JP2000051855A - Water treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the contamination of a filter membrane by installing an ozone-oxidation apparatus for ozone-oxidizing raw water in the pre-stage of a membrane filter. SOLUTION: An ozone contact column which injects ozone into raw water to oxidize it is installed in the pre-stage of a precision filter membrane for membrane filtration. A reverse osmosis membrane is provided in the post-stage of the filter membrane to constitute a water treatment apparatus. When ozone oxidation treatment is implemented in the pre-stage of a membrane filter which is used for the pre-treatment of a reverse osmosis apparatus, polymeric humic acid and fulvonic acid which are TOC components in the raw water are reduced, and organic components are also decomposed into low molecular weight components. In this way, these acids are adsorbed/adhered on/to the membrane surface of the membrane filter so that the increase of membrane filtration resistance is prevented and the organic substance contamination of the membrane filter can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention can be used as a water purifier for producing drinking water and various kinds of water, or as an advanced treatment apparatus for further treating biologically treated water, by suppressing organic contamination of a membrane filtration apparatus. To a water treatment device that can

[0002]

2. Description of the Related Art In recent years, due to organic contamination of industrial water and water intake water sources, TOC components comprising humic acid and fulvic acid, which are metabolites of microorganisms, have increased, and the membrane contamination of water treatment facilities using membranes has tended to increase. It is in. Generally, a system consisting of coagulation, sedimentation, and sand filtration is used as a pretreatment for a reverse osmosis membrane (RO) device. However, when the concentration of organic substances in raw water increases, ferric chloride, polyaluminum chloride, and sulfuric acid bands are used. It is necessary to add a large amount of a coagulant such as Also, when the coagulant is added in such an excessive amount, a small amount of coagulant in a dissolved state that cannot be coagulated remains in the treated water, and the coagulant reaggregates in the process of being concentrated in the reverse osmosis membrane, There is a problem in that it adheres to the surface of the reverse osmosis membrane and increases the frequency of chemical cleaning (= shortens the chemical cleaning interval).

[0003] Instead of such a classic pretreatment process, if membrane filtration is performed using a membrane filtration device such as a microfiltration device or an ultrafiltration device, as described above, without adding a large amount of a flocculant, Further, only by adding a small amount of coagulant, it is possible to suppress the contamination of the reverse osmosis membrane, reduce the frequency of chemical cleaning (= longer the chemical cleaning interval), and improve the operation efficiency of the reverse osmosis membrane device.

[0004]

However, in the method of performing membrane filtration using a microfiltration device or an ultrafiltration device as a pretreatment of the above-mentioned reverse osmosis membrane device, the high molecular weight polymer, which is the TOC component in the raw water, is used. Since humic acid and fulvic acid are adsorbed and deposited on the membrane surface of the membrane filtration device, the membrane filtration resistance is increased. In addition, membrane contamination by polymeric humic acid or fulvic acid cannot be removed by water backwashing, which is generally known as a means for cleaning microfiltration membranes and ultrafiltration membranes.
It becomes necessary to perform cleaning with chemicals. Furthermore, in the case of reusing biologically treated water from sewage and industrial wastewater, since the TOC component consisting of humic acid and fulvic acid, which are microbial metabolites, is present in the biologically treated water, the aforementioned industrial pollution caused by organic pollution has progressed. It had the same problems as the treatment of water and water supply. The present invention has been made based on such findings, and it is an object of the present invention to provide a water treatment apparatus having a high TOC component removal performance and capable of suppressing membrane contamination of a microfiltration membrane or an ultrafiltration membrane. Things.

[0005]

The water treatment apparatus of the present invention comprises:
An ozone oxidation treatment device that oxidizes raw water with ozone, a membrane filtration device that separates and removes suspended and insoluble substances in water by passing ozone-oxidized water, and a dissolved material that passes through membrane filtration water And a reverse osmosis membrane (RO) device for removing water. In addition, it is desirable to provide a reducing agent supply means for adding a reducing agent to the membrane filtration water passing through the RO device.

First, each device constituting the water treatment apparatus of the present invention will be described. As the ozone oxidation treatment device applied to the present invention, any type of gas-liquid contact device can be used as long as it can contact an ozone-containing gas with 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 ozone dissolved is at least the reaction equivalent required to oxidize organic substances in the raw water, preferably 2 to 20 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 it is usually about 1 to 60 minutes depending on the TOC concentration and the ozone concentration. And

[0007] The membrane filtration device 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 reverse osmosis membrane (R) applied to the present invention
O) The apparatus separates and removes salts and ionic substances by the action of reverse osmosis membrane, and any type of membrane and apparatus generally known can be used. The water recovery rate, operating pressure and the like are not limited at all.

