They are vanishingly small, quite unremarkable under a microscope and anything but exotic. Yet microalgae, found anywhere from oceans, lakes and swamps to soils, rocks and icy mountain tops, are the Earth’s clean, green micro-machines.
With voracious appetites for carbon dioxide, these micro-organisms harness solar energy to convert the greenhouse gas into just about everything we need. And now, to help ameliorate the ravages of global warming, algae are being used to produce biofuels for vehicles and aviation fuels to power tomorrow’s airliners.
Algae, the world’s fastest-growing photosynthetic organisms, accumulate up to 80 per cent of their dry weight in oil. This endows them with huge, as yet untapped, potential for global fuel production — especially biodiesel and hydrogen gas, says Nick Coleman, a senior lecturer in microbiology at Sydney University.
By cultivating particular strains of algae, scientists can produce oils for specific purposes. “The various algae can be grown in freshwater or marine environments,” Dr Coleman says.
Their biomass can double every eight to 12 hours, and they produce oil year round, unlike most seasonal crops, says Aidyn Mouradov, an associate professor of plant biotechnology at RMIT University in Bundoora.
Algae are more productive, he explains, than other energy crops such as corn, soy or oil palm. “For example, algae can produce 10 times more than palm oil and require 10 times less land area.” This is important as biofuel crops have been severely criticised for occupying valuable arable land that could otherwise be used to grow food.
Algae farming, in fact, requires neither agricultural land — the micro-organisms can be grown on land too poor to use for traditional crops — nor clean freshwater. “They thrive on saline, brackish and waste waters,” Professor Mouradov says, noting that they can be grown on excess nutrients in sewage wastewater. “This leads to a win-win situation with a waste turned into an asset,” he explains.
Finally, algae can produce a range of value-added products: ethanol, hydrogen, pigments, biopolymers and food for animals and humans. To top it off, they make great bio-fertilisers. “These are getting very popular because they are eco-friendly and more cost-effective than chemical fertilisers,” Professor Mouradov says.
Fuelling the future
Bunker fuel used by ships is highly polluting, so any attempt to replace it with algal oil would benefit the environment.
With this in mind, Maersk, the world’s biggest shipping company, recently tested a mix of algal oil and bunker fuel on a ship sailing from Europe to India. The US Navy, meanwhile, trialled algal fuel on a decommissioned destroyer. Both experiments proved successful, although evaluations are continuing.
Several experiments using algal oil for aircraft jet engines have also shown promise.
And, in a move greeted with caution by GM sceptics, US biotechnologist Craig Venter, who first sequenced the human genome, plans to genetically engineer algal fuel that could be grown and harvested in the oceans.
Like all bio-derived fuels, algae take carbon dioxide out of the air as they grow, Dr Coleman says. “So the ultimate fuel produced is carbon-neutral. That is, when you burn it, you are just putting back into the atmosphere some carbon dioxide that the algae took out.
“This is different to burning fossil fuels, where carbon that has been locked underground for millions of years is put back into the atmosphere. If you use the algae to make hydrogen, then it’s like a double win — in this case, you are taking carbon dioxide out of the air, and making a fuel that is carbon-free.”
Algae are much more versatile and adaptable than higher plants: they can be grown literally anywhere there is sunlight and water, Dr Coleman says. “Areas that are too dry, too hot, or too cold to support trees or other plants can still potentially be used for algae.
Deserts are an obvious place for algae farms, since the land cannot be used for much else and there is plenty of sunlight. “The issue there is providing water and other nutrients — nitrogen, phosphorus, potassium and iron. But this is not difficult using a closed system where the water is trapped, and cannot evaporate,” Dr Coleman says.
Challenges for algal farming include the mechanics of harvesting the algae, in post-processing — for instance, converting natural algal oils into biodiesel — and in the risk of virus contamination. “All monocultures, whether plants, animals or algae are unstable ecosystems, and are at higher risk of being wiped out by viral pathogens compared to complex multi-species ecosystems,” Dr Coleman says.
A variety of viruses are known to prey on algae; these could enter algae farms in water or by wind, he says. “There are also tiny animals that love to eat algae, so you would have to keep these at bay as well.”
Algae on our doorstep
Australia is ideally placed to farm algae. It has abundant sunlight and wide-open spaces that are arid or semi-arid and so cannot be used for other forms of agriculture.
Algae production facilities, in fact, have been established in most states. The first commercial facilities were started in Western Australia where a $3 million project is under way in Karratha. Algae cultivated in large ponds are harvested to extract oil to produce biodiesel.
Scaling up algae production for commercial use has been an issue since the early days of interest in algal production, says Susan Blackburn of CSIRO’s marine and atmospheric division and the head of the Australian National Algae Culture Collection.
She says the best way to produce algae for commercial purposes is using photo-bioreactors that maximise the availability of light.
“As well as light for growth, microalgae require nutrients rather like a hydroponics system,” Dr Blackburn explains. “Supplying the necessary nutrients in sufficient quantities is a challenge.” One way to address this, she says, is to use municipal wastewater systems.
The CSIRO is developing a management system for algal fuels. “As well, the organisation has a wealth of knowledge on Australian native microalgae and a bank of more than 1000 strains held in the Australian National Algae Culture Collection,” Dr Blackburn notes. The collection also holds strains that have potential for aviation fuel.
Aurora Algae, a US-based company, has invested in commercial algal production for biofuels in Australia. “It will surely be followed soon by others,” Dr Blackburn says.
But it’s not all plain sailing. “Factors against us in Australia include poor links between research institutions and industry, the high cost of labour and a lack of strong commitment from the government to support research in this area,” Dr Coleman says.
In addition to their other applications, algae can be used as food for animals and people, as well as live feed for aquaculture animals. To this end, the CSIRO has been supplying the Australian aquaculture industry, as well as more than 60 other countries, with “starter cultures” for hatching aquaculture animals.
“The potential for animal feeds and fertilisers as co-products with the developing algal industry is great,” Dr Blackburn says. “Even with the oil fraction removed for biodiesel, the remaining biomass is protein-rich and contains many other bioactive compounds.”
Microalgae, for example, are the fundamental marine source of the long-chain polyunsaturated fatty acids omega-3 and omega-6. These are crucial for human health, as well as that of aquaculture animals.
Other high-value products include pigments, such as betacarotene and astaxanthin that are used in the human nutraceutical industry. The so-called “super-food” Spirulina, meanwhile, is also a type of algae.
“Despite these examples, the potential of algal products is largely untapped,” Dr Blackburn says.
Some algae are toxic. “It would be bad if an algae farm got contaminated with a toxic form, which might happen fairly easily in an open environment,” says Dr Coleman.
Blue-green algae — a type of photosynthetic bacteria, such as anabaena — cause toxic algal blooms in rivers.
All the same, blue-green types make great nitrogen-rich fertilisers as they “fix” their own nitrogen from the environment. “This means they can effectively make protein out of air,” Dr Coleman says. “No higher plants are capable of this, with the exception of legumes.”
“In a nutshell, algae offer a green, universal solution for most of the challenges we face in our everyday lives,” says Professor Mouradov. “Applications of algae in science and technology are restricted only by our creativity and knowledge.”
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