Enhanced nitrobenzene biotransformation by graphene-anaerobic sludge composite

BACKGROUND Traditional anaerobic bioprocesses have failed to achieve the efficient biotransformation of nitrobenzene. Thus, graphene-anaerobic sludge composite as a novel biocatalyst was proposed for the enhancement of nitrobenzene biotransformation. RESULTS Reduced graphene oxide/anaerobic sludge (RGO/AS) composite presented good settling performance when graphene oxide (GO) was added into an AS system for 24 h cultivation. The presence of RGO resulted in enhanced nitrobenzene biotransformation by AS, and the highest removal efficiency of nitrobenzene was observed with initial GO (3-5 mu m) vs sludge ratio of 0.075 (w/w). Dehydrogenase activity in the RGO/AS system increased approximately 2-fold over that in the AS system and redox active species appeared in supernatant from the RGO/AS system. The ratio of acetate to propionate increased in the RGO/AS system during glucose fermentation, and nitrobenzene biotransformation by both AS and RGO/AS systems was independent of methanogenesis, but dependent on acetogenesis. Moreover, bound and free extracellular polymeric substances (EPS) from RGO/AS composite were involved in direct biotransformation of nitrobenzene, and bound EPS might interact with secreted redox active species to accelerate nitrobenzene biotransformation by extracellular electron transfer. CONCLUSION RGO/AS composite was efficient for the treatment of nitrobenzene wastewater. (c) 2013 Society of Chemical Industry