Full Scale Biological Pre-Treatment of Scrubber wastewaters for selenate removal

1. Full Scale Biological Pre-Treatment of Scrubber wastewaters for selenate removal Jeremy Driver Alabama Power Company Environmental Affairs Lab & Field Services 205.664.6188 jddriver@southernco.com

2. Flue Gas is high in SO2 • SO2 reacts with limestone to form CaSO4 or gypsum • Additional pollutants are removed

3. Gypsum Slurry Clarification

4. APC Plant Barry Background Information • Current NPDES limit on Ash Pond Discharge includes Hg • 12 ppt Hg • Treatment system in place to meet this limit by injecting FeCl3 and NaOH (Physical – Chemical Treatment) • Potential future NPDES limits may include Se and other elements • Physical - Chemical treatment is not sufficient for removing selenate, an oxidized soluble form of Se • Biological treatment is needed to reduce selenate

5. Scrubber Slurry Clarification Pond

6. Wastewater Flow Diagram Service Water Scrubber Scrubber Slurry Clarifying Pond Biofilm Cell 2 Biofilm Cell 1 Biofilm Cell 3 Discharge Ash Sluice Sump Other Minor WW Primary Settling Pond FeCl3 Iron Clarification Pond Ash Pond Mobile River

7. Ash Pond FeCl3 Treatment With Biofilm Pre-Treatment Total Flow 20 MGD <12 ppt Hg $1M /yr Chemical cost on FeCl3 and NaOH Successful now for over a year River Discharge Three Biofilm Cells ½ acre each Primary Settling Pond Iron Clarification Pond Chemical Injection Clarified Scrubber Slurry Wastewater Ash Sluice and Other Minor Wastewater

8. Vertical Flow System(Biofilm or Bio-reduction) Glycerin SeO4-2 Soluble SeO3-2 Wood Chips Se0 In-soluble

9. Vertical Flow System(Biofilm or Bio-reduction)

10. Full Scale Biofilm Treatments • 2 of 3 Seasonal Treatments (completed) • Fall 2011 • Winter 2012 • Summer 2012 (ongoing) • Flow rate 180 - 220 gpm (~ 0.3 MGD) • Clarified Scrubber WW Influent • 65% Diluted (unsaturated) Service Water • Diluted by winter rains • Complete Chemical Analyses • ICP-MS-interference correction system • EPA 200.7 • Peroxide

11. Biofilm Pretreatment Results

12. Full Scale Treatment of Clarified Scrubber Wastewater

13. Preliminary Biofilm Results • Relatively Inexpensive & Robust • Low capital and maintenance cost • Requires carbon feed for bacteria food source • (e.g., glycerin, 140mL/min) • Bacteria can withstand time periods with no flow • Effective pretreatment directly integrated into existing ash pond physical - chemical treatment system • Pollutant Removal • Se (mostly Selenate) , Method 200.7 (98%) • Hg (82%) • Presently Being Evaluated • Low volume wastewater treatment • Looking at different ways that we can integrate the biofilm treatment system in the overall wastewater treatment in order to achieve higher pollutant reduction

14. Future evaluations • Additional physical-chemical treatment of minor waste water with pretreated Scrubber wastewater from the biofilm. Scrubber Scrubber Slurry Clarifying Pond Biofilm Cell 1 Biofilm Cell 2 Service Water Ash Sluice Sump Biofilm Cell 3 Discharge Other Minor WW FeCl3 Primary Settling Pond Ash Settling Pond FeCl3 Iron Clarification Pond Mobile River Ash Pond

15. Questions?