Page 7 - North American Clean Energy January February 2014

Installed capacity of

geothermal heat pumps to
more than double by 2020

Geothermal heat pump (GHP) systems are being
Microbiologists reveal unexpected installed in nearly every region of the world in
residential, commercial, institutional, and industrial
properties of methane-producing microbe
applications with great success, according to a

Navigant Research report. Despite recent setbacks
For 40 years, scientists thought they understood how certain bacteria work together to anaerobically digest in deployments due to the economic downturn, the
biomass to produce methane gas—important in bioenergy and the major source of greenhouse gas. But, future looks bright for the global GHP market. he
now microbiologists at the University of Massachusetts Amherst have for the irst time demonstrated that research irm forecasts that worldwide installed

one of the most abundant methane-producing microorganisms on earth makes direct electrical connections capacity of GHP systems will grow by nearly 150%
with another species to produce the gas in a completely unexpected way.
over the next seven years—from 52.7 gigawatts-
“We discovered that Methanosaeta have the ability to reduce carbon dioxide (CO) to methane,” researcher thermal (GWt) to 127.4 GWt.
2and microbiologist Derek Lovley explains. “hey do this by a remarkable mechanism in which they make “he renewable energy policies that led to strong

electrical connections with other microorganisms, something methanogens have never been known to do growth in the GHP market in the last decade are
before.”
still in place, and will drive expansion as the global
Methanosaeta species are important for a couple of reasons. For one, they are so active in methanogenic economy improves,” said Mackinnon Lawrence,
wetlands that they are considered the most prodigious methane producers on the planet. his is a concern principal research analyst with Navigant Research.

because atmospheric methane is 20 times more efective at retaining heat than CO2, and as tundra soils “Although their overall penetration remains low,
warm due to climate change even greater methane releases are expected. Also, methane produced in GHP installations are gaining traction in both
anaerobic biomass digesters is economically important as one of the few proven, economical, large-scale the construction industry and the regulatory
bioenergy strategies in use today.
environment, and this high-eiciency technology will

Methane-producing microbial communities have been studied for decades, but as Lovley notes, “All this likely play a larger role in both new build and retroit
time we were missing a major pathway of methane production.”
projects going forward.”
His group’s study of Methanosaeta started when they found that digesters converting brewery wastes to Navigant Research
methane contained large quantities of the microorganism Geobacter. Geobacter cannot produce methane,
www.navigantresearch.com
but it does break down more complex substrates to compounds that methane-producing bacteria can use.
he UMass Amherst teams knew from previous studies that Geobacter grow electrically conductive
ilaments, known as microbial nanowires, which can transport electrons outside the cell to make electrical
connections with minerals, electrodes or other cells. Methanosaeta were the dominant methane-producing

microorganisms in the digesters, and known to convert acetate to methane, but analysis of the gene
expression in the digester revealed that Methanosaeta were also highly expressing genes for converting
carbon dioxide to methane. he researchers speculated that Geobacter were feeding Methanosaeta electrons

through their nanowires to promote Methanosaeta’s methane production from CO2.
Further studies in which individual Geobacter and a Methanosaeta species were cultured together
conirmed these suspicions. Lovley and his colleagues used radioactive tags to demonstrate that COwas
2 being reduced to methane. hey dubbed this transfer via microbial nanowire “direct interspecies electron

transfer,” or DIET. It was conirmed when they used a strain of Geobacter genetically altered to prevent it
from producing nanowires, and the process did not work.
Lovely says the discovery of DIET challenges the concept held for decades that natural, methane-
producing microbial communities primarily exchange electrons through the production and consumption of

hydrogen gas. DIET is a much more direct, and potentially more eicient mechanism for feeding electrons to 100% renewables
methane-producing bacteria.
“Now we need to improve predictions of how methane-producing microbial communities will respond Last November was a noteworthy month. According
to climate change. Microbial communities using DIET may react much diferently than those that rely on to the “Energy Infrastructure Update” report from

hydrogen exchange,” he says.
the Federal Energy Regulatory Commission’s Oice
here are also short-term practical implications. “Once you realize that there are methane producers that of Energy Projects, solar, biomass, wind, geothermal,
can directly feed on electrons, you start thinking diferently about how to optimize methane production and hydropower units provided 394 megawatts
from wastes,” the microbiologist notes. “Although generating methane from wastes is one of the oldest (MW)—or 100%—of all new electrical generation

bioenergy strategies, and is practiced even in small villages in developing countries, its application on a large placed in-service in November 2013. here was no
scale has been limited because it is slow.”
new capacity during the month from natural gas,
Trying to speed methane production in large-scale operations can disrupt the microbes’ highly coal, oil, or nuclear power. Renewable energy sources
coordinated activity and systems can fail. “Electrical circuitry that evolved for microbes to make methane also provided 99% of all new electrical generating

from organic matter in swamps at their own leisurely pace may not match our wish for a faster process in capacity in October.
waste digesters,” says Lovely. “Just as you need to upgrade electrical service in your house when you add Federal Energy Regulatory Commission
more appliances, we made need to use synthetic biology or other engineering approaches to increase the www.ferc.gov
capacity to move current through methanogenic microbial communities in digesters.”

More at http://xlink.rsc.org/?doi=10.1039/C3EE42189A
UMass Amherst | www.umass.edu