TWI855997B - Processing device and processing method for water containing hardness component - Google Patents

Abstract

An object of the invention is to provide a processing device and a processing method for processing water that contains a hardness component which, when performing reverse osmosis processing of the hardness component-containing water following a softening treatment, can reduce the amount of the hardness component in the concentrate that flows into the next stage. A processing device 1 for a hardness component-containing water comprises a reaction chamber 12 in which at least one or other of an alkali agent and a carbonate compound is added to a water to be processed which contains the hardness component to insolubilize the hardness component, a solid-liquid separation device 16 which performs solid-liquid separation of the obtained insolubilized matter, a reverse osmosis membrane processing device 20 which uses a reverse osmosis membrane to process the liquid obtained from the solid-liquid separation into a concentrate and a permeate, and a return pipe 38 which returns at least a portion of the obtained concentrate to a stage prior to the solid-liquid separation device.

Description

Device and method for treating water containing hardness components

The present invention relates to a device and method for treating water containing hardness components.

As a method to reduce the volume of wastewater, reverse osmosis membranes have been used to concentrate wastewater and recycle permeate water. In recent years, the demand for reducing wastewater volume has increased, and the concentration rate of wastewater has been increased as much as possible. More and more factories have even achieved ZLD (Zero Liquid Discharge).

Therefore, there are methods to further concentrate the concentrated water of the reverse osmosis membrane by further reverse osmosis membrane treatment or evaporation concentration. In this way, once the concentration ratio of the drainage is increased, the risk of scaling caused by hardness components in the drainage will also increase accordingly. Once scaling occurs, the reverse osmosis membrane will be blocked, resulting in a decrease in the amount of water that penetrates, or the heat transfer surface of the evaporation concentration will be covered by scale, reducing the heat transfer efficiency.

In view of this, it is ideal to reduce the hardness component in the wastewater as much as possible through softening treatment, etc. before reverse osmosis membrane treatment. As described in Patent Document 1, a method for softening wastewater containing hardness components is known, in which the hardness component in the wastewater is converted into calcium carbonate or magnesium hydroxide and precipitated to separate the solid and liquid. When the hardness component contained in the wastewater is calcium, the calcium carbonate in the softened water after the solid-liquid separation will be saturated, so the following method can be adopted: oxygen is added to increase the solubility of calcium carbonate, and decarbonation is performed to inhibit the precipitation of calcium carbonate in the later stage.

The softened water obtained by this softening treatment usually has a few mg/L to tens of mg/L of dissolved hardness components. Since the calcium hardness component will be removed as calcium carbonate, the calcium concentration of the softened water depends on the concentration of carbonate ions remaining in the softened water; the higher the carbonate ion concentration, the lower the calcium hardness component will be, but relatively more carbonate injection is required, which is more costly. Since the magnesium hardness component will be removed as magnesium hydroxide, the magnesium concentration of the softened water will change with the pH. If the pH is above 11.0, the magnesium hardness component can be removed to less than 1 mg/L; but if it reaches pH10.5, the magnesium hardness component will remain at around several mg/L to tens of mg/L.

As mentioned above, even if the hardness component in the wastewater is reduced by softening treatment before reverse osmosis membrane treatment, there will still be residual hardness components in the softened water. Therefore, if the concentration ratio of the reverse osmosis membrane in the later stage is further increased, the scaling risk in the later stage will increase.

In order to further remove the hardness components remaining in the softened water, there is also a method of using ion exchange resin for treatment, but the treatment cost will increase. [Known technical literature] [Patent literature]

[Patent Document 1] Japanese Patent No. 5906892

[Identify the problem that the invention is trying to solve]

The purpose of the present invention is to provide a device and method for treating water containing hardness components, which can reduce the amount of hardness components in the concentrated water flowing out to the later stage by "performing reverse osmosis membrane treatment after softening water containing hardness components". [Technical means for solving the problem]

The present invention is a treatment device for water containing hardness components, comprising: a reaction tank for adding at least one of an alkali and a carbonate compound to the water to be treated containing the hardness components to make the hardness components insoluble; a solid-liquid separation means for performing solid-liquid separation of the obtained insoluble matter; a reverse osmosis membrane treatment means for treating the obtained solid-liquid separation liquid with a reverse osmosis membrane to obtain concentrated water and permeate; and a return means for returning at least a portion of the obtained concentrated water to the front section of the solid-liquid separation means.

