Analysis on Levels of Disinfection Byproducts in Municipal Water Supplies of a City in 2013-2016

Objective To explore the levels of disinfection byproducts in municipal water supplies, and provide the basis for controlling the contamination of disinfection byproducts.

Methods The water quality monitoring of all municipal waterworks in the city was carried out in 2013-2016 according to the national standards. The analysis of data was based on different years, forms of water supply, disinfection processes, facility scales, plant levels and seasons of water supply to find out the cause of unqualification by descriptive epidemiological method.

Results Among 12 indexes, dichloromethane and carbon tetrachloride were not detected in water samples, and the detection rate of other 10 indexes were varied from 12.88% to 100.00%. The overall unqualification rate of disinfection byproducts was 37.50%.As chloroform, trihalomethanes, dichloroacetic acid and trichloroacetic acid were selected as symbolic indexes to compare the unqualification of water samples, the unqualification rate of river-source water were higher than those of reservoir-source water; adding chlorine before filtration was higher than that after filtration; and the difference of chloroform and trihalomethanes were statistically significant. Disinfection byproducts were more produced in larger scale and higher level facilities, and the difference of chloroform and trihalomethanes were statistically significant. In the comparison of different disinfectants, the residual byproducts in water samples disinfected by liquid chlorine was higher than those by chlorine dioxide, and the differences of chloroform, trihalomethanes, dichloroacetic acid and trichloroacetic acid were all statistically significant. More disinfection byproducts was discovered in water with lower turbidity and the differences of chloroform, trihalomethane were statistically significant. In different seasons of water supply, only the difference of dichloroacetic acid in water was statistically significant.

Conclusions In general the contamination of disinfection byproducts in municipal water supplies of the city was low. Because the uncertainty of using chlorine dioxide for disinfection could not be suitable for small scale waterworks without reliable management; and supervision should be strengthened by relevant authorities. Reducing the particle size of sand in V-type filter would become the most effective and practical measures to control disinfection byproducts in drinking water.