Microalgae and immobilized TiO₂/UV-A LEDs as a sustainable alternative for winery wastewater treatment

This work intends to promote the growth of microalgae biomass with simultaneous remediation of an agro-industrial wastewater. Winery wastewater (WW) was used as growth media for the cyanobacteria Arthrospira maxima and the green microalgae Scenedesmus obliquus, Auxenochlorella protothecoides and Chlorella vulgaris, under mixotrophic and heterotrophic conditions. The latter species stands out under mixotrophic conditions, with removals of TOC and TN above 90%. Biomass production and pollutant removal were influenced by the initial WW concentration. Maximum removal values within 8 days of incubation were 92, 91, 49 and 40% for COD, TN, polyphenols and P-PO₄, respectively, and 147.5 mg L^-1 d^-1 of biomass productivity. C. vulgaris biomass showed higher carotenoid content (maximum of 8.7 mg/g) when grown in WW, compared to autotrophic conditions (6.5 mg/g), making the bioremediation process more viable with the production of valuable by-products such as pigments. As the pollutant load removed by the microalgae does not allow reach the legal limits of release treated waters in natural water courses, a tertiary treatment process was applied. A post-treatment by photocatalysis in a UV LEDs photoreactor with TiO₂-supported in Raschig rings was proposed for the removal of COD and polyphenols from a high loaded WW. The heterogeneous photocatalytic process was efficient in removing 80% of total polyphenols and 40% of COD, allowing the release of the treated water in superficial water courses since complies with the legal limits (COD below 150 mg L^-1).