JP2009072766A - Water treating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treating method suitable for regenerating sewage like factory wastewater containing biodegradable organic matter as a main component, causing less fouling in a nanofiltration membrane or a reverse osmosis membrane, like particularly an organic acid or hydrocarbon, by the nanofiltration membrane or reverse osmosis membrane, and a water treating method suppressing fouling by organism metabolite at the nanofiltration membrane and/or reverse osmosis membrane, and keeping a biological treatment facility compact, in this water treating method. <P>SOLUTION: Water 21 to be treated is subjected to membrane separation using the nanofiltration membrane and/or reverse osmosis membrane and separated into permeated water and condensed water, and the condensed water is subjected to a biological treatment for solid-liquid separation. A membrane separation activated sludge method is used as a method for biological treating for solid-liquid separation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a water treatment method for regenerating factory waste water or the like with a nanofiltration membrane or a reverse osmosis membrane.

  2. Description of the Related Art Conventionally, there is a water treatment facility for purifying sewage such as sewage and industrial wastewater as shown in FIG. In FIG. 2, the sewage 2 supplied to the aeration tank 1 is sent to the sedimentation basin 3 as a mixed solution together with activated sludge after organic matter in the sewage is oxidatively decomposed by microorganisms in the aeration tank. In addition, in the sedimentation basin 3, the activated sludge 4 and the supernatant water (secondary treated water) 5 are separated, the activated sludge 4 is returned to the aeration tank 1, and the secondary treated water 5 is condensed into the coagulating sedimentation basin 6 Sent to. In this agglomeration sedimentation basin 6, suspended matters contained in the secondary treated water 5 are mostly flocked due to the aggregating action of the aggregating agent, but some flocs that could not be removed here follow. It is removed by the filtration layer of the sand filtration pond 7 to become the tertiary treated water 8 and sent to the reverse osmosis membrane separation device 9. In the reverse osmosis membrane separation device 9, the liquid that permeates the reverse osmosis membrane 10 is taken out as clear water 11 from which salts and chromaticity components have been removed, and the salts and chromaticity that have not permeated the reverse osmosis membrane 10. The concentrated liquid 12 containing the components is separated and discharged.

  In recent years, a membrane separation activated sludge method in which a precision membrane or an ultrafiltration membrane module is installed in a biological treatment tank and biological treatment and solid-liquid separation can be performed simultaneously has been developed and is becoming popular. A sewage and wastewater treatment method has been proposed in which treated water treated using this membrane separation activated sludge method is subjected to membrane separation treatment using a reverse osmosis membrane or the like (see, for example, Patent Document 1).

  When membrane separation treatment is performed using a reverse osmosis membrane, the water to be treated is separated into permeated water that has permeated through the membrane and concentrated water that has not permeated through the membrane. Therefore, a treatment method has also been proposed in which the concentrated water generated in the membrane separation treatment using the reverse osmosis membrane is returned to the preceding membrane separation activated sludge tank (biological treatment tank).

  However, in the wastewater treatment method in which the membrane separation treatment is performed by the reverse osmosis membrane after the membrane separation activated sludge method, the biological metabolite contained in the permeated water obtained by the membrane separation activated sludge method clogs the reverse osmosis membrane. There was a so-called fouling problem.

In addition, the entire amount of wastewater generated must be biologically treated, and the number of activated sludge tanks (biological treatment tanks) required for treatment increases, which complicates operation and requires not only a large site area but also construction costs, There was a problem that the running cost was high.
JP-A-4-305287

  In particular, the present invention is a water treatment method for regenerating and treating factory wastewater with a nanofiltration membrane or a reverse osmosis membrane, which suppresses fouling caused by biological metabolites in the nanofiltration membrane or reverse osmosis membrane, and makes the biological treatment equipment compact. The purpose is to suppress it.

