JP5807634B2 - Reverse osmosis membrane treatment method - Google Patents

Description

  The present invention relates to a method of treating water to be treated containing a pollutant using a reverse osmosis membrane (hereinafter sometimes referred to as RO membrane), and more specifically, water to be treated having a high FI (fouling index). The present invention relates to a method for treating a membrane using a reverse osmosis membrane to prevent contamination and deterioration of the membrane.

  Since the RO membrane has a high solute rejection rate, the clear permeated water obtained by the RO membrane treatment has a good water quality and can be effectively reused in various applications. However, if the water to be treated contains pollutants that contaminate the RO membrane, such as turbidity and organic matter, the reverse osmosis membrane is contaminated by these substances, and the permeation flux of the RO membrane increases as the treatment continues. There are problems such as a decrease or a desalting rate.

  When water treatment is performed using the RO membrane, in order to prevent such contamination (fouling) of the RO membrane and increase the treatment efficiency, water supplied to the RO membrane device is supplied with the fouling defined in JIS K3802. Evaluate with the ring index (FI) or the silt density index (SDI) defined in ASTM D4189, and for example, the FI value or the SDI value is 3 to 4 or less so that this value is less than the predetermined value. Pretreatment (flocculation treatment, solid-liquid separation, activated carbon treatment) is performed so that the reverse osmosis membrane feed water is clarified to some extent, thereby reducing the permeation flux and the operating pressure in the reverse osmosis membrane device. A method is being implemented to avoid the obstacles and continue stable operation.

  In the circulating cooling water system, when the cooling water that has cooled the heat source is cooled by the cooling tower, a part of the water evaporates, so that pollutants such as turbidity and organic matter are concentrated. Since bacteria that cause slime are mixed from the outside and slime generated in the cooling tower is peeled and mixed, sterilization as a countermeasure against slime is also necessary. That is, even if contaminants such as turbidity and organic matter are removed, if bacteria are contained in the treated water, the bacteria grow on the membrane surface and the permeation flux of the RO membrane decreases, so the treated water It is sterilized by adding a bactericidal agent to prevent contamination of the membrane surface due to bacterial growth.

  As a disinfectant, free chlorine agents such as chlorine and sodium hypochlorite are widely used in general aqueous systems, but these deteriorate the RO membrane as an oxidant and lower the performance, thus reducing the oxidization property. As a method, Patent Document 1 (Japanese Patent Laid-Open No. 1-104310) proposes a method of adding a free chlorine agent to sterilize and then adding ammonium ions to produce chloramine. However, Patent Document 1 does not show in detail at which stage and how to apply to treated water containing pollutant substances.

  Patent Document 2 (Japanese Patent Laid-Open No. 2006-263510) proposes a slime inhibitor for membrane separation containing a combined chlorine agent composed of a chlorine-based oxidizing agent and a sulfamic acid compound. Patent Document 2 shows that the above-mentioned combined chlorine agent contains free chlorine at a certain ratio in the water to be treated, and has a similar relationship in the equilibrium relationship. And in order to acquire a bactericidal effect, it uses by the density | concentration in which free chlorine is detected in to-be-processed water, and in an Example, free chlorine density | concentration is used at 2-6 mg / L, and total chlorine density | concentration is used at 20-60 mg / L. Yes.

  However, RO membranes, in particular RO membranes made of polymer membranes having nitrogen-containing groups such as polyamide and aramid, are susceptible to free chlorine, and there is a problem that membrane separation performance such as desalination rate and removal rate deteriorates. It is important to perform the RO membrane treatment without containing free chlorine. For this reason, Patent Document 3 (Japanese Patent Laid-Open No. 9-57067) shows that after sterilizing with a free chlorine agent, a reducing agent such as sodium bisulfite is added to erase the sterilizing agent, and RO membrane treatment is performed. ing. In Patent Document 3, the concentration of copper is limited because it is still insufficient even if the reducing agent is added and the bactericidal agent is erased. It is said that erasing is necessary to prevent the deterioration of the RO membrane.

Japanese Unexamined Patent Publication No. 1-104310 Japanese Unexamined Patent Publication No. 2006-263510 Japanese Unexamined Patent Publication No. 9-57067

  In order to solve the conventional problems as described above, the object of the present invention is to remove the pollutant from the treated water containing the pollutant by a simple mechanism and simple operation, and to make it in a biologically inactive state. An object of the present invention is to propose a method for efficiently treating the RO membrane while preventing contamination and deterioration of the RO membrane.

