Enhancement and monitoring of pollutant removal in a constructed wetland by microbial electrochemical technology

A bench-scale constructed wetland combined with microbial electrochemical technology (MET-CW) was run for 400 days with groundwater contaminated with benzene, methyl-tert-butyl ether (MTBE), and ammonium (NH4+). Four vertically stacked anode modules were embedded into a sand bed and connected with a stainless steel cathode placed in an open water pond. In the zone of presence of anode modules, significantly more benzene and MTBE were removed in the MET-CW compared to the control CW without MET in the first 150 operation days. Benzene was identified as primary electron donor at the anode. Benzene removal and current densities were linearly correlated, implying the potential of the system for electrochemically monitoring benzene biodegradation. Compound-specific isotope analysis (CSIA) indicated that benzene was initially activated by monohydroxylation forming intermediates which were subsequently oxidized accompanied by extracellular electron transfer, leading to current production. NH4+ removal was not stimulated by MET.