JP3213555B2 - Water treatment method and water treatment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to raw water containing salts,
For example, the present invention relates to a water treatment method and a water treatment apparatus for desalinating leached sewage and the like in a general waste final disposal site.

[0002]

2. Description of the Related Art At present, wastes are generally disposed of in landfills after incineration. The leachate generated at this final disposal site contains calcium, nitrogen, silicon dioxide, etc., leached from the incinerated waste, and when discharged as it is, for example, calcium ions become carbonate ions and sulfate ions. There has been a problem that it reacts to form an insoluble calcium salt and adheres as a scale to pipes and equipment, thereby deteriorating the equipment.

Therefore, conventionally, wastewater is first stored in a flow rate control tank 21 and then removed by a calcium removal tank 22 by a water treatment apparatus as shown in FIG. After the calcium is removed in the biological treatment tank 23, it is denitrified, and further coagulated and settled.
Sludge and treated water are separated by 24, and the treated water is treated as treated water after passing through a sand filtration tank 25, an activated carbon treatment tank 26, and a chelate adsorption treatment 27.

[0004]

However, when leachate is treated with such a water treatment apparatus, components such as calcium, nitrogen, and phosphorus can be removed, but salts other than calcium, such as silicon dioxide, magnesium, Sodium, chloride ions, sulfate ions, and other soluble salts cannot be removed, and if discharged as such into rivers, etc. as treated water, the rivers and soil may be contaminated by these salts. Had occurred.

[0005] As a method of removing salts in raw water that cannot be removed by the above-mentioned water treatment apparatus, sewage treatment using a permeable membrane such as a reverse osmosis membrane may be considered. This reverse osmosis membrane
When the raw water containing salts is permeated, the permeation membrane separates the concentrated water into which the salts are concentrated and the treated water from which the salts have been removed to remove the salts, and can also remove the salts other than the calcium.

However, when raw water containing silicon dioxide is permeated through such a reverse osmosis membrane, if silicon dioxide is present on the concentrated side, the concentration of salts in the concentrated water after permeation increases and the concentration of silicon dioxide increases. Is a low-solubility salt with lower solubility than other salts, so silicon dioxide may exceed the solubility on the concentrated side of the membrane, adhere to the membrane surface as scale, and reduce the processing capacity of the reverse osmosis membrane. . Also,
This silicon dioxide, once deposited as a scale, was difficult to clean even with chemicals such as acids and alkalis.

Further, the dissolved silicon dioxide which did not adhere as a scale at this time remains in the concentrated water, and cannot be removed even if the concentrated water is subjected to crystallization or other film treatment. In addition, silicon dioxide is still contained in the treated water discharged from the water treatment device, and the quality of the treated water is reduced. Also, when low-solubility salts such as calcium sulfate and calcium carbonate are contained in the raw water, the quality of the treated water is lowered as in the case of the silicon dioxide.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is an object of the present invention to easily perform a desalination treatment of sewage such as leachate containing low solubility salts such as silicon dioxide by using a reverse osmosis membrane. It is an object of the present invention to provide a water treatment method and a treatment apparatus which can perform the above.

[0009]

SUMMARY OF THE INVENTION The present invention has been made as a water treatment method and a water treatment apparatus in order to solve such a problem, and the feature of the water treatment method is that raw water containing low solubility salts is used. In a water treatment method for separating into treated water and concentrated water containing salts by passing through a reverse osmosis membrane, after removing low-solubility salts from the raw water by low-solubility salt removal means, passing through the reverse osmosis membrane, The concentrated water separated by the reverse osmosis membrane is filtered by an NF membrane, and the permeated water filtered by the NF membrane is further passed through a reverse osmosis membrane for concentrated water treatment to discharge the separated highly concentrated water .
The concentrated water filtered by the NF membrane is subjected to crystallization treatment,
It is to introduce a supernatant generated during the crystallization treatment into the NF film .

A feature of the water treatment apparatus is that, on the upstream side of the reverse osmosis membrane apparatus 1 which permeates raw water containing low-solubility salts and separates it into treated water and concentrated water containing salts, low-solubility salts are supplied from the raw water. An NF membrane device (2) for filtering concentrated water separated by the reverse osmosis membrane device (1), and a permeate filtered by the NF membrane device (2). There a reverse osmosis unit for concentrated water processing is transmitted (3), the discharge passage for discharging the highly concentrated water, which is separated by reverse for the concentrated water treatment osmosis unit (3) and (a), the NF
Crystallization in which concentrated water filtered by the membrane device (2) is introduced
And a supernatant liquid generated in the crystallization tank (4).
An introduction path (B) for introducing into the NF membrane device (2) is provided .

