Electrochemical Flow Anode For Treating Methylisothiazolinone And Its Application In Reverse Osmosis Concentrate Treatment

With the increasing demand for high-quality reclaimed water,reverse osmosis（RO）membrane treatment process has been widely applied in the industrial field.During the RO process,a certain quantity of reverse osmosis concentrates（ROCs）can be produced,which pose a great challenge to environmental security and human’s health safety.Electrochemical advanced oxidation processes（EAOPs）is receiving increasing attention due to its simple equipment,environmental compatibility,and effectiveness in degrading non-biodegradable pollutants.Based on the electrochemical flow through reactor and optimized anode materials,the degradation performance,oxidation mechanism,environmental risks of ROCs and methylisothiazolinone（MIT,which is a typical pollutant in ROCs）were investigated.MP-Ti-ENTA/SnO₂-Sb electrode was prepared on the porous nanotube array intermediate layer（MP-Ti-ENTA）by sol-gel method,and its oxygen evolution potential was about 2.45 V（vs.NHE）.The conversion lifetime can reach to 1.83 years（current density:20 mA/cm²）,and the reaction rate constant for MIT can reach 1.2～1.5min^-1.In addition,the electrochemical flow through system and ozone oxidation have the lowest EE/O(0.24–1.83 k Wh m^-3)for MIT degradation,which shows the potential of electrochemical flow through anodes for cost-effective water purification.When the MIT removal efficiency reaches over 90%.The removal efficiency of COD and TOC are only 23.8%and 12.7%,respectively.It also indicates that the MIT compound is easily destroyed,but difficult to be fully mineralize into carbon dioxide.The phenomenon may be explained by that MIT degradation path oxidized the carbon-carbon double bonds on the molecule through active oxidizing substances.It causes the MIT molecule to break down and form a refractory carboxylic acid.Control experiments on active oxidizing species（O₃ and H₂O₂）show that the degradation of non-radical contribution could be negligible.Based on the radical shielding experiment,it is estimated that hydroxyl radicals account for about 75.8%of the degradation contribution,while the direct electron transfer reaction（DET）accounts for 24.2%of MIT degradation contribution.According to the fitting analysis of radical dynamics reaction,the second reaction rate constant between MIT and hydroxyl radicals is 3.75×10⁹ M s.In addition,with the range of current densities（2.5～10mA/cm²）,the effective HO·concentration in the electrocatalytic filtration process is 4.0×10^-13～7.1×10^-13 mol/L.The electrochemical treatment of ROCs using MP-Ti-ENTA/SnO₂-Sb flow anode was investigated.The average current efficiency was 60.5～77.4%,and the corresponding COD removal efficiency per unit energy consumption was 60.2～80.7 g COD/k Wh.After electrolysis,the humic acid humus,benzene ring-containing protein and soluble microbial metabolites in ROCs were completely removed,and only fulvic acid humus was detected.Meanwhile,the biodegradability index of ROCs has been greatly improved.In addition,the acute toxicity of ROCs was equivalent to the 0.73mg/L Zn²⁺toxicity level at the initial time,and it decreased to 0.41 mg/L Zn²⁺toxicity level after 30 min of electrolysis.