‘Green’ fuel may not be so green

 So-called green biofuels might not be as good for the environment as scientists hoped, according to Massey research.

Algae can be used to produce a form of green crude, with the possibility of freeing societies and nations from their reliance on fossil fuels, yet this seemingly natural wonder has a dirty secret.

It thrives in fresh, brackish or salty water in places too hot, dry or infertile for other forms of agriculture, and grows many times faster than conventional crops, consuming quantities of carbon dioxide (CO2) as it does so.

So why aren’t we already topping up our tanks with green biofuel produced from algae? Price. As yet, algal biofuels are many times more expensive than the conventional kinds. But their cost may not be the only barrier. There is also the matter of algae’s environmental credentials which, it turns out, are not entirely impeccable.

In 2009, Professor Benoit Guieysse and his colleagues at the School of Engineering and Advanced Technology at Massey University were surprised to find that nitrous oxide (N2O), also known as laughing gas, was seeping from a batch of microalgae. This was not a good thing. Algae may be good at consuming the greenhouse gas CO2, but, per molecule, N2O has nearly 300 times the ability of CO2 to trap heat in the atmosphere, and is also an ozone-depleting pollutant.

Professor Guieysse was intrigued and concerned. “So I did a couple of simple calculations, which showed that the emissions seemed significant. Then I looked for confirmation.”

He found the algae were indeed producing N2O and, subsequently, that how much of it was produced changed with the culture conditions. Adding nitrite, for example, increased the production of N2O, and incubating the algae in the dark increased it further still.

“When the experimental microalgae were deprived of light and fed with nitrite, the emissions of N20 increased by a factor of 40.”

Not only does the finding have worrying implications for the use of algae in biofuel production and wastewater treatment, but it could also upset the scientific consensus that most atmospheric N2O originates from bacteria involved in the nitrogen cycle.

Significant discoveries

Professor Benoit GuieysseProfessor Benoit Guieysse Professor Guieysse’s research bridges the frontiers of environmental microbiology (the study of microorganisms and microbial communities) and environmental biotechnology (the design, modelling and scale-up of environmental bioprocesses). His challenge is now to understand how and why algae synthesise N2O, and possibly work out how to cultivate algae in a manner that minimises how much N2O is produced. He and his colleagues have begun screening algal species and have already made significant discoveries in narrowing down N2O synthesis pathways in a well-studied algae species.

Professor Guieysse does not regard the N2O problem as insurmountable, and the results to date show these emissions can be kept low by, for example, cultivating the right algae under the proper conditions. He also believes that as universities such as Massey and private enterprise tackle the problems, algal iotechnologies will become cheaper and more environmentally friendly, forming the basis of new industries. Whether one of these will be a major biofuel industry, however, remains to be seen.

"When the experimental microalgae were deprived of light and fed with nitrite, the emissions of N20 increased by a factor of 40."


Research start date

  • 2012

Research end date

  • 2016



Contact Professor Benoit Guieysse

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