JP2014113591A - Water treatment method and water treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method and a water treatment system each capable of removing, both quickly and stably, formaldehyde from a body of raw water including the formaldehyde.SOLUTION: The water treatment method of the present invention includes a reaction step of generating α-hydroxysulfonate ions by adding a bisulfite to a body of raw water and then inducing the reaction of aldehydes included within the raw water and bisulfite ions at a pH of 5-7 and an ion exchange step of removing the α-hydroxysulfonate ions by using an anion exchange resin. It is desirable to remove the α-hydroxysulfonate ions by using a reverse osmotic membrane prior to the ion exchange step. The water treatment system 1 of the present invention, furthermore, includes an addition means 2 for adding a bisulfite to a body of raw water, a mixing means 3 for mixing the raw water and a bisulfite, and an ion exchange means 9 for removing α-hydroxysulfonate ions by using an anion exchange resin. It is desirable for the water treatment system 1 to additionally possess a reverse osmotic membrane module 5.

Description

  The present invention relates to a water treatment method and a water treatment system capable of removing formaldehyde from raw water containing formaldehyde.

  Wastewater discharged from factories and the like may contain harmful substances such as formaldehyde. In addition, harmful substances such as formaldehyde may be detected from raw water for drinking or food processing (for example, groundwater).

  Conventionally, as a method for removing these organic substances from raw water containing organic substances such as formaldehyde, a method including a step of decomposing these organic substances using biological treatment is known. For example, Patent Document 1 discloses a method for treating high-temperature wastewater containing organic substances such as formaldehyde at a high temperature of 40 ° C. or higher while aeration is performed using a membrane bioreactor provided with a separation membrane. In Patent Document 2, after treating the organic wastewater with activated sludge, the activated sludge treated water is solid-liquid separated by a separation membrane installed so as to be in contact with the activated sludge treated water, and membrane permeated water is obtained. A method for producing reclaimed water purified by subjecting the membrane permeate to a reverse osmosis membrane is disclosed.

JP 2007-268468 A JP 2008-73622 A

  However, in the methods described in Patent Documents 1 and 2, it takes a lot of time to culture microorganisms to obtain activated sludge, and it is not easy to perform wastewater treatment quickly. In addition, due to environmental changes, the composition and state of microorganisms in activated sludge are affected, and the efficiency of wastewater treatment tends to fluctuate, making it difficult to operate the wastewater treatment system stably.

  For example, a reverse osmosis membrane (hereinafter also referred to as “RO membrane”), an ion exchange resin, and a porous adsorbent are generally used as a means for quickly and stably treating wastewater. However, when trying to remove formaldehyde contained in raw water using these means, the problem is that formaldehyde is a low molecular weight compound having a molecular weight of 30 and having no charge. For example, RO membranes tend to block the transmission of substances having a molecular weight of more than 60 and substances having a charge, whereas they tend to pass through substances having a molecular weight of 60 or less that have no charge. Therefore, formaldehyde easily passes through the RO membrane, and the removal rate of formaldehyde by the RO membrane is only 20 to 30%. Moreover, since formaldehyde has no electric charge, it does not adsorb to the ion exchange resin by ion exchange. Therefore, it is difficult to sufficiently remove formaldehyde contained in raw water with an ion exchange resin. Furthermore, porous adsorbents such as activated carbon have a small amount of formaldehyde adsorbed, and it is difficult to sufficiently remove formaldehyde contained in raw water using the porous adsorbent.

  An object of this invention is to provide the water treatment method and water treatment system which can remove formaldehyde from the raw | natural water containing formaldehyde rapidly and stably.

  The present invention is a water treatment method for removing aldehydes from raw water containing aldehydes, comprising adding bisulfite to the raw water, reacting the aldehydes contained in the raw water with bisulfite ions at pH 5-7, -It relates to the water treatment method including the reaction process which produces | generates a hydroxysulfonic acid ion, and the ion exchange process which removes the alpha-hydroxysulfonic acid ion using an anion exchange resin.

  The water treatment method further includes a membrane separation step of removing α-hydroxysulfonic acid ions using a reverse osmosis membrane, and the ion exchange step is preferably a step performed after the membrane separation step.

  Further, the present invention is a water treatment system for removing aldehydes from raw water containing aldehydes, comprising mixing bisulfite addition means for adding bisulfite to raw water, raw water and bisulfite, The aldehydes contained in the mixture are reacted with hydrogen sulfite ions generated from the hydrogen sulfite at pH 5 to 7 to produce α-hydroxysulfonate ions, and α-hydroxysulfonate ions are subjected to anion exchange. The present invention relates to a water treatment system comprising ion exchange means for removing resin.

  The water treatment system preferably further includes a membrane separation means for removing α-hydroxysulfonic acid ions using a reverse osmosis membrane.

  ADVANTAGE OF THE INVENTION According to this invention, the water treatment method and water treatment system which can remove formaldehyde from the raw water containing formaldehyde rapidly and stably can be provided.

1 is an overall configuration diagram of a water treatment system 1 according to a first embodiment. It is a whole block diagram of the water treatment system 1A which concerns on 2nd Embodiment. It is a graph which shows the result of having measured the quantity of formaldehyde which remains after making formaldehyde and sodium hydrogensulfite or sodium thiosulfate contained in raw | natural water react.

