Efficient reduction of nitrobenzene by sulfate-reducer enriched biocathode in microbial electrolysis cell

This study aimed to enhance treatment of wastewater containing nitrobenzene (NB) and sulfate using biocathode enriched with sulfate-reducing bacteria in microbial electrolysis cell (MEC). Artificial wastewater with 50 mg L^-1 NB and 200 mg L^-1 sulfate was used as the catholyte. With 0.8 V applied voltage, removal efficiencies of NB and sulfate reached 98% and 34%, respectively, within 36 h. Aniline and sulfide were the main reductive products in the catholyte with concentrations increased to 0.32 and 0.51 mM, which accounted for 97% and 78% of the removed NB and sulfate, respectively. Sulfate-reducer Desulfovibrio sp. and Wolinella sp. played the dominant role in the biocathode for the reductions of sulfate and NB. Analyses of scanning electron microscope and X-ray photoelectron spectroscopy showed the formation of elemental S on the biocathode surface. The relative abundance of sulfur-oxidizing bacterium Thioclava sp. reached 24% on the biocathode. The results indicated that the oxidation process from S^2- to S⁰ occurred on the biocathode, which provided electrons to biofilm for NB reduction. The MEC with sulfate-reducer enriched biocathode can be used as an alternative to treat complex wastewater containing NB and sulfate.