### 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/an aerobic biological systems to reduce certain

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

impoundments, chemical precipitat ion, or aerobic biologi cal treatment processes. EPA prepared

an updated summary of pilot tests, full-scale sy stems, 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 treatmen t system operates a fixed-film bioreactor

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

permanent porous substrate that is inoculat ed 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. A ttachment A presents a summary of these systems

tested, operated, or under constr uction 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 th at lead to nitrifica tion/denitrification and

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

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

wastewater; five fixe d-film anoxic/anaerobic and one suspen ded 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 Stan dard 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 ConstructionGE ABMet Coal Power ExperienceDate Location Pre-Treatment & NotesPilot 12005 Pennsylvania, USA Raw FGD purge stream after hydro-cyclones. Dibasic acid used in FGD.Pilot 22007North Carolina,USALime softening, chemical precipitation, clarification feeding ABMet.Pilot 32007North Carolina,USAChemical precipitation and clarification feeding ABMet. Dibasic acid used in FGD.Pilot 42008 West Virginia, USA Lime softening, chemical precipitation, clarification, pH adjustment feeding ABMet.Duke – Roxboro2008North Carolina,USASettling pond.Duke - Belews Creek2008North Carolina,USALime softening, chemical precipitation, clarification, pH adjustment feeding ABMet.Pilot 52008 Belgium Lime softening, chemical precipitation, clarification, pH adjustment feeding ABMet.Duke - Allen2009North Carolina,USALime softening, chemical precipitation, clarification, pH adjustment feeding ABMet.Duke - Mayo2009North Carolina,USASettling pond.Pilot 62009 Georgia, USA Solids removal/clarification feeding ABMet.Pilot 72010North Carolina,USALime softening, chemical precipitation, clarification, pH adjustment feeding ABMet.AEP - Mountaineer2011 North-East USALime softening, chemical precipitation, clarification, pH adjustment for FGD combinedwith landfill leachate feeding ABMet.Pilot 82012North Carolina,USALime softening, chemical precipitation, clarification, pH adjustment feeding ABMet, highsulfur coal test, oxidant present in feed waterSE US Power Plant2013 South-East USA Ash landfill leachate, pH adjustment via acid addition.Pilot 92013 Indiana, USA Lime softening, chemical precipitation, clarification, pH adjustment feeding ABMet.Eastern US Power Plant2014 Mid-Atlantic, USA Lime softening, chemical precipitation, clarification, pH adjustment feeding ABMet.