The present invention is the following reverse osmosis membrane treatment method.
(1) A method for reverse osmosis membrane treatment of water to be treated containing pollutants,
A pretreatment process for removing pollutants from the water to be treated in the presence of free chlorine;
A membrane separation step of separating the pretreated water with a reverse osmosis membrane in the presence of a bound chlorine agent,
The total chlorine concentration of pretreated water obtained from the pretreatment step is 3 to 10 mg / L, the free chlorine concentration is 0.2 to 10 mg / L,
A reverse osmosis membrane treatment method, wherein the total chlorine concentration of pretreatment water supplied to the membrane separation step is 1 to 5 mg / L, and the free chlorine concentration is 0.1 mg / L or less.
(2) The method according to (1) above, wherein after adding a reducing agent to the pretreated water obtained from the pretreatment step, a combined chlorine agent is added and supplied to the membrane separation step.
(3) The method according to (1) or (2) above, wherein in the pretreatment step, a bound chlorine agent is added to remove the pollutant.
(4) The method according to any one of (1) to (3) above, wherein the combined chlorine agent comprises sulfamic acid or a salt thereof and a free chlorine agent.
(5) The method according to any one of (1) to (4) above, wherein the pretreatment step comprises an operation of removing one or more pollutants selected from agglomeration treatment, solid-liquid separation and activated carbon treatment.
(6) The method according to any one of (2) to (5) above, wherein the reducing agent is bisulfite.

The present invention is the following reverse osmosis membrane treatment method.
(1) A method for reverse osmosis membrane treatment of water to be treated containing pollutants,
A pretreatment process for removing pollutants from the water to be treated in the presence of free chlorine;
A membrane separation step of separating the pretreated water with a reverse osmosis membrane in the presence of a bound chlorine agent,
Contaminating material before the processing step, the total chlorine concentration of pretreated water obtained is 3-10 mg / L, as free chlorine concentration of 0.2 to 10 mg / L, while sterilization in the presence of free chlorine Remove
After adding the reducing agent to the pretreated water obtained from the pretreatment step,
Add bound chlorinating agent consisting of sulfamic acid or its salt and free chlorinating agent,
Reverse osmosis membrane total chlorine concentration of 1 to 5 mg / L of pretreated water to be supplied to the membrane separation process, the free chlorine concentration which is characterized that you fed to membrane separation step under conditions such that less 0.05 mg / L Processing method.
(2) In the pretreatment step, with the addition of combined chlorine agent, the method of mounting the above (1) SL and removing contaminating substances.
(3) The method according to (1) or (2) above, wherein the pretreatment step comprises an operation of removing one or more pollutants selected from agglomeration treatment, solid-liquid separation and activated carbon treatment.
(4) The method according to any one of (1) to (3) above, wherein the reducing agent is bisulfite.

  In the present invention, the water to be treated for RO membrane treatment is water to be treated containing a pollutant. Contaminating substances are substances that contaminate RO membranes, and are substances that adhere to RO membranes and reduce membrane separation performance such as permeation flux and desalination rate. Turbidity, organic matter, colloids, etc. are common However, it also includes those that increase contamination by growth, such as microorganisms. Since such pollutants are contained in water obtained from ordinary water sources, all of these waters are the subject of the present invention. In the present invention, water to be treated having a particularly high FI (fouling index) is used. Suitable for processing.

  FI is an index of the contamination with respect to the RO membrane, and the water to be treated having a high FI has a high contamination with the RO membrane. Such treated water with a high FI often contains a large amount of microorganisms in addition to turbidity, organic matter, colloid, and the like, and the contamination of the RO membrane is often increased by the growth of microorganisms. Such treated water with a high FI is more collected water such as wastewater than natural water. In particular, in the circulating cooling water system, salt and turbidity are concentrated, and slime generated in the cooling tower is peeled off. Therefore, a large amount of adherent microorganisms are contained, and therefore, pretreatment is required in a state where there is no growth of microorganisms.

