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All municipal solid waste in Fairfax County that is not recycled
through curbside or drop off programs ends up at the Covanta
waste-to-energy facility located at the I-95 Landfill in Lorton.
In the waste-to-energy conversion, the volume of trash is reduced
by 90%.
Every day about 150 to 200 trucks, each carrying as much as
20 tons of trash, arrive at the facility. The trucks enter a
huge garage-type structure and dump the trash on the tipping
floor.
A bulldozer pushes the trash into a pit that has a maximum
capacity of 16,000 tons but typically holds 8,000 tons. Big
cranes pick up the trash and feed it into the hopper, which
goes to the boiler. This is where combustion happens.
The trash is burned on a grate at 2,400 degrees Fahrenheit,
24 hours a day, seven days a week. The heat from the combustion
heats water in tubes, which creates steam. The steam turns the
turbine, which combined with a generator, generates electricity.
The steam leaves the turbine and goes to cooling tanks. The
steam is then returned to a liquid state with cooling water.
During the process the cooling water can be seen evaporating
as water vapor clouds above the cooling tower.
The ash from the incinerated trash is sifted for ferrous and
nonferrous metals, which are recycled. About 25,000 tons of
ferrous metals and 600 tons of nonferrous metals are removed
per year. The remaining ash is land filled, which represents
only about 25% of the original weight of the trash.
The combustion air goes through several forms of air pollution
control equipment to remove nitrogen oxides, sulfur dioxide,
hydrogen chlorides, mercury, and dioxins.
 Ammonia
is sprayed into the furnace to remove nitrogen oxides which,
when released into the atmosphere, can contribute to a “ground
level” ozone or smog. From the furnace, the combusted
air goes to a scrubber that neutralizes acid gases—sulfur
dioxide and hydrogen chloride—which contribute to acid
rain. Carbon is sprayed into the combusted air to help remove
mercury and dioxins. Finally, the combusted air goes through
fabric filters in the “bag house.” The bag house
works like a big vacuum cleaner in reverse. There are 2,520
bags which are each 14 feet long. As the dirty gas goes through
the bags, more than 99 percent of particulate matter is removed.
Clean gas rises and goes out through one of four stacks.
The plant generates 79 megawatts of electricity, enough to
power about 75,000 homes. Covanta sells the electricity to Virginia
Dominion Power, and Fairfax County receives a portion of the
revenue.
The county has a contract with Covanta to process trash until
2011 with the option to extend the contract to 2021.
Fairfax County guarantees the delivery of 930,750 tons of waste
to the facility. Until 2003, about three-fourths of the waste
came from Fairfax County and the rest from Washington, D.C.
Today, the county’s population exceeds one million and
generates enough trash to fill the facility. A small amount
of waste from D.C., Prince William and Loudoun Counties is currently
being taken at the facility; however, these amounts are less
than in previous years. Most DC waste is taken to landfills
south of here.
Kent Burton, Senior Vice President of National Environmental
Strategies and a consultant to Covanta, is eager to talk about
the solid waste industry. “Solid waste management, from
the standpoint of protecting public health, is relatively new,”
said Burton.
“A hundred years ago, we disposed of our garbage with
little regard for ground water contamination or air emissions.
The evolution in waste management started when people realized
that how we disposed of our waste had environmental consequences.
It was the Europeans who got creative with trash disposal because
there was less land available for burying it. They devised technologies
to improve and control combustion of trash. The Germans discovered
that if you burn trash hot enough, the energy can turn a turbine.
The Martin grate, which is the type used at Fairfax, is the
most used technology for burning municipal solid waste in the
world. It was introduced to the U.S. in the 1970’s.”
Derek Porter, a chemical engineer, is the business manager
for Covanta Fairfax. “In the 1970’s and 80’s,
interest in the waste-to-energy process increased because landfills
were running out of space. However, in the 1990’s landfills
increased capacity so interest in WTE slowed. In the last few
years, as capacity for landfills is again going down, interest
in WTE is up. This is particularly true in New York where land
is too expensive to use for landfills and in Florida where the
water table is so high that municipalities cannot dig deep enough
to bury trash.
“WTE has grown,” added Burton. “It is absolutely
the most environmentally sound way to deal with garbage. In
the northeast and other populated areas, it is economically
comparable to other disposal methods. If you look at the environmental
benefits, there is no comparison.”
“In 1989, when the Clean Air Act passed, there was a
separate title specifically addressing WTE” said Burton.
“Many environmental activists were pushing for strict
recycling—all waste material should be converted to its
original use. However, it would be astronomically expensive
and impractical to recycle everything. The Clean Air Act required
WTE facilities to be at the leading edge with respect to air
emissions. New facilities had to meet stringent emissions criteria
and older facilities had to be retrofitted. (Covanta Fairfax
was built after 1989.) In 2003 the EPA completed a facility
by facility inspection of WTE facilities. It was an amazing
report. The EPA said that taken together, these retrofits make
for an industry that has less environmental impact than almost
any other source of electricity in the country. For example,
these retrofits reduced dioxins by 99% and mercury by 90%.”
WTE accounts for 15-16% of waste management in the U.S. Recycling
falls in the high teens. According to Burton, more recycling
occurs in communities with WTE than in communities without it.
He credits communities like Fairfax County for taking the lead
in municipal solid waste management.
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