Study On The Application Of Reagents To The Secondary Water Supply

As is known to us, when tap water flows to the secondary water supply facilities, the water will be contaminated by the secondary water supply facilities or influenced by external factors. It is a very serious problem closely related with general inhabitant, which has aroused much attention in environmental sanitation. At present, the secondary water problems are mainly in chlorine reduction, microbial indicators of failure and so on. Therefore, it is urgent to find a safe, economical and efficient disinfection processes.This paper takes the secondary water as an example. To solve the problems of low chlorine and unqualified microbial indexes, the disinfectants sodium hypochlorite and chlorine dioxide were used in secondary water disinfection research. By the simulation of different water quality conditions, the generation of disinfectants decay and byproducts were investigated in static and dynamic conditions. For this, it would provide a scientific basis for the secondary water disinfection processes and water quality management. The followings are the main research conclusions.(1) In the static system of sodium hypochlorite (NaClO), the chlorine decay and the generation of trichloromethane and carbon tetrachloride reduced with the increase of ammonia dosage. The increase of CODMn and pH in raw water can promote the formation of trichloromethane and carbon tetrachloride. In the tested water samples,methylene chloride, trichloroethane, dibromo-chloro-methane, and other disinfection byproducts were not detected. In the static system of chlorine dioxide (ClO2), after 4 h of adding ClO2, the rate of ClO2 attenuation was accelerated with the increase of ClO2 dosage. The increase of ammonia dosage, CODMn and pH in raw water can promote ClO2 attenuation and the formation of chlorate and chlorite. The order is: ammonia dosage < CODMn < pH. The static system indicates that: by-products would exceed after 36 h if CODMn was more than 3.13 mg/L, even though 0.1 mg/L of sodium hypochloritewas added to the secondary water. However, by-products would not exceed if chlorine dioxide was choosed as disinfectant.(2) In the dynamic system of sodium hypochlorite, by-products would not exceed in 12 h if CODMn was less than 3 mg/L, ammonia dosage was less than 0.5 mg/L, 6.5 < pH < 8.5, 0.1 mg/L of sodium hypochlorite was added to the secondary water, and the hydraulic rerention time was 48 h. In the same condition, by-products may exceed if sodium hypochlorite was added with the dosage of more than 2.0 mg/L. In the dynamic system of chlorine dioxide, by-products would not exceed in 12 h if CODMn was less than 3 mg/L, ammonia dosage was less than 0.5 mg/L, 6.5 < pH < 8.5, 0.05 mg/L of chlorine dioxide was added to the secondary water, and the hydraulic retention time was 48 h. In the same condition, by-products may exceed if chlorine dioxide was added with the dosage of more than 0.7 mg/L.(3) Models of static and dynamic disinfect system were built. The costs between the two disinfectants was investigated, as well as the whole input of disinfect system.