Your problem may be where you add the DTC and what it is reacting with.  DTC
is a reducing agent and if you have a metal oxide in solution, it reduces to
the metal and oxygen.  You may have a lot of oxygen in solution that is
causing the problem.  If this is an old installation and a new problem, you
may want to look upstream to see what processes have changed recently.

DTC should be added late in the clarification stage, as a secondary step to
polish the waste stream.  I you add it early, you loose the advantage of
hydroxide precipitation.  DTC should be added last as a polishing step to
take out any residual metal.  It's a very expensive way to precipitate metal.

I think our newsletter number 4 or 5 talked about DTC use.

Bob Mesick 
Remco Engineering
Water and Wastewater Treatment Systems
http://remco.com/home.htm
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