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

Abstract

Anaerobic digestion (AD) represents a high-efficiency approach for resource recovery from organic wastewater. The metabolic imbalance and sluggish electron transfer between syntrophic anaerobic microorganisms is the key limiting factor for methanogenesis in AD process. To better address this issue, a carbonized Fe-based metal-organic framework (CMIL-800) was strategically developed in this study. The CMIL-800 was characterized by the integration of uniformly dispersed Fe single atoms and their ultrafine clusters with the carbon substrate, which fundamentally minimized the interfacial charge-transfer resistance and established localized potential differences on the interface to actively drive interspecies electron transfer in AD process. Furthermore, the exceptional charge capacity and proton-conduction capability of CMIL-800 can provide multiple-mediatory pathways for maintaining microbial metabolic equilibrium and accelerating methane conversion. Experimental results showed that the AD efficiency was effectively improved via the addition of CMIL-800. 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.