JPH1043506A - Pre-treatment of raw material water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of efficiently clarifying and having large throughput as a method for pretreating a raw material water containing a suspended material. SOLUTION: This pre-treating method of the raw material water is performed by adding a cationic organic high molecular flocculant into the raw material water containing the suspended material in the quantity that the product of the concn. of the suspended material and the concn. of the flocculant in the raw material solution becomes 0.02-0.5 when the concentration unit is expressed by mg/1. In the case of using a granular filter media as the filter media of filtration, the filtration is more stabilized by using the granular filter media having 300-800μm effective diameter and uniformity coefficient of <=1.6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method for highly clarifying raw water containing suspended substances, for example, concentration by reverse osmosis, electrodialysis, etc.
It can be used for pretreatment in fields such as desalting and separation and purification, and pretreatment in the treatment of industrial water.

[0002]

A problem in reverse osmosis and electrodialysis is contamination of the membrane. The raw material water often contains organic substances and inorganic substances as colloidal substances and suspended substances (hereinafter referred to as “suspended substances”). Since the suspended matter in the raw water causes contamination of the membrane, a pretreatment method capable of preventing such contamination is desired. Therefore, various methods have conventionally been used as a method for removing suspended substances in raw water. For example, a method of filtering using a particulate filter medium such as sand as a filter medium, a membrane, a ceramic filter, a synthetic resin filter, or the like, a method of adding a flocculant to form a floc of a suspended substance, and performing a filter, and the like. A method of forming a floc by adding it, followed by sedimentation separation or flotation separation is exemplified.

[0003] Several examples are described below. First, as a field in which the electrodialysis method is used, production of salt by an ion exchange membrane electrodialysis method (hereinafter, referred to as “salt production”).
There is. In the ion exchange membrane electrodialysis apparatus used for salt production, an anion exchange membrane and a cation exchange membrane are alternately arranged, and a mesh-shaped plastic spacer is inserted between the anion exchange membrane and the cation exchange membrane.
The following narrow passage is maintained, and a uniform flow of the raw water is maintained in this passage. Since seawater as raw water is passed through such a special device, it is important to suppress contamination of the ion exchange membrane and blockage of the passage between the membranes in order to ensure stable operation of the ion exchange membrane electrodialysis device. Issues. Therefore, the prerequisite for seawater pretreatment is that the suspended solids in the raw water can be removed as quickly as possible, and since a large amount of seawater is used to produce the salt, the filtration capacity is low. It is necessary to be large and to be able to highly clarify the filtered water. At present, generally in the field of salt production, a gravity type or pressure type filtration method using a particulate filter medium such as sand having an effective diameter of 200 μm to 1000 μm is often used.

[0004] However, the ion exchange membrane electrodialyzer recently used for salt production tends to reduce the electric resistance by further narrowing the gap between the ion exchange membranes and reduce the production cost. Due to the increasing demand for labor saving by realizing long-term continuous operation, the current state of the art has reached the limit with conventional processing methods. In other words, in order to narrow the gap between the ion exchange membranes and prolong the operation of the ion exchange membrane dialysis device, it is necessary to prevent the contamination of the membranes and block the passages between the membranes, and supply them. This problem is difficult to solve unless the suspended solids in the raw water are further reduced and clarified.

Another field in which the reverse osmosis method is used is desalination of seawater. Two modules of a spiral type and a hollow fiber type are widely used in desalination apparatuses as reverse osmosis membranes for obtaining fresh water by removing inorganic salts and organic substances in seawater. The spiral element is wound around a water collecting pipe around a reverse osmosis membrane and a spacer, and the hollow fiber type element is made by incorporating a bundle of hollow fibers as a reverse osmosis membrane and bonding the ends thereof. In any of the modules, the surface of the reverse osmosis membrane has a dense structure, which is a kind of filtration. Therefore, if there is a suspended substance in the raw water, it is deposited on the membrane and lowers the water permeability. Therefore, it is essential for the stable operation of the apparatus to supply a raw water of clear and stable quality by pretreatment. Condition.

