MCES Mercury Reduction Strategy

Mercury background

Mercury is a unique element found in everyday uses such as batteries, thermometers, thermostats, fluorescent lights, and dental fillings. Because mercury is an element, it can not be created or destroyed, but can be transferred between air, water and soil in one form or another. When it is released to the environment, mercury can cause serious problems. Public health concerns are growing because mercury can bioaccumulate in fish tissue and cause neurological damage in animals and humans who eat fish.

The Minnesota Department of Health (MDH) and others believe that the concentration of mercury in fish in many Minnesota lakes is already too high. As a result, the MDH advises people--especially young children and women of childbearing age---to limit their intake of fish from certain lakes and rivers.

Mercury Sources

Mercury is widespread in the environment and comes from numerous sources, both natural and human (anthropogenic). Nearly all the mercury in lakes results from air emissions, such as emissions from coal-fired power plants, waste incinerators (including sewage sludge incinerators), and natural sources. Airborne mercury is eventually deposited in water or on the ground where surface runoff carries it into water.

Wastewater treatment plants receive mercury in wastewater from residential, commercial, and industrial sources, including dental clinics and medical facilities. Some wastewater treatment plants incinerate the wastewater solids, or sludge, that are removed during the wastewater treatment process. Sewage sludge incineration is a source of mercury air emissions, although its contribution is small compared to many other anthropogenic sources.

MCES historical mercury trends

Overall, mercury loading to MCES wastewater treatment plants is decreasing. Since 1990, the amount of mercury in the metropolitan wastewater system has decreased by 53 percent. Today, less than 3/4 fluid ounce of mercury is dispersed among 300 million gallons of wastewater reaching MCES treatment plants every day. The reduction of mercury in the metropolitan sanitary system is due to MCES's Industrial Waste Section pretreatment program, better management of mercury wastes by commercial facilities, and changes in consumer products to reduce mercury content.

Mercury transport and fate within the wastewater treatment plant

MCES has measured mercury in the wastewater that comes to its plants and found that most mercury is removed along with solid material in the treatment process. MCES currently incinerates 95 percent of wastewater solids, capturing most airborne emissions in scrubbers. Some mercury is emitted to the air on particles too small to be collected with conventional air pollution equipment. About 5 percent of wastewater solids are applied to agricultural land, and preliminary studies indicate that mercury may also be released to the air from these land-applied solids.

New technology is being developed to control mercury emissions from wastewater incinerators, but the technology is expensive and it does not destroy mercury. Currently, no sewage sludge incinerator in North America has used this new technology to control mercury. The best method for reducing mercury emissions from wastewater treatment plants is to prevent mercury from getting into the sanitary sewer system in the first place.

MCES Mercury Reduction Strategy

Since 1994, the Industrial Waste Section has been working to identify and minimize sources of mercury discharged to the sanitary sewer. MCES has proposed lowering its mercury limit from 100 micrograms per liter (µg/l), or parts per billion to 2 µg/l for facilities discharging to the sanitary sewer.

To further support mercury reduction efforts, in April 1998 the Metropolitan Council formally adopted a new Mercury Reduction Strategy which states the following: "To protect public health and the environment, and in support of the state's initiatives to reduce mercury contamination in fish, the Council will develop the most cost-effective balance of mercury pollution control and prevention approaches to achieve the long-term improvement of the water and air quality for the region."

A MCES staff team was created to implement the strategy and has set a goal of reducing mercury discharged to the sanitary sewer system and eliminating the use of mercury within MCES facilities. MCES expects to reduce mercury emissions from its facilities through a combination of pollution control (treating air emissions from MCES facilities) and prevention (minimizing sanitary sewer discharges). Initiatives include:

Pollution Prevention efforts in the community through continuing partnerships with industry;
Pollution prevention efforts within MCES, including reducing the use of devices and materials that contain mercury; and
Installing emission and discharge pollution control equipment at MCES wastewater treatment plants.

Other mercury reduction initiatives through partnerships

MCES is a partner with 27 other environmental, regulatory and industrial leaders in the statewide Mercury Contamination Reduction Initiative. Coordinated by the Minnesota Pollution Control Agency (MPCA), the group is identifying sources of mercury and considering reduction strategies. Criteria include reduction potential, flexibility, feasibility, permanence, fairness and cost-effectiveness.

MCES is a partner with federal, state and local agencies to study mercury and PCB pollution in the Minnesota River Basin. Six additional monitoring sites are being established on the Minnesota River through legislative funding of $550,000 for 1998 and 1999.

MCES also works with the Association of Metropolitan Sewerage Agencies, a national professional organization, to develop recommendations to the U.S. Environmental Protection Agency on future pollution prevention strategies to reduce mercury emissions nationwide.

Minnesota Dental Association partnership

MCES and the Minnesota Dental Association formed a partnership in January 1998 to evaluate advanced technologies that will remove more dental amalgam from wastewater generated at dental clinics. Amalgam, which contains mercury, is currently collected with basic filters. But improved technology would remove even more waste amalgam. The partnership will also ensure that dental clinics properly manage the waste amalgam that is collected in filtration equipment.

Metro Plant Solids facility

After two years of study, in July 1998 the Metropolitan Council selected new technology that will be used at the Metro Plant to treat the solids removed from wastewater. The new facility will reduce mercury emissions initially by 70 percent from existing levels, as well as reducing other emissions and odors, improving operational efficiency and saving money.

The existing incinerator facility, now nearing the end of its useful life, will be replaced with new "fluidized-bed" incinerators and all new air pollution control equipment. The new facility will produce ash for agricultural application and for construction materials, such as concrete and asphalt. Heat from the facility will be captured and reused for plant operations.

Accountability

The 17-member Metropolitan Council, appointed by the governor, oversees MCES administration and management, principally through its Environment Committee.

Revised: 01/22/99

Contact: Jeff Syme (651)-602-1109