Microalga is one of the most compelling microbial biomasses for biodiesel production. Various pretreatment processes, namely, enzyme treatment, lysis by acid, ultrasonicator, microwaves, autoclave, and 40% NaCl, for nitrogen replete and depleted algal cultures of Nannochloropsis oculata had been carried out to check the most feasible and effective technique to disrupt cells for procuring lipids, for which concentrations were determined. Fatty acid composition, essential functional groups, and cell disruption were analyzed by GC-MS, FT-IR Spectroscopy, and Nile Red fluorescent microscopy, respectively. The present investigation showed that lipid yield was higher in nitrogen depleted cells than that in normally nourished cells. GC-MS revealed the presence of major fatty acids—palmitic, oleic, stearic, arachidic, lauric, and linoleic acids. Highest efficiency was found when cells were pretreated using acid for 3？h. The lipid content was calculated as 33.18% and 54.26% for nitrogen rich cells and nitrogen starved cells, respectively. This work thus aided in identifying the most eligible pretreatment process to avail lipids from cells, to convert them to eco-friendly and nonpolluting biodiesel. 1. Introduction Increasing population and uncontrolled urbanization have created serious problems of energy requirement. Due to a sudden hike in energy consumption, it is anticipated that there would be deterioration in oil reserves by 2050. Continuous use of fossil fuels resulted in effect on environment by increasing greenhouse gas emission leads to climatic changes [1]. Therefore, there is a current demand to find out the alternative eco-friendly fuel against petrodiesel. Biodiesel has been considered as a major alternative for fossil fuel, as it is a biodegradable, renewable and nontoxic fuel [2]. Fatty acid methyl esters originating from vegetable oils and animal fats are known as biodiesel. It does not contribute net carbon dioxide or sulfur to the atmosphere and emits less gaseous pollutants than the petrodiesel [3]. Plants and algae are good candidates, as alternative energy sources, as they obtain their energy from the sunlight and build up their biomass by removing carbon dioxide from atmosphere through photosynthesis [4]. Recently, there is much interest in lipid production from microalgae because they have multiple advantages over traditional energy crops [5]. Microalgae have a high photosynthetic efficiency, rapid growth rate, shorter doubling time, and higher biomass production rate and utilize very less land than conventional crops [6, 7]. Biodiesel
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