WASHINGTON — Advanced cellulosic biofuels made from switchgrass and leftover corn stalks are dramatically greener than first-generation alternatives made from corn, according to a new analysis commissioned by the Environmental Working Group.
The assessment, which relies on two scientists’ evaluation of the carbon intensity of gasoline and some renewable fuels, could buttress calls to overhaul federal biofuel mandates. On Tuesday, two House Science subcommittees are holding a joint hearing on the federal renewable fuel standard, which obligates refiners to blend biofuels into gasoline.
Refiners have argued the RFS needs a major rewrite, because they are hitting a blend wall where they can no longer incorporate enough ethanol to meet the law’s volume targets without exceeding a 10 percent threshold acceptable for use in all cars and trucks.
In pushing for changes, some oil industry organizations and other groups with a stake in the outcome — including livestock producers and anti-hunger activists — have seized on studies questioning the environmental benefits of traditional corn-based ethanol that currently makes up the bulk of the federal mandate.
The Environmental Working Group paper could add fuel to their argument that the RFS is too reliant on corn-based ethanol, instead of sophisticated next-generation alternatives that have been tougher to commercialize.
“When the renewable fuel standard was established, corn ethanol was touted as being cleaner than gasoline, but 10 years later we know it’s just the opposite,” said Emily Cassidy, an Environmental Working Group research analyst who authored the paper. “It’s time to break up the corn ethanol monopoly to make room for next-generation biofuels that could reduce carbon emissions.”
Supporters of the current law — including Corn Belt lawmakers — note that some of the next-generation biofuels now in production are being manufactured by the same companies that produce traditional ethanol derived from corn.
The corn-based ethanol business can improve the economics of their next-generation biofuels production. Tinkering with the renewable fuel standard to advantage next-generation alternatives at the expense of traditional corn-based biofuels could jeopardize that business model.
But in its paper, EWG argues the traditional ethanol mandate is crowding out next-generation alternatives, rather than sustaining their development. “The limited market for ethanol is saturated by corn ethanol, so elimination of the corn ethanol mandate will create a powerful incentive for greater investment in cellulosic ethanol,” the paper said.
At the same time, the Environmental Working group is pushing Congress to extend the cellulosic biofuels mandate beyond its planned 2022 expiration. And the organization wants lawmakers to require a broader array of environmental effects from various biofuels to be factored into the renewable fuel standard. The mandate should “require consideration of the impacts of biofuels production and use on air, water and soil quality — not just on greenhouse gas emissions.”
The new EWG paper takes such a broad look at gasoline, traditional corn-based ethanol and alternatives made with switchgrass or corn stover. Two University of California at Davis scientists assessed the carbon dioxide emissions associated with those four fuels over their entire life cycle, taking into account not just the initial production and combustion of the fuel but also the land-use changes and other factors that go into the feedstocks used to create it.
Ethanol made from switchgrass — a prairie grass that grows throughout Texas — was found to have a life-cycle carbon intensity that is 47 percent lower than that of gasoline. “Switchgrass ethanol is significantly better for the climate than gasoline or corn ethanol,” the paper said. That exceeds a calculation by the Environmental Protection Agency — with the discrepancy likely explained by a larger estimate of domestic land use changes associated with switchgrass.
But growing switchgrass “provides other environmental benefits,” the EWG paper said, noting that it can be grown on land unsuitable for foo and animal feed crops, can reduce fertilizer pollution in local waterways and can slow soil losses.
Ethanol made from corn stover — the leftover stalks and leaves after a corn field is harvested — was found to have the lowest carbon footprint of all. Because the stover is typically pulled from a field where corn has already been harvested, “it requires no additional land to produce ethanol feedstoc.”
There are other environmental drawbacks to stover, the EWG white paper said, noting that it acts as a barrier to rain and wind, helping to suppress erosion.
The life-cycle carbon intensity of renewable fuels is an important consideration in federal law. Corn-based ethanol is required to produce 20 percent fewer greenhouse gases than gasoline.
The inspector general of the Environmental Protection Agency just launched an investigation into whether EPA has updated its life-cycle analysis of renewable fuels since initial models produced six years ago.