Comparison of Pretreatment Methods for Wheat Straw Densification by Life Cycle Assessment Study

Abstract

Abstract. Compaction and pelletization processes increase the bulk density and energy density of biomass, making it easy to handle, transport, and utilize. Abundant amounts of wheat straw biomass are produced every year. This article presents a life cycle assessment (LCA) study to compare five different pretreatment methods during wheat straw pelletization. The system boundary was defined from a wheat straw bale (from field production) to transporting pellets to the customer. Steam explosion (SE), microwave alkaline (MA), binder addition (BD), radio frequency alkaline (RF), and torrefaction (TF) as well as no pretreatment (base case) are potential pretreatment methods prior to pelletization. SimaPro software incorporating the Ecoinvent database and literature data were used to conduct this LCA study. The environmental impact of each pretreatment method was evaluated in terms of global warming potential, acidification, eutrophication, human toxicity, marine aquatic ecotoxicity, ozone layer depletion, abiotic depletion, freshwater aquatic ecotoxicity, photochemical oxidation, terrestrial ecotoxicity, and non-renewable energy use. The results revealed that TF and BD, especially involving the addition of wood residue, had lower environmental impacts compared to the other pretreatment methods including the base case. The SE and RF pretreatment methods had more negative environmental impacts compared to the other pretreatment methods including the base case. All pretreatment options except SE can reduce the global warming potential and human toxicity. A densification system involving BD, TF, and MA can conserve non-renewable energy resources compared to the other pretreatment options.