More good news on the viability of biofuels as transportation fuel alternatives has emanated from the research field, providing advocates with even more persuasive arguments against EPA’s short-sighted proposal to reduce blending requirements under the Renewable Fuel Standard (RFS).
One study represents some of the latest research showing a steepening drop in the carbon intensity of a wide range of biofuels when compared to fossil-fuel derived transportation fuels.
Meanwhile, another study undertaken at Michigan State University over the past seven years shows perennial crop feedstocks positively resolve some of the unknowns of how converting large tracts of the Midwest’s marginal farming land to perennial biofuel crops could affect the balance of water between rainfall, evaporation and movement of soil water to groundwater.
The carbon-related study, recently published in the Advances in Applied Agricultural Science (AAAS) Journal and written by a team that included Steffen Mueller of the University of Illinois at Chicago’s Energy Resources Center and Wally Tyner, of Purdue University, assesses different life cycle modeling approaches for handling the corn and corn stover systems for respective biofuel and feed production. Corn stover (cobs, stalks and leaves) is used as a cellulosic feedstock for ethanol, or as a replacement for corn and hay or corn silage in animal feed.
The researchers note that while corn stover is an important part of the life cycle of corn, either as fuel or as animal feed, most lifecycle analysis (LCA) models treat them separately from grain ethanol.
The team estimated that the carbon intensity of corn grain ethanol alone is 62 grams of carbon per megajoule (a unit of energy), or 62 g/MJ, which is 33 percent less than the 93 g/MJ measured for gasoline. Cellulosic ethanol made strictly from corn stover, the research shows, generates emissions of only 8.7 g/MJ, or 91 percent lower emissions than gasoline. Furthermore, corn grain ethanol combined with treated stover or corn stover ethanol reduces the composite numbers to 56 and 52 g/MJ respectively, which represent drop-offs in carbon intensity when compared to gasoline of 39 and 44 percent respectively.
The study notes that some environmental concerns have been raised over excessive harvest of stover or other non-grain crop biomass, which, when retained in the field helps build organic matter, sustain carbon levels and recycle nutrients. But the authors cite other studies that show as U.S. corn yields have been increasing over the years – and thereby increasing stover yields ‑ removing a portion of the stover from the field reduces nitrous dioxide emissions and improves carbon production in the soil.
In humid climates such as the U.S. Midwest, evaporation returns more than half of the annual precipitation to the atmosphere, with the remainder available to recharge groundwater and maintain stream flow and lake levels.
A recent study from the Great Lakes Bioenergy Research Center (GLBRC) and published in Environmental Research Letters looks at how efficiently “second generation” biofuel crops use rainwater and how these crops affect overall water balance. Led by Michigan State professor and GLBRC scientist Stephen Hamilton, the study is the first multi-year effort to compare the water use of conventional corn crops to the perennial cropping systems of switchgrass, miscanthus, native grasses, restored prairies and hybrid poplar trees.
Hamilton and his team established different test cropping systems in 2008 and installed soil-water sensors at various depths through the root zone, continuously monitoring the soil water content ever since.
The bottom line? The perennial system’s evapotranspiration ‑ the sum total of water lost while the plant is growing ‑ did not differ greatly from corn. It’s a finding that contrasts sharply with earlier studies that contended there was particularly high water use by perennials in areas with high water tables. The study was done in Michigan’s temperate humid climate and on the kind of well-drained soil characteristic of the marginal farming land expected to be used for perennial feedstocks for biofuels.
Hamilton says the message to be taken from the study is that in many settings, including the upper Midwest and probably in eastern North America in general, perennials will likely use no more water than traditional grain crops and the soil’s water balance would not be adversely affected.
These are the kinds of findings emerging on a regular basis and should be duly noted by lawmakers and policy makers plotting the nation’s path to a clean energy future, whether its complying now with the biofuel blending requirements long established by the RFS or supporting the development of advanced biofuels that will power our cars, trucks and aircraft in the decades ahead.