Distribution Characteristics of Disinfection Byproducts in Drinking Water Distribution Systems of Different Disinfection Methods

Abstract:

This study analyzes the distribution characteristics and influencing factors of three types of disinfection by-products（DBPs）—trihalomethanes （THMs）， haloacetic acids （HAAs）， and halonitriles （HANs）—in water samples from drinking water distribution systems in the southeastern coastal region of China. These distribution systems utilize three different secondary disinfectants： chlorine， chloramine and chlorine dioxide. The results indicate a relatively low risk for exceeding DBPs limits in the three cities studied. Among the collected 117 water samples， 10 exceeded the standard limit for THMs， while other DBPs were within compliance. Water distribution systems using chlorine as a disinfectant showed significantly higher concentrations of THMs and HANs in comparison with other water distribution systems. Chlorine dioxide effectively reduced the formation of THMs in comparison with the chlorine. Chloramines were used in Shanghai， however， the concentration of HAAs was 5 to 19 times higher than that in the other three systems， potentially due to higher levels of HAA precursors in the source water. Concentration of disinfectants and DBPs in drinking water varied with distances. In the SH-NH₂Cl system， disinfectant concentration showed an negative correlation with distance （r = -0.57）. This system also changed in nitrate， nitrite， and ammonia nitrogen concentrations along the distance， suggesting gradual chlorine decrease and nitrification in the distribution systems， leading to the oxidation of ammonia to nitrite and nitrate. In the WJ-Cl₂ system， a significant correlation was found between DBPs and distance. The concentration of HANs decreased with distance （r =-0.49）， while HAAs concentration displayed an increase along the path （r = 0.45）. Moreover， long stagnation time within premise plumbings can also impact water physicochemical qualities. This study reveals the concentration and variation of DBPs in distribution systems water using different types of secondary disinfectants. The findings provide a basis for water quality assessment and risk control in various regions.

Key words:disinfection by-products;trihalomethanes;haloacetonitrile;haloacetic acid