8.1. SR 03-18-2013 - Laserfiche WebLink

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3.2.3. Grit Removal Following flow measurement, wastewater flows to the vortex grit removal process. The existing grit tank is an exterior tank located just east of the Headworks Building. The existing grit tank has a 10 foot diameter and a side water depth of 11 1/2 feet. The maximum capacity of the existing grit removal system is 7.0 MGD with a bypass inplace for peak instantaneous flows. The grit settled at the bottom of the tank is pumped to a grit classifier, where grit is further washed before it is discharged into a dumpster for disposal. The existing grit removal process would meet the requirements for Design Option No. I and No. 2. 3.2.4. Primary Clarifiers Following grit removal, wastewater flows to a splitter structure where it is evenly split between two primary clarifiers. The existing primary clarifiers are each 40 feet in diameter with a side water depth of 9 feet. Maximum AWW flow and PHWW flow of each clarifier are 1.25 MGD and 1.51 MGD, respectively. The combined maximum AWW and PHWW flows are 2.50 MGD and 3.02 MGD, respectively. The existing clarifiers do not meet AWW and PHWW flow requirements for Design Options No. I and No. 2. In Addition, the existing collection mechanism in both primary clarifiers is in need of replacement due to their age. 3.2.5. Trickling Filters Following the primary clarifiers, wastewater flows to the trickling filter pump station where it is pumped to the top of the trickling filters. The existing filters consist of two trickling filters that are each 26 feet deep with a 45 foot diameter. The top 2 feet of media is a cross flow type while the bottom 24 feet is a vertical flow type plastic media. The specific surface area of the media is 30 square feet per cubic foot. Each trickling filter has a two-arm distributor to evenly apply wastewater on the media. City of Elk River—T12.104758 Page 10 Wastewater Treatment Facility Plan Prepared by Bolton&Menk,Inc.