  In the present invention, the pollutant on the RO membrane is removed by removing the pollutant in the presence of free chlorine in the pretreatment process from the water to be treated containing such a pollutant, in particular, the water to be treated having a high FI. In the membrane separation step, the pretreated water is subjected to membrane separation with a reverse osmosis membrane in the presence of a combined chlorine agent. At this time, the total chlorine concentration of pretreatment water obtained from the pretreatment step is 3 to 10 mg / L, the free chlorine concentration is 0.2 to 10 mg / L, and the total chlorine concentration of pretreatment water supplied to the membrane separation step is 1. When the free chlorine concentration is set to ˜5 mg / L and the free chlorine concentration is 0.1 mg / L or less, the RO membrane can be prevented from being contaminated and deteriorated, and the RO membrane can be processed efficiently.

  In order to make free chlorine exist in the pretreatment step and the pretreated water obtained from the pretreatment step has the above total chlorine concentration and free chlorine concentration, a free chlorine agent and / or a combined chlorine agent can be added. However, in the pretreatment step, the combined chlorine agent is added to remove the pollutant, and the pretreatment water is added in the pretreatment step so that the total pretreatment water concentration and the free chlorine concentration are as described above. It is preferable to adjust the amount. In order to make the pretreatment water supplied to the membrane separation step have the above total chlorine concentration and free chlorine concentration, a reducing agent can be added to the pretreatment water obtained from the pretreatment step, and a combined chlorine agent can be added. .

Free chlorine, combined chlorine and total chlorine in the present invention are shown in JIS K 0400-33-10: 1999, and the concentration of Cl ₂ is determined by the DPD method using N, N-diethyl-1,4-phenylenediamine. Measured. Free chlorine is chlorine existing in the form of hypochlorous acid, hypochlorite ion or dissolved chlorine, combined chlorine is chlorine existing in the form of chloroamine and organic chloroamine, and total chlorine is free chlorine, combined chlorine or Chlorine is present in both forms.

A free chlorine agent is a chemical | medical agent which produces | generates the said free chlorine, Elemental chlorine and hypochlorous acid are illustrated as an active free chlorine agent, and hypochlorite is illustrated as a latent free chlorine agent. A bonded chlorine agent is an agent that forms the above-mentioned bonded chlorine, but chloroamine is a chlorine derivative of ammonia in which 1, 2 or 3 hydrogen atoms are substituted with chlorine atoms (monochloroamine (NH ₂ Cl), dichloroamine (NHCl ₂ )). ), Nitrogen trichloride (NCl ₃ )) and all organic nitrogen compounds quantified by the measurement method of the same standard, including chlorine derivatives of sulfamic acid.

  Examples of the free chlorine agent that can be used in the present invention include the above chlorine gas, 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 Alternatively, a salt thereof can be used. Examples of the salt include alkali metal salts such as sodium and potassium, alkaline earth metal salts such as barium, other metal salts such as nickel, ammonium salts, and the like. One or more of these can be used. Of these, hypochlorous acid is preferable because of its excellent handleability.

  In the bound chlorine agent used in the present invention, the nitrogen compound to which the free chlorine is bound is ammonia or a compound thereof, melamine, urea, acetamide, sulfamide, cyclolamic acid, sulfamic acid, toluenesulfonamide, succinimide, Examples thereof include phthalimide, isocyanuric acid, N-chlorotoluenesulfonamide, uric acid, saccharin, and salts thereof. The bonded chlorine agent used in the present invention is a compound in which the above-mentioned free chlorine is bonded to these nitrogen compounds. As the combined chlorine agent used in the present invention, those obtained by mixing and reacting the above nitrogen compound and free chlorine agent, particularly those obtained by mixing and reacting each in the state of an aqueous solution are preferable. The concentration of the aqueous solution is 5 to 10% by weight, preferably 5.5 to 7.5% by weight in terms of total chlorine concentration.

  Examples of such bonded chlorinating agents include chloramine shown in Patent Document 1, chloramine-T (N--), as well as chlorinated amines composed of a chlorine-based oxidizing agent and a sulfamic acid compound described in Patent Document 2. Sodium salt of chloro-4-methylbenzenesulfonamide), chloramine-B (sodium salt of N-chloro-benzenesulfonamide), sodium salt of N-chloro-paranitrobenzenesulfonamide, trichloromelamine, mono- or di-chloro Sodium salt or potassium salt of melamine, sodium salt or potassium salt of trichloro-isocyanurate, mono- or di-chloroisocyanuric acid, sodium salt or potassium salt of mono- or di-chlorosulfamic acid, monochlorohydantoin or 1,3 -Dichlorohydan In or 5,5-alkyl derivatives.