[First Embodiment]
A water treatment system 1 according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is an overall configuration diagram of a water treatment system 1 according to a first embodiment of the present invention.

  As shown in FIG. 1, the water treatment system 1 which concerns on 1st Embodiment removes formaldehyde from the waste_water | drain (raw water W1) containing formaldehyde discharged | emitted in a factory etc., for example, and can be reused as industrial water etc. Reclaimed water (treated water W4) is produced. Examples of the wastewater containing formaldehyde include wastewater collected after sterilizing a packaged food or drink such as a beverage can or canned food in a sterilization apparatus such as a retort kettle or a pastorizer. Formaldehyde contained in the wastewater collected after sterilization as described above is considered to have eluted from the paint of the pattern printed on the side of the packaged food and drink.

  Moreover, as shown in FIG. 1, the water treatment system 1 which concerns on 1st Embodiment removes formaldehyde from groundwater etc. (raw water W1) containing formaldehyde, for example, and uses drinking water or water for food processing (treated water W4). To manufacture. The ministerial ordinance concerning water quality standards stipulates that the concentration of formaldehyde contained in tap water must be 0.08 mg / L or less. The treated water W4 used as drinking water or food processing water preferably has a formaldehyde concentration of 0.08 mg / L or less, as in the case of the water quality standard.

  As shown in FIG. 1, a water treatment system 1 according to this embodiment includes a bisulfite ion source compound addition device 2 as a bisulfite ion source compound addition means, a mixing tank 3 as a mixing means, and a pressure pump 4. And a reverse osmosis membrane module (hereinafter also referred to as “RO membrane module”) 5 as a removing means, valves 6 and 7, and a porous adsorbent bed tower 8 as a removing means. The water treatment system 1 includes water flow lines L1, L2, L3, and L7, a concentrated water line L4, a drainage line L5, and a concentrated water reflux line L6. The “line” in the present specification is a general term for lines capable of flowing a fluid such as a flow path, a path, and a pipeline.

  According to the water treatment system 1, in the mixing tank 3, formaldehyde (a kind of aldehydes) contained in the raw water W1 is reacted with hydrogen sulfite ions (α- A kind of hydroxysulfonate ion). Hydroxymethane sulfonate ion has a molecular weight of 111 and has a charge, and therefore is removed by the RO membrane module 5 and the porous adsorbent bed tower 8. The treated water W4 is supplied as water from which formaldehyde has been removed.

  The hydroxymethanesulfonate ion is decomposed into formaldehyde and bisulfite ion in the presence of an alkali such as sodium hydroxide and sodium carbonate by the reverse reaction shown in the above chemical reaction formula. Therefore, in the water treatment system 1, in order to prevent formaldehyde from being regenerated by decomposition of hydroxymethanesulfonate ions in addition to converting formaldehyde into hydroxymethanesulfonate ions in the mixing tank 3, the RO membrane module 5 and the porous Hydroxymethanesulfonic acid ions are removed by the adsorbent bed tower 8.

  Hereinafter, each part of the water treatment system 1 will be described in detail. The water flow line L <b> 1 is a line that supplies the raw water W <b> 1 to the mixing tank 3. This raw water W1 contains formaldehyde. The raw water W1 may contain organic components other than formaldehyde. The upstream end of the water flow line L1 is connected to a supply source (not shown) of the raw water W1. The downstream end of the water flow line L1 is connected to the mixing tank 3.

  The bisulfite ion source compound addition device 2 is a means for adding a bisulfite ion source compound that dissolves in water to generate bisulfite ions to the raw water W <b> 1 supplied to the mixing tank 3. The bisulfite ion source compound may be added as it is to the raw water W1, or may be added to the raw water W1 as an aqueous solution. The bisulfite ion source compound added to the raw water W1 as it is is dissolved in the raw water W1 to generate bisulfite ions. In addition, when the bisulfite ion source compound is added to the raw water W1 as an aqueous solution, bisulfite ions are already generated from the bisulfite ion source compound in the aqueous solution. The hydrogen sulfite ion generated by dissolving the hydrogen sulfite ion source compound in water reacts with formaldehyde contained in the raw water W1 to generate hydroxymethanesulfonic acid ions.

  The bisulfite ion source compound is not particularly limited as long as it is dissolved in water to generate bisulfite ions, and examples thereof include bisulfite, pyrosulfite, dithionite, sulfite, and sulfite. It is done. Examples of the salt include alkali metal salts such as sodium salt and potassium salt. The bisulfite ion source compounds exemplified above and the reaction products of these bisulfite ion source compounds and formaldehyde are reducing agents, but their reducing action is mild, so there is little adverse effect on removal means such as RO membranes. . Further, since the bisulfite ion source compounds exemplified above have low toxicity and can be used as food additives, these bisulfite ion source compounds remain in the treated water obtained by the present invention. Even so, the treated water can be safely used for drinking or food processing. Among them, when used for the reaction with formaldehyde, a low concentration may be used, and a bisulfite such as sodium bisulfite and potassium bisulfite is preferable in that the pH does not need to be adjusted. A hydrogen sulfite ion source compound may be used individually by 1 type, or may use 2 or more types together.

