title: Integrating enzyme fermentation in lignocellulosic ethanol production: life-cycle assessment and techno-economic analysis.
abstract: BACKGROUND
  Cellulase enzymes have been reported to contribute with a significant share of the total costs and greenhouse gas emissions of lignocellulosic ethanol production today. A potential future alternative to purchasing enzymes from an off-site manufacturer is to integrate enzyme and ethanol production, using microorganisms and part of the lignocellulosic material as feedstock for enzymes. This study modelled two such integrated process designs for ethanol from logging residues from spruce production, and compared it to an off-site case based on existing data regarding purchased enzymes. Greenhouse gas emissions and primary energy balances were studied in a life-cycle assessment, and cost performance in a techno-economic analysis.
  
  
  RESULTS
  The base case scenario suggests that greenhouse gas emissions per MJ of ethanol could be significantly lower in the integrated cases than in the off-site case. However, the difference between the integrated and off-site cases is reduced with alternative assumptions regarding enzyme dosage and the environmental impact of the purchased enzymes. The comparison of primary energy balances did not show any significant difference between the cases. The minimum ethanol selling price, to reach break-even costs, was from 0.568 to 0.622 EUR L-1for the integrated cases, as compared to 0.581 EUR L-1for the off-site case.
  
  
  CONCLUSIONS
  An integrated process design could reduce greenhouse gas emissions from lignocellulose-based ethanol production, and the cost of an integrated process could be comparable to purchasing enzymes produced off-site. This study focused on the environmental and economic assessment of an integrated process, and in order to strengthen the comparison to the off-site case, more detailed and updated data regarding industrial off-site enzyme production are especially important.
authors.affiliation: Division of Environmental and Energy Systems Studies, Department of Technology and Society, Lund University, John Ericssons väg 1, 22363 Lund, Sweden.
authors.forename: Johanna
authors.identifier: 0000-0001-7215-4162
authors.initials: J
authors.lastname: Olofsson
authors.affiliation: Department of Applied Biotechnology and Food Science, Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and Economics, Muegyetem rkp. 3, Budapest, 1111 Hungary.
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Barta
authors.affiliation: Division of Environmental and Energy Systems Studies, Department of Technology and Society, Lund University, John Ericssons väg 1, 22363 Lund, Sweden.
authors.forename: Pål
authors.initials: P
authors.lastname: Börjesson
authors.affiliation: Department of Chemical Engineering, Lund University, Naturvetarvägen 14, 22362 Lund, Sweden.
authors.forename: Ola
authors.initials: O
authors.lastname: Wallberg
keywords: Bioethanol; Cellulases; Greenhouse gases; LCA; Off-site; On-site; Process economics; Second generation (2G)