|M.Sc Student||Abutayeh Hiba|
|Subject||Bioethanol Production from Agriculture Wastes|
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Carlos Dosoretz|
|Dr. Hassan Azaiza|
|Full Thesis text - in Hebrew|
Olive oil production in the Middle East is an important agricultural industry which produces large quantities of olive mill solid wastes (OMSW). OMSW as a waste constitutes an environmental nuisance and as such is considered as cheap raw material for producing of second generation bioethanol. Global interest in ethanol is increasing and it accounts for more than 94% of the bio-fuel global production.
Lignocellulose degradation produces hexoses and pentoses. The most efficient microorganisms producing ethanol from glucose are unable to utilize pentoses. Even engineered strains of Saccharomyces cerevisiae and Escherichia coli which utilize pentoses but their effectiveness are still limited.
The main objective of this study was to search for endogenous microorganisms in the OMSW which have great potential of fermenting sugars from OMSW.
Yeasts were isolated and identified as Issatchenkia orientalis, and Pichia galeiformis/manshurica. The two strains were characterized for their ability to produce ethanol from pentoses and hexoses and OMSW hydrolysate, and compared to the baker yeast, S. cerevisiae.
As part of improving the fermentation process of the three yeasts in the hydrolysate medium, the strains were adapted to OMSW hydrolysate. The adaptation displayed a positive impact on the fermentation process. In terms of xylose utilization and ethanol production, all three strains were able to utilize xylose and produce xylitol but no ethanol production. I. orientalis showed better kinetics and less sensitivity to xylose repression to ethanol production process from glucose compared to the reference yeast S. cerevisiae and the P. galeiformis/manshurica strain.
There was a positive effect on yeast growth after the detoxification of OMSW hydrolysate using activated carbon at 60°C for 60 min incubation. Pretreatment was performed using 2% sulfuric acid at 100°C, where several inhibitors were detected including furfural, HMF, formic acid and acetic acid.
Separate Hydrolysis and Fermentation (SHF) process on hydrolysate undergo detoxification, and I. orientalis showed the best efficiency in producing bioethanol on glucose. Using Simultaneous Saccharification and Fermentation (SSF) process after pretreatment of OMSW, ethanol yield was 3 g/100 g dry OMSW (for the three yeasts). Furfural up to a concentration of 2 g/l didn’t inhibit fermentation and bioethanol production.
OMSW seems to be a potential cheap raw material for bioethanol production, but inferior to other agriculture wastes because of lower structural hydrocarbon content and higher lignin content. In order to have OMSW economically feasible for bioethanol production there is need to obtain yeasts able to utilize both pentoses and hexoses.