JP2011056411A - System and method for desalination of water to be treated - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system for desalination of water to be treated employing a reverse osmosis membrane capable of reducing the load on the reverse osmosis membrane by effectively removing a suspended matter from the water prior to the filtration of the water by means of the reverse osmosis membrane and also capable of preventing the generation of scale at a low cost. <P>SOLUTION: The desalination system employing the reverse osmosis membrane method includes a filtration means in which the suspended matter is separated from the water to be treated and a reverse osmosis membrane filtration means installed at the downstream side of the filtration means as viewed in the direction of treating the water from the upstream side to the downstream side for filtering and desalinating the water. The desalination system is characterized in that the filtration means is a ceramic membrane filtration means for filtering out the suspended matter from the water using a ceramic-made microfiltration membrane or a ceramic-made ultrafiltration membrane and also in that a decarbonation means is further included which is installed at the upstream side of the ceramic membrane filtration means as viewed in the direction of treating the water from the upstream side to the downstream side for removing carbonic acid from the water. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a system and method for desalinating water to be treated such as brine or seawater, and in particular, desalinates water to be treated by appropriately pretreating the water to be treated and filtering it with a reverse osmosis membrane. In particular, the present invention relates to a desalination system and a desalination method for water to be treated, in which a load on a reverse osmosis membrane is reduced.

  Conventionally, a membrane separation method (reverse osmosis method) using a reverse osmosis membrane (RO membrane) is known as a general method for obtaining fresh water from treated water such as brine or seawater.

  In general, in a seawater desalination system using a reverse osmosis method, seawater that is to be treated is agglomerated by using a flocculant such as suspended substances in the seawater, and aggregated suspended substances are removed from the seawater. For this purpose, seawater is desalinated while preventing the occurrence of early clogging of the reverse osmosis membrane by filtering with a reverse osmosis membrane after sand filtration for the purpose.

  However, sand filtration that filters treated water using a layer of gravel or sand cannot sufficiently separate and remove suspended solids from seawater, so conventional seawater desalination systems have a reverse osmosis membrane. There was a problem that early clogging could not be sufficiently suppressed (the load on the reverse osmosis membrane could not be sufficiently reduced).

  In response to such problems, in a seawater desalination system, it is also possible to remove suspended substances from seawater using a membrane filtration device using an organic material microfiltration membrane or an ultrafiltration membrane instead of a sand filtration device. Conceivable. However, since seawater contains a lot of hardness components such as calcium and magnesium, the seawater desalination system using the membrane filtration device described above, when trying to remove suspended solids from seawater, There is a problem that the hardness component is deposited (scaling) in the form of carbonate (calcium carbonate, magnesium carbonate, etc.) as well as a pump and piping.

  Therefore, in a seawater desalination system using a membrane filtration device, it is necessary to perform a softening treatment by a crystallization method in which hardness components are precipitated and removed in the form of carbonate or the like before membrane filtration of seawater. However, when the softening treatment is performed by the crystallization method, a large amount of inorganic sludge (calcium carbonate or magnesium carbonate) is discharged, which increases the amount of waste and increases the cost.

  Therefore, it is possible to effectively remove suspended substances from the water to be treated before filtering the water to be treated by the reverse osmosis membrane, thereby reducing the load on the reverse osmosis membrane and generating scale at low cost. It has been desired to develop a desalination system and a desalination method using a reverse osmosis membrane that can be suppressed.

  This invention aims to solve the above-mentioned problem advantageously, and the desalination system of the treated water of the present invention comprises filtration means for separating suspended substances in the treated water from the treated water, A reverse osmosis method provided with a reverse osmosis membrane filtration means for filtering the treated water to be desalted by being provided on the downstream side of the filtration means when viewed in the direction of treating the treated water from the upstream side to the downstream side. The filtration means is a ceramic membrane filtration means for separating suspended substances from the treated water using a ceramic microfiltration membrane or a ceramic ultrafiltration membrane, It is characterized by further comprising a decarbonation means for removing carbonic acid in the for-treatment water on the upstream side of the ceramic membrane filtration means as viewed in the direction of treating the treated water from the upstream side to the downstream side. Thus, if the suspended matter is separated from the treated water using a ceramic microfiltration membrane or a ceramic ultrafiltration membrane, the suspended matter is effectively separated and removed from the treated water, and reverse osmosis is performed. The load applied to the membrane can be reduced. Moreover, if a decarbonation means is provided, generation | occurrence | production of the scale in a desalination system can be suppressed.

