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Electrochemical Oxidation Process Contribution in Remediating Complicated Wastewaters

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  • International Collage of Engineering and Management ICEM
Wastewater Engineering: Types, Characteristics and Treatment Technologies
Available online at http://www.ijsrpub.com/books
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81
Wastewater Engineering: Types, Characteristics and
Treatment Technologies
Chapter 4: Electrochemical Methods
Wastewater Engineering: Types, Characteristics and Treatment Technologies
Available online at http://www.ijsrpub.com/books
©2014 IJSRPUB
82
Electrochemical Oxidation Process Contribution in Remediating Complicated
Wastewaters
Mohammed J. K. Bashir1,*, Jun-Wei Lim1, Shuokr Qarani Aziz2, Salem S. Abu Amr3
1,*Department of Environmental Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman,
31900 Kampar, Perak, Malaysia
3Department of Civil Engineering, College of Engineering, University of SalahaddinErbil, Iraq
2School of Civil Engineering, Engineering Campus, Universiti Sains Malaysia,14300 Nibong Tebal, Penang, Malaysia
*Corresponding Author: jkbashir@utar.edu.my; Tel: 605-4688888 ext: 4559; Fax: 605-4667449
Abstract. In recent years, electrochemical oxidation process has gained increasing interest due to its exceptional technical
features to eliminate a wide range of pollutants exist in various types of wastewaters, e.g., refractory organic matter, nitrogen
species, microorganisms, etc. Serve as a clean, adaptable and powerful tool in removing pollutants, this review paper focuses
on the fundamental mechanisms of electrochemical oxidation process and provides discussions on the possible applications in
wastewater treatment. To top it off, special attention on the most recent developments and challenges are as well highlighted in
this review.
Keywords: Electrochemical, Wastewater, Oxidation Process
1. INTRODUCTION
Basically, wastewater treatment aims to improve the
quality of wastewater before discharging to the
receiving water bodies by using reliable technology.
The conventional sequence of wastewater treatment
starts with draining the wastewater in a central,
separated location and subjecting the wastewater to
several treatment processes. Wastewater treatment can
be generally categorized by the character of the
treatment process operation being used such as
biological, chemical or physical methods. Wastewater
treatment via biological technology is the most
economical means of treatment and normally utilizes
for the removal of biodegradable organic pollutants
presented in the wastewater. Nevertheless, the
presence of toxic and refractory substrates in the
wastewater would virtually foil the biological
treatment process as these substrates are potentially
inhibiting the bioactivity of microorganism (Grimm et
al., 1998). Among the various techniques, the use of
electro-chemical oxidation process in the wastewater
treatment has engrossed many researchers attention,
particularly in remediating industrial wastewater. To
date, electrochemical oxidation processes have been
shown to be a valuable option for the elimination of
refractory organic compounds from various types of
wastewaters (Bashir et al., 2013). Electrochemical
oxidation is highly capable and efficient in reducing
the organic compounds from various types of
wastewater as compared with other types of physio-
chemical technologies which only bring about phase
transfer of the contaminants in question with no
chemical destruction is taking place.
Similarly, Kapalka et al. (2009) stated that the
electrochemical oxidation process is a clean, versatile
and powerful tool for the destruction of organic
pollutants in wastewater. Furthermore,
electrochemical method presents many significant
gains since it does not require any ancillary chemical,
appropriate for large range of pollutants removal and
does not require high pressures and temperatures for
the reaction to commence. However, the efficiency of
the electro-oxidation techniques depends strongly on
the operation conditions and on the nature of the
electrode materials (Wang et al., 2008). Recently, the
strict wastewater discharge limits with health quality
standards obligation set by legislation may be met by
applying electrochemical oxidation. Wastewaters
generated from municipal landfill and a wide diversity
of industries including the food, textile, and tannery
productions have been successfully treated by this
process. Thus, due to its high competence together
with its disinfection capabilities, electro-oxidation is a
suitable technique for water reuse programs. On the
other hand, treatment costs have to be cut down prior
to full-scale application of this technology.
Accordingly, the employment of electrochemical
oxidation together with other technologies and the use
of renewable energy sources to operate this process
are two significant steps required to reduce the overall
operational cost (Anglada et al., 2009).