In the aforementioned device for treating water containing hardness components, it is preferred that the destination to which the concentrated water is returned by the returning means is the reaction tank.

In the aforementioned treatment device for water containing hardness components, it is preferred to return the concentrated water so that the CaCO ₃ concentration in the reaction tank reaches above 100 mg/L.

The aforementioned device for treating water containing hardness components preferably further comprises: an ion concentration measuring means for measuring the ion concentration of the concentrated water; and adjusting the amount of the concentrated water returned by the returning means according to the measured value.

Furthermore, the present invention is a method for treating water containing hardness components, comprising the following steps: an insolubilization step, in which at least one of an alkali and a carbonate compound is added to the treated water containing the hardness components to insolubilize the hardness components; a solid-liquid separation step, in which the obtained insoluble matter is separated into solid and liquid; a reverse osmosis membrane treatment step, in which the obtained solid-liquid separation liquid is treated with a reverse osmosis membrane to obtain concentrated water and permeate; and a return step, in which at least a portion of the obtained concentrated water is returned to the previous stage of the solid-liquid separation step.

In the aforementioned method for treating water containing hardness components, it is preferred that in the returning step, the destination of the concentrated water is a reaction tank to which at least one of the alkali agent and the carbonate compound is added.

In the aforementioned method for treating water containing hardness components, it is preferred to return the concentrated water so that the CaCO ₃ concentration in the reaction tank reaches above 100 mg/L.

In the aforementioned method for treating water containing hardness components, it is preferred to measure the ion concentration of the concentrated water and adjust the amount of the concentrated water returned in the returning step according to the measured value. [Effects of the Invention]

The present invention enables an apparatus and method for "performing reverse osmosis membrane treatment after softening water containing hardness components" to reduce the amount of hardness components in concentrated water flowing out to the subsequent stage.

The following describes the implementation of the present invention. This implementation is an example of the implementation of the present invention, and the present invention is not limited to this implementation.

FIG1 schematically shows an example of a device for treating water containing hardness components according to an embodiment of the present invention, and explains its structure.

The treatment device 1 for water containing hardness components comprises: a reaction tank 12 for adding at least one of "alkali" and "carbonic acid compound" to the water to be treated containing hardness components to "insolubilize" the hardness components; a sedimentation tank 16 for performing solid-liquid separation of the obtained insoluble matter as a solid-liquid separation means; and a reverse osmosis membrane treatment device 20 for treating the obtained solid-liquid separation liquid with a reverse osmosis membrane as a reverse osmosis membrane treatment means to obtain concentrated water and permeate water. The treatment device 1 for water containing hardness components may also be further equipped with: a treated water tank 10 for storing the treated water; a polymer reaction tank 14 for adding a polymer gelling agent to the reaction solution obtained in the reaction tank 12 to perform a gelling reaction; and a solid-liquid separation liquid tank 18 for storing the solid-liquid separation liquid obtained in the sedimentation tank 16.

