Effect of biochar addition on microbial community and methane production during anaerobic digestion of food wastes: The role of minerals in biochar.

The effect of biochar addition on the microbial community and methane (CH4) production during anaerobic digestion was experimentally investigated, focusing on the role of minerals in biochar. The biochar was prepared from pine sawdust by pyrolysis at 650 °C and 900 °C, respectively, and a subsample was leached with citric acid. The cultures with the addition of biochar, leached biochar, Fe, and leached biochar combined with Fe, respectively, were placed in bench-scale bioreactors for anaerobic digestion. Daily biogas production was measured by volume displacement method and analysed for CH4 concentration, which allowed the cumulative CH4 yield (YM) and daily CH4 production rate (RM) to be determined. Culture samples were also taken daily for volatile fatty acids (VFAs) and microbial community analysis. Compared to the control without biochar addition, the addition of raw biochar significantly increased YM by 46.9% and RM by 43.0%, while leached biochar only increased the YM by 33.2% and RM by 18.2%, respectively. The Fe-containing minerals in biochar were found to enhance VFA degradation and increase population of Clostridia and Methanosaeta, improving the CH4 production.