JP2014057920A - Water treatment method - Google Patents

Abstract

To provide a water treatment method capable of separating, collecting and reusing a magnetic adsorbent and a filter aid in water without increasing the size of a magnetic separation tank and without clogging a filter. .
SOLUTION: When the most frequent pore diameter of the filter is A, the volume-converted average particle diameter of the filter aid is B, and the particle spacing of the filter aid constituting the precoat layer is C, the filter and the filter aid are The relationship of A ≦ C, 2 ≦ B ≦ 50 μm and 0.2 ≦ C ≦ 15 μm is satisfied, the filter has a flat and horizontal filter surface, and the filter aid contains nonmagnetic inorganic particles.
[Selection figure] None

Description

  The embodiment described here relates to a water treatment method for separating and reusing a water treatment adsorbent (magnetic inorganic particles) and a filter aid (nonmagnetic inorganic particles) for purifying wastewater. .

  Recently, the effective use of water resources has been required due to industrial development and population growth. In order to effectively use water resources, it is important to purify and reuse various wastewaters such as industrial wastewater and domestic wastewater. In order to purify the wastewater, it is necessary to separate and remove water insoluble matters and impurities contained in the water. Examples of methods for purifying wastewater include membrane separation methods, centrifugal separation methods, activated carbon adsorption methods, ozone treatment methods, and suspended matter precipitation removal methods by adding flocculants. Using these water treatment methods, valuable materials contained in the wastewater are collected. In addition to these, there is a magnetic separation method using magnetic particles as an adsorbent as a method for recovering valuable materials from wastewater. For example, in the magnetic separation method for recovering metals in wastewater as valuable resources, an alkali agent is added to the wastewater to cause solid metal ions to precipitate in water, and magnetic particles are added to adsorb the precipitated metal particles in water to the magnetic particles. , Separating the solid-liquid magnetic particles adsorbing the metal particles from the waste water, detaching the metal particles from the magnetic particles in the separated material, and separating the separated metal particles from the magnetic particles magnetically, the separated metal particles Are recovered as valuables and the separated magnetic particles are reused.

Japanese Patent Laid-Open No. 9-14018

  However, in the conventional water treatment method, there is a problem in that the amount of waste water that can be actually treated is small and the treatment efficiency is low because the range in which the magnetic force of the magnet reaches is limited to a narrow space in the magnetic separation tank. . Increasing the capacity of the magnet or increasing the number of magnets to solve this problem not only increases the equipment size and increases the capital investment cost, but also increases the number of magnets in and out of the tank. In addition, the magnets may come into contact with each other or collide with each other, which is problematic from the viewpoint of safety and health.

  Further, as another conventional method, for example, a filtration method or a coagulation precipitation method may be used. However, in the former, when fine particles are filtered with a filter, the filter is likely to be clogged. In the latter case, the flocculant has a problem that the purity of the recovered product tends to decrease.

  The present invention has been made to solve the above problems, and separates and collects the magnetic adsorbent and the filter aid in water without increasing the size of the magnetic separation tank and without clogging the filter. It is an object to provide a water treatment method that can be reused.

  The water treatment method according to the embodiment described herein includes (a) adding a magnetic adsorbent to raw water, adsorbing foreign matter contained in the raw water to the magnetic adsorbent, and (b) adsorbing from the magnetic adsorbent. (C) magnetically separating the magnetic adsorbent from the water containing the desorbed foreign matter, (d) adding water to the separated magnetic adsorbent, and (E) On the other hand, a filter aid containing nonmagnetic inorganic particles is prepared, and a solid filter having a flat filter arranged so that the filter surface is substantially horizontal is prepared. Preparing a liquid separator; (f) adding a dispersion medium to the filter aid and stirring and mixing to prepare a suspension containing the filter aid; and (g) adding the suspension to the solid solution. Pumped to a liquid separator, the suspension is filtered through the filter, and the filter aid is placed on the filter. To form a precoat layer of the filter aid on the filter. In this case, the most frequent pore size of the filter is A, the volume-converted average particle size of the filter aid is B, and the precoat When the particle interval of the filter aid constituting the layer is C, the filter and the filter aid satisfy the relations of A ≦ C, 2 ≦ B ≦ 50 μm, and 0.2 ≦ C ≦ 15 μm, respectively (h) The water to be treated produced in the step (d) is passed through the precoat layer and the filter, and the magnetic adsorbent is solid-liquid separated from the water to be treated, and the magnetic adsorbent is deposited on the precoat layer, Thereby, a deposited double layer in which a filter aid and a magnetic adsorbent are laminated on the filter is formed, and (i) peeling water is sprayed on the deposited double layer to peel the deposited double layer from the filter, thereby Magnetic adsorption And (j) a magnetic separation tank having a magnetic member for adsorbing the magnetic adsorbent, and (k) from the solid-liquid separation device. The peeled material liquid is supplied to the magnetic separation tank, the peeled material liquid is stirred and mixed in the magnetic separation tank, the magnetic adsorbent contained in the peeled material liquid is adsorbed on the magnetizing member, and the magnetic adsorbent is magnetized. While adsorbing to the member, the filter aid-containing liquid containing the filter aid is discharged from the magnetic separation tank, thereby magnetically separating the filter aid and the magnetic adsorbent in the stripped liquid. (L) The filter aid-containing liquid discharged in the step (k) is reused in the step (e), (m) the adsorption of the magnetic adsorbent by the magnetized member is released, and the desorbed magnetism A magnetic adsorbent-containing liquid is prepared by adding a dispersion medium to the adsorbent, and the magnetic adsorbent-containing liquid The discharged from the magnetic separator tank, and wherein the reused in (n) the step (m) at the discharge is the magnetic adsorbent-containing liquid said step (a).

The block diagram which shows the outline | summary of the apparatus used for the water treatment method of embodiment. (A) is a schematic cross-sectional view showing a magnetic adsorbent (magnetic primary particles) coated with a coating material, and (b) is a schematic cross-sectional view showing a magnetic adsorbent (aggregated secondary particles) in which a large number of magnetic foundation particles are aggregated. . The flowchart which shows the water treatment method which concerns on embodiment. (A)-(e) is process drawing which shows the water treatment method which concerns on embodiment. The expanded cross-sectional schematic diagram which shows the deposition double layer of the filter aid / magnetic adsorbent on a filter. The characteristic line figure which shows an example of distribution of the pore diameter of a filter.

  Various embodiments for solving the above problems will be described below.

