8.1. SR 03-18-2013 - Laserfiche WebLink

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Table 3.1 Digestion Facilities Elk River Wastewater Treatment Facility Primary Digester Secondary Digester Diameter, ft 55 35 SWD, ft 20 19.5 Volume, ft' 47,460 18,700 gallons 355,000 140,000 Temperature, °F 98 Ambient Biosolids Concentrations, % 1-4 2 The digestion process reduces both the total biosolids volume and the amount of pathogens and vectors found in the biosolids, resulting in biosolids of less quantity and better quality. The anaerobic digester capacities are determined by Volatile Suspended Solids (VSS) loading and minimum time and temperature requirements. For completely mixed digesters, a loading rate of 80 lb VSS/1,000 ft3 is allowed. A minimum detention time of 15 days is required to meet the US EPA 503 regulations for Class B biosolids. From the existing data, the concentration of biosolids wasted to the primary digester is 1.9 percent solids with a VSS content of 85 percent. If the solids are continuously wasted at the above mentioned characteristics the maximum capacity of the primary digester would be 23,700 gallons per day. To run the primary digester at the maximum volatile solids loading rate, the City would need to thicken the influent sludge to 2.25 percent solids. At a concentration of 2.25 percent solids concentration the primary digester can process 4,470 lbs/day of biosolids. The estimated biosolids production rate for Design Option No. 1 and No. 2 are 13,400 lbs/day and 17,150 lbs/day, respectively. Based upon the future loadings the City would need to expand the biosolids handling facilities. City of Elk River T12.104758 Page 13 Wastewater Treatment Facility Plan Prepared by Bolton&Menk,Inc.