Degradation of Sulfamethoxazole using Palladium-based Electrocatalytic Reactive Electrochemical Membranes

Increased antibiotic resistance in bacteria has caused concern over the release of antibiotics into the environment. In this research, degradation of the antibiotic sulfamethoxazole (SMX) was studied using electrochemical reduction and oxidation in a flow through reactor as a function of potential and permeate flux. Electrochemical destruction of SMX was accomplished in flow-through, single pass operation mode using porous titanium suboxide (Ti4O7) reactive electrochemical membranes (REMs) and Pd-Cu doped Ti4O7 REMs (Pd-Cu/Ti4O7 REMs). Results for electrochemical reduction showed that the removal 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) (residence time: ~7.2 s), which is an approximate 1-log improvement in the reduction of SMX. By contrast, electrochemical oxidation experiments in the same operation mode using Ti4O7 REMs achieved 95.7 ± 1.0 % removal of SMX at 2.03 V/SHE at a permeate flux of 300 LMH without the addition of catalytic metals. A mathematical model characterizing reactive transport of SMX in the REMs was developed and calibrated to the experimental data. The calibrated model was able to accurately predict SMX permeate concentrations as a function of applied electrode potential and permeate flux rates. Products from electrochemical reduction experiments were analyzed using liquid chromatography-tandem mass spectroscopy. Based on the detected product, it was proposed that SMX was reduced by a hydrogen atom transfer reaction that was mediated by the Pd-Cu/Ti4O7 REM.