| Due to water pollution,many emerging contaminants,such as disinfection by-products,antibiotics and resistance genes(ARGs),had been detected in tap water,posing a threat to human health.In order to obtain cleaner drinking water,household water purifiers have been rapidly applied in China in the past two decades.However,there is still a lack of research on the removal of trace level contaminants by the household water purifiers.Therefore,in this study,concentrations and removal rates of typical trace level contaminants(trihalomethanes(THMs),antibiotics and ARGs in the a five-stage ultrafiltration water purifier was studied,and ARGs distribution and characteristic of microorganism in five filters with a long-term operation,and investigated the usage of household water purifiers in Tianjin.The five-stage ultrafiltration water purifier used in the experiment was composed of polypropylene(PP)filter,granular activated carbon(GAC)filter,compressed activated carbon(CTC)filter,ultrafiltration(UF)filter and after-treatment activated carbon(ATAC)filter.At the initial stage of operation,the removal rates of total residual chlorine,TOC and THMs were 85%,59%and 37%.The removal rates of azithromycin(AZI),erythromycin(ERY)and roxithromycin(ROX)were above 90%,and the removal rate of macrolide antibiotics(MLAs)was 91%.The total reduction of ARGs by the purifier was 0.71～2.43 log,while the UF filter and ATAC filter had significant reduction of ARGs,which values were 0.07～1.63 and 0.04～1.75 log,respectively.After a long-term operation(a flow of 1400 L,operation time of 6 months),the purification capacity of PP filter,GAC filter and CTC filter declined significantly and the filters had the potential to become new sources of contaminants.The removal rate of TOC was only 20%.The purifier didn’t significantly remove antibiotics from tap water.The experiment of high-concentration antibiotics(0.75～1.08μg/L)showed that the adsorption of antibiotics by the purifier didn’t reach saturation,and the removal rate was 50%～81%.The concentration of ARGs in the filters used for a long term operation was 10~1～10~4 copies/L.The biomass and ARGs concentrations on the UF filter were the highest.On phylum level,the dominant flora of five filters were Proteobacteria,Acidobacteria and Chloroflexi.On genus level,the dominant flora were Bradyrhizobium,Novosphingobium,Sphingorhabdus,Amphiplicatus and Sphingopyxis.The survey of 26 household water purifiers discovered that a long-term operation(6～12 months)of filters was widespread,and the purification efficiency of water purifiers declined,resulting in antibiotics and ARGs enrichment and release.The concentrations of total THMs,antibiotic and ARGs in the tap water of 26 household water purifiers were 25.86～62.45μg/L,0.90～10.94 ng/L and 2.94×10~1～9.20×10~5copies/L,respectively.The average removal rate of total THMs concentration in tap water by household water purifiers was 46%.34%of household water purifiers removed above 70%of total THMs concentration.8%of household water purifiers removed more than 70%antibiotics,and 54%of purifiers did not removed total concentration of antibiotics.The removal rate of total ARGs concentration of the household water purifiers was-2.85～2.91 log,and total ARGs concentration of effluent from 35%of household water purifiers had increment. |
