Toxicity-oriented water quality engineering

The fundamental goal of water quality engineering is to ensure water safety to humans and the environment.Traditional water quality engineering consists of monitoring,evaluation,and control of key water quality parameters.This approach provides some vital insights into water quality,however,most of these parameters do not account for pollutant mixtures-a reality that terminal water users face,nor do most of these parameters have a direct connection with the human health safety of waters.This puts the real health-specific effects of targeted water pollutant monitoring and engineering control in question.To focus our attention to one of the original goals of water quality engineering-human health and environmental protection,we advocate here the toxicity-oriented water quality monitoring and control.This article presents some of our efforts towards such goal.Specifically,complementary to traditional water quality parameters,we evaluated the water toxicity using high sensitivity toxicological endpoints,and subsequently investigated the performance of some of the water treatment strategies in modulating the water toxicity.Moreover,we implemented the toxicity concept into existing water treatment design theory to facilitate toxicity-oriented water quality control designs.Suggestions for the next steps are also discussed.We hope our work will intrigue water quality scientists and engineers to improve and embrace the mixture water pollutant and toxicological evaluation and engineering control.

Assessing microbial and chemical exposure risks of Giardia in indoor swimming pool water disinfected by chlorine

Swimming pools adopt chlorination to ensure microbial safety. Giardia has attracted attention in swimming pool water because of its occurrence, pathogenicity, and chlorine resistance. To control Giardia concentrations in pool water and reduce the microbial risk, higher chlorine doses are required during disinfection. Unfortunately, this process produces carcinogenic disinfection byproducts that increase the risk of chemical exposure. Therefore, quantitatively evaluating the comparative microbial vs. chemical exposure risks that stem from chlorination inactivation of Giardia in swimming pool water is an issue that demands attention. We simulated an indoor swimming pool disinfection scenario that followed common real-world disinfection practices. A quantitative microbial risk assessment coupled with a chemical exposure risk assessment was employed to compare the Giardia microbial exposure risk(MER) and the trihalomethane chemical exposure risk(CER) to humans. The results demonstrated a 22% decrease in MER-and CER-induced health exposure risk, from 8.45E-5 at 8:00 to 6.60E-5 at 19:00. Both the MER and CER decreased gradually, dropping to 3.26E-5 and 3.35E-5 at 19:00, respectively. However, the CER exceeded the MER after 18:30 and became the dominant factor affecting the total exposure risk. Past the 18 hr mark, the contribution of trihalomethane CER far exceeded the risk aversion from microbial inactivation, leading to a net increase in total exposure risk despite the declining MER. Swimmers may consider swimming after 19:00, when the total exposure risk is the lowest. Lowering water temperature and/or p H were identified as the most sensitive factors to minimize the overall health exposure risk.