  The mixing tank 3 mixes the raw water W1 supplied to the mixing tank 3 through the water flow line L1 and the bisulfite ion source compound added to the raw water W1 in the mixing tank 3 by the bisulfite ion source compound addition device 2. This is a means for reacting formaldehyde contained in the raw water W1 with hydrogen sulfite ions to produce hydroxymethane sulfonate ions. The mixing tank 3 is connected to the downstream end of the water flow line L1. Connected to the downstream side of the mixing tank 3 is a water passage line L2 through which raw water W1 containing hydroxymethanesulfonate ions generated in the mixing tank 3 can be passed. The downstream end of the water flow line L2 is connected to the primary inlet port of the RO membrane module 5.

  The pressurization pump 4 is provided in the water flow line L2. The pressurizing pump 4 is a device that sucks the raw water W <b> 1 supplied from the mixing tank 3, pressurizes it, and discharges it toward the RO membrane module 5. The operation (drive and stop) of the pressurizing pump 4 is controlled by a control device (not shown).

  The RO membrane module 5 separates the raw water W1 discharged from the pressurizing pump 4 into permeated water W2 from which hydroxymethanesulfonate ions have been substantially removed and concentrated water W3 from which hydroxymethanesulfonate ions have been concentrated. It is equipment to process. The RO membrane module 5 is connected to the downstream end of the water flow line L2.

  The RO membrane module 5 includes a single or a plurality of RO membrane elements (not shown). The RO membrane module 5 membrane-separates the supply water W1 with these RO membrane elements to produce permeated water W2 and concentrated water W3. The RO membrane includes a nanofiltration membrane (NF membrane) having pores looser than those of a normal RO membrane. Therefore, as the RO membrane module 5, an NF membrane module having an NF membrane can also be used.

  The RO membrane module 5 is connected to a water passage line L3 through which the permeated water W2 can pass and a concentrated water line L4 through which the concentrated water W3 can pass. The upstream end of the water flow line L3 is connected to the secondary port of the RO membrane module 5. The downstream end of the water flow line L3 is connected to the porous adsorbent bed tower 8. The water flow line L3 supplies the permeated water W2 produced by the RO membrane module 5 to the porous adsorbent bed tower 8.

  The concentrated water line L4 is a line for sending the concentrated water W3 from the RO membrane module 5. The upstream end of the concentrated water line L4 is connected to the primary outlet port of the RO membrane module 5. A branch portion J1 is provided at the downstream end of the concentrated water line L4. The concentrated water line L4 branches into the drainage line L5 and the concentrated water reflux line L6 at the branch portion J1.

  The drainage line L5 is a line for draining a part of the concentrated water W3 from the RO membrane module 5 to the outside of the water treatment system 1. The upstream end of the drainage line L5 is connected to the concentrated water line L4 at the branch portion J1. A valve 6 is provided in the drain line L5. The valve 6 can open and close the drain line L5.

  The concentrated water reflux line L6 is a line for refluxing the remainder of the concentrated water W3 from the RO membrane module 5 to the upstream side of the pressurizing pump 4 in the water flow line L2. The upstream end of the concentrated water reflux line L6 is connected to the concentrated water line L4 at the branch portion J1. The downstream end portion of the concentrated water reflux line L6 is connected to the water flow line L2 at the branch portion J2. The branch part J2 is disposed between the mixing tank 3 and the pressure pump 4. A valve 7 is provided in the concentrated water reflux line L6. The valve 7 can open and close the concentrated water reflux line L6. That is, the RO membrane module 5 is configured to be capable of membrane separation processing by crossflow.

  The porous adsorbent bed tower 8 adsorbs and removes hydroxymethanesulfonic acid ions remaining in the permeated water W2 by the porous adsorbent. The porous adsorbent bed tower 8 is connected to the downstream end of the water flow line L3. The porous adsorbent bed tower 8 accommodates a porous adsorbent bed. Examples of the porous adsorbent used for the porous adsorbent bed include powdered, granular, or fibrous activated carbon and activated alumina. On the downstream side of the porous adsorbent bed tower 8, a water flow line L7 through which the treated water W4 produced by the porous adsorbent bed tower 8 can flow is connected.

  The water flow line L7 is a line for sending the treated water W4 produced in the porous adsorbent bed tower 8 to a customer. The upstream end of the water flow line L7 is connected to the porous adsorbent bed tower 8. The downstream end of the water flow line L7 is connected to a demand destination device or the like (not shown).

  In addition, although illustration is abbreviate | omitted, raw water W1, permeated water W2, and concentrated water W3 are in the water flow lines L1, L2, L3, and L7, the concentrated water line L4, the drainage line L5, and the concentrated water reflux line L6 described above. In addition, a pump for sending the treated water W4 and the treated water W5 (see FIG. 2), a valve for opening and closing the flow path, and the like are appropriately provided. These pumps and valves are also controlled by a control device (not shown).

