“There are three important explanations for why this bacterium, which is called Caldicellulosiruptor saccharolyticus, produces more hydrogen gas than others. One is that it has adapted to a low-energy environment, which has caused it to develop effective transport systems for carbohydrates and the ability to break down inaccessible parts of plants with the help of enzymes. This in turn means it produces more hydrogen gas. The second explanation is that it can cope with higher growth temperatures than many other bacteria. The higher the temperature, the more hydrogen gas can be formed”, summarises Karin Willquist, doctoral student in Applied Microbiology at Lund University. She will soon be presenting a thesis on the subject.
The third explanation is that the CS bacterium can still produce hydrogen gas even in difficult conditions, for example high partial hydrogen pressure, which is necessary if biological hydrogen gas production is to be financially viable.
On the other hand, the bacterium does not like high concentrations of salt or hydrogen gas. These affect the signalling molecules in the bacterium and, in turn, the metabolism in such a way that it produces less hydrogen gas.
“But it is possible to direct the process so that salt and hydrogen gas concentrations do not become too high”, points out Karin Willquist.
When hydrogen is used as an energy carrier, for example in car engines, water is the only by-product. However, because the hydrogen gas production itself, if it is carried out by a conventional method, consumes large amounts of energy, hydrogen gas is still not a very environmentally friendly energy carrier.
Reforming of methane or electrolysis of water are currently the most common ways to produce hydrogen gas. However, methane gas is not renewable and its use leads to increased carbon dioxide emissions.
Electrolysis requires energy, usually acquired from fossil fuels, but also sometimes from wind or solar power. Hydrogen gas can also be generated from wind power, which is an environmentally friendly alternative, even if wind power is controversial for other reasons.
“If hydrogen gas is produced from biomass, there is no addition of carbon dioxide because the carbon dioxide formed in the production is the same that is absorbed from the atmosphere by the plants being used. Bio-hydrogen gas will probably complement biogas in the future”, predicts Karin Willquist.
Today there are cars that run on hydrogen gas, e.g. the Honda FCX, even if they are few in number. The reason for this is that it is too expensive to produce hydrogen gas and there is no functioning hydrogen infrastructure.
“A first step towards a hydrogen gas society could be to mix hydrogen gas with methane gas and use the existing methane gas infrastructure. Buses in Malmö, for example, drive on a mixture of hydrogen gas and methane gas”, says Karin Willquist.
Caldicellulosiruptor saccharolyticus was isolated for the first time in 1987 in a hot spring in New Zealand. It is only recently that researchers have really begun to realise the potential of the bacterium.