JP2003053390A - Clear water production system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a clear water production system in which a NF(nanofiltration) membrane means is stably operated over a long period in high recovery rate and highly-cleaned clear water is produced in high recovery rate. SOLUTION: In the clear water production system in which the clear water is produced by treating raw water at a coagulating sedimentation means, a filtration means and the NF membrane means in order, a means using a coagulation method or a means using a crystallization method is interposed in the way or at the tail of the coagulating sedimentation means or a means using an ion exchange method is interposed in the way of the filtration means and the NF membrane means, and a concentration of supply water to the NF membrane means is reduced to a concentration not to generate scale at the NF membrane and the NF membrane means is operated at >=90% recovery rate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water purification system, and more particularly to a nanofiltration membrane (na).
No-filtration membrane: NF membrane) is provided, and fresh water such as river water, lake water, and groundwater is used as raw water.
The present invention relates to a purified water production system capable of stably operating the raw water with a high recovery rate for a long time when producing purified water such as drinking water by highly treating the raw water with the NF membrane.

[0002]

2. Description of the Related Art Conventionally, when producing purified water from fresh water (hereinafter referred to as raw water) such as river water, lake water, groundwater, etc., flocculation treatment of turbid components of raw water, precipitation treatment of generated flocs, and further, The resulting treated water is sequentially filtered to remove turbid components in the raw water. Then, the obtained treated water is subjected to, for example, chlorine sterilization treatment to produce drinkable purified water.

Recently, however, factory wastewater, agricultural wastewater,
Since the pollution of raw water is progressing by domestic wastewater, it is necessary to remove various pollutants mixed in from the wastewater when manufacturing purified water. With respect to such a problem, an advanced treatment system is operated in which treated water after the filtration treatment is further treated with an NF membrane to remove various pollutants.

The system will be described below with reference to FIG. This system is mainly composed of a coagulation-sedimentation means, a filtration means, and an advanced treatment means using an NF membrane, which are connected in series. In this system, most of the turbid components in the raw water are precipitated and removed as flocs by the flocculation-precipitation means, and the remaining turbid components in the obtained treated water are further removed by the filtration means. However, since the above-mentioned contaminants have not been removed at this point, these contaminants are removed by the next advanced treatment means using the NF film. In the above-mentioned system, if a chlorine sterilization means for adding chloramine, NaOCl, Cl ₂ or the like to the treated water is arranged at the subsequent stage of the advanced treatment means using an NF membrane, disinfection by-products such as trihalomethanes can be obtained. The production is reduced, and the safety of the purified water obtained can be increased.

The operation of this system is usually carried out as follows. First, raw water was introduced into the rapid mixing pond,
A flocculating agent such as polyaluminum chloride, aluminum sulfate; ferrous sulfate, ferric sulfate, etc. is added thereto, and the whole is stirred at a high speed to rapidly disperse the flocculating agent in the raw water to produce a turbidity. The quality components are aggregated to form microflocs.

The amount of the coagulant added at this time is usually Al.
The converted amount or Fe converted amount is about several ppm to 10 ppm.
Further, for the aggregation by the rapid mixing described above, the pH value is adjusted to about 6 to 8 by adding an alkali such as caustic soda, or an acid such as hydrochloric acid or sulfuric acid as necessary. Then, the treated water in which the above-mentioned micro flocs are dispersed is transferred to a slow stirring tank, where the whole is slowly stirred to promote the association of the micro flocs to form coarse flocs.

At this time, the agitation is performed slowly so that the formed coarse flocs are not destroyed during the agitation. For such agitation, the slow agitation tank is equipped with, for example, a paddle type, a vertical diversion. The agitation method such as the horizontal type and the right-and-left bypass method is adopted. The treated water in which the above-mentioned coarse flocs are dispersed is then transferred to the sedimentation basin. As a sedimentation pond,
For example, a single-layer type, a hierarchical type, or a sloping plate type lateral flow type sedimentation pond is used. Then, coarse flocs are precipitated in this sedimentation basin, and supernatant water (treated water) is produced.

The treated water obtained through the rapid mixing basin, the slow agitation basin and the sedimentation basin as described above usually has a turbidity of 5 degrees by appropriately selecting the operating conditions of each treating means. Below, it is preferably adjusted to about 0.1 to 2 degrees. The reason for this is to reduce the load on the filtration means that subsequently processes this supernatant water. The turbidity referred to here is an index defined as a relative value to the turbidity when the turbidity in a state in which 1 L of standard kaolin is contained in 1 L of purified water is 1 degree, and is usually JIS K01.
It is measured by the transmitted light measurement method and the scattered light measurement method specified in 01 "Industrial water test method".