  Next, a water treatment method (operation of the water treatment system 1) by the water treatment system 1 according to the first embodiment will be described with reference to FIG. The water treatment method by the water treatment system 1 includes a reaction step in which formaldehyde contained in the raw water W1 is reacted with bisulfite ions to generate hydroxymethane sulfonate ions, and a removal to remove hydroxymethane sulfonate ions generated in the reaction steps. And a process.

  First, the reaction process will be described. When the water treatment system 1 is operated, the raw water W1 is supplied to the mixing tank 3 via the water flow line L1. On the other hand, a hydrogen sulfite ion source compound that dissolves in water to generate hydrogen sulfite ions is added to the raw water W <b> 1 supplied to the mixing tank 3 by the hydrogen sulfite ion source compound addition device 2. In the mixing tank 3, the raw water W1 and the hydrogen sulfite ion source compound are mixed, and the formaldehyde contained in the raw water W1 reacts with the hydrogen sulfite ions generated from the hydrogen sulfite ion source compound to generate hydroxymethanesulfonic acid ions. To do.

  The reaction conditions in the reaction process will be described. The reaction time is preferably about 10 minutes to 10 hours. If reaction time is in said range, it can suppress that reaction fully progresses and the produced | generated hydroxy methanesulfonate ion decomposes | disassembles and formaldehyde is regenerated | regenerated.

  The molar ratio of hydrogen sulfite ion to formaldehyde (hydrogen sulfite ion / formaldehyde) is usually 1 or more. In addition, when calculating the said molar ratio, it is necessary to subtract the number of moles of oxidizing agents, such as sodium hypochlorite contained in the raw water W1, from the number of moles of hydrogen sulfite ion. Since the bisulfite ion acts as a reducing agent, it reacts with the oxidizing agent contained in the raw water W1 and is lost. By subtracting the number of moles of the oxidizing agent contained in the raw water W1 from the number of moles of hydrogen sulfite ions, the effective mole ratio of hydrogen sulfite ions and formaldehyde can be calculated.

  The pH during the reaction is preferably from 3 to 9, and more preferably from 5 to 7. If the pH during the reaction is within the above range, the reaction proceeds sufficiently, and in the removal step, the removal function of hydroxymethanesulfonate ions by the RO membrane module 5 and the porous adsorbent bed tower 8 is provided. Hard to damage.

  The reaction temperature is preferably 5 to 95 ° C, more preferably 20 to 60 ° C. If the reaction temperature is within the above range, it is easy to proceed the reaction at a sufficient reaction rate.

  Next, the removal process will be described. The raw water W1 containing hydroxymethanesulfonic acid ions generated in the mixing tank 3 is supplied to the pressurizing pump 4 through the water passage line L2. The raw water W1 pressurized by the pressurizing pump 4 is further supplied to the RO membrane module 5 through the water passage line L2. The raw water W1 supplied to the RO membrane module 5 is subjected to membrane separation treatment into permeated water W2 and concentrated water W3 by the RO membrane of the RO membrane module 5. In the permeated water W2, the amount of hydroxymethanesulfonate ions is greatly reduced.

  Concentrated water W3 generated in the RO membrane module 5 passes through the concentrated water line L4, the branched portion J1, and the concentrated water reflux line L6 by opening and closing the valves 6 and 7 as appropriate. Reflux to line L2. In addition, a part of the concentrated water W3 generated in the RO membrane module 5 is opened and closed as appropriate by opening and closing the valves 6 and 7 to the system of the water treatment system 1 via the concentrated water line L4, the branch portion J1, and the drainage line L5. Drained outside.

  The permeated water W2 produced by the RO membrane module 5 is supplied to the porous adsorbent bed tower 8 through the water passage line L3. The permeated water W <b> 2 supplied to the porous adsorbent bed tower 8 passes through the porous adsorbent bed accommodated in the porous adsorbent bed tower 8. At that time, the hydroxymethanesulfonic acid ions remaining in the permeate W2 are adsorbed in contact with the porous adsorbent in the porous adsorbent bed and removed from the permeate W2. Thereby, the treated water W4 in which the amount of hydroxymethanesulfonate ions is further reduced can be obtained. The treated water W4 produced by the porous adsorbent bed tower 8 is supplied to a demand destination device or the like (not shown) via a water passage line L7.

  In the treated water W4, the concentration of formaldehyde is preferably 0.08 mg / L or less. In the treated water W4, the total organic carbon (hereinafter also referred to as “TOC”) is preferably 5 mgC / L or less.

  According to the water treatment system 1 which concerns on 1st Embodiment mentioned above, the following effects are show | played, for example.

  Formaldehyde contained in the raw water W1 is changed into hydroxymethane sulfonate ions in the mixing tank 3 by reaction with bisulfite ions. In the RO membrane module 5, hydroxymethanesulfonate ions are removed at a high removal rate, and the permeated water W2 in which the amount of hydroxymethanesulfonate ions is significantly reduced is obtained. In the porous adsorbent bed tower 8, a small amount of hydroxymethanesulfonate ions remaining in the permeate W2 is removed at a high removal rate, and treated water W4 in which the amount of hydroxymethanesulfonate ions is further reduced is obtained. . Thus, according to the water treatment system 1 according to the first embodiment, formaldehyde can be removed from the raw water W1 containing formaldehyde with a high removal rate.