The present invention for solving this problem has the following configuration.
(1) The water to be treated is separated into permeated water and concentrated water by membrane separation treatment using a nanofiltration membrane and / or a reverse osmosis membrane, and the concentrated water is biologically treated and subjected to solid-liquid separation treatment. Water treatment method.
(2) The method according to (1), wherein the biological treatment and solid-liquid separation method is a membrane separation activated sludge method.
(3) The above (1) or (1), wherein at least a part of the treated water obtained by the biological treatment and the solid-liquid separation treatment is subjected to membrane separation treatment with a nanofiltration membrane and / or a reverse osmosis membrane in the subsequent stage. The water treatment method as described in 2).
(4) The water treatment method according to (3) above, wherein the latter nanofiltration membrane and / or reverse osmosis membrane is a low fouling reverse osmosis membrane.
(5) At least a part of the treated water obtained by the biological treatment and solid-liquid separation treatment is refluxed as water to be treated in the nanofiltration membrane and / or reverse osmosis membrane in the previous stage of biological treatment. The water treatment method according to (1) or (2) above.
(6) After at least a part of the treated water obtained by the biological treatment and the solid-liquid separation treatment is subjected to any one or more of activated carbon treatment, ultrafiltration membrane treatment and ozone treatment, The water treatment method according to the above (1) or (2), wherein the nanofiltration membrane and / or the reverse osmosis membrane before treatment is refluxed as water to be treated.

  According to the method of the present invention, sewage such as factory waste water, which is mainly composed of biodegradable organic substances that are unlikely to cause fouling of nanofiltration membranes or reverse osmosis membranes, such as organic acids and hydrocarbons, is subjected to nanofiltration. In a water treatment method in which regeneration treatment is performed using a membrane or a reverse osmosis membrane, fouling of the nanofiltration membrane or the reverse osmosis membrane can be suppressed, and the biological treatment facility can be suppressed in a compact manner.

  The water treatment method of the present invention is particularly suitable for treating sewage such as industrial wastewater, which is mainly composed of biodegradable organic substances that are unlikely to cause fouling of nanofiltration membranes or reverse osmosis membranes, such as organic acids and hydrocarbons. The sewage is separated into permeated water and concentrated water using a nanofiltration membrane and / or a reverse osmosis membrane, and the concentrated water is subjected to biological treatment and solid-liquid separation treatment.

  In the present invention, since biological treatment is not performed before the nanofiltration membrane and / or reverse osmosis membrane, fouling of the nanofiltration membrane and / or reverse osmosis membrane due to biological metabolites can be suppressed. Further, in the present invention, only the concentrated water after being separated into permeated water and concentrated water by the nanofiltration membrane and / or reverse osmosis membrane is biologically processed, so that the biological treatment facility can be kept compact.

  In FIG. 1, an example of the schematic of the water treatment apparatus used for the water treatment method of this invention is shown. However, the water treatment method of the present invention is not limited to this embodiment.

  The water 21 to be treated is pumped to the nanofiltration membrane and / or the reverse osmosis membrane 23 by the pressure pump 22 to obtain the permeated water 24 and the concentrated water 25. The concentrated water 25 obtained by the nanofiltration membrane and / or the reverse osmosis membrane 23 is sent to the biological treatment tank 27 for biological treatment and solid-liquid separation by the filtration membrane 26.

  The treated water 21 of the present invention refers to the supply water supplied to the nanofiltration membrane and / or the reverse osmosis membrane 23. The properties of the water 21 to be treated are not particularly limited, but it is difficult to foul with a nanofiltration membrane or a reverse osmosis membrane such as an organic acid or a hydrocarbon, and a biodegradable organic substance is a main component. preferable. In addition, raw water such as waste water that has been pretreated such as MF membrane treatment, UF membrane treatment, activated carbon treatment, etc. is treated water 21 to reduce fouling of the nanofiltration membrane and / or reverse osmosis membrane 23. Also good.

  In order to improve the handleability and physical durability of the filtration membrane, the device of the filtration membrane 26 installed in the tank is, for example, a flat membrane element in which a filtration membrane is bonded to both sides of the frame with a filtrate channel material sandwiched between them. It is desirable to have a structure. The device structure of the filtration membrane 26 is not particularly limited, and an element using a hollow fiber membrane may be used. However, the flat membrane element structure is based on a shearing force when a flow velocity parallel to the membrane surface is applied. Since the effect of removing dirt is high, it is suitable for the present invention. The flat membrane element structure includes a rotating flat membrane structure.

