Biomass and Methane
Biomass is a collective term that means producing energy from plants or animals. One common method is burning plant material to heat water and generate electricity. Feedstock for biomass power facilities generally includes agricultural waste left over from harvesting, energy crops grown specifically for use as biomass, forestry remains after timber harvesting, and wood left over from mill operations.
To provide the most sustainable alternatives, it's best to use plant material waste that is close to the biomass plant to avoid transportation impacts. Trees commonly farmed for use in biomass in the northern United States include hybrid poplars and willow; in the southeast, sycamore and sweet gum work well. These trees are amenable as feedstock because they grow quickly and will grow back after being harvested close to the ground.
Grasses are also used as feedstock — mostly frequently, switch-grass, sugar cane, and elephant grass. Corn remains from harvesting for the food market are also used as a feedstock for biomass energy production. Corn specifically for use as fuel is not as sustainable as other plants because it requires pesticides, fertilizers, and energy to grow and frequently has to be transported to energy facilities, often negating the benefits of using it as a renewable resource.
Facilities can operate with either a pure biomass feedstock or with combined biomass and coal. Although biomass material does contain sulfur and nitrogen compounds, these are present at lower concentrations than coal and emit lower levels of sulfur dioxide and nitrogen oxides when burning.
The other common method of creating biomass includes digesting organic material like sludge or manure to produce methane, which is then burned, or flared, to produce electricity. Wastewater treatment plants are beginning to digest sludge at their facilities and then use the methane generated to help operate the treatment plant. In New York City, the North River facility uses electricity generated from digested methane to run some of the plant's operations.
The EPA runs two programs that assist with converting methane into electricity. The AgSTAR program works with swine and dairy farmers who are interested in purchasing and operating methane digesters. The Landfill Methane Outreach Program (LMOP) works to forge relationships between landfill owners and electric utility business.
In Marin County, California, the Straus Family Creamery uses the electricity generated from methane digesters not only to run their organic dairy but to charge up Albert Straus's electric car. And the dairy didn't stop with organic farming and digesting methane. The backup generator and the feed truck have both been converted to biodiesel. The family is in the process of converting all their farm vehicles to biodiesel.
Methane can also be obtained from landfills. The decomposition of waste produces methane, which can be collected and piped to generators where it is then converted to electricity and put out on the grid. The Omaha Public Power District uses methane that's generated by the decomposition of landfill waste as fuel. By utilizing the methane, the utility is able to generate 3 million watts of electricity — enough to run about 2,000 homes.
The Tennessee Valley Authority utilizes three sources of renewable energy, generating electricity from wind-powered turbines, solar generation sites, and methane gas from a wastewater treatment plant.