Grit Tank Screw for Abington Waste Water Treatment Plant Abington, PA

General Description

The Abington WWTP can treat over 6 MGD for the growing suburban city. Like many active facilities, the plant managers saw a need to replace aging equipment. The plant was originally designed over 50 years ago, and many systems have been replaced or improved over the years. The existing grit removal process was breaking down due to the elements, the corrosive environment, and material selections. KWS Environmental worked closely with the Plant Engineering Manager to redesign the grit removal equipment to better suit the environment and improve the expected life cycle of the equipment with less down time. The new grit removal process includes an aerated grit tank, a grit cyclone, and grit classifier. The KWS Environmental solution eliminated the need for additional sealing elements as the screw shaft is sealed with a high quality mechanical seal. The sealing element is the most critical element in the system as the water column is being held back by the seal, and it the seal allows for the motor and other electrical items to be in a dry space.

Design Parameters

1. Product Type: – Grit
2. Material Density – 120 Lbs. per Cubic Foot
3. Capacity – 7 Cubic Feet per Hour
4. Duty – 7 Days a Week, 4 Hours per Day

KWS Advantages

Submerged grit applications require a provider that knows how to design for long life, abrasion, corrosion, pressure, and upset conditions. The choice was KWS Environmental. The KWS Environmental solution included a custom grit removal screw with AR235 construction, water-purged mechanical shaft seal, custom hanger bearing supports, safety stop switch, and commissioning support. Designed to fit in the limited space allowed by the existing aeration tank and grit removal building, the screw is submerged under 15-feet of raw sewage. KWS Environmental personnel assisted the contractor in determining the necessary measurements of the tank to design the custom hanger supports and went out to site to take the measurements.

The custom hanger supports were made to fit the sloped tank walls without requiring modification of the concrete and facilitated near perfect alignment of the screws. KWS Environmental designed the system to overcome a full load of grit, which can be experienced during high flow events like thunderstorms or prolonged rain events. The hanger bearings, which are submerged in the tank, include extended grease lines for greasing above the water line. The KWS Environmental engineering team led the contractor step-by-step through the delicate process of installing the special Chesterton mechanical shaft seal used on the project.

Special Features

KWS Environmental provided abrasion resistant (AR235) screws capable of long term submersion in a corrosive and abrasive aqueous environment. The custom hanger supports were made to fit the sloped tank walls without requiring modification of the concrete and facilitated near perfect alignment of the screws. The drive support integrated a mechanical seal for the drive shaft to hold back the water column. The drive support end also seals against the concrete tank wall. This arrangement eliminated the need for troublesome chain drives, hydraulic components, or a submersible motor.