JP2012183472A - Water treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the flow rate reduction of a permeate while suppressing the water quality deterioration of the permeate, in a water treatment method that filters raw water containing silica and hardness components using a reverse osmosis membrane device.SOLUTION: While adding a scale dispersant containing polycarboxylic acid and phosphonic acid from a second adding device 23, the raw water is supplied to the reverse osmosis membrane device 20 through a supply path 10 to separate the raw water into a permeate and a concentrate by the reverse osmosis membrane module 24. The permeate flows through a treated water passage 30 to be used for required purposes, and the concentrate flows to a drain passage 40. The pH of the concentrate is adjusted by a pH adjuster, which is added from a first adding device 22 to the raw water, to control the Langelier index equal to or more than 0 and equal to or less than 0.3. The recovery rate of the permeate in the reverse osmosis membrane module 24 is controlled to maintain the concentration of silica equal to or less than 150 mgSiO/L.

Description

  The present invention relates to a water treatment apparatus, and more particularly to a water treatment apparatus for filtering raw water containing silica and hardness components using a reverse osmosis membrane apparatus.

  In the manufacturing process of semiconductors and pharmaceuticals, from the viewpoint of improving product quality and ensuring safety, a large amount of purified water from which contaminated components such as dissolved natural components and suspended substances are removed is used. Such purified water is produced, for example, by subjecting raw water such as industrial water, tap water, or groundwater to filtration using a reverse osmosis membrane device.

  In the production of such purified water, since continuous mass production is required, it is necessary to stably maintain the amount of filtrate (permeated water) in the reverse osmosis membrane device. However, the reverse osmosis membrane device highly separates the contaminated components contained in the raw water with the reverse osmosis membrane, and as a result, the concentration of the contaminated components increases on the primary side of the reverse osmosis membrane, that is, on the introduction side of the raw water. Since the concentrated water comes into contact, fouling and scale occur on the primary side, and the amount of permeate tends to gradually decrease. Here, fouling refers to a phenomenon in which suspended substances, organic substances, etc. in raw water are deposited or adsorbed on the membrane surface of the reverse osmosis membrane, and can cause a reduction in the amount of permeated water in the reverse osmosis membrane. On the other hand, scale is a deposit of hardness components such as calcium and silica, which are mainly contained as natural components, in raw water, which causes the permeated water volume in the reverse osmosis membrane to decrease by blocking the pores of the reverse osmosis membrane. obtain.

  Generally, in reverse osmosis membrane devices, increasing the recovery rate, that is, the proportion of permeated water obtained relative to raw water, increases the concentration of contaminated components in concentrated water, and decreases the amount of permeated water due to fouling and scale in a short time. Therefore, by controlling the recovery rate to be low, an increase in the concentration of contaminating components in the concentrated water can be suppressed, and a stable permeated water amount can be maintained for a relatively long period of time. However, in this case, since the amount of permeated water is reduced, the treatment efficiency of raw water (that is, the production efficiency of purified water) is impaired.

  As a countermeasure against such a problem, Patent Document 1 discloses a method of adding an acid so that the pH of the raw water becomes about 5.5 while adding a scale inhibitor to the raw water. However, as described in Patent Document 1, this method has a problem that the quality of the permeated water is deteriorated and cannot be overlooked in the production of purified water.

  Incidentally, in the method described in Patent Document 1, the quality of the permeated water decreases because the excessive addition of acid changes the hydrogen carbonate ions and carbonate ions contained in the raw water into free carbonic acid (dissolved carbon dioxide gas). This is because carbonic acid permeates through the reverse osmosis membrane.

Japanese Patent Laid-Open No. 9-206749 (paragraph 0010, paragraph 0013 and paragraph 0045 and paragraph 0050, comparative example 1)

  An object of the present invention is to suppress a decrease in the flow rate of permeated water while suppressing deterioration in the quality of the permeated water in water treatment in which raw water containing silica and a hardness component is filtered using a reverse osmosis membrane device.

The present invention relates to a water treatment apparatus for filtering raw water containing silica and a hardness component. This water treatment apparatus filters raw water from a raw water supply path and raw water from the supply path, and transmits permeated water and concentrated water. A reverse osmosis membrane device for separating the water, a treatment water channel for discharging permeated water from the reverse osmosis membrane device, a drainage channel for discharging concentrated water from the reverse osmosis membrane device, and a supply path. The first adjusting means for adjusting the pH of the raw water, the second adjusting means for adjusting the recovery rate of the permeated water in the reverse osmosis membrane device, and the scale dispersant added to the raw water provided in the supply path Addition device for adding, water quality inspection device for inspecting the quality of concentrated water discharged through the drainage channel, and for calculating the Langeria index of concentrated water based on the water quality inspected by the water quality inspection device Calculation means and run of concentrated water As the rear index is maintained at 0.3 or less, and, as the silica concentration of concentrated water is kept below 150mgSiO 2 / _L, and a water quality control means for controlling the first adjusting means and second adjusting means I have.

