Electro-Coagulation and Electro-Oxidation in Water and Wastewater Treatment

Electrocoagulation (EC) is a process that originates from conventional chemical coagulation. EC treatment is generally characterized by simple equipment, ease of operation, short retention time, and negligible use of equipment for adding chemicals, which would contribute to reducing the operating cost in large scale applications. The suitability of EC processes for decentralized sanitation and water treatment in extreme conditions (e.g., in the Nordic regions and remote areas) is explored. Use of EC as primary treatments, secondary treatments, tertiary treatments, and combinations with other treatments is discussed. Details on how to integrate EC into different treatment processes are also given. Effluents from municipal wastewater treatment plants can contain residual phosphorus concentration above the recommended values; the potentially high environmental impact of such high phosphorous concentration (e.g., eutrophication resulting from excess nutrients) is discussed.

For raw water and wastewater, many treatment methods are currently in use. In conventional treatment processes, coagulation-flocculation, followed by gravity sedimentation, is the most common process for removal of colloidal particles from raw water and wastewater. This chapter focuses on the application of the electrocoagulation (EC) process for treating raw water, which was introduced in London in 1889. Fundamentals of EC process treatment of raw water and wastewater are detailed, along with associated advantages and disadvantages. In addition, experimental features, such as current density, anode and cathode material, and the effects of operating parameters on the efficiency of EC processes are evaluated.

The anodic oxidation process has been used for several decades for the treatment of color and certain organic pollutants such as phenol, cyanides, and aniline. For instance, for leachate treatment, electro-oxidation (EO) has yielded satisfactory results when the EO processes are used as a pretreatment step to reduce the load of chemical oxygen demand (COD) and ammoniacal nitrogen or as a tertiary treatment for the degradation of recalcitrant organic pollutants. This chapter focuses on the origins and principles of the EO process, which is considered one of the most powerful treatment methods in water and wastewater treatment. Advantages and disadvantages of this process, along with challenges, are discussed from a variety of perspectives. Also explored are the limitations associated with industrial applications of this method because of relatively high energy consumption, compared to other electrochemical methods.

Several modeling techniques have recently evolved that can accurately simulate and predict the outcome of the electrocoagulation (EC) process. This chapter details some modeling techniques applied to EC processes using various computational tools. The modeling techniques used include artificial neural network (ANN), response surface methodology (RSM), adsorption-based models, and mathematical kinetic equation-based models. The distinct core concepts of these techniques are identified with respect to modeling EC processes; each one has been successfully applied to outcome prediction. Details are also provided on the various critical elements of ANN design.

The electro-oxidation (EO) process has received much attention in recent years because it can be used as an alternative to traditional wastewater treatment methods with increased flexibility. In this chapter, details, and fundamentals of different modeling approaches, including phenomenological, Response Surface Methodology (RSM), and Artificial Neural Networks (ANNs), used for the EO process are provided. Kinetic analysis of the EO process is also reviewed. Identifying the design variables that have the most impact on the EO process and calculating the response variables are the main goals of the Design of Experiment (DoE). The most used DoE methods for EO processes are factorial design, central composite design, Box-Behnken design, Taguchi's design, and Doehlert design.

When wastewater moves through the applied electric field in the electrocoagulation (EC) process, various phenomena, such as ionization, electrolysis, hydrolysis, and electrophoresis may occur. Ultrasound and low pH (i.e., pH < 3) can accelerate free radical and hydroxyl radical formation. However, there is no proof of advanced oxidation processes (AOP) during the EC process. Therefore, AOP and EC processes must be combined for these phenomena to enhance the efficiency of wastewater treatment. This chapter reviews fundamentals and recent developments involving integrated EC processes; these include treatment techniques such as EC-photo-assisted, Sono-EC, EC-Fenton, EC-EO, EC-Peroxidation, and Ozone Assisted-EC processes. The EC process can remove organic, inorganic, and microbial pollutants in water and wastewater by in situ generation of coagulants through electrodes and can be applied as a pre- or posttreatment step, depending on wastewater type.

The combined electro-oxidation (EO) process is an efficient method for the treatment of water and wastewater. It involves the oxidation of organic pollutants, either by direct oxidation of hydroxyl radicles at anode surfaces, or by indirect oxidation in which oxidants are produced by chemical compounds. The factors that determine EO treatment efficiency are electrode material, electrochemical cell design, mass-transport regimen, electrode potential, current density, current input, and electrolysis medium. This chapter provides a review and extensive discussion on the coupling of the EO process with other chemical treatment processes such as TiO₂ photo-assisted processes, sono-electro-oxidation processes, electrochemical-peroxidation processes, electroperoxone processes, electro-Fenton processes, EO filtration processes, and membrane technology. Factors affecting these processes are identified, and case studies are presented.

To address the major challenge of providing clean water to the growing world population, numerous studies have investigated the potential of electrocoagulation (EC) processes for removal of organic and inorganic contaminants (such as heavy metals, ammonia, pharmaceuticals, and hydrocarbons) from water and wastewater. This chapter provides a brief description of treatment of wastewater from various sources using the EC process. It discusses the removal of metals, ions, and anionic species such as fluoride and phosphate from wastewater. Subsequently, EC process procedures for landfill leachate treatment and agroindustrial wastewater are described. Treatment of wastewater from the cheese whey industry, slaughterhouses, restaurants, textiles, and laundry is then examined. Details are included on implementation of EC processes for drinking water treatment.

