton in 2.2 L reactor
followed by sequencing batch biofilter
reactor (SBBR) was used for treating
200 ppm of 4-CP
H
2
O
2
showed higher influence on the degradation rate
rather than Fe
+2
and temperature. Moreover, higher
H
2
O
2
dose improved the biodegradability of the
solution.
48
Cibacron brilliant
yellow 3G-P
Combined photocatalysis (1 mgL
-1
TiO
2
) and aerobic biological (activated
sludge) treatment was used for 100
mgL
-1
of the target.
Higher decolorization rate was observed under
aerobic treatment of partially photocatalytically pre-
treated solution. Acclimated sludge also increased the
oxygen uptake rate of the solution.
9-10
Winery
wastewater
Solar homogeneous and
heterogeneous photo-Fenton process
was employed in the presence of 10
mLL
-1
H
2
O
2
for treating winery
wastewater (COD= 3300 and TOC =
969 mgCL
-1
)
Unlike the heterogeneous photo-Fenton,
Homogeneous method required additional H
2
O
2
during
the experiments. Homogeneous performed higher
degradation rate and TOC reduction rather than
heterogeneous photo-Fenton. The heterogeneous
Fenton method was advantageous because further
precipitation was not necessary.
49
Cellulose effluent
The effluent from the acid stages of
the bleaching process of Eucalyptus
urograndis wood was examined by
activated sludge followed by UV
radiation (200 ml batch reactor)
Activated sludge increased the wastewater color but it
was very effective for COD and BOD reduction. UV
radiation was helpful for decolorization and it showed
lower ability for COD and BOD removal. The
combined system did not show any improvement for
further BOD and COD reduction.
50
Mixed industrial
wastewater
Pathogen removal and re-growth of
an UASB effluent was studied with
ozonation, UV, UV/H
2
O
2
, peracetic
acid (PAA)
Increasing the ozonation time did not improve the
pathogen removal. 350 mgL
-1
H
2
O
2
, 15 V% PAA, and
120 sec UV radiation was effective for above 99%
pathogen inactivation. In higher temperature (35
0
C)
pathogen re-growth was higher.
51
Semiconductor
wastewater
Combined physical (fixed bed air
stripping column), chemical (Fenton
Air stripper was used to recover isopropyl alcohol
(IRA). IPA recovery was enhanced by increasing air
52
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 131
process), and biological (sequencing
batch reactor (SBR)) was employed
for treating a semiconductor
wastewater and recover isopropyl
alcohol.
flow rate, temperature and separation time. Fenton
was very effective at pH between 2 and 5. Lower
FeSO
4
dose (lower than 5 mgL
-1
) showed greatest
COD reduction. The removal rate was also increased
under higher H
2
O
2
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
(2,4-DCP)
100 ppm 2,4-DCP was treated in
combined ozonation and biological
treatment (activated sludge and
acclimated biomass with phenol)
Ozonation improved the biodegradability of the
solution from 0 to 0.25 and 0.48 for BOD
5
/COD and
BOD
21
/COD. Activated sludge (non-acclimated with
phenol) showed better removal rate than that of
acclimated to phenol.
53
Linear
alkylbenzene
sulfonate (LAS)
76.6 L Pilot plant cylindrical
photoreactor (UV/H
2
O
2
) for 12, 25, 50,
100 mgL
-1
LAS
Biodegradability was increased during LAS
photocatalysis especially for lower concentration of
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.
54
Methyl tert-butyl
ether (MTBE)
3 L batch glass photoreactor
equipped with 2 different UV lamps
with wavelengths 365 and 254 nm
employed for UV/H
2
O
2
and UV/TiO
2
followed by biodegradation using SBR
Over 90% MTBE removal achieved by UV/H
2
O
2
within
1 h. Optimal H
2
O
2
dose was 14 times greater than
MTBE dose. UV-254 was more effective than UV-365
for both UV/H
2
O
2
and UV/TiO
2
in degrading MTBE.
UV/H
2
O
2
and UV/TiO
2
were not effective for enhancing
the biodegradability of solution.
55
Wool scouring
effluent
Flocculation followed by aerobic
biological treatment is being used to
treat and UV/H
2
O
2
was used as a
post-treatment process. Biological
treatment was also used as a post-
treatment process.
BOD
5
was increased during UV/H
2
O
2
from <10 to 86
mgL
-1
. COD and TOC were removed by 75 and 85%,
respectively. Decolorization was complete in less than
30 min. pH variation was ineffective on COD and TOC
reduction. Higher COD removal was achieved in
integrated AOP and Biological post-treatment.
56
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 132
Oily wastewater
from the lubricant
unit
UV/H
2
O
2
followed by biological
(Pseudomonas putida DSM 437)
treatment used to treat oily
wastewater containing ethylene
glycol, phenol, p-cresol, o-cresol.
Direct biological results were
compared to integrated system
Biodegradation alone showed 60% COD reduction.
Fe
+3
/UV/H
2
O
2
improved COD reduction rather than
UV/H
2
O
2
from 5 to 30% within 10 min. Integrated
photolysis and biological showed greater organics
removal relative to direct biodegradation. For example
ethylene glycol was 100% removed from the solution.
COD removal was increased from 60 to 72% by
integrated process.
57
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 133
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/H
2
O
2
, UV/O
3
, UV/TiO
2
, 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
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 134
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
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 135
- 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]:
constant rate methods individual ofsummation Linear
constant ratereaction Combined
effect Synergetic =
(1)
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.
