Enhanced mitigation of antibiotic resistance genes in anaerobic digestion of food waste using biochar-supported nanoscale zero-valent iron

Food waste (FW) is a crucial biomass resource and reservoir of antibiotic resistance genes (ARGs). Biochar-supported nanoscale zero-valent iron (BC-nZVI) can enhance methane production in the anaerobic digestion (AD) of FW. However, the mechanisms underlying the effects of BC-nZVI on the fate of ARGs during AD are remain unclear. Here, the impacts of BC-nZVI on the fate of total ARGs were investigated, by analyzing dynamics of representative types of ARGs including intracellular and extracellular ARGs (iARGs and eARGs). We found a significant decrease in the abundance of the most ARGs during AD treated with BC-nZVI. Specially, the relative abundance of iARGs (tet32, ermF, sul1, and tetW) decreased by 30.58 %, 11.38 %, 16.69 %, and 3.65 %, respectively, while that of eARGs (tet32, ermF, sul1, and tetW) decreased by 95.09 %, 48.18 %, 88.55 %, and 71.41 %, respectively. The relative abundances of intracellular and extracellular intI1 decreased by 17.42 % and 41.96 %, respectively. BC-nZVI enhanced microbial metabolism, prevented SOS response activation, reduced the expression of type IV secretion systems, and decreased extracellular polymeric substance secretion, which could contribute to the decrease in ARGs. These findings indicate that BC-nZVI can effectively mitigate the risk of ARGs in AD by reducing their abundance and inhibiting their horizontal transfer.