  In the method of the embodiment described here, a precoat method using nonmagnetic inorganic particles as a filter aid is used, and a precoat layer of nonmagnetic inorganic particles is formed on the filter, and the precoat layer on the filter is formed. Water to be treated is passed through to deposit the magnetic adsorbent (magnetic inorganic particles for water treatment) on the precoat layer, and the filter aid / magnetic adsorbent double layer is peeled off from the filter. By magnetically separating the magnetic adsorbent and the filter aid therein, the magnetic adsorbent and the filter aid can be separated and recovered efficiently. That is, by using the precoat method, the magnetic adsorbent is separated and recovered at a high concentration, and the magnetic separation tank used in the subsequent magnetic separation step becomes small and compact.

  In the method of the embodiment described here, when the precoat layer is formed on the filter, the most frequent pore diameter of the filter is A, the volume conversion average particle diameter of the filter aid is B, and the filtration constituting the precoat layer When the particle interval of the auxiliary agent is C, the filter and the filtration auxiliary agent are respectively configured so as to satisfy the relationships of the following formulas (1) to (3).

A ≦ C, (1)
2 ≦ B ≦ 50 μm (2)
0.2 ≦ C ≦ 15 μm (3)
Here, the pore diameter A of the filter may be a known numerical value such as a metal mesh sieve, but if unknown, it is measured by a mercury intrusion method. This mercury pressure method uses the high surface tension of mercury to apply pressure to cause mercury to penetrate into the pores of the powder, and obtains the specific surface area and pore distribution from the pressure and the amount of mercury that is injected. It is.

  The pore diameter of the filter can be determined using, for example, an automatic porosimeter autopore IV9500 series manufactured by Shimadzu Corporation. At this time, the most frequent pore diameter A is used as the pore diameter of the filter. This most frequent pore diameter A is the differential value of the cumulative amount of mercury injected into the pores with the filter pore diameter (μm) on the horizontal axis and the filter pore volume (ml / g) on the vertical axis. Can be obtained using the characteristic diagram of FIG. In the figure, the pore diameter at the peak Pf of the pore diameter distribution F is the most frequent pore diameter A.

  Moreover, the mutual space | interval C of the particle | grains of a filter aid here can be calculated | required, for example using Shimadzu Corporation automatic porosimeter autopore IV9500 series. In the porosimeter, the gap between particles is regarded as a hole, and the interparticle distance C is determined from the pressure at which mercury enters the hole. Since the measurement of the porosimeter is performed under pressure, this value and the pore diameter C of the precoat layer of the filter aid deposited on the filter almost coincide. The mode value of the pore distribution obtained at this time is defined as the representative pore diameter C between the particles. However, if the filter aid has a porous structure, a peak when mercury enters the pores is also obtained, so two peaks of the pore diameter of the porous structure and the pore diameter between particles are obtained. In this case, a peak having a large pore diameter can be defined as a pore diameter between particles. In addition, the representative pore diameter C of the precoat layer is set to the mode value in the same manner as the pore diameter A of the filter.

In the embodiment described herein, in terms of volume average particle diameter B of the filter aid, namely the particle size d ₁ of particle 50 shown in FIG. 2 in the range of 2 to 50 [mu] m. When the volume conversion average particle diameter B is less than 2 μm, the particles 50 are too densely aggregated, the mutual distance C between the particles becomes too small, and it becomes difficult to obtain an effective water flow rate. Here, when the volume-converted average particle diameter B of the filter aid is less than 2 μm, the filter aid is not deposited on the filter, or even if the filter aid is deposited on the filter, the filter aid particles are filtered at the initial stage of the filtration process. This causes an initial leak that passes through the pores.

  On the other hand, if the volume-converted average particle diameter B exceeds 50 μm, the particles 55 are coarsely aggregated on the filter and the mutual interval C between the particles 55 becomes too large, so that the fine magnetic particles 50 can be easily passed. The function of cannot be fully demonstrated. Also, if the volume average particle size B of the filter aid exceeds 50 μm, the dispersibility of the particles in water will deteriorate, the filter aid will not deposit uniformly on the filter, and the surface will be unevenly uneven. Layers are easily formed. Further, excessive particles having an average particle diameter B exceeding 50 μm may cause magnetic particles to pass between the particles of the filter aid, and an effective filter effect may not be obtained.

  Furthermore, the volume conversion average particle diameter B of the filter aid is more preferably in the range of 10 to 25 μm. When the volume-converted average particle diameter B is 25 μm or less, the removal efficiency of the magnetic particles 55 is further increased. On the other hand, when the volume conversion average particle diameter B is 10 μm or more, the water flow rate is further increased and the treatment efficiency is improved. Thus, the filter aid having a volume-converted average particle diameter B of 10 to 25 μm has a good balance between the removal efficiency of the magnetic adsorbent particles and the water flow rate.

(Filter aid)
In the embodiment described here, a filter aid serving as a precoat layer forming material is designed so that the magnetic adsorbent (magnetic inorganic particles) can be separated and recovered without using a flocculant. That is, inorganic particles having various performances and characteristics such as dispersibility, detachability, hydrophobicity, releasability, shape stability, water insolubility and nonmagnetic properties are employed as filter aids.

  Hereinafter, various performances and characteristics required for the filter aid will be described.

  The dispersibility is a performance necessary for preparing a suspension of inorganic particles (filter aid). When inorganic particles are added to a solvent such as water and stirred, the inorganic particles are preferably dispersed rapidly and uniformly in the solvent. If the inorganic particles are excellent in dispersibility, a uniform suspension without unevenness in particle concentration can be obtained by stirring for a short time.

  The detachability is a performance necessary for separating the filter aid from the magnetic adsorbent / filter aid mixture. This is because when the filter aid (non-magnetic inorganic particles) is adsorbed on the magnetic adsorbent (magnetic inorganic particles), a considerable amount of energy is required to separate the adsorbed filter aid from the magnetic adsorbent. . For this reason, it is preferable that the filter aid has detachability with respect to the magnetic adsorbent, in other words, it has preferably almost no adsorptivity with respect to the magnetic adsorbent.

  Hydrophobicity is a characteristic required to facilitate separation of the filter aid from the water to be treated and to facilitate deposition of the magnetic adsorbent on the filter aid precoat layer. Although it is not necessary for the entire surface of the filter aid to be hydrophobic, it is easy to separate the filter aid from the water to be treated if at least a part of the surface of the filter aid is hydrophobic. Also, as the filter aid becomes more hydrophobic, a smaller particle size magnetic adsorbent can be deposited on the filter aid precoat layer. When strong hydrophobic filter aids (inorganic particles) are adjacent to each other, it becomes difficult for the magnetic particles to pass through the gaps between the inorganic particles, and even if the magnetic particles are small particles, the magnetic particles bridge on the surface of the inorganic particles. Because there are things to do. For example, even if the magnetic particles have a particle size smaller than the most frequent mutual spacing C, the magnetic particles can be deposited on the inorganic particle precoat layer by forming a bridge.

