That is a coincidence. I have now run two BW wet limestone FGDs, one in MO and now one in FL. We are not currently restricted on Thallium. We have a treated combined discharge from 5 units and only one has a scrubber. I would agree in theory that the activated carbon would remove the Thallium...
I can't say I've had this problem. Treating FGD waste for much of anything can present some problems. What type of scrubber do you have? What are you scrubbing, and what is the Thallium level?