Study On The Effects Of Supply Water Switching On The Water Quality And Biofilm In A Model Drinking Water Distribution System

Water is an indispensable substance for life,and access to safe,reliable drinking water in sufficient quantities is even more important for good health and well-being.With the improvement production and living standards,the shortage of water resources has become increasingly prominent,a growing number of contaminants are entering water supplies,and people have more strict requirements on water quality.Based on the above reasons,water treatment workers have been committed to developing more advanced water treatment technology to improve the water quality of the water plants.In many areas,the water supply pattern of multi-source such as groundwater,surface water and external reservoir water has gradually formed for throttling.It can be said that these methods greatly alleviate the water shortage and improve the water quality of the water treatment plants.However,along with the rapid development of these technologies,a series of "red water" problems caused by the deterioration of drinking water quality are common worldwide.For a long time,people mainly pay attention to the water quality of drinking water,but there is little systematic research on the process of water distribution.Although the upgraded water treatment processes has been applied to improve drinking water quality,the change of supply water quality has caused the deterioration in the distribution network,resulting in the serious phenomenon of "red water" in the user's tap water.Water quality testing proves that when the water quality changes,it will lead to a series of physical,chemical and biological changes such as the release of organic matter accumulated in the original pipe network and the biofilm detachment,breaking the balance in the original pipe network,thus greatly threatening water safety.Therefore,it is of great significance to research the effect of supply water switching on the water and biofilm in the pipe network to correctly evaluate the safety of the terminal tap water.In this paper,the five kinds of water supply pipe materials,such as ductile cast iron pipe,copper pipe,stainless steel pipe,polyethylene and polyvinyl chloride,which are commonly used in water supply system pipe network,and glass material are used as water-passing carriers to simulate supply water switching in high temperature resistant borosilicate glass bottles.Two types of water quality were supplied to these pipes,respectively including the laboratory tap water out and tap water after five levels of deep filtration treatment of water,test water in the test jars is replaced every two days with fresh test water to simulate the hydraulic retention time in the net.After more than two months of cultivation,change the supply water quality to reveal the potential changes of the main water and biofilm in the reaction bottles before and after the supply water switching.And the differences of supply water switching between different pipes are compared to find out more suitable and environment-friendly ones to improve drinking water quality.The simulation experiment carried out in the laboratory was to research chemical indexes and bacteria in the water sample and biofilm before and after water source switching on the basis of ICP-MS and flow cytometry measurement,and analyze the effects of water quality changes on water samples and biofilm of different pipes.And the results showed that:(1)In the first stage(before supply water switching),the DOC in the water inside the pipe shows a downward trend in the first week,and the DOC value of some pipes with high carbon content will slightly increase,indicating that the substances contained in the pipe have migrated.After the water source switch,the DOC concentration of water in different pipes is higher than that in the water,which indicates that in addition to the carbon migration of pipes,the falling off of biofilm and organic sediment also occurs.(2)In addition to PVC pipes,the concentration of Ca in other pipes is the same as that in water,that is,the concentration of Ca is not affected by supply water switching.The concentration of Fe and Al in different pipes increased after supply water switching,which indicated that Fe and Al were released to some extent.(3)In the first stage(before supply water switching),the bacterial concentration in the water in the pipes increased compared with that in the water.The bacterial content in the water samples of different pipes was CI > Cu > PVC > SS > PE > G.The microbial biomass per unit area of each pipe is: PVC > CI > SS > G > PE > Cu.(4)In the second stage(after supply water switching),the microbial biomass of water in all pipes increased significantly,about 10 times of the influent concentration,and the biofilm biomass of all pipes decreased to varying degrees,but the water source switching had no effect on the microbial activity.(5)By comparing the changes of biomass in different pipes before and after water source switching,it can be concluded that: Cu>CI>PVC>SS>G>PE,which indicates that copper pipes are more vulnerable to impact and PE pipes are the most stable when dealing with supply water switching.Therefore,PE pipes are ideal pipes for supply water switching,and stainless steel pipes are ideal metal materials.