Reducing Highway Runoff Pollution and Producing A Low-Cost Biorefinery Feedstock

Abstract

The emerging bioeconomy can offer climate change mitigation, energy security and independence, and rural economic development. Cellulosic ethanol can alleviate economic dependence on petroleum-derived fuels. Cellulosic ethanol biorefineries are economically hindered by complex conversion processes, which contribute to significant capital investment, and high feedstock costs; both of which contribute to significant operating expenses. In this study, a hypothesized cellulosic ethanol biorefinery, located in Centralia, Washington, is modeled to convert a 250,000 oven dry tons (ODT) of cellulosic biomass, hybrid poplar, into ethanol annually. This study applies integrates two approaches to reduce operating and capital costs of the proposed biorefinery with the goal of producing an economically competitive product. Marginal land on roadsides can potentially produce a valuable agronomic product, hybrid poplar, that can be transported to a biorefinery for conversion to ethanol. Poplar production on roadsides can be achieved at a lower cost than traditionally poplar plantations because other parties are incentivized to manage roadside poplar for the valuable ecosystem services it provides. This research shows that combining roadside poplar with traditional dedicated poplar feedstocks can reduce the feedstock cost of the biorefinery from $74.35/ODT to $69.35/ODT. Strategic design and management of roadside poplar, in the form of vegetated filter strips (VFS), can provide valuable ecosystem services. VFSs have been shown to reduce the concentration of pollutants in runoff. Highway runoff pollution is responsible for damaging many roadside ecosystems. This analysis finds that implementing roadside VFSs in Western Washington can reduce 25% of TSS, copper, and zinc, 20% of phosphorus and nitrogen, and 20% of lead discharges from urban roadways in highly sensitive aquatic areas and 40% of TSS, copper, and zinc, 15% of phosphorus and nitrogen, and 30% of lead discharges from rural roadways in highly sensitive aquatic areas. Feedstock cost reduction can be achieved by displacing high-cost dedicated poplar resources with residual poplar resources and poplar resources that provide ecosystem services. Capital costs can be reduced by constructing a biorefinery around a pre-existent powerplant, omitting the need for certain equipment to be newly constructed. This research found that these integrated approaches of cost reduction can reduce the minimum ethanol selling price (MESP) of a cellulosic ethanol biorefinery from $4.15/gallon to $2.89/gallon.