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Article updated on 18/02/20 by Susha Cheriyedath
Algal biofuel is an alternative to fossil fuel, which is generated by specific algae species from carbon dioxide. These algae species are primarily unicellular or diatom microalgae that produce high carbohydrate compositions suitable for ethanol production, high lipid compositions suitable for biodiesel production or high hydrocarbon compositions that are suitable for producing renewable distillates.
Increase in fuel costs and consumption, and depletion of natural fuel resources have created a demand for research into alternative forms of fuels in the last decade. Several companies and government agencies are funding research to try and make algae fuel production commercially viable.
The optimum selection of the algal species for biofuel production is based on the ability to sustain the culture, growth rate of the species, the biomass specific contents of proteins, carbohydrates, and lipids, and the overall supporting photosynthesis environment.
- Algae are tiny biological factories that use photosynthesis to convert CO2 and sunlight into energy-rich chemicals.
- There are more than 30,000 freshwater and saltwater species of algae.
- Nearly 1000 algae species that have been studied so far exhibit the potential for producing biofuel.
Fuels from Algae
The lipid (oily) part of the algae biomass can be extracted and converted into biodiesel by a process similar to that used for any other vegetable oil.
Butanol can be made from algae or diatoms using a solar-powered biorefinery. This fuel was found to have an energy density 10% less than gasoline, and greater than that of either methanol or ethanol.
The green waste left over from the algae oil extraction can be used to produce butanol.
Additionally, it was found that macroalgae can be fermented by Clostridria to form butanol and other solvents.
Biogasoline produced from algae biomass can be used in internal combustion engines. Methane, which is the chief component of natural gas, can be produced from algae using several methods - pyrolysis, gasification or anaerobic digestion.
Algae can also be used to produce green diesel, also known as renewable diesel through a hydrocracking refinery process that breaks down molecules into shorter hydrocarbon chains used in diesel engines.
Algae can produce up to 300 times more oil per unit area than conventional crops such as palms, soybeans, rapeseed or jatoba. The following three primary ways to grow algae for biofuel production have been identified:
Open Pond System
The open pond system is one of the easiest methods for the cultivation of algae with high oil content. In this method, algae are grown in open ponds under very warm and sunny environments.
Although it is the simplest form of algae production, it also has some major drawbacks. Open systems using a monoculture are also vulnerable to viral infection. To enhance algae production using this method, water temperature needs to be controlled.
The closed-loop system was adapted to produce algae more quickly and efficiently than the open pond system. In this method, algae are placed in clear, plastic bags to allow them to be exposed to sunlight.
These bags are stacked high and protected from external elements using a cover. The clear plastic bag provides enough exposure to sunlight to increase the rate of algae production.
The greater the algae production, the greater the amount of oil will be extracted. Unlike the open pond method, this method prevents algal contamination.
Most of the companies that use algae as a source of biofuels employ borosilicate glass tubes known as bioreactors that are exposed to sunlight. Within these tubes, the algae can be grown at maximum levels, even to the point they can be harvested every day.
This method results in a very high output of algae and oil for producing biofuels. However, running a photobioreactor is more expensive and difficult than using the open pond system, but may provide a high level of control.
Benefits of Algal Fuel
The key benefits of algae and algal fuels are listed below:
- Algae require much less land to grow when compared to other traditional row crops, such as corn. Also, algae can be grown on non-arable, nutrient-poor land that does not support conventional agriculture.
- Algae farms for producing biofuel can thrive without petroleum-based fertilizers, freshwater for irrigation of arable land.
- Algae can be grown rapidly at large scale and generate up to 50 times more oil per acre than other row crops like soybeans and corn.
- Algae biofuels help reduce the country’s energy dependence.
- Algae use photosynthesis to capture sunlight energy for producing carbohydrates and oxygen thereby creating a natural biomass oil product.
- Algae can grow in seawater as well as high-saline water. Several species of algae can also grow in wastewater from treatment plants and water-containing phosphates, nitrates, and other contaminants.
- Algae fuels are biodegradable and non-toxic as they do not contain sulfur.
- Unlike fossil fuels, harvested algae release CO2 when burnt, but it is absorbed by new growing algae.
Algae-based biofuel is a promising energy source that is in the late stages of development. Although producing biofuel with algae is not yet a cost-equivalent solution to the replacement of gasoline, further optimization of current methodologies and economies of scale may change this for some markets in the future.