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removal is required. Denitrification is supported with C:N ratios as low as approximately 3:1, <br />below this ratio, supplemental carbon will be required to facilitate the denitrification process. <br />Table 5 — Carbon:Nitrogen:Phosphorus Ratios <br />CBODs TN Phos <br />Loading Condition C:N:P Ratio <br />(Ib/day) (lb/day) (lb/day) <br />Design Conditions 7,220 1,362 273 100: 19: 3.8 <br />Current Load <br />Leachate <br />Current Load + Leachate <br />3,153 719 <br />6,510 1,350 <br />7,220 - 9,663 2,069 <br />74 100: 22: 2.3 <br />10.3 100: 20: 0.16 <br />84.3 100: 21 : 0.87 <br />100:29: 1.17 <br />Alkalinity is consumed by the nitrification process at a rate of 7.14 lb as CaCO3 per lb of <br />nitrogen oxidized to nitrate. Therefore, with a projected influent nitrogen concentration of 90- <br />100 mg/L, a minimum alkalinity concentration of approximately 1,000 mg/L is required. <br />4.5 UV Disinfection System Performance <br />The existing ultraviolet (UV) disinfection system is designed to achieve a dose of <br />30,000 µWs/cm2 at a peak design flow of 7.0 MGD and a UV transmittance (UVT) of <br />61 percent. This dose is designed to achieve compliance with the required effluent fecal coliform <br />limit of 200 per 100 mL. <br />As indicated previously, landfill leachate has a distinct color that reduces the UVT and <br />effectiveness of the UV disinfection system. A bench scale study evaluated UVT reduction with <br />a combination of raw leachate and treated municipal wastewater. The theoretical impact on UV <br />system performance was calculated based on the measured the UVT values of the blended <br />solutions. This conservative evaluation assumes color in the leachate is not removed through the <br />biological activated sludge treatment process. <br />Results of the UVT evaluation are summarized below. The results indicate the need for pilot <br />testing with activated sludge treatment as the existing UV disinfection system cannot achieve the <br />design UV dose of 30,000 µWs/cm2 with the blended flow until the influent flow exceeds <br />5 MGD. <br />City of Elk River, Minnesota —121.109643 Page 16 <br />Elk River/Waste Management Leachate Study Prepared by Bolton & Menk, Inc. <br />