JP7403387B2 - Coagulation membrane filtration system and coagulation membrane filtration method - Google Patents

Description

The present invention relates to a coagulating membrane filtration system and a coagulating membrane filtration method, and in particular to a coagulating membrane filtration system and a coagulating membrane filtration method for filtering coagulated treated water obtained by mixing a coagulant into water to be treated using a separation membrane. .

Traditionally, sand filtration has been the mainstream solid-liquid separation process in water purification, but in recent years, microfiltration membranes (MF membranes) and ultrafiltration membranes (UF membranes) have been used, which are expected to achieve more advanced solid-liquid separation. The introduction of low-pressure membrane filtration is progressing.

Nowadays, membrane filtration is increasingly being applied to renewal equipment due to aging of medium-sized and large-scale water treatment plants, but in these cases, surface water such as river water is used as raw water for water supply. From the viewpoint of removing soluble substances such as chromaticity components, aggregation treatment is often combined as membrane pretreatment.

Coagulation treatment as a pretreatment is effective in reducing biopolymers, which are the cause of organic membrane contamination, which is one of the issues with membrane filtration methods. arise.

In flocculation in water purification treatment, aluminum-based flocculants such as polyaluminum chloride (PACl) and aluminum sulfate (Alm) are used, so residual aluminum present in the flocculation treatment water becomes a substance that causes membrane contamination.

Membrane contamination due to aluminum derived from the flocculant in coagulation membrane filtration systems is a major problem from the viewpoint of maintaining stable operation of the system and economical efficiency, and countermeasures against membrane contamination have been studied and implemented from various aspects. There are many unknown points that cannot be explained rationally.

In the case of a conventional coagulation-sedimentation rapid sand filtration system, the coagulation treatment system consists of a rapid stirring tank that mixes the flocculant, and a slow stirring tank that grows the micro flocs formed in the rapid stirring tank into large flocs that can be subjected to sedimentation treatment. It consists of and.

According to Non-Patent Document 1, it is shown that the hydraulic residence time of the rapid stirring tank should be approximately 1 to 5 minutes, and the hydraulic residence time of the slow stirring tank is 20 to 40 minutes. It is said that the degree of

When combining a flocculation treatment system as a pretreatment for membrane filtration such as MF membrane or UF membrane, the pore size of the membrane is 0.01 to 0.1 μm, so the pore size formed by rapid stirring treatment is about several to several tens of μm. If flocs of size , so-called micro flocs, are formed, they can be removed by the physical sieving effect of the membrane, so it is reasonable to think that slow stirring treatment to form large flocs is not necessary. It is.

However, in reality, flocculation treatment systems are designed to suppress membrane contamination due to flocculation flocs and residual aluminum derived from flocculants, but the mechanism of membrane contamination caused by flocculants is not accurately understood, so excessive It is not an exaggeration to say that equipment design is being carried out without proper design basis. Additionally, in order to avoid such problems, pilot-scale long-term demonstration experiments are often conducted, but this results in extremely large costs.

For example, when using a casing-type hollow fiber membrane module as a filtration membrane, the membrane manufacturer clearly states in the instruction manual and other materials that when coagulation treatment is performed as a pretreatment, the treated water that has undergone coagulation and precipitation must be supplied to the membrane. are doing.

The reason for this is that the membrane packing density of the casing-type hollow fiber membrane module, that is, the membrane area per casing internal volume, is relatively large, so when highly adhesive flocs flow in, the membranes become bunched together, resulting in an intermembrane blockage phenomenon. Another reason is that hollow fiber membranes are polymeric membranes and membrane clogging due to residual aluminum is likely to occur.

However, although flocculation treatment is necessary to reliably achieve tap water quality standards, in the case of relatively clear raw water, slow agitation treatment and sedimentation treatment are excessive equipment, and the benefits of membrane filtration cannot be achieved. Significantly reduced. Even if slow stirring treatment is to be carried out, its purpose and scale should be rationally designed.

