Influence Of Source Water And Advanced Treatment Processes On Bacterial Community And Antibiotic Resistance Genes In Drinking Water Supply Systems

With the expansion of cities and the implementation of the urban-rural integrated water supply strategy,drinking water supply systems with multiple water sources and complex pipeline networks has become the new normal.Faced with the risk of microorganism and antibiotice resistance gene（ARG）pollution in different water sources,the selection of appropriate advanced treatment processes according to the characteristics of source water is the key to solve such problems.However,previous research on water sources and advanced treatment processes was limited by multiple variables,which could not realize the systematic comparative analysis.Meanwhile,previous studies,which only focused on the quality of treated water,ignored the impact of source water and advanced treatment processes on the microorganisms and ARGs in the water distribution systems.Therefore,the water microbial quality of the customers’tap water has not been effectively evaluated.To fill this gap,this study utilized high-throughput sequencing,high-throughput quantitative PCR（HT-qPCR）and flow cytometry method（FCM）to systematically investigate the influence of water sources and advanced treatment processes on the microorganisms and ARGs in drinking water supply systems.In this study,two groups of water supply systems with multiple water sources or advanced treatment processes in Jiangsu were investigated.Additionally,a pilot-scale drinking water treatment system with multiple disinfection processes in parallel was used to explore the shift of antibiotic resistome,bacterial community and their potential correlations.Overall,the main research conclusions are listed as belows.（1）The influence of different source water on the bacterial community in the drinking water supply systems was evaluated by flow cytometry,16S rRNA approaches,and Source Tracker analysis.The results showed that treated water from different source water could both meet the drinking water prescribe standard well.Although the same treatment process was utilized,a larger number of damaged cell and higher bacterial regrowth rate were found in the treated water from CD DWTP,indicating the variation of the source water may lead to microbial deterioration during pipeline transportation.Additionally,according to Source Tracker analysis,the contribution of source water to treated water was only 0.3-1.1%,and the contribution of treated water to pipe water decreased by 66.9-92.5%along the pipeline transportation.The advanced water treatment process played an important role in reshaping and determined the microbial characteristics of treated water,and the pipeline transportation ultimately determined the microbial community in tap water.It is highlighted that hihger relative abundance of Pseudomonas spp.was found in particle-associated bacteria,suggesting that PAB are potential reservoirs for high-risk bacteria.Higher abundance of Pseudomonas spp.was also found in the intersection region resulted from frequent water quality and hydraulic fluctuation.Overall,it is necessary to select an appropriate advanced treatment process and enhance the microbial stability in the distribution systems with full description of water quality.And more comprehensive controlling strategies are needed for the microbial risks of the particle-associated bacteria and water supply intersection region in complex water supply systems.（2）In a pilot-sacle drinkging water treatment system,we explored the effects of multiple disinfection units related to quaternary ammonium salt resin NDMPand ozone-biological activated carbon（O₃-BAC）on the community and relative abundance of bacteria and ARGs using metagenomic approaches.The results showed a good disinfection efficiency of all multiple disinfection processes.Among them,the quaternary ammonium salt resin and its disinfection process combined with chlorine showed a broad-spectrum removal efficiency and could avoid the enrichment of drug-resistant bacteria.Meanwhile,18 representative ARGs were screened from the ARGs,which were not only difficult to be removed by all disinfection processes,but also significantly influened the resistome and had a greater health risk.And these 18 ARGs could be further used as an important part of drinking water ARGs database for risk evaluation.Based co-occurrence network analysis,it was revealed that bacterial community shift may be the key factor driving the change of antibiotic resistome during disinfection and benefit the source tracing of ARGs and optimization appropriate disinfection process in practical applications.（3）Using 16S rRNA approaches and HT-qPCR,we investigated the effects of O₃-BAC and quaternary ammonium salt resin NDMP on microbial communities and the absolute abundance of ARGs in the full-scale drinking water supply systems.The results showed that both processes could remove more than 99.7%bacteria and reduce the absolute abundance of ARGs by 71.4-90.0%from source water.However,theα-diversity,subtypes of detected ARGs and absolute abundance of ARGs increased during pipeline transportation,indicating that the pipeline may be an important source of bacteria and ARGs.It is highlighted that the absolute abundance of ARGs in the pipeline transportation was significantly correlated with the number of bacteria（p<0.05）,suggesting that the increasing of ARG concentration resulted from the proliferation of bacteria.Only by improving the bacterial removal effeciency as well as the microbial stability in the pipeline transportation,the enrichment and diffusion of ARGs could be better controlled.In addition,due to the different mechanisms of organic matter degradation and bacterial removal,the microbial stability of pipe water treated by NDMP resins was better.Therefore,the NDMP resins are of great practical value in drinking water advanced treatment..