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

Significance 

A microalgae biorefinery is a facility that integrates microalgae fractional process and conversion processes to transform biomass into a variety of bio-based products like food, feed, chemicals and bio-energy such as fuels, power and heat. The main goal of the biorefinery is to optimize the use of the microalgae; reduce waste production, and maximize profitability and benefits. Ideally, this process is done through cell disruption methods which are essential pretreatments that are carried out to increase the bioavailability of microalgae constituents and maximize product recovery in the downstream processes of the microalgae biorefinery. This downstream process takes up a large part of the operational cost and thus it is necessary to utilize cell disruption technologies that are low cost and will result in high product quality of compounds such as lipids, proteins, carbohydrates and residual biomass. In order to increase the efficiency of the downstream process, recent studies have proposed a combination of pretreatment techniques to maximize the recovery of bio compounds at minimum energy consumption.

Building on this knowledge, researchers from the National Autonomous University of Mexico UNAM, Dr. Regina González-Balderas and Dr. M.T. Orta Ledesma, in collaboration with Professor Sharon Velásquez-Orta at the Newcastle University applied individual and combined application of cell disruption techniques, known as Ultrasound and Ozone pretreatments, to compare the efficiency of the recovery of microalgae bio compounds and phosphorous from Scenedesmus obliquus cultivated in wastewater. Their work is currently published in the research journal, Chemical Engineering & Processing: Process Intensification.

Subsequent to the study of the individual pretreatment effects on the recovery of the same micro algae, Scenedesmus obliquus, the research team assessed their combined application in sequence. The sequential process consisted first of ultrasound to induce cell disruption recover proteins and lipids followed by ozone to recover carbohydrates and phosphorous. After each pretreatment, lipids, proteins, carbohydrates and total phosphorous released into the aqueous phase was quantified separately. There after, the remaining microalgal bio compounds were extracted from the pre-treated cell pellet in the following order: lipids, proteins, and carbohydrates.

Results of individual application showed that ultrasound released protein to the aqueous phase (99 %), and increased microalgal lipid viability from 11 to 90 %. Whilst ozone pretreatment induced carbohydrate release to the aqueous phase 28 %. Combined, the maximum yields of recovered lipids, proteins, carbohydrates and phosphorus by the combined pretreatment were approximately, 89%, 91%, 63% and 75 %, respectively.

In summary, the study applied individual and combined application of ultrasound and ozone pretreatments for the tandem recovery of microalgae bio-compounds (lipids, proteins, and, carbohydrates) and phosphorus from Scenedesmus obliquus cultivated in wastewater. During the dual pretreatment test, 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. Overall, the combined pretreatment intensified microalgae fractionation achieving high bio-compounds and phosphorus recovery yields; reducing solvent waste by 95 % and extraction time by 90 %, in comparison to bio compounds extraction without pretreatment.

Reference

R.M. González-Balderas, S.B. Velásquez-Orta, M.T. Orta Ledesma. Biorefinery process intensification by ultrasound and ozone for phosphorus and bio compounds recovery from microalgae. Chemical Engineering & Processing: Process Intensification (2020) volume 153, pages 107951.

Go To Chemical Engineering & Processing: Process Intensification

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