  Examples of the membrane structure of the filtration membrane 26 include a porous membrane and a composite membrane in which a functional layer is combined with the porous membrane, but are not particularly limited. Specific examples of these membranes include polyacrylonitrile porous membrane, polyimide porous membrane, polyethersulfone porous membrane, polyphenylene sulfide sulfone porous membrane, polytetrafluoroethylene porous membrane, polyvinylidene fluoride porous membrane, polypropylene Examples of the porous film include a porous film and a porous film such as a polyethylene porous film, and a polyvinylidene fluoride porous film and a polytetrafluoroethylene porous film are particularly preferable because of high chemical resistance. Furthermore, a composite film in which a rubbery polymer such as cross-linked silicone, polybutadiene, polyacrylonitrile butadiene, ethylene propylene rubber, or neoprene rubber is compounded as a functional layer can be given as a functional layer.

  The membrane pore size of the filtration membrane 26 is preferably a pore size such that activated sludge can be solid-liquid separated into a solid component and a dissolved component. If the membrane pore size is large, the membrane permeability is improved, but the possibility that a solid component is contained in the membrane filtrate tends to increase. On the other hand, if the membrane pore size is small, the possibility that a solid component is contained in the membrane filtrate is reduced, but the membrane permeability tends to be lowered. Specifically, it is preferably 0.01 to 0.5 μm, and more preferably 0.05 to 0.5 μm.

  The biological treatment tank 27 is not particularly limited as long as it can store the concentrated water 25 and immerse the filtration membrane 26, and a concrete tank, a fiber reinforced plastic tank, or the like is preferably used. Moreover, the inside of the processing tank 27 may be divided into a plurality of parts, and a part of the divided tanks may be used as a tank for immersing the filtration membrane 26 and the other as an anaerobic tank or a denitrification tank. The water to be treated may be circulated between the tanks that are divided from each other.

  The activated sludge introduced into the biological treatment tank 27 is generally used for wastewater treatment or the like, and as the seed sludge, drawn sludge from other wastewater treatment facilities is usually used. In the membrane separation activated sludge method, the operation is performed at a sludge concentration of about 2,000 mg / L to 20,000 mg / L. The activated sludge method makes it possible to purify water by using microorganisms as contaminants in wastewater.

  The pressurizing pump 22 is not particularly limited as long as it can pressurize filtered water, and is a centrifugal pump, diffuser pump, spiral mixed flow pump, mixed flow pump, piston pump, plunger pump, diaphragm pump, gear pump, screw Pumps, vane pumps, cascade pumps, jet pumps, etc. can be used, but because they can be easily pressurized to the pressure required for reverse osmosis treatment, centrifugal pumps, diffuser pumps, piston pumps, plunger pumps, cascade pumps, A jet pump or the like is preferably used.

  The nanofiltration membrane and / or reverse osmosis membrane 23 is required to have a performance capable of reducing the solute in the filtered water to a concentration that can be used as reclaimed water. Specifically, the present invention provides various ions such as salt and mineral components such as seawater and brine, for example, divalent ions such as calcium ion, magnesium ion, sulfate ion, sodium ion, potassium ion, Blocks monovalent ions such as chloride ions, and soluble organic substances such as humic acid (molecular weight Mw ≧ 100,000), fulvic acid (molecular weight Mw = 100 to 1,000), alcohol, ether, saccharides, etc. It is required to have the performance to A nanofiltration membrane is defined as a filtration membrane with an operating pressure of 1.5 MPa or less, a fractional molecular weight of 200 to 1000, and a rejection rate of sodium chloride of 90% or less. What has performance is called a reverse osmosis membrane. A reverse osmosis membrane close to a nanofiltration membrane is also called a loose RO membrane.

  Nanofiltration membranes and reverse osmosis membranes have hollow fiber membranes and flat membranes, and the present invention can be applied to both. Further, in order to facilitate handling, a fluid separation element (element) in which a hollow fiber membrane or a flat membrane is housed in a housing can be used. When this fluid separation element uses a flat membrane-like semipermeable membrane as a nanofiltration membrane or a reverse osmosis membrane, for example, as shown in FIG. 5, around a cylindrical central pipe 39 having a large number of holes, It is preferable that a membrane unit including a semipermeable membrane 40, a permeate flow passage material 42 such as a tricot, and a supply water flow passage material 41 such as a plastic net is wound, and these are housed in a cylindrical casing. . It is also preferable to form a separation membrane module by connecting a plurality of fluid separation elements in series or in parallel. In this fluid separation element, the supply water 35 is supplied into the unit from one end, and the permeated water 37 that has permeated the semipermeable membrane 40 before reaching the other end is supplied to the central pipe 39. The flow is withdrawn from the central pipe 39 at the other end. On the other hand, the supply water 35 that has not permeated the semipermeable membrane 40 is taken out as concentrated water 36 at the other end.

