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Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
July, 2002

Metal Precipitation in a Full Biological Treatment Plant

Q. Is it okay to use sodium dimethyldithiocarbamate to precipitate metal in a full biological treatment plant?

A. Absolutely not. Thiocarbamates (including sodium dimethyldithiocarbamate) are toxic to waste water organisms (bacteria that treat the waste water) and are sometimes used as biocides for recirculated cooling water such as that used in cooling towers or heat exchangers. Thiocarbamates are used in some chemical precipitation waste water pretreatment systems to drop out heavy metals. EPA is currently looking at limiting (or maybe even banning) thiocarbamates IF the final treated water is discharged to a POTW or direct to US waters, due a recent major fish kill linked to thiocarbamates. As with any compound the dosage is the issue. It is probably not a problem at a few parts per billion, but apparently is quite toxic even around 1 ppm to bacteria and fish. I suspect that it is not much use for precipitating metals at the PPB level, therefore I would strongly suggest avoiding its use.



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