الفهرس 
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Abstract
Algae grown on wastewater treatment plant for bioremediation purpose can be utilized also for biodiesel production. This study investigated the dominant/ predominant species (Euglena sanguinea, Spirulina maxima and Chlorella sp.) which represent 75-80% among other species in the sample, sampled from the domestic wastewater treatment plant during the study period. Their lipids are extracted by standalone solvents (methanol, ethanol and diethyl ether) and solvent mixtures (chloroform-methanol (1:1), hexane-isopropanol (3:2) and hexane-ethanol (1:1)). The current study focused on the capability of ultrasonic-assisted extraction (UAE) and microwave-assisted extraction (MAE) for improving the extracted lipid quantitatively (by calculation of lipid yield gravimetrically) and qualitatively (by analysis of fatty acid composition generated through gas chromatography).The present findings supported that the extracted lipids from the domestic wastewater algal biomass have the suitable fatty acid composition for biodiesel production. MAE is more efficient than UAE and conventional extraction techniques using methanol. It was noted that the maximum lipid content of S. maxima was approximately 38.2±0.65%. A similar high efficiency was obtained for E. sanguinea (36.3±0.37%) and Chlorella sp. (37.9±0.13%) as well. Extraction through MAE and UAE achieved higher lipid yield with reduced reaction times. These results are supported by the cells morphology using scanning electron microscope (SEM) after the extraction process through three techniques. SEM showed that MAE had the most distributive effect for algae cells compared to UAE and conventional reflux. Through the all used extraction techniques, the extracted lipids of wild mixed culture dominated by S. maxima are higher than that of E. sanguinea and Chlorella sp. This can be attributed to the differences in cell size, shape and structure of algae species, and the characteristics of the wastewater. The current study stated that standalone solvents are more efficient than solvent mixtures at extracting total lipids. Applying MAE, methanol produced much higher lipid yields from E. sanguinea (36.3±0.37%) and Chlorella sp. (37.9±0.13%) than other solvents used where ethanol recovered higher lipid yields from S. maxima (43.78±0.15 %). Results indicate that a strong linear relation between the solvent polarity (represented by the dielectric constant) and yield percent. Gas chromatography (GC) analysis is done to identify and quantify the fatty acid of two mixed cultures, under various extraction techniques and solvent systems. Palmitic acid (C16) was the main fatty acid for lipids of Spirulina, Euglena and Chlorella sp. applying the three techniques (with methanol). For S. maxima, E. sanguinea and Chlorella sp., the concentration of saturated fatty acids (SFAs) is higher than the unsaturated fatty acids (USFAs) when UAE was applied. High content of SFAs in algal lipid is desirable for increasing energy and oxidative stability of biodiesel synthesized. According to MAE fatty acid profile resulted by six solvent systems, methanol can extract highest concentration of palmitic acid (45.5%) from Chlorella sp. The highest Palmitic acid percentage of Spirulina lipid (49.54%) is obtained with hexane: ethanol, where Euglena lipid was (48.2%) with chloroform: methanol.