The Study On Electrochemical Technology For Treating Methylisothiazolinone And Its Application In Reverse Osmosis Concentrate

Recently,methylisothiazolinone?MIT?has been widely used in reverse osmosis system to suppress the growth and propagation of microorganisms.The discharge of reverse osmosis concentrate?ROC?containing high concentrations of MIT to natural water bodies poses great threats to natural environment and human health.The electrochemical oxidation process is a promising technology for treating MIT since it is effective,environment-friendly and no secondary pollution.Therefore,we systematically investigated the electrochemical oxidation for treating MIT and its application in ROC in this study.Ti/SnO₂-Sb₂O₃/?,?-PbO₂ electrode was fabricated and the characteristic of MIT degradation using electrochemical oxidation were studied.Ti/SnO2-Sb2O3/?,?-PbO2shows the oxygen evolution potential of 2.09 V?vs.NHE?,which favors for producing HO·on electrode.The electrochemical degradation of MIT consists with the pseudo-first-order reaction kinetics and the reaction rate constant was determined as 1.62×10^–322.12×10^–3 min^–1.A high electron utilization was observed on electrode.68.8%electrons that are used for COD removal can be used for mineralizing MIT into CO₂.Results show that energy consumption to eliminate one order MIT concentration?EE/O?is 1.0⁴3.5 kWh/m³ to achieve 90%MIT degradation when MIT concentration is100⁴00 mg/L and current density is 2.5⁵0 mA/cm².Compared with other MIT treatment technologies,electrochemical oxidation demonstrates advantages of relatively low energy consumptions and more environment-friendly.The HO·and H₂O₂ production are enhanced when the applied current density is increased using a Ti/SnO₂-Sb₂O₃/?,?-PbO₂ for MIT electrochemical oxidation.The direct oxidation and indirect oxidation were calculated to be 37.7%and 62.3%on electrode,respectively.HO·oxidation was proven to be the main mechanism of MIT degradation.A new and distinct pathway of MIT degradation was found in electrochemical oxidation.The C=C bond is firstly broken down to achieve further oxidation.The introduction of TiO₂-NTs into SnO₂-Sb electrode can increase the electrochemical activity and stability of a novel Ti/TiO₂-NTs/SnO₂-Sb anode.EE/O for MIT oxidation is 0.74²7.42 kWh m^–3,which is lower than Ti/SnO₂-Sb₂O₃/?,?-PbO₂electrode.It was found that decreasing the space between two electrodes and/or increasing fluid velocity can increase mass transfer coefficient and reaction rate as well as reducing energy consumption.The effectiveness factor???can be used to evaluate the mass transfer resistance and this index can be popularized to other electrochemical oxidation processes.The degradation performance of ROC by using Ti/SnO₂-Sb₂O₃/?,?-PbO₂ and Ti/TiO₂-NTs/SnO₂-Sb was investigated.Results show that the performance of Ti/TiO₂-NTs/SnO₂-Sb electrode to degrade organic compounds is better than Ti/SnO₂-Sb₂O₃/?,?-PbO₂ electrode.MIT degradation efficiency reached 99%after 1 h electrochemical oxidation with the use of the two electrodes.However,Ti/TiO2-NTs/SnO2-Sb electrode pose no threat on heavy metal dissolution?Pb?.Chloride ion concentration in ROC influences chlorine evolution reaction.By rising the concentration of Cl^-can decrease the voltage and energy consumption and enhance the removal of COD in electrochemical oxidation process.