That is, as described above, since the present invention has a means for removing low-solubility salts such as silicon dioxide from raw water such as leachate containing salts, the low-solubility salts precipitated on the reverse osmosis membrane, particularly on the concentration side, are removed. It can be prevented from adhering to the film surface as a scale.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. First, the configuration of the water treatment apparatus according to the present embodiment will be described. Reference numeral 1 shown in FIG. 1 denotes a reverse osmosis membrane apparatus into which raw water from which silicon dioxide obtained by a coagulation sedimentation apparatus F has been removed is introduced. As shown, a plurality of sets of reverse osmosis membrane portions 14 each having a disk-shaped reverse osmosis membrane 12 provided between disk-shaped spacers 13 are stacked in a cylindrical device main body 11.

A raw water flow path 15 for introducing raw water is provided on the inner peripheral surface of the apparatus main body 11 of the reverse osmosis membrane apparatus 1.
Raw water is introduced to the surface of the reverse osmosis membrane 12 from the above. An end plate 16 is provided above the reverse osmosis membrane section 14 so as to withstand a pressure higher than the osmotic pressure.

Reference numeral 18 denotes a treated water pipe penetrating the central portion of the reverse osmosis membrane section 14. The treated water pipe 18 discharges the treated water separated by the reverse osmosis membrane 12. Reference numeral 19 denotes a concentrated water pipe for discharging the concentrated water concentrated by each reverse osmosis membrane 12 to the outside of the apparatus main body 11.

Since the reverse osmosis membrane device 1 includes a plurality of reverse osmosis membrane sections 14 in which the disc-shaped reverse osmosis membranes 12 are provided between the disc-shaped spacers 13 as described above, A wide flow path can be ensured when the treated water is allowed to permeate. Therefore, for example, after long-term use, the surface of the reverse osmosis membrane can be easily cleaned.

The coagulation / sedimentation apparatus F is an apparatus for adding a coagulant to raw water stored in a coagulation / sedimentation tank to coagulate and remove silicon dioxide contained in the raw water. After the silicon dioxide in the water is precipitated, only the supernatant water is introduced into the reverse osmosis membrane device 1 by filtration or the like.

Reference numeral 2 denotes a nanofilter (NF membrane) as a permeable membrane through which the concentrated water separated by the reverse osmosis membrane device 1 is introduced and filtered. Salts of the above negative ions, for example, Ca
N that can remove CO ₃ and CaSO ₄ by filtration
This is an F film apparatus.

Reference numeral 3 denotes a high-pressure reverse osmosis membrane device for concentrated water treatment provided for further desalting the permeated water filtered by the NF membrane device 2. As in the osmosis membrane device 1, a plurality of modules each having a disc-shaped reverse osmosis membrane provided between spacers are stacked in a cylindrical device main body. The high-pressure reverse osmosis membrane device 3 is formed so as to be capable of performing a separation process of applying a higher pressure than the reverse osmosis membrane device 1 to highly concentrate the concentrated water.

Reference numeral 4 denotes a crystallization tank into which the concentrated water separated in the NF membrane device 2 and the high-pressure reverse osmosis membrane device 3 is introduced.
In the crystallization tank 4, salts remaining in the treated water are precipitated as solids 6.

The supernatant generated in the crystallization tank 4 is N
It is sent to the F membrane device 2 via the introduction path B together with the concentrated water introduced from the osmosis membrane device 1, filtered by the NF membrane device 2, and then circulated to the high pressure reverse osmosis membrane device 3.

Further, a part of the concentrated water separated in the high-pressure reverse osmosis membrane device 3 is directly treated as a highly concentrated water from the discharge path A, and the remaining concentrated water is sent to the crystallization tank 4.

Reference numeral 5 denotes a second reverse osmosis membrane device into which the treated water separated by the reverse osmosis membrane device 1 is introduced. The second reverse osmosis membrane device 2 also has the same configuration as the reverse osmosis membrane device 1. .

The treated water separated in the second reverse osmosis membrane device 5 is directly discharged as purified water from the main body of the device, while the concentrated water is introduced into the reverse osmosis membrane device 1 together with raw water.
The treated water separated by the high-pressure reverse osmosis membrane device 3 is introduced into the second reverse osmosis membrane device 5.

Next, a treatment method for treating leachate by the leachate treatment apparatus 20 having the above configuration will be described.

