Persulfate contribution to photolytic and pulsed corona discharge oxidation of metformin and tramadol in water

Abstract

Degradation and mineralization of antidiabetic metformin (MTF) and opioid tramadol (TMD) in water were studied in UV photolytic oxidation and pulsed corona discharge (PCD) combined with extrinsic persulfate (PS) as UV/PS and PCD/PS systems. The effect of PS dose variation on the oxidation rate and efficiency was assessed. The UV/PS combination showed considerable effect in MTF and TMD removal, enhancing the removal of TOC up to 60–65% at maximum applied PS dose, thus providing the highest cost efficiency. As for the PCD/PS oxidation, the synergy was noticed for MTF, moderately increasing the oxidation rate and mineralization at somewhat increased expense. The PS addition to PCD treatment, however, demonstrated no effect on TMD oxidation. The highest energy efficiency in MTF and TMD degradation was thus showed by non-assisted PCD treatment with an energy yield at 90% conversion of the target compound of 5.6 and 13 g kW-1 h-1, respectively, confirming its practical applicability. The effective mineralization of the target compounds in persulfate photolysis makes it promising for use in advanced water purification. To assess the environmental safety of the studied oxidation processes, the acute toxicity of the treated MTF and TMD solutions to luminous bacteria (Vibrio fischeri) was examined.