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Mercury in Wastewater Discharge

We are a captive electrozinc (acid chloride) plating shop. Our wastewater treatment process is a simple one - metals precipitation via pH adjustment, clarifier, filter press. A recent water monitoring event revealed high levels of Mercury (.0010 mg/l) in our wastewater discharge. Any ideas regarding the source or treatment for mercury?

Karen Walters
- Lexington, Kentucky
2000

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At that level (1 ppb), it could be that someone broke a thermometer!

James Totter, CEF
- Tallahassee, Florida
2000

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1 of 2 simultaneous responses Karen, have you checked the mercury level in the incoming water. Unless the decimal point is misplaced, it is likely to be in the water supply.

Mandar Sunthankar
- Fort Collins, Colorado
2000

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2 of 2 simultaneous responses Assuming that Hg is not present as impurities in your zinc bath check the quality of your caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] used for neutralising. You should be using diaphragm grade NaOH to avoid Hg impurities. R

Roger Bridger
- Croydon, UK
2000

Mercury can be removed by precipitation with sodium sulfide. The mercury can then be filtered out and disposed of as hazardous wastes. However I agree at these levels, it would take a very accurate lab to tell wether you actually precipitated all the mercury or not. O.OO1 mg/l must be very close to the detection limit.

Don Piett
INCO Ltd - Thompson, Manitoba, Canada
2000

If you are using HCl have it checked for Mercury. In the past I have traced mercury back to a HCl supply over 1 ppm.

John Ring
- Wheaton, Illinois
2000

One of our key customers, a large metal finishing job-shop, is being pursued by the Michigan taxing authority for payment of sales tax on wastewater treatment chemicals. We have historically treated these chemicals as part of the industrial process and therefore exempt from sales tax. Have any of your readers faced this issue in the past?

Eric Earl
- Grand Rapids, Michigan
2000

In Illinois, if the purchased product is consumed in the manufacture of a product (i.e. coolant or chemicals) it is considered taxable (sales tax). Only if a component actually becomes a part of the company's finished product does it become exempt from sales tax. Hope this helps.

Dan Brewer
chemical process supplier - Gurnee, Illinois
2000