DISINFECTION BY-PRODUCT ANALYSIS AND MODELING IN A WATER DISTRIBUTION SYSTEM

摘要

Minimizing the risks of disinfection by-products (DBPs) while maintaining adequate protection from microbial contamination is one of the dilemmas water utilities and regulating agencies are faced with today. The study of disinfection by-products (DBPs) has gained importance in the past decade because of the increased emphasis that regulatory agencies have placed on DBP control. DBPs are formed during water treatment when disinfectants and oxidants react with organic and inorganic matter. Since chlorine is used in a large majority of treatment plants in the United States, the chlorinated by-products are the most prevalent. The two chlorinated by-products that are regulated are trihalomethanes (THMs) and haloacetic acids (HAAs). The formation of both THMs and HAAs increases with time when a chlorine residual is present, leading to higher concentrations in the distribution system than in the finished water at the treatment plant. Regulations on DBPs are based on concentrations in the distribution system rather than at the end of the treatment process. Water quality models are often used in attempt to analyze various water quality parameters in the distribution system. The goal of this research project was to develop a site-specific water quality model to simulate the formation of THMs and HAAs (all nine species) in the Gwinnett County, Georgia water distribution system using a first-order saturation growth model with the distribution system modeling program WaterCAD?. These model predictions were compared with measured values from field sampling. The modeling effort produced results with varying success. The results from the HAA modeling appeared to be reasonably successful, having better agreement between predicted and measured concentrations than the THM modeling. While the measured and predicted results were statistically different, the results were of practical value in determining relative changes in water quality that can be expected at various locations throughout the distribution system. The results provided a reasonable indication of the effects of the distribution system on water quality and on the ability to model THMs and HAAs with distribution system hydraulic modeling software.