Historically, humans have harnessed biomass-derived energy since the time when people began burning wood to make fire. Even in today’s modern era, biomass is the only source of fuel for domestic use in many developing countries. Biomass is all biologically-produced matter based in carbon, hydrogen and oxygen. The estimated biomass production in the world is 104.9 petagram (104.9 * 1015 g) of carbon per year, about half in the ocean and half on land.
Wood remains the largest biomass energy source today; examples include forest residues (such as dead trees, branches and tree stumps), yard clippings, wood chips and even municipal solid waste. Wood energy is derived by using lignocellulosic biomass (second generation biofuels) as fuel. This is either using harvested wood directly as a fuel, or collecting from wood waste streams. The largest source of energy from wood is pulping liquor or “black liquor,” a waste product from processes of the pulp, paper and paperboard industry. In the second sense, biomass includes plant or animal matter that can be converted into fibers or other industrial chemicals, including biofuels. Industrial biomass can be grown from numerous types of plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane, bamboo, and a variety of tree species, ranging from eucalyptus to oil palm (palm oil).
Based on the source of biomass, biofuels are classified broadly into two major categories. First generation biofuels are derived from sources such as sugarcane and corn starch etc. Sugars present in this biomass are fermented to produce bioethanol, an alcohol fuel which furthermore can be used directly in a fuel cell to produce electricity or serve as an additive to gasoline. However, utilizing food based resource for fuel production only aggravates the food shortage problem further. Second generation biofuels on the other hand utilize non-food based biomass sources such as agriculture and municipal waste. It mostly consists of lignocellulosic biomass which is not edible and is a low value waste for many industries. Despite being the favored alternative, economical production of second generation biofuel is not yet achieved due to technological issues. These issues arise mainly due to chemical inertness and structural rigidity of lignocellulosic biomass.
Plant energy is produced by crops specifically grown for use as fuel that offer high biomass output per hectare with low input energy. Some examples of these plants are wheat, which typically yield 7.5–8 tons (tonnes?) of grain per hectare, and straw, which typically yield 3.5–5 tons (tonnes?) per hectare in the UK. The grain can be used for liquid transportation fuels while the straw can be burned to produce heat or electricity. Plant biomass can also be degraded from cellulose to glucose through a series of chemical treatments, and the resulting sugar can then be used as a first generation biofuel.
The main contributors of waste energy are municipal solid waste (MSW), manufacturing waste, and landfill gas. Energy derived from biomass is projected to be the largest non-hydroelectric renewable resource of electricity in the U.S between 2000 and 2020.
Biomass can be converted to other usable forms of energy like methane gas or transportation fuels like ethanol and biodiesel. Rotting garbage, and agricultural and human waste, all release methane gas—also called “landfill gas” or “biogas.” Crops, such as corn and sugar cane, can be fermented to produce the transportation fuel, ethanol. Biodiesel, another transportation fuel, can be produced from left-over food products like vegetable oils and animal fats. Also, biomass to liquids (BTLs) and cellulosic ethanol are still under research.
There is a great deal of research involving algae, or algae-derived, biomass due to the fact that it’s a non-food resource and can be produced at rates 5 to 10 times those of other types of land-based agriculture, such as corn and soy. Once harvested, it can be fermented to produce biofuels such as ethanol, butanol, and methane, as well as biodiesel and hydrogen. Efforts are being made to identify which species of algae are most suitable for energy production. Genetic engineering approaches could also be utilized to improve microalgae as a source of biofuel.
The biomass used for electricity generation varies by region. Forest by-products, such as wood residues, are common in the United States. Agricultural waste is common in Mauritius (sugar cane residue) and Southeast Asia (rice husks). Animal husbandry residues, such as poultry litter, are common in the UK.
As of 2015, a new bioenergy sewage treatment process aimed at developing countries is being trialed; the Omni Processor is a self-sustaining process which uses the sewerage solids as fuel in a process to convert the waste water into drinking water and with surplus electrical energy being generated for export.