The Study Of The Catalytic Oxidation Removal Of Ammonium/manganese From Surface Water By Manganese Co-oxides Film At Pilot Scale

Ammonium and manganese are major pollutants in surface water source in China.The removal of manganese and ammonium from surface water sources is one of the critical issues that needs to be solved in China.The objective of this study is to explore the ammonium and manganese removal from surface water by the chemical catalytic oxidation technology which is different from conventional biological and chemical-physical processes,and as well as to establish a new process for manganese and ammonium removal from surface water.The main experimental results are as follows:(1)A method for sustaining the activity of manganese co-oxide film was proposed.The capability of co-oxide film for ammonium removal from surface water decreased gradually when dealing with effluent from the sedimentation tank of a surface water plant.By dosing phosphate into surface water,ammonium removal activity of the co-oxide film could be sustained.The dosage of the phosphate should be in the range of 5-30 ?g/L based on the change of the temperature and phosphate can be dosed intermittently with water temperature above 14 ? to sustain the activity of the manganes.The activity of the manganese co-oxide was relatively stable when the water sources were treated directly.The activity for manganese removal was still stable in a long period of time without phosphate doing and would be further increased with running time.(2)The influence factors and process parameters on ammonium and manganese removal from surface water were determined.The main influence factors on ammonium and manganese removal from surface water include dissolved oxygen,pH,water temperature,turbidity.In summer and autumn,the activity of the co-oxide film was high.Therefore,the concentration of the oxygen was the condition that limits the ammonium removal.Moreover,ammonium could be removed by the filter with the filter bed comprised with virgin quartz sands and the co-oxide film coated sand to reduce the cost.In winter,the activity of the filter media was relatively low.By increasing the height of the filter bed and provide more oxgen from the bottom of the filter ammonium with concentration higher than 3.0 mg/L could be removed effectively.For seasonal manganese pollutants,ammonium and manganese could be removed simultaneously in summer.If the water pH value is lower than 7.01,the adjustment of the pH is necessary to ensure the manganese removed completely.Under persistent manganese pollution conditions,the oxide film can effectively remove ammonium and manganese from the water even when the water temperature is as low as 5.5?.(3)The reason for the decreased activity of the filter media has been found and the mechanism of phosphate sustaining the catalytic activity of the filter media has been explored.By the analyzing the the morphology,element species and elemental chemical state of the co-oxide film by SEM,EDS and XPS methods,it indicated that aluminum can combine with the oxygen atom or hydrogen group connecting with Mn(?)which is the active species of the manganese co-oxide film and resulted in the depletion of the numbers of the active sites and the decrease of the catalytic ability by comparing the changes of the elements species,atomic percent,elements distribution and chemical state of the co-oxide film.After the addition of phosphate,the aluminum content on the surface of the oxide film decreased by 60.53%,and the chemical catalytic activity was 2.07 to 2.15 times that of the case without adding phosphate.By analyzing the transformation procedure of phosphate and aluminium,it was found that the stronger binding force between aluminum and phosphate prevented aluminum from combining with manganese co-oxide film and therefore,the catalytic activity of the co-oxide film was sustained.(4)The mechanism of the chemical catalytic oxidation removal of ammonium by the manganese co-oxide film was further clarified.The mechanism of the catalytic oxidation for ammonium removal was determined further through infrared spectra and other means.The surface of the co-oxide was weakly acid.In surface water,the hydroxide groups on the co-oxide film would lose a proton making the surface negative charged and adsorbing the ammonium ion in water easily.The quasi-free holes and quasi-free electrons can appear in the co-oxide film due to the variable valence of the Mn and Ca2+,Mg2+ and oxygen vacancy in the co-oxide film and can activate the ammonium ion and oxygen molecular making the oxidation reaction proceding easily and oxidizing ammonium to be nitrate.