The supernatant water (treated water) obtained by the treatment of the above-mentioned stirring and precipitation means is then transferred to the filtration means, and further,
Removal of suspended components is promoted. As this filtering means,
Usually sand filtration, micro-filtration membrane
e: filtration means using MF membrane, or ultrafiltration membrane (ult
A filtration means using a ra-filtration membrane (UF membrane) is adopted.

Among these means, in the case of sand filtration, for example, a filter layer formed by laminating granular filter media such as sand, anthracite, or garnet in a single layer or multiple layers, for example, 1
The supernatant water to be treated is passed through an upward flow type or a downward flow type at a flow rate of 20 to 150 m / d to remove suspended components of the supernatant water by adhering to the surface of the filter medium and sieving the filter layer. .
By this sand filtration, the above-mentioned clearing of the supernatant water is further promoted.
The conditions such as the thickness of the filter layer for sand filtration and the particle size of the filter medium are appropriately selected so that the SDI of the obtained treated water is 5 or less, preferably 3 or less.

In the case of this sand filtration, when the filter layer is in a state of completely capturing the suspended components, the filter layer is clogged and the filtering action begins to decrease. Therefore, it is usually an intermittent process using purified water. Backwashing is done. In addition, the above-mentioned SDI
The (silt density index) refers to the degree of clogging per minute of a membrane filter with a pore size of 0.45 μm based on suspended matter contained in water. The smaller this value, the less suspended matter. It means being clear.

Next, in the case of a filtration means using an MF membrane or a UF membrane, when the above-mentioned supernatant water is flowed on one membrane surface at a predetermined operating pressure, the permeated water is transmitted from the other membrane surface at a certain permeation flux. Is obtained. At that time, turbidity components smaller than the pores formed in the membrane move to the permeate side, but turbidity components larger than the pores do not pass through the membrane and remain on one membrane surface side. To do.

Therefore, when the above-mentioned supernatant water is filtered through the MF membrane or the UF membrane, the concentration of the suspended water component and the permeated water in which the suspended water component of a certain size is removed are increased. It is separated into concentrated water. In this case, since the pores of the UF membrane are usually smaller than the pores of the MF membrane, smaller turbidity components can be clarified. However, these filtration means use permeated water after the membrane treatment. Is operated so that the SDI of 3 is 3 or less, preferably 2 or less.

For example, polyacrylonitrile (PA
N), polyvinylidene fluoride (PVDF), polyethylene (PE), polypropylene (PP), polysulfone (PS), cellulose acetate, or various ceramics, and the membrane is composed of hollow fiber or flat membrane MF membrane module or UF. The membrane module is operated at an operating pressure of about 0.01 to 0.3.
By operating under the conditions of MPa and permeation flux of 0.3 to 5 m / d, the above-mentioned SDI permeate can be obtained.

The treated water treated by such a filtration means is then transferred to the NF membrane means, and undergoes advanced treatment there. Specifically, various substances to be removed which have not been removed by the filtering means are removed. That is,
For example, low to medium molecular weight organic substances such as humic acid and fulvic acid; pesticides such as simazine and atrazine; diosmin,
Odorants such as 2-methylisoborneol; disinfection by-product precursors containing trihalomethane precursors; Ca ²⁺ and M
Hardness components such as g ²⁺ ; Fe ²⁺ , Mn ²⁺ , Al ³⁺ , SO ₄
2 or more valences ions such as ² can be effectively removed.

As such an NF film, for example, a film made of crosslinked polyamide or cellulose acetate is used. Then, using a membrane module assembled by bundling the hollow fibers or spirally winding the flat membrane, an operating pressure of 0.2 to 0.7 MPa and a permeation flux of 0.2 to 2 are usually used.
The altitude processing described above is performed under the condition of m / d.

[0017]

As described above, in the case of the purified water manufacturing system shown in FIG. 4, the purified water obtained by the advanced treatment with the NF membrane is of high quality because, for example, pesticides are also removed. By the way, in a purified water production system, it is important to efficiently produce a large amount of desired high-quality purified water from raw water to be treated. That is, it is necessary to have a system that can obtain purified water with a high recovery rate.

