Mechanistic Modeling of Photocatalytic Water Disinfection

The main goal of this research was to develop a mechanism-based model for photocatalytic disinfection of bacteria in water using suspended catalyst pthesiss in batch reactors. The photocatalytic disinfection process occurs as a semiconductor photocatalyst, most commonly titanium dioxide (TiO2), is irradiated with light of wavelength less than 380 nm to produce hydroxyl radicals and other highly reactive oxidants which can inactivate microorganisms. Photocatalytic disinfection involves a complex interaction of many fundamental mechanisms such as light absorption and scattering by semiconductor pthesiss, electrochemical surface reactions, and heterogeneous colloidal stability. Current models, based largely on chemical reacting systems, do not adequately account for these fundamental mechanisms. Even the Langmuir model developed for heterogeneous systems cannot describe the interactions of such large colloidal pthesiss. As a result, it is difficult to assess the combined effects of many important factors which go into the design of a photocatalytic disinfection system. A mechanistic modeling approach is desirable because it provides a framework to understand the influence of many important parameters on the disinfection process. It requires a description of the physical properties of the catalyst, the nature of the suspending electrolyte solution, the physical and chemical properties of the cell surface, and the energetic aspects that influence the interaction of the pthesiss. All these aspects are interrelated. While it is customary to envision the adsorption of reactants unto a catalyst surface, for photocatalytic disinfection involving suspended catalyst pthesiss, multiple catalyst pthesiss adhere to the bacterial surface. In this work a mechanistic model has been developed that simulates the effect of light intensity and catalyst concentration on the disinfection process. The simulations show good agreement with the experimental data for stable colloidal suspensions, that is, suspensions in which rapid aggregation of cells and TiO2 do not occur. Increased disinfection rates and high levels of inactivation can be achieved by maintaining a relatively low catalyst-to-microbe ratio while maximizing the light intensity. The influence of pH and ionic strength on the disinfection process have been included in the model, but these are only expected to be accurately predicted when the solution remains stable