Increased risks of antibiotic resistant genes (ARGs) induced by chlorine disinfection in the reverse osmosis system for potable reuse of reclaimed water.

The reverse osmosis (RO) process has been applied extensively in wastewater reclamation for industrial and potable reuse. To prevent biofouling, chlorine disinfection was usually used in pretreatment. However, this study found that chlorine disinfection could significantly increase risks of antibiotic resistant genes (ARGs) in the RO system. With the increase of chlorine concentration from 0 to 5 mg/L, the accumulative relative abundance of 14 common ARGs in the membrane foulants increased by 49.6%. Among these ARGs, tolC, acrA and acrB (resistance to multiple drugs) showed the highest increament after chlorine disinfection. Especially, the relative abundance of tolC in the group with 5 mg/L chlorine increased by 113.3% compared with the control group. These ARGs tended to be enriched in a few bacterial genus, including Candidatus, Thiomonas, Silanimonas, Xanthomonas and Pseudomonas. These results indicated that the foulants on RO membranes might become a potential sink of ARGs. Considering the possibility of membrane breach, the ARGs may contaminate the permeate and bring great biological risks.