الفهرس 
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Abstract
This investigation aims to achieve two main targets:-
1. To contribute to the efforts that are made to mitigate carbon dioxide concentration in the atmosphere. This gas is an important component of greenhouse gases that impart to the environmental problem known as global warming.
2. To contribute to the work of other investigators searching for subutitutes of petroleum refinery products from renewable sources.
To achive these two targets, three microalgal species:- Chlorella vulgaris and Scenedesmus obliquus (green algae), Spirulina platensis (blue algae) were cultivated and fed with CO2 in different concentrations.
Each type of the three species of microalgae were used seperatly in the closed system with different concentration of CO2 as follows :-
Group I: - included culture of the three micoalgae with air only (using air compressor).
Group II: - included culture of the three micoalgae with 2% CO2 (using air compressor and CO2)
Group III: - included culture of the three micoalgae with 5% CO2 (using air compressor and CO2).
Group IV: - included culture of the three micoalgae with 10% CO2 (using air compressor and CO2).
• Biomass collection:-
At the end of cultivation of the three types of microalgae the biomass was collected, dried and then weighed. It was found that Spirulina platensis yields high biomass during cultivation with 2% CO2 concentration and air only, while Chlorella vulgaris yields high biomass during cultivation with 5% CO2 concentration and Scenedesmus obliquus yields high biomass during cultivation with 10% CO2 concentration.
• Biodiesel production:-
The oil extracted from each type of microalgae (separately) was subjected to transesterification to obtain the biodiesel results obtained showed that Spirulina platensis yields high biodiesel during cultivation with air only and 2% CO2 concentration,but Chlorella vulgaris yields high biodiesel during cultivation with 5% CO2 concentration and Scenedesmus obliquus yields high biodiesel during cultivation with 10% CO2 concentration.
It was worthy to determine the physico–chemical characteristics of the biodiesel obtained from the species Scenedesmus obliquus that gave the higher yield. from the present results it can be concluded that flash point, kinematic viscosity at 40 ºC, cetan number, cloud point, pour point, heating value and density of the biodiesel obtained fit the international specifications, and are superior to that of petroleum diesel, especially in cetane number and flash point.