Microbes make methane from CO2 and electricity

[FourScore]

http://www.dailykos.com/story/2009/3/31/715030/-Microbes-make-methane-from-CO2-and-electricity

Microbes make methane from CO2 and electricity
by Keith Pickering
Tue Mar 31, 2009 at 11:24:25 AM PDT

Penn State engineers have described a new process that utilizes microbes and electric current to produce methane (CH4) from water and carbon dioxide.

The process, called electromethanogenesis, is 80% efficient in the lab. If a non-fossil source of electricity is used, such as wind or solar, this process could be a source of non-fossil carbon-neutral fuel, extracting from the air the same CO2 it emits when burned.

One vexing problem of renewable energy is that the sun doesn't always shine and the wind doesn't always blow. And it's difficult to store the energy created by wind and solar projects, leaving renewables less reliable than traditional dirty methods of power generation. The key to solving this problem is finding a way of storing renewable energy.

Renewable advocates have long imagined a future "hydrogen economy" in which wind, solar, or even thermonuclear electricity is converted to hydrogen via electrolysis. The hydrogen would be stored and used as fuel for heating and transportation. But there are some major problems with this vision. Even after 200 years of research, the electrolysis of hydrogen from water is not terribly efficient, at about 50-70% (though it can be theoretically larger). Also, hydrogen is quite difficult to transport and to store.

The electromethanogenesis process is already more efficient than hydrogen electrolysis, and methane is easy to store and transport using existing natural gas and LP infrastructure. (Natural gas is mostly methane, so the existing national pipeline system for natural gas would work fine for this source.) The potential here could be huge.

Chemistry

Burning methane is the simplest hydrocarbon reaction:

CH4 + 2(O2) --> 2(H2O) + CO2 + energy

Electromethanogenesis is the reverse reaction:

2(H2O) + CO2 + energy --> CH4 + 2(O2)

The trick to the whole thing is to coat the cathode of an electrochemical cell with a biofilm of methanogenic bacteria. In the Penn State experiments, they used the species Methanobacterium palustre and got good results. The bacteria (okay, okay, they are really archaea, not bacteria -- but only biologists care about the difference) actually accept electrons from the cathode to do their work.

As for exactly how the archaea do their magic -- we don't know yet.

Science Daily article:
http://www.sciencedaily.com/releases/2009/03/090330111257.htm
Peer-reviewed abstract:
http://pubs.acs.org/doi/abs/10.1021/es803531g