HU201893B - Process for chemical removing nitrate and nitrite content of waters - Google Patents

Abstract

The proposed method involves the addn. of a stoichiometric amt. of reducing chemical pref. hydrazine, and an inhibitor to prevent the formation of ammonia pref. hydrogen peroxide. After mixing in the reagents the pre-treated water is passed to a chemical reactor contg. a granular material having a large surface area, pref. activated carbon. The purified water and the gaseous nitrogen liberated are removed. If necessary post-chlorination is carried out. - The method requires minimal capital investment, it has large clean-up capacity, and produces no waste prods. needing further treatment. The method can be carried out continuously or intermittently.

Description

The present invention relates to a process and an apparatus for removing nitrate and / or nitrite from water (e.g., surface water, drinking water, groundwater, groundwater, waste water).

In the last few decades, the concentration of nitrate in the raw water used for drinking water has increased significantly. One reason for the increase is that drinking water supply has outperformed sewage treatment capacity. Other important nitrate contaminants are the proportion of nitrogenous fertilizers used in agriculture that are not absorbed by plants. Increased nitrate concentration in drinking water may increase the likelihood of serious human diseases (eg meteoglobinaemia, malignancy).

Recognizing the problem of nitration of water resources, research has recently begun worldwide to develop ways to remove nitrate. In order to prevent nitration, procedures have been developed for the removal of nitrogen in the third stage of wastewater treatment, and new solutions have been developed in the field of water utilization to reduce the nitrate concentration in raw water intended for drinking water. Existing nitrate decontamination procedures are based on biological, physical and chemical processes. physico-chemical process.

Biological denitrification is the most commonly used process in wastewater. The advantage is not only the low investment cost but also the simple operation. By using a carbon source that is not harmful to health, the process is also applied to drinking water (Hungarian Patent No. 186,653). However, in this case, the treated water should be protected against any bacterial toxins or germs that may be formed. against pathogenic bacteria, and post-cleaning can be a significant factor in increasing specific cleaning costs. Another biological process applicable to wastewater and drinking water is the intracellular nitrate reduction with lower-level apathogenic fungi (Hungarian Patent No. 186,451).

In the high capacity range, this process can also achieve a low specific purification cost, but due to biological processes in the biological reactor, which are only slightly controllable, a significant amount of after-treatment of the treated water is required for drinking water. The common disadvantage of all biological processes is that they are not intermittent and require several days for purification of the living culture.

Known nitrate removal procedure for potable water based on the physico-chemical principle is the adsorption of nitrate on a selective ion exchanger in the chloride cycle (Scholze, C .: Die Nitrate Imination in Dér Trinkwasseraubereitung - Acta Hydrochim. Hydrobiol. The advantage of ion exchange processes is their simplicity, but the disadvantage is that the selectivity of the resins is not clear (eg in case of high sulphate waters the process becomes expensive), and the treatment and placement of the regenerate unsolvable.

Known procedures for the removal of nitrates from waters by reverse osmosis and electrodialysis, however, are extremely energy-intensive and therefore expensive. The use of these methods should be considered only in special cases.

It is an object of the present invention to provide a novel process which overcomes the above-mentioned drawbacks of existing processes and more efficiently and economically addresses the removal of nitrate and / or nitrite.

The present invention is based on the discovery that the nitrate and / or nitrite content of the waters on the active surface of the catalyst can be easily and rapidly reduced by converting the majority of the nitrate and / or nitrite to nitrogen gas. The stoichiometric amount of reducing agent is sufficient to remove the nitrate and / or nitrite. As a reducing agent hydrazine or. hydrazine salts, activated carbon as catalyst. During the reaction, trace amounts of oxidizing agent (eg H2O2-O) must be added to the water to be purified to prevent ammonia formation. During the chemical reaction, nitrate or nitrite is reduced and nitrogen gas, water and hydrogen ions are formed. Quantitatively takes place within 3 to 10 minutes No adverse reaction products are formed during the reaction and any excess reducing agent is completely decomposed on the activated carbon surface of the catalyst.

The process of the present invention comprises mixing at least a stoichiometric amount of a chemical reducing agent (e.g., hydrazine) corresponding to the nitrate and / or nitrite content to be removed to the water to be treated. The chemical water is fed into a chemical reactor containing a high surface area particulate material (e.g., activated carbon). Water de-nitrated and / or nitrite-free, if necessary (eg drinking water), is post-chlorinated. The resulting nitrogen gas is removed from the reactor.

