Labile carbon feedstocks trigger a priming effect in anaerobic digestion: An insight into microbial mechanisms.

The mechanisms underlying the advanced performance in anaerobic co-digestion (AcoD) are crucial but remain elusive. This study conducted AcoD of swine manure, rice straw and apple waste (AW, mainly consisting of labile carbon) or fructose (a pure labile carbon), and monitored microbial community abundances, activities and transcriptional profiles in the digestate and on straw. The transformation efficiencies of manure (not straw) to CH were promoted in AcoD co-fed manure and AW (by 39 ± 13%) or fructose (by 65 ± 14%), compared to the control mono-fed manure, implying labile carbon could trigger a priming effect underlying AcoD advantage. Although digestate-associated and straw-associated communities existed in a same bioreactor, the priming effect mainly linked to the former and was attributed to enhancements in deterministic turnover of active communities, in activities of Firmicutes taxa involved in substrate hydrolysis, and in acetoclastic methanogenesis. These findings provide novel insights to elaborate AcoD processes.