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    Taiwan's Feng Chia University has succeeded in boosting the production of hydrogen from biomass to 15 liters per hour, one of the world's highest biohydrogen production rates, a researcher at the university said Friday. The research team managed to produce hydrogen and carbon dioxide (which can be captured and stored) from the fermentation of different strains of anaerobes in a sugar cane-based liquefied mixture. The highest yield was obtained by the Clostridium bacterium. Taiwan News - November 14, 2008.

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Thursday, December 04, 2008

Perennial biomass crops build soil carbon

Converting farm fields to energy crops can increase or decrease greenhouse gas emissions, depending on where – and which – biofuel crops are used, University of Illinois researchers report this month. The researchers analyzed data from dozens of studies to determine how planting new biomass crops can influence the carbon content of the soil. Their findings will appear next month in the first issue of the journal Global Change Biology Bioenergy - a new scientific journal in the Global Change Biology series, published by Blackwell.

Plants use the sun's energy to convert carbon dioxide from the atmosphere into the organic carbon that makes up leaves, stems and other plant parts. As plants decay, this carbon goes into the soil. Organic carbon is an important component of soil health and also influences atmospheric carbon dioxide levels. Whenever the soil is disturbed, as occurs when land is plowed or cleared of vegetation, some of this carbon returns to the atmosphere in the form of carbon dioxide.

From the time that John Deere invented the steel plow, which made it possible to break the prairie sod and begin farming this part of the world, the application of row crop agriculture to the Midwest has caused a reduction of soil carbon of about 50 percent, says Evan DeLucia, a professor of plant biology at Illinois and corresponding author on the new study.

Any debate on the environmental consequences of using plants to produce liquid fuels should also consider how each option affects soil carbon, DeLucia said.
The biggest terrestrial pool of carbon is in the soil. The top meter of soil holds more than three times the amount of carbon stored in either vegetation or the atmosphere, so if you do little things to change the amount of carbon in the soil it has a huge impact on the atmosphere and thus global warming. - Evan DeLucia
Unlike corn, which must be replanted every year, perennial grasses such as switchgrass and Miscanthus preserve and increase carbon stores in the soil. These and other grasses have been proposed as high-energy alternative feedstocks for biofuel production:
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Currently, ethanol is produced by fermenting the starch in corn kernels, but significantly more liquid fuel energy can be harvested from the stems and leaves of plants. The technology for producing this "cellulosic" ethanol is still quite expensive, but many believe that it will displace corn ethanol as the technology advances.

About 20 percent of the corn crop currently goes into ethanol production in the U.S., DeLucia said, "so we began with the hypothesis that it might be good for soil carbon to put a perennial biofuel crop on the landscape instead of corn."

The researchers analyzed published estimates of changes in soil organic carbon in landscapes converted from natural or agricultural land to biofuel crops. They focused on corn, sugar cane, Miscanthus, switchgrass and native prairie grasses. They also evaluated the impact of harvesting and using corn stover (the plant debris left over after corn is harvested) as a cellulosic biofuel source.

Their analysis showed that converting native land (grassland or forest) to sugarcane dramatically reduced soil carbon, creating a carbon deficit that would take decades to repay. While perennial grasses add carbon to the soil each year, DeLucia said, it could take up to a century for the sugar cane to rebuild soil carbon to former levels on native land.

Harvesting the corn residue for cellulosic ethanol production also reduced the carbon in the soil. The more plant residue was removed, the more the soil carbon declined.

Planting perennial grasses on existing agricultural lands had the most beneficial effect on soil carbon, the researchers found. Although there was an initial drop in carbon as fields were converted from corn to Miscanthus, switchgrass or native perennial grasses, the loss was fairly quickly offset by yearly gains in soil carbon as the grasses became established.