In the "treatment device 1 for water containing hardness components" of Figure 1, the outlet of the treated water tank 10 and the treated water inlet of the reaction tank 12 are connected by a pipe 26 via a pump 22. The outlet of the reaction tank 12 and the inlet of the polymer reactor 14 are connected by a pipe 28. The outlet of the polymer reactor 14 and the inlet of the sedimentation tank 16 are connected by a pipe 30. The solid-liquid separation liquid outlet of the sedimentation tank 16 and the inlet of the solid-liquid separation liquid tank 18 are connected by a pipe 32. The sludge outlet of the sedimentation tank 16 is connected to the sludge pipe 58. The outlet of the solid-liquid separation liquid tank 18 and the inlet of the reverse osmosis membrane treatment device 20 are connected by a pump 24 via a pipe 34. The permeate outlet of the reverse osmosis membrane treatment device 20 is connected to the permeate water pipe 36. The concentrated water outlet of the reverse osmosis membrane treatment device 20 and the return water inlet of the reaction tank 12 are connected by the return pipe 38 via a valve 54; the return pipe 38 is used as a return means to return at least a part of the obtained concentrated water to the front section of the sedimentation tank 16. The concentrated water outlet on the return pipe 38 and the valve 54 are connected by the concentrated water pipe 40 via a valve 56. The reaction tank 12 is connected to: a carbonate compound adding pipe 42 used as a carbonate compound adding means, and an alkali adding pipe 44 used as an alkali adding means; and is provided with a stirring device 50 having a stirring blade as a stirring means. The polymer reaction tank 14 is connected to a polymer gelling agent adding pipe 46 as a polymer gelling agent adding means; and is provided with a stirring device 52 having a stirring blade as a stirring means. The pipe 32 is connected to a pH adjusting agent adding pipe 48 as a pH adjusting agent adding means.

The method for treating water containing hardness components and the operation of the device 1 for treating water containing hardness components according to this embodiment are described.

Water containing hardness components as treated water is stored in the treated water tank 10 as needed, and is sent to the reaction tank 12 by the pump 22 through the pipe 26. In the reaction tank 12, at least one of an alkali and a carbonate compound is added to the water containing hardness components to insolubilize the hardness components (insolubilization step). The alkali is added to the reaction tank 12 through the alkali addition pipe 44, and the carbonate compound is added to the reaction tank 12 through the carbonate compound addition pipe 42. In the reaction tank 12, the reaction liquid can also be stirred by the stirring device 50.

The insolubilization reaction is represented by the following chemical formula, for example. For the calcium hardness component as a temporary hardness component, calcium hydroxide (Ca(OH) ₂ ) is used as an alkali, and it is insolubilized into calcium carbonate. Alternatively, for the calcium hardness component as a permanent hardness component, sodium carbonate (Na ₂ CO ₃ ) is used as a carbonate compound, and it is insolubilized into calcium carbonate. For the magnesium hardness component, sodium hydroxide (NaOH) is used as an alkali, and it is insolubilized into magnesium hydroxide. Ca（HCO ₃ ） ₂ ＋Ca（OH） ₂ →2CaCO ₃ ↓＋2H ₂ O CaCl ₂ ＋Na ₂ CO ₃ →CaCO ₃ ↓＋2NaCl MgCl ₂ ＋2NaOH→Mg（OH） ₂ ↓＋2NaCl

The reaction solution obtained in the insolubilization step is transported from the reaction tank 12 to the polymer reaction tank 14 through the pipe 28. In the polymer reaction tank 14, a polymer gelling agent is added to the reaction solution through the polymer gelling agent adding pipe 46 as needed to perform a gelling reaction (gelling step). In the polymer reaction tank 14, the gelling solution can also be stirred by the stirring device 52.

The gelling liquid obtained in the gelling step is transferred from the polymer reaction tank 14 to the sedimentation tank 16 via the pipe 30. In the sedimentation tank 16, the obtained insoluble matter is separated into solid and liquid by natural sedimentation or the like (solid-liquid separation step).

The solid-liquid separation liquid obtained in the solid-liquid separation step is transported from the sedimentation tank 16 to the solid-liquid separation liquid tank 18 through the pipe 32 as needed and stored there. A pH adjuster can also be added to the solid-liquid separation liquid through the pH adjuster adding pipe 48 in the pipe 32 as needed to adjust the pH of the solid-liquid separation liquid (pH adjustment step). The pH adjustment can also be performed in the solid-liquid separation liquid tank 18. On the other hand, the sludge obtained in the solid-liquid separation step is discharged through the sludge pipe 58.

