Energy

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.

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.

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.

Mark Finkelstein, Luca’s vice president of bioscience, says that the company has tested its methods in coal beds where wells had been drilled to collect natural gas (about 10 percent of the natural gas mined in the United States comes from coal beds). Many of these wells had stopped producing natural gas, or produced too little to be profitable. After treatment, production increased, and the wells became profitable again, Finkelstein says. The new funding will allow Luca to apply its techniques to more wells and continue research to understand the microorganisms involved, with the goal of further increasing methane production.

Finkelstein says that based on initial results, the company’s process could extend the lifetime of natural-gas wells. Conventional techniques for extracting natural gas from coal kill the gas-producing organisms found naturally in these coal beds, first, by removing the water that they need, and second, by exposing them to oxygen, which is deadly to them. By carefully maintaining conditions favorable to the microorganisms, the company allows them to continue digesting the coal and producing methane. The company could also employ its techniques to collect useful fuel from coal that’s inaccessible to conventional mining, Finkelstein says.

Scott says that it’s still unclear how much of the coal reserves in the United States can be converted into methane. Much depends on the nature of the coal bed, including factors such as the surface area of the coal that the microbes feed on. Eventually, for example, waste produced by the microbes could cause them to die off. Scott is also concerned about public reaction to the use of microbes, even though they occur naturally in coal beds, especially in areas where the coal beds are the source of drinking water. (However, he says, the microbes aren’t harmful to humans.)

Ultimately, Stiegel says, the success of the company will depend on the costs of Luca’s process and the price of natural gas. But he says that as a way to reduce carbon emissions and develop more sources of domestic energy, “it’s an intriguing approach.”

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