Combined process of adsorption and electrochemical oxidation to degrade sulfamethazine using low-grade charcoal

To address the limited capacity and frequent replacement of conventional adsorbents, this study proposed a hybrid adsorption-electrochemical oxidation (EO) system to remove sulfamethazine (SMZ) using discarded low-grade charcoal as a functional adsorptive electrode. Under an electrical current of 10 mA, medium-sized charcoal particles (0.15 – 2 mm) increased SMZ removal from 23.6% (adsorption alone) to 95.1%. Surface characterization indicated that EO modified the pore structure and introduced oxygen-containing functional groups on the charcoal surface. This facilitated the degradation of adsorbed SMZ into intermediates such as p-benzoquinone and low-molecular-weight organic acids, regenerating adsorption sites and sustaining removal performance. To reduce energy consumption, a sequential operation strategy – initial adsorption followed by integrated EO – was implemented, achieving comparable removal with lower energy input. Although batch reusability tests showed a decline in SMZ removal from 100% to 39% over four cycles, a continuous stirred-tank reactor (CSTR) demonstrated markedly improved stability. The hybrid CSTR system maintained SMZ removal above 80% for 192 h, whereas the standalone adsorption lost its removal capacity within 6 h. These results highlight the potential of low-grade charcoal as a sustainable and cost-effective adsorptive electrode, offering a viable strategy for continuous treatment of water contaminated with antibiotics.