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<br />TECHNICAL MEMO <br /> <br />To: <br />From: <br />Subject: <br /> <br />Date: <br /> <br />Distribution <br />Dawn Homer, Eric Evans ~ <br />Pretreatment Improvements <br />November 17, 2004 r-Ic:MJard R. Green Company <br /> <br />INTRODUCTION <br /> <br />The headworks at the City of Elk River Wastewater Treatment Facility (WWTF) serves to <br />pretreat wastewater flowing into the plant with the primary objective of protecting <br />downstream pumps and equipment. Bar screens remove rags and large objects ITom <br />wastewater, which migbt otberwise be caught in downstream pumps. Grit removal systems <br />protect equipment ITom excessive abrasion. By removing grit at the head of the plant, <br />digester and aeration basin (future) grit accumulation is reduced. Additionally, the <br />Pretreatment Building contains flow measurement and influent sampling. The Minnesota <br />Pollution Control Association (MPCA) inspected the current plant headworks and <br />determined that the City needs to upgrade the pretreatment equipment, becallse the flow <br />capacity is inadequate and the existing manual bar screen is unacceptable. <br /> <br />Design of the proposed headworks improvements follows Ten State Standards (Great Lakes <br />- Upper Mississippi River - GLUMR). Selected standards of interest include: <br /> <br />Bar Screens: <br />. At design average flow conditions, approach velocities should be no less than <br />1.25 feet per second (FPS) and no greater than 3.0 FPS. <br />. Dual channels shall be provided and equipped with necessary gates to isolate flow <br />ITom any screening unit. <br />. The channel invert should be 3 to 6 inches below the invert of the incoming <br />sewer. <br />. Entrance channels should be designed to provide equal and uniform distribution <br />of flow to the screens. <br />. A convenient and adequate means for removing screenings shall be provided. <br />. Facilities must be provided for handling, storage, and disposal of screenings in a <br />manner acceptable to the regulatory agency. <br />. Floor design and drainage shall be provided to prevent slippery areas. <br /> <br />Grit Removal: <br />. A single manually or mechanically cleaned grit chamber with bypass is <br />acceptable for small wastewater treatment plants serving separate sanitary sewer <br />systems . <br />. Inlet turbulence shall be minimized in channel type units. <br /> <br />1 <br />