Wastewater treatment method and device using reverse osmosis membrane

Abstract

A wastewater treatment method using a reverse osmosis membrane, in which raw water is separated into permeate water and concentrated water by adding a scale dispersant to the raw water and performing reverse osmosis membrane treatment, and the concentrated water is subjected to crystallization treatment, characterized in that a deactivator that deactivates the scale dispersant is added to the concentrated water. A ferric salt and a cationic polymer are added as inactivators.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for treating wastewater using a reverse osmosis membrane, and more particularly to a method and apparatus for adding a dispersant to the water supplied to the reverse osmosis membrane. More specifically, the present invention relates to a method and apparatus for treating wastewater using a reverse osmosis membrane suitable for treating mining wastewater. Background Art

[0002] As a method for removing dissolved components from mining wastewater such as mine drainage, there is a method in which a scale dispersant is added to the mine drainage water and the concentrated water is treated using a forward osmosis membrane or a reverse osmosis membrane to crystallize the resultant concentrated water (Patent Document 1).

[0003] Patent Document 2 describes a method in which a scale dispersant is added to raw water containing salts (e.g., leachate from a final waste disposal site), the concentrated water is subjected to reverse osmosis membrane treatment, and the concentrated water is further subjected to reverse osmosis membrane treatment and crystallized in a crystallization tank.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-215686.

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 11-165171. Summary of the Invention

[0008] Problems to be solved by the invention

[0009] By adding a dispersant to the feed water of a reverse osmosis membrane (hereinafter sometimes referred to as RO), scale deposition in the RO device is suppressed.

[0010] However, when dispersants were added to RO feed water, the crystallization efficiency of RO concentrated water was found to decrease. This is presumably because the dispersants remaining in the concentrated water hindered the crystallization of salts and the like.

[0011] The present invention aims to provide a wastewater treatment method and apparatus using a reverse osmosis membrane, wherein a scale dispersant is added to wastewater for reverse osmosis membrane treatment and the concentrated water is subjected to crystallization treatment, wherein the wastewater treatment method and apparatus using a reverse osmosis membrane can increase the crystallization amount.

[0012] Means for solving problems

[0013] The present invention is summarized as follows.

[0014] [1] A method for treating wastewater using a reverse osmosis membrane, wherein a scale dispersant is added to raw water, the raw water is subjected to reverse osmosis membrane treatment to separate the raw water into permeate water and concentrated water, and the concentrated water is subjected to crystallization treatment, wherein a deactivating agent for deactivating the scale dispersant is added to the concentrated water.

[0015] [2] The wastewater treatment method using a reverse osmosis membrane according to [1], wherein an iron salt and a cationic polymer are added as the deactivating agent.

[0016] [3] The wastewater treatment method using a reverse osmosis membrane according to [2], wherein the iron salt is ferric chloride or ferric sulfate, and the cationic polymer is DMA-epi (Dimethylamine-epichlorohydrin dimethylamine-epichlorohydrin polycondensate) and / or pDADMAC (Poly diallyl dimethyl ammoniumchloride).

[0017] [4] A wastewater treatment device using a reverse osmosis membrane, wherein the wastewater treatment device using a reverse osmosis membrane comprises: a scale dispersant adding mechanism for adding a scale dispersant to raw water; a reverse osmosis membrane device for treating the raw water to which the scale dispersant has been added; a deactivator adding mechanism for adding a deactivator for the scale dispersant to concentrated water of the reverse osmosis membrane device; and a crystallization tank for performing crystallization treatment on the concentrated water to which the deactivator has been added.

[0018] [5] The wastewater treatment device using a reverse osmosis membrane according to [4], wherein an iron salt and a cationic polymer are added as the deactivating agent.

[0019] [6] The wastewater treatment device using a reverse osmosis membrane according to [5], wherein the iron salt is ferric chloride or ferric sulfate, and the cationic polymer is DMA-epi and / or pDADMAC.

[0020] Effects of the Invention

[0021] According to the present invention, in a method and apparatus for adding a dispersant to wastewater for RO treatment and then subjecting the RO concentrated water to crystallization treatment, the addition of a deactivating agent to the RO concentrated water suppresses the crystallization-inhibiting effect of the dispersant during the crystallization treatment, allowing for efficient crystallization. Furthermore, this improves the quality of the treated water.

