JP2001191086A - Water treating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treating apparatus which can be operated or worked stably, is improved in performance for removing a TOC component and can be used as a water purifying apparatus which produces drinkable water and various kinds of service water or a high-degree treating apparatus which further treats biologically treated water to a higher degree. SOLUTION: This water treating apparatus comprises an ozonating means which ozonates raw water, a membrane filtering means which separates and removes suspended materials and insoluble substances in water by passing the water which is subjected to ozonating treatment therethrough and a deionizing means which deionizes a membrane filtration water. Therein, an acid adding means is disposed on a front stage of the ozonating means or/and on the ozonating means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water purification device which can stably operate (operate) and improve the TOC component removal performance, and can produce drinking water and various kinds of water.
Alternatively, the present invention relates to a water treatment apparatus that can be used as an advanced treatment apparatus for further treating biologically treated water.

[0002]

2. Description of the Related Art In order to maintain the operation of a desalination apparatus using a reverse osmosis membrane (RO) in a stable state for a long period of time, a coagulation treatment and precipitation, or A system that combines equipment such as floating and sand filtration has been generally adopted. However, this conventional method requires an aggregating operation using an aluminum-based flocculant such as aluminum sulfate or polyaluminum chloride, or an iron-based flocculant such as ferric chloride or polyiron sulfate. Complicated operations such as adjustment of the amount of coagulant added and adjustment of pH conditions corresponding to the fluctuation were required. Furthermore, when the organic matter concentration in the raw water increases, it is necessary to add a large amount of a coagulant.However, when the coagulant is added in such an excessive amount, a small amount of a coagulant in a dissolved state that cannot be coagulated is generated. And the flocculant remains in the RO
Re-agglomerates in the process of being concentrated in and adheres to the surface of the RO membrane,
There was also a problem of increasing the frequency of chemical cleaning (= shortening the chemical cleaning interval).

In recent years, ultrafiltration (UF) membranes and microfiltration (M
F) With the technical advance of the membrane, a system in which the membrane filtration using the UF membrane and the MF membrane is combined as the RO pretreatment instead of the conventional sand filtration has come to be used. In this method, agglomerated treatment is not necessarily required because a turbid component larger than the used pore diameter of the membrane can be reliably removed.
Therefore, the contamination of the reverse osmosis membrane by the coagulant can be suppressed, the frequency of chemical cleaning can be reduced (= the chemical cleaning interval is lengthened), and the operating efficiency of RO can be improved.

[0004]

However, the above U
In the method combining membrane filtration using F membrane and MF membrane as pretreatment of RO, in addition to clay minerals and microorganisms to be removed, dissolved organic components typified by polymeric humic acid and fulvic acid Is also adsorbed and deposited on UF and MF membranes,
Particularly in the case of raw water having a high concentration thereof, frequent washing operations were required. In addition, membrane contamination by polymeric humic acid or fulvic acid cannot be removed by water backwashing, which is generally known as a cleaning means for UF and MF membranes, so it was necessary to perform chemical cleaning. . Also, if the membrane filtration flux is set low to extend the chemical washing cycle,
A new problem arises in that a large membrane area is required and the construction cost of the apparatus is increased. Furthermore, although a very small part of the dissolved organic components is removed by the UF film or the MF film as described above, since it depends on the RO in the latter stage, the burden is large, and particularly high removal is required. In ultrapure water production requiring a high rate, a complicated system such as arranging ROs in multiple stages has been required. In view of this, the present applicant has proposed in Japanese Patent Application No. 10-228862 a method in which an ozone oxidation treatment device is arranged in front of a membrane filtration device to decompose dissolved organic components in raw water by ozone.
It has been found that the film contamination of the F film and the MF film is suppressed, and that the film has a sufficient ability to remove dissolved organic components. However, after further intensive studies, the present invention has an even greater effect.