  Here, it is preferable that the desalination system of the present invention further includes a flocculant addition means for adding a flocculant to the water to be treated between the ceramic membrane filtration means and the decarboxylation means. This is because if the coagulant adding means is provided, suspended substances in the water to be treated can be aggregated, and the suspended substances can be reliably separated and removed from the water to be treated by the ceramic membrane filtration means.

  In the desalination system of the present invention, the decarbonation means is a first pH adjusting means for reducing the pH of the water to be treated to 5 or less and a direction in which the water to be treated is treated from the upstream side to the downstream side. It is preferable to provide an aeration means, a deaeration means, or both of them provided downstream from the first pH adjustment means. This is because if the aeration or deaeration is performed after the pH is adjusted to 5 or less, the carbonic acid component can be efficiently removed from the water to be treated, and the generation of scale can be suppressed.

And it is preferable that the desalination system of this invention is further equipped with the 2nd pH adjustment means which adjusts pH of to-be-processed water to 6-10 between the said decarboxylation means and the said coagulant | flocculant addition means. This is because if the flocculant is added after adjusting the pH of the water to be treated to 6 to 10, the suspended substances in the water to be treated can be effectively aggregated. In the desalination system of the present invention, since the pH is adjusted by the second pH adjusting means after decarboxylation, the water to be treated is carbonate ion (CO ₃ ²⁻ ) or bicarbonate ion during pH adjustment. The buffering action by (HCO ₃ ⁻ ) is not exhibited, and the amount of chemicals used for pH adjustment can be reduced.

  The desalination method of the water to be treated of the present invention includes a filtration step for separating suspended substances in the water to be treated from the water to be treated, and a reverse osmosis membrane for filtering the water to be treated after the filtration step with a reverse osmosis membrane A ceramic membrane that separates suspended matter from the water to be treated using a ceramic microfiltration membrane or a ceramic ultrafiltration membrane. It is a filtration process, It is characterized by further including the decarboxylation process which removes the carbonic acid in to-be-processed water before the said ceramic membrane filtration process. Thus, if the suspended matter is separated from the treated water using a ceramic microfiltration membrane or a ceramic ultrafiltration membrane, the suspended matter is effectively separated and removed from the treated water, and reverse osmosis is performed. The load applied to the membrane can be reduced. Moreover, if a decarbonation means is provided, generation | occurrence | production of the scale in a desalination system can be suppressed.

  Here, the desalination method of the present invention further includes a flocculation step of adding a flocculant to the water to be treated and aggregating suspended substances in the water to be treated between the decarboxylation step and the ceramic membrane filtration step. It is preferable to include. This is because if the coagulation step is provided, suspended substances in the water to be treated can be coagulated and the suspended substances can be reliably separated and removed from the water to be treated in the ceramic membrane filtration step.

  In the desalination method of the present invention, the decarboxylation step includes a first pH adjustment step in which the pH of the water to be treated is 5 or less, and aeration in which the water to be treated after the first pH adjustment step is aerated. It is preferable to include a process, a degassing process for degassing, or both of them. This is because if the aeration or deaeration is performed after the pH is adjusted to 5 or less, the carbonic acid component can be efficiently removed from the water to be treated, and the generation of scale can be suppressed.

Furthermore, it is preferable that the desalination method of this invention further includes the 2nd pH adjustment process which adjusts pH of to-be-processed water to 6-10 between the said aggregation process and the said decarboxylation process. This is because if the flocculant is added after adjusting the pH of the water to be treated to 6 to 10, the suspended substances in the water to be treated can be effectively aggregated. In the desalination method of the present invention, since the pH is adjusted in the second pH adjustment step after decarboxylation, the water to be treated is carbonate ion (CO ₃ ²⁻ ) or hydrogen carbonate at the time of pH adjustment. The buffering action by ions (HCO ₃ ⁻ ) is not exhibited, and the amount of chemicals used for pH adjustment can be reduced.

