Approaching zero discharge concept in refineries by solar–assisted photo-Fenton and photo-catalysis processes

[Display omitted] •Decrease in a refinery wastewater generation by reuse has been explored.•Solar light-assisted AOPs have been applied to decrease the energy consumption.•Photo-Fenton process showed best performance as secondary and tertiary treatment.•Biodegradability, toxicity and final TOC and COD values were improved.•Fe concentration in photo-Fenton process has been decreased to discharging limits. To undertake a better water management in Oil&Gas sector, it is essential to decrease the wastewater generation by increasing the current reused water rates. Focused on this motivation, this study presents the performances of solar-assisted photo-Fenton and heterogeneous photo-catalysis on refinery wastewater treatment for reuse purposes with the aim of zero discharge. While initial tests were made on synthetic refinery wastewater, real case studies were performed with two types of refinery effluent in order to test the feasibility of using AOPs either as a secondary or tertiary treatment. Even though heterogeneous photo-catalysis and a combined process showed promising results for the treatment of the refinery effluents, photo-Fenton treatment revealed a superior effectiveness for application in both secondary and tertiary treatment, considering the improvements on TOC removal, toxicity and biodegradability. Photo-Fenton as secondary treatment resulted as efficient as the biological treatment, reaching final TOC values ca. 20 mg/L and 88% of COD removal presenting values lower than those achieved after the biological treatment. Moreover, a marked increase in the BOD5/COD ratio from 0.38 to 0.83 was obtained. Furthermore, as a tertiary treatment, photo-Fenton process either with H2O2/COD = 10 and H2O2/Fe2+ = 50 or H2O2/COD = 4 and H2O2/Fe2+ = 10 provided a final TOC value