Patent Document 1 discloses that water to be treated is mixed with a so-called ultra-high basicity PACl solution having a basicity of 70% in a rapid stirring tank to form fine flocs, and then the fine flocs are coarsened in a slow stirring tank. Disclosed is a membrane filtration method in which coagulated treated water is obtained, and the coagulated treated water is dead-end filtered using a filtration membrane. According to this, by using a so-called ultra-high basicity PACl solution with a basicity of 70%, membrane contamination can be reduced more than the commonly used normal basicity PACl with a basicity of 50%.

Patent No. 5614644

Published by Japan Water Works Association, Water Facility Design Guidelines 2012

In the case of the conventional sand filtration method, from the viewpoint of water quality standards, the optimal coagulant injection rate and coagulation pH are determined by a jar test, focusing on turbidity, color, organic matter index, etc., but in the case of the membrane filtration method, Coagulation conditions must also be selected from the viewpoint of membrane contamination.

However, the rapid stirring time, the presence or absence of slow stirring, and the stirring time when slow stirring is required, which should be fixed conditions, are selected from the same viewpoint as the conventional coagulation-sedimentation sand filtration system, and are extremely difficult. It is empirical and never rational.

As mentioned above, the hydraulic retention time of the rapid stirring tank and the hydraulic retention time of the slow stirring tank of Non-Patent Document 1 are based on the assumption of the conventional coagulation sedimentation rapid sand filtration system, and are not suitable for the coagulation membrane filtration system. It has not been considered whether it is optimal.

Further, Patent Document 1 discloses the use of an ultra-high basicity PACl solution as a flocculation treatment agent suitable for flocculation treatment as a pretreatment for membrane filtration, but fine flocs formed in a rapid stirring tank are transferred to a slow stirring tank. The method of coarsening by stirring for a long time is considered to be the flocculation processing conditions suitable for the conventional flocculation-sedimentation sand filtration system.

In view of the above problems, an object of the present invention is to provide a coagulation membrane filtration system having a coagulation processing section suitable for water purification treatment using a separation membrane. Furthermore, an object of the present invention is to provide a coagulation membrane filtration method having a coagulation treatment process suitable for water purification using a separation membrane.

As a result of extensive studies by the inventors, it has been found that there are two broad categories of membrane contamination factors that have a significant effect on coagulation membrane filtration systems. One is aluminum nanoparticles smaller than 100 nm contained in the flocculant, and the other is aggregate particles with organic matter (composite of organic matter and aluminum), which are also smaller than 100 nm in size and are also aluminum nanoparticles. It can be said to be a nanoparticle.

In the former case, these aluminum nanoparticles are added to the water to be treated by injecting a flocculant during rapid stirring, and in the latter case, the substance to be flocculated and the flocculant are mixed together in less than a few seconds when the flocculant is injected. React and generate.

These aluminum nanoparticles are very small (less than 100 nm) and have a dilute concentration, so they are difficult to aggregate and become coarse by themselves, so they remain in the coagulation treatment water and cause membrane contamination. It is important to remove these aluminum nanoparticles before the filtration process.

As a result of further intensive studies, the inventor found that micro flocs on the order of submicrons (approximately 0.1 to 1 μm), so-called sub-micro flocs, which cannot be seen with the naked eye, and relatively small micro flocs of several μm (1 to 10 μm) It was confirmed that the removal mechanism of aluminum nanoparticles is the formation process of aluminum nanoparticles, and the collision and incorporation of aluminum nanoparticles into these sub-microflocs and microflocs. On the contrary, it was found that the formation process of large flocs that can be visually observed during slow stirring treatment and the contact between these large flocs and aluminum nanoparticles were not the mechanism for removing aluminum nanoparticles.

In addition, for forming sub-micro flocs and micro flocs that are effective in removing aluminum nanoparticles, rapid stirring with a high stirring speed is more effective than the conventional slow stirring for forming flocs. It was found that the growth of aluminum nanoparticles can be achieved through the collision of flocs with aluminum nanoparticles.

In addition, the inventor found that when rapid stirring alone is used for a sufficient period of time, the removal rate of aluminum nanoparticles often reaches a plateau and does not improve. The present invention was made based on the discovery that aluminum nanoparticles that could not be removed by rapid stirring can be incorporated into sub-micro flocs and micro flocs by performing a short slow stirring process.

