Development of computer-based first-principles kinetic models for aqueous phase advanced oxidation processes
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Advanced oxidation processes (AOPs) are attractive technologies to remove organic compounds in water. AOPs produces highly reactive hydroxyl radicals that can react with organic contaminants and further degrade these compounds with the radical initiated chain reactions. These chain reactions are very complicated and various intermediates and byproducts are produced during the degradation processes. These intermediates and byproducts are of great concern since they may have adverse effect on human health. So there is need to have a detailed and quantitative insight into the degradation mechanisms and fates of intermediates and byproducts of organic compounds in AOPs. A number of studies have investigated the degradation mechanisms of organic compounds in AOPs. However, these studies have the following limitations: first, these studies conduct experiments to determine the degradation mechanisms, which are extreme time consuming and prohibitive to be applied for all organic contaminants in water; second, the degradation mechanisms that are proposed in these studies contain lumped reactions, which can prevent us from obtaining detailed insight into the degradation process; third, the kinetic models developed in these studies are required to solve ordinary differential equations, which might be too stiff to be solved for complicated degradation mechanisms. In this study, several computer-based first-principles kinetic models have been developed to overcome the above limitations. These computer-based first-principles kinetic models can automatically predict the degradation mechanisms for given parent compounds in aqueous phase AOPs and calculate the concentration profiles of all species involved in the degradation mechanisms. To be specific, we developed a computer-based first-principles kinetic model with ODE solver, which can successfully simulate the degradation process for small parent compounds. We also developed a computer-based kinetic Monte Carlo (KMC) model that can solve the generated pathway without solving ODEs. Hence, the difficulty of stiffness encountered by traditional ODE based kinetic models can be avoided. This KMC model can successfully simulate the degradation processes of both small and large parent compounds. Last, we developed an on-the-fly KMC model that can have improved computational efficiency as compared with the KMC model. Our approach is sufficiently general to be applied to a wide range of contaminants.