Evaluation of ZnO Catalyst Supported on Zeolite NaA in the Photocatalytic Degradation of Vinasse Pretreated by Coagulation/Flocculation

Abstract

The research for a proper disposal of vinasse is a serious concern for countries that produce ethanol from sugar cane such as Brazil. The wastewater of its production process is generated with an extremely hightoxic load. In this work, samples of in natura vinasse were submitted to a pre-treatment by coagulation/flocculation process, applying the Tanfloc® SG in order to obtain a clarified vinasse and improve the performance of photocatalytic degradation. The pre-treated vinasse (clarified) was characterized by chemical oxygen demand (COD), colour, turbidity and absorbance reductions. Coagulation/flocculation reduced 80 % of colour, 70 % of turbidity, 40 % of COD and 43 % of absorbance at 270 nm (region of maximal absorption of vinasse). The sludge obtained from this process was submitted to thermogravimetric and differential thermal analysis (TGA/DTA), verifying its potential for use as fuel in furnaces of boilers in power plants. Catalysts based on zinc oxide supported on commercial zeolite NaA under the following compositions were prepared by wet impregnation: 5 % ZnO/NaA and 10 % ZnO/NaA (wt%). The catalysts were characterized by X-ray diffraction (XRD), N2 physical adsorption (BET), atomic absorption (AA), photoacoustic spectroscopy (PAS), infrared spectroscopy (FTIR), energy dispersive X-ray (EDX), scanning electron microscopy (SEM), and then applied in photocatalytic reactions of clarified vinasse. The efficiency of the combined treatment coagulation/flocculation/photocatalysis was evaluated by means of COD and UV-Vis absorbance reductions. It was found that 10 % ZnO/NaA showed better activity, with an increase of 50 % and 36 % reduction in COD and absorbance, respectively, when compared to plain zeolite NaA.