That is, the invention according to claim 1 for achieving the above object,
A coagulation membrane filtration system comprising: a coagulation treatment section in which a coagulant is mixed with water to be treated and subjected to coagulation treatment; and a membrane filtration section that filters coagulation treated water obtained in the coagulation treatment section through a separation membrane. hand,
The flocculation treatment section includes a rapid stirring tank and a slow stirring tank located downstream of the rapid stirring tank, and the hydraulic residence time of the water to be treated in which the flocculant is mixed in the rapid stirring tank is equal to It is characterized by a retention time longer than the hydraulic retention time in a slow stirring tank.

According to this configuration, the hydraulic residence time in the rapid stirring tank in the flocculation processing section is longer than the hydraulic residence time in the slow stirring tank, so that aluminum nanoparticles can be incorporated into sub-micro flocs and micro flocs. is promoted. This reduces the amount of aluminum nanoparticles remaining in the flocculation treated water and avoids membrane contamination caused by these residual aluminum nanoparticles.Therefore, the flocculation treatment section is suitable for water purification using a separation membrane. A coagulating membrane filtration system can be provided.

The invention according to claim 2 is the coagulation membrane filtration system according to claim 1, characterized in that the hydraulic residence time in the rapid stirring tank is 6 minutes or more.

According to this configuration, it is possible to ensure sufficient hydraulic residence time in the rapid stirring tank for the incorporation of aluminum nanoparticles into sub-micro flocs and micro flocs, and therefore, more effectively It is possible to reduce the amount of aluminum nanoparticles remaining in the aluminum nanoparticles.

The invention according to claim 3 is the coagulation membrane filtration system according to claim 1 or 2, characterized in that the hydraulic residence time in the slow stirring tank is 3 minutes or more.

According to this configuration, the aluminum nanoparticles remaining after rapid stirring can be incorporated into the sub-micro flocs and micro flocs more effectively, and therefore the aluminum nanoparticles remaining in the coagulation treatment water can be further effectively reduced. be able to.

The method for coagulating membrane filtration of water to be treated according to the invention according to claim 4 includes:
A flocculation treatment step in which a flocculant is mixed with the water to be treated and subjected to flocculation treatment, a membrane filtration step in which the flocculation treated water obtained in the flocculation treatment step is filtered through a separation membrane, and a coagulation treatment step in which the flocculant is a rapid stirring process for rapidly stirring the added water to be treated, and a slow stirring process for slowly stirring the water to be treated after the rapid stirring process, and the hydraulic residence time of the rapid stirring process is It is characterized in that it is longer than the hydraulic residence time of the slow stirring process.

According to this configuration, the hydraulic residence time of the rapid stirring process in the flocculation treatment step is longer than the hydraulic residence time of the slow stirring process, so that the incorporation of aluminum nanoparticles into sub-micro flocs and micro flocs is facilitated. promoted. This reduces the amount of aluminum nanoparticles remaining in the flocculation treated water and avoids membrane contamination caused by the residual aluminum nanoparticles, thus making the flocculation treatment process suitable for water purification using separation membranes. A coagulation membrane filtration method can be provided.

According to the flocculation membrane filtration system of the present invention, the hydraulic residence time in the rapid stirring tank in the flocculation processing section is longer than the hydraulic residence time in the slow stirring tank, so that sub-micro flocs and Incorporation into microflocs is promoted. This reduces the amount of aluminum nanoparticles remaining in the flocculation treated water and avoids membrane contamination caused by these residual aluminum nanoparticles.Therefore, the flocculation treatment section is suitable for water purification using a separation membrane. A coagulating membrane filtration system can be provided.

Therefore, the pre-coagulation treatment for membrane filtration can be optimized, reducing the pre-treatment time and overall system operation time compared to conventional methods, while avoiding membrane contamination caused by residual aluminum nanoparticles. Not only can the life cycle of the separation membrane be extended, but also the amount of time the system will be interrupted due to membrane regeneration or replacement can be reduced.