[0005]

The water treatment apparatus of the present invention comprises:
Ozone oxidation treatment means for oxidizing raw water with ozone, membrane filtration means for separating and removing suspended and insoluble substances in water by passing ozone oxidized water, and deionization for deionizing membrane filtered water A water treatment apparatus provided with a treatment means, wherein an acid addition means is provided in a preceding stage of the ozone oxidation treatment means and / or in the ozone oxidation treatment means.
In addition, it is desirable to provide a reducing agent supply means for adding a reducing agent to the membrane filtered water passing through the deionizing means.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, each device constituting the water treatment apparatus of the present invention will be described. As the ozone oxidation treatment means applied to the present invention, any type of gas-liquid contact device can be used as long as it can contact the ozone-containing gas with the raw water. For example, raw water is sprinkled from a sprinkler provided at the top of the tank in which water is temporarily stored in the tank, and an ozone-containing gas is sparged from an air diffuser provided near the bottom of the tank, and the gas and water come into countercurrent contact. A countercurrent gas-liquid contactor can be used. Further, a device in which a packed bed is provided in the contact tank may be used, or water and ozone may be simply supplied to the lower part of the water storage tank. The amount of dissolved ozone is at least the reaction equivalent required to oxidize the organic matter in the raw water, preferably from 2 to 2.
The amount is set to 0 times. Further, it is desirable to consider the residence time of the water in which ozone is dissolved so that the oxidation reaction is performed before the water is supplied to the membrane filtration device, and although it depends on the TOC concentration and the ozone concentration, it is usually about 1 to 60 minutes. And Then, it is preferable to pass water through the membrane filtration device while ozone remains. This is to decompose and remove fouling substances deposited on the membrane surface.

The membrane filtration means applied to the present invention may be an ultrafiltration device (UF) or a microfiltration device (M
Although F) is generally used, any type of device that is generally known can be used, and any of a flat membrane, a hollow fiber membrane, and a tubular membrane may be used. A pressurized type for obtaining permeated water or a reduced pressure type for immersing the membrane device in a water tank and depressurizing the permeated water side to obtain permeated water may be used. The membrane is made of an ozone-resistant material such as ceramic, tetrafluoroethylene, or polyvinylidene fluoride.

Further, the deionizing means applied to the present invention is not particularly limited, but a reverse osmosis membrane (RO) device which does not require a regenerating treatment with a chemical, an electric regenerating type deionizing device, Preferably, a dialysis device is used. Particularly preferably, an RO device having an ability to remove organic substances is used. This RO apparatus separates and removes salts and ionic substances by the action of a reverse osmosis membrane, and any type of membrane or apparatus generally known can be used. The water recovery rate, operating pressure and the like are not limited at all. Depending on the quality of the raw water and the desired quality of the water, the deionization means may be provided in a plurality of stages, or two or more types may be used in combination. For example, an RO device may be provided in multiple stages, or an electric regeneration type deionization device may be provided downstream of the RO desalination device.

Further, the acid addition means applied to the present invention is, for example, such that the acid is added from an acid storage tank to a water storage tank provided in front of the ozone oxidation treatment means via a chemical injection pipe and a chemical injection pump. Or may be added into the ozone oxidation treatment means, or may be added to both. The acid is not particularly limited,
It is preferable to use a mineral acid, and particularly, sulfuric acid and hydrochloric acid can be suitably used. Furthermore, the amount of acid added can be increased by increasing the number of sites where ozone attacks by modifying the surface charge density and chemical properties such as hydrophobicity of organic components such as humic substances in the raw water. The amount is such as to promote oxidation, and specifically, pH 6 or less, preferably about pH 3 to 6. If the pH is lower than 3,
It is not very desirable in terms of corrosion and the like.

