Second-generation biofuels facing challenges
With ethanol and biodiesel coming under fire for driving up food prices and putting biodiversity at risk, the EU has committed to 'second-generation' biofuels as a cleaner alternative.
Second-generation biofuels are made from ligno-cellulosic biomass - the "woody" part of plants - that do not compete with food production. Sources include residues from crop and forest harvest such as leaves, tree bark, straw or woodchips as well as the non-edible portions of corn or cane.
However, converting the woody biomass into liquid sugars requires costly technologies involving pre-treatment and fermentation with special enzymes, meaning that second-generation biofuels cannot yet be produced economically on a large scale.
"It is unlikely that second-generation biofuels will be competitive with first generation by 2020," said the European Commission's Joint Research Centre in a 2008 study. And if they do, they will use largely imported biomass anyway, the JRC added, as latest studies indicate there will not be enough wood available to meet energy needs while continuing to supply Europe's existing wood industries.
Algae: High yields, no competition for land
To overcome these problems, some start-ups have now turned to so-called third-generation biofuels.
The United States Department of Energy (DoE) defines those as crops "designed exclusively for fuel production" such as perennial grasses, fast-growing trees and algae. These plants are not normally cultivated for agro-alimentary uses and have a particularly high percentage of biomass, it says.
Chief among those are algae. They are considered the most efficient organisms on earth, because of their rapid growth rate (some species can double their biomass in a day) and their high oil content.
Research into algae for the mass-production of oil is mainly focused on microalgae or phytoplankton – organisms capable of photosynthesis that are less than 0.4 mm in diameter.
"Algae can produce more biomass and more biofuel molecules much more efficiently in time and space than any terrestrial plant," says Greg Mitchell of the Scripps Institute of Oceanography, University of California, San Diego (UCSD). "For example, algae can produce 100 times more vegetable oil per acre per year than soy beans and 10 times more than oil palm," he told WIPO Magazine, a publication of the World Intellectual Property Organisation.
According to US oil giant ExxonMobil, which recently launched a $600 million research and development project on the issue, algae could yield more than 2,000 gallons of fuel per acre per year of production (7,580 litres). Approximate yields for other fuel sources are far lower, it pointed out:
- Palm — 650 gallons per acre per year (2,463 litres).
- Sugar cane — 450 gallons per acre per year (1,705 litres).
- Corn — 250 gallons per acre per year (947 litres).
- Soy — 50 gallons per acre per year (190 litres).
As a consequence, algae need much less land to grow than conventional biofuels, ending the potential for conflict with food production which comes with increased energy crop cultivation.
No need for freshwater
Algae have many other advantages. Aside from better yields, they are able to grow on ocean or wastewater, avoiding tapping into scarce freshwater resources for irrigation.
Algae grow best in seawater, which comes in virtually unlimited supply, says Raffaello Garofalo, executive director at the European Algae Biomass Association (EABA). And the micro-organism seems to be particularly fond of polluted seawater, which helps it grow at exponential rates.
"In all polluted sea places, there is a phenomenon which happens naturally called eutrophisation, which means there is an over-growth of algae," says Garofalo. "Precisely because pollution brings excess nutrients to the algae and therefore they grow exponentially."
The idea, he says, is to feed polluted water to the algae via transparent plastic tubes which industry specialists call photo-bioreactors. The algae absorb the pollution as a nutrient, and the water can then be returned back to the sea cleaner than when it entered, he explains. In the meantime, the algae have grown into biomass, which can be used for biofuels.
As a result, algae can be grown on so-called marginal lands, such as in desert areas where the groundwater is saline. Besides, they can feed on waste nutrients, including polluted water produced by the oil and gas industries.
In addition, microalgae have proved to grow more quickly when fed with carbon dioxide, the main global warming gas. When injected into a photo-bioreactor, the CO2 helps the plant grow faster while at the same time providing a way of "recycling" the CO2.
If algae plants are fitted next to factories or power stations, this could even open prospects for reducing emissions from industry.
"You could for example put algae next to a cement plant or a thermo-electric plant and you inject the carbon coming out of the plant in the bioreactor," Garofalo explains. "This means that the CO2, instead of coming out of the chimney, goes into the bioreactor to produce algae, which is burnt a second time as a fuel and then only goes into the atmosphere. So the same CO2 can be re-used twice."
In Arizona, GreenFuel, a private company, has developed a large-scale algae-to-biofuel plant, which uses CO2 emissions from a nearby power plant, the Arizona Public Service Redhawk power facility. The facility, which opened in 2005, won the 2006 Platts Emissions Energy Project of the Year Award.
Cost the main challenge
However, a number of challenges remain before algae can reach mainstream commercial applications, with uncertainties about cost the greatest obstacle.
Various algae species typically cost between US$5–10 per kg dry weight, according to US reports, with further research looking into ways of reducing capital and operating costs to make algae oil production commercially viable.
Bernard Raemy, executive vice-president at the Carbon Capture Corporation (CCC), a US-based company which claims to be a leader in the nascent algae-based biofuel industry, acknowledges that algae face a string of challenges. Speaking to WIPO Magazine, Raemy said these include "algae harvesting, dewatering, drying, lipid extraction and conversion". "Coordinated research efforts are required to bring research from the lab to the field," he said.
