Grit Screws for Yonkers Wastewater Treatment Plant in Yonkers, NY

General Description

The Yonkers Joint Wastewater Treatment Plant is maintained by the Westchester Department of Environmental Facilities. The Plant treats sewage from 22 municipalities and 7 separate sewer districts. The plant handles sewage flows from as far north as Mount Kisco and to communities in southern Westchester in the Bronx River Valley. The plant serves 504,562 people, roughly 55 percent of the County. Yonkers Joint Wastewater Treatment Plant contacted KWS to replace nine existing grit screws in three concrete tanks that are utilized in the wastewater treatment plant to treat sewage.

Design Parameters

1. Product Type: Grit
2. Material Density: 90 to 120 Lbs. per Cubic Foot
3. Capacity: 150 Cubic Feet per Hour
4. Duty: Intermittent

KWS Advantages

KWS worked closely with the GHD Group, a consulting engineering firm and Mace Contracting to ensure the grit screws, shafts, and hangers were designed properly to fit the concrete tanks. A KWS engineer traveled to site to take field measurements of the existing system. KWS used the latest 3D CAD modeling techniques to model the special hanger mounts in the concrete slab to ensure proper fitment in the field. As a result, the installation phase went very smoothly. After installation a certified KWS engineer performed equipment startup and operator training before the system was put into successful service.

KWS Special Features

KWS provided hard surfaced screws to eliminate excessive wear on flights while conveying the abrasive grit material. Hard surfacing improves component longevity, reduces maintenance events, down time, and lowers overall operating costs. Hard surfacing was applied using conventional GMAW welding methods. For this application, KWS selected ½-inch thick flights and applied Postalloy Flitewear 3 hard surfacing on the carrying side and periphery of all flights. Flitewear 3 is very high carbon, chromium hard surfacing wire with Brinell Hardness of 601-627 and Rockwell Hardness of 58-62 Rc. Flitewear 3 is recommended for severe abrasive applications.

KWS provided heavy duty screws to span the 61-foot-long concrete tanks. To minimize the quantity of screws needed, KWS designed each screw section with 8-inch heavy-wall pipe to handle loading and reduce overall deflection of each screw section. Each screw section was supported by shafts and hangers. The hangers were constructed from 316-stainless steel for reduce corrosion. Hanger or journal bearings were machined from 1045-carbon steel and heat treated to a hardness of 55 Rc.

The screws are submerged in wastewater and convey grit that settles out by gravity. The drive shaft penetrates the grit chamber wall and is sealed using a grease-purged, adjustable flanged gland seal. KWS flanged gland seals can hold pressures up to 25-psig.