Many plants can be turned into biofuels – but which ones should we use and what methods are best?
A
On paper, biofuels seem the ideal replacement for oil, coal and gas, the fossil fuels we depend upon, and which drive global warming and disrupt weather patterns by releasing carbon dioxide into the atmosphere. But the past decade has seen the biofuel industry face tough questions over whether it can truly claim to be ‘green’. One of the biggest criticisms of biofuel crops – at least those that produce the fuel ethanol – has been their impact on food markets and on traditional land use. Direct impacts – for example, cutting down forests to make way for a biofuel crop – are usually obvious, says Professor Bill Laurance director of the Centre for Tropical Environmental and Sustainability Science at James Cook University. But, in his experience, indirect impacts can be no less devastating for the environment and are far more of a challenge to anticipate.
B
Let’s take Brazil, for example. When farmers in the US opted out of soy in favour of corn as a biofuel crop, soy prices soared, suddenly making it an attractive crop for Brazilian farmers. In turn, this increased demand for freshly deforested cropland 1n Brazil. Similar situations are occurring all over the world. But while deforestation can certainly load to economic benefits for farmers, it also puts biodiversity at risk. Then, once a biofuel crop has been planted on deforested land, farmers need to ensure that it grows as well as it can. That means applying large quantities of fertiliser, and while this helps the plants to shoot up, there is also the possibility it will lead to the contamination of local rivers.
C
Not all biofuels have been grown on land, but the once-popular idea of generating them from microscopic algae grown in ponds or tanks has largely been forgotten. Professor Rachel Burton leader of the ARC Centre of Excellence for Plant Cell Walls at the University of Adelaide, thinks that there is a smarter way forward for biofuels and it starts with selecting the right crop for land not usually used for agriculture. Burton and others are looking to tough plants that grow on land too dry or salty for conventional crops. Australia, for example, could turn to crops such as agave, hemp or the native saltbush and wild-growing sorghum for the biofuels of the future, she says.
D
Researchers must also consider economic factors, however. While plant oils can be extracted and turned into biodiesel for vehicles and machinery, currently the process is very expensive – much more so than the process for fossil fuels. Dr Allan Green is innovation leader for bio-based products at CSIRO Agriculture and Food. His solution is to make plants oilier by genetically altering them so that they produce oil in their leaves, not just in their fruit or seeds. With more oil being produced on a particular section of land by the same number of plants, it would become cheaper to harvest and extract the oil. The technology, which has so far only been tested in tobacco, shows that oil production can be boosted to a third or more of a tobacco leaf’s weight. If used in a different crop – one that already produces oil in its seeds or fruit – the hope is that oil output could be doubled, though that idea is yet to be put to the test.
E
A technology which is becoming increasingly popular in the biofuel industry is hydrothermal liquefaction. This is a process which uses heat and pressure to break apart molecules in whole plants and remove oxygen, so that the raw material is turned into ‘bio-crude oil’. Then, just as we need to refine the crude oil made from fossil fuels, the plant-based oil is also refined. After this, it can then be turned into different kinds of fuel. One advantage of the hydrothermal liquefaction process is that many kinds of plant can be used. And if this process could run on energy from solar panels or wind farms, it would be much more environmentally sustainable.
F
New processing technologies are giving biofuel producers hope that, in future, they won’t be limited to plants designed to be biofuel-only crops. Perhaps they will be able to choose species that deliver added benefits or sources of income. Hemp crops, for instance, could be used for their oil, but also for their fibre. Some car manufacturers have already used it as a soundproofing material in their vehicles, and others may do the same. And according to Kirsten Heimann, associate professor at the College of Science and Engineering at James Cook University, it might be possible, say, for algae not just to act as a biofuel, but to decontaminate water. Burton believes this kind of multi-purpose use for biofuel crops is the way forward. ‘It’s much more sophisticated thinking,’ she says. ‘Biofuels maybe don’t need to be as cheap as we think they do, because you can make money out of the other things.’ Eventually, the biofuel industry could well develop into a very diverse one, with no one crop or process dominating the market, according to Green. ‘The amount of fuel we need to move away from petroleum is massive, so there’s plenty of space for all technologies,’ he says.
