A novel approach for harvesting Scenedesmus sp. microalgae from real wastewater by using adsorbents of magnetite-based nanoparticles (Fe 3 O 4 NPs) was tested in this study for the first time for this microalgae. Using these NPs, the harvesting efficiency was even higher than 95%. The optimal conditions (0.14 gNPs/L, a short magnetic separation time of only 8 min and 27 min of contact time) were found using the response surface methodology. The best fitting of the adsorption equilibrium results was achieved by the Langmuir isotherm model, and the maximum adsorption capacity for Scenedesmus sp. reached 3.49 g dry cell weight (DCW)/g Fe 3 O 4 NPs. Zeta potential measurements and the Dubinin-Radushkevich isotherm model analysis pointed out that the main adsorption mechanism between Scenedesmus sp. cells and Fe 3 O 4 NPs was electrostatic interaction.Finally, Fe 3 O 4 NPs were six times successfully reused by combining an alkaline treatment with an ultrasonication process, which implies microalgae lysis. The results herein obtained highlight the potential for magnetic separation of microalgae from wastewater, which is capable of reaching a high harvesting efficiency in a very short time.

Lignocellulolytic enzymes from low-cost sources are gaining attention as a tool to reduce production costs. Such enzymes can be obtained sustainably by diverse fungal strains via solid-state fermentation (SSF) of lignocellulosic-derived residues as substrates. Besides, these enzymes allow hydrolyzing the same residue, releasing fermentable sugars that can be transformed into valueadded products. This study shows a two-stage valorization approach for the lignocellulosic leftover brewer's spent grain (BSG): first, by producing lignocellulolytic enzymes through the SSF of BSG using three fungal strains and, second, by using the selfproduced enzymes to hydrolyze the same BSG and obtaining sugar-rich hydrolysates that serve as an alternative carbon source for polyhydroxyalkanoates (PHA) production. From the evaluated set, Aspergillus niger and Thermoascus aurantiacus produced the highest xylanase activities compared with Trichoderma reesei (268 ± 24, 241 ± 10, and 150 ± 24 U per gram of dry BSG, respectively). Also, A. niger extracts resulted in the most effective for releasing sugars from BSG, obtaining up to 0.56 g per gram of dry BSG after 24 h without any pretreatment needed. Thus, the sugar-rich hydrolysate obtained with A. niger was used as a source for producing PHA by using two bacterial strains, namely, Burkholderia cepacia and Cupriavidus necator. Maximum PHA yield was achieved by using C. necator after 48 h with 9.0 ± 0.44 mg PHA•g −1 dry BSG. These results show the significant potential of BSG as raw material for obtaining value-added bioproducts and the importance of multiple valorization schemes to improve the feasibility of similar residue-based systems.