Modeling partial oxidation of a commercial textile surfactant formulation with the H₂O₂/UV-C process

In the present study, the reaction conditions required for the partial oxidation of a commercial nonionic textile surfactant, an alkyl polyethoxylate, with the H₂O₂/UV-C treatment process were optimized using central composite design and response surface methodology (CCD-RSM). CCD-RSM allowed for the development of empirical quadratic equations that satisfactorily predicted COD and TOC removal efficiencies under all studied experimental conditions. Analysis of variance revealed that the variables "H ₂O₂ concentration" and "initial surfactant COD" were found to be the process independent parameters most positively and negatively affecting the treatment performance, respectively, whereas the process variable "treatment time" had a smaller influence on COD and TOC removal efficiencies. According to the established polynomial regression models, for the degradation of the nonionic surfactant at an initial COD of 450 mg L^-1 and pH of 10.5, the optimized treatment conditions were 15 mM H₂O₂ and a reaction time of 80 min. In order to achieve the treatment targets (complete surfactant removal accompanied by 60% COD and TOC elimination to meet the national discharge consents into receiving water bodies) either H₂O₂ concentration or photochemical treatment time had to be increased. Activated sludge inhibition experiments conducted with nonionic surfactant solution being subjected to photochemical oxidation under optimized reaction conditions indicated that the inhibitory effect of the nonionic surfactant could be completely eliminated during H ₂O₂/UV-C treatment and the partial degradation intermediates were more biodegradable than the original textile surfactant.