Complex FGD wastewater decisions need to be made

Lots of effort will going into providing the facts and insights to make sure utilities can negotiate the wastewater rules and limits with their new FGD systems. These decisions are complex. Take for example the decision whether to use dibasic acid (DBA) for improvement of scrubber efficiency. On one hand you can generate allowances at $ 800/ton. On the other hand you wiill probably have to installa biological treatment plant.

We talked to Chris Edmonds of U.S. Filter. His company can furnish a biological treatment system to meet requirements even if DBA is used. So the utility has to weigh the allowance revenue generation against the cost of the acid and the capital and operating cost of the incremental additional treatment systems.

There are many other wastewater decisions which have to be made. Most purchasers will not be able to simply discharge the gypsum wash water purge stream to the ash pond. Edmonds points out that it may be necessary to remove the heavy metals, suspended solids and other contaminants as well as adjust the pH.. U.S. Filter is supplying systems with clarifiers, filter presses, reaction tanks and other hardware for this purpose.

One contaminant of concern in several states including Pennsylvania and North Carolina is selenium. The compound is very difficult to remove. U.S. Filter has found that the solution to be a suspended growth bioreactor which converts the selenium to the elemental form where it can be separated.