The solid-liquid separation liquid is transported to the reverse osmosis membrane treatment device 20 through the pipe 34 by the pump 24. In the reverse osmosis membrane treatment device 20, the solid-liquid separation liquid is treated in the reverse osmosis membrane to obtain concentrated water and permeate (reverse osmosis membrane treatment step). The permeate obtained in the reverse osmosis membrane treatment step is discharged through the permeate water pipe 36 and then recycled or discarded. At least a part of the concentrated water obtained in the reverse osmosis membrane treatment step is returned to the reaction tank 12 through the return pipe 38, and the reaction tank 12 belongs to the previous section (return step) of the sedimentation tank 16 (solid-liquid separation step). At least a portion of the concentrated water may also be returned to the solid-liquid separation tank 18.

As mentioned above, in the method and apparatus for treating water containing hardness components of the present embodiment, after the softening treatment of the water containing hardness components (insolubilization step, gelation step, solid-liquid separation step), reverse osmosis membrane treatment is used to concentrate the solid-liquid separation liquid containing hardness components, and at least a portion of the concentrated water is returned to the front stage of the solid-liquid separation step.

This can reduce the amount of hardness components in the concentrated water flowing out to the later stage. Even if further reverse osmosis membrane treatment or evaporation concentration treatment is performed at the later stage of reverse osmosis membrane treatment, these equipment can be miniaturized. Furthermore, the reverse osmosis membrane treatment and evaporation concentration treatment at the later stage of reverse osmosis membrane treatment suppress the precipitation of hardness components and enable the system to operate stably.

The destination of the concentrated water by the return means is not particularly limited as long as it is the preceding section of the sedimentation tank 16 (solid-liquid separation step). For example, at least a portion of the concentrated water can be returned to at least one of the treated water tank 10, the reaction tank 12, the polymer reaction tank 14, and the pipes 26, 28, and 30; however, it is more ideal because the hardness component in the concentrated water can promote the precipitation of calcium carbonate or magnesium hydroxide in the reaction tank 12 by returning the concentrated water to the reaction tank 12 to which at least one of the alkali and the carbonate compound is added. For example, the precipitation reaction of calcium carbonate proceeds by precipitating calcium carbonate on the surface of the generated crystals. Therefore, it is expected that the reaction time can be shortened when calcium carbonate particles are already present or the concentration of the calcium hardness component is high.

In this case, it is preferred to return the concentrated water so that the concentration of calcium carbonate (CaCO ₃ ) in the reaction tank 12 becomes 100 mg/L or more, and it is more preferred to return the concentrated water so that it becomes 1000 mg/L or more. If the concentration of calcium carbonate (CaCO ₃ ) in the reaction tank 12 is less than 100 mg/L, it may be difficult to promote the precipitation of calcium carbonate in the reaction tank 12.

The more concentrated water is sent back to the sedimentation tank 16 (solid-liquid separation step), the less hardness load can be applied to the reverse osmosis membrane treatment. However, if the water to be treated contains sodium chloride (NaCl) and other ions that are difficult to remove by gelation precipitation, these components may be concentrated in the system. If the concentration ratio is too high, the osmotic pressure will increase, and the reverse osmosis membrane operating pressure will increase. Therefore, it is ideal to have a certain amount of concentrated water sent to the reverse osmosis membrane treatment. In order to adjust the amount of concentrated water delivered to the rear section of the reverse osmosis membrane treatment, it is preferred to have an ion concentration measuring means, such as measuring the ion concentration of the concentrated water, and to adjust the amount of concentrated water returned by the return means according to the measured value. For example, the following method can be adopted: measuring the conductivity in the concentrated water, and adjusting the amount of concentrated water delivered to the rear section of the reverse osmosis membrane treatment so that the conductivity reaches below a predetermined value. The adjustment of the delivery amount of concentrated water is, for example, to adjust the opening of valves 54 and 56.

