Removing Water-Based Paint Solids from Rinse Water

If you would rather not flush water laden with acrylic paint solids down the drain, they can be removed prior to disposing of the water. This process consists of chemically treating the contaminated water to cause the solids to flocculate, followed by filtering to remove them from the water. The materials and equipment needed are available locally and/or via mail order from the Vendor List found at the end of this article. The chemicals are hazardous so read label precautions and keep everything out of the reach of children. Safety goggles and a dust mask are recommended. The process described is intended for nonindustrial users of acrylic paints.

Start by assembling the supplies listed below. Decide on the process batch size. Using 5 gallon pails allows you to process up to 2½ gallons at a time. A 1 gallon pail and matching funnel allows for up to a ¾ gallon batch.

  1. Add 10 grams of granular aluminum sulfate for each gallon of water. This is about ½ Tablespoon, well rounded. So, 2½ gallons would require about 25 grams, or 1¼ Tablespoons. Dissolve this material in a small jar with several ounces of water before adding to waste water. Then, add to waste water and stir vigorously.
  2. Add 9 grams of powdered lime per gallon being processed (a scant ¾ Tablespoon). Stir in vigorously and observe. The flocculation of solids should start occurring within a couple of minutes. You should start to see a clear layer of water forming as the solids settle to the bottom. If, after several minutes, flocculation has not occurred, repeat steps 1 and 2.
  3. Check the pH of clear water. It should be between 5 and 9. If lower, adjust by adding lime. If higher, adjust by adding aluminum sulfate.
  4. Assemble the filtering equipment as shown. Use 2 coffee filters at a time. Pour the water through the filters after flocculation has occurred. The water will take several hours (over night) to completely pass through the filter. The resulting filtrate should be clear and should be flushed to a sanitary sewer. The solid filtered residue should be disposed of in a licensed landfill.

Supplies Needed to Process Rinse Water

Vendor List

  • Filters may be found at restaurant supply houses. We use “Brew Rite” 18″x7.5″ for the 1 gallon setup and 25″x11″ for the 5 gallon, purchased from Smith Restaurant Supply Co, Inc., 500 Erie Boulevard East, Syracuse, NY 13202; Phone (315)474-8731.
    Filters are also available from Coffee Wholesale USA, Po Box 1614, Round Rock, Texas, 78680; Phone (512)388-9700. Ask for the 18″ or 24″ size, manufactured for 3 or 10 gallon coffee urns.
  • Funnels need to be large enough to rest on rim of pail. Check with industrial supply firms, such as McMaster-Carr, 473 Ridge Road, Dayton, NJ 08810; Phone (908)329-3200. Order the 13.5″ diameter #4360T6 for the 5 gallon setup and the 9″ #4144T4 for the 1 gallon. (Search for “funnel”)
  • Pails, such as the polyethylene type that hold our products, work fine.
  • Aluminum Sulfate and Hydrated Lime are common soil amendments available from gardening centers.
  • pH paper is available from laboratory supply houses.
  • Measuring spoons should be purchased and kept separate from kitchen utensils.
  • Safety Equipment (goggles and dust masks) are available at Northern Safety.

4 Responses to Removing Water-Based Paint Solids from Rinse Water

  1. Lisa Petrulis April 28, 2019 at 11:03 am #

    I see this was written in 1996, is it still the best solution?

    • Sarah Sands April 29, 2019 at 10:58 am #

      Hi Lisa – Thanks for asking. This process really does remain the best and most effective approach and it has held up quite well over the years. So definitely feel free to rely on it. And if you have any other questions, just ask!

  2. Lorraine November 5, 2019 at 4:45 pm #

    Can the waste water be reused to wash brushes and containers?

    • Greg Watson November 11, 2019 at 1:54 pm #

      Hi Lorraine,
      We recommend discarding the filtered water after the paint solids are removed.
      Thank you,
      Greg Watson

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