Uso do óxido de zinco (ZnO) e energia solar na descoloração do efluente de indústria processadora de frutas

Abstract

This paper aimed to apply heterogeneous Zinc Oxide (ZnO), Commercial and Pechini, based catalysts in the solar photocatalytic treatment of the fruit processing effluent from the city of João Pessoa – PB, evaluating its discoloration over time. Initially, the physicochemical characterization of the effluent was performed, following the Standard Methods for Examination of Water and Wastewater, followed by three steps of the photocatalytic process. In the first stage, three preliminary tests were performed for each, varying: the concentration of ZnO, the application of Hydrogen Peroxide (H2O2) and the reaction time for the effluent at natural pH, defining the most favorable conditions for the process; An adsorption test for said effluent was also performed in this first step. In the second stage, two experiments were carried out, applying the 2³ factorial design for the heterogeneous photocatalysis Advanced Oxidative Process (AOP) for the two aforementioned types of ZnO, aiming at effluent discoloration. The pH was set at six and the conditions of concentration of ZnO, amount of H2O2 and reaction time were varied. In the third step, the reuse efficiency of the two ZnO catalysts was evaluated by two test cycles, under the best conditions achieved in the second stage. The results of test one of the first step revealed the need for the addition of H2O2 in order to increase effluent discoloration; Thus, in the second test of the step, 25% of the amount of H2O2 needed alone was added to each sample to degrade the effluent's Chemical Oxygen Demand (COD), based on a H2O2 factor of 0.3, providing 75% of color removal for both catalysts used, with ZnO Pechini achieving the result in the shortest time (180 minutes); the third test showed that the adsorption process was a little significant to the discoloration process. In the second stage, maximum color removals of 66% with 25% H2O2 and 0.25 g.L-1 ZnO Pechini and 71% with 5% H2O2 and 0.75 g.L-1 Commercial ZnO were achieved. These results indicated that the most significant factor for the process is the catalyst concentration. Finally, the results of the third stage showed that the reused Pechini and Commercial ZnO do not lose their photocatalytic efficiency, degrading up to 75% of the effluent color in both recycling trials. However, Pechini ZnO has greater potential for full-scale application due to its lower recycling loss rate (25% per cycle), in relation to the Commercial ZnO (losses over 40%).