Microwave Thermolysis and Lipid Recovery from Dried Microalgae Powder for Biodiesel Production

Third-generation microalgae-derived biodiesel has become increasingly important in recent years because of the depletion of fossil fuels and to reduce global dependence on oil from crop sources that may use or displace agricultural land for food crops. This work investigates the microwave treatment of dried microalgae powder to improve the oil extraction efficacy. This study has revealed that the lipid yield from Nannochloropsis oculata dried powder with microwave thermal treatment at 50% microwave power (443 W) was greater than that with 100% power (943 W). However, the efficacy of the cell wall destruction after 5 min microwave thermal treatment at full power was higher (70.0 +/- 2.30%) than that at 50% power (46.0 +/- 2.05%). The greatest lipid yield at 943 W was achieved with 1 min treatment, 0.093 +/- 0.001 gg(-1) of dry algae weight, with 17.3 +/- 1.19% cell lysis at 42.2 degrees C. Initially, the lipid content yield increased from 0.082 +/- 0.002 to 0.093 +/- 0.001 gg(-1) dry algae weight compared to the control sample (with no treatment applied). With the increase in temperature, the lipid yield was reduced because of oxidation at elevated temperatures. With the reduced power setting (443 W), the highest lipid yield of 0.149 +/- 0.003 gg(-1) of dry algae weight was achieved after 5 min of treatment, with 46.0 +/- 2.05% cell lysis at 58.5 degrees C. Statistically, the treatment time and temperature are correlated strongly to the extracted lipid yield. The kinetic study showed that the rate constant for lipid extraction with microwave pre-treatment was higher at 443 W compared to the control sample and the higher microwave power level. The extracted lipid was analysed and found to have physical and chemical properties that were comparable to those of vegetable seed oils and they were suitable for use as a feedstock to produce biodiesel.