Amperometry for real-time and on-site monitoring of phenol and H₂O₂ during the treatments

In conventional wastewater treatment processes, a predetermined quantity of chemicals is introduced at the onset, without ongoing monitoring of the treatment progress. Thus, it is difficult to perform timely intervention in the treatment process. Herein, we develop an amperometry-guided wastewater treatment strategy based on a green oxidation process with H₂O₂ and an iron-tetraamidomacrocyclic ligand (Fe-TAML) catalyst. During the process, users can monitor both phenol and H₂O₂ concentrations in real time and then intervene by adding more H₂O₂ to accelerate the reaction. As a proof of concept, a wastewater sample containing 9.3 ppm of phenol is treated by using the amperometry-guided strategy with 1 dosage of Fe-TAML (0.45 ppm) and 3 dosages of H₂O₂ (1.86 ppm). After the treatment, phenol concentration in the wastewater decreases to 0 ppm after 21 min. In contrast, with only 1 dosage of Fe-TAML (0.45 ppm) and 1 dosage of H₂O₂ (1.86 ppm), the reaction slows down after 5 min and stops prematurely. After that, the reaction kinetics of ppb-level phenol are investigated, in which the phenol rate and the rate constant are estimated. Compared to conventional detections, the designed amperometry shows faster response, lower limit of detection (LOD, phenol: 11 ppb, H₂O₂: 80 ppb) and consumable cost, easier operation, and no pollution generated. This example demonstrates the importance of early intervention during wastewater treatment with the help of real-time information.