  As the material of the semipermeable membrane 40, a polymer material such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer, or the like can be used. In addition, the membrane structure has a dense layer on at least one side of the membrane, and on the asymmetric membrane having fine pores gradually increasing from the dense layer to the inside of the membrane or the other side, or on the dense layer of the asymmetric membrane. Either a composite membrane having a very thin separation functional layer formed of another material may be used.

  However, among them, a composite membrane having a high pressure resistance, high water permeability, and high solute removal performance and having an excellent potential and using polyamide as a separation functional layer is preferable. In particular, when seawater is used as raw water, it is necessary to apply a pressure equal to or higher than the osmotic pressure in the first semipermeable membrane unit, and an operating pressure of at least 5 MPa is often applied substantially. In order to maintain high water permeability and blocking performance against this pressure, a structure in which polyamide is used as a separation functional layer and is held by a support made of a microporous membrane or a nonwoven fabric is suitable. Moreover, as the polyamide semipermeable membrane, a composite semipermeable membrane having a separation functional layer of a crosslinked polyamide obtained by polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide on a support is suitable.

  The separation functional layer is preferably made of a cross-linked polyamide having high chemical stability with respect to acid or alkali, or made of a cross-linked polyamide as a main component. The crosslinked polyamide is preferably formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide, and at least one of the polyfunctional amine or the polyfunctional acid halide component preferably contains a trifunctional or higher functional compound.

  Here, the polyfunctional amine refers to an amine having at least two primary and / or secondary amino groups in one molecule. For example, two amino groups are any of ortho, meta, and para positions. Aromatic polyfunctional amines such as phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene and 3,5-diaminobenzoic acid bonded to benzene in the positional relationship of Aliphatic amines such as ethylenediamine and propylenediamine, alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 1,3-bispiperidylpropane and 4-aminomethylpiperazine be able to. Of these, aromatic polyfunctional amines are preferred in view of selective separation, permeability, and heat resistance of the membrane. Examples of such polyfunctional aromatic amines include m-phenylenediamine, p-phenylenediamine, 1, 3,5-triaminobenzene is preferably used. Furthermore, it is more preferable to use m-phenylenediamine (hereinafter referred to as m-PDA) from the standpoint of availability and ease of handling. These polyfunctional amines may be used alone or in combination.

  The polyfunctional acid halide refers to an acid halide having at least two carbonyl halide groups in one molecule. Examples of trifunctional acid halides include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, 1,2,4-cyclobutanetricarboxylic acid trichloride, and bifunctional acid halides include biphenyl dicarboxylic acid. Aromatic difunctional acid halides such as acid dichloride, biphenylene carboxylic acid dichloride, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalene dicarboxylic acid chloride, aliphatic difunctional acid such as adipoyl chloride, sebacoyl chloride Mention may be made of alicyclic bifunctional acid halides such as halides, cyclopentane dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, tetrahydrofuran dicarboxylic acid dichloride. Considering the reactivity with the polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional acid chloride, and considering the selective separation property and heat resistance of the membrane, the polyfunctional aromatic acid chloride is preferable. Preferably there is. Among them, it is more preferable to use trimesic acid chloride from the viewpoint of easy availability and easy handling. These polyfunctional acid halides may be used alone or in combination.

  The support including the microporous support membrane is a layer that does not substantially have separation performance, and is provided to give mechanical strength to the separation functional layer of the crosslinked polyamide having substantial separation performance. For example, a material in which a microporous support film is formed on a substrate such as a fabric or a nonwoven fabric is used.

  The microporous support membrane itself is a layer that does not substantially have separation performance, and is used to give mechanical strength to the separation functional layer having substantially separation performance. It is preferable to use a support film having such a structure that has a fine hole or a gradually small fine hole from one surface to the other surface, and the surface of the single surface is 100 nm or less.

