Study On Bio-stability And Influence Factors Of Water In Regional Water Distribution System Of Urban And Rural Areas

Drinking water is deliveried to millions of households through water distribution system of urban and rural areas after treatment from waterworks. During this period, the bacteria could grow and reproduce using organic nutrient substrates in water, causing the tap water microbial unsafe. This paper took the actual pipe network in Yancheng as objects. Both of water quality changes and bacterial diversity of actual pipe network were studied. On these basis, the influence of various factors on bio-stability of water by small and pilot scale experiment were also analyzed.For water quality analysis of output water and actual pipe outlets, the main conclusions are as follows:The pH, turbidity, residual chlorine, ammonia, nitrate, nitrite and total number of colonies of each detection point can meet drinking water health standards except for the oxygen consumption with overproof of 12.7%. Differences between water quality indifferent pipe network detection points are mainly caused by the position and working conditions. Turbidity, residual chlorine, oxygen consumption and total number of colonies of each point have a certain relationship with temperature. The higher temperature, the higher turbidity and total number of colonies, the lower residual chlorine and oxygen consumption. Turbidity shows a significant correlation with total number of colonies; Chlorine presents a negative correlation with total number of bacteria; oxygen consumption displays a certain positive correlation with total number of colonies. Water quality of four network detection points are in the state of bio-stability.For bulk decay, the main conclusions of the study are as follows:Initial chlorine residual and pH have a negative correlation with chlorine decay coefficient. The higher initial chlorine concentration (or pH), the smaller chlorine decay coefficient. Initial total organic carbon(TOC) concentration and temperature have a positive correlation with chlorine decay coefficient. The higher initial TOC concentration (or temperature), the greater residual chlorine decay coefficient.For small pilot study of bio-stability, it used the new/old pipe tests and its shear force was provided by magnetic stirrer. The main conclusions of the study are as follows:The trend of BDOC over time is identical under different initial chlorine. The concentration of biodegradable dissolved organic carbon(BDOC) decreases first, then increases, and then decreases over residence time. The higher initial chlorine concentration, the lower BDOC value under the same residence time, the higher bio-stability. The trend of BDOC is consistent with above under different pH. The higher pH, the lower BDOC, the higher bio-stability. Pipes have a great impact on BDOC content, which BDOC value of the new pipe is significantly lower than the old pipe, the new galvanized steel is slightly lower than PE pipe, the old galvanized steel pipe is slightly lower than the old cast iron pipe.For pilot study of distribution biostability, pipe rings under different conditions in the pilot network were used, which including different pipe materials and different flow rates which were adjusting by valves with the same pipe. The main conclusions are as follows: BDOC content of different pipes (or flow rate) has an overall downward trend over time in the pilot network, and HPC has an overall upward trend. BDOC degrades rapidly in the beginning of the experiment, which is mainly due to oxidative decomposition of chlorine. The degradation of BDOC is relatively slow in the later stages of the experiment, which is mainly due to microbial oxidation decomposition. BDOC content is lower in the post-test, which HPC tends to balance. BDOC content and HPC of steel pipeline is relatively smaller throughout the experimental stage, and BDOC concentration and HPC of PE pipeline is relatively large. There is no obvious difference between other pipes. The greater velocity, the quicker chlorine decay, the larger BDOC content, which resulting in larger HPC.High-throughput sequencing was applied to five samples, which including output water of Chengxiwaterworks(sample 1), output water of Chengdong waterworks(sample 2), water before pressure pump(sample 3), water after pressure pump(sample 4) and biofilm in the wall of the actual network(sample 5). The results are as follows:25 phylum and 430 genus are detected in five samples, which indicating that the five samples have a high bacterial diversity. The dominant phylum of sample one to sample four have a certain similarity, which including: Firmicutes, Cyanophyta / chloroplast, Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes. The sample of biofilm is slightly different, which not including cyanophyta. The dominant bacteria genus of biggest abundance is Enterococcus. The sizes of shannon index of five samples respectively are:sample 2>sample 1> sample 3> sample 5> sample 4. By tree based on Bray-Curtis index we found that sample 2, sample 3 and sample 4 are the most similar and clustered into a small class; sample 1 has a greater distance with others and is displayed on the further branch; sample5 appears the furthest branch.