Mathematical modeling of ozone decomposition processes in wastewater treatment: A lumped kinetic approach with initial ozone demand

Ozone-based processes involve complex reaction networks and exhibit matrix-dependent decomposition patterns when dosed to wastewater effluents. Existing models for ozone decomposition are either too complex or not sufficiently descriptive of the regime manifested during initial ozone demand and decay. Models incorporating detailed reactions have shown limited applicability due to the high number of initial states and state variables involved. This study introduces a new mathematical model that balances accuracy and complexity in describing the main phases of ozone decomposition in secondary wastewater effluents. Specifically, a simplified model is proposed based on lumped variables, including initial ozone demand, two classes of organic matter (slow and fast reacting), radical forming (and ozone-decomposing) compounds, radical scavengers, and a hypothetical target contaminant. Results revealed that the model can predict with reasonable accuracy both the rapid initial ozone demand (occurring at very short timescales <10¿s) and the slower ozone decomposition processes (occurring at longer timescales >30¿s). A global sensitivity analysis was also conducted to further model refinement and simplification, which led to the elimination of three reactions connected to the generation and consumption of radicals (threshold || = 0.05). Satisfactorily low residual values (RMSE=7·10-6 M) were observed in all cases. Finally, the adequacy of the model was further tested against an independent set of ozone decomposition experiments obtained from the literature, confirming its suitability in describing ozone decomposition in secondary wastewater effluents with initial ozone demand.