JP2016120457A - Filtration treatment system and filtration treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filtration treatment system where, after nanofiltration membrane treatment of water to be treated, in filtration treatment of performing reverse osmosis membrane treatment, the slime inhibition (sterilization) of a nanofiltration membrane and a reverse osmosis membrane by a simple method can be performed.SOLUTION: There is provided a filtration treatment system comprising: a nanofiltration membrane treatment device 12 where the treatment of water to be treated is performed by using a nanofiltration membrane; a reverse osmosis membrane treatment device 14 where the treatment of nanofiltration membrane permeable water from the nanofiltration membrane treatment device 12 is performed by using a reverse osmosis membrane; and slime inhibitor feeding means which feeds a slime inhibitor permeating the nanofiltration membrane in the prestage of the nanofiltration membrane treatment device 12, and further, less deteriorating the nanofiltration membrane and the reverse osmosis membrane than hypochlorous acid.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a filtration treatment system and a filtration treatment method for performing reverse osmosis membrane treatment after membrane filtration treatment using a nanofiltration membrane.

  As a method for obtaining fresh water such as industrial water and drinking water from seawater, for example, Patent Document 1 discloses that seawater is first treated with a nanofiltration membrane (NF membrane), and then the permeate is treated with a reverse osmosis membrane to obtain fresh water. The method of obtaining is described.

  In such treatment, hypochlorous acid is usually added to the raw water for the purpose of suppressing slime formation. However, since hypochlorous acid remains in the permeated water of the nanofiltration membrane treatment in the previous stage, when performing reverse osmosis membrane treatment with a reverse osmosis membrane in the latter stage, hypochlorous acid flows into the reverse osmosis membrane treatment device. End up. Polyamide reverse osmosis membranes that are generally widely used are vulnerable to hypochlorous acid, and the reverse osmosis membranes deteriorate when exposed to hypochlorous acid. In addition, the nanofiltration membrane also has a problem of being deteriorated by hypochlorous acid depending on the material.

  Therefore, it was necessary to remove the remaining hypochlorous acid by adding a reducing agent or using activated carbon before the nanofiltration membrane treatment or reverse osmosis membrane treatment. In addition, in order to suppress slime production in the nanofiltration membrane and reverse osmosis membrane, it was necessary to add a slime inhibitor (bactericidal agent) that hardly deteriorates these membranes again.

JP 2002-282855 A

  An object of the present invention is to provide a filtration system capable of performing slime suppression (sterilization) of a nanofiltration membrane and a reverse osmosis membrane by a simple method in a filtration treatment in which water to be treated is treated with a reverse osmosis membrane after being treated with a nanofiltration membrane. And providing a filtration method.

  The present invention relates to a nanofiltration membrane treatment means for treating water to be treated using a nanofiltration membrane, and a reverse osmosis membrane for treatment of nanofiltration membrane permeated water from the nanofiltration membrane treatment means using a reverse osmosis membrane. A slime inhibitor supplying means for supplying a slime inhibitor that permeates the nanofiltration membrane in the previous stage of the nanofiltration membrane treatment means, wherein the slime inhibitor that permeates the nanofiltration membrane is bromine-based Oxidizing agent, or a reagent containing a reaction product of a bromine compound and a chlorine-based oxidizing agent and a sulfamic acid compound, or a bromine-based oxidizing agent, or a reaction product of a bromine compound and a chlorine-based oxidizing agent, and a sulfamic acid compound A hypobromite stabilizing composition, which is a drug containing a reaction product of chlorinated oxidant and a drug containing a chlorinated oxidant and a sulfamic acid compound, or a reaction product of a chlorinated oxidant and a sulfamic acid compound. Hypochlorite stabilizing composition is drug-free; isothiazolone compounds; chloramine compounds, nitro alcohol compounds; halo cyanoacetamide compound; at least is one filtration system.

  In the filtration system, at least one of the nanofiltration membrane concentrated water from the nanofiltration membrane processing means and the reverse osmosis membrane concentrated water from the reverse osmosis membrane processing means is returned to the previous stage of the nanofiltration membrane processing means. It is preferable to provide return means.

  The present invention relates to a nanofiltration membrane treatment step for treating treated water using a nanofiltration membrane, and a reverse osmosis membrane for treatment of nanofiltration membrane permeated water from the nanofiltration membrane treatment step using a reverse osmosis membrane A slime inhibitor supplying step for supplying a slime inhibitor that permeates the nanofiltration membrane in the previous stage of the nanofiltration membrane treatment step, and the slime inhibitor that permeates the nanofiltration membrane is bromine-based Oxidizing agent, or a reagent containing a reaction product of a bromine compound and a chlorine-based oxidizing agent and a sulfamic acid compound, or a bromine-based oxidizing agent, or a reaction product of a bromine compound and a chlorine-based oxidizing agent, and a sulfamic acid compound A hypobromite stabilizing composition, which is a drug containing a reaction product of chlorinated oxidant and a drug containing a chlorinated oxidant and a sulfamic acid compound, or a reaction product of a chlorinated oxidant and a sulfamic acid compound. Hypochlorite stabilizing composition is drug-free; isothiazolone compounds; chloramine compounds, nitro alcohol compounds; halo cyanoacetamide compound; at least is one filtering processing method.

