A portable SlurryCup™ and Grit Snail® sludge degritting system solves a costly grit deposition problem at Bird Island Wastewater Treatment Plant.
The Bird Island Wastewater Treatment Plant (WWTP) in Buffalo, NY, is one of the largest capacity treatment plants in the Northeast US, serving about 550,000 residents in the city and surrounding suburbs and providing primary treatment of sewerage since it opened in 1938. A $200 million upgrade project added secondary treatment processes in the late 1970s. The plant processes flows of up to 180 MGD on a dry day, 600 MGD during wet-weather periods and 360 MGD in its secondary treatment processes.
The plant’s operator, the Buffalo Sewer Authority, installed a new paddle-wheel, mechanically-induced vortex type system in 2004, improving the performance of the grit-removal operation. But the grit that had passed through the basic chain-and-flight system for years had accumulated in the aeration basins to the point where it had buried the fine-bubble diffusers in 1-2 ft of grit.
The Sewer Authority considered a number of solutions to clean the grit out of the 16 aeration basins. Leaders considered hiring contractors, but found the costs too high. They considered using pumps, vactor trucks or centrifuge systems, which had downsides; some involved the use of harmful chemicals, while others required the plant to implement difficult work processes.
Buffalo Sewer Authority chose to use a portable sump pump to feed grit slurry to a SlurryCup™ grit washing unit from the aeration basin, while a Grit Snail® dewatering escalator is used to remove water from the captured grit.
During its first phase of operation, Buffalo Sewer Authority used the mobile system to remove 60 tons of grit from four of the 16 aeration basins over a period of six months.
Plant Superintendent Jim Keller estimates that the system will save the WWTP more than a million dollars over the life of the project. Some of the savings come from being able to avoid the costs of hauling heavily weighted organic sludge away from the plant and from not having to pay for polymers or the large amounts of costly high-quality city water needed for belt press sprays, but the biggest cost saving is in reduction in energy: since the grit has been removed from the four tanks, Keller said that electricity consumption in that area has dropped by more than 15%.
"We needed a way to clean out the grit that’s been sitting in these tanks for over a decade. We feel like we made the right decision, we’ve invested in equipment that performs well, needs minimal manpower and significantly lowers our operating costs." - Jim Keller, Plant Superintendent