According to the study of the present inventor, high-molecular humic acid which is a TOC component in raw water is obtained by performing ozone oxidation treatment before a membrane filtration means used as a pretreatment of a deionization treatment means. And fulvic acid are oxidatively decomposed to reduce high molecular components. Moreover, in the ozone oxidation treatment, the ozone oxidation is promoted by the acid added from the acid addition means. Since the ozone-oxidized water is passed through the membrane filtration unit, the UF membrane and the MF membrane in the membrane filtration unit trap organic components that can be easily removed by backwashing. In addition, by passing water through the membrane filtration means in the presence of ozone, contaminants deposited on the membrane surface can be oxidized and decomposed. Further, when an RO device is used in the subsequent deionization means, the permeation of the TOC component is prevented by the RO membrane device. Also, in charged deionization processing means such as an electric regeneration type deionization device and an electrodialysis device, the organic component is decomposed by the ozone oxidation treatment to reduce the molecular weight and the charged TOC component increases. Is removed. However, since a part of the TOC component has been removed by the preceding membrane filtration means, the load of the TOC component on the deionization treatment means is reduced. Therefore, the water treatment apparatus of the present invention can be operated (operated) stably and has high TOC component removal performance. In the case of a polyamide RO device, since the RO film is also charged, the TOC
The effect of increasing the component blocking performance (removability) is also provided. As described above, the water treatment apparatus of the present invention promotes apparent ozone oxidation by the acid addition means, thereby suppressing fouling due to organic substances in the membrane, setting a high membrane filtration flux, and increasing the removal rate of the TOC component. Can be done.

[0011] The water treatment apparatus of the present invention treats water containing a relatively low concentration of organic matter to produce purified water, industrial water,
It is suitable for obtaining clear water such as process water, and can be used, for example, as a water purification device for producing drinking water and various types of water from river water, lake water, groundwater, and the like. In addition, the wastewater containing relatively high concentration of organic matter, human waste, and various types of industrial wastewater, etc., should be used as an advanced treatment device that treats biologically treated water obtained by biological treatment to make it more advanced and reused. Can be.

[0012] Further, a coagulation step may be carried out before the membrane filtration means. That is, a coagulant may be added to raw water to form a flocculated floc and then subjected to membrane filtration, or may be subjected to membrane filtration without addition. Addition of a coagulant results in higher-purity treated water. This aggregation step may be performed at any position as long as it is before the membrane filtration means, and may be performed before or after the ozone oxidation treatment means. As the above flocculant,
Known inorganic coagulants such as iron chloride, iron sulfate, aluminum chloride, aluminum sulfate, aluminum oxide, and polyaluminum chloride can be used. Further, a polymer flocculant such as a polyacrylamide flocculant can be used.

Incidentally, when water is passed through the ozone oxidation treatment means to decompose the polymeric humic acid or fulvic acid, which is a TOC component, components that are easily biodegradable such as carboxylic acid are produced. Therefore, this may pass through the membrane filtration means and cause microbial contamination in a deionization treatment means such as an RO device at the subsequent stage. That is, despite the microorganisms in the raw water being sterilized by the ozone oxidizing means, even if the treated water subjected to the ozone oxidizing treatment is subjected to membrane filtration and introduced into the deionizing treatment means, the deionized water is still mainly due to the above. In some cases, the frequency of chemical cleaning of the processing means cannot be increased.

In such a case, the residual ozone is reduced by adding a reducing agent in the preceding stage of the deionizing means, and the water supplied to the deionizing means is made to have a reducing atmosphere so that microorganisms can be reduced. Proliferation can be suppressed.

As means for supplying the above-mentioned reducing agent at the preceding stage of the deionizing means, the reducing agent is added from a reducing agent storage tank to a water tank provided before the deionizing means via a chemical injection pipe and a chemical injection pump. Alternatively, the water may be injected into a water supply pipe to the deionization processing means. As this reducing agent, sodium thiosulfate, sodium bisulfite, hydrazine or the like is employed, but preferably sodium bisulfite is used. Further, the amount of the reducing agent added is such that residual ozone is eliminated and a reducing atmosphere is obtained. Preferably, the oxidation-reduction potential (ORP) should be negative, and the amount of the reducing agent added can be controlled using an ORP meter.

As described above, in the water treatment apparatus provided with the reducing agent supply means for adding the reducing agent to the membrane filtered water passing through the deionizing means, the membrane contamination of the UF membrane, the MF membrane, the RO membrane, etc. is suppressed. This not only improves the filtration performance, but also has the effect of increasing the TOC removal performance of the entire processing system.

The water treatment apparatus of the present invention may be one in which steps other than those described above are added as appropriate. For example, if a silica dispersant is used in combination, the economic efficiency can be improved.

