Simultaneous removal of sulfamethazine and sulfate via electrochemical oxidation and capacitive Deionization: Mechanisms of in-situ activation and strategies of the hybrid system

Electrochemical oxidation (EO) is a well-established method for pollutants removal. However, excessive addition of oxidant during EO may cause secondary pollution. Moreover, the unprocessed ions in the wastewater can cause further contamination. This research introduces a hybrid process that combines EO with capacitive deionization (CDI), in situ catalytically utilizing sulfate (SO42-) and removing sulfamethazine (SMZ). This process realized by layered porous MXene-modified biochar electrodes (BCM) that demonstrate electrocatalytic and adsorption properties. The electrochemical oxidation system, constructed using BCM cathode and boron-doped diamond anode, harnesses in situ generation of oxidants from SO42-, leading to the complete degradation of 30 mg/L sulfamethazine in 30 min through adsorbed radicals and metastable active species at the biphasic interface. Subsequently, the BCM-2 exhibits excellent CDI performance at 1.2 V, achieving a desalination capacity of 15.40–65.97 mg/g in 100–1000 mg/L Na2SO4 solution. By combining EO with CDI, BCM simultaneously removes sulfamethazine and sulfate, resulting in a 60 % reduction in total organic carbon and a 14.4 % decrease in electrical conductivity after one process cycle. Moreover, BCM exhibits favorable cytocompatibility.