Oklahoma city upgrades WWTP’s sludge handling system using intelligent equipment
Perry, Okla., is located approximately 60 miles north of Oklahoma City and serves as the county seat for Noble County. According to the U.S. Census Bureau, Perry had an estimated population of 5,018 in 2016, and it includes approximately 2,200 households. Perry’s wastewater treatment plant has a maximum rating of 2 million gal per day (mgd) and receives an average of 500,000 gal per day (gpd) of wastewater. The plant consists of a manual coarse bar screen, two aeration basins, two clarifiers and disinfection by chlorination.
In December 2015, Perry elected to build a new sludge thickening and conditioning basin at the plant. This included installation of a 30-cu-yd sludge dewatering container filter, or sludge box. In addition, a polymer injection system was installed, five existing sludge-drying beds were retrofitted, and return activated sludge (RAS) pumps at the existing clarifiers were replaced, with a total project cost of $350,000.
Sludge was previously moved at the plant by two rail-mounted submersible non-clog pumps that were old, failing and often clogged due to material bypassing the bar screen at the lift station. However, the primary impetus for their replacement was the new sludge box thickening and conditioning system, which consists of a polymer mixing and injection system and a dumpster-like structure to dewater biosolids so that they can be stored and stabilized on the retrofitted sludge-drying beds until land-applied. The city needed to discharge sludge at two different rates—one for sludge returning to the headworks RAS and another for sending material to the sludge box. The system is designed to speed up dewatering biosolids as a replacement for the existing sand drying beds.
Perry’s consulting engineer—Monsoon Consultants of San Luis Obispo, Calif.—originally recommended two different-sized pumps in its design—one for return and one for waste to accommodate the sludge box requirements.
Local Xylem distributor Automatic Eng., however, stepped in and suggested Concertor pumps so that each station would have 100% redundancy.
Concertor pumps combine a fully integrated control system with IE4 motor efficiency, N-hydraulics and intelligent functionalities. The control system automatically adapts to the changing pumping environment, delivering the optimal level of performance at a low cost of ownership. Built-in intelligence also makes it easy to set up and operate, and it allows for a small footprint, including controls.
Meanwhile, the adaptive N-impeller moves axially upward when needed, allowing bulky fibrous material and debris to smoothly pass through. After the debris has passed, the hydraulic pressure returns the impeller to its original position. This not only prevents clogging and reduces stress on the shaft, seals and bearings, but also enables a sustained low usage of energy.
The ability to quickly and easily change flow rates was very appealing to the Perry wastewater treatment plant staff. As for replacement, nothing unusual was encountered in the project: The old pumps were simply pulled out and replaced with the Concertors. Pump controls were added in a new building, which also houses the polymer mixing and injection system.
The new pumps went into service in April and May 2017, and the staff has experienced no clogging. Perry’s flow rates for this application vary based on the head requirements between the clarifiers and range between 85 and 370 gpm, depending on the pump speed. Personnel are awaiting commencement of a SCADA project, which is expected to dramatically smooth varying the pump flow rate, speed and power settings.
“The new Concertor pumps have been operating flawlessly and have given our operator the flexibility to perfectly match our RAS flows, either in the return mode or the wasting mode, with the ever changing conditions that we experience on a daily basis,” said Blaine Reely of Monsoon Consultants, the project design engineer.