Operational thresholds and microbial mechanisms in high-solid anaerobic membrane bioreactors treating swine...

This study investigated swine wastewater treatment using a high-solid anaerobic membrane bioreactor (HSAnMBR), focusing on microbial adaptive mechanisms and process stability under stepwise-increased organic loading rates (OLRs: 5-26 g COD/L/d). The HSAnMBR achieved high efficiency at OLRs ≤ 17 g COD/L/d, with COD removal > 96 % and optimal methane yield (0.28 L CH₄/g COD_removed). However, OLR elevation to 26 g COD/L/d induced volatile fatty acid (VFA) accumulation (5.57 g/L), causing acute methanogenic inhibition that reduced methane yield efficiency by 39 %. System functionality was rapidly restored within 10 days after OLR reduction to 21 g COD/L/d. Microbial analysis revealed divergent diversity dynamics: bacterial alpha diversity peaked at 14 g COD/L/d before declining, while archaeal diversity increased continuously, enhancing functional redundancy. Sludge acclimation enriched key functional taxa (such as Clostridium_sensu_stricto and hydrogenotrophic methanogens), forming a resilient "metabolic complementarity-functional substitution" network that maintained process stability under VFA stress. Metagenomic evidence confirmed metabolic pathway restructuring, including upregulation of hydrogenotrophic methanogenesis genes (e.g., coenzyme F₄₂₀ biosynthesis) and a decline in acetoclastic dominance. This work deciphers the microbial mechanisms enabling high-load operation of HSAnMBRs, establishing the foundation for energy-efficient swine wastewater valorization.