It thrives in fresh, brackish or salty water in places too hot, dry or infertile for other forms of agriculture. It grows many times faster than conventional crops, consuming quantities of carbon dioxide (CO2) as it does so. And it can be used to produce a form of ‘green crude’, freeing societies and nations from their reliance on fossil fuels.
So why aren’t we 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 price 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 Associate Professor Benoit Guieysse and colleagues at Massey’s School of Engineering and Advanced Technology 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 310 times the ability of CO2 to trap heat in the atmosphere, and it is also an ozone-depleting pollutant.
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 that the algae were indeed producing N2O, and, subsequently, that by changing the parameters he could vary how much of it was produced.
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 upset the scientific consensus that most atmospheric N2O originates from bacteria involved in the nitrogen cycle.
Guieysse’s challenge is now to 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 postgraduate student Quentin Bechet is working on a computer model that will incorporate various parameters to predict the scale of N2O emissions resulting from the full-scale outdoor cultivation of microalgae.
Guieysse does not regard the N2O problem as insurmountable. He believes that as universities, such as Massey, and private enterprise tackle the problems one by one, algal biotechnologies will become cheaper and more environmentally friendly, forming the basis of new industries. Whether one of these will be a major biofuel industry remains to be seen.
Guieysse’s project Is algal photosynthesis sustainable? is funded by a 2011 Marsden allocation of $774,000.
Visiting PhD student Cynthia Alcántra
PhD student Quentin Bechet
Associate Professor Benoit Guieysse
