Electroflotation: A demonstration
In 1996 a project was developed by Hughes Research Laboratory and funded in June 1997 by the Air Force for a full-scale demonstration of electroflotation of the removal of oils and greases from aqueous cleaner solutions/rinses and removal of paint solids from paint booth wastewaters.
By John H. Stallings and First Lt. Saulo Cepeda-Calderon
Electroflotation* is the process of generating a controlled stream (blanket) of dispersed hydrogen and oxygen gas bubbles that rise through a wastewater solution attaching to insoluble contaminants to form a "flotosludge". The concentration of the bubbles can be more than 5 million per liter, allowing for a high rate of contaminant removal.
Demonstration Unit
The first part of the project called for the construction in the USA of an electroflotation demonstration unit to the exact specifications set forth by Kolesnikov*. Trionetics, Inc., Twinsburg (near Cleveland), OH constructed the unit for Raytheon. The unit was designed exactly to the specifications but used improved materials of construction and was built in accordance with U.S. safety requirements. Trionetics completed the unit in April 1998.
Kolesnikov tested and approved the demonstration unit at the Trionetics factory in Twinsburg, OH, after which Raytheon and Air Force representatives accepted it for shipment to Tucson, AZ.
Testing/Validation
Testing at AFP 44 in Tucson included the removal of paint from a waterfall paint booth sump and removal of a water-insoluble oil from an aqueous cleaning solution.
In order to test paint separation, a test solution was extracted from a waterfall-type paint booth that catches overspray from catalytic urethane and epoxy solvent-based paints. Adry-film lubricant coating was used. The water used in the feed to the paint booth was domestic water. The total electroflotation test time was five hours.
The unit achieved 11% per hour removal of paint solids. The 280-W/hr power consumption is considered to be low for this type unit.
During the initial electroflotation process, observations revealed that the paint pigments, paint resins, and other electrofloated material formed a cake on the surface of the solution. Later, after several skimmings, the electrofloated material formed a thinner and less-dense gelatinous film on the surface. The efficiency of the system began to fall off after five hours following resin carrier depletion in the paint, indicating the need for a flocculent to act as a flotation carrier for the remaining paint solids. Collected skimmed concentrate was about 30% paint solids.
In order to test water-insoluble oil separation, a test solution was prepared using Daraclean 282 from W.R. Grace at a pH of 9.8. The oil contaminant selected was MIL-H-5606 hydraulic oil. The hydraulic oil (100ml) was added to 170 gallons of the cleaner solution and vigorously mixed to emulsify it. The unit extracted 72% of the oil after six hours of operation.
Observations showed that the surfactant in the aqueous cleaner formed a bubble package with the gas bubbles evolving from the electrofloter's anodes/cathodes—producing a pink-colored foam that was easily skimmed. The oil that was not removed had collected in the foam at the corners and edges of the electrofloter tanks where it could not be reached by the skimmer.
The recycled cleaner solution was tested for water breaking on test strips and a break free surface was observed. The higher conductivity of the aqueous cleaner allowed the rectifiers to be set higher than in previous tests, achieving an even lower power use.
Conclusion
The demonstration showed that the electroflotation process would remove paint overspray from water solutions and oil from aqueous cleaners. However, a flotation aid is needed to help produce a floating cake or foam that can be skimmed to the collection container.
The Air Force funded an extension and scope of work modification to construct and install one or more electroflotation unit(s) for removal of paint solids from the waterfall paint booth(s).
* Vladimir Kolesnikov invented and developed Electroflotation. He is with the Mendeleyev University of Chemical Technology, Moscow, Russia. Paul Fecsik, of Hughes Aircraft Company, now Raytheon Systems Company, first learned of the technology in 1993. In 1995, Hughes purchased a laboratory scale electroflotation unit, and preliminary verification testing was conducted at the Hughes Research Laboratory in Malibu, CA.
About the authors: John H. Stallings and First Lt. Saulo Cepeda-Calderon at the time of the presentation were with the U.S. Air Force, Air Force Materiel Command, Aerospace Systems Center, Acquisition Environmental Management, 1801 Tenth St., Ste. 2, Wright-Patterson AFB OH 453433-7626
The previous Case Study was adapted from an excerpt of the paper 99-638, "Innovative Pollution Prevention Program at Air Force Owned Raytheon Operated Facility Incorporating Russian Technology," presented at the Air & Waste Management Association's 92nd Annual Meeting & Exhibition, June 20-24, 1999, St. Louis, MO.