Among these, the combined chlorine agent composed of a free chlorine agent and a sulfamic acid compound disclosed in Patent Document 2 contains sulfamic acid and is preferable because it has slime peelability. In particular, the mixing ratio of the sulfamic acid compound and the free chlorine agent is preferably 1: 0.45-0.60, preferably 1: 0.45-0.55 in terms of N: effective chlorine (molar ratio). The concentration of the aqueous solution is 5 to 10% by weight, preferably 5.5 to 7.5% by weight in terms of total chlorine concentration. The sulfamic acid is amidosulfuric acid represented by R ¹ R ² NSO ₃ H (1), and R ¹ and R ² are each independently H and a hydrocarbon group having 1 to 6 carbon atoms. As such sulfamic acid, sulfamic acid in the narrow sense in which R ¹ and R ² are each H is preferable, but N-methylsulfamic acid, N, N-dimethylsulfamic acid, N-phenylsulfamic acid and the like can also be used. These sulfamic acids may be used in a free (powdered) acid state, or may be a salt such as an alkali metal salt such as a sodium salt or a potassium salt. The above-mentioned N: effective chlorine (molar ratio) is the number of moles of sulfamic acid constituted by N and the number of moles of Cl ₂ of the chlorinated oxidant measured according to JIS K 0400-33-10: 1999. It corresponds to the ratio. The concentration of the aqueous solution, the JIS K 0400-33-10: free chlorine and combined chlorine concentration is measured by 1999 is a value represented by the total chlorine concentration calculated as Cl _2.

  In the present invention, prior to the membrane separation step, a pretreatment step of removing pollutants from the water to be treated in the presence of free chlorine is performed. In the pretreatment process, the operation for removing the pollutant is not limited as long as it can remove turbidity, organic matter, colloid, microorganisms, and other substances that show contamination to the RO membrane, and a known one is adopted. it can. As a preferable operation, an operation for removing one or more pollutants selected from flocculation treatment, solid-liquid separation and activated carbon treatment can be employed, and a combination of flocculation treatment, filtration separation and activated carbon treatment is particularly preferred.

  In the present invention, the pretreatment step for removing such pollutants is performed in the presence of free chlorine, and the total chlorine concentration in the pretreatment water obtained from the pretreatment step is 3 to 10 mg / L, preferably 5 to 7 mg. / L, the pretreatment step is performed so that the free chlorine concentration is 0.2 to 10 mg / L, preferably 1 to 5 mg / L. Performing the pretreatment step in the presence of free chlorine means maintaining the pretreatment step in a sterilized state. Even in the conventional pretreatment, sterilization may be performed before or after these separation operations. However, microorganisms may grow in the liquid storage part or the retention part provided before or after the separation operation. In some cases, microorganisms may flow out into the pretreated water and grow on the RO membrane. Therefore, in the present invention, the pretreatment step is performed in the presence of free chlorine to prevent the microorganisms from flowing out into the pretreated water. To do.

  The pretreatment step is performed in the presence of free chlorine so that the total chlorine concentration of pretreated water obtained from the pretreatment step is 3 to 10 mg / L and the free chlorine concentration is 0.2 to 10 mg / L. For this purpose, the free chlorine agent may be added, but the combined chlorine agent can be added together with or in place of the free chlorine agent. Combined chlorinating agents have lower oxidizing power (ORP) than free chlorinating agents, but nitrogen compounds hold and store free chlorine and have a function of gradually releasing them, so they have excellent sustainability and release of free chlorine. Thereafter, the free chlorine is retained and stored only by adding free chlorine, and recovered as a combined chlorine agent, which is preferable.

  As described above, the combined chlorine agent contains free chlorine in a certain ratio in the water to be treated, and has an equilibrium relationship similar to that. By adding the combined chlorine agent, the entire process of the pretreatment step is performed. If the total chlorine concentration can be controlled to be 3 to 10 mg / L and the free chlorine concentration is 0.2 to 10 mg / L, the chlorine concentration in the pretreatment process can be controlled only by adding the combined chlorine agent. Such a combined chlorine agent may be added only once at the beginning of the pretreatment step, or may be added continuously or intermittently to maintain the total and free chlorine concentrations. In any case, since the chlorine concentration can be measured and controlled, the control is easy.

