INTRODUCTION

Fast depletion of fossil fuel based energy sources and global warming has necessitated the transition to renewable and sustainable energy sources. Biodiesel from various renewable feed stocks of plants, microalgae and animal fat, has been attempted as viable alternative sources of energy (Vasudevan & Briggs 2008). Microalgae being primary producers in aquatic ecosystems are a viable third generation of biofuel due to abundant availability and higher accumulation of lipid. Biodiesel has dual advantages (Chisti 2008) of mitigating carbon dioxide and as a substitute for petroleum. They also have certain advantages compared to other energy crops, including a high growth rate, shorter generation time, higher biomass production (Ramachandra et al. 2009) and lower degree of unsaturation and effective accumulation of lipids in algal cells at the end of growth stage (Casadevall et al. 1985, McGinnis et al. 1997).

A standard lipid extraction process from microalgae is prioritized based on its lipid specificity, entailing minimization of co-extraction of non-lipid contaminants and selective towards desirable lipid  fractions viz., neutral lipids containing mono-, di-, and trienoic fatty acid chains (Medina et al. 1998, Fajardo et al. 2007). The various steps involved in the biodiesel production using microalgae are isolation of species, mass cultivation, harvesting, lipid extraction (disruption of cell wall), and the conversion of the triglycerides into fatty acid methyl esters (transesterification) (Lee et al. 2010).

Cell disruption forms the most defining initial step for extraction of lipids. Various cell disruption techniques such as microwave assisted, sonication, osmotic shock, autoclaving, french press; lyophilization and bead beating have been used to extract lipids for different microalgae - Botryococcus sp. (Lee et al. 1998), Chlorella vulgaris, and Scenedesmus sp. (Lee et al. 2008). However, the consensus on optimal technique for microalgae has not yet been achieved. This study evaluates disruption methods like sonication, bead beating, sonication - hexane solvent, sonication – supercritical nitrogen, supercritical nitrogen – manual, bead beating - hexane solvent and bead beating - supercritical nitrogen for the microalgae Microcystis sp. for different time intervals to evaluate the time and the disruption method required for maximum lipid yield.