[0006] In addition, industrial water greatly varies in required water quality depending on the type of industry in which it is used and the intended use.
Suspended substances are deposited on pipes, manufacturing equipment, boilers, and the like to cause a decrease in efficiency and the like, which hinders the use of the substances for treating products. Therefore, clarification of industrial water is required. As in the above examples, in the field of application of the present invention, there is a strong demand for an economical and highly finable raw water pretreatment method.

Therefore, several methods have been proposed.
For example, Japanese Patent No. 1042319 discloses a method of performing sand filtration in the presence of the following amount of flocculant in which floc formation is observed in salt water containing a suspended substance having an SS concentration of 5 ppm or less. As a coagulant, an inorganic coagulant,
Any of the organic polymer flocculants can be used, and the flocculant concentration is 0.2 ppm to 3 pp as described in the Examples.
m. In this method, the coagulant addition concentration is 0.2
ppm or more, the formed floc becomes large,
As the surface layer of the sand filtration is liable to be clogged, the pressure loss over time increases considerably. The concentration of the flocculant added is closely related to the SS concentration of the suspended substance, and to find conditions that optimize the water quality of the filtered water and the pressure loss over time of the filter layer,
Knowledge about the coagulant concentration and the concentration of the suspended substance is required, and it has been found that it is extremely difficult to stably clarify by sand filtration simply by specifying the coagulant concentration.

Although it is described that inorganic and organic coagulants can be widely used as coagulants, remarkable differences are observed in coagulability depending on the types of coagulants, and it has been found that the selection of coagulants is important. did. As another method, if a ceramic filter, a synthetic resin filter, a membrane filtration, or the like is used, the treated water can be clarified, but it is not suitable for low-cost and large-volume treatment. A method of clarifying by filtration after sedimentation separation and flotation separation has also been proposed, but there is a problem that the equipment becomes large.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a reverse osmosis method,
As a pretreatment method of raw water used in electrodialysis, water treatment, and the like, a pretreatment method of efficiently removing suspended substances in raw water and clarifying the same is provided.

[0010]

Means for Solving the Problems The present inventors have developed a reverse osmosis method,
To pre-treat raw water to be supplied to electrodialysis, water treatment, etc., use a cationic organic polymer flocculant in a specific range where the product of the concentration of the suspended substance and the flocculant concentration in the raw water is By adding an amount of water and filtering, the water quality of the filtered water can be remarkably clarified as compared with the conventional method, the rise in pressure loss over time can be reduced, and the granular filter medium can be used as a filter medium. The present invention has been completed based on the finding that such characteristics can be further utilized when filtration using is used.

[0011] In the raw material water, suspended matter is several hundred μm to several μm.
m or less. If normal filtration, for example, sand filtration is used, particles having a particle size of 20 μm to 30 μm or more can be removed. However, the water quality target of the raw water required by the reverse osmosis method or the electrodialysis method is a conventional technology. It is getting more severe for the reasons described in the article. Therefore, the quality of the filtered water that can achieve such severe conditions will be described, for example, using an ion exchange membrane electrodialysis method, which is one of industrial applications.

Sand filtration, which is one of the pretreatment methods, is applied to seawater supplied by an ion exchange membrane electrodialysis method, followed by secondary filtration, followed by filtration through a 10 μm polypropylene thread-wound cartridge filter. As a result of supplying to an electrodialysis apparatus and evaluating the obstructiveness, it was found that if such pretreatment was performed, the obstruction between ion exchange membranes was small, and stable operation was possible for a long period of time. Then, the water quality was evaluated by three measurement methods, a turbidity meter manufactured by Hach and a multisizer manufactured by Coulter Counter Co., and FI measurement as shown in the examples. As a result, the turbidity was 0.1 (NTU) or less, The number is 200 (pieces / ml) or less, and the FI value is 3 (% /
Minutes) It was found that the water quality was as follows.

