JP2003154372A - Method and apparatus for removing sulfate ion and method for treating wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for removing sulfate ions which can efficiently remove sulfate ions from wastewater, an apparatus for the method, and a method for treating wastewater containing sulfate ions without generating hydrogen sulfide. SOLUTION: In the method for removing sulfate ions, water containing sulfate ions is treated at pH 9.5-13 in the presence of calcium ions and aluminum ions to deposit hydrated calcium sulfate and hydrated aluminum sulfate. In the apparatus for removing sulfate ions, the water containing sulfate ions is brought into contact with seed crystals in the presence of calcium ions and aluminum ions. The apparatus for removing the sulfate ions has a fluidized bed type reaction tower for keeping the seed crystals in a fluidized state, an inlet for supplying water containing sulfate ions to the reaction tower, an outlet for extracting treatment water from the reaction tower, and a circulating line for circulating part of the treatment water into the reaction tower. In the method for treating the wastewater, the wastewater containing sulfate ions, after the hydrated calcium sulfate and the hydrated aluminum sulfate are deposited, is subjected to anaerobic microorganism treatment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for removing sulfate ions. More specifically, the present invention relates to a method for removing sulfate ion capable of efficiently removing sulfate ion from wastewater containing sulfate ion and reducing the sulfate ion to a concentration below the solubility of calcium sulfate. The present invention relates to an apparatus and a method for treating wastewater containing sulfate ions that does not generate hydrogen sulfide.

[0002]

[Prior Art] Semiconductor factories, thermal power plants, pharmaceutical factories,
Process wastewater and general wastewater discharged from food manufacturing plants, drinking water manufacturing plants, pulp and paper mills, fiber spinning plants, etc. are required to be discharged or voluntarily controlled, or to be collected and reused, depending on the water quality. To satisfy the required water quality,
The coagulation treatment, the precipitation treatment, the biological treatment, the oxidative decomposition, the filtration, the evaporation, the ion exchange and the like methods are used alone or in combination. In recent years, the reuse of water in factories has progressed due to stricter standards for discharged water quality, depletion of water resources, rising water and sewerage costs in manufacturing costs, and environmental ISO efforts in some regions. Biological treatment is suitable for decomposing relatively concentrated organic matter in water,
It is widely used for reducing COD components and removing nitrogen components by combining aerobic treatment and anaerobic treatment. The anaerobic treatment is suitable for treating wastewater having a high organic matter concentration as compared with the aerobic treatment because the amount of sludge generated is small. However, when anaerobic treatment is carried out, if sulfate ions are present in water at a concentration of several hundreds to several thousands mg / L, the sulfate ions are reduced to generate hydrogen sulfide. Hydrogen sulfide not only has a strong odor and is toxic, but also causes corrosion of equipment and pipes, or becomes an obstacle to effective use of gas. Since a large amount of adsorbents and alkaline agents are required to remove hydrogen sulfide in biogas, even if anaerobic treatment is performed at low cost, the anaerobic treatment results due to the cost of gas treatment. There is a lot of drainage that cannot be applied. Even if the sulfate ion is several hundred mg / L, the above problem occurs, so 100
It is desired to reduce the concentration to less than mg / L, but in the treatment by precipitation of calcium sulfate, several thousand mg / L of sulfate ion remains. When the concentration of sulfate ion is high, the ion exchange treatment is not practical because the regeneration frequency is high and the waste treatment liquid must be treated. Furthermore, if calcium sulfate is present in water at a concentration close to the saturation concentration, in a system using that water, calcium sulfate will be deposited as scales on the pipes, equipment, etc., if the environment such as temperature and pH changes slightly. It will cause scale failure. For this,
There has been a demand for development of a treatment method capable of effectively removing sulfate ions contained in wastewater.

