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Attachment 1

Definition of Model Facility and FGD Wastewater Treatment Technologies

This attachment describes the characteristics of EPA’s “model plant,” including basic 

descriptions of the operation and the assumed FGD wastewater characteristics. This information 

is intended to be used to design, size, and cost the FGD wastewater treatment systems. In 

addition, a summary of the FGD chemical precipitation wastewater treatment system used as part 

of the basis for the best available technology economically achievable (BAT) effluent limitations 

guidelines and standards (ELGs) for the steam electric industry is provided for reference.

Power Plant and FGD Wastewater Characteristics

EPA’s “model plant” has the following characteristics:

 Eastern bituminous coal burned in boilers;

 Limestone sorbent used in FGD absorber;

 Forced oxidation system used to generate gypsum;

 Gypsum solids are removed prior to wastewater treatment;

 Plant is located in the Mid-Atlantic region of the country; and

 FGD wastewater treatment system is located outdoors.

Table A-1 presents the characteristics of the FGD wastewater that Liberty Hydro can assume will 

enter the wastewater treatment system. EPA refers to this influent waste stream as “scrubber 

purge”. It is assumed that this scrubber purge has already been through a solids removal process. 

A range of concentrations, as well as an average concentration, is provided for all constituents 

and parameters.

Table A-1. Scrubber Purge Wastewater Characteristics

Analyte Units Average 

Concentration 

Concentration Range

Minimum 

Concentration

Maximum 

Concentration

Total Metals

Aluminum μg/L 453,085 49,000 2,550,000

Antimony μg/L 25.44 6.50 100

Arsenic μg/L 598 10.66 5,250

Barium μg/L 3,653 400 21,300

Beryllium μg/L 23.16 0.05 136

Boron μg/L 181,634 98.10 1,200,000

Bromide μg/L 171,252 6,000 1,400,000

Cadmium μg/L 45.05 4.00 840.00

Calcium μg/L 3,284,684 610,000 9,700,000

Chromium μg/L 427 19 8,490

Cobalt μg/L 306 52 968

Copper μg/L 264 11 3,280

Iron μg/L 312,751 64,000 2,670,000

Lead μg/L 400 67 2,120
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Analyte Units Average 

Concentration 

Concentration Range

Minimum 

Concentration

Maximum 

Concentration

Lithium μg/L 192 93 500

Magnesium μg/L 1,577,895 258,000 14,000,000

Manganese μg/L 38,651 1,980 486,000

Mercury ng/L 454,000 200 4,200,000

MeSe μg/L 3.42 1.40 6.30

MeSe(IV) μg/L 3.07 1.20 15.40

Molybdenum μg/L 293 27.00 1,350

Nickel μg/L 472 106 6,560

Nitrate μg/L 69,500 36,000 120,000

Nitrate (as N) μg/L 15,724 12,000 27,000

Potassium μg/L 47,105 19,900 84,500

SeCN μg/L 3.57 0.43 22.80

Selenate μg/L 314 37.20 2,470

Selenite μg/L 90.35 0.60 1,120

Selenium μg/L 4,057 274 26,200

SeMe μg/L 2.85 0.63 9.20

Silicon μg/L 133,692 99,000 163,000

Silicon Dioxide μg/L 285,923 211,000 349,000

Silver μg/L 11.95 1.00 387

Sodium μg/L 123,654 16,300 950,000

Thallium μg/L 30.67 2.00 195.00

Tin μg/L 398 50 1,860

Titanium μg/L 4,748 940 29,700

Vanadium μg/L 1,700 120 10,700

Zinc μg/L 1,009 50 21,000

Dissolved Metals

Aluminum μg/L 1,769 200 29,000

Antimony μg/L 5.81 2.00 13

Arsenic μg/L 11.85 4.00 79.92

Barium μg/L 301 85 700

Beryllium μg/L 2.88 2.00 12.00

Boron μg/L 278,792 13,000 820,000

Cadmium μg/L 98.29 4.00 510.00

Calcium μg/L 2,050,000 550,000 5,200,000

Chromium μg/L 8.03 8 8.70

Chromium hexavalent μg/L 10 10 10

Cobalt μg/L 230 20 500

Copper μg/L 17.27 4 110

Iron μg/L 200 200 200

Lead μg/L 2 2 2

Magnesium μg/L 3,694,583 400,000 11,000,000

Manganese μg/L 25,431 9 470,000

Mercury ng/L 8,730 1.2 187,000

Molybdenum μg/L 132 40 960

Nickel μg/L 1,070 71 2,500

Selenium μg/L 669 42.40 5,780

Silver μg/L 2 2 2

Sodium μg/L 289,667 28,000 590,000

Thallium μg/L 14.91 2 49

Tin μg/L 200 200 200

Titanium μg/L 20 20 20
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Analyte Units Average 