  In the pretreatment process, if an operation for removing pollutants in the presence of free chlorine, for example, agglomeration treatment, filtration separation, etc. in the presence of free chlorine, the microorganisms in the water to be treated are sterilized, turbidity, organic matter, Since it is separated and removed together with colloids and the like, and the total chlorine concentration and free chlorine concentration are maintained at a predetermined value or more throughout the pretreatment step, microorganisms do not remain in the pretreatment water.

In the present invention, such pretreated water is subjected to membrane separation by RO membrane in the presence of bound chlorine agent in the membrane separation step, and the total chlorine concentration of the pretreated water is 1 to 5 mg / L, preferably 1 to 3 mg. / L, free chlorine concentration is 0 . It supplies to a membrane separation process on the conditions used as 05 mg / L or less. Since RO membranes which may be damaged by free chlorine, free chlorine concentration supplied Suruga under the following conditions 0.05 mg / L, microorganisms and in such condition, flowing out without being sterilized by the pretreatment step, The possibility that microorganisms mixed in the membrane separation process grow cannot be excluded. For this reason, the total chlorine concentration of the pretreatment water supplied to the membrane separation step is maintained within the above range to prevent the growth of microorganisms .

  In order to make the pretreatment water supplied to the membrane separation process have the above total chlorine concentration and free chlorine concentration, a reducing agent is added to the pretreatment water obtained from the pretreatment process, and a part of residual chlorine is eliminated. It is possible to adjust the total chlorine concentration and free chlorine concentration by adding an excess reducing agent to the pretreated water obtained from the pretreatment step, erasing all of the residual chlorine, and then adding a combined chlorine agent. When adjusted to, the total chlorine concentration and free chlorine concentration of the pretreatment water supplied to the membrane separation step can be accurately adjusted, which is convenient for preventing the deterioration of the RO membrane. The reducing agent added to the pretreated water is not limited as long as it removes at least a part of residual chlorine, but a bisulfite such as sodium bisulfite is preferable.

When the pretreatment water supplied to the membrane separation step is set to the above total chlorine concentration and free chlorine concentration in this way, the sterilizing atmosphere of the pretreatment water sterilized in the pretreatment step is maintained, and microorganisms grow on the RO membrane. Thus, it is possible to prevent the film surface from being contaminated. In the membrane separation process, the water to be treated is concentrated by the RO membrane treatment, so that the bactericidal concentration can be maintained even if a part of the residual chlorine is erased. The state which prevents contamination can be maintained for a long time.

According to the present invention, in a method for treating a water to be treated containing a pollutant with a reverse osmosis membrane, a pretreatment step for removing the pollutant from the water to be treated in the presence of free chlorine, and the pretreated water is combined with chlorine. A membrane separation step of membrane separation with a reverse osmosis membrane in the presence of an agent. In the pretreatment step , the total chlorine concentration of the pretreated water obtained is 3 to 10 mg / L, and the free chlorine concentration is 0.2 to 10 mg / L After removing the pollutant in a sterilized state in the presence of free chlorine so as to be L and adding a reducing agent to the pretreated water obtained from the pretreatment step, sulfamic acid or a salt thereof and a free chlorine agent was added combined chlorine agent comprising a membrane total chlorine concentration of 1 to 5 mg / L of pretreated water to be supplied to the separation step, supplied to the membrane separation step under conditions that free chlorine concentration of less than 0.05 mg / L So , it is easy to treat the treated water containing pollutants. With this simple mechanism and simple operation, it is possible to remove the pollutants and bring them into a biologically inactive state to prevent the RO membrane from being contaminated and deteriorated, and to efficiently perform the RO membrane treatment.

