Derived from algae, algae biofuel is a sustainable alternative to liquid fossil fuels, and it is also an alternative to more well-known biofuels such as corn-derived biofuel and sugarcane-derived biofuel.
Algae biofuel is also known as algae fuel, algae oil and algal oil. When made from seaweed, i.e. macroalgae, it can be referred to as seaweed biofuel/seaweed oil.
Algae can be converted into different types of fuels – including biodiesel, biogasoline, biobutanol, biogas, methane and ethanol – depending on the technique and which part of the cells are used. The fatty content of the algae can be turned into biodiesel and similar products, while the carbohydrate content can be fermented to produce products such as bioethanol or butanol.
Doesn´t compete with food-crop production
Algae biofuel do not require farmland for its production, since it is grown in water. It, therefore, has the potential to be produced in places that are unsuitable for growing food crops.
The United States Department of Energy estimates that 150,000 square miles (39,000 square kilometres) would be sufficient to yield enough algae biofuel to replace all the petroleum fuel used in the United States. 150,000 square miles is 0.42% of the U.S. map. To put it into perspective, seven times as much land is currently used to grow corn in the U.S.
Smart water use
Algae suitable for the production of algae oil does not require fresh water to be cultivated. It can be grown in saline water and brackish water, and the water doesn´t even have to be very ”clean”.
When fossil fuels are burned, they release carbon dioxide into the atmosphere that was removed from the atmosphere a very long time ago. They, therefore, contribute to an increase of carbon dioxide in our current atmosphere.
When algae oil is burned, it also releases carbon dioxide, but only the carbon dioxide that the algae captured when they were alive – which was very recently. Thus, the burning of algae oil does not contribute to the increase of carbon dioxide in the atmosphere.
Biodiesel from algae
Biodiesel is a fuel derived from plant lipids or animal lipids. Some species of algae are highly suitable for the production of biodiesel, as they are 60% or more lipids (in the form of oil) when dried. To understand how astonishing this is, it helps to know that soybean crops typically convert 2-3% of their biomass into oil.
The famously high-yielding oil-crop Elaeis oil palm yields approximately 5 950 litres of oil per hectare in a year. The yield of oil from algae is approximately 58,000 – 135,000 litres per hectare per year.
Biobutanol from algae
When the oil has been extracted from the algae to produce biodiesel, the left-over waste can be used to produce butanol (biobutanol). Butanol can be used as fuel in an internal combustion engine, and most gasoline engines can use butanol without any need for modifications.
Biobutanol is derived from biomass (e.g. algae) while petrobutanol is derived from fossil fuels. Biobutanol made from algae has an energy density that is higher than ethanol and methanol, but roughly 10% lower than gasoline.
Compared to terrestrial plants, macroalgae has a high methane production rate and is, therefore, a great choice for making biogas, as biogas is composed mainly of methane and carbon dioxide.
It is also possible to make biogas from microalgae since the carbohydrates and protein in them can be converted into biogas through anaerobic digestion. The biogas yield is lower than for macroalgae.
Instead of stopping at biogas, it is possible to make pure methane gas from algae. Several methods are available, including gasification and pyrolysis techniques where methane is extracted under high temperature and pressure. It is also possible to use a step-by-step process involving anaerobic bacteria, acidogenic bacteria and methanogenic bacteria.