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Carbon dioxide sequestration by microalgae is receiving increased attention in alternative impact of increasing CO2 in the atmosphere. For this study, we have chosen three different microalgae such as Chlorococcum humicola, Chlorella vulgaris and Scenedesmus quadricauda were treated with 3 W/m2 UV-B radiation in different time durations (10, 15, 30, 45 and 60 min) and supplemented with bold basal medium. Parameters such as Total Chlorophyll, protein, Carbohydrate, and CO2 fixation rate were determined. Based on the parameters Scenedesmus quadricauda is used for carbon sequestration study. Different concentrations of sodium bicarbonate (0.2%–1%) were supplemented to bold basal medium for carbon utilization it can act as an alternative source of atmospheric CO2. In this maximum amount of chlorophyll content were observed in 0.6% of Sodium bicarbonate. The uttermost amount of CO2 fixation rate and lipid content was recorded at 0.4% sodium bicarbonate concentration. Finally, the result indicated that Scenedesmus quadricauda could be used for CO2 mitigation and having a rich source of polyunsaturated fatty acid. Further urea and glucose in the media positively influence growth and CO2 fixation rate of micro algae. These carbon and PUFA rich microalgae can be used as dietary feed fish usually obtain necessary nutrients via bioaccumulation through the food chain. Thus, this study proves to be an encouraging source of discovery of alternating the dietary source for fish and also helping in carbon utilization process in a natural way. Keywords: Carbon sequestration, Microalgae, Scenedesmus quadricauda, PUFA, CO2 Fixation

AA5083 is an alloy of military-grade aluminum used to make lightweight combat vehicles. Combining this material with traditional welding methods results in the formation of grain agglomerations, alloy separation, porosity, and pores. To overcome these shortcomings, Friction stir welding was utilized. In this work, the problems arising from friction stir welding are reduced by performing the process underwater. A relative study was also conducted to determine the impact of various tool pin profiles. particularly straight hexagonal, straight cylindrical, straight threaded, and tapered cylindrical. Friction stir welding and Underwater friction stir welding were used for welding Aluminium alloy AA5083 alloys of 150 x100 × 6 mm, constant tool rotational speed of 1200 rpm, tool transverse speed of 40 mm/min, and tool tilt angle of 0°. This study revealed that the straight hexagonal pin produced joint in an underwater cooling medium had a greater tensile strength (UTS) of 295 MPa and a joint efficiency of 78 %.