Assessment of kinetic modeling for oxidation of humic substances in mature landfill leachate by solar photocatalysis using ZnO–TiO2

Abstract The treatment of leachate from landfills is an important issue from an environmental point of view, as such leachates are classified as hazardous materials. This issue has received the attention of researchers in several regions of the world, especially in developing countries. Conventional biological treatment of leachate from mature landfills has not yielded consistent results, mainly because of the recalcitrance of humic substances. Little is known about the kinetic complexity of leachate treatment by oxidative methods, representing a barrier to process scale-up from benchtop experiments. In this study, a modeling approach was applied to describe the photodegradation of humic substances in a plug flow reactor connected to a stirred tank. The kinetic model provided an R2 of 0.974. Rate constants for humic acids (HA) and fulvic acids + humans (FAH) were 2.96 and 1.03 × 10− 3 min− 1, respectively. Statistical models for the degradation reaction had R2 values of 0.96 for HA and 0.99 for FAH. 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 significant difference in conversion between replicate runs, suggesting a uniform diffusion of fractions through catalysts.