| Antibiotic resistance genes (ARGs) are emerging pollutants. Wastewater treatment plants (WWTPs) represent as an important reservoir of ARGs into the environment, it is important to control ARGs in the effluents from WWTPs to reduce the contamination and ecological risk of ARGs in the environment. The paper studied the effects of several advanced wastewater treatments technologies (disinfection, Advanced Oxidation Process:AOPs, coagulation) on removal of ARGs and intI1 in secondary effluents from a WWTP. The effects of Fenton oxidation and coagulation on inactivation of ARGs and intI1 from screened wastewater were investigated as well. The objective of this study was to search suitable technologies to inactivate ARGs in the wastewater. The results of this research are as follows:1. The disinfection study investigated removal of ARGs by chlorination, ultraviolet (UV) disinfection and ozonation. The results showed that chlorine disinfection could achieve3.16-4.46 log removal for ARGs and 2.98 log for intI1 at chlorine dose of 160 mg/L with contact time of 180min. For other disinfectors, UV irradiation could achieve 2.48～3.04 log removal for ARGs and 2.61 log for intI1 at 12477 mJ/cm2; ozonation inactivated 1.83～3.00 log ARGs and 1.68 log intI1 at dose of 177.6 mg/L. In addition, UV irradiatioin followed by chlorine disinfection had synergistic effect, it could improve removal efficiency under common doses of UV irradiation (62,125 mJ/cm2) and chlorination (5～40 mg/L), the removal values increased 0.03～0.79 log for ARGs and 0.15～1.30 log for intI1。2. Effects of AOPs (Fenton reagents, UV/H2O2) on the removal of ARGs in the secondary wastewater from a WWTP were investigated. The results showed that for AOPs, treatment effect of Fenton reagents was slightly better than UV/H2O2 method. For Fenton reagents, when pH value was 3.0 with H2O2 concentration of 0.01 M and Fe2+/H2O2 molar ratio of 1/10, after reaction time of 2h, the removal rate were achieved 2.58～3.78 log for ARGs and 3.66 log for intll in secondary wastewater. For UV/H2O2 method, when pH value was 3.5 with H2O2 concentration of 0.01M, after UV irradiation time of 30 min,2.83～3.47 log for ARGs and 2.98 log for intll were achieved. In addition, Fenton reagents could achieve better removal rate of ARGs in screened wastewater than in secondary wastewater.3. Effects of commonly used coagulant (poly aluminum chloride:PAC1 and ploy ferric sulfate:PFS) on the removal of ARGs and intll in screened water and secondary effluent were investigated, respectively.The optimal dosages of coagulants and pH value were investigated. The results indicated that the removal of target genes first increased and then decreased with increasing coagulant dosage. The maximum removal for ARGs for the screened water were achieved when adding 60 mg/L PAC1 (as Al) with the removal of 2.33～2.97 log and adding 74 mg/L PFS (as Fe) with removal of 0.98～2.11 log, respectively. For secondary effluent, the optimal dosages were 30 mg/L for PAC1 and 28 mg/L for PFS, with the removal of ARGs of 1.85～2.64 log and 1.81～2.46 log, respectively. For pH, when increasing pH value from 3 to 10, the removal of ARGs decreased for PAC1 coagulation, but first increased and then decreased for PFS coagulation. The optimization pH for removing ARGs were 3 for PAC1 and 5～6 for PFS, respectively. Cogulation by PAC1 could achieve better removal of genes than PFS.The effects of different technologies on removal of ARGs were:chlorination disinfection> Fenton oxidation> UV/H2O2 oxidation> UV irradiation> ozonation> PAC1 coagulation> PFS coagulation. However, in chlorination, it was needed high chlorine dose for remarkable removal of ARGs, increasing the possibility of production of disinfection by-products. Taking into account the lower secondary pollution; economic and other actual operability factors, chlorination (FC dosage of 40 mg/L; reaction time of 120 min), combined UV and chlorination process (UV irradiation of 62 mJ/cm2 dosage followed by chlorination with 5 mg/L FC dosage) were recommended for removal of ARGs in secondary effluents. |
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