Study of the effectiveness of a ZnO–TiO2 formulation in the degradation of humic substances in mature leachate by solar photocatalysis Brazil

Abstract

Treatment of landfill leachate is an important environmental issue, especially in developing countries such as Brazil. Advanced oxidation processes (AOPs) have been considered interesting treatment alternatives. In this study, ZnO–TiO₂ mixtures were incorporated into a paint polymer matrix and fixed onto supports. Paints were applied by overlapping coat layers on plates, resulting in high film thickness (600 ± 80 µm). Treatment of mature leachate by an AOP was conducted in a plug flow reactor connected to a stirred tank under solar irradiation. The objective was to evaluate the degradation of humic acid (HA) and fulvic acid + humins (FAH). The highest HA and FAH removal efficiencies were 62% ± 4.9% and 16% ± 4.2%, respectively. The kinetic model provided a coefficient of determination (R²) of 0.974. Rate constants for HA and FAH removal were 2.96 and 1.03 × 10⁻³ min⁻¹, respectively. Statistical models for HA and FAH degradation had R² values of 0.96 and 0.99, respectively. Both approaches indicated that HA degradation is greater at acidic pH and higher TiO₂ concentrations. FAH degradation was favored by acidic pH and higher ZnO concentrations. Statistical models showed the same mean difference in conversion between replicate runs of HA and FAH, suggesting a uniform diffusion of fractions through catalysts.

Keywords: heterogeneous photocatalysis, humic and fulvic acid, landfill leachate treatment, titanium dioxide, zinc oxide.