Food waste enhanced anaerobic digestion of biologically pretreated yard waste: Analysis of cellulose crystallinity and microbial communities

[Display omitted] •A joint pretreatment method for yard waste using sludge and food waste was proposed.•An increase of 20.3–53.1% was achieved in reduction of cellulose and hemicellulose.•23% cellulose crystallinity decreased during pretreatment period due to food waste.•Methane yield increased by 35% by co-pretreatment of sludge and 10 wt% food waste.•Bacteria Sphaerochaeta and Cellulosibacter were selectively enriched by 5–10 times. Solid waste treatment through anaerobic digestion (AD) technology contributes to energy recycling and reuse of various solid organic wastes. However, yard waste (YW) is generally recalcitrant to AD due to the presence of high cellulose and hemicellulose content, which are difficult to be hydrolyzed. In this study, to enhance hydrolysis efficiency, YW was biologically pretreated with digested sludge and supplemented with food waste (FW) before AD process. Effects of FW supplementation on pH, SCOD, cellulose and hemicellulose content and cellulose crystallinity were examined. The optimal amount of FW supplementation was determined to be 10 wt%. An increase of 6.5–20.3% in cellulose reduction and an increase of 14.8–53.1% in hemicellulose reduction in digesters was achieved within the optimal pretreatment time of 4 days. After hydrolysis, cellulose crystallinity decreased by 23% from 71% in the control digester, which was responsible for improved biodegradability of cellulose in YW. FT-IR analysis of hydrolysis mixture confirmed that partial hydrogen bonds were destroyed in digesters with supplementation of 10 wt% FW, leading to a higher extent of degradation of the feedstock. In the batch AD of FW supplemented YW, results indicated that methane yield was 35% higher than that of the control digester without FW supplementation. Pyrosequencing analysis indicated that the abundance of bacterial genus Sphaerochaeta and Cellulosibacter in subsequent digestion were enhanced by 10- and 5-folds by 10 wt% FW supplementation, respectively, and were deemed to be responsible for the enhanced anaerobic digestion performance.