  And as for the desalination method of this invention, it is preferable that the said aeration process is a process of aerating gas with the flow volume of 6-23 times the flow volume of to-be-processed water with respect to to-be-processed water. If the gas is aerated so that the flow ratio of the water to be treated and the gas (water to be treated: gas) is 1: 6 to 1:23, the carbonic acid component can be efficiently removed from the water to be treated. It is.

  According to the present invention, it is possible to effectively remove suspended substances from the water to be treated before filtration of the water to be treated by the reverse osmosis membrane to reduce the load on the reverse osmosis membrane, and at a low cost. The desalination system and the desalination method of the to-be-processed water using a reverse osmosis membrane which can suppress generation | occurrence | production of a scale can be provided.

It is explanatory drawing which shows the seawater desalination system which concerns on this invention. It is a graph which shows the relationship between the operation time and the membrane differential pressure | voltage of a ceramic membrane filtration apparatus in the seawater desalination system which concerns on the Example and comparative example of this invention. It is a graph which shows the influence which pH of seawater has on the total amount of carbonation in decarboxylation processing water.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, an example of the desalination system of the present invention shown in FIG. 1 is a seawater desalination system 100 for producing seawater by desalinating seawater as water to be treated. Is decarboxylated and coagulated and filtered through a reverse osmosis membrane. In the desalination system of the present invention, fresh water may be produced using brine or the like as treated water.

Here, as seawater processed with the seawater desalination system 100 shown in FIG. 1, hardness (calcium carbonate conversion) is 5000-6000 mg / L, pH is 8.0-8.5, and total carbonic acid concentration is 1500-500, for example. Examples include seawater having 2000 μmol / kg and SDI of 5.5 to 6.5. The total carbonic acid concentration refers to carbonic acid (H ₂ CO ₃ ) and carbonate ions (CO ₃ ²⁻ ) in seawater measured by a closed method using a total alkalinity measuring instrument (manufactured by Kimoto Electronics Co., Ltd.). ) And bicarbonate ion (HCO ₃ ⁻ ). Also, SDI (Silt Density Index) refers to a value calculated using the following calculation formula, measured according to ASTM (Standard Test Method for Silent Density Index of Water D4189-95).
SDI ₁₅ = (1-T ₀ / T ₁₅ ) × 100/15
T ₀ : Time (seconds) required to filter 500 ml of the initial sample when the sample is filtered at a pressure of 206 kPa using a membrane filter having a pore diameter of 0.45 μm and a diameter of 47 mm
T ₁₅ : Time (seconds) required for further filtering 500 ml of the sample after 15 minutes of filtration

  As shown in FIG. 1, a seawater desalination system 100 includes a raw water intake device 10 that takes seawater from the sea, and a decarboxylation device 30 that is provided on the downstream side of the raw water intake device 10 and removes carbonic acid in seawater. And a ceramic membrane filtration device 70 provided on the downstream side of the decarboxylation device 30 for separating suspended substances from the seawater, and a freshwater obtained by filtering the seawater provided on the downstream side of the ceramic membrane filtration device 70. The reverse osmosis membrane filtration device 90 is provided.

  And in the seawater desalination system 100, the 1st pH adjustment apparatus 20 which adjusts the pH of seawater between the raw | natural water acquisition apparatus 10 and the decarboxylation apparatus 30, and the seawater which adjusted pH are 1st pH adjustment. A pump 31 for sending from the device 20 to the decarboxylation device 30 is provided, and a second for adjusting the pH of the seawater from which the carbonic acid component has been removed is provided between the decarboxylation device 30 and the ceramic membrane filtration device 70. The pH adjusting device 40, the flocculant adding device 50 for adding the flocculant to the seawater, the ceramic membrane filtration raw water tank 60 for storing the seawater to which the flocculant has been added, and the seawater to which the flocculant has been added to the ceramic membrane filtration raw material A pump 71 for sending the water from the water tank 60 to the ceramic membrane filtration device 70 is sequentially provided. Further, between the ceramic membrane filtration device 70 and the reverse osmosis membrane filtration device 90 of the seawater desalination system 100, a ceramic membrane filtration water tank 80 for storing seawater filtered by the ceramic membrane filtration device 70, and a ceramic membrane filtration A high pressure pump 91 for sending the seawater filtered by the device 70 from the ceramic membrane filtration water tank 80 to the reverse osmosis membrane filtration device 90 is provided.

