Environmental sustainability of bioethanol production from wheat straw in the UK

Abstract

A UK-based environmental sustainability study on bioethanol production from wheat straw was conducted using a Life Cycle Assessment (LCA) approach. Five pathways with leading pretreatment technologies (dilute acid, steam explosion with and without catalyst, liquid hot water, and wet oxidation) were modelled using process simulation software AspenPlus™, and their advantages and disadvantages were evaluated from an environmental perspective. In a contribution analysis of the environmental profiles for the near-term prospective scenarios, results indicated that the enzyme is a main contributor in all pathways. In addition to enzyme production, acid catalyst and base for its subsequent neutralisation also cause significant environmental burdens for dilute acid and steam explosion with catalyst pathways. By comparing the five wheat straw production pathways with petrol, it was suggested that those using pretreatment with steam explosion, liquid hot water and wet oxidation can be environmentally favourable over petrol. However, a sensitivity analysis conducted by expanding the ethanol system boundary to include the consequential effects of removing wheat straw from the field, suggested an increase in the overall environmental burdens of ethanol life cycles but certain wheat straw ethanol pathway (i.e. with steam explosion pretreatment) still remain environmentally favourable over petrol.