Magnetically controlled non-conductive microbial carrier-mediated anaerobic digestion of sewage sludge

Magnetic porous microspheres (MPMs) have been used to enhance the anaerobic digestion (AD) of sludge. However, the feasibility of using MPMs as magnetically controlled microbial carriers in long-term AD remains unclear. Herein, without replenishment of MPMs, the methanogenic performance, main physicochemical properties of sludge and methanogenic metabolomics in 150-day MPM-mediated AD were comprehensively investigated. A substantial highly active anaerobes were found to adhere to MPMs, which maintained strong magnetic controllability and structural stability and significantly enhanced methane production (P < 0.001) and the methane proportion in biogas (P < 0.05) from AD at different hydraulic retention times (HRTs). The significant positive correlations between the interfacial Lewis acid-base (AB) interaction (R² > 0.79, P < 0.01) and daily methane production (R² > 0.52, P < 0.01) with water-mediated proton-coupled electron transfer (PCET) indicate that MPM-enhanced AB interactions can accelerate electron transfer by promoting proton movement in interfacial water molecules, thus enhancing methanogenesis during AD. Statistical analyses of variations in activities or contents of key bioenergetic substances on and within anaerobic cell membranes in AD confirmed this observation and simultaneously indicated that MPMs significantly enhanced the bioenergetics of CO₂-reduction methanogenesis by promoting intracellular water-mediated PCET. Microbial community changes show that during the AD under different HRTs, MPMs significantly enriched bacteria capable of decomposing complex organics into acetate and hydrogen in an attached state, as well as free acetotrophic methanogens and attached hydrogenotrophic and hydrogen-dependent methylotrophic methanogens, thereby optimising the spatial distribution of methanogenic consortia. Metagenomics and genome-centric metagenomic analyses confirmed that MPMs significantly enhanced the hydrogen-dependent methanogenesis pathways of the attached methanogenic consortia and promoted energy-conserving metabolic cooperation between free and attached methanogenic consortia, reducing resource competition. Basic economic and environmental analyses revealed that the annual economic benefit increased by 112.2% and carbon emissions decreased by approximately 1.34 × 10⁵ tons CO₂/year with MPM-mediated AD relative to conventional AD. These findings can provide an important reference for the development of exogenous material-mediated AD technology.