Single-cell organisms living in oceans and ponds could provide a fresh new source of energyby Philip Hunter / June 21, 2010 / Leave a comment
Ocean bound: could harnessing the energy produced by algae cure the world of its oil dependency?
The environmental disaster caused by the Gulf of Mexico oil spill has underscored our urgent need for alternative energy sources. But existing ones—like wind, wave and solar—all have their drawbacks, while nuclear fusion remains stillborn despite its long-term promise of almost unlimited power. For a while there was hope that converting biomass from crops such as corn and sugarbeet would make a serious dent in fossil fuel consumption, but this is likely to remain a marginal solution since it would take too much land away from food crops. Now microalgae—single-cell organisms living in either sea or fresh water—have emerged as the most promising new biomass candidate.
There are some 500,000 species of microalgae living in our oceans, rivers and ponds. Because they are single-cell organisms, they are highly efficient at converting light into energy (photosynthesis), unlike more complex plants that comprise millions of cells. During photosynthesis microalgae also produce hydrogen, to protect themselves from excess light energy, and it’s this that has interested US researchers, because hydrogen can be used as fuel and also to generate electricity.
Experiments have already shown that microalgae cells can be engineered to yield much greater amounts of hydrogen than they do naturally, and that they can even generate electricity directly. The cells also naturally produce organic oils, or lipids, that can be converted into biodiesel which closely resembles the diesel used for heating and internal combustion engines.
There is also the longer-term possibility of going further, and engineering microalgae to produce biofuels (including biodiesel) directly, without having to convert from organic oils as an intermediate step. This may be achieved by re-engineering the photosynthesis process to yield hydrocarbons like petrol or diesel, by combining water and carbon dioxide, and removing the oxygen by reduction. This would make them a potentially effective source of biofuels, and perhaps even direct generators of electricity.
Refining these processes is a work in progress, but it is telling that some leading experts, such as the US National Renewable Energy Laboratory (NREL), the largest federal agency dedicated to sustainable energy research, declined to comment for this article because it is currently filing patents. Indeed, Craig Venter, who recently claimed to have created “artificial life,” has singled out production of biofuels from algae as an important future application of his work. He believes that emerging techniques capable of transplanting whole genomes between different species of bacteria could make it easier to develop strains of algae that produce hydrogen in much larger quantities than existing species.
Researchers have established that algae could theoretically convert 10 per cent of the solar energy falling upon them into biofuels, compared with, say, only 0.05 per cent for corn-grain ethanol. Remembering the false dawns associated with nuclear power after the second world war and, more recently, with biofuel crops themselves, there are good reasons to be wary of any promise of unlimited energy. There are also good reasons to be suspicious of any claims to have developed a completely green source of energy, given that most algae farms would almost certainly be offshore, where our environmental record has been poor. Significant engineering would have to be involved to collect the fuel and bring it to shore on a large scale.
Yet there are also growing grounds for optimism. It has been shown that algae could be harnessed in “algal bioreactor” tanks covering a much smaller surface area than biofuel crops—which would avoid stealing fertile land from food production. Mike Seibert, a research fellow at NREL, estimates that replacing all the petrol used in the US with corn-grain ethanol would take a cornfield “of the order of 1,000 miles a side.” With algae, the same amount of energy could be produced in an area of “about 110 miles on a side”—1 per cent of the space. And unlike crops grown on land, the critical raw materials needed for the process, such as phosphorus, nitrogen and iron, are provided in water, so they would be permanently on tap. This means that algae could even clean up pollution at the same time, by taking heavy metals out of the water. The environmental impact, then, could actually be a positive one.
But there are problems, and they come under three headings: harvesting the sunlight, converting it into a suitable fuel or energy form, and then collecting that energy. Research so far has concentrated on the first two issues. One of the significant harvesting problems is close to being solved by a team at the University of California, Berkeley. Algae produce chlorophyll, which turns water containing large numbers of them green. By breeding yellow rather than green algae, the amount of sunlight absorbed by each cell is reduced to a level where energy conversion is much more efficient. At the same time, more light is left over to penetrate deeper into the water, to other cells lower down, so that more light energy can be converted into biofuels.
Meanwhile, a team at Stanford University has made another potentially important discovery, by showing that algae can be wired up with sharp nano-size electrodes made of gold, in order to generate an electric current. Harnessing the electrical output of billions of such cells might seem a distant prospect, but at least it has been shown that it can be done. The more immediate possibility, though, is of yielding biofuels rather than electricity.
Timescales are impossible to predict at this early stage but, unlike nuclear fusion, the process is not all or nothing: there is the chance of starting relatively small and producing modest amounts of power and fuel in pilot projects. And some are already taking place. The NREL, for example, has recently applied for patents covering bioengineering techniques for microalgae. Algae biofuel projects are also starting to gather steam in Europe, with a further stimulus likely to follow thanks to a €3m (£2.5m) EU-funded report on algae biofuel technologies due in October 2010. In March, Britain’s Carbon Trust, an organisation charged with accelerating the drive to a low-carbon economy, announced the funding of a two-phase challenge involving a number of universities to develop algae biofuel production in open seawater ponds, with the target of achieving commercial-scale biofuel by 2020. The first phase, with funding up to £8m, involves fundamental research to be completed by 2012, the second £10m phase will test biofuel production in small pilot projects between 2013 and 2016; full-scale production processes will follow after that.
If any of these projects do come to fruition, the future could indeed be green. Or possibly yellow.