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Original Date: 03/08/1999
Revision Date: 01/18/2007
Information : Treating Bilgewater Using Critical/Super Critical Carbon Dioxide
The Applied Research Laboratory at the Pennsylvania State University (ARL Penn State) is working with the Navy to derive a better way of treating contaminated bilgewater in deployed Naval ships. Bilgewater from ships usually contains hydrocarbons from minor leaks and spills of hydraulic fluids, fuels, and lubricating oils. Because of this contamination, bilgewater must be treated before being discharged. The Navy’s primary treatment method is a parallel plate separator, which uses polymer beds designed for a 15-parts per million (PPM) discharge. The compliance goal is five PPM, with the system actually achieving approximately 100 PPM. Problems associated with the current system include performing periodic, manual underway changeouts; storing spent polymer onboard; and transporting spent polymer back to port which creates additional disposal costs. In addition, parallel plate separators continue to be plagued by biological growth that releases noxious hydrogen sulfide gas and clogs the separation panels.
ARL Penn State has evaluated the user of Near - Critical/Supercritical carbon dioxide (NC/SCC02) extraction for treating bilgewater. This technology uses high-pressure carbon dioxide as a solvent to remove organic materials from water. The carbon dioxide solvent is recycled, resulting in a highly concentrated waste stream that can be processed along with other oily wastes. No carbon dioxide is produced in this process, so greenhouse gas emissions are not a concern.
Investigations used a laboratory scale batch NC/SCCO2 system to effectively treat simulated bilgewater, reducing oil and grease contamination from 300 ppm to approximately 3 mg/liter even when 25 mg/liter of surfactant mixture was included. Attempts to transition to a steady counterflow extraction process were less successful, highlighting the unusual phase behavior of a seawater carbon dioxide mixture.
For shipboard use, an NC/SCCO2 system would require several batch reactors operating in parallel to achieve continuous operation. Although the batch process has been demonstrated in the laboratory, the process needs to be optimized for shipboard use. A prototype must be developed and demonstrated on shore and at sea.
For more information see the
Point of Contact for this survey.
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