With regard to such a problem, in a system not using an NF membrane, for example, the washing wastewater when backwashing sand filtration is once cleaned by the wastewater treatment means, and the clean backwash water is returned to the raw water. A circulation treatment method is known in which coagulation-precipitation treatment and filtration treatment are sequentially performed. According to this method, since a part of the treated raw water is reused, the recovery rate of purified water from the raw water is high.

However, even if the NF membrane means is simply combined with this circulation treatment system to assemble the purified water production system, the purified water production system produces the purified water highly processed by the NF membrane means at a high recovery rate. Is difficult. It is true that the circulation treatment type filtration means supplies a large amount of treated water with an SDI of 3 or less to the NF membrane means.
However, since the NF membrane means can operate only at a recovery rate of about 80%, the overall recovery rate of the purified water production system is limited even though a large amount of treated water is supplied from the filtration means. receive.

For example, when operating the NF membrane means, the operating pressure is increased and the permeation flux is increased so that the recovery rate is 9%.
This is because, when the operation is performed under the condition of 0%, scale is generated in the concentrated water and fouling occurs on the membrane surface of the NF membrane in a short time operation, and the amount of permeated water is reduced. That is, in the case of the purified water manufacturing system having the NF membrane means shown in FIG. 4, there is a problem that it is difficult to stably operate with a high recovery rate for a long period of time.

In the present invention, by incorporating the design concept described later and the concrete means based on it into the system shown in FIG. 4, it is possible to stably operate the NF membrane means for a long time with a high recovery rate which has never been seen before. As a result, an object of the present invention is to provide a purified water production system capable of producing highly purified purified water as a whole with a high recovery rate.

[0022]

In order to achieve the above-mentioned object, in the present invention, there is provided a purified water production system for producing purified water by sequentially treating raw water with a flocculation-precipitation means, a filtration means and an NF membrane means. There is provided a water purification system characterized in that the NF membrane means is operated at a recovery rate of 90% or more.

More specifically, a softening treatment means is interposed in the middle or the end of the coagulation-precipitation means, or in the middle of the filtration means and the NF membrane means, and the hardness component of the water supplied to the NF membrane means is changed. A purified water production system for reducing the concentration to a concentration at which scale does not occur in an NF membrane, wherein the calcium ion concentration of the concentrated water produced by the NF membrane means is C
(Mg / L), sulfate ion concentration is S (mg / L), alkalinity is A (mg / L asCaCO ₃ ), and pH is H. : (C / 40) × (S / 96) × 10 ⁻⁶ <1.0 × 10 ⁻⁵ (1)

[0024]

[Equation 3]

There is provided a water purification system in which the above conditions are satisfied at the same time. In that case, the calcium ion concentration is C ₀ (m
g / L), sulfate ion concentration is S ₀ (mg / L), and alkalinity is A ₀ (mg / L as CaCO ₃ ),
When the NF membrane means incorporated in the target purified water production system is operated at a recovery rate that does not generate scale in the wash water, the calcium ion exclusion rate of the NF membrane is r.
Assuming that _c (%), the sulfate ion exclusion rate are r _s (%), and the alkalinity exclusion rate is r _A (%), the calcium ion concentration of the obtained concentrated water is C ′ (mg / L), Sulfate ion concentration is S '(mg / L), alkalinity is A' (mg / L as C
aCO ₃ ), the following formula:

[0026]

[Equation 4]

(However, R represents the recovery rate (%) of the nifiltration membrane means.) C ', S', A'calculated based on the respective values of C, S, A. A predictive and designed water purification system is provided.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION
By operating the F membrane means at a recovery rate of 90% or more, N
It is a system for producing purified water with a high recovery rate as a whole and in a stable state for a long period of time while realizing advanced treatment by F membrane means. The core point in that case is 90% of the NF membrane means.
It is about to be operated at the above recovery rate. The operation of the NF membrane means in that case is realized based on the following technical idea.

First, when the NF membrane means is operated at a high recovery rate of 90% or more, as described above, scale is likely to be generated in the concentrated water, the amount of permeated water is reduced, and the recovery rate is reduced in a short time. To do. Therefore, in order to maintain the operation with a high recovery rate of 90% or more for a long period of time, it is sufficient to suppress the scale generation in the concentrated water separated and manufactured during the operation of the NF membrane means. It is preferable that no scale is generated.

