Method for evaluating membrane fouling property of coagulated treated water, coagulation membrane filtration method, and coagulation membrane filtration system

Abstract

To provide a membrane clogging evaluation method of coagulation-treated water and a coagulation membrane filtration system that can easily and quickly evaluate a membrane clogging property of coagulation-treated water on site without evaluating the membrane clogging property of coagulation-treated water in separate equipment during coagulation membrane filtration, and to provide a method for evaluating the membrane clogging property of the coagulated water that can easily and quickly evaluate the membrane clogging property of the coagulation-treated water during coagulation membrane filtration.SOLUTION: There is provided a membrane clogging evaluation method, including: a coagulation treatment step (S100); a membrane filtration step (S110); a ΔAl calculation step (S120) for calculating ΔAl, which is a difference between an aluminum concentration of supernatant water of coagulation-treated water and an aluminum concentration of membrane filtrate water; and an operating condition changing step (S140) in which operating conditions of at least one of the coagulation treatment step (S100) and the membrane filtration step (S110) are changed from the operating conditions before the change based on the calculated value of ΔAl. The present invention also provides a coagulation membrane filtration system 100 and a method for evaluating membrane clogging properties of the coagulation-treated water.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for evaluating the membrane fouling property of coagulated treated water, a coagulation membrane filtration method, and a coagulation membrane filtration system, and particularly to a method for evaluating the membrane fouling property of coagulated treated water that occurs during the coagulation membrane filtration process, a coagulation membrane filtration method using this method, and a coagulation membrane filtration system.

Background Art

[0002] Conventionally, sand filtration has been the mainstream solid-liquid separation process in water purification treatment. However, in recent years, the introduction of low-pressure membrane filtration methods using microfiltration membranes (MF membranes) and ultrafiltration membranes (UF membranes), which can achieve more advanced solid-liquid separation, has been progressing.

[0003] For example, there are many cases where membrane filtration is applied to the renewal equipment accompanying the aging of medium and large-scale water purification plants. In such cases, since surface water such as river water is used as the raw water for tap water, coagulation treatment is often combined as a pre-treatment before the membrane from the viewpoint of removing dissolved substances such as chromaticity components.

[0004] Coagulation treatment as a pre-treatment before the membrane is also effective in reducing biopolymers, which are causative substances of organic membrane fouling, one of the problems of the membrane filtration method. On the other hand, the problem of membrane fouling due to residual coagulants occurs. In particular, in coagulation in water purification treatment, aluminum-based coagulants such as polyaluminum chloride (PACl) and aluminum sulfate (Alm) are used, so residual aluminum present in the coagulated treated water becomes a causative substance of membrane fouling.

[0005] Residual aluminum in the coagulated treated water is divided into aluminum particles at the micro level on the order of μm, soluble aluminum that can be filtered through a 0.45-μm membrane, and nano-aluminum particles on the order of several nm to several tens of nm that have a negative charge due to the influence of their positive charge and hardly pass through the 0.45-μm membrane. Among these, the aluminum particles at the micro level are in the form of being incorporated into coarse particles such as microflocs. Since these microflocs can be removed by the physical sieving effect of the membrane and thus do not pose a problem, but the nano-aluminum particles cause membrane fouling, it is important to know the presence of nano-aluminum particles in the coagulated treated water for understanding the membrane fouling property of the coagulated treated water.

[0006] Patent Document 1 is a patent document related to a patent application by the applicant of the present application. In the purified water treatment by coagulation membrane filtration, it discloses that the hydraulic residence time in the rapid stirring process of the water to be treated is set to be equal to or longer than the hydraulic residence time in the slow stirring process. The removal of nano-aluminum particles from the coagulated treated water occurs in the floc formation process, which is the collision and incorporation into coarse particles such as microflocs. According to the invention of Patent Document 1, the incorporation of nano-aluminum particles into sub-microflocs and microflocs is promoted, and it becomes possible to effectively reduce the nano-aluminum particles remaining in the coagulated treated water.

[0007] Patent Document 2 proposes an attempt to suppress membrane fouling by measuring and controlling the zeta potential of nano-aluminum particles (reported to be about 20 to 500 nm). Specifically, the membrane-filtered water to be subjected to membrane treatment is irradiated with electromagnetic waves, mixed with a coagulant after the irradiation of the electromagnetic waves to form flocs, the zeta potential of the mesoparticles (i.e., nano-aluminum particles) in the pretreated water containing these flocs is measured, and the properties of the electromagnetic waves irradiated are controlled so that the measured zeta potential of the mesoparticles approaches 0 mV. According to the invention of Patent Document 2, pretreated water that can sufficiently suppress the occurrence of membrane fouling when subjected to membrane filtration can be obtained.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Non-Patent Document

[0009]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] According to the invention of Patent Document 1, although it is possible to effectively reduce the nanoaluminum particles remaining in the coagulated treated water, the nanoaluminum particle concentration has not actually been measured.

[0011] In Patent Document 2, the zeta potential of mesoparticles (nanoaluminum particles) is measured. However, nanoparticle counters such as zeta potential measurement devices are very expensive and require skilled analysis techniques. Also, since they are basically not measurement devices for instrumentation, it is not practical to apply them to actual water treatment facilities.

[0012]

[0013] ​Furthermore, unlike conventional sand filtration, in membrane filtration, a sedimentation basin is not required, so the flocculated treated water directly becomes the membrane feed water. In this case, however, the above-mentioned micro-level aluminum particles, nano-aluminum particles, and dissolved aluminum are mixed in the membrane feed water, and it is very difficult to determine the aluminum concentration of the nano-aluminum particles that cause membrane fouling from among them.

