Mechanism study of improving anaerobic co-digestion performance of waste activated sludge and food waste by Fe3O4

Abstract

A large amount of waste activated sludge (WAS) and food waste (FW) are produced every year in China. Anaerobic co-digestion is considered to be an effective way to solve this problem. This study applied FW/WAS mixture as co-substrate to create different digestive environment, aiming to understand the mechanism of Fe₃O₄ particles in promoting AD performance. The results showed that the addition of Fe₃O₄ presented various performances when facing different digestive acidification stress brought by different mixing ratios of WAS and FW. Methanogenic pathways and microbial communities varied with substrates' properties. For group A (WAS mono-digestion), the acetoclastic methanogens dominated, 20 mg/g VS (according to the iron element) Fe₃O₄ could promote methane production, while 200 mg/g VS Fe₃O₄ would inhibit microbial activity. The promoted methane production by Fe₃O₄ was attributable to the promotion of sludge hydrolysis. For group B (WAS: FW = 1:0.5, based on VS addition, similarly hereinafter), Fe₃O₄ triggered direct interspecific electron transfer (DIET) between bacteria and methanogens. For group C (WAS: FW = 1:1), the hydrogenotrophic methanogens dominated, bacteria excreted more non-conductive polysaccharides in EPS to resist unfavorable environment, thereby it prevented their contact with Fe₃O₄ particles. So, it was difficult for Fe₃O₄ to trigger DIET and promote the digestive performance of batch experiments in such condition.

Keywords: Anaerobic co-digestion; Direct interspecific electron transfer; Extracellular polymeric substances; Food waste; Microbial community; Waste activated sludge.