Coupling the electrocatalytic dechlorination of 2,4-D with electroactive microbial anodes.

Abstract

This work proves the feasibility of dechlorinating 2,4-D, a customary commercial herbicide, using cathodic electrocatalysis driven by the anodic microbial electrooxidation of sodium acetate. A set of microbial electrochemical systems (MES) were run under two different operating modes, namely microbial fuel cell (MFC) mode, with an external resistance of 120 Ω, or microbial electrolysis cell (MEC) mode, by supplying external voltage (0.6 V) for promoting the (bio)electrochemical reactions taking place. When operating the MES as an MFC, 32% dechlorination was obtained after 72 h of treatment, which was further enhanced by working under MEC mode and achieving a 79% dechlorination. In addition, the biodegradability (expressed as the ratio BOD/COD) of the synthetic polluted wastewater was tested prior and after the MES treatment, which was improved from negative values (corresponding to toxic effluents) up to 0.135 in the MFC and 0.453 in the MEC. Our MES approach proves to be a favourable option from the point of view of energy consumption. Running the system under MFC mode allowed to co-generate energy along the dechlorination process (-0.0120 kWh mol-1 ), even though low removal rates were attained. The energy input under MEC operation was 1.03 kWh mol-1 -a competitive value compared to previous works reported in the literature for (non-biological) electrochemical reactors for 2,4-D electrodechlorination.