When measuring the conductivity of concentrated water to adjust the delivery volume of concentrated water, it is better to keep the osmotic pressure at a value that does not exceed the upper limit of the pressure of the reverse osmosis membrane treatment; it is better to keep it below 30000μS/cm, and more preferably below 20000μS/cm. If the conductivity of concentrated water exceeds 30000μS/cm, the osmotic pressure of the reverse osmosis membrane will become higher, and there may be a problem of exceeding the pressure limit of the reverse osmosis membrane.

In the latter stage of the reverse osmosis membrane treatment, as a means of further concentrating the concentrated water, reverse osmosis membrane treatment, heating evaporation concentration treatment, forward osmosis membrane treatment, electrodialysis treatment, etc. can be cited; however, from the viewpoint of reducing the treatment cost, reverse osmosis membrane treatment is preferred. If the treatment method and treatment device of water containing hardness components of this embodiment are used, even if a reverse osmosis membrane treatment is added in the latter stage of the reverse osmosis membrane treatment, the treatment can be stably performed.

The water containing hardness components to be treated includes, for example, groundwater, industrial water, and factory drainage. The amount of calcium hardness components in the water containing hardness components is, for example, 50 to 5000 mg-CaCO ₃ /L; and the amount of magnesium hardness components is, for example, 10 to 1000 mg-CaCO ₃ /L. When the water containing hardness components contains silica, the amount of silica in the water containing hardness components is, for example, 10 to 400 mg/L.

As the alkali used in the insolubilization step, for example, calcium hydroxide (Ca(OH) ₂ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), etc. can be mentioned. Among these, calcium hydroxide and sodium hydroxide are preferred from the viewpoint of chemical cost. As the carbonate compound used in the insolubilization step, for example, sodium carbonate (Na ₂ CO ₃ ), sodium bicarbonate (NaHCO ₃ ), carbonic acid gas, etc. can be mentioned. Among these, sodium carbonate is preferred from the viewpoint of chemical cost.

The amount of the alkali and the carbonate compound added in the insolubilization step is preferably in the range of 1.0 mol to 1.2 mol, more preferably in the range of 1.0 mol to 1.1 mol, relative to the amount of the calcium hardness component (1 mol) in the water containing the hardness component as the treated water. Furthermore, it is preferably in the range of 2.0 to 2.4 mol, more preferably in the range of 2.0 to 2.2 mol relative to the amount of the magnesium hardness component (1 mol). If the amount of the alkali and the carbonate compound added in the insolubilization step is less than the equivalent mole relative to the amount of the hardness component (1 mol) in the water containing the hardness component, the insolubilization reaction may not proceed sufficiently; and if it is added excessively, it may be disadvantageous from the viewpoint of chemical cost, etc.

The reaction temperature in the insolubilization step is not particularly limited, and is, for example, in the range of 15°C to 30°C.

Examples of polymer gelling agents used in the gelling step include acrylamide-based polymer gelling agents and acrylate-based polymer gelling agents. Among these, acrylamide-based polymer gelling agents are preferred from the viewpoint of chemical cost and the like.

The amount of polymer gelling agent added in the gelling step is preferably in the range of 0.5 to 5.0 mg/L, more preferably in the range of 1 to 2 mg/L. If the amount of polymer gelling agent added in the gelling step is less than 0.5 mg/L, the gelling reaction may not proceed sufficiently; and if it is added excessively, it may be disadvantageous from the perspective of chemical cost, etc.

The reaction temperature in the gelling step is not particularly limited, and is, for example, in the range of 15°C to 30°C.

