Biorefinery process intensification by ultrasound and ozone for phosphorus and biocompounds recovery from microalgae

Abstract This study applies individual and combined application of ultrasound and ozone pretreatments for the tandem recovery of microalgae biocompounds (lipids, proteins, and, carbohydrates) and phosphorus from Scenedesmus obliquus cultivated in wastewater. Results of individual application showed that ultrasound released protein to the aqueous phase (99 ± 3%), and increased microalgal lipid viability from 11 to 90 ± 2%. Whilst ozone pretreatment induced carbohydrate release to the aqueous phase 28 ± 1%. Combined ultrasound and ozone pretreatment were studied in sequence mode. Ultrasound was first applied to release proteins and expose lipids, followed by ozone to induce carbohydrates and phosphorus release. The maximum yields of recovered lipids, proteins, carbohydrates and phosphorus by the combined pretreatment were 89 ± 1%, 91 ± 8%, 63 ± 1%, and 75 ± 1% respectively. In the dual pretreatment best experimental parameters applied for ultrasound were: biomass concentration of 25 g/L and applied energy of 200 kW h/kg dry biomass. Ozone pretreatment used 27 mg O3/L, contact time 25 min and pH of 11. The combined pretreatment intensified microalgae fractionation achieving high biocompounds and phosphorus recovery yields; reducing solvent waste by 95% and extraction time by 90%, in comparison to biocompounds extraction without pretreatment.