Removal Effects And Mechanism Study On The Chemical Odorants In Drinking Water By Selected Oxidation Process

In recent years,the taste and odor（T&O）problems of drinking water occur repeatedly in many countries throughout the world.The drinking water industry is facing huge challenges.The lives and health of residents have been affected and threatened.The safety of drinking water has attracted much attention.Due to social development and the large-scale use and random discharge of chemical organics such as benzene,ether,phenol and indole in production and life,the frequent detection of phenol and indole organics in source water gives rise to concern about the taste and odor problems mainly caused by some chemicals.As the current conventional treatment processes of drinking water treatment plants,coagulation,precipitation,filtration,etc.,are difficult to remove odorants effectively,it is necessary to add enhanced removal methods in the drinking water treatment process for further treatment.And chemical oxidation technology is widely used in actual production because of its advantages of convenient and high efficiency.This article mainly focuses on two typical oxidants,sodium hypochlorite（NaClO）and potassium permanganate（KMnO₄）,with 3-methylphenol（3-MP）,2,6-dichlorophenol（2,6-DCP）,indole and 3-methylindole（3-MI）four chemical odorants are the main targets.The removal of of 3-MP,2,6-DCP,indole and 3-MI by NaClO and KMnO₄,the oxidation kinetics,the influence of pH and NOM factors,the reaction mechanism and the oxidation effect in actual water are studied.It is expected to provide basic data reference for the control of phenols and indoles in chemical odor emergencies in the drinking water treatment process.Under the condition of pH 7,the removal and oxidation kinetics of the mixed solution of3-MP,2,6-DCP,indole and 3-MI with different dosages of NaClO and KMnO₄ were investigated.The results of the oxidation effect experiment showed that under the condition of pH 7,NaClO oxidation could almost completely remove indole and 3-MI,and could remove3-MP and 2,6-DCP effectively;while the oxidation of KMnO₄ is close to complete removal of3-MI,and could be effectively removed for 3-MP and 2,6-DCP,but it could not be effectively removed for indole.And except that the oxidation effect of 3-MP and 2,6-DCP by NaClO is obviously enhanced with the increase of NaClO dosage,the rest of the oxidation process is basically not affected by the dosage of oxidant.The kinetics of four odorants by NaClO and KMnO₄ oxidation were analyzed using the competitive kinetics with 3-MP as the competitor.The results of oxidation kinetic showed that the oxidation process of 3-MP,2,6-DCP,indole and 3-MI by NaClO and KMnO₄ basically accorded with the second-order kinetic model.Among them,the order of the kinetic constants of four target odorants by NaClO oxidation was:3-MI,Indole,3-MP,2,6-DCP.The order of the kinetic constants of four target odorants by KMnO₄ oxidation was:2,6-DCP,3-MI,3-MP,Indole.Under the condition of pH 5-9,the effect of different pH on the removal of four target odorants by NaClO and KMnO₄ oxidation was investigated,and the results showed that pH has a great influence on the removal of 3-MP and 2,6-DCP by NaClO and KMnO₄ oxidation.3-MP has a better removal under alkaline conditions,and 2,6-DCP could be better oxidized and removed under neutral conditions.For indole and 3-MI,pH only slightly affects the removal of indole by KMnO₄ oxidation,while the removal of other oxidation processes are basically the same under different pH conditions.The oxidation kinetics affected by pH.showed that under neutral conditions,the removal of 3-MP and 2,6-DCP by NaClO oxidation and the removal of 2,6-DCP and 3-MI by KMnO₄ oxidation faster.Under acidic conditions,the reaction rate of Indole and 3-MI by NaClO oxidation was faster.Under alkaline conditions,the reaction rate of 3-MP by KMnO₄ oxidation was faster.The reaction rate of indole by KMnO₄ oxidation was less affected by pH.The effect of NOM from 2.0 to 8.0 mg·L^-1 on the removal of target odor substances by NaClO and KMnO₄ oxidation in the experiment was investigated.The results showed that the NOM in the aqueous solution would reduce the removal of the target odorants by NaClO oxidation.The NOM has a promoting effect on the oxidation process of KMnO₄.The products produced of four target odor substances by the process of NaClO oxidation showed that NaClO mainly degraded 3-MP and 2,6-DCP through chlorination reaction,and four chlorinated products were detected;while for indole and 3-MI,the degradation is through the chlorination reaction and the hydroxylation reaction,and three intermediate products were detected.The possible reaction path was speculated in the paper.The research on the oxidation removal of four target odorants in actual water showed that the removal of odorants under actual water background conditions is mainly affected by the NOM concentration in the water.