Magnetite encapsulated in carbon shell particles (FeO@C) to boost anaerobic methanogenesis of chloramphenicol wastewater.

Magnetite (FeO) is extensively applied to enhance efficacy of anaerobic biological treatment systems designed for refractory wastewater. However, the interaction between magnetite, organic pollutants and microorganisms in digestion solution is constrained by magnetic attraction. To overcome this limitation and prevent magnetite aggregation, the core-shell composite materials with carbon outer layer enveloping magnetite core particles (FeO@C) were developed. The impact of FeO@C with varying FeO mass ratios on the anaerobic methanogenesis capability in the treatment of chloramphenicol (CAP) wastewater was investigated. Experimental results demonstrated that FeO@C not only enhanced chemical oxygen demand (COD) removal efficiency and biogas production by 2.42-13.18% and by 7.53%-23.25%, respectively, but also reduced the inhibition of microbial activity caused by toxic substances and the secretion of extracellular polymeric substances (EPS) by microorganisms responding to adverse environments. The reinforcing capability of FeO@C increased with the rise in FeO content. Furthermore, High-throughput pyrosequencing illustrated that FeO@C enhanced the relative abundance of Methanobacterium, a hydrogen-utilizing methanogen capable of participating in direct interspecies electron transfer (DIET), by 5%. Metagenomic analysis indicated that FeO@C improved the decomposition of complex organics into simpler compounds by elevating functional genes encoding key enzymes associated with organic matter metabolism, acetogenesis, and hydrogenophilic methanogenesis pathways. These findings suggest that FeO@C have the potential to strengthen both the hydrogenophilic methanogenesis and DIET processes. This insight offers a novel perspective on the anaerobic bioaugmentation of high-concentration refractory organic wastewater.