Nano Fe3O4-modified graphene enhancing the removal of sulfamethoxazole under anaerobic digestion and sulfate reduction conditions through improved direct interspecies electron transfer

Abstract

Sulfamethoxazole (SMX) present in pharmaceutical wastewater may pose significant risks to ecological health. This study evaluated the role of redox mediator nano Fe₃O₄-modified graphene (GF) to facilitate SMX biotransformation in a sulfate reduction reactor (Rs) and an anaerobic digestion reactor (Ra). The results revealed that the SMX removal in Rs and Ra after GF addition reached 92% and 97%, respectively. By stimulating the secretion of humus-like substances (containing quinone group), riboflavin, and conductive proteins, GF enhanced direct interspecies electron transfer (DIET) among microorganisms in both Rs and Ra. Additionally, in both systems, the relative abundance of genes encoding cytochrome c oxidase and type IV pilus assembly proteins decreased. These metabolic shifts reduced the reliance of DIET on cytochrome c and ciliates while enhancing energy utilization. The results confirmed that GF can serve as an effective additive for enhancing SMX degradation in anaerobic systems.