Effects of Ultrasonic and Microwave Pretreatment on Lipid Extraction of Microalgae and Methane Production from the Residual Extracted Biomass

The extraction of lipids from microalgae cells ofBotryococcus brauniiandChlorella vulgarisafter ultrasonic and microwave pretreatment was evaluated. Cell disruption increased the lipid extraction efficiency, and microwave pretreatment was more effective compared with ultrasonic pretreatment. The maximum lipid yield fromB. brauniiwas 56.42% using microwave radiation and 39.61% for ultrasonication, while fromC. vulgaris, it was respectively 41.31% and 35.28%. The fatty acid composition in the lipid extracts was also analyzed. The methane yield from the residual extracted biomass pretreated by microwaves ranged from 148 to 185 NmL CH4/g VS forC. vulgarisand from 128 to 142 NmL CH4/g VS forB. braunii. In the case of ultrasonic pretreatment, the methane production was between 168 and 208 NmL CH4/g VS forC. vulgaris, while forB. brauniiranging from 150 to 174 NmL CH4/g VS. Anaerobic digestion showed that lipid-extracted biomass presented lower methane yield than non-lipid-extracted feedstock, and higher amount of lipid obtained in the extraction contributed less methane production. Anyway, anaerobic digestion of the residual extracted biomass can be a suitable method to increase economic viability of energy recovery from microalgae.

Automated summary

The study evaluated the lipid extraction from microalgae cells of Botryococcus braunii and Chlorella vulgaris after ultrasonic and microwave pretreatment. Microwave pretreatment was found to be more effective in enhancing lipid extraction efficiency. Anaerobic digestion of the residual extracted biomass showed a decrease in methane production compared to non-lipid-extracted feedstock. However, the residual extracted biomass can still be a suitable method for energy recovery from microalgae.