The Future of Electricity
Solving the mercury problem
In 14 months, on December 15, 2003, the Environmental Protection Agency (EPA) will propose regulations on a new category of emissions for electric power plants--mercury.
This naturally occurring element was once commonly used in thermometers, dental work, many everyday products, and in the refining of other metals. But in the last several years research has found that mercury can cause health problems in children and women of child-bearing age.
Tiny amounts of mercury are often part of the coal burned to generate electricity. This is a special concern for electric co- operatives in Kentucky, since burning coal generates nearly all the electricity in the state.
Figuring out how to regulate and reduce mercury emissions is so important to the industry that utility experts are meeting with the EPA in an intensive effort to define terms and develop workable solutions.
Although we've known for years that burning coal can release mercury, during the last three decades more priority has been given to other power plant emissions, such as sulfur dioxides and nitrogen oxides.
Mercury has received very little public attention for two reasons. First, relatively small quantities of mercury are released during coal combustion. While annual sulfur dioxide and nitrogen oxide emissions nationally are measured in millions of tons, the entire American electric utility industry emitted only 90,000 pounds of mercury during the year 2000. In Kentucky, the annual mercury emissions at East Kentucky Power Cooperative (one of three electricity generating entities that serve the state's co-ops) are about 678 pounds--less than 1 percent of the national total.
Second, the way mercury moves through the environment is different from other emissions, making it a less obvious problem.
Bob Wayland, leader of the Combustion Group for the EPA's Office of Air Quality Planning and Standards in Research Triangle Park in North Carolina, says scientists are "just beginning to understand the whole mercury cycle."
Wayland, who specializes in atmospheric chemistry, points out that people don't commonly breathe mercury and get sick. Mercury must be ingested, that is, taken in with food, to cause problems, and the effects are usually gradual.
When tiny amounts of mercury enter the atmosphere as a byproduct of burning coal, the mercury atoms eventually fall to the Earth's surface and enter water. Once in the water, either in nearby streams, rivers, and lakes or far-away oceans, normal biological processes transform elemental mercury into a highly toxic form, methyl mercury.
That methyl mercury builds up in the bodies of fish and other animals that eat fish. As the poisons "bio-accumulate" they become more concentrated. Too much mercury in a person's diet can eventually lead to serious problems with the nervous system and the brain. Studies show that those most susceptible to mercury exposure are children in the formative years and women of child-bearing age.
A simple way to help prevent human health problems associated with mercury is to avoid eating certain kinds of fish. Indeed, "fish advisories" are posted and publicized in many places.
The newer focus tries to prevent mercury from entering natural water systems in the first place.
The first efforts to control the release of mercury involved dental and medical practices as well as municipal garbage incinerators. But those sources of mercury account for only about one-fourth of the problem. The bulk of mercury entering the Earth's atmosphere comes from coal-fired power plants. That problem has utility company engineers, scientists, and accountants all sharpening their pencils and peering at computer models.
Instead of setting an arbitrary number (such as parts per million or billion) for mercury emissions, the EPA has been collecting data to find out which power plants have the lowest emissions of mercury. The regulations being developed now will reflect the best results obtained by plants using existing technology--with some important qualifications.
Bill Wemhoff, a senior environmental manager for the National Rural Electric Cooperative Association in Arlington, Virginia, points out, "Different kinds of coal have different amounts of mercury, as well as other elements. The chlorine content of coal seems to affect the amount of mercury that can be removed with existing technologies such as scrubbers, SCRs, and particulate removal systems."
Removing mercury while removing other pollutants with existing technologies such as flue gas desulfurization is known as a "co-benefit." But co-benefits alone may not be able to get mercury emissions low enough to satisfy regulators.
"If a particular kind of coal has no chlorine in it," Wemhoff says, "the mercury goes right out the stack anyway. A different technology may be required since right now there's no proven technology to deal strictly with mercury."
One promising new method involves "activated carbon injection," ACI for short. Still in the experimental laboratory stage, ACI captures the mercury and puts it into the residual ash. But such a method raises more questions: Would changes in color and composition make the mercury-laden ash unsuitable for other uses such as manufacturing processes? Would this ash with mercury be considered a non-hazardous waste and permitted in landfills, or would it have to be disposed of differently?
Other mercury-removal technologies under consideration include changes to the entire combustion process.
The question of cost unites all these tentative solutions. Will limiting mercury emissions cost thousands of dollars per pound removed, or tens of thousands of dollars? And how will those costs affect electric rates?
When the EPA proposes the mercury regulations at the end of 2003, it will allow comments and fine-tuning adjustments before presenting the final rules on December 15, 2004. Those rules will become effective in December 2007, whether or not all the questions have been answered.
The battle to control mercury is likely to take a long time, with improvements coming along in a series of small steps.
To learn more about how mercury can affect you, and to find out what the EPA is doing to reduce mercury pollution, visit www.epa.gov/mercury.