[0022] The mechanism by which crystallization inhibition is suppressed by the addition of a deactivator is not entirely clear, but it is speculated that the following effects are exerted by the iron salt and the cationic polymer. The iron salt binds to the dispersant, thereby suppressing the binding of the scale component and the dispersant. In addition, the iron salt acts as an active site for generating crystallization, and the scale component binds to the iron salt to promote the aggregation of the scale component. The cationic polymer neutralizes the charge of the dispersant to suppress the crystallization inhibition effect of the dispersant. In addition, when the dispersant is a polymer, the cationic polymer forms a gel with the dispersant, suppressing the crystallization inhibition effect of the dispersant. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flowchart showing a wastewater treatment method and apparatus using a reverse osmosis membrane according to an embodiment.

[0024] Figure 2 is a graph showing the results of the test example.

[0025] Figure 3 is a graph showing the results of the test example.

[0026] Figure 4 is a graph showing the results of the test example.

[0027] Figure 5 is a graph showing the results of the test example.

[0028] Figure 6 is a graph showing the results of the test example.

[0029] Figure 7 This is a diagram of the test device.

[0030] Figure 8 is a graph showing the results of the test example. DETAILED DESCRIPTION

[0031] Below, refer to Figure 1 An embodiment will be described. Figure 1 This diagram shows the flow of a wastewater treatment method and apparatus using a reverse osmosis membrane according to an embodiment. Raw water (in this embodiment, mine wastewater) is introduced into an RO device 3 via a water supply line 1. Scale dispersant is added to the water supply line 1 by a scale dispersant addition mechanism 2. The dispersant addition mechanism 2 consists of a tank for dispersant aqueous solution, an injection pump, and injection piping.

[0032] The permeated water of the RO device 3 is taken out as the first treated water.

[0033] The concentrated water from the RO unit 3 is introduced into a stirring tank 5 via a pipe 4. In this stirring tank 5, a deactivating agent is added via a deactivating agent adding mechanism 6 and stirred using a stirrer 5a. The RO concentrated water with the added deactivating agent is introduced into a crystallization tank 7 for crystallization. The crystallized product is discharged via a pipe 8. It should be noted that a portion of the precipitate may be returned to the crystallization tank 7.

[0034] A portion of the outflow water from the crystallization tank 7 is returned to the water supply line 1 through the line 10 , and the remaining portion is taken out as second treated water through the line 9 .

[0035] As raw water, mine drainage such as gold mines, coal mines, and mining leachate is preferred. The total concentration of salts in these mine drainages is generally around 20,000 mg / L to 200,000 mg / L, and they generally contain high concentrations of sulfate.

[0036] As scale dispersants, in addition to inorganic polyphosphates such as sodium hexametaphosphate and sodium tripolyphosphate, and phosphonic acids such as hydroxyethylene diphosphonic acid and phosphonobutane tricarboxylic acid, polymer scale dispersants can also be used. The polymer scale dispersant may be one having only a carboxyl group and no sulfonic acid group, and preferably a polymer having both a sulfonic acid group and a carboxyl group.

[0037] Examples of polymer scale dispersants include polymers having suitable sulfonic acid groups and carboxyl groups, such as copolymers of monomers having sulfonic acid groups and monomers having carboxyl groups, or further examples include terpolymers with other monomers copolymerizable with these monomers. Examples of monomers having sulfonic acid groups include conjugated diene sulfonic acids such as 2-methyl-1,3-butadiene-1-sulfonic acid, unsaturated (meth)allyl ether monomers having sulfonic acid groups such as 3-(meth)allyloxy-2-hydroxypropanesulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidepropanesulfonic acid, styrenesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, allylsulfonic acid, isopentenesulfonic acid, or salts thereof. Preferred examples include 3-allyloxy-2-hydroxy-1-propanesulfonic acid (HAPS) and 2-acrylamide-2-methylpropanesulfonic acid (AMPS). These monomers may be used alone or in combination.

[0038] On the other hand, examples of monomers having a carboxyl group include acrylic acid (AA), methacrylic acid, crotonic acid, isocrotonic acid, vinyl acetate, atropic acid, maleic acid, fumaric acid, itaconic acid, hydroxyethyl acrylic acid, or salts thereof. Acrylic acid and methacrylic acid are preferred. One of these may be used alone, or two or more may be mixed and used.

[0039] Examples of monomers copolymerizable with these monomers include olefins such as isobutylene, and amides such as N-tert-butylacrylamide (N-tBAA) and N-vinylformamide.

[0040] The weight average molecular weight of the polymer scale dispersant is preferably about 1,000 to 20,000.

[0041] The amount of the scale dispersant added is preferably about 20 to 60 mg / L, particularly preferably about 20 to 40 mg / L.

[0042] Iron salts and cationic polymers are used as deactivators added to RO concentrated water. Iron salts such as ferric chloride and ferric sulfate are preferred.

