Development of a semiconductor tree branch-like photoreactor for textile industry effluent treatment.

Abstract

This paper aimed to develop a new photocatalytic reactor design with a rotary tree branch structure for wastewater treatment in the textile industry. The brass sheet calcined at 500 °C (B500) was used as the photocatalyst and as a substrate for ZnO nanoparticle immobilization (B500ZnO). The photoreactor performance was evaluated toward the photodegradation of an aqueous solution of Reactive Black 5 dye (AS-RB5), raw wastewater (RW), and treated wastewater (TW). X-ray diffraction (XRD) and scanning electron microscopy (SEM) results illustrated ZnO nanowire formation over B500 and B500ZnO substrates. The bandgap values of these samples were estimated by diffuse reflectance measurements. The effects of dye concentration, the type of radiation, and ZnO NP deposition on the degradation of AS-RB were evaluated. Decreases in chemical oxygen demand (COD) greater than 82% were obtained using solar irradiation and artificial light as the energy source. Regarding calcined brass sheet reutilization, a decrease of 45% in the photocatalytic activity efficiency after 5 cycles was noted due to the effect of photocorrosion of the ZnO nanowires. The photoreaction of the RW and TW effluents showed COD values of 21 and 35%, respectively, which are below the limits established by state environmental control. With respect to RB5 addition to the TW effluent (TW-RB5), a discoloration of 62% was noticed after 3 h of photodegradation. Furthermore, the toxicity tests of the AS-RB5 and TW-RB5 samples did not display toxic intermediates after the photoreaction since 80% of the seeds germinated. Finally, the photoreactor exhibited good performance regarding the decrease in effluent pollutant charge, in addition to the efficient discoloration of RB5 dye.