By the way, the main body of the scale is Ca²⁺In
Hardness component and SO in treated water represented _Four ^2-, HCO₃ ^-Such
Calcium sulfate (CaSO_Four) And
Calcium carbonate (CaCO₃). These CaSO_Four
And CaCO₃The amount of Ca produced in concentrated water is
SO_FourAnd CaCO₃Depending on the solubility of the
Is rate-controlled. That is, of these components for concentrated water
If the solubilities are high, these will form as scale
If the solubility is low, the scale is
Generated in concentrated water.

The NF membrane means is, as described above, 2
Highly charged multivalent ions (eg Ca ²⁺ , Mg ²⁺ , S
O ₄ ²⁻ ) has a high rejection rate, so the concentrated water obtained by separation with an NF membrane means Ca ²⁺ , SO ₄ ²⁺ , and HC
The concentration of scale factors such as O ₃ ⁻ is high. Now, let us consider the conditions under which CaSO ₄ is not produced in concentrated water.

First, the solubility product (K _sp ) of CaSO ₄ at room temperature is calculated by the following formula: K _sp = [Ca ²⁺ ] · [SO ₄ ^{2 −} ] = 1.0 × 10 ^-5 (1A) It is represented by. In this case, [Ca ²⁺ ], [S
The concentration unit of O ₄ ²⁻ ] is mol / L in all cases. Therefore, the calcium ion concentration ([Ca ²⁺ ]) in the concentrated water obtained by separation during the operation of the NF membrane means is C (mg
/ L), sulfate ion concentration ([SO ₄ ^2- ]) S (mg /
L), if the product of [Ca ²⁺ ] and [SO ₄ ²⁻ ] is more than the above K _sp value (= 1.0 × 10 ⁻⁵ ), CaS
If O ₄ is produced as a scale and is smaller than the K _sp value, scale (CaSO ₄ ) is not produced in the concentrated water.

Here, when the concentration units of [Ca ²⁺ ] and [SO ₄ ²⁻ ] are respectively expressed in mg / L, [Ca ²⁺ ] · [S
O ₄ ²⁻ ] is the following formula:

[0034]

[Equation 5]

[0035] Therefore, in the concentrated water obtained by the NF membrane means, the following formula:

[0036]

[Equation 6]

If the above condition is satisfied, the concentrated water is scaled.
(CaSO_Four) Fouling of NF membrane means
Does not occur, and the amount of permeated water does not decrease.
The recovery rate can be maintained at a high level. next
CaCO in concentrated water₃Consider the conditions for not generating
It "Industrial water and wastewater treatment" (Okamoto et al., Nikkan Kogyo Shimbun
Company)²⁺And HCO ₃ ^-From water containing CaCO
₃Is generated or not is determined by the alkali of the water.
Degree A_MAnd [Ca²⁺] Saturated pH value (pHs) controlled by
And the saturation index, which is the difference between the actual pH value (H) of the water:
It is said that I = H-pHs may be used as an index.

That is, if I> 0, the scale (Ca
CO ₃ ) is produced, and if I <0, CaCO ₃ is dissolved and scale formation does not occur. Therefore, CaCO
The condition for not generating ₃ is represented by the following formula: pHs> H ... (2A).

According to the above-mentioned literature, the pHs value is calculated by the following formula: pHs = pK ₂ -pK _sp + pCa + pA _M + α (2B) (where pK ₂ is the second dissociation constant of carbonic acid and its value is 10.
33, pK _sp is the value at 8.32 in the solubility product of calcium carbonate, pCa is -log [Ca ^2+], pA _M
Represents -log [A _M ]. Note that [Ca ²⁺ ] and [A _M ]
The unit of each is mol / L. ).

[0040] Here, since since it is pH <9 is α term in Equation (2B) can be ignored, after all, the formula (2B) has the _{formula: pHs = pK 2 -pK sp +} pCa + pA M ......... (2C) Becomes Therefore, the equation (2A) from the formula (2C), the following formula: if they meet the _{pK 2 -pK sp + pCa + pA} M <H ......... (2D), CaCO 3 is not able to generate in the water as a scale.

