A manufacturer wanted to expand their operation of the paint booth. The paint booth’s capacity was limited by the emissions of Hexavalent Chromium.
The existing paint boot had a filtration system to collect the overspray as a primary control device. A previous consultant suggested adding a water scrubber as a secondary control device. They proposed to monitor the discharge water stream to show that the scrubber was in proper operation.
Adding a scrubber as a secondary control device is not an efficient use of control technology. Further, measuring the concentration in the water discharge stream does not effectively measure the control. If the filtration system collected more materials, then the hexavalent chrome going to the scrubber would be reduced and the concentration in the discharge would be less.
I decided to look at the entire process. The paint in the spray booth was a mixture of 3 component paint mixture, which only one has hexavalent chrome. The Hexavalent Chrome emissions were calculated by assuming all of the Hexavalent Chrome that was in the paint were emitted.
The procedure called for mixing the paint for 30 minutes prior to spraying. I had an independent laboratory test the mixture after 30 minutes. The hexavalent chromium in the combine mixture was reduced to Tri-valent Chrome and considerably less before the mixing of the 3 components. The manufacturer was able to increase the production without adding additional air pollution control devices.