Heavy rains and clogged pumps were leading to frequent overflows at the Fairwood Lift Station in Hot Springs, Arkansas. A Xylem solution featuring the award-winning Flygt N-pump technology and a Godwin Dri-Prime backup pump will now keep the station fully operational – even during power outages.
The city of Hot Springs recently undertook a comprehensive overhaul of its municipal wastewater infrastructure, which serves 23,000 customers. The aim of the overhaul was to implement a more proactive maintenance program and address issues arising from capacity constraints and aging equipment. The project included a complete revamp of its Fairwood Lift Station.
The 5.8 million gallon per day Fairwood Lift Station, one of 76 major stations in the Hot Springs system, was experiencing frequent overflows. In particular, the station struggled during heavy rainfall events or when pumps clogged because of increasingly popular “disposable” products such as duster heads, cleaning cloths, and disinfecting wipes. These products can build up on the leading edge of the pump impeller and become entangled, reducing the efficiency of the pump or even causing a complete stoppage.
Self-cleaning and clog resistant impellers
Since the Hot Springs utility already had extended success with high-performance Flygt N-pumps installed elsewhere in the treatment system, it chose N-pumps for the new Fairwood station as well. The station was equipped with Xylem’s Flygt model NP-3231/765N-pumps. The 335-HP submersible pumps will be operated via variable speed drive and are designed to deliver 4,050 GPM each.
The award-winning N-pump technology incorporates patented clog-resistant impellers designed to handle debris-laden wastewater more efficiently than other pumps through the combination of a self-cleaning impeller and a relief groove incorporated in the pump volute.
Horizontally positioned leading edges of the impeller deliver superior hydraulic performance and energy efficiency by self-cleaning the stringy material carried in the wastewater flow away from the leading edge of the pump impeller.
Real-time control and protection
A new Flygt MultiSmart station controller will also provide both real-time control and protection along with historical and communications options. The installed MAS 711 pump monitoring system records pump starts and stops, pump vibration, station power quality and energy usage, and pump bearing and seal temperatures.
The system will calculate and record the daily inflow and outflow of the station in gallons per day. All of this information will be available to the city for monitoring and review, allowing them to better operate the pumps and more easily determine the root cause of any future problems.
A backup system during power outages
The potential environmental impact of sanitary sewer overflows at the Fairwood facility mandated a backup system that would continue operation during a power outage. Utility field operations manager Bobby Harris, together with design engineer Jerry Williams, PE, the principal of local engineering consultant Engineers, Inc., chose the Godwin Dri-Prime Backup pump unit as a backup for the Fairwood Station.
Powered by a 425-HP natural gas engine, the HL250M DBS pump will operate on an above-ground foundation adjacent to the wet well. The heavy-duty pump was well suited for the backup mission because of its self-priming feature and ability to handle the high discharge pressure and high suction lift conditions at the new Fairwood station, which underwent some dimensional redesign to accommodate increased flow requirements.
“The availability of a natural gas connection on-site will eliminate the risks of aging diesel fuel gelling in the generator fuel tank and the potential for fuel spills that could reach the nearby creek,” Harris said. “It will also reduce the city’s fuel costs during an outage of the submersibles.”