In other words, if the above formula (2D) is satisfied in the concentrated water obtained by separation with the NF membrane means, CaCO ₃ will not be produced as a scale in the concentrated water. There will be no. Here, Cmg the [Ca ^2+] in the concentrated water produced / L, the [A _M] Am
Displayed in g / L as CaCO ₃ respectively, pHs
Is the following formula:

[0042]

[Equation 7]

It becomes Therefore, in the concentrated water obtained by the NF membrane means, the following formula:

[0044]

[Equation 8]

If the relationship of is satisfied, scale (CaCO ₃ ) is not generated in the concentrated water, fouling of the NF membrane means does not occur, and the amount of permeated water does not decrease.
The recovery rate in the membrane means can be maintained at a high level. In the purified water production system of the present invention, the concentrated water obtained by the NF membrane means simultaneously satisfies the formulas (1) and (2),
Therefore, the concentrated water contains CaSO ₄
And CaCO ₃ are not generated.

In this case, C in equations (1) and (2)
The value, the S value, and the A value are related to the target recovery rate (R%) of the NF membrane means as follows, and the C ′ value and the S ′ value, respectively.
Values, A'values are predicted, and these predicted values are compared with the C value, S value, and A value in the above formulas (1) and (2), and in these predicted values, formulas (1) and (2) If the above conditions are not satisfied at the same time, the simultaneous satisfaction of the formulas (1) and (2) is attempted by introducing the means described below into the system.

First, the calcium ion concentration is C ₀ (mg /
L), the sulfate ion concentration is S ₀ (mg / L), and the alkalinity is A ₀ (mg / L as CaCO ₃ ), the water to be treated (supply water) is prepared and placed in the water purification system for construction. An NF film means to be prepared is prepared. This NF membrane means has a calcium ion exclusion rate of rc (%) when the membrane separation of the feed water is operated at a recovery rate that does not generate scale.
Sulfuric acid ion exclusion rate is rs (%), alkalinity exclusion rate is r
It is assumed to indicate _A (%).

Using the feed water and the NF membrane means, the operating conditions of the NF membrane means (for example, operating pressure 0.2 to 0.2) with a target recovery rate R (%) of, for example, 90% or more in the purified water production system to be constructed. Membrane separation of the feed water is performed at 1 MPa and a permeation flow rate of 0.2 to 3 m / d) to separate the feed water into concentrated water and permeate. Calcium ion concentration C '(mg / L) and sulfate ion concentration S'in the concentrated water obtained at this time
(Mg / L), alkalinity A '(mg / L as CaC
O ₃ ) is calculated from each of the following equations.

[0049]

[Equation 9]

The C'value, S'value, and A'value obtained from the equations (3), (4), and (5) are all of the above-mentioned properties by using the feed water having the above-mentioned properties. It is a predicted value of calcium ion concentration, sulfate ion concentration, and alkalinity of concentrated water obtained when the NF membrane means is operated at the target recovery rate. Therefore, these values are used as C, S, and
Substituting each into A, and if the formula (1) and the formula (2) are established at the same time, the purified water production system to be constructed does not cause the generation of scale, and has the above-mentioned target recovery rate (R). It is possible to judge that the operation can be maintained.

On the other hand, when these values are substituted into C, S, and A of the equations (1) and (2), respectively, and if the equations (1) and (2) do not hold at the same time, the It can be determined that a scale is generated when the purified water production system is operated at the target recovery rate (R). This is mainly due to the high concentration of calcium ions in the water supplied to the NF membrane means, that is, the concentration of the hardness component. Therefore, in the purified water production system of the present invention, the softening treatment means is arranged on the upstream side of the NF membrane means to reduce the concentration of the hardness component of the water supplied to the NF membrane means, and the above equation (1) and equation ( 2)
By realizing the simultaneous establishment of the above, the high recovery rate operation of the NF membrane means is enabled.

Specifically, as shown in FIG. 1, whether the coagulation method is applied at the time of rapid mixing, the crystallization method is applied to the supernatant water after the precipitation treatment, or the water supplied to the NF membrane means is used. It is preferable to remove the hardness component by applying an ion exchange method to. Here, the coagulation method is carried out by adding an alkali such as caustic soda to the raw water at the time of rapid mixing to adjust the pH to 9 to 11, and further adding slaked lime thereto. Ca and Mg in raw water
Bicarbonate, which is the hardness component, is insoluble in CaCO ₃ and M
Change to g (OH) ₂ . Then, since these are removed by the precipitation process and the filtration process in the latter stage, the concentration of the hardness component of the water supplied to the NF membrane means is reduced. However, in this coagulation method, since the pH value of the treated water is high, it is necessary to adjust the pH value to an appropriate value in the latter stage.

