Electrocoagulation/oxidation/flotation by direct pulsed current applied to the removal of antibiotics from Brazilian WWTP effluents

Emerging contaminants such as pharmaceutical residue brings harmful effects to the environment and human health as well. In Brazil, wastewater treatment plants (WWTPs) for influents and effluents do not remove efficiently that kind of residue due to the conventional biological-like treatment. In this context, alternative treatments, such as electrocoagulation can be used to achieve better removal efficiency based on electrolytic treatment. In this work, electrocoagulation processes (ECOF) were applied to remove antibiotics, such as trimethoprim (TMP) and amoxicillin (AMX) using a direct pulsed current (DPC). The electrocoagulation process was conducted using different anodes (304 and 316L steel electrodes and 1050 aluminum electrodes), and were evaluated experimental parameters such as corrosion rate, pH of the working solution and operational costs. In comparison with other electrodes, the 1050 aluminum electrode showed the larger corrosion rate, longer service life and smaller operational costs (energy and electrode consumptions). In addition, using of the pulsed direct current reduced the consumption energy of the electrocoagulation process by 30% when compared to the same process using direct current. During electrocoagulation process, the electrodes showed a complex hydrolysis equilibrium due to charge density transfer of the electrodes themselves which resulted in an acid-base equilibrium between hydrolysis products and AMX/TMP molecules. For 1050 aluminum electrodes, the pH of the electrolyte during electrocoagulation process changed from 3.0 to 5.5, and the cationic equilibrium containing Al3+ and Al(OH)(2+) along the studied molecules was proposed. The same equilibrium approach was used in iron present in the steel electrodes: once the pH ranged from 3.0 to 7.0, the proposed equilibrium for this system evolves Fe3+, Fe(OH)(2) and Fe(OH)(3) compounds. To investigate the reactivity between AMX/TMP molecules and the electrodic surfaces, DFT calculations were conducted, and the analysis of molecular parameters in the experimental processes showed a passivation effect of AMX and TMP molecules towards 1050 aluminum electrode while AMX presented a corrosion effect in steel electrodes. Therefore, the 1050 aluminum electrode presented the best efficiency over steel electrodes in electrocoagulation process for AMX and TMP removal in wastewater, having potential to be applied in large scale application in a WWTP. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Emerging contaminants like pharmaceutical residues pose harmful effects on the environment and human health, with conventional wastewater treatment plants in Brazil failing to efficiently remove them. Electrocoagulation processes show promise in achieving better removal efficiency, with the 1050 aluminum electrode demonstrating superior performance in removing antibiotics like trimethoprim and amoxicillin, making it a potential candidate for large-scale application in wastewater treatment plants.