Water-based Paint Disposal

Q. I’ve read about the careful disposal of oil-based paints and solvents to prevent contaminants from entering our water system, but I’ve never heard anything about special care for water-based paints. Don’t they use some of the same toxic pigments?

A. It’s true—even water-based paints pose some level of risk when you dispose of palette scrapings and rinse water. Although their potential for damaging water supplies is nowhere near as high as that from oil-based products that contain solvents, watercolor and acrylic emulsion paints do indeed contain pigments that may be potentially harmful to the environment.

The following disposal methods can help you keep a clear conscience. For palette scrapings, the easiest approach is to collect them in a can or jar and allow them to dry or solidify. The full, covered container can then be safely thrown away in your household trash or at a licensed landfil—unless the mixture contains cadmium or cobalt pigments, which could leach into a landfill. You could collect these paints separately and take them to your local hazardous waste disposal facility. But you’ll probably want to simplify matters for yourself by taking your dried paints—including old tubes—to such a location.

The safe disposal of rinse water containing paint residue is a little trickier. I’ve tried filtering the water through a paper coffee filter as many times as it takes to make the water clear. I allow the residue on the filter to dry, then throw it in the trash or take it to a collection point. But the water, even though it appears clear, still contains pigment.

Golden Artist Colors has developed a method that treats the wastewater, causing the pigments to clump together and separate completely from the water.

The process uses chemicals that can cause irritation to the skin or burning (aluminum sulfate and hydrated lime, which are common soil-treatment chemicals available from a gardening supply store), so you must use caution and follow label instructions carefully. You’ll also need plastic buckets, a large funnel, pH papers to check the acidity/alkalinity of the water, measuring spoons and large coffee filters—all of which can be found in hardware stores, restaurant supply houses or discount stores.

The basic procedure is to dissolve the aluminum sulfate in water, add it to your wastewater, add powdered hydrated lime to that mixture and allow it to settle. The solids will fall to the bottom of the container, leaving a layer of clear water on top. The water should be filtered and the resulting solids disposed of in a licensed landfill. The clear water should then be tested for its pH—which should be between 5 and 9, or neutral—and then flushed into a municipal sewer. Again, paints containing cadmium or cobalt pigments must be taken to a hazardous waste disposal facility rather than flushed (although they can be filtered using this method).

For a complete description of Golden’s process, go to www.goldenpaints.com/water.htm.

With undergraduate and graduate degrees from St. Norbert College and the University of Wisconsin—Madison, Scott Zupanc made his living as a teacher for many years; now he does freelance carpentry so that he can spend most of his time with nature—painting in a farmhouse near Spring Green, Wisconsin, or in a cabin “up north.” “I look forward to painting whatever needs to be painted. I’ve always had an interest in doing prints, and I’m waiting for that possibility to happen,” says Zupanc, who for the second year in a row has won the Kenneth M. Shuck Memorial Award in the Watercolor USA Honor Society annual exhibition.

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