Another advantageous effect is obtained by using a column filled with activated carbon as the chemical reactor.

To prevent ammonium formation, a trace amount of an inhibitor (e.g., hydrogen peroxide) is added to the water to be treated.

The process is illustrated by way of example by way of a drawing.

Figure 1 is a flowchart of a possible embodiment of the method.

The nitrate appetite containing the nitrite-containing water to be treated 1 is passed through a rapid mixer 4 and then a stoichiometric amount of reducing agent 2 (hydrazine) and a 100 mg / l inhibitor 3 (hydrogen peroxide) are added via a metering pump. The chemical water is stirred and after a residence time of thirty seconds, the pre-treated water 5 is introduced into the top of reactor 6. The reactor 6 is a packed column having a load 7 of a high surface area particulate material 8 supported by a bed plate 9 mounted with plastic filter candles. Then, after a ten-minute residence time, the nitrate and / or nitrite depleted water 10 is discharged to the bottom of the reactor and the nitrogen gas 11 to the top. If necessary (eg in the case of drinking water) 12 post-cloning is performed.

To illustrate the process of the present invention, experimental results are reported.

HU 201893 Β

Table I

Nitrate removal from drinking water with stoichiometric reducing agent and residence time in 10 minute reactor

Quantity of water per fill volume NO'3 g m ' ³ PH of NH ⁺ 4 KOIsMn mg # ³ g m ' ³ raw water 139 <1 2.0 7.4 5 5.3 46 3.2 7.2 10 0.7 36 2.3 7.1 Discharged 15 1.5 18 0.8 7.3 water 20 0.7 18 0.7 7.2 25 1.8 22 0.7 7.1 30 2.9 13 05 7.1

The results indicate that the process can produce purified water with a very low nitrate concentration in a residence time of 10 minutes, which differs from raw water quality.

Π. spreadsheet

Removal of nitrate from wastewater generated during ion exchanger regeneration. With a stoichiometric amount of reducing agent and a residence time of 10 minutes.

NO'3 N-2 g nr ³ g m ' ³ NH + 4 g m ' ³ so ² - ₄ g ni ' ³ Sewage 2500 0.70 0,150 65,000 accessible sewage 52 0.13 0.52 64,800

The results show that the rate of the reaction increases proportionally with the increase in nitrate concentration, so that no increase in residence time is required in the event of an increase in nitrate concentration. The reaction is highly selective for nitrate and is not interfered with by other ions, such as sulfate ions, which are highly concentrated in water.

ΙΠ. spreadsheet

Simultaneous removal of nitrate and nitrite. The residence time is 10 minutes

The reducing agent NO'2 g m ' ³ NI-3 g m ' ³ stoichiometric ratio of ΝΟ3 to NO2 raw water 313 308 0,125 201 269 Discharged 0.250 27 255 WATER 0.50 <1 187 1.0 <1 109

Based on the results, it can be stated that in the presence of nitrate and nitrite, the more unstable nitrite is reduced first and then the nitrate is reduced by increasing the concentration of the reducing agent.

Advantageous effects of the invention may be summarized as follows:

During the process, the content of nitrate and / or nitrite to be treated is converted to non-polluting N2 gas, i.e., the process is concentrated to a smaller volume but eliminates nitrate contamination;

- No need for post-treatment of de-nitrated water;

Due to the simplicity of the equipment and the extremely short residence time, the investment cost is low;

- 2-3 times more nitrate and / or nitrate per process volume compared to existing technologies. nitrite can be removed over time (10-20 kg NO'3 m ³ per charge and daily).

Claims (3)

1. A process for the chemical removal of nitrate and / or nitrite in water (surface water, groundwater, tributary water, drinking water, sewage), characterized in that the water to be treated (1) is at least stoichiometric with a chemical mixed with a reducing agent (2), then the pretreated water (5) is fed to a chemical reactor (6) containing a high surface area particulate material (8), the water (10) depleted of nitrate and / or nitrite and the nitrogen gas (11) performing post-chlorination (12). Process according to Claim 1, characterized in that the activated carbon column (6) is used as a chemical reactor. Method according to any one of claims 1 and 2, characterized in that an inhibitor (e.g. hydrogen peroxide) (3) is added to the water (1) to be treated to prevent the formation of ammonia. -3GB 201893 ra feet