"Consistent with our hypothesis, the perennial feedstocks like Miscanthus and switchgrass start building soil carbon very, very early on," DeLucia said. "From a purely carbon perspective, our research indicates that putting perennial biofuel crops on landscapes that are dominated by annual row crops will have a positive effect on soil carbon."

The finding "seems to walk you right into the food for fuel debate," DeLucia said, referring to the controversy over using agricultural land for fuel production. But because the U.S. is already devoting about 20 percent of its corn crop to ethanol production, he said, it would make sense to eventually use that land to produce a much higher yielding biofuel feedstock that has the added benefit of increasing organic carbon in the soil.

DeLucia and his colleagues will present their findings this month at the 2008 Fall Meeting of the American Geophysical Union. Evan DeLucia is also an affiliate of the Institute for Genomic Biology and the Energy Biosciences Institute at the University of Illinois.

Quicknote on biochar
It's interesting to note that DeLucia has not yet looked at biochar, a new technology that turns the equation on its head. With biochar, crops are grown to turn them into a stable form of carbon that can be permanently sequestered in soils (or biomass waste is used). This sequestration via biochar is quasi-permanent - the carbon stays locked up for hundreds to thousands of years.

This is in contrast with the carbon sequestered either by no-till farming or by perennial grass crops as the one studied by DeLucia. These forms of carbon sequestration are only temporary. In the no-till case, the biomass in the soil is turned into CO2 and other GHG gases very rapidly. After a few years, all the carbon has been released back into the atmosphere. Biochar, on the contrary, locks up the C for centuries.

Biochar is made by pyrolysing biomass. Interestingly, during this pyrolysis process - heating in the absence of air or in a low oxygen environment - hydrogen-rich 'waste' gases can be captured and used to produce energy. If used to replace fossil fuels, this bio-energy is no longer carbon-neutral, but effectively carbon-negative because of the total amount of C used as a feedstock, around 50% is sequestered into soils.

One of the most interesting research pathways into bioenergy farming systems, will be the study of growing carbon-sequestering polycultures of perennial crops, and using them in biochar concepts.

Liquid or solid biofuels?
Another point to note is that turning cellulose into biofuels is not the most efficient way to use a given stream of biomass. A considerable number of studies shows that on a farm-to-wheel basis, using biomass for the generation of electricity used in (plugin-) electric vehicles is much more efficient than converting that biomass into a liquid or gaseous fuel for use in internal combustion engines. A still more efficient way to use biomass is in combined heat and power (CHP) or for pure heat generation.

A recent Canadian study, for example, showed that using solid biofuels generate heat presents a five to 10-fold increase in the capacity to offset greenhouse gas emissions, compared to first-generation biofuels (earlier post). Cellulosic ethanol would be more efficient than first-generation fuels, but they remain liquid energy sources - that is, the cellulose undergoes an energy-intensive conversion process - to be used in the rather inefficient internal combustion engines.

The future of biomass for transportation may well be the production of energy crops for biochar, the waste-energy of which is used to generate carbon-negative electricity for use in electric vehicles (driving such a car would mean that you would not simply be generating "zero emissions", you would actually generate "negative emissions" and take CO2 out of the atmosphere -- see "the strange world of carbon-negative energy"). Such integrated biomass energy and char concepts, would be coupled to smart-grids and to the other renewables that are going to power the electric transportation future.

Picture: Converting agricultural land to perennial grasses, such as Miscanthus, has a beneficial effect on soil carbon. Credit: Photo by Don Hamerman

Global Change Biology Bioenergy - Article not yet available at the time of publishing.

Energy Biosciences Institute.

Biopact: Study: solid biofuels 570% more efficient than corn ethanol in reducing GHG emissions - September 10, 2008

More on perennials as bioenergy crops:
Biopact: Tallgrass Prairie Center to study polyculture prairie hay for bio-electricity: combining conservation and restoration with bioenergy - December 03, 2007

Biopact: Carbon negative biofuels: from monocultures to polycultures - December 08, 2006


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