  In this water treatment apparatus, the water quality control means usually controls the first adjustment means so that the Langeria index is maintained at 0 or more. Moreover, a 1st adjustment means is an injection | pouring apparatus for inject | pouring a pH adjuster into raw | natural water, for example. The pH adjuster used here is usually at least one of an acidic drug that lowers the pH of raw water and an alkaline drug that increases the pH of raw water.

The present invention according to another aspect relates to a water treatment method of filtering raw water containing silica and a hardness component using a reverse osmosis membrane device, and the water treatment method is reverse osmosis of raw water added with a scale dispersant. It includes a step of supplying to the membrane device and separating the permeated water and the concentrated water, and the Langeveria index of the concentrated water is maintained at 0.3 or lower and the silica concentration is maintained at 150 mgSiO ₂ / L or lower.

  In this water treatment method, the Langeria index is usually maintained at 0 or higher. In this water treatment method, the concentration of the concentrated water is usually controlled by adjusting the pH of the raw water to control the Langeria index of the concentrated water, and adjusting the recovery rate of the permeated water in the reverse osmosis membrane device. To control.

  The scale dispersant used in the present invention contains, for example, polycarboxylic acid and phosphonic acid.

In the present invention, when raw water containing silica and a hardness component is filtered using a reverse osmosis membrane device, the Langeria index of concentrated water is maintained at 0.3 or lower, and the silica concentration is maintained at 150 mgSiO ₂ / L or lower. Therefore, it is possible to suppress a decrease in the flow rate of the permeated water while suppressing deterioration in the quality of the permeated water.

1 is a schematic view of a water treatment apparatus according to an embodiment of the present invention. The flowchart which shows operation | movement of the said water treatment apparatus.

With reference to FIG. 1, the water treatment apparatus which concerns on one Embodiment of this invention is demonstrated. In the figure, the water treatment apparatus 1 is composed of silica (meaning all silicas defined in “44. Silica (SiO ₂ )” in Japanese Industrial Standards JIS K0101: 1998 “Industrial Water Test Method”) and hardness. Raw water containing components (calcium ions and magnesium ions), for example, industrial water, tap water, groundwater (shallow well water, deep well water, spring water or underground water, etc.), surface water (river water or lake water, etc.) or factory effluent or The purified water is produced by filtering the mixed water of these arbitrary combinations. The raw water supply path 10, the reverse osmosis membrane device 20, the treated water channel 30, the drainage channel 40, and the control device 50 are mainly used. In preparation.

  The supply path 10 is for supplying raw water from a raw water supply source (not shown) to the reverse osmosis membrane device 20, and includes a water supply control valve 21 for controlling supply and stop of raw water and raw water. The 1st addition apparatus 22 and the 2nd addition apparatus 23 for adding a chemical | medical agent with respect to are provided in this order.

  The first addition device 22 (an example of the first adjustment means) is for injecting a pH adjusting agent into the raw water supplied to the reverse osmosis membrane device 20, and includes a first portion 22a and a second portion 22b. I have. The 1st site | part 22a is a site | part for inject | pouring the acidic chemical | medical agent which reduces the pH of raw | natural water with respect to raw | natural water. The acidic drug used here is not particularly limited and is, for example, an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid, and is usually used as an aqueous solution. On the other hand, the 2nd site | part 22b is a site | part for inject | pouring the alkaline chemical | medical agent which raises the pH of raw | natural water with respect to raw | natural water. The alkaline agent used here is, for example, a hydroxide or carbonate of an alkali metal such as sodium or potassium, and is usually used as an aqueous solution.

  Each of the first part 22a and the second part 22b has a storage part for a pH adjusting agent and an injection part for injecting the pH adjusting agent from the storage part into the raw water. It has a control valve for adjusting the injection amount.

  The second addition device 23 is for adding a scale dispersant to the raw water supplied to the reverse osmosis membrane device 20, and adds a storage portion of the scale dispersant and the scale dispersant from the storage portion to the raw water. And an addition part for. The addition unit has a control valve for adjusting the amount of the scale dispersant added.

