Aerated Grit Tank Conveyance Upgrade Cox Creek Water Reclamation Facility in Curtis Bay, MD

General Description

The Cox Creek Water Reclamation Facility (WRF) is the largest of 7 wastewater treatment facilities in Anne Arundel County, MD. Each year, these 7 facilities collect and treat 12 billion gallons of wastewater from 118,154 area customers. Located at a tributary to the Chesapeake Bay, the Cox Creek WRF upgrades represent the largest capital investment in county history.

In an effort to reduce environmental impact, the county decided to upgrade the Cox Creek WRF facility to handle up to 45 mgd at peak flow and meet the Bay Restoration Program pollutant limits. The total project value is in excess of $162 million, which includes significant upgrades to the bioreactor, high flow management system, headworks upgrades and many other improvements. The plant’s headworks were also given a much needed overhaul.

With storm water surges periodically burying the grit screws and overwhelming the capacity of the system, the new, upgraded design prescreens for particulates over a specific size, thereby reducing the overall grit load. The original aerated grit chambers were poorly designed to remove the settled grit, and the conveyor components would be routinely buried in grit. The new design lengthens the grit screws and modifies the pumping point to more efficiently deliver the grit to the pumps without burying the conveyor motors and other critical components. KWS Environmental provided a very unique and robust design to solve all of the existing problems.

Design Parameters

1. Product Type – Grit
2. Material Density – 120 Lbs. per Cubic Foot
3. Capacity – 115 Cubic Feet per Hour
4. Duty – 7 Days a Week, 24 Hours per Day

KWS Advantages

KWS Environmental started working with PC Construction at an early phase to help identify existing problems with the grit removal system. KWS made specific site visits to discuss installation concerns and determine critical dimensions. Engineers from KWS Environmental provided PC Construction with information for the existing grit tanks that were critical to success of the design. KWS also worked directly with the Anne Arundel County equipment operators to determine the operating conditions that cause the most stress on the system.

KWS Environmental designed grit screws to fit different grit tanks at the facility. The design prioritized maximizing the longevity of the system and minimizing equipment downtime. Designed to fit in the limited space allowed by the grit tanks, the new KWS grit conveyors extend the length of the tanks. A custom trough was designed to be integrated to the tank bottom. KWS Environmental and Black & Veatch worked together to coordinate the layout of the new grit conveyors to resolve interference issues with existing equipment. KWS used 3D modeling techniques to provide a solution without numerous submittal iterations or field modifications.

Special Features

KWS Environmental provided a complete grit conveyance system including grit screws, structural supports, hydraulic power units and control system. The grit screws are continuously submerged, and due to the 60-foot length; multiple hanger assembles are required per tank. KWS designed extra heavy duty hanger assemblies including bronze journal bearings with flushing grooves. Each bearing in the system is flushed with non-potable water to prevent grit from wearing the bearings prematurely. The speed sensors for each grit screw can handle continuous submersion and meet IP68 specifications. The submerged hydraulic motors are enclosed in housings purged with water to prevent the accumulation of destructive grit. The independent hydraulic power units are designed to resist corrosion and reduce equipment down time.