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.
- 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.
- 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.
- 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.
- 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.
- 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.
34 thoughts on “Removing Water-Based Paint Solids from Rinse Water”
I see this was written in 1996, is it still the best solution?
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!
Can the waste water be reused to wash brushes and containers?
We recommend discarding the filtered water after the paint solids are removed.
Can the waste filtered water be drained?
After the process, the water can be safely poured down the drain. It should not be reused for painting.
just curious as to why it shouldn’t be re-used for painting.
Tap water typically has microbes that do not get filtered out with this process. These can grow in the waste water, cause odor and make the filtered waste water unpleasant to use and may spoil paint mixtures more quickly. For best results, it is recommended to use fresh water for painting.
I’ve called most every garden center in California that I can drive to, they say that they can’t carry hydrogenated lime or aluminum sulfate because FDA forbids it. What other options will work. I don’t want to ruin my pipes or septic. Thank you!
Hello Arielle. I’m not sure why you are not able to obtain hydrated lime in a DIY center such as Lowes or Home Depot. Quickcrete Hydrated Lime is a very common additive in plastering walls and garden centers. https://www.lowes.com/pd/QUIKRETE-50-lb-Hydrated-Lime/3567274 Alumuminum Sulphate, or “Alum” is a very common material as well. https://www.homedepot.com/p/20-lb-Ammonium-Sulfate-21-0-0-LG-40006-50/303701525 . I assume that both are readily available at the home centers, but you may need to go to the store and speak with gardening center manager there to make sure they understand what you are looking for. We also have a brand new kit for doing this process, linked here for you: https://www.goldenpaints.com/crashpaintsolids – Mike Townsend
Can this be done in larger batches? I use a 10-gallon pail for water disposal….
great that you are treating your painting water as well! Yes, this can be done in larger batches and you would simply have to adjust the amounts of lime powder and aluminum sulfate accordingly.
The water that is filtered into the pail seems rather murky. Can it be refiltered?
I couldn’t find the larger filters where I live, so I used smaller filters arranged to cover the funnel as much as possible.
The other solution I had was to cut a hole in the lid of the pail to set the funnel in. It works quite well and I don’t need a huge funnel. I’m using a 9 inch funnel.
Yes, you can attempt to refilter. You could use the chemicals again or just try to pass through the coffee filter and see if you catch more solids. It is possible since you are not using a single filter that some material is passing around the smaller filters. Larger filters are available online from retailers such as Amazon.
Hi, Can I make large batches of the powdered Sulfate and Lime into solutions for later use?
It’s possible to mix the material and use it over time, but the lime will settle and require very vigorous remixing so we do not recommend it. Also, these would not be good to have around in non-child-proof containers if this is a family household.
Can you add too much of either? Tried this once and it worked like a charm. The next time I wasn’t getting floculation, but I did have some foaming. Waited a few minutes and added more of each and then nothing….
Hoping you can help!
Not sure what may have happened there. Assuming everything was added in the correct order, the #1 solution should flocculate the solids and then the #2 solution should bring it back to a more neutral PH for disposal. Please let us know if you continue to have issues. Give us a call at 800-959-6543 and ask for technical support.
Could you explain the purpose of flocculating the solids?
Surely they disperse again a bit when you move the water simply through agitation?
Would simply pouring the water through the filter, without using the chemicals, not achieve the same result?
Flocculating the solids is an important step to this process. It renders the solids into clumpy masses that are too large to stay in solution. They do not reenter the mixture after they have been flocculated. The pigments and acrylic solids need to be flocked together so they get caught in the filter. Otherwise they will flow through as colored water. Some of the color may get captured, but it is markedly less effective.
Does the paint solid turn to a powder? What are uses for the paint after filtering the water away?
What remains is a dried clump of pigment and acrylic solids. We recommend discarding this material after separating it from the water, as it is difficult to say what it might be used for and if it would be a stable addition to any sort of home-made art material. This product should be fine to add to your solid waste stream.
We hope all is well in the studio!
Thank you! I am going to implement this strategy at my school to reduce our microplastic waste in the art department!
Thank you! I am going to use this process to recycle paint water in my school’s art department!