  The scale dispersant used here is not particularly limited as long as it is water-soluble, and examples thereof include polycarboxylic acids such as acrylic acid polymers, methacrylic acid polymers, and maleic acid polymers, polysulfonic acids, and the like. Examples thereof include phosphonic acid. Two or more kinds of these scale dispersants may be used in combination. The scale dispersant is usually used as an aqueous solution.

  As the scale dispersant, since it is possible to effectively suppress the calcium carbonate-based scale from adhering to the membrane surface of the reverse osmosis membrane in the reverse osmosis membrane module 24 to be described later on the reverse osmosis membrane device 20, polycarboxylic acid and Those containing phosphonic acid are preferred. As an example of such a scale dispersant, BWA WATER ADDITIVES trade name “Flocon 260” which is an aqueous solution containing polycarboxylic acid and phosphonic acid and having a concentration of 33 to 37% by weight can be mentioned.

  The reverse osmosis membrane device 20 is for filtering raw water from the supply path 10 and mainly includes a reverse osmosis membrane module 24 and a pressure pump 25.

  The reverse osmosis membrane module 24 includes a single or a plurality of reverse osmosis membrane elements (not shown). The reverse osmosis membrane element that forms the reverse osmosis membrane element is a membrane that can prevent the permeation of fine contaminant components having a molecular weight of several dozens in the raw water. A low nanofiltration membrane (NF membrane) may be used.

  The pressurizing pump 25 can pressurize the raw water from the supply path 10 and supply it to the reverse osmosis membrane module 24. The raw water from the supply path 10 is supplied to the reverse osmosis membrane module 24 in a state of being pressurized by the pressure pump 25 at a pressure higher than the osmotic pressure of the reverse osmosis membrane. Part permeates the reverse osmosis membrane element. Thereby, in the reverse osmosis membrane element, the raw water is separated into permeated water from which the contaminating components have been removed (that is, purified water) and concentrated water having an increased concentration of the contaminating components.

  The treatment water channel 30 is a path for sending out the permeated water generated in the reverse osmosis membrane device 20, and a tank for temporarily storing the permeated water, and various devices (for example, semiconductor manufacturing apparatus) using the permeated water. , Pharmaceutical manufacturing equipment and steam boiler equipment).

  The drainage channel 40 is a path for discharging the concentrated water generated in the reverse osmosis membrane device 20 from the device, and the circulation path 41, the water quality inspection device 42, and the drainage control valve 43 are arranged in this order from the reverse osmosis membrane device 20 side. I have.

  The circulation path 41 is for circulating a part of the concentrated water from the reverse osmosis membrane apparatus 20 to the supply path 10, branches from the drainage path 40, and is between the second addition device 23 and the pressure pump 25. To the supply path 10.

  The water quality inspection device 42 is for measuring the quality of the concentrated water flowing through the drainage channel 40, and a sampling path 410 for collecting a part of the concentrated water branched from the drainage channel 40 as a sample for water quality inspection. have. The sampling path 410 is branched into a plurality of parts, and each branch path has a pH sensor 411 for measuring the pH value of the concentrated water, a temperature sensor 412 for measuring the temperature of the concentrated water, and the electric conduction of the concentrated water. An electrical conductivity sensor 413 for measuring the rate, a hardness sensor 414 for measuring the calcium hardness of the concentrated water, and a total alkalinity sensor 415 for measuring the total alkalinity of the concentrated water. As the pH sensor 411, the temperature sensor 412, and the electrical conductivity sensor 413, various types used for water quality inspection can be used.

  As the hardness sensor 414, a general colorimetric sensor is used. The colorimetric sensor adds a coloring reagent (for example, 2-hydroxy-1- (2′-hydroxy-4′-sulfo-1′-naphthylazo) -3-naphthoic acid) to the collected concentrated water sample. The color development of the sample is detected as a change in absorbance at a specific absorption wavelength, and the calcium hardness is determined based on the absorbance.

The total alkalinity measured by the total alkalinity sensor 415 is expressed by converting the amount of alkali components contained in the concentrated water as bicarbonate, carbonate, hydroxide, etc. into the amount of calcium carbonate (CaCO ₃ ). This is what is referred to as acid consumption (pH 4.8) in various JIS standards relating to water quality analysis. The general total alkalinity sensor 415 is of a colorimetric type, and this indicates the color development of a sample when a coloring reagent (for example, methyl orange) is added to the collected concentrated water sample. Is detected as a change in absorbance, and the total alkalinity is determined based on the absorbance.

  The drainage control valve 43 is for controlling the amount of concentrated water discarded from the reverse osmosis membrane device 20.