  In the filtration method, at least one of the nanofiltration membrane concentrated water from the nanofiltration membrane treatment step and the reverse osmosis membrane concentrated water from the reverse osmosis membrane treatment step is returned to the previous stage of the nanofiltration membrane treatment step. It is preferable to include a returning step.

  In the present invention, a filtration treatment system and filtration capable of performing slime suppression (sterilization) of the nanofiltration membrane and the reverse osmosis membrane by a simple method in the filtration treatment in which the water to be treated is treated with the reverse osmosis membrane after the nanofiltration membrane treatment. A processing method can be provided.

It is a schematic structure figure showing an example of a filtration processing system concerning an embodiment of the present invention. It is a schematic block diagram which shows the other example of the filtration processing system which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

<Filtration treatment system and filtration treatment method>
The outline of an example of the filtration processing system which concerns on embodiment of this invention is shown in FIG. 1, and the structure is demonstrated. The filtration processing system 1 includes a nanofiltration membrane processing apparatus 12 including a nanofiltration membrane as nanofiltration membrane processing means, and a reverse osmosis membrane processing apparatus 14 including a reverse osmosis membrane as reverse osmosis membrane processing means. The filtration processing system 1 may include a raw water tank 10 and a nanofiltration membrane permeated water tank 16.

  In the filtration processing system 1 of FIG. 1, a raw water pipe 24 is connected to the inlet of the raw water tank 10, and the outlet of the raw water tank 10 and the inlet of the nanofiltration membrane processing apparatus 12 are connected by a raw water supply pipe 26 via a pump 18. Has been. The permeated water outlet of the nanofiltration membrane treatment device 12 and the inlet of the nanofiltration membrane permeated water tank 16 are connected by a nanofiltration membrane permeated water pipe 28, and the outlet of the nanofiltration membrane permeated water tank 16 and the inlet of the reverse osmosis membrane treatment device 14 are The nanofiltration membrane permeated water supply pipe 30 is connected via the pump 20. A nanofiltration membrane concentrated water pipe 34 is connected to the nanofiltration membrane concentrated water outlet of the nanofiltration membrane treatment device 12. A reverse osmosis membrane concentrated water pipe 36 is connected to the reverse osmosis membrane concentrated water outlet of the reverse osmosis membrane treatment apparatus 14, and a reverse osmosis membrane permeated water pipe 32 is connected to the reverse osmosis membrane permeated water outlet. A slime inhibitor supply pipe 38 is connected downstream of the pump 18 in the raw water supply pipe 26 as slime inhibitor supply means.

  Operation of the filtration method and filtration system 1 according to the present embodiment will be described.

  The raw water that is the water to be treated is stored in the raw water tank 10 through the raw water pipe 24 as necessary, and then supplied to the nanofiltration membrane treatment apparatus 12 through the raw water supply pipe 26 by the pump 18. Here, on the downstream side of the pump 18 in the raw water supply pipe 26, the slime inhibitor is supplied to the raw water through the slime inhibitor supply pipe 38 (slime inhibitor supply process). In the nanofiltration membrane treatment apparatus 12, insoluble components and the like are removed from the water to be treated by the nanofiltration membrane (nanofiltration membrane treatment step). The slime inhibitor may be added in the raw water tank 10.

  The nanofiltration membrane permeated water subjected to the nanofiltration membrane treatment is stored in the nanofiltration membrane permeated water tank 16 through the nanofiltration membrane permeated water piping 28 as necessary, and then passed through the nanofiltration membrane permeated water supply piping 30 by the pump 20. It is supplied to the reverse osmosis membrane treatment device 14. In the reverse osmosis membrane treatment apparatus 14, reverse osmosis membrane treatment is performed by the reverse osmosis membrane (reverse osmosis membrane treatment step). On the other hand, the nanofiltration membrane concentrated water obtained by the nanofiltration membrane treatment is discharged through the nanofiltration membrane concentrated water piping 34.

  The reverse osmosis membrane concentrated water obtained by the reverse osmosis membrane treatment is discharged through the reverse osmosis membrane concentrated water pipe 36, and the reverse osmosis membrane permeated water is discharged through the reverse osmosis membrane permeated water pipe 32.

  In the filtration treatment method and filtration treatment system according to the present embodiment, nanofiltration membrane treatment is performed to prevent clogging of the nanofiltration membrane treatment device 12 and to suppress slime formation, to prevent clogging of the reverse osmosis membrane treatment device 14 and to suppress slime production, and the like. A slime inhibitor that passes through the nanofiltration membrane in the front stage of the device 12 and does not deteriorate the nanofiltration membrane and the reverse osmosis membrane as compared with hypochlorous acid is supplied. When a slime inhibitor is added at the front stage of the nanofiltration membrane treatment apparatus 12, the sterilization component appropriately passes through the subsequent reverse osmosis membrane treatment apparatus 14, and the reverse osmosis membrane treatment apparatus 14 is sterilized together with the nanofiltration membrane treatment apparatus 12. be able to. Moreover, since the slime inhibitor is less likely to deteriorate the nanofiltration membrane and the reverse osmosis membrane than hypochlorous acid, the reducing agent is added at the front stage of the reverse osmosis membrane treatment apparatus 14 and an activated carbon tower is installed. In addition, it is not necessary to re-add the slime inhibitor in the previous stage of the reverse osmosis membrane treatment apparatus 14, and the system is simplified.

