Effects of zero-valent iron and carbon core-shell particles on methanogenic metabolic pathways in anaerobic system containing chloramphenicol wastewater

Antibiotic pharmaceutical wastewater poses significant risks to human health and the environment. Anaerobic biological treatment technologies offer a promising solution by converting organic pollutants in wastewater into biogas. However, the efficiency of traditional anaerobic systems is often limited by the rate of interspecies hydrogen electron transfer. Iron-based and carbon-based materials, serving as electron transfer mediators, can enhance direct interspecies electron transfer (DIET) and improve treatment efficiency. In this study, a novel iron‑carbon core-shell material, consisting of zero-valent iron (ZVI) wrapped in graphite carbon (ZVI@C-MP), was developed to enhance the anaerobic treatment of chloramphenicol-containing wastewater. The results demonstrated that the addition of ZVI@C-MP (3.0 g/L) enhanced COD removal efficiency by 10.16 %, increased methane yield from 159.25 to 238.71 mL/g COD removed, and improved chloramphenicol (CAP) removal efficiency by 11.16 % within 3 h of treatment compared with the control. ZVI@C-MP facilitated the formation of a dense biofilm on its surface, reducing the inhibitory effects of toxic substances on microbial activity. Furthermore, it enhanced microbial dehydrogenase activity and increased coenzyme F₄₂₀ content by 26.63 % and 78.81 %, respectively. The conductivity of anaerobic granular sludge (AGS) was also increased by 16.18 %. Moreover, the addition of ZVI@C-MP led to a significant increase in the relative abundance of key microbial genera, including Clostridium sensu (32.23 %) and Methanosaeta (20.13 %). Metagenomic analysis revealed that ZVI@C-MP promoted the relative abundance of genes encoding key enzymes involved in the methanogenic metabolism of organic matter, with particular enhancement in genes associated with the DIET process. These changes collectively resulted in improved microbial metabolic activity and enhanced conversion of organic matter into methane.