[0003]

DISCLOSURE OF THE INVENTION The present invention is capable of efficiently removing sulfate ions from wastewater containing sulfate ions and reducing the sulfate ions to a concentration below the solubility of calcium sulfate. The present invention has been made for the purpose of providing a removing method and removing apparatus for the above, and a method for treating wastewater containing sulfate ions that does not generate hydrogen sulfide.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that sulfate ion-containing water has a pH of 9.5 to 13 in the presence of calcium ions and aluminum ions. It was found that sulfate ions dissolved in water can be removed to a low concentration by treating with water to precipitate as a hydrated sulfate of calcium and aluminum, and the present invention has been completed based on this finding.
That is, according to the present invention, (1) sulfuric acid ion-containing water is added in the presence of calcium ions and aluminum ions to obtain a pH of 9.
The method of removing sulfate ions, characterized by precipitating a hydrated sulfate of calcium and aluminum by treatment with 5 to 13 (2), wherein the sulfate ions according to item 1 are carried out in the presence of seed crystals. Removal method of (3) seed crystal is natural zeolite, synthetic zeolite or calcium aluminate compound, removal method of sulfate ion according to the second item, (4) sulfate ion-containing water, calcium ion and aluminum ion coexistence Below, a device for removing sulfate ions to be brought into contact with seed crystals, the fluidized bed type reaction tower in which the seed crystals are kept in a fluidized state,
An apparatus for removing sulfate ions, comprising a supply port for sulfate ion-containing water to the reaction tower, an outlet for extracting treated water from the reaction tower, and a circulation line for circulating a part of the treated water into the reaction tower. , And (5) Wastewater containing sulfate ions is treated in the presence of calcium ions and aluminum ions at pH 9.5 to 13 to precipitate hydrated sulfate salts of calcium and aluminum, and then anaerobic. A method for treating wastewater, which is characterized by biological treatment.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of the present invention, sulfate ion-containing water is treated at a pH of 9.5 to 13 in the presence of calcium ions and aluminum ions to precipitate hydrated sulfate salts of calcium and aluminum. . According to the method of the present invention, the concentration of sulfate ion in water can be easily adjusted to 100 mg SO ₄ ^2- /
It can be reduced to L or less. According to the method of the present invention,
When the sulfate ion-containing water is treated at pH 9.5 to 13 in the presence of calcium ion and aluminum ion, the reactions represented by the formulas [1] and [2] occur sequentially,
A hydrated sulfate of calcium and aluminum, that is, a sparingly soluble ettringite is formed and precipitated, and sulfate ions in water are removed. ^{_{6Ca 2+ + 3SO 4 2+ 2Al 3+}} + 12OH - → Al 2 O 3 · 3CaSO 4 · 3CaO · 6H 2 O ... [1] Al 2 O 3 · 3CaSO 4 · 3CaO · 6H 2 O + 26H 2 O → Al ₂ O ₃ · 3CaSO ₄ · 3CaO · 32H ₂ O ... [2] In the method of the present invention, the amounts of calcium ion and aluminum ion coexisting with the sulfate ion are stoichiometrically calculated by the formula [1]. It is preferable that the amount is or more. That is, it is preferable that the amount of calcium ions is 2 mol times or more that of sulfate ions, and the amount of aluminum ions is 1.5 mol times or more of sulfate ions. Since the waste water often contains calcium ions as well as sulfate ions, the calcium ion concentration in the waste water is measured, and when the calcium ions are insufficient, a calcium compound can be added to reach the required amount. Although it is rare that the wastewater contains aluminum ions, it is preferable to measure and confirm the aluminum ion concentration in the wastewater in advance. Sulfate ion can be analyzed by barium chromate absorptiometry, gravimetric method, ion chromatography, nephelometry and the like. Calcium ions can be analyzed by chelate titration method, flame atomic absorption method, ion chromatography method, ion electrode method, nephelometry and the like. Aluminum ion is quinolinol absorptiometry, flame atomic absorption, I
It can be analyzed by CP emission spectrometry. Examples of the calcium compound to be added include calcium chloride and calcium hydroxide. Examples of the aluminum compound to be added include sodium aluminate, aluminum chloride, aluminum nitrate and the like.

