Bioenergy-Fermentation Wood Chemistry PSE 406 Bioenergy-Fermentation

Agenda What is fermentation? Fermentation inhibitors Separate Hydrolysis and Fermentation (SHF) and Simultaneous Saccharification and Fermentation (SSF)

Bioconversion of biomass to ethanol (pretreatment) Liquid phase Sugars Ethanol Pretreatment Fermentation Biomass Lignin Recovery Solid phase Cellulose Hydrolysis Fermentation Sugars Ethanol

Fermentation Defined as: Cellular metabolism under anaerobic conditions (absence of oxygen) for the production of energy and metabolic intermediates Many organisms can “ferment” (i.e., grow anaerobically) Not all produce ethanol as an end-product of fermentation Butanol Acetic acid Propionic acid Lactic acid

Strain selection Choice of microorganism for ethanol production has traditionally been a Yeast Yeast: Single cell microorganism Fungi Facultative anaerobe Most common industrial fermenter is Saccharomyces cerevisiae (baker’s or brewer’s yeast) Why?

Why S. cerevisiae? Has been selected over thousands of years High ethanol yield and productivity Relatively simple to culture G.R.A.S organism Robust: High ethanol tolerance Resistant to inhibitors

Fermentation (1)

Fermentation (2) Conversion factor 0.51 1g/L of glucose: 0.51g/L ethanol (maximum)

Inhibitors 5 groups of inhibitors Released during pretreatment and hydrolysis Acetic acid and extractives By-products of pretreatment and hydrolysis HMFs and furfurals, formic acid Lignin degradation products Aromatic compounds Fermentation products Ethanol, acetic acid, glycerol, lactic acid Metals released from equipment

HMFs and Furfurals Reactions occuring during hydrolysis of lignocellulosic materials. The furan derivatives and phenolic compounds will react further to form some polymeric material

HMFs, Furfurals Figure 29 Utilisation of 5-HMF and furfurals during SSF at various solid consistencies by Saccharomyces cerevisiae. Error bars represent the range of duplicate experiments.

Experimental Corn fibre Hydrolysis SHF Corn fibre SSF Steam Explosion (solid +liquid fraction) Corn fibre Hydrolysis Fermentation SHF 50°C, pH 4.8 48 hours 30°C, pH 6 12 hours Steam Explosion (solid +liquid fraction) Corn fibre SSF 37°C, pH 5 24 hours

Pros and cons of SHF and SSF Separate temp. for each step (hydrolysis 50°C, fermentation 30°C) Possibility of yeast and enzyme recovery Cons Requires two sets of fermenters End-product inhibition Pros Minimized end-product inhibition Requires only one set of fermenters Cons Difficulties in recovery and yeast and enzyme recycling Temperature/pH compromise (37°C)

SHF versus SSF SSF (91%-6C)-24 hours Corn fibre SHF (75%-6C)-60 hours Steam Explosion (solid +liquid fraction) SSF (91%-6C)-24 hours Corn fibre 95% SHF (75%-6C)-60 hours

SSF versus SHF Hexose consumption and ethanol production during SSF and SHF at 37°C with 10, 20 and 40 FPU g cellulose-1 of the combined water soluble and insoluble fractions at 8% (w/v) consistency solids at an IU:FPU ratio of 2:1. Error bars represent the range of duplicate experiments. The numbers in the legend show the relative ethanol yield (%) and ethanol productivity (g L-1 h-1). The ethanol productivity was calculated as ethanol produced (g L-1) within first 12 hours for SSF and 12+48 hours for SHF