From dump to pump: "Green garbage" center opens in Ohio
When stuff rots but oxygen is absent, bacteria produce methane, which many landfills collect to fuel electric generators. But because landfill gas contains many contaminants, these generators can pollute the air.
If contaminants could cheaply be removed from landfill gas, this waste product could make a clean fuel for cars and trucks.
Having finished our preamble, we turn to a facility at the Columbus, Ohio, landfill that in September started cleaning landfill gas and storing the methane as compressed natural gas (CNG), which makes an excellent fuel for specially-equipped cars and trucks – a gasoline replacement made from pure garbage!
The cleaned methane is already being used to power a car and a truck owned by Solid Waste Authority of Central Ohio, the landfill’s owner; another eight vehicles are scheduled to be converted to CNG in the next couple of years.
Eventually, the authority plans to expand the process to capture the remaining 92 percent of the landfill gas, with the CNG going to more vehicles, or into a natural-gas pipeline. “We can produce the equivalent of 250,000 gallons of gasoline each year now,” says John Remy, director of communications for the waste authority. “In the second phase, we will have 3 million gallons equivalent.”
Why would a landfill operator be interested in extracting and cleaning methane? Because methane:
is an excellent (and merchantable) source of energy for heat, transport, or electricity;
can explode in the basements of neighboring houses if it’s trapped in the landfill; and
is about 20 times more effective than carbon dioxide in causing global warming.
Methane (CH4), the major component of natural gas, is a metabolic product of ancient bacteria called methanogens. Because methanogens thrive only when oxygen is absent, they are called anaerobes, and the decay process is called anaerobic digestion.
Although landfill gas has long been collected and burned, FirmGreen, Inc., which designed and installed the separator, claims advantages over competitors. According to Tony Wong, the company director of business development, the problem is purity -- all sorts of gases can emerge from a garbage dump, and the blend can vary from day to day -- yet to power vehicles or pump the gas into the natural-gas supply, the methane must be about 95 percent pure.
The cleaning process relies on cold carbon dioxide, says Wong. "When we go to minus 40 ° F to minus 60 ° F, something really elegant happens. The carbon dioxide that was already present in the gas -- we are not adding any solvent that later has to be removed -- starts to liquefy, forming a mist that magically falls through gravity,” and this mist removes contaminants. (Carbon dioxide is also used as a solvent to remove caffeine from coffee.)
Terry Devitt, editor; Nathan Hebert, project assistant; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive