Removal of organochlorine pollutants from DNAPL-saturated groundwater using electrolysis with MMO anodes

Abstract

This work evaluates the electrolysis of groundwater saturated with dense non-aqueous phase liquid (DNAPL) from lindane production wastes using mixed metal oxide (MMO) anodes to remove 26 Chlorinated Organic Compounds (COCs). Synthetic groundwater saturated with DNAPL from an industrial landfill was employed, and the influence of the current density (5–50 mA cm−2) was studied. Results show that removing COCs from DNAPL-saturated groundwater in 300 min is possible, reaching a final conversion of 0.99 when current densities of 50 mA cm−2 are applied. Under these operating conditions, the mineralisation conversion achieved is above 0.80. Low molecular weight COCs are rapidly oxidised because the evaporation also contributes to decrease their concentration in groundwater. Chlorine-based electrogenerated oxidants are the main species responsible for the removal of COCs. Toxicity and biodegradability tests performed on treated groundwater reveal that EC50 increases above 65 %, and 100 % biodegradability is obtained. The highest energy efficiencies are obtained during the treatment at 5 mA cm−2 (over 0.03 m3 kW-1h−1 for all COCs) due to the minimisation of parallel oxidation reactions promoted at higher current densities.