Stuyvesant Environmental Contracting is currently operating the largest sand separation and dewatering facilities ever constructed in the United States. The site is located at the Fox River Cleanup Project, located in Green Bay, Wisconsin. Stuyvesant completed the design, procurement, construction, and commissioning in less than one year.

Stuyvesant Environmental Contracting is working on this project according to the integrated approach in a team with Tetra Tech EC being the prime contractor and J.F. Brennan being the marine contractor.

The estimated project duration is seven years for sediment processing; operations started 1 May 2009.

The Lower Fox River Operable Units (OUs) 2 - 5 project in Wisconsin include sand separation, dewatering, and disposal of approximately 3.8 million cubic yards of sediment. Dewatering with membrane filter presses (advanced plate and frame presses) was selected as the most economical and efficient means of dewatering the sediment prior to off-site disposal. The tonnage of filter cake produced is minimized through sand separation and the use of membrane filter presses. The design of the desanding and dewatering system required careful balancing of the flow of solids and water through the entire system, from point of dredging through final production of sand and filter cake.

Sediment sampling and bench-scale testing was performed in November 2007. The objectives of the testing included the development of a proper description of the sediment characteristics as well as selection and sizing of the appropriate sediment processing approach and equipment. Disposal costs and beneficial use options were considered during the selection process, while the estimated dredge production rate was critical when sizing the equipment.

Sediment is being hydraulically dredged using three units and pumped directly to the desanding and dewatering facility. The facility is designed to accommodate a maximum flow of 6,000 gallons per minute at approximately five to ten percent dry solids. Marine operations are able to dredge 250 in-situ cy per hour. Sediment from OUs 2 - 5 typically contains 30-40 percent sand, which is separated from the sediment and beneficially reused. Coarse and fine sand separation units separate sand in the range of 63 microns to 150 microns. Silt and clay fines removed during desanding operations are pumped to the dewatering process equipment, which includes pre-thickener tanks, polymer dosage equipment, sludge holding tanks, and membrane filter presses.

The filter presses designed for the Fox River are sized to process approximately 14 cubic yards of solids per hour per press, with a compression factor of 1.3 and a cycle time of 75 minutes. The number of presses required was calculated based on the anticipated range of flow rates through the dewatering system, an assumed uptime for the presses ranging from 75 to 100 percent, a range of 20 to 40 percent sand removal, and the hourly production rate for each press. It was determined that eight presses are needed; and that space two additional presses will be installed as contingency. Each press, manufactured by Andritz-Austria, consists of 188 two by two meter plates.