Feature: Algal biofuels and the future of renewable energy

The 21st century will see humanity face many great challenges, including managing climate change, promoting sustainable economic growth and accommodating our growing global population. However, one of the most immediate concerns is our dependence on non-renewable sources of energy, which not only have an uncertain future in terms of supply, but that also exacerbate the effects of climate change.

According to Associate Professor Ben Hankamer, who works on renewable energy biofuel production from microalgae at the University of Queensland, even if fossil fuels will be around for a while, they’re far from an ideal energy source for the future. “Regardless of what everyone thinks about fuel security and the price of oil, the fact is that whatever supplies we have left will become more and more expensive to get out of the ground and supply to users,” he says.

“Therefore, it makes sense environmentally and economically to establish green jobs and develop new industries with the ultimate aim of building a sustainable economic base. If we can get clean, renewable technologies to a usable point, the fluctuations in oil prices will cease to be the issue they are, and we will be in a much better position in terms of economic stability. Because, in the end, all of our economies and our responses to climate change depend on stable fuel supplies.”

Read about the International Solar Bio-fuels Consortium established by Associate Professor Ben Hankamer

Having truly ‘clean and green’ fuels means having a sustainable source of energy to drive them. Of course, numerous choices are already being explored worldwide – solar, wind, wave power, geothermal, amongst others – with the largest potential source, by far, being the Sun.

Each day the Earth receives enough solar energy to meet global energy needs 10,000 times over, with less than a fraction of one per cent of the Earth’s land mass required to catch sufficient energy to power the world. But photovoltaics is not the only way to utilise the power of the Sun; plants have been turning solar radiation into chemical energy for millions of years.

The first generation of biofuels, like ethanol made from plant biomass such as corn, wheat and sugar cane, have already been explored. However, such biofuels require a significant portion of the world’s usable land and have sparked the recent and heated ‘fuel versus food’ debate.

In fact, with only about 10 per cent of the total land area on the planet classed as arable, there is simply not enough room to grow even those crops needed for biofuel production, and that’s not considering the land required for food production. Although alternative, non-food crops, like some native grasses that grow on non-arable land, are now being looked at for fuel production, the problem of land usage remains an intractable issue.

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Enter algae

Hankamer has always been interested in the processes by which plants catch sunlight and store it as chemical energy and, in particular, how this works in certain varieties of unicellular green algae. He also realised some time ago that this process in algae could form the basis of a sustainable source of energy products or biofuels. The last decade has seen an explosion of research and development in the field of microalgal cultivation and technology aiming for large-scale biofuel production.

Hankamer’s specific area of research at the University of Queensland’s Institute for Molecular Bioscience in Brisbane is the structural biology and biochemistry of the photosynthetic machinery that drives the first step of all biofuel production from algae. His group takes several different molecular approaches, concentrating on the development of new technologies for protein structure determination.

By solving the three-dimensional structure of key membrane proteins and macromolecular assemblies in the photosynthetic machinery, Hankamer’s team hopes to optimise the efficiency of the algal they work with for biofuel production. “Knowing more about the structure of these proteins will enable us to fine tune the photosynthetic machinery through genetic engineering, and then model interactions within the system to seek a commercially viable efficiency of solar-energy transfer in these cells.”

A select group of algae seem best suited for such applications due to their naturally high solar-conversion efficiency. The green microalgae, Chlamydomonas reinhardtii, is one of the main stars, with certain cyanobacteria also being tried as promising candidates. Genetic engineering of some of these algal strains in recent years, including by Hankamer’s group, has resulted in even higher energy conversion efficiencies, particular for the production of biohydrogen, as well as the ability to ‘work’ under different conditions, such as in saline and wastewater streams or at CO₂ levels comparable with industrial environments.

The ultimate aim of Hankamer’s research is to see vast algal cultures growing in large-scale bioreactors on non-arable land, basically doing what algae do best, which is to take sunlight and use it to convert water into hydrogen and oxygen, with a bit of scientific tweaking here and there to boost efficiency and to tailor the output to different purposes. The Queensland Government has already offered support to Hankamer’s project, providing endorsement and significant financial support, and Hankamer expects commercial partnerships will be procured in time.

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Multitasking algae

Once the algae are growing happily, the range of products on offer from these single-celled organisms is impressive. Potentially the most promising of these in terms of sustainable fuels is hydrogen, and Hankamer has been interested in algal H2 production for many years.

“To meet the emissions reductions targets that we will need to in the not-too-distant future, we really need a carbon-free energy and the only real alternative is hydrogen,” says Hankamer. “Most developed countries have a road map for hydrogen planning, including Australia, and California and Europe are building the infrastructure right now for delivering hydrogen-powered cars en masse. The major bottleneck is being able to make enough hydrogen and make it sustainably.”

Other algal bioproducts include methane from fermented algae, biodiesel from extracted oils, ethanol from carbohydrate extracts, and many other less-obvious choices that are being increasingly sought for alternative fuel systems, such as butanol. The algae could also be used as biomass for cattle feed or even dried and used for carbon sequestration in a form called bio-char, since algae efficiently absorb CO₂ while they are growing.

Depending on how regulations evolve in the future, this last application could be important as a storage medium for carbon that could be then returned to the soil. The potential also exists to make high-value products from processed algae with medicinal, nutritional or nutraceutical properties, such as beta-carotene, which is used in the food industry as a colouring and vitamin additive. Ideally, several bioproducts could result from the one algal factory, such as dried algae being used as biomass after it has gone through the biohydrogen stream.

Of course, for any of these promising ideas in algal biotechnology to proceed beyond the promising blue-sky research stage, they have to be economically viable in the real world, where the biofuels produced will running head-to-head with fossil fuels. As such, a very important part of Hankamer’s research was to examine industrial feasibility models of microalgal systems to identify the key economic drivers and potential bottlenecks. To this end, his team has just completed a major feasibility study, published in Nature Biotechnology, that shone a positive light on the approach.

“Overall, the feasibility study showed that developing the microalgal systems has real economic potential and identified some key factors that we need to address to get there,” says Hankamer.

“Basically, we need to bring down bioreactor costs, optimise biomass production and co-develop a range of high-value products alongside the biofuel production. This will involve a lot more time and money to take our models and test out the practicalities in the real world.

We also have many basic biological questions yet to answer to help address the process efficiency and cost, and our current research is targeting all of these areas. In short, our analyses have validated the technologies being developed by us and others, and fully justify taking the project to the next stage and towards commercial reality.”