Fe/Co-modified Enteromorpha bio-hydrochar enhanced anaerobic digestion of chicken manure with sulfadimethazine: focusing on synergistic mechanism and microbial community succession

Residual antibiotics in chicken manure may interfere with the stability of anaerobic digestion (AD) and inhibit resource utilization efficiency. In this study, we aimed to enhance chicken manure bio-methanation in AD with high-concentration of sulfamethazine (SMZ) by adding metal (Fe, Co)-modified Enteromorpha-based hydrochar (Co-HC, Fe-HC). The results showed that Fe-HC and Co-HC increased the degree of acidogenesis by 1.25 times and 1.58 times, respectively. The maximum protein concentration in EPS was increased by 47.64% and 72.5% after adding Fe-HC and Co-HC. However, only Co-HC demonstrated notable improvements in both methane production and SMZ removal efficiency. Electrochemical analysis showed that Co-HC possessed a richer variety of oxygen and nitrogen functional groups, along with superior electron exchange capabilities compared to Fe-HC. Furthermore, microbiological assessments revealed that Co-HC enriched syntrophic bacteria (such as Syntrophomonas and Mesotoga), facilitating direct interspecies electron transfer (DIET) and subsequently enhancing biomethane production. The abundance of genes involved in electron transfer increased significantly with Co-HC, with a maximum increase of 75.86% in Co1.5-HC treatment. Additionally, the elimination of antibiotic resistance genes (sul1, sul2) increased by 65.66% in the Co1.5-HC treatment. This study offers a theoretical foundation and empirical support for the synergistic improvement of livestock and poultry manure containing high antibiotic concentrations, thereby helping to overcome challenges posed by recalcitrant substances. Enteromorpha bio-hydrochar (HC) improved chicken manure digestion with high sulfadimethazine.Co-HC contributed high electronic exchange capacity with pyridine-N, graphite-N and C-O functional groups.Co-HC outperformed Fe-HC at the same dose in enhancing both methanogenesis and acidogenesis.Addition of 1.5 mmol L-1 Co-HC significantly enhanced both SMZ degradation and the elimination of ARGs (sul1, sul2).Co-HC significantly upregulated mtrA, boosting DIET cooperation between bacteria and methanogens.