Eliminate clogs and save energy.
Located on the north shore of Long Island, New York, Stony Brook University’s enrollment was rising rapidly. Its facilities were multiplying at a vigorous rate, but parts of the campus infrastructure had not kept pace with its expansion — most notably the lift station that pumps the school's wastewater to its treatment plant.
The pumps in the Stony Brook Lift Station clogged so frequently that crews for Suffolk County Department of Public Works (SCDPW) anticipated the event as part of their weekly routine.
“The clogging became quite predictable,” recalls Ron Warren, Maintenance Director of the Division of Sanitation, Operations & Maintenance. “Every week to 10 days we'd have to go out there and free an impeller that had become jammed with rags or some other debris.”
The beleaguered 3-MGD facility was just one of 87 pump stations and 24 wastewater treatment plants maintained by the Department. Built when the campus was smaller and generated less flow, the station and its original equipment simply couldn't keep up with the greater demands of a much larger university center and three outlying areas that comprise the Stony Brook of today.
The Stony Brook station was designed with a 20,000-gallon wetwell and three 60-HP end-suction pumps mounted horizontally in the dry pit. Approximately two years ago, when the pumps were clogging as often as twice a week, SCDPW asked GA Fleet Associates to recommend a workable solution that SCDPW's own engineering staff and crews could implement.
After reviewing the original specifications and spending several months monitoring the station's flow, Fleet recommended replacing the three existing 60-HP pumps with N-Pumps from ITT Flygt. This new type of pump has an innovative self-cleaning impeller incorporating a volute with a special relief groove that prevents rags, high-fibrous material, grease or solids from clogging the pump. The Fleet team based its recommendations on the results of tests at other installations where fouled impellers had been a recurring problem. During those tests, the N-pumps not only operated for extended periods without becoming clogged, they also achieved dramatic energy savings.
G. A. Fleet further recommended changing the sizes of the three pumps to a combination of two, 60-HP Flygt Model NZ3300 pumps to handle peak flows (Figure 1), and a Base-Load pump to handle the low-flow conditions (See Sidebar). Instead of a third 60-HP unit, however, the Base-Load pump Fleet specified was a 20-HP Model NZ3152 model that would help reduce the station's energy consumption. Additional upgrades included a Flygt MultiTrode® Liquid Level Control System, a conductivity probe-based system that is fully compatible with SCDPW's new SCADA system which operates on Citex software. SCDPW plans to add more MultiTrode systems and gradually network eight stations with SCADA as a first step towards a full-blown, continuously monitored operation.
This $85,000 lift station upgrade retained the horizontal alignment of the old pumps, translating into immediate savings on re-piping. Following the completion of the retrofit, GA Fleet initiated month-long testing. Over the course of that month, the station recorded a fairly typical 2.1 MGD flow - but with a marked reduction in energy costs. “Although the university has its own power grid, we can make some good assumptions about our improved energy use,” Warren notes. “For the first 24 days the station was online with the SCADA, the 20-HP Base-Load pump operated 533 hours, compared to 25 and 17 hours each for the 60-HP Peak-Load units.” Equally important is the fact that there were no incidents of clogging at the once clog-plagued station. That alone saved $240 in labor costs-every 7-10 days.
Today, Stony Brook's Base-Load pumping system continues to run as designed-smoothly and efficiently.