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CENTRIFUGE DEWATERING DEMONSTRATION LEADS TO MAJOR CHANGES AT THE 250-MGD METROPOLITAN WASTEWATER TREATMENT PLANT

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In the mid-1990s, the Metropolitan Council Environmental Services (MCES) determined that improved raw sludge dewatering with new high-solids centrifuges could initiate significant changes to the solids processing system at the 250-mgd Metropolitan Wastewater Treatment Plant (Metro Plant), which is located in St. Paul, Minnesota. However, at that time, Metro Plant operations and maintenance personnel expressed skepticism about raw sludge dewatering performance, processing costs, and labor implications of the associated phase-out of the existing thermal conditioning treatment system. In response to these challenges and to prove performance and long-term costeffectiveness, a full-scale centrifuge dewatering demonstration program was implemented. This technical paper presents the findings and the associated changes now occurring at the Metro Plant, that have resulted from the success of the centrifuge demonstration program.

Representatives from MCES operations/maintenance/engineering/construction management and its consultant collaborated for several years to resolve significant issues. This effort provided the framework for procurement, installation, and evaluation of the equipment. The investment in project planning provided a smooth start-up and quick resolution to process problems during the demonstration.

Side-by-side testing was conducted on two full-scale sludge dewatering centrifuges for twelve months. Raw sludge feeding encompassed a large variety of sludge blends, including septic sludge conditions, to define performance variation. The test program also evaluated polymer usage, power requirements, auxiliary and control systems, operations and maintenance cost, and labor requirements of the centrifuge system.

Demonstration results were better than expected. The centrifuges consistently produced sludge cake of 30 to 32 percent solids with a polymer dose of only 5 to 7 active pounds per dry ton of feed sludge. Centrifuge cake burned efficiently in the existing multiple hearth incinerators and required less fuel (compared to heat-treated, roll press-dewatered cake).

With success of the demonstration program, MCES is now proceeding with major system changes at the Metro Plant. These changes include the implementation of a full-scale raw sludge centrifuge dewatering system and the eventual phase-out of the existing thermal conditioning and roll press dewatering systems. The increased efficiencies improved MCES' competitive position while fostering buy-in from Metro Plant staff.
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Document Type: Research Article

Publication date: 2001-01-01

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