CS268962B1 - A method for removing nitrite from water - Google Patents

Abstract

The essence of the method of removing nitrites from water is that the treated water is filtered through sand, which is previously prepared with higher manganese oxides. Autotrophic nitrifying microorganisms, which oxidize nitrites to nitrates, adhere firmly to this preparation layer. When washing a filter filled with such a prepared filling, these microorganisms are not removed from the surface of the filter filling grains, so nitrification of nitrites occurs immediately after the start of the next filtration cycle. Filter fillings can also be used advantageously for the simultaneous separation of suspension from water resulting from water coagulation or deironing and demanganizing of water.

Description

The invention relates to the removal of nitrites from water during its treatment into drinking water.

To remove nitrites from surface and especially groundwater when treating them to drinking water, oxidation processes are mainly used to oxidize them to nitrates, □as the oxidizing agent chlorine, hypochlorites or ozone are used. 3Other oxidizing agents such as potassium permanganate or hydrogen peroxide are ineffective. The disadvantage of chlorine is that in the presence of some organic substances in the treated water, carcinogenic chlorinated substances can be formed, which is of course undesirable for drinking water. In addition, in the presence of ammonium ions in the treated water, nitrite oxidation occurs at a sufficient rate beyond the turning point of the chlorination curve, which leads to the need to use higher doses of chlorine. When using ozone, which is a very effective oxidizing agent, the disadvantage is the high investment and operating costs associated with water ozonation. Nitrites can also be removed from water by biological methods using autotrophic ^{citrification} bacteria or heterotrophic denitrification and denitrification bacteria. The disadvantage of conventional bacteriological procedures is that suspension culture cannot be used for the production of drinking water, and biofilm reactors cannot be used where the filter with the biofilm carrier is washed for technological reasons, because the bacteria are washed out at the same time, causing the filter to lose its ability to remove nitrites from the water for a certain period of time.

The above-mentioned shortcomings are eliminated by the method of nitrite removal according to the invention, the essence of which lies in the fact that nitrification of nitrites is carried out biologically with the help of autotrophic nitrifying bacteria, for which sand prepared with manganese oxides (Mn^^ and Mn^) serves as a carrier. Manganese oxides on sand grains are prepared before the nitrification process is put into operation by the action of a potassium permanganate solution on the sand.

The advantages of removing nitrites from water according to the invention lie primarily in the possibility of combining two operations into one technological unit - simultaneous removal of nitrites and suspended solids from water. This allows for significant savings in investment and operating costs. Furthermore, there is no need to dose any chemicals into the water.

The importance of the manganese oxide preparation layer lies in the fact that this layer roughens the otherwise smooth surface of the sand grain, on which nitrifying microorganisms would have difficulty adhering and would be washed out of the sand bed both during operation and especially during the regeneration phase (washing) of the filter, which would result in only partial or no removal of nitrites from the treated water. Autotrophic nitrifying bacteria adhere very firmly to the unprepared layer, so sand fillings prepared in this way can also be used as fillings for water filters for the separation of suspended substances, suspensions formed during water coagulation or during the iron and manganese removal of groundwater containing nitrites. The filter cartridge prepared in this way can be advantageously used as a nitrification and filtration medium in the final treatment of water from biological denitrification processes, where the water after denitrification usually contains unacceptable concentrations of nitrites and at the same time bacteria, which are removed from the water by water coagulation.

The first incorporation of the filter cartridge prepared according to the invention occurs spontaneously during filtration of the treated water and usually lasts several weeks. During this phase, autotrophic nitrifying microorganisms, mainly bacteria of the genus Nitrobacter, are cultivated in the cartridge. After the first incorporation, the filter cartridge can be used as a nitrifying and filtering unit for the separation of suspended substances. After washing the filter cartridge in the usual way, i.e. with water and air, or with water only, there is no longer any need to incorporate a filter for removing nitrites, because nitrifying bacteria are not removed from the surface of the prepared sand grains by ordinary washing. For the good course of nitrite removal, it is only necessary that the water contains dissolved oxygen.

The invention can be used in water treatment plants where nitrites, nitrites together with iron or even manganese, or nitrites together with bacterial contamination or organic substances that can be removed from the water by coagulation are present in the treated water.

CS 268962 Bl

Example of nitrite removal from water according to the invention:

A filter bed filled with sand prepared with manganese oxides was operated, the sand was pre-treated with a 2% solution of potassium permanganate. The diameter of the grains of the sand filling was in the range of 0.9 to 1.1 mm. Water with a nitrite concentration of 1 mg.l" ¹ was then used for the filter column. The column operation parameters were as follows: filter layer 1.2 m, filtration rate 6 mh"^. The column incorporation took 40 days. The incorporation of the filter filling was necessary to spontaneously cultivate a sufficient amount of autotrophic nitrifying bacteria on the surface of the filter material grains, necessary for the biological oxidation of nitrites to nitrates. After this incorporation phase, nitrites were removed from the water with 100% efficiency. The nitrite concentration in the filtered water was then increased to 10 ^mg.l.l. Even at this concentration, the nitrite removal efficiency was 100%; the removal efficiency was also independent of step changes in the input nitrite concentration. The filter cartridge was then washed with water and the filtration was restarted. The nitrite removal efficiency was 100% immediately after the start of the filtration cycle.

Claims (1)

SUBJECT OF THE INVENTION A method of removing nitrites from water during its treatment into drinking water, namely by biological nitrification during water filtration through sand, characterized in that the water is filtered through sand that is previously prepared with higher manganese oxides.