Harnessing the power of microbes

THE planned development of a £15m science centre at Oldham Sixth-Form College sees the town bucking the national trend by having more students than ever taking the subjects. Tonight, in the latest in a series of Friday features, we look at alternative energy sources from living scources with Dr Paul Humphreys, Senior Lecturer in Microbiology at the School of Applied Sciences, University of Huddersfield.

When people think of alternative fuel or energy sources, bacteria and other microbes are rarely the first things that come to mind.

However, with their ability to live in extreme environments and use and generate energy from substrates as far apart as iron, wood, sewage and sun light, microbes present some interesting alternatives to conventional fuel and energy sources.

When this natural diversity of microbial metabolism is combined with genetic engineering the potential for microbial fuel and energy generation becomes even more exciting. One well-established microbial fuel production process is the generation of alcohol to fuel cars.

This alcohol is produced by the fermentation of sugar by yeasts. The resulting alcohol can either be blended with petrol or used exclusively to power cars. Blends with low levels of alcohol (e.g. 10 per cent) can be used by most modern cars, but where higher levels of alcohol are involved some engine modifications are required.

Flexi -fuel

The use of alcohol in vehicle fuels was pioneered in Brazil where flexi-fuel cars and light vehicles running on fuels with 20-25 per cent ethanol are common place.

These advances have given Brazil the world’s first sustainable biofuels economy.

Another approach to microbial fuel production which is receiving considerable attention at the moment is the extraction of oil from micro algae, some of which are microscopic relatives of common sea weeds.

These microbes produce high levels of oils such as polyunsaturated fatty acids which can be pressed out of the harvested cells.

A big advantage of using algae in this way is the fact that they only need light and carbon dioxide to grow.

They can also produce up to 30 times more oil than some plant crops.

Although the use of algal biofuels is very much in the development stage, there have been some notable high profile tests.

These have included the test flight of a Boeing 737 which had one engine powered by a 50:50 mix of algal biofuel.

These microalgae can be grown in either bioreactors or on land in open ponds. Once the oil has been recovered from the algae the remaining biomass can then be used for other processes including methane generation.

The most attractive forms of microbial energy generation are those which involve microbial conversion of wastes into fuels.

A good example of this is the generation of methane during a process called anaerobic digestion; a process that only takes place in the absence of oxygen.

This is far from a new technology, anaerobic digestion and the re-use of the methane generated has been around for along time, especially when applied to the disposal of sewage and farm waste.

However, this technology can be applied to a much wider range of organic waste such as food, household and construction wastes.

Unfortunately anaerobic digestion does not work well with wastes which contain large amounts of woody material.

One emerging application of microbes in energy generation is the construction of microbial fuel cells.

These employ microbes to convert chemical energy into electrical energy which can then be utilised as normal.

The microbes and an energy source are placed in a sealed chamber with an anode.

This is separated from the cathode chamber by an ion exchange membrane, and the two electrodes are connected electrically.

Electricity is generated as the microbes degrade their energy source and transfer electrons to the anode.

In many microbial fuel cells a chemical mediator is required to facilitate the transfer of electrons from the bacteria to the anode.

However, more recent research has discovered that some bacteria, especially those able to reduce metals such as iron, are able to transfer electron directly without the need for a mediator.

This electron transfer is possible because these bacteria have surface structures and enzymes which are electrochemically active.

One of the attractions of microbial fuel cells is their ability to use a range of carbon compounds and a lot of research has focussed on the use of waste waters in sewage plants.

This type of fuel cell hase also been proposed for the running of research equipment in remote locations such as the deep oceans.

Given the range of potential applications microbes may have in future energy generation, it appears clear that some of the smallest living things on the planet may be able to make a significant contribution to future energy demands and take some of the pressure off the use of fossil fuels.