8.1. SR 03-18-2013 - Laserfiche WebLink

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SECTION 3.0 EVALUATION OF EXISTING WASTEWATER TREATMENT FACILITIES 3.1 General This section evaluates the existing wastewater treatment facility and its ability to treat the proposed design flows and loadings. Any problems with the existing equipment will also be discussed. The overall wastewater treatment facility is best evaluated by analyzing each of the main process units and their respective treatment capacities. The current process consists of screening, vortex grit removal, primary clarifiers, trickling filters, final clarifiers, sand filters, ultraviolet (UV) disinfection, and anaerobic sludge digestion and storage. The existing site plan is presented in Figure 3.1. The current rated capacity as stated in the NPDES permit is 2.2 MGD (AWW) and a CBOD5 loading of 200 mg/L. In this report, the existing treatment processes are evaluated to handle the requirements of hydraulic and organic loadings for Design Option No. 1 and No. 2. 3.2 Liquid Treatment Process 3.2.1. Screening Wastewater enters the treatment facility and flows through two mechanical bar screens. The screens are installed in 2 1/2 foot wide by 3 foot deep channels. Each screen has a capacity of 7.00 MGD with a clear opening of 3/4 inch. Each screen is redundant to the other in case of mechanical breakdown. The existing screens would meet the design requirements for Design Option No. 1, but would need modifications to meet the requirements for Design Option No. 2. 3.2.2. Flow Measurement Following the screens, wastewater flows through a parshall flume for flow measurement. The existing parshall flume has a 12-inch throat width with a maximum flow measurement capacity of 10.4 MGD. The existing parshall flume would meet the flow measurement requirements for both Design Options. City of Elk River—T12.104758 Page 9 Wastewater Treatment Facility Plan Prepared by Bolton&Menk,Inc.