The advanced water treatment systems including ozonation and GAC adsorption have been introduced to many plants in recent few decades. As a result, some trade-offs have arisen between the reduction of chlorine disinfection byproducts and the increase in ozone treatment byproducts. However, due to differences in health effects of each substance comparing their impact on human health is difficult. Therefore, we compared the health effects using the risk expected values as a common index which was derived from the disability-adjusted life years (DALY). Four trihalomethanes and two haloacetic acids chosen as representative chlorine disinfection by-products, and bromate ion chosen as an ozone treatment by-product were compared before and after introduction of new treatment processes. Further the oral exposure to drinking water, and the inhalation exposure to trihalomethanes by showering were estimated.
The total risk expected value has been decreased from 4.8×10−4 [year−DALY/lifetime exposure] to 3.2×10−4 [year−DALY/lifetime exposure], which is about about 30％ reduction after the introduction of the new treatment processes.