  The reaction between formaldehyde and bisulfite ions in the mixing tank 3 proceeds sufficiently at room temperature or under heating. Therefore, a wide range of water temperatures can be used as the raw water W1. For example, even hot water such as waste water after retort sterilization can be used as the raw water W1. Therefore, it is not necessary to adjust the temperature of the raw water W1 in order to advance the reaction in the mixing tank 3, and formaldehyde can be removed from the raw water W1 with high energy efficiency.

  In the RO membrane module 5 and the porous adsorbent bed tower 8, a part of organic components and a part of inorganic components other than formaldehyde and hydroxymethanesulfonate ions can be removed. Therefore, in the treated water W4, the amount of these components is also reduced.

[Second Embodiment]
Next, a water treatment system 1A according to a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is an overall configuration diagram of a water treatment system 1A according to the second embodiment of the present invention. In the second embodiment, differences from the first embodiment will be mainly described. In the second embodiment, the same or equivalent components as those in the first embodiment will be described with the same reference numerals. In the second embodiment, the description overlapping with the first embodiment is omitted as appropriate.

  As shown in FIG. 2, a water treatment system 1A according to the present embodiment includes a bisulfite ion source compound addition device 2, a mixing tank 3, a pressure pump 4, an RO membrane module 5 as a removing means, a valve 6 and 7 and an anion exchange resin bed column 9 as a removing means. Further, the water treatment system 1A includes water flow lines L1, L2, L3, and L8, a concentrated water line L4, a drainage line L5, and a concentrated water reflux line L6. That is, 1 A of water treatment systems which concern on 2nd Embodiment differ in the point provided with the anion exchange resin bed tower 9 instead of the porous adsorbent bed tower 8 of the water treatment system 1 which concerns on 1st Embodiment.

  The anion exchange resin bed column 9 adsorbs and removes hydroxymethanesulfonic acid ions remaining in the permeated water W2 by an anion exchange resin (for example, a Cl-type strongly basic anion exchange resin). The anion exchange resin bed tower 9 is connected to the downstream end of the water flow line L3. The anion exchange resin bed tower 9 accommodates an anion exchange resin bed. On the downstream side of the anion exchange resin bed tower 9, a water flow line L8 through which the treated water W5 produced by the anion exchange resin bed tower 9 can be passed is connected.

  The water flow line L8 is a line for sending the treated water W5 produced in the anion exchange resin bed tower 9 to a customer. The upstream end of the water flow line L8 is connected to the anion exchange resin bed tower 9. The downstream end of the water flow line L8 is connected to a demand destination device or the like (not shown).

  Next, a water treatment method (operation of the water treatment system 1A) by the water treatment system 1A according to the second embodiment will be described with reference to FIG. The water treatment method by the water treatment system 1A according to the second embodiment is substantially the same as the water treatment method by the water treatment system 1 according to the first embodiment, and is removed by the RO membrane module 5 and the porous adsorbent bed tower 8. Instead of the process, it includes a removal process by the RO membrane module 5 and the anion exchange resin bed tower 9. Therefore, duplication description is abbreviate | omitted about the part similar to the water treatment method by the water treatment system 1 which concerns on 1st Embodiment, and the operation | movement in the removal process by the anion exchange resin bed tower 9 is demonstrated.

  The permeated water W2 produced by the RO membrane module 5 is supplied to the anion exchange resin bed column 9 through the water passage line L3. The permeated water W <b> 2 supplied to the anion exchange resin bed tower 9 passes through the anion exchange resin bed accommodated in the anion exchange resin bed tower 9. At that time, the hydroxymethanesulfonic acid ions remaining in the permeated water W2 are adsorbed in contact with the anion exchange resin in the anion exchange resin bed and are removed from the permeated water W2. Thereby, the treated water W5 in which the amount of hydroxymethanesulfonate ions is further reduced can be obtained. The treated water W5 produced by the anion exchange resin bed tower 9 is supplied to a demanding device or the like (not shown) via a water passage line L8.

  In the treated water W5, the concentration of formaldehyde is preferably 0.08 mg / L or less. Moreover, in the treated water W5, it is preferable that TOC is 5 mgC / L or less.

  According to 1 A of water treatment systems which concern on 2nd Embodiment mentioned above, the following effects are show | played, for example.

  In the water treatment system 1A according to the second embodiment, an anion exchange resin bed column 9 is used instead of the porous adsorbent bed column 8 in the water treatment system 1 according to the first embodiment. In the anion exchange resin bed tower 9, a small amount of hydroxymethanesulfonate ions remaining in the permeate W2 are removed at a high removal rate, and treated water W5 in which the amount of hydroxymethanesulfonate ions is further reduced is obtained. . Thus, according to the water treatment system 1A according to the second embodiment, formaldehyde can be removed from the raw water W1 containing formaldehyde with a high removal rate.

  In the RO membrane module 5 and the anion exchange resin bed tower 9, a part of organic components other than formaldehyde and hydroxymethanesulfonate ions and at least a part of inorganic components can be removed. Therefore, the amount of these components is also reduced in the treated water W5. Other effects are the same as those achieved by the water treatment system 1 according to the first embodiment.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and can be implemented in various forms.

