Tertiary Wastewater Treatment Processes Can Be a Double-Edged Sword for Water Quality Improvement in View of Mitigating Antimicrobial Resistance and Pathogenicity

Despite the high removal efficiency for chemical pollutants by tertiary wastewater treatment processes (TWTPs), there is no definite conclusion in terms of microbial risk mitigation yet. This study utilized metagenomic approaches to reveal the alterations of antibiotic resistance genes (ARGs), virulence factor genes (VFGs), their co-occurrence, and potential hosts during multiple TWTPs. Results showed that the TWTPs reduced chemical pollutants in wastewater, but the denitrifying biofilter (DB) significantly increased the absolute abundances of selected antibiotic-resistant bacteria and ARGs, and simultaneously elevated the relative abundances of ARGs and VFGs through the enrichment of multidrug resistance and offensive genes, respec-tively. Moreover, the co-occurrence of ARGs and VFGs (e.g., bacA-tapW, mexF-adeG) was only identified after the DB treatment and all carried by Pseudomonas. Then, the ultraviolet and constructed wetland treatment showed good complementarity for microbial risk reduction through mitigating antibiotic resistance and pathogenicity. Network and binning analyses showed that the shift of key operational taxonomic units affiliating to Pseudomonas and Acinetobacter may contribute to the dynamic changes of ARGs and VFGs during the TWTPs. Overall, this study sheds new light on how the TWTPs affect the antibiotic resistome and VFG profiles and what TWTPs should be selected for microbial risk mitigation.

Automated summary

Although tertiary wastewater treatment processes (TWTPs) have high removal efficiency for chemical pollutants, their impact on microbial risk mitigation is uncertain. This study used metagenomic approaches to investigate the changes of antibiotic resistance genes (ARGs), virulence factor genes (VFGs), and their co-occurrence during multiple TWTPs. It was found that the denitrifying biofilter (DB) increased the abundance of antibiotic-resistant bacteria and ARGs, as well as the relative abundance of ARGs and VFGs through the enrichment of multidrug resistance and offensive genes. Complementary microbial risk reduction was achieved through ultraviolet and constructed wetland treatment. The study provides new insights into the effects of TWTPs on the antibiotic resistome and VFG profiles, and aids in selecting appropriate TWTPs for microbial risk mitigation.