JP5303501B2 - Water treatment method and water treatment apparatus - Google Patents

Description

  The present invention relates to a water treatment method and a water treatment apparatus for desalinating raw water containing calcium ions and sulfate ions, for example, leachate generated from a final disposal site for waste.

  At present, waste is generally landfilled at a final disposal site after incineration. Rainwater that falls on the final disposal site soaks into landfill waste awaiting stabilization and becomes leachate that dissolves the substances contained in the waste. If this leachate seeps into the external environment, it can cause water pollution. In particular, the leachate often contains calcium or the like derived from incinerated waste, and if it is discharged as it is to the outside environment, there is a problem that it adheres as a scale in piping or treatment equipment.

  For this reason, conventionally, a lime soda method has been performed in which sodium carbonate is added to the leachate as a calcium remover, and the calcium content in the leachate is removed as calcium carbonate. After removing the calcium content, treatment such as denitrification treatment and coagulation sedimentation treatment was performed, and the treated water was drained out of the treatment facility. However, this treatment method can reliably remove the calcium content, but requires a large amount of sodium carbonate, and thus the treatment cost is high.

  There is also a technique for incorporating an electrodialyzer into a water treatment apparatus for desalting, but there is a problem that the treatment cost increases when a large amount of concentrated water is generated by electrodialysis. If the concentration of concentrated water is as high as possible, the processing cost can be suppressed, but it has been difficult to concentrate 10 times or more with an electrodialysis apparatus.

  Here, the leachate containing salt is permeated through the reverse osmosis membrane to separate the treated water and the concentrated solution containing salts, the concentrated solution is filtered through the permeable membrane, and the permeated water of the permeable membrane is further processed for concentrated water treatment. A water treatment method and a water treatment apparatus characterized by allowing permeation through a reverse osmosis membrane and discharging highly concentrated water while crystallizing the concentrated water filtered by the permeable membrane and introducing the supernatant into the permeable membrane. It is disclosed in Patent Document 1.

  Since the water treatment method and the water treatment apparatus disclosed in Patent Document 1 treat raw water containing salts with a reverse osmosis membrane, salts such as calcium, magnesium, sodium, chloride ions, sulfate ions, phosphorus, nitrogen content, etc. Can be reliably separated to obtain demineralized water. In addition, after the concentrated water of the reverse osmosis membrane is treated with the permeable membrane, it is further permeated to the reverse osmosis membrane for concentrated water treatment. Is easy.

Japanese Patent No. 3098965

  The water treatment method and water treatment apparatus disclosed in Patent Document 1 have a high concentration rate of leachate containing salt and the like, and salt removal is easy. However, when the salt concentration of the raw water is high, there is a problem that it is likely to precipitate on the reverse osmosis membrane surface or in the pipe. Further, when the salt concentration is low, there is a problem that the salt concentration of the concentrated water filtered by the permeable membrane is not sufficiently high, and the crystallization treatment efficiency is low. For this reason, under conditions where the salt concentration of the raw water changes greatly, there is a possibility that the desalting ability cannot be fully exhibited, and there is room for improvement in that respect.

  The present invention provides a water treatment method and water that can sufficiently exhibit the ability to remove calcium sulfate, even when the salt concentration in the raw water is high or low, and can reduce the amount of calcium remover used as much as possible. An object is to provide a processing apparatus.

  The present inventors diligently studied a method for maintaining high calcium sulfate removal efficiency while preventing clogging of the membrane even when the calcium concentration and sulfate ion concentration in the raw water causing scale generation change greatly. did. As a result, attention was paid to the fact that the calcium sulfate concentration in the concentrate can be brought into a supersaturated state by treating raw water containing calcium ions and sulfate ions with a permeable membrane device. Furthermore, if a calcium sulfate seed crystal is added to the concentrated solution in which the calcium sulfate concentration is supersaturated, and a portion of the crystallized calcium sulfate is recovered as a calcium sulfate seed crystal, a calcium remover is no longer necessary. The headline and the present invention were completed.

