JPH09122690A - Method for decomposing organic nitrogen and water treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove org. nitrogen by incorporating an nitrite into water contg. org. nitrogen such as urea which can not be removed by means of an ultrapure water production system. SOLUTION: A stock water such as industrial water is introduced into an NaNO2 injecting tank 3 through a pipeline 20 and a pipeline 21 provided with a stock water tank 1 and sodium nitrite (NaNO2 ) is injected therein from an NaNO2 tank through a pipeline 22. In this instance, the concn. of org. nitrogen is detected by means of an org. nitrogen analyzer 2 provided on the pipeline 20 and the org. nitrogen is efficiently removed by controlling the amt. of injection of NaNO2 based on this detected value. The water injected with NaNO2 in the injection tank 3 is then fed into a flocculation-solid-liq. separation means 5, wherein a flocculant is incorporated to perform solid-liq. separation. Then, the separated water is introduced from a tank 6 for separated water to a filter device 7 to store it in a tank 8 for the filtered water and then, ion exchange treatment is performed by means of an ion exchange pure water apparatus 9 and then, the org. nitrogen is removed by means of a reverse osmotic membrane separation apparatus 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing organic nitrogen and a water treatment apparatus, and more particularly to efficiently removing organic nitrogen such as urea which cannot be removed by a conventional ultrapure water production system. , TOC (total organic carbon) significantly reduced, and a device therefor.

[0002]

2. Description of the Related Art Conventionally, an ultrapure water production system for producing ultrapure water from raw water such as city water, groundwater, and industrial water is basically a pretreatment system 41 and primary pure water as shown in FIG. It is composed of a system 42 and a secondary pure water system 43. In each unit of this ultrapure water production system, the T
It is a reverse osmosis membrane separation device, an ion exchange deionized water device, and a low pressure ultraviolet oxidation device that reduces the OC component by means such as separation, adsorption and decomposition.

The TOC reduction mechanism in each device unit is as follows.

Reverse osmosis membrane separator: A filtration method using a reverse osmosis membrane, which removes ionic and colloidal TOC.

Ion exchange deionized water device: Removes TOC components adsorbed or ion exchanged on ion exchange resins.

Low-pressure UV oxidizer: TOC is decomposed into organic acid and further CO ₂ by the 185 nm UV emitted from a low-pressure UV lamp. The decomposed organic matter is removed by the ion exchange resin in the subsequent stage. Particularly, it is used for decomposing volatile organic substances.

Further, among the apparatus units constituting the conventional ultrapure water production system, only the reverse osmosis membrane separation apparatus removes TOC derived from organic nitrogen such as urea in raw water.

[0008]

However, the removal rate of the organic nitrogen in the reverse osmosis membrane separator is about 85%, and the organic nitrogen cannot be completely removed.

Therefore, in the conventional ultrapure water production system, ultrapure water having a sufficiently reduced TOC can be obtained when organic nitrogen is not mixed as a TOC component in the raw water. When industrial water mixed with organic nitrogen as the TOC component is used as raw water, the organic nitrogen remains as the TOC component in the ultrapure water obtained, and the TOC target value is 5
It cannot satisfy ppb and below.

Further, the organic nitrogen, which cannot be removed by the reverse osmosis membrane separator and flows into the low-pressure ultraviolet oxidizer, produces an acid (nitric acid) by ultraviolet oxidization, so that the electrical resistivity is greatly reduced. As a result, the conductivity of the ultrapure water obtained is
The value is about 5 times the actual organic nitrogen concentration.

In the conventional ultrapure water production system, TOC derived from organic nitrogen can be reduced by adding a reverse osmosis membrane separation device, but the addition of the device requires equipment cost, maintenance and installation. Space is not preferable in all respects.

The present invention solves the above-mentioned conventional problems and efficiently removes organic nitrogen such as urea which cannot be removed by the conventional ultrapure water production system, and the TOC is remarkably reduced. It is an object of the present invention to provide a method for decomposing organic nitrogen and a water treatment device capable of obtaining water.

[0013]

The method for decomposing organic nitrogen according to the present invention is characterized by adding nitrite to water containing organic nitrogen.

By adding nitrite, organic nitrogen such as urea can be efficiently decomposed and removed.
It is possible to obtain treated water with significantly reduced water content.