  Here, the raw water intake apparatus 10 includes a pump 11 for sending seawater pumped from the sea to the raw water tank 13, and an oxidant addition means 12 provided between the pump 11 and the raw water tank 13. And in this raw | natural water intake apparatus 10, since oxidizing agents (bactericidal agents), such as sodium hypochlorite (NaClO), are added with the oxidizing agent addition means 12 with respect to the seawater as to-be-processed water, seawater desalination In the system 100, clogging of biological membranes in the ceramic membrane filtration device 70 and the reverse osmosis membrane filtration device 90 and generation of algae in the piping are unlikely to occur.

  The first pH adjusting device 20 is for adjusting the pH of the seawater to 5 or less, preferably 4 or more, and is a chemical pump for adding sulfuric acid as a pH adjusting agent to the seawater in the first pH adjusting tank. 21, a stirrer 22 for stirring the seawater in the first pH adjustment tank, a pH sensor 23 for measuring the pH of the seawater, and a pH for feedback control of the chemical pump 21 based on the measured value of the pH sensor 23 And a controller 24. And in this 1st pH adjustment apparatus 20, the pH of seawater is adjusted to 5 or less, Preferably it is 4-5 by controlling the addition amount of the sulfuric acid from the chemical pump 21 with the pH controller 24. FIG. Here, from the viewpoint of effectively removing carbonic acid from seawater by the decarboxylation device 30, it is preferable to lower the pH of the seawater as much as possible by the first pH adjustment device 20, but the seawater exhibits a buffering action. Since the pH does not easily change, the pH of the seawater is preferably 4 or more from the viewpoint of the cost of adding the chemical. In addition, as a chemical | medical agent used for adjustment of pH, although it is preferable to use a sulfuric acid from a viewpoint of cost or handleability, inorganic acids, such as hydrochloric acid and nitric acid, can also be used without being specifically limited to a sulfuric acid.

The decarboxylation device 30 removes carbon dioxide from the seawater as carbon dioxide by aeration of a gas such as air to the seawater whose pH has been lowered by the first pH adjustment device 20. In 30, the total carbonic acid concentration of the seawater whose pH has been lowered is lowered to, for example, 30 to 40 μmol / kg according to the following chemical equilibrium formulas (I) to (III).
CO ₃ ²⁻ + H ⁺ ⇔ HCO ₃ ⁻ (I)
HCO ₃ ⁻ + H ⁺ ⇔ H ₂ CO ₃ (II)
H ₂ CO ₃ ⇔ H ₂ O + CO ₂ (III)

The decarboxylation device 30 is cylindrical and made of plastic that does not rust due to salt in the seawater. In the decarboxylation device 30, seawater introduced from above is made into fine water droplets by the distributor 32, and the inside The contact area between the air introduced from the air introduction pipe 34 at the lower part of the apparatus and seawater is increased by contacting the polypropylene filler 33 filled in the container. Therefore, in this decarboxylation apparatus 30, seawater and air efficiently come into contact with each other, so that carbonic acid components (carbonic acid, carbonate ions and hydrogen carbonate ions) in the seawater move into the air in the form of carbon dioxide, and the air together with the air It is discharged from the discharge pipe 35 and decarboxylation is performed. Note that the flow rate of air aerated in the decarboxylation device 30 is sufficient to remove the carbonic acid component in the seawater, and is a flow rate that does not cause air entrainment by the seawater descending from the top, for example, the flow rate of seawater. It is preferably 6 to 23 times. More specifically, the flow rate of air can be 40 to 160 L / min, preferably 60 to 90 L / min, for example, when seawater is decarboxylated at a rate of 10 m ³ / day.

