8.1. SR 03-18-2013 - Laserfiche WebLink

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The extended aeration basin will be designed with a solids retention time of 20 days, organic loading of 15 lb/day/1,000 cubic feet of basin volume, a food to mass (F/M) ratio between 0.04-0.10 lbs CBOD5/lbs MLVSS/day, a Mixed Liquor Suspended Solids (MLSS) between 2,000-5,000 mg/l, and 1.1 lbs OZ/lbs of peak hourly CBOD5. A series of concrete aeration basins with a total volume of 1.8 MG would be provided to meet the design loading conditions. The basins would be approximately 80 feet wide by 160 feet long with a side water depth of 18 feet. A selector basin for biological phosphorus removal would also be provided with an approximate volume of 240,000 gallons. During the activated sludge process the biomass grows and reproduces as the organic matter in the wastewater is consumed. To avoid excessively high MLSS and effluent solid losses, periodic solids wasting is required. Wasting of solids would occur from the final clarifiers after settling and would be used to maintain a desired MLSS concentration within the aeration basin. In addition, Return Activated Sludge (RAS) would be returned to the aeration basins from the final clarifiers to maintain a healthy and active biomass within the system. To accommodate the RAS/WAS pumping needs a new RAS/WAS building would be constructed. This building would house new sludge pumps and flow meters so return and waste flows could be accurately controlled and measured. The location of the aeration basins and RAS/WAS building are shown in Figure 4.1. 4.2.1.7. Final Clarifiers The existing Final Clarifiers have maximum PHWW flow capacity of 5.28 MGD which is 0.40 MGD short of design year PHWW flow. It is proposed that the City reevaluate the final clarifiers in the future when the peak hourly flows to the facility reach 90 percent of the capacity of the final clarifiers. Although the capacity of the final clarifiers is adequate for Design Option No. 1, other improvements will be investigated to improve the operation of the existing clarifiers. Those improvements will include the addition of covers to inhibit algae growth and improved flow control and measurement for return and waste flows. City of Elk River—T12.104758 Page 19 Wastewater Treatment Facility Plan Prepared by Bolton&Menk,Inc.