In the conventional pretreatment method, it is difficult to improve the water quality up to the target value and satisfy the condition of performing a large amount of filtration. By using the pretreatment method of the present invention, such a strict water quality target can be achieved, and a large amount of treatment can be performed. Hereinafter, the present invention will be described in more detail. Originally, the flocculant was added for the purpose of increasing the size and strength of the floc,
In the case of performing the filtration treatment, the formation of a suspended substance layer on the surface of the filter layer was promoted, so that the filter layer was easily clogged. This state is almost surface filtration, and the pressure loss of the filtration layer increases rapidly with time, the cycle of filtration → washing → filtration becomes short, the quality of filtered water, the amount of filtered water, etc. fluctuate, and the operation of the filter Becomes unstable.

Therefore, the type of the flocculant is appropriately selected, and the amount of the flocculant to be added is expressed by the product of the concentration of the suspended substance in the raw water and the concentration of the flocculant. By setting the amount to fall within the range of 0.02 to 0.5, the floc of the suspended substance in the raw water can be controlled. This makes it possible to use the inner volume more volumetrically, so that clarification of the filtrate and reduction of the pressure loss of the filter layer can be achieved at the same time. The present invention is a preprocessing method using such a concept.

The flocculant includes an inorganic flocculant and an organic polymer flocculant. The organic polymer flocculant has cationic, anionic and nonionic properties. Thousands to tens of thousands, high polymerization degree molecular weights of several hundred thousand to ten million. In the present invention, as a result of evaluating the cohesiveness with the suspended substance in the raw water and the compatibility with the filtration, it was found that the cationic organic polymer coagulant is most effective. The cationic organic polymer flocculant preferably has a molecular weight of 1,000,000 to 8,000,000 and may be any of a weak cation, a medium cation, or a strong cation, but is preferably a medium cation.

The cationic organic polymer flocculant is of a known type such as polyvinylimidazoline, polyalkylaminoacrylate, polyalkylaminomethacrylate, Mannich-modified polyacrylamide, or a natural polymer such as chitosan. I don't care. The cationic organic polymer flocculant used in the present invention may be used in combination with an anionic organic polymer flocculant, a nonionic organic polymer flocculant or an inorganic flocculant. Combination with the addition of an oxidizing substance such as sodium does not matter.

The concentration of the flocculant added to the raw water is affected by the effective diameter of the filter medium, the properties of the suspended substance, and the like, but has a very large relationship with the concentration of the suspended substance in the raw water. I found that. This relationship can be expressed by the product of the concentration of the flocculant and the concentration of the suspended substance in the raw water. When both the concentrations of the flocculant and the suspended substance are expressed in units of mg / l, the value is 0.02 to 0.02. It turned out to be 0.5. If the product of the concentration of the flocculant and the concentration of the suspended substance is less than 0.02, the flocculant cannot be exhibited because the amount of the flocculant is too small compared to the amount of the suspended substance in the raw water. Therefore, improvement in the quality of the filtered water cannot be expected. Conversely, if it exceeds 0.5, the abundance of the coagulant will be excessive, and the suspended solids in the raw water will be coagulated to form large flocs, instead of volume filtration which is a major feature of the present invention, This results in surface filtration that blocks the surface of the filter layer, and the pressure loss of the filter layer over time increases so that the filtration becomes unstable.

When the concentration exceeding 0.5 is added as described above, the quality of the filtered water may not be sufficiently improved due to a change in the charge of the suspended substance in the raw water and re-stabilization. When the flocculant is a solid, the flocculant is uniformly dissolved in water using a conventional dissolution method such as a stirrer, and if it is a liquid, it is diluted with water to an appropriate concentration. Used. The stirring at the time of addition can be used without any particular problem as long as it is a method capable of promptly dispersing the flocculant solution in the raw water from stirring by a normal stirrer to stirring by a pump. The flocculant can be added without particular limitation before the raw water is filtered, but it is better to add the flocculant in a step where the concentration of the suspended substance in the raw water is high, even if the concentration of the flocculant is low. Since the effects of the present invention can be expected, it is preferable to add to the raw material water having a high concentration of the suspended substance. The raw water to be treated in the present invention is preferably weakly acidic to weakly alkaline.

