electrochemical oxidation process contribution in remediating complicated wastewaters

Wastewater Engineering: Types, Characteristics and Treatment Technologies

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Wastewater Engineering: Types, Characteristics and

Treatment Technologies

Chapter 4: Electrochemical Methods


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Electrochemical Oxidation Process Contribution in Remediating Complicated

Wastewaters

Mohammed J. K. Bashir1,*

, Jun-Wei Lim1, Shuokr Qarani Aziz

2, Salem S. Abu Amr

3

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: [email protected]; 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 (Krbahti and Tanyola 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.



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.


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 L1 H2SO4

Pt 1.6 0.5 mol L1 H2SO4

IrO2 1.6 0.5 mol L1 H2SO4

Graphite 1.7 0.5 mol L1 H2SO4

PbO2 1.9 1.0 mol L1 H2SO4

SnO2 1.9 0.5 mol L1 H2SO4

TiO2 2.2 1.0 mol L1 H2SO4

Si/BDD 2.3 0.5 mol L1 H2SO4

Ti/BDD 2.7 0.5 mol L1 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,



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.


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 pH7.5 (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



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 (Krbahti

and Tanyola, 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 cm

3 /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 80A/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.


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

(Krbahti and

Tanyola, 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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