Algal biofuels Full bloom or dead in the water?

Could algae be the fuel of the future? This extremely diverse group of simple organisms is prominent in efforts to develop a green energy source to replace oil, but there are substantial hurdles to be overcome In November 2013, the Society of Biology gathered together experts from the world of biofuels to discuss the future of this remarkable group of organisms in energy production. The debate title, ‘Full bloom or dead in the water’ was testament to the varied opinions about whether algae has potential as an energy source. Both unicellular microalgae and macroalgae, such as seaweed, are being used in a range of products known as ‘advanced biofuels’ thanks to their rich energy content and minimal land use. It is hoped they will reduce our dependence on oil and reduce global carbon emissions. Algae are photoautotrophic organisms, turning simple inorganic compounds including CO₂ and water into complex, energy-rich hydrocarbons using light as an energy source. The question is; can we harness this for our energy needs? Part of the appeal of algae is that they could theoretically be used to produce liquid fuels. Transport accounts for a quarter of UK carbon emissions, but is proving the hardest part of the economy to decarbonise. In all European countries, 10% of transport energy must come from renewable sources by 2020, so the stakes are high. Initial attempts to grow our way out of an energy crisis relied on so-called first generation biofuels. These are made from sugar, starch, or vegetable oil, often using traditional food crops such as corn or soya beans. Dry plant matter (lignocellulose) is the most abundant raw material in the world for the production of ethanol by fermentation, and producing bioethanol from plants is a well-established technology. First generation biofuels, however, have been criticised for using crops for fuel production instead of food, which can arguably drive up food prices and cause more carbon emissions through deforestation as more land is needed to satisfy both food and energy needs. At the event, Oliver Chadwick from the Department for Transport explained that estimates of overall emissions from certain biofuels may be worse than crude oil. “To provide biofuel for one lane of cars requires a strip of land the length of that lane, and 8km wide,” he said. “Conventional biomass is just not efficient in terms of land use.” Research is now focussed on advanced generation biofuels, which do not use edible plant matter, and this is where algae come in. Some species of microalgae can convert up to 60% of their biomass to oils (compared to 2-3% in soy beans). Because they don’t produce complex differentiated tissues such as stems and leaves, algae grow faster than land-based crops. Plus, marine macroalgae doesn’t even have to be grown on land (although the sea is an ecosystem in its own right, so shifting biofuel production from land to ocean requires careful management). Professor Rod Scott from the University of Bath was a speaker at the debate, and his research aims to develop strains of microalgae especially for biofuel production. He said: “You can do much better than terrestrial plants using algae. To provide 50% of the US’s fuel requirements with corn oil, you’d need 846% of the available crop area in the US, which is clearly just impossible.” [caption id="attachment_37350" align="alignright" width="200"] Algae as fuel: Algae can be turned into fuel via anaerobic digestion (producing methane), transesterification (biodiesel and glycerol), pyrolysis (‘biocrude’ and hydrogen) and hydrothermal liquefaction (biocrude and hydrogen)[/caption] If we are to produce algal biofuel on a sufficient scale for transport fuel, research needs to take place into both the strains of algae and the processes by which it is converted into fuel. Mixing algal biomass with a solvent and catalyst produces a diesel-like substance called biodiesel, plus glycerol. Newer techniques are also emerging which mean products are not limited to biodiesel. Pyrolysis involves heating algae to very high temperatures (500-700°C) in the absence of oxygen to produce a bio-char (charcoal) and a wider range of fuel products. Hydrothermal liquefaction puts whole unprocessed algal material under pressure and temperatures of 250-350°C with water to produce ‘biocrude’ and hydrogen gas. These processes essentially mimic the natural production of oil. Crude oil itself is formed from ancient algae, as well as other marine plankton. Algaenan, a tough hydrocarbon polymer found in algal cell walls, is turned to oil when layers of plankton are buried under the seabed and subjected to extreme heat and pressure. Producing oil this way takes about 30 million years. Replicating the process in real time, at a scale vast enough to contribute to global demand, is the challenge. Processes like pyrolysis can produce an oil equivalent from algae in about a day. But it’s important to consider quite how much oil we use before getting excited about algal fuels. Scott said: “At the moment we use 90 million barrels of oil, over 14 billion litres, every single day. You can fiddle around with a flask of new fuel and think we’re doing quite a good job, but we use a staggering amount of oil.” There are great costs involved in growing and processing algae compared to just piping oil out of the ground. Algal cells produce more hydrocarbons when they are starved of nitrogen, so it is a two-step process, where the cells that are to be starved must be separated from the ones still growing. Also, the more microalgae you try to grow in one space, the less light gets through to each cell, meaning growth rate falls. Andrew Spicer is scientific director of Algenuity, a company that provides support services to the emerging algal fuel industry. He says microalgal biofuel production will need to be stepped up from current levels of 100,000 tonnes a year to millions of tonnes per year if it is to replace petrol. Influential reports on biofuels say it is biology not industry that will help drive this, through strain selection and genetic engineering. Yet Spicer says it won’t be easy to translate bioengineering to industrial agriculture: genetically modified organisms are often hard to grow, but also many governments restrict the growth of them outdoors. “To assume you can genetically modify an algal cell to produce more biofuel, and then expect it to grow it en masse, is perhaps naïve,” admitted Spicer. Microalgae are starting to enter the genome editing realm. Metabolic engineering of biochemical pathways could achieve improved productivities, lower costs and improved energy balance. If we are accurately altering individual nucleotide bases, will this still be classed as genetic modification? It is under current legislation. Will it be acceptable to grow these algal in large scale, outdoor facilities? The technology may not be here yet, but part of paving the way is to open the ethical debate. Creative thinking about the uses of algae is also opening doors to new possibilities. One approach to the problems of scale and cost is to combine production of algal biofuels with another process. Many algal biofuel companies are changing direction to produce more expensive algal products rather than fuels. When algae are used to produce higher value products, such as pharmaceuticals, bioenergy could be produce as a ‘by-product’. Macroalgae such as seaweed grows in vast quantities and can be farmed from the sea, or recovered from the beach. It also can provide valuable environmental services. Fish farms, for example, are serious polluters, with waste nitrogen damaging ecosystems. Some species of algae can contribute to waste water treatment and be converted into biofuel. Yet before anything can be called a biofuel it must show its green credentials, said Dr Michelle Stanley, director of the NERC Algal Bioenergy Special Interest Group. “Seaweed beds on the ocean floor have an important role in preventing coastal erosion and removing beached kelp interferes with coastal ecosystems,” she said, “so you can’t just come along and take it all away.” Stanley shared a prediction that 447 TJ of energy can be produced by macroalgae by 2020. That’s about 0.2% of current road fuel demands. China is well ahead when it comes to growing seaweed in shallow waters, producing an estimated 10 million tonnes a year. Elsewhere, production is still low. Stanley said: “It all falls to pieces when it comes to economics. Costs can vary from €50 per tonne for nearshore, floating kelp, to €400 for offshore kelp, to €2500-plus for experimental systems.” Ultimately, algae are likely to be a valuable part of a range of products gradually replacing oil, said Stanley, not a miracle alternative.  “I’m of the view that one fuel won’t solve the energy crisis. People are fixated by the idea that there is one fuel out there and there won’t be. Microalgae will not fuel the UK, because of the land mass required, but it could provide a valuable contribution and other services like removing excess nutrients from waste water.” It’s up to governments around the world to keep backing research and put the infrastructure in place to support the production and use of algae as fuel. The UK Government will soon be calling for evidence on advanced biofuels to inform its future energy strategy, including the emerging algae technologies mentioned in this article. The EU is also considering changing European renewable energy targets to take into account land use consequences, which could lead to additional support or subtargets for algal biofuels in transport. But, for the time being, algal biotechnologists will continue to burn the midnight oil in the hope of making a viable biofuel for the future.   Our dependence on oil 14, 000,000,000,000 - litres of oil used per day globally Transport accounts for 25% of global carbon emissions 98% - proportion of transport fuel produced from oil Authors Rebecca Nesbit, press officer at the Society of Biology and Tom Ireland, managing editor of The Biologist, the Society of Biology’s magazine