Removal Of Soluble Manganese By Chlorination-filtration With Catalysis Of In-situ Manganese Modified Zeolite

The problem of excessive manganese in water is widespread all over the world.In the last century,China has made a lot of research on iron and manganese removal from ground water and achieved remarkable results.In recent year-s,the concentration of manganese in the surface water supply such as reservoir-s and lakes,has been exceeding the limit level of 0.1mg Mn/L at a specific time.In addition,the safety of drinking water in rural areas is becoming increasingly prominent,and the removal of manganese from groundwater in rural areas without centralized water supply facilities or with intermittent small-scale centralized water supply is still a problem.In this paper,the in-situ manganese modified zeolite was used to achieve rapid and stable manganese removal under chlorination conditions.At the same time,the influencing factors,operating conditions and mechanism of in-situ manganese modified zeolite chlorine catalytic oxidation manganese removal were studied.The main conclusions were as follows:（1）The preparation method of in-situ manganese modified zeolite is simple and convenient.It can firmly load a considerable amount of manganese oxide on the surface of zeolite,and its adsorption performance is obviously stronger than manganese sand.It can remove manganese rapidly and steadily adding chlorine before filtration.（2）The influencing factors of manganese removal by in-situ manganese modified zeolite chlorine catalytic oxidation process were studied.It was found that the dosage of chlorine was insufficient and the concentration of manganese in effluent was higher than 0.1mg Mn/L.The excessive chlorine dosage caused higher concentration of the residual chlorine in effluent.The optimal dosage of chlorine was 0.87 mg/L under the experimental conditions with the concentration of manganese in influent being 1 mg/L and the residence time being 11.8 min.Shortening the residence time,the effect of manganese removal becomes worse.The residence time should be more than 7.9minutes.Increasing the filtration rate,the depth of the filter layer should increase to ensure enough residence time for that the concentration of manganese of the effluent is lower than 0.1mg Mn/L.Mn²⁺is mainly removed in the upper part of the filter,and the removal rate of Mn²⁺can reach 90%at 5cm.Low concentration of organic matter had no effect on the removal of manganese,while high concentration of organic matter made the removal of manganese worse.Ferric hydroxides and Ca²⁺had no effect on manganese removal.（3）Backwashing has no effect on the removal of manganese by in situ chlorine catalytic oxidation filtration of manganese modified zeolite.Manganese absorbed by in-situ manganese modified zeolite absorbs dissolves into water again during backwashing,while Mn²⁺adsorbed under chlorination condition is oxidized to solid manganese oxide,and there is almost no Mn²⁺in backwashing water.The filter using in-situ manganese modified zeolite-quartz sand as filtration media can effectively remove manganese when chlorine is added before the filtration.In-situ manganese modified zeolite chlorine catalytic oxidation filtration process has a good removal effect on manganese in groundwater and Songhua River water,and the disinfection by-product in effluent is trace.（4）The mechanism of in-situ manganese modified zeolite chlorine catalytic oxidation filtration for manganese removal is that Mn²⁺is adsorbed by in-situ manganese modified zeolite firstly,and then oxide by chlorine with catalysis of manganese oxide multiphase interface forming new manganese oxides.The process of manganese removal is the result of the balance of adsorption and oxidation processes occurring simultaneously in the filter layer.The influence on adsorption and oxidation will affect the concentration of Mn²⁺in the effluent.The manganese oxides formed by chlorine oxidation of Mn²⁺are amorphous,including manganese oxides with various valences,such as MnO,Mn₃O₄ and MnO₂.The available chlorine required for manganese oxidation of 1 mg is less than 1.3 mg.The catalytic component of manganese oxide is Mn₃O₄.