Pulsed Electric Field Treatment for Efficient oil Extraction from Nannochloropsis salina Microalgae: A Green and Sustainable Approach

Abstract

Microalgae have emerged as a promising feedstock for biofuel production due to their ability to accumulate significant quantities of lipids. However, efficient extraction of these intracellular lipids remains a critical challenge. This study investigated pulsed electric field (PEF) and ultrasonic treatments for disrupting the robust cell walls of Nannochloropsis microalgae and extracting intracellular oils. A custom PEF setup with corrugated steel electrodes treated Nannochloropsis salina slurries under varying electric field strengths, pulse frequencies, processing times, and biomass concentrations. The Taguchi method optimized PEF parameters to maximize oil yields. Optimal PEF conditions of 20 kV/cm, 400 Hz, 30 min, and 20 g/L facilitated enhanced oil extraction by reversibly electroporating the cells. After PEF treatment, a solvent extraction process using chloroform and methanol recovered the released oils, yielding a maximum of 0.52 g_oil/g_{dry biomass} while consuming 39.6 kJ/kg of energy. Notably, PEF outperformed ultrasonic treatment, achieving higher oil yields with minimal temperature rise that could degrade cellular components. Microscopic observations confirmed oil droplet release and cell membrane permeabilization after PEF, without significant cell debris. The results showcase PEF as an efficient, non-thermal, and environmentally friendly pretreatment approach for extracting oils from robust microalgae like Nannochloropsis, making it viable for microalgae-based biofuel and industrial applications involving oil extraction.