Biomass

How it works

Biomass is any biological material used as fuel. Biomass can be burned directly or be first converted to a different form of fuel. The carbon implications and other environmental issues related to the use of biomass depend greatly on the fuel stock used and the method of utilization. Fuel stocks that require little in the way of energy or nutrient inputs and which require minimal processing generally have lower emissions and environmental impacts.

Fuel Stock

Woody Biomass: The most common forms of biomass in the Northeast are woody – wood chips and wood pellets.   Woody biomass currently comes from a variety of sources – waste from sawmills, residue from logging operations, and clean community waste such as tree trimmings.  As demand for this fuel source increases, woody biomass may start to be harvested as a crop in its own right, rather than as a bi-product.  Some quick-growing woody species such as willow are being examined as possible woody energy crops.

Perennial Grasses: Some varieties of native prairie grasses such as switchgrass have low nutrient demands, wide ranges of appropriate growing conditions, and rapid growth rates, which make them potentially useful as biomass fuel stock. Currently there is little growth and utilization of perennial grasses as a fuel stock, but there is growing interest and research in that direction.

Agricultural crops: Most of the liquid biofuel (primarily ethanol) in the United States is currently produced from corn. Oil producing crops such as soybeans and sunflowers can be used to make biodiesel. Conventional methods of growing these crops depend on large inputs of energy, fertilizers, and pesticides.

Microalgae: Several species of microalgae synthesize neutral lipids, sometimes accumulated as much as 50% of their cell dry weight. Those lipids can be converted to liquid biofuels, much like the oil in more conventional crops like soybeans. Microalgae can be grown with non-fresh water sources and without using high value crop land, and potentially have much greater yields than other biofuel stocks. Systems and technology for utilizing microalgae as biofuel are in their infancy, requiring further research and resources to meet any significant proportion of the world’s energy needs.

Animal Waste and Landfill Gas: Organic waste such as manure and buried trash in landfills release methane as they decompose. That gas can be captured and burned for fuel rather than released in to the atmosphere. Methane is a potent greenhouse gas, so utilizing it as a biomass fuel is doubly effective in greenhouse gas mitigation.

Waste Streams: Some particular waste streams can be used as biofuels. Used cooking oil can be burned directly or converted to biodiesel, clean woody waste such as tree trimmings can be burned, etc. General municipal waste is frequently burned for energy (especially in the Northeast where landfill space is limited).

Utilization

Direct Burn: The simplest way to utilize biomass is to directly burn it for thermal energy. Depending on the efficiency of the burner used, significant portions of the energy is wasted in direct burning.

Biofuels: Many biomass fuel stocks can be converted in to liquid fuels, which can be burned in place of diesel fuel, heating oil, or gasoline. The two most common forms of biofuel current are biodiesel and ethanol, and the most common fuel stocks for those biofuels are corn and soybeans. Energy is required to convert biomass fuel stocks to liquid biofuels, and the agricultural practices used for some crops (such as corn and soybeans) have high energy and high chemical inputs. As a result, the net energy and environmental benefits of biofuels are currently unclear. Fuel stocks that require fewer energy and chemical inputs (such as algae) and conversion processes that require less energy could lead to biofuels with much higher net energy and lower net emissions.