[0014] If the aluminum concentration of the nano-aluminum particles cannot be determined, either actual coagulation membrane filtration is performed and the membrane filtration conditions are controlled while observing an increase in the filtration resistance, or membrane filtration is performed using an experimental facility equipped with a membrane having the same physical properties as the membrane used in the water purification facility in advance, and the membrane fouling property of the flocculated treated water is evaluated by determining the filtration constant of the flocculated treated water. However, in the former case, the membrane fouling property of the flocculated treated water cannot be evaluated in advance, and in the latter case, another evaluation facility is required for evaluating the membrane fouling property of the flocculated treated water, and it also takes time for the evaluation.

[0015] The present invention has been made in view of the above problems, and an object thereof is to provide a coagulation membrane filtration method and a coagulation membrane filtration system capable of easily and quickly evaluating the membrane fouling property of flocculated treated water on-site without evaluating the membrane fouling property of flocculated treated water using separate equipment during coagulation membrane filtration.

[0016] Another object of the present invention is also to provide a method for evaluating the membrane fouling property of flocculated treated water that can easily and quickly evaluate the membrane fouling property of flocculated treated water during coagulation membrane filtration.

Means for Solving the Problems

[0017] In order to achieve the above object, the inventors conducted intensive studies and found that when measuring nano aluminum particles, which are the cause of membrane fouling, in the flocculation-treated water in which micro-level aluminum particles, nano aluminum particles, and soluble aluminum are mixed, only nano aluminum particles and soluble aluminum are present in the supernatant obtained by allowing a part of the flocculation-treated water to settle, and micro-level aluminum particles are not present. They also noted that only soluble aluminum is present in the membrane-filtered water after membrane filtration.

[0018] By determining the difference between the aluminum concentration in the supernatant of the flocculation-treated water and the aluminum concentration in the membrane-filtered water, it is possible to easily calculate the concentration of nano aluminum particles in the flocculation-treated water, which is difficult to directly measure. They also found that the calculated concentration of nano aluminum particles in the flocculation-treated water has a significant correlation with the apparent cake filtration constant when the flocculation-treated water is membrane-filtered through a separation membrane, thus completing the present invention.

[0019] That is, the above object is achieved by a flocculation membrane filtration method characterized by having a flocculation treatment step of mixing a flocculant with the water to be treated to obtain flocculation-treated water, a membrane filtration step of membrane-filtering the flocculation-treated water obtained in the flocculation treatment step through a separation membrane selected from a microfiltration membrane and an ultrafiltration membrane to obtain membrane-filtered water, a ΔAl calculation step of calculating ΔAl, which is the difference between the aluminum concentration in the supernatant of the flocculation-treated water and the aluminum concentration in the membrane-filtered water, and an operating condition change step of changing at least one of the operating conditions of the flocculation treatment step and the membrane filtration step from the operating conditions before the change based on the calculated value of ΔAl.

[0020] A preferred embodiment of the method for treating the wastewater generated in the water purification treatment according to the present invention is as follows. (1) In the operating condition change step, when the value of ΔAl calculated in the ΔAl calculation step exceeds 0.5 mg / L, at least one of the operating conditions of the flocculation treatment step and the membrane filtration step is changed from the operating conditions before the change so that the value of ΔAl becomes 0.5 mg / L or less. (2) Also, in the operation condition change step, when the value of ΔAl calculated in the ΔAl calculation step exceeds 0.3 mg / L, at least one of the operation conditions of the coagulation treatment step and the membrane filtration step is changed from the operation conditions before the change so that the value of ΔAl becomes 0.3 mg / L or less. (3) Further, there is an apparent cake filtration constant calculation step of calculating an apparent cake filtration constant K2 when the coagulated treated water is membrane-filtered with a separation membrane, and the operation condition change step changes at least one of the operation conditions of the coagulation treatment step and the membrane filtration step from the operation conditions before the change based on the calculated value of ΔAl and the calculated value of K2.

[0021] Also, the above object is achieved by a coagulation membrane filtration system having a coagulation treatment means for performing coagulation treatment on the water to be treated added with a coagulant to obtain coagulated treated water, a membrane filtration means for membrane-filtering the coagulated treated water obtained by the coagulation treatment means with a separation membrane selected from a microfiltration membrane and an ultrafiltration membrane to obtain membrane-filtered water, a first measuring means for measuring the aluminum concentration in the supernatant of the coagulated treated water, and a second measuring means for measuring the aluminum concentration in the membrane-filtered water, a control unit that calculates a value of ΔAl, which is the difference between the aluminum concentration in the supernatant of the coagulated treated water measured by the first measuring means and the aluminum concentration in the membrane-filtered water measured by the second measuring means, and controls a change in at least one of the operation conditions of the coagulation treatment means and the membrane filtration means from the operation conditions before the change based on the calculated value of ΔAl.

[0022] Furthermore, the above object is achieved by a method for evaluating the membrane fouling property of coagulated treated water for coagulation membrane filtration in which the coagulated treated water obtained by coagulating the water to be treated is membrane-filtered, the method comprising: a ΔAl calculation step of calculating ΔAl, which is the difference between the aluminum concentration in the supernatant of the coagulated treated water and the aluminum concentration in the membrane-filtered water; and a membrane fouling property evaluation step of evaluating the membrane fouling property of the coagulated treated water based on the calculated value of ΔAl.