  A nanofiltration membrane (NF membrane) refers to a membrane having a sodium chloride rejection of 5% or more and less than 93% under evaluation conditions of an operating pressure of 0.3 to 1.5 MPa. The NaCl rejection of the nanofiltration membrane is preferably less than 93%. If the NaCl rejection of the nanofiltration membrane is less than 93%, the slime inhibitor permeates appropriately to the subsequent stage, and the reverse osmosis membrane treatment device 14 can be sterilized together with the nanofiltration membrane treatment device 12. When the NaCl rejection of the nanofiltration membrane is 93% or more, the slime inhibitor is almost blocked and the subsequent reverse osmosis membrane treatment device 14 cannot be sufficiently sterilized.

  The slime inhibitor that permeates through the nanofiltration membrane is not particularly limited as long as 5% by weight or more of the added slime inhibitor permeates. Specific examples of the slime inhibitor that permeates the nanofiltration membrane include a bromine-based oxidant, a reaction product of a bromine compound and a chlorine-based oxidant, and a sulfamic acid compound, or a bromine-based oxidant, Or a hypobromite stabilizing composition which is a drug containing a reaction product of a reaction product of a bromine compound and a chlorine-based oxidant and a sulfamic acid compound; a drug containing a chlorine-based oxidant and a sulfamic acid compound, or And hypochlorous acid stabilization composition which is a drug containing a reaction product of a chlorinated oxidant and a sulfamic acid compound; isothiazolone compound; chloramine compound; nitroalcohol compound; halocyanoacetamide compound and the like. The slime inhibitor that permeates these nanofiltration membranes is less likely to degrade the nanofiltration membrane and reverse osmosis membrane than hypochlorous acid.

  Examples of the isothiazolone compound include 2-methyl-4-isothiazolin-3-one, 2-ethyl-4-isothiazolin-3-one, 2-octyl-4-isothiazolin-3-one, and 5-chloro-2-methyl. -4-isothiazolin-3-one, 5-chloro-2-octyl-4-isothiazolin-3-one, 4,5-dichloro-2-methyl-4-isothiazolin-3-one, 4,5-dichloro-2 -Octyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, and the like.

  Examples of the chloramine compound include monochloramine, dichloramine and the like.

  Examples of the nitroalcohol compound include 2-bromo-2-nitropropane-1,3-diol, 2-bromo-2-nitrobutane-1,3-diol, and 3-bromo-3-nitropentane-2,4- Diol, 2,2-dibromo-2-nitro-1-ethanol, 2-nitro-1,3-propanediol, tris (hydroxymethyl) nitromethane, 2-bromo-2-nitro-1,3-diacetyloxypropane, 3,3-dibromo-3-nitro-2-propanol, 2-chloro-2-nitroethanol, 2-chloro-2-nitro-1,3-propanediol, 3-chloro-3-nitro-2-propanol, etc. Is mentioned.

  Examples of the halocyanoacetamide compound include 2-bromo-3-nitrilopropionamide, 2,2-dibromo-3-nitrilopropionamide (DBNPA), 2-chloro-2-bromo-3-nitrilopropionamide, 2- Chloro-3-nitrilopropionamide, 2,2-dichloro-3-nitrilopropionamide, N-methyl-2,2-dibromo-3-nitrilopropionamide, N-propyl-2-chloro-2-bromo-3- Nitrilopropionamide and the like can be mentioned.

  In the filtration treatment method and filtration treatment system according to the present embodiment, as the slime inhibitor, “bromine-based oxidant” or “reaction product of bromine compound and chlorine-based oxidant” and “sulfamic acid compound” It is preferred to use a drug containing. Thereby, it is thought that a hypobromite stabilization composition produces | generates in raw | natural water.

  Further, in the filtration treatment method and filtration treatment system according to the present embodiment, as the slime inhibitor, “reaction product of bromine-based oxidant and sulfamic acid compound” or “reaction of bromine compound and chlorine-based oxidant” It is preferable to use a hypobromite stabilizing composition which is a “reaction product of a product and a sulfamic acid compound”.

  These hypobromite stabilizing compositions can sterilize the reverse osmosis membrane treatment device 14 together with the nanofiltration membrane treatment device 12 while suppressing deterioration of the nanofiltration membrane and the reverse osmosis membrane. Since the hypobromite stabilizing composition hardly deteriorates the reverse osmosis membrane, it is not necessary to add a reducing agent or install an activated carbon tower or the like in the previous stage of the reverse osmosis membrane treatment apparatus 14. It is not necessary to re-add the slime inhibitor in the previous stage of the reverse osmosis membrane treatment apparatus 14, and the system is simplified.

  Specifically, in the filtration treatment method and filtration treatment system according to the present embodiment, for example, in the raw water, “bromine”, “bromine chloride” or “reaction product of sodium bromide and hypochlorous acid”, “ A sulfamic acid compound ".

  In the filtration method and the filtration system according to the present embodiment, for example, in the raw water, “reaction product of bromine and sulfamic acid compound”, “reaction product of bromine chloride and sulfamic acid compound”, or A “reaction product of sodium bromide and hypochlorous acid and a sulfamic acid compound” is supplied.

  For example, in the raw water tank 10 or the raw water supply pipe 26, “bromine-based oxidizing agent” or “reaction product of bromine compound and chlorine-based oxidizing agent” and “sulfamic acid compound” or reaction products thereof are added to the raw water. May be injected by a chemical injection pump or the like. “Brominated oxidant” or “reaction product of bromine compound and chlorinated oxidant” and “sulfamic acid compound” may be added separately, or may be added after mixing in stock solutions. Good.

