Biogas

Biogas has a role in sustainable energy production. It is a combustible gaseous fuel that is collected from the microbial degradation of organic matter in anaerobic conditions.  Biogas is principally a mixture of methane (CH₄) and carbon dioxide (CO₂) along with other trace gases.  Biogas can be collected from landfills, covered lagoons, or enclosed tanks called anaerobic digesters. 

Feedstocks

Digesters

Biogas Use

Residues

Research Projects

Research Publications

Is biogas the same as biofuel?

Biogas is only one of many types of biofuels, which include solid, liquid or gaseous fuels from biomass.  Any combustible fuel derived from recent (non-fossil) living matter (biomass) may be considered a biofuel, including ethanol derived from plant products, biodiesel from plant or animal oils, as well as, biogas from biomass.  All biofuels are produced from sources which are renewable and are included as a subset of renewable energy sources that also include energy produced from solar, hydro, tidal, wind, and geothermal sources.  Biogas, like natural gas, has a low volumetric energy density compared to the liquid biofuels, ethanol and biodiesel.  However, biogas may be purified to a natural gas equivalent fuel for pipeline injection and further compressed for use as a transportation fuel.  Methane, the principal component in biogas, has four times the volumetric energy density of hydrogen (H₂) and is suitable for use in many types of fuel cell generators.

Energy Content of Biofuels

Comparative energy crop yields

There is no “silver bullet” in producing fuel from a sustainable energy crop. Fuel yields are limited by photosynthetic efficiency (less than 3% of solar energy is captured in even high yield crops), the efficiency of the conversion process, and the energy used in the production and conversion process (a significant cost for ethanol production). On a per acre basis, biogas production is far more efficient in capturing the energy found in energy crops. While the convenience and energy density of liquid fuels is an admirable target, if maximizing energy recovery from biomass and wastes is targeted, biogas production is the best choice. Further, even where ethanol and biodiesel production is used, biogas production from their waste products can improve the energy balance of the overall conversion process.

Energy Yields from Conversion of Energy Crops to Biofuels:

Frequently Asked Questions

• What is biogas?

  Biogas is the gaseous emissions from anaerobic degradation of organic matter (from plants or animals) by a consortium of bacteria.  Biogas is principally a mixture of methane (CH₄) and carbon dioxide (CO₂) along with other trace gases.  Methane gas, the primary component of natural gas (98%), makes up 55-90% by volume of biogas, depending on the source of organic matter and conditions of degradation.  Biogas is produced in all natural environments that have low levels of oxygen (O₂) and have degradable organic matter present.  These natural sources of biogas include: aquatic sediments, wet soils, buried organic matter, animal and insect digestive tracts, and in the core of some trees.  Man’s activities create additional sources including landfills, waste lagoons, and waste storage structures.  Atmospheric emissions of biogas from natural and man-made sources contribute to climate change due to methane’s potent greenhouse gas properties.  Biogas technology permits the recovery of biogas from anaerobic digestion of organic matter using sealed vessels, and makes the biogas available for use as fuel for direct heating, electrical generation or mechanical power and other uses.  Biogas is often made from wastes but can be made from biomass energy feedstocks as well.

• What can biogas be made from?

  Biogas is commonly made from animal manure, sludge settled from wastewater, and at landfills containing organic wastes.  However, biogas can also be made from almost any feedstock containing organic compounds, both wastes and biomass (energy crops).  Carbohydrates, proteins and lipids are all readily converted to biogas.  Many wastewaters contain organic compounds that may be converted to biogas including municipal wastewater, food processing wastewater and many industrial wastewaters.  Solid and semi-solid materials that include plant or animal matter can be converted to biogas.

• Can biogas be used in place of fossil fuels? How?

  Methane is the principal gas in biogas.  Methane is also the main component in natural gas, a fossil fuel. Biogas can be used to replace natural gas in many applications including: cooking, heating, steam production, electrical generation, vehicular fuel, and as a pipeline gas.

• Why aren't we doing more with biogas? What are the barriers to increasing biogas production and use?

  Biogas is being collected and used to generate electricity or steam at many landfills, wastewater plants and breweries in Florida.  However, many opportunities for biogas production are yet to be implemented.  Until recently, the low cost of fossil fuels has hindered implementation of biogas production.  There is a limited awareness of the potential and advantages of biogas production by citizens, government officials, and in the business sector that has limited interest in biogas production.  More education, demonstration and investment in biogas technology would help overcome these barriers.

• How much biogas can be produced in Florida annually?

  The broad types of wastes and biomass feedstocks that are suitable for production of biogas and limited data on production levels and biogas yields make it difficult to accurately calculate the total amount of biogas, which can be produced in the state.  If the annual biogas potential from only municipal wastewater, dairy manure, poultry manure, MSW, and energy crops is estimated, a rough potential of 205.7 billion cu ft of natural gas equivalent results, which is half of the 400 billion cu ft of natural gas used for electrical generation in Florida in 2003. 

• What are the environmental impacts of producing/using biogas?

  Biogas production can reduce the pollution potential in wastewater by converting oxygen demanding organic matter that could cause low oxygen levels in surface waters.  Nutrients, like nitrogen and phosphorous are conserved in biogas effluents and can be used to displace fertilizers in crop production.

• Does biogas contribute to climate change?

  While combustion of biogas, like natural gas, produces carbon dioxide (CO₂), a greenhouse gas, the carbon in biogas comes from plant matter that fixed this carbon from atmospheric CO_2.  Thus, biogas production is carbon-neutral and does not add to greenhouse gas emissions.  Further, any consumption of fossil fuels replaced by biogas will lower CO₂ emissions.   

• Can I make/use biogas at home or at my place of business?

  Biogas can be made at home or at a business from food waste, yard and grass trimmings, and some organic solid wastes.  However, efficient use of biogas is more readily accomplished at larger scales.  A typical home might cook for an hour per day on biogas from home waste sources.

• How much does biogas cost to make?

  With prices for natural gas around $7 per 1000 cu. ft.  depending on the particular application this is very similar to estimates for the cost of biogas production.

• Where can I find more information?

  Useful Links to Biogas Information

  Florida

  Florida Energy Summit (FL Department of Agriculture and Consumer Services)

  Dairy Manure Management at University of Florida-IFAS Extension

  United States

  AgSTAR - The AgSTAR Program is an effort jointly sponsored by the U.S. Environmental Protection Agency (EPA), the U.S. Department of Agriculture, and the U.S. Department of Energy to encourage the use of methane recovery (biogas) technologies for reducing methane emissions from manure management.

  American Biogas Council

  Energy Efficiency and Renewable Energy Biomass Program (U.S. Department of Energy)

  Global Methane Initiative - an international initiative that advances cost-effective, near-term methane recovery and use as a clean energy source.

  Climate Friendly Farming (Washington State University)

  International

  AD Nett (The European Anaerobic Digestion Network)

  European Biogas Association

  Anaerobic Granular Sludge Bed Technology Pages

  Beginners Guide to Biogas

  European Biomass Association

  IEA(International Energy Agency)

  Swiss Association for Anaerobic Digestion