  The control device 50 is for controlling the operation of the water treatment device 1, and is a central control device that controls the operation, a storage device that stores an operation program and various data of the water treatment device 1, and an information input / output device. It is an electronic information processing organization provided with (none of which is shown). The input unit of the input / output device is in communication with the water quality inspection device 42 and receives measurement data from the pH sensor 411, temperature sensor 412, electrical conductivity sensor 413, hardness sensor 414, and total alkalinity sensor 415. Is possible. In addition, an operation panel 51 for manually inputting various data and commands necessary for the operation of the water treatment apparatus 1 is communicated to the input unit. On the other hand, the output side of the input / output device receives measurement data and other information from the water supply control valve 21, the first addition device 22, the second addition device 23, the pressurization pump 25, the drainage control valve 43, and the water quality inspection device 42. A display device 52 for displaying or guiding manual input of required information is in contact, and a required operation signal can be transmitted to each of these units.

  The operation program stored in the storage device includes a calculation program for calculating the Langeria index of concentrated water and a water quality control program for the concentrated water.

  The Langeria index is a general index for evaluating the tendency of scale generation in water systems. A positive value indicates that calcium carbonate is more likely to precipitate as the absolute value increases, and a negative value increases the absolute value. It shows that calcium carbonate hardly precipitates. When the Langeria index is 0, calcium carbonate is in an equilibrium state where neither precipitation nor dissolution occurs. For this reason, when the Langeria index of concentrated water is less than 0, it is difficult for scales due to calcium carbonate to be generated on the membrane surface of the reverse osmosis membrane module 24, and conversely, when it exceeds 0, the reverse osmosis membrane module Scales of calcium carbonate are easily generated on the 24 film surfaces.

The Langeria index (LSI) of the concentrated water is usually obtained by the following equation (1).
LSI = pH-pHs (1)

In Formula (1), pH is a pH value of concentrated water. Further, pHs is a theoretical pH value when the calcium carbonate is in an equilibrium state where the calcium carbonate is not dissolved or precipitated in the concentrated water, and is obtained by the following equation (2).
pHs = 9.3 + A value + B value−C value−D value (2)

  In equation (2), the A value is a correction value determined by the evaporation residue concentration. Since the evaporation residue concentration has a correlation with the electric conductivity, the evaporation residue concentration can be obtained from the electric conductivity using a predetermined conversion formula. The B value is a correction value determined by the water temperature. The C value is a correction value determined by the calcium hardness. The D value is a correction value determined by the total alkalinity.

  As apparent from the equation (1), the Langeria index of the concentrated water decreases as the pH of the concentrated water decreases and increases as the pH increases. Therefore, the Langeria index of concentrated water can be controlled by adjusting the pH of the concentrated water.

  The Langeria index calculation program obtains the A to D values by calculating from the measurement data of each sensor of the water quality test apparatus 42 using a predetermined relational expression or referring to a predetermined numerical table. . Then, pHs is obtained from the obtained A to D values by the equation (2), and the Langeria index is calculated by the equation (1) from the pHs and the actually measured pH by the pH sensor 411. Various numerical tables necessary for calculating the Langeria index can be stored in a storage device.

  On the other hand, the water quality control program is for controlling the Langeria index and the silica concentration of the concentrated water by controlling the first addition device 22, the pressurizing pump 25 and the drainage control valve 43 by a process described later.

  Next, the basic operation of the water treatment apparatus 1 will be described. In the water treatment apparatus 1, when the water supply control valve 21 is opened and raw water is supplied from the raw water supply source to the supply path 10, the scale dispersant is added to the raw water continuously or at regular intervals from the second addition device 23. In addition, the pressure is increased by the pressurizing pump 25 to the osmotic pressure in the reverse osmosis membrane module 24 and supplied to the reverse osmosis membrane module 24. The raw water supplied under pressure to the reverse osmosis membrane module 24 partially passes through the reverse osmosis membrane (that is, is filtered), and is discharged from the treatment water channel 30 as permeated water from which impurities are removed. On the other hand, the remaining raw water is washed away into the drainage channel 40 as concentrated water in which the concentration of the contaminated components whose permeation is blocked by the reverse osmosis membrane is increased. Part of the concentrated water that has flowed to the drainage channel 40 flows to the circulation path 41 and joins the raw water flowing through the supply path 10. The remaining concentrated water that does not circulate to the circulation path 41 is discarded from the drainage control valve 43.

