U of Ill. economists analyze weedy invaders-to-energy concept

By Sue Retka Schill | December 11, 2013

Could weeds, particularly problematic invasive ones, become a reliable cellulosic ethanol feedstock? It isn’t likely in the near-term due to a fundamental dilemma, suggest a group of University of Illinois researchers. “Biorefineries require a consistent and abundant source of biomass to operate profitably. Landowners and conservationists, on the other hand, primarily seek to eradicate invaders permanently,” they wrote in a recent FarmDocDaily post, “Turning Weeds Into Ethanol – Why Not?”

Most of the discussion to date in the literature is about the concern that certain nonnative bioenergy feedstocks could become invasive, but others have suggested biofuel producers be rewarded for helping eradicate current invasive species.

University of Illinois ag economists Lauren Quinn, Elise Scott and Bryan Endres examined the issue in a paper published last month that looked at the economic constraints.    

Focusing on cellulosic ethanol conversion technologies, one constraint would be specificity regarding cell wall composition for those biorefineries in development planning to use corn stover. “Invaders - whose chemical composition is likely untested - would not necessarily be acceptable at cellulosic biorefineries. For those cellulosic biorefineries capable of converting an array of different feedstocks, the distance weedy or invasive biomass would have to travel to the appropriate biorefinery would, in most cases, be prohibitively expensive.” The volume of materials required, plus the cost of labor and processing would also likely be prohibitive.

There may also be ecological constraints, they suggest, with the potential for landscape disturbance to create further problems. Restoration costs might negate any potential profits, they add. “One study has estimated that control of giant reed in California riparian areas and subsequent restoration can total $25,000 per acre (0.4 ha). The estimated sale price of giant reed biomass for conversion into ethanol at $800 per acre simply would not justify the cost of its removal without further incentives.”

Typical state and federal noxious weed regulations would also need to be adapted, since many prohibit the sale of materials on the noxious weed lists, restricting their transport as well.

Biomass combustion may be the better use, but presents its own challenges, with the uncertain future of how regulators will ultimately view the greenhouse gas reduction benefits.

“Perhaps as the biomass-to-ethanol industry matures over the next half century, technical innovation may reduce the currently insurmountable logistical and economic concerns associated with utilizing existing invasive feedstocks for viable sources of liquid fuel,” the Illinois researchers conclude. “In the meantime, however, this concept of invaders-to-energy currently tossed about in policy discussion warrants careful scrutiny grounded in economic, ecological, and legal aspects of the bioenergy supply chain.”