The filter medium used for filtration is a granular filter medium having a single layer or a multilayer of sand, garnet, pumice, anthracite, ilmenite, etc .; In addition, a filter medium exhibiting a filtration phenomenon called deep filtration, such as a filter medium of a woven fabric, a nonwoven fabric, a membrane filter medium, or the like, such as plastic, can be used without particular limitation. Here, the depth filtration is filtration mainly for the purpose of clarification filtration. Strain filtration is performed to remove solids by hooking the gaps of the filter medium, and cake filtration is performed by forming cake on the surface of the filtration layer and filtering. Unlike this, the filtration is a filtration utilizing a filtration phenomenon such that particles having a smaller particle size than the pores can be removed while flowing in the pores of the filter layer. For this reason, it is necessary that the filter layer has a thickness several hundred times as large as the size of the suspended substance particles in the raw water, and the present invention uses a filter medium capable of forming such a thickness.

Although the volume filtration of the present invention does not use the phenomenon of strain filtration or cake filtration by using such a filter medium, it does not use the phenomenon of deep-layer filtration mainly. Therefore, this is a filtration method in which the filter layer is used effectively in volume. In the case of granular filter media, such as sand, which is a typical example of this volume filtration, the effective diameter is 1
A filter having an effective diameter of 300 μm to 800 μm can be used. Under these conditions, the rise in pressure loss over time of the filter layer is small, and the quality of the filtered water is good. The coagulant and the filter layer are very well matched, and the filter can be operated stably. When the effective diameter of the filter medium is smaller than 300 μm, the increase in pressure loss over time of the filter layer becomes extremely large. Conversely, when the effective diameter of the filter medium is larger than 800 μm, the increase in pressure loss is small. In addition, since the quality of the filtered water decreases, stable operation of the filter becomes difficult under any conditions.

Here, the effective diameter refers to the size of the opening of the sieve that passes by 10% on a weight basis. In addition, the uniformity coefficient refers to the size / effective diameter of the sieve that passes through 60% on a weight basis, and the sieving operation uses a dry sieving test method according to JIS-K0069. The degree of ionicity of the flocculant is expressed by mol% of charged molecules in all molecules, 50 mol% or more is strongly cationic, 20 mol% to 50 mol% is medium cationic, and 20 mol% or less is strong cationic. It is called weakly cationic. The concentration of the suspended substance is a value measured using the method for measuring a suspended substance in the industrial water test method of JIS-K0101.

[0022]

A cationic organic polymer flocculant is added to the raw water, and the product of the concentration of the suspended substance in the raw water and the flocculant concentration is:
Their concentrations are expressed in units of mg / l, from 0.02 to 0.
By adding and filtering in an amount that falls within the range of 5, the filtration layer can be effectively used in volume, and the obtained filtered water has turbidity,
Both the number of particles and the FI value can be improved to a high degree. When filtering using a granular filter medium, the effective diameter is 3
If a filter medium having a uniformity coefficient of 1.6 or less with a size of from 00 μm to 800 μm is selected, the filtration is further stabilized.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. (Example 1) A primary filtration tower in which a 500 mmφ vinyl chloride pipe was filled with sand having an effective diameter of 380 μm and a uniformity coefficient of 1.4 to a thickness of 600 mm was filled with seawater containing 7 mg / l of a suspended substance. The mixture was filtered at a flow rate of 5 m / hr, and then the obtained primary filtered water was treated with a cationic organic polymer coagulant Hi-Set C-341 (trade name) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. After adding 0.2 mg / l and stirring with a pump,
Filtration was performed at 15 m / hr through a secondary filtration tower having the same specifications as the primary. Measure the pressure drop gradient with time of the secondary filtration tower, the turbidity of the secondary filtered water using a turbidimeter 2100N manufactured by Hach, the number of particles using a multisizer manufactured by Coulter Counter, and the FI value by FI measurement. did. Table 1 shows the results.