In the crystallization method, caustic soda, for example, is added to the supernatant after the precipitation treatment to bring its pH value to about 10, and this supernatant is contacted with, for example, ground calcium carbonate as a fluid medium, The Ca component in the treated water is reduced by crystallizing the calcium component in the supernatant as calcium carbonate on the fluidized medium. The ion exchange method is a method in which the hardness component is ion-exchanged into sodium salt or the like, and for example, the water supplied to the NF membrane means may be passed through the Na-type weak cation exchange resin.

As described above, by disposing the above-mentioned softening treatment means on the upstream side of the NF membrane means, it is possible to reduce the concentration of the hardness component in the water supplied to the NF membrane means. As a result, the equations (1) and (2) can be simultaneously established, and the NF membrane means can be operated at a high recovery rate of 90% or more. Of the above-mentioned softening treatment means, application of means using a coagulation method is practically limited to rapid mixing. Although the crystallization method can be carried out anywhere, it is preferable to apply it before the filtration means in view of preventing the leakage of the obtained calcium carbonate to the downstream side, and considering the reuse of the obtained calcium carbonate. It is preferable to apply after precipitation with less turbid components. Although the ion exchange method can be carried out anywhere, it is preferably applied between the filtration means and the NF membrane means from the viewpoint of suppressing the contamination of the ion exchange resin.

FIG. 2 shows another water purification system of the present invention. This purified water manufacturing system is the system shown in FIG. 1, which is premised on the high recovery operation of the NF membrane means, and the washing wastewater obtained by backwashing the filtering means, for example, sand filtration, is passed through the wastewater treatment means. It is a system that reuses the raw water by returning it to the raw water.

In this system, the high recovery rate operation of the NF membrane means has already been realized, and at the same time, the raw water to be treated is reused, so that the system as a whole has a high recovery rate of purified water. improves. In the purified water manufacturing system of the present invention, it is preferable to dispose activated carbon charging means for raw water as shown in FIG. 3 on the premise of the configuration shown in FIG. 1 or 2.

By introducing activated carbon into the raw water, odor substances, pesticides, low molecular weight organic substances, etc., which are difficult to remove by the coagulation-sedimentation means and filtration means in the latter stage, are adsorbed and removed in advance, and the load of the NF membrane means Can be reduced,
Finally, synergistically with the effect of the NF membrane means, higher quality purified water can be produced. This activated carbon charging means is composed of a raw water quality measuring device, a controller, and an activated carbon charging device.

In this means, the water quality of the raw water is first measured by the water quality measuring device, and the water quality data is transmitted to the controller. The controller is preset to emit a signal when certain water quality conditions are met. The water quality data from the water quality measuring device is input to the controller, where it is compared with preset water quality conditions, and if the water quality data matches the set water quality conditions, the controller sends an operation signal to the activated carbon charging device. Then, a predetermined amount of activated carbon is fed into the raw water from the activated carbon feeding device.

The charged activated carbon is not included in the feed water of the NF membrane means because it is removed by the coagulation-sedimentation means and the filtration means in the subsequent stage, which hinders the high recovery rate operation of the NF membrane means. It won't come.

[0060]

Example 1 (1) Measurement of r _c , r _s , and r _A of the NF membrane means used. First, the river water was subjected to coagulation sedimentation and sand filtration in order to remove turbidity components and to obtain clear water with the following properties.

C ₀ value: 50 mg / L, S ₀ value: 26 mg / L,
A ₀ value: 120 mg / L as CaCO ₃ , pH (H) value:
7.4. Then, NF membrane (manufactured by Toray Industries, Inc., Lomembura SU-61)
0) with respect to the upper supernatant water, water temperature 32 ° C., the operating pressure 0.56MPa, perform membrane separation at a recovery rate of 25% of conditions, r _c for the upper supernatant water of the NF membrane, r _s, the r _A I asked.
It should be noted that no scale is generated in the concentrated water during the above operation.

As a result, the calcium ion exclusion ratio r _c was 64.0%, the sulfate ion exclusion ratio was 99.8%, and the alkalinity exclusion ratio was 60.2%. (2) System operation A system of the present invention was assembled by arranging a softening treatment means using a crystallization method in the supernatant water after sand filtration. It should be noted that hydrochloric acid was injected into the water supplied to the NF membrane means so that the pH value became 7.4.