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 136
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 H
2
O
2
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.
processes individualby t enhancemenbility biodegrada Total
process combinedby t enhancemenbility Biodegrada
t enhancemenbility biodegrada Synergetic =
(2)
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/H
2
O
2
[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]:
CODK
COD
COD
+
=
max
µµ
(3)
where µ and µ
max
are the specific and maximum specific growth rates of microorganisms, K
COD
is the half
saturation constant, and COD is standing for any limiting organic source (COD concentration),
respectively. In case of K
COD
<< COD that is applicable to no inhibition, Monod equation can be simplified
as follows [90, 94]:
(
)
maxmax
1
µµµ
≅
+
== CODK
COD
dt
VSSd
Vss
COD
(4)
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]:
CODCOD
VSSVSS
Y
CODVSS
−
−
=
0
0
/
(5)
where VSS
o
and VSS are the initial and final volatile suspended solids in the bioreactor, and COD
o
– 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:
[ ]
[
]
[
]
[ ]
[
]
[
]
[ ] [ ]
−
−
+
==−
0
0max
/
.
1
VSSVSS
CODCOD
CODK
COD
Ydt
CODd
VSS
CODCODVSS
µ
µ
(6)
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 137
[
]
[
]
[
]
[ ] [ ]
[
]
[
]
[ ] [ ]
( )
0
max
0
0
max
)( VSSVSSK
CODVSS
VSSVSSK
CODVSS
dt
CODd
CODCOD
−
−
−
=−
µ
µ
(7)
If A =
[
]
[
]
[ ] [ ]
)(
0
0
max
VSSVSSK
CODVSS
COD
−
µ
, B =
[
]
[ ] [ ]
( )
0
max
VSSVSSK
VSS
COD
−
µ
, and K
COD
<< [COD], after integration of the
equation, following equation can be achieved:
[
]
[ ]
Bt
CODBA
CODBA =
+
+
0
ln
(8)
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/H
2
O
2
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]:
[ ] [ ] [ ]
isynergy
CL
i
ii
C
Ci
OH
ipyr
i
CKe
C
ICKCK
dt
dC
i
ii
i
−
−
++=−
∑
−
∑
ε
ε
ε
φ
303.2
0
1...
.
(9)
where , , , and are quantum yield, light intensity, molar absorptivity, and the compounds’
concentration. K
pyr
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/H
2
O
2
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, H
2
O
2
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
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 138
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:
BCP
F
θθθ
++=
(10)
where
P
θ
,
C
θ
, and
B
θ
(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 θ
p
and θ
b
should be
positive where
C
θ
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/H
2
O
2
(AOPs) and activated carbon.
Estimated fixed costs of different treatment methods based on the depreciation period (40 years) are
provided as follow [99]:
Photoreactors:
( )
×
××
×+
=L
m
V
FC
C
C
C
1000
1
3652440
500,140000,85
3
θ
(11)
where FCC ($/L) is a typical UV/H
2
O
2
fixed cost, and V
C
(m
3
) is the volume of the photoreactor. (h) is
the residence time of the wastewater in the photoreactor. The fixed cost for a UV/H
2
O
2
process is usually
$58,000 plus the cost of UV lamp which is $15,000 per year. The maximum allowable useful life estimate
under U.S.A. income tax regulations is 40 years which can be considered as depreciation time.
Activated carbon:
( )
×
××
=L
m
V
FC
P
P
P
1000
1
3652440
000,58
3
θ
(12)
where FCp ($/L) represents the fixed cost of a typical activated carbon column and V
p
(m
3
) is the volume
of the column. $58,000 is the capital cost for a typical activated carbon column.
Biological reactor:
( )
( )
××
+
×××
=
B
B
B
B
BV
V
FC
θ
θ
3652440
403,368365244072
(13)
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 139
where FC
B
($/L) shows a typical activated sludge capital cost based on the bioreactor volume (V
B
) and
the residence time (
B
θ
). $368,403 is the capital cost for a typical biological treatment and $72 is also
required for the treatment of 1 m
3
wastewater.
8.3 Maintenance and operating costs
The operating cost of different processes is necessary to be optimized. The operating cost of AOPs is
also high due to the continuous addition of reagents such as H
2
O
2
and Fe
+2
. Physical treatment methods
utilizing an adsorbent are considered to be an additional expense for regeneration. Operating and
maintenance cost of typical UV/H
2
O
2
, activated carbon, and biological processes are provided as follows
[90, 99]:
( )
×
×
=L
m
V
OMC
C
C
C1000
1
36524
2000
3
θ
(14)
where is the operating and maintenance costs for a typical UV/H
2
O
2
system and $2,000 is the
operating cost estimated for 40 years.
( )
×
×
+
=L
m
V
V
OMC
P
p
P
P1000
1
36524
29.0200,1
3
θ
(15)
where OMC
P
is the maintenance and operating cost of a typical activated carbon column. $1,200 is the
operating and maintenance cost estimated for 40 years, and 0.29 [$/m
3
] is the cost for the regeneration
and reactivation of the carbon bed.
( )
( )
×
×
+
××
=L
m
V
V
OMC
B
B
B
B
B1000
1
36524
295,363652458.4
3
θ
θ
(16)
where OMC
B
is the maintenance and operating cost of a typical biological treatment. $36, 295 is the
operating and maintenance cost predicted for 40 years plus the 4.58 [$/m
3
].
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
M. Mohajerani, M. Mehrvar & F. Ein-Mozaffari
International Journal of Engineering (IJE) Volume (3) : Issue (2) 140
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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