Advantages of the Invention

[0023] According to the present invention, the concentration of nano-aluminum particles in the coagulated treated water can be simply and rapidly calculated as ΔAl without preparing another membrane filtration facility or the like. Further, since this ΔAl has a significant correlation with the apparent cake filtration constant K2 when the coagulated treated water is membrane-filtered with a separation membrane, the membrane fouling property of the coagulated treated water can be simply and rapidly evaluated using ΔAl as an index at the site of water purification treatment.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0025] <Coagulation Membrane Filtration Method> The coagulation membrane filtration method of the present invention is implemented as a solid-liquid separation process for water purification. The coagulation membrane filtration method of the present invention includes a coagulation treatment step, a membrane filtration step, a ΔAl calculation step, and an operating condition change step. Hereinafter, it will be described with reference to FIGS. 1 to 4. FIG. 1 is a flowchart for explaining the coagulation membrane filtration method of the present invention, FIG. 2(a) is a clogging model diagram of cake filtration, FIG. 2(b) is a model diagram for explaining the increase in resistance due to deposited particles p on a filter medium (a bundle of circular tubes) by replacing the fact that the circular tube t has become longer, FIG. 3 is a flowchart showing a first example of the operating condition change step of the coagulation membrane filtration method of the present invention, and FIG. 4 is a flowchart showing a second example of the operating condition change step of the coagulation membrane filtration method of the present invention. [Coagulation treatment step (S100)] In this step, a coagulant is mixed with the water to be treated to obtain coagulated treated water. Tap water source water is used as the water to be treated. Examples of tap water source water include river water, groundwater, dam lake water, marsh water, spring water, and groundwater.

[0026] In the present invention, the coagulant is an aluminum-based coagulant, and examples thereof include polyaluminum chloride and sulfate band. In the specific implementation of the present invention, inorganic coagulants other than aluminum-based coagulants and polymer coagulants may be separately added.

[0027] The mixing of the coagulant may be performed in a pipe such as an in-line mixer, or may be performed by stirring in a stirring tank. Preferably, the mixing of the coagulant is carried out in the rapid stirring tank at the front stage of the coagulation treatment section including a combination of a rapid stirring tank at the front stage and a slow stirring tank at the rear stage. By mixing the aluminum-based coagulant into the water to be treated, coagulated treated water in which micro-level aluminum particles, nano-aluminum particles, and dissolved aluminum are mixed is obtained.

[0028] As described above, micro-level aluminum particles refer to aluminum particles on the order of μm, soluble aluminum refers to aluminum that can be filtered through a 0.45-μm membrane, and nano-aluminum particles refer to nano-aluminum particles on the order of several nm to several tens of nm that hardly pass through the 0.45-μm membrane having a negative charge due to the influence of its positive charge (the above is the coagulation treatment step (S100)).

[0029] [Membrane filtration step (S110)] In this step, the coagulated treated water obtained in the coagulation treatment step (S100) is membrane-filtered with a separation membrane selected from a microfiltration membrane and an ultrafiltration membrane to obtain membrane-filtered water.

[0030] As described above, the separation membrane is selected from a microfiltration membrane and an ultrafiltration membrane, and the type of the separation membrane may be any of a polymer membrane, an inorganic membrane, an MF membrane, and a UF membrane. However, a polymer membrane that can use an immersion-type membrane module, particularly, a membrane made of PVDF that is physically and chemically strong, is preferable, and an MF membrane that can also use an immersion-type membrane module is also preferable. In addition, a hollow fiber membrane is preferably used for the shape of the membrane in terms of volume efficiency.

[0031] From the viewpoint of energy saving, a membrane with a pore size of 0.05 μm or more that can utilize the water level difference is preferable, and further, from the viewpoint of suppressing membrane fouling by organic substances, a membrane with a minimum diameter of 0.05 μm is optimal.

[0032] The structure of the membrane filtration device may be either a casing type or a tank immersion type, but the tank immersion type, which has high applicability to raw water with high turbidity, is preferable.

[0033] The membrane-filtered water obtained by membrane filtration is retained in a treatment water tank (not shown) as treated water for a certain period of time and used as purified water (the above is the membrane filtration step (S110)).

[0034] [ΔAl calculation step (S120)] In this step, ΔAl, which is the difference between the aluminum concentration of the supernatant of the coagulated treated water and the aluminum concentration of the membrane-filtered water, is calculated.

[0035] First, prior to calculating ΔAl, measure the aluminum concentration of the supernatant of the flocculated treated water and the aluminum concentration of the membrane-filtered water.

[0036] The supernatant of the flocculated treated water is preferably obtained by collecting the flocculated treated water obtained in the flocculation treatment step (S100) in a container such as a 500-ml beaker, allowing it to stand for 3 to 5 minutes to precipitate the flocs, and collecting approximately 20 mL of the upper part of the water surface with a digital pipette. By collecting the supernatant of the flocculated treated water in this procedure, it is possible to separate the coarse particles and the nanoparticle group containing nanoaluminum particles.

[0037] If the standing time of the flocculated treated water is less than 3 minutes, the sedimentation of the coarse particles is insufficient, and it is preferably in the range of 3 to 5 minutes, more preferably 5 minutes. If it is longer than that, the nanoaluminum particles may coagulate and settle, which is not preferable.

