OVERVIEW: This paper provides an overview of some fundamental aspects of electrochemical oxidation and gives updated information on the application of this technology to waste-water treatment. In recent years, electrochemical oxidation has gained increasing interest due to its outstanding technical characteristics for eliminating a wide variety of pollutants normally present in waste-waters such as refractory organic matter, nitrogen species and microorganisms.IMPACT: The strict disposal limits and health quality standards set by legislation may be met by applying electrochemical oxidation. However, treatment costs have to be cut down before full-scale application of this technology. Deployment of electrochemical oxidation in combination with other technologies and the use of renewable sources to power this process are two steps in this direction. APPLICATIONS: Effluents from landfill and a wide diversity of industrial effluents including the agro-industry, chemical, textile, tannery and food industry, have been effectively treated by this technology. Its high efficiency together with its disinfection capabilities makes electro-oxidation a suitable technology for water reuse programs. c 2009 Society of Chemical IndustryKeywords: electrochemical oxidation; waste-water treatment; process development; advanced oxidation processes

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During the electrochemical oxidation of real wastewaters, the different species present in the effluent may interact creating complex scenarios making the prediction of the behavior of the whole system difficult. In this paper the different phenomena that occur during the electro-oxidation process of landfill leachate at a pilot plant scale with boron-doped diamond (BDD) anodes are elucidated. The total BDD anode area of the pilot plant was 1.05 m2. The evolution of the concentration of chloride ions, chlorate, and inorganic carbon and the value of pH and redox potential were found to be inter-related. In turn, the concentration of chloride affected the oxidation of ammonia, which took place through indirect oxidation by active chlorine. Moreover, chloride ions competed with organic matter to be oxidized at the anode. The effect of current density was also investigated. Organic matter and ammonia oxidation were highly influenced by the applied current density value. A change in the mechanism of organic matter oxidation was observed when high current densities were applied. Two mathematical models, previously applied to the oxidation of synthetic wastewaters in the literature, were able to predict the evolution of chemical oxygen demand and ammonia for low current density values.

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Two of the main drawbacks to be overcome before full scale implementation of boron-doped diamond electro-oxidation were addressed in this work; its energy consumption and hazard of formation of chlorinated organics. This was framed within a study in which the technical and economic feasibility of BDD electro-oxidation of landfill leachate was evaluated at pilot scale. On one hand, its technical feasibility was assessed based on COD and NH(4)(+) removal, allowing the selection of the operation conditions that provide optimal energy efficiency, and special attention was paid to the risk of formation of undesired by-products such as nitrite, nitrate ions and trihalomethanes. On the other hand, treatment costs were estimated based on energy consumption required to reach the disposal limits to natural watercourses established by legislation. The results were compared with those of other commonly used AOPs. Under the operating conditions studied, the concentration of COD decreased below the disposal limit (160 mg L(-1)) and ammonia concentration reached values as low as 30 mg L(-1). The energy consumption needed was estimated at 54 kWh/m(3) and the formation of chlorination by-products appeared to be low as the maximum total trihalomethane concentration detected was 432 microg/L.

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