Retrofitting a HeadCell®, SlurryCup™ and Grit Snail® grit removal, washing and dewatering system provided a significant performance improvement over Fox Lake WWTP's aerated grit basin.
The existing aerated grit basin (AGB) grit removal system at Fox Lake, IL, was at the end of its useful life and needed to be replaced. There were two requirements for the replacement: they wanted to retrofit the new equipment in the existing area and to eliminate grit deposition in the grit basin which was very difficult to remove. Steve Vella, Fox Lake’s plant Supervisor, saw the HeadCell® at WEFTEC in Chicago. He liked the stacked tray concept, and thought it would be the ideal solution to their plant’s grit problem. He had seen similar operational principles in lamella systems. The stacked tray design would allow them to increase their surface area which would increase their grit system performance, while staying within the existing area used by the AGB.
In order to get the performance required to prevent grit from depositing within the plant they needed to double the surface area for settling grit. The stacked tray design of the HeadCell® allowed them to significantly increase their surface area while staying within their existing footprint. An isolation wall was poured to section off a portion of the old aeration basin making a dry pit for the grit pumps. The rest of the basin was used to house the HeadCell® trays. A SlurryCup™ and Grit Snail® replaced the old cyclone / screw washing and dewatering system.
Prior to taking the aerated grit basin (AGB) out of service, a grit study was performed on it. At the design peak flow, the aerated grit basin should have been removing 225 micron grit. At lower flows the AGB should have performed even better, unfortunately it did not. Testing was performed during low flow conditions of only 1.2 mgd when the aerated grit basin should have been removing all sand particles 50 micron and larger. The data revealed that the separator was only capturing 58% of incoming grit. To make matters worse, the cyclone / screw washing and dewatering system was retaining just 17% of the material delivered to it. This further reduced the overall system efficiency to only capturing 10% of influent grit.
Testing on a day with flows of 10 mgd proved the new HeadCell® system to be 88% efficient overall. The HeadCell® grit collection chamber was 95% efficient and the SlurryCup™ and Grit Snail® washing and dewatering system retained 93% of the grit delivered to it. The new system provided a significant performance improvement over the previous AGB.