It is a flowchart of the reverse osmosis membrane processing method of embodiment. It is a graph which shows the change of the production water amount of Example 1, and a differential pressure | voltage. 2 is a graph showing changes in the desalting rate of Example 1. It is a graph which shows the change of the production water amount of Comparative Example 1, and a differential pressure | voltage. 6 is a graph showing changes in the desalting rate of Comparative Example 1. It is a graph which shows the change of the amount of production water of comparative example 2, and differential pressure. 6 is a graph showing changes in the desalting rate of Comparative Example 2.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a cooling water system including a cooling tower 2. Reference numeral 10 denotes a pretreatment process, which includes a water tank 11 to be treated, a flocculation tank 12, a filtration tank 13, and an activated carbon treatment tank 14. Reference numeral 20 denotes a membrane separation step, which includes a pretreatment water tank 21, a safety filter 22, and an RO membrane treatment device 23. The RO membrane treatment device 23 is divided into a concentrate chamber 25 and a permeate chamber 26 by an RO membrane 24.

  In the cooling water system 1, the cooling water is supplied from the cooling water pit 3 of the cooling tower 2 through the line L1, the return water is circulated from the line L2 to the cooling water pit 3, and the circulating water is cooled and circulated by the cooling tower 2. It is configured. By cooling by evaporating a part of the water in the cooling tower 2, the cooling water is concentrated and contaminating substances and microorganisms are mixed from the louver 4. Therefore, a scale inhibitor, a slime control agent, etc. are added to the cooling water pit 3. The cooling water treatment is performed by adding.

  In the pretreatment process 10, a part of the cooling water from the cooling water pit 3 is treated as water to be treated and drawn out to the water tank 11 to be treated through the line L4 and stored. An aqueous solution of a free chlorine agent and / or a combined chlorine agent is added from the line L5 to the water tank 11 to be treated so that the water to be treated can remove contaminants in the presence of free chlorine. Water to be treated containing free chlorine is supplied to the coagulation tank 12 from the water tank 11 to be treated through the line L6, and an inorganic coagulant such as PAC is added from the line L7, and a polymer coagulant such as polyacrylamide is added from the line L8 and stirred. Then, agglomeration treatment is performed. As a result, turbidity, organic matter, colloids, microorganisms, etc. in the water to be treated are taken into the flocs.

  The aggregation treatment liquid is supplied from the line L9 to the filtration tank 13, and the aggregation floc is separated by filtration. The filtered water is supplied from the line L10 to the activated carbon treatment tank 14 to adsorb and remove organic substances and other pollutants that cannot be removed by the coagulation treatment. Thereby, microorganisms etc. are sterilized and removed together with other pollutants such as turbidity, organic matter and colloid in the water to be treated, and the pretreated water maintains a bactericidal atmosphere. The combined chlorine agent added to the water tank 11 to be treated from the line L5 so that the total chlorine concentration of pretreated water obtained from the pretreatment step 10 is 3 to 10 mg / L and the free chlorine concentration is 0.2 to 10 mg / L. Although the amount is determined, divided injection to other places or continuous injection may be performed. In addition, when it has the activated carbon treatment tank 14 like this Embodiment, since activated carbon decomposes | disassembles free chlorine, a free chlorine density | concentration will become large exceeding 0.2 mg / L so much in the exit of the activated carbon treatment tank 14. There is nothing. The upper limit of 10 mg / L is the concentration when the activated carbon treatment tank 14 is not provided.

  In the membrane separation process 20, the treated water in the activated carbon treatment tank 14, that is, the pretreated water obtained from the pretreatment process 10, is introduced into the pretreated water tank 21 from the line L11 and stored. At this time, a reducing agent such as sodium hydrogen sulfite is added from the line L12 to the line L11, and the total chlorine concentration and the free chlorine concentration contained in the pretreated water are made zero. Then, the combined chlorine agent is added from the line L13 to the pretreatment water tank 21, and the total chlorine concentration of the pretreatment water in the pretreatment water tank 21 is adjusted to 1 to 5 mg / L, and the free chlorine concentration is adjusted to 0.1 mg / L or less.

  The pretreatment water in the pretreatment water tank 21 is pressurized by the pump P from the line L15 through the safety filter 22 and supplied from the line L15 to the concentrated liquid chamber 25 of the RO membrane treatment device 23, and the RO membrane treatment is performed by the RO membrane 24. I do. As a result, the permeate that has permeated into the permeate chamber 26 circulates from L16 to the cooling water pit 3 of the cooling tower 2, and the concentrate concentrated in the concentrate chamber 25 is discharged out of the system from L17. By adjusting the total chlorine concentration of the pretreatment water in the pretreatment water tank 21 to 1 to 5 mg / L and the free chlorine concentration to 0.1 mg / L or less, the sterilization state of the pretreatment water supplied to the RO membrane 24 is changed. It is possible to prevent the microorganisms from growing on the RO membrane and contaminating the membrane surface.

