Carbon supported iron-single atoms/ultrafine atom clusters mediated electron-proton coupling transfer for enhanced anaerobic digestion

Anaerobic digestion (AD) represents a high-efficiency approach for resource recovery from organic wastewater. The metabolic imbalance between different anaerobic microorganisms is the key limiting factor for methanogenesis in AD process. To overcome this bottleneck, a carbonized Fe-based metal-organic framework material (CMIL-800) was developed in this study. This material integrated uniformly dispersed Fe single-atoms as well as their ultrafine clusters on the carbon, which generating stable potential differences for actively driving charge transfer in the AD system. Meanwhile, the superior charge capacity and proton transfer properties of CMIL-800 provided additional assurance for microbial metabolic mediation and methane conversion. Experimental results showed that the CMIL-800 can effectively improve the chemical oxygen demand (COD) removal and net methane production during AD process. Kinetic isotope effect (KIE) tests and extracellular polymeric substances (EPS) structural evolution results provided powerful evidence for a simultaneous enhancement in electron and proton transfer rates within the AD system. Moreover, a significant increase in the abundance of genes associated with methanogenesis, proton transfer, and electron transport was also observed, further confirming the multi-dimensional regulatory effects of CMIL-800 on metabolic imbalances among syntrophic anaerobes. In summary, this work provided a novel and efficient strategy for optimizing AD performance.