Electrochemical oxidation (EO) is an effective method for treating wastewater and for disinfection of water. This chapter provides an overview of EO processes employed to remove environmental pollutants from wastewater (WW). Persistent organic pollutants enter the WW treatment facilities from rain, agricultural, domestic, and industrial WW. The presence of pathogens in WW causes serious health problems for treatment plant personnel and community members living near facilities. Also discussed are the main sources of pollution in agricultural WW: toxic substances; organic and inorganic compounds such as heavy metals, pesticides, or plant protection products; phenols; and derivatives used in the farming industry to improve crop yield.

As an emerging technology for water and wastewater treatment, electrocoagulation (EC) unites the concept of coagulation-flocculation (a physicochemical process) with electrochemistry. The existing literature on comparison of classical chemical coagulation (CC), adsorption, and EC have juxtaposed these technologies with respect to their pollutant removal efficiencies and availability of detailed information on which technology is better in terms of energy efficiency, economics, or pollutant removal. In this chapter, the authors critically review the existing literature and provide a technical comparison of the three processes. Wastewater treatment applications of EC in the tannery, food, and pulp and paper industries, as well as in refineries and in municipal treatment plants are examined. Some available software tools that can assist in performing real-life technoeconomic analysis using software resources are evaluated.

Electro-oxidation (EO) has shown enormous potential in wastewater treatment and organic pollutants oxidation. In this chapter, the principles of action, operating conditions, and performance factors associated with EO are described and compared with Fenton, ozonation, photocatalysis, and sonochemical processes. The treatment of organic pollutants by EO processes and economic comparison of these processes are also reviewed. EO can eliminate the organic load of industrial effluents; on the contrary, ozonation and Fenton oxidation may lead to the accumulation of significant amounts of oxidation-refractory compounds. Sonochemistry, ultrasound-based treatment to degrade pollutants applied to water treatment, is evaluated as an advanced oxidation process. Applications of EO when used in the context of biological processes are also explored; these include transforming non-biodegradable compounds into biodegradable products, use in final treatment for the complete oxidation of organic compounds to carbon dioxide.

In this chapter, the authors investigate the scale-up and design criteria of EC, focusing on economics, crucial factors, reactor types and operating conditions, current commercial plants and companies, types of wastewater and pollutants, and current challenges and possible solutions. EC is a method that, unlike coagulation, prevents the introduction of soluble anions (sulfate or chloride) into a system. An EC reactor's configuration consists of an electrolytic cell with one anode and one cathode in simplest form. Optimum operating conditions of EC are examined, along with treatment of various types of wastewaters and removal of some contaminants by EC.

In recent decades, electro-oxidation (EO) has gained increasing interest for treatment of water and wastewaters, mainly because of its high efficiency in the removal of biorefractory substances. EO has been employed to treat the wastewater generated in various industries. This chapter provides an overview of fundamental aspects of EO in wastewater treatment and the scale-up of this technology in the context of essential design parameters. The EO mechanism and EO design criteria are summarized. Some coupled systems employed for EO-based wastewater treatment are described. The remediation of several types of wastewaters by EO is then explored, with a focus on the different contaminates. Finally, critical challenges pertinent to EO and recommendations to surmount the implementations are presented.

This chapter investigates applications of electro-coagulation (EC) and electro-oxidation (EO) processes in wastewater treatment. EC and EO processes are compared with other treatment methods (membrane technology, commercial adsorbents, low-cost adsorbents, and chemical coagulation) in terms of treatment efficiency and economics. The factors impacting cost in electrocoagulation and electro-oxidation processes and other treatment processes are also discussed; the major operating cost component for an EO process is the cost of equipment/reactors, which is a fixed cost and is only an initial requirement. Other major costs that are directly associated with the operation of a treatment system are: cost for power consumption to run the treatment system, cost of electrode material, and cost of reagents needed for the cleaning of electrodes. Also explored are electro-chemical treatment methods that have recently attracted significant attention as eco-friendly processes for wastewater treatment; these include electro-oxidation and electrocoagulation.

Electro-coagulation (EC) has proved to be a low-cost treatment technology because of its ability to effectively remove an extremely wide range of pollutants in diverse types of water and wastewater, as well as its inherent simplicity of design and operation. Electro-oxidation (EO) is an application of electrochemical properties to remove many types of organic, inorganic, and microbial pollutants from water via direct and/or indirect oxidation inside the electrolysis cell. Objectives for future applications of EC and EO treatment include addressing limitations and new approaches to minimize formation of toxic by-products and loss of efficiency, improving design and operation, minimizing power consumption, and identifying the direction of future development. Therefore, in this chapter, the drawbacks of the EC and EO processes are discussed, with recommendations for future research to make EC and EO more obvious economic and environmental choices for treatment of water and wastewater.

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