Biomass is organic material which has stored sunlight in the form of chemical energy. Biomass fuels include wood, wood waste, straw, manure, sugar cane, and many other byproducts from a variety of agricultural processes.

Biomass is a renewable energy source because the energy it contains comes from the sun. Through the process of photosynthesis, chlorophyll in plants captures the sun's energy by converting carbon dioxide from the air and water from the ground into carbohydrates, complex compounds composed of carbon, hydrogen, and oxygen. When these carbohydrates are burned, they turn back into carbon dioxide and water and release the sun's energy they contain. In this way, biomass functions as a sort of natural battery for storing solar energy. As long as biomass is produced sustainably—with only as much used as is grown—the battery will last indefinitely.

From the time of Prometheus to the present, the most common way to capture the energy from biomass was to burn it, to make heat, steam, and electricity. But advances in recent years have shown that there are more efficient and cleaner ways to use biomass. It can be converted into liquid fuels, for example, or cooked in a process called "gasification" to produce combustible gases. And certain crops such as switchgrass and willow trees are especially suited as "energy crops," plants grown specifically for energy generation.

Amongst the fastest growing trees, in good conditions, hybrid poplars will shade a 1 story house in three years Hardy and rugged will grow almost anywhere.

Willows or poplars shouldn't be planted within 140 feet of a house or drains to be safe. They have very vigorous far reaching roots and are thirsty enough to make the soil expand and contract with the uptake of water so threatening foundations.

Solid industrial residues (paper, fibers, textile, pulp, etc.) and liquid industrial residues (which could be used for production of biodiesel, ethanol, etc.).

Industrial solid waste can be managed either on site—at the facility where it is generated—or transported off site to commercial facilities. Whether on-site or off-site, industrial solid waste can be disposed of through the use of municipal and industrial wastewater facilities; land disposal facilities such as landfills, waste pits—principally for petroleum exploration waste—and deep underground injection wells; and incineration or waste-to-energy incineration facilities like cement kilns. A variety of treatment, recycling, and other management options - such as stabilization and solidification - also exist for many types of industrial wastes. Nearly 99 percent of hazardous wastes are managed on site at the facility itself or treated and discharged through a wastewater treatment facility. About 74 percent of all hazardous wastes are managed through wastewater treatment facilities. In some cases, the industrial wastewater is simply sent directly to a municipal wastewater treatment plant, while in others  the level of hazardous waste is decreased to a certain level by treatment, and then discharged, either through a publicly owned (wastewater) treatment works or from the industrial facility itself. Most of the other waste managed on site is injected underground into deep wells.

Municipal solid waste (MSW) is a waste typethat includes predominantly household waste (domestic waste) with sometimes the addition of commercial wastes collected by a municipality within a given area. They are in either solid or semisolid form and generally exclude industrial hazardous wastes. The term residual waste relates to waste left from household sources containing materials that have not been separated out or sent for reprocessing.

Solid waste disposal categories

General Solid Waste or Municipal Solid Waste (MSW) is typical waste generated from residential and non-industrial commercial sources.

Industrial Solid Waste is waste that is the result of a variety of industrial process. That is a process where a new, physical product is manufactured from a set of input materials. Mining and electric power generation are usually included in the industrial category for the purpose of classifying solid waste.

Residual Solid Waste is a subset of industrial wastes that many U.S. states regulate separately from miscellaneous industrial waste. Residual wastes are wastes or "residue" that are left over from a specific process. Residual wastes tend to be fairly homogeneous in composition and have a relatively lower environmental impact compared to most industrial solid wastes. Residual wastes often have a mineral composition; one example is Flue Gas Desulfurization (FGD) waste from electric power generation. Because residual wastes are fairly consistent, many states allow the generators of these wastes to dispose of them in captive landfills that are designed only for that particular residual waste.

Construction and Demolition Debris (C&DD), as the name suggests, are the result of the construction and/or demolition of roads, buildings or other physical structures. Traditionally these wastes were allowed to be disposed in their own class of landfills because it was believed that they did not pose a serious threat to the environment. Construction and demolition debris landfills were constructed to less stringent standards than general solid waste landfills. However, abuses of the system, and new data showing adverse environmental impacts from C&DD landfills, have led to increasing regulations on the disposal of C&DD.

Infectious Wastes may include things like hospital waste, animal carcasses, or any other waste with the potential to spread infectious diseases.

Asbestos Waste: In the United States, many people are surprised to find that many states do not regulate asbestos the way they regulate most other hazardous wastes. This is because asbestos is fairly inert chemically, and when buried in the ground it poses a minimal environmental threat. In fact, asbestos was commonly used to filter beer in the brewing industry. The primary health threat from asbestos comes from inhaling the microscopic fibers deep into the lung tissue and mesothelium. Since the airborne threat is contained once asbestos is buried, many states allow asbestos to be disposed in landfills with general solid waste, provided the waste is handled with extra safety procedures.

Converting Biomass to Energy

An approach that may increase the use of biomass energy in the short term is to burn it mixed with coal in power plants—a process known as "co-firing." Biomass feedstock can substitute up to 20 percent of the coal used in a boiler. The benefits associated with biomass co-firing include lower operating costs, reductions of harmful emissions, and greater energy security. Co-firing is also one of the more economically viable ways to increase biomass power generation today. In 2000, the Chariton Valley Biomass Project, a joint effort including Alliant Energy, the U.S. Department of Energy, and local biomass groups, began testing the co-firing of switchgrass with coal at Alliant's Ottumwa Generating Station in Iowa. The project has proved so successful that in 2005, Alliant received permission to build a permanent biomass processing facility at the plant, capable of co-firing up to five percent of its energy with switchgrass.

A number of noncombustion methods are available for converting biomass to energy. These processes convert raw biomass into a variety of gaseous, liquid, or solid fuels that can then be used directly in a power plant for energy generation. The carbohydrates in biomass, which are comprised of oxygen, carbon, and hydrogen, can be broken down into a variety of chemicals, some of which are useful fuels. This conversion can be done in three ways:
*** Thermochemical. When plant matter is heated but not burned, it breaks down into various gases, liquids, and solids. These products can then be further processed and refined into useful fuels such as methane and alcohol. Biomass gasifiers capture methane released from the plants and burn it in a gas turbine to produce electricity. Another approach is to take these fuels and run them through fuel cells, converting the hydrogen-rich fuels into electricity and water, with few or no emissions.
*** Biochemical. Bacteria, yeasts, and enzymes also break down carbohydrates. Fermentation, the process used to make wine, changes biomass liquids into alcohol, a combustible fuel. A similar process is used to turn corn into grain alcohol or ethanol, which is mixed with gasoline to make gasohol. Also, when bacteria break down biomass, methane and carbon dioxide are produced. This methane can be captured, in sewage treatment plants and landfills, for example, and burned for heat and power.
*** Chemical. Biomass oils, like soybean and canola oil, can be chemically converted into a liquid fuel similar to diesel fuel, and into gasoline additives. Cooking oil from restaurants, for example, has been used as a source to make "biodiesel" for trucks. (A better way to produce biodiesel is to use algae as a source of oils.)