Similar effects can be obtained with the coagulation membrane filtration method of the present invention.

It is a schematic diagram explaining coagulation membrane filtration system 10 concerning a first embodiment of the present invention. It is a schematic diagram explaining coagulation membrane filtration system 100 concerning a second embodiment of the present invention. It is a flow chart explaining the coagulation membrane filtration method of the present invention. (a) A blockage model diagram of cake filtration, and (b) a model diagram illustrating an increase in resistance due to accumulated particles p on a filter medium (bundle of circular tubes) by replacing it with an increase in the length of the circular tube t. It is a bar graph showing the apparent cake filtration constant (K _VVHP ) of each coagulation-treated water of Examples and Comparative Examples.

Preferred embodiments of the present invention are shown below.

<Coagulation membrane filtration system>
FIG. 1 is a schematic diagram illustrating a coagulation membrane filtration system 10 according to a first embodiment of the present invention. As shown in the figure, the coagulation membrane filtration system 10 includes a coagulation processing section 40 in which a coagulant is mixed with the water to be treated 1 and subjected to coagulation treatment, and a coagulation processing section 40 located downstream of the coagulation processing section 40. It has a membrane filtration section 60 that filters the obtained coagulated treated water with a separation membrane.

Water source water is used as the water to be treated 1. Examples of water supply raw water include river water, groundwater, dam lake water, lake water, underground water, and groundwater.

Although there are no restrictions on the type of flocculant, aluminum-based flocculants such as polyaluminum chloride and aluminum sulfate are preferred. Furthermore, the basicity is not limited in any way and may be anywhere from 50 to 90%.

In this embodiment, the water to be treated 1 flows into the powdered activated carbon mixing tank 2 using a pump or a water level difference, and at the same time, powdered activated carbon is injected from the powdered activated carbon injection equipment 3. This powdered activated carbon treatment is not directly related to the present invention, but since the powdered activated carbon has a negative charge, it is expected that residual aluminum particles will be adsorbed and attached in the tank responsible for the subsequent agglomeration treatment. Therefore, it is preferable to combine it with the present invention.

The appropriate contact time in the powdered activated carbon mixing tank 2 is about 20 to 40 minutes if the substance to be treated is an odor substance, and it is suitable for organic substances that are disinfection byproducts such as color components and trihalomethane precursors. In this case, approximately 15 to 30 minutes are required. Additionally, if the subsequent membrane filtration device is a tank immersion type, an adsorption reaction of powdered activated carbon can be expected in the membrane immersion tank, so a residence time (corresponding to contact time) in powdered activated carbon mixing tank 2 of about 3 minutes is sufficient. It is.

Of course, depending on the quality of the raw water, the powdered activated carbon treatment may be omitted.

The aggregation processing section 40 includes a rapid stirring tank 4 and a slow stirring tank 5 located downstream of the rapid stirring tank 4.

In this embodiment, the water to be treated 1 that has been subjected to powdered activated carbon treatment is sent to a rapid stirring tank 4 (consisting of rapid stirring tanks 41, 42, and 43 in FIG. 1). Accordingly, an alkaline agent such as caustic soda or an acid agent such as sulfuric acid is injected, and a pH adjuster is injected so that the coagulation pH at the time of injecting the flocculant becomes a predetermined value. The injection position of the chemical may be either a front tank at a position such as the powdered activated carbon mixing tank 2 or the rapid stirring tank 41. Next, a flocculant is injected by the flocculant injection device 44.

The illustrated embodiment is an example, and the rapid stirring tank 4 may be composed of three rapid stirring tanks, two tanks or less, or a single tank. Of course, you can use more than three tanks. If the residence time becomes short due to a single tank or a small number of tanks, short-circuit currents will occur and the mixing condition will deteriorate, so the tank configuration and structure should take this into consideration.

The standard residence time in one tank is about 3 minutes, but there is no restriction at all as long as the structure satisfies the above requirements.

