The Study On Catalytic Oxidation Of Ammonia In Groundwater By Co-oxides Of Iron And Manganese

According to the latest report, that nearly 22% of cities use the groundwater water for drinking water resource, making the groundwater an important part of drinking water supplement in China. As for the northwest district, in which the groundwater was depended in high degree for drinking resource, the pollution of groundwater water increased seriously, and the ammonia nitrogen, iron, and manganese exceeds the standard commonly. As a result, the removal of ammonia, iron and manganese is an important problem which is need to be solved for the drinking water safety of our country. It is found that after a long peroid operation, on the surfaces of quartz sands formed the co-oxides filter film, which has catalytic effect on oxidation of ammonia. In this paper, the synergy catalytic oxidation mechanism of manganese and ammonia in groundwater is studied, the results and the conclusions are as follows:(1) The iron in the raw water could be removed by the quartz sand filter bed in the height of 1.5m once the operation of filter was started. Under the condition of stable water quality, after the filter column run continuously in 20 days and 40 days, the pollution of manganese and ammonia nitrogen in water were removed successively; filtration cycle reached in about 180 hours after 60 days operation and then gradually decline to about 50hours; After ozone oxidation treatment, filtration cycle can be extended and recovered period are nearly 4 times of that before the treatment.(2) The scanning electronic microscope(SEM), electron energy spectrum(EDS), X-ray diffraction(XRD) and nitrogen adsorption(BET) were used to characterized the morphologies, chemical composition and crystal structures of quartz sands which was operated continuously in different periods. It is found that on the surfaces of quartz sand gradually formed amorphous co-oxides filter film, and the specific surface area, pore properties of filter sands were improved; the filter film was consisted of the elements such as calcium, magnesium and aluminum at the first periods of formation, and was consisted of iron and manganese oxide, carbonate when the function of filter film was completely formed;(3) The ozone and sodium azide were used to exclude the biological nitrification in the filter colume which was operated for 170 days, and the effects of ammonia removal was detected.It is shown that the ozone inactivation has no effect on the removal of ammonia and the ammonia removal efficiency could be recovered after 48 hours since the sodium azide was intrduced, indicate the existance of catalytic oxidation effects on the filter sands surface.(4) The adsorption properties of ammonia, mamganese and iron were studied by batch experiments and the adsorption sites and adsorption states were studied by XPS, TPD methods. The result indicates that adsorption effect of every reactant in filter sands surface were all improved over running time. While adsorption types and adsorption sites varied with composition of filter film. Adsorption sites of manganese and ammonia on mature filter sands surface were oxygen atoms in the structure of Mn-O and the iron and mamgamese atoms in the form of metal oxides respectively. Adsorption of dissolved oxygen on mature filter sands surface was weak chemical effect. Adsorption state is O2- and Adsorption sites are Si atom,Fe atom and Mn atom.(5) L-H(E-R) reaction mechanism of catalytic oxidation of manganese, ammonia and nitrite nitrogen which is the middle product of ammonia oxidation was studies by packing basket batch reactor based on derivation of L-H reaction kinetics equation. The result indicated that: the reaction of manganese ion catalytic oxidation happened between adsorbed manganese ion and free dissolved oxygen molecules. adsorption activation process of manganese ion is the rate-controlling step. The reaction of ammonia catalytic oxidation happend between adsorbed dissolved oxygen and free ammonia. Adsorption process of dissolved oxygen is the rate-controlling step. The reaction of nitrite nitrogen catalytic oxidation happend between adsorbed nitrite nitrogen and free dissolved oxygen molecules in the liquid phase. Adsorption process of nitrite nitrogen is the rate-controlling step.(6) According to the self-catalytic oxidation mechanism of mamganese, the kinetics model of the manganese synergy catalytic oxidation of ammonia was established and the the model parameters were determined by Newton-Marqurlt method.