| Extended usage of antibiotics in medical, livestock breeding and fish farmingcauses the rising of bacteria resistance in the environment, which may consequentlylead to the generation, transmission and diffusion of antibiotic resistance genes(ARGs). Wastewater treatment systems contains a significant amount ofmicroorganisms, integrons, antibiotics and heavy metals, which may lead to theformation, horizontal transmission and expansion of ARGs. Therefore wastewatertreatment plants (WWTPs) are becoming an important store unit for ARGs.Real-time fluorescence quantitative PCR was used in this research to detect theARGs in the water and sludge samples from local WWTPs. These ARGs are:tetracycline resistance genes (tetA, tetO, tetW), sulfonamide resistance genes (sul I,sul II) and β-lactam resistance genes (blaCTX-M) as well as class I integrons. Thedistribution of ARGs in one local WWTP was monitored for half a year and theremoval mechanisms for each treatment unit were investigated.All the6ARGs were detected in the inflow of the WWTPs. The concentration ofthe6ARGs vaired from plant to plant, in general, the concentrations of the tetW werehigher than other tetracycline resistance genes. For the sulfonamide resistance genes,the concentration of sul II were higher than those of sul I. The overall concentrationsof sulfonamide resistance were higher than the tetracycline resistance genes. β-lactamresistance genes were relatively lower in the four WWTPs. The detectedconcentrations of the ARGs were higher in the influent than in the effluent, althoughthe concentrations were still high in the effluent. The total concentration of the6ARGs, tetO, tetW, sul I, blaCTX-Mshowed positive correlations to the total conentrtionof16SrDNA. The concentration of sul I was positively correlated to the concentrationof int I1.ARGs can not be effectively removed by grilles, grit chamber and sedimentationtanks, while can be obviously removed by biological treatment units. Total removalamount of0.5~2.0magnitude was chieved for the6ARGs, intI1and16SrDNA.Wastewater treatment plants that utilized the A/A/O process showed advantage forARGs removal. The dewatered sludge contains a significant amount ofmicroorganisms and a high concentration of ARGs. 6-month monitoring in one WWTP showed that the6ARGs were all100%detected. Grilles, grit chamber and sedimentation tanks could not effectively removethe ARGs, while a1~2magnitude removal was achieved in the biological treatmentunits. Ultraviolet disinfection process showed only a0.2~0.3magnitude removal ofthe ARGs. The biological treatment units in CASS process showed a moderateremoval efficiency on tetA, tetO, and tetW, while the relative abundance of sul I, sulII and blaCTX-Mincreased a little bit. To reduce the biomass concentration is the mainmechanism for ARGs removal in the WWTP, however, further removal principal ofeach treatment unit are need to carried out.Granular activated carbon (GAC) and shapeless activated carbon were used toenhance the ARGs removal from the effluent of the WWTP. The result showed thatthe shapeless activated carbon had a better ARGs removal efficiency, which was onemagnitude. Ozone disinfection was also used to enhance the ARGs removal from theeffluent, the result showed that with the increase of ozone dosage, the ARGs removalefficiency increased, while when the ozone dosage increased to60mg/L, the ARGsremoval tended to stable. The removal of tetracycline resistance genes, sulfonamideresistance genes and int I1reached one magnitude and the removal efficiency was80%. In terms of the ARGs removal efficiency, three post treatment processes is inthis order: Actived Carbon> Ozone> Ultraviolet. Since activated carbon can alsohelp the removal of TOC, TN and TP, it is considered as an appropriate process forfurther removal the ARGs in the WWTP effulent. On this basis,we develop acombined process-"wastewater secondary treatment+ozonation+activated carbon "to enhance the ARGs removal. |
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