Specifically, the present invention
In a water treatment method for separating raw water containing calcium ions and sulfate ions into treated water and concentrated water by a permeable membrane device,
Concentrated water is returned to the raw water tank through the crystallization reaction tank and the precipitation tank,
Circulate a part of the concentrated water to the inlet side of the permeable membrane device,
In the crystallization reaction tank, calcium sulfate seed crystals are added to the concentrate, and the calcium ions and sulfate ions in the concentrate are crystallized as calcium sulfate crystals.
In the precipitation tank, the calcium sulfate crystals in the concentrated water sent from the crystallization reaction tank are precipitated and the supernatant is returned to the raw water tank.
A part of the calcium sulfate crystals precipitated in the precipitation tank is recovered as a calcium sulfate seed crystal into the crystallization reaction tank,
The remainder of the calcium sulfate crystals precipitated in the settling tank is discharged out of the system.
The present invention relates to a water treatment method.

The present invention also provides:
A raw water tank for storing raw water containing calcium ions and sulfate ions;
A permeable membrane device for separating raw water sent from the raw water tank into treated water and concentrated water;
A water return route for returning the concentrated water to the raw tank,
A circulation path for circulating a part of the concentrated water to the inlet side of the permeable membrane device;
A water treatment device comprising:
In the water return path, a crystallization reaction tank for adding calcium sulfate seed crystals to the concentrate in the tank to crystallize calcium ions and sulfate ions in the concentrate as calcium sulfate crystals,
A precipitation tank is provided for precipitating calcium sulfate crystals in the concentrated water sent from the crystallization reaction tank and returning the supernatant to the raw water tank.
A part of the calcium sulfate crystals precipitated in the precipitation tank is recovered as a calcium sulfate seed crystal from the precipitation tank through the recovery path to the crystallization reaction tank,
The remainder of the calcium sulfate crystals precipitated in the settling tank is discharged out of the system.
The present invention relates to a water treatment apparatus.

  The calcium sulfate crystals precipitated in the precipitation tank are crystallized in the crystallization reaction tank so that the amount of calcium sulfate crystals in the crystallization reaction tank is 0.01 times or more the amount of calcium sulfate supersaturated in the crystallization reaction tank. It is preferable to send it back to. The water treatment method and the water treatment apparatus of the present invention crystallize calcium content in raw water as calcium sulfate, and a part thereof is used as a crystallizer for concentrated water in the permeable membrane device, so that the calcium removal agent is almost used. Without this, a high calcium removal rate can be maintained.

  Here, “the amount of calcium sulfate supersaturated in the crystallization reaction tank” means “(amount of calcium sulfate ionized−amount of calcium sulfate corresponding to the saturation solubility)” in the crystallization reaction tank. . When this value is a positive value, it is considered that calcium sulfate in the crystallization reaction tank is supersaturated.

  The calcium sulfate concentration in the concentrated water of the permeable membrane device is preferably 1.01 or more times the saturation concentration.

  The membrane surface flow rate of the water to be treated (raw water + part of concentrated water) in the permeable membrane device is preferably 5000 m / hour or more and 15000 m / hour or less. This is to prevent the scale from adhering to the permeable membrane.

In the water treatment method of the present invention, a portion of the retentate, Ru is circulated to the inlet side of the permeable membrane device. The water treatment apparatus of the present invention, further Ru comprising a circulation path for circulating a portion of the concentrated water to the inlet side of the permeable membrane device. By adopting such a configuration, it is possible to concentrate the concentrated water to a saturation concentration of calcium sulfate or higher without circulating the concentrated water of the permeable membrane device to the path after the crystallization reaction tank.

  The permeable membrane of the permeable membrane device is preferably in the form of a flat membrane to which scale does not easily adhere.

  The treated water of the permeable membrane device can be further treated by a reverse osmosis membrane (RO membrane) device. By selectively removing bivalent or higher-valent metal ions contained in the raw water with the permeable membrane device, stable operation is possible when treating the treated water of the permeable membrane device with the RO membrane device.