In the method of the present invention, sulfate ion-containing water is treated in the presence of calcium ions and aluminum ions at a pH of 9.5 to 13, more preferably a pH of 10 to 12.3. There is no particular limitation on the method for adjusting the pH, and the pH can be adjusted by adding an alkali or an acid as appropriate according to the pH of the raw water. At this time, a basic or acidic aluminum salt, calcium salt, or the like can be added instead of the alkali or acid. The order of adding the calcium compound, the aluminum compound, the alkali or the acid is not particularly limited, and they can be added in any order. If the pH of the sulfate ion-containing water treated under the coexistence of calcium ions and aluminum ions is less than 9.5, the sulfate ion removing effect may be significantly reduced. When the pH of the sulfate ion-containing water treated in the coexistence of calcium ions and aluminum ions exceeds 13, sulfate ions can be removed, but the proportion of fine crystal particles with poor sedimentation increases. There is a risk. In the method of the present invention, when the sulfate ion-containing water is treated in the presence of calcium ions and aluminum ions, seed crystals (seed c)
rystal) is preferably present. A seed crystal is a substance that becomes a nucleus of a crystal when the crystal is precipitated from a solution,
By allowing the seed crystal to exist, the rate of crystal precipitation can be increased. Further, since crystals grow using seed crystals as nuclei, it is possible to prevent the generation of fine crystal particles and improve the operability of the subsequent solid-liquid separation treatment, but the solid-liquid separation device can be omitted. . The seed crystal used in the method of the present invention is
There is no particular limitation as long as it is a substance that can be a nucleus of ettringite crystals, for example, natural zeolite, synthetic zeolite, calcium aluminate compound, clay mineral, silica sand,
Calcium carbonate etc. can be mentioned. Among these, natural zeolite, synthetic zeolite and calcium aluminate compound can be particularly preferably used. Examples of the natural zeolite include clinoptilolite and mordenite. Examples of the synthetic zeolite include A-type, X-type, and Y-type zeolites. The calcium aluminate compounds, for _{example, CaO · Al 2 O 3 (} CaAl 2 O 4), 3
In addition to CaO.Al ₂ O ₃ (Ca ₃ Al ₂ O ₆ ), substances with different ratios of CaO and Al ₂ O ₃ , and further CaSO ₄ and H ₂
Examples thereof include O-added substances. Examples of clay minerals include montmorillonite, bentonite, and smectite.

The particle size of the seed crystal used in the method of the present invention is not particularly limited, and the particle size can be appropriately selected based on the shape of the reaction apparatus depending on the water quality of the sulfate ion-containing water.
Usually, it is preferably 0.05 to 5 mm. When a seed crystal is used under fluidized bed reaction conditions, the grain size is usually 0.05-
It is preferably 0.3 mm, but it is also possible to use a seed crystal having a particle size of 0.3 mm or more and to carry out the treatment at a liquid passing linear velocity (LV) of 30 m / h or more. When used in a suspension reaction tank, the seed crystal preferably has a particle size of 0.05 to 0.2 mm. In the method of the present invention, the existing form of the seed crystal is not particularly limited, and in the presence of calcium ion and aluminum ion, the contact between the sulfate ion-containing water and the seed crystal is performed by a fluidized bed reactor, a suspension tank reactor, or the like. Can be done using.
In a fluidized bed type reactor, sulfate ion-containing water is supplied from the lower part of the device and is passed in an upward flow. At this time, a part of the treated water can be circulated so that the flow rate of the seed crystal particles is increased. By performing the circulation treatment, it is possible to reduce the degree of supersaturation of precipitated crystals at the inlet of the reactor, prevent undesired precipitation of crystals at the inlet of the reactor, and prevent precipitation of fine crystals. In the method of the present invention, when a part of fine crystal particles produced by the reaction flows out into the treated water, a filtering device, a sedimentation separation device or the like may be installed in the subsequent stage to remove the outflowing fine particles. The fine crystal particles separated and removed by filtration, sedimentation and the like can be returned to the reactor and used as seed crystals. By using fine particles as seed crystals, large crystal particles can be grown. In the method of the present invention, when the sulfate ion-containing water is treated in the presence of calcium ions and aluminum ions without using seed crystals, the precipitated suspension is subjected to coagulation sedimentation, pressure floating, filtration, membrane filtration. It can be separated by, for example.