In particular, a means for adding nitrite to water containing organic nitrogen, a means for coagulating the nitrite-added water to perform solid-liquid separation, and ion-exchanged water separated by the solid-liquid separation means. According to the water treatment device of the present invention, which comprises an ion exchange device for treatment and a reverse osmosis membrane separation device for membrane separation treatment of ion exchange treated water, the nitrite remaining in the decomposition reaction of organic nitrogen and the reaction product By removing the substances with an ion exchange device and further removing the residual organic nitrogen with a reverse osmosis membrane separation device, treated water of extremely high water quality can be obtained.

Such a water treatment apparatus of the present invention requires only a simple nitrite injection means (nitrite dissolution tank, chemical injection pump and chemical injection pipe) to be attached to the existing equipment, and TOC
Since it is not necessary to add a device for reduction, it is possible to reduce equipment cost and maintenance.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the method for decomposing organic nitrogen and the water treatment apparatus of the present invention. In the following, sodium nitrite (NaN) is used as the nitrite.
O ₂ ) is used as an example, but as the nitrite,
Not limited to NaNO ₂ , KNO ₂ or the like may be used.

In this embodiment, raw water such as industrial water is passed through a pipe 20, a raw water tank 1, and a pipe 21 provided with a pump P ₁ to supply N water.
introduced into ANO ₂ injection tank 3, NaNO ₂ tank 4 performs injection of NaNO ₂ from the pipe 22 with a pump P ₂ from but, this time, preferably the pipe of organic nitrogen concentration of the raw water 2
It is detected by the organic nitrogen analyzer 2 provided at 0, and the organic nitrogen is efficiently removed by controlling the injection amount of NaNO ₂ based on the detected value.

Normally, the detected value of this organic nitrogen is 5
When it becomes 0 ppb or more, NaNO ₂ is preferably injected, and the amount of NaNO ₂ injected is preferably about 5 to 50 times the organic nitrogen in the raw water.

The reaction of the injected NaNO ₂ and organic nitrogen, in the apparatus of FIG. 1, NaNO ₂ injection tank 3, coagulation and
It is carried out in the solid-liquid separation means 5 and the separation water tank 6. Therefore, the residence time during this period becomes the reaction time. In the present invention,
This retention time (hereinafter referred to as "NaNO ₂ retention time")
Is preferably carried out for 1 hour or more, particularly about 3 hours.

The water into which NaNO ₂ has been injected in the NaNO ₂ injection tank 3 is sent to the flocculation / solid-liquid separation means 5 through the pipe 23,
After adding an aggregating agent such as polyaluminum chloride or aluminum sulfate to perform the aggregating treatment, a solid-liquid separation treatment is performed. As the coagulation / solid-liquid separation means 5, means such as coagulation (floating under pressure) filtration or coagulation sedimentation can be adopted. This aggregation
The solid-liquid separation treatment can be performed efficiently according to a conventional method without being affected by the injection of NaNO _{2 according to} the present invention.

The water separated by the flocculation / solid-liquid separation means 5 is supplied to the pipe 2
4, is introduced into the filtration device 7 via a pipe 25 provided with a separating water tray 6 and the pump P _3, it is pooled from line 26 to the filtering water tank 8. The water in the filtered water tank 8 is ion-exchanged by the ion-exchange pure water device 9 through the pipe 27 equipped with the pump P ₄ . As this ion exchange pure water device 9, there are two beds and three towers,
Various types such as 3 beds 4 towers type or 4 beds 5 towers type can be used. By this ion exchange treatment, organic nitrogen and Na
Reaction products with NO ₂ and residual NaNO ₂ are efficiently removed. In the apparatus of the present embodiment, the organic nitrogen concentration of the raw water detected by the organic nitrogen analyzer 2, this in order to control the NaNO ₂ injection amount based on the detected value, less residue of NaNO _2, ion exchange net The load on the water device 9 is reduced.

The ion-exchange treated water is then supplied to the pipe 28,
The reverse osmosis membrane separation device 11 performs a membrane separation process via a pipe 29 equipped with the tank 10 and a pump P ₅ , and the organic nitrogen still remaining by the reaction with NaNO ₂ is removed. The TOC of the treated water at that time is already 5 ppb or less, but preferably, the permeated water of the reverse osmosis membrane separation device 11 is further introduced into the microfiltration membrane separation device 12 through the pipe 30 to further remove fine particles. As a result, TOC is treated as treated water from the pipe 31.
It is possible to obtain high-purity water having a water content of 2 ppb or less.

The apparatus shown in FIG. 1 shows one embodiment of the present invention, and the present invention is not limited to the apparatus shown in the figure as long as it does not exceed the gist of the present invention.