The solid-liquid separation method in the solid-liquid separation step is not particularly limited; for example, in addition to a sedimentation tank that utilizes natural sedimentation, sand filtration, membrane filtration, and the like can also be cited. Among these, a sedimentation tank that utilizes natural sedimentation is preferred from the viewpoint of equipment cost, etc.

Examples of the pH adjuster used in the pH adjustment step include acids such as chloric acid and sulfuric acid, and alkalis such as sodium hydroxide.

In the pH adjustment step, the pH is preferably adjusted to a range of pH 4 to 10, more preferably to a range of pH 5 to 8. If the pH is less than 4, there may be an excess of acid; if the pH exceeds 10, the scale inhibition effect of calcium carbonate may be insufficient.

Since the solubility of hardness components in acidic areas is high (see Figure 5), they are not easy to precipitate. However, when water containing hardness components contains silica components, the solubility of silica components in acidic areas is low (see Figure 6) and it is easy to precipitate. Therefore, it is sufficient to make the hardness components insoluble and then remove them (solid-liquid separation) by the above method, and then treat them at a pH of 9.5 or above in the reverse osmosis membrane treatment step.

If the water containing hardness components contains silicon dioxide, another reaction tank (second reaction tank) may be set in the reaction tank 12 or in the front section or rear section of the reaction tank 12, and a magnesium compound may be added to make the silicon dioxide insoluble, and then removed by the above-mentioned solid-liquid separation step. In this case, reverse osmosis membrane treatment can be performed at any pH value.

Examples of magnesium compounds used for insolubilizing the silicon dioxide component include magnesium hydroxide (Mg(OH) ₂ ), magnesium chloride (MgCl ₂ ), magnesium oxide (MgO), and other inorganic salts of magnesium. Among these, magnesium hydroxide is preferred from the viewpoint of chemical cost.

The amount of magnesium compound added is preferably in the range of 0.5 mol to 5.0 mol, more preferably in the range of 1.0 mol to 2.5 mol, relative to the amount of silicon dioxide in the treated water (1 mol). If the amount of magnesium compound added is less than 0.5 mol relative to the amount of silicon dioxide in the treated water (1 mol), the insolubilization reaction may not proceed sufficiently; and if it exceeds 5.0 mol, it may be disadvantageous from the perspective of chemical cost, etc.

The reverse osmosis membrane used in the reverse osmosis membrane treatment is not particularly limited, and may be, for example, a polyimide reverse osmosis membrane. [Example]

The present invention will be described in more detail with reference to the following embodiments and comparative examples; however, the present invention is not limited to the following embodiments.

<Example 1 and Comparative Example 1> A water flow test was conducted in the experimental equipment of the flow chart shown in Fig. 2 (Example 1) and Fig. 3 (Comparative Example 1). In Example 1, part of the concentrated water was returned to the reaction tank.

(Treatment water) Treatment water: Factory effluent water (containing hardness components) Ca = 200mg-CaCO ₃ /L, Mg = 50mg-CaCO ₃ /LHCO ₃ ^- = 200mg-CaCO ₃ /L

In Example 1, the treated water was circulated to the reaction tank at a flow rate of 140 L/h. In the reaction tank, calcium hydroxide (Ca(OH) ₂ ) was added as an alkali agent to adjust the pH to 10.8-11.0; and 100 mg-CaCO ₃ /L sodium carbonate (Na ₂ CO ₃ ) was added as a carbonate compound. In the polymer reaction tank, 2 mg/L ORFLOCK M-4020 (manufactured by ORGANO Co., Ltd.) was added as a polymer gelling agent. As for the solid-liquid separation device, a sedimentation tank was used for solid-liquid separation. The solid-liquid separation liquid was circulated to the solid-liquid separation liquid tank at a flow rate of 200 L/h. The solid-liquid separation liquid was circulated to a 4-inch RO element (LFC-3, manufactured by Nitto Denko) as a reverse osmosis membrane treatment device at a flow rate of 720 L/h. The permeate water was obtained at a flow rate of 120 L/h by reverse osmosis membrane treatment, and the concentrated water was circulated to the solid-liquid separation tank at a flow rate of 520 L/h, and returned to the reaction tank at a flow rate of 60 L/h, and then sent to the concentration device at the rear stage at a flow rate of 20 L/h. In Example 1, the concentrated water was returned to make the CaCO ₃ concentration in the reaction tank 155 mg/L. The results are shown in Table 1.