A preferred sulfate ion removing apparatus of the present invention is a sulfate ion removing apparatus in which sulfate ion-containing water is brought into contact with seed crystals in the presence of calcium ions and aluminum ions, and the seed crystals are in a fluidized state. Having a fluidized bed type reaction tower kept at 1, a supply port for sulfate ion-containing water to the reaction tower, an outlet for extracting treated water from the reaction tower, and a circulation line for circulating a part of the treated water into the reaction tower . FIG. 1 is a process system diagram of one embodiment of the sulfate ion removing apparatus of the present invention.
In the apparatus according to this embodiment, a supply port 4 for sulfate ion-containing water and a supply port for an aluminum compound aqueous solution are provided in the lower part of the fluidized bed type reaction tower 1 in which the seed crystals are kept in a fluidized state. Alkaline or acid is added to the sulfate ion-containing water to a prescribed pH
Adjusted to. An outlet 5 for extracting treated water is provided at the upper part of the reaction tower, and a part of the treated water is circulated to the bottom of the tower by a pump 2. By adjusting the circulation amount of treated water,
The state of seed crystal development can be controlled. The rest of the treated water flowing out from the outflow port 5 is sent to the subsequent step as treated water from which sulfate ions have been removed. Further, a crystal extraction port 6 is provided at the bottom of the reaction tower 1, and the crystal grains grown and enlarged in the reaction tower are periodically discharged. In the example shown,
The treated water flowing out from the reaction tower 1 is guided to the solid-liquid separation tank 3,
Even if crystal particles are mixed in the treated water, the solid-liquid separation tank 3
It is designed to be separated by. Normally, by setting the upper surface of the fluidized development layer of crystals below the upper end of the reaction tower 1 with a margin, seed crystals do not mix with the treated water and flow out, so the solid-liquid separation tank 3 is omitted. You may. In the wastewater treatment method of the present invention, wastewater containing sulfate ions is treated at a pH of 9.5 to 13 in the presence of calcium ions and aluminum ions to precipitate hydrated sulfate salts of calcium and aluminum. After that, anaerobic organism treatment. According to the method and apparatus for removing sulfate ions of the present invention, the sulfate ion concentration of the treated water can be reduced to about 1/10 of the concentration reached by the gypsum deposition method. For this reason, it becomes difficult for calcium sulfate scale to precipitate from the treated water. Further, according to the wastewater treatment method of the present invention, even if the anaerobic biological treatment is performed, the amount of hydrogen sulfide generated is very small, and the concern about corrosion or the like is eliminated.

