Enhanced efficiency of membrane-based bioreactors using activated carbon in the reduction of genotoxicity and antibiotic resistance during decentralized wastewater treatment.

Increasing attention is being devoted to the spread of antibiotic resistance through discharges from wastewater treatment plants. Research in this area aims to elucidate the impact of discharges on aquatic ecosystems and the associated public health and environmental consequences. This study examines the efficiency of a decentralized wastewater system with two membrane bioreactors (MBRs), both with and without the inclusion of powdered activated carbon (PAC), in influencing the gut resistome of Xenopus laevis larvae. The Xenopus gut resistome was analyzed using dilutions of treated effluent at 1/300, 1/100, 1/10, and undiluted (1/1) to quantify changes in relative abundances of ARGs under both treatment regimes. The findings demonstrate the efficiency of MBR treatment in globally reducing genotoxicity and ARGs but exposure to MBR-treated effluent without PAC resulted in a global increase in ARGs within the gut microbiota, with median log2 fold changes in ARG relative abundances showing an increase at each dilution level. Notably, genes such as aph3-iii, blaSHV-1, ermD1, bacA, mcr-1, sul1, and ermE were up-regulated, especially under conditions of higher effluent concentration. This pattern suggests that although MBR systems reduce the overall levels of ARG in effluents, the remaining ARGs could still influence the gut microbiota of aquatic organisms exposed to these waters, potentially contributing to the environmental resistome. On the other hand, the inclusion of PAC in the MBR treatment resulted in a global decrease in the abundances of ARGs at dilutions. In the PAC-treated effluent, the log2 fold changes of ARGs indicated a decrease at dilutions of 1/300, 1/100, and 1/10, while only the undiluted effluent displayed a slight increase (+0.26). The results highlight the efficacy of PAC as an additional barrier to ARGs and Xenopus gut microbiota dysbiosis, supporting its incorporation into wastewater treatment systems to improve ecological safety. This study highlights the potential benefits of PAC in wastewater treatment to control the spread of ARGs, in line with environmental and public health strategies to mitigate the spread of antibiotic resistance in aquatic environments.