Resolution No. 4793 - Laserfiche WebLink

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MWMC FACIUI'IES PLAN subsequent anoxic selector of the following cell where derfitrificafion occurs. Therefore, the capital and operating costs associated with the nitrified mixed liquor pumping equipment are el/m/hated. RAS pumping/s required and RAS performs a dual function of biomas,s return as well as nitrate redrculation from the secondary clarifiers. The step-feed anoxic selector process provides for control of sludge settleabffity through selective organism growth, effectively reducing the sludge volume index (SVI). The reduction in SVIs enables the secondary clarifiers to be rated for a higher design solids loading rate. It is the effect of this increase in biological capacity in combination with improved sludge settleabflity that would allow the WPCF to increase its capacity using the existing aeration basin volume and secondary darifiers. It was assumed that as part of the secondary treatment modifications, the secondary clarffiers would be modified to include baffling to increase their capacity and provide a more reliable effluent qual/ty, as outlined in section 6.2.2. To fl,nplement this technology at the WPCF, the existing complete-nfix/plug-flow aeration basins would have to be sigrfificantly modified to provide complete ~vgxed anoxic selector zones physically separated from the aerobic zones. This may be accomplished by constructing a new dividing wall along the length of each cell in each bas/n to provide an a_noxic selector having approxLmately 20 percent of the total aeration volume. This would provide four identical cells in each basin containing an anoxic selector followed by an aerobic zone. Primary effluent could then be distributed to each of these cells in various quantifies to accommodate seasonal effluent requirements. Dry weather operations requiring nitrification could distribute primary effluent in the proportion of 25 percent to each cell, whereas wet weather operations where no nitrLficaiton is required could be distributed in the proportion of 33 percent to each of the last three cells in the aeration basin. Table 6.2.1-1 summarizes the dry and ,,vet season design criteria used for analysis of the step-feed anoxic selector process. TABLE 6.2.1-1 Design Cntena: Step-Feed Anoxic Selector Process MWMC Facifities Plan, Eugene-Springfield Parameter Dry Season Wet Season Temperature, degrees C 15.6 12.5 Nitnfication Safety Factor 2.0 N/A Aerobic Volume 80% 80% Aerobic SRT, days 7.8 4 Anoxic Volume 20% 20% Anoxic MCRT, days 1.7 1.0 PE Flow Split 25% to 4 cells, or 33% to 3 ceils 33% to 3 cells SV~, mJ/g 110 120 Table 6.2.1-2 sttmmarizes the facility requirements for the modified system to meet the 2025 projected flow and loads.