CHEMECOLOGY, October 1995, Vol. 24, No. 8
CHEMECOLOGY is published by the Chemical Manufacturers Association,
2501 M Street, N.W., Washington, D.C. 20037. Effective January
1996: 1300 Wilson Boulevard, Arlington, VA 22209. ISSN 0738-7776.
CMA is a nonprofit trade association of United States and Canadian company members.
The Art of Reducing Wastewater From Paint-Making Equipment
Just as you have to clean your paint brushes after creating your latest masterpiece, paint manufacturers clean their equipment to ensure the quality of the next batch of paint. Although you can probably pour the used water down the sink, paint manufacturers have much more than a cupful to dispose--more like 400,000 gallons a year for PPG Industries--and it's considered hazardous.
But in a stroke of genius, PPG found a way to cut its waste water by almost 78 percent and put the rest back to use. A team of engineers at the company's Cleveland plant developed a system that filters out waste to the point that the plant can reuse most of the water for future cleaning. Then PPG disposes of the stuff that the filters removed.
Membrane Magic
The Cleveland facility makes automobile coatings, specifically the metal primer used to prevent corrosion. Car coatings and paints are either water based or solvent based, like the water-based or oil-based paint you might use. The equipment to make them must be cleaned to remove traces of the other kind, just as you would clean your brushes. Typically this takes hundreds of gallons of water each week. Until a couple years ago, all of that tainted water from PPG's plant was taken away and treated as hazardous waste.
Now only a fraction of that water is shipped off-site for treatment. PPG's new system combines ultrafiltration and reverse osmosis (two ways of using membranes to get waste particles out of a liquid) to concentrate the contaminants.
Many paint makers already use ultrafiltration to keep large particles out of the gallons you buy at the hardware store. PPG's team, which included environmental staff, technicians, production personnel and managers, developed a new application based on knowledge they already had, says Maura Tinter, the environmental representative. They set up the ultrafiltration unit to take out suspended solids and high molecular weight particles.
Before the water reaches that system, it is prefiltered to take out the largest solids. In ultrafiltration, the water goes through a filter, like pouring a liquid through a cheesecloth. The water passes to the next step and the particles stay behind in the filter.
That still leaves some impurities, though, so the water moves on to reverse osmosis. In that process, a membrane with even smaller holes catches even smaller impurities. It doesn't take out everything, you wouldn't want to drink it, Tinter says. But it's clean enough to go back and clean more equipment.
In fact, the process returns 95 percent of the original water to the storage tank for reuse in washing down machinery. The remaining 5 percent caught by the filters is highly concentrated waste, which is burned.
Since PPG has less waste to get rid of, the company uses less fuel to ship it to the disposal site. Instead of 65 trips to the disposal facility, the tanker trucks only go four times a year now. And the reduced amount of waste that goes there takes less energy to incinerate. The Department of Energy estimates that the change saves 3.6 billion Btu per year, and saves PPG more than $200,000 a year. Now that's a work of art.
[photo] Cleaning up after making paint can be more complex than cleaning up after using it.
Last Updated: July 23, 1996