Adverse Impacts of Enhanced TOC Removal on a Colorado Front Range Source

摘要

In 1996, the City of Englewood (City) initiated the upgrade of the Charles Allen WaterrnTreatment Plant (WTP) to improve plant reliability and to meet the more stringentrnrequirements of the proposed microbial and disinfection by-product (DBP) regulations.rnPilot-scale evaluation of free chlorine application to the raw, settled, and filtered watersrnproduced interesting results regarding the formation of DBPs in relation to the removal ofrnnatural organic matter (NOM) as measured by total organic carbon (TOC). DBPs,rnparticularly the brominated and mixed choro-bromo trihalomethanes (THMs) andrnhaloacetic acids (HAAs), were observed at higher concentrations as TOC removal wasrnimproved through filtration or higher coagulant doses as compared to TOC levels in thernsettled waters. These increases in DBP concentration combined with the shift inrnspeciation resulted in an estimated 15 to 20 percent greater carcinogenic risk based onrnavailable health effects data. The marginal improvements for TOC removal beyond thatrnobserved for turbidity removal also resulted in increased solids production and projectedrntreatment costs. This report discusses the procedures, results, and implications of therncoagulation and DBP testing conducted for the City of Englewood.