The City of Cashmere owns and operates a lagoon system wastewater treatment facility (WWTF); however, the WWTF’s treatment capacity was not able to keep up with recent increases in environmental regulations. RH2 was tasked to prepare a Facility Plan and design upgrades that will meet the new total maximum daily load phosphorus limitations.
The WWTF upgrade was designed for an average day flow of 1.1 MGD and includes a new headworks with screening and a vortex grit removal unit and classifier; equalization and activated sludge basins; 40-foot circular clarifiers; open channel UV disinfection; a dissolved air flotation unit for thickening; an aerobic digester; and a belt filter press for sludge handling.
The vortex grit unit and classifier will be installed partially outdoors with screens to minimize costs. The equipment includes weather protections and a bypass to accommodate grit unit maintenance.
An activated sludge process configuration was designed to achieve enhanced biological phosphorus removal. This was one of the key design criteria to maximize effluent phosphorus reduction. The design was a modified form of the Bardenpho process and was selected with multiple anoxic and aerobic stages. Each aerobic stage includes a grid of fine bubble diffusers.
Different UV disinfection systems were evaluated and a horizontal, open channel system with two banks in series in one channel was selected to reduce costs, minimize operating complexity, provide reliable disinfection, and ensure proper disinfection during minimum and maximum week flows.
The facility upgrades are currently under construction and should be completed in early 2014.