Metal finishing Q&As since 1989

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Aluminum Hydroxide Polymer Control

I work in tech support for a manufacturer of analytical sensors (pH, conductivity, dissolved O2, etc).

An aluminum anodizer contacted me about reducing costs on the polymer addition on the waste treatment end of their process. Aluminum Hydroxide is byproduct of anodizing. The customer adds a polymer to an open tank to settle out (flocculate) the Aluminum Hydroxide. The aluminum hydroxide is then disposed of.

Our initial thought was to use turbidity to help indicate the level of suspended solids in the tank. Are there any other common industry methods used to control the amount of polymer addition? I haven't been able to learn enough about how the polymer reaction works to see if it can be controlled by pH, conductivity, or other methods.

Steve Hammond
- Reno, Nevada, USA
2006

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Reduce what cost?

Are they trying to economize by cutting back on the amount of polymer solution? My recollection is that this is the least expensive of the chemicals added in a waste treatment operation. I've not seen (in my admittedly limited experience) any kind of feedback control used to regulate floc addition, except a level sensor. Usually, as long as waste is being fed to the system, it is added at a constant rate.

A great place to look for cost savings in an operation of this nature is the rate of sodium hydroxide addition in the neutralization step. Finessing this helps reduce the settled sludge volume, sometimes a great deal.

Dave Wichern
Consultant - The Bronx, New York
2006

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Polymer is the least expensive of all wastewater treatment chemicals (lb per lb it is the most expensive, but the small amount usually required means it is the smallest cost item overall) Perhaps more efficient use of the polymer or using the right polymer for the application is the answer here. At what pH is the stream being precipitated. The pH is crucial.

Visual control of the polymer is the only way to control. If you have a consistent stream then it would be a matter of setting the feed rate correctly and monitoring. If the stream changes regularly then constant monitoring will be required to ensure proper flocculation.

Gordon Djani
- Greenville, South Carolina
2006

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Steve

Is your customer being regulated by their POTW for aluminum in their waste water discharge?

Willie Alexander
- Colorado Springs, Colorado
2006