America's First Potable Water Flotation-Filtration Plant

This chapter delves into the critical issues surrounding water treatment, focusing on the effective control of disinfection byproducts (DBPs), lead, copper, and total coliform bacteria in drinking water. It begins by outlining the research objectives, emphasizing the significance of stringent water quality standards to safeguard public health. Various control measures for disinfectants and their byproducts, lead and copper contamination, and the mitigation of coliform bacteria levels are explored. The authors introduce the research location, facilities, and chemical processes at the award-winning Lenox Water Treatment Plant (LWTP), the first potable water flotation plant built in America. This chapter provides a comprehensive overview of traditional and innovative technologies for reducing harmful contaminants. Key sections include the reduction of trihalomethane levels through conventional and advanced treatment methods and the performance of a dissolved air flotation-filtration (DAFF) process system. This chapter serves as a valuable resource for researchers, practitioners, and policymakers striving to enhance water treatment practices and ensure safe drinking water. Special emphasis is placed on the two investigation periods of 1981–1983 (LWTP start-up period) and 2019–2023 (LWTP recent operational period). The innovative Lenox plant primarily uses chemical coagulation-precipitation, DAFF, and disinfection processes. Before the plant’s installation in 1982, the total trihalomethane (TTHM) levels in Lenox tap water ranged from 19.3 to 88.5 ppb, along with numerous other water quality violations. Following the implementation of the DAFF system, TTHM levels in Lenox tap water have been reduced by more than 50%. During the recent period of 2019–2023, Lenox tap water quality has been excellent: TTHM = 32–40 ppb (MCL = 80 ppb), HAA5 = 24–30 ppb (MCL = 60 ppb), chloroform = 11–15 ppb, total coliform = zero % positive (MCL = 5% positive), nitrate = 0.5–0.8 ppm (MCL = 10 ppm), copper = 0.3–0.6 ppm (MCL = 1.3 ppm), lead = 2–5 ppb (MCL = 15 ppb), and turbidity = 0.12–0.15 NTU (MCL = 1 NTU). Without pre-chlorination (or pre-disinfection), the innovative Lenox flotation-filtration (DAFF) system removes 80%–100% of coliform bacteria from raw water. Two major process improvements are noticeable: (a) the damaging stage for generating most THM by pre-chlorination is avoided; chlorine dosage in subsequent post-chlorination is significantly reduced by 10%–40%. Residual chlorine is maintained in the range of 0.8–0.9 ppm from 2019 to 2023 (MCL = 4 ppm). Since the filter backwash wastewater (amounting to 15% of raw water input) is fully recycled for drinking water production, there are two additional advantages compared to conventional water purification systems: (a) a 15% saving in chemicals for water purification, (b) elimination of wastewater facilities and chemicals, and (c) production of 15% more potable water. The findings from this investigation can be applied to the combined DAFF system (such as Krofta Sandfloat DAFF) or any manufacturer’s water purification system consisting of dissolved air flotation (DAF) and filtration connected in series.