The second pH adjusting device 40 is for adjusting the pH of the decarboxylated seawater to 6 to 10, and is a chemical for adding sodium hydroxide as a pH adjusting agent to the seawater in the second pH adjusting tank. Based on the pH value of the seawater in the pump 41, the stirrer 42 for stirring the seawater in the second pH adjusting tank, and the flocculant adding device 50 provided in the subsequent stage of the second pH adjusting device 40 And a pH controller 43 for feedback control. In the second pH adjusting device 40, the pH of the seawater is adjusted to 6 to 10, preferably 6 to 9.5 by controlling the amount of sodium hydroxide added from the chemical pump 41 with the pH controller 43. To do. Here, since the seawater after decarboxylation does not show a buffering action by carbonate ions (CO ₃ ²⁻ ) or bicarbonate ions (HCO ₃ ⁻ ), the second pH adjuster 40 adjusts the pH to a small amount. Can be done with sodium hydroxide. However, when the pH of the seawater is more than 10, calcium and magnesium contained in the seawater may precipitate as hydroxides and generate scale, so the pH of the seawater should be 6-10. Preferably, it is 6-9.5. In the seawater desalination system 100, since the carbonic acid component is removed from the seawater by the decarboxylation device 30, even if the pH of the seawater is increased by the second pH adjustment device 40, the hardness component (magnesium, Calcium etc.) hardly precipitate as carbonate. Incidentally, as a chemical used for adjusting the pH, sodium hydroxide is preferably used from the viewpoint of cost and handleability, but is not particularly limited to sodium hydroxide.

The flocculant addition device 50 adds a flocculant such as ferric chloride to the seawater whose pH has been adjusted by the second pH adjustment device 40 to agglomerate suspended substances (SS, organic matter) contained in the seawater. A chemical pump 51 for adding ferric chloride (FeCl ₃ ) as a coagulant to the seawater in the coagulation tank, and an agitator 52 for stirring the seawater in the coagulation tank, A pH sensor 53 for measuring the pH of seawater in the flocculant adding device 50 used for feedback control of the chemical pump 41 of the second pH adjusting device 40 is provided. And in this coagulant | flocculant addition apparatus 50, ferric chloride is added so that it may become a density | concentration of 0.1-3 mg / L (iron conversion), preferably 1.5-2 mg / L (iron conversion), for example, Aggregates suspended matter in seawater.

  The ceramic membrane filtration device 70 includes three ceramic membrane modules 72 having a ceramic microfiltration membrane or a ceramic ultrafiltration membrane arranged in parallel. And in this ceramic membrane filtration apparatus 70, a suspended substance (aggregate) is removed from seawater using the ceramic membrane 73 with high intensity | strength and chemical resistance, and filtration with a high flux, and it is in the latter part. The load applied to the provided reverse osmosis membrane filtration device 90 can be reduced. It should be noted that the ceramic membrane module 72 uses a known method and apparatus (not shown) to back flow periodically or when the differential pressure increases to prevent or eliminate clogging of the ceramic membrane 73. When the ceramic membrane filtration device 70 is backwashed (hereinafter referred to as “backwashing”), for example, one of the three ceramic membrane modules 72 is backwashed, and the remaining Seawater desalination can be performed continuously by continuing filtration of seawater with two units.

  The reverse osmosis membrane filtration device 90 uses a known reverse osmosis membrane 92, and seawater does not pass through the reverse osmosis membrane filtration device 90 and fresh water that has permeated the reverse osmosis membrane 92 and the reverse osmosis membrane 92. Separated into concentrated water. And the fresh water which permeate | transmitted the reverse osmosis membrane 92 is used as drinking water etc., after performing pH adjustment and a sterilization process arbitrarily. On the other hand, the concentrated water that has not permeated the reverse osmosis membrane 92 is treated as waste water.

  And in the seawater desalination system 100 mentioned above, since the carbonic acid component is removed from seawater with the decarboxylation apparatus 30, precipitation of carbonate can be suppressed at low cost. In addition, since the suspended matter is removed from the seawater by the ceramic membrane filtration device 70, the reverse osmosis membrane 92 is not easily clogged.

