5. Conclusion

effluent or simultaneous EC and EOx treatment with an appropriate electrode configuration. The aim of sequential EC-EOx is to propose a new approach that combines the synergistic effects of the two methods [47]. Simultaneous EC-EOx offers a hybrid system integrating monopolar (MP) EOx and bipolar (BP) EC in a single reactor that also provides all the advantages of sequential EC-EOx [19]. Recent studies on combined EC-EOx treatment of different kinds of wastewater are presented

Table 3. Simultaneous EC-EOx treatment results of various wastewaters for selected examples in the literature.

Electrical conductivity

(mS/cm)

ranges for parameters

Electrode material Al-Fe Al COD removal:

3–7 5

conditions

) 0.91

pH 8 Color removal:

) 800

) 800

) 2

) 10

) 0.6

Electrolysis time (min) 6 COD removal:

) 30 COD removal:

~94% SEEC: 0.02 kWh/g

100%

100% COD removal: 100% BOD5 removal: 100%

> 97% SEEC: 12 kWh/m<sup>3</sup>

Initial pH 3–9 6

Temperature (C) 10–30 20 Current intensity (A) 0.5–1.5 1

Parameters Optimum

Current density (mA/cm<sup>2</sup>

Current density (mA/cm<sup>2</sup>

Current density (A/m<sup>2</sup>

Treatment time (min) 5

Treatment time (min) 425

Treatment time (min) 30

pH 8 Current density (A/m<sup>2</sup>

Treatment time (min) 150

Electrolysis time (min) 90 Current density (mA/cm<sup>2</sup>

Current density (mA/cm<sup>2</sup>

Optimum conditions Results at optimum conditions

Turbidity removal:

31.6 kWh/kg COD Operating cost: 1.33 \$/m3

Results at optimum conditions

Turbidity removal:

87% Color removal: 100%

100% SEEC:

Ref. Wastewater Electrode material Parameters Research

in Tables 3 and 4.

[18] Textile (synthetic)

[51] Car wash (real)

Ref. Wastewater Electrode

[8] Industrial park (real) EC:

material

EC: Al

EOx: Graphite

Fe

EOx: Anode: BDD Cathode: Fe

EC: Anode: Fe Cathode: Stainless steel

EOx: Anode: BDD Cathode: Stainless steel

[47] Current density (A/dm<sup>2</sup>

[26] Pulp and paper mill (real)

82 Wastewater and Water Quality

Anode: MP graphite Cathode: MP graphite Sacrificial electrode: BP Al or Fe

> Due to the increasing need for freshwater resources and the large number of pollutants produced by the industries, it becomes more and more important to treat and reuse wastewater. For this purpose, effective, economical, and easy-to-operate wastewater treatment technologies need to be developed. Because of the fact that electrochemical treatment methods have various

advantages, they are still investigated extensively. Besides being simple and effective, they are able to remove almost all kinds of pollutants at the same time. They are also eco-friendly and clean due to in situ generation of metal hydroxides and hydroxyl radicals. Many EC and EOx studies have been published on the treatment of industrial wastewaters such as olive mill, textile, dairy, pulp and paper, tannery, pharmaceutical, bilge, refinery, slaughterhouse, food processing, potato chips manufacturing, and leather. It is reported that EC and EOx methods have been successfully applied for removing COD, BOD, oil, phenol, lignin, phosphate, arsenic, color, turbidity, chromium, sulfate, total coliforms, boron, nickel, copper, and pharmaceuticals from wastewaters. Recent studies were briefly presented in this chapter, and it is observed that a minimum of 54.16% COD, 90.4% color, 90% BOD, 37% turbidity, 94.4% phenol, 42.9% phosphate, 72% TOC, and 97% TSS removal efficiencies and a maximum of 45.28 kWh/m3 SEEC were achieved by applying combined treatment. Since EC is a fast and efficient method for wastewaters containing suspended solids but also an inefficient method for the removal of persistent dissolved organic pollutants and EOx is able to mineralize persistent organic pollutants completely but also a slow and energy-consuming method for the removal of suspended solids, combining these two processes offers a practical hybrid by taking advantage of the synergistic effects. According to the results, it can be concluded that combined EC-EOx process is an efficient alternative for industrial wastewater treatment in terms of pollutant removal and more research on applications to the industrial wastewaters are required.

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