  The ratio of the equivalent of “sulfamic acid compound” to the equivalent of “bromine-based oxidizing agent” or “reaction product of bromine compound and chlorine-based oxidizing agent” is preferably 1 or more, and is in the range of 1 or more and 2 or less. It is more preferable. If the ratio of the equivalent of “sulfamic acid compound” to the equivalent of “bromine-based oxidizing agent” or “reaction product of bromine compound and chlorine-based oxidizing agent” is less than 1, the active ingredient may not be sufficiently stabilized. If it exceeds 2, the production cost may increase.

  The effective halogen concentration in the raw water is preferably in the range of 1 to 10 mg / L in terms of effective chlorine concentration. If it is this range, the latter reverse osmosis membrane processing apparatus 14 can be disinfected efficiently. If the effective halogen concentration in the raw water is less than 1 mg / L, free halogen may not be detected in the subsequent stage of the nanofiltration membrane treatment apparatus 12, and a sufficient slime suppression effect may not be obtained. If the effective halogen concentration in the raw water is more than 10 mg / L, it may cause deterioration of the nanofiltration membrane or reverse osmosis membrane when water is passed for a long time, and may cause corrosion of metallic materials such as piping. There is.

  Examples of bromine-based oxidizing agents include bromine (liquid bromine), bromine chloride, hypobromite, bromate, bromate, and the like.

  Among these, the preparations of “bromine and sulfamic acid compound” or “reaction product of bromine and sulfamic acid compound” using bromine are the preparations of “hypochlorous acid, bromine compound and sulfamic acid” and “bromine chloride”. It is more preferable because it has less chloride ions and is less likely to cause corrosion of metal materials such as pipes, compared to the formulation of “and sulfamic acid”.

  That is, in the filtration method and filtration system according to the present embodiment, it is preferable that bromine and a sulfamic acid compound are present in the raw water, or a reaction product of bromine and a sulfamic acid compound is present.

  Examples of bromine compounds include sodium bromide, potassium bromide, lithium bromide, ammonium bromide and hydrobromic acid. Of these, sodium bromide is preferable from the viewpoint of formulation cost and the like.

  Examples of the chlorine-based oxidizing agent include chlorine gas, chlorine dioxide, hypochlorous acid or a salt thereof, chlorous acid or a salt thereof, chloric acid or a salt thereof, perchloric acid or a salt thereof, chlorinated isocyanuric acid or a salt thereof. Etc. Among these, examples of the salt include alkali metal hypochlorites such as sodium hypochlorite and potassium hypochlorite, alkaline earth hypochlorite such as calcium hypochlorite and barium hypochlorite. Metal salts, alkali metal chlorites such as sodium chlorite and potassium chlorite, alkaline earth metal chlorites such as barium chlorite, and other metal chlorites such as nickel chlorite , Alkali metal chlorates such as ammonium chlorate, sodium chlorate and potassium chlorate, and alkaline earth metal chlorates such as calcium chlorate and barium chlorate. These chlorine-based oxidants may be used alone or in combination of two or more. As the chlorine-based oxidant, sodium hypochlorite is preferably used from the viewpoint of handleability.

The sulfamic acid compound is a compound represented by the following general formula (1).
R ₂ NSO ₃ H (1)
(In the formula, R is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

  Examples of the sulfamic acid compound include sulfamic acid (amidosulfuric acid) in which both two R groups are hydrogen atoms, N-methylsulfamic acid, N-ethylsulfamic acid, N-propylsulfamic acid, N- A sulfamic acid compound in which one of two R groups such as isopropylsulfamic acid and N-butylsulfamic acid is a hydrogen atom and the other is an alkyl group having 1 to 8 carbon atoms, N, N-dimethylsulfamic acid, N, Two R groups such as N-diethylsulfamic acid, N, N-dipropylsulfamic acid, N, N-dibutylsulfamic acid, N-methyl-N-ethylsulfamic acid, N-methyl-N-propylsulfamic acid, etc. One of two R groups such as a sulfamic acid compound and N-phenylsulfamic acid, both of which are alkyl groups having 1 to 8 carbon atoms, An atom, the other is sulfamic acid compound or a salt thereof, such as an aryl group having 6 to 10 carbon atoms. Examples of the sulfamate include alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt, strontium salt and barium salt, manganese salt, copper salt, zinc salt, iron salt, cobalt salt, Other metal salts such as nickel salts, ammonium salts, guanidine salts and the like can be mentioned. The sulfamic acid compounds and salts thereof may be used alone or in combination of two or more. As the sulfamic acid compound, sulfamic acid (amidosulfuric acid) is preferably used from the viewpoint of environmental load.

  In the filtration method and filtration system according to the present embodiment, an alkali may be further present. Examples of the alkali include alkali hydroxides such as sodium hydroxide and potassium hydroxide. From the viewpoint of product stability at low temperatures, sodium hydroxide and potassium hydroxide may be used in combination. Further, the alkali is not solid and may be used as an aqueous solution.

  Examples of the nanofiltration membrane of the nanofiltration membrane treatment apparatus 12 include organic nanofiltration membranes (NF membranes) made of polyethersulfone (PES), piperazine amide, cellulose acetate, polyamide, and the like. The filtration treatment method and filtration treatment system according to the present embodiment can be suitably applied particularly to nanofiltration membranes made of polyethersulfone (PES), piperazine amide, cellulose acetate, and polyamide. These materials can permeate the hypobromite stabilizing composition regardless of the material.