  The peelability is a characteristic necessary for peeling the filter aid precoat layer from the filter. This peelability is a property related to the above-mentioned hydrophobicity in the filter aid. If the releasability of the filter aid is excellent, there is an advantage that the amount of stripping water used can be reduced.

  Shape stability is a characteristic required to separate and recover the filter aid and reuse it repeatedly. When the filter aid is excellent in shape stability, it is less likely to deteriorate over time, and can be used as a precoat layer forming material with good reproducibility over a long period of time.

  Water insolubility is a property required for water to form a precoat layer of filter aid on the filter in a uniform thickness. For this reason, it is preferable to use a calcium salt compound or a silicate compound insoluble in water as a filter aid.

  Non-magnetism is a characteristic necessary for magnetically separating the filter aid from the magnetic adsorbent in the mixed solution. In the magnetic separation step, only the magnetic adsorbent is adsorbed on the magnet, and the nonmagnetic filter aid remains in the mixed solution, whereby the filter aid is magnetically separated from the magnetic adsorbent.

  The filter aid is preferably composed of inorganic compound particles containing calcium, or inorganic compound particles containing silicon. This is because these inorganic compounds have a small specific gravity and a large difference in specific gravity from magnetic particles (metal or metal oxide particles) that are to be separated and recovered, and thus are easily separated from the magnetic particles by the action of gravity. Further, the filter aid can be a calcium salt compound or a silicate compound insoluble in water.

  The calcium-containing filter aid may be a natural ore or a simple substance of a purified calcium compound. Natural ores include, for example, aragonite, urexite, melilite, onfasite, uvalite, scheelite, velobskite, hedenburgite, zoisite, fisheye stone, dolomite, creedite, peamontite, spar stone, dihydrate gypsum, titanite , Charoite, anorthite, diopside, ash iron pyroxene, johansen pyroxene, tremolite, rhodonite, pigeonite, horn blend, augite, becrotite, vesuvianite, calcite, calcite, meteorite, montmorillonite, actinolite, epidote, clinozoite, Apatite is mentioned. Examples of the purified calcium compound include calcium carbonate, calcium sulfite, calcium hydroxide, calcium sulfate, calcium titanate, and calcium tungstate. Among these, calcium carbonate having a low solubility in water and ore (eg, aragonite, dolomite) containing calcium carbonate as a main component are preferable. Moreover, it is preferable that the inorganic particle of a filter aid is a substance which does not have a hydrate or a hydroxyl group. This is because a substance having a hydrate or a hydroxyl group has a softer property than other substances, so that particles may be fitted into the pores of the filter and the filter may be clogged.

  Also, as silicon-containing filter aids, silicate minerals (olivine, pyroxene, amphibole, mica, quartz, feldspar, etc.), clay minerals (kaolin, montmorillonite, etc.), or pure silica (SiO2), etc. Can be used. As the silicon-containing filter aid, silica with high purity is more preferable. It should be noted that clay minerals are difficult to control the particle size, and when laminated on a filter, they may adhere strongly to the clay and become unfilterable. Care must be taken when using them.

  The outline manufacturing method of a filter aid is demonstrated.

  The raw material is finely pulverized using an arbitrary pulverizer, and the pulverized product is classified to produce a powder having a desired particle size (nonmagnetic inorganic particles serving as a filter aid). Examples of the method for pulverizing the filter aid raw material include a ball mill, a Henschel mixer, and a roll. The average particle diameter is calculated based on the result measured by the laser diffraction method. Specifically, a trade name: SALD-DS21 type measuring device manufactured by Shimadzu Corporation can be used as an apparatus using a laser diffraction method. Here, the “average particle diameter” refers to a volume-converted average particle diameter. The volume conversion average particle diameter B of nonmagnetic inorganic particles (filter aid) is measured using such an apparatus.

(Magnetic adsorbent)
The magnetic adsorbent is porous magnetic particles having an average particle diameter of 15 to 90 μm. For example, as shown in FIG. 2A, the surface of the magnetic particles 51 is coated with a coating material 52 such as a fluorine organic compound. Yes. When the magnetic particles 51 are coated with a fluorine organic compound, the coating material 52 can be coated so as to have a coverage of 50 to 20000 μg / g in terms of fluorine. The magnetic adsorbent may be an aggregate 53 in which the polymer-coated magnetic particles 50 are aggregated as shown in FIG. In order to adsorb fats and oils, it is necessary that the properties of the solid surface be hydrophobic. Since the magnetic adsorbent contains a fluorine organic compound in which the coating layer has a coating rate of 50 to 20000 μg / g in terms of fluorine, its surface properties are hydrophobic. When the coverage of the fluorine organic compound is less than 50 μg / g in terms of fluorine, sufficient hydrophobicity cannot be obtained, and the adsorption of oil is inhibited. On the other hand, when the coverage of the fluorine organic compound exceeds 20000 μg / g in terms of fluorine, it becomes difficult to desorb oil adsorbed from the magnetic particles because the hydrophobicity is too strong.

  Various shapes such as a spherical shape, a polyhedron, and an indeterminate shape can be adopted as the shape of the magnetic particles, and a polyhedral structure with a spherical shape or a rounded corner is particularly preferable. These shaped particles are excellent in shape stability and exhibit stable performance with high reproducibility when used repeatedly. On the other hand, magnetic particles with sharp edges having sharp edges are not preferable. This is because if the magnetic particles have sharp edges, the surface of other particles and the coating layer are likely to be damaged, and the shape may change and the adsorption performance may fluctuate greatly during repeated use.

  Various inorganic particles or metal particles can be used as the core material of the magnetic particles. Magnetite, titanite, pyrrhotite, magnesium ferrite, cobalt ferrite, nickel ferrite, barium ferrite, fused silica, crystalline silica, glass, talc, alumina, calcium silicate, calcium carbonate, barium sulfate, magnesia, silicon nitride as inorganic particles And ceramic particles such as boron nitride, aluminum nitride, magnesium oxide, beryllium oxide, and mica. Examples of metal particles include aluminum, iron, copper, and alloys thereof.

  Further, various ferrite compounds can be suitably used for the core material of the magnetic particles. Ferrite compounds such as iron, iron-based alloys, magnetite (magnetite), titanite (ilmenite), pyrrhotite (pilotite), magnesia ferrite, manganese magnesium ferrite, manganese zinc ferrite, cobalt ferrite, nickel ferrite, nickel zinc ferrite, barium Ferrite, copper zinc ferrite, etc. can be used.

