Hydraulic Simulation and Variable Speed Pump Selection of a Dual-Function Pumping Station: Pumping Treated Water to a Reclaimed Water System or Deep Injection Well System

The Three Oaks Wastewater Treatment Facility, located in Fort Myers, Florida, is owned and operated by Lee County Utilities (LCU). The treated effluent will be pumped into a 6-mgd reclaimed water system if the water quality meets FDEP (Florida Department of Environmental Protection) requirements. Otherwise, the plant effluent will be pumped into deep injection well system for further treatment. A total of four pumps including one standby pump were proposed. For the reclaimed water system, the hydraulic simulation using WaterCAD suggests that the design flow and head for each pump shall be 1500 gpm and 100 ft, respectively. For the deep injection well system, engineering calculations and on-site test recommend that the design flow and head for each pump shall be 1800 gpm and 140 ft, respectively. In Florida, complex effluent pumping systems are commonly preferred because of extensive reuse of treated effluent and a seasonal wet weather disposal using deep injection wells or ASR (Aquifer Storage and Recovery) wells. Therefore, only one pumping station with one set of pumps is selected, per LCU's request. This challenging task leads to an ideal selection of variable speed pumps in order to meet the two very different performance criteria. The hydraulic simulation and engineering calculations both prove that the selected variable speed pumps can effectively meet both two scenarios (reclaimed water system and deep injection well system) without extra costs of another pumping station and additional four pumps.