Study and Upgrade of a Pharmaceutical Wastewater Treatment Plant for Nutrient Removal

Merck & Co., Inc. operates an activated sludge wastewater treatment plant in Elkton, VA (Stonewall WWTP) to treat wastewater generated in the production of pharmaceuticals by chemical synthesis and fermentation. The original discharge permit for the WWTP imposed limits on BOD, COD, TKN, ammonia, cyanide, TSS and the Pharmaceutical Effluent Guideline compounds. The Chesapeake Bay Program has now imposed a cap on the amount of nitrogen and phosphorus that the facility can discharge. The cap was based on the typical allocation allowed for municipal wastewater treatment plants in the Shenandoah and Potomac River Basin which would require an effluent TN of 4.0 mg/L and an effluent TP of 0.3 mg/L on an annual average basis. It was not possible, however, for Merck to meet these proposed nutrient limits because the wastewater characteristics are highly variable, nitrogen and/or phosphorus is occasionally limiting and some of the nutrient constituents are refractory. Based on a detailed analysis of the Stonewall WWTP wastewater, including a kinetic model of the process, it was concluded that limits of 12 mg/L TN and a 1.2 mg/L TP were appropriate. Discussions with the Commonwealth of Virginia DEQ and Technical Advisory Committee (TAC) led to a petition being filed with the State Water Control Board (SWCB) to change the waste load allocation. Conditional approval for limits of 12 mg/L TN and 1.2 mg/L TP was obtained resulting in waste load allocations of 43,857 lbs/yr for TN and 4,384 lbs/yr for TP. Merck then upgraded the wastewater treatment plant on an accelerated schedule in an effort to establish final permit limits based on the demonstrated performance of the plant following a year of operation. The conclusions of the study and the results of the first year of operation are presented herein in support of the ruling (9VAC 25-720-50C).