Letter 31012

Water Rinse Tank Dumping vs. Replenishing  

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I work for a non-profit technical assistance organization, that provides pollution prevention information and dissemination to agencies and businesses trying to minimize wastes and conserve resources. 

Apologies that this is not an ACTUAL situation, and for my naiveté, but I am looking at conserving rinse water by the use of conductivity or other sensors (e.g., TDS, pH) to ensure the water is adequately clean. If one intermittently adds fresh water based on the conductivity/other control set points, and filters/pumps out some of the contaminants, do you still have to fully dump the tank? How would you determine the conditions when the tank should be fully dumped?

Michelle Gaither
Technical assistance - Seattle, WA, US

Rinse tanks do not need to ever be dumped under normal circumstances. Conductivity meters are relatively inexpensive and quite indicative of the contamination situation. But it is very difficult to determine how dirty is too dirty any way other than empirically.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

I might suggest that what you are describing is done all of the time with swimming pools, I've never seen anyone dump a pool just because the water got dirty. A rinse tank is just like a little swimming pool, maybe some of the same theory can be applied to rinse tanks.

Sheldon Taylor    supply chain electronics Wake Forest, No. Carolina

I must disagree with Mr. Mooney on the "never dump" idea. My area of the country has terribly hard water and high TDS. At the end of the week certain rinse tanks (mostly cyanide rinses) look fairly clean and don't test real high on TDS, but when we drain them there is 2 inches of "muck" in the bottom that I assume is coprecipitating bath elements (carbonates?) and the high calcium/magnesium in my raw water. This has been a problem if allowed to build up.

We ended up installing an industrial sized RO unit and my water problems went away (although we found that the high hardness was helping quite a bit on the waste treatment side.

There is always going to be situations that you as a consultant will get blindsided by.

In my opinion.

Regards and good luck.

Trent Kaufman electroplater - Galva, Illinois

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