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

FULL SCALE BIOLOGICAL PRE-TREATMENT OF SCRUBBER WASTEWATERS FOR SELENATE REMOVAL

Jeremy DriverAlabama Power CompanyEnvironmental Affairs Lab & Field Services205.664.6188 jddriver@southernco.com

Flue Gas is high in SO2

SO2 reacts with limestone to form CaSO4 or gypsum

Additional pollutants are removed

GYPSUM SLURRY CLARIFICATION

APC PLANT BARRY BACKGROUND INFORMATION

Current NPDES limit on Ash Pond Discharge includes Hg12 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

SCRUBBER SLURRY CLARIFICATION POND

WASTEWATER FLOW DIAGRAMScrubber Slurry Clarifying Pond

Biofilm Cell 3 Discharge

Iron Clarification

Pond

Primary Settling Pond

Ash PondMobile River

Ash Sluice Sump

Other Minor WW

Service Water

Scrubber

Biofilm Cell 1

Biofilm Cell 2

FeCl3

Ash Pond FeCl3 Treatment With Biofilm Pre-Treatment

Three Biofilm Cells ½ acre each

Primary Settling Pond

Iron Clarification Pond

River Discharge

ChemicalInjection

Total Flow 20 MGD<12 ppt Hg

$1M /yr Chemical cost on FeCl3 and NaOH

Successful now for over a year

Clarified Scrubber Slurry Wastewater

Ash Sluice and Other Minor Wastewater

VERTICAL FLOW SYSTEM(BIOFILM OR BIO-REDUCTION)

SeO3-2

SeO4-2

Se0

Glycerin

In-soluble

SolubleWood Chips

VERTICAL FLOW SYSTEM(BIOFILM OR BIO-REDUCTION)

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

BIOFILM PRETREATMENT RESULTS

FULL SCALE TREATMENT OF CLARIFIED SCRUBBER WASTEWATER

Season Biofilm Cells (#)

Time (d)

Avg. Flow (gpm

)

No Flow (%)

Infl. Se

(ppb)

Effl. Se

(ppb)

Se Remova

l (%)

Water Temp (C)

Samples (#)

Fall 2011

2 52 180 9 2,103

29 99 16 11

Winter 2012

2 41 213 0 590 13 98 16 13

Summer 2012

3 85 206 2 951 25 97 29 17

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

FUTURE 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

Scrubber Biofilm Cell 1

Biofilm Cell 2

FeCl3

Ash Settling Pond

FeCl3

QUESTIONS?