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 ABSTRACT 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 H 2 O 2 (UV/H 2 O 2 ) is one of the most common AOPs used in practice. In this work, we propose a kinetic model to simulate the UV/H 2 O 2 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. 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/H 2 O 2 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. Preliminary model results demonstrate that the UV/H 2 O 2 model was successful in reproducing previously published results (Figure 6). 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/H 2 O 2 AOP, which converts organic contaminants into carbon dioxide (CO 2 ), instead of transporting the contaminants across different treatment phases, such as in adsorption processes. This project applies an innovative approach to the UV/H 2 O 2 model, taking into account spatial variations of radical concentrations in the reactor. By improving an already robust UV/H 2 O 2 AOP model, there is obvious potential for polishing conventionally treated wastewater. INTRODUCTION UV/H 2 O 2 MODEL OBJECTIVES METHODOLOGY CHEMICAL REACTIONS ACKNOWLEDGEMENTS RESULTS Figure 1: Student conducting UV/H 2 O 2 AOP experiments. 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 2: This one-reactor setup assumes uniformity of all chemical concentrations. Figure 3: This two-reactor setup considers each reactor 1 and reactor 2 as separate reactors and assumes uniformity of all chemical concentrations in each reactor. CONCLUSIONS The adjusted UV/H 2 O 2 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/H 2 O 2 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. Figure 4: This three-reactor setup considers each reactor 1, reactor 2, and reactor 3 as separate reactors and assumes uniformity of all chemical concentrations in each reactor. Figure 5: Light intensity attenuated by absorption. Figure 7: (Left) The decomposition of PC using the original single-reactor UV/H 2 O 2 model. (Middle) The decomposition of PC using the improved two-reactor UV/H 2 O 2 model. (Right) The decomposition of PC using the improved three-reactor UV/H 2 O 2 model. Figure 6: The decomposition of p-cresol for three initial H 2 O 2 concentrations using the UV/H 2 O 2 model. [PC] 0 =240μM and λ=250nm. (Left) Figure from Rojas et al. (2010). (Right) From this research. No.Reaction Rate constant, k (M -1 s -1 ) or equilibrium constant, K R1 H 2 O 2 + hn → 2HO·f=0.5 (primary quantum yield) R2·OH + H 2 O 2 → O 2 · - + H 2 O + H + k 2 = 2.7  10 7 R3·OH + HO 2 - → O 2 · - + H 2 O k 3 = 7.5  10 9 R4·OH + HCO 3 - → CO 3 · - + H 2 O k 4 = 8.5  10 6 R5·OH + CO 3 2- → CO 3 · - + OH - k 5 = 3.9  10 8 R6·OH + HO 2 · → O 2 + H 2 O k 6 = 6.6  10 9 R7·OH + O 2 · - → O 2 + OH - k 7 = 8.0  10 9 R8·OH + ·OH → H 2 O 2 k 8 = 5.5  10 9 R9·OH + CO 3 · - → Products k 9 = 3.0  10 9 R10O 2 · - + H 2 O 2 → ·OH + O 2 + OH - k 10 = 1.3  R11O 2 · - + CO 3 · - → O 2 + CO 3 2- k 11 = 6.5  10 8 R12O 2 · - + HO 2 · + H 2 O → H 2 O 2 + O 2 + OH - k 12 = 9.7  10 7 R13HO 2 · + HO 2 · → H 2 O 2 + O 2 k 13 = 8.6  10 5 R14HO 2 · + H 2 O 2 → ·OH + O 2 + H 2 Ok 14 = 3.7 R15CO 3 · - + H 2 O 2 → HCO O 2 · - + H + k 15 = 8.0  10 5 R16CO 3 · - + HO 2 - → HCO O 2 · - k 16 = 3.0  10 7 R17CO 3 · - + CO 3 · - → 2CO 3 2- k 17 = 2.0  10 7 R18PC + ·OH → Products k PC = 1.2  R19NP + ·OH → Products k NP = 1.33  R20C 3 H 8 O + ·OH → Products k IPOH = 1.9  10 9 R21C 2 H 6 O + ·OH → Products k EtOH = 1.9  10 9 E1 H 2 O 2  HO H + K a1 = E2 HO 2 ·  O 2 · - + H + K a2 = E3 H 2 CO 3  HCO H + K a3 = E4 HCO 3 -  CO H + K a4 = Below are the elementary chemical reactions involved in the UV/H 2 O 2 model. Kinetic and equilibrium constants are at 25°C. Reactions E1 to E4 are considered to equilibrate instantaneously. Learning the Model: In order to validate the efficacy of the UV/H 2 O 2 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/H 2 O 2 model 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. 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.