Optimisation of ultrasonication pretreatment on microalgae Chlorella Vulgaris & Nannochloropsis Oculata for lipid extraction in biodiesel production

A wide variety of nutritious products and biofuels can be produced from microalgae. Their applications span across various sectors such as food, medical, and energy industries. Microalgal cell disruption is a crucial aspect in the production processes as it facilitates the extraction of bio-products stored within them. One of the commonly extracted compounds from microalgae is lipids, which constitute a high percentage of their composition. In this study, we conducted ultrasonic pre-treatment on two different microalgae species, namely Chlorella vulgaris and Nannochloropsis oculata. The pre-treatment involved ultrasonic frequencies of 37 and 80 kHz, exposure times of 10, 15, and 20 min, and extraction times of 2, 3, and 4 h. By utilising ultrasonic frequencies, we induced acoustic cavitation to break the microalgae cell walls and extract lipids. The experimental design followed a Response Surface Methodology (RSM) to evaluate the effect of ultrasonication pretreatment parameters on lipid extraction. In comparison to previously published studies, our findings indicate that higher frequencies of ultrasonication lead to increased lipid extraction from microalgae. The highest lipid yield achieved in our study was 11.54% for Chlorella vulgaris and 17.91% for Nannochloropsis oculata, using the input factors of 80 kHz frequency, 20 min of running time, and 4 h of extraction time. Our results contribute to the existing body of knowledge by demonstrating the efficacy of ultrasonic pre-treatment in lipid extraction from microalgae. By providing a quantitative comparison with previous studies, this study highlight the novel aspects of work and its potential implications for the production of biofuels and other valuable products from microalgae.