JP2018176116A - Water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent decomposition of chlorine and generation of harmful substances such as trihalomethane when suppressing biofouling in a water treatment device by addition of a chlorine type oxidizing agent to supply water or generation of chlorine by electrolysis, and to suppress biofouling in an RO membrane device by eliminating the need of adding a reducing agent at an inlet side of an RO membrane or installing an activated carbon column.SOLUTION: A water treatment method is a method for supplying supply water to a water treatment device after making free chlorine present in the supply water by adding a chlorine type oxidizing agent to the supply water or by generating chlorine by electrolysis. In the water treatment method, before making free chlorine present in the supply water, a nitrogen compound is added as a chlorine stabilizer to the supply water.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a water treatment method, and more particularly, to a water treatment method for suppressing biofouling in a water treatment apparatus such as a reverse osmosis membrane (RO membrane) apparatus for seawater desalination.

  As a means for treating industrial water, city water, well water, seawater, river water, lake water, factory wastewater and the like to produce pure water and the like, RO membrane devices are widely used. In this case, a chlorine-based oxidizing agent such as chlorine, sodium hypochlorite or sodium chlorite is added to the water to be treated (feed water) in order to suppress biofouling caused by microorganisms contained in the water to be treated. Be done. In addition, generation of chlorine by electrolysis is also performed.

  When RO film treatment is performed on water containing free chlorine by addition of a chlorine-based oxidizing agent or electrolysis, the RO film is oxidatively deteriorated. In particular, in the case of a polyamide-based RO film, it is easily oxidized and deteriorated. Therefore, conventionally, an activated carbon tower is installed at the front stage of the RO membrane apparatus to remove residual oxidant such as chlorine (Patent Document 1), or sodium bisulfite (SBS) or sodium sulfite etc. at the front stage of the RO membrane apparatus. A treatment such as adding a reducing agent to decompose and remove chlorine (Patent Document 2) is performed.

  However, when an activated carbon tower is installed, there is a disadvantage that biofouling occurs in the tower to contaminate the post-stage apparatus, initial cost is increased, etc. Generally, residual oxidation due to addition of a reducing agent The agent has been decomposed and removed.

FIG. 2 is a system diagram showing an example of a conventional seawater desalination plant, and in FIG. 2 (a) by the addition of a chlorine-based oxidizing agent, the sea water is supplied to the raw water tank 1 by the water pump in FIG. A chlorine-based oxidizing agent such as sodium chlorate (NaClO) is added, and then an inorganic flocculant such as ferric chloride (FeCl ₃ ) is added in the process of being supplied from the raw water tank 1 to the reaction tank 2 After being coagulated in tank 2 and then filtered in double-layer filter 3, it is subjected to RO membrane processing by RO membrane device 6 through water supply tank 4 and security filter 5, and RO membrane permeated water is taken out as treated water, At the inlet side of the security filter 5, a reducing agent such as sodium bisulfite (SBS) is added to decompose and remove the residual oxidizing agent. In FIG. 2 (b) by electrolysis, seawater is electrolyzed by the electrolytic device 7, and seawater containing chlorine generated by the electrolysis passes through the raw water tank 1 and is aggregated and filtered as in FIG. 2 (a). Thereafter, a reducing agent such as SBS is added and processed in the RO membrane device 6.
In addition, as a result that free chlorine is not present in the feed water due to the addition of this reducing agent, in order to prevent the occurrence of biofouling in the RO membrane device, bonding with little deterioration effect on the RO membrane after the addition of the reducing agent Chlorine-based slime control agents (for example, "Kuribata IK-110" manufactured by Kurita Kogyo Co., Ltd.) may be added.

JP 10-337563 A JP-A-7-308671

The above-described conventional seawater desalination RO membrane processing has the following problems.
(1) Free chlorine produced by the addition of chlorine-based oxidizing agents such as sodium hypochlorite and electrolysis of seawater is easily decomposed by organic substances in the seawater, bromine and iodine, so the decomposition fraction is supplemented to There is a large amount of chemical addition and power consumption to obtain sufficient ring suppression effect.
(2) Addition of a chlorine-based oxidizing agent to seawater generates harmful chlorine, such as trihalomethane, which is a problem particularly in drinking water applications.
(3) In order to prevent the oxidation deterioration of the RO membrane, the treatment is required by the addition of a reducing agent on the inlet side of the RO membrane and the installation of an activated carbon tower, and the treatment is complicated.
(4) Since the free chlorine is removed by the addition of a reducing agent and the activated carbon treatment at the front stage of the RO membrane device, the suppression of biofouling in the RO membrane device is insufficient.
(5) The problem of the above (4) can be solved by adding the combined chlorine slime control agent at the inlet of the RO membrane device, but in this case, the amount of the agent to be added is further increased.

