Microwave treatment of wet algal paste for enhanced solvent extraction of lipids for biodiesel production

The role of microwave treatment as a precursor to lipid extraction from Nannochloropsis oculata using solvent extraction was investigated. Two microwave power settings were used, corresponding to wall plug powers of 635 and 1021 W. To limit the maximum temperature rise of the wet algal samples, exposure times were capped to 15 s intervals and followed by 15 min of cooling. Samples were treated in total from 1 to 5 min of microwave treatment (i.e. 1 min was 4 × 15 s treatments). The lysed fraction increased with exposure time for both power levels and the extracted lipids closely followed the lysed fraction. The highest extracted lipid content, after 5 min, was 0.036 g/g dry algae weight (g/g) for 635 W (68.86% cell lysis), while with 1021 W the yield was 0.052 g/g (92.81%). The control sample, which did not receive any microwave treatment, was only 0.016 g/g dry algae weight. Significance was observed between treatment time, cell lysis and lipid yield, (p < 0.05). For the 5 min of treatment, the lipid produced per total number of Joules consumed was found for each microwave power setting; yielding values of 1.889 × 10−4 g/g/kJ (635 W) and 1.697 × 10−4 g/g/kJ (1021 W).