In Comparative Example 1, the treated water was circulated to the reaction tank at a flow rate of 140 L/h. In the reaction tank, calcium hydroxide (Ca(OH) ₂ ) was added as an alkali agent to adjust the pH to 10.8-11.0; and 100 mg-CaCO ₃ /L sodium carbonate (Na ₂ CO ₃ ) was added as a carbonate compound. In the polymer reaction tank, 2 mg/L ORFLOCK M-4020 (manufactured by ORGANO Co., Ltd.) was added as a polymer gelling agent. As for the solid-liquid separation device, a sedimentation tank was used for solid-liquid separation. The solid-liquid separation liquid was circulated to the solid-liquid separation liquid tank at a flow rate of 140 L/h. The solid-liquid separation liquid was circulated to a 4-inch RO element (LFC-3, manufactured by Nitto Denko) as a reverse osmosis membrane treatment device at a flow rate of 684 L/h. Through the reverse osmosis membrane treatment, permeate water was obtained at a flow rate of 84 L/h, and concentrated water was circulated to the solid-liquid separation tank at a flow rate of 544 L/h, and the liquid was sent to the subsequent concentration device at a flow rate of 56 L/h. The results are shown in Table 2.

The amount of Ca and Mg in water was measured using an ion chromatography curve (IC761, manufactured by Metrohm Corporation); the amount of HCO ₃ ^- was converted by measuring the value of inorganic carbon using a total organic carbon analyzer (TOC-3000, manufactured by Shimadzu Scientific Instruments).

[Table 1]

[Table 2]

In Example 1, a portion of the concentrated water is returned to the reaction tank as the front stage of the sedimentation tank (solid-liquid separation tank) to reduce the Ca load and Mg load of the RO concentrated water, so that the amount of hardness components flowing out to the rear stage of the reverse osmosis membrane treatment device is reduced. In contrast, in Comparative Example 1, since the concentrated water is not circulated, the hardness components flowing out to the rear stage of the reverse osmosis membrane treatment device are larger.

<Example 2> The destination of the concentrated water was discussed. Since the precipitation reaction of CaCO ₃ is carried out by precipitating CaCO ₃ on the surface of the generated crystals, it is conceivable that the reaction time can be shortened when CaCO ₃ particles are pre-existing or the concentration of Ca is high.

[Bottle test sequence] Add 0, 100, 1000, 10000 mg/L of CaCO _3- containing sludge to the raw water (Ca=250 mg-CaCO ₃ /L). Then add 417 mg-CaCO ₃ /L of Na ₂ CO ₃ to them and use sodium hydroxide (NaOH) to adjust to pH11. In the bottle test, react at 120 rpm. After filtering with a 0.45μm filter, measure the Ca concentration of the treated water.

The results of the bottle test are shown in Figure 4. The graph in Figure 4 represents the Ca concentration (mg-CaCO ₃ /L) relative to the reaction time (min).

As mentioned above, it is known that by returning the concentrated water of CaCO ₃ to the reaction tank so that the CaCO ₃ concentration becomes 100 mg/L or more, the precipitation of CaCO ₃ can be promoted.

As described above, according to the embodiments, after softening water containing hardness components, the amount of hardness components in the concentrated water flowing out to the subsequent stage can be reduced by using an apparatus and method for reverse osmosis membrane treatment.

