Pollution Prevention
Ask the Expert Question-and-Answer Archive

by George Cushnie
March, 2008

Rinse Water

Q. We have a large anodizing facility which uses 6000 gallons of water per day as rinse. We calculated that one rack/cycle of parts consumes 100 gallons of water for rinsing. It is your typical sulfuric acid anodizing process: Soak cleaner, rinse, nitric dip, rinse, sulfuric anodizing, rinse, cold seal, rinse. I am the Environmental Coordinator and it appears that this rinsing is excess.

A. Six thousand gallons per day does not sound excessive to me, if you are a large anodizing shop.  As a rough rule of thumb, an average anodizing shop uses about 1.96 gallons of water per dollar of sales and the better performing shops use 0.6 gal/$ of sales.  Poor performers are using over 3 gal/$ of sales.  These numbers come from the Metal Finishing Benchmarking Study.

As an example, if I assume your shop does $3 million/year in anodizing sales, and if you were a good performing shop, you would be expected to use 5,880,000 gal. per year (3,000,000 * 1.96 = 5,880,000).  If you were working 300 days/year, that would translate to 19,600 gal per day.  Plug in your actual sales and see how well you are doing.

Although nearly every shop has some room for improvement, you should not cut back your water use to the point where you are getting inadequate removal of dragout from the parts.  If that happens, then you will carry over process solution to other tanks and will need to dump and remake you baths more frequently. On the other hand, there are a number of ways to reduce water use and actually improve the quality of your rinsing.  Check out the dragout reduction and rinse water reduction sections of the "Bluebook." There are a lot of good suggestions here on keeping the dragout in the process tank and optimizing the use of rinse water. No mater how good of a performer you are, you will probably find something here that will make a positive impact.

A good resource for evaluating alternative rising configurations is the STERCs Rinse Systems Calculator.  Using this tool, you can evaluate the effect of adding another rinse tank.

The STERC can help you track water use, electricity use, sludge generation, etc. from year to year and will show how you facility stacks up against other anodizing shops.  To participate in this program, go to http://www.strategicgoals.org and fill out the 2007 Worksheet.  There are instructions on the worksheet that tell you where to send completed forms.

Id like to hear back from you once you have had a chance to read over my response and look at these various tools.  Please let me know if this has been helpful or not.  Also, Id be more than happy to give you some additional guidance if you have some other questions.

Good luck,

George