According to the Water Facility Design Guidelines 2012, the desirable value of the agitation intensity (velocity gradient) G value for conventional floc formation ponds is 10 to 75 1/s, and conversely, the agitation intensity that achieves a rapid agitation effect is the G value Considering this, the value is larger than 75 1/s.

In this embodiment, if the quality of the raw water is poor and the flocculant injection rate is relatively high, or if the flocculation pH is relatively low at about 6, it will be necessary to increase the residence time in the rapid stirring tank 4, and the overall In order to stir uniformly, it is preferable to design a rapid stirring tank with three tanks.

In such a case, it is preferable that the stirring strengths of the rapid stirring tanks 41 and 42 be approximately the same, and that the stirring strength of the rapid stirring tank 43 be lower than that of the former two tanks.

The stirring intensity of the rapid stirring tanks 41 and 42 is preferably 150 1/s or more, more preferably 150 to 250 1/s, most preferably 250 1/s or more, in terms of G value.

The flocculated water after the rapid stirring process is sent to the slow stirring tank 5, and by performing the slow stirring process, while forming apparent flocs, aluminum nanoparticles are formed into sub-micro flocs and micro flocs. Import is performed.

It is desirable that the slow stirring process in the slow stirring tank 5 be performed with a G value in the range of 10 to 75 1/s, but the stirring intensity of the rapid stirring tank 43 immediately preceding it is 100 to 150 1/s. It is preferable to operate within a G value range of approximately

The reason for this is that under the above-mentioned aggregation conditions, the number of aluminum nanoparticles generated in the rapid stirring tanks 41 and 42 becomes very large, and there is a high possibility that the slow stirring tank 5 alone will not have the ability to incorporate them into the flocs. . Therefore, by creating a stirring intensity region between the rapid stirring tanks 41 and 42 and the slow stirring tank 5, the aluminum nanoparticles can be incorporated into the flocs while maintaining a high contact efficiency with the sub-micro flocs and micro flocs. This is to perform a flocculation process that more reliably suppresses membrane contamination.

In the present invention, the hydraulic residence time of the water to be treated mixed with the flocculant in the rapid stirring tank 4 is longer than the hydraulic residence time in the slow stirring tank 5. As a result, the amount of aluminum nanoparticles remaining in the coagulation-treated water is reduced, and membrane contamination of the separation membrane in the subsequent membrane filtration section 60 caused by the remaining aluminum nanoparticles can be avoided.

Note that the hydraulic retention time (also referred to as HRT) herein refers to the time during which the water to be treated stays in each of the rapid stirring tank 4 and the slow stirring tank 5. For example, the hydraulic residence time in each tank can be calculated from the flow rate of the water to be treated and the volume of each tank.

The hydraulic residence time in the rapid stirring tank 4 is 2 minutes or more, preferably 3 minutes or more, and more preferably 6 minutes or more.

The hydraulic residence time in the slow stirring tank 5 is 1 minute or more, preferably 2 minutes or more, and more preferably 3 minutes or more.

The water to be treated, that is, the flocculation treated water, which has passed through the flocculation processing unit 40 (in FIG. 1, the rapid stirring tank 4 and the slow stirring tank 5) is sent to the membrane filtration unit 60.

The type of separation membrane in the membrane filtration section 60 may be a polymer membrane, an inorganic membrane, a MF membrane, or a UF membrane. A membrane made of strong PVDF is preferable, and an MF membrane that can be used with a submerged membrane module is also preferable. In addition, the shape of the membrane is preferably a hollow fiber membrane in terms of volume efficiency.

From the viewpoint of energy saving, a membrane with a pore diameter of 0.05 μm or more is preferable so that the water level difference can be utilized, and furthermore, from the viewpoint of suppressing membrane clogging by organic matter, a membrane with a minimum diameter of 0.05 μm is optimal.

The structure of the membrane filtration device may be either a casing type or a tank immersion type, but the tank immersion type is preferable because it is highly applicable to highly turbid raw water.

The membrane-filtered coagulated treated water is retained as treated water in the treated water tank 7 for a certain period of time and is used as purified water 8. The treated water (membrane filtration water) in the treated water tank 7 is used for backwashing the separation membrane, but at that time, an oxidizing agent such as sodium hypochlorite is added to the backwash water and the water is passed through the separation membrane. .