[0038] Subject the obtained supernatant of the flocculated treated water to the measurement of the aluminum concentration.

[0039] The membrane-filtered water can be directly subjected to the measurement of the aluminum concentration as the membrane-filtered water obtained in the membrane filtration step (S110).

[0040] The measurement of the aluminum concentration can be carried out by a colorimetric method (absorbance photometry), atomic absorption spectrometry, ICP emission spectrometry, ICP mass spectrometry, etc. From the viewpoint of simply and rapidly measuring the aluminum concentration, it is preferable to adopt the colorimetric method (absorbance photometry).

[0041] When measuring the aluminum concentration by colorimetry (absorbance photometry), commercially available measuring instruments such as a portable aluminum measuring instrument (product number: HI 96712, manufactured by Hanna Instruments) and an aluminum measuring instrument (product number: MF2PTM-7712H, manufactured by Shiro Sangyo) can be used. When using a commercially available spectrophotometer such as an ultraviolet-visible spectrophotometer (product number: UVmini-1240, manufactured by Shimadzu Corporation), for example, the absorbance of the reaction solution at 535 nm is measured by absorbance photometry using an Eriochrome Cyanine Red reagent (ECR), and the concentration of the aluminum to be determined can be obtained.

[0042] After measuring the aluminum concentrations of the supernatant of the flocculated treated water and the membrane-filtered water, ΔAl is obtained by subtracting the aluminum concentration of the membrane-filtered water from the aluminum concentration of the supernatant of the flocculated treated water (the above is the ΔAl calculation step (S120)).

[0043] [(Optional) Apparent cake filtration constant (K2) calculation step (S130)] This step is an optional step. In this step, the apparent cake filtration constant (K2) when membrane-filtering the flocculated treated water with a separation membrane is calculated.

[0044] The measurement of the apparent cake filtration constant (K2) can be performed by a cake filtration formula based on the cake filtration blocking model (for example, refer to "2013 SPRING Pall News, Volume 117, Pages 10 - 15", edited and published by Marketing & Communication Group, Nippon Pall Co., Ltd., written by Masato Tsuneya).

[0045] The cake filtration blocking model is a model in which, assuming that the filter medium is a bundle of circular tubes with a uniform inner diameter and length, the loaded particles accumulate on the surface of the filter medium (bundle of circular tubes) without blocking the circular tubes. In that case, as shown in Fig. 2(a), the thickness of the deposited particles p (cake layer) increases in proportion to the amount of particles p loaded on the bundle of circular tubes t. Here, the increase in resistance due to the deposited particles p can be replaced by the circular tube t becoming longer as shown in Fig. 2(b).

[0046] Then, by applying the Hagen-Poiseuille equation to the filter medium and proceeding with the calculation while also considering the above-mentioned cake filtration blocking model, in the case of constant-pressure filtration, the following equation (1)

[0047] [Chemical formula] (In equation (1), J represents the flow rate per unit filtration area (m 3 / m 2 ·s), J0 represents the initial flow rate per unit filtration area (m 3 / m 2 ·s), K2 represents the apparent cake filtration constant (1 / m, also referred to as the blocking coefficient), and v represents the filtrate volume per unit area (m 3 / m 2 ).) In the case of constant-flow-rate filtration, the following equation (2) [Chemical formula] (In equation (2), ΔP represents the differential pressure at both ends of the circular tube (Pa), ΔP0 represents the initial differential pressure at both ends of the circular tube (Pa), K2 represents the apparent cake filtration constant (1 / m, also referred to as the blocking coefficient), and v represents the filtrate volume per unit area (m 3 / m 2 ).) can be obtained respectively.

[0048] Since the apparent cake filtration constant is known as an index indicating the membrane fouling property of the flocculated treated water, when determining the change of the operating conditions in the subsequent operating condition change step (S140), by measuring the apparent cake filtration coefficient K2 of the flocculated treated water obtained in the flocculation treatment step (S100) in this step, the membrane fouling property of the flocculated treated water can be more comprehensively judged based on ΔAl and K2.

[0049] [Operating Condition Change Step (S140)] In this step, based on the calculated value of ΔAl, at least one of the operating conditions of the flocculation treatment step (S100) and the membrane filtration step (S110) is changed from the operating conditions before the change.

[0050] Examples of the operating conditions to be changed include flocculation treatment conditions and membrane filtration conditions.

[0051] Examples of the flocculation treatment conditions include, for example, the injection rate of an aluminum-based flocculant, agitation conditions, and pH. For example, the injection rate of the aluminum-based flocculant and the flocculation pH can be adjusted (to the optimum values) so that the concentration of nano-aluminum particles in the flocculation-treated water is minimized, and by increasing the agitation time in the agitation tank, the incorporation of nano-aluminum particles into microflocs or sub-microflocs is promoted, and the concentration of nano-aluminum particles in the flocculation-treated water can be reduced.

[0052] Examples of the membrane filtration conditions include, for example, changing the operating conditions to lower the filtration flow rate. According to this, the time until membrane fouling occurs can be extended.

[0053] An example of changing the operating conditions of this step will be described with reference to FIG. 3. As shown in FIG. 3, in step S140-1, it is determined whether ΔAl is 0.5 mg / L or less. If ΔAl exceeds 0.5 mg / L (NO determination), the process proceeds to step S140-2. If ΔAl is 0.5 mg / L or less (YES determination), the process returns to the flocculation treatment step (S100) without changing the operating conditions.

