Electrochemical treatment of drainage water from toxic dump of pesticides and degradation products

Polluted drainage water from a dump of toxic chemical waste containing organophosphoric pesticides and their natural degradation products was treated with electrochemical oxidation in order to investigate the applicability of the technique in remediation of natural complex polluted water. The dump is located adjacent to the sea in sand dunes, the natural salinity of the investigated water was 0.7 w/w% and sodium chloride served as main electrolyte. A commercial available flow cell with a tubular design, Ti/Pt-90-Ir-10 anode, and 316 SS cathode was applied, and the electrolysis experiments were conducted in a batch recirculation experimental set-up. COD measurements showed that the overall oxidation of organic and inorganic substances followed first-order kinetics by the current densities investigated, 310-1131 mA cm(-2), and the COD removal rate increased by increased current density and to a minor extent by increased salinity up to 2.0 w/w%. Evaluation of ICE and energy consumption showed that further optimization is possible and needed. The target organic pollutants parathion, methyl-parathion, malathion, ethylaminoparathion, paraoxon, and several phosphoric triesters were all degraded during the treatment except O,O,O-triethylphosphoric acid, a compound formed during the electrochemical process with a highly stable low energy structure, rendering it recalcitrant to participate in the oxidation reaction. The degradation of the subjected organics was found to be caused by indirect oxidation by the hypochlorous/hypochlorite pair as the main oxidizing agent, produced by the anodic oxidation of chloride. The study has showed that electrochemical chloride mediated indirect oxidation is a relevant, neat and possible solution for the remediation of organophosphoric pesticide polluted natural water. (C) 2008 Elsevier Ltd. All rights reserved.