  Examples of the reverse osmosis membrane of the reverse osmosis membrane treatment apparatus 14 include an organic reverse osmosis membrane (RO membrane) such as polyamide. If the membrane material of the reverse osmosis membrane is polyamide, membrane deterioration due to the hypobromite stabilizing composition hardly occurs and high blocking performance can be exhibited.

  The filtration method and filtration system according to the present embodiment can be suitably applied particularly to polyamide polymer membranes that are currently mainstream as reverse osmosis membranes (RO membranes). Polyamide polymer membranes have a relatively low resistance to oxidizing agents, and when free chlorine or the like is continuously brought into contact with the polyamide polymer membrane, the membrane performance is significantly reduced. However, in the filtration treatment method and filtration treatment system according to the present embodiment, such a remarkable decrease in membrane performance hardly occurs even in the polyamide polymer membrane.

  In the filtration method and filtration system according to this embodiment, the pH of the raw water that is the treated water is preferably 5.5 or more, more preferably 6.0 or more, and 6.5 or more. More preferably. If the pH of the raw water is less than 5.5, the pH of the water supplied to the reverse osmosis membrane treatment device 14 (the nanofiltration membrane permeated water) becomes less than 5.5, and the amount of permeated water may decrease. In addition, the upper limit of the pH of the raw water is not particularly limited as long as it is not higher than the normal upper limit pH of the reverse osmosis membrane (for example, pH 10), but considering the scale precipitation of hardness components such as calcium, the pH is, for example, It is preferable to operate at 9.0 or less. When using the filtration method and the filtration system according to the present embodiment, the reverse osmosis membrane of the reverse osmosis membrane treatment device 14 is deteriorated and treated water (reverse osmosis membrane permeation) by operating at a raw water pH of 5.5 or higher. It is possible to secure a sufficient amount of permeated water while suppressing the deterioration of water quality and exhibiting a sufficient slime suppressing effect.

  In the reverse osmosis membrane treatment device 14, when a scale is generated at pH 5.5 or higher of the nanofiltration membrane permeate to the reverse osmosis membrane treatment device 14, a dispersant is used in combination with a slime inhibitor for scale inhibition. Also good. Examples of the dispersant include polyacrylic acid, polymaleic acid, and phosphonic acid. The amount of the dispersant added to the feed water (prefiltered water) is, for example, in the range of 0.1 to 1,000 mg / L as the concentration in the concentrated water.

  Moreover, in order to suppress the occurrence of scale without using a dispersant, for example, the silica concentration in the reverse osmosis membrane concentrated water is less than or equal to the solubility, and the Langelia index that is an index of calcium scale is less than or equal to 0, Adjusting the operating conditions such as the recovery rate of the reverse osmosis membrane treatment device 14 may be mentioned.

  The filtration treatment method and filtration treatment system according to the present embodiment treat, for example, brine, surface water, well water, seawater, waste water from a factory, and the like. The TOC of the water to be treated is, for example, in the range of 0.1 mg / L to 1000 mg / L.

  The schematic structure of the other example of the filtration processing system which concerns on embodiment of this invention is shown in FIG. In the filtration processing system 3 of FIG. 2, the nanofiltration membrane concentrated water outlet of the nanofiltration membrane treatment device 12 and the raw water tank 10 are connected by a concentrated water return pipe 42 as a return means. Further, the reverse osmosis membrane concentrated water outlet of the reverse osmosis membrane treatment device 14 is connected to the middle of the concentrated water return pipe 42 by a concentrated water return pipe 44 as a return means. On the upstream side of the connection point between the concentrated water return pipe 42 and the concentrated water return pipe 44, a nanofiltration membrane concentrated water pipe 46 is connected to the concentrated water return pipe 42, and a reverse osmosis membrane concentrated water is connected to the concentrated water return pipe 44. A pipe 48 is connected.

  With this configuration, at least one of at least a part of the nanofiltration membrane concentrated water from the nanofiltration membrane treatment device 12 and at least a part of the reverse osmosis membrane concentrated water from the reverse osmosis membrane treatment device 14 is a nanofiltration membrane treatment device. 12 is returned to the raw water tank 10 which is the previous stage (returning step). Thereby, the usage-amount of a slime inhibitor can be reduced and the recovery rate of reverse osmosis membrane permeated water improves.

<Composition for filtration treatment>
The composition for filtration treatment according to the present embodiment contains, for example, “bromine-based oxidant” or “reaction product of bromine compound and chlorine-based oxidant” and “sulfamic acid compound”, and You may contain an alkali.

  Moreover, the composition for filtration treatment according to the present embodiment includes, for example, “a reaction product of a bromine-based oxidant and a sulfamic acid compound”, or “a reaction product of a bromine compound and a chlorinated oxidant, and a sulfamic acid compound”. And “a reaction product of” and may further contain an alkali.

  The bromine-based oxidizing agent, bromine compound, chlorine-based oxidizing agent, and sulfamic acid compound are as described above.

  As the composition for filtration treatment according to the present embodiment, one containing bromine and a sulfamic acid compound from the viewpoint of low corrosiveness to a metal material such as piping and less by-product of bromic acid, or Those containing a reaction product of bromine and a sulfamic acid compound are preferred.