[0054] In step S140-2, the operating conditions are changed so as to reduce the value of ΔAl. As the operating conditions to be changed, the above-described flocculation treatment conditions and membrane filtration conditions can be selected and implemented. After changing the operating conditions, the process returns to the flocculation treatment step (S100).

[0055] Furthermore, when changing the operating conditions, not only the value of ΔAl but also the value of the apparent cake filtration constant (K2) may be considered. Hereinafter, the case of considering the value of K2 in addition to ΔAl will be described with reference to FIG. 4 as the second example of changing the operating conditions of this step. As shown in FIG. 4, in step S140-3, it is determined whether ΔAl is 0.5 mg / L or less and K2 is 10 (1 / m) or less. When ΔAl exceeds 0.5 mg / L and K2 exceeds 10 (1 / m) (NO determination), when ΔAl exceeds 0.5 mg / L and K2 is 10 (1 / m) or less (NO determination), and when ΔAl is 0.5 mg / L or less and K2 exceeds 10 (1 / m) (NO determination), the process proceeds to step S140-4. When ΔAl is 0.5 mg / L or less and K2 is 10 (1 / m) or less (YES determination), the process returns to the flocculation treatment step (S100) without changing the operating conditions.

[0056] In step S140-4, the operating conditions are changed so as to reduce the values of ΔAl and K2. As the operating conditions to be changed, the flocculation treatment conditions and the membrane filtration conditions already described can be selected and implemented. After changing the operating conditions, the process returns to the flocculation treatment step (S100).

[0057] Therefore, according to the flocculation membrane filtration method of the present invention, the concentration of nanoaluminum particles derived from the flocculant, which causes membrane fouling in membrane filtration, can be easily and quickly calculated as ΔAl, and by using this ΔAl as an index of the membrane fouling property of the flocculated treated water, the operating conditions can be quickly changed at the site of the water purification treatment, and the operating conditions of the flocculation membrane filtration can be optimized.

[0058] Furthermore, by using ΔAl and K2 in combination as indexes of the membrane fouling property of the flocculated treated water, it becomes possible to more accurately evaluate the membrane fouling property of the flocculated treated water.

[0059] In the above-described operation condition change step (S140), when ΔAl exceeds 0.5 mg / L, the operation conditions of coagulation membrane filtration are changed. However, from the viewpoints of maintaining stable operation of coagulation membrane filtration and economy, it is preferable to change the operation conditions of coagulation membrane filtration when ΔAl exceeds 0.3 mg / L.

[0060] Also, from the ΔAl calculation step (S120) to the operation condition change step (S140), it may be executed under the control of the control unit as in the coagulation membrane filtration system described later. However, it is also possible for a person to measure the aluminum concentration of the supernatant of the coagulated treated water and the membrane-filtered water, calculate ΔAl (and optionally measure K2), and change the operation conditions of coagulation membrane filtration based on the values of this ΔAl (and K2).

[0061] <Coagulation Membrane Filtration System> FIG. 5 is a block diagram for explaining the coagulation membrane filtration system 10 of the present invention. As shown in the figure, the coagulation membrane filtration system 10 of the present invention includes a coagulation treatment means 12 that performs coagulation treatment on the water to be treated 1 to which a coagulant 2 is added to obtain coagulated treated water 3, a membrane filtration means 14, a first measurement means 16, a second measurement means 18, and a control unit 20.

[0062] Regarding the water to be treated 1, the coagulant 2, and the coagulated treated water 3, they are the same as those in the above-described coagulation membrane filtration method, so the description thereof is omitted here.

[0063] Examples of the coagulation treatment means 12 include an in-line mixer and a stirring tank equipped with stirring means. The coagulation treatment means 12 preferably includes a rapid stirring tank and a slow stirring tank located downstream of the rapid stirring tank.

[0064] The coagulant 2 is injected into the water to be treated 1 by a coagulant injection device (not shown) at a position upstream of the coagulation treatment means 12 or in the coagulation treatment means 12. In FIG. 5, the coagulant 2 is injected into the water to be treated 1 by the coagulation treatment means 12.

[0065] When the flocculation treatment means 12 includes a rapid agitation tank and a slow agitation tank located downstream of the rapid agitation tank, the rapid agitation tank may be a single tank or a plurality of tanks arranged in series. When there are a plurality of tanks, it is preferably three tanks or less, and particularly preferably three rapid agitation tanks. Considering the agitation intensity of rapid agitation in terms of the G value (velocity gradient) of the agitation intensity according to the Waterworks Facility Design Guidelines 2012, it is 100 1 / s or more, and the G value of the slow agitation tank is in the range of 10 to 75 1 / s.

[0066] In the flocculation treatment means 12, flocculation treatment is performed on the water to be treated 1 to which the flocculant 2, which is an aluminum-based flocculant, is added, thereby obtaining flocculation-treated water 3 in which micro-level aluminum particles, nano-aluminum particles, and dissolved aluminum are mixed.

[0067] The membrane filtration means 14 is a means for obtaining the membrane-filtered water 4 by membrane-filtering the flocculation-treated water 3 obtained by the flocculation treatment means 12 with a separation membrane selected from a microfiltration membrane and an ultrafiltration membrane. Information on the separation membrane such as the type and pore size of the separation membrane has been described in the above flocculation membrane filtration method, and the description thereof is omitted here.

[0068] The first measurement means 16 is a means for measuring the aluminum concentration in the supernatant of the flocculation-treated water 3, and the second measurement means 18 is a means for measuring the aluminum concentration in the membrane-filtered water 4.

