Remediation of groundwater polluted with lindane production wastes by conductive-diamond electrochemical oxidation

Abstract

This work studies the remediation of groundwater saturated with dense non-aqueous phase liquid (DNAPL) from lindane production wastes by electrochemical oxidation. DNAPL-saturated groundwater contains up to 26 chlorinated organic compounds (COCs), including different isomers of hexachlorocyclohexane (HCH). To do this, polluted groundwater was electrolysed using boron-doped diamond (BDD) and stainless steel (SS) as anode and cathode, respectively, and the influence of the current density on COCs removal was evaluated in the range from 5 to 50 mA cm−2. Results show that current densities higher than 25 mA cm−2 lead to the complete removal and mineralisation of all COCs identified in groundwater. The higher the current density, the higher the COCs removal rate. At lower current densities (5 mA cm−2), chlorobenzenes were completely removed, and degradations above 90 % were reached for COCs with more than five chlorine atoms in their molecules. The use of BDD anodes promotes the electrochemical generation of powerful reactive species, such as persulfate, hypochlorite or hydroxyl radicals, that contribute to the degradation and mineralisation of COCs. The applied current density also influences the generation of these species. Finally, no acute toxicity towards Vibrio fischeri was observed for the treated groundwater after the electrochemical oxidation performed at 5 and 10 mA cm−2. These findings demonstrate that electrochemical oxidation with BDD anodes at moderate current densities is a promising alternative for the remediation of actual groundwater contaminated with DNAPLs.