The above system was operated using the river water described above. The calcium concentration in the feed water to the NF membrane means was reduced to 1.3 mg / L. Therefore, the water supplied to the NF membrane means has a C ₀ value of 1.3 mg / L and an S ₀ value of 26 mg / L.
L, A ₀ value: 120 mg / L as CaCO ₃ , pH value:
It is 7.4. For this supply water, the water temperature is 32 ° C,
Advanced treatment was performed under the conditions of operating pressure of 0.56 MPa and recovery rate of 95%.

The amount of water produced was 7.32 m ³ / d. 750
The amount of water produced after running for 7 hours is 7.21 m ³ / d,
Almost no decrease in the amount of water produced was recognized even during continuous operation with a recovery rate of 95%. At this time, the value on the left side of the equation (1) is 1.2 × 10 ⁻⁶ , and the value on the left side of the equation (2) is 7.5, so that the equation (1) and the equation (2) are simultaneously calculated. It has been established.

Comparative Example 1 In the application of the crystallization method in the system of Example 1, the amount of sodium hydroxide added was reduced so that the calcium ion concentration in the water supplied to the NF membrane means was 3.0 mg / L. Except that the operation was performed under the same conditions as in Example 1.
As a result, the amount of water produced immediately after the start of operation was 7.21 m ³ / d, but after 750 hours of operation, it was 3.42 m ³ / d.
It has been halved to d. That is, it was not possible to maintain operation at a recovery rate of 95%.

In this case, the equation (1) was established, but the equation (2) was not established. Comparative Example 2 In the application of the crystallization method in the system of Example 1, the amount of sodium hydroxide added was reduced and the calcium ion concentration in the feed water to the NF membrane means was 15.0 mg / L.
The operation was performed under the same conditions as in Example 1, except that

As a result, the amount of water produced immediately after the start of operation was 7.4.
It was 1 m ³ / d, but it decreased to 2.95 m ³ / d after 200 hours of operation. That is, it was not possible to maintain operation at a recovery rate of 95%. In this case, the expressions (1) and (2) were not satisfied. Example 2 A system in which a softening treatment means using a coagulation method was arranged during rapid mixing was assembled. In addition, hydrochloric acid was injected into the water supplied to the NF membrane means so that the pH value became 7.0.

The above system was operated using the river water described above. The calcium concentration in the feed water to the NF membrane means was reduced to 5.0 mg / L. Water temperature of this supply water is 3
Advanced treatment was performed under the conditions of 2 ° C., operating pressure of 0.56 MPa, and recovery rate of 90%. The amount of water produced was 7.25 m ³ / d. 750
The amount of water produced after the operation for 7 hours was 7.12 m ³ / d, and almost no decrease in the amount of water produced was observed even during continuous operation with a recovery rate of 90%.

Under this operation, the expressions (1) and (2) are simultaneously established. Example 3 A system in which a water softener using a Na-type weak cation exchange resin was placed in the supernatant water after sand filtration was assembled. The above system was operated using the river water described above. The calcium concentration in the feed water to the NF membrane means was reduced to 1.0 mg / L.

This feed water was subjected to advanced treatment under the conditions of a water temperature of 32 ° C., an operating pressure of 0.56 MPa and a recovery rate of 95%.
The amount of water produced was 7.15 m ³ / d. The amount of water produced after 750 hours of operation was 7.09 m ³ / d, and the recovery rate was 95%.
Almost no decrease in the amount of water produced was observed even after continuous operation.

Under this operation, the equations (1) and (2) are both satisfied. Example 4 The same system as in Example 1 was assembled and operated under the same conditions as in Example 1 except that a UF membrane (Torefil CP20-1010 manufactured by Toray Industries, Inc.) was used instead of sand filtration as the filtering means. did.

[0072] desalination amount after the start of operation is 7.45m ³ / d, desalination amount after operation 750 hours 7.41m ³ /
d, and almost no decrease in the amount of water produced was recognized even during continuous operation at a recovery rate of 95%. The purified water production yield of the system as a whole was 88%. It should be noted that under this operation, the equations (1) and (2) are simultaneously established.

Example 5 In Example 4, a system for returning the UF membrane backwash drainage to the river water was assembled, and the system was operated under the same conditions as in Example 4. As a result, the purified water production yield of the entire system was improved to 93%, and the return effect was confirmed.

