Laserfiche WebLink
would be designed to provide biological phosphorus removal and would be <br /> approximately 110 feet wide by 180 feet long with a side water depth of 18 feet. <br /> During the activated sludge process more biomass is produced as bacteria consume the <br /> organic matter in the wastewater. To avoid excessively high MLSS and effluent solid <br /> losses, periodic solids wasting is required. Wasting of solids would occur from the final <br /> clarifiers and would be used to maintain a desired MLSS concentration within the <br /> aeration basin. In addition, RAS would be returned to the aeration basins from the final <br /> clarifiers to maintain a healthy and active biomass within the system. To accommodate <br /> the RAS/WAS pumping needs a new RAS/WAS building would be constructed. This <br /> building would house new sludge pumps and flow meters so return and waste flows <br /> could be accurately controlled and measured. The location of the aeration basins and <br /> RAS/WAS building are shown in Figure 4.3. <br /> 4.2.2.7. Final Clarifiers <br /> The existing Final Clarifiers have a maximum PHWW flow capacity of 5.28 MGD. Ten <br /> States Standards recommends that the Final Clarifiers receiving activated sludge with <br /> chemical phosphorous removal should be designed for a surface overflow rate of 900 <br /> gpd/ft2. To meet the PHWW flow of 7.27 MGD at the design year the existing facility <br /> would need an additional 55 foot diameter secondary clarifier. <br /> Since the existing Final Clarifiers have adequate capacity for future flows over the next <br /> several years it is not recommended to construct a new secondary clarifier at this time. <br /> The city should reevaluate the needs for an additional secondary clarifier as peak flows <br /> reach 90 percent of the capacity of the Final Clarifiers. However, improvements to the <br /> existing clarifiers should be considered and include the addition of covers to inhibit algae <br /> growth and improved flow control and measurement for return and waste flows. <br /> 4.2.2.8. Filters <br /> The existing gravity filters have a design flow of 7.0 MGD. The PHWW flow for Design <br /> Option No. 2 at the design year 2035 is 7.27 MGD. Therefore, the existing facility is <br /> 0.27 MGD short in capacity. To optimize filter operation, modifications for the filter <br /> City of Elk River—T12.104758 Page 23 <br /> Wastewater Treatment Facility Plan Prepared by Bolton&Menk,Inc. <br />