  In addition, the desalination system of the to-be-processed water of this invention is not limited to the said example, For example, a decarbonation apparatus removes carbon dioxide from seawater by deaerating carbon dioxide under reduced pressure. It may be a device.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the following Example at all.

Example 1
Seawater (total hardness: 5650 mg / L (CaCO ₃ conversion), calcium hardness: 820 mg / L (CaCO ₃ conversion), pH: 8.15, total carbonic acid concentration: 2091 μmol /, using the seawater desalination system shown in FIG. kg, SDI: 6.28) was subjected to a desalination treatment (seawater supply amount: 10 m ³ / day). In the first pH adjusting device, the pH of seawater was adjusted to 4.2, and in the second pH adjusting device, the pH of seawater was adjusted to 9.6. The amount of ferric chloride added was such that the iron concentration in seawater was 2 mg / L, and the filtration flux in the ceramic membrane filtration device was 4 m / day. Furthermore, the supply amount of air to the decarboxylation device was 80 L / min (seawater supply amount: air supply amount≈1: 12), and the ceramic membrane filtration device was regularly backwashed every 40 minutes.

  And the change of the membrane differential pressure (25 degreeC conversion) in a ceramic membrane filtration apparatus was measured. Moreover, SDI of the seawater filtered with the ceramic membrane was measured according to ASTM. The results are shown in FIG. Under the above processing conditions, even if the operation was continued for 150 days or more, carbonate scale did not occur in the piping of the seawater desalination system.

(Comparative Example 1)
The same seawater desalination system as used in Example 1 was used except that a softening device using a crystallization method was used instead of the first pH adjusting device and the decarboxylation device, and the same as in Example 1. Seawater was desalinated under the treatment conditions. And the change of the membrane differential pressure (25 degreeC conversion) in a ceramic membrane filtration apparatus and SDI of the seawater filtered with the ceramic membrane were measured like Example 1. FIG. The results are shown in FIG. Under the above treatment conditions, when the operation was continued for 14 days, carbonate scales were generated in the piping of the seawater desalination system.

  From Table 1, according to the seawater desalination system of Example 1, it is possible to filter ceramic membrane filtrate with a low SDI water quality with a reverse osmosis membrane (the load on the reverse osmosis membrane can be reduced). I understand. Moreover, it turns out that the membrane differential pressure | voltage of a ceramic membrane does not rise easily from the seawater desalination system of Example 1 provided with a decarboxylation apparatus from FIG.

(Reference Example 1)
Using the decarboxylation device of the seawater desalination system shown in FIG. 1, aeration air volume: 80 L / min, seawater inflow volume: 6.9 L / min for seawater whose pH is changed in the range of 4.8 to 7.3 Decarboxylation was performed under the condition of minutes. And the total carbonic acid density | concentration in the seawater before decarboxylation and the seawater after decarboxylation was measured with the total alkalinity titration apparatus (Kimoto Electronics Co., Ltd. make, ATT-05). The results are shown in FIG.

  From FIG. 3, it can be seen that the total carbonic acid concentration can be sufficiently reduced if the decarboxylation treatment is performed after the pH of the seawater is adjusted to 6 or less.

(Reference Example 2)
Using the decarboxylation device of the seawater desalination system shown in FIG. 1, seawater having a pH of 4.2 was decarboxylated under the conditions of an aeration air volume of 80 L / min. And the pH of the decarboxylated seawater was adjusted to 7.01 using sodium hydroxide. And the seawater adjusted pH is stirred at a stirring speed of 50 rpm in an open system, (ii) stirred at a stirring speed of 120 to 150 rpm in an open system, and (iii) at a stirring speed of 120 to 150 rpm in a closed system. Stir. And the total carbonic acid density | concentration after stirring for 48 hours was measured with the total alkalinity titration apparatus (Kimoto Electronics Co., Ltd. make, ATT-05). The results are shown in Table 2.
The same stirring operation and measurement of the total carbonic acid concentration were also performed on seawater whose pH was adjusted to 8.15 or 9.14 after decarboxylation. The results are shown in Table 2.