  The composition for filtration treatment according to the present embodiment has higher oxidizing power and significantly higher slime suppressing power and slime peeling power than a combined chlorine-based slime inhibitor such as chlorosulfamic acid.

  Unlike the oxidizing agent such as hypochlorous acid, the composition for filtration treatment according to this embodiment hardly deteriorates the reverse osmosis membrane. Further, since the concentration can be measured on site in the same manner as hypochlorous acid or the like, more accurate concentration management is possible.

  The pH of the composition is, for example, more than 13.0, more preferably more than 13.2. When the pH of the composition is 13.0 or less, the effective halogen in the composition may become unstable.

  The bromic acid concentration in the composition for filtration treatment is preferably less than 5 mg / kg. When the bromic acid concentration in the composition for filtration treatment is 5 mg / kg or more, the quality of the treated water may deteriorate.

<Method for producing composition for filtration treatment>
The composition for filtration treatment according to the present embodiment includes, for example, mixing a bromine-based oxidant and a sulfamic acid compound, or mixing a reaction product of a bromine compound and a chlorine-based oxidant with a sulfamic acid compound. Obtained and further mixed with alkali.

  As a method for producing a composition for filtration treatment containing bromine and a sulfamic acid compound or a composition for filtration treatment containing a reaction product of bromine and a sulfamic acid compound, water, an alkali and a sulfamic acid compound are used. It is preferable to include a step of adding bromine to the mixed liquid to react under an inert gas atmosphere. By adding and reacting under an inert gas atmosphere, the bromate ion concentration in the composition becomes lower, which is preferable.

  The inert gas to be used is not limited, but at least one of chamber element and argon is preferable from the viewpoint of manufacturing and the like, and nitrogen is particularly preferable from the viewpoint of manufacturing cost and the like.

  The oxygen concentration in the reactor upon addition of bromine is preferably 6% or less, more preferably 4% or less, further preferably 2% or less, and particularly preferably 1% or less. If the oxygen concentration in the reactor during the bromine reaction exceeds 6%, the amount of bromic acid produced in the reaction system may increase.

  The addition ratio of bromine is preferably 25% by weight or less, more preferably 1% by weight or more and 20% by weight or less based on the total amount of the composition. If the bromine addition rate exceeds 25% by weight relative to the total amount of the composition, the amount of bromic acid produced in the reaction system may increase. If it is less than 1% by weight, the sterilizing power may be inferior.

  The reaction temperature during the addition of bromine is preferably controlled in the range of 0 ° C. to 25 ° C., but more preferably in the range of 0 ° C. to 15 ° C. from the viewpoint of production cost and the like. When the reaction temperature at the time of bromine addition exceeds 25 degreeC, the production amount of the bromic acid in a reaction system may increase, and when it is less than 0 degreeC, it may freeze.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

[Preparation of Stabilized Hypobromite Composition a]
Under nitrogen atmosphere, liquid bromine: 16.9% by weight (wt%), sulfamic acid: 10.7% by weight, sodium hydroxide: 12.9% by weight, potassium hydroxide: 3.94% by weight, water: remaining Minutes were mixed to prepare composition a. The pH of the composition was 14, and the effective halogen concentration (effective chlorine equivalent concentration) was 7.5% by weight. The detailed method for preparing the stabilized hypobromite composition a is as follows.

  Add 1436 g of water and 361 g of sodium hydroxide to a 2 L four-necked flask sealed by continuous injection while controlling the flow rate of nitrogen gas with a mass flow controller so that the oxygen concentration in the reaction vessel is maintained at 1%. Next, after adding 300 g of sulfamic acid and mixing, 473 g of liquid bromine was added while maintaining cooling so that the temperature of the reaction solution was 0 to 15 ° C., and 230 g of 48% potassium hydroxide solution was added. The target composition a having a sulfamic acid 10.7% by weight ratio to the total amount of the composition, bromine 16.9%, and an equivalent ratio of sulfamic acid to an equivalent of bromine of 1.04 was obtained. The pH of the resulting solution was 14 as measured by the glass electrode method. The bromine content of the resulting solution was 16.9% as measured by a redox titration method using sodium thiosulfate after bromine was converted to iodine with potassium iodide, and the theoretical content (16.9% ) Of 100.0%. In addition, the oxygen concentration in the reaction vessel during the bromine reaction was measured using “Oxygen Monitor JKO-02 LJDII” manufactured by Zico Corporation. The bromic acid concentration was less than 5 mg / kg.

[Filtration treatment]
Using the membrane treatment apparatus provided with each separation membrane shown in Table 1, 10 mg / L of the stabilized hypobromite composition a was added to the raw water at an effective halogen concentration, and the effective halogen concentration of the permeated water was measured.

  The effective halogen concentration is measured by the DPD method using a residual chlorine measuring apparatus (manufactured by Hach, “DR-4000”), and converted into an effective chlorine concentration. The NaCl rejection of the separation membrane was measured by ion chromatography.

(Experimental conditions)
Raw water: NaCl solution (NaCl concentration: 500 mg / L)
Operating pressure: 0.75 MPa
Raw water pH: 7
Test temperature: 25 ° C

  Nanofiltration membranes (NF membranes) with a NaCl rejection of 93% or less permeate the stabilized hypobromite composition a, whereas stabilized reverse bromite compositions a with a reverse osmosis membrane (RO membrane) of 99% or more. Did not penetrate.

