Effect of extracellular polymeric substances removal and re-addition on anaerobic digestion of waste activated sludge

Extracellular polymeric substances (EPS) play a key role in anaerobic digestion of excess sludge. The influence of EPS removal and re-addition on sludge anaerobic digestion were investigated by batch experiment. The results showed that both EPS removal and re-addition improved sludge anaerobic digestion, the cumulative methane production increased by 14.9 % and 50.4 %. EPS removal promoted sludge hydrolysis and acidification, the soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFAs) concentration increased by 31 % and 29 %. The re-addition of EPS increased the substrate of sludge fermentation, resulting in 1.64 and 1.77 times higher SCOD and VFAs concentration than that of control group. In addition, EPS contained lots of electrochemically active substances, and re-adding EPS increased the electron transfer system activity in anaerobic digestion by 164 %, which enhanced significantly methane production. Both removal and re-addition of EPS altered the microbial community structure in anaerobic digestion, the bacteria with hydrolysis and acidification functions were enriched, such as Chloroflexi and Desulfobacterota. Methanobacterium and Methanosaeta were the dominant methanogens in anaerobic digestion systems, and their relative abundance were increased by removing and re -adding EPS.