Microalgae biomass pre-treatment with deep eutectic solvent to optimize lipid isolation in biodiesel production

While microalgae are promising biomass candidates for biodiesel production, efficient lipid extraction is hindered by the strong cell walls. Cell wall disruption is an essential processing step for improving lipid yields from microalgae biomass. Conventional methods use toxic organic solvents (e.g., mixtures of chloroform and methanol or hexane) to extract microalgal lipids. This study with Chlorella pyrenoidosa investigates a novel microalgal pretreatment by a deep eutectic solvent (choline chloride:acetic acid) to increase cell wall disruption prior to lipid extraction. Deep eutectic solvent and ultrasonic homogenization should be best performed after 5 min of pretreatment. Biomass was characterized before and after the pretreatment to understand the mechanism. To optimize the lipid extraction yield, the effect of various variables (methanol to n-butanol, solvent to biomass ratio, time, and temperature) on lipid extraction yield was investigated using a single-factor experiment. The maximum lipid yield (19.25%) was extracted at 1:4 methanol to n-butanol and a 30 (v/w) solvent to biomass ratio over 120 min at 60 °C. Fatty acid methyl esters were obtained through transesterification reactions from extracted lipid of optimized condition and biodiesel quality was studied in comparison with European and US standards. The dominant fatty acids were C16:0 (29.54%), C18:2 (18.42%), and C18:3 (19.50%) and properties of biodiesel are within the European and US standards. This novel pretreatment method, coupled with lipid yields and characterization, documents the significant potential for microalgae biodiesel as an alternative, sustainable energy source.