- Nassau County Department of Public Works
- RJ Industries, Inc., Cameron Engineering & Associates, LLP, Suez North America.
- East Rockaway, New York
- Our Role
- Lead Designer, Geotechnical, Structural, Electrical, Process Engineering, Construction Services
- 70 mgd
- Construction Cost
- $16.3 million
- 2 years
- Set an industry model for upgrading grit removal equipment
- Doubled the amount of grit removed per day through leading technology
- Improved water quality in the Reynolds Channel, where treated effluent is released.
The status quo is not good enough—that was the driving force behind the Nassau County Department of Public Works (NCDPW)’s initiative to update the grit removal system at its Bay Park Sewage Treatment Plant (STP). Placed into operation in 1986, the existing system included three detritor tanks containing a complex arrangement of conveyors, belts, scrapers, and other large moving parts. After three decades, the original equipment was rusting and degrading, requiring extensive and costly repairs.
NCDPW first considered rehabilitating the grit facility with new versions of the same 1980s technology. This straightforward solution would require minimal effort, as the plant was already outfitted to accommodate it. Still, NCDPW wasn’t satisfied that upgrading to new detritor tanks was the best approach to achieve maximum efficiency in grit removal. Grit includes sand, cinder, seeds, coffee grounds, food waste particles, and other heavy solids. If not removed, grit causes abrasive wear and tear on pumps, tanks, and other equipment in downstream processes, increasing maintenance demands and costs.
Gannett Fleming recommended and implemented a leading-edge grit removal technology for the Bay Park STP: vortex grit chambers. In a vortex system, the flow enters a cylindrical tank tangentially, creating a rotational movement caused by curved chamber walls. Grit settles by gravity into the bottom of the chamber and into a grit collection tank, while effluent exits at the top. Vortex chambers are not commonly seen in wastewater facilities, as most large facilities were built more than 30 years ago, at least a decade before vortex systems existed.
The team used an innovative jet grouting solution to replace the 1980s-era detritor tanks with modern vortex grit chambers. The ground improvement technology used high-pressure, high-velocity jets of water, air, and grout to erode the underlying soil and create an in-situ column of soil-cement grout. Each adjacent soil-cement column was overlapped by 6 inches to create a continuous impermeable barrier that could support the foundation. Engineers used these soil-cement columns to form a bathtub, effectively sealing the perimeter walls and base slab from the groundwater. This process was used to excavate a 900-square-foot-wide area for each of the three vortex chambers 20 feet deep. The bathtub stabilized the building and kept the groundwater outside the excavation limits.
- Each of the three vortex grit chambers have two 30-horsepower pumps; one pump removes the grit and the other is backup to ensure system consistency and reliability
- Custom-designed bypass system enabled the team to take the old tanks offline and install the new ones without impacting customer service
- New downstream classifiers and cyclones improve grit removal efficiency
- Renovated HVAC system isolates and provides proper ventilation for the hazardous and non-hazardous areas of the plant
- New emergency gas detection and exhaust system with roof-mounted, axial upblast exhaust fans remove explosive air from the plant upon detection, improving safety.
- Reduced grit in the wastewater reduces impacts on downstream equipment and increases service life by an anticipated 20 percent
- Vortex chambers are energy free, reducing the plant’s energy costs by a projected $50,000 annually
- Less machinery translates to an estimated 20 percent annual decrease in maintenance costs.
- National Recognition Award, 2018, American Council of Engineering Companies, Engineering Excellence Awards
- Diamond Award, 2018, American Council of Engineering Companies of New York, Engineering Excellence Awards.