POWER October 2012 - 71

WATER & POWER
Evaluating Technologies to
Address Proposed Effluent
Guidelines
Upcoming revisions to U.S. federal effluent guidelines are anticipated to include
new discharge limits for mercury and selenium in flue gas desulfurization
wastewater, in addition to other potential revisions. Collaborative R&D is
helping inform the rulemaking and is evaluating the cost and performance
of technology options that might be used to meet the new targets.
By Paul Chu, Electric Power Research Institute
T
he U.S. Environmental Protection Agency
(EPA) is revising effluent guidelines
for the steam electric power industry
that could change how many power plants
manage and treat wastewater. The proposed
EPA rule is scheduled for release for comment
in November 2012; final rule approval
is expected by April 2014. Once finalized, the
EPA's guidelines may impose new limits on
wastewater discharges at power plants that
would be incorporated into the plant permitting
process. The specific details of the guidelines
remain unknown at present, but they
may include the first-ever nationwide limits
on mercury and selenium discharges from
flue gas desulfurization (FGD) systems and
may also include new limits on fly and bottom
ash transport water, landfill leachate, and
metal cleaning wastes.
Among the potential range of outcomes,
new limits on mercury and selenium in FGD
wastewater discharges could represent the most
significant consequences for the power generation
industry-for coal plants in particular.
To support its rulemaking, the EPA issued
an Information Collection Request (ICR) in
June 2010-an extensive industry questionnaire
to obtain data on water management
practices at power plants. The agency also
conducted sampling and analytical studies at
eight power plant FGD wastewater treatment
systems. The EPA has been using the data
to gauge the applicability and overall performance
and costs of wastewater treatment
options. Ultimately, the agency will identify
the " best available technology " (BAT) and
propose new standards based on this technology's
expected performance.
For power plants, the costs to comply
with potential new limits on mercury and
October 2012 | POWER
selenium discharge could be significant and
will depend upon the treatment approach as
well as which pollutants are regulated and
at what level. The Electric Power Research
Institute (EPRI) estimated that capital costs
could range from $25 million to $50 million
for a physical/chemical FGD wastewater
treatment system to more than $100 million
for a thermal zero liquid discharge (ZLD)
wastewater treatment system. Multiplying
those costs by the number of potentially
affected power plants pushes the potential
price tag for this regulation well into the billions
of dollars. In addition to the costs for
removing mercury and selenium from FGD
wastewater, there are numerous technical
challenges. As a result, FGD wastewater
treatment has been a high priority for research
and development (R&D).
R&D for Informed Decisions
To inform the rulemaking process and support
scientifically based decision-making,
EPRI is conducting a parallel evaluation of
the EPA's ICR data. The evaluation is part
of EPRI's multiyear collaborative R&D program
that also includes characterization of
FGD wastewaters, evaluation of mercury and
selenium chemistry in FGD wastewaters, and
evaluation of an array of wastewater treatment
technologies. EPRI's technical analyses
inform all stakeholders, including the EPA,
industry, and the public, so regulatory decisions
can draw upon a foundation of independent
information.
Focus on FGD, Mercury,
and Selenium
Many FGD systems have been or will be installed
to reduce air emissions of sulfur dioxwww.powermag.com
ide,
as well as mercury and selenium from
coal-fired power plant stack gases; however,
these systems may create new waste management
challenges.
Also known as wet scrubbers, FGD systems
use a slurry of water and limestone or
other alkaline material to remove sulfur dioxide
from power plant exhaust gases. Sulfur,
mercury, and selenium occur naturally in coal
and are released during combustion. Mercury
and selenium exist primarily in vapor phase
in flue gas. They may pass through the power
plant's particulate control device, such as the
electrostatic precipitator (ESP), and thus are
captured in the wet FGD system. The majority
of the mercury and selenium becomes sequestered
in the FGD solids. Small amounts,
often in the parts per billion (ppb) range, end
up in the FGD wastewater. The revised effluent
guidelines will likely affect the way FGD
wastewater (and other wastewater) is managed
before it can be discharged.
Although the proposed federal effluent
guidelines have yet to be released, many states
already regulate mercury and selenium in
FGD wastewater. Some northern Midwestern
states, for example, have established mercury
discharge limits at 1.3 to 12 parts per trillion
(ppt) and selenium limits at 10 to 100 ppb. It is
unclear whether existing treatment technology
can consistently and reliably reduce concentrations
to these levels for all FGD wastewaters
on a continuous basis. The limited data
available demonstrate significant variability
in trace element removal (especially for mercury)
among different power plants and FGD
systems, as well as within operational parameters
of a single FGD system. A number
of factors may affect treatment performance,
such as the coal properties, FGD design and
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POWER October 2012

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