MEMORANDUM 

TO: Steam Electric Rulemaking Record 

FROM: ERG 

DATE: April 19, 2013 

SUBJECT: Status of Biological Treatment Systems to Remove Selenium 

Some coal-fired power plants use anoxic/anaerobic biological systems to reduce certain 

pollutants (e.g., selenium, mercury, nitrates) more effectively than has been possible with surface 

impoundments, chemical precipitation, or aerobic biological treatment processes. EPA prepared 

an updated summary of pilot tests, full-scale systems, and systems under construction at power 

plants for anoxic/anaerobic biological treatment systems used to remove selenium and other 

pollutants. 

One type of anoxic/anaerobic biological treatment system operates a fixed-film bioreactor 

that consists of an activated carbon bed, such as granular activated carbon (GAC) or some other 

permanent porous substrate that is inoculated with naturally occurring, beneficial 

microorganisms that reduce selenium and other metals.1

 Chapter 7.1.3.2 of the Technical 

Development Document for the Proposed Effluent Limitations Guidelines and Standards for the 

Steam Electric Power Generating Point Source Category (EPA 821-R-13-002) provides a more 

detailed discussion of this type of system. Attachment A presents a summary of these systems 

tested, operated, or under construction as of March 27, 2013 by GE. 

In addition to the GE ABMet systems, one plant (GenOn Energy’s Conemaugh 

Generating Station) has installed another type of anoxic/anaerobic biological treatment system 

that consists of suspended growth flow-through bioreactors instead of fixed-film bioreactors. 2

,

3

Both designs share the fundamental processes that lead to nitrification/denitrification and 

reduction of metals in anoxic and anaerobic environments. In summary, six steam electric power 

plants operate biological treatment systems that target the removal of selenium in FGD 

wastewater; five fixed-film anoxic/anaerobic and one suspended growth biological treatment 

systems to treat FGD wastewater . Other power plants are considering installing the biological 

treatment technology to remove selenium and at least one plant is moving forward with 

construction. 

 

1

 Sonstegard, Jill, et al. 2010. ABMet®: Setting the Standard for Selenium Removal. (October). DCN SE02040.

2

 Eastern Research Group, Inc. (ERG). 2012. Draft Site Visit Notes for GenOn Energy’s Conemaugh Generating 

Station. (23 August). DCN SE01801.

3

 This suspended growth system has been pilot tested at least in one additional power plant. See DCN SE03883. 
Attachment A 

List of ABMet Pilot Tests, Full-Scale Systems, and Systems Under Construction 
GE ABMet Coal Power Experience

Date Location Pre-Treatment & Notes

Pilot 1 2005 Pennsylvania, USA Raw FGD purge stream after hydro-cyclones. DibasPilot 2 2007 North Carolina, USA Lime softening, chemical precipitation, clarificatio

Pilot 3 2007 North Carolina, USA Chemical precipitation and clarification feeding ABMet. 

Pilot 4 2008 West Virginia, USA Lime softening, chemical precipitation, clarification, pH a

Duke – Roxboro 2008 North Carolina, USA Settling pond.

Duke - Belews Creek 2008 North Carolina, USA Lime softening, chemical precipitation, clarification, pH a

Pilot 5 2008 Belgium Lime softening, chemical precipitation, clarification, pH aDuke - Allen 2009 North Carolina, USA Lime softening, chemical precipitation, clarification, pH a

Duke - Mayo 2009 North Carolina, USA Settling pond.

Pilot 6 2009 Georgia, USA Solids removal/clarification feeding APilot 7 2010 North Carolina, USA Lime softening, chemical precipitation, clarification, pH a

AEP - Mountaineer 2011 North-East USA Lime softening, chemical precipitation, clarification, pH adj

with landfill leachate feeding ABM

Pilot 8 2012 North Carolina, USA Lime softening, chemical precipitation, clarification, pH adju

sulfur coal test, oxidant present in feed 

SE US Power Plant 2013 South-East USA Ash landfill leachate, pH adjustment via acPilot 9 2013 Indiana, USA Lime softening, chemical precipitation, clarification, pH aEastern US Power Plant 2014 Mid-Atlantic, USA Lime softening, chemical precipitation, clarification, pH a