Process Performance and Microbial Communities in Anaerobic Co-digestion of Sewage Sludge and Food Waste with a Lower Range of Carbon/Nitrogen Ratio

In anaerobic digestion (AD) system, the C/N ratio can affect utilization efficiency of organic matter and microbial community structure, thereby influencing methane production. This study investigated that the C/N ratio in AD of sewage sludge (SS) suitably enhanced by adding food waste (FW) to improve methane production efficiency. The effects of different C/N ratios (9, 11, 13, and 15) on dry thermophilic anaerobic co-digestion of SS and FW and the microbial community structure were researched. The cumulative methane production at C/N ratio of 11 reached 165.68 +/- 11.88 mL/g VSadded which increased by 1.23 times compared with the mono-digestion of SS; and the cumulative methane production increased by 8.15 - 63.55% at C/N ratios of 9, 13, and 15. The methanogenic pathway changed from acetoclastic methanogenesis process to hydrogenotrophic methanogenesis process with the increasing of C/N ratio. Redundancy analysis explained that the C/N ratio had obvious effects on the variation of the microbial phylum and genus, which contributed 21.63% and 29.27%, respectively. The C/N ratio of 11 enriched the dominant bacterial phyla (Firmicutes and Thermotogae) and increased the methanogens diversity at genus level. This research found an approach that could improve methane production in the lower C/N range.