According to the study of the present inventor, high-molecular humic acid and fulvic acid, which are TOC components in raw water, are subjected to ozone oxidation treatment before the membrane filtration device used as pretreatment of the RO device. The acid is oxidatively decomposed to reduce the amount of high molecular components. Then, even if the easily biodegradable components generated by the ozone oxidation treatment pass through the membrane filtration device, the permeation thereof is prevented by the RO device, so that the removal of TOC does not pose a problem. In addition, organic components are decomposed into molecules by the ozone oxidation treatment, and T
Since the OC component is increased, a charged RO such as a polyamide-based RO also has an effect of increasing the rejection of the TOC component. Thus, the water treatment apparatus of the present invention prevents the polymeric humic acid or fulvic acid, which is the TOC component in the raw water, from adsorbing and depositing on the membrane surface of the membrane filtration device, thereby increasing the membrane filtration resistance. At the same time, organic matter contamination of the membrane filtration device can be suppressed. In addition, by passing water through the membrane filtration device in the presence of ozone, these contaminants deposited on the membrane surface can be oxidized and decomposed, so that a clean membrane surface is always maintained and the membrane filtration flux can be set high.

[0010] 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 selecting clear water such as process water. For example, it can be used 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.

[0011] Further, a coagulation step may be performed at a stage preceding the membrane filtration device. 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 an arbitrary position as long as it is in front of the membrane filtration device, and may be performed before or after the ozone oxidation treatment device. 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.

[0012] When water is passed through the ozone oxidation treatment apparatus 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 device and cause microbial contamination in the RO at the subsequent stage. That is,
Despite the sterilization treatment of microorganisms in raw water by ozone oxidation treatment, even if the treated water subjected to ozone oxidation treatment is membrane-filtered and introduced into a reverse osmosis membrane, the chemical cleaning frequency of RO is still the main reason for the above. May not be long.

In such a case, by adding a reducing agent before the RO device, the residual ozone is reduced, and the water supplied to the RO film is reduced to a reducing atmosphere.
The growth of microorganisms can be suppressed.

As means for supplying the above-mentioned reducing agent at the preceding stage of the RO device, the reducing agent may be added from a reducing agent storage tank to a water storage tank provided in front of the RO device via a chemical injection pipe and a chemical injection pump. Alternatively, the water may be injected into a water supply pipe to the RO device. 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 filtration water passing through the RO apparatus, the microfiltration membrane or the ultrafiltration membrane or the membrane contamination of the RO is suppressed, In addition to improving the filtration performance, the effect of increasing the TOC removal performance of the entire processing system is also provided.

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, the water treatment apparatus may be configured such that water is passed through an electric regeneration type desalination apparatus downstream of the RO apparatus. Alternatively, after adjusting the pH to pH 9 or more, water may be passed through an electric regeneration type desalination apparatus.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in the upper half of FIG. 1, a means for injecting ozone into raw water and oxidizing it (ozone contact tower) and a means for membrane-filtering this ozone oxidized water (microfiltration membrane) include A water flow experiment was performed by a water treatment apparatus according to an embodiment of the present invention provided with a reverse osmosis membrane (hereinafter, referred to as case 1). The above-mentioned ozone contact tower was of a countercurrent contact type, and the microfiltration membrane was a polyethylene tetrafluoride (PTFE) membrane, and a spiral membrane module consisting of a flat membrane with a nominal pore size of 0.2 μm was used.
In addition, this element pushes air into the treated water at 7.5 minute intervals to backwash and introduce air into the raw water,
Air scrubbing was performed, and the dirt on the membrane surface was discharged out of the system. Further, 5 mg / L of sodium bisulfite is added as a reducing agent to the membrane filtration treatment water to remove ozone remaining in the membrane filtration water, and to reduce the growth of microorganisms by reducing the atmosphere to form a reverse osmosis membrane (RO). Supplied. The reverse osmosis membrane (RO) employed a spiral module made of a polyamide-based material.