[0043] The amount of iron salt added (mg / L) is preferably about 0.1 to 5 times the amount of scale dispersant added (mg / L), particularly preferably about 0.5 to 2 times. The amount of iron salt added can be adjusted in consideration of conditions such as the salt concentration of the raw water.

[0044] As the cationic polymer, for example, at least one of DMA-epi (dimethylamine-epichlorohydrin dimethylamine-epichlorohydrin polycondensate) and pDADMAC (poly diallyl dimethyl ammonium chloride) is preferred.

[0045] The weight average molecular weight of the cationic polymer may be, for example, 1,000 to 1,000,000, preferably 50,000 to 800,000, and more preferably 100,000 to 700,000. The weight average molecular weight of the cationic polymer may be 10,000 or less, for example, approximately 1,000 to 10,000.

[0046] When the cationic polymer is DMA-epi, the weight average molecular weight of DMA-epi may be, for example, 50,000 to 200,000. When the cationic polymer is pDADMAC, the weight average molecular weight of pDADMAC is, for example, preferably 100,000 to 800,000, more preferably 300,000 to 600,000.

[0047] In addition, the weight average molecular weight is a weight average molecular weight calculated|required by gel permeation chromatography (GPC) with respect to standard polystyrene.

[0048] The iron salt and the cationic polymer may be mixed into one dose and then added, or may be added separately.

[0049] The amount (mg / L) of the cationic polymer added is preferably about 0.05 to 5 times, and particularly preferably about 0.5 to 2.5 times, the amount (mg / L) of the scale dispersant added.

[0050] The ratio of the amount of iron salt added (mg / L) to the amount of cationic polymer added (mg / L) (amount of iron salt added: amount of cationic polymer added) is preferably about 1:0.1 to 10, particularly about 1:0.5 to 2.

[0051] By adding the deactivating agent, the precipitation amount of calcium sulfate, calcium carbonate, calcium hydroxide, calcium phosphate, sodium bicarbonate, calcium fluoride, barium sulfate, silicon dioxide, etc. increases.

[0052] [Example]

[0053] [Test Example 1]

[0054] In a beaker, the following deactivator 1 or 2 was added to simulated raw water (simulated mine drainage) containing the following scale dispersant and stirred. After a predetermined time (0, 20, 40, or 60 minutes), the simulated raw water was filtered using a 0.1 μm filter, and the dissolved calcium concentration was measured.

[0055] <Simulated raw water>

[0056] CaCl2: 2300mg / L.

[0057] Na2SO4:7100mg / L.

[0058] The scale dispersant used is a phosphonic acid scale dispersant: 40 mg / L, or an AA / AMPS scale dispersant: 80 mg / L.

[0059] pH: 3.5, 5 or 8.

[0060] <Inactivator 1>

[0061] Ferric chloride: 1 mg / L was added to the scale dispersant at 1 mg / L.

[0062] <Inactivator 2>

[0063] Ferric chloride: 1 mg / L was added to the scale dispersant at 1 mg / L.

[0064] The cationic polymers were DMA-epi (weight average molecular weight 120,000): 0.1 mg / L was added to 1 mg / L of the scale dispersant; and pDADMAC (weight average molecular weight approximately 450,000): 1 mg / L was added to 1 mg / L of the scale dispersant.

[0065] The results of the determination of each Ca dissolution concentration are as follows Figure 2As shown in the figure, in either case, the longer the time after adding the deactivator, the lower the dissolved Ca concentration after filtration. This indicates that the deactivator suppresses the dispersing effect of the dispersant, facilitating Ca precipitation, and removing Ca by the filter. Compared to Deactivator 1 using only an iron salt, Deactivator 2, which combined an iron salt and a cationic polymer, tended to have a superior deactivation effect.

[0066] [Test Example 2]

[0067] The same conditions as in Test Example 1 were used except that simulated raw water containing humus and to which a scale dispersant was added was used, and no filter was used. After a predetermined time, the supernatant was collected and the dissolved Ca concentration was measured.

[0068] <Simulated raw water>

[0069] CaCl2: 2300mg / L.

[0070] Na2SO4:7100mg / L.

[0071] Humus: calculated as DOC (Dissolved Organic Carbon) is 100 mg / L.

[0072] The scale dispersant used is a phosphonic acid scale dispersant: 40 mg / L, or an AA / AMPS scale dispersant: 80 mg / L.

[0073] pH: 3.5, 5 or 10.

[0074] The results of the determination of each Ca dissolution concentration are as follows Figure 3 shown.