  Note that it is not necessary that all of the magnetic particle cores are made of a magnetic material. For example, a bonded body in which very fine magnetic particles are bonded with a nonmagnetic binder may be used as the magnetic particle core. Moreover, the surface of the magnetic particles may be hydrophobized with an alkoxysilane compound such as methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, or phenyltriethoxysilane.

  The surface of the magnetic particles can be coated with various coating materials. The coating material is required to have a property (solvent insolubility) that is not dissolved by an organic solvent (cleaning solvent). As the coating material, various polymer compounds such as acrylic resin, styrene resin, phenol resin, fluororesin, silicone resin, trialkoxysilane condensate can be used. By coating the surfaces of the magnetic particles with these resins, the hydrophobicity necessary for adsorbing hydrophobic substances such as fats and oils can be obtained. This makes it possible to adsorb hydrophobic substances in water not only in a liquid state but also in a solid state. For example, solid fats and oils that are in a solid state at room temperature such as lard can be adsorbed.

  The inventors of the present application have confirmed by experiments that the magnetic particles precipitated in water by synthesis are approximately 0.1 to 5 μm. In addition, it has been confirmed that the particle diameters of metal particles contained in metal polishing wastewater and processing wastewater that are difficult to remove fall within the same range. As a method of capturing magnetic particles in this range, the particle size of the filter aid is limited so that solid-liquid separation can be easily performed with a filter having a specific pore size. By filtering the magnetic particles together with such a filter aid, the magnetic particles are trapped in the gaps between the filter aid particles, and the magnetic particles can be separated.

(filter)
As the filter, filter cloth, metal mesh, porous ceramic and porous polymer can be used. Among these, a filter cloth is particularly preferable for the filter. The filter cloth is preferably made of a woven fabric woven with synthetic fiber threads such as polypropylene, nylon, and polyester. Here, the “woven fabric” means a fiber having a certain degree of hardness and a smooth surface. The fiber hardness (waist strength) is clogged if it is too soft, so it should be hard to some extent. It is important that the surface roughness of the fabric as a woven fabric is not rough, and is preferably smooth and smooth to some extent.

  The material of the filter in the embodiment described herein is, for example, preferably that the filter cloth is a woven fabric in which the fibers are woven in a weaving manner such as satin weaving, twill weaving, plain weaving, double weaving, etc. Most preferred is a woven or twilled woven fabric. The filter cloth materials include Pyrene (registered trademark of Mitsubishi Rayon Polypropylene Fiber), Tetoron (trade name of Toray and Teijin's polyester fibers), Nylon (a general term for polyamide fibers including nylon 6,6 and nylon 6) It is preferable to use a synthetic fiber such as

  The pore diameter of the filter includes known ones and unknown ones such as a metal mesh sieve. If the pore size of the filter is unknown, use the mercury intrusion method. The mercury pressure method uses the high surface tension of mercury to apply pressure to inject mercury into the pores of the powder, and obtains the specific surface area and pore distribution from the pressure and the amount of mercury injected. is there.

(Microfiltration membrane)
A microfiltration membrane (MF membrane) made of a porous polymer membrane is preferably used as the filter. Here, the “microfiltration membrane” refers to a membrane having pores having a pore diameter of 50 nm to 10 μm (10 ⁴ nm).

  The relationship between the filter aid and the filter constituting the precoat layer will be further described with reference to FIGS.

  As shown in FIG. 4 (a), the suspension is supplied to the filter 33 of the solid-liquid separator at a predetermined pressure (0.2 to 0.3 MPa) of 0.5 MPa or less, and as shown in FIG. 4 (b). A filter aid 55 is deposited on 33 to form a precoat layer. Next, as shown in FIG. 4 (c), the water to be treated is supplied to the filter 33 at a predetermined pressure (0.2 to 0.3 MPa) of 0.5 MPa or less, and as shown in FIG. The magnetic adsorbent 50 is deposited on the filter to form a filter aid / magnetic adsorbent bilayer 56. Next, as shown in FIG. 4E, peeling water is sprayed from the side of the solid-liquid separator to peel the deposited double layer 56 from the filter 33.

  As shown in FIG. 5, the filter aid constituting the deposited double layer 56 is such that the particle spacings C1 to C3 of the inorganic particles 55 on the filter 33 satisfying the above formula (1) satisfy the above formulas (1) and (3). The volume-converted particle diameter B of the inorganic particles 55 satisfies the above formula (2).

  When the relationship of C <A where the inorganic particles 55 and the filter 33 do not satisfy the above formula (1) is satisfied, the particles that can be captured by the filter 33 are smaller than the particles that can capture the laminated filter aid, and the filter 33 itself is clogged. May end up.

  On the other hand, if the value of the inter-particle spacing C is less than 0.2 μm, the pore size between the filter aids is too small to obtain an effective amount of water. On the other hand, if the interparticle spacing C exceeds 15 μm, the precoat layer may not have sufficient interparticle spacing C to capture the magnetic particles.

  The particle spacing of the filter aid will be described with reference to FIG.

In the embodiment described here, in the distribution of the particle spacing C of the filter aid, the pore size distribution width D _S smaller than the mode particle spacing Cp is larger than the mode particle spacing Cp. Preferably it is wider than _L.

  In such a non-normal distribution or extreme value distribution, since there is a wide distribution from a small interval to a large interval between particles, for example, as shown in FIG. Get caught. At this time, even if the mutual intervals C1 to C3 of the filter aid particles 55 are blocked by the magnetic particles 50, the surrounding filter aid particles 55 are deformed by the magnetic particles 50 being sandwiched between the filter aid particles 55. As a result, the open pores of the filter aid particles 55 expand, and the magnetic particles 50 are fitted into the expanded open pores. This action improves the ability of the filter aid particles 55 to capture the magnetic particles 50 having a diameter smaller than the most frequent particle spacing Cp. The mutual interval C of the filter aid particles 55 can be measured using, for example, Autopore IV 9500 series (trade name) manufactured by Shimadzu Corporation.

In the distribution of the particle spacing of the filter aid constituting the precoat layer, when the most frequent particle spacing is C1, the 90% diameter is C2, and the 10% diameter is C3, the relationship of logC2-logC1 <logC1-logC3 is satisfied. It is preferable. Here, “90% diameter” means that the cumulative distribution has a diameter of 90%, and “10% diameter” means that the cumulative distribution has a diameter of 10%. In other words, in the distribution of the particle spacing of the filter aid, the distribution width D _S of the particle spacing smaller than the mode particle spacing Cp is wider than the distribution width D _{L of the} particle spacing larger than the mode particle spacing Cp. Means. That is, the particle dispersion (variation) is increased when the interparticle pore size is smaller, and the particle dispersion (variation) is decreased when the interparticle pore size is larger. In such a distribution (a non-normal distribution that deviates from the normal distribution), since there is a wide distribution from the small gaps between the particles, even if fine particles in the water are first caught in the small gaps, The particles can be captured by the open pores whose diameter has been changed by sandwiching the particles. This action improves the ability to capture particles having a diameter smaller than the mode interparticle pore diameter. Accordingly, those having such a pore size distribution between particles have a wide distribution in pore sizes smaller than the mode. When the particles have a wide distribution in such a small particle diameter, for example, small particles can be captured, and the captured small particles narrow the pore diameter, so that even smaller particles can be removed. Conversely, if there are many pore sizes between particles larger than the mode, the probability of capturing small particles first decreases, and the capture rate of small particles may decrease.

