The U.S. EPA Stage 2 Disinfectants and Disinfection Byproducts Rule (S2DDBR) requires potable water utilities to maintain total trihalomethane (TTHM) concentrations below 80 µg/L at all locations within distribution systems beginning in 2012 due to adverse health-effect risks. Air stripping effectively volatilizes TTHMs due to their low Henrys law constants. However, commercially available air-stripping systems do not optimize processing due to inefficient water mixing and aeration, and require large capital and operations and maintenance expenditures. This proposal describes TTHM reduction results from the initial field test of a diffused aeration (DA) prototype combined with SolarBees existing solar-powered circulation (SPC) technology in Las Vegas Valley Water Districts Elkhorn 2 reservoir (LV). The goal of the proposed research is to optimize DA parametric values for TTHM reduction to enable commercialization of a SPC-DA system that maximizes processing and operational efficiencies. Existing systems use DA for mixing and TTHM volatilization, requiring DA deployment on reservoir bottoms. TTHMs saturate air bubbles within 2 feet of rise. DA deployment at 25 feet requires 12.5-times the power required at 2 feet, resulting in 300 HP blowers in 10,000,000 gallon reservoirs. SPC currently improves water quality by circulating water throughout reservoirs to prevent thermal stratification and evenly distribute water column constituents without grid power. However, circulation alone does not sufficiently volatize TTHMs. SolarBee's prototype DA uses 7.5-HP gridpowered blowers to deliver air to distribution boxes mounted atop SPC units. The distribution boxes supply air to DA manifolds suspended 2 feet below the surface. Measurements of TTHM reduction in SolarBee's 12,000-gallon test tank using 1-6 manifolds indicated that five SPC-DA units (37.5-HP total), each with 32 5-line manifolds, 5 feet in length staggered across a 40-foot diameter, were needed for LVs 10,000,000-gallon reservoir. TTHM concentrations in LV decreased by 33 percent within 3 days of SPC-DA deployment. Comparable results were obtained repeatedly during alternating SPC-DA on/off periods. We propose to systematically investigate in our test tank the DA parameters of manifold depth, treatment zone diameter, lines/manifold, line (therefore manifold) length and interline spacing, airhole size, angle and spacing, and cfs/unit. The prototype SPC-DA system effectively reduced TTHM concentrations and reduced power requirements by 87.5 percent relative to traditional systems. We anticipate that the proposed research will further increase TTHM reduction by 50 percent and reduce power usage by 80 percent. Phase II research will field-test optimized SPC-DA in LV and two additional sites. Optimized SPC-DA will provide utilities with a highly efficient system for meeting the U.S. EPA S2DDBR for TTHMs. Supplemental
Keywords: water, drinking water, potable water, trihalomethane, TTHM, air stripping, diffused aeration, solar-powered circulation, TTHM volatilization, SBIR
