Evaluation and comparison of algal cell disruption methods: Microwave, waterbath, blender, ultrasonic and laser treatment

Third generation biodiesel production from microalgae currently necessitates many stages, some of which are complex and energy consuming, cell disruption is such an example. Microalgal strains which are prime candidates for oil extraction normally possess a robust cell wall which prevents the release of intracellular products, and breaking them can be energy intensive. This study investigated several laboratory scale methods (solid and liquid shear, thermolysis, and microwave and laser treatments) to disrupt Nannochloropsis oculata cells with a view to monitor the treatment efficiency and induced damage traits. Bright field microscopy analysis was used to quantify the reduction of intact cells as a function of time, whilst measuring the treatment’s cumulative energy requirements. A figure of merit was defined to assess the relative energy consumption, taking into consideration the percentage disruption, energy consumed and the volume fraction utilised of the system. The greatest disruption was achieved with laser treatment, with a mean value of 96.53 ± 0.92% (standard error of the mean, n = 30; 16.0 MJ/L of laser power, scaled to per litre); microwave treatment 94.92 ± 1.38% (74.6 MJ/L); mechanical solid shear yielded cell disruption of 92.95 ± 0.97% (540 MJ/L); thermolysis 87.72 ± 1.82% (20.1 MJ/L); liquid shear ultrasonication was least effective with a mean disruption of 67.66 ± 1.97% (132 MJ/L).