[0075] [Test Example 3]

[0076] The same conditions as those of Test Example 1 were used except that the following simulated raw water with a high salt concentration and to which a scale dispersant was added was used, and the above-mentioned Deactivator 1, Deactivator 2, or the following Deactivator 3 (added in an amount twice that of Deactivator 2) was used as the deactivator.

[0077] <Simulated raw water>

[0078] CaCl2: 2300mg / L.

[0079] Na2SO4:7100mg / L.

[0080] NaCl: 3000mg / L.

[0081] The scale dispersant used is a phosphonic acid scale dispersant: 40 mg / L, or an AA / AMPS scale dispersant: 80 mg / L.

[0082] pH: 6.8.

[0083] Conductivity: 25.0ms / cm.

[0084] <Inactivator 3>

[0085] Ferric chloride: 2 mg / L was added to 1 mg / L of scale dispersant.

[0086] The cationic polymers were DMA-epi (weight average molecular weight 120,000): 0.2 mg / L was added to 1 mg / L of the scale dispersant; and pDADMAC (weight average molecular weight approximately 450,000): 2 mg / L was added to 1 mg / L of the scale dispersant.

[0087] The results of the determination of each Ca dissolution concentration are as follows Figure 4 shown.

[0088] [Test Example 4]

[0089] The same conditions as those of Test Example 1 were set except that the following simulated raw water to which a scale dispersant was added was used, and the following seed crystals were added together with the deactivating agent.

[0090] <Simulated raw water>

[0091] CaCl2: 2300mg / L.

[0092] Na2SO4:7100mg / L.

[0093] The scale dispersant used is a phosphonic acid scale dispersant: 40 mg / L, or an AA / AMPS scale dispersant: 80 mg / L.

[0094] pH: 5.

[0095] <Seed Crystal>

[0096] CaSO4: 50000mg / L.

[0097] The results of the determination of each Ca dissolution concentration are as follows Figure 5 shown.

[0098] [Test Example 5]

[0099] The same conditions as those of Test Example 4 were set except that simulated raw water with a high salt concentration and to which a scale dispersant was added was used.

[0100] <Simulated raw water>

[0101] CaCl2: 2300mg / L.

[0102] Na2SO4:7100mg / L.

[0103] NaCl: 3000mg / L.

[0104] The scale dispersant used is a phosphonic acid scale dispersant: 40 mg / L, or an AA / AMPS scale dispersant: 80 mg / L.

[0105] pH: 5.

[0106] Conductivity: 25.0ms / cm.

[0107] The results of the determination of each Ca dissolution concentration are as follows Figure 6 shown.

[0108] [Test Example 6]

[0109] use Figure 7 The device was subjected to a continuous sludge circulation test under the following test conditions.

[0110] (i) The following seed crystals were added to the simulated raw water to which the scale dispersant was added, and the water was treated in coagulation tank T1, coagulation tank T2, and crystallization tank T3. The Ca dissolved concentration of the treated water was measured. The sludge obtained in T3 was returned to the inlet of T1, and the sludge circulation rate (sludge circulation rate R = sludge return flow rate / input flow rate × 100 (%)) was set to 30%. The results are shown in Figure 8 The curve is from 23 / 8 / 2022 to 24 / 8 / 2022.

[0111] <Device Overview>

[0112] Solidification tank T1: 0.5L.

[0113] Coagulation tank T2: 0.5L.

[0114] Anionic polyacrylamide was added as a coagulant at 2.5 mg / L.

[0115] Crystallization tank T3: 3L (diameter 200 mm, height 395 mm).

[0116] Processing capacity: 2L / hour.

[0117] Holding time: 30 minutes (T1), 30 minutes (T2), 90 minutes (T3).

[0118] <Simulated raw water>

[0119] CaCl2: 2300mg / L.

[0120] Na2SO4:7100mg / L.

[0121] As the scale dispersant, a phosphonic acid-based scale dispersant is used: 40 mg / L.

[0122] pH: 5.

[0123] <Seed Crystal>

[0124] CaSO4: 50000mg / L.

[0125] Then, a continuous sludge circulation test was conducted in the same manner as in the above (i) except that the test conditions were changed as follows.

[0126] (ii) Seed crystals were added and the following deactivator was added. The circulation rate was set to 30%. The results are shown in Figure 8 The curve is from 31 / 8 / 2022 to 1 / 9 / 2022.

[0127] <Inactivation agent>

[0128] Ferric chloride: 0.5 mg / L was added relative to 1 mg / L of scale dispersant.

[0129] The cationic polymers were DMA-epi (weight average molecular weight 120,000): 0.05 mg / L was added to 1 mg / L of the scale dispersant; and pDADMAC (weight average molecular weight approximately 450,000): 0.5 mg / L was added to 1 mg / L of the scale dispersant.

