Analysis Of The Current Situation And Characteristics Of Secondary Water Supply System In A District Of A City In The South Of China Study On Water Quality Optimization Measures

Due to the problems of supervision and management,secondary water supply has become the blind area of "the last kilometer" treatment for water supply security.Taking the secondary water supply in a southern region as the research object,this paper systematically investigates the operation and management characteristics of the secondary water supply and identifies the key factors of water quality assurance;combines the key factors to carry out pilot-scale simulation experiments,and grasps the changing law of the secondary water supply quality;on this basis,a guide manual for the operation and management of the secondary water supply is compiled,which guides and evaluates the construction of the secondary water supply demonstration project.128 secondary water supply points were investigated by questionnaire.The results showed that the overall situation of secondary water supply was not optimistic.There were non-standard construction(57.38 % of water tanks were covered and locked,39.34 % of ventilation holes were not equipped with anti-mosquito devices),serious aging of facilities(57.81 % of secondary water supply facilities had been used for more than nine years,31.25 % of pipe aging,and non-standard management(84.38 %).Water quality monitoring system,79.69 % without video security system)and other phenomena.Through monitoring and evaluating the quality of water quality in the secondary water supply links of factory water,pipe network water,secondary water supply and tap water,it is found that the water quality has changed greatly in the secondary water supply links.The comprehensive standard-reaching rate has decreased from 100.00 % to 96.65 %,and the six indexes of turbidity,pH,free chlorine,total bacteria,aluminum and iron have decreased.The water quality of 20 typical secondary water supply points was analyzed.It was found that the water quality was affected by the construction age,tank material,posotions in tank,management mode and other factors.Different water tank materials,internal location and residence time have great influence on the water quality of secondary water supply tank.After 9 weeks of continuous operation,the turbidity of cement material increased most obviously,and the pH exceeded the standard.At the same time,the free chlorine value of water samples in the water tank of cement and ceramic tile material decreased more obviously than the initial value,and bacteria were easy to grow.Proteobacteria(Proteobacteria)and Actinobacteria(Actinobacteria)were the most abundant in the water tank.At the same time,the proportion of nitrate reducing bacteria and nitrate oxidizing bacteria reached the peak in the third week,and the species abundance and community diversity gradually decreased during operation.The corrosion resistance of the two stainless steel materials increases with the operation of the water tank.According to the analysis of different positions inside the water tank,the turbidity of the lower water samples is generally higher than that of the upper water samples,and there is Cross-Change between the upper and lower positions of pH.The free chlorine value of the lower water samples is generally lower than that of the upper water samples,and the total bacterial count is generally higher than that of the upper water samples.The species abundance and community diversity of the samples with different materials at the lower part of the water tank were lower than those of the upper part of the same period.During the 48 h residence time,residual chlorine of cement and ceramic tile materials decays rapidly and bacteria grow seriously.At the same time,the pH value of cement water tank keeps rising and reaches 8.97 after 48 h.The simulation of tank flow pattern shows that there is a large range of dead water area in the existing tank,and the water quality in the middle-dead water area tends to deteriorate due to the long residence time.Ceramic tile material is not suitable for secondary water supply tank because of its poor ability to maintain residual chlorine concentration and bacterial breeding.Cement material is not suitable for secondary water supply tank because of its fast decay of residual chlorine and easy increase of pH.Plexiglass,PP,304 stainless steel and 316 stainless steel have strong ability to guarantee water quality,so they can be considered as secondary water supply tank material.Based on the investigation and experimental results,the Rules for Construction,Operation and Maintenance of Secondary Water Supply Facilities are compiled,with emphasis on the design of tanks,pipelines and other ancillary facilities,as well as information management system and operation and maintenance system.The operation effect of standardized pumping house was monitored.The residual chlorine,turbidity,pH and conductivity did not exceed the standard.