Photocatalytic treatment as a polishing step for the degradation of bio‐recalcitrant fractions of winery wastewater under solar, UVA‐LED, and blacklight irradiation

Abstract BACKGROUND This study investigates, for the first time, the most beneficial conditions for photocatalytic oxidation under ultraviolet (UV) irradiation provided by either a solar simulator, UVA light‐emitting diode (UVA‐LED), or UVA blacklight lamp (UVA‐BL) as a post‐treatment step for the degradation of the residual COD and color in winery wastewater (WiWW) after biological treatment. RESULTS The effect of WiWW dilution (0, 50%), TiO 2 concentration (0–1000 mg/L), catalyst type (TiO 2 , ZnO), pH (3, 6, 8.4), H 2 O 2 addition (0–1000 mg/L), and treatment time on process efficiency was evaluated. At the best‐assayed conditions (1000 mg/L TiO 2 , 1000 mg/L H 2 O 2 ), COD removal percentages in the range of 94–97% were obtained and color was removed by 99% within 180 min of treatment under all irradiation sources. The process was enhanced when the WiWW was subjected to 50% dilution and its pH was adjusted to 6. Among the three irradiation sources, UVA‐BL led to a marginally higher photocatalytic performance than solar and UVA‐LED, both of which achieved similar removal efficiencies. Regarding energy efficiency, UVA‐LED was found to be up to 1.7 times more energy efficient than UVA‐BL/TiO 2 . Finally, in most cases, the phytotoxicity of secondary effluent was eliminated during solar photocatalytic treatment. CONCLUSION Alteration of basic operating parameters significantly improved process efficiency. In all cases, LED‐driven photocatalysis combined high removal performance and energy efficiency, proving to be an appropriate and sustainable alternative to solar photocatalysis for 24 h operation or for supplementary application during the harvest, when the majority of WiWW is generated. © 2022 Society of Chemical Industry (SCI).