  From Table 2, it can be seen that if decarboxylation is performed using the decarboxylation device of the seawater desalination system shown in FIG.

  According to the present invention, it is possible to effectively remove suspended substances from the water to be treated before filtration of the water to be treated by the reverse osmosis membrane to reduce the load on the reverse osmosis membrane, and at a low cost. The desalination system and the desalination method of the to-be-processed water using a reverse osmosis membrane which can suppress generation | occurrence | production of a scale can be provided.

DESCRIPTION OF SYMBOLS 10 Raw water acquisition apparatus 11 Pump 12 Oxidizing agent addition means 13 Raw water tank 20 First pH adjustment apparatus 21 Chemical pump 22 Stirrer 23 pH sensor 24 pH controller 30 Decarbonation apparatus 31 Pump 32 Distributor 33 Filler 34 Air introduction pipe 35 Air discharge pipe 40 Second pH adjustment device 41 Chemical pump 42 Stirrer 43 pH controller 50 Coagulant addition device 51 Chemical pump 52 Stirrer 53 pH sensor 60 Ceramic membrane filtration raw water tank 70 Ceramic membrane filtration device 71 Pump 72 Ceramic membrane module 73 Ceramic membrane 80 Ceramic membrane filtration water tank 90 Reverse osmosis membrane filtration device 91 High pressure pump 92 Reverse osmosis membrane

Claims (9)

Filtering means for separating suspended substances in the water to be treated from the water to be treated, and water to be treated provided downstream of the filtering means as viewed in the direction of treating the water to be treated from the upstream side to the downstream side. A desalination system using a reverse osmosis method, comprising a reverse osmosis membrane filtration means for filtering to desalinate,
The filtration means is a ceramic membrane filtration means for separating suspended substances from water to be treated using a ceramic microfiltration membrane or a ceramic ultrafiltration membrane,
The treated water further comprising a decarbonation means for removing carbonic acid in the treated water on the upstream side of the ceramic membrane filtration means when viewed in the direction of treating the treated water from the upstream side to the downstream side. Desalination system.   The desalination system according to claim 1, further comprising a flocculant addition means for adding a flocculant to the water to be treated between the ceramic membrane filtration means and the decarboxylation means.   The decarbonation means includes a first pH adjusting means for reducing the pH of the water to be treated to 5 or less, and a downstream of the first pH adjusting means as seen in the direction of treating the water to be treated from the upstream side to the downstream side. The desalination system according to claim 1 or 2, further comprising aeration means, deaeration means, or both of them provided on the side.   The second pH adjusting means for adjusting the pH of the water to be treated to 6 to 10 is further provided between the decarboxylation means and the flocculant addition means. Desalination system. A desalination method for water to be treated comprising a filtration step for separating suspended substances in the treatment water from the treatment water, and a reverse osmosis membrane filtration step for filtering the treatment water that has passed through the filtration step with a reverse osmosis membrane. And
The filtration step is a ceramic membrane filtration step of separating suspended substances from the water to be treated using a ceramic microfiltration membrane or a ceramic ultrafiltration membrane,
A desalination method for water to be treated, further comprising a decarboxylation step of removing carbonic acid in the water to be treated before the ceramic membrane filtration step.   6. The method according to claim 5, further comprising a coagulation step of adding a flocculant to the water to be treated to coagulate suspended substances in the water to be treated between the decarboxylation step and the ceramic membrane filtration step. The desalination method described.   The decarboxylation step includes a first pH adjustment step for adjusting the pH of the water to be treated to 5 or less, an aeration step for aeration of the water to be treated after the first pH adjustment step, or a deaeration step for deaeration, or Both of them are included, The desalination method of Claim 5 or 6 characterized by the above-mentioned.   The desalination according to claim 6 or 7, further comprising a second pH adjustment step of adjusting the pH of the water to be treated to 6 to 10 between the aggregation step and the decarboxylation step. Method.   The desalination method according to claim 7 or 8, wherein the aeration step is a step of aeration of gas at a flow rate of 6 to 23 times the flow rate of the water to be treated.

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