Improving anaerobic digestion performance after severe acidification: Unveiling the impacts of Fe3O4-bentonite composites in co-digestion of waste activated sludge and food waste

Acidification recovery in anaerobic digestion of food waste is challenging. This study explored its in-situ recovery using a co-substrate of food waste and waste activated sludge. Fe3O4 and bentonite were used as conductor and carrier, respectively, to enhance AD performance under severe acidification. The application of Fe3O4-bentonite resulted in a 152% increase in cumulative methane in the Fe3O4-bentonite 10 digester, demonstrating its effectiveness in restoring the acidified AD system. In acidified systems, bentonite enhanced the diversity and richness of microbial communities due to its buffering capacity. The excessive non-conductive polysaccharides excreted by bacteria in extracellular polymeric substances reduced the possibility of electron transfer by Fe3O4. However, in the synergistic application of Fe3O4 and bentonite, this resistance was alleviated, increasing the possibility of direct interspecies electron transfer, and accelerating the consumption of volatile fatty acids. This approach of integrating carrier and conductive materials is significant for in-situ restoration of acidified systems.