Treatment of winery wastewater by sulphate radicals: HSO5−/transition metal/UV-A LEDs

In this study, the effectiveness of the HSO5−/Mn+/UV process on the treatment of winery wastewater (WW) was investigated. The optimal operating conditions were determined: [HSO5−] = 2.5 mM; [M2(SO4)n] = 1.0 mM; pH = 6.5 and reaction temperature = 323 K. Under the given conditions, 51%, 42% and 35% of COD removal was achieved using respectively Fe(II), Co(II) and Cu(II) as catalysts. Different UV sources were tested with the previously selected optimal conditions in order to increase the treatment efficiency. The highest COD removal (82%) was achieved using a UV-A LEDs system (70 W/m2). These conditions were also promising for the treatment of WW with COD concentrations of 5000 mg O2/L, reaching 79% and 64% of COD and TOC removal, respectively, after 180 min of treatment. At 323 K, the most effective treatment was obtained when Co(II) was used as catalyst (79% and 64% of COD and TOC removal), while at ambient temperature (293 K) the highest COD (65%) and TOC (52%) removals were obtained with Fe(II) catalyst. Moreover, it was demonstrated that the use of HSO5−/Mn+ in several consecutive doses was more efficient than adding the reagents as a single dose at the beginning of the reaction. A comparison between the performance of the HSO5−/Fe(II)/UV-A LED process and the conventional photo-Fenton demonstrated important advantages associated with the HSO5−/Fe(II)/UV-A LED process, including the absence of the costly pH adjustment and of the hydroxide ferric sludge which characterise the photo-Fenton treatment process. The HSO5−/Mn+/UV-A LED process demonstrates a high COD and TOC removal efficiency, and it can be considered a promising technology for application in real scale agro-food wastewater treatment plants.