Effects Of UV/H₂O₂ And Activated Carbon Filtration On Water Quality In Drinking Water Distribution Systems

Drinking water safety is vital to public health and social development.The supply of high quality drinking water is a top priority for people.Although the finished water in most drinking water treatment plants can reach the drinking water standards,the users'tap water might be contaminated due to the secondary pollution of drinking water distribution systems?DWDSs?.Based on this,this study compared the effects of three different water treatment processes?sand filtration,activated carbon filtration,UV/H₂O₂-activated carbon filtration?on the influent,effluent,and biofilms of the simulated DWDSs,in order to investigate the control effects of UV/H₂O₂ advanced oxidation process combined with activated carbon filtration on organic matter,disinfection by-products?DBPs?,and microorganisms,especially opportunistic pathogens?OPs?.In addition,the effects of sulfadiazine on drinking water and the ability of UV/H₂O₂-activated carbon treatment to control over the sulfadiazine's influences were investigated by adding antibiotic sulfadiazine to raw water in the subsequent process.The main research contents and conclusions are as follows:?1?Three types of water treatment processes,such as sand filtration,activated carbon filtration,UV/H₂O₂-activated carbon filtration,were set up to investigate their influences on the influent water quality of DWDSs.The results showed that UV/H₂O₂advanced oxidation process could enhance the filtration function of the activated carbon.After UV/H₂O₂-activated carbon filtration treatment,the influent of DWDSs kept the lowest concentration of dissolved organic carbon?DOC?as well as fulvic acid and humic acid,causing lower DBPs concentrations including THMs and HAAs during sterilizing stage.Moreover,the concentration of biodegradable dissolved organic carbon?BDOC?,assimilable organic carbon?AOC?was the lowest in the influent of UV/H₂O₂-activated carbon filtration DWDSs.Furthermore,the microbial community structure was changed,and the microbial diversity was the lowest.The opportunistic pathogens were also effectively controlled.?2?Three simulated DWDSs were established,and the treated water samples of three treatment processes were separately flowed into the simulated DWDSs.Water treatment processes and DWDSs are equivalent to two sequential systems.Among the three types of DWDSs effluent,the effluent of UV/H₂O₂-activated carbon filtration DWDSs had the lowest concentrations of various organic matter which utilized by microorganisms.Then,the effluent of UV/H₂O₂-activated carbon filtration DWDSs also kept DBPs to a minimum.Meanwhile,the inhibition of the regrowth of microorganisms was the most obvious in the effluent of UV/H₂O₂-activated carbon filtration DWDSs according to the lowest indicators of microbial activity,resistance capability,and diversity.The relative aboundance of?-proteobacteria which were pathogens were the least in the microbial community structure.So,UV/H₂O₂-activated carbon filtration treatment process had well controlled the continued conversion of DBPs and the regrowth of microorganisms,especially the opportunistic pathogens.?3?The biofilms of three simulated DWDSs were made further investigation.The concentration of organic matter that microorganisms utilized was lower,and the cholorine concentration was higher under the same dosage in UV/H₂O₂-activated carbon filtration DWDSs.On this conditions,the aggregation of extracellular polymeric substances?EPS?secreted by biofilms was the lowest,so the microorganisms were easily inactivated in UV/H₂O₂-activated carbon filtration DWDSs.Besides the 16S rRNA of total bacteria and opportunistic pathogens,the activity and resistance capability of microorganisms were also remained at the lowest level in the biofilms in UV/H₂O₂-activated carbon filtration DWDSs.Moreover,the microbial diversity and the relative aboundance of four kinds of proteobacteria were controlled at the lowest level.All in all,the UV/H₂O₂-activated carbon filtration could well inhibit the formation of biofilms in DWDSs.?4?Adding trace mounts of antibiotic sulfadiazine to raw water,the operation of three types of water treatment processes and simulated DWDSs were maintained.The results showed that the addition of sulfadiazine would increase the microbial risk of drinking water.In particular,the aggregation of EPS increased,whitch led to the enhancement of the the protective effect of biofilms on microorganisms and the inactivation of microorganisms in DWDSs.Finally,the antibiotic resistance genes increased,and the microbial activity showed an upward trend.However,the research results showed that UV/H₂O₂-activated carbon filtration treatment process could well reduce the impact of sulfadiazine on water quality in DWDSs among the three types of water treatment processes.