  According to the water treatment method and the water treatment apparatus of the present invention, when the calcium ion concentration and the sulfate ion concentration in the raw water are high, the calcium sulfate crystals can be immediately removed in the crystallization reaction tank and the precipitation tank. On the other hand, when the calcium ion concentration and the sulfate ion concentration in the raw water are low, the concentration of these ions is gradually concentrated to the calcium sulfate saturation concentration or more by circulating the concentrated water in the permeable membrane. Calcium sulfate crystals can be efficiently removed in the deposition reaction tank and the precipitation tank. For this reason, even if the calcium ion concentration and the sulfate ion concentration in the raw water vary greatly, it is possible to maintain a high calcium sulfate removal rate while preventing clogging of the permeable membrane.

  Moreover, since a part of the calcium sulfate crystal generated with the treatment of raw water is recovered as a crystallization agent, external crystallization agent addition is almost unnecessary, and the cost performance is excellent.

It is a flowchart which shows an example of the water treatment apparatus of this invention. It is a flowchart which shows another example of the water treatment apparatus of this invention. It is a flowchart of the water treatment apparatus currently disclosed by patent document 1. FIG. 4 is a graph showing experimental results of Example 1. It is a graph (seed crystal amount 1 time-10 times) which shows the experimental result of Example 2. FIG. It is a graph (seed crystal amount 30 times-100 times) which shows the experimental result of Example 2. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to the following description.

<Embodiment 1>
FIG. 1 is a flowchart showing an example of the water treatment apparatus of the present invention. Raw water containing calcium ions and sulfate ions such as leachate is first stored in the raw water tank 1. Solids such as earth and sand contained in the raw water are preferably removed using a filter or the like before the raw water is supplied to the raw water tank 1.

  The raw water is supplied to the inlet (lower side in FIG. 1) of the permeable membrane device 3 via the path 2. Here, a nanofiltration (NF) membrane device is used as the permeable membrane device. A pump (not shown) is provided in front of the inlet of the permeable membrane device 3 in the path 2 to increase the pressure of the raw water supplied to the permeable membrane device 3. The NF membrane of the permeable membrane device 3 permeates monovalent ions (sodium ions, chlorine ions, etc.) in the raw water and does not permeate ions more than divalent (calcium ions, sulfate ions, etc.). For this reason, divalent or higher ions in the raw water are selectively concentrated, and the concentrated water is taken out from the outlet (upper side in FIG. 1) of the permeable membrane device 3 to the path 5. On the other hand, the treated water from which divalent or higher valent ions have been removed is taken out from the path 12. It is preferable to concentrate the calcium sulfate concentration of concentrated water to 1.01 or more times the calcium sulfate saturation concentration.

  The route 5 may be branched to provide the circulation route 4, and a part of the concentrated water may be returned to the inlet of the permeable membrane device 3 by the circulation route 4. According to this configuration, it is possible to concentrate calcium sulfate in the water to be treated without circulating the equipment after the path 5. Moreover, since the pressure of the concentrated water of the permeable membrane apparatus 3 can be utilized, it becomes possible to reduce the power of the pump installed in front of the inlet of the permeable membrane apparatus 3 of the path 2. That is, it becomes possible to reduce the size and power consumption of the pump.

  It is preferable that the permeable membrane device 3 includes a flat membrane-like NF membrane to which calcium sulfate scale hardly adheres. In order to prevent the scale from adhering to the NF membrane, it is preferable to adjust the membrane surface flow rate of the water to be treated (raw water + concentrated water) in the NF membrane device to 5000 m / hour or more and 15000 m / hour or less.

  In the crystallization reaction tank 6, calcium sulfate seed crystals are added to the concentrated water. The concentrated water in the crystallization reaction tank 6 has a calcium sulfate concentration equal to or higher than a saturated concentration, but calcium sulfate does not crystallize in the same state. However, by adding granular calcium sulfate as seed crystals to the concentrated water, calcium sulfate in the concentrated water is crystallized using the seed crystals as nuclei, and calcium sulfate crystals are precipitated. In the crystallization reaction tank 6, it is preferable to stir the concentrated water for a certain time after adding the seed crystal.