In the operation of the water treatment apparatus 1, recovery is performed by controlling the flow rate of permeated water from the reverse osmosis membrane module 24 (F ₂ ) and the flow rate of concentrated water discarded from the drainage control valve 43 (F ₃ ). The rate can be adjusted. Here, the recovery rate is the ratio (%) of the flow rate (F ₂ ) of the permeated water to the flow rate (F ₁ ) of the raw water supplied to the reverse osmosis membrane module 24 (ie, F ₂ / F ₁ × 100). Say. In the present embodiment, F ₁ is the flow rate of raw water supplied from the water supply control valve 21.

Next, the operation of the water treatment apparatus 1 will be described more specifically with reference to the operation flowchart shown in FIG. In this water treatment method, first, a sample of raw water is collected and analyzed for the silica concentration of raw water (mgSiO ₂ / L). The silica concentration of the raw water can be measured by a chemical analysis method using a commercially available measuring reagent kit or the like, but can also be measured using a commercially available automatic measuring device.

When the operator starts the water treatment device 1, the operation program displays an information input guide on the display device 52 of the control device 50 in step S1, and waits for the operator to input the raw water silica concentration in step S2. . When the silica concentration of raw water checked by the operator is input from the operation panel 51, the operation program shifts from step S2 to step S3, and calculates the recovery rate to be set in the reverse osmosis membrane device 20. More specifically, the recovery rate at which the silica concentration of the concentrated water can be maintained at 150 mgSiO ₂ / L or less is calculated based on the silica concentration of the input raw water.

Here, when the recovery rate is set high, the concentration rate of the raw water is increased (that is, the concentration of impurities in the concentrated water is increased), and when the recovery rate is set low, the concentration rate of the raw water is decreased (that is, the concentrated water is increased). Contaminant component concentration in the case becomes low). For this reason, when the silica concentration of raw | natural water is known, if the concentration rate of raw | natural water is controlled by adjustment of a recovery rate, the silica concentration of concentrated water can be controlled as a result. For example, when the collection rate is set to 90%, the concentration rate of raw water is about 10 times. In this case, if the silica concentration of the raw water is, for example, 10 mgSiO ₂ / L, the silica concentration of the concentrated water is maintained 10 times the concentration in the raw water, that is, about 100 mgSiO ₂ / L. This is an appropriate recovery rate for maintaining the silica concentration of concentrated water at 150 mg SiO ₂ / L or less. On the other hand, if the silica concentration of the raw water is 20 mgSiO ₂ / L, for example, the silica concentration of the concentrated water is maintained at about 200 mgSiO ₂ / L, which is 10 times, so the recovery rate of 90% Inappropriate recovery rate for maintaining below 150 mg SiO ₂ / L.

The recovery rate calculated based on the concentration rate of the raw water is an upper limit value capable of maintaining the silica concentration of the concentrated water at 150 mgSiO ₂ / L or less. Such a recovery rate of the upper limit value may not be able to maintain the silica concentration of concentrated water at 150 mgSiO ₂ / L or less when a situation occurs in which the silica concentration temporarily increases in the raw water. In addition, the recovery rate is usually preferably set to 90% or less from the viewpoint of avoiding a reduction in raw water treatment efficiency due to fouling on the membrane surface of the reverse osmosis membrane module 24. Therefore, in consideration of these circumstances, it is preferable that the recovery rate calculated in step S3 is usually set to be smaller than the upper limit value by correcting the upper limit value.

When the concentration of silica in the concentrated water exceeds 150 mgSiO ₂ / L, silica-based scale is likely to be generated on the membrane surface of the reverse osmosis membrane module 24, so that the amount of permeated water decreases in a relatively short time, and the raw water The processing efficiency decreases.

  Next, the operation program proceeds to step S4. In this step, the display device 52 displays the completion of the initial preparation and waits for the operator to input an operation start command for the water treatment device 1. Then, when the operator inputs an operation start command through the operation panel 51, the operation program proceeds to step S5 and starts operation of the water treatment device 1.

In step S <b> 5, the operation program first opens the water supply control valve 21 and flows the raw water from the supply source to the supply path 10. Thereby, the water treatment apparatus 1 starts the basic operation described above. In this step, the flow rate of the permeated water (F ₂ ) in the reverse osmosis membrane module 24 and the flow rate of the concentrated water to be discarded (F ₃ ) are increased so that the recovery rate calculated in step S3 is achieved. It adjusts by control of the rotation speed of the pump 25 and the opening degree of the drainage control valve 43. Thus, the silica concentration of concentrated water is maintained below 150mgSiO ₂ / L.

