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topic 0324

Can carbamates in wastewater treatment create false cyanide readings?

A discussion started in 1996 and continuing through 2000.
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We have instituted the use of carbamate as a chemical polishing agent to further break down cyanide complexes, allowing us to meet our effluent permit numbers. The problem arises in the last couple of roll-offs, we have seen a rise in cyanide present in the sludge as determined through spectrophotometry (Hach). This test is a screen used by the hazardous landfill. The interesting phenomenon is that the cyanide numbers increase with time. If a distillation is done and the extract treated for sulfides, the sludge is well within parameters for disposal. Does anyone have a clue as to what is happening? Is the carbamate breaking down, releasing sulfur and causing false readings? Has anyone seen this before?

Ric Wade


We have seen similar behavior in other waste water treatment systems and are very interested in the details of your problem.

Scott Bowers
water treatment


Sodium Dimethyl Dithiocarbamate is made from carbon disulfide, dimethyl amine and caustic. The metal carbamates that form a very stable but can be oxidized over time to produce sulfites or sulfates in solution and/or will react with stronger reductants to release sulfur into solution. Does the cyanide procedure use sodium sulfide as a reductant?

Robert R. Odle
- Greenville, South Carolina

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