  Here, when the calcium ion concentration and the sulfate ion concentration in the raw water supplied from the raw water tank are high, the calcium ion concentration and the sulfate ion concentration in the concentrated water of the permeable membrane device 3 are equal to or higher than the saturation concentration of calcium sulfate in a short period of time. Can reach. In that case, the concentrated water is sent to the crystallization reaction tank 6 in a short period of time, and the calcium sulfate is removed in the precipitation tank 8 as crystals.

  On the other hand, even when the calcium ion concentration and the sulfate ion concentration in the raw water are low, the concentrated water of the permeable membrane device 3 circulates through the paths 5 → 7 → 11 → 2, thereby reducing the calcium ion concentration and the sulfate ion concentration in the concentrated water. The saturation concentration of calcium sulfate can be exceeded.

  FIG. 3 shows a water treatment device disclosed in Patent Document 1. In the water treatment device 21 of FIG. 3, raw water is treated by a reverse osmosis filtration membrane device (RO membrane device) 22, and the concentrated water of the RO membrane device 22 is further treated by an NF membrane device 23. Then, calcium sulfate is precipitated and removed from the concentrated water of the NF membrane device 23 in the crystallization tank 24. In this configuration, when the calcium ion concentration and the sulfate ion concentration in the raw water are low, the calcium ion concentration and the sulfate ion concentration in the concentrated water of the NF membrane device 23 are also low, and the amount of treated water in the crystallization tank 24 is large. As a result, a large-scale crystallization tank 24 is required, the crystallization rate of calcium sulfate in the crystallization tank 24 must be lowered, and a large amount of calcium removing agent is also required.

  However, in the water treatment apparatus of the present invention, the concentrated water is continuously circulated between the circulation path 4 and the permeable membrane apparatus 3, so that the calcium ion concentration and the sulfate ion concentration in the raw water are reduced to calcium sulfate. It can concentrate to more than the saturation concentration of. That is, with such a configuration, even when the calcium ion concentration and the sulfate ion concentration in the raw water are low, the concentrated liquid having a low concentration rate is not treated in large quantities in the crystallization reaction tank 6 and the precipitation tank 8. For this reason, the volume of the crystallization reaction tank 6 and the precipitation tank 8 may be small, and the calcium sulfate crystallization rate in the precipitation tank 8 is also high.

  In the water treatment method and the water treatment apparatus of the present invention, by adding a calcium sulfate seed crystal, the supersaturated calcium sulfate is crystallized using the seed crystal as a nucleus, which is larger than the case where there is no seed crystal. As crystallization. As a result, the precipitation rate of calcium sulfate crystals is high in the precipitation tank 8.

  Next, the concentrated liquid in the crystallization reaction tank 6 is supplied to the precipitation tank 8 via the path 7. In the sedimentation tank 8, large calcium sulfate crystals with high sedimentation are deposited at the bottom. For this reason, the removal rate of calcium sulfate in the precipitation tank 8 is high, and the time required for precipitation is also short.

  The calcium sulfate crystals precipitated at the bottom of the settling tank 8 are appropriately extracted from the discharge path 9 as a crystallization slurry. A recovery path 10 is connected to the discharge path 9, and a part of the calcium sulfate crystals is returned to the crystallization reaction tank 6. The returned calcium sulfate crystal functions as a seed crystal for crystallizing calcium sulfate in the concentrated liquid in the crystallization reaction tank 6.

  The amount of calcium sulfate crystals returned from the precipitation tank 8 to the crystallization reaction tank 6 is that the amount of calcium sulfate crystals in the concentrated water in the crystallization reaction tank 6 is supersaturated in the crystallization reaction tank 6. It is preferable to adjust so that it may be 0.01 times or more. In addition, in order to measure the suspended solid concentration of concentrated water, it is preferable to provide a suspended solid concentration measuring device in the crystallization reaction tank 6.

  The supernatant of the precipitation tank 8 from which the calcium sulfate crystals have been removed is supplied to the raw water tank 1 via the path 10 and reused. That is, the raw water and the concentrated water of the permeable membrane device 3 are returned to the raw water tank 1 in the order of the raw water tank 1 → the permeation membrane device 3 → the crystallization reaction tank 6 → the precipitation tank 8 → the raw water tank 1. 10 is functioning as a water return route). Thus, in the water treatment device of the present invention, when raw water is treated by the permeable membrane device 3, the need for extracting drain water is low, and a water recovery rate close to 100% can be achieved.

