Item A-MWMC Facilities Plan - Laserfiche WebLink

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3. EXISTING WASTEWATER FACILITIES Effluent Bisposal Current effluent disposal practices consist of discharging plant effluent into the Willamette River. The WPCF has historically met all regulatory requirements for secondary effluent disposal with one exception. On May 17, 1991 the daffy mass limit was exceeded for TSS and BOD. Effluent is preferentially disposed of through a submerged diffuser in the Willamette River. The NPDES permit requires the use of the submerged diffuser from May 22 through October 31. Peak wet weather flows over 103 mgd consist of blended primary and secondary disinfected effluent. The wet weather hydraulic capacity of the WPCF is estimated at 175 mgd, although higher flow rates approaching 215 mgd have been achieved. The current practice for discharging peak wet weather flows in excess of the submerged diffuser outfall capacity is to overflow into a bankside outfall. These overflows occur at a weir located at the outfall control structure. The current NPDES permit allows the bankside outfall to be used from November 1 through May 21 to accommodate peak wet weather flows. Thickening WAS is currently thickened at the WPCF with the use of GBTs. The GBT facility houses two 3-meter gravity belts, a polymer distribution system, and the thickened WAS pumps. WAS flows either by gravity or pumped flow from the RAS control structure to the GBT facility. The WAS flow rate is metered and controlled with flow control vanes at the RAS and/or GBT control structure. Prior to thickening, the WAS is conditioned with a cationic polymer. Thickened WAS is typically around 5 percent solids and is pumped directly to the digester for anaerobic digestion. Table 3.2.2-5 summarizes the waste activated sludge unit process and associated equipment. TABLE 3.2.2-5 WPCF Waste Activated Sludge Thickening Unit Processes and Equipment MWMC Facilities Plan, Eugene-Springfield Capacity, (each/total Equipment Type Quantity firma/totalb) Gravity Belt Thickeners 3-meter, 95% solids capture, 5% solids, 2 48,250/48,250/96,500 lb/day MWWW SLR= 2010 lb/hr, MWWW HLR = 120 gpm/m WAS feed pumps Screw centrifugal with adjustable frequency 2 800/800/1,600 gpm drive (AFD), 15 hp Thickened Waste Progressive cavity with AFD, 20 hp. 2 120/120/240 gpm Activated Sludge Pumps Polymer System Liquid tote polymer system, 17 lb/ton 2 i7/17/34 lb/ton capacity Notes: a Total firm capacity is with largest unit out of service. bTotal capacity is with all units in service. Anaerobic Digestion Three primary anaerobic digesters located at the WPCF stabilize primary sludge and secondary WAS. Each digester is 85 feet in diameter and contains a fixed cover. Table 3.2.2-6 summarizes the anaerobic digestion unit processes and associated equipment. MWMC_3.0_REV11.DOC 3-13