The Catalytic Oxidation Removal Of Ammonium And Manganese From Groundwater Using Iron-manganese Co-oxide Film

At present,the pollution of ammonium and manganese in groundwater become increasingly serious in China,and excessive ammonium and manganese in drinking water can directly harm human health.Ammonium can be oxidized to nitrate and nitrite in human body induces carcinogenic nitrosamines and methemoglobinemia.If excessive manganese was ingested in the body,which will make the central nervous system damage,cause memory loss,induce pneumonia,and lead to chronic poisoning.So the simultaneous efficient removal of ammonium and manganese in groundwater plays an important role in the guarantee of drinking water.By oxidizing manganese and ferrous ion in raw water using potassium permanganate continuously,the iron-manganese co-oxides film?MeOx?was quickly formed on the surface of virgin quartz sand in a pilot-scale filter column.Ammonium and manganese can be efficiently removed by the co-oxide film.In this paper,the catalytic oxidation mechanism of ammonium and manganese in groundwater and the other related research were studied,and the main results and the conclusions are as follows:?1?The ripening period of sands was shortened,and the kinetic model of film growth was established.The ripening period of sands was shortened to about 26 days after process optimization,which was shortened 2 to 3 times than the processing of biofilm.The film on the surface of sands has exhibited efficient and long-term stability for the removal of ammonium and manganese.The kinetic model of oxide film growth was established,and the thickness of the film growth shown a linear dependence on the time in an operation period.Two years of operation results show that the kinetic model can describe the growth thickness of the oxide film accurately and the theoretical film peeling time under different influent manganese concentrations.The backwashing interval was decreased two times as a sign of film peeling,and the thickness of the oxide film should not exceed 150 ?m.?2?The main influencing factors of ammonium removal were determined.When the influent contains only ammonium,the higher dissolved oxygen concentration of the influent,the higher of the ammonium removal loading.A maximum removal loading of ammonium was 22.2 g/?m3×h?by the oxide film,which was far higher than the removal loading of ammonium by other biological conditions?1.5-6 g/?m3×h??.When the filtration rate was 7-18 m/h,and the ammonium concentration in influent was 1.0-1.6 mg/L,ammonium could be efficiently removed.The change of iron concentration in influent has obvious impact on the removal of ammonium.The change of manganese concentration seemed to have no impact on the removal of ammonium,but the ammonium in the influent affected on the manganese removal.The ripening sands have exhibited efficient and long-term stability for the simultaneous removal of ammonium,manganese and iron after continuous operation for six months.The film exhibited a high oxidation activity when the temperature was down to 6.6 ?.A decrease in pH would weaken ammonium removal due to the fluctuation of pH.High concentration of Na+,K+ and Cl-have no impact on the ammonium removal.High concentrations of Mg²⁺ and Ca²⁺ weaken the role of the ammonium removal.The ripening sands from entire filter layer for the removal of ammonium and manganese have catalytic ability.Middle and lower filter layer "inefficient" is mainly due to the lack of the dissovled oxygen.When the height of ripening sands was 100 cm,and the efficiently removal of ammonium and manganese can be restored after 3.5 days,even if the system was stopped running for 60 days.?3?Chemical catalytic oxidation of the oxide film was further verified,and the mechanism was discussed preliminarily.The pilot-scale catalytic oxidation filter system was inactivated synergistically by UV,ozone and hydrogen peroxide.Removal efficiency of ammonium and manganese by the oxide film could also reach up to 90% even after the bacteria were inactivated completely in both the film and water.So chemical catalytic oxidation play a leading role in the removal of ammonium and manganese.The results have changed a view of biological oxidation as a main role for ammonium removal which is widely recognized at home and abroad,and a new technology and process for ammonium removal in water was proposed.A chemical catalytic oxidation mechanism for ammonium removal was proposed by the characterization?SEM,XRF and XPS?: O2 adsorption on the film surface to form adsorbed O2,then quickly desorbed to form the active state intermediates ·O;The reaction between an oxidized ·O and adsorbed NH4+ to produce [NH] and H+,and the formation of the final product NO3-from [NH] and oxidized ·O.?4?The catalytic oxidation process of Mn²⁺ is in accordance with the pseudo first-order kinetics,and its catalytic oxidation mechanism was discussed preliminarily.The adsorption process of Mn²⁺ on the oxide film can be described by Lagergren pseudo first-order kinetics equation,and the correlation coefficient R2 is above 0.98.log([Mn²⁺]t/[Mn²⁺]0)versus the empty bed contact time?EBCT?was linear.The value of k for the low initial Mn²⁺ concentrations?0.57 min-1?was significantly higher than that for the high initial Mn²⁺ concentrations?0.14 min-1?,which was due to limited number of active sites on the surface of sands.The oxidation process of Mn²⁺ does not need to consume the DO.The results of XPS has showed the existence of [?Mn-OH] on the surface of film.Finally,a chemical catalytic oxidation mechanism for Mn²⁺ removal was proposed: the reaction between adsorbed Mn²⁺ and [?Mn-OH] to produce hydrolysis complex,a small amount of the complicated product would form some new oxide film.?5?The film peeling conditions of oxide film was optimized and determined.To select a suitable solvents for treatment of the overgrown film on the surface of the filter sands,which could not only recover the backwashing interval of the filter,but also ensure that the water quality of effluent should be within the permitted limits.Several film peeling solvents including ozone,hydrogen peroxide,chlorine dioxide,sodium sulfite and hydrochloric acid were examined to peel off the overgrown film from the sand surface.Overgrown film from the sand surface was peeled off after treatment by film peeling solvents.Based on the batch tests,the optimized dosage for ozone was found to be 30.1 g/?L·filter·h?,and in regrad to hydrogen peroxide,chlorine dioxide and sodium sulfite they were all 4.10?g/L·filter?.The optimized dosage of hydrochloric acid was found to be 5.11 g/?L·filter?.The optimized time for all film peeling solvents were found to be 40 min.Based on the pilot-scale experiments,compared with the other four film peeling solvents,hydrochloric acid had the best peeling result,the most significant effect on the recovery of backwashing interval?from 35.2 h to 61.6 h?,and the lowest cost.Therefore,hydrochloric acid was recommended for peeling off the overgrown film.