  The above-mentioned support can be selected from various commercially available filter materials such as “Millipore Filter VSWP” (trade name) manufactured by Millipore and “Ultra Filter UK10” (trade name) manufactured by Toyo Roshi Kaisha, , “Office of Saleen Water Research and Development Progress Report”, “No. 359 (1968). As the material, polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride and other homopolymers or blends are usually used, but chemically, mechanically and thermally stable polysulfone is used. It is preferred to use.

  For example, a dimethylformamide (DMF) solution of the above polysulfone is cast on a densely woven polyester fabric or nonwoven fabric to a certain thickness, and the resulting solution is dissolved in an aqueous solution containing 0.5% by weight of sodium dodecyl sulfate and 2% by weight of DMF. By wet coagulation with, a microporous support membrane having a fine pore having a diameter of several tens of nm or less on the surface is obtained. As a material for the microporous support membrane, polyamide and polyester are preferably used in addition to polysulfone.

  Below, the processing flow which shows the embodiment of the water treatment method of this invention is outlined.

  First, the water 21 to be treated is separated into permeated water 24 and concentrated water 25 by the nanofiltration membrane and / or reverse osmosis membrane 23. The operating conditions (filtration flux, recovery rate, etc.) of the nanofiltration membrane and / or reverse osmosis membrane 23 depend on the type of nanofiltration membrane and reverse osmosis membrane used, and also depending on the requirements of the quality of treated water and permeated water. While it can be determined as appropriate, the filtration flux is preferably determined with the intention of minimizing membrane fouling. Regarding the recovery rate, which is the ratio of the permeated water to the water to be treated, it is preferable that the recovery rate is high. Further, if the recovery rate is too high, the solute that cannot be completely dissolved is deposited on the film surface, and the membrane is damaged or the flow path is blocked. Therefore, it is necessary to set the recovery rate within a range where it does not precipitate. Of course, if a scale inhibitor is added to prevent precipitation, precipitation can be suppressed to some extent, so that the recovery rate can be set high. In addition, when the recovery rate is too high, the recovery rate can be maintained high by reducing the flow rate of the water to be treated. However, if the flow rate of the water to be processed is reduced to an extremely small amount, retention on the membrane surface is likely to occur ( That is, the concentration polarization becomes large and the performance is deteriorated). Therefore, it is necessary to maintain the treated water flow rate within the recommended range. Therefore, in order to maintain the flow rate of water to be treated within an appropriate range, the nanofiltration membrane and reverse osmosis membrane may be multi-staged to increase the recovery rate.

  Thereafter, the concentrated water 25 is sent to the biological treatment tank and biologically treated in the biological treatment tank 27. Various combinations of biological treatments are possible depending on the component concentration of the concentrated water 25, the required water quality of the treated water after solid-liquid separation, and the like. For example, when the organic matter concentration (COD, BOD, TOC, etc.) of the concentrated water 25 is high (for example, 2,000 mg COD / L or more), it is preferable to perform anaerobic treatment after first performing anaerobic treatment. Further, when the nitrogen component concentration of the concentrated water 25 is high in the organic component ratio (for example, the COD / N ratio is 20 or less), it is preferable to introduce a nitrification denitrification method. Further, when the concentration of phosphorus component in the concentrated water 25 is high in the organic component ratio (for example, the COD / P ratio is 100 or less), it is preferable to introduce a biological phosphorus removal method or a flocculant-added phosphorus removal method.

  Examples of solid-liquid separation methods after biological treatment include gravity precipitation, sand filtration, MF (microfiltration) membrane and UF (ultrafiltration) membrane filtration. The biological treatment preferably includes aerobic treatment as described above, but the concentrated water 25 is biologically treated and solid-liquid separated in that aerobic treatment and solid-liquid separation can be performed in the same tank. As a method, it is preferable to employ a membrane separation activated sludge method.

