Investigation on thermal pyrolysis of microalgae grown in winery wastewater: biofuels and chemicals production

Abstract

Current innovations in microalgae technology include the use of wastewater as a cultivation medium for renewable energy generation and wastewater treatment. In this study, thermal pyrolysis was performed on a co-culture of Chlorella vulgaris and Arthrospira platensis grown in winery wastewater fed continuously into a membrane photobioreactor. The yield and composition of the reaction gases, reaction liquids, and solid residues collected at different reaction times and pyrolysis temperatures were compared with those of the same co-culture grown in its conventional medium. In general, the gaseous fraction resulted rich in combustible compounds. The highest yield in liquid products (55 %) was obtained by thermal pyrolysis of the co-culture grown in winery wastewater at 500 °C. Liquid fraction was made up of a mixture of oxygenated and nitrogenated compounds that are suitable as chemical intermediates and can therefore contribute to making the pyrolysis treatment economically feasible. For example, this fraction resulted particularly rich in crotonic acid, useful for the synthesis of copolymers (crotonic acid-vinyl acetate) and probably derived from the thermal cracking of polyhydroxy alkenoate. The results of this study suggest that thermal pyrolysis may be a good strategy to recover the energy potential of microalgae co-cultures used to treat wastewater. Graphical abstract