FlexRake Screens Prove to Be Efficient Solutions for Lift Stations and a Treatment Plant

Greater New Haven authority solves a screening problem with maintenance-free and reliable bar screens backed by quality support.

FlexRake Screens Prove to Be Efficient Solutions for Lift Stations and a Treatment Plant

The new bar screens have been installed at the East Shore Water Pollution Abatement Facility as well as at pump stations in the collections system.

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The Greater New Haven Water Pollution Control Authority serves the Connecticut communities of New Haven, Hamden, East Haven and Woodbridge.

Focused on wastewater management, the authority oversees a system that includes 555 miles of collection pipeline, 30 pump stations and a 40 mgd (design) advanced secondary wastewater treatment plant.

The authority has always found it essential to budget responsibly and keep rates as low as possible. That includes choosing efficient equipment that requires minimal maintenance and repair. After experiencing difficulty with aging bar screens at the treatment plant and lift stations, the authority looked for replacements.

Since 2013, the authority has replaced several of the old bar screens with FlexRake screens from Duperon.

Inherited trouble

Wastewater treated by the authority at its East Shore Water Pollution Abatement Facility is discharged to Long Island Sound and must meet federal and state effluent quality standards. In the heart of the authority’s territory sits Yale University.

When formed in 2005, the Greater New Haven authority took over all assets of the existing wastewater system, inheriting bar screens installed in the 1980s when the plant and lift stations were built. The screens worked but were unreliable and expensive to maintain.

They used a traditional catenary design: a series of vertical steel bars 1 to 3 inches apart with cross-secting scraper bars at 5-foot centers, driven by motor, gear reducer and sprockets. Maintenance to the components was labor intensive, according to Thomas V. Sgroi, P.E., director of engineering with Duperon.

A better way

In line with its commitment to do everything “smarter and better,” the authority looked for remedies, led by Charlie Biggs who had served as the New Haven wastewater treatment facilities’ operations and engineering coordinator since 1988.

Biggs manages maintenance for all vertical assets at the plant and pump stations. He recalls his introduction to Duperon at a Connecticut wastewater trade show where the company had a mobile demonstration trailer.

“They had the same type of screen as our equipment — catenary bar screens,” Biggs says. “The same concept, but different proprietary chain design and a different scraping bar. It’s much, much more user friendly and a much neater installation, all-cast stainless steel, easier to repair and corrosion resistant. That’s very important at a wastewater plant. Basically, the screen was simple but robust.”

The authority was especially interested in the design of the FlexRake bar screens, in which only the chain is below the water. Sgroi and colleagues believed that could make a real difference in uptime. They invited Duperon representatives for a visit.

“We really liked their style,” Sgroi says. “Their equipment spoke for them. They weren’t trying to sell their product; they really were trying to solve our problem. And the technology was different — not your typical mechanical bar screen. It’s more like a link system, rigid and effective.”

Keeping rates low

The authority tested the first FlexRake screen in 2013 and has since replaced old screens with seven FlexRake screens at four locations: two at the East Street Pump Station, each with 35 mgd capacity; two at the Boulevard Pump Station, also 35 mgd each; one at the Morris Cove Pump Station, 18 mgd; and two at the East Shore Main Plant, with 20 mgd average flow. The plan is to add new screens at two other locations to provide increased capacity.

Authority leaders say the new screens have produced significant savings on maintenance and repair. The old screens needed to be rebuilt every 1.5 to three years, at costs from $25,000 to $30,000 apiece. In addition, each rebuild meant downtime of up to a month to wait for specialized parts. When the screens were out of service, a high-flow event created potential for a backup.

The authority estimates it would have cost $300,000 on average to rebuild the old screens over the last four years. Chains also would have had to be replaced every two years; they would stretch so much that links had to be removed to shorten the chains so they wouldn’t drag.

The cost estimate doesn’t include the regular maintenance required by the operations team to keep them running. It was also labor-intensive to clean up the debris that built up over time on the screens, chains and surrounding areas. Then there was the downtime and its associated risk.

Job well done

The first FlexRake screens have been in operation for four years. “They’ve been running fine, better than fine,” Biggs says. “We grease them as recommended every quarter; that takes 10 to 15 minutes. We change the oil once a year, and that’s about a couple hours per unit each time. The maintenance is minimal, a lot less. After four years, the chains aren’t even worn. We haven’t needed to replace a part in four years.”

Besides saving money, the new screens are much more effective. At the Boulevard Pump Station, for example, the influent comes from a combined sewer. During a New England autumn, the stations are inundated with leaves, which would blind the old screens. Now the leaves are spread all over the room and all over the conveyer, overflowing from the dump containers because the screens do their job so well.

Sgroi, who has worked closely with the Duperon team over the past six years, observes, “They work with us, brainstorming a problem. They feel like an extension of our staff. We feel safer or more comfortable with the company that invented the technology, but more important, the customer service and willingness to listen are second to none. 

“We like that they put a lot of effort into research and development, and we’re now looking into some of their other equipment. The FlexRake screens have been absolutely reliable and maintenance-free, saving us tremendous time and money. We employ 60 people. If three of them aren’t pulled off their work to fix problem equipment, we can have their time spent elsewhere. Having maintenance-free, reliable equipment allows us to have money for other projects.”

About the authors

Thomas V. Sgroi, P.E., (tsgroi@gnhwpca.com) is director of engineering with Duperon. Charlie Biggs (cbiggs@gnhwpca.com) is operations and engineering coordinator with the Greater New Haven Water Pollution Control Authority.


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