[0018]

EXAMPLE [Example] As shown in FIG. 1, sulfuric acid was added to raw water (acid adding means) to make the pH acidic, then ozone was injected, and means for oxidizing treatment (ozone contact tower) was provided. An embodiment in which a means (MF membrane) for membrane filtration of ozone oxidized water is provided in the stage, and sodium bisulfite is added to the membrane filtered water (reducing agent supply means) in the subsequent stage, and then water is passed through the RO device A water-passing experiment was performed using a water treatment device.
The above ozone contact tower is a countercurrent contact type (residence time: 18 m
in). The MF membrane is made of polyethylene tetrafluoride (PTF
E) Spiral membrane module consisting of a flat membrane with a nominal pore diameter of 0.2 μm (Kurita Kogyo Co., Ltd. “K
M0212R ") was used. In addition, air was pushed into the treated water side at 7.5 minute intervals to backwash the element, and air was also introduced into the raw water side, air scrubbing was performed, and dirt on the MF membrane surface was discharged out of the system. Furthermore, 5 mg / l of sodium bisulfite was added as a reducing agent to the MF membrane filtrate to remove dissolved ozone remaining in the MF membrane filtrate and to reduce the microorganisms by reducing the atmosphere to supply the RO water to the RO apparatus. . The RO film is a spiral type module made of polyamide-based material ("E" manufactured by Nitto Denko Corporation).
S-10 "). The raw water used in the experiment was underground water in a paddy field and had high chromaticity and high TOC because of low turbidity but high humic substance content.

[Comparative Examples 1 and 2] Comparative Example 1 was the same as the above-mentioned Example except that ozone was not added, and Comparative Example 2 was the same as the above-mentioned Example except that no acid was added.
And

[Water flow conditions] The above embodiment and comparative examples 1 and 2
Table 1 below summarizes the water flow conditions in the water treatment device of No.

[Table 1]

[Water flow test result 1; Filtration stability of MF membrane]
Water was continuously passed for 3 to 5 days under the above-mentioned water passing conditions, and the rate of increase in the differential pressure speed was determined from the membrane differential pressure after air scrubbing performed once a day, and the filtration stability of the MF membrane was evaluated. The results are shown in Table 2.

[Table 2] As is clear from Table 2 above, in the embodiment of the present invention in which the raw water was subjected to ozone oxidation treatment by adding an acid, and further the water was passed under the condition that residual ozone was detected in the membrane filtration water, the membrane filtration flux was 5%. Even at a high flux of 0.0 m / d, the rate of increase in the membrane differential pressure was extremely low, and it was confirmed that stable water flow was possible. On the other hand, in Comparative Example 1 in which ozone was not injected, the membrane differential pressure increasing rate was extremely high.
It was confirmed that chemical cleaning needs to be performed once a week at a high frequency. Furthermore, in Comparative Example 2 in which ozone was injected but no acid was added, although not as high as in the example, the rate of rise in the membrane differential pressure was low, so that stable water flow was possible.

[Water flow test result 2: TOC of MF membrane filtered water]
And removal rate] The raw water TOC and the TOC of the MF membrane filtered water during the continuous water flow period were measured. The results are shown in Table 3. Also, MF
The TOC removal rate by the membrane was calculated and shown together.

[Table 3] As is clear from Table 3 above, in the embodiment of the present invention in which the raw water was subjected to ozone oxidation treatment by adding an acid, and furthermore, water was passed under the condition that residual ozone was detected in the membrane filtered water, the T
The OC removal rate was as high as 63%, and it was confirmed that the burden on the RO at the subsequent stage was reduced. On the other hand, in Comparative Example 1 in which ozone was not injected, TOC removal was hardly recognized. Furthermore, in Comparative Example 2 in which ozone was injected but no acid was added, the TOC removal rate was higher than that of Comparative Example 1 and the effect of ozone injection was recognized, but a clear difference was recognized as compared with the Example. The TOC removal rate was low.

[Permeation test result 3: TOC and removal rate of RO permeated water] T of MF membrane filtered water and RO permeated water during continuous water passage
The OC was measured, and the results are shown in Table 4. The TOC removal rate by RO was calculated and shown together.