  An object of the present invention is to provide a water treatment method which solves the problems of the above-mentioned conventional method.

  As a result of intensive studies to solve the above problems, the present inventor added a nitrogen compound as a chlorine stabilizer to the feed water prior to the generation of chlorine due to the addition of a chlorine-based oxidizing agent or electrolysis, By stabilizing chlorine, it is possible to prevent the decomposition of chlorine and the formation of trihalomethane etc., and to prevent the oxidation deterioration of the RO membrane by reducing the concentration of free chlorine, and the reducing agent at the RO membrane inlet side It has been found that biofouling of the RO membrane can be effectively suppressed while eliminating the need for the addition of carbon and the installation of an activated carbon tower.

  That is, the present invention provides the following.

[1] A water treatment method comprising adding a chlorine-based oxidizing agent to feed water to a water treatment apparatus or causing free chlorine to be generated by generating chlorine by electrolysis and then supplying it to the water treatment apparatus; A water treatment method comprising adding a nitrogen compound as a chlorine stabilizer to the feed water prior to the presence of free chlorine in the feed water.

[2] The water treatment method according to [1], wherein the water treatment device is a reverse osmosis membrane device.

[3] The water treatment method according to [1] or [2], wherein the supplied water is seawater.

[4] The water treatment method according to any one of [1] to [3], wherein the nitrogen compound is a sulfamic acid compound and / or an organic nitrogen compound.

[5] The water treatment method according to any one of [1] to [4], wherein hypochlorite and / or dichloroisocyanuric acid is added to the feed water as the chlorine-based oxidizing agent.

[6] The water treatment method according to any one of [1] to [5], wherein 0.3 to 50 mg / L of the nitrogen compound is added to the feed water.

[7] In any one of [1] to [6], the residual chlorine concentration of the feed water after the presence of the free chlorine is maintained at 0.1 to 10 mg-Cl ₂ / L. Water treatment method.

  According to the present invention, prior to the addition of a chlorine-based oxidizing agent or the generation of chlorine by electrolysis, a nitrogen compound is added to the feed water as a chlorine stabilizer, and thereafter free chlorine added or generated in the feed water is stabilized. The decomposition can prevent the decomposition of chlorine and the formation of harmful substances such as trihalomethane. In addition, by making chlorine be present in the feed water as stabilized chlorine and reducing the free chlorine concentration, the RO membrane oxidation deterioration property of the feed water is reduced, so the addition of the reducing agent at the RO membrane inlet side and the activated carbon tower In addition, the treatment can be simplified, and the stabilized chlorine can effectively suppress biofouling in the RO membrane apparatus.

It is a systematic diagram of the seawater desalination installation which shows an example of embodiment of the water treatment method of this invention. It is a systematic diagram of the conventional seawater desalination plant. It is a graph which shows the result of example 1 of an experiment. It is a graph which shows the result of example 2 of an experiment. 7 is a graph showing the results of Experimental Example 3. 7 is a graph showing the results of Experimental Example 4; 7 is a graph showing the results of Experimental Example 5; It is a graph which shows the result of Experimental example 6. It is a graph which shows the result of the comparative example 1 of an experiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Fig.1 (a), (b) is a systematic diagram which shows an example of the desalination installation of the seawater to which the water treatment method of this invention is applied, The freshwater of the seawater shown to FIG. 2 (a), (b), respectively The same code | symbol is attached | subjected to the member which plays the same function as the equipment.
As shown in FIGS. 1 (a) and 1 (b), according to the water treatment method of the present invention, chlorine is stabilized prior to the generation of chlorine by the addition of a chlorine-based oxidizing agent such as sodium hypochlorite (NaClO) or electrolysis. A nitrogen compound is added to the feed water as an agent to stabilize the chlorine in the feed water.

