Electroactive biofilm enhances synergistic degradation of sulfamethoxazole and roxarsone in actual livestock wastewater: extracellular electron transfer drives metabolic network remodeling

Abstract

Livestock wastewater is characterized by high concentrations of organic matter and diverse antibiotics. A major challenge in its anaerobic treatment is the effective degradation and thorough removal of coexisting antibiotic contaminants. In this study, an external voltage was applied to establish an electroactive biofilm, thereby enhancing the co-metabolic degradation of sulfamethoxazole and roxarsone. Application of +0.6 V (Ag/AgCl) increased the 72 h TOC removal efficiency to 52.1 %. At the same time, sulfamethoxazole and roxarsone removal efficiencies reached 90.8 % and 100 %, respectively. The results from liquid chromatography-mass spectrometry (HPLC-MS/MS) and density functional theory calculations revealed sulfamethoxazole degradation pathways: N–O bond cleavage and hydroxylation. Roxarsone degradation primarily involved nitro group reduction and C–As bond cleavage. The pharmacophore of sulfamethoxazole was effectively removed, and inorganic arsenic from roxarsone degradation was efficiently immobilized. Toxicity analysis confirmed that the electroactive biofilm notably reduced toxic intermediate accumulation. Elevated concentrations of NADH and ATP in the electroactive biofilm indicated enhanced microbial substrate metabolism and generation of more electron donors. The higher absolute abundance of the sulfamethoxazole degradation gene (SadABC) in the electroactive biofilm indicated that sulfamethoxazole degrading enzyme (sadABC) gained more electrons. Microbiome analysis revealed the upregulation of genes linked to extracellular electron transfer, the tricarboxylic acid (TCA) cycle, nitro-reduction, and sulfate reduction pathway, confirming the electroactive biofilm enhances substrate metabolism and co-metabolic antibiotic degradation. Electroactive biofilm offers a viable strategy for antibiotic removal in livestock wastewater.