Evaluation of lignocellulosic biomass, pretreatment methods, and microorganisms for industrial production of bioethanol. Part 1

The hydrolysates have been evaluated regarding enzymatic convertibility and inhibitor content. Fermentations have been carnied out using the thermophilic strain Thermoanaerobacter mathranii A3M4 and the mesophilic strain Zymomonas mobilis 39676 (pZB4L). It was seen that T. mathranii A3M4 was capable of converting the xylose in the hydrolysates more effective than Z. mobilis 39676 (pZB4L). On the other hand the experiments showed that a greater fraction of the xylose was converted to ethanol by Zymomonas mobilis 39676 (pZB4L) than by T. mathranii A3M4 - because the morganism also produce acetate and lactate. Furthermore the screening experiments showed a relationship between the applied pretreatment method and the inhibitor level of the resulting hydrolysates. It was shown that hydrolysates produced by steam explosion were more inhibitory towards the fermenting microbial strains than hydrolysates produced by wet oxidation. Both microorganisms had higher ethanol yields on wheat straw hydrolysate than yellow poplar hydrolosate, which - as expected - indicates that fewer inhibitory compounds are generated from wheat straw. It was found that Zymomonas mobilis 39676 (pZB4L) was more affected by inhibitors than the thermophilic strain Thermoanaerobacter mathranii A3M4. Thus the xylose fermentation of Zymomonas mobilis 39676 (pZB4L) decreased dramatically in hydrolysate concentrations above 25% (corresponding to a concentration of 15g-biomass/1 before pretreatment). In general the conducted experiments showed that adaption to the hydrolysates is a importart factor in optimizing fermentations based on lignocellulosic hydrolysates - regardless of the pretreatment method and the choice of fermenting organism. Methods for extraction and purification of the cellulose and hemicellulose fractions conceming structural analysis has been developed and optimized in collaboration with research center RISØ. Furthermore methods has been developed for analyzing extracted and purified carbohydrate: fractions by High Performance Liquid Chromatography (HPLC), methylation analysis and SizeExclusion Chromatography (SEC) with Light _Scattering (LS) detection. A part of there studies has been carried out in an existing project (EFP97 ENS 1383/97-0009), hence the presentation of methods and results has been gathered and presented in the End Report of the EFP97 project. The difference of the two fermentation strategies Simultaneous Saccharification and Fermentation (SSF) and Separate hydrolysis and Fermentation (SHF) has been evaluated on wheat straw hydrolysate using Novozyme and Celluclast enzymes together with the yeast strain Saccharomyces cerevisiae. The hydrolysate was avet oxidized wheat straw produced at RISØ from an initial concentration of 60 g-straw per liter of water. It was shown that there was no difference in the final concentration of ethanol for the two fermentation strategies. However the experiments showed a difference of 35% in the ethanol productivity of the two evaluated systems. SSF was found to be fastest With a productivity of 0.069g-EtOH/1/h compared to the SHF productivity of 0.051g-EtOHl/h