Energy crisis lifeline: ‘Green diesel’ produced from microalgae could replace fossil fuels

E10 biofuel: Department for Transport explains why it’s ‘better'

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Biofuel is the name given to any liquid fuel derived from biomass — that is, material like plant matter, algae, or animal waste. Unlike fossil fuels, which took millions of years to form, biofuels are produced rapidly and can therefore be easily replenished, meaning that they are categorised as renewable. This does not mean, however, that biofuels are always inherently good for the environment. While their production can absorb carbon dioxide from the atmosphere — and many burn cleaner than fossil fuels — some still result in a net increase of greenhouse gases.

In their study, engineer Professor José Coelho Vargas of the Federal University of Paraná, Brazil, and his colleagues worked with the microalgae species Tetradesmus obliquus.

This particular tiny aquatic organism has elongated, spineless cells and can commonly be found in freshwater environments — and can biosynthesise hydrocarbons, which would be used to produce fuel.

The team said: “Microalgae are autotrophic organisms that can fix carbon dioxide as a primary carbon source.

“Therefore, due to the combination of high biomass productivity and great efficiency in synthesising and accumulating fatty acids, they emerge as ideal hydrocarbon production beings.”

A particular advantage of producing biofuel from microalgae — over crops like corn or sugarcane — is that it can be grown in so-called photobioreactors.

Because these can be built up vertically, they have a much more compact footprint, making industrial-scale production easier to realise.

The researchers grew T. obliquus in large-scale photobioreactors.

Each comprised more than 12,000 feet of clear PVC tubing, giving the algae access to sunlight for photosynthesis.

For a cultivation medium, the team used bio-digested swine manure, a substance that is rich in carbon, nitrogen and phosphorus.

After 15 days, the team removed the dry biomass from the reactors.

From this, they extracted oil — via the addition of a mixture of hexane and ethanol — for subsequent distillation.

In tests of the resulting fuel, the team found that the so-called “lower heating value” of their distilled oil was comparable to that of low-sulphur diesels, at 41,952 compared with 42,093 kilojoules per kilogram.

The team reported: “A lower heating value approximately equal to fossil low-sulphur diesel and high ignition quality qualify microalgae-derived ‘green’ diesel for diesel engines utilisation.”

In future, they said, green diesel could be used as an advanced motor fuel to replace fossil fuels “without engine performance loss”.

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With their initial study complete, the researchers have said that follow-up work is needed to address the economic and logistical challenges of scaling up and commercialising production of their green diesel.

Alongside this, they added, biofuel production could potentially be optimised by using genetic engineering to enhance the hydrocarbon synthesis pathway in microalgae.

The researchers concluded: “Microalgae-derived biofuels could be part of the solution to the growing fossil oil demand problem, and contribute to climate change mitigation.”

The full findings of the study were published in the journal Chemical Engineering & Technology.

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