Accelerating anaerobic digestion of lignocellulosic digestate via chelator-mediated Fenton treatment and microbial community acclimatization

As a major byproduct of anaerobic digestion (AD), lignocellulosic digestate contains carbon-rich organic material that can be used as a soil amendment in agriculture or further valorized to maximize biomethane recovery—the focus of this research. We previously reported that chelator-mediated Fenton (CMF) treatment enhanced biomethane yield from lignocellulosic residues, with the extent of improvement varying based on the level of substrate oxidation and the microbial composition of the inoculum. The inoculum-dependent results suggested that acclimatizing the inoculum to CMF-treated digestate can further enhance AD by promoting the enrichment of a core microbial community. To test this hypothesis, we conducted four sequential AD runs under thermophilic conditions to examine how inoculum acclimatization affects the biodegradation of CMF-treated digestate with low or high oxidant dosages. CMF treatment alone yielded a four- to sixfold increase in methane production compared to untreated controls. Subsequent acclimatization further improved methane productivity by eliminating lag phases, maximizing methane production rates for both substrates, and significantly shortening the time to reach maximum biomethane potential (BMP). Digestate oxidized at the lower dosage exhibited an additional 20% increase in BMP following acclimatization, approaching methane yields previously observed only in highly oxidized digestates. These improvements coincided with microbial community restructuring, characterized by a decrease in alpha diversity and enrichment of microorganisms commonly associated with hydrolysis and acidogenesis. Microbiome acclimatization to CMF-treated digestates revealed a previously underappreciated adaptive response to chemically oxidized substrates, leading to improved anaerobic digestion kinetics and the potential to reduce oxidant usage while sustaining process performance.