Avaliação do processo combinado fotocatalítico e biológico para descoloração e remoção de matéria orgânica de efluentes têxteis

Abstract

The textile industry requires large amounts of water, dyes and chemicals in their activity, generating wastewater, solid waste, air emissions, noise and odors that cause direct impact to the environment. In addition, synthetic dyes are responsible for residuals with intense color, acting as a source of pollution and interfering with the natural photosynthetic processes. These dyes have high chemical and photolytic stability, making them recalcitrant, mutagenic and they are hard to remove using conventional treatments, for example, coagulation/flocculation, sedimentation and activated sludge. In face to an environmental legislation increasingly severe and the growing awareness of the consumers, manufacturers have been required to find more appropriate solutions for the treatment of this type of wastewater. The combination of physical-chemical and biological processes has been studied as an effective and economically viable alternative. This study aims to assess the combination of advanced oxidation process (AOP) and biological treatment of textile wastewater. In this study, aqueous solutions of individual reactive dyes (red, yellow and navy blue), synthetic textile wastewater (dyes solutions + additives) and, finally, a real industrial textile wastewater were used. The decoloration was evaluated by UV-VIS spectrophotometry scan between 380 and 900 nm, while the organic matter removal by total organic carbon (TOC) analysis. The POA employed heterogeneous photocatalysis with ZnO/UV or TiO2/UV, concentration of 0.6 mg/ml solution, with an incidence time of UV radiation ranging between 30 and 120 minutes. In the tests with each individual dye aqueous solutions (50 mg/L), the decoloration observed in both photocatalytic systems was higher than 88%, and the TOC removal was between 26% and 44%, with a treatment time between 30 and 45 min. The treatment of the synthetic wastewater (SW 1) containing dyes + surfactant and real wastewater (RW), with ZnO, was not efficient after 120 min of UV radiation incidence. The photocatalysis of these effluents (RW) using TiO2/UV and the same time of reaction, achieved better results, yielding 38% of color removal and 28% of TOC removal. Comparing both photocatalysts, the better catalytic performance, both in color and in TOC removings was obtained with TiO2, which has much higher surface area than ZnO. The combined treatment using aerobic bioprocess for 48 hours with acclimated sludge after POA, using both catalysts, showed decoloration of the SW 1 above 97% and removal of TOC greater than 80%. For the RW, the combined process using TiO2 promoted 96.8% of decoloration and TOC removal of 63.2%. The process coupling photocatalysis and bioprocess has proven to be promising for the treatment of textile wastewater