Effects of green waste participation on the co-digestion of residual sludge and kitchen waste: A preliminary study

Anaerobic co-digestion has been extensively applied in treating residual sludge (RS) and kitchen waste (KW). However, some problems still occur in co-digestive system. This study tries to add green waste (GW) as co-substrate into RS/KW co-digestive system to improve methane production and system stability. The results showed that K4 group (RS:KW:GW = 2:1:0.5, based on VS addition, similarly hereinafter) presented the highest specific methane yield (SMY) of 303.4 mL/g VS, as well as the highest acetic acid (HAc) concentration at the primary stage. An appropriate amount of GW addition into co-substrate mixture was conducive to guaranty continuous degradation and conversion of the organics, and it could also improve the stability of the digestive system and optimize volatile fatty acids (VFAs) composition structure. Buswell formula was used and showed that the highest biodegradability index (BI) was obtained in K4 (97.0%) and K5 (98.2%). Besides, the fitting results of kinetic models were used to analyze methane production and hydrolytic process. The enzymes activity and microbial diversity results of K4 group can also verify the results above.