Irradiation-assisted electrochemical processes for the removal of persistent organic pollutants from wastewater

Abstract

This work focused on the removal of persistent organic pollutants (POPs) from wastewater using irradiation-assisted electrochemical technologies, i.e. sonoelectrolysis, photoelectrolysis and sono-photoelectrolysis. Single-irradiation processes (sonolysis and photolysis) and electrochemical oxidation using conductive diamond anodes (current density of 30 mA cm -2 ) were also evaluated for comparison. Three POPs with different molecular structures (sulfamethoxazole, metoprolol and caffeine, initial concentration of 100 mg dm -3 ) were studied to evaluate the robustness of the selected technologies and the oxidation mechanisms involved in each case. Results show that the single application of the irradiation technologies led to the removal of only a small amount of POPs and no mineralisation, with the nature of the pollutant showing a marked effect; the opposite was observed for the single application of conductive diamond electrochemical oxidation (CDEO), which is a highly robust and efficient technology for the degradation of all types of POPs. Sonoelectrolysis, photoelectrolysis and sono-photoelectrolysis processes (ultrasound conditions: 200 W, ultraviolet conditions: 254 nm, 4 W) may show synergistic, antagonistic or nil effects with respect to a single electrochemical oxidation event, depending on the nature of the treated molecule. The differences observed may be related to the different chemical nature of the organic species studied, indicating an important role of mediated oxidation processes, which may be enhanced with ultrasounds and ultraviolet radiation techniques.

The Role of Mediated Oxidation on the Electro-irradiated Treatment of Amoxicillin and Ampicillin Polluted Wastewater

“…In order to clarify this point, Figure 6 compares the synergistic effect (estimated according to equation 14) of the electro-irradiated treatment of AMX and AMP solutions and of other compounds previously studied in the literature [32,51] under similar operation conditions. In light of the obtained results, it can be said that although irradiation by UV light or US generates SO 4 and Cl species, and also promotes the formation of OH, this is not reflected in an improvement of the degradation process.…”

Treatment of persistent organic pollutants in wastewater using hydrodynamic cavitation in synergy with advanced oxidation process

“…Adewuyi and Khan (2012) provided a framework model for robust and rigorous development of sonochemical systems and reactors (Adewuyi and Khan 2012). Effective mineralisation of POPs, however, depends on the combination of ultrasonicator with other AOPs (de Vidales et al 2015).…”

Degradation of Atenolol with Electrochemical Oxidation at Mixed Metal Oxide Electrodes Assisted by UV Photolysis

“…Active anodes such as mixed metal oxide (MMO) electrode showed low capability to directly degrade organic pollutants, while non‐active anodes such as boron‐doped diamond (BDD) exhibited higher ability to destroy recalcitrant contaminants due to its higher overpotential for oxygen evolution . Besides, common electrolytes including phosphate, chloride, and sulfate have been usually used to generate • OH, ozone, chlorine, ferrate, and other oxidants during electrochemical oxidation processes . In this study, MMO (IrO 2 /Ta 2 O 5 /Ti) electrodes were used to in situ generate the active chlorine in the presence of NaCl electrolytes.…”

“…–. The literature indicated that the combination of UV photolysis and single electrolysis oxidation can help promote the generation of hydroxyl radicals and the removal efficiency over the expected separate contributions . In this respect, UV photolysis can be used to expand the applicability of electrolysis processes and destroy the organic contaminants in water.…”