On the other hand, as a comparative example, as shown in the lower half of FIG. 1, water used for agglomeration (coagulation tank) and sand filtration (sand filtration tower) conventionally used as a pretreatment of a reverse osmosis membrane. A water flow experiment was conducted with the treatment equipment (hereinafter referred to as case2). Ferric chloride was used as a flocculant, and flushing washing with sodium bisulfite was performed once a day for microbial control.

Table 1 summarizes these experimental conditions.

[Table 1]

FIG. 2 shows the transition of the transmembrane pressure difference. During the water flow period in this experiment, the rate of increase of the transmembrane pressure per day was 0.0021 [MPa / da for each of cases 1 and 2.
y], 0.0056 [MPa / day], and the ozone oxidation treatment and membrane filtration as the pretreatment of the reverse osmosis membrane (RO) are performed as compared with case 2 in which the coagulation and sand filtration are performed as the pretreatment of the reverse osmosis membrane (RO). Case1 was more stable. This can be attributed to the fact that the microfiltration membrane used as the pretreatment has higher removability of suspended solids than sand filtration, and the sterilization effect of ozone and the suppression of microbial growth by sodium bisulfite injection. .

Table 2 shows the average water quality in the above two types of water flow tests, where TOC and E26 were used as organic matter indices.
0 was indicated. E260 is an ultraviolet absorbance having a wavelength of 260 nm, and was measured based on a high correlation with humic substances.

[Table 2]

According to Table 2, the water supplied to the reverse osmosis membrane (RO)
That is, when comparing the microfiltration water and the sand filtration water, TOC,
Although there is no significant difference from E260, T
OC was lower in case1. This is because organic substances such as humic substances are degraded by ozone and the TOC in a charged state
It is considered that the component increased. From the above experimental results, the introduction of the ozone oxidation treatment and the membrane filtration into the pretreatment of the reverse osmosis membrane (RO) enables the stable operation of the reverse osmosis membrane (RO) device and the high TOC removal rate. confirmed.

[0024]

As described above in detail, according to the water treatment apparatus of the present invention, the ozone oxidation treatment can oxidatively decompose the polymeric humic acid and fulvic acid, which are the TOC components in the raw water, It can be easily removed with a reverse osmosis membrane device. In addition, since the organic component is decomposed into molecules by the ozone oxidation treatment to reduce the molecular weight and increase the TOC component in a charged state, a charged reverse osmosis membrane such as a polyamide reverse osmosis membrane has:
The rejection of those TOC components is increased. Therefore, the water treatment apparatus of the present invention can suppress the organic contamination of the membrane filtration apparatus, and can set the membrane filtration flux high, and as a result,
Suitable for obtaining clear water such as purified water, industrial water, process water by treating water containing relatively low concentration of organic matter, for example, water purification equipment for producing drinking water and various types of water from river water, lake water, groundwater, etc. Advanced treatment equipment that can be used as wastewater, and further treats biologically treated water obtained by biologically treating sewage, human waste, and various types of industrial wastewater that contain relatively high concentrations of organic matter as recycled water. Can be used as In particular, in the case where a reducing agent supply means for adding a reducing agent to the membrane filtration water passing through the reverse osmosis membrane device is provided, the water supplied to the reverse osmosis membrane 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 reverse osmosis membrane device can be improved.

[Brief description of the drawings]

FIG. 1 is an experimental flow (flow system diagram) of case 1 and case 2 according to an embodiment of the present invention.

FIG. 2 is a graph showing a change in transmembrane pressure between case1 and case2 in the embodiment of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA03 GA06 GA07 HA18 HA19 HA28 HA32 HA41 HA61 HA93 JA53A KA02 KA33 KB13 KB30 KC14 KD01 KD02 KD08 KD21 KD26 KD30 MA01 MA02 MA03 MC03 MC29 MC30X MC54X PB02 PB04 PB05 PC08 AA03 AA04 AA20 AB07 AB32 BA06 BA07 BB02 BD02 CA09

Claims (2)

[Claims] 1. An ozone oxidation treatment device for oxidizing raw water with ozone, and passing water subjected to ozone oxidation treatment to form a suspended substance in the water,
A water treatment apparatus comprising: a membrane filtration device for separating and removing insoluble substances; and a reverse osmosis membrane device for removing dissolved substances by passing membrane filtration water. 2. The water treatment apparatus according to claim 1, further comprising a reducing agent supply means for adding a reducing agent to the membrane filtered water passing through the reverse osmosis membrane device.