In this case, the product of the concentration of the flocculant and the concentration of the suspended substance in the raw water (hereinafter referred to as "concentration product") was 0.3 mg / l of the suspended substance in the primary filtered water. So
0.06. In this example, as compared with Comparative Example 1, the increase in pressure loss over time of the filtration layer was almost the same, and the water quality of the filtered water was improved by about 1/2 in all of the turbidity, FI value, and number of particles. Therefore, even when the concentration of the suspended substance such as the primary filtered water is low, the quality of the filtered water can be improved. The measurement was carried out using a Coulter Counter Multisizer with an aperture of 100 μm, a sample volume of 2 μl, and a stirring scale of 3. The Hach turbidimeter uses formazine as a turbidity standard solution for calibration,
Expressed in NTU or turbidity units. FI measurement is 2.1
Under a constant pressure of (kg / cm ² ), the solution was filtered with a polycarbonate membrane filter having a pore size of 8 μm manufactured by Advantech Co., Ltd., and the time for filtering 500 ml immediately after the start of the filtration was T ₀ , and further continuously flowed for 15 minutes. Later, 500
When the time of filtering the ml and _{T 1, FI = (T 1} -T
₀ ) × 100 / (T ₁ × 15).
The pressure drop gradient over time is the value expressed as the pressure change per unit time, when the raw water is supplied to the filtration tower at a constant flow rate, and the pressure change at the supply port to the filtration tower is divided by the time. Say The unit is expressed in kg / cm ² · hr.

(Example 2) Under the same conditions of seawater, apparatus, method, type of coagulant and concentration of coagulant as in Example 1, 0.7 mg of sodium hypochlorite was added before secondary filtration.
/ L was added and filtered, and the measurement was performed by the same items and methods as in Example 1. Table 1 shows the results. Even if an oxidizing substance such as sodium hypochlorite is added together with the flocculant, the quality of the filtered water can be improved as in this example.

(Comparative Example 1) The same seawater, apparatus and method as in Example 1 were used, and filtration was performed without adding a coagulant. The measurement was performed using the same measurement method. Table 1 shows the results. (Comparative Example 2) In the same seawater, apparatus and method as in Example 1, the same type of coagulant was added at 0.05 mg / l, followed by filtration.
The pressure loss gradient over time of the secondary filtration and the quality of the filtered water were measured using the same measurement method as in Example 1. The concentration product in this case was 0.015. Table 1 shows the results.

[0027]

[Table 1]

Example 3 0.025 mg / l of a cationic organic polymer flocculant Hi-Set C-341 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was added to seawater containing 6 mg / l of a suspended substance, and 7 After stirring with a stirrer for minutes, a filtration tower filled with sand having an effective diameter of 380 μm and a uniformity coefficient of 1.4 at a thickness of 600 mm was filled into a 40 mmφ vinyl chloride pipe at a rate of 7.5 m / m.
Flowed through for hr and filtered. The pressure drop gradient with time of the filtration tower, the turbidity measured by a turbidity meter manufactured by Hach and the number of particles measured by a multisizer manufactured by Coulter Counter were measured as the quality of filtered water. The pressure drop gradient with time is the change in pressure at the supply port to the filtration tower when the raw water is supplied to the filtration tower at a constant flow rate. And the unit is cm / hr. (Hereinafter referred to as “pressure loss gradient”)

The density product in this case is 0.15. Table 2 shows the results. If the coagulant is not added as in Comparative Example 3, the quality of the filtered water will be several times worse. In the case of the nonionic organic polymer flocculant and the anionic organic polymer flocculant as the flocculants as in Comparative Examples 5 and 6, improvement in the quality of the filtered water cannot be expected as much as the flocculants. When the flocculant is added at a low concentration below the concentration range of the present invention as in Comparative Example 7,
The quality of the filtered water deteriorates. When the effective diameter of the filter is 300 μm or less as in Comparative Example 8, the pressure loss gradient becomes extremely high, and the stable operation of the filter is hindered. When the effective diameter of the filter medium is 800 μm or more as in Comparative Example 9, the quality of the filtered water deteriorates.

