Inhibiting the increase of antibiotic resistance genes during drinking water distribution by superior microbial interface using Fe modified granular activated carbon

The effects of biological activated carbon treatment using Fe2O3-modified granular activated carbon in inhibiting antibiotic resistance genes in simulated drinking water distribution systems was compared with unmodified granular activated carbon as a reference. Fe2O3-modified biofiltration resulted in a sustained inhibition of resistance genes during drinking water chlorination and distribution (relative abundance in simulated tap water after the modified and unmodified filtration was 1.31% and 9.40%, respectively). A new electron transfer pathway occurring in attached biofilms on Fe2O3-modified granular activated carbon surface, which was identified using X-ray photoelectron spectroscopy and the phenanthroline spectrophotometric method, enhanced the extracellular electron transfer rate and weakened the pressure of organic micropollutants on microorganisms. Hence, the relative abundance of resistance genes (36.32%) and integron (8.79%) on modified carbon was considerably lower than that on unmodified carbon (115.59% and 13.85%, respectively). Meanwhile, the secreted extracellular polymeric substances on modified carbon presented higher flocculating efficiency and better mechanical stability, resulting in the suspended extracellular polymeric substances in downstream water exhibiting stronger electrostatic repulsion. The particle-attached biofilms in downstream distribution systems consistently failed to form larger aggregates, inhibiting horizontal gene transfer, and overall microbial metabolism. Based on network analysis, 11 OTUs in the water samples from raw water to simulated tap water formed an extremely interrelated module with no links to target resistance genes and integron. Therefore, a range of microbial variations triggered by the microbial interface on modified carbon successfully controlled the transfer of antibiotic resistance genes-associated risk from biological activated carbon effluent to tap water. Our findings revealed that enhancing the microbial interface using Fe2O3-modified granular activated carbon is a promising option for inhibiting the antibiotic resistance genes increase in tap water.