In the summer of 2004, Freese & Nichols, Inc. was developing the design of a major wastewater treatment plant expansion project for the city of The Colony, Texas. Having enjoyed earlier wastewater project success when specifying N-Pumps from Flygt, Freese & Nichols, Inc. once again requested N-Pump selections from Flygt. The project design called for pumping raw sewage with a firm capacity of 14 MGD when utilizing 2 duty pumps, with a third pump designated as a standby. Given that the raw sewage application was at the main lift station for the city's main wastewater treatment plant, the engineer requested that Flygt select pumps that could be operated by variable frequency drives (VFDs). The engineer believed that VFDs would allow the city flexibility with their pumping rates to the wastewater treatment plant to match incoming flows and to help create a stable biological environment for the wastewater treatment processes.
After further discussion with Freese & Nichols, it was determined that the majority of the total dynamic head (TDH) was static head. Having had experience with previous projects where similar high static head conditions often lead to inefficient and ineffective use of VFDs, Flygt recommended that 2-speed pumps be considered for use in this project. The engineer agreed that this would be a beneficial action.
The challenge for designers was the requirement to utilize the existing pump station and wet-well civil works to house the new pumps. In addition to the existing pump station being quite old, the engineers had to deal with a wet-well that was a circular structure. The concept was to modify and divide the existing structure into halves with half being utilized as the new raw sewage influent pump station and the other half serving as the return and waste activated (RAS/WAS) pump station.
Using design concepts and elements from previous "pump-in-the-round" designs, Flygt developed and offered a design that fulfilled the project demands. The recommendations were for the circular pump station to be divided, resulting in 2 separate pump stations. A recommendation included guidance on pump spacing and station grouting to minimize turbulence and maximize performance of the raw sewage and RAS/WAS pumps.
Having such an active position in the design development of this project, Flygt began discussing the possibility of a pump pre-purchase arrangement with the municipality. The project would include 3 NP-3300.675, 82 kW/110 hp raw sewage submersible pumps and 3 NP-3202-641, 33 kW/45 hp RAS/WAS submersible pumps to be located in the other half of the modified circular pump station. Because of Flygt’s detailed assistance in pump selection and wet-well design recommendations, the integrity shown and trust developed during the initial and detailed design of this project, the engineer recommended the direct purchase of the pumping equipment by the city. The city accepted the engineer's recommendation and Flygt was awarded the $200,000 USD project as the sole pump equipment supplier.