About the project
Production of ethanol from lignocellulosic materials is a very complex process, which consists of various interdependent steps, such as pretreatment of the raw material, enzymatic hydrolysis of the polysaccharides into sugar monomers, fermentation of the sugars to ethanol, and purification of ethanol. Life cycle assessment (LCA) is a potential tool for comparing and analyzing environmental performance of different pathways for lignocellulosic ethanol as well as finding hot spots for future improvements. Several previous LCA’s have identified the production of cellulase enzymes as a process that have a large impact on overall results, especially regarding energy consumption and greenhouse gas (GHG) emissions.
The aim of the present study was to investigate GHG performance, primary energy use and ethanol production cost from two different process designs regarding cellulase enzymes for lignocellulosic ethanol production: (i) integrated in ethanol plant versus (ii) purchased from a centralized facility. On-site cellulase production in a full-scale bioethanol plant was modelled together with the whole ethanol production process, and the economic impact of the enzyme fermentation step on the ethanol production cost was assessed.
The results show that primary energy efficiency is somewhat higher in the cases with integrated enzyme production, but no major differences are identified. Regarding GHG emissions, results show that by using part of the lignocellulosic feedstock for enzyme production by the microorganism, emissions from bioethanol in a well-to-wheel perspective can be reduced significantly, compared to a scenario using purchased enzymes from a centralized facility. Information regarding purchased enzymes is scarce and data is connected to large uncertainties. The sensitivity analysis shows that assumptions regarding purchased enzymes, such as dosage and type of energy utilized in production, largely affect the comparison with an integrated enzyme production approach.
ResultsLife cycle assessment and techno-economical analysis of on-site enzyme production in 2nd generation bioethanol
Ola Wallberg, Lund University
Zsolt Barta, Pål Börjesson and Johanna Olofsson, Lund University
September 2014 - April 2015
Total project cost
220 000 SEK
The f3 partners