Bioenergy Resources and Technologies

Overview

The Food and Agriculture Organization (FAO) defines bioenergy as all energy derived from biofuels, which are fuels derived from biomass (that is, matter of biological origin). These biofuels can be subdivided into three types, solid, liquid, and gas and by origin, forest, agriculture, and municipal waste .

In the past decade, bioenergy has seen an uptick in interest from the international community. While instability in oil regions has been one factor in the shift towards renewable energy resources, other factors such as demand for self-supply energy commodities, increase in energy security, stimulate rural development, reduce the impact of energy use on climate change, and provide a clean more environmentally friendly energy source have played a large role in the promotion of bioenergy resource development .

The basic bioenergy process involves the translation of organic material into an end product, including biogas, which can then be used to produce energy.

Check out the video lecture about Bioenergy Resources and Technologies by Miguel Franco, Powering Agriculture Task Support Order (PASTO) & Director at Tetra Tech - Bionenergy and Environment.

Further information on the mentioned MOOC: Powering Agriculture – Sustainable Energy for Food and related materials you can find here.

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Organic Material

Organic material comes from a variety of resources, including municipal, industrial, and agricultural activities. The main feedstocks used today to produce bioenergy are:

Food Waste

Food waste can come from a variety of sources, including grocery stores, restaurants, cafeterias, and homes. Some types of food waste packaging can also be digested, such as paper food packaging, cardboard boxes, paper towels, napkins, and wax paper.

Farm Manures and Slurries

Manure produced through agricultural operations like on dairy farms or hog farms provides an excellent feedstock for anaerobic digestion. The digestate that is produced is also of a higher caliber fertilizer than that of undigested manure.

Agro-industrial Wastewaters

Many agro-industries generate wastewaters with high levels of organic matter that generate biogas due to their typical wastewater treatment and disposal practices. These agroindustries include palm oil mills, sugar processing and refining, ethanol production, and food processing facilities.

Crop Residues

Crop residues can come from either crops grown for traditional purposes like corn for food or tobacco for cigarettes, or they can come from crops that are grown specifically for the production of energy. These crops include sugar cane, sugar beets, grassy crops like switch grass, starchy crops like wheat, maize or potatoes, and woody crops in the tree family that are traditionally used for combustion purposes .

Regarding access to resources, basic data should show that a sufficient amount of organic waste is constantly available and of adequate quality. Securing a guaranteed and regular feedstock supply for biogas plants should not be taken for granted. In practice, this means that all elements of the waste management value chain must contribute to the smooth functioning of the entire system – i.e. the collection, transport, handling and storage of the biowaste feedstock.

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Bioenergy Technologies

Choosing the appropriate technology for converting organic matter into bioenergy is key to optimizing energy production. The technologies available today for bioenergy conversion can be broken up into three general categories: thermochemical, biochemical and other processes.

Thermochemical processes

Direct combustion: Direct combustion is the most common form of bioenergy and is typically employed at fossil-fuel fired power plants. The process involves the combustion of solid biomass feedstock, most often some type of woody waste, in the presence of excess oxygen in boiler in order to produce steam which is then converted to electricity. The heat produced from the combustion process can also be used in direct thermal applications such as to heat a building (Sass Byrnett, et al., 2009).

Typically cellulosic materials that are not viable for the treatments described above due to their difficult nature to break down can be made into ethanol. Materials such as grass, wood waste, and crop residue are all good feedstocks for both thermochemical and biochemical conversion. Thermochemical conversion uses heat and chemicals to break down the cellulose in the feedstock to make syngas. The specific processes are:

Pyrolysis: Pyrolysis uses high temperatures and pressure in the absence of oxygen to decompose organic matter, which can result in gas, pyrolysis oil (bio-oil), or charcoal (bio-char). Biooil is the most common product as it has the most end-uses such as for thermal energy that can be used to heat buildings or water, or for power generation. The temperature of the reaction determines the end-product .

Gasification: Gasification converts solid fuel to gas through either a chemical or heat process. Solid biomass like woody waste is heated to a high temperature (above 700 degrees Celsius) with limited oxygen. This in turn converts the feedstock into a flammable synthesis gas known as “syngas”. Syngas is then either combusted to produce steam in a boiler for electricity or heat for thermal applications .

Biochemical Processes

Biochemical conversion can use a variety of high temperature, high pressure acid, enzymes, or other treatment techniques to break down the lignin and hemicellulose that surround the cellulose. Hydrolysis using enzymes and acids then breaks down the cellulose into sugar which in turn is fermented to produce ethanol . The related processes are:

Anaerobic Digestion: Anaerobic digestion involves the decomposition of organic or biological waste by microorganisms in the absence of oxygen. This process produces a gas composed largely of methane and carbon dioxide (CO2). The methane can be used to produce electricity or heat in much the same manner as with the above described methods .

Fermentation: Starchy plants are often used in the biochemical fermentation process to convert sugars into alcohol. This is the most common process used to produce ethanol from corn and sugarcane .

Other processes

Transesterification: Transesterification is a process that converts oils or fats into biodiesel. The process involves the removal of water and contaminants from the feedstock, the mixing with alcohol (typically methanol), and a catalyst (such as sodium hydroxide). Fatty acid methyl esters and glycerin are produced as byproducts of the process. The glycerin can be used in pharmaceuticals and cosmetics, while the esters are considered biodiesel and can be used as vehicle fuel or for other fuel purposes (Sass Byrnett, et al., 2009).

Further Biomass Conversion Technologies can be found here.

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Conclusion

The basic bioenergy process is the translation of organic material into a final product that is used to produce energy. The main feedstock to produce bioenergy include:

• Food waste
  
• Farm manures and slurries
  
• Agro-industrial wastewaters
  
• Crop residues.
  

Bioenergy technologies can be divided into 3 types:

• Thermochemical processes – pyrolysis and gasification
  
• Biochemical processes – anaerobic digestion and fermentation
  
• Other processes - transesterification
  

Bioenergy resources are abundant yet underutilized throughout the world. With the wide range of available feedstocks such as farm manure, food waste, crop residues, and wastewater and many different treatment methods ranging from traditional combustion processes to fermentation and anaerobic digestion processes, there are many opportunities across many sectors to implement bioenergy projects.

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Further Reading

• Water and Energy for Food (WE4F) portal on energypedia
• Reader of the MOOC "Powering Agriculture - Sustainable Energy for Food"
  
• Bioenergy Decision Support Tool by UNEP
  
• Bioenergy for Agricultural Production
  
• Bioenergy in Powering Agriculture
  
• Bioenergy Portal on energypedia
  
• Bioenergy Development - Issues and Impacts for Poverty and Natural Resource Management
  
• State Bioenergy Primer. Information and Resources for States on Issues, Opportunities, and Options for Advancing Bioenergy
  
• Biomass Conversion Technologies
  

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References

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