4.4. SR 03-20-2017 - Laserfiche WebLink

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Additional aeration may be required to satisfy the oxygen demand associated with the oxygen demand and nitrification if the allocated CBOD5 and TKN treatment capacities are exceeded. 4.4 Biological Treatment Performance Evaluation of the treatability of combined municipal wastewater and leachate utilized the Environmental Pollution Agency (EPA) Local Limits Development Guidance. This document provides guidance regarding toxic and inhibitory compounds as well as anticipated removal efficiencies through the typical biological treatment processes. Comparison of the EPA documented inhibition values (Appendix G of Local Limits Development Guidance) and the anticipated blended pollutant concentrations identified one parameter that approaches the threshold level for inhibition. The reported range of zinc inhibition is 0.3-10 mg/L for activated sludge and 0.08-0.5 mg/L for nitrification. Zinc concentrations in the leachate ranged from 0.03-6.64 mg/L and the blended wastewater concentrations are projected at 0.2-0.4 mg/L when only accounting for mass received in the leachate. Complete nitrification of the estimated influent nitrogen concentration of 90-100 mg/L will result in an effluent nitrate concentration in the similar range. If denitrification, (conversion of nitrate to nitrogen gas) is required to meet future total nitrogen limits, additional recycle pumping and supplemental carbon may be required. Future nitrogen limits may be as low as 10 mg/L total nitrogen. Biological treatment relies on carbon: nitrogen:phosphorus (C:N:P) ratios in the appropriate range to support biological activity. Optimum C:N:P ratios are in the range of 100:10:1 and 100:5:1. Projected ratios at start-up and design conditions for the Elk River WWTF are summarized in Table 5. As indicated, the additional of leachate results in a C:P ratio closer to 100:1, therefore, more phosphorus will be utilized through the biological processes, thereby reducing chemical feed requirements. A C:N ratio of approximately 100:20 (5:1) results in all loading conditions. The impact of this elevated nitrogen concentration will not be evident until total nitrogen City of Elk River, Minnesota —121.109643 Page 15 Elk River/Waste Management Leachate Study Prepared by Bolton & Menk, Inc.