Amperometry for real-time and on-site monitoring of phenol and HO 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 HO and an iron-tetraamidomacrocyclic ligand (Fe-TAML) catalyst. During the process, users can monitor both phenol and HO concentrations in real time and then intervene by adding more HO 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 HO (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 HO (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, HO: 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.