The Bacteria-removal Capacity Of Copper-loaded Zeolite As Rainwater Retention Media

The pathogenic microorganisms pollution of urban waters is a latent threat to the public health.In the old districts of cities with combined drainage system,stormwater runoff is often polluted by domestic sewage.Pollution is aggravated with the mass inflow of the sewage-contaminated stormwater with excessive pathogenic microorganisms.Among all the existing bacteria-removal technology,the bioretention has more advantages whose bacteria-removal capacity will be significantly improved with bacteria-removal media.However,there are still deficiencies in research on its application in the on sewage-contaminated stormwater runoff and the properties of bacteria-removal media.In order to solve such problems,this paper prepared copper-loaded zeolites and silver-loaded zeolites as baceteria-removal media,and optimized the preparation conditions of copper-loaded zeolites.The bacteria-eliminating capacity of fine sand,silver-loaded zeolite and copper-loaded zeolite were studied via shake flask tests and retention column tests in both E.coli dilution and sewage-contaminated stormwater.And the best media was selected to investigate its bacteria-eliminating capacity in different rainfall intensity and sewage-contaminated stormwater.The main conclusions are as follows:Among the three important preparation conditions,the stirring temperature and the stirring time had more significant effects on the copper loading than the roasting time?p<0.05?.The best preparation conditions of copper-bearing zeolite were as follows:the stirring time with CuCl₂ solution was 2 hours,the stirring temperature was 80°C,and the roasting time was 2 hours,in which the copper loading quantity was 7.04 mg/g.After preparation,the specific surface area and pore volume of the zeolite increased,and the pore diameter slightly decreased.The main structure of the zeolite remained,and there were more small particles on the surface.In shake flask tests and retention column tests of fine sand,silver-loaded zeolite and copper-loaded zeolite,the E.coli removal rate ranking was copper-loaded zeolite?column?,silver-loaded zeolite?column?,natural zeolite,fine sand?control column?.The presence of COD,TN,TP reduced the E.coli removal rate.Both zeolite columns maintained good removal performance?above 88.84±2.04%?when the influent E.coli concentrations ranged from 10⁷ CFU/L to 10⁵ CFU/L.The results of comparative experiments showed that the addition of bacteria-removing media would improve the stormwater filter's bacteria removal capacity significantly.And copper-loaded zeolite was better than silver-loaded zeolite even under similar preparation conditions.With the increase of the rainfall intensity and COD,TP,TN,the E.coli removal rate of copper-loaded zeolite retention decreased.However,the E.coli removal rate copper-loaded zeolite column stayed more than 89.67%when the rainfall intensity was under30mm/6h?heavy rain?and the pollution were moderate?COD,TP,TN concentrations were 398.05±1.53 mg/L,3.52±0.05 mg/L,and 31.95±0.04 mg/L,respectively?.After 2grade filtration of copper-loaded zeolite column,the E.coli concentration in the effluent decreased to 5.25±1.48 CFU/m L,with a removal rate of 99.48%,meeting the environmental quality standard of surface water of Class V.