Algae that pull CO2 out of the air to produce oxygen, protein, oil and carbohydrates have a number of benefits over corn in biofuel production, according to the US Department of Energy’s Argonne National Laboratory. They can be grown in a closed system almost anywhere, from deserts to roof tops, and they do not compete for food or fertile soil. They are also easier to harvest because there are no roots or fruit, and they grow dispersed in water.
And algal spores are everywhere, as consultant Thomas Byrne pointed out: ‘A glass of water if left standing will eventually develop algal growth, so there is no push for genetically modified algae.’ Byrne told delegates at the BIO World Congress on Industrial Biotechnology & Bioprocessing (C&I 2008, 11, 24) that algae is a very viable product as it can double in volume in six hours. It is also outside the food vs fuel debate – it provides both fuel and animal feed.
Oils extracted from algae make an excellent biodiesel feedstock that doesn’t need to be dewaxed – something that is seen by aerospace major Boeing as a major factor in future aviation fuel development, noted Byrne, who is secretary of the recently formed Algal Biomass Organization (see Box). Algal protein, although not cellulosic, can also be used as an ethanol feedstock using an appropriate enzyme technology. Byrne believes that algal biofuels should be seen as part of the renewable solution.
Like other forms of biomass, algae do need fertiliser, light, CO2 and micronutrients, but without the restriction of a six-month growing season. But as Byrne pointed out, the fertiliser can be obtained from anaerobic digesters, the CO2 could be free, and micronutrients do not represent a high cost input. A large amount of water does have to be moved around but it does not have to be good quality potable water and is preferably brackish.
In terms of algal cultivation, Byrne emphasised that there is no single system that will work everywhere, and the system has to match the space, the nutrients and resources available. ‘One needs to match the technology to the location,’ he said. In terms of space, ponds need the most and they can be subject to contamination, while bioreactors have a smaller footprint but generally have higher utility requirements, and tubes offer better contamination control but, although cheaper than bioreactors, they have a larger footprint. Hybrids comprising ponds tied into bioreactors can offer enhanced growth while requiring less space and utility input.
Ben Cloud, from KL Renewables, also noted that there are plenty of systems available to produce algal biomass, but they all need to be large scale to be economic. His company is looking to launch a low cost scalable alternative in November 2008, with a capital cost of around $25 000/acre, using a minimum facility size of 40 acres, and operating and maintenance costs of $5000-20 000/year.
The KL Renewables solution is based on a ‘super trough’ approach using proven agricultural components.The covered ‘V’-shaped troughs lined with polyliner incorporate an aeration system at the bottom and a lighting system that doesn’t require additional energy but ensures photosynthesis continues overnight. A flocculantbased harvesting system is part of each field system. A demonstration facility is already in operation at Casa Grande, just outside Phoenix, Arizona, and yields of 50-100 t/acre have so far been achieved. Cloud believes that with further R&D this could be increased to 100-150 t/acre.
Cloud calculates that using the KL approach on an area of 15m acres would have a capital cost of $375bn and produce the equivalent of 1bn bbl of diesel, assuming 25% of the biomas oil is used for fuel production. In addition, approximately 77% of the yield would be available as animal feed. Regarding the production of oil from the algal biomass, Cloud noted that supercritical CO2 offers a very attractive route.
He sees two potential markets for the KL technology: small agricultural facilities, either stand-alone or co-located, with their own capital and management: and large-scale turn-key operations that could be co-located with ethanol or geothermal plants, or even paper pulp mills contributing their waste water streams. Cloud believes that the small-scale facility is possible now while the larger operations might take three to four years to realise.
Algae also feature in the first project of Innoventures Canada (I-CAN). A consortium of organisations and agencies, including Shell, PetroCanada and the governments of Canada and the state of Alberta, I-CAN is looking at the use microalgae to convert CO2 to value-added products.
The first part of the I-CAN project is an assessment and demonstration of the potential of algae for sequestering flue gas as a feedstock for producing biomass for transformation into products that might include fuels and chemicals. In describing the Carbon Algae Recycle System (CARS), Quinn Goretzky from the the Alberta Research Council said the aim is to produce an industrial scale system that will work all year round in the Canadian climate while generating a positive return.
A feasibility report was expected to be published during June 2008, while a demonstration facility is expected to be completed by 2020, with a scaled-up facility scheduled for 2010/12.
Algae are not just being considered as a biomass source for the production of bioethanol and diesel. Researchers at the Argonne National Laboratory are looking at chemically manipulating algae for the production of another renewable fuel – hydrogen. Some forms of algae incorporate an enzyme, hydrogenase, that enables the algae to produce small amounts of hydrogen.
David Tiede, senior chemist at Argonne said that hydrogenase is believed to eliminate excess reducing equivalents that are produced under high light conditions, but there is little benefit to the plant itself. Tiede’s team is working to discover the part of the enzyme involved and to introduce it into the photosynthesis process to produce larger quantities of hydrogen. ‘Biology can do it, but it’s making it do it at 5-10% yield that’s the problem,’ said Tiede.
‘We believe there is a fundamental advantage in looking at the production of hydrogen by photosynthesis as a renewable fuel,’ he added. ‘Right now, ethanol is being produced from corn, but generating ethanol from corn is a thermodynamically much more inefficient process.
‘If you have terrestrial plants like corn, you are restricted to where you could grow them,’ said Tiede. ‘There is a problem now with biofuel crops competing with food crops because they are both using the same space. Algae provide an alternative, which can be grown in a closed bioreactor analogous to a microbial fermentor that you could move any place.’
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