Improved TTHM Reduction Processing and Operational Efficiencies in Potable Water Distributions Systems Using Solar-Powered Circulation with Diffused, Near-Surface Aeration
The U.S. EPA Stage 2 Disinfectants and Disinfection Byproducts Rule (S2DDBR) requires potable water utilities to maintain total trihalomethane (TTHM) concentrations below 80µg/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 Henry’s law constants. However, commercially available air-stripping systems do not optimize processing due to inefficient water mixing and aeration, and require large capital and O&M expenditures. This proposal describes TTHM reduction results from the initial field test of a diffused aeration (DA) prototype combined with SolarBee’s existing solar-powered circulation (SPC) technology in Las Vegas Valley Water District’s 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 maximized 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-ft of rise. DZ deployment at 25-ft requires 12.5-time the power required at 2-ft, resulting in 300 HP blowers in 10,000,000 gal 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. Our prototype DA uses 7.5-HP grid-powered blowers to deliver air to distribution boxes mounted atop SPC units. This distribution boxes supply air to DA manifolds suspended 2-ft below the surface. Measurements of TTHM reduction in our 12,000-gal test tank using 1-6 manifolds indicated that five SPC-DA units (37.5-HP total), each with 32 5-line manifolds 5-ft in length staggered across a 40ft diameter, was needed for LV’s 10,000,000-gal reservoir. TTHM concentrations in LV decreased by 33% within 3-d ays 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, air-hole size, angle and spacing and CFS/unit. The prototype SPC-DA system effectively reduced TTHM concentrations and reduced power requirements by 87.5% relative to traditional systems. We anticipate that the proposed research will further increase TTHM reduction by 50% and reduce power usage by 80%. Phase II research will field-text optimized SPC-DA in LV and tow additional sites. Optimized SPC-DA will provide utilities with a highly efficient system for meeting the U.S. EPA S2DDBR for TTHMs.
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