[Table 4] As is clear from Table 4 above, in the embodiment of the present invention in which the raw water was subjected to ozone oxidation treatment by adding an acid, and furthermore, water was passed under conditions where residual ozone was detected in the membrane filtration water, the TOC of the RO permeated water was Showing a very low value of 0.035 mg / l,
It was confirmed that advanced treatment for obtaining a water quality of 0.05 mg / l or less was possible. On the other hand, in Comparative Example 1 in which ozone was not injected and in Comparative Example 2 in which ozone was injected but no acid was added, the TOC removal rate in RO was close to that of the Example, but the Example High water quality such as was not obtained. From the above experimental results, the ozone oxidation treatment means and the membrane filtration means such as MF membrane were introduced into the pretreatment of the deionization treatment means such as RO, and the ozone oxidation treatment means was further added with an acid, so that the membrane filtration means and It was confirmed that the deionization processing means can be operated stably and the TOC removal rate is high.

[0024]

As described in detail above, according to the water treatment apparatus of the present invention, the ozone oxidation treatment is performed under acidic conditions by adding an acid, so that the polymeric humic acid as the TOC component in the raw water is obtained. And fulvic acid can be oxidatively decomposed and easily removed by membrane filtration means and deionization treatment means. In addition, since the organic components are decomposed into lower molecules by the ozone oxidation treatment and the charged TOC component is increased, the charged deionization treatment means such as a polyamide-based reverse osmosis membrane can reduce such TOC components. Deterrence increases. Therefore, the water treatment apparatus of the present invention can suppress the organic substance contamination in the membrane filtration means, enhance the removability of the TOC component, set the membrane filtration flux high, and reduce the load on the deionization treatment means. Can also. As a result, it is possible to stably operate (operate) and improve the TOC component removal performance, and it can be easily applied without particularly a complicated system to ultrapure water production requiring a high removal rate. can do. And the water treatment apparatus of the present invention is suitable for treating clear water such as purified water, industrial water, and process water by treating water containing a relatively low concentration of organic matter, for example, from river water, lake water, groundwater, and the like. It can be used as a water purification device for producing drinking water and various types of water, and further advanced treatment of biologically treated water obtained by biologically treating sewage, human waste, and various factory wastewater containing relatively high concentrations of organic matter. It can be used as an advanced treatment device to make recycled water. In particular, in the case where a reducing agent supply unit for adding a reducing agent to the membrane filtration water passing through the deionizing unit is provided, the water supplied to the deionizing unit becomes a reducing atmosphere, and the growth of microorganisms can be suppressed. . As a result, the frequency of chemical cleaning can be reduced (= the chemical cleaning interval is lengthened), and the operation efficiency of the deionization processing means can be improved.

[Brief description of the drawings]

FIG. 1 is a flow (flow system diagram) showing one embodiment of a water treatment apparatus of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) C02F 1/44 C02F 1/44 K 1/70 1/70 Z F term (reference) 4D006 GA03 GA06 GA07 GA07 HA61 KA02 KA03 KA31 KA33 KA43 KA52 KA53 KA55 KA57 KA71 KB13 KB21 KB30 KC03 KC13 KC14 KD02 KD08 KD11 KD21 KE05P KE06P KE11Q KE12P KE13P BA KE15Q KE30Q MA01 MA02 MA03 MA02 P03 MC05 P03 MC03 MC01 MC03 BB02 BD02 BD06 BD08 CA09 CA10 CA13 CA16

Claims (2)

[Claims] 1. Ozone oxidation treatment means for oxidizing raw water with ozone, membrane filtration means for passing ozone-oxidized water through to separate suspended substances and insoluble substances in water, and deionizing membrane filtered water A water treatment apparatus provided with a deionization treatment means for treating, wherein an acid addition means is provided before the ozone oxidation treatment means and / or in the ozone oxidation treatment means. 2. The water treatment apparatus according to claim 1, further comprising a reducing agent supply unit for adding a reducing agent to the membrane filtration water flowing through the deionization processing unit.