Economics of growing poplar for the dual purpose of biorefinery feedstock and wastewater treatment

Poplar is recognized as an excellent biorefinery feedstock because of year-round availability and ease of fractionation. Further, poplar is commonly used to provide ecosystem services such as for riparian buffers or phytoremediation. While biofuels offer many environmental and socioeconomic benefits, commercial scale biorefineries are not prominent in the U.S. in part because of feedstock availability and cost. To reduce feedstock cost, we investigated incorporation of hybrid poplar grown to receive treated municipal wastewater into our supply curves, using a Western Washington location as a case study. We first developed supply curves for purpose-grown hybrid poplar feedstock, a likely biorefinery feedstock for the Pacific Northwest, to supply a biorefinery in Washington State. It was found that there was abundant land within 100 km to grow enough poplar to supply a larger scale biorefinery – as much as 800 Gg per year - and that the plant gate cost of the poplar biomass is in the range of $75 - $85 per Mg feedstock. Most of this land was pastureland, mitigating fuel vs. food concerns. We then incorporated wastewater treatment poplar into the supply curves. The amount of feedstock that could be grown to receive wastewater was limited; approximately 54 Gg per year. However, for a modest sized biorefinery (150 Gg poplar per year) the wastewater treatment poplar provided 36% of the feedstock and reduced the plant gate feedstock cost by 14%. Expanding the use of ecosystem services poplar would enable even large scale biorefineries to see substantial benefits from this lower cost feedstock.