  In addition, unlike the water treatment apparatus in FIG. 3, monovalent ions contained in the raw water are not concentrated in the path of the raw water tank 1 → the permeation membrane apparatus 3 → the crystallization reaction tank 6 → the precipitation tank 8 → the raw water tank 1. The increase in osmotic pressure is small and it is possible to operate at a low pressure. Since the NF membrane device can be operated at a lower pressure than the RO membrane device, in the water treatment device of the present invention, the pump for feeding the raw water and the concentrated water is more in comparison with the case where monovalent ions are concentrated. A low-pressure and small type is sufficient, and power consumption can be saved.

  In addition, since the treated water of the permeable membrane device 3 has calcium ions and sulfate ions removed, it is difficult for scales to occur in piping and the like. In the case where the monovalent ion concentration is high, it is preferable that the RO membrane device is used as necessary, and then drained out of the system (see Embodiment 2).

<Embodiment 2>
FIG. 2 is a flowchart showing another example of the water treatment apparatus of the present invention. The water treatment device shown in FIG. 1 is common except that the treated water of the permeable membrane device 3 is further treated by the RO membrane device 13. Here, description of the common parts is omitted.

  The treated water of the permeable membrane device 3 is supplied to the RO membrane device 13 via the path 12. A part of the concentrated water of the RO membrane device 13 is circulated to the route 12 by the circulation route 14, but since calcium ions and sulfate ions are removed by the permeable membrane device 3, scale adheres to the RO membrane. Hateful. The remaining concentrated water of the RO membrane device 13 may be connected to the route 2 via the route 15 and supplied to the permeable membrane device 3.

  A part of the treated water of the RO membrane device 13 is stored in the cleaning tank 18 via the path 16 and used as cleaning water for cleaning the RO membrane of the RO membrane device 13. The remainder of the treated water of the RO membrane device 13 is stored in the RO treated water tank 19 via the path 17 and taken out of the system as appropriate. Since the monovalent ions are also removed from the treated water of the RO membrane device 13, it can be safely drained into the environment.

  The permeated water of the RO membrane device 13 stored in the cleaning tank 18 can be returned to the path 2 and / or the path 12 via the path 20 and reused.

[Example 1]
Using the water treatment apparatus having the configuration shown in FIG. 1, the concentration ratio is 1.05, 1.10, 1.20, 1.30, 1.40 times with respect to leachate in which calcium sulfate is saturated. Concentration was performed using an NF membrane. The rejection of Ca ²⁺ and SO ₄ ²⁻ by the NF film was assumed to be 100%. Concentrated water Ca ²⁺ and SO ₄ ²⁻ were measured, and the ion product was calculated by multiplying the molar concentration. The result is shown in FIG. From the relationship between each concentration ratio and ion product value, it was confirmed that calcium sulfate is supersaturated in concentrated water if it is up to 1.3 times concentrated, but supersaturated components are precipitated in 1.4 times concentrated (1 .3 times to 1.4 times, there is almost no difference in ion product).

[Example 2]
Using the water treatment apparatus having the configuration shown in FIG. 1, seed crystals (calcium sulfate) 1 to 100 times the amount of supersaturated calcium sulfate were added to the leachate concentrated 1.2 times and stirred. . The SS component (suspended material) was filtered, and Ca ²⁺ and SO ₄ ²⁻ in the filtrate were measured. The results are shown in FIGS. The stirring time of 0 hr means before the seed crystal is charged.

  The smaller the amount of seed crystals, the slower the crystallization progressed, and at 30 times or more, the stirring time was about 30 minutes, and most of the supersaturated calcium sulfate was deposited. In addition, crystallization progressed to a lower concentration as the seed crystal amount increased.

  The water treatment method and water treatment apparatus of the present invention are useful in technical fields such as leachate or wastewater treatment having a high concentration of ions that cause scale.