Concentration 

Concentration Range

Minimum 

Concentration

Maximum 

Concentration

Vanadium μg/L 18.13 10 97

Zinc μg/L 1,721 30 11,000

Classicals

Acidity μg/L 80,250 20,000 150,000

Alkalinity μg/L 72,750 36,000 140,000

Ammonia as N mg/L 6.05 0.50 49

Biochemical Oxygen Demand mg/L 10 2 110

Chemical Oxygen Demand mg/L 391 40 1,400

Chloride mg/L 5,933 950 16,000

Cyanide μg/L 772 10 19,000

Fluoride μg/L 10,200 8,400 12,000

Nitrate-Nitrite (as N) mg/L 52.02 0.55 230

Sulfate mg/L 3,362 780 36,000

Total Dissolved Solids mg/L 18,276 6,900 68,000

Total Kjeldahl Nitrogen mg/L 31.21 1.30 130

Total Phosphorus mg/L 3.66 0.05 30

Total Suspended Solids mg/L 15,487 1,100 67,000

Parameter Units Average Range

Minimum Maximum

Operating Conditions

Flow Rate gpm 350 100 800

pH S.U. 7.4 6.78 8.1

Temperature oC 38.2 38.2 38.2

*The values in this table are a rough estimate of FGD purge wastewater characteristics using available data; therefore, these

values should only be used as guidance and not for any calculations

Chemical Precipitation Treatment System

During pH elevation and gypsum desaturation, the pH is raised, typically to 8.5-9.2 using 

calcium hydroxide (Ca(OH)2) or sodium hydroxide (NaOH). Abundant metals, such as 

aluminum, iron and manganese form hydroxides. Addition of lime or caustic also causes 

desaturation of gypsum in the stream. Seed sludge is recycled from the downstream clarifier to 

provide sites for gypsum crystal growth. This process desaturates the stream and prevents scale 

from forming on the equipment.

For coagulation, an iron salt such as ferric chloride is used. The iron salt helps denser flocs to 

form, thus enhancing clarifier performance. In addition, the iron salt may co-precipitate other 

metals and some organic matter.

Sulfide chemicals (e.g., trimercapto-s-triazine (TMT), Nalmet®, Metclear, sodium sulfide) may 

be added to enhance the precipitation and removal of heavy metals, such as mercury. While 

precipitation due to hydroxide addition can remove some heavy metals, precipitation due to 

sulfide addition can remove additional heavy metals because metal sulfides have lower 

solubilities than metal hydroxides. FGD wastewater chemical precipitation systems may include 

various configurations of lime, ferric chloride, and sulfide addition stages, as well as clarification 

stages.
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Typically, after the coagulation step, polymer is added to aid in solids formation. Next, the 

wastewater undergoes clarification using a reactor-clarifier design. After clarification, the pH is 

adjusted to neutral using hydrochloric acid (HCl).

Proposed BAT ELG Limits

As you are aware, EPA proposed BAT limits for FGD wastewater based on the operation of a 

chemical precipitation system (as described above) and the operation of GE’s ABMet biological 

treatment system. Table A-2 presents the proposed BAT limits for FGD wastewater. When 

providing the costs for Liberty Hydro’s ZVI treatment system, EPA requests that the system 

design be sized appropriately to meet the proposed BAT limits and that the costs provided reflect 

the appropriately sized system.

Table A-2. Pollutant Limits for the Proposed Effluent Limitations Guidelines (ELG) and 

Standards for the Steam Electric Power Generating Point Source Category

Pollutant Daily Average Monthly (30-day) 

Average Units

Arsenic 8 6 μg/L

Mercury 242 119 ng/L

Selenium 16 10 μg/L

Nitrate-Nitrite (as N) 0.17 0.13 mg/L