Microbes Make 'Clean' Methane
Microbes that convert electricity into methane gas could become an important source of renewable energy, according to scientists from Stanford and Penn State universities.
Researchers at both universities are raising colonies of microorganisms -- methanogens -- with the remarkable ability to turn electrical energy into pure methane, the key ingredient in natural gas. The goal is to create large microbial factories to transform clean electricity from solar, wind or nuclear power into renewable methane fuel and other valuable chemical compounds for industry.
"Most of today's methane is derived from natural gas, a fossil fuel," said Alfred Spormann, professor of chemical engineering and civil and environmental engineering at Stanford. "And many important organic molecules used in industry are made from petroleum. Our microbial approach would eliminate the need for using these fossil resources."
He added that all of the carbon dioxide released during combustion is derived from the atmosphere, and all of the electrical energy comes from renewables or nuclear power, which are also carbon dioxide free.
Methane-producing microbes could help solve the problem of what to do with surplus electricity generated by photovoltaic power stations and wind farms.
"While conceptually simple, there are significant hurdles to overcome before electricity-to-methane technology can be deployed at a large scale," said Bruce Logan, Evan Pugh Professor and Kappe Professor of Environmental Engineering, Penn State. "That's because the underlying science of how these organisms convert electrons into chemical energy is poorly understood."
Burning natural gas accelerates global warming by releasing carbon dioxide that's been trapped underground for millennia. The researchers wan to take a "green" approach to methane production. They envision large bioreactors filled with methanogens – single-cell organisms that produce methane.
Methanogens cannot grow in the presence of oxygen. Instead, they regularly dine on atmospheric carbon dioxide and electrons borrowed from hydrogen gas. The byproduct of this microbial meal is pure methane, which methanogens excrete into the atmosphere.
The researchers plan to use this methane to fuel airplanes, ships and vehicles. In the ideal scenario, cultures of methanogens would be fed a constant supply of electrons generated from emissions-free power sources, such as solar cells, wind turbines and nuclear reactors. The microbes would use these clean electrons to metabolize carbon dioxide into methane, which can then be stockpiled and distributed via existing natural gas facilities and pipelines when needed.
Microbial methane is much more ecofriendly than ethanol and other biofuels, the researchers noted. Corn ethanol, for example, requires acres of cropland, as well as fertilizers, pesticides, irrigation and fermentation.
Methanogens are much more efficient, because they metabolize methane in just a few quick steps.
For this new technology to become commercially viable, a number of fundamental challenges must be addressed.
In 2009, Logan's lab was the first to demonstrate that a methanogen strain known as Methanobacterium palustre could convert an electrical current directly into methane. For the experiment, Logan and his Penn State colleagues built a reverse battery with positive and negative electrodes placed in a beaker of nutrient-enriched water.
"The microbes were about 80 percent efficient in converting electricity to methane," Logan said.
At Penn State, Logan's lab is designing and testing advanced cathode technologies that will encourage the growth of methanogens and maximize methane production. The Penn State team is also studying new materials for electrodes, including a carbon-mesh fabric that could eliminate the need for platinum and other precious metal catalysts.
"Many of these materials have only been studied in bacterial systems but not in communities with methanogens or other archaea," Logan said. "Our ultimate goal is to create a cost-effective system that reliably and robustly produces methane from clean electrical energy. It's high-risk, high-reward research, but new approaches are needed for energy storage and for making useful organic molecules without fossil fuels."
A three-year grant from the Global Climate and Energy Project at Stanford funds this project.
SOURCE: The Pennsylvania State University