(Water treatment system)
Hereinafter, a water treatment system used in the water treatment method of the present embodiment will be described with reference to FIG.

  The water treatment system 1 includes a water storage tank 2, a solid-liquid separation device 3, a magnetic separation tank 4, a filter aid tank 5, a stirring and mixing tank (mixing tank) 6, a pretreatment agent addition device 7, a filter aid addition device 8, A treatment water supply source and a magnetic powder concentrated water storage tank (not shown) are provided. These devices and apparatuses are connected to each other by a plurality of piping lines L1 to L12. Various pumps P1 to P9, valves V1 to V4, measuring instruments and sensors (not shown) are attached to the piping lines L1 to L12. Detection signals are input from these measuring instruments and sensors to the input section of a controller (not shown), and control signals are output from the output section of the controller to the pumps P1 to P9 and valves V1 to V4, respectively, and their operations are controlled. It has become so. As described above, the entire water treatment system 1 is comprehensively controlled by a controller (not shown).

  A magnetic adsorbent supply tank, an adsorption tank, a desorption tank, a magnetic separation tank, and a treated water supply pump (not shown) are provided on the upstream side of the inflow line L1 of the water storage tank 2, respectively. A magnetic adsorbent in the form of a slurry or suspension is supplied from the magnetic adsorbent supply tank into the adsorption tank. In the adsorption tank, fats and oils contained in factory wastewater are adsorbed by a magnetic adsorbent (magnetic powder), and the water to be treated is sent from the adsorption tank to the desorption tank. In the desorption tank, the adsorbed fats and oils are desorbed from the magnetic adsorbent with a hydrophilic organic solvent and sent to the magnetic separation tank. In the magnetic separation tank, the magnetic adsorbent is magnetically separated from the sewage containing the desorbed oil and fat, and the sewage containing the desorbed oil and fat is discharged from the magnetic separation tank, while water is added to the separated magnetic adsorbent to obtain a desired coating. Treated water is prepared. And the to-be-processed water containing a magnetic powder is sent to the water storage tank 2 from the magnetic separation tank via the line L1 by the drive of the to-be-processed water supply pump.

  The water storage tank 2 is a tank for temporarily storing water to be treated containing magnetic powder flowing in from the line L1, and includes a screw type agitator 21. A pretreatment agent is added to the water to be treated in the water storage tank 2 from the pretreatment agent addition device 7 as necessary. The pretreatment agent is added to the water to be treated in order to reduce damage to the inner surface of the equipment and piping and the filter 33 from the water to be treated. In particular, the pretreatment agent reduces damage to the filter 33 from the water to be treated. As the pretreatment agent, a pH adjusting agent such as an acid or an alkali, or an oxidizing agent or a reducing agent can be suitably used. For example, when the water to be treated is acidic, sodium hydroxide is added as a pretreatment agent to neutralize the water to be treated. When the water to be treated is alkaline, hydrochloric acid is added as a pretreatment agent to neutralize the water to be treated. In the embodiment described here, no flocculant is added as a pretreatment agent. In this embodiment, the filter aid used as the precoat layer forming material is designed so that the magnetic powder can be recovered without using a flocculant.

  The solid-liquid separator 3 incorporates a filter 33 that partitions the interior into an upper space 31 and a lower space 32. The filter 33 is a microfiltration membrane that is mounted substantially horizontally in the container of the solid-liquid separator 3. The upper space 31 of the solid-liquid separation device is connected to the water storage tank 2 via a to-be-treated water supply line L2 having a pressure feed pump P1. Further, a peeling water supply line L31 having a pump P3 and a peeled material discharge line L4 are connected to the side portions of the upper space 31, respectively.

  On the other hand, the lower space 32 of the solid-liquid separator is connected to a treated water distribution line L3 having three three-way valves V1, V2, and V3. At the first three-way valve V1, the above-described separation water supply line L31 branches from the treated water distribution line L3. A treated water line L32 having a pump P2 branches off from the treated water distribution line L3 at the second three-way valve V2. At the third three-way valve V3, two lines L33 and L34 are branched from the treated water distribution line L3. One branch line L33 has a pump P4 and is connected to a magnetic separation tank 4 described later. The other branch line L34 has a pump P5 and is connected to a stirring and mixing tank 6 described later.

  The magnetic separation tank 4 has a screw type agitator 41 for agitating the washing discharged water received from the upper space 31 of the solid-liquid separation device through the peeled material discharge line L4, and also contains the magnetic adsorbent in the water and the filter aid. A bar magnet 42 for separating the agent is provided. The bar magnet 42 is housed in a cylindrical protective tube provided in the tank 4 while being supported by a cylinder mechanism (not shown) so as to be movable up and down.

  In addition to the separated product discharge line L4, a treated water utilization line L33, an industrial water supply line L11, and a tap water supply line L12 are connected to the upper part of the magnetic separation tank 4, respectively. A part of the treated water that has passed through the filter 33 of the solid-liquid separator is introduced into the magnetic separation tank 4 from the line L33. Further, from the line L11, industrial water of a supply source (not shown) is introduced into the magnetic separation tank 4. Further, tap water is introduced into the magnetic separation tank 4 from the line L12.

  On the other hand, a magnetic powder concentrated water discharge line L8 and a filter aid return line L5 are connected to the lower part of the magnetic separation tank 4, respectively. The discharge line L8 is configured to discharge concentrated water containing magnetic powder at a high concentration from a magnetic separation tank 4 to a storage tank (not shown) by driving a pump P9. The return line L5 is configured to return the filter aid separated from the magnetic separation tank 4 to the filter aid tank 5 by driving the pump P6.

  The filter aid tank 5 has a built-in purifier for removing foreign substances from the water containing the used filter aid. The filter aid tank 5 regenerates the used filter aid introduced from the magnetic separation tank 4 with a purifier, and the regenerated filter aid is agitated via the filter aid supply line L6 by driving the pump P7. The mixing tank 6 is supplied.

