Design and operation of a bench-scale process development unit for the production of ethanol from lignocellulosics

Eva Palmqvist, Bärbel Hahn-Hägerdal, Mats Galbe, Mats Larsson, Kerstin Stenberg, Zsolt Szengyel, Charlotte Tengborg, Guido Zacchi

Research output: Contribution to journalArticle

114 Citations (Scopus)


A bench-scale unit for the development of an enzymatic process for the bioconversion of lignocellulosics to ethanol has been used to study the recycling of waste-water streams to minimize fresh-water requirements and reduce effluent streams. Willow, after impregnation with sulphur dioxide, was sream-pretreated, enzymatically hydrolysed, and the sugars produced were fermented using S. cerevisiae. The fermentation broth was distilled and the stillage was fractionated by evaporation into six separate condensate fractions and a residue. The overall yield of ethanol from willow was 65% of the theoretical yield based on total fermentable sugars. The inhibitory effect of the evaporation condensates was assessed by fermentation using S. cerevisiae. The non-volatile residue of the stillage was found to be inhibitory to fermentation. The ethanol yield decreased from 0.37 g/g in a pure sugar reference to 0.31 g/g in the residue and the average ethanol fermentation rate decreased from 6.3 g/(lh) to 2.7 g/(l h), respectively. The evaporation condensates, containing the volatile components, showed no negative effects on fermentation. The intermediate evaporation condensate fractions, fractions 4 and 5, had the lowest chemical oxygen demand (COD), 1560 and 1120 mg/l, compared with 33300 mg/l for the stillage. Therefore, these fractions can be released directly into the effluent without further treatment.

Original languageEnglish
Pages (from-to)171-179
Number of pages9
JournalBioresource Technology
Issue number2
Publication statusPublished - Nov 1 1996


  • Enzymatic process
  • Ethanol production
  • Inhibitors
  • Lignocellulosics
  • Steam treatment
  • Waste-water recycling
  • Willow

ASJC Scopus subject areas

  • Bioengineering
  • Environmental Engineering
  • Renewable Energy, Sustainability and the Environment
  • Waste Management and Disposal

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