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Leachate originating in landfills where municipal solid wastes are disposed is a wastewater with a complex composition that could have a high environmental impact. The primary goal of this research was to investigate the feasibility of removing refractory organic pollutants and ammonium nitrogen from landfill leachate by electrochemical oxidation. The effects of current density, pH, and chloride concentration on the removal of both chemical oxygen demand (COD) and ammonium nitrogen were investigated. Titanium coated with lead dioxide (PbO 2 ) or tin dioxide (SnO 2 ) was used as the anode. An effective process was achieved in which the leachate was decolorized, COD was removed up to a value of 100 mg L -1 , and ammonia was totally eliminated. Average current efficiency of about 30% was measured for a decrease of COD from 1200 to 150 mg L -1 , while efficiency of about 10% was measured for a near complete removal of ammonium nitrogen, starting from an initial value of 380 mg L -1 . Results indicated that the organic load was removed by both direct and indirect oxidation. Indirect oxidation by chlorine or hypochlorite originating from oxidation of chlorides is believed to be mainly responsible for the nitrogen removal.

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In this work the products of the oxidation at BDD anode of chloride ions in aqueous solutions were identified during galvanostatic electrolyses performed in a filter-press reactor operating both in batch and continuous mode. A set of experiments were preformed in order to study the effect of operating conditions (current density, residence time, hydrodynamics and chloride concentration) on distribution and concentration of electrolysis by-products. As a comparison experiments were also performed using a commercial DSA anode. A simple mathematical model was formulated, and the model predictions agree with the experimental data in a wide range of experimental conditions. The results of this work showed that at low chloride concentrations electrolysis with BDD anode produce a mixture of powerful oxidant: low current density, high mass transfer conditions and low residence time were found as optimal conditions to maximize the concentration of oxidants and minimize the concentration of chlorates. The proposed reaction mechanism may also justify the controversial effect of chloride ions in wastewater treatments: the electrolysis carried out with BDD anodes and electrolyte containing chloride concentration higher 1 g/L could meet the target of the process only if the active chlorine is effective in oxidation of the pollutant that must be removed

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