Study on the performance of HNO3-modified biochar for enhanced medium temperature anaerobic digestion of food waste.

Abstract

Biochar can help promote direct interspecies electron transfer (DIET) and increase methane production; the surface redox groups play a constructive role in these processes. This study attempted to improve the anaerobic digestion (AD) performance by modifying biochar with HNO3 to increase its redox activity. A comparative experimental study, raw biochar (BC0) and biochar treated with HNO3 for 6h (BC6), were conducted to investigate the effect of HNO3 treatment on the medium temperature AD performance of food waste. Both BC0 and BC6 can enhance CH4 yield and facilitate the degradation of volatile fatty acids. The enhanced yield of CH4 was 36% for BC0 and 90% for BC6, respectively. Biochar can also enhance methanogenesis, presumably owing to direct interspecific electron transfer (DIET). Compared with BC0, BC6 had a higher redox activity and a smaller conductivity. It was supposed that BC0 mediated DIET through its conductivity, whereas BC6 accelerated DIET by surface redox groups.