[0074]

As is apparent from the above description, the purified water production system of the present invention can stably operate the NF membrane means at a high recovery rate of 90% or more for a long period of time. Therefore, this purified water production system is capable of producing highly treated, high-quality purified water over a long period of time with a high recovery rate by removing pesticides, low molecular weight organic substances, odorous substances, etc. as well as turbid components. And its industrial value is great.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a preferred example of a purified water production system of the present invention.

FIG. 2 is a schematic view showing an example of another purified water manufacturing system of the present invention.

FIG. 3 is a schematic view in which activated carbon charging means is arranged in the purified water manufacturing system of the present invention.

FIG. 4 is a schematic diagram showing a conventional water purification system using an NF membrane means.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 9/00 C02F 9/00 504E 4D066 B01D 9/02 601 B01D 9/02 601B 602 602E 603 603C 608 608A 24 / 02 36/04 36/04 61/16 61/16 C02F 1/42 B C02F 1/42 1/44 H 1/44 1/52 Z 1/52 1/58 J 1/58 B01D 23/16 23 / 10 Z (72) Inventor Keiichi Ikeda 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Toray Co., Ltd. Shiga Plant (72) Inventor ▲ Ryota Takagi 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Expression company F term in Shiga plant (reference) 4D006 GA06 GA07 HA01 HA41 HA61 JB20 KA01 KB11 KB13 KB15 KB30 KE30Q MA01 MA03 MC03 MC18 MC22 MC23 MC29 MC39 MC54 MC62 PB04 PB05 PB27 PB70 4D015 BA19 BA22 BA23 B B05 CA14 DA03 DA05 DA15 DA16 EA36 EA37 FA22 4D025 AA03 AB19 BA08 DA05 DA10 4D038 AA02 AB59 BA04 BB08 BB09 BB17 BB18 4D041 BA01 BA21 BB04 BB08 BB21 CA03 CA04 CB03 4D066 AB02 AB04 AB07 AC08

Claims (7)

[Claims] 1. A water purification system for producing purified water by sequentially treating raw water with a coagulating sedimentation means, a filtration means and a nanofiltration membrane means, wherein the nanofiltration membrane means has a recovery rate of 90% or more. A water purification system characterized by being operated at 2. A softening treatment means is provided midway or at the end of the flocculation-precipitation means, or in the middle of the filtration means and the nanofiltration membrane means, and water supplied to the nanofiltration membrane means is provided. The water purification system according to claim 1, wherein the concentration of the hardness component is reduced to a concentration at which scale does not occur in the nanofiltration membrane. 3. The concentration of calcium ions in the concentrated water produced by the nanofiltration membrane means is C (mg / mg /
L), sulfate ion concentration S (mg / L), alkalinity A
(Mg / L as CaCO ₃ ), and when pH is H, between C, S, A and H, the following formula: (C / 40) × (S / 96) × 10 ⁻⁶ <1.0 × 10 ^-5 [Equation 1] The water purification system according to claim 1 or 2, wherein the above are established at the same time. 4. A calcium ion concentration of C ₀ (mg /
L), the concentration of sulfate ion is S ₀ (mg / L), and the alkalinity is A ₀ (mg / L as CaCO ₃ ), the nanofiltration is arranged in the target water purification system. When the membrane means is operated at a recovery rate that does not generate scale in concentrated water, the nanofiltration membrane has a calcium ion exclusion rate of r _c (%), a sulfate ion exclusion rate of r _s (%), an alkali Assuming that the rejection rate is r _A (%), the calcium ion concentration of the obtained concentrated water is C ′ (mg /
L), the sulfate ion concentration is S ′ (mg / L), and the alkalinity is A ′ (mg / L as CaCO ₃ ), the following formula: (However, R represents the recovery rate (%) of the nifiltration membrane means.) C ′,
The water purification system according to claim 3, which is designed by predicting the respective values of C, S, and A with S ′ and A ′. 5. The purified water production system according to claim 2, wherein the softening treatment means is means using a coagulation method, means using a crystal folding method, or means using an ion exchange method. 6. The means for using sand filtration as the filtration means,
The purified water manufacturing system according to claim 1, which is one or more of a means using a microfiltration membrane or a means using an ultrafiltration membrane. 7. The purified water production system according to claim 1, wherein the wash water of the filtering means is returned to the raw water.