  In this case, by removing the pollutants in the presence of free chlorine throughout the pretreatment process, the microorganisms contained in the water to be treated are removed together with other pollutants in a sterilized state, In order to prevent microorganisms from remaining and to maintain a bactericidal state, even if the concentration of free chlorine in the pretreatment water supplied to the membrane separation step is 0.1 mg / L or less, a bactericidal atmosphere is created by the combined chlorine agent. It can be maintained, and contamination of the RO membrane due to the growth of microorganisms can be prevented.

  Examples of the present invention and comparative examples will be described below.

[Example 1]:
Cooling water pretreatment and RO treatment were performed according to FIG. The quality of the cooling water as the water to be treated is pH: 6.8, electric conductivity: 589 mS / m, acid consumption (4.8): 28 mg / L (as CaCO ₃ ), TOC: 6.6 mg / L _{, Cl: 1380mg / L, SO} 4: 955mg / L, Na: a 979 mg / L.

  In the pretreatment step 10, two kinds of aqueous solutions of 0.4% by weight of sulfamic acid and 0.3% by weight of sodium hypochlorite (as effective chlorine) are respectively added to the water tank 11 to be treated and agglomerated in the coagulation tank 12. Treatment, filtration separation in the filtration tank 13, and activated carbon treatment in the activated carbon treatment tank 14 were performed. For aggregation treatment, 2 mg / L of PAC 80 mg / L and a polymer flocculant Cliff Rock PA-331 (trade name, manufactured by Kurita Kogyo Co., Ltd.) were added and stirred to form a floc. Filtration separation was carried out by passing SV = 10 through a two-layer filtration layer using a filter medium composed of sand having a particle size of 0.45 mm, uniformity coefficient of 1.4 and anthracite having a particle size of 0.9 mm. In the activated carbon treatment, the activated carbon treatment was performed by passing SV = 15 through an activated carbon layer using coal-based activated carbon Crycol WG-160 (trade name, manufactured by Kurita Kogyo Co., Ltd.). The amount of sulfamic acid 0.4 wt% aqueous solution and sodium hypochlorite 0.3 wt% aqueous solution added to the water tank 11 to be treated is 5 mg / L in total chlorine concentration of activated carbon treated water and 0.5 mg in free chlorine concentration. / L was adjusted as a control value.

Water quality of the activated carbon treated water is pH: 7.4, electric conductivity: 746 mS / m, acid consumption (4.8): 38 mg / L (as CaCO ₃ ), TOC: 6.5 mg / L, Cl: 1770 mg / L, SO ₄ : 1150 mg / L, Na: 985 mg / L. Table 1 shows the total chlorine concentration and free chlorine concentration of treated water and activated carbon treated water.

  When the activated carbon treated water in the activated carbon treatment tank 14 is introduced from the line L11 to the pretreatment water tank 21, a 10% by weight sodium hydrogen sulfite aqueous solution is added from the line L12 so that the sodium hydrogen sulfite is 15 mg / L. The total chlorine concentration and free chlorine concentration in water were set to zero. Then, a combined chlorine agent comprising a mixed aqueous solution (pH> 13) of 10% by weight of sodium hydroxide, 16% by weight of sulfamic acid and 6% by weight of sodium hypochlorite (as effective chlorine) is added from the line L13 to the pretreatment water tank 21. Bound chlorine agent was added. The amount of the combined chlorine agent added to the pretreatment water tank 21 was controlled so that the total chlorine concentration at the outlet of the pretreatment water tank 21 was 1.2 mg / L and the free chlorine concentration was 0.05 mg / L.

  The pretreatment water in the pretreatment water tank 21 is pressurized to 1.5 MPa from the line L14 through the safety filter 22 and from the line L15 by the pump P, and is supplied to the concentrated liquid chamber 25 of the RO membrane treatment device 23. The RO membrane treatment was performed. The RO membrane treatment apparatus used was an aromatic polyamide RO membrane 4-inch spiral RO membrane element (Nitto Denko Corporation, ES20-D4) filled in one vessel.

