Biochar enhanced biological nitrobenzene reduction with a mixed culture in anaerobic systems: Short-term and long-term assessments

Biochar as a multi-functional material has been widely used in the fields of catalysis and pollutant removal, but its feasibility to enhance biologic nitrobenzene reduction with the mixed culture and the long-term impact on nitrobenzene removal and microbial structure are lack of a clear clarification. This study aimed at evaluating the feasibility of biochar to enhance anaerobic reduction of nitrobenzene with a mixed culture. We initially investigated the effect of the biochar addition on nitrobenzene removal in short-term experiments and then possible enhancement mechanisms for the biochar were explored. Additionally, the impacts of different key parameters on biological nitrobenzene reduction were studied in the presence of biochar. Moreover, the longterm influence of the biochar on biological nitrobenzene removal with the mixed culture was also evaluated. The results showed that the estimated pseudo first-order rate constant of nitrobenzene removal in the presence of 1.0 g L(-1 )biochar was four times higher than that without biochar addition. The possible enhancement mechanisms may be owing to that biochar could activate the nitrobenzene molecules and accelerate the electron transfer between microbe and nitrobenzene. Additionally, the stimulating level of the biochar on biological nitrobenzene removal remarkably varied under different conditions. Long-term experiments demonstrated that biochar could not only increase nitrobenzene removal rate but also improve the system stability, which may be related to the shift of microbial communities that the relative abundance of nitrobenzene reduction related bacteria as well as electrochemically active bacteria was enriched in biochar addition systems.