AWWA WQTC58842

The objective of this study was to review water treatment plant (WTP) operation practices in order to decrease the level of Trihalomethanes (THMs) at the outlet of the WT plants and in the distribution system. Specific objectives of this project were: to characterize conditions that lead to the formation of THMs after the final chlorination for several water treatment (WT) plants in the United Kingdom; to provide recommendation to prevent or limit THMs formation by optimizing the natural organic matter (NOM) removal and chlorination operating conditions. A global approach was implemented to identify the adverse conditions of THM occurrence on several industrial production sites in the United Kingdom. Four different industrial case studies were chosen to illustrate different water quality, different treatment train and different strategies to solve the THM issue. The study was performed during the 2001/2003 period for sites 1 and 2, and in 1999/2001 for sites 3 and 4. The study contained the following tasks: plant operation audits on several WTPs treating surface waters through clarification and polishing treatment for some of them, with capacities ranging from 15 to 200 Ml/day (around 4 to 53 MGD); extensive quality monitoring of raw waters and of finished waters leaving the different WTPs to identify the THM levels at the outlet of the WT plants and their evolution in the distribution systems; building of a database containing information related to resources, plant operation practices and THM occurrences in treated water in different parts of the distribution systems; implementation of laboratory-studies to generate the missing data from the plants; and, from full-scale data and predicted values for THM formation establishment of recommendations to prevent and limit THM formation by optimizing the NOM removal and chlorination operating conditions according raw water quality variations. Includes 21 references, tables, figures.