Modeling electrochemical oxidation and reduction of sulfamethoxazole using electrocatalytic reactive electrochemical...

In this research, degradation of the antibiotic sulfamethoxazole (SMX) was studied using electrochemical reduction and oxidation in single pass, flow-through mode using porous titanium suboxide (Ti₄O₇) reactive electrochemical membranes (REMs) and Pd-Cu doped Ti₄O₇ REMs (Pd-Cu/Ti₄O₇ REMs). Electrochemical reduction of SMX increased from 3.8 ± 0.3% for the Ti₄O₇ REM to 96.1 ± 3.9% for the Pd-Cu/Ti₄O₇ REM at -1.14 V/SHE and at a permeate flux of 300 L m^-2 h^-1 (LMH) (liquid residence time: ∼1.8 s). By contrast, electrochemical oxidation using Ti₄O₇ REMs achieved 95.7 ± 1.0% removal of SMX at 2.03 V/SHE and a permeate flux of 300 LMH (liquid residence time: ∼9.0 s) without the catalyst addition. We developed a reactive transport mathematical model and calibrated it to the SMX experimental data. The calibrated model predicted SMX permeate concentrations at fixed potentials and as a function of permeate flux. Based on products from SMX reduction, we proposed that SMX was reduced by a hydrogen atom transfer reaction that was mediated by the Pd-Cu/Ti₄O₇ REM. Toxicity tests indicated that electrochemical oxidation/reduction lowered solution toxicity. The results of this work indicate that a tandem electrochemical reduction/oxidation approach using the REM-based technology is a potential treatment strategy for sulfonamide-contaminated pharmaceutical wastewater.