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Researchers Show Direct Bacterial Production of Methane from Electricity and CO2

30 March 2009

Researchers at Penn State University, led by Dr. Bruce Logan, have found that methane can be directly produced using a biocathode containing methanogens in electrochemical systems (abiotic anode) or microbial electrolysis cells (MECs; biotic anode) by a process called electromethanogenesis.

The results show that electromethanogenesis can be used to convert electrical current produced from renewable energy sources (such as wind, solar, or biomass) into a biofuel (methane) as well as serving as a method for the capture of carbon dioxide. A paper on the work was published online 26 March in the ACS journal Environmental Science and Technology.

At a set potential of less than -0.7 V (vs Ag/AgCl), carbon dioxide was reduced to methane using a two-chamber electrochemical reactor containing an abiotic anode, a biocathode, and no precious metal catalysts. At -1.0 V, the current capture efficiency was 96%. Electrochemical measurements made using linear sweep voltammetry showed that the biocathode substantially increased current densities compared to a plain carbon cathode where only small amounts of hydrogen gas could be produced. Both increased current densities and very small hydrogen production rates by a plain cathode therefore support a mechanism of methane production directly from current and not from hydrogen gas. The biocathode was dominated by a single Archaeon, Methanobacterium palustre. When a current was generated by an exoelectrogenic biofilm on the anode growing on acetate in a single-chamber MEC, methane was produced at an overall energy efficiency of 80% (electrical energy and substrate heat of combustion).

—Cheng et al. (2009)

Methanogenic microorganisms do produce methane in marshes and dumps, but scientists thought that the organisms turned hydrogen or organic materials, such as acetate, into methane. However, while trying to produce hydrogen in microbial electrolysis cells, the researchers found that the cells produced much more methane than expected.

We were studying making hydrogen in microbial electrolysis cells and we kept getting all this methane. We may now understand why...All the methane generation going on in nature that we have assumed is going through hydrogen may not be. We actually find very little hydrogen in the gas phase in nature. Perhaps where we assumed hydrogen is being made, it is not.

—Bruce Logan, Kappe Professor of Environmental Engineering

Microbial electrolysis cells do require an electrical voltage to be added to the voltage that is produced by bacteria using organic materials to produce current that evolves into hydrogen. The researchers found that Archaea, using about the same electrical input, could use the current to convert carbon dioxide and water to methane without any organic material, bacteria or hydrogen usually found in microbial electrolysis cells.

“We have a microbe that is self perpetuating that can accept electrons directly, and use them to create methane.”
—Bruce Logan

Logan, working with Shaoan Cheng, senior research associate; Defeng Xing, post doctoral researcher, and Douglas F. Call, graduate student, environmental engineering, confirmed that the microscopic organisms produced the methane. The researchers created a two-chambered cell with an anode immersed in water on one side of the chamber and a cathode in water, inorganic nutrients and carbon dioxide on the other side of the chamber. They applied a voltage, but recorded only a minute current. The researchers then coated the cathode with the biofilm of Archaea and not only did current flow in the circuit, but the cell produced methane.

The process does not sequester carbon, but it does turn carbon dioxide into fuel, said Logan. “If the methane is burned and carbon dioxide captured, then the process can be carbon neutral.

Logan suggests the method for off peak capture of renewable energy in a portable fuel. Methane is preferred over hydrogen because a large portion of the US infrastructure is already set up to easily transport and deliver methane.

The National Science Foundation and Air Products and Chemicals, Inc. supported this project.

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March 30, 2009 in Biomethane, Fuel Cells | Permalink | Comments (4) | TrackBack (0)

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Comments

Feul from CO2. Now there is some good news. If this is something that could be adapted to any commercial source of CO2 using solar, wind or waste heat to generate electricity, then we really have something to celebrate.

"...overall energy efficiency of 80%..."

This is impressive. Labs are not production so there is no test of longevity, but interesting.

"Methane is preferred over hydrogen because a large portion of the US infrastructure is already set up to easily transport and deliver methane."

This is what I believe too. If you want to get off imported oil sooner (we have done very little the past 35 years) then you need to go with what you have. Natural gas pipelines are here and we can power trucks and buses with natural gas. That takes major consumers of energy OFF oil all together.

China figured out that Methane was the way to go
vs Ethanol and Hydrogen, and George Olah, distinguished
professor at USC, has been pushing for Methane for
years. This is good news. Methane/CNG is the way to
go if we can avoid having to get it from petroleum.
Backwater countries have more CNG capable cars than
we do. The only problem we have to solve now is
trunk space.

Getting methane from non fossil sources would be good for trucks and buses. They use lots of fuel every day and getting them off using oil is something to go for.

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