2. ELECTROCHEMICAL OXIDATION
PROCESS
Electrochemical oxidation process has been
recognized as one of the most effective techniques in
degrading pollutants present in textile wastewater,
landfill leachate, simulated wastewater, olive mill
wastewater, paper mill effluents, and industrial paint
wastewater (Körbahti and Tanyolaç 2003; Un et al.,
2008; Bashir et al., 2009 ). The electrochemical
reactor in the laboratory experiments is shown in
Bashir et al.
Electrochemical Oxidation Process Contribution in Remediating Complicated Wastewaters
83
Figure 1. Figure 2 shows the conceptual diagram of
electrochemical reactor for wastewater treatment,
which includes a direct current (DC) power supply, a
cathode, an anode, and the electrolyte (a medium that
provides the ion transport mechanism between the
anode and the cathode necessary to maintain the
electrochemical process).
Fig. 1: The electrochemical reactor in the laboratory experiments. (1) DC power supply, (2) magnetic stirrer, (3) cover, (4)
electrodes, (5) magnetic bar-stirrer, (6) wastewater and (7) electric wire (Source: Bouhezila et al., 2011).
Fig. 2: Conceptual diagram of an electrochemical reactor (Source: Anglada et al., 2009)
Electrochemical oxidation of impurities in
wastewater is accomplished through two different
mechanisms as demonstrated in Figure 3: (1) direct
anodic oxidation, where the pollutants are destroyed at
the anode surface and (2) indirect oxidation where
mediators (NaCL, HClO, H2S2O8, etc) are
electrochemically produced to achieve the oxidation.
It should be clear that during electro-oxidation of
aqueous effluents, both oxidation mechanisms may
coexist (Chiang et al., 1995). Generally, the
mechanism of electrochemical degradation of
wastewater is a complex phenomenon involving
coupling of electron transfer reaction with a dissociate
chemisorptions step.
Wastewater Engineering: Types, Characteristics and Treatment Technologies
Chapter 4: Electrochemical Methods
84
Fig. 3: Schemes for direct and indirect electrolytic treatment of pollutants (Chiang et al., 1995).
2.1. Direct oxidation
Direct oxidation of pollutants takes place in two steps:
(i) diffusion of pollutants from the bulk solution to the
anode surface and (ii) oxidation of pollutants at the
anode surface. As a result, the effectiveness of the
electrochemical oxidation will depend on the
correlation between mass transfer of the substrate and
electron transfer at the electrode surface. The rate of
electron transfer is determined by the electrode
activity and current density. In general, there are two
different pathways of anodic oxidation of organic
substances as shown henceforth (Drogui et al., 2007):
Electrochemical conversion. Organic
substances (R) are partially oxidized as presented in
Eq. 1. Thus, a following treatment is needed to
completely destroy the oxidized substrates.
R → RO + e− (1)
Electrochemical incineration (combustion).
Organic substances are transformed into water, carbon
dioxide and other inorganic constituents as presented
in Eq. 2.
R → CO2 + H2O + Salts + e− (2)
2.1. Indirect oxidation
During indirect electrochemical oxidation, a strong
oxidizing agent is electro-generated at the anode
surface and subsequently destroys the organic
compounds in the bulk solution. The most widespread
electrochemical oxidant is chlorine which is produced
via the oxidation of chloride at the anode. Throughout
indirect oxidation, the agents produced on the anode
that are responsible for oxidation of inorganic and
organic matters could be chlorine and hypochlorite,
hydrogen peroxide, peroxodisulfuric acid, and ozone
(Li et al., 2010; Scialdone et al., 2009). Accordingly,
throughout the electrochemical oxidation of
wastewater, the impurities removal principally
occurred due to indirect oxidation, utilizing
chlorine/hypochlorite produced by anodic oxidation of
chlorine that existing or being added in the aqueous. A
chain of reactions that involve chlorine/hypochlorite
indirect oxidation are presented in Eqs. 3-9.
