الفهرس 
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Abstract
The present work was designed to investigate the production of
bioethanol from agricultural feedstock (sugarcane bagasse and potato
peels) using Zymomonas mobilis ATCC 29191 and Saccharomyces
cerevisiae ATCC 7754, exposed to different doses of gamma irradiation
(0, 0.1, 0.3, 0.5, 1 and 1.5 kGy). The effect of different pretreatments of
sugarcane bagasse and potato peels on resulting sugars (initial sugars),
which were later fermented to bioethanol, was also tested and compared
to non-hydrolyzed feedstock. These pretreatments were done as follows:
a) Hydrolysis of sugarcane bagasse and potato peels with dilute acid at
two concentrations of sulphuric acid (H2SO4), 2 and 6 % (v/v),
running at 100 and 120°C for 30 and 60 min of retention time.
b) Exposing both feedstock to gamma rays (at 25, 50 and 75 kGy) as
either substitute to acid treatment or combined with acid to obtain
more sugar in hydrolyzate for the bioethanol production.
c) Use of co-culture of Sacch. cerevisiae and Z. mobilis, to increase the
sugar conversion efficiency.
Results could be summarized as follows:
1. Irradiation of Z. mobilis and Sacch. cerevisiae significantly reduced
the cell counts of both organisms in all treatments, regardless of the
feedstock they grew on.
2. Use of irradiated Z. mobilis on non-hydrolyzed feedstock reduced the
final bioethanol yield produced either from sugarcane bagasse or
potato peels. Sacch. cerevisiae irradiated at 0.3 kGy produced the
highest yield of bioethanol (4.9 g L-1), utilizing about 75.4 % (w/w)
of total sugars on non-hydrolyzed sugarcane bagasse, whereas the
maximum bioethanol obtained from non-hydrolyzed potato peels was
2.4 g L-1, produced by Sacch. cerevisiae irradiated at 0.1 kGy. Total sugars concentration obtained from non-hydrolyzed sugarcane
bagasse and potato peels were 14.2 and 6.7 g L-1, respectively.
3. Results of dilute acid hydrolysis of sugarcane bagasse and potato
peels experiments are summarized as follows:
The highest bioethanol concentration obtained from sugarcane
bagasse was 10.3 g L-1, produced by Sacch. cerevisiae irradiated at
0.3 kGy from hydrolyzate of 2% (v/v) H2SO4 at 120°C for 60 min
treatment. from the same treatment, the highest bioethanol
concentration obtained by Z. mobilis was 4.4 g L-1, when
irradiated at 0.1 kGy. This acid treatment produced 23.7 g L-1 of
sugars from the feedstock.
The highest bioethanol concentration obtained from potato peels
was 7.5 g L-1, produced by Sacch. cerevisiae irradiated at 0.3 kGy
from hydrolyzate of 6% (v/v) H2SO4 at 100°C for 60 min
treatment, compared to 5.7 g L-1 produced by Z. mobilis irradiated
at 0.1 kGy. This treatment produced 24 g L-1 of sugars from the
feedstock.
4. Use the co-culture of Z. mobilis irradiated at 0.1 kGy and Sacch.
cerevisiae irradiated at 0.3 kGy (at ratio 1:1) was tested to produce
bioethanol from both feedstocks, hydrolyzed with different acid
pretreatments. Results showed the following:
Significant increases in the final bioethanol concentration,
conversion coefficient sugar utilizing efficiency and cell counts on
neutralized acid hydrolyzed feedstock were scored.
The highest final bioethanol concentration (11.3 g L-1) was
obtained from sugarcane bagasse hydrolyzed by 2 % (v/v) H2SO4
at 120 °C for 60 min, with the highest sugar utilizing efficiency of
98.7 % (w/w).
from potato peels, the highest final bioethanol concentration was
10.7 g L-1, which was obtained from feedstock hydrolyzed by
6 % (v/v) H2SO4 at 100 °C for 60 min.
5. When feedstock irradiated by γ–rays (0, 25, 50 and 75 kGy),
amounts of bioethanol were higher than these obtained from
non-hydrolyzed feedstock. The highest bioethanol production
obtained by co-culture was 8.2 g L-1 from sugarcane bagasse
irradiated at 75 kGy, compared to 3.5 g L-1 from potato peels
irradiated at 75 kGy.
6. Gamma irradiation was combined with acid hydrolysis treatments,
where both feedstock were irradiated at 0, 25, 50 and 75 kGy, then
followed by hydrolysis with 2 % H2SO4 (v/v) at 120°C for 30 and
60 min in case of sugarcane bagasse, and by 6 % H2SO4 (v/v) at
100 °C for 30 and 60 min, in case of potato peels. The resulted
hydrolyzates were used to produce bioethanol using single and
co-culture cultivation of Z. mobilis irradiated at 0.1 kGy and Sacch.
cerevisiae irradiated at 0.3 kGy. Results indicated the following:
The highest final bioethanol concentration (15.6 g L-1) was
produced by the co-culture cultivation on the acid hydrolyzed
sugarcane bagasse irradiated at 75 kGy with 93.7 % (w/w) of
utilized sugar efficiency.
from potato peels, the highest final bioethanol concentration
(12.1 g L-1) was obtained by co-culture cultivation on the acid
hydrolyzed potato peels irradiated at 75 kGy with 87.6 % (w/w)
of utilized sugar efficiency.
The highest cell counts were recorded by co-culture cultivation
on the acid hydrolyzed sugarcane bagasse and potato peels,
irradiated at 75 kGy (13.6 and 11.8 CFU x 105 ml-1, respectively).
from the above mentioned results, it could be concluded that
feedstock responded differently when treated with dilute acid to release
the sugars in order to ferment them to bioethanol. The best treatment to
produce the outmost of bioethanol was 2 % (v/v) H2SO4 at 120°C for 60
min for sugarcane bagasse, irradiated at 75 kGy, and 6 % (v/v) H2SO4 at
100°C for 60 min for potato peels, irradiated at 75 kGy, which were then
fermented by a co-culture of Z. mobilis irradiated at 0.1 kGy and Sacch.
cerevisiae irradiated at 0.3 kGy.
Results of this study also indicated that the concentration of total
sugars of sugarcane bagasse and potato peels significantly increased due
to dilute acid hydrolysis with or without irradiation of feedstock.
Consequently, utilization of gamma irradiation in the saccharification
stage is an advantage to reduce the cost of bioethanol and utilize the plant
waste with high lignin content.