Paint sludge plant


Construction of paint sludge disposal plant

Deutsche Version

For more than thirty years, a regional craft enterprise, which now includes around sixty qualified painters, has been practicing its very own kind of environmental protection, which deserves praise. However, as the volume of work and thus of consumables has increased over the years, the waste disposal system for cleaning paint rollers and brushes, pasting machines and plastering trowels has been quite limited.

The normal procedure of painting companies around the world is to simply dispose of the paint residue into the sewage system when washing the tools, which does not seem to be a problem, since this sludge does not contain any chemicals or other substances that endanger groundwater and nature. Nevertheless, in our eyes the quantities have become quite alarming and there is still no regulation for the disposal of these waste materials.

In 2020, the owner approached me to design, configure and also put into action a paint sludge disposal plant concept that was not available for purchase until now, i.e. „build the thing“.

The sludge must never come to a stand still!

After a few weeks of planning, construction drawings and many a discussion about wastewater volume, consistency of the sludge that falls off, and the frequency of use by the employees, one particular feature emerged: the sludge must never stand still. Because otherwise – and this was shown by the experience of the previous years of „disposing of the sludge by hand“ – the pumps, the pipes, the containers and everything that came into contact with this wastewater, which was saturated with paint residues, would stick together.

Not an easy task, especially since the plant would not be in constant use, because in the winter naturally prioritize other work than, for example, in the spring and summer time. Exterior painting results in more plaster-based paints, i.e. coarser grain and higher silicate content, whereas the interior painting of a hospital, for example, tends to produce more water-based solutions.

The all-encompassing solution, i.e. a plant with several washing tables, a waste water tank for collecting the sludge, but also the appropriate circulation of the sludge masses, an automatic discharge into a cementation container, in which cement dust was to be added to the aqueous sludge, in order to subsequently dry out this mass in manually provided containers and feed it into the „construction waste container“, proved to be almost unsolvable.

Room size just under 20 square meters

Last but not least, the circulation process had to function just as smoothly and without supervision on Sundays and holidays as it did on public holidays or at night. Continuous recirculation, on the other hand, was not possible, since the sludge was also supposed to thicken, and thus had to settle, but was not allowed to settle permanently, since otherwise it would dry out and completely and irrevocably stick to the equipment.

The picture shows the wash boxes, each controlled by a Kränzle, which automatically clean the paint rollers from all sides in a 10-second wash cycle using five water nozzles each. The wastewater sludge runs into the round 1000 liter wastewater tank stored under the wash tables. Round and with integrated backwash to circulate the sludge several times during the day and night to not let it settle, but at the same time to slightly thicken it to reduce wastewater.

The entire plant can convert up to one and a half tons of paint sludge / week into concrete-like construction waste, the wastewater itself, which runs into the sewer system after the procedure, has drinking water quality, so to speak – well, a little filtering and flavoring would still have to be done, but it neither carries the paint residue sludge with it, nor is it chemically contaminated.

Three wash stations – 10 seconds per soiled paint roll

The result is a three-wash station system with a 1 cubic meter sludge tank, automatic shut-off of the fresh water supply in the event of a pipe break or similar. In addition, the discharge of the sludge is controlled by an electromagnetic three-way valve at the push of a button, but the challenge was also that the lines could not be allowed to stand still over the Christmas period, for example, so they had to be flushed continuously to prevent them from becoming full of sludge.

One thousand liter slurry cement flocculation tank

with timer-controlled whisk and automatic cement feeding for hardening of the waste product

The feeding of the cement dust should be dosed automatically, also such a device was not available for sale on the market, thus own construction. A whisk that mixes the slurry with the cement to enrich it for faster thickening had to meet certain conditions in the flocculating slurry tank, because the entire contents must be kept in motion and vigorously mixed during the cementing process. Deposits are not acceptable, because they immediately become hard as concrete and thus destroy the equipment.

The plant has been running smoothly for a year now, and I am honestly proud of it.

Source text and photos: Rolf Göbel

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