First, leachate leached from a waste treatment plant is introduced as raw water into the coagulation sedimentation apparatus F. In the coagulating sedimentation apparatus F, a coagulating sedimentation agent is added to the raw water in the coagulating sedimentation tank, and the silicon dioxide is coagulated while stirring, and the floc is settled. Can be obtained. Sulfuric acid bands, iron chloride, polyaluminum chloride and the like can be used as the coagulating sedimentation agent.

Since silicon dioxide has a low solubility and a solubility of about 140 to 150 mg / l at 35 ° C., when raw water having a higher concentration is directly passed through the reverse osmosis membrane, it is deposited on the membrane as scale. May cause
Particularly, on the concentration side of the reverse osmosis membrane, the concentration of salts in the concentrated water is high, so that silicon dioxide tends to precipitate. When the silicon dioxide is dissolved, it remains in the concentrated water and is subjected to another membrane treatment, for example, in the reverse osmosis membrane device 1, the NF membrane device 2, the high pressure reverse osmosis membrane device 3, or the crystallization device 4. It is further concentrated and causes scale.

Therefore, it is possible to easily remove the cause of scale by removing silicon dioxide in raw water in a process prior to membrane treatment, and at the same time, it is possible that silicon dioxide is concentrated and present in the water treatment apparatus 20. And does not remain in the treated water.

Further, the raw water from which the silicon dioxide has been removed by the coagulation and sedimentation apparatus F is introduced into the reverse osmosis membrane apparatus 1, and the reverse osmosis membrane apparatus 1 has a disk-shaped reverse osmosis membrane 12 as described above. Are laminated, the surface of the reverse osmosis membrane 12 and the spacer
When pressure is applied when raw water flows between 13, the reverse osmosis membrane 12 permeates only water and the treated water that has been desalinated accumulates inside the membrane, and the treated water is installed vertically in the center of the apparatus main body 11 The treated water is discharged from the reverse osmosis membrane device 1 through the treated water pipe 18 as treated water, while the raw water is discharged from the reverse osmosis membrane device 1 as concentrated water through the concentrated water pipe 19 passing between the reverse osmosis membrane 12 and the spacer 13. Is done.

Next, the concentrated water is introduced into the NF membrane device 2 and the salts in the concentrated water, particularly, the salts such as CaCO ₃ and CaSO ₄ are removed.
After the negative ions having a valency or higher are effectively removed by filtration, the permeated water is introduced into the high-pressure reverse osmosis membrane device 3.

On the other hand, the treated water discharged from the reverse osmosis membrane device 1 is further desalted in the second reverse osmosis membrane device 5 and discharged as high-purity treated water. This second reverse osmosis membrane device 5
Is returned to the reverse osmosis membrane device 1 together with the raw water, so that it is possible to reliably remove even a small amount of salts and prevent the concentrated water from being discharged out of the device.

Since the raw water to be treated in the reverse osmosis membrane device 1 does not contain silicon dioxide, silicon dioxide does not precipitate as scale on the reverse osmosis membrane.

Further, the concentrated water generated in the NF membrane device 2 and a part of the highly concentrated water generated in the high-pressure reverse osmosis membrane device 3 are introduced into the crystallization tank 4. In the crystallization tank 4, salts contained therein can be precipitated and removed as solids.

The supernatant liquid generated in the crystallization tank 4 is again introduced into the NF membrane device 2 via the introduction path B together with the concentrated water from the reverse osmosis membrane device 1. As described above, since some of the salts are precipitated as solids in the crystallization tank 4, the amount of salts discharged as concentrated water can be further reduced.

Further, the treated water separated in the high-pressure reverse osmosis membrane device 3 is introduced into the second reverse osmosis membrane device 5 together with the treated water discharged from the reverse osmosis membrane device 1, and is subjected to a desalination treatment without fail.

In the above embodiment, the coagulating sedimentation apparatus F is provided as a means for removing silicon dioxide. However, the means for removing silicon dioxide is not limited thereto. Any means may be used as long as it can remove silicon dioxide in raw water. Further, in the case of raw water containing low-solubility salts such as calcium sulfate and calcium carbonate other than silicon dioxide, it is only necessary to provide a means capable of removing these low-solubility salts.

In the above embodiment, the concentrated water generated in the reverse osmosis membrane device 1 is introduced into the NF membrane device 2 and further processed in the high-pressure reverse osmosis membrane device 3. Treating the retentate in this manner is not a condition. However, when the concentrated water from the reverse osmosis membrane device is treated with a permeable membrane such as an NF membrane and a high-pressure reverse osmosis membrane device, the concentrated water is further concentrated and discharged as a liquid having a high salt concentration. There is an advantage that the processing is easy because only a small amount is required. In this case, if the treatment with the NF membrane and then the treatment with the permeable membrane are performed, ions having two or more valences can be selectively removed from the NF membrane.
Since it can be removed by the membrane, it is possible to effectively prevent the subsequent formation of scale on the permeable membrane.