  The nitrogen compound to be added for stabilization of chlorine is not particularly limited as long as it can stabilize chlorine in feed water as stabilized combined chlorine or activated combined chlorine, and there is no particular limitation. And sulfamic acid compounds such as sodium salt, potassium salt, calcium salt and ammonium salt of sulfamic acid, and organic nitrogen compounds such as glycine, taurine, threonine, ornithine (L ornithine), alanine and phenylalanine (L phenylalanine). These nitrogen compounds may be used alone or in combination of two or more.

  The amount of these nitrogen compounds added to the feed water depends on the type of nitrogen compound used, the amount of the chlorine-based oxidizing agent added in the latter stage, the amount of chlorine generated by electrolysis, and thereby the concentration of chlorine to be maintained in the feed water Although it varies depending on the condition etc., it is preferably about 0.3 to 50 mg / L, particularly about 0.3 to 20 mg / L. If the addition amount of the nitrogen compound is too small, chlorine in the feed water can not be stabilized sufficiently, and if too much, the treatment cost becomes high or causes fouling, which is unsuitable.

In the present invention, a nitrogen compound as a chlorine stabilizer is added in the above-mentioned suitable addition amount, and after the nitrogen compound is sufficiently uniformly diffused in the feed water, a chlorine-based oxidizing agent is added or it is electrolyzed It is preferable to generate chlorine. For example, when adding a chlorine-based oxidizing agent, as shown in FIG. 1 (a), a nitrogen compound as a chlorine stabilizer is added on the discharge side of the water pump, After homogenization while staying in the water tank 1, it is preferable to add a chlorine-based oxidizing agent such as NaClO together with an inorganic coagulant such as FeCl ₃ at the outlet side of the raw water tank 1. Further, in the case of electrolysis, as shown in FIG. 1 (b), a chlorine stabilizer is added on the discharge side of the water pump so that the chlorine can be generated as well as uniform during electrolysis in the electrolytic device 7. It is preferable to do.

  As shown in FIG. 1 (a), when a chlorine-based oxidizing agent is added after adding a chlorine stabilizer, any conventionally known chlorine-based oxidizing agent can be used, but from the viewpoint of product safety From the above, hypochlorite such as sodium hypochlorite or dichloroisocyanurate such as dichloroisocyanuric acid, sodium dichloroisocyanurate and the like are preferable, and it is particularly preferable to use sodium hypochlorite or dichloroisocyanuric acid. . These chlorine-based oxidizing agents may be used alone or in combination of two or more.

The addition amount of the chlorine-based oxidizing agent is usually 0.1 to 1.0 mg / L, particularly about 0.3 to 0.7 mg / L, although it varies depending on the generation tendency of the biofouling of the water system to be treated. Preferably, the residual chlorine concentration at the inlet of the RO membrane device is 0.3 to 1.0 mg-Cl ₂ / L, particularly 0, by adding a chlorine-based oxidizing agent in the above range after the addition of the nitrogen compound of the chlorine stabilizer. It is preferable to control so as to be about 0.5 to 0.7 mg-Cl ₂ / L. If the residual chlorine concentration at the inlet of the RO membrane device is less than the above lower limit, sufficient biofouling suppression effect can not be obtained, and if it exceeds the above upper limit, it depends on the proportion of free chlorine in the residual chlorine, but the RO membrane There is a risk of deterioration.

  In addition, even in the case of electrolysis, the electrolysis conditions are controlled so that the concentration of residual chlorine at the inlet of the RO membrane device is in the above range due to the generation of chlorine due to the electrolysis after the addition of the nitrogen compound of the chlorine stabilizer. Is preferred.

