On-line FTIR as a novel tool to monitor Fenton process behavior

• On-line FTIR is shown as a suitable alternative for real-time reaction control.
• FTIR was successfully applied to monitor the Fenton oxidation of model compounds.
• FTIR-based real-time control allowed the finest Fenton’s process optimization.
• The proposed methodology saved much time for analyses monitoring Fenton processes.

The efficiency of advanced oxidation processes is usually optimized by measuring the evolution of some water quality parameters sampling aliquots at pre-selected time intervals, such as particular undesired contaminants contents, or the reduction of chemical oxygen demand and total organic carbon. Besides providing good information regarding overall treatment performance and dynamics, this methodology also implies large analytical time consumption, and does not offer the actual full sequence of compounds appearing and disappearing during oxidation. On-line Fourier transform infrared spectroscopy is herein reported as a very useful tool for this purpose. In particular, it was successfully applied to monitoring the Fenton’s oxidation of three model compounds (phenol, acetic acid, and oxalic acid) performed in continuous, providing precise control of the effect of reagents over time. Hydroxylation reactions resulted in the formation of hydroquinone and catechol as the main aromatic by-products being generated along the oxidation of phenol by the Fenton process. All phenolic substances (phenol, hydroquinone, benzoquinone, and catechol) were totally removed along the reaction. Carboxylic acids (oxalic and acetic mainly) were significantly present as final by-products of the oxidation process, highlighting their oxyrecalcitrant behavior. On-line FTIR successfully enabled monitoring the Fenton process, and it provided a precise control of the effect of reagents along reaction time. Applications for a future on-line control of Fenton processes in industry may be developed in order to optimize the use of reagents and the potential combination with biological treatment stages; therefore reducing the operational cost of this advanced oxidation treatment.

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