Using Biomass for Energy (College Board AP® Environmental Science): Study Guide

Biomass energy

• Biomass refers to organic material that comes from plants and animals

• It is a renewable source of energy derived from living or recently living organisms

• Biomass can be used as an alternative to hydrocarbon fuels

Types of biomass

• Wood and agricultural products: include firewood, wood chips, and agricultural residues

• Solid waste: municipal solid waste (MSW) can be used to produce energy

• Landfill gas and biogas: methane gas produced from the decomposition of organic material in landfills

• Alcohol fuels: ethanol and biodiesel produced from crops like corn and sugarcane

Energy conversion processes

• Direct combustion by burning biomass directly to produce heat

• Thermochemical conversion includes processes like pyrolysis and gasification to convert biomass into liquid or gaseous fuels

• Biochemical conversion by using microorganisms to convert biomass into biofuels through processes like anaerobic digestion and fermentation

Advantages of biomass

• Renewable: biomass can be replenished over a short period

• Carbon neutral: CO₂ released during biomass combustion is offset by the CO₂ absorbed during the growth of the biomass

• Waste reduction: waste materials are utilized that would otherwise contribute to landfill mass

• The cost of burning biomass for heat energy is low

• Low sulfur content: biomass usually has less sulfur than fossil fuels, which reduces acid rain formation

Disadvantages of biomass

• Land use: large areas of land are needed to grow biomass crops, which can lead to deforestation and habitat loss

• Air pollution: burning biomass releases pollutants, including particulates, carbon monoxide, carbon dioxide, and volatile organic compounds

• Acid rain: burning biomass releases nitrogen oxides, which contributes to acid rain formation

• Energy efficiency: biomass energy conversion processes can be less efficient compared to fossil fuels

Applications

• Electricity generation: biomass can be burned in power plants to produce electricity.

• Heating: biomass is used in residential and industrial heating systems.

• Vehicular fuels: biofuels like ethanol and biodiesel are used as alternatives to gasoline and diesel

Biofuels

Ethanol

• Ethanol, also known as ethyl alcohol, is a renewable biofuel produced primarily through the fermentation of sugars by yeast

• It is commonly used as a fuel additive to reduce greenhouse gas emissions and enhance octane levels in gasoline

• Ethanol is less energy dense than gasoline, so ethanol-powered cars get lower mileage

• Pure 100% ethanol is hard to find and can technically be drunk as a very strong alcoholic drink

• U.S. laws state that fuel alcohol must be undrinkable and mixed to 95.5% and would be taxed as alcohol unless it is mixed with gasoline

Production methods

• Fermentation is the most common method, where sugars from crops like corn, sugarcane, and wheat are fermented by yeast to produce ethanol

• Cellulosic ethanol is produced from non-food plant materials such as agricultural residues, grasses, and wood chips

  • This method is more sustainable but currently less efficient and more costly

Advantages of ethanol

• Renewable: as ethanol is produced from biomass, it can be replenished over a short period

• Reduced emissions: when burned, ethanol produces fewer greenhouse gases compared to fossil fuels

• Energy security: reduces dependence on imported oil and supports local agriculture

• Job creation: the ethanol industry creates jobs in agriculture, production, and distribution, boosting local economies

• Market diversification: ethanol provides an alternative market for agricultural products, helping to stabilize crop prices and provide additional income for farmers

Disadvantages of ethanol

• Land use: large areas of land are required to grow crops for ethanol production, which can lead to deforestation and competition with food production

• Food prices: the diversion of crops like corn and sugarcane for ethanol production can lead to higher food prices, affecting food security

• Energy balance: the energy required to produce ethanol can sometimes be close to or exceed the energy it provides (i.e. the energy return on energy investment for ethanol is low)

• Water use: ethanol production requires significant amounts of water, which can strain local water resources

• Subsidies: ethanol production often relies on government subsidies, which can be a financial burden on taxpayers and may not be sustainable in the long term

Applications

• Fuel additive: ethanol is commonly blended with gasoline to create E10 (10% ethanol) or E85 (85% ethanol) fuels

• Industrial uses: used as a solvent, in the production of personal care products, and in the beverage industry

Environmental impact

• Carbon neutrality: the CO₂ released during ethanol combustion is offset by the CO₂ absorbed by the plants during their growth

• Soil and water: intensive farming for ethanol crops can lead to soil degradation and water pollution from fertilizers and pesticides