  The stirring and mixing tank 6 has a screw type stirrer 61, and water is added as a dispersion medium to the filter aid supplied from the filter aid tank 5 and stirred and mixed to prepare a suspension containing the filter aid. To do. The stirring and mixing tank 6 is replenished with fresh calcite particles unused as a filter aid from a filter aid addition device 8. A treated water utilization line L34 is connected to the upper part of the stirring and mixing tank 6, and a part of the treated water that has passed through the filter 33 of the solid-liquid separator is supplied to the stirring and mixing tank 6. It has come to be used.

  Further, a filter aid suspension supply line L7 having a pump P8 communicates with an appropriate place of the stirring and mixing tank 6. The filter aid suspension supply line L7 joins at an appropriate position of the treated water supply line L2. A mixture (suspension) containing the filter aid from the supply line L7 is added to the water to be treated flowing through the water supply line L2. A check valve V4 is attached to the suspension supply line L7 so as to prevent backflow of the water to be treated from the water storage tank 2 to the stirring and mixing tank 6 through the line L2.

(Water treatment method)
Next, a water treatment method using the above apparatus will be described with reference to FIGS. In the embodiment described here, after separating and removing oils and fats from factory wastewater using a magnetic adsorbent, a case where the used magnetic adsorbent is separated and recovered by a precoat method using a filter aid is described. .

  Factory wastewater, which is raw water, is introduced into an adsorption tank (not shown). This industrial wastewater contains a lot of fats and oils as impurities. An appropriate amount of magnetic adsorbent (magnetic powder) is added from an unillustrated tank to the adsorbing tank, mixed with stirring, and fats and oils contained in the raw water are adsorbed to the magnetic adsorbent (step S1). Next, water containing fat and oil adsorption magnetic powder is supplied from an adsorption tank to a desorption tank (not shown), and a hydrophilic organic solvent is brought into contact with the fat and oil adsorption magnetic powder in the desorption tank, and magnetic properties are obtained by the action of the organic solvent. The adsorbed oil and fat is desorbed from the powder (step S2).

  Next, water containing the desorbed oil and fat and magnetic powder is sent from the desorption tank to the magnetic separation tank, and the magnetic powder is magnetically separated from the waste water containing the desorbed oil and fat in the magnetic separation tank (step S3). The sewage containing the desorbed oil and fat is discharged from the magnetic separation tank, and only the magnetic powder is left in the magnetic separation tank (step S4). As a result, the magnetic powder is physically separated from the water containing fats and oils. Next, tap water is supplied as a dispersion medium to the magnetic powder in the desorption tank, and the magnetic powder and water are stirred and mixed to prepare water to be treated containing magnetic powder in the form of slurry or suspension (step S5). .

  On the other hand, a filter aid is supplied from the filter aid tank 5 and / or the filter aid addition device 8 to the stirring and mixing tank 6, and an appropriate amount of water is added thereto, and the filter aid and water are stirred in the stirring and mixing tank 6. Mix and adjust the suspension containing the filter aid (step S6). For example, a slurry containing calcium carbonate fine particles having an average particle diameter of 17 μm is supplied as a filter aid. The filter aid contained in the suspension has a concentration capable of forming a desired precoat layer on the filter 33 of the solid-liquid separator 3. The content of the filter aid in the suspension is preferably in the range of 10,000 to 200,000 mg / L, for example.

  Next, the pumps P8 and P1 are started, the suspension is pumped from the stirring and mixing tank 6 to the solid-liquid separator 3, and the suspension is supplied to the filter 33 (FIG. 4 (a)). The filter aid in the suspension is filtered by the filter 33, whereby a precoat layer of the filter aid 55 is formed on the filter 33 as shown in FIG. 4B (step S7). In this case, the supply of the suspension to the filter 33 is performed by applying a pressure of 0.5 MPa or less by the pressure pump P1. Furthermore, it is more preferable that the pressure of the suspension applied to the filter 33 is in the range of 0.2 to 0.3 MPa. At this time, the liquid component of the suspension quickly permeates through the filter 33 due to the synergistic action of the pressure and gravity generated by driving the pressure pump P, and the filter aid, which is a solid component in the suspension, is captured by the filter 33. As a result, a precoat layer having a uniform thickness is formed on the filter 33. In addition, it is preferable to make the thickness of the precoat layer of a filter aid into the range of 0.5-10 mm on average.

  In the precoat layer forming step S7, the filter 33 is attached so as to close the inlet of the solid-liquid separator 3, so that the pressure drop of the suspension in the solid-liquid separator 3 is reduced as much as possible. Filter the suspension by Specifically, the upper space 31 defined by the container wall of the solid-liquid separation device 3 and the filter 33 is made smaller, and the pressurized suspension is pushed into the small space 31 with a small volume, so that the filter Separation of solid (filter aid) and liquid by 33 is promoted. At this time, the liquid component of the suspension quickly permeates through the filter 33 due to the synergistic action of the pressure and gravity generated by driving the pressure pump P1, and the solid component (filter aid) in the suspension is captured by the filter 33. As a result, a precoat layer of a filter aid is formed on the filter 33.

  A treated water supply pump (not shown) is activated, and treated water containing magnetic powder is introduced into the water storage tank 2 from a magnetic separation tank (not shown) (step S8). Next, the pH of the water to be treated in the water tank 2 is measured by a pH sensor (not shown), and when the water to be treated largely deviates from neutrality, the pretreatment agent addition device 7 supplies the water to be treated in the water tank 2 to the front. A treatment agent is added to adjust the pH of the water to be treated (step S9).

  Next, the pump P1 is activated, and the water to be treated is supplied from the water storage tank 2 to the solid-liquid separator 3 (step S10). Thereby, the magnetic particles 50 in the water to be treated are filtered, the magnetic particles 50 are deposited on the precoat layer of the nonmagnetic inorganic particles 55, and the nonmagnetic inorganic particles 55 are deposited on the filter 33 as shown in FIG. / A deposited double layer 56 in which magnetic particles 50 are laminated is formed (step S11). In this case, the filter aid (nonmagnetic inorganic particles) 55 constituting the deposited double layer 56 is such that the particle intervals C1 to C3 satisfy the above formulas (1) and (3) on the filter 33 satisfying the above formula (1). Each satisfies and the volume conversion particle diameter B satisfies the above formula (2). When the inorganic particles 55 and the filter 33 have a relationship of A ≦ C satisfying the above formula (1), the particles that can be captured by the filter 33 are smaller than the particles that can capture the laminated filter aid 55 as shown in FIG. Therefore, the filter 33 is not clogged.

