AWWA WQTC56972

Treatment of surface water supplies by conventional methods is becoming increasingly complex as utilities must comply with increasingly stringent current and future water quality regulations. In-depth knowledge of chemical process options is necessary to produce a high-quality water that meets both aesthetic and health-related criteria. Consequently, a bench-scale study was undertaken to assess the impact of a variety of different chemical treatment options on a surface water for which a new water treatment plant is currently being planned. A 100-gallon water sample was collected from the Savannah River, a typical flashy surface water that is low in alkalinity (median 14 mg/L, maximum 20 mg/L as CaCO3), low in organic content (median TOC 2.9 mg/L, maximum 4.5 mg/L) and low in turbidity but subject to run-off related excursions (annual median 2 NTU, maximum 130 NTU). The major water quality issues affecting design of the new treatment plant are common to many water utilities around the United States: chlorinated disinfection byproducts (DBPs), particularly total trihalomethanes (TTHMs) and haloacetic acids (HAAs), and taste and odor episodes associated with algal activity in upstream river impoundments. Control of seasonal iron and manganese episodes occurring in the raw water, associated with turnover in upstream impoundments, is also a concern. A wide range of strategies was evaluated for the common water quality problems of DBPs, taste and odor, and iron and manganese. Of all the treatment scenarios tested, ozone was the most effective for addressing all of these concerns. Chlorine dioxide did not produce beneficial effects at doses acceptable with respect to chlorite formation. When cost and operational complexity were considered, the inclusion of KMnO4 and PAC addition in a conventional process train was the most effective for DBP control, as well as providing the flexibility to address seasonal taste, odor, iron and manganese episodes. Includes 6 references, tables, figures.