| With the continuous development of urban construction,cities and towns have successively built high-rise buildings to meet people’s growing housing needs,which has rapidly expanded the water supply scope of the whole region.However,the original urban pipe network was insufficient water supply capacity,the present stage of city pipe network upgrade speed cannot meet the needs of the water supply in a short time,so intensive water supply and secondary pressurized water supply in suburbs are widely used.While solving the problem of water supply,the drinking water in the secondary water supply system is accompanied by potential microbial risk during its stay in the tank.After the disinfection process,the bacteria dormant in the living unculturable state(VBNC)revive and become culturable.This paper focuses on the secondary water supply drinking water microbiological safety issues,in order to deal with and alleviate the microbial problems in drinking water,a systematic experiment was established to develop an ultraviolet disinfection device for secondary water supply system.According to the relationship between the number of living bacteria and absorbance under the specific wavelength condition of the best storage tank material,the hydraulic retention time of ultraviolet disinfection and the change of the number of living bacteria,as well as their influence on the bacterial culture ability,the necessity and feasibility of designing the parameters of the ultraviolet disinfection device were discussed.The main conclusions are as follows:(1)Three materials of 304 stainless steel,PE and plexiglass are used to simulate the water storage tank to analyze the water storage effect.By understanding the high-rise buildings and centralized water supply areas of nearby communities,most of the water storage materials are concrete,304 stainless steel,PE,plexiglass,but considering external factors such as long-distance transportation,the experimental simulation water tank is made of 304 stainless steel,PE,and plexiglass.The main detection indicators were:total hardness,oxygen consumption,total number of colonies and free residual chlorine.Comprehensive index change analysis,water storage effect:organic glass material>304 stainless steel material>PE material;There was a negative correlation between total hardness and pH value of water quality;For the three kinds of materials,the total number of bacterial colonies in water showed the change rule of slow growth,exponential growth and rapid decline.(2)Taking Escherichia coli(CMCC 44103)and Pseudomonas aeruginosa(ATCC 27853)as the research objects,the influence of different disinfection hydraulic retention time on the growth of the two strains was analyzed.The two strains were inoculated and cultured for about 8 hours,and the number of live bacteria of Escherichia coli and Pseudomonas aeruginosa reached 1.3664×1011CFU/mL,3.0201×1011CFU/mL.After the UV lamp was sterilized continuously for 5s,10s,30s,1min,3min,and 5min,the plate count method showed that after the water sample was disinfected for 10 seconds,the number of viable bacteria of the two decreased to 3.1×106CFU/mL、4.7×107CFU/mL,and after the continuous disinfection for 1min,the inactivation effects of E.coli and P.aeruginosa based on lg(N0/Nt)were 9.684 9.401,and the inactivation efficiency was as high as 99.999%.The results shows that UV sterilization has a good killing effect on bacteria after continuous sterilization for 1 min.In order to further verify that the strain entered the VBNC state under the disinfection environment,the resuscitation experimental analysis was performed on the treatment group.By comparing the plate culture results of the two treatment groups strains and the growth curve of the strains after inoculation.The images showed that after the plate culture dish was continuously cultured under the appropriate conditions for 48h,no obvious colony growth was observed in the culture dish.The treatment group can enter the logarithmic growth phase after inoculation and culture at 3 7℃ and 120r/m for 7-12h.After 16h of inoculation culture,the OD600 value of E.coli(5min in the treatment group)was 1.177,according to the linear relationship(OD600:y =16.382x+0.7226),the number of live bacteria was 2.0×1011CFU/mL,the OD585 value of Pseudomonas aeruginosa is 2.096,and the number of live bacteria was 1.120×1012CFU/mL(OD585:y=55.214x-3.7476).It can be inferred that bacteria can become VBNC state after UV disinfection,and can be revived by inoculation culture under suitable conditions,and the recovery time is positively correlated with the duration of sterilization.(3)Based on the experimental data,a UV disinfection device used in the secondary water supply system was designed and developed.The device was equipped with a UV lamp of 50W,a disinfection dose of 435MJ/cm2,a pump flow rate of 0.523L/s,and a hydraulic retention time of≥60S,the device has a good disinfection effect.The daily treatment scale of the device is 15.1m3-18.8m3/d,the average daily consumption is 5.2 yuan,and the water treatment cost is 0.27-0.34 yuan/m3,which has good economy.Applicable markets for the device mainly include communities with secondary water supply systems,high-rise buildings,or remote areas with surface water or deep wells as water sources and good water quality.The device has great promotion space and application prospect. |
