Response of hydrolysis, methanogenesis, and microbial community structure to iron dose during anaerobic digestion of food waste leachate

Anaerobic digestion (AD) of biodegradable organics depends heavily diverse functional genera, but an attempt to simultaneously enhance the various AD phases including the rate-limiting step (hydrolysis acidification) and methanogenesis has often remained a challenge. Although zero-valent iron (ZVI) supplementation had been proposed by many, its effect on the biomethanation process and microbial community evolution has not been fully explored. In this study, the response of hydrolysis acidification, methanogenesis, kinetics, pollutant removal efficiency, and microbial community evolution to various doses of ZVI employed in AD of food waste leachate was investigated and reported. When 10 g/L ZVI was dosed in the AD system, hydrolysis acidification, COD removal, biomethanation, and methane percentage were elevated by 18.9%, 67%, 39%, and 36%, respectively, as opposed to the control reactor (R1). Kinetics (R2 of 0.998) revealed shorter lag phase (ƛ = 4.18 days) in ZVI-dosed reactors in contrast to longer periods (6.54 days) in R1. Methane production rate constant (k), sludge activity, and methane production rate estimated were 0.066 (day−1), 0.83 gCH4/gVSS, and 64.20 mLCH4/gVSS/day, respectively, suggesting ZVI promoted methane production rate. Hydrolytic and methanogenic phyla including Firmicutes, Chloroflexi, Bacteroidetes, and Euryarchaeota were more enriched in ZVI-dosed reactors as opposed to R1. Acetoclastic-(Methanosaeta) and hydrogenotrophic-(Methanobacterium) methanogens were the most abundant genera of the archaea within ZVI-dosed assays, indicating acetoclastic methanogenesis was the main pathway.