1: Raw water tank 2, 5, 7, 11, 12, 15, 16, 17, 20: Path 3: Permeation membrane device 4, 14: Circulation path 6: Crystallization reaction tank 8: Precipitation tank 9: Discharge path 10: Collection path 13: RO membrane device 18: Washing tank 19: RO treatment water tank 21: Water treatment device of Patent Document 1 22: RO membrane device 23: NF membrane device 24: Crystallization tank 25: Solid matter containing salts 26: High pressure RO membrane device 27: second RO membrane device

Claims (12)

In a water treatment method for separating raw water containing calcium ions and sulfate ions into treated water and concentrated water by a permeable membrane device,
Concentrated water is returned to the raw water tank through the crystallization reaction tank and the precipitation tank,
Circulate a part of the concentrated water to the inlet side of the permeable membrane device,
In the crystallization reaction tank, calcium sulfate seed crystals are added to the concentrate, and the calcium ions and sulfate ions in the concentrate are crystallized as calcium sulfate crystals.
In the precipitation tank, the calcium sulfate crystals in the concentrated water sent from the crystallization reaction tank are precipitated and the supernatant is returned to the raw water tank.
A part of the calcium sulfate crystals precipitated in the precipitation tank is recovered as a calcium sulfate seed crystal into the crystallization reaction tank,
The remainder of the calcium sulfate crystals precipitated in the settling tank is discharged out of the system.
A water treatment method characterized by the above.   The calcium sulfate crystals precipitated in the precipitation tank are adjusted so that the amount of calcium sulfate crystals in the crystallization reaction tank is 0.01 times or more of the amount of calcium sulfate supersaturated in the crystallization reaction tank. The water treatment method according to claim 1, wherein the water treatment method is returned to the crystallization reaction tank.   The water treatment method according to claim 1 or 2, wherein the concentration of calcium sulfate in the concentrated water of the permeable membrane device is 1.01 or more times the saturation concentration.   The water treatment method according to any one of claims 1 to 3, wherein a membrane surface flow rate of water to be treated in the permeable membrane device is 5000 m / hour or more and 15000 m / hour or less. The water treatment method according to any one of claims 1 to 4 , wherein the permeable membrane of the permeable membrane device has a flat membrane shape. The water treatment method according to any one of claims 1 to 5 , wherein the treated water of the permeable membrane device is further treated by a reverse osmosis membrane device. A raw water tank for storing raw water containing calcium ions and sulfate ions;
A permeable membrane device for separating raw water sent from the raw water tank into treated water and concentrated water;
A water return route for returning the concentrated water to the raw tank,
A circulation path for circulating a part of the concentrated water to the inlet side of the permeable membrane device;
A water treatment device comprising:
In the water return path, a crystallization reaction tank for adding calcium sulfate seed crystals to the concentrate in the tank to crystallize calcium ions and sulfate ions in the concentrate as calcium sulfate crystals,
A precipitation tank is provided for precipitating calcium sulfate crystals in the concentrated water sent from the crystallization reaction tank and returning the supernatant to the raw water tank.
A part of the calcium sulfate crystals precipitated in the precipitation tank is recovered as a calcium sulfate seed crystal from the precipitation tank through the recovery path to the crystallization reaction tank,
The remainder of the calcium sulfate crystals precipitated in the settling tank is discharged out of the system.
The water treatment apparatus characterized by the above-mentioned. The calcium sulfate crystals precipitated in the precipitation tank are adjusted so that the amount of calcium sulfate crystals in the crystallization reaction tank is 0.01 times or more the amount of calcium sulfate supersaturated in the crystallization reaction tank. The water treatment apparatus according to claim 7 , which is returned to the crystallization reaction tank. The water treatment device according to claim 7 or 8 , wherein a concentration of calcium sulfate in the concentrated water of the permeable membrane device is 1.01 or more times a saturation concentration. The water treatment apparatus according to any one of claims 7 to 9 , wherein a membrane surface flow velocity of water to be treated in the permeable membrane apparatus is 5000 m / hour or more and 15000 m / hour or less. The permeable membrane of the permeable membrane device is a flat membrane, the water treatment apparatus according to any one of claims 7 to 10. The water treatment device according to any one of claims 7 to 11 , further comprising a reverse osmosis membrane device for further treating the treated water of the permeable membrane device.

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