Climate change and its effects have been rising all around the world. The impact of climate change is present in every aspect, including the depletion of fossil fuels. These can also lead to increase in atmospheric carbon and pollute the environment. So, the need to find alternative energy sources has increased ten folds.
An alternative method of replacing fossil fuels is biofuel production. Biofuel is the fuel generated by biomass decomposition with microorganisms’ help. Biodiesel, bioethanol, biogas, and biohydrogen are some types of biofuel formed by the biological degradation of biomass. Biomass refers to the organic matter material from algae, plants, and animals.
Microbes play an essential role in biofuel production. Different microbes decompose different types of biomasses to produce biofuel.
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Types of Biofuels
Biofuels are classified into three types based on the raw materials used; first-generation, second-generation, third-generation, and fourth-generation. The first-generation biofuels use food crops as raw materials for biofuel production.
The second generation biofuels use waste material from plants and animals. Third-generation biofuels use microalgae for production. The fourth generation biofuels includes formation of synthetic gas or syngas.
Let’s discuss the most commonly found biofuels; biodiesel, biogas, biohydrogen, and bioethanol.
- Biodiesel: This type of biofuel belongs to the first generation of biofuels. The transesterification of fats from animal and vegetable oils by microorganisms produces biodiesel.
- Bioethanol: This type of biofuel belongs to the first generation of biofuels. Bacteria ferment sugar and starch from food crops to produce ethanol.
- Biogas: This type of biofuel is second-generation biofuel. The raw materials include waste from animals and plants, including municipal waste. These kinds of organic matter are termed lignocellulosic biomass.
- Biohydrogen: This type of biofuel belongs to the third-generation biofuels. Biohydrogen uses starch and cellulose as raw materials. Microalgae helps in the production of biohydrogen. Two pathways to produce this biofuel are direct biohydrogen production by microalgae or utilization of microalgae biomass.
Another basis for determining categories of biofuels is based on their state; biogas, solid and liquid biofuels. Liquid biofuels include biodiesel, bioethanol, etc. The biogas include methane, carbon dioxide, hydrogen gas, etc. Solid includes wood wastes from furniture carvings/making, black liquor, etc.
The Role of Microbes in Biofuel Production
Microbes are the most crucial part of biofuel production. These have roles in the decomposition and degradation of raw materials. Metabolic pathways of the microorganisms are the principal method of decomposition of biomass. Some of the essential roles played by microbes are as follows:
- Fermentation: The conversion process of biomass (especially biomass rich in cellulose, hemicellulose, or lignin) into alcohol (ethanol) is called fermentation. It is carried out by yeast like Saccharomyces cerevisiae.
- Enzyme production: The enzymes like hemicellulase and cellulase are produced by some bacteria. These enzymes can reduce lignocellulose (composed of cellulose, hemicellulose, and lignin) and other forms of biomass into simple carbohydrates.
- Esterification and transesterification: Biodiesel is also produced by the esterification of animal fats and vegetable oils. Esterification and transesterification are the reactions between vegetable oil or animal fats with alcohol.
- Algae: Microalgae or microscopic algae help produce algal biofuels/biodiesel. The algae can easily convert sunlight and CO2 into lipids. The algae have high lipid content which converts into biodiesel. Its cultivation occurs in bioreactors, tanks, and ponds.
- Synthetic gas production: Microbes that convert biomass into carbon monoxide (CO) and hydrogen (H2) produce synthetic gas or syngas (CO+H2). The gas is processed to produce methanol. The microbes involved are Clostridium and Ruminococcus.
- Methanogenic archaea: Anaerobic digestion of organic waste like animal manure or food waste produces methane or biogas. The microbes mainly involved in the production are methanogenic archaea that convert organic matter into methane gas under anaerobic conditions. The biogas thus produced can be useful as a natural gas source directly or after processing to remove impurities.
Importance of Biofuels
Biofuels provide energy for power plants, vehicles, and other critical manufactured technologies. These have much importance. Some of the importance of biofuels are as follows:
- Release of carbon dioxide during combustion of the biofuels is less, so these are known as carbon neutral fuels.
- These can replace the use of finite fossil fuels.
- The combustion of biofuels does not emit greenhouse gasses compared to fossil fuels.
Limitation of Biofuels
Although biofuels are highly important and positively impact the climate, they have some limitations. Some of them are as follows:
- The food crops that produce bioethanol and biodiesel have increased concerns over food security. There might be high competition in food production and rising food prices.
- Production of biofuel can also cause some impact on the environment, like deforestation, use of fertilizers and pesticides for faster growth may damage soil quality, and excessive use of water.
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- Kumar, Ravinder & Kumar, Pradeep. (2017). Future Microbial Applications for Bioenergy Production: A Perspective. Frontiers in Microbiology. 8. 10.3389/fmicb.2017.00450. (Image list table)
- Keasling, J., Garcia Martin, H., Lee, T.S. et al. Microbial production of advanced biofuels. Nat Rev Microbiol 19, 701–715 (2021). https://doi.org/10.1038/s41579-021-00577-w
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