Anodic reactions:
2Cl→ Cl2 + 2e (3)
6HOCl + 3H2O 2ClO3 + 4Cl + 12H+ + 1.5O2 +
6e (4)
2H2O → O2 + 4H+ + 4e (5)
Bulk reactions:
Cl2 +H2O → HOCl + H+ + Cl (6)
HOCl → H+ + OCl (7)
Cathodic reactions:
2H2O + 2e- → 2OH + H (8)
OCl + H2O + 2e → Cl + 2OH (9)
The hypochlorite (OCl) generated in bulk solution
(Eqs. 6 and 7) is a strong oxidizing agent that can
oxidize aqueous organic substances (Scialdone et al.,
2009). In addition to the common oxidants that can be
electrochemically produced, metal catalytic mediators
(Ag+2, Co+3, Fe+3, etc.) are also employed for the
generation of hydroxyl radicals, as seen in the electro-
Fenton system. Nevertheless, the use of metal ions
may result in the treated effluent to be more toxic than
that its initial state. Therefore, the system of this kind
needs a separation step to recover the metallic species
Bashir et al.
Electrochemical Oxidation Process Contribution in Remediating Complicated Wastewaters
85
(Anglada et al., 2009), leading to the unfavorable
intricate treatment process.
2.3. Process Design Issues
Electrode materials, cell design (configuration),
working conditions and energy consumption have to
be taken into the consideration when it comes to the
building up of the electrochemical oxidation system.
2.3.1. Electrode material
The choice of electrode materials is very important
since it affects the selectivity and the efficiency of the
process. The complexity of electrode performances
and lack of adequate information insights make it
unfeasible to choose the optimum electrode for a
given process on a theoretical basis. The preliminary
selection is depending on process experience and this
is then tested and refined during an extensive
development program. In fact, it is complicated to
expect the achievement of an electrode material or to
characterize its lifetime without extended studies
under realistic operation conditions (Klamklang et al.,
2012).
Essentially, the electrode materials must have the
following properties (Anglada et al., 2009; Klamklang
et al., 2012):
(a) High physical stability; the electrode material
must have good mechanical strength, good resistance
to erosion and must be resistant to cracking.
(b) High chemical stability; the electrode material
must be resistant to corrosion, unwanted oxide or
hydride formation and the deposition of inhibiting
organic films under all conditions.
(c) Suitable physical shape; it should be feasible to
make the material into the required shape, to assist
sound electrical connections and also to allow simple
fixing and replacement at a variety of scales.
(d) Electrical conductivity; conductivity must be
practically high throughout the electrode system
including the current feeder, electrode connections
and the entire electrode surface exposed to the
electrolyte.
(e) Catalytic activity and selectivity; the electrode
material must sustain the desired reaction and in some
cases, significant electro-catalytic properties are vital.
The electrode material must encourage the desired
chemical change while inhibiting all competing
chemical changes.
(f) Low cost/life ratio; the use of reasonably priced
and durable electrode materials must be favored.
Competition between organics oxidation at the
anode and the side reaction of oxygen evolution
should be considered to assess the choice of an anode
material. The oxidation of water to oxygen (Eq. 5)
happens at about 1.2 V versus normal hydrogen
electrode. Yet, a higher voltage is required for
electrochemical oxidation of water to take place at the
anode. The oxygen evolution over potential of a
number of electrode materials is illustrated in Table 1
(Chen, 2004).
Table 1: Potential of oxygen evolution of different anodes, V versus normal hydrogen electrode (Chen, 2004)
Anode
Potential (V)
Conditions
Pt
1.3
0.5 mol L−1 H2SO4
Pt
1.6
0.5 mol L−1 H2SO4
IrO2
1.6
0.5 mol L−1 H2SO4
Graphite
1.7
0.5 mol L−1 H2SO4
PbO2
1.9
1.0 mol L−1 H2SO4
SnO2
1.9
0.5 mol L−1 H2SO4
TiO2
2.2
1.0 mol L−1 H2SO4
Si/BDD
2.3
0.5 mol L−1 H2SO4
Ti/BDD
2.7
0.5 mol L−1 H2SO4
There are some general guidelines to assist the
choice of an electrode material. In general, low O2
overvoltage anodes are distinguished by a high
electrochemical activity toward oxygen evolution and
low chemical reactivity toward oxidation of organic
compounds. Efficient pollutants oxidation at these
anodes may take place at low current densities. A
significant reduction of the current efficiency is
expected at high current densities due to the
production of oxygen. Conversely, at high O2
overvoltage anodes, higher current densities may be
used with minimal involvement from the oxygen
evolution side reaction. Thus, high O2 overvoltage
anodes are generally preferred. For example, boron-
doped diamond (BDD) anodes have been confirmed
to yield higher organic oxidation rates and superior
current efficiencies than other commonly used metal
oxides including PbO2 and Ti/SnO2-Sb2O5 (Anglada et
al., 2009).
