Undesirable risks of ozone-resistant bacteria (ORB): biofilm formation potentials and control strategy

Increasing disinfectant usage in urban water systems has heightened concerns regarding the enrichment of disinfection-resistant bacteria, particularly those capable of forming robust biofilms. Although chlorine-resistant bacteria and their associated risks are relatively well characterized, the characteristics and control strategies of ozone-resistant bacteria (ORB) remain insufficiently explored. Here, we examined seven previously classified ORB strains with varying ozone resistance to experimentally validate their biofouling risks and investigate efficient control methods. Cellular surface hydrophobicity and growth-related traits were associated with between-strain variation in biofilm formation potential. After investigating the inhibitory patterns of methylisothiazolinone (MIT) and 2,2-dibromo-3-nitrilopropionamide (DBNPA), we developed a synergistic control strategy using low concentrations of them, which effectively inhibited the biofilm formation of ORB and reduced extracellular polymeric substances. A likely synergistic mechanism involved the different targets in the cellular proteins, which may cause more severe damage to ORB. This approach was subsequently evaluated in a typical scenario, a water reclamation reverse osmosis system. When the reclaimed water contained ORB, the normalized flux of reverse osmosis membrane decreased by 12% after ozone treatment but increased by 13% after subsequent synergistic treatment with MIT and DBNPA. The synergistic treatment was also associated with a lower approximated relative abundance of fouling-related ORB and a lower predicted biofilm-forming potential of the microbial community. In summary, our findings bridged the gap between fundamental characteristics of ORB and practical biofouling risk, highlighted the potential of a synergistic biofilm control approach, and provided preliminary insights for mitigating the risks posed by ORB in advanced water treatment processes.