Research challenge: Bringing costs down
In the United States, several R&D activities have taken place since the 1950s. The largest was the Aquatic Species Programme, launched in 1978 by the US Department of Energy (DOE). The programme focused on finding the best strains which produce the highest yield and have the highest lipid content, while resisting fluctuations in temperature, particularly when cultivated in outdoor ponds.
Over 3,000 strains of microalgae were collected and screened, with the number later narrowed down to 300. However, no single strain was found to be perfect for all kinds of climate or water and the programme was closed in 1996, when US gasoline prices went down to $26/litre.
According to a review by the US National Renewable Energy Laboratory (NREL), outdoor mass production of algae in open ponds faces a number of challenges, including:
- Temperature variations, which affects productivity and growth;
- Invasion by native microalgae species, which may wipe out the cultivated strain;
- Water loss due to evaporation, and;
- Lower lipid content of algae produced in ponds.
When cultivated in photo-bioreactors, other issues come up, mainly:
- Finding the right type of plastic or glass for the transparent tubes in order to prevent algae from accumulating and obstructing the light;
- The cost of bringing the water via pipelines when algae are grown in desert areas, and;
- High maintenance cost of the installations.
It is therefore still an open question whether algae are best grown in photo-bioreactors or in open ponds. And the economics are a large part of the problem, as widespread mass production of algae for biofuel production is being hampered by the cost of the equipment and structures needed to begin growing algae in large quantities.
"For most algae applications we are still in fundamental research," says the EABA's Garofalo. "There is still research in order to identify the algae kinds or families which are most appropriate in order to produce biofuels. There is still research on what is the best bioreactor shape or plastic that is best to do this."
Harvesting and oil extraction
Then comes the question of how to harvest the plants. "Because algae are micro-organisms of a size ten times smaller than hair, you cannot harvest them with a net for example," Garofalo says.
Options for harvesting include centrifugation or chemical flocculation, which pushes all the microalgae together, but there are high costs associated with these processes too.
Whatever the species concerned, harvesting algae and extracting the oil from it appears to be "one the most critical steps" in producing algae-based biofuels, according to research foreseen under the European Commission's FP7 research programme.
The project, called Aquafuels, intends to bring together researchers and industry in order to streamline European algae research in the future.
But with oil prices up again, new research is being carried out with renewed enthusiasm. And genetic modification seems to open entirely new prospects, with new algae strains being tested for their capacity. The US national biofuels action plan, published in October 2008, appears to hedge its bets on genetic engineering: "Third generation feedstocks should be developed to increase drought and stress tolerance; increase fertiliser and water use efficiencies; and provide for efficient conversion," the plan says.
Environmental impact and energy balance
In addition, open questions still remain about the potential environmental impacts of biodiesel production from microalgae.
A life-cycle assessment of algae biofuels, performed by French scientists at INRA, raised concerns over the environmental impact of the whole process chain, from biomass production to biodiesel combustion.
Their findings, published in the Environmental Science & Technology journal in July 2009, confirmed the potential of microalgae as an energy source but also raised doubts about the energy balance of the whole process.
Looking at the energy required for the production of fertilisers and construction of infrastructure buildings, the scientists made a distinction between different algae culture and oil extraction techniques.
The study compared two different culture conditions - nominal fertilising and nitrogen starvation - as well as two different extraction options - dry or wet extraction.
"When taking into account all the energy debt of the process chain, it appears that only the wet extraction on low-nitrogen grown algae has a positive balance," the scientists write. In comparison, "other scenarios lead to negative energetic balance despite a 100% energy extraction from the oilcake".
Indeed, the scientists found that 90% of the energy consumed in the production process was dedicated to lipid extraction, compared to 70% with wet extraction. As a result, the energy balance "can be rapidly jeopardised, ending up with a counter-productive production chain," the scientists warn.
"It is then clear that specific research must investigate new processes in lipid recovering with limited drying of the biomass," they stress.
In conclusion, the study highlights "the imperative necessity of decreasing the energy and fertiliser consumption of the process". According to the scientists, the low-nitrogen culture "obviously has lower fertiliser requirements but also implies a lower drying and extraction effort," making this route more promising.
Future profitability lying outside biofuels
However, selecting the right algae strain and production process is not the only challenge which must be met before algae biomass can hit the commercial mainstream.
According to the European Algae Biomass Association (EABA), the key to future commercial profitability is to understand that there is more to algae than just biofuels production.
"It will never be economically viable to produce biodiesel or bioethanol from algae biomass if we don’t think about the co-products," says the EABA's Garofalo. "For instance, when you produce biodiesel, the lipid or the oil part of the algae represents about 25-30% of the product. But what do you do with the remaining 70%? We call it a by-product but actually it is the same product in terms of weight."
Aside from biofuels and jet fuels, the EABA says other applications include nutrients, pharmaceuticals, animal feed or bio-based products. In all these sectors, the EABA says algae and aquatic biomass hold an outstanding potential to achieve a real revolution towards a fully sustainable economy.