| Cyanobacterial extracellular polymeric substance(EPS)is a polymer produced by cyanobacteria cells.Cyanobacterial EPS has a high organic content,which is an important internal component of dissolved organic matter in water source.Free cyanobacterial EPS is not easy to be removed in the conventional water treatment process,which leads to the residual cyanobacterial EPS entering the water supply network and becoming an important pollution source.Urban water supply network is an important part of urban water supply system,which undertakes the safe transportation of all drinking water.Several studies have shown that:Even if the water quality indexes of the treated water in the water purification plant meet the national sanitary standards for drinking water,if there are trace organic matters in the water,heterotrophic bacteria will grow and breed in the process of water supply and delivery,the safety of drinking water quality will not be guaranteed,the health of residents will be threatened,and the orderly development of cities in China will be affected.Aiming at the situation that residual cyanobacterial EPS enters the water supply network after conventional water treatment process,taking the influence of cyanobacterial EPS on the biological stability of the water supply network as the research goal,this study mainly focuses on and analyzes the degradation and transformation of cyanobacterial EPS in the water supply network under different internal environment conditions of the pipeline,as well as its influence mechanism on the conventional water quality index and biological stability of the water supply network,and probes into the dynamic connection In order to find a way to reduce the influence of cyanobacterial EPS on the water quality of water supply network,the influence of cyanobacterial EPS with different content on the regular water quality index and biological stability of water supply network is studied.The research contents are as follows:(1)The migration and transformation of cyanobacteria EPS in water supply pipes with different biofilm conditions were studied.As a polymer,cyanobacteria EPS increased the total organic carbon content in the water after entering the pipe network.Some of them react with chlorine and are decomposed into small molecular organics,which are important components of organic matter mainly composed of dissolved microbial metabolites and humus like substances.With the increase of time,bacteria and other microorganisms in the water began to grow and propagate using small molecular organic matter as food and energy sources,and the remaining cyanobacteria EPS continued to be decomposed and utilized.At the same time,the growth and propagation of autotrophic bacteria transformed inorganic carbon into organic carbon,the dissolved organic matter in the water increased,and the organic component accumulation of cyanobacteria EPS and other organic matters increased(2)The influence of EPS on water quality and bacterial growth was studied in the water supply pipeline with different membrane conditions.When the drinking water contains residual cyanobacteria EPS,the cyanobacteria EPS is easy to react with chlorine,so as to consume residual chlorine,reduce the amount of chlorine,weaken the inhibition of residual chlorine on microorganisms,recover the activity of bacteria in the water,and gradually start to grow and reproduce,and use the cyanobacteria EPS as the nutrient matrix and energy source,accelerate the activity of microorganisms,greatly increase the number of bacteria,increase the total number of bacteria by 18-20 times,at the same time,reverse When it acts on the conventional water quality indexes such as residual chlorine and turbidity,it accelerates the decay rate of residual chlorine,which leads to the turbidity of the water in the pipe network exceeding the upper limit of the sanitary standard for drinking water after 12-24 hours.In the process of the interaction between the growth of microorganisms and the water quality indexes of the pipe network,the content of organics that can be absorbed and utilized by bacteria in the water increases.BDOC increases by 37.2-39.5%and AOC increases by 365-393%within 72 hours The biological stability of water quality is reduced and the safety of water quality is threatened.(3)The effects of EPS concentration on the conventional water quality index,organic matter content,biological stability and bacterial growth were studied.In the water supply network containing cyanobacteria EPS,the higher the concentration of cyanobacteria EPS,the higher the content of organic matter in the water,and after 72h,the TOC content in the drinking water of the network containing different concentrations of cyanobacteria EPS increased by 1.86-3.8 times compared with the initial time;the higher the concentration of cyanobacteria EPS,the faster the decay of residual chlorine,and with the increase of the concentration of cyanobacteria EPS,the amount of residual chlorine decreased to 0 after 72h,48h or even 36h of system operation.The higher the concentration of cyanobacteria EPS,the faster the growth and reproduction of bacteria and other microorganisms,and the increase of the number of bacteria.After 72h,the total number of bacteria in the drinking water of the pipe network containing different concentrations of cyanobacteria EPS increased by 21-26 times compared with the initial time;the BDOC content of the pipe network containing different concentrations of cyanobacteria EPS increased by 41.4-43.9%in 72h,and the AOC increased by 331-395%in 72h.The biological stability of the water quality decreased,which easily led to the water supply pipe The water quality of the network does not meet the water quality safety standards,and there is a secondary pollution problem.Therefore,in the current water supply network system,especially in the period of cyanobacteria outbreak,it is very important to regulate the input of EPS reasonably and effectively for the biological stability and water quality safety of the network. |
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