The Importance of Water, Climate Change, and Water Policy for Bioethanol Derived from Hybrid Poplar (Populus spp.) in Washington State

Abstract

Biofuels outperform fossil fuels on many environmental indicators, except for water consumption. With climate change, shifting water resource availability may affect the feasibility of growing feedstock for biofuel refineries in certain locations. In this research, water consumption was analyzed for bioethanol production from cradle to gate, using hybrid poplar (Populus spp.) feedstock and an acetogen pathway conversion process. Volumetric water consumption was quantified using the water footprint methodology by Hoekstra et al. (2011). The water footprint for two hypothetical biorefineries near Mount Vernon, WA and Spokane, were analyzed for rainfed and irrigated feedstock in three crop yield scenarios under current climate conditions and under two climate change scenarios. Results show that water use for bioenergy from hybrid poplar in Washington State ranges from 10-70 m3/GJ, which is lower than the United States average and on the small end of the range for bioenergy (10-250 m3/GJ). Results vary by climate and crop production, with the rainfed crop using 30% less water than the irrigated crop. The proportion of green, blue and grey water footprints varied for each site as well, with the Mount Vernon site’s footprint dominated by green water (precipitation) and the Spokane site’s footprint dominated by blue water (irrigation). Climate scenarios show larger water footprints and increased water stress for the hot/dry scenario. In Washington State, there are limited opportunities to obtain uninterruptible senior water rights inexpensively, so Washington water code constrains water availability for both irrigation and biorefinery conversion process water. Rain-fed crops or crops irrigated with reclaimed water avoid some of these policy constraints. The water policy landscape is highly complex, and water policy objectives are often different from the objectives of renewable fuel, land use, or air quality policies. These policies are highly site specific, and need to be evaluated for each potential production site.