  For example, in the first embodiment, the porous adsorbent floor tower 8 and the water flow line L7 may be omitted, and the downstream end of the water flow line L3 may be connected to a demanding device or the like (not shown). Good. In this configuration, the permeated water W2 manufactured by the RO membrane module 5 is used as treated water. As described above, in the permeated water W2, the amount of hydroxymethanesulfonate ions is greatly reduced. Therefore, the permeated water W2 can be used as treated water.

  In the first embodiment, the pressurization pump 4, the RO membrane module 5, the valves 6 and 7, the water flow line L3, the concentrated water line L4, the drainage line L5, and the concentrated water reflux line L6 are omitted, and the water flow line L2 The downstream end may be connected to the porous adsorbent bed tower 8. In this configuration, the hydroxymethanesulfonate ions generated in the mixing tank 3 are adsorbed and removed by the porous adsorbent in the porous adsorbent bed tower 8. Thereby, the treated water W4 in which the amount of hydroxymethanesulfonate ions is greatly reduced can be obtained.

  In the second embodiment, the pressurization pump 4, the RO membrane module 5, the valves 6 and 7, the water flow line L3, the concentrated water line L4, the drainage line L5, and the concentrated water reflux line L6 are omitted, and the water flow line L2 The downstream end may be connected to the anion exchange resin bed tower 9. In this configuration, the hydroxymethanesulfonate ions generated in the mixing tank 3 are adsorbed and removed by the anion exchange resin in the anion exchange resin bed column 9. Thereby, the treated water W5 in which the amount of hydroxymethanesulfonate ions is significantly reduced can be obtained.

  In the first and second embodiments, in order to monitor whether or not the removing unit functions normally, a configuration in which a TOC measuring unit is appropriately provided may be employed. In the removing means of these embodiments, a part of the organic component such as hydroxymethanesulfonate ion is removed, so that there is a difference in TOC before and after the removing means. By monitoring this difference, it is possible to detect a decrease in the function of the removing means. As a specific configuration, for example, a configuration in which a TOC measuring unit is provided between the pressurizing pump 4 and the RO membrane module 5 and in the water passage line L3 can be cited. In this configuration, the difference in TOC before and after the RO membrane module 5 can be monitored by the TOC measuring means. When the difference in TOC is equal to or less than a predetermined value, it is determined that the RO membrane has deteriorated and the TOC removal rate by the RO membrane module 5 has decreased, and the RO membrane is replaced. Similarly, the difference in the TOC before and after the porous adsorbent bed tower 8 or the anion exchange resin bed tower 9 is monitored, and when the difference in the TOC becomes a predetermined value or less, the porous adsorbent bed tower 8 or It is determined that the TOC removal rate by the anion exchange resin bed column 9 has decreased, and the porous adsorbent is exchanged or the anion exchange is regenerated or exchanged. Instead of the TOC measuring means, a bisulfite ion measuring means or a hydroxymethane sulfonate ion measuring means may be used. In each of the above measurement means, for example, measurement is performed using ultraviolet absorbance, oxidation-reduction potential, or the like.

  In 1st and 2nd embodiment, it is good also as a structure which provided the water softening processing apparatus in the upstream of the mixing tank 3. FIG. The water softening apparatus is to remove hardness components (calcium ions and magnesium ions) contained in the raw water W1 by adsorbing them with a cation exchange resin. By softening the raw water W1 with a water softening device, the removal rate of hydroxymethanesulfonate ions by the removing means such as the RO membrane, the porous adsorbent, the anion exchange resin, and the like is easily improved.

  In 1st and 2nd embodiment, it is good also as a structure which provided pH adjustment means, such as an acidic chemical | medical agent addition apparatus and a basic chemical | medical agent addition apparatus. Thereby, since pH of raw | natural water W1, permeated water W2, etc. is adjusted suitably, in mixing tank 3, formaldehyde and bisulfite ion can be made to react by optimal pH, RO membrane module 5, porous In the adsorbent bed column 8 and the anion exchange resin bed column 9, hydroxymethane sulfonate ions can be removed at an optimum pH, and the removal rate of hydroxymethane sulfonate ions can be improved. For example, in the first and second embodiments, the pH adjusting means may be provided on the upstream side of the mixing tank 3, between the branch portion J2 and the pressurizing pump 4, and at least at one location of the water flow line L3. Good.

  In 1st and 2nd embodiment, you may mix the treated water W4 or the treated water W5, and the dilution water which does not contain formaldehyde, and may supply it to a customer. Thereby, water in which the amount of remaining formaldehyde is further reduced can be obtained. The dilution water is preferably water that does not contain formaldehyde, hydroxymethanesulfonate ions, and other organic components.

