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Archive for July 2008

Biosolids = Grass = Fuel

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High grade bio fuel from grass land.

I agree completely that the most promising biofuels experiments are those using mixed native grasses. We discuss Tilman’s work and its many potential benefits on page 95-96 of Earth: The Sequel. These include:

– increased storage of carbon in the soil
– improved soil structure
– water infiltration and fertility
– radically reduced need for energy inputs (tilling, seeding, fertilizing)
– avoidance of competition with food production
– reduced pollutant run-off
– enhanced biodiversity, with all its benefits

I also agree that corn ethanol is generally a bad idea, given its poor energy/carbon balance, land and water impacts, and effects on food price and availability.

For net energy analysis, I rely on the work by Alex Farrell and Daniel Sperling of the University of California. They have developed a low-carbon fuel standard by assessing the “global warming impact” (GWI) of each fuel, measured as grams of carbon dioxide per megajoule of fuel burned. The GWI for gasoline is 92, for corn ethanol 76, for Brazilian sugarcane-based ethanol 36, and for cellulosic ethanol just 4.

Amyris’ fuels, because they’re made from sugarcane, currently offer about the same net reductions in carbon emissions as sugarcane ethanol. However, by making pure hydrocarbons and avoiding the distilling process, their energy inputs are lower. Their long term goal is to have the sugar inputs originate in cellulosic materials, like those native prairie grasses.

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