In step S <b> 5, the operation program starts addition of the scale dispersant by the second addition device 23. Here, the operation program refers to the flow rate (F ₁ ) of raw water supplied from the water supply control valve 21 to the supply path 10 and controls the concentration of the scale dispersant in the raw water. It is necessary to set the concentration of the scale dispersant in the raw water so that the generation of scale on the membrane surface of the reverse osmosis membrane module 24 is suppressed, and the concentration is generally set higher. In this embodiment, the silica concentration of the concentrated water is maintained at 150 mg SiO ₂ / L or less, and the Langeveria index of the concentrated water is maintained within a range of 0.3 or less as described later, so that 1 to 5 mg / L It can function effectively only by setting it to a minute amount. As a result, the concentrated water discarded from the drainage control valve 43 suppresses an increase in chemical oxygen demand (COD) due to the scale dispersant, and is unlikely to give an environmental load.

  Furthermore, in step S <b> 5, the operation program activates the water quality inspection device 42 and starts the water quality inspection of the concentrated water sample that is always collected from the drainage path 40 through the sampling path 410.

  In the next step S <b> 6, the operation program determines whether or not the operator has input a stop command for the water treatment apparatus 1 from the operation panel 51. When the operator inputs a stop command, the operation program proceeds to step S7, closes the water supply control valve 21 and stops other devices. Thereby, supply of the raw | natural water to the reverse osmosis membrane apparatus 20 stops, and the water treatment apparatus 1 complete | finishes operation | movement.

  On the other hand, during operation of the water treatment apparatus 1, the operation program calculates a Langeria index (LSI) of the concentrated water in step S8. Here, the pH, temperature, electrical conductivity, hardness, and total alkalinity measured by the pH sensor 411, temperature sensor 412, electrical conductivity sensor 413, hardness sensor 414, and total alkalinity sensor 415 of the water quality inspection device 42, respectively. The above-described A to D values are obtained by referring to a predetermined numerical table from each data, and the Langeria index is calculated from the above-described equations (2) and (1).

  It is determined whether or not the Langeria index calculated in step S8 is in the range of 0 to 0.3 in the next step S9. When it is determined that the Langeria index is out of the above range, the operation program proceeds to step S10, and the control operation of the concentrated water Langeria index is executed.

  Here, when the Langeria index exceeds 0.3, the operation program operates the control valve of the first portion 22 a in the first addition device 22 to inject the acidic chemical into the raw water flowing through the supply path 10. Thereby, the pH of the concentrated water decreases and the Langeria index becomes small. On the other hand, when the Langeria index is less than 0, the operation program operates the control valve of the second portion 22 b in the first addition device 22 to inject the alkaline chemical into the raw water flowing through the supply path 10. Thereby, the pH of the concentrated water increases and the Langeria index increases. Thus, since the 1st addition apparatus 22 is equipped with both the 1st site | part 22a for adding an acidic chemical | medical agent, and the 2nd site | part 22b for adding an alkaline chemical | medical agent, the Langelia index of concentrated water is obtained. It is possible to quickly and stably control the narrow range described above.

  The operation program repeats Step S8 and Step S9 during operation of the water treatment apparatus 1, that is, unless the operator inputs a stop command from the operation panel 51. When necessary, the operation program executes Step S10. Control is performed so that the Langelia index is in the range of 0 to 0.3.

By the operation program as described above, in the water treatment apparatus 1, during operation, the Langeria index of the concentrated water is maintained at 0 or more and 0.3 or less, and the silica concentration of the concentrated water is maintained at 150 mgSiO ₂ / L or less. The For this reason, the reverse osmosis membrane module 24 can suppress the generation of calcium carbonate scale and silica scale in the reverse osmosis membrane, and can stably maintain the flow rate of the permeated water for a long period of time. Further, the maintenance of the flow rate of the permeated water is not achieved by simply adjusting the pH of the concentrated water to be lowered, but precisely controlling the Langeria index of the concentrated water within a narrow range of 0 or more. Therefore, it can be achieved while suppressing the injection amount of the pH adjuster, particularly the acidic drug, with respect to the raw water. As a result, hydrogen carbonate ions and carbonate ions contained in the raw water are prevented from changing to free carbonic acid (dissolved carbon dioxide gas), and the amount of free carbonic acid permeating the reverse osmosis membrane is reduced to suppress deterioration in the quality of the permeated water. Can do.

Modification (1) The silica concentration of raw water may be stable depending on the geological circumstances of the water source depending on the type of raw water. In this case, unless there is a circumstance where the silica concentration of the raw water fluctuates due to seasonal changes or the like, it is not necessary to measure the silica concentration of the raw water every time the water treatment apparatus 1 is operated and to input the measured value. In such a case, the water treatment apparatus 1 described above stores the silica concentration input by the operator at the first start-up in the control device 50, and at the subsequent start-up, the operation program steps S1 to S3 are omitted. You can also

(2) In the above-mentioned embodiment, the silica concentration of raw water is measured in advance, and the recovery rate is adjusted so that the silica concentration of concentrated water is maintained at 150 mgSiO ₂ / L or less based on the measured value. A sensor for measuring the silica concentration of the concentrated water may be further provided in the water quality inspection device 42, and the recovery rate may be adjusted so that the measured value of the silica concentration by this sensor is maintained at 150 mgSiO ₂ / L or less.

