Disinfection of Antibiotic-resistant Bacteria in Sewage and Hospital Effluent by Ozonation

Abstract

ABSTRACT The present status of antimicrobial-resistant bacteria (AMRB) and antimicrobial-susceptible bacteria (AMSB) in hospital effluent, sewage treatment plant (STP) influent, STP secondary effluent, STP effluent (chlorination), STP effluent (ozonation), and river water were analyzed in an urban river in Japan by a 2-year monitoring survey. The results revealed the existence of multiple AMRB grouped into six classes whose numbers were in the hospital effluent at 19 to 2,800 CFU/mL, in the STP influent at 9 to 3,133 CFU/mL, in the STP secondary effluent at 1 to 148 CFU/mL, in the STP effluent (chlorination) at N.D. to 191 CFU/mL, and in the river water at N.D. to 28 CFU/mL In the case of the STP effluent (ozonation) the level of AMRB was, however, quite low ranging from N.D. to several CFU/mL, roughly 1/10 to 1/100 of the concentrations detected in the STP effluent (chlorination). The bacterial community structure analysis indicates that only ozonation changed the constitution of bacterial phyla. Rates of antimicrobial resistance were high among MDRA (82% in hospital effluent and 79% in STP influent), MDRP (35% and 40%), and MRSA (93% and 87%). MRSA showed resistance against chlorine treatment but could be gradually disinfected by ozonation. When the hospital effluent and the model STP wastewater prepared by mixing STP influent and STP secondary effluent in a 1:9 ratio were directly treated with ozone, both AMRB and AMSB were inactivated effectively with variance in the time among bacteria, accompanied by a change in the constitution of phyla similar to the observation in the case of the STP effluent (ozonation). Ozonation inactivated almost all target bacteria (>99.9%) after 10 min treatment (CT value: 1.0 mg·min/L). Changing taxonomic diversity of micro-organisms based on 16S rRNA gene sequencing by ozonation showed that ozonation inactivated not only AMRB but also removed antimicrobial resistance genes (AMRGs) in the wastewater. As a result of the present study, a recommendation was evoked to operate ozonation treatment directly for the hospital effluent immediately after flowing out, leading to desirable contribution to reduce environmental pollution, and the potential hazard to human health caused not only by the AMRB and AMSB but also infectious diseases. Extension of the present results opens a new way to assess environmental risks associated with the spread of AMRB and AMSB in aquatic environments to keep the water environment safe and to maintain human health. To our knowledge, this is the first report to show the inactivation profiles of AMRB and AMSB in real STP wastewater together with hospital effluent by direct ozonation.