1.··· Treatment device for water containing hardness components 10.··· Treatment water tank 12.··· Reaction tank 14.··· Polymer reaction tank 16.··· Solid-liquid separation tank 18.··· Solid-liquid separation liquid tank 20.··· Reverse osmosis membrane treatment device 22, 24.··· Pumps 26, 28, 30, 32, 34.··· Pipe 36.··· Permeate water pipe 38.··· Return pipe 40.··· Concentrated water pipe 42.··· Carbonate addition pipe 44.··· Alkali addition pipe 46.··· Polymer gelling agent addition pipe 48.··· pH adjuster addition pipe 50, 52.··· Agitator 54, 56.··· Valve 58.··· Sludge pipe

[Figure 1] is a schematic diagram showing an example of a treatment device for water containing hardness components according to an embodiment of the present invention. [Figure 2] is a schematic diagram showing a treatment device used in Example 1. [Figure 3] is a schematic diagram showing a treatment device used in Comparative Example 1. [Figure 4] is a graph showing the Ca concentration (mg-CaCO ₃ /L) relative to the reaction time (min) in Example 2. [Figure 5] is a graph showing the solubility of calcium carbonate (mg/L) relative to the pH value of water at 25°C. [Figure 6] is a graph showing the solubility of silicon dioxide (mgSiO ₂ /L) relative to the pH value of water at 25°C.

1‧‧‧Device for treating water containing hardness components

10‧‧‧Treatment sink

12‧‧‧Reaction tank

14‧‧‧Polymer reactor

16‧‧‧Solid-liquid separation tank

18‧‧‧Solid-liquid separation tank

20‧‧‧Reverse osmosis membrane treatment device

22, 24‧‧‧Pump

26, 28, 30, 32, 34‧‧‧Piping

36‧‧‧Penetrating water pipes

38‧‧‧Return the pipes

40‧‧‧Concentrated water piping

42‧‧‧Carbonate compound adding piping

44‧‧‧Alkali adding piping

46‧‧‧Polymer gelling agent adding piping

48‧‧‧pH adjuster addition piping

50, 52‧‧‧Stirring device

54, 56‧‧‧Valve

58‧‧‧Sludge piping

Claims (4)

A treatment device for water containing hardness components comprises: a reaction tank for adding at least one of an alkali and a carbonate compound to the treated water containing hardness components to insolubilize the hardness components; a solid-liquid separation means for performing solid-liquid separation of the obtained insoluble matter; a reverse osmosis membrane treatment means for treating the obtained solid-liquid separation liquid with a reverse osmosis membrane to obtain concentrated water and permeate; and a return means for returning at least a portion of the obtained concentrated water to the front section of the solid-liquid separation means; the destination to which the concentrated water is returned by the return means is the reaction tank; the concentrated water is returned so that the _CaCO3 concentration in the reaction tank reaches above 100 mg/L. For example, the device for treating water containing hardness components in item 1 of the patent application scope further includes: an ion concentration measuring means for measuring the ion concentration of the concentrated water; and adjusting the amount of the concentrated water returned by the returning means according to the measured value. A method for treating water containing hardness components comprises the following steps: an insolubilization step, in which at least one of an alkali and a carbonate compound is added to the treated water containing the hardness components to insolubilize the hardness components; a solid-liquid separation step, in which the obtained insoluble matter is separated into solid and liquid; a reverse osmosis membrane treatment step, in which the obtained solid-liquid separation liquid is treated with a reverse osmosis membrane to obtain concentrated water and permeate; and a return step, in which at least a part of the obtained concentrated water is returned to the preceding section of the solid-liquid separation step; in the return step, the destination to which the concentrated water is returned is a reaction tank to which at least one of the alkali and the carbonate compound is added; the concentrated water is returned so that the CaCO in the reaction tank is deionized. _3. The concentration reaches above 100 mg/L. For example, in the method for treating water containing hardness components as described in item 3 of the patent application scope, the ion concentration of the concentrated water is measured, and the amount of the concentrated water returned in the return step is adjusted according to the measured value.