[0009]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, the concentration of sulfate ion was measured by JIS K 0102 41.3 ion chromatographic method, and the concentration of calcium was measured by JIS K 01.
02 50.2 flame atomic absorption spectrometry, and the aluminum concentration was measured by JIS K 0102 58.2 flame atomic absorption spectrometry. Example 1 Sulfate ion 500 mg SO ₄ ^2- / L and calcium 100 mg Ca
Wastewater containing / L was treated. Calcium chloride (879 mg / L) was added to this waste water to adjust the molar ratio of sulfate ion to calcium ion to 1: 2, and a sodium hydroxide aqueous solution was further added to adjust the pH to 12.2 to obtain water to be treated. From the bottom of the reaction tower with an inner diameter of 40 mm and a height of 2,320 mm,
The water to be treated was passed upward at a flow rate of 6 L / h, and at the same time, at a position 100 mm from the bottom of the reaction tower, sodium aluminate (NaAl) having an aluminum concentration of 1,000 mgAl / L was used.
The O ₂ ) aqueous solution was injected at a rate of 0.57 L / h. Also,
Water to be treated was withdrawn at a position of 2,000 mm from the bottom of the reaction tower and circulated to the bottom of the reaction tower at a flow rate of 25.8 L / h. For one day after the start of water flow, the fine reaction product flowed out into the treated water in a suspended state, but the amount of fine particles that flowed out tended to decrease when water flow was continued for about one week. After that, almost transparent treated water was obtained. 10 days after the start of water flow, when the quality of the treated water became stable, sulfate ion 95 mg SO ₄ ^2- / L,
The removal rate was 81% by weight, the calcium content was 83 mgCa / L, and the removal rate was 83% by weight. Example 2 Sulfate ion 500 mg SO ₄ ^2- / L and calcium 1,000 mg
Wastewater containing Ca / L was treated. Since there is a large excess of calcium ions, without adding calcium chloride,
The treatment was performed in the same manner as in Example 1 except that the pH was adjusted to 12.2 by adding an aqueous sodium hydroxide solution. Similar to the case of Example 1, the fine reaction product was flown out into the treated water in a suspended state for 1 day after the start of water passage, but the treated water became stable 10 days after continuing the water passage. . When the quality of treated water is stable, sulfate ion 81 mg SO ₄ ^2- / L, removal rate 84
% By weight, calcium 178 mg Ca / L, removal rate 82
% By weight. Amount of sulfate ion removed (ΔSO ₄ : 41
9mg / L) compared to the removal amount of calcium ion (ΔC
a: 822 mg / L) is large. This is Ca
It is considered that the CO ₃ precipitation reaction proceeded in parallel.

Example 3 Sulfate ion 500 mg SO ₄ ^2- / L and calcium 500 mg Ca
Wastewater containing / L was treated. Since the calcium ions are excessive, the pH was adjusted to pH 12.2 by adding an aqueous solution of sodium hydroxide without adding calcium chloride to obtain water to be treated. Same inner diameter of 30 mm and height of 2, 3
A 20 mm reaction tower was filled with 300 mL of clinoptilolite natural zeolite having a particle size of 0.08 to 0.15 mm, and treated water was passed from the lower part of the reaction tower in an upward flow at a flow rate of 6 L / h,
At the same time, at a position 100 mm from the bottom of the reaction column, sodium aluminate (NaA with an aluminum concentration of 1,000 mg Al / Lg) was used.
The 10 ₂ ) aqueous solution was injected at a rate of 0.57 L / h. Further, water to be treated was withdrawn at a position of 2,000 mm from the bottom of the reaction tower and circulated to the bottom of the reaction tower at a flow rate of 25.8 L / h. When the quality of treated water is stable, sulfate ion 95 mg SO ₄ ^2- /
L, removal rate 81% by weight, calcium 84 mgCa /
L, the removal rate was 83% by weight. After the treatment was completed, a part of the zeolite was taken out from the reaction tower and dried at 105 ° C. for 1 day, and the surface thereof was analyzed by the X-ray diffraction method. FIG. 2A is an X-ray diffraction pattern, and FIG. 2B is the detected peak position. Further, FIG. 2 (c) shows the peak position of ettringite, and FIG. 2 (d) shows the peak position of clinoptilolite. Comparing FIG. 2 (a) and FIG. 2 (b), it can be seen that the peak marked with ● in FIG. 2 (a) belongs to ettringite. Further, the other peaks almost coincide with the peak positions of clinoptilolite shown in FIG. 2 (d), and it can be seen that the peaks are derived from the zeolite used as the seed crystal. From this result, it was confirmed that ettringite crystals were precipitated on the surface of zeolite.