2.3.2. Cell design
Maintaining high mass transfer rates as the main
reactions that occur in electrochemical process
transpire on electrode surfaces are the most important
issue in cell design. To improve mass transfer,
Wastewater Engineering: Types, Characteristics and Treatment Technologies
Chapter 4: Electrochemical Methods
86
techniques such as gas sparging, high fluid velocity,
use of baffles and incorporation of several types of
turbulence promoters are frequently employed. In
obtaining a high mass transfer rate, the cell
construction should account for simple access to and
exchange of cell parts (Wendt and Kreysa, 1999).
Figure 4 summaries the various features that should be
considered in the design of an electrochemical reactor
(Anglada et al., 2009).
Fig. 4: Categorization of electrochemical reactors in regards to cell configuration, electrode geometry and flow type (Anglada
et al., 2009).
Two types of electrodes, principally of 2-
dimensional and 3-dimensional construction subsist.
The 3-dimensional assures a high value of electrode
surface to cell volume ratio. Both types can be
classified into static and moving electrodes as shown
in Figure 4. Accordingly, the utilization of moving
electrodes increases the mass-transport coefficient
owing to the turbulence promotion. However, among
the 2-dimensional electrodes, static parallel and
cylindrical electrode cells are used in the major
reactor designs in the latest studies. Cell designs using
the parallel plate geometry in a filter press
arrangement are generally used because of the
simplicity of scale-up to a larger electrode size by
merely adding electrodes or increasing number of cell
stacks (Rajeshwar and Ibanez, 1997). Furthermore,
cell configuration (divided and undivided) needs to be
considered. In divided cells, the anolyte and catholyte
are separated via a porous diaphragm or an ion
conducting membrane. The selection of the separating
diaphragm or membrane in divided cells is equally
vital as the selection of electrode materials. In general,
divided cells choice should be avoided whenever
possible, as separators are expensive and tightening of
a divided cell (reduction of electrode gap) is difficult
and encounters a host of mechanical and corrosion
problems (Wendt and Kreysa, 1999).
2.3.3. Operation conditions
(a) The current density (CD) is among the most
important factors that usually control electrochemical
oxidation processes through the reaction rate. It
should be clear that an increase in CD does not
necessarily result in the increase of oxidation
efficiency; the effect of current density on the
treatment level depends on the features of the effluent
to be treated. On the other hand, the use of higher CD
generally results in higher operating costs due to the
increase of energy use.
(b) An increase in the temperature leads to more
efficient processes by global oxidation. While direct
oxidation processes remain almost unaffected by
temperature, this fact may be explained in terms of the
presence of inorganic electro-generated reagents. An
enhancement with rising temperature of the mediated
Bashir et al.
Electrochemical Oxidation Process Contribution in Remediating Complicated Wastewaters
87
oxidation processes by inorganic electro generated
reagents (active chlorine, peroxodisulfate) has been
reported. But, operation at ambient temperature is
preferred as it offers electrochemical processes with
less temperature requirements than those of the
equivalent non-electrochemical counterparts (i.e.,
incineration, supercritical oxidation) (Canizares et al.,
2006).
(c) The physicochemical features of the wastewater
(e.g., electrolyte nature and amount, pH value and
initial concentration of pollutants) also affect the
electrochemical oxidation process. The higher the
concentration of electrolyte is used, the higher the
conductivity and the lower cell voltage for a given
current density are recorded. Thus, treatment by
electrochemical oxidation is more suitable and cost
efficient when the wastewaters contain high salinity.
The effect of pH value is similar temperature, affects
mostly indirect oxidation processes (Anglada et al.,
2009). In chloride mediated reactions, the pH value
may influence the oxidation rate. During indirect
oxidation, chlorine evolution occurs at the anode (Eq.
3). At pH values < 3.3, the primary active chloro
species is Cl2 while at higher pH values its diffusion
away from the anode is coupled to its
disproportionation reaction to form HClO at pH<7.5
(Eq. 6) and ClO at pH>7.5 (Eq. 7). Theoretically,
operation at acidic conditions could be the finest
option as chlorine is the strongest oxidant followed by
HClO. Accordingly, higher pH values would improve
the electro-oxidation of pollutants, as HClO and ClO
are almost unaffected by desorption of gases and they
can act as oxidizing reagents in the total volume of
wastewater (Canizares et al., 2006).
