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Removal of Chromium VI from wastewater

I am University of Vermont civil engineering student doing a project for a wastewater engineering class. We were given a list of constituents and there average concentrations from three wells and also discharge requirements. The main problem area is the amount of chromium VI (0.5 mg/L), and III (5 mg/L). We have to design a treatment process that will meet the discharge requirements which for the chrome are 0.1 mg/L. Any information on different treatment methods that are used with advantages and disadvantages would be very helpful. Thank you for your time.

Sincerely,

Matthew M [surname deleted for privacy by Editor]
- Burlington, Vermont 2003

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2003

See letter 18899. Of the conventional methods, I suggest chemical reduction using sodium hydrosulfite ⇦ this on eBay or Amazon zincaffil links] , + coagulant such as Fe+3, pH adjust, + polymer flocculent, settling and filtering. Use about 2:1 Fe:Cr and a final pH of 8.5-8.75, and the co-precipitation should give a final [Cr] < 0.1 ppm.

For the given low influent levels, electrocoagulation (electrochemical reduction + coagulation) is probably a viable method as well. The least expensive plates (Fe) should give the lowest effluent levels.

Both of these methods have the advantage of not requiring acidification in order to accomplish the Cr⁺⁶ reduction; thus, no acid metering pump and less alkali [Ca(OH)₂, Mg(OH)₂ or NaOH] are needed.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

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