Treatment of Reactive Dye Hydrolysates with UV-C- and Ozone-Activated Percarbonate and Persulfate

Color removal from dyehouse effluent remains a challenging pollution problem. Until now, no effective, economic and at the same time environmentally friendly treatment option has been proposed. In this study, the performance of photochemically/chemically-activated peroxides in the degradation of commercially important reactive dyestuffs was investigated considering actual process conditions and feasibility concerns. For this purpose, Reactive (Black 5; RB5-Red 21; RR21) dyebath effluents were prepared to study the effects of the “green” peroxides percarbonate (PC) and persulfate (PS) on UV-C and ozone treatments with respect to color (peak absorbance) and total organic carbon (TOC) parameters. UV-C activation of PC and PS (1.5 mM PC; 0.5 mM PS; UV-A = 0.5 W/L; pH 8) resulted in fast and complete color as well as 64–71% TOC removals after 60 min treatment, respectively. High-rate ozonation (71 mg min⁻¹ O₃; pH 11) which was already quite effective in terms of color (100% at an ozone dose of 180 mg) and TOC (38% at an ozone dose of 2100 mg) removals, could not be enhanced for TOC removal upon PS (36% at an ozone dose of 2100 mg) or PC addition (31% at an ozone dose of 2100 mg). Radical quenching probe chemicals confirmed the involvement of hydroxyl and sulfate radicals in UV-C-activated peroxide treatments, whereas ozone absorption increased with PS (from 38 to 51%) but decreased with PC addition (from 38 to 34%) due to sulfate and carbonate radical formation that changed ozone chemistry and stability during dyebath effluent treatment. Acute toxicity decreased from 21 to 10% (UV-C/PS treatment of RB5 effluent) and from 33 to 20% (O₃/PS treatment of RR21 effluent) according to the activated sludge inhibition tests. Graphical Abstract: [Figure not available: see fulltext.].