2.3.4 Energy Consumption
The energy expenditure should be reduced to
minimize the power costs. The total power
requirement has contributions for both electrolysis and
movement of either the solution or the electrode. The
design of both electrodes and cell has a chief role in
reducing power needed. Therefore, a very open flow-
through porous electrode will have a low pressure
drop linked with it, giving rise to modest pumping
costs and facilitating reactor sealing. A high surface
area electrode which itself a turbulence promoter in
bed electrode, will give rise to a moderately high mass
transfer coefficient and active area without the need
for high flow rates through the cell; the pumping cost
will again be moderately low (Klamklang et al.,
2012). The maintenance of a low cell voltage requires
awareness to electrodes and cell design. The following
aspects should be considered:
(a) The counter electrode reaction should be
selected to reduce the reversible cell voltage. Thus, a
suitable and stable electrode material is required.
(b) The over-potentials at both electrodes should
be minimized through using electro catalysts.
(c) The electrodes, current feeders, and connectors
should be prepared from greatly conducting materials.
(d) Electrode and cell design should allow a small
inter-electrode or electrode membrane gap. The
electrode may touch the membrane as in zero-gap or
solid polymer electrolyte cells.
(e) A separator should be avoided by suitable
selection of the counter electrode chemistry or a thin
conductive membrane should be applied.
3. APPLICATIONS OF ELECTROCHEMICAL
OXIDATION IN WASTEWATER TREATMENT
Being touted as an effective treatment process, the
performance of electrochemical oxidation process in
treating various types of complicated wastewater
containing various pollutants has been studied. Also,
considerable efforts have been contributed recently to
elimination micro-contaminants using electrochemical
oxidation process. In general, microorganisms can be
deactivated via direct electrochemical process or by
the creation of ‘‘killer’’ agents, for example ·OH
(Lazarova and Spendlingwimmer 2008; Polcaro et al.,
2007). The combination of pollutants removal with
disinfection of wastewaters in a single treatment step
poses an attractive option, mainly in water recovery
and reuse where effectual removal of pathogens is
critical to protect public health. Table 2 presents the
effectiveness of electrochemical oxidation process in
treating variety of wastewaters.
Post-treatment of slaughterhouse wastewater via
electrochemical oxidation process was studied by
Awang et al. (2011). The most favorable conditions
were determined as 220 mg/L influent COD, 30
mA/cm2 current density and 55 min reaction time.
This resulted in 96.8% of color removal, 81.3% of
BOD removal and 85.0% of COD removal. Under the
optimal operation conditions (initial pH 6.9, current
density of 10 mA/cm2, conductivity of 3,990 micro
S/cm, and electrolysis time of 10 min), the removal
efficiencies of the textile wastewater by
electrochemical oxidation were 78% of COD and 92%
of turbidity. The energy and electrode consumptions
at the optimum conditions were calculated to be 0.7
kWh/kg COD (1.7 kWh/m3) and 0.2 kg Fe/kg COD
(0.5 kg Fe/m3), respectively (Kobya et al., 2009).
Landfill leachate treated electrochemically using
graphite carbon electrodes by Bashir et al. (2009), the
highest COD removal of 68% was achieved under the
operational conditions of 4 h reaction time and 79.9
mA/cm2 current density, while the initial COD was
Wastewater Engineering: Types, Characteristics and Treatment Technologies
Chapter 4: Electrochemical Methods
88
1414 mg/L. In another study conducted by Moraes
and Bertazzoli (2005), about 73% of COD, 57% of
TOC, 86% of color removals at a current density of
116.0 mA/cm2 and 180 min of reaction were attained.
They used oxide-coated titanium as an anode
electrode. The electrochemical treatment of industrial
water-based paint wastewater was examined in a
continuous tubular reactor. The effects of reaction
time on COD, color and turbidity removals was
investigated at 30 °C, 35 g/L electrolyte and
7496 mg/L of initial COD concentrations with
66.8 mA/cm2 current density. The optimum residence
time in the reactor was fixed at 6 h for a cost driven
approach, enabling COD, color and turbidity removal
of 44.3%, 86.2% and 87.1%, respectively (Körbahti
and Tanyolaç, 2009).
