Effects of temperature, pH, and C/N ratio of sugarcane wastewater processing (vinasse) on Phormidium autumnale heterotrophic cultivation

Agro-industrial wastewater treatment processes using microalgae have been attractive due to high commercial-value biomass obtainment and contaminant removal efficiency. Cyanobacteria cultivation with the generation of biomass and bioproducts, such as proteins, lipids, carbohydrates, and pigments, is known by the term microalgae biorefinery. In this context, the present study aimed to heterotrophically cultivate Phormidium autumnale in sugarcane vinasse and evaluate its contaminant removals, emphasizing its value-added bioproduct production. The highest biomass productivity was reached at 35 degrees C, corresponding to 127.20 mg L-1 d-1, in a C/N ratio of 16 and pH of 7.5, with removals of organic carbon, nitrogen, and phosphorus of 49 %, 47 %, and 28 % respectively. In the batch cultivation, removals of organic carbon (67 %) and nitrogen (70 %) were obtained, with maximum productivity in terms of biomass equivalent to the best performance of the tests performed on an orbital shaker (CCRD). Biomass generated by P. autumnale showed 21.33 % proteins, 4.26 % lipids, 197.53 mg g-1 blue phycocyanin pigment, and a varied carbohydrate composition, such as glucose (79.46 mg L-1), arabinose (44.53 mg L-1), mannose (9.84 mg L-1), galactose (2.76 mg L-1), and xylose (14.44 mg L-1). These monosaccharides are ideal in the formation of exopolysaccharides (EPS) and 0.91 g L-1 of total reducing sugars (TRS). Our results demonstrated the ability of P. autumnale to treat sugarcane vinasse, which becomes a medium for its cultivation, removing representative amounts of carbon and nitrogen, besides producing several bioproducts, such as pro-teins, lipids, phycocyanin pigment, and carbohydrates.