  Thus, it was suggested that the nanofiltration membrane and the reverse osmosis membrane can be sterilized by a simple method in the filtration treatment in which the water to be treated is treated with the reverse osmosis membrane after the nanofiltration membrane treatment.

[Preparation of Stabilized Hypobromite Composition b]
Sodium bromide: 11% by weight, 12% sodium hypochlorite aqueous solution: 50% by weight, sodium sulfamate: 14% by weight, sodium hydroxide: 8% by weight, water: the remainder was mixed to prepare composition b. Prepared. The pH of the composition b was 14, and the effective halogen concentration (effective chlorine equivalent concentration) was 6% by weight. The detailed preparation method of the composition b is as follows.

  17 g of water was put into a reaction vessel, 11 g of sodium bromide was added and dissolved by stirring, 50 g of 12% aqueous sodium hypochlorite solution was added and mixed, and then 14 g of sodium sulfamate was added and stirred. After dissolution, 8 g of sodium hydroxide was added, stirred and dissolved to obtain the desired composition b.

[Composition c]
Each composition of stabilized hypobromite composition b was added separately into water.

[Composition d]
Composition d containing bromine chloride, sodium sulfamate, sodium hydroxide was used. The pH of the composition d was 14, and the effective halogen concentration (effective chlorine equivalent concentration) was 7% by weight.

[Composition e]
A 12% aqueous sodium hypochlorite solution was used.

[Composition f]
Sodium bromide: 15% by weight, 12% sodium hypochlorite aqueous solution: 42.4% by weight were separately added to water.

[Composition g]
12% sodium hypochlorite aqueous solution: 50% by weight, sulfamic acid: 10% by weight, sodium hydroxide: 8% by weight, water: residue were mixed to prepare composition g. The pH of composition g was 14, and the effective halogen concentration (effective chlorine equivalent concentration) was 6% by weight.

[Comparison test of RO membrane rejection rate, impact on permeated water, and oxidizing power]
Under the following conditions, the compositions a to g were added to the raw water of the reverse osmosis membrane device, and the influence on the RO membrane rejection rate, the influence on the permeated water, and the oxidizing power were compared.

(Test conditions)
Test apparatus: Flat membrane test apparatus Separation membrane: Polyamide polymer reverse osmosis membrane ES20 manufactured by Nitto Denko Corporation
・ Operating pressure: 0.75 MPa
Raw water: Sagamiharai water (pH 7.2, conductivity 240 μS / cm)
Drug: Compositions a to g are added so that the effective halogen concentration (effective chlorine equivalent concentration) is 10 mg / L.

(Evaluation method)
・ Effect on RO membrane rejection rate: Conductivity rejection rate after 30 days of water flow (%)
(100- [permeated water conductivity / feed water conductivity] × 100)
・ Effect on the permeated water: Effective halogen concentration (effective chlorine equivalent concentration, mg / L) in the permeated water 1 hour after the addition of the chemical was measured using a residual chlorine measuring device ("DR-4000" manufactured by Hach). Measured by DPD method / Oxidation power: Measures redox potential (ORP) of feed water after 1 hour using redox potential measuring device (RM-20P type ORP meter, manufactured by Toa DKK)

[Comparison test of bactericidal activity]
Under the following conditions, compositions a to g were added to simulated water, and the bactericidal power was compared.

(Test conditions)
-Water: Simulated water prepared by adding normal bouillon to Sagamiharai water and adjusting the general bacterial count to 10 ⁵ CFU / ml.-Drug: Compositions ag to 1 mg as effective halogen concentration (effective chlorine equivalent concentration) / L added (Measurement method of effective halogen concentration: measured by DPD method using residual chlorine measuring device (manufactured by Hach, “DR-4000”))

(Evaluation method)
・ Measures the number of general bacteria 24 hours after the addition of chemicals using a bacterial count kit (manufactured by Sanai Oil, BioChecker TTC)

  The test results are shown in Table 2.

  Compositions a to d maintained a high RO membrane rejection rate, had low effective halogen concentration (effective chlorine equivalent concentration) of permeated water, and high oxidation power and bactericidal power. Among the compositions a to d, the composition a retained the highest RO membrane rejection rate and had the lowest effective halogen concentration (effective chlorine equivalent concentration) of permeated water.

  Although the composition e had high oxidizing power and bactericidal power, the RO membrane rejection rate decreased and the effective halogen concentration (effective chlorine equivalent concentration) of permeated water was also high. The composition f had a high effective halogen concentration (effective chlorine equivalent concentration) in the permeated water, although the oxidizing power and the bactericidal power were high. Composition g had almost no reduction in the RO membrane rejection rate, and the permeated water had a low effective halogen concentration (effective chlorine equivalent concentration), but had low oxidizing power and low bactericidal power.

  Thus, by supplying the slime inhibitor that permeates the nanofiltration membrane to the front stage of the nanofiltration membrane treatment in the filtration treatment system that performs the reverse osmosis membrane treatment after the membrane filtration treatment using the nanofiltration membrane, reverse osmosis is achieved. It was found that the deterioration of the membrane and the deterioration of the quality of the treated water can be suppressed and a sufficient slime suppressing effect can be obtained.

[Comparison experiment of bromate ion concentration in permeated water]
The bromate ion concentration of permeated water with and without nitrogen gas purge during composition preparation was compared.

