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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 122 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. |