In the present invention, in particular, by stabilizing the chlorine produced by the chlorine-based oxidizing agent or chlorine produced by electrolysis with a nitrogen compound, the residual chlorine concentration at the inlet of the RO membrane device is in the above range, and the free chlorine concentration is 0.2. By controlling the concentration to be 1 mg-Cl ₂ / L or less, particularly 0.05 mg-Cl ₂ / L or less, it is possible to prevent the oxidative degradation of the RO membrane due to free chlorine and sufficiently obtain the biofouling suppressing effect. It is possible to eliminate the need for the addition of the reducing agent at the front stage of the RO membrane device and the installation of the activated carbon tower.
In particular, the ratio of combined chlorine (total of activated combined chlorine and stabilized combined chlorine) to residual chlorine at the RO membrane apparatus inlet is preferably 90% or more, and further, 80% or more of stabilized combined chlorine Is preferred. And, by controlling the kind and the addition amount of the nitrogen compound as the chlorine stabilizer so as to become such a ratio, it is possible to obtain a good biofouling suppressing effect after preventing the deterioration of the RO film. it can.

  Here, free chlorine, activated combined chlorine, and stabilized combined chlorine correspond to chlorine measured by the method described in the section of Examples described later, and residual chlorine refers to these free chlorine, activated It is the sum of combined chlorine and stabilized combined chlorine.

  In the present invention, as described above, by controlling the residual chlorine concentration, the addition of a reducing agent at the inlet of the RO membrane device and the installation of an activated carbon tower can be omitted, but any of these operations and devices are excluded. However, if necessary, a small amount of reducing agent may be added.

  Although FIG. 1 exemplifies the case where the present invention is applied to seawater desalination equipment, in the present invention, the water treatment apparatus is not limited to the RO membrane apparatus, but addition of a chlorine-based oxidizing agent or bio-fouling suppression is possible. Although it electrolyzes, in order to prevent deterioration of an apparatus, it can apply also to the water treatment by water treatment apparatuses, such as an ion exchange apparatus which needs to remove free chlorine in the entrance side. Further, the supply water is not limited to seawater, and can be applied to cases where river water, well water, lake water, various drainages, etc. are used as supply water. However, from the viewpoint of solving problems such as decomposition of chlorine, formation of organic chlorine compounds such as trihalomethane, and RO membrane deterioration, the effect of the present invention is particularly effectively exhibited when applied to desalination equipment using seawater RO membrane apparatus. Ru.

  Hereinafter, the present invention will be more specifically described by way of experimental examples instead of the examples.

In the following experimental examples, for measuring the chlorine concentration (mg-Cl ₂ / L), each chlorine concentration was determined by the following measuring method or calculating method using a pocket chlorine measuring instrument "HACH2470" manufactured by Toa DKK.

Free chlorine concentration: After 5 to 30 seconds with DPD (Free) reagent, a reagent for measuring free chlorine
Chlorine concentration measurement result (mg-Cl ₂ / L)
Activated bound chlorine concentration: 300 with DPD (Free) reagent, a reagent for free chlorine measurement
From the chlorine concentration measurement result after ₂ seconds (mg-Cl ₂ / L), the above free chlorine concentration
The value obtained by subtracting the measurement result of (mg-Cl ₂ / L) Stabilized combined chlorine concentration: 180 by DPD (Total) reagent which is a reagent for total chlorine measurement
From the chlorine concentration measurement result (mg-Cl ₂ / L) after 1 _second , a test for free chlorine measurement
Measurement result of chlorine concentration after 300 seconds by DPD (Free) reagent which is a medicine
The value obtained by subtracting (mg-Cl ₂ / L) Residual chlorine concentration: Sum of the above free chlorine concentration, activated combined chlorine concentration, and stabilized combined chlorine concentration
(Mg-Cl ₂ / L)

  A beaker test was performed using Oarai seawater as seawater.

[Experimental Example 1]
An experiment was conducted to investigate the effect of adding sulfamic acid as a chlorine stabilizer to seawater.
After adding 30 mg / L of sulfamic acid to seawater and stirring and mixing uniformly for 1 minute, add 1.5 mg-Cl ₂ / L of sodium hypochlorite, and check each chlorine concentration after 5 minutes and after 60 minutes The
Separately, after adding sodium hypochlorite 1.5 mg-Cl ₂ / L to seawater, 30 mg / L of sulfamic acid was added after 1 minute, and each chlorine concentration after 5 minutes and after 60 minutes was examined.
These results are shown in FIG.
In FIG. 3, "(after) sulfamic acid" shows the case where sulfamic acid is added after sodium hypochlorite addition, and "(previous) sulfamic acid" is the case where sulfamic acid is added before sodium hypochlorite addition. Indicates The same applies to the following Experimental Examples 2 to 6.

