Bacteria make light work of hydrogen production
Industry collaborations bring renewable energy advances
17 June 2009
Energy demands are increasing across the world. Developed countries consume the most energy per person – nine times the amount used in 1800 in the UK – is projected to rise as our houses, cars and offices are loaded with more power-hungry gadgets.
Part of the solution is local or home-energy generation. Rooftop solar panels and wind turbines are growing in popularity, yet the potential exists for food and garden waste to contribute to heating homes and charging phones.
It’s technology that could have an unparalleled impact on the wellbeing of the planet if it realises its full potential. Living standards and life expectancy are closely tied to per capita energy use and as they rise in India and China, the two most populous countries in the world, the need to offset climate change by reducing fossil fuel use has never been greater.
Step off the gas
Using hydrogen is one proposed solution to the energy crisis. Combusting it does not add carbon dioxide to the atmosphere, or the air pollutants associated with burning fossil fuels. What’s more, it has about 2.6 times more energy per unit mass than petrol.
Red streaks indicate mutant E. coli strains that can utilise maltose as a carbon source. Image: Frank Sargent
Consequently, hydrogen can be used to power planes, trains, and automobiles – as well as the Space Shuttle – but charging electric fuel cells opens up hundreds more down-to-earth applications. But before we get carried away in a hydrogen balloon, there are real reasons to keep our feet on the ground.
Because hydrogen is less dense than petrol a storage tank has to be three times the size of a petrol tank. But that is a lesser concern compared to how to make it. You can’t dig it up like oil or coal because hydrogen in its elemental form is rare on the Earth; most hydrogen produced for industry is derived from natural gas (methane) which nullifies any environmental credentials.
The answer could lie in the natural world. Some bacteria produce hydrogen as a byproduct of normal microbial metabolism. Bacteria such as E. coli (ref 1) manage this because they possess an enzyme called hydrogenase that produces hydrogen during the fermentation of carbohydrates – the same process that produces bread and beer – only with bacteria instead of yeast.
Another tasty snack – chocolate – inspired Lynne Macaskie of the University of Birmingham to exploit this trick. Macaskie needed clean hydrogen to power fuel cells to biologically recover the precious metals platinum and palladium from waste. "One day I thought ‘Mmmmm… we’ve got a Cadbury’s factory down the road, why don’t we just use the chocolate waste to make our own hydrogen?’" she says.
What started out as a hobby took on a life of its own. In an example of research at the interface between bioscience and engineering, Macaskie used a link grant from sister Research Council EPSRC and a BBSRC studentship to develop the technology. And it was more than a deft manoeuvre to get free sweets. Behind the move lay the opportunity for a cunning double-whammy: the bacteria producing the hydrogen were the same ones recovering the precious metals using the same hydrogenase chemical reaction in reverse(ref 2, ref 3). "The same bacteria do both tricks," says Macaskie. "So the whole idea is to close the loop and get zero emissions."
Platinum is more expensive than gold. There are no natural sources in Europe so it is liable to significant price fluctuations. Incredibly, it’s so valuable that recovering it from roadside waste is attractive, where it accumulates after being ejected by cars’ platinum-rich catalytic converters.
"70% of the converters’ precious metals are lost during driving," says Macaskie’s PhD student Angela Murray. She is set to take advantage of a BBSRC Enterprise Fellowship Award, beginning October 2009, to commercialise the technique (see Hydrogen entrepreneurs below).
Although biohydrogen technology is ready for large-scale pilot plant, further gains can be made by tinkering with the bacteria to make them more efficient (ref 4, ref 5). An alternative approach could be to do away with the bacteria altogether and concentrate on using and improving the action of the key hydrogenase enzyme.
3D structure of the hydrogenase enzyme
"We can take out the enzyme and attach it to electrodes and it makes gas on its own," says Macaskie’s collaborator Frank Sargent from the University of Dundee. "With bacteria you produce tons of spent bacterial waste. But with the enzyme in a device you wouldn’t have that."
The problem, Sargent says, is that enzymes never live as long as you want them to. The answer is to create a more resilient enzyme to carry out the same core functions. "We’re trying to engineer a hydrogenase that would be stable, tolerant to oxygen and long-lived so you could use it as a material in the near future," he says. It’s an approach that fuses protein engineering and synthetic biology to scrutinise a natural enzyme’s best features and then reengineer an artificial protein
And it’s a mission-critical approach. Sargent says that you can produce about two litres of biohydrogen gas from a dry weight gram of bacteria fermenting for 8-10 hours. But currently that’s only enough to power a radio, or a small electric motor on a fan for a few minutes.
