Development of a pretreatment method based on Fenton-like reaction combined with hydrodynamic cavitation for lipid extraction from wet microalgae

Microalgal biorefineries, a green alternative to traditional refineries, require integrated processes and are economically viable, for the much-anticipated commercialization of microalgae-derived products. This study demonstrated that cell disruption for lipid extraction could be effectively performed using wet microalgae harvested with ferric chloride by combining a Fenton-like reaction with hydrodynamic cavitation (HC). HC boosted the already powerful Fenton-like reaction even further through cavitation and its resultant increases in temperature and mixing intensity. The extraction efficiencies for lipids and chlorophyll increased from 43.1% to 77.4%, and from 22.4% to 97.2%, respectively, and depended on the pH and hydrogen peroxide concentration. Statistical analysis showed that not only mild but also optimum condition suitable for both lipid extraction and chlorophyll removal was 0.79% hydrogen peroxide at pH 3.41; under these conditions, the simulated lipid yield was estimated to be 70.4% with 82.8% chlorophyll removal. Despite the advantages of process integration and high lipid extraction rates, the extracted lipids appeared highly viscous and substantially stickier than the products of conventional methods, likely due to the presence of residual iron particles. In conclusion, the Fenton-HC reaction offers a workable alternative for lipid extraction from wet microalgae, particularly when microalgae are harvested by ferric chloride-based flocculation.