(Embodiment 4) In the same seawater, apparatus and method as those in Embodiment 3, a filter material is used with an effective diameter of 600 μm and a uniformity coefficient of 1.
The mixture was filtered using pumice of No. 5, and the pressure loss gradient of the filtration layer and the quality of the filtered water were measured using the same measurement method as in Example 3. Table 2 shows the results. Compared with Example 3, the pressure loss gradient can be reduced by increasing the effective diameter of the filter medium.
If the coagulant is not added as in Comparative Example 4, the quality of the filtered water will be extremely poor. (Comparative Example 3) Filtration was performed using the same seawater, apparatus and method as in Example 3 without adding a coagulant, and the pressure loss gradient of the filtration layer and the quality of the filtered water were measured using the same measurement method as in Example 3. . Table 2 shows the results.

(Comparative Example 4) Filtration was carried out using the same seawater, apparatus and method as in Example 4 without the addition of a flocculant, and the pressure loss gradient of the filtration layer and the quality of the filtered water were measured in the same manner as in Example 3. Measured. Table 2 shows the results. (Comparative Example 5) Nonionic organic polymer flocculant Hi-Set P-700 (trade name) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was added in an amount of 0.1 mg / l as a flocculant using the same seawater, apparatus and method as in Example 3. After filtration, the pressure loss gradient of the filtration layer and the quality of the filtered water were measured using the same measurement method as in Example 3. Table 2 shows the results.

Comparative Example 6 0.1 mg of an anionic organic polymer flocculant Hi-Set P-710 (trade name) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was used as a flocculant in the same manner as in Example 3 using the same seawater, apparatus and method. / L, followed by filtration, and the pressure loss gradient of the filtration layer and the quality of the filtered water were measured using the same measurement method as in Example 3. Table 2 shows the results. (Comparative Example 7) The same type of coagulant was added in the same manner as in Example 3 by adding seawater, the same coagulant at 0.0025 mg / l, and filtration was performed. The measurement was performed using the same measurement method. The concentration product in this case is 0.
015. Table 2 shows the results.

(Comparative Example 8) Seawater, equipment,
The method, the type of flocculant, and the flocculant concentration, filtration was performed using sand having an effective diameter of 250 μm and a uniformity coefficient of 1.4 as a filter medium, and the pressure loss gradient of the filtration layer and the quality of the filtered water were measured in the same manner as in Example 3. It measured using. Table 2 shows the obtained results. (Comparative Example 9) With the same seawater, apparatus, method, type of flocculant and flocculant concentration as in Example 8, an effective diameter of 1000 μm as a filter medium
m, and filtration was performed using sand having a uniformity coefficient of 1.5, and the pressure loss gradient of the filtration layer and the quality of the filtered water were measured using the same measurement method as in Example 3. Table 2 shows the obtained results.

[0034]

[Table 2]

Example 5 To a seawater containing 9 mg / l of a suspended substance, 0.05 mg / l of a cationic organic polymer flocculant Hiset C-545 (trade name) manufactured by Daiichi Kogyo Seiyaku was added. After stirring for 30 minutes by pump circulation, 1000m
A 10-denier polyester yarn filter medium made of Unitika is supplied to an iron filter having an inner rubber lining of
38m / hr into a primary filter packed with a thickness of 00mm
And filtered. 500mmφ as secondary filtration
The sand of Example 1 was filled to a thickness of 600 mm into a vinyl chloride pipe, and the mixture was filtered at 15 m / hr through a filtration tower. The pressure loss gradient of the primary filter and the quality of the secondary filtered water were measured by the same measurement method as in Example 3. The density product in this case is 0.45. Table 3 shows the results. Thus, the effect of the present invention can be expected even if a filter medium other than the granular filter medium is used. (Comparative Example 10) The addition of the flocculant was stopped using the same seawater, apparatus, and method as in Example 5, and the pressure loss gradient of the filtration layer and the quality of the filtered water were measured using the same measurement method as in Example 3. Table 3 shows the results.

