| In recent years, antibiotics have been identified as widespread contaminants of treated drinking waters and wastewaters. As a consequence, concerns have been raised that antibiotic resistant bacteria (ARB) or antibiotic resistance gene (ARG) transport between aquatic compartments may enhance the spread of antibiotic resistance amongst non-resistant bacterial communities by means of horizontalgene transfer processes. Thus, a systematic evaluation of the capability of common disinfection technologies to ensure the destruction of bacterial DNA, in addition to pathogen inactivation, seems warranted.In this study, five tetracycline resistance genes(tetA, tetM, tetO, tetQ and tetW) and two sulfonamide resistance genes (sulⅠ and sulⅡ) were evaluated in secondary effluents of a municipal wastewater treatment plant in Zhejiang areas using polymerase chain reaction (PCR) and real-time quantitative polymerase chain reaction (qPCR). And the aim of this study was to compare three different disinfect processes (ultraviolet, chlorination and ozone) and the efficacy of three disinfectants in effluents in reducing the risk of antibiotic resistance pollution.Our experimental results indicated that the selected antibiotic resistance genes were detected in secondary effluents of the wastewater treatment plant in differ periods.The abundance of sulⅠ was highest with tetW lowest. Significant reductions in ARGs were observed in the UV disinfection effluent process of the WWTP and the removal of ARGs reached 0.04～0.98 orders of magnitude.The abundance of ARGs were exponentially decreased with the increase of disinfectant dosage after UV disinfection treatment (R2=0.68～0.92). Through high dose of UV disinfection, tetracycline antibiotic resistance genes except tetQ of the effluents were nearly removed completely, but sulⅠ not. In 0～5mg/L available chlorine concentration, contact time for 30 min, the abundance of ARGs were decreased linearly with the increase of chloride concentration (R2=0.77～0.99). SulⅠ was nearly removed completely by high chlorine concentration (5～50mg/L available chlorine) while tetQ was not. In concentration of 2 mg/L ozone disinfection treatment, the abundance of tetracycline resistance genes had a higher removal than UV and chlorine, but the removal ability was not significantly enhanced by increasing the concentration of ozone.Sulfa antibiotics resistance genes sull and sulll were removed more effectively by chlorine disinfection, the removal rate of which reached 99.21 and 99.61%. The strains of total culturable bacteria, tetracycline resistant bacteria, sulfamethoxazole resistant bacteria and multiple drug-resistant bacteria in the effluent were reduced after treated by UV and chlorine, ozone disinfection. The ozone sterilization ability was stronger, respectively reduced the concentration of tetracycline resistant bacteria and sulfamethoxazole resistant bacteria 2.46 and 2.10 orders of magnitude in the concentration of 2 mg/L ozone.Correlation analysis indicated that the abudance of some ARGs and corresponding drug-resistant bacteria had significant correlation (P<0.05); Decreases of microorganisms was the main reason for the removal of ARGs in disinfection process; Class I integron gene intll was significantly correlated with sulfa antibiotics resistance gene sull in the effluents of the WWTP, while in the three methods of disinfection process, intll and some ARGs including sull also showed a significant correlation, indicated that class I integron played an important carrier in the process of pollution and transfering of ARGs.The experiment of DNase I treatment showed that UV and ozone disinfection result in apoptosis and DNA of the bacteria released into the environment, antibiotic resistance genes mostly existed in the free DNA in the treated wastewater. And in the effluents after chlorination treatment, only part of antibiotic resistance genes exists in the free DNA. |
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