<Preparation of Stabilized Hypobromite Composition a '>
In the same manner as the stabilized hypobromite composition a, in a nitrogen atmosphere, liquid bromine: 17% by weight (wt%), sulfamic acid: 10.7% by weight, sodium hydroxide: 12.9% by weight, water A composition a ′ was prepared by mixing potassium oxide: 3.95 wt% and water: residue. The pH of the composition a ′ was 14, the effective halogen concentration (effective chlorine equivalent concentration) was 7.5% by weight, and the bromic acid concentration was less than 5 mg / kg.

<Preparation of Stabilized Hypobromite Composition h>
In the atmosphere without nitrogen purge, liquid bromine: 17% by weight (wt%), sulfamic acid: 10.7% by weight, sodium hydroxide: 12.9% by weight, potassium hydroxide: 3.95% by weight, Water: the residue was mixed to prepare composition h. The pH of the composition h was 14, the effective halogen concentration (effective chlorine equivalent concentration) was 7.4% by weight, and the bromic acid concentration was 63 mg / kg.

(Test conditions)
Test apparatus: Flat membrane test apparatus Separation membrane: Polyamide polymer reverse osmosis membrane ES20 manufactured by Nitto Denko Corporation
・ Operating pressure: 0.75 MPa
Raw water: Sagamiharai water (pH 7.2, conductivity 240 μS / cm)
・ Drug: Stabilized hypobromite compositions a ′ and h are added so that the effective halogen concentration (effective chlorine equivalent concentration) is 50 mg / L.

(Evaluation method)
-The bromate ion concentration of the permeated water was measured by ion chromatography-post column absorptiometry.

  The test results are shown in Table 3.

  In the stabilized hypobromite composition a ′, the bromate ion concentration in the feed water and the permeated water was less than 1 μg / L. In the stabilized hypobromite composition h, the bromate ion concentration in feed water and permeated water was higher than that in the stabilized hypobromite composition a '.

  DESCRIPTION OF SYMBOLS 1,3 Filtration processing system, 10 Raw water tank, 12 Nanofiltration membrane processing apparatus, 14 Reverse osmosis membrane processing apparatus, 16 Nanofiltration membrane permeated water tank, 18, 20 Pump, 24 Raw water piping, 26 Raw water supply piping, 28 Nanofiltration membrane Permeate pipe, 30 Nanofiltration membrane permeate supply pipe, 32 Reverse osmosis membrane permeate pipe, 34,46 Nanofiltration membrane concentrate water pipe, 36,48 Reverse osmosis membrane concentrate water pipe, 38 Slime inhibitor supply pipe, 42, 44 Concentrated water return piping.

Claims (4)

A nanofiltration membrane treatment means for treating the water to be treated using the nanofiltration membrane;
Reverse osmosis membrane treatment means for treating nanofiltration membrane permeated water from the nanofiltration membrane treatment means using a reverse osmosis membrane;
A slime inhibitor supply means for supplying a slime inhibitor that permeates the nanofiltration membrane in the preceding stage of the nanofiltration membrane treatment means;
With
The slime inhibitor that permeates the nanofiltration membrane is a bromine-based oxidant, a reaction product of a bromine compound and a chlorine-based oxidant, and a sulfamic acid compound, or a bromine-based oxidant, or a bromine compound. Hypobromite stabilizing composition, which is a chemical containing a reaction product of chlorinated oxidant and a reaction product of sulfamic acid compound; chemical containing chlorinated oxidant and sulfamic acid compound, or chlorinated A hypochlorous acid stabilizing composition which is a drug containing a reaction product of an oxidant and a sulfamic acid compound; isothiazolone compound; chloramine compound; nitroalcohol compound; halocyanoacetamide compound; Filtration processing system. The filtration system according to claim 1,
A return means for returning at least one of the nanofiltration membrane concentrated water from the nanofiltration membrane treatment means and the reverse osmosis membrane concentrated water from the reverse osmosis membrane treatment means to the previous stage of the nanofiltration membrane treatment means; Filtration processing system characterized by. A nanofiltration membrane treatment process for treating the water to be treated using the nanofiltration membrane;
A reverse osmosis membrane treatment step of treating the nanofiltration membrane permeated water from the nanofiltration membrane treatment step using a reverse osmosis membrane;
A slime inhibitor supply step for supplying a slime inhibitor that permeates the nanofiltration membrane in the previous stage of the nanofiltration membrane treatment step;
Including
The slime inhibitor that permeates the nanofiltration membrane is a bromine-based oxidant, a reaction product of a bromine compound and a chlorine-based oxidant, and a sulfamic acid compound, or a bromine-based oxidant, or a bromine compound. Hypobromite stabilizing composition, which is a chemical containing a reaction product of chlorinated oxidant and a reaction product of sulfamic acid compound; chemical containing chlorinated oxidant and sulfamic acid compound, or chlorinated A hypochlorous acid stabilizing composition which is a drug containing a reaction product of an oxidant and a sulfamic acid compound; isothiazolone compound; chloramine compound; nitroalcohol compound; halocyanoacetamide compound; Filtration treatment method. The filtration method according to claim 3,
Including a returning step of returning at least one of the nanofiltration membrane concentrated water from the nanofiltration membrane treatment step and the reverse osmosis membrane concentrated water from the reverse osmosis membrane treatment step to the previous stage of the nanofiltration membrane treatment step. A filtration method characterized by.

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