  Next, the pump P3 is activated, and peeling water is sprayed from the side nozzle of the solid-liquid separator 3 onto the deposited double layer 56 on the filter 33, and as shown in FIG. Is peeled off (step S12). Further, the water supply pressure by the pump P3 is increased, the spraying force of the stripping water sprayed from the nozzle is increased, and the stripped material is discharged from the upper space 31 of the solid-liquid separator. The discharged exfoliation is introduced into the magnetic separation tank 4 through the line L4 (step S13).

  When the inside of the magnetic separation tank 4 is filled with the exfoliated material and an appropriate amount of tap water and / or treated water is introduced into the magnetic separation tank 4, the screw type agitator 41 is activated to agitate the exfoliated material and the water. Next, the bar magnet 42 is lowered by a cylinder mechanism (not shown), the bar magnet 42 is inserted into the protective tube, and a magnetic field is applied to the stirring suspension. Since the magnetic particles 50 are attracted to the protective tube by the magnetic force of the magnet 42, the magnetic particles 50 are magnetically separated from the suspension.

  The stirring of the mixed water in the magnetic separation tank 4 is stopped, the pump P6 is started in a state where the magnetic particles 50 are adsorbed and held on the magnet protective tube, and the water containing the filter aid 55 is discharged from the magnetic separation tank 4 ( Step S14). Thereby, the magnetic particles 50 are separated from the filter aid 55 in water. In this separation step S14, since the specific gravity difference between the filter aid 55 and the magnetic powder 50 is large, the separation of both is further facilitated. The filter aid 55 is returned to the filter aid tank 5 together with the discharged water, regenerated in the filter aid tank 5, sent from the filter aid tank 5 to the stirring and mixing tank 6, and reused for the formation of the precoat layer. (Step S14 → Step S6). Thus, the filter aid 55 can be repeatedly used in the cycle of precoat layer formation → magnetic powder capture → solid-liquid separation → magnetic separation / recovery → precoat layer formation.

  In the magnetic separation tank 4, after discharging the filter aid-containing water, the magnet is raised by the cylinder mechanism, the magnet is withdrawn from the protective tube, the magnetic field applied to the magnetic particles 50 is lost, and the magnetic particles are removed from the magnet protective tube. Drop 50.

  Next, water is supplied into the magnetic separation tank 4 through at least one of the lines L11, L12, and L33, and the magnetic particles 50 and the water in the magnetic separation tank are stirred and mixed by the screw stirrer 41 so that the magnetic particles are mixed. Magnetic powder concentrated water containing 50 in high concentration is prepared, and this magnetic powder concentrated water is discharged from the magnetic separation tank 4 (step S15). The discharged magnetic powder concentrated water is sent to a magnetic powder tank (not shown) and reused as an adsorbent for adsorbing fats and oils (step S15 → step S1). In this way, the magnetic adsorbent 50 can be repeatedly used in the cycle of oil / fat adsorption → oil / fat desorption → solid-liquid separation → magnetic separation / recovery → oil / fat adsorption.

  Examples and comparative examples will be described below.

Example 1
A test for separating and recovering various magnetic adsorbents was performed using the processing apparatus of FIG. A suspension containing 1000 mg / liter of nickel fine particles was prepared as the water to be treated. Nickel fine particles as a magnetic adsorbent had an average particle size of about 1 μm. As the filter 33, a filter cloth having a most frequent pore diameter A of 7 μm was used. As the filter aid 55, a powder obtained by pulverizing calcite with a ball mill and selecting so that the volume-converted average particle diameter B is 13 μm was used. Wind power was used to select calcite powder used as filter aid 55. The selected calcite powder was added to water and mixed by stirring to prepare a suspension containing calcite powder. This suspension was supplied to the solid-liquid separator 3 to form a precoat layer on the filter 33. The particle spacing C of the calcite particles constituting the precoat layer was about 4.1 μm. As shown in FIG. 6, the distribution of the particle spacing C of the filter aid was wider when the particle spacing was smaller than the most frequent particle spacing of 4.1 μm.

  First, water to be treated was introduced into the water storage tank 2 and stirred uniformly with a screw stirrer 21. Next, suspension-like or slurry-like calcite particles are supplied from the filter aid tank 5 and the filter aid supply device 8 into the mixing tank 6, diluted with water, and stirred by a screw stirrer 61. A suspension containing about 5% by mass of calcite particles was prepared. This suspension was supplied to the solid-liquid separator 3, and calcite particles 55 were deposited on the filter 33 to form a precoat layer having a thickness of about 1 mm.

  Next, the water to be treated is supplied from the water storage tank 2 to the solid-liquid separator 3, nickel particles 50 are further deposited on the precoat layer of the calcite particles 55, and nickel particles 50 / calcite particles 55 are laminated. A deposited bilayer 56 was formed. As a result, almost all of the nickel particles 50 could be solid-liquid separated from the water to be treated.

  Next, part of the treated water was returned to the upper space 31, and this was sprayed from the nozzle as stripping water, so that the deposited double layer 56 was stripped from the filter 33. This peeled material was sent to the magnetic separation tank 4, tap water was added, and while stirring with a screw stirrer 41, the magnet 42 was inserted into a protective tube in the tank and a magnetic force was applied. The nickel particles 50 were adsorbed on the outer periphery of the magnet protective tube by the magnetic force of the magnet 42, and the nickel particles 50 were magnetically separated from the calcite particles 55 in the peeled material. As a result, a slurry of calcite particles 55 was obtained at the bottom of the magnetic separation tank 4.

  The slurry of calcite particles 55 was discharged from the magnetic separation tank 4 and transferred to the filter aid tank 5. Next, when a part of the treated water was introduced into the magnetic separation tank 4 and the magnetic force applied to the magnet 42 was turned off and stirred, a concentrated solution of nickel particles was obtained. This concentrated solution was recovered using pump P9.

  The filter aid recovered in the filter aid tank 5 was sent again to the mixing tank 6 and could be used again.

(Example 2)
Example except that the average particle diameter of nickel particles to be treated was 4 μm, the average pore diameter of filter cloth was 15 μm, the average particle diameter of calcite particles was 42 μm, and the average pore diameter between filter aids was 14 μm. The nickel particles and calcite particles were separated and recovered under the same conditions as in 1. As a result, the entire amount of nickel particles was separated and recovered, and calcite particles were also separated and recovered. The recovered nickel particles and calcite particles could be reused repeatedly.

(Comparative Example 1)
When the test was performed under the same conditions as in Example 1 except that the filter surface of the filter 33 of the solid-liquid separator 3 was changed from horizontal to vertical, the nickel particles were not sufficiently solid-liquid separated from the water to be treated. It was confirmed that a large amount of nickel particles was mixed in the permeated water (treated water) and was washed out of the system without being separated and recovered.