Example 4 Treatment was carried out in the same manner as in Example 3 except that the pH of the waste water was adjusted to 11.0. When the quality of treated water is stable,
Sulfate ion was 350 mg SO ₄ ^2- / L, the removal rate was 30% by weight, calcium 269 mgCa / L, the removal rate was 46% by weight. Example 5 The treatment was carried out in the same manner as in Example 3 except that the pH of the waste water was adjusted to 9.9. When the quality of treated water is stabilized, sulfate ion 370mgSO ₄ ^2- / L, a removal rate 26% by weight was calcium 287mgCa / L, removal rate 43% by weight. Example 6 The filling amount of zeolite was 600 mL, and the pH of waste water was 9.9.
The treatment was performed in the same manner as in Example 3 except that When the quality of treated water is stable, sulfate ion 305mg SO ₄
^2- / L, removal rate 39% by weight, calcium 277 mg
It was Ca / L and the removal rate was 45% by weight. Example 7 Sulfate ion 1,750 mg SO ₄ ^2- / L and calcium 1,60
Wastewater containing 0 mgCa / L was treated. Sodium aluminate (NaAlO ₂ ) aqueous solution was added to this waste water to make the aluminum concentration 330 mg Al / L, and further sodium hydroxide aqueous solution was added to adjust the pH to 12.0,
It was treated water. Same inner diameter of 30 mm and height of 2,
A 320 mm reaction tower is filled with 500 mL of granular limestone having a particle size of 0.08 to 0.3 mm, and the treated water is supplied from the lower part of the reaction tower in an amount of 3 L /
The solution was passed at a rate of h. When the quality of the treated water was stable, sulfate ions were 793 mg SO ₄ ^2- / L, the removal rate was 55% by weight, calcium 536 mgCa / L, the removal rate was 67% by weight.

[0012]

According to the method and apparatus for removing sulfate ions of the present invention, the sulfate ion concentration of treated water is reduced to about 1/10 of the concentration reached by the gypsum precipitation method. be able to. For this reason, it becomes difficult for calcium sulfate scale to precipitate from the treated water. Further, according to the wastewater treatment method of the present invention, even if the anaerobic biological treatment is performed, the amount of hydrogen sulfide generated is very small, and the concern about corrosion or the like is eliminated.

[Brief description of drawings]

FIG. 1 is a process system diagram of one embodiment of a sulfate ion removing apparatus of the present invention.

FIG. 2 is an X-ray diffraction pattern and peak positions.

[Explanation of symbols]

1 Fluidized bed type reaction tower 2 pumps 3 Solid-liquid separation tank 4 supply ports 5 Outlet 6 Crystal outlet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 3/28 C02F 3/28 Z (72) Inventor Norito Ikemiya 3-4, Nishishinjuku, Shinjuku-ku, Tokyo No. 7 Kurita Industry Co., Ltd. (72) Inventor Nobuhiro Oda No. 3-7-4 Nishi-Shinjuku, Shinjuku-ku, Tokyo F-term inside Kurita Industry Co., Ltd. (reference) 4D038 AA08 AB36 AB81 AB88 BA02 BA04 BB13 BB19 4D040 AA01

Claims (5)

[Claims] 1. Sulfate ion-containing water is treated at a pH of 9.5 to 13 in the presence of calcium ions and aluminum ions to precipitate hydrated sulfate salts of calcium and aluminum. Removal method. 2. The method for removing sulfate ions according to claim 1, wherein the treatment is carried out in the presence of seed crystals. 3. The method for removing sulfate ions according to claim 2, wherein the seed crystal is a natural zeolite, a synthetic zeolite or a calcium aluminate compound. 4. A fluidized bed reactor in which a sulfate ion-removing device is brought into contact with seed crystals in the presence of calcium ions and aluminum ions, the seed crystals being kept in a fluidized state. A sulfate ion-containing water supply port to the reaction tower, an outlet for extracting treated water from the reaction tower, and a circulation line for circulating a part of the treated water into the reaction tower. apparatus. 5. Waste water containing sulfate ions in the presence of calcium ions and aluminum ions at a pH of 9.5 to 1
A method for treating wastewater, which comprises treating anaerobic organisms after treating with 3 to precipitate hydrous sulfate of calcium and aluminum.