Comparison of the degradation of multiple amine-containing pharmaceuticals during electroindirect oxidation and electrochlorination processes in continuous system. (15th September 2021)

• Record Type: Journal Article
• Authors: Liu, Yu-Jung; Hu, Ching-Yao; Lo, Shang-Lien
• Is Part Of: Water research. Volume 203(2021)
• Publication Date: 2021-09-15
• Subjects: Multiple amine-containing pharmaceuticals -- Dimer -- Electroindirect oxidation -- Electrochlorination -- Toxicity -- Scavenger; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.117517
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Mass transfer governs the amine-containing pharmaceutical degradation by the electrochemical process. Radicals are the main reactants in the batch system with and without chloride. Free chlorine is the main reactant in the continuous system. Co-existing amine-containing pharmaceuticals may be transferred to dimers. Abstract: The degradation of pharmaceuticals by electrochemical oxidation (EO) in simulated wastewater containing multiple pharmaceuticals was compared between batch and continuous reactors. Despite the excellent efficiencies achieved in batch experiments, the practical/large-scale applications of EO-degrading amine-containing pharmaceuticals has not yet been accomplished. This paper presents the results of continuous experiments with one of the most promising electrochemical configurations of Pt/Ti electrodes before proceeding to application. In the continuous electrooxidation system (without chloride), direct oxidation on the electrode surface and oxidation by hydroxyl radicals were the main pathways. Due to their short lifespans, the radicals could not be transferred to the bulk solution, and the removal of pharmaceuticals followed the order of sulfamethoxazole (SMX) > paracetamol (PAR) > diclofenac (DIC). In the electrochlorination system (with chloride), oxidation by residual chlorine was the main pathway. The removal of pharmaceuticals followed the order of sulfamethoxazole (SMX) > diclofenac (DIC) > paracetamol (PAR). High SMX removal was realized because of the high reaction rate of SMX with free chlorine. Among the pharmaceuticals, PAR had the lowest removal because it is a neutral species with a low mass transfer rate without the attraction of electrostatic force. These results are consistent with the predictions from our previous batch-scale study, which showed that the reaction rate of dissociated compounds could be increased by the addition of electrostatic force. Furthermore, multiple coexisting pharmaceuticals, such as SMX and PAR or DIC, may form dimers that can be transferred to complex structures and cause higher toxicity. Graphic abstract: Image, graphical abstract