Evaluation of various cell drying and disruption techniques for sustainable metabolite extractions from microalgae grown in wastewater: A multivariate approach

This study attempted to determine the yield of extractable metabolites and the cost of oil production from Scenedesmus obliquus cultivated in municipal wastewater. The microalgae achieved a biomass concentration of 1.64 g L⁻¹ as well as pollutant removal efficiencies of 87.86% COD, 86.16% NH₄⁺-N, and ≈100% PO₄³⁻-P. The harvested microalgae were subjected to different drying and cell disruption techniques for lipid extraction, and the residual biomass was used to recover proteins and carbohydrates. Principal component analysis was employed to evaluate the metabolic yields obtained from sun-, freeze-, and oven-drying methods and microwave-, sonication-, autoclaving-, and osmotic shock-disruption techniques. The lipid yield varied between 4.90± 0.42% for sun-dried biomass subjected to osmotic shock and 25.39± 1.08% for freeze-drying with microwave-assisted extraction. Protein yield of the whole microalgae cells (31.26± 3.76%) was comparable (p > 0.05) to that resulting from lipid-extracted microalgae by either autoclaving or osmotic shock. Carbohydrate yield of the intact microalgae cells (19.80± 1.49%) was comparable (p > 0.05) to that of lipid-extracted microalgae from amongst all the cell disruption methods. Results of a techno-economic analysis indicated that the cost of oil production from microalgae varied between $0.883 and $2.088 per liter. These results revealed the feasibility of using a sequential extraction of lipids followed by proteins and carbohydrates.