Iowa State researchers study effects of cellulosic feedstocks for ethanol production
February 25th, 2021
AMES, Iowa – A new Iowa State University study considers an increase of growing cellulosic feedstocks for ethanol production and the effect it could have on land use and water quality, specifically nitrogen loss, in the Mississippi Atchafalaya River Basin.
Kelsie Ferin, a graduate student in agronomy, conducted a modeling study based on the Renewable Fuel Standard (RFS2) mandate which set a goal to include 16 billion gallons of cellulosic ethanol production into gasoline by 2022. To assess the impact of this mandate, she ran scenarios to predict how planting cellulosic feedstocks would have on the environment and the economy.
Ferin’s advisor, Andy VanLoocke, associate professor in agronomy, also took part in the research, which was published recently in the peer-reviewed journal, Environmental Science and Technology.
“The fundamental question is if we grew particular crops in the Mississippi River Basin, would we change the amount of nitrogen that we lose in the Gulf of Mexico?” VanLooke said.
Three scenarios were tested and analyzed for nitrogen loss: A baseline, which reflects ethanol production of 7.5 billion gallons of 100% corn grain-based ethanol produced prior to the renewable fuel standard; a mid-production scenario, producing 15 billion gallons of corn grain ethanol; and a high production example, producing 16 billion gallons of cellulosic ethanol using corn stover, miscanthus and switchgrass.
“The amount of ethanol production went from 7.5 billion gallons of corn grain ethanol in the baseline to 15 billion gallons of corn grain ethanol in the scenarios,” Ferin said. “Our modeling simulations resulted in the 15 billion gallons corn grain ethanol scenario having 8% greater nitrogen loss relative to the baseline. For the full corn grain and cellulosic ethanol scenario, it was between 16-17% more nitrogen loss.”
Miscanthus and switchgrass are perennial grasses capable of reducing nitrogen loss from soil and water when incorporated into the current landscape. However, this benefit is greater when these grasses are replacing active cropland (i.e. corn and soybean production area) rather than on idle cropland.
“Based on current markets, growing them on the active corn and soybean acres wouldn’t turn a profit based on the economic model,” VanLoocke said. “If we did plant the perennial grasses on active cropland, we would improve the water quality in our scenarios. It just didn’t make enough money to do so.”
A sensitivity study was also conducted where 100% of the cellulosic ethanol was produced with miscanthus and switchgrass – no corn stover. In this case, the economic model determined 68% would be planted on active cropland, resulting in a 10% decrease in nitrogen loss relative to the corn grain and cellulosic ethanol production scenario.
“There’s no mandate that says 100% [of cellulosic ethanol] will come from miscanthus or switchgrass. We just wanted to assess how big of an impact they could have on our current landscape,” Ferin said.
Environmentally speaking, it is better to plant miscanthus and switchgrass on active cropland. Economically speaking, Ferin said the research showed it is more profitable to use the active cropland for corn and soybeans.
Ferin and VanLoocke’s research was supported by the new Department of Energy Bioenergy Research Center - Center for Advanced Bioenergy and Bioproducts Innovation (CABBI), which focuses on increasing the value of bioenergy crops with a “plants as factories” approach.
Ferin and VanLoocke said if CABBI is successful, crops like miscanthus and switchgrass containing valuable oils, fatty acids and other bioproducts in their stems could be extracted and sold separately from the lower-value cellulosic biomass. There is potential to grow more cellulosic feedstocks if they can be utilized for products other than ethanol.
“There needs to be other innovations around cellulosic feedstocks to get over the economic hump,” VanLoocke said. “The future of cellulosic ethanol depends on innovations, like finding more value within the crops that we are growing so we can market to multiple markets and be more diverse.”