Fuel from Coal-Eating Microbes

A process for converting coal into natural gas could help reduce emissions.

Luca Technologies, a startup based in Golden, CO, has raised $76 million to scale up a process that uses coal-digesting microorganisms to convert coal into methane. The process is designed to operate underground, inside coal beds. Methane, the key component of natural gas, can then be pumped out and used to generate electricity or power vehicles.

Gas bugs: Methane-generating bacteria on a coal sample from Wyoming's Powder River Basin, viewed by scanning electron microscopy. Credit: Luca Technologies

If the process proves economical, it could help reduce carbon-dioxide emissions, since burning natural gas releases half as much carbon dioxide as does burning coal. It could also reduce or eliminate the anticipated need to import natural gas in the future, says Gary Stiegel, the technology manager for gasification at the National Energy Technology Laboratory, in Philadelphia. As little as one-hundredth of 1 percent of the coal in the United States converted into methane by microbes would supply the country's current annual natural-gas demands, says Andrew Scott, a former professor of economic geology at the University of Texas at Austin. Scott is the founder of Altuda Energy Corporation, based in San Antonio, TX, which is developing a similar process.

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Most natural gas is the product of heat and pressure over millions of years. But Scott, working at the University of Texas in the mid-1990s, helped show that a significant fraction of natural gas is constantly being produced by microorganisms that feed on coal. First, one type of microbe breaks the long hydrocarbon molecules found in coal into shorter molecules. Other microbes convert these molecules into organic acids and alcohols. Finally, microbes called methanogens feed on these and produce methane.

The researchers at Luca have learned to increase the amount of methane that these microorganisms produce, both in laboratory experiments and inside coal beds, by adding various nutrients and otherwise changing the chemistry of the microbes' living environment. The task was made difficult by the fact that some coal beds host as many as a thousand different microbes, some of which can interfere with methane production. What's more, the combination of microbes varies from location to location. The company developed combinations of nutrients that favored the methane-producing organisms.