[0130] (iii) In the above (ii), the circulation rate was set to 20%. The results are shown in Figure 8 The curve is from 5 / 9 / 2022 to 6 / 9 / 2022.

[0131] (iv) In the above (ii), the circulation rate was set to 0%. The results are shown in Figure 8 The curve is from 8 / 9 / 2022 to 12 / 9 / 2022.

[0132] (v) In the above (ii), the circulation rate was set to 10%. The results are shown in Figure 8 The curve is from 13 / 9 / 2022 to 15 / 9 / 2022.

[0133] (vi) In the above (iv), the deactivating agent was changed to the following (circulation rate 0%). The results are shown in Figure 8 The curve is from 22 / 9 / 2022 to 26 / 9 / 2022.

[0134] <Inactivation agent>

[0135] Ferric chloride: 1 mg / L was added to the scale dispersant at 1 mg / L.

[0136] The cationic polymers were DMA-epi (weight average molecular weight 120,000): 0.1 mg / L was added to 1 mg / L of the scale dispersant; and pDADMAC (weight average molecular weight approximately 450,000): 1 mg / L was added to 1 mg / L of the scale dispersant.

[0137] (vii) In the above (iv), the deactivator was changed to the following (circulation rate 0%). The results are shown in Figure 8 The curve is from 27 / 9 / 2022 to 28 / 9 / 2022.

[0138] <Inactivation agent>

[0139] Ferric chloride: 0.25 mg / L was added to 1 mg / L of scale dispersant.

[0140] The cationic polymers were DMA-epi (weight average molecular weight 120,000): 0.025 mg / L was added to 1 mg / L of the scale dispersant; and pDADMAC (weight average molecular weight approximately 450,000): 0.25 mg / L was added to 1 mg / L of the scale dispersant.

[0141] (viii) In the above (vii), the circulation rate was changed to 10%. The results are shown in Figure 8 The curve is 29 / 9 / 2022.

[0142] The above test examples show that the addition of a deactivator significantly reduces the dissolved Ca concentration. It is also clear that the deactivator increases the amount of crystallization. Furthermore, sludge recycling (returning the precipitate to the T1 inlet) further reduces the dissolved Ca concentration. Sludge recycling can reduce the amount of deactivator added.

[0143] Although the present invention has been described in detail using specific embodiments, it is apparent that a person skilled in the art can make various modifications within the scope of the present invention.

[0144] This application is based on Japanese patent application No. 2023-003225 filed on January 12, 2023, the entire contents of which are incorporated herein by reference.

[0145] Description of Reference Numerals

[0146] 1: Water supply pipeline.

[0147] 2: Scale dispersant adding mechanism.

[0148] 3: RO device.

[0149] 5: Mixing tank.

[0150] 6: Inactivation agent adding mechanism.

[0151] 7: Crystallization tank.

Claims

1. A wastewater treatment method using a reverse osmosis membrane, wherein a scale dispersant is added to raw water, the raw water is subjected to reverse osmosis membrane treatment to separate the raw water into permeate water and concentrated water, and the concentrated water is subjected to crystallization treatment, characterized in that: A deactivating agent for deactivating the scale dispersant is added to the concentrated water.

2. The wastewater treatment method using a reverse osmosis membrane according to claim 1, wherein: As the deactivating agent, an iron salt and a cationic polymer are added.

3. The wastewater treatment method using a reverse osmosis membrane according to claim 2, wherein: The iron salt is ferric chloride or ferric sulfate, and the cationic polymer is dimethylamine-epichlorohydrin polycondensate and / or polydiallyldimethylammonium chloride.

4. A wastewater treatment device using a reverse osmosis membrane, wherein: The wastewater treatment device using a reverse osmosis membrane has: Scale dispersant adding mechanism, used for adding scale dispersant into raw water; A reverse osmosis membrane device is used to treat the raw water to which the scale dispersant is added; a deactivating agent adding mechanism for adding a deactivating agent of a scale dispersant to concentrated water of the reverse osmosis membrane device; and The crystallization tank is used to perform crystallization treatment on the concentrated water to which the deactivating agent is added.

5. The wastewater treatment device using a reverse osmosis membrane according to claim 4, wherein: As the deactivating agent, iron salt and cationic polymer were added.

6. The wastewater treatment device using a reverse osmosis membrane according to claim 5, wherein: The iron salt is ferric chloride or ferric sulfate, and the cationic polymer is dimethylamine-epichlorohydrin polycondensate and / or polydiallyldimethylammonium chloride.

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