Degradation of direct black 22 textile dye using the photo-Fenton and electro-Fenton processes: a comparative study

Abstract The dyes present in textile effluents have a complex structure and low biodegradability, making it necessary to use efficient treatments such as advanced oxidation processes (AOP). The aim of this study was to compare the efficiency of photo-Fenton (PF) and electro-Fenton (EF) AOPs in the degradation of direct black dye 22 (PD22), defining the best experimental conditions and evaluating the kinetics and toxicity of the proposed treatments. Initially, for the PF system, using UV-C and sunlight radiation, 99.08% and 99.98% degradations were reached, respectively for [H2O2] = 20 mg·L− 1 and [Fe] = 1.0 mg·L− 1. From the volume variation study, it was observed that the increase in volume did not compromise the degradation of the dye. For the EF process, the [Fe] that promoted the highest percentage of degradation (95.16%) was equal to 1 mg·L− 1. The volume study for the EF process also did not interfere significantly in the efficiency of the process. The PF and EF systems presented satisfactory adjustments to the proposed kinetic models, suggesting that the treatment follows a pseudo-first-order kinetics. The ecotoxicological tests showed no toxicity for the thyme seed after using the EF process. Therefore, it is evident that different AOP techniques can be applied in the treatment of PD22.