الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
This study aims to produce bioethanol by using the microalgal species,
Chlorella vulgaris. Depending on the ability of microalgae to grow by using
simple requirements and their photo conversion efficiency and can synthesize
and accumulate large quantities of carbohydrate biomass for bioethanol
production. This research aimed to study the effect of different media
compositions and then evaluate the influence of different culture conditions
on the growth of microalga Chlorella vulgaris to optimize the best culture
condition for maximum biomass production. Then studied different
hydrolysis methods to get the highest amount of carbohydrates and reducing
sugars. Fermentation of the hydrolyzed samples by using Saccharomyces
cerevisiae which convert reducing sugars to bioethanol.
Algae are simple organisms containing chlorophyll and they use light
for photosynthesis. Algae can grow phototrophically or heterotrophically.
Phototrophic algae convert carbon dioxide in atmosphere to organic
compounds such as carbohydrate. Conversely, heterotrophic algae continue
their development by utilizing organic carbon sources (Wen and Chen,
2003). Algae can grow in every season and everywhere such as salty waters,
fresh waters and brackish area etc. However for their cultivation, generally
the most widely used are growth systems like open ponds and closed
photobioreactors systems are used for large scale production.
Effect of different nutrient composition on growth pattern forms to
select the best medium for Chlorella vulgaris. Five culture media (BG-11,
Modified Bold Basal, Chu-10, Zarrouk’s and Khul) were carried out to select
a suitable medium for best growth of Chlorella vulgaris.
Summary
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Estimation of growth through Optical density (OD), cell count (CC)
and Chlorophyll content of Chlorella vulgaris in different culture conditions,
in spite of all culture conditions started with slightly similar initial inocula.
Among all five culture conditions, the obtained results clearly indicated that
the best growth of Chlorella vulgaris was obtained in modified Chu-10
medium as compared to those in other media.
Then we study the effects of culture conditions such as Nitrogen source,
pH values, light source and aeration on the growth rate by using Chu-10
modified medium. This help to detect the best growth factors that give the
maximum growth rate of Chlorella vulgaris, to get the maximum amount of
biomass that would be used as a raw biomass in bioethanol production.
Growth media formulations were varied to optimize the growth media
composition for maximized algal biomass production. The effects of culture
conditions as Nitrogen source, pH values, light source and Aeration on growth
and the contents of chlorophyll a, chlorophyll b, of Chlorella vulgaris were
determined. The best Nitrogen source was ammonium nitrate (NH4NO3) and
importance of aeration and natural light exposure for maximum growth of
algal biomass.
Bioethanol production from algae requires four major unit operations
including: pretreatment, hydrolysis, fermentation and distillation. Because
algal biomass has its own characteristics, such as soft organization and high
moisture content, the pretreatment of the algae is easier than that of
lignocellulosic biomasses. Physical, chemical and biological processes have
been used for pretreatment of algal materials. The goal of these experiments
was to determine the optimal pretreatment process for the extraction of
reducing sugars to facilitate the fermentation and the simultaneous production
of bioethanol from the microalga Chlorella vulgaris. Concerning chemical
pretreatments, the maximum reducing sugar concentration from Chlorella
vulgaris biomass after acidic pretreatment was recorded when the biomass
pretreated with 2% sulfuric acid (H2SO4) at 120 °C for 30 min and bioethanol
released from the biomass was increased gradually from the 1st day (2.79 g
/100 g dried biomass) to the 5th day (14.32 g /100 g dried biomass). While
lower carbohydrate and reducing sugars were obtained as well as lower
bioethanol production composed with those produced from acid pretreatment.
Using physical pretreatment, the use of microwave induced lower
carbohydrate and reducing sugars as well as produced bioethanol
concentration from Chlorella vulgaris biomass Ultrasound pretreatment gave
results represented by higher carbohydrate, reducing sugars and consequently
bioethanol products.
At biological pretreatment, work was done on two biomass samples.
The first sample was treated with 1% NaOH for one hr. before the biological
pretreatment with Aspergillus niger. While the second biomass sample had no
treatments.
At the 1% NaOH pretreated samples, the highest sugar was released on
the maximum amount of reducing sugars at the 1st day 6.996 (g /100 g dried
biomass) which increased by Aspergillus niger gradually till reaching 16.052
(g /100 g dried biomass) at the 6th day. While the maximum amount of
bioethanol at the 1st day 10.95 (g /100 g dried biomass) which increased
gradually till reaching 16.77 (g /100 g dried biomass) at the 4th day. While the
1% NaOH untreated samples, the highest sugar was released on 6th day of
saccharification. The Chlorella vulgaris biomass at the synthetic media
released the maximum amount of reducing sugars 8.552 (g /100 g dried
biomass) at the 1st day which increased by Aspergillus niger gradually till
reaching (19.835 g /100 g dried biomass) at the 6th day and the produced
bioethanol increased at the synthetic media to record the maximum amount of
bioethanol (3.68 g /100 g dried biomass) at the 1st day which increased
gradually till reaching (25.20 g /100 g dried biomass) at the 5th day.
The biological treatment was the best method tested for cellular
disruption and sugar extraction. At this study we used Saccharomyces
cerevisiae for fermentation. We detected the reducing sugar produced and the
released bioethanol by using spectrophotometric methods.
Pretreatment is estimated to be the most costly step in the production of
algal bioethanol. Such a pretreatment method must be simple and must avoid
high consumption of expensive chemicals and high energy demands.
Furthermore, polysaccharides from the algal biomass should be hydrolyzed
directly without sugar degradation, which might produce fermentation
inhibitors.
Among the different methods, the use of dilute sulfuric acid is currently
one of the most effective and includes the most promising technologies for
industrial applications. To further decrease the cost of the pretreatment step in
the algae feedstocks conversion to ethanol, it is essential to minimize sugar
losses, to increase solids concentration as high as possible and to keep low
reactors and associated equipment costs. Additionally, from a basic research
point of view, one approach that is receiving more attention is the study of the
effects of pretreatment at a more fundamental level. The composition of algal
cell wall is very complex and research at cellular, ultrastructural and even
molecular levels could contribute to understand the diverse catalytic reactions
acting on biomass as well as the consequences of pretreatments. This
knowledge should be applied to achieve an integrated and efficient biomass
conversion process to ethanol.
As a recommendation; because microalgae contain high capacity of
vegetable oils, biodiesel production from microalgae still the most ideal main
product. However, the diversity of biofuels production from microalgae is
necessary to improve the overall energy balance. One of the successful
examples is to use the microalgae biomass residue (after lipid extraction) for
bioethanol production because high concentrations of carbohydrates still
remain in the biomass. This is a good strategy in reutilizing the waste to
produce another source of energy. Useful chemical can be extracted from the
algae and residue contained rich cellulose that can be utilized as raw material
for bioethanol production. Even after the ethanol production, the leftover
residue still contains good amount of organic matter and useful minerals and
eventually could be used as biofertilizer.