8.1. SR 03-18-2013 - Laserfiche WebLink

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Peak Instantaneous Wet Weather Flow(PIWW) 7.10 MGD Carbonaceous Biochemical Oxygen Demand (CBOD5) 8,518 lb/day Total Suspended Solids (TSS) 7,808 lb/day Total Kjeldahl Nitrogen (TKN) 1,065 lb/day Total Phosphorus (P) 213 lb/day Construction activities include primary clarifiers, trickling filter improvements, activated sludge addition, covers for the existing final clarifiers, and UV disinfection improvements. The new clarifiers and activated sludge tanks are partially below grade,cast- in-place concrete facilities. Erosion control will be provided for the excavated material. Excess material will be wasted off-site with prompt establishment of a vegetative cover. A detailed description of improvements for each process is provided below. Primary Clarifiers To meet flow requirements the existing facility would need an additional 2.66 MGD of capacity. This could be accomplished by the addition of two 40-foot diameter clarifiers that could be brought in to service in two phases. One additional 40-foot clarifier would provide enough total capacity for a flow of 4.52 MGD. Once flows reached 90%of the capacity of the three clarifiers the fourth clarifier could be brought on line which would increase the total capacity of the primary clarifiers to 6.03 MGD. With all four primary clarifiers online the system would meet the design requirements. Staging the addition of the third and fourth clarifiers would provide easier operation at current flows. Sizing of the additional clarifiers was based on Ten States Standards which states that the primary clarifiers receiving waste activated sludge would be designed for a surface overflow rate of 1200 gpd/ft2. Trickling Filters Improvements to the trickling filters will include modifications to the trickling filter operation and recirculation piping. The modifications would include operation of the two trickling filters in parallel with pumping and piping modifications to achieve a recirculation rate of 100 percent. Other possible modifications include improvements to the distribution arm, controls, ventilation, and access ways. Activated Sludge Process Since the existing trickling filters do not have enough capacity to treat all the flows and loadings, an additional biological wastewater treatment process is required. In order to provide a reliable, easy to operate system, an extended aeration activated sludge process would be constructed. 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 Ibs CBOD5/Ibs MLVSS/day, a Mixed Liquor Suspended Solids(MLSS) between 2,000-5,000 mg/I, and 1.1 Ibs 02/Ibs of peak hourly CBOD5. A concrete aeration basin containing three cells with a total volume of 1.8 MG would be provided to meet the design loading conditions. The basin would be approximately 115 feet square with a side water depth of 18 feet. During the activated sludge process more biomass is produced as bacteria consume the organic matter in the wastewater. 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. Sand Filters The existing gravity filters have a design flow of 7.0 MGD and will have adequate capacity to meet the flow of 5.68 MGD for the design year 2035. To optimize filter operation, modifications of the filter controls, media, and the chlorine feed system will be evaluated. Modifications to the chlorine feed system shall include an inline chlorine analyzer to protect against over chlorination. Disinfection System Capacity of the existing UV system is 3.0 MGD which is 2.67 MGD short in capacity for design flows. To meet the design requirements, new UV equipment would need to be installed in the existing spare channel which would increase the total capacity to 6.0 MGD. Additional improvements would include replacing the effluent weir on the existing UV channel with a fixed depth finger weir. Electrical/Controls The existing control system does not include a central control system for the entire wastewater treatment facility. Upgrades to the control system should include a central control system that will allow the operators to monitor and control all units of the treatment process from one location. Biosolids Handling Facilities www.pca.state.mn.us 651-296-6300 800-657-3864 TTY 651-282-5332 or 800-657-3864 • Available in alternative formats wq-wwtp2-20 • 8117112 Page 2 of 7