[0069] As the first measurement means 16 and the second measurement means 18, the equipment described in the above flocculation membrane filtration method can be appropriately used. The first measurement means 16 and the second measurement means 18 are controlled by a control unit 20 described later.

[0070] The control unit 20 is a computer equipped with a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), etc. The control unit 20 expands the program stored in the ROM onto the RAM and causes the CPU to execute the corresponding processing. Note that the above program is not limited to being stored in the ROM, and it may be stored in an NVRAM (Non-Volatile Randam Access Memory).

[0071] The control unit 20 calculates the value of ΔAl, which is the difference between the aluminum concentration in the supernatant of the flocculation-treated water 3 measured by the first measuring means 16 and the aluminum concentration in the membrane-filtered water 4 measured by the second measuring means 18, and based on the calculated value of ΔAl, controls the change of at least one of the operating conditions of the flocculation treatment means 12 and the membrane filtration means 14 from the operating conditions before the change.

[0072] The method for calculating ΔAl is the same as the ΔAl calculation step (S120) of the above flocculation membrane filtration method except that the control unit 20 is limited to calculating ΔAl, so the description thereof is omitted here.

[0073] After calculating ΔAl, the control unit 20 determines whether ΔAl has reached a predetermined value as described in the first example of the operating condition change step (S140) of the above flocculation membrane filtration method. If it exceeds the predetermined value, a signal is sent to at least one of the flocculation treatment means 12 and the membrane filtration means 14 to change its operating conditions. If it does not exceed the predetermined value, no signal is sent, and thus its operating conditions are not changed.

[0074] The types of the operating conditions of at least one of the flocculation treatment means 12 and the membrane filtration means 14 are the same as those in the operating condition change step (S140) of the above flocculation membrane filtration method, so the description thereof is omitted here.

[0075] Further, after changing the operation conditions or after deciding not to change the operation conditions, the control by the control unit 20 may end, or ΔAl may be calculated again after a predetermined time, and based on the result, control for changing (or not changing) the operation conditions of at least one of the flocculation treatment means 12 and the membrane filtration means 14 may be repeated.

[0076] Also with the flocculation membrane filtration system 10 of the present invention, similar to the flocculation membrane filtration method of the present invention, the concentration of nano-aluminum particles derived from the flocculant that causes membrane fouling in membrane filtration can be easily and quickly calculated as ΔAl, and by using this ΔAl as an index of the membrane fouling property of the flocculation-treated water, the operation conditions can be quickly changed at the site of water purification treatment, and the operation conditions of flocculation membrane filtration can be optimized.

[0077] <Method for evaluating membrane fouling property of flocculation-treated water> The method for evaluating the membrane fouling property of the flocculation-treated water of the present invention is a method for evaluating the membrane fouling property of the flocculation-treated water obtained by subjecting the water to be treated to flocculation treatment and then performing membrane filtration. Since there is no difference in the water to be treated, flocculation treatment, flocculation-treated water, and membrane filtration from the above-described flocculation membrane filtration method, the description thereof will be omitted here.

[0078] The method for evaluating the membrane fouling property of the flocculation-treated water of the present invention includes a ΔAl calculation step and a membrane fouling property evaluation step. Hereinafter, it will be described with reference to FIG. 6. FIG. 6 is a flowchart for explaining the method for evaluating the membrane fouling property of the flocculation-treated water of the present invention.

[0079] [ΔAl calculation step (S200)] In this step, ΔAl, which is the difference between the aluminum concentration of the supernatant of the flocculation-treated water and the aluminum concentration of the membrane-filtered water, is calculated. Since this step is not different from the ΔAl calculation step (S120) of the above-described flocculation membrane filtration method, the description thereof will be omitted here (above, ΔAl calculation step (S200)).

[0080] [Membrane fouling property evaluation step (S210)] In this project, based on the value of ΔAl calculated in the ΔAl calculation step (S200), the membrane fouling property of the flocculated treated water is evaluated.

[0081] The inventor has discovered that in the purified water treatment process by coagulation membrane filtration, when performing coagulation treatment by adding an aluminum-based coagulant, the ΔAl obtained has a good correlation with the apparent cake filtration constant (K2) obtained when membrane-filtering the coagulated treated water in the same purified water treatment process.

[0082] Since the apparent cake filtration constant (K2) is known as an index of membrane fouling property, by adding an aluminum-based coagulant to the water to be treated in advance and performing coagulation treatment under various conditions, obtaining the apparent cake filtration constant (K2) and ΔAl when membrane-filtering the obtained coagulated treated water (and also the membrane-filtered water for ΔAl), obtaining the relational expression between the two, obtaining the value of ΔAl for the coagulated treated water and its membrane-filtered water with an unknown apparent cake filtration constant (K2), and applying the value of ΔAl to the relational expression, it is possible to obtain the value of the apparent cake filtration constant (K2) without performing a long-term membrane filtration test. And since the value of the apparent cake filtration constant (K2) serves as an index of membrane fouling property, it becomes possible to simply and quickly evaluate the membrane fouling property of the coagulated treated water by calculating the value of ΔAl.

