Scenedesmus obliquus microalga‐based biorefinery – from brewery effluent to bioactive compounds, biofuels and biofertilizers – aiming at a circular bioeconomy

The circular bioeconomy concept relies on the exploitation of wastes as a feedstock of different biotechnological processes to obtain, as much as possible, a huge spectrum of biochemical components through a biorefinery platform. This work deals with the treatment of brewery effluent through the cultivation of Scenedesmus obliquus microalga and the use of the biomass in a complex biorefinery. The treatment proved efficient in the removal of nutrients (N, P and COD removals of 88, 30 and 71% respectively). Several compounds and products were obtained from the biomass, such as: (a) phenols (0.249–1.016 mg GAE mL −1 ) and flavonoids (0.05–0.167 mg CE mL −1 ) by subcritical water extraction (SWE) at 120 °C, the extraction efficiency being five times higher at 200 °C; (b) biohydrogen by dark fermentation (67.1 mL H 2 g VS −1 ); (c) bio‐oil (64%), biochar (30%) and biogas (6%) by pyrolysis; and (d) enhanced capacity of germination/growth of wheat and barley seeds by S. obliquus culture and biomass (pellet, after centrifugation); better results were obtained with the biomass cultivated in brewery effluent (when compared with synthetic medium), and the biomass pellet was better than the whole culture; barley seeds treated with the pellet from the brewery effluent had the highest germination index (GI) of 85 compared with the control (tap water) GI of 35. The innovative study emphasis was on reducing microalgae production costs, providing environmental benefits in a biorefinery‐based S. obliquus platform.