Mercury is a naturally occurring metal that is found in
several forms. Metallic mercury is a silver white odorless liquid at normal
room temperature and pressure. If heated, the liquid metal will evaporate
into a colorless, odorless gas. Mercury is also found in the form of
sulfur-, chlorine-, and oxygen-bearing compounds and amalgams.
Exposure to mercury occurs from breathing mercury vapor,
ingesting contaminated water or food, or via transdermal migration. At high
levels, mercury exposure may result in damage to the brain, the kidneys, and
developing fetuses.
FLUE GAS
In 1999, EPA estimated that approximately 75
tons of mercury were found in the coal delivered to power plants each year
and about two thirds of this mercury was emitted to the air, resulting in
about 50 tons being emitted annually. This 25-ton reduction was achieved
through existing pollution controls such as fabric filters (for particulate
matter), scrubbers (for SO2) and SCRs (for NOx). As more scrubbers and SCRs
are installed to comply with the Clean Air Interstate Rule and other
regulations, and as mercury control technology is used in response to state
mercury regulation, emissions may decrease.
There are a number of currently available
control technologies that coal-fired power plants can use to reduce their
emissions of mercury to the atmosphere. For example, controls for sulfur
dioxide, oxides of nitrogen and small particles that have already been
installed remove some of the mercury before it is released from the stack.
The effectiveness of these technologies for mercury removal varies,
depending on characteristics of the coal and the configuration of the power
plant. In some cases a plant might consider changing the type of coal that
it burns in order to get better mercury control from its existing control
devices.
Control technologies specifically used to
reduce mercury emissions from coal fired power plants have recently begun to
be used on some power plants with success. The most highly advanced
technology, activated carbon injection (ACI) has been used on facilities
that burn municipal solid waste for the past decade. Particles of activated
carbon are injected into the exit gas flow, downstream of the boiler. The
mercury attaches to the carbon particles and is removed in a traditional
particle control device.
SOLIDS
Current Regulations:
- the U. S. Environmental
Protection Agency (EPA) has set a limit of two (2) parts of mercury
per one billion parts of drinking water, and requires that discharges or
spills of greater than one (1) pound of mercury be reported,
- the U.S. Food & Drug Administration (FDA) has set a permissible
limit of one (1) part methyl mercury in a million parts of seafood,
- the U.S. Occupational
Safety & Health Administration (OSHA) has set a limit of one (1)
milligram of mercury per ten (10) cubic meters of workplace air that
should not be exceeded during any part of the workday, and
- the EPA requires:
- thermal treatment of listed hazardous wastes having a total
mercury content of 260 parts per million, or higher, prior to
disposal,
- thermal treatment of characteristic hazardous wastes containing
260 parts per million, or greater, which fail TCLP testing prior to
disposal, and
- either thermal treatment, or other acceptable treatment, of
characteristic hazardous astes which contain mercury in amounts less
than 260 parts per million and which fail TCLP testing
Regulations addressing permissible levels of mercury are
being reevaluated by several agencies.
The following sites are recommended for additional detail
and the most current regulations in effect.
CDC (Centers for Disease Control and Prevention)
http://www.cdc.gov
NIOSH (National Institute for Occupational Safety and Health)
http://www.cdc.gov/niosh/homepage.html
U.S. Department of Health and Human Services
http://www.os.dhhs.gov
U.S. Environmental Protection Agency
http://www.epa.gov
U.S. Occupational Safety & Health Administration
http://www.osha.gov
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