[0036]

[Table 3]

(Example 6) Sand of an effective diameter of 380 µm and a uniformity coefficient of 1.4 was poured into a pipe of 40 mmφ made of vinyl chloride by 60.
The suspended substance was placed in a primary filtration tower packed to a thickness of 0 mm.
To seawater containing 4 mg / l, 0.2 mg / l of chitosan dissolved in 0.1 N acetic acid was added, and the mixture was stirred with a stirrer for 7 minutes, and then filtered at 7.5 m / hr. The pressure drop gradient of the filtration tower and the quality of the filtered water were measured using the same measurement method as in Example 3. The density product in this case is 0.08. Table 4 shows the results. The effect of the present invention can be expected even when a natural polymer-based cationic polymer flocculant is used. (Comparative Example 11) Filtration was carried out using the same seawater, apparatus and method as in Example 6, and after adding 10 mg / l of chitosan, filtration was carried out. The pressure loss gradient of the filtration layer and the water quality of the filtrate were measured in the same manner as in Example 3. It measured using. The density product in this case is 4. Table 4 shows the results. Addition of a high flocculant concentration higher than the concentration product range of the present invention may deteriorate the quality of filtered water as in this example.

[0038]

[Table 4]

(Embodiment 7) The same filtration device as in Embodiment 1,
The type of the coagulant, the concentration of the coagulant, and the filtered water obtained by filtering the seawater by the filtration method are applied to a small 28 cm-long and 24 cm-wide small ion exchange membrane electrodialyzer (hereinafter referred to as "dialyzer") without passing current. A constant flow rate was supplied at a linear flow rate of 4 cm / sec, and the pressure at the inlet of the dialyzer was measured to evaluate the obstruction. Table 5 shows the results. The initial pressure at the start of supplying the filtered water gradually increases over time due to the progress of clogging of the dialysis device, contamination of the membrane, and the like. If a pressure change over time from this initial pressure is expressed per unit time as a pressure gradient, the operable pressure of the dialyzer is limited, so that the pressure gradient determines the operable time of the dialyzer. In order to enable long-time operation, it is necessary to make this pressure gradient as small as possible. Example 7
Compared with Comparative Example 12, the pressure gradient of Example 7 was about 1
Since it is reduced to about / 4, it can be understood that the number of days in which the dialysis device can be operated can be extended several times by performing the pretreatment of the present invention. (Comparative Example 12) Filtration water obtained by filtering seawater by the same filtration apparatus and filtration method as in Comparative Example 1 was supplied to the same dialysis apparatus as in Example 7 under the same conditions as in Example 7, and The pressure at the inlet was measured. Table 5 shows the results.

[0040]

[Table 5]

[0041]

According to the present invention, the type of the coagulant to be added is selected, and the amount of the coagulant to be added is set to 0.02 to 0.2 of the product of the concentration of the suspended substance in the raw water and the concentration of the coagulant. Electrodialysis, reverse osmosis, and water pretreatment can improve the quality of filtered water and stabilize filtration by adding and filtering, and when using a particulate filter medium for filtration, by selecting the effective diameter. It is possible to provide a method for pretreatment of raw water suitable for, for example, the following.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C02F 1/56 C02F 1/46 103

Claims (2)

[Claims] 1. A raw material water containing a suspended substance is charged with a cationic organic polymer flocculant, and the product of the concentration of the suspended substance and the concentration of the flocculant in the raw water is such that both these concentrations are in mg / l. A method for pretreatment of raw water, comprising adding an amount in the range of 0.02 to 0.5 expressed in units, followed by filtration. 2. A coagulant is added to raw water at a concentration required from the relationship of claim 1 so that the effective diameter is 300 μm to 80 μm.
Filtration using a particulate filter medium having a uniformity coefficient of 1.6 μm or less at 0 μm, followed by supplying to an ion exchange membrane electrodialysis apparatus for electrodialysis after the pretreatment according to claim 1. Dialysis method.