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Biochar For CO2 Reduction

March 15, 2010 | A version of this story appeared in Volume 88, Issue 11

Pertaining to the article "Geoengineering Steps Toward Reality," the use of waste as an agent for the removal of CO2 emissions by pyrolysis to "biochar" has been supported by Al Gore, James Hansen, and James Lovelock (C&EN, Nov. 23, 2009, page 28). They recommend that organic waste be used as terra preta del indio, a soil conditioner, perhaps first used in native Amazonia. The idea of biochar soil addition as a CO2 sequestrate provides the vital concept of an indisputably carbon-negative component in the control of the carbon cycle and hence a potential antidote to global warming. However, on its own, char manufacture will not do much to remove CO2 while fossil fuels are still used. The incorporation of a biochar model allows one to propose three complementary directions to combat CO2 emissions:

1. The addition of biochar to soil. This will increase productivity and potentially avoids the use of underground injection of CO2 for carbon fixation. Essentially, dry biomass is retorted, producing powdery charcoal and pyrolysis gas and oil that can be used for sustainable fuel and electricity generation. Though an excellent idea for using agricultural waste, in my opinion, it is not appropriate for municipal and industrial waste. Urban waste is heterogeneous, full of toxic heavy metals and organic chemicals that on charring would probably form novel brews of carcinogens that should not be added to soil. It might be safer to gasify or steam reform municipal and industrial waste, hazardous waste, and sewage sludge to syngas. Syngas could form the basis of a municipal petrochemical complex or "sustainability center," and, along with the methane from an anaerobic wastewater plant, provide clean water, petrochemicals, metals, and fuel for a city's needs. By contrast, in small towns and villages a simple retort still could be used for the production of biochar, etc.

2. Constructing a hydrogen/electricity-based economy (as a substitute for fossil fuels). The hydrogen economy is already being established in Europe. The geysers of Iceland are used to turn steam turbines and generate hydrogen by electrolysis. Wind is used in Denmark and Scotland for similar purposes. Solar-powered steam turbines are being installed in the U.S. Because of the difficulty of storing electricity, power could be stored or transported from remote locations as electrolytic hydrogen derived from water.

3. Initiating the novel legal development of "green rights." Analogous to mineral rights, the purchase of green rights could give the owner an incentive to preserve and develop the vegetation of key areas of biodiversity with CO2 sequestration. These rights would be sold worldwide to governments, individuals, and businesses that wished to purchase carbon credits or offsets. The money could be supervised by the United Nations or another international body. Competing demand for tropical lumber, soybeans, beef, and palm oil by developed countries may have to be reduced using a carbon tariff. Ways of marrying green rights with "slash and char" would need to ensure that areas set aside for biodiversity are relatively contiguous and that agricultural development would not interfere with the development of new international carbon reserves. A similar approach could be adopted for coral reefs.

I believe it may be possible to completely cease our reliance on fossil fuels by replacing them with hydrogen and also permanently remove excess carbon dioxide from the atmosphere using biochar within a relatively short space of time—perhaps only as little as seven years. That is the time it would take to replace most fossil-fuel-powered vehicles with electric ones and to cover the world in biochar. The technology is already available.

Paul Comet


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