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A kinetic model describing Fenton and photo-Fenton degradation of paracetamol (PCT) and consumption of hydrogen peroxide (HO) was proposed. A set of Fenton and photo-Fenton experiments (18 runs in total) was performed by fixing the initial concentration of PCT to 40 mg L and varying the initial concentrations of HO and ferrous ion, Fe. The experimental set-up was a well-stirred annular photoreactor equipped with an actinic BL TL-DK 36 W/10 1SL lamp. Experimental results highlighted that PCT is no more detected by HPLC analysis within a minimum reaction time of 2.5 and a maximum reaction time of 15.0 min. Besides, a maximum conversion of total organic carbon (TOC) of 68.5% was observed after 75 min of reaction in case of using UV radiation and the highest concentrations of the Fenton reagents. The experimental data were used to fit the kinetic model. The radiation field inside the reactor was taken into account through the local volumetric rate of photon absorption, evaluated by assuming a line source model with spherical and isotropic emission. The kinetic parameters were estimated by using a non-linear least-squares regression procedure and root mean square errors (RMSE) were calculated in order to validate the feasibility of the proposed model. A good agreement between experimental and predicted data was observed and the lowest values of RMSE resulted in 5.84 and 9.59% for PCT and HO normalized concentrations, respectively.

Fenton, photo-Fenton, and photo-induced oxidation, were investigated and compared for the treatment of 0.26 mmol L−1 of paracetamol (PCT) in a deionised water matrix, during a reaction span of 120.0 min. Low and high Fenton reagent loads were studied. Particularly, the initial concentration of Fe2+ was varied between 0.09 and 0.18 mmol L−1 while the initial concentration of H2O2 was varied between 2.78 and 11.12 mmol L−1. The quantitative performance of these treatments was evaluated by: (i) measuring PCT concentration; (ii) measuring and modelling TOC conversion, as a means characterizing sample mineralization; and (iii) measuring cytotoxicity to assess the safe application of each treatment. In all cases, organic matter mineralization was always partial, but PCT concentration fell below the detection limit within 2.5 and 20.0 min. The adopted semi-empirical model revealed that photo induced oxidation is the only treatment attaining total organic matter mineralization ( ξ MAX = 100% in 200.0 min) at the expense of the lowest kinetic constant (k = 0.007 min−1). Conversely, photo-Fenton treatment using high Fenton reagent loads gave a compromise solution ( ξ MAX = 73% and k = 0.032 min−1). Finally, cytotoxicity assays proved the safe application of photo-induced oxidation and of photo-Fenton treatments using high concentrations of Fenton reagents.

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The photo-Fenton process is a photochemical process that has proved to be highly efficient in degrading new potentially harmful contaminants. Despite of this, scarce attention has been paid to the development of systematic procedures and optimisation strategies to efficiently operate such a process. The present work aims at investigating the effectiveness of a model-based approach in carrying out the dynamic optimisation of the recipe of a photo-Fenton process, performed in fed-batch mode (reactant dosage). This work has addressed and solved multiple optimisation problems, searching for the optimal hydrogen peroxide (HO) dosage profile, and Pareto frontiers have been built accordingly in order to point out the interaction between three main process efficiency parameters, such as processing time, total amount of HO used, and Total Organic Carbon (TOC) removal. Such a study allows mapping the best operating conditions and provides a decision-making oriented overview of the process. An economic study has also been carried out with the aim of finding out the optimal HO dosage profile that guarantees the minimum operating cost under a varying set of operational and environmental constraints, such as TOC removal. This work has adopted and properly adapted the model by Cabrera Reina et al. (2012) in order to describe the evolution of the system under a flexible reactant dosage. Cabrera Reina et al. (2012) proposed a semi-empirical kinetic model to track paracetamol degradation using the photo-Fenton process and experimentally validated this model for a pollutant load range between 4 and 25 mmol L of TOC (e.g. industrial wastewaters). Dynamic optimisation has been addressed applying a direct simultaneous optimisation method using this extended model. Results have been presented and discussed in regard of optimal HO dosage under both economic and environmental constraints. The model-based optimisation approach has allowed a fast practical recipe adjustment with reduced experimental work.