Electrochemical treatment of organic pollutants
from paper mill effluent was investigated by El-
Ashtoukhy et al. (2009). The results showed that the
percentage of COD and color removals were 97% to
100%, respectively. Energy consumption calculation
shows that energy consumption ranges from 4 to
29 kWh/m3 of effluent depending on the operating
conditions. In another study, the electrochemical
oxidation of paper mill effluents was investigated via
a dimensionally stable anode of composition Ti/RuPb
(40%) Ox. The results indicated that about 99% of
COD and 95% of color and polyphenols were
removed after 15 min of electrolysis. The UV-Vis
spectrum illustration confirmed the formation of
hypochlorite ions (ClO-) during the electrolysis
process, indicating that the electrochemical oxidation
proceeds via an indirect mechanism with the
participation of hypochlorite ions (Zayas et al., 2011).
In the case of olive oil mill wastewater, the removal
rates of organics increased with the increase of
applied current density, sodium chloride level,
recirculation rate and temperature. The original COD
concentration of 41,000 mg/L was reduced to 167
mg/L, 99.85% of turbidity removal, 99.54% of oil-
grease removal were achieved after 7 h electrolysis at
the conditions of 135mA/cm2, 2M NaCl, 7.9 cm3 /s,
and 40C (Un et al., 2008). The effect of current
density (40-120A/m2) and initial pH (3-11) on the
Pharmaceutical wastewater treatment efficiency by
electro oxidation process was investigated
(Deshpande et al., 2012).Under optimum operating
conditions (CD 80  A/m 2; pH 7.2), the process used
aluminum electrodes resulted in 24% of COD
removal after 25 min, whereas the process used
carbon electrode achieved 35.6% of COD removal
after 90 min of treatment (Deshpande et al., 2012). An
investigation of tannery wastewater treatment using
graphite cathodes and Ti/SnO2/PdO2/RuO2 anode,
with a current density of 2.1 A/dm2 was carried out.
After 55 min of the process the catholyte was
transferred into the anodic space and the process was
continued. After 55 min of electro-Fenton process, the
COD was reduced by 52.0%. Electrooxidation
continued by the anodic process resulted in
elimination of ammonia in 55 min and a total
reduction of COD by 72.9% (Naumczyk and
Kucharska, 2011).
Due to its unique performance in treating various
types of wastewater especially industrial wastewater
and landfill leachate which contain large amount of
the toxic and non-biodegradable pollutants as
aforementioned, it can be concluded that
electrochemical oxidation process represents a useful
solution when the existence of refractory and toxic
pollutants prevents the use of conventional biological
treatments. Under suitable operation conditions, a
total removal of COD, color, ammonia and
microorganisms can be achieved.
4. OPORTUNITIES AND CHALLENGES
The appearance of pollutants that are unmanageable
by conventional biological and chemical treatments
together the means of stricter restrictions enforced by
new legislation have resulted in much research work
focus on wastewater treatment via electro-oxidation
processes. Electrochemical oxidation has been found
to be an environmentally caring technology with
capability to remove completely non-biodegradable
organic compounds and eliminate nitrogen species.
Recently, the researchers in this field directed their
work towards two lines: (i) replacement of
conventional processes by electrochemical oxidation
and (ii) integration of electrochemical oxidation into a
treatment plant. As electrical energy is mainly
consumed in electrochemical oxidation process, the
use of photovoltaic (PV) modules as a power supply is
also expected to reduce the operating costs
(Klamklang et al., 2012; Anglada et al., 2009).
Indeed, high energy consumption is generally
required, limiting the further full-scale marketable
application. Two steps have been taken to reduce
treatment costs; (i) the use of this technology in
combination with other techniques as either a pre-
treatment or as a polishing step and (ii) the use of
renewable energy sources to power electrochemical
oxidation (Anglada et al., 2009). In addition to the
energy consumption, during the process design some
critical issues are important to be considered
especially in the design of electrodes and cells. These
include cost, safety, simplicity of maintenance, and
ease to use. It is also necessary that the performance
of the electrodes is maintained during the expected
operating life of the cells (Klamklang et al., 2012).
Although it has been confirmed that
electrochemical oxidation is a technically practicable
Bashir et al.
