F ULL S CALE B IOLOGICAL P RE - T REATMENT OF S CRUBBER WASTEWATERS FOR SELENATE REMOVAL Jeremy Driver Alabama Power Company Environmental Affairs Lab & Field Services

Flue Gas is high in SO 2 SO 2 reacts with limestone to form CaSO 4 or gypsum Additional pollutants are removed

G YPSUM S LURRY C LARIFICATION

APC P LANT B ARRY B ACKGROUND I NFORMATION Current NPDES limit on Ash Pond Discharge includes Hg 12 ppt Hg Treatment system in place to meet this limit by injecting FeCl 3 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

S CRUBBER S LURRY C LARIFICATION P OND

W ASTEWATER F LOW D IAGRAM Scrubber Slurry Clarifying Pond Biofilm Cell 3 Discharge Iron Clarification Pond Primary Settling Pond Ash Pond Mobile River Ash Sluice Sump Other Minor WW Service Water Scrubber Biofilm Cell 1 Biofilm Cell 2 FeCl 3

Ash Pond FeCl 3 Treatment With Biofilm Pre-Treatment Three Biofilm Cells ½ acre each Primary Settling Pond Iron Clarification Pond River Discharge Chemical Injection Total Flow 20 MGD <12 ppt Hg $1M /yr Chemical cost on FeCl 3 and NaOH Successful now for over a year Clarified Scrubber Slurry Wastewater Ash Sluice and Other Minor Wastewater

V ERTICAL F LOW S YSTEM (B IOFILM OR B IO - REDUCTION ) SeO 3 -2 SeO 4 -2 Se 0 Glycerin In-soluble Soluble Wood Chips

V ERTICAL F LOW S YSTEM (B IOFILM OR B IO - REDUCTION )

F ULL S CALE B IOFILM T REATMENTS 2 of 3 Seasonal Treatments (completed) Fall 2011 Winter 2012 Summer 2012 (ongoing) Flow rate 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 Peroxide

B IOFILM P RETREATMENT R ESULTS

F ULL S CALE T REATMENT OF C LARIFIED S CRUBBER W ASTEWATER SeasonBiofilm Cells (#) Time (d) Avg. Flow (gpm) No Flow (%) Infl. Se (ppb) Effl. Se (ppb) Se Removal (%) Water Temp (C) Samples (#) Fall , Winter Summer

P RELIMINARY B IOFILM R ESULTS 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 (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

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

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