[Experimental Examples 2 to 6]
The effect of each addition was examined in the same manner as in Experimental Example 1 except that 7.5 mg / L of each of the following was added instead of 30 mg / L of sulfamic acid, and the results are shown in FIGS.
Example 2: Glycine Example 3: phenylalanine Example 4: threonine Example 5: ornithine Example 6: taurine

[Comparative Experiment 1]
Sodium hypochlorite (NaClO) of 1.5 mg-Cl ₂ / L or 2.5 mg-Cl ₂ / L was added to seawater, and each chlorine concentration was measured after 5 minutes or after 60 minutes, and the results are shown in FIG. It was shown to.

The following can be understood from FIGS.
In the case of addition of only sodium hypochlorite, the addition of 1.5 mg-Cl ₂ / L causes the residual chlorine concentration to drop to a residual chlorine concentration of 0.4 mg-Cl ₂ / L after 60 minutes. resulting in less than _1.2mg-Cl 2 / L even after 60 minutes at high concentrations the addition of _5mg-Cl 2 / L (Fig. 9).
On the other hand, addition of a nitrogen compound as a chlorine stabilizer followed by sodium hypochlorite increases the concentration of activated combined chlorine and stabilized combined chlorine even though the concentration of free chlorine decreases, The residual chlorine concentration can be maintained higher than when only sodium chlorate is added, and the residual chlorine concentration is 1.2 even after 60 minutes by the addition of sodium hypochlorite 1.5 mg-Cl ₂ / L. It can be maintained at about 1.5 mg-Cl ₂ / L. However, even if it is the same nitrogen compound, such an effect is not acquired when adding after sodium hypochlorite addition (FIGS. 3-8).

From these results, according to the present invention, after a nitrogen compound is previously added as a chlorine stabilizer, a chlorine-based oxidizing agent such as sodium hypochlorite is added, or free chlorine is generated by electrolysis. Can stabilize chlorine in the feed water,
1) It is possible to suppress the decomposition and consumption of chlorine due to organic matter, bromine and iodine in seawater, so reduce the amount of chlorine-based oxidant addition necessary for suppressing biofouling and reduce the power consumption of the electrolytic device be able to.
2) By reducing the concentration of free chlorine, it is possible to reduce the effects of deterioration of the RO membrane and the like. In some cases, biofouling of the RO membrane can be suppressed without performing decomposition treatment in a reducing agent or an activated carbon tower before the RO membrane device.
3) Stabilization of chlorine can suppress the formation of harmful substances such as trihalomethane.
It can be seen that such excellent effects can be obtained.
In addition, the effect of the present invention can be obtained by simply stabilizing the chlorine-based oxidizing agent with the nitrogen compound and adding it as a combined chlorine-based oxidizing agent, since the effect as in the prior addition can not be obtained by post-addition of nitrogen compounds. It turns out that is completely different.

1 original water tank 2 reaction tank 3 two-layer type filter 4 water supply tank 5 security filter 6 RO membrane device 7 electrolyzer

Claims (7)

In the water treatment method, a chlorine-based oxidizing agent is added to feed water to a water treatment apparatus, or free chlorine is made to exist by generating chlorine by electrolysis and then supplied to the water treatment apparatus,
A water treatment method comprising adding a nitrogen compound as a chlorine stabilizer to the feed water prior to the presence of free chlorine in the feed water.   The water treatment method according to claim 1, wherein the water treatment device is a reverse osmosis membrane device.   The water treatment method according to claim 1, wherein the supply water is seawater.   The water treatment method according to any one of claims 1 to 3, wherein the nitrogen compound is a sulfamic acid compound and / or an organic nitrogen compound.   The water treatment method according to any one of claims 1 to 4, wherein hypochlorite and / or dichloroisocyanuric acid is added to the feed water as the chlorine-based oxidizing agent.   The water treatment method according to any one of claims 1 to 5, wherein 0.3 to 50 mg / L of the nitrogen compound is added to the feed water. The water treatment method according to any one of claims 1 to 6, wherein the residual chlorine concentration of the feed water after the presence of the free chlorine is maintained at 0.1 to 10 mg-Cl ₂ / L. .

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