Biogas Efficiency and Microbial Community Characteristics in Thermophilic Anaerobic Digestion of Kitchen Waste

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Anaerobic digestion of kitchen waste (KW) for biogas production has significant promise both economically and environmentally. However, low biogas production and fluctuating methane concentration remain key challenges that need to be overcome to make this a viable solution. This study implements a two-stage evaluation framework to link temperature-dependent microbial characteristics with process optimization. First, high-throughput sequencing was performed across a wide temperature gradient (25 °C, 37 °C, 45 °C, 50 °C, 55 °C, and 60 °C) to characterize the baseline microbial community screening and succession trajectories of methanogenic archaea. Based on the identified thermophilic transition threshold, five batch anaerobic reactors were subsequently configured under the target thermophilic condition (50 ± 1 °C) with substrate-to-inoculum (S/I) ratios calculated on a volatile solids (VS) basis (1:0, 1.5:1, 1:1, 1:1.5, and 1:2) to evaluate the biomethane potential, organic removal rates, and volatile fatty acid (VFA) conversion. The results showed that an optimal S/I ratio of 1:1 was crucial for maximizing methane production performance, achieving the highest cumulative biogas yield of 1494.07 mL/g VS and methane yield of 746.28 mL/g VS. Notably, Methanoculleus and Candidatus Methanoplasma were identified as the core functional methanogens enriched at high-temperature stages. Both genera are obligate hydrogenotrophic methanogens that consume H2 and CO2 as substrates, and their enrichment plays a vital syntrophic role in alleviating intermediate acid accumulation and maintaining steady methanogenesis. This study provides clear theoretical insights and experimental data supporting the efficient thermophilic utilization of KW via precise microbial load balancing.

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