[0083] Furthermore, the inventor has obtained the finding that in the purified water treatment process by coagulation membrane filtration, when performing coagulation treatment by adding an aluminum-based coagulant, it is preferable that the apparent cake filtration constant (K2) when membrane-filtering the obtained coagulated treated water is 10 (1 / m) or less. And from the relational expression between the above-mentioned apparent cake filtration constant (K2) and ΔAl, since the value of ΔAl when the apparent cake filtration constant (K2) is 10 (1 / m) is 0.5 (mg / L), when the value of ΔAl calculated in the ΔAl calculation step (S200) is 0.5 (mg / L) or less, it can be evaluated that the membrane fouling property of the coagulated treated water is good.

[0084] Furthermore, when the value of ΔAl calculated in the ΔAl calculation step (S200) is 0.3 (mg / L) or less, since the apparent cake filtration constant (K2) becomes even smaller, it can be evaluated that the membrane fouling property of the flocculated treated water is even better.

[0085] In addition, when evaluating the membrane fouling property of the flocculated treated water, it is preferable to combine not only the value of ΔAl but also the value of the apparent cake filtration constant (K2) from the viewpoint of more accurately evaluating the membrane fouling property of the flocculated treated water. In this case, when the value of the apparent cake filtration constant (K2) is 10 (1 / m) or less, it can be evaluated that the membrane fouling property of the flocculated treated water is good, and when the value of the apparent cake filtration constant (K2) is 5 (1 / m) or less, it can be evaluated that the membrane fouling property of the flocculated treated water is even better (above, membrane fouling property evaluation step (S210)).

[0086] Therefore, according to the method for evaluating the membrane fouling property of the flocculated treated water of the present invention, the nano-aluminum particle concentration in the flocculated treated water can be easily and quickly calculated as ΔAl without preparing another membrane filtration facility or the like. In addition, since this ΔAl has a significant correlation with the apparent cake filtration constant when the flocculated treated water is membrane-filtered with a separation membrane, the membrane fouling property of the flocculated treated water can be easily and quickly evaluated using ΔAl as an index at the site of water purification treatment.

[0087] Note that after evaluating the membrane fouling property of the flocculated treated water using ΔAl (and K2) as an index, the operating conditions of the flocculation membrane filtration can be optimized by changing the operating conditions of the flocculation membrane filtration based on this evaluation result.

[0088] Also, in FIG. 6, when the membrane fouling property evaluation step (S210) ends, all the steps of the method for evaluating the membrane fouling property of the flocculated treated water of the present invention end, but it is also possible to repeat the ΔAl calculation step (S200) and the membrane fouling property evaluation step (S210) after a predetermined time.

[0089] Hereinafter, the present invention will be described more specifically by way of examples.

Examples

[0090] <Example 1> (1) Water to be treated and coagulation treatment conditions As the water to be treated (raw water), river water in winter during a relatively clear period at a water purification plant where a membrane filtration facility is installed (turbidity: 2.7 degrees, chromaticity: 4.1 degrees, pH = 7.5, TOC: 0.7 mg / L, UVA 260 : 0.086 (5 cm cell)) was used.

[0091] To this water to be treated, polyaluminum chloride (PACl, basicity 50%) was added, and coagulation treatment was carried out using a 500 mL beaker.

[0092] The coagulation conditions were set as coagulation pH = 7.0 and PACl injection rate = 25 mg / L. These are the same conditions as the on-site operation conditions at the time of collecting the water to be treated. The stirring conditions are as shown in Table 1 below.

[0093]

Table 1

[0094] (2) Measurement of apparent cake filtration constant (K2) (1) 80 mL each of the coagulation-treated water obtained under the water to be treated and coagulation treatment conditions was collected, and this was passed through the membrane by constant-pressure filtration of the total amount (suction pressure 90 kPa) using a suction pump, and the change in the amount of filtered water over time was measured. Then, based on the cake filtration theory from the results, the apparent cake filtration constant (K2) was determined.

[0095] Note that as the membrane, a VVHP membrane (hydrophobic PVDF membrane, pore diameter 0.1 μm) manufactured by Merck was used, and a glass filter holder for flat membranes with a diameter of 25 mm was used.

[0096] (3) Measurement of ΔAl (1) Approximately 20 mL of the upper part of the water surface after 5 minutes of standing sedimentation obtained under the water to be treated and coagulation treatment conditions was collected with a digital pipette and used as the supernatant of the coagulation-treated water. For the same coagulation-treated water, in (2) the measurement of the apparent cake filtration constant (K2), it was passed through the membrane to obtain membrane-filtered water.

[0097] The aluminum concentrations of the supernatant water of the flocculation-treated water and the membrane-filtered water were measured according to JIS K 0102-2008 "58.4 Inductively Coupled Plasma Optical Emission Spectrometry".

[0098] Then, ΔAl, which is the difference between the aluminum concentration of the supernatant water of the flocculation-treated water and the aluminum concentration of the membrane-filtered water, was calculated. For the flocculation-treated water obtained under the conditions of Treatment Conditions 1 to 3 in Example 1, the values of K2 and ΔAl are shown in Table 2 below.

[0099]

Table 2

[0100] Also, FIG. 7 is a graph plotting the values of K2 and ΔAl for the flocculation-treated water obtained under the conditions of Treatment Conditions 1 to 3 in Example 1, with K2 on the vertical axis and ΔAl on the horizontal axis.

[0101] As shown in Table 2 and FIG. 7, in any treatment condition, as the stirring time becomes longer, the values of ΔAl and K2 can be made smaller. Also, regarding Treatment Condition 1, when only rapid stirring is performed, the reduction widths of K2 and ΔAl reach a plateau when rapid stirring is performed for 6 minutes. On the other hand, as in Treatment Condition 2, when only 2 minutes of rapid stirring is performed, in order to make K2 10 (1 / m) or less and ΔAl 0.5 (mg / L) or less, slow stirring for 9 minutes or more is required, and the stirring time for flocculation treatment becomes long in order to reduce the concentration of nano-aluminum particles in the flocculation-treated water.

