(86c) Parameter Estimation of a Model of Advanced Oxidation Processes

In a previous work, a mathematical model of advanced oxidation processes (AOPs) was developed.¹ It was based on the mole balance equations of species and the kinetic information offered by the reaction mechanism. The model described the treatment of ciprofloxacin (CIP) in aqueous solution using the ozonation process. Intermediate compounds of CIP degradation were neglected, and the key model parameters were the volumetric mass transfer coefficient in the liquid phase (k_La) and the liquid hold up (β).

The present work focusses on parameter estimation of the model describing the CIP oxidation considering the reactions of intermediate compounds and total organic carbon (TOC) with the ozone molecule and hydroxyl radical. These reactions were inserted in the reaction mechanism according to a possible degradation mechanism of CIP reported in the literature.² A sensitivity analysis was performed in order to evaluate the influence of kinetic constants on the model predictions. The kinetic constants were varied one by one and the predicted concentration profiles of CIP and ozone in the gas phase at the column outlet were analyzed. The model parameters k_La, β and kinetic constants were estimated from available experimental data minimizing the differences between the experimental and predicted concentrations of CIP and ozone in the gas phase.³ In addition, reparameterization for the kinetic constants was used. The optimization problem was solved using the fmincon solver of Matlab^®. Values for the initial guesses of the model parameters were taken from the literature, and upper and lower bounds for the parameters were defined.^4,5 In all cases, the accuracy of the model predictions was estimated by means of the root mean square error (RMSE).

Once the parameters were estimated, simulations of the process taking into consideration the experimental conditions were performed. The model was capable to fit adequately the experimental CIP and gas phase ozone concentrations. Process simulations with the estimated parameters considering the intermediates (k_La, β and kinetic constants) were compared with simulations using estimated parameters (k_La and β) neglecting the reactions of intermediates and TOC. The comparison allowed to study the role of intermediate compounds. These compounds consume ozone affecting the ozonation process. When the intermediates were neglected, the model overestimated the ozone concentrations in the gas phase for all the experimental conditions. The model was not capable to fit adequately the ozone concentrations in the gas phase even working with estimated parameters from the available experimental data. It is necessary to take into consideration the reactions of intermediate compounds of CIP degradation and TOC in order to obtain a good agreement between the model predictions and the experimental data. The mathematical model of advanced oxidation processes with the estimated parameters can be used to test different experimental conditions and design experiments that lead to a maximization of degradation.

References

1.Abreu Zamora MA, Teixeira ACSC, Le Roux GAC. Modelling and simulation of advanced oxidation process: application to the treatment of ciprofloxacin in aqueous solution by ozonation process. Comput. Aided Chem. Eng. 2017; 40: 553-558. In: 27^th European Symposium on Computer Aided Process Engineering.

2.De Witte B, Dewulf J, Demeestere K, Van Langenhove H. Ozonation and advanced oxidation by the peroxone process of ciprofloxacin in water. J. Hazard. Mater. 2009; 161(2-3):701-708.

3.Bardauil Baptistucci C. Degradação do antibiótico ciprofloxacina em solução aquosa por meio de processo oxidativo avançado baseado em ozônio. Master's Thesis. Chemical Engineering Department, University of São Paulo, 2012.

4.Beltrán FJ, González M, Acedo B, Rivas FJ. Kinetic modelling of aqueous atrazine ozonation processes in a continuous flow bubble contactor. J. Hazard. Mater. 2000; 80(1-3):189-206.

5.Dodd, MC, Buffle MO, Von Gunten U. Oxidation of antibacterial molecules by aqueous ozone: Moiety-specific reaction kinetics and application to ozone-based wastewater treatment. Environ. Sci. Technol. 2006; 40(6):1969-1977.

ACKNOWLEDGEMENT: Antonio Carlos S. C. Teixeira would like to express his acknowledgement to FAPESP for its financial support through grant number 2013/50218-2