POWER May 2012 - 18

Pacific Northwest National Laboratory on converting some of its
chemicals to drop into jet fuel. British airline Virgin Atlantic,
which has partnered with LanzaTech, is already committed to
begin trials using LanzaTech-produced jet fuel on its ShanghaiNew
Delhi-London route within a few years. " The biofuels that
will succeed must be compatible with existing engines, pipelines
and refineries, " Holmgren said.
Auckland-based LanzaTech has been operating a pilot plant at
a New Zealand Steel plant since 2008 that it says is capable of
generating 16,000 gallons of ethanol made from carbon monoxide
a year. Recently, LanzaTech agreed to allow the steel company and
its Australian parent company Bluescope Steel to use the technology
commercially. Meanwhile, the 2005-founded company has begun
building demonstration projects in China, working with major
steel manufacturers Baosteel and Capital Steel to turn waste gases
into ethanol. The 100,000-gallon demonstration plant to convert
waste flue gas at Baosteel is expected to begin production later
this year. A full-scale commercial facility-which LanzaTech anticipates
will be the " world's first steel waste to ethanol and chemicals
plant " -is planned to be operational by 2013.
Last November, LanzaTech also announced plans to work with
Chinese coal producer Yankuang Group to produce fuels and
chemicals from synthesis gas produced by gasification. A more
recent deal with Indian Oil and Jindal Power and Steel will result
in a facility to convert plant gases into ethanol in India.
The company also recently bought the old Range Fuel site in
Georgia-a project now renamed " Freedom Pines " -that had
been awarded millions in federal funding under the Bush and
Obama administrations-to convert regionally sourced waste
wood into renewable fuels. It is also working with the DOE, the
Defense Advanced Research Projects Agency, and the Federal Aviation
Administration to adapt its technology to produce aviation
fuels for commercial and military use. Separately, the company is
also working with the Chinese Academy of Sciences on research,
development, and commercialization of related technologies.
This process to convert flue gases to fuel has garnered much
attention from investors. In addition to racking up clean technology
accolades (it was Global Cleantech " Company of the Year "
for 2011), LanzaTech is being backed by Malaysian national oil
company Petronas, Malaysian engineering firm Dialog Group, and
investing groups Khosla Ventures and Qiming Venture Partners.
Technique Generates Salinity Gradient
Power and Cleans Wastewater
Exploiting the difference in salt concentrations between the freshwater
runoff from river mouths at the point where they meet saltwater
reservoirs such as seas and oceans to harness power isn't a
new thing. Salinity gradient power has been recognized since the
1950s. Its massive global potential was estimated in the 1970s on
the basis of average ocean salinity and annual global river discharges
at between 1.4 TW and 2.6 TW. The most prominent technique to
exploit the salinity gradient at river mouths is called reversed electrodialysis
(RED), and it basically entails letting a salt solution and
freshwater flow through a stack of alternating cathode and anode
exchange membranes. The chemical potential difference between the
freshwater and saltwater generates a voltage.
In a new article in the journal Science, however, researchers at
Pennsylvania State University argue that RED's potential applications
are limited to coastal areas, and are impractical, owing to
the need for a large number of membrane pairs (a RED module
with a capacity of 250 kW, for example, is almost the same size
as a shipping container). But the researchers say that the RED
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POWER | May 2012
process could be improved using salt solutions that could be
continuously regenerated with waste heat (of more than 40C)
and conventional technologies that would allow a much wider
application of salinity-gradient power. One possibility is to use
the method on water containing food waste, domestic waste, and
animal waste-which, the researchers claim, could represent a
17-GW power capacity in the U.S. alone.
Their proposed technique essentially combines the use of microbial
fuel cells-which use exoelectrogenic bacteria, or bacteria
found in wastewater that consume organic material and
produce an electric current-and RED to create what they call a
" microbial reverse-electrodialysis cell " (MRC, Figure 6).
MRC can work with natural seawater, but the organic matter in
seawater will foul the membranes in RED stacks without extensive
precleaning and treatment, the researchers found. So, rather
than relying on seawater, the researchers used an ammonium bicarbonate
solution, which mimics seawater but will not foul RED
membranes. " The ammonium bicarbonate is also easily removed
from the water above 110 F, " they suggest. " The ammonia and
carbon dioxide that make up the salt boil out, and are recaptured
and recombined for reuse. "
In tests using the ammonium bicarbonate MRC, the researchers
reached a maximum power density (using acetate) of 5.6 watts per
square meter of cathode surface area-five times greater than that
produced using just the bacteria, and without a dialysis stack-
and nearly 3 W per square meter with domestic wastewater. Maximum
energy recovery with acetate reached 29.5% to 30.5%.
The researchers tested the MRC only in a fill-and-empty mode,
but eventually a stream of wastewater could be run through the
cell, they say. Not having to process wastewater was a major energy
saver, said article co-author Bruce Logan, Kappe Professor of
Environmental Engineering. " The bacteria in the cell quickly used
up all the dissolved organic material, " he added. " This is the portion
of wastewater that is usually the most difficult to remove and
requires trickling filters, while the particulate portion which took
longer for the bacteria to consume, is more easily removed. "
According to Logan, MRCs can be configured to produce electricity
or hydrogen, making both without contributing to greenhouse
gases such as carbon dioxide. " The big selling point is that
it currently takes a lot of electricity to desalinate water and using
the microbial desalination cells, we could actually desalinate wa6.
Power from salty water. A new technique engineered by
Penn State researchers that combines bacterial degradation of wastewater
with reverse electrodialysis-a method to extract power from a
saltwater-freshwater gradient-promises to produce power anywhere.
This image shows the researchers' microbial reverse dialysis test cell,
which produced 5.6 watts per square meter. Courtesy: Penn State
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POWER May 2012

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