Comparison of reactive azo dye removal with UV/HO, UV/SO and UV/HSO processes in aqueous solutions.

Advanced oxidation processes (AOPs) are an effective choice for removal of reactive azo dyes used in the textile industry due to high solubility and low degradability. Within the scope of this study, reactive orange 122 (RO122) azo dye was removed using the UV-based AOPs of ultraviolet (UV) radiation, UV/hydrogen peroxide (UV/HO), UV/persulfate (UV/SO), and UV/peroxymonosulfate (UV/HSO). Oxidant concentration, initial solution pH, initial RO122 concentration, different anions (Cl, NO and SO), and solution temperature effects were compared. With only UV radiation (254 nm), 19.5% RO122 removal occurred at the end of 120 min. The RO122 removal reduced with the UV/oxidant processes at pH 9. Experimental results revealed RO122 removal followed pseudo-first-order (PFO) kinetics. There was a linear correlation identified between initial oxidant concentration and the PFO kinetic rate constant (k). Among the three UV-based processes, with oxidant concentration 50 mg/L, temperature 20 °C, and pH 5, RO122 removal efficiency was in the order UV/HO > UV/HSO > UV/SO. RO122 removal rate increased as initial oxidant concentration and temperature increased and reduced as initial RO122 concentration increased. Energy requirements and oxidant costs were assessed. The UV/HO process was concluded to be the most efficient and economic process for RO122 removal.