In the first embodiment, the coagulation membrane filtration system 10 includes the powdered activated carbon mixing tank 2, the pH adjustment device 45, and the rapid stirring tank 4 consisting of three tanks, but these configurations are not essential. For example, when comparatively clear tap water raw water is used as the water to be treated 1 and the pH of the water to be treated 1 after addition of a coagulant is assumed to be close to the coagulation pH, the coagulation according to the second embodiment below may be used. It is also possible to take the form of a membrane filtration system.

FIG. 2 is a schematic diagram illustrating a coagulation membrane filtration system 100 according to a second embodiment of the present invention. As illustrated, the coagulation membrane filtration system 100 includes a coagulation processing section 40-2 having one rapid stirring tank 4-2 and one slow stirring tank 5-2, and a membrane filtration section 60-2.

A flocculant injection device 44-2 is provided in the rapid stirring tank 4-2. A powder activated carbon mixing tank and a pH adjustment device 45 are not provided.

In the present embodiment, the water to be treated 1 is supplied to the rapid stirring tank 4-2, and after the addition of the coagulant, rapid stirring is performed, and then slow stirring is performed in the slow stirring tank 5-2. The hydraulic residence time of the water mixed with the flocculant in the rapid stirring tank 4-2 is longer than the hydraulic residence time in the slow stirring tank 5-2.

The flocculated treated water after the slow stirring is filtered by a separation membrane in the membrane filtration section 60-2, and stored as treated water in the treated water tank 7-2 to become purified water.

<Coagulation membrane filtration method for treated water>
The present invention further provides a coagulation membrane filtration method for water to be treated. FIG. 3 is a flowchart illustrating the coagulation membrane filtration method of the present invention.

As illustrated, the coagulation membrane filtration method of the present invention includes a coagulation treatment step (S110) and a membrane filtration step (S120).

[Aggregation treatment step (S110)]
In this step, a flocculant is mixed with the water to be treated, and flocculation treatment is performed. The water to be treated and the flocculant are as described in the above section of the flocculating membrane filtration system.

The flocculation treatment includes a rapid stirring process in which water to be treated to which a flocculant has been added is rapidly stirred, and a slow stirring process in which water to be treated after the rapid stirring process is slowly stirred.

Considering the G value, the stirring intensity of the rapid stirring process is preferably 150 1/s or more, more preferably 150 to 250 1/s, most preferably 250 1/s or more, and is higher than that of the slow stirring process. The stirring intensity is preferably such that the G value is in the range of 10 to 75 1/s.

In addition, when the rapid stirring process is performed by multiple rapid stirrings, the stirring intensity of the rapid stirring tank located immediately before the tank in which the slow stirring process is performed is in the G value range of about 100 to 150 1/s. It is preferable to drive with

In this step, the hydraulic residence time of the rapid stirring process is greater than or equal to the hydraulic residence time of the slow stirring process.

As a result, the amount of aluminum nanoparticles remaining in the coagulation treatment water is reduced, and it is possible to avoid membrane contamination of the separation membrane in the subsequent membrane filtration step (S120) caused by the residual aluminum nanoparticles. (S110)).

[Membrane filtration step (S120)]
In this step, the flocculation treated water obtained in the flocculation treatment step (S110) is filtered through a separation membrane.

In this step, for the configuration of the separation membrane and the membrane filtration device having the separation membrane, the configuration described in the item of the coagulation membrane filtration system above can be used.

The filtrate water filtered through the separation membrane is retained in the treated water tank as treated water for a certain period of time, and is used as purified water 8.

The effects of the flocculation membrane filtration system and flocculation membrane filtration method of the present invention can be easily evaluated by the method of measuring the apparent cake filtration constant as shown below, and the flocculation treatment conditions can be determined. Can be done.

