Integrated microalgae biorefinery using produced water: Simultaneous obtaining of biomass, biofuels and exopolysaccharides

Produced water (PW), a waste product of the oil industry, can be integrated into microalgae biorefinery systems not only for its bioremediation but also for the production of industrially relevant biomolecules, supporting the circular economy. Accordingly, the growth of microalgal species Chlorolobion braunii, Chlorella zofingiensis, Monoraphidium griffithii (freshwater), Dunaliella tertiolecta, Isochrysis galbana, and Phaeodactylum tricornutum (marine) was tested in media containing PW concentrations from 0 % to 100 %. PW concentrations >50 % supported microalgae growth, with the highest biomass production observed for I. galbana at PW80% (1.58 g L⁻¹). Among the tested species, D. tertiolecta exhibited the highest lipid content at PW80% (37.26 %), while C. braunii showed the highest carbohydrate content at PW50% (24.51 %). The biodiesel produced in PW exhibited a fatty acid profile comparable to that obtained in the standard medium, with characteristics similar to those of commercially available biodiesel, highlighting the potential of PW as a substrate for biorefinery processes. The tested microalgae also produced bioethanol in quantities exceeding those reported in the literature for cultures grown in the standard medium (0.60–16.81 mL). Cultivation in PW also led to substantial production of exopolysaccharides, particularly by I. galbana, which yielded 0.56 g L⁻¹ at PW80%. This species also demonstrated high bioremediation efficiency, achieving complete removal of phosphorus and nitrate and reducing iron concentrations by >88 % in the PW80% medium. These results demonstrate the technical feasibility of using PW for microalgae cultivation and the concurrent production of biofuels and EPS while also supporting effective waste bioremediation.