Modeling Advanced Oxidation Processes for Water Treatment

1. Modeling Advanced Oxidation Processes for Water Treatment Ashley N. Anhalt, A. Eduardo Sáez, Robert G. Arnold, and Mario R. Rojas Department of Chemical and Environmental Engineering The University of Arizona CHEMICAL REACTIONS METHODOLOGY ABSTRACT • Learning the Model: • In order to validate the efficacy of the UV/H2O2 model, data from previously published research were successfully reproduced. • Accurate comparisons between these graphs and those previously developed demonstrate an understanding of the model. • Fixing the Model: • Originally, the UV/H2O2model functioned as one reactor (Figure 2), in which the concentrations of the radicals are assumed to be uniform throughout the reactor. • This assumption of uniformity throughout the reactor is inaccurate. • We adjusted the model by dividing the reactor into multiple equivalent sections (Figures 3 and 4). • By considering two or three individual reactors, the model better accounts for light intensity effects and spatial variations of radical concentrations. • Comparisons between the one-reactor setup, the two-reactor setup, and the three-reactor setup allow for insight as to how depth influences the chemical degradations. • Many conventional wastewater treatment processes only partially remove trace organics that result from human use, including hormones and pharmaceuticals. • Advanced oxidation processes (AOPs) can be used to remove the chemicals that remain. Ultraviolet Photolysis of H2O2 (UV/H2O2) is one of the most common AOPs used in practice. • In this work, we propose a kinetic model to simulate the UV/H2O2 process taking into account the destruction of trace organics by radicals generated in multiple reactions. • This research predicts the degradation of organic contaminants over a wide range of conditions and illustrates the potential for polishing conventionally treated wastewater with AOPs. Below are the elementary chemical reactions involved in the UV/H2O2 model. Kinetic and equilibrium constants are at 25°C. Reactions E1 to E4 are considered to equilibrate instantaneously. INTRODUCTION • Typical wastewater treatment processes do not completely remove organics, such as pharmaceuticals and endocrine disrupters. • An advanced treatment method which removes these unwanted chemicals in a cost-efficient manner is highly desirable. • This research simulates and analyzes a UV/H2O2 AOP, which converts organic contaminants into carbon dioxide (CO2), instead of transporting the contaminants across different treatment phases, such as in adsorption processes. • This project applies an innovative approach to the UV/H2O2 model, taking into account spatial variations of radical concentrations in the reactor. • By improving an already robust UV/H2O2 AOP model, there is obvious potential for polishing conventionally treated wastewater. Figure 3: This two-reactor setup considers each reactor1 and reactor2as separate reactors and assumes uniformity of all chemical concentrations in each reactor. Figure 4: This three-reactor setup considers each reactor1, reactor2, and reactor3as separate reactors and assumes uniformity of all chemical concentrations in each reactor. Figure 2: This one-reactor setup assumes uniformity of all chemical concentrations. Figure 5: Light intensity attenuated by absorption. CONCLUSIONS RESULTS • The adjusted UV/H2O2 models, which take into account the spatial variations of radical concentrations, are improved models. • Expanding this multiple-reactor approach to other data sets and different conditions would be rewarding future research. • As originally hypothesized, the degradation of organic contaminants is predictable over a wide range of conditions. • This UV/H2O2 model illustrates the promise for effectively and efficiently removing potentially harmful contaminants in water. • The implications of these results are significant. • Determining a consistently successful and cost-effective method for the removal of these pollutants is essential. Preliminary model results demonstrate that the UV/H2O2 model was successful in reproducing previously published results (Figure 6). Figure 1: Student conducting UV/H2O2 AOP experiments. Figure 6:The decomposition of p-cresol for three initial H2O2concentrations using the UV/H2O2 model. [PC]0=240μM and λ=250nm. (Left) Figure from Rojas et al. (2010). (Right) From this research. UV/H2O2 MODEL OBJECTIVES The new multiple-reactor approaches take into account spatial variations of radical concentrations. The figure below (Figure 7) demonstrates slight improvement in the accuracy of the multiple-reactor models compared to the original single-reactor model. ACKNOWLEDGEMENTS • To oxidize unwanted compounds remaining in wastewater. • To characterize the mechanism and kinetics behind the decomposition of nonylphenol (NP) and p-cresol (PC), two chemicals in wastewater that serve as surrogates for endocrine disruptors. • To improve an already robust UV/H2O2 AOP model by taking into account spatial variations of radical concentrations. • To predict the degradation of organic contaminants over a wide range of conditions, thus broadening the model’s applications. • I would like to thank: • Dr. Maria Teresa Velez, the Director of the University of Arizona Undergraduate Research Opportunities Consortium (UROC) • Donna Treloar, the Director of the University of Arizona Summer Research Institute (SRI) • This research was supported by the Western Alliance to Expand Student Opportunities (WAESO) ‘Senior Alliance’ Louis Stokes Alliance for Minority Participation (LSAMP) National Science Foundation (NSF). Figure 7: (Left) The decomposition of PC using the original single-reactor UV/H2O2 model. (Middle) The decomposition of PC using the improved two-reactor UV/H2O2 model. (Right) The decomposition of PC using the improved three-reactor UV/H2O2 model.