Specifically, by conducting a membrane filtration test on the flocculated water after flocculation treatment, a cake layer consisting of aluminum nanoparticles is formed on the surface layer of a separation membrane (MF membrane, etc.), and from the filtration resistance, the flocculation treated water is quantifies the concentration of aluminum nanoparticles indirectly. The results of this membrane filtration test are then analyzed using general cake filtration theory, the apparent cake filtration constant (often referred to as Kc) is calculated, and these are compared. From a practical standpoint, it is intuitively understandable and very convenient.

The apparent cake filtration constant can be measured using the cake filtration equation based on the occlusion model of cake filtration (for example, Masato Kadoya, published by Marketing Communication Group, Japan Pall Co., Ltd., 2013 SPRING Pall News, Vol. 117) (See pages 10 to 15).

The occlusion model for cake filtration means that when the filter medium is assumed to be a bundle of circular tubes with uniform inner diameter and length, the loaded particles do not block the circular tubes and create a volume on the surface of the filter medium (bundle of circular tubes). This is a model of continuing to do so. In that case, as shown in FIG. 4(a), the thickness of the deposited particles p (cake layer) increases in proportion to the amount of particles p loaded onto the bundle of circular tubes t. Here, the increase in resistance due to the deposited particles p is replaced by an increase in the length of the circular tube t shown in FIG. 4(b).

（式（１）中、Ｊは単位ろ過面積あたりの流量（ｍ^３／ｍ^２・ｓ）を、Ｊ_０は単位ろ過面積あたりの初期流量（ｍ^３／ｍ^２・ｓ）を、Ｋｃはケーキろ過定数（１／ｍ）、閉塞係数ともいう）を、ｖは単位面積あたりのろ液量（ｍ^３／ｍ^２）を、それぞれ示す。）を、
定流量ろ過の場合には、以下の式（２）

（式（２）中、ΔＰは円管両端での差圧（Ｐａ）を、ΔＰ_０は円管両端での初期差圧（Ｐａ）を、Ｋｃはケーキろ過定数（（１／ｍ）、閉塞係数ともいう）を、ｖは単位面積あたりのろ液量（ｍ^３／ｍ^２）を、それぞれ示す。）
を、それぞれ得ることができる。 Then, by applying Hagen-Poiseuille's equation to the filter medium and proceeding with calculations taking into account the blockage model of cake filtration described above, in the case of constant pressure filtration, the following equation (1) is obtained.

(In formula (1), J is the flow rate per unit filtration area (m ³ /m ²・s), J ₀ is the initial flow rate per unit filtration area (m ³ /m ²・s), and Kc is the cake The filtration constant (1/m) (also referred to as occlusion coefficient) and v represent the filtrate volume per unit area (m ³ /m ² ), respectively. )of,
In the case of constant flow filtration, the following equation (2)

(In formula (2), ΔP is the differential pressure (Pa) at both ends of the circular tube, ΔP ₀ is the initial differential pressure (Pa) at both ends of the circular tube, Kc is the cake filtration constant ((1/m), occlusion (also referred to as the coefficient), and v indicates the filtrate volume per unit area (m ³ /m ² ), respectively.
can be obtained respectively.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited only to these Examples.

1. Membrane and Filter Holder In the following examples and comparative examples, a VVHP membrane (hydrophobic PVDF membrane, pore size 0.1 μm) manufactured by Merck & Co. was used as the membrane, and a glass filter holder for flat membranes with a diameter of 25 mm was used.

2. Membrane filtration test (measurement of apparent cake filtration constant)
In the following Examples and Comparative Examples, 240 mL of sample water was passed through the membrane using a suction pump with constant pressure filtration (suction pressure 90 kPa), and the change over time in the amount of filtrated water was measured, and the equation (1) above was used. By applying this, the cake filtration constant Kc, that is, the value of _KVVHP (1/m) was determined.

<Examples 1 to 4 and Comparative Examples 1 to 2>
The water to be treated includes relatively clear winter river water (turbidity: 0.7 degrees, chromaticity: 3.3 degrees, pH 7.3, TOC: 0.9 mg/L, UVA260: 0.114). (5 cm cell)) was used.