[0102] Therefore, as in Treatment Condition 3, it was found that when 6 minutes of rapid stirring is performed, the values of K2 and ΔAl can be sufficiently reduced even by performing slow stirring for 1 to 2 minutes thereafter.

[0103] Also, as shown in FIG. 7, a good correlation was confirmed between ΔAl and K2, and thus it was found that the value of K2 can be predicted by measuring ΔAl. Similarly, it is also possible to predict ΔAl from the value of K2. <Example 2> ΔAl and K2 were also measured in the membrane feed water of the actual equipment.

[0104] The water to be treated was the same as that in Example 1.

[0105] The purified water treatment flow of the actual equipment is: rapid agitation section (hydraulic retention time (HRT): 2 minutes, 130 rpm) → slow agitation section (HRT: 20 minutes, 30 rpm) → sedimentation tank → membrane filtration equipment. The flocculation conditions were set as flocculation pH = 7.0 and PACl injection rate = 25 mg / L.

[0106] The measurement conditions for ΔAl and K2 were the same as those in the items of Example 1. The measurement results were ΔAl = 0.29 (mg / L) and K2 = 6.93 (1 / m). In the purified water treatment flow of the actual equipment, ΔAl was in the range of 0.5 (mg / L) or less, and K2 was in the range of 10 (1 / m) or less. It was found that the membrane fouling property of the flocculated treated water at the site was small and it was good operating conditions.

Explanation of symbols

[0107] 10 Coagulation membrane filtration system 12 Flocculation treatment means 14 Membrane filtration means 16 First measurement means 18 Second measurement means 20 Control unit

Claims

1. A coagulation treatment step of mixing a coagulant containing an aluminum-based coagulant with the water to be treated to obtain coagulated treated water; A membrane filtration step of subjecting the coagulated treated water obtained in the coagulation treatment step to membrane filtration with a separation membrane selected from a microfiltration membrane and an ultrafiltration membrane to obtain membrane-filtered water; A ΔAl calculation step of calculating ΔAl, which is the difference between the aluminum concentration of the supernatant of the coagulated treated water and the aluminum concentration of the membrane-filtered water; An operating condition change step of changing at least one of the operating conditions of the coagulation treatment step and the membrane filtration step from the operating conditions before the change based on the calculated value of ΔAl; A coagulation membrane filtration method, characterized by comprising the above steps.

2. In the operating condition change step, when the value of ΔAl calculated in the ΔAl calculation step exceeds 0.5 mg / L, at least one of the operating conditions of the coagulation treatment step and the membrane filtration step is changed from the operating conditions before the change so that the value of ΔAl becomes 0.5 mg / L or less. The coagulation membrane filtration method according to Claim 1.

3. In the operating condition change step, when the value of ΔAl calculated in the ΔAl calculation step exceeds 0.3 mg / L, at least one of the operating conditions of the coagulation treatment step and the membrane filtration step is changed from the operating conditions before the change so that the value of ΔAl becomes 0.3 mg / L or less. The coagulation membrane filtration method according to Claim 1.

4. Furthermore, it has an apparent cake filtration constant calculation step of calculating an apparent cake filtration constant K2 when the coagulated treated water is membrane-filtered with the separation membrane, The operating condition change step changes at least one of the operating conditions of the coagulation treatment step and the membrane filtration step from the operating conditions before the change based on the calculated value of ΔAl and the calculated value of K2. The coagulation membrane filtration method according to any one of Claims 1 to 3.

5. A coagulation treatment means for performing coagulation treatment on the water to be treated added with a coagulant containing an aluminum-based coagulant to obtain coagulated treated water; A membrane filtration means for subjecting the coagulated treated water obtained by the coagulation treatment means to membrane filtration with a separation membrane selected from a microfiltration membrane and an ultrafiltration membrane to obtain membrane-filtered water; A first measuring means for measuring the aluminum concentration in the supernatant of the coagulated treated water; A coagulation membrane filtration system having a second measuring means for measuring the aluminum concentration in the membrane-filtered water. Calculate the value of ΔAl, which is the difference between the aluminum concentration in the supernatant of the flocculated treated water measured by the first measuring means and the aluminum concentration in the membrane-filtered water measured by the second measuring means, and based on the calculated value of ΔAl, control the change of at least one of the operating conditions of the flocculation treatment means and the membrane filtration means from the operating conditions before the change. A flocculation membrane filtration system, further comprising a control unit.

6. A method for evaluating the membrane fouling property of flocculated treated water for flocculation membrane filtration in which the flocculated treated water obtained by flocculating the water to be treated is membrane-filtered, comprising: The flocculation treatment is a treatment for obtaining the flocculated treated water by mixing a flocculant containing an aluminum-based flocculant with the water to be treated. A ΔAl calculation step of calculating ΔAl, which is the difference between the aluminum concentration in the supernatant of the flocculated treated water and the aluminum concentration in the membrane-filtered water. A membrane fouling property evaluation step of evaluating the membrane fouling property of the flocculated treated water based on the calculated value of ΔAl. A method for evaluating the membrane fouling property of flocculated treated water, characterized by comprising the steps.

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