TEM of Rhodobacter sphaeroides bacteria showing carbon-storage and photosynthetic sites.
Image: Lynne Macaskie
Private companies, too, are trying to increase the power. Mark Wells at BioHydrogen Ltd, based at the entrepreneurial bioscience centre The Sheffield Incubator, says they are introducing a programme of modifications into E. coli to boost the hydrogen yield. The highest yield that wild type bacteria are capable of is 4 units (moles) of hydrogen per unit glucose (or any C6 sugar), compared to the maximum yield chemically possible of 12 units per unit glucose. "That gap is the gap between what is feasible now and what is commercially viable, which is at around 8-10 moles," he says.
There are other ways to increase the efficiency. Biophotolysis uses light energy only using cyanobacteria but is far from commercialisation. However, photofermentation uses a photosynthetic bacterium, Rhodobacter sphaeroides, which can generate additional hydrogen from the waste organic acids (acetate) left over from the primary fermentation.
Combined approaches using light and chemical energy are being explored by Macaskie, Sargent and colleagues (ref 6, ref 7, ref 8) via a BBSRC-supported PhD project and the spinout company Biowaste2Energy. The Europe-wide Hyvolution project based at the University of Wageningen in the Netherlands is also developing the technology.
Maximising the energy return is crucial. Critics of the ‘hydrogen economy’ say it will never be truly viable because hydrogen is an energy carrier, not a primary energy resource, and always takes more energy to recover than is available by using it (ref 9).
But Wells says that this applies to all renewable fuels, and that renewable biohydrogen production could displace the large volumes of petrochemical-derived hydrogen in chemical industry, regardless of whether the hydrogen economy takes off. "To move to a sustainable economy we must find new ways of producing fuels and chemicals from renewable resources," he says. "Hydrogen production from biomass has great potential to help meet this challenge."
Biomass is readily available in domestic dwellings – the source of one-third of the UK’s demand for electricity – where up to 20M tonnes of food waste are produced. Hence, Macaskie has moved on from chocolate to experimenting with food wastes, an approach that Sargent finds appealing. "Lynne’s great idea is to use household waste that can be fermented. You buy a packet of dry bacteria in a shop and that will then produce gas in your garden shed, which you can convert to electricity or store it and use for something else," he says.
It’s an opportunity for another double-whammy: the biohydrogen produced from food waste may not meet even 10% of a current home’s energy demand, but energy and financial savings are made elsewhere because waste is not carted off to landfill and charged £48 per tonne.
Mark Wells, whose BBSRC PhD studentship has developed the technology confirms that savings can be made. "From one tonne of organic waste we could extract enough hydrogen gas to run a home for a week (about 168 kWh)," he says. "This would offset about 55,000 litres (or 100kg) of CO2," and that’s not including the saving made from regular waste disposal.
Combined with other eco-housing initiatives, domestic or community-level biohydrogen production could yet earn a place alongside the more familiar solar panels and wind turbines. It’s a vision that Sargent and Macaskie have shared with British and European Parliament politicians during the Royal Society MP and MEP Scientist Pairing Schemes, respectively.
"I talked about the need for alternative fuels and the power of microbiology and they all agreed that this kind of cutting-edge modern science was the way ahead in the UK," says Sargent. "After a week at Westminster, you meet a lot of people and you come away thinking you spoke to someone who might make a difference." Macaskie reports positive responses from Brussels. "MEPs are hungry for up to date yet impartial information."
There is approximately £60M of precious metals on the streets of Britain. "We are aiming to initially recover 0.5% of that, worth about £2-300K," says Angela Murray. Based on catalyst demand for platinum and palladium, which in the UK alone is nearly £100M per year, if just 1% of annual platinum and palladium is biorecovered a market of at least £67M over twenty years: more than enough sustain further innovation and employment – and that’s assuming today’s prices.
To financially develop the impact of the precious metal recovery technology, Murray is ready to begin a BBSRC-Royal Society of Edinburgh Enterprise Fellowship, beginning October 2009, with business training delivered by the Hunter Centre for Entrepreneurship, Strathclyde University. "Specific modules will help develop the business along each step of the way," says Murray, who stresses other benefits. "Mining is hugely damaging to the environment, so our recycling technology will have positive effect."
A spin-out company have been formed, Roads to Riches, to develop the physical processes to take on a variety to wastes. BBSRC-funded patent-pending biohydrogen technology has also gone out to another new business, Biowaste2energy Ltd, which has invested in a pilot set up that has been running continuously for 140 days. Macaskie, who has been collaborating with C-Tech Innovation to this end, via a Royal Society Industrial Fellowship, says the next stage for industry will be big enough to fit on a lorry.
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