  Compared with the gravity precipitation activated sludge method, the membrane-separated activated sludge method can retain a high concentration of activated sludge in the biological treatment tank, saving space and generating excess sludge (waste). There are advantages such as reduction. The concentrated water 25 is obtained by concentrating the water to be treated 21, and the contained component concentration inevitably increases. However, the higher the contained component concentration, the more prominent the merit. In addition, the treated water obtained by membrane separation activated sludge method has the feature that the treated water quality is superior compared to the case of solid-liquid separation treatment by gravity precipitation method or sand filtration method after biological treatment. In addition, there is an advantage that fouling of the nanofiltration membrane and / or reverse osmosis membrane can be suppressed even when the treated water subjected to biological treatment and solid-liquid separation treatment is further treated with a nanofiltration membrane and / or a reverse osmosis membrane.

  As the membrane separation activated sludge method, a method (immersion type) in which the filtration membrane 26 is installed in at least a part of the space in the biological treatment tank 27 where biological treatment is performed, and the filtration membrane is immersed in the biologically treated water. The activated sludge in the biological treatment tank 27 may be sent to a membrane filtration apparatus including the filtration membrane 26 installed outside the biological treatment tank 27 (external circulation type), but from the viewpoint of energy saving and space saving. Therefore, the former immersion type is preferred. Moreover, as a method of performing membrane filtration to obtain membrane permeated water, there are a method of drawing with a suction pump from the secondary side of membrane filtration, a method of utilizing a water head difference, and the like. The concentration of activated sludge in contact with the filtration membrane is preferably 2,000 mg / L to 20,000 mg / L. In addition, an aeration device is installed below the filtration membrane, and oxygen-containing gas (air, etc.) is supplied from the aeration device (blower, etc.) installed in communication with the aeration device, and adheres to the membrane surface. It is preferable to perform membrane filtration while separating the activated sludge component from the membrane surface. The residence time in the biological treatment tank 27 of the water to be treated is usually 1 hour to 72 hours, but it is preferable to adopt an optimum one depending on the state of the water to be treated and the biological treatment conditions. Moreover, you may install the apparatus which adds a flocculant, and may add a flocculant to the to-be-processed water containing the activated sludge stored in the biological treatment tank 3. FIG. The membrane filtration flux (membrane filtration flow rate per unit membrane area) is preferably 0.1 to 1.0 m / d. Further, after the concentrated water 25 is anaerobically treated, the membrane separation activated sludge treatment may be performed.

  Further, in order to increase the ratio of the permeated water of the nanofiltration membrane and / or reverse osmosis membrane to the water to be treated 21, treated water obtained by biological treatment and solid-liquid separation treatment as illustrated in FIG. 3 or FIG. Further processing may be performed with a nanofiltration membrane and / or a reverse osmosis membrane.

  FIG. 3 shows water treatment in which treated water subjected to biological treatment and solid-liquid separation treatment is treated with a nanofiltration membrane and / or reverse osmosis membrane 29 different from the nanofiltration membrane and / or reverse osmosis membrane 23 in the previous stage of biological treatment. It is an example of the water treatment apparatus used for a method. At this time, the nanofiltration membrane and / or the reverse osmosis membrane 29 at the later stage of the biological treatment are chemically fouled (chemical fouling) in which dissolved organic matter adheres to the membrane surface, and microorganisms grow by using the dissolved organic matter as a nutrient source. A low-fouling reverse osmosis membrane that is unlikely to cause biofouling (biological soiling) adhering to the surface is preferable. Examples of low-fouling reverse osmosis membranes include TML20 manufactured by Toray Industries, Inc. and LF10 manufactured by Nitto Denko Corporation (the surface of the membrane is neutral, a hydrophilic group is introduced, adsorption of charged substances and heavy metals such as iron colloids) Membranes made difficult to be affected by), reverse osmosis membranes such as Hydranautic LFC1, LFC3 and Dow BW30-365FR. In addition, if the concentration of solutes and suspended substances in filtered water is low, there is a particular problem even if a nanofiltration membrane that is a liquid separation membrane that blocks particles and polymers smaller than about 2 nm is used as a reverse osmosis membrane. Absent. The method for determining the operating conditions at this time can also be determined in the same manner as the nanofiltration membrane or reverse osmosis membrane described above. However, in biological treatment, salt removal is basically difficult, so the salinity concentration Therefore, it is necessary to pay more attention to the influence of osmotic pressure and the possibility of scale deposition.

