Degradation of target pollutants under simultaneous competition from coexisting compounds: Electron-beam treatment of a real hair dye wastewater

Abstract

Water pollution resulting from the extensive production and consumption of hair dyes has been threatening human health and aquatic ecosystems globally. Gaining knowledge on the presence of compounds in real hair dye wastewater and developing efficient treatment are emerging issues. This paper studies the electron beam irradiation of a real hair dye industrial wastewater. The COD_Cr of the industrial wastewater was reduced by 35 % through EB irradiation at 9 kGy. Four dyestuff intermediates (phenol, 5-amino-o-cresol, 5-amino-4-chloro-o-cresol and 5-amino-6-chloro-o-cresol) were identified as the target pollutants through compositional analysis of the wastewater. The removals of target pollutants in single-component solutions reached 75.7 %–89.7 % at 9 kGy The influence of coexisting background components on the degradation of targets was investigated and the interaction between different targets was evaluated during the irradiation treatment. Compared with pure single solutions, the required doses for 50 % removal of the targets in the wastewater increased by 0.1–5.8 times. Quantitative assessment of the competing effects of non-target components and the selectivity of reactive species is performed. OH and O₂⁻ show much lower selectivity toward the targets than reducing radicals (e_aq⁻ and H). Among them, O₂⁻ exhibits the lowest selectivity toward phenol with a logf value of −0.51. The main breakdown products of the target pollutants are quinones, diphenols and carboxylic acids.