Several technologies exist for dewatering sediment, a key component ofsediment remediation projects that involve sediment removal and disposal. Factors influencingthe type of dewatering system selected include: dewatering costs; availability ofarea for the dewatering process; whether the dewatering equipment needs to be placed ina building and the associated cost for the building; costs for construction of on-site dewateringand disposal facilities; the cost of process additives required (e.g., polymers and/orcoagulants); availability of disposal space on site; and costs for off-site transportation anddisposal of dewatered sediments. Since landfill disposal costs in the United States typicallyrange from $20 to $50 per ton ($22 to $56 per metric ton), minimizing the tonnageof dewatered sediment requiring disposal can result in significant savings for a project, inaddition to increasing the project’s environmental stewardship. For sediment remediationmega-sites such as the Fox River Operable Units (OUs) 2 - 5 in Wisconsin, where approximately3.8 million cubic yards (2.9 million cubic meters) of sediment are targetedfor removal beginning in the spring of 2009, dewatering with membrane filter presses hasbeen selected as the most economical and efficient means of dewatering the sedimentprior to disposal or reuse. A detailed analysis of available sediment data was performedto design an appropriate dewatering system that would be able to accommodate theplanned dredge production rates, variations in material and concentrations, and overallproject schedule. In addition, a pilot-scale bench test was performed using sediment fromselected dredge areas to determine the appropriate filter clothes to be used in the membranepresses; to identify the best chemicals for conditioning (secondary objective) of thesediment; and to verify the number of presses necessary for dewatering. Based on thedata analysis and pilot test, a system of eight membrane filter presses with a total maximumfilter cake production of approximately 14 cubic yards (10.7 cubic meters) per hourwas selected.
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