ACHIEVING LOW EFFLUENT NITROGEN LEVELS AT A UNIQUE NUTRIENT REMOVAL FACILITY

The City of Plant City Wastewater Reclamation Facility (WRF) is a permitted 8.0 million gallon per day (mgd) annual average daily flow (AADF) nutrient removal facility. The WRF is a unique municipal wastewater treatment facility because industrial discharges account for 40 percent of the influent flow and the influent organic loadings are highly variable. Nitrogen removal is achieved through simultaneous nitrification/denitrification in the completely mixed aeration basins and ferrous sulfate is added to precipitate phosphorus in the final clarifiers. The current effluent discharge limits are 5.0 mg/L BOD5, 5.0 mg/L TSS, 3.0 mg/L TN, and 1.0 mg/L TP. In order to service the future anticipated population growth, upgrade options were evaluated to identify a preferred biological treatment upgrade. The overall project objective was to maximize the use of existing facilities and expand the treatment capability at the existing site to a target AADF of 12.0 mgd, while continuing to meet their stringent 5-5-3-1 permit limits under the unique influent conditions faced by the City. In order to accomplish the project objectives, available upgrade alternatives were reviewed followed by an initial screening and short-listing of six viable alternatives. Based on an economic and non-economic evaluation, optimization of the existing system was selected for implementation. A phased implementation strategy was recommended to achieve the ultimate treatment goal of 12 mgd. It entails optimizing existing process and applying polymer, if required to enhance settleability and increase treatment capacity to 7.5 mgd AADF. The rated capacity may be increased further to 9.0 mgd AADF by operating at an elevated MLSS of 4,000 mg/L and by adding a new clarifier. The addition of a second clarifier would allow 10 mgd AADF to be treated. These improvements will not compromise the ability of the City to consider process technologies such as denitrification filters, addition of new aeration tanks, integrated fixed film reactors, and membrane bioreactors to achieve expansion to 12 mgd in the future.