To this water to be treated, polyaluminum chloride (PACl, basicity 50%) was added at an injection rate of 20 mg/L, and flocculation treatment was performed using a 500 mL beaker.

The stirring conditions were as follows: coagulation pH 7.0, rapid stirring treatment (130 rpm) → slow stirring treatment (30 rpm), each treatment time was changed to perform flocculation treatment, obtain flocculation treated water, and filter the apparent cake. A constant (K _VVHP ) (hereinafter also simply referred to as K _VVHP ) was determined.

The stirring time and apparent cake filtration constant (K _VVHP ) of the obtained coagulated treated water are as shown in Table 1 and FIG. 5 below. In addition, in the table, the label ``Sudden 3 - Slow 0'' (Comparative Example 1) indicates that the hydraulic residence time of the rapid stirring treatment is 3 minutes, and the hydraulic residence time of the slow stirring treatment is 0 minutes (i.e., This indicates that the slow stirring process was not performed. The same applies to the explanations of the labels of other Examples and Comparative Examples.

According to Table 1 and Figure 5, in the case of rapid stirring only (Comparative Example 1 (3-slow 0), Comparative Example 2 (6-slow 0)), the longer the treatment time, the lower the value of _KVVHP . Although it does, it doesn't go down enough.

In addition, under the conditions of rapid stirring for 3 minutes, which is the range of conventional rapid stirring processing, the value of K _VVHP decreases as the time of subsequent slow stirring increases, but it is the closest to the conventional coagulation processing conditions. Even in Comparative Example 4 (sudden 3-slow 9), the _KVVHP value was 4.5.

Furthermore, compared to the case of rapid stirring alone for 3 minutes (Comparative Example 1 (fast 3 - slow 0)), Example 1 (fast 3 - slow 3), in which slow stirring was added for the same 3 minutes, was better. , K _VVHP values decreased.

On the other hand, when rapid stirring was performed for 6 minutes or longer and slow stirring was performed, the value of K _VVHP was lower than either the case of rapid stirring alone or the case of adding slow stirring to 3 minutes of rapid stirring.

Furthermore, although the value of K _VVHP was lower after 9 minutes of rapid stirring than after 6 minutes, the difference was small, and it was considered that the optimum rapid stirring time was 6 to 9 minutes.

1 Water to be treated 10, 100 Coagulation membrane filtration system 40, 40-2 Coagulation treatment section 4, 4-2, 41, 42, 43 Rapid stirring tank 5, 5-2 Slow stirring tank 60, 60-2 Membrane filtration section

Claims (4)

a flocculation treatment section in which an aluminum-based flocculant is mixed with the water to be treated and flocculation treatment is performed;
A coagulation membrane filtration system comprising: a membrane filtration section that filters the coagulation-treated water obtained in the coagulation treatment section through a separation membrane,
The aggregation processing section includes a rapid stirring tank and a slow stirring tank located downstream of the rapid stirring tank,
A polymer flocculant is not added to the water to be treated in the flocculation treatment section,
A coagulation membrane filtration system, wherein a hydraulic residence time of the water to be treated mixed with the aluminum-based flocculant in the rapid stirring tank is longer than a hydraulic residence time in the slow stirring tank. The coagulating membrane filtration system according to claim 1, wherein the hydraulic residence time in the rapid stirring tank is 6 minutes or more. The coagulation membrane filtration system according to claim 1 or 2, wherein the hydraulic residence time in the slow stirring tank is 3 minutes or more. A flocculation treatment step of mixing an aluminum flocculant into the water to be treated and performing flocculation treatment;
a membrane filtration step of filtering the flocculation treated water obtained in the flocculation treatment step with a separation membrane;
a rapid stirring process in which the aggregation treatment step rapidly stirs the water to be treated to which an aluminum-based coagulant has been added;
a slow stirring process of slowly stirring the water to be treated after the rapid stirring process;
has
A polymer flocculant is not added to the water to be treated in the flocculation treatment step,
A coagulation membrane filtration method for water to be treated, characterized in that a hydraulic residence time in the rapid stirring process is longer than a hydraulic residence time in the slow stirring process.

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