  In 1st and 2nd embodiment, it may replace with raw water W1 containing formaldehyde, raw water W1 containing other aldehydes, for example, acetaldehyde (molecular weight 44), or raw water W1 containing formaldehyde and acetaldehyde may be used. Acetaldehyde, like formaldehyde, has a molecular weight of 60 or less and has no electric charge. Therefore, acetaldehyde is removed from raw water containing acetaldehyde using removal means such as RO membranes, porous adsorbents, anion exchange resins and the like. It is difficult to remove at a high removal rate. When acetaldehyde is reacted with bisulfite ion, 1-hydroxyethanesulfonate ion (molecular weight 125), which is a kind of α-hydroxysulfonate ion, is generated. Since 1-hydroxyethanesulfonic acid ion has a molecular weight exceeding 60 and has a charge, it can be removed at a high removal rate using the above-mentioned removing means in the same manner as hydroxymethanesulfonic acid ion. Therefore, according to the present invention, acetaldehyde can be removed from raw water containing acetaldehyde, and formaldehyde and acetaldehyde can also be removed from raw water containing formaldehyde and acetaldehyde.

  Examples of the present invention will be described below, but the scope of the present invention is not limited to these examples.

[Preparation of raw water]
50 mL of waste water (pH 7) after retort sterilization was collected. Diluted aqueous solution 0.5 mL obtained by diluting 37% by weight aqueous formaldehyde solution with water to 1/1000 (volume ratio) is added to the waste water, and raw water used in Examples 1-4 and Comparative Examples 1 and 2 below. Got. When measured with a GC / MS and a TOC meter, the formaldehyde concentration in this raw water was 3.3 mg / L, and the TOC was 0.88 mgC / L.

[Examples 1-4, Comparative Examples 1 and 2] Reactivity of formaldehyde and bisulfite ion Sodium bisulfite, which is a reducing agent, to have the concentration shown in Table 1 with respect to 50.5 mL of the raw water prepared above. Alternatively, sodium thiosulfate was added, and the addition reaction was carried out by stirring at the reaction temperature shown in Table 1 for 30 minutes. The amount of formaldehyde contained in the raw water after the addition reaction was relatively measured by the MBTH method. That is, 3-methyl-2-benzothiazolinone hydrazone (hereinafter referred to as “MBTH”) is added to the raw water after the addition reaction, and formaldehyde and MBTH are subjected to a color development reaction, and the absorbance of the color reaction product is measured spectrophotometrically. Measured with a meter. The amount of formaldehyde contained in the raw water after the addition reaction was compared based on the peak height of the color reaction product at 620 nm. The results are shown in FIG. In carrying out the MBTH method, a commercially available pack test (manufactured by Kyoritsu Riken) was used.

注）亜硫酸水素ナトリウム又はチオ硫酸ナトリウムとホルムアルデヒドとのモル比

Note) Molar ratio of sodium bisulfite or sodium thiosulfate to formaldehyde

  As shown in FIG. 3, in Comparative Example 1 where raw water was used untreated, a peak appeared at 620 nm. In Examples 1 to 4 using sodium hydrogen sulfite as the reducing agent, no peak was observed at 620 nm. From this, it can be seen that when the molar ratio of sodium bisulfite to formaldehyde is 1 or more, most of the formaldehyde contained in the raw water has reacted with sodium bisulfite and disappeared.

  Further, from Examples 1 and 2, it was confirmed that the reaction between sodium bisulfite and formaldehyde proceeded in a short time of 30 minutes at room temperature or 60 ° C. On the other hand, in Comparative Example 2 using sodium thiosulfate instead of sodium bisulfite as a reducing agent, the peak height at 620 nm is the same as that of Comparative Example 1, and formaldehyde and sodium thiosulfate are completely reacted. I understand that I did not. Sodium bisulfite produces bisulfite ions, whereas sodium thiosulfate does not produce bisulfite ions. Therefore, it turns out that formaldehyde was converted into hydroxymethanesulfonic acid ions by reaction with bisulfite ions and disappeared from the raw water.

[Example 5] Removal of formaldehyde by a system using an RO membrane In the first embodiment shown in Fig. 1, water using a water treatment system having a configuration in which the porous adsorbent bed tower 8 and the water flow line L7 are omitted. An experiment corresponding to the treatment method was performed. Sodium bisulfite was added to 50.5 mL of the raw water prepared above so that the concentration was 63 mg / L (molar ratio of sodium bisulfite to formaldehyde: 5.5), and the mixture was stirred at room temperature for 30 minutes. Reaction with sodium hydrogen sulfite. The raw water after the reaction was introduced into the RO membrane module via a pressure pump. As the RO membrane, a reverse osmosis membrane element TMG20 manufactured by Toray Industries, Inc. was used, the pressure by the pressure pump was set to 0.6 MPa, and the operation was performed at a recovery rate of 50%. About the concentrated water and permeate which flowed out from RO membrane module, formaldehyde concentration and TOC were measured using GC / MS and a TOC meter. The results are shown in Table 2.

注）検出限界未満

Note) Below detection limit

  When the results are compared between raw water and concentrated water in Table 2, the amount of formaldehyde is greatly reduced by reacting sodium bisulfite with formaldehyde at a molar ratio of 5.5, and the reaction product is From the separation by the RO membrane module, it can be seen that the TOC other than formaldehyde was concentrated in the concentrated water.

  When the results are compared between the concentrated water and the permeated water in Table 2, the TOC in the concentrated water was 4.10 mgC / L, whereas the TOC in the permeated water was 0.60 mgC / L. It can be seen that about 85% of the TOC was removed on the basis of the concentrated water. Moreover, it turns out that formaldehyde was not detected from permeated water.

