Feeding regime selectively enriching acetoclastic methanogens to enhance energy production in anaerobic digestion systems

Applying the r/K selection theory to explore the distribution patterns of acetoclastic methanogens under varying conditions is rare, although it can offer a basis for optimizing community structure and enhancing methane production in anaerobic digestion systems. Different operating modes (sequencing batch reactors, SBRs; and continuous-flow reactors, CFRs) and solids retention times (SRTs; 15 and 50 days) were adopted to acclimate different acetoclastic methanogens in acetate-fed anaerobic reactors. SBRs exhibited a significantly higher CH 4 production rate than CFRs ( P = 0.037). Methanosarcina exhibited a higher relative abundance in SBRs (13.7 ∼ 16.1 %) than in CFRs (0.2 ∼ 0.3 %), aligning with its typical r-strategist characteristics. Methanothrix showed a higher enrichment in CFRs (33.1 ∼ 39.6 %) compared to SBRs (26.8 ∼ 29.9 %) at the same SRT, indicating K-strategist behavior. The SBRs had the potential to co-enrich both types of methanogens. Feeding regimes played a more pivotal role in the distribution of methanogens than SRT. The dominant bacteria, such as Desulfococcus and Mesotoga , as well as the archaeon Methanothrix , were auxotrophic in some essential amino acids, implying potential cross-feeding interactions. This study provides key insights into ecological strategies by linking microbiology with environmental technologies to enrich target methanogenic communities and enhance methane production. • Methanosarcina exhibited a higher relative abundance in SBRs than in CFRs. • Methanothrix showed a higher enrichment in CFRs compared to SBRs. • SBRs tended to enrich both Methanosarcina and Methanothrix. • Methanothrix might engage in cross-feeding of essential amino acids.