(3) In the above-described embodiment, control is performed so that the Langeria index of concentrated water is in the range of 0 or more and 0.3 or less. However, in the present invention, the lower limit of the Langeria index can be omitted. . However, in that case, a relatively large amount of a pH adjusting agent (acidic agent) is added to the raw water in order to achieve the required Langeria index in the concentrated water, resulting in permeation of the reverse osmosis membrane. The amount of free carbonic acid increases and the quality of the permeated water decreases. Therefore, the Langeria index is preferably set to 0 or more, and even if it is set to a negative value, it is preferably limited to about -0.2 to 0.

  In addition, the raw water from a supply source can control the Langelia index | exponent of concentrated water to 0.3 or less by the pH adjustment by addition of an acidic chemical | medical agent from the general water quality except the special case. For this reason, in the water treatment apparatus 1, the 1st addition apparatus 22 which consists only of the 1st site | part 22a for adding an acidic chemical | medical agent can also be normally used.

  On the other hand, when the pH of the raw water itself from the supply source is in the acidic range, for example, when the raw water is a factory effluent and the pH is about 5-6, the Langeria index of the concentrated water is the pH of the raw water. Even without adjusting the value, it is often 0.3 or less, particularly a negative value. In such a case, in order to improve the quality of the permeated water, the first addition device 22 consisting only of the second portion 22b for adding the alkaline agent is used, and the Langeria index of the concentrated water is added while appropriately adding the alkaline agent to the raw water. Is preferably increased to around 0.3.

(4) In the above-described embodiment, the first addition device 22 is provided with the second portion 22b for adding the alkaline chemical, and the pH of the raw water is increased by adding the alkaline chemical to the raw water from there. If the quality of the raw water is appropriate, an aeration method (a method for removing free carbonic acid using gas-liquid contact between air and raw water) can be employed as a means for increasing the pH of the raw water.

(5) In the above-described embodiment, the cross flow method in which the circulation path 41 is provided in the drainage channel 40 is adopted for the purpose of efficiently using the raw water and suppressing the discarded amount of the concentrated water. The present invention can be similarly implemented even when the crossflow method is not employed.

(6) In each of the above-described embodiments, the supply path 10 may further include a water softening device on the upstream side (raw water supply source side) of the first addition device 22. The water softening device removes the hardness component contained in the raw water by exchanging it with a monovalent cation (for example, sodium ion) using a cation exchange resin, and converts the raw water into softened water. is there. In a general water softening device, the calcium hardness of raw water can be reduced to 0.1 mg / L or less.

  As clearly shown in the above-described equation (2), the Langerian index of the concentrated water is determined based on the calcium hardness of the raw water, and is reduced by reducing the calcium hardness of the raw water. Therefore, the use of a water softening device makes it easier to control the Langerian index of the concentrated water within a predetermined range by suppressing the addition of a pH adjuster, particularly an acidic agent, to the raw water. It becomes easy.

Examples 1-3
A test water supply adjusted to a water quality having an electrical conductivity of 159 mS / m, a hardness of 414 mg CaCO ₃ / L, a silica concentration of 44 mg SiO ₂ / L, a total alkalinity of 90 mg CaCO ₃ / L and a pH of 7.6 is prepared. Stored in tank. Then, through the supply path extending from the tank, this supply water is continuously pressurized while being pressurized with a pressure pump to a reverse osmosis membrane module loaded with one reverse osmosis membrane element (model name “RE8040-BLF” of Eunjin Chemical Co., Ltd.). Was operated under the conditions of a permeate flow rate of 1000 L / h, a recovery rate of 75%, and a temperature of 25 ° C. The permeate flow rate was controlled by adjusting the number of rotations of the pressure pump. Water flow to the reverse osmosis membrane module was a cross flow method, and a part of the concentrated water was circulated to the supply path so that the circulating flow rate in the system was 5 times the permeate flow rate. During such a feed water treatment operation, a portion of the concentrated water is periodically collected as a sample, the silica concentration of the concentrated water is approximately 135 to 150 mg SiO ₂ / L, and the electrical conductivity of the concentrated water is approximately It confirmed that it was maintained at 510-530 mS / m.

