A Comprehensive Study of the Electrochemical Oxidation of Diclofenac Sodium in Reverse-Osmosis Concentrate: Analysis, Reaction Kinetics, and the Effect of Electrolyte Composition

Abstract

Electrochemical oxidation (EO) is the most promising treatment for pharmaceutical removal in an aqueous matrix, though there are limited studies investigating the EO of pharmaceuticals in a real matrix such as reverse osmosis concentrate (ROC). High electrical conductivity causes less energy consumption for EO and massive chloride concentration in ROC make it suitable for its use as an electrolyte. The application of ROC as an electrolyte for the EO of diclofenac sodium (DCF) using an indigenously prepared Ti/Ru-Sn-Sb-Ox anode is explored in this study. The removal rate increased with an increase in current density from 5 to 10 mA/cm2 for both DCF and intermediate products (IPs). The 0.005 p-value obtained using a paired t-test indicated that the results obtained using methanol as a quenching agent matched those obtained by immediate analysis (without quenching) at a 99.5% confidence level. Thus, methanol is the most suitable quenching agent in this study. The composition of electrolyte in terms of sulfate to chloride mass ratio was found to affect the removal of DCF and IPs. The maximum removal (approximately 95%) of DCF was obtained in the presence of a sulfate-to-chloride mass ratio ranging from 0.85 to 1.35. The phytotoxicity level increased from 3% to 9% after 120 min of EO, which is not significant compared with similar previous studies.