UV light photo-Fenton degradation of polyphenols in oolong tea manufacturing wastewater

Abstract

The UV light photo-Fenton degradation of oolong tea polyphenols in tea manufacturing effluent that color the wastewater to a dark brown has been examined. In order to elucidate the photo-Fenton degradation mechanism of oolong tea polyphenols and find the optimal dosages of the Fenton reagents, systematic study has been conducted. For the UV light photo-Fenton degradation of oolong tea effluent being 70 mg-(polyphenol) L−1, the optimum dosages of Fenton reagents were found to be 20 mgL−1 of total Fe and 500 mgL−1 of H2O2. The polyphenol degradation could be divided into two stages. The polyphenols concentration rapidly decreased to around 30% of the initial concentration within 2 min and the degradation rate significantly slowed down in the subsequent stage. After 60 min of UV light irradiation, 97% polyphenol removal was obtained. The initial quick degradation of oolong tea polyphenols suggests that hydroxyl radical generated by the photo-Fenton process might preferentially attack polyphenols having high antioxidant activity by scavenging hydroxyl radicals. Almost complete decolorization of the oolong tea effluent was achieved after 80 min. About 96% mineralization of 63 mgL−1 TOC loading was achieved within 60 min and then further mineralization was rather slow. The complete COD removal of 239 mgL−1 COD loading was obtained after 100 min. The present results indicate that the UV light photo-Fenton degradation process can treat tea manufacturing wastewaters very effectively.