Further, in the above-described embodiment, the crystallization tank 4 is provided in the treatment of the concentrated water, and the concentrated water generated by depositing the salts as a solid substance is made more phenomena. That is not a condition.

In the above embodiment, the reverse osmosis membrane device 1 is used.
The treated water separated in the above is treated by the second reverse osmosis membrane device 5 further provided on the downstream side, but providing such a second reverse osmosis membrane device is not a condition. However, if a plurality of stages of reverse osmosis membrane treatment are performed as in the above embodiment, the quality of the treated water will be further improved.

In the above embodiment, a reverse osmosis membrane device using a disc-shaped flat reverse osmosis membrane was used as the reverse osmosis membrane device. A reverse osmosis membrane of any shape such as a hollow fiber type, a spiral type and a tubular type may be used.

Further, in the above embodiment, leachate was treated as raw water. However, the present invention is not limited to leachate, and desalination treatment of water containing low-soluble salts such as silicon dioxide discharged from general equipment is used. Applicable to

[0041]

As described above, the present invention can be applied to the case where leachate discharged from a disposal site contains low-concentration salts such as silicon dioxide at a high concentration before desalination. Since low-solubility salts are removed, it is possible to prevent scale from being formed on the reverse osmosis membrane. Therefore, desalination of water such as leachate can be reliably performed without deteriorating the membrane function.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a water treatment apparatus as an example of an embodiment of the present invention.

FIG. 2 is a schematic sectional view of a reverse osmosis membrane device.

FIG. 3 is a schematic configuration diagram of a conventional water treatment apparatus.

[Explanation of symbols]

 Reference Signs List 1 reverse osmosis membrane device (reverse osmosis membrane) 2 NF membrane device (permeable membrane) 3 high-pressure reverse osmosis membrane device (reverse osmosis membrane for concentrated water treatment) 4 crystallization tank F coagulation settling device

Continuation of the front page (72) Inventor Yoshimitsu Fukao 2-5-4 Yoneya, Takarazuka-shi, Hyogo (72) Inventor Kiyoshi Kinoshita 1-15-29, Minamino, Shijonawate-shi, Osaka (56) References JP-A-51-100976 ( JP, A) JP-A-58-6297 (JP, A) JP-A-8-290164 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/44 B01D 61/00 -61/58

Claims (6)

(57) [Claims] 1. A water treatment method for permeating raw water containing low-solubility salts through a reverse osmosis membrane to separate treated water and concentrated water containing salts, wherein the low-solubility salts are removed from the raw water by a low-solubility salt removing means. Then, the concentrated water separated by the reverse osmosis membrane is filtered through a NF membrane, and the permeated water filtered by the NF membrane is further passed through a reverse osmosis membrane for concentrated water treatment. The separated highly concentrated water is discharged, and further filtered by the NF membrane.
The concentrated water is crystallized, and the supernatant generated during the crystallization is removed.
A water treatment method, wherein the method is introduced into the NF membrane . 2. The water treatment method according to claim 1, wherein the low-solubility salts removing means removes the low-solubility salts by coagulating and precipitating the low-solubility salts. 3. The water treatment method according to claim 1, wherein the low solubility salt contained in the raw water is silicon dioxide. 4. A low solubility salt for removing low solubility salts from raw water upstream of a reverse osmosis membrane device (1) for permeating raw water containing low solubility salts and separating into treated water and concentrated water containing salts. An NF membrane device (2) for removing concentrated water separated by the reverse osmosis membrane device (1);
The reverse osmosis membrane device for concentrated water treatment (3) through which the permeated water filtered by the F membrane device (2) is transmitted, and the highly concentrated water separated by the reverse osmosis membrane device for concentrated water treatment (3) are discharged. Discharge path (A), and the concentration filtered by the NF membrane device (2).
A crystallization tank (4) into which water is introduced, and the crystallization tank
The supernatant generated in (4) is introduced into the NF membrane device (2).
A water treatment apparatus, wherein an introduction path (B) is provided . 5. The water treatment apparatus according to claim 4 , wherein said low solubility salt removing means is a coagulation sedimentation apparatus. 6. The water treatment apparatus according to claim 4, wherein the low solubility salt contained in the raw water is silicon dioxide.