Electrochemical Oxidation Process Contribution in Remediating Complicated Wastewaters
89
option to eliminate organic pollutants, the partial
oxidation of ammonia to nitrate ions has been
reported. The deployment of electrochemical
oxidation in combination with other process such as
ion exchange (Cabeza et al. 2007) as a post treatment
step could be a plausible solution to this issue.
Consequently, Comninellis et al. (2008) had
demonstrated the promising results obtained from the
treatment of industrial wastewaters via combined
methods involving electrochemical oxidation have
built up foundation for upcoming works. Contriving a
sustainable process based on the combination of
efficient technologies is one of the key obstructions
that need to be overcome before full-scale
implementation of electrochemical oxidation.
Table 2: Application of electrochemical oxidation process in waste water treatment
Type of wastewater
Electrode material
Performance
references
Slaughterhouse
Wastewater
aluminum
96.8% color, 81.3% BOD, and 85.0%
COD removals.
Awang et al.(2011)
Textile Wastewater
iron electrode
78% COD, and 92% turbidity removals
Kobya et al. (2009)
Textile Wastewater
graphite electrodes
100% dye removal
Kariyajjanavar et al.
(2011)
Landfill leachate
graphite Carbone
68%COD, 84% color, and 70% BOD
removals.
Bashir et al. (2009)
Landfill leachate
30% RuO2 and 70% TiO2
coated titanium
73% COD, 57% TOC, 86% color
removals
Moraes and
Bertazzoli, (2005)
Industrial paint
wastewater
stainless steel
44.3% COD, 86.2% color, and 87.1%
turbidity removals
(Körbahti and
Tanyolaç, 2009)
paper
mill effluents
-A cylindrical lead sheet as
anode
- a cylindrical stainless steel
sheet as cathode
97% COD, and 100% color removals
El-Ashtoukhy et al.
(2009)
paper
mill effluents
-Ti/RuPb(40%)Ox as anode
-Ti/PtPd(10%)Ox as
cathode.
99% COD and 95% of color and
polyphenols removals
Zayas et al. (2011)
Olive oil mill
Effluents
RuO2 coated Ti
99.6% COD, 99.85% turbidity, and
99.54% oil-grease removals
Un et al.(2008)
Pharmaceutical
Wastewater
Carbon electrode
35.6% COD removal
Deshpande et al.
(2012)
Tannery
Wastewater
-graphite cathodes
-Ti/SnO2/PdO2/RuO2 anode
72.9 % COD removal
Naumczyk and
Kucharska (2011)
5. CONCLUSION
Wastewater treatment by electrochemical oxidation
process was established in a laboratory scale for many
years. However, electrochemical oxidation
technologies have not reached real application
maturity in commercial scale perhaps due to the
limitation of comparatively high capital investment
and the cost of electricity supply. Consequently,
operating cost reduction and efficient electrode
materials manufacturing are the main problems need
to be overcome before the site-scale accomplishment
of electrochemical oxidation in wastewater treatment.
ACKNOWLEDGEMENTS
The authors are grateful for the financial support
provided by the Universiti Tunku Abdul Rahman
(UTAR) through grant No:
IPSR/RMC/UTARRF/2012-C2/M03.
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treatment: fundamentals and review of
applications Emerging Technologies. J Chem
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Wastewater Engineering: Types, Characteristics and Treatment Technologies
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... Among the powerful advanced decay techniques, the unintended electrooxidation process is a viable alternative to microscopically destroying large amounts of weight, especially eliminating contaminants, and high conductivity wastewater conditions. It will be a promising technology using powerful oxidants to destroy the natural load of these processes (ACS) [35]. Electron transfer to the anode (reaction (3)) produces ACS from chloride in the Journal of Environmental and Public Health water and communicates with water to produce hypochlorous acid (kickback (4)). ...
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Advanced oxidation comprises a range of similar but different chemical processes aimed at tackling pollution in water, air and soil. Over the past few decades, multidisciplinary research has been carried out to study a broad spectrum of topics such as understanding of process fundamentals, elucidation of kinetics and mechanisms, development of new materials, modelling, process integration and scale-up. This article identifies and discusses certain directions that seem to advance R&D on advanced oxidation for water/wastewater treatment. Copyright © 2008 Society of Chemical Industry