  The above is an experiment corresponding to a water treatment method using a water treatment system having a configuration in which the porous adsorbent bed tower 8 and the water flow line L7 are omitted in the first embodiment shown in FIG. If the permeated water obtained in this experiment is brought into contact with the porous adsorbent or the anion exchange resin, it can be expected that treated water with further reduced TOC can be obtained. Therefore, in the water treatment system 1 of the first embodiment further having the porous adsorbent bed tower 8 and the water treatment system 1A of the second embodiment further having the anion exchange resin bed tower 9, the removal performance is further improved. Obviously.

[Examples 6 and 7] Removal of formaldehyde by a system using an RO membrane An experiment corresponding to a water treatment method using a water treatment system similar to that of Example 5 was performed. Cooled retort effluent (pH 7.2, water temperature 33 ° C.) different from the above examples and comparative examples is used as raw water, and the molar ratio of sodium bisulfite to formaldehyde is 17.7 with respect to this raw water. Sodium bisulfite was added to the mixture, and the mixture was stirred for 20 minutes in Example 6 and for 30 minutes in Example 7 to react formaldehyde with sodium bisulfite. The raw water after the reaction was introduced into the RO membrane module via a pressure pump. As the RO membrane, Toray Industries, Inc. reverse osmosis membrane element TMG20 was used, and the pressure by the pressure pump was set to 0.6 MPa, and the operation was performed at a recovery rate of 80%. The formaldehyde concentration and TOC were measured using GC / MS and a TOC meter for the raw water before and after the addition of sodium bisulfite, and the concentrated water and permeated water flowing out from the RO membrane module. The results are shown in Tables 3 and 4.

注）検出限界未満

Note) Below detection limit

注）検出限界未満

Note) Below detection limit

  In Tables 3 and 4, when the results were compared between the raw water before addition and the raw water after addition, it was found that the reaction between sodium bisulfite and formaldehyde progressed by adding sodium bisulfite to the raw water containing formaldehyde. I understand. Since the water after the addition of sodium bisulfite is concentrated, the concentration of formaldehyde in the concentrated water increases, but formaldehyde was not detected in the permeate.

[Comparative Example 3] Removal of formaldehyde by a system not using sodium bisulfite An experiment for removing formaldehyde with an RO membrane module alone was conducted without adding sodium bisulfite to the raw water. Waste water (pH 6.8) after retort sterilization different from the above Examples and Comparative Examples was used as raw water and introduced into the RO membrane module via a pressure pump. As the RO membrane, Toray Industries, Inc. reverse osmosis membrane element TMG20 was used, and the pressure by the pressure pump was set to 0.6 MPa, and the operation was performed at a recovery rate of 80%. About the concentrated water and permeated water which flowed out from raw | natural water and RO membrane module, the formaldehyde density | concentration was measured using GC / MS. The results are shown in Table 5.

  When the results are compared between the concentrated water and the permeated water in Table 5, the formaldehyde concentration in the concentrated water was 0.51 mg / L, whereas the formaldehyde concentration in the permeated water was 0.39 mg / L. It can be seen that the separation in the membrane module only removed about 24% formaldehyde on a concentrated water basis. Further, the formaldehyde concentration of the permeated water greatly exceeded 0.08 mg / L, which is the quality standard of tap water.

1, 1A Water treatment system 2 Bisulfite ion source compound addition device (bisulfite ion source compound addition means)
3 Mixing tank (mixing means)
4 Pressure pump 5 Reverse osmosis membrane module (removal means)
6, 7 Valve 8 Porous adsorbent bed tower (removal means)
9 Anion exchange resin bed tower (removal means)
L1, L2, L3, L7, L8 Water flow line L4 Concentrated water line L5 Drainage line L6 Concentrated water return line W1 Raw water W2 Permeated water (treated water)
W3 Concentrated water W4, W5 Treated water

Claims (4)

A water treatment method for removing aldehydes from raw water containing aldehydes,
A reaction step of adding bisulfite to raw water and reacting aldehydes contained in the raw water with bisulfite ions at pH 5 to 7 to produce α-hydroxysulfonic acid ions;
An ion exchange step of removing the α-hydroxysulfonic acid ion using an anion exchange resin;
Including water treatment method. Further comprising a membrane separation step of removing the α-hydroxysulfonate ion using a reverse osmosis membrane,
The water treatment method according to claim 1, wherein the ion exchange step is a step performed after the membrane separation step. A water treatment system for removing aldehydes from raw water containing aldehydes,
Bisulfite addition means for adding bisulfite to raw water,
The raw water and the bisulfite are mixed, and the aldehydes contained in the raw water are reacted with bisulfite ions generated from the bisulfite at pH 5 to 7 to produce α-hydroxysulfonic acid ions. Means,
An ion exchange means for removing the α-hydroxysulfonic acid ion using an anion exchange resin;
A water treatment system comprising.   The water treatment system according to claim 3, further comprising a membrane separation unit that removes the α-hydroxysulfonate ion using a reverse osmosis membrane.

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