For example, an organic nitrogen analyzer is not always necessary, and the organic nitrogen concentration is always high (for example, 100 p
If it is a system into which raw water (pb or more) is introduced, the method of constantly injecting NaNO ₂ without analyzing organic nitrogen may be used. Also in this case, the organic nitrogen in the raw water is analyzed in advance, and the Na content is 5 to 50 times that of the organic nitrogen.
It is preferable to inject a fixed amount of NO ₂ .

The raw water may be analyzed based on TOC instead of organic nitrogen. In this case, the raw water is sequentially passed through the activated carbon tower and the mixed bed type ion exchange tower before the TO
It is preferable to inject with 1 to 10 times the TOC value of NaNO ₂ when the TOC value becomes 150 ppb or more as analyzed by a C meter.

Further, the NaNO ₂ injection tank is not always required, and if the NaNO ₂ residence time is sufficiently secured, the NaNO ₂ injection tank may be injected into the coagulation tank or the pump outlet of the pipe from the raw water tank to the coagulation tank. You may inject a line. Also,
If the NaNO ₂ residence time cannot be sufficiently secured at this injection point, line injection may be performed into the raw water introduction pipe to the raw water tank.

Further, the microfiltration membrane separation device is not always required, and in the present invention, even when the permeated water of the reverse osmosis membrane separation device is treated water without providing the microfiltration membrane separation device, the TOC is 5 ppb or less. High quality treated water can be obtained.

[0030]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 Ultra pure water was produced in the apparatus shown in FIG. 1 using synthetic water prepared by adding urea as the organic nitrogen to the concentration shown in Table 1 to the working water as raw water, and the outlet of each apparatus was produced. The TOC (by wet method) and the organic nitrogen concentration of water were measured, and the results are shown in Table 1.

The injection amount of NaNO ₂ is 1630 ppb.
The NaNO ₂ residence time was about 3 hours.

Comparative Example 1 Treatment was carried out in the same manner as in Example 1 except that NaNO ₂ was not injected, and the measurement results of TOC (by wet method) and the concentration of organic nitrogen in the outlet water of each device are shown. Shown in 1.

[0034]

[Table 1]

As is clear from Table 1, according to the present invention, high purity water having TOC of 5 ppb or less can be obtained by efficiently decomposing and removing organic nitrogen by injecting NaNO ₂ .

On the other hand, in Comparative Example 1 in which NaNO ₂ was not added, organic nitrogen was removed in the reverse osmosis membrane separation device, but the TOC was not sufficient, and the TOC caused by residual organic nitrogen was It is not possible to obtain treated water of sufficiently high purity.

[0037]

As described in detail above, according to the method for decomposing organic nitrogen of the present invention, organic nitrogen is efficiently decomposed and removed by nitrite, and TOC resulting from organic nitrogen is at an extremely low concentration. It is possible to obtain high-quality treated water.

Further, according to the water treatment apparatus of the present invention, the decomposition and removal of the organic nitrogen by the nitrite effectively removes the organic nitrogen which cannot be treated by the conventional ultrapure water production system. After removal, TOC is 5ppb or less, and further 2
It is possible to produce ultrapure water having a purity as high as ppb or less. In particular, in the water treatment device of the present invention, without adding a device for removing TOC caused by organic nitrogen to an extremely low concentration, it is possible to improve the water quality by simply installing a chemical injection facility for nitrite in the existing facility. It can be improved and is industrially extremely advantageous.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a method for decomposing organic nitrogen and a water treatment device of the present invention.

FIG. 2 is a system diagram showing a conventional ultrapure water production system.

[Explanation of symbols]

1 Raw Water Tank 2 Organic Nitrogen Analyzer 3 NaNO ₂ Injection Tank 4 NaNO ₂ Tank 5 Aggregation / Solid-Liquid Separation Means 6 Separation Water Tank 7 Filtration Device 8 Filtration Water Tank 9 Ion Exchange Pure Water Device 10 Tank 11 Reverse Osmosis Membrane Separation Device 12 Precision Filtration membrane separator

Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C02F 1/58 C02F 1/58 A

Claims (2)

[Claims] 1. A method for decomposing organic nitrogen, comprising adding nitrite to water containing organic nitrogen. 2. A means for adding nitrite to water containing organic nitrogen, a means for coagulating the water to which nitrite is added to perform solid-liquid separation, and ion-exchanged water separated by the solid-liquid separation means. A water treatment device comprising an ion exchange device for treatment and a reverse osmosis membrane separation device for membrane separation treatment of ion exchange treated water.