  Table 2 shows the total chlorine concentration and free chlorine concentration at the outlet of the activated carbon treatment tank 14, the inlet and outlet of the pretreatment water tank 21.

  Although continuous operation was performed for 3 months under the above conditions, the RO membrane did not deteriorate, the differential pressure of the RO membrane did not increase, and no slime trouble occurred. Changes in the production water volume and differential pressure during this period are shown in FIG. 2, and changes in the desalination rate are shown in FIG. 3. Since the differential pressure does not increase from the start of operation and the permeated water volume does not decrease, a clogging failure due to slime occurs. It can be confirmed that it is not. Moreover, since the desalination rate has not decreased since the start of operation, it can be confirmed that the RO membrane is contaminated or the RO membrane is deteriorated and the water quality of the production water is not lowered.

[Comparative Example 1]
In Example 1, the amount of product water and the pressure difference when a chlorine agent is further added to the pretreatment water supplied to the RO membrane and the total chlorine concentration is 13 mg / L and the free chlorine concentration is 0.2 mg / L. The change is shown in FIG. 4 and the change in the desalting rate is shown in FIG.

[Comparative Example 2]
In Example 1, the amount of produced water and the change in the differential pressure are shown in FIG. 6 as a treatment result when no chlorine agent is added to the water to be treated in the pretreatment step and the free chlorine concentration is 0.0 mg / L. The change in rate is shown in FIG. 7, where a decrease in flux due to slime formation is observed.

[Reference Test Examples 1 to 3]:
The mixed drainage of the cooling water blow water and other waste water used in Example 1 was passed for 3 days without addition of a slime control agent, and the contaminated safety filter was disassembled, and a 10 cm × 10 cm of contaminated substances adhered. The filter was taken out and used as a test piece. The test piece was immersed in 300 mL of pure water for 3 days in a test solution in which the same combined chlorine agent as that added to the pretreatment water tank 21 in Example 1 was added to adjust the total chlorine concentration and the free chlorine concentration. Table 3 shows the turbidity of each test solution and the visual observation result of the filter after 3 days. As shown in Table 3, when the total chlorine concentration is about 1.7 mg / L, the contaminants attached to the filter cannot be removed sufficiently, and when the total chlorine concentration is 8 mg / L, the contaminants are sufficiently removed. Since it can remove, it turns out that it is necessary to perform a pretreatment with such a chlorine concentration.

  The present invention relates to a method for treating treated water containing a pollutant using a reverse osmosis membrane, and in particular, to treat treated water having a high FI (fouling index) such as a cooling water system using a reverse osmosis membrane. It can be used in a method for preventing membrane deterioration and performing membrane separation treatment.

  1: cooling water system, 2: cooling tower, 3: cooling water pit, 4: louver, 10: pretreatment step, 11: water tank to be treated, 12: flocculation tank, 13: filtration tank, 14: activated carbon treatment tank, 20: Membrane separation step, 21: pretreatment water tank, 22: security filter, 23: RO membrane treatment device, 24: RO membrane, 25: concentrate chamber, 26: permeate chamber.

Claims (4)

A method for treating a water to be treated containing a pollutant with a reverse osmosis membrane,
A pretreatment process for removing pollutants from the water to be treated in the presence of free chlorine;
A membrane separation step of separating the pretreated water with a reverse osmosis membrane in the presence of a bound chlorine agent,
Contaminating material before the processing step, the total chlorine concentration of pretreated water obtained is 3-10 mg / L, as free chlorine concentration of 0.2 to 10 mg / L, while sterilization in the presence of free chlorine Remove
After adding the reducing agent to the pretreated water obtained from the pretreatment step,
Add bound chlorinating agent consisting of sulfamic acid or its salt and free chlorinating agent,
Reverse osmosis membrane total chlorine concentration of 1 to 5 mg / L of pretreated water to be supplied to the membrane separation process, the free chlorine concentration which is characterized that you fed to membrane separation step under conditions such that less 0.05 mg / L Processing method. In the pretreatment step, with the addition of combined chlorine agent, claim 1 Symbol placement method and removing a contaminant substance. The method according to claim 1 or 2 , wherein the pretreatment step comprises an operation of removing one or more contaminants selected from agglomeration treatment, solid-liquid separation, and activated carbon treatment. The method according to any one of claims 1 to 3 , wherein the reducing agent is bisulfite.

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