Photons to fuel

An investment of £27m has been made in bioenergy research to find out if fuel can be developed from agricultural wastes and non-food crops. Stuart Nathan reports.

The Isle of Wight is an unusual place to look for answers to major environmental problems. But then, the Isle of Wight is an unusual place. The first dinosaur fossils were found there and it was the home of the British space programme. But who would have thought that the key to making sustainable biofuels could be found in the intestines of a microscopic organism that is eating away at the foundations of the island’s piers — the unlikely named gribble?

The pesky gribble is one of the most important research targets of the newly formed UK Sustainable Bioenergy Centre, a ‘virtual institution’ spread around the country at major bioscience facilities. The Biotechnology and Biological Science Research Council (BBSRC) has awarded the centre its largest ever bioenergy grant, £27m over five years. This, said Prof Douglas Kell, chief executive of the BBSRC, is because there is a definite — although maddeningly uncertain — deadline for biofuels research. ‘One day, fossil fuels will run out,’ he said. ‘We can say that with certainty. All we’ll have is what we can derive from sunlight. There are a lot of steps from photons to fuel, but it’s something we have to look into.’

The focus of the centre, which is based at Rothamsted Research in Hertfordshire along with the Universities of Cambridge, Dundee, York and Nottingham, is to find ways of producing ethanol and butanol from agricultural wastes and non-food crops that can be grown on marginal land. The definition of ‘marginal land’ is one of the thorny issues of biofuels, but Angela Karp, who leads the centre’s research at Rothamsted, said that there is no shortage. ‘If you take all the land currently cultivated for food out of the equation, and then take out all the land that’s of environmental interest, such as areas of natural beauty, cultural heritage, sites of special scientific interest and landscape features, we’ve calculated that we’ve got at least three million hectares we could grow these crops on,’ she added. ‘And we probably wouldn’t need more than that.’

One of the things that excites Karp about the project is that one of the likeliest candidates for energy crops is an old, established part of the British landscape and a traditional crop —  willow. She indicates a twig about a foot long and as thick as a pencil. ‘Stick this in the ground, and within a few years you’ll have five to 10 stems as big as this.’ Karp hefts two wrist-thick five-foot staves. ‘And I had to cut that in half to get it on the train.’ Moreover, she said, unlike first-generation fuel crops — the maize and rapeseed used to make biodiesel — willow doesn’t need good land to grow, doesn’t need large amounts of energy-intensive nitrogen fertilisers, and is a perennial plant, so the land doesn’t need cultivating and resowing every year. Even better, she added, willow is a great biodiversity supporter — many varieties of insect live on it, which attracts bird life and small mammals and gives them a home.

This is something where the UK has a long history — longer even than the UK itself. The willow that Karp sawed in half to lug onto the train is one of the same varieties that had been planted here for millennia for material to weave baskets. Back in the 1920s, when basketmaking began to decline, prescient Rothamsted researchers set up a resource to retain different varieties of willow, and this variation forms a major part of Karp’s end of the research.

Wood, she said, is a difficult material to exploit for biofuels. It produces a huge amount of biomass in a short time, and is very efficient at converting sunlight and carbon dioxide into cellulose — the natural polymer of glucose that is the basis for bioethanol production. But the cellulose is knitted into a complicated network of cell walls made from tough lignin, another biopolymer that gives the tree its strength, resilience and resistance to weather. ‘These crops are already used to provide heat and electricity,’ Karp added. The fields around Drax power station in Yorkshire support large crops of willow and another fast-growing, poor soil-tolerant energy crop, the African grass Miscanthus, which is chopped into pellets and fed into the station’s furnaces. ‘But we don’t want to burn it. We want to make fuel.’

That involves breaking down the structure of the wood to unlock the cellulose. ‘We need to understand how the cell walls are put together, so that we can then breed a variety where the cellulose and the lignin can be uncoupled more easily, but where the lignin still gives the plant its strength and keeps it standing upright,’ she said.

One strand of this cell-wall research is being coordinated by the University of Dundee, looking at how lignin properties can be altered in barley straw to make the cellulose more accessible. Meanwhile, researchers at Cambridge and Newcastle universities are working with Shell and enzyme specialist firm Novozymes to both develop plants that will release cellulose more easily, and enzymes to perform that unlocking process. Enter: the gribble.

‘There are three sources for enzymes that will release the sugars and liquefy them,’ said Katherine Smart, professor of brewing sciences at Nottingham University. ‘One is bacterial, another is fungal, and the other is the gribble.’ These little marine borers live exclusively on wood, much to the annoyance of the Isle of Wight tourism board, but this means that their intestines must contain enzymes that can metabolise the wood into digestible sugars. ‘So once we have that liquefied sugar mix, the next step is to convert them into fuels. We’ve opted for ethanol, which we can make using yeasts, and butanol, where we’ll use bacteria.’ The plant, enzyme and fermentation research will all involve genetic techniques, she added, but the final results should be achievable by conventional plant crossing and breeding techniques because of the large number of diverse varieties available.

The target for the centre is to develop technologies and plant lines that will be exploitable by industry in five years’ time, which means that commercial fuel blends could be on the market within a decade, said Smart. This seems to be very ambitious, but Karp pointed out that a good start has already been made. ‘We’re not starting from scratch by any means. We’re building on improvement in breeding lines, materials, microbes and plants from all the laboratories that are taking part in the centre, but we’re focusing all of that onto the target of biofuels.’

Prof Kell believes that, even with car companies looking intensely at electric vehicles, biofuels will continue to be important. ‘Their big attraction is the large energy density they have, compared with lithium-hydride batteries or any other energy carrier, and that’s unlikely to change. We can burn them directly or use them in fuel cells, and that decision is open to the marketplace; but nothing changes the fact that liquid transport fuels have an energy density that is completely unbeatable.’ Car companies have already invested large amounts in developing flexible fuel engines that can run on blends containing different amounts of bioethanol, he said.

‘At the moment, we can make 19g of ethanol from 100g of straw. We have 10 million tonnes of straw in the UK. Based on that, and the amount of straw we currently produce that isn’t being used for other purposes, this could replace about 10 per cent of the fossil fuels used in transport at current conversion capacities. And improving those capacities is a major part of the project,’ added Kell.

To ensure that the centre develops sustainable systems, it also houses social scientists, economists and other engineers to study the various implications of its technologies. The vision, said Kell, is to develop a mobile factory, which could visit various energy crop growers and convert their crops into biofuel on site, which could then be transported by tanker into the fuel infrastructure.

‘It’s difficult to imagine a situation where we wouldn’t have to import anything,’ Karp said. ‘But as technology develops, who knows? We could end up self-sufficient, with our cars running on willow and straw.’

And hopefully, the Isle of Wight’s piers will survive for long enough to see it.