(Example 3)
A liquid containing magnetite particles (magnetic adsorbent) having an average particle diameter of 0.1 μm obtained by oxidizing a solution containing iron oxide as water to be treated at a temperature of 60 ° C. or higher using the same apparatus as in Example 1. Produced. A microfiltration membrane having an average pore diameter of 1 μm was prepared as a filter. Further, calcite particles having an average particle diameter of 2 μm and an average pore diameter of 0.3 μm were prepared as filter aids. The test was conducted in the same manner as in Example 1. As a result, the entire amount of magnetite particles was separated and recovered from the water to be treated, and calcite particles were also separated and recovered. The recovered magnetite particles and calcite particles could be reused repeatedly.

Example 4
The test was conducted in the same manner as in Example 1 except that the filter aid was changed from calcite to a calcium carbonate reagent (manufactured by Wako Pure Chemical Industries), the average particle size was 17 μm, and the pore size between the filter aids was 6.8 μm. It was. As a result, the entire amount of nickel particles was separated and recovered from the water to be treated, and calcium carbonate particles were also separated and recovered. Moreover, the recovered nickel particles and calcium carbonate particles could be reused repeatedly.

(Example 5)
The test was conducted in the same manner as in Example 1 except that the filter aid was changed from calcite to spherical fused silica, the average particle size of the filter aid was 13 μm, and the pore size between the filter aids was 4.0 μm. As a result, the entire amount of nickel particles was separated and recovered from the water to be treated, and spherical fused silica particles were also separated and recovered. The recovered nickel particles and spherical fused silica particles could be reused repeatedly.

1 ... Water treatment system, 2 ... Water tank, 21 ... Screw type stirrer,
3 ... Solid-liquid separator (membrane filter), 33 ... Filter (filter cloth),
4 ... magnetic separation tank, 5 ... filter aid tank,
6 ... stirring and mixing tank (mixing tank), 61 ... screw type stirrer,
7 ... Pretreatment agent addition device, 8 ... Filter aid addition device,
50 ... magnetic adsorbent (magnetic primary particles, magnetic powder), 51 ... magnetic particles, 52 ... coating material,
53 ... Magnetic adsorbent (aggregates of magnetic primary particles, aggregated magnetic powder),
55 ... Filter aid (non-magnetic inorganic particles),
P1-P9 ... Pump, V1-V4 ... Valve,
L1 ... treated water introduction line, L3 ... treated water line, L31 ... peeling water supply line (first treated water utilization line), L32 ... treated water carry-out line, L33 ... second treated water utilization line, L34 ... first 3 treated water utilization line,
L4 ... exfoliation discharge line, L5 ... filter aid return line, L6 ... filter aid supply line, L7 ... mixing line, L8 ... magnetic powder concentrated water discharge line, L9 ... pretreatment agent supply line, L10 ... magnetic powder supply line.

Claims (7)

(A) adding a magnetic adsorbent to the raw water, adsorbing foreign matter contained in the raw water to the magnetic adsorbent,
(B) desorbing foreign matter adsorbed from the magnetic adsorbent;
(C) magnetically separating the magnetic adsorbent from water containing desorbed foreign matter,
(D) water is added to the separated magnetic adsorbent to produce water to be treated containing the magnetic adsorbent at a desired concentration;
(E) On the other hand, preparing a filter aid containing non-magnetic inorganic particles, and preparing a solid-liquid separation device having a flat filter arranged so that the filter surface is substantially horizontal,
(F) adding a dispersion medium to the filter aid and stirring and mixing, thereby preparing a suspension containing the filter aid;
(G) The suspension is pumped to the solid-liquid separator, the suspension is filtered by the filter, and the filter aid is deposited on the filter, whereby the filter aid is deposited on the filter. In this case, the most frequent pore diameter of the filter is A, the volume conversion average particle diameter of the filter aid is B, and the particle spacing of the filter aid constituting the precoat layer is C. The filter and filter aid satisfy the relationship of A ≦ C, 2 ≦ B ≦ 50 μm, and 0.2 ≦ C ≦ 15 μm,
(H) The water to be treated produced in the step (d) is passed through the precoat layer and the filter, the magnetic adsorbent is separated from the water to be treated by solid-liquid separation, and the magnetic adsorbent is placed on the precoat layer. Deposit, thereby forming a deposited bilayer on which the filter aid and magnetic adsorbent are laminated on the filter;
(I) spraying peeling water on the deposited double layer, peeling the deposited double layer from the filter, thereby providing a peeled liquid containing a magnetic adsorbent, a filter aid, and peeling water;
(J) Meanwhile, a magnetic separation tank having a magnetized member for adsorbing the magnetic adsorbent is prepared,
(K) The exfoliated liquid is supplied from the solid-liquid separator to the magnetic separation tank, the exfoliated liquid is stirred and mixed in the magnetic separation tank, and the magnetic adsorbent contained in the exfoliated liquid is applied to the magnetizing member. While adsorbing and adsorbing the magnetic adsorbent to the magnetized member, the filter aid-containing liquid containing the filter aid is discharged from the magnetic separation tank, and thereby the filter aid in the exfoliated liquid and Magnetically separated from the magnetic adsorbent,
(L) Reusing the filter aid-containing liquid discharged in the step (k) in the step (e),
(M) Release the adsorption of the magnetic adsorbent by the magnetized member, add a dispersion medium to the desorbed magnetic adsorbent to produce a magnetic adsorbent-containing liquid, and discharge the magnetic adsorbent-containing liquid from the magnetic separation tank And
(N) Reusing the magnetic adsorbent-containing liquid discharged in the step (m) in the step (a).
A water treatment method characterized by the above. In the distribution of particle spacing C of the filter aid, characterized in that towards the distribution width D _S of particle spacing Cp is smaller than the pore diameter of the modal it is wider than the distribution width D _L of pore diameter Cp larger pore diameter most frequent The method according to claim 1.   In the distribution of the particle spacing C of the filter aid constituting the precoat layer, when the most frequent particle spacing is C1, the cumulative distribution is 90%, the C2 is the cumulative particle spacing, and the cumulative distribution is 10%, the C3 is the particle spacing. The method according to claim 1, wherein a relationship of logC2−logC1 <logC1−logC3 is satisfied.   The method according to any one of claims 1 to 3, wherein the filter aid comprises particles of an inorganic compound containing calcium or silicon.   5. A method according to any one of the preceding claims, wherein the filter comprises a fabric made of a woven fabric of yarn.   The method according to any one of claims 1 to 4, wherein the filter is a microfiltration membrane made of a porous polymer membrane.   The method according to any one of claims 1 to 6, wherein a pretreatment agent is added to the water to be treated in the step (d).

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