  FIG. 4 is an example of a water treatment apparatus used in a water treatment method in which a part of treated water subjected to biological treatment and solid-liquid separation treatment is returned to the nanofiltration membrane and / or reverse osmosis membrane in the previous stage of biological treatment.

  At this time, the ratio of the treated biological water that has been subjected to biological treatment and solid-liquid separation that is refluxed is preferably higher because the recovery rate of permeated water in the nanofiltration membrane and / or reverse osmosis membrane with respect to the water to be treated 21 becomes higher. Care must be taken because there is a risk of fouling of the nanofiltration membrane and / or reverse osmosis membrane due to deterioration of permeate quality and solute precipitation. The ratio of reflux can be determined as appropriate depending on the type of nanofiltration membrane or reverse osmosis membrane in the pre-stage of biological treatment, and depending on the quality of the water to be treated 21 and / or the quality of the refluxed water and the quality of the permeated water. It is also possible to monitor the water quality of the water to be used and to reduce or stop reflux when the water quality deteriorates.

  In addition, the filtration flux needs to be set so that membrane fouling does not occur, and should be determined by the quality of the water supplied by the nanofiltration membrane or reverse osmosis membrane. It is preferable to set to about 10 to 20 L / m 2 · h. In addition, the biological metabolites are subjected to post-treatments such as activated carbon treatment, UF (ultrafiltration) membrane treatment, ozone treatment, etc., before the treated water that has undergone biological treatment and solid-liquid separation treatment is returned to the nanofiltration membrane or reverse osmosis membrane. The method of reducing the fouling substance of the nanofiltration membrane by reverse osmosis membrane etc. can be taken.

  The water treatment method of the present invention can be mainly applied to industrial wastewater treatment, but its application range is not limited to these.

It is the schematic which shows an example of the water treatment apparatus used for the water treatment method of this invention. It is the schematic which shows an example of the water treatment apparatus used for the conventional water treatment method. It is the schematic which shows another example of the water treatment apparatus used for the water treatment method of this invention. It is the schematic which shows another example of the water treatment apparatus used for the water treatment method of this invention. It is the schematic which shows an example of a reverse osmosis membrane fluid separation element.

Explanation of symbols

21: Water to be treated 22: Pressure pump 23: Nanofiltration membrane / reverse osmosis membrane 24: Permeated water in nanofiltration membrane / reverse osmosis membrane 25: Concentrated water in nanofiltration membrane / reverse osmosis membrane 26: Filtration membrane 27 : Biological treatment tank 28: Treated water subjected to biological treatment and solid-liquid separation treatment 29: Nanofiltration membrane / reverse osmosis membrane 35 after biological treatment 35: Supply water 36: Concentrated water 37: Permeated water 38: Telescope prevention plate 39: Center pipe 40: Semipermeable membrane 41: Supply water channel material 42: Permeate channel material

Claims (6)

Water to be treated is separated into permeated water and concentrated water by subjecting the water to be treated to membrane separation using a nanofiltration membrane and / or a reverse osmosis membrane, and the concentrated water is subjected to biological treatment and solid-liquid separation treatment. Processing method. The water treatment method according to claim 1, wherein the biological treatment and solid-liquid separation treatment is a membrane separation activated sludge method. The water according to claim 1 or 2, wherein at least a part of the treated water obtained by the biological treatment and solid-liquid separation treatment is subjected to membrane separation treatment by a nanofiltration membrane and / or a reverse osmosis membrane in the subsequent stage. Processing method. The water treatment method according to claim 3, wherein the latter nanofiltration membrane and / or reverse osmosis membrane is a low fouling reverse osmosis membrane. 2. At least a part of the treated water obtained by the biological treatment and solid-liquid separation treatment is refluxed as treated water for the nanofiltration membrane and / or reverse osmosis membrane in the previous stage of biological treatment. Or the water treatment method of 2. At least a part of the treated water obtained by the biological treatment and solid-liquid separation treatment is subjected to any one or more of activated carbon treatment, ultrafiltration membrane treatment, and ozone treatment, and then subjected to biological treatment. The water treatment method according to claim 1, wherein the nanofiltration membrane and / or reverse osmosis membrane is refluxed as water to be treated.

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