Degradation of methylisothiazolinone biocide using a carbon fiber felt-based flow-through electrode system (FES) via anodic oxidation

Methylisothiazolinone (MIT) is one of the most widely used non-oxidizing biocides, however its toxicity may pose a threat to ecosystems. A carbon fiber felt-based flow-through electrode system was used for MIT degradation in an aqueous solution. An excellent degradation rate (similar to 90%) was achieved at a low applied cell voltage (2.5 V) and a high feed water flux (3 m(3) h(-1) m(-2)) that corresponds to a short resistance time of similar to 11 s. In-situ sampling experiments and electrochemical characterization indicated that MIT was degraded via a direct anodic oxidation mechanism. In terms of electrode sequence, anode-cathode system (by placing the anode upstream from the cathode) exhibited an improved MIT degradation performance and energy efficiency compared with a reversed cathode-anode system (by placing the anode downstream from the cathode), because the former arrangement prevented parasitic reactions and provided a higher anode potential. Effluent analysis by time-of-flight mass spectrometry and luminescent bacteria acute toxicity showed that the organic sulfur atom was oxidized to the sulfoxide or sulfone structure and then hydrolyzed to release from the MIT molecule, which led to a significant toxicity reduction. No obvious performance loss was observed over 5 h of continuous operation with a total treated MIT solution up to 1400 times the cell volume and an energy requirement of 0.03 kWh m(-3). These promising data make the carbon fiber felt-based flow-through electrode system attractive for effective and low-cost water purification.