  In the operation described above, the pH of the feed water flowing to the reverse osmosis membrane module is adjusted to 6 to 6.6 by adding sulfuric acid to adjust the pH of the concentrated water to about 8 to 9, and in Example 1, the Langeria index ( LSI) was controlled to -0.2, in Example 2, the index was controlled to 0.1, and in Example 3, the index was controlled to 0.3. Further, BWA WATER ADDITIVES trade name “Flocon 260” was added as a scale dispersant to the supplied water so that the concentration was 2.5 mg / L as the stock solution.

Comparative Example 1
The feed water was treated under the same conditions as in Examples 1 to 3 except that the Langerian index of concentrated water was controlled to 0.5 by adjusting the addition of sulfuric acid to the feed water.

Comparative Example 2
The feed water was treated under the same conditions as in Examples 1 to 3 except that the Langeria index of concentrated water was not controlled by adding sulfuric acid to the feed water.

Comparative Example 3
Except for the point that the Langerian index of the concentrated water was controlled to 0.2 by adjusting the addition of sulfuric acid to the feed water, and the silica concentration of the concentrated water was increased to about 170 mgSiO ₂ / L by increasing the recovery rate. The feed water was treated under the same conditions as in Examples 1 to 3.

Comparative Example 4
Except that the scale dispersant was not added to the feed water, the feed water was treated under the same conditions as in Example 3 in which the Langeria index was controlled to 0.3.

Comparative Example 5
The feed water was treated under the same conditions as in Examples 1 to 3 except that the Langeria index of concentrated water by adding sulfuric acid to the feed water was not controlled and the scale dispersant was not added to the feed water.

In each of Evaluation Examples 1 to 3 and Comparative Examples 1 to 5, the change in effective pressure of the reverse osmosis membrane element during the water treatment operation was measured over time. Then, the water permeation coefficient of the permeated water was calculated from the measured value of the effective pressure, the set value of the permeated water flow rate, and the effective membrane area of the reverse osmosis membrane element when a predetermined time elapsed. In addition, since the water permeation coefficient in the initial state varies somewhat depending on individual differences of the reverse osmosis membrane elements, the numerical value at the time when one hour has elapsed from the start of the water treatment operation is used as the initial value. Moreover, the electrical conductivity of the permeated water was measured after 24 hours from the start of the water treatment operation. The electrical conductivity is an index indicating the quality of the permeated water. The lower the value, the smaller the ionic component (contaminated component) in the permeated water, that is, the better the water quality. The results are shown in Table 1. In Comparative Example 5, since the water permeation coefficient after 120 hours had dropped to less than 15% of the initial value, the water treatment operation was stopped at this point. Table 1 shows the Langeria index, the silica concentration, and the electrical conductivity of the concentrated water. The numerical values shown are average values during the water treatment operation.

  According to Table 1, in Examples 1 to 3, the water permeation coefficient after 150 hours was maintained at 96 to 97% of the initial value, which is due to the scale adhesion of the reverse osmosis membrane element as compared with Comparative Examples 1 to 5. It turns out that obstruction | occlusion is suppressed notably. In Examples 1 to 3, the electrical conductivity of the permeated water is the same as that of Comparative Examples 1 to 5, and it is understood that permeated water with good water quality is obtained. Furthermore, according to Examples 1 to 3, since the conductivity of the permeated water tends to be slightly higher when the Langerian index of the concentrated water is less than 0, the Langerian index of the concentrated water is maintained at 0 or more. It can also be seen that it is preferable.

DESCRIPTION OF SYMBOLS 1 Water treatment apparatus 10 Supply path 20 Reverse osmosis membrane apparatus 22 1st addition apparatus 23 2nd addition apparatus 30 Treated water channel 40 Drainage channel 42 Water quality inspection apparatus 50 Control apparatus

Claims (9)

A water treatment device for filtering raw water containing silica and hardness components,
The raw water supply path;
A reverse osmosis membrane device for filtering the raw water from the supply path and separating it into permeated water and concentrated water;
A treatment water channel for discharging the permeated water from the reverse osmosis membrane device;
A drainage channel for discharging the concentrated water from the reverse osmosis membrane device;
First adjusting means for adjusting the pH of the raw water provided in the supply path;
A second adjusting means for adjusting the recovery rate of the permeated water in the reverse osmosis membrane device;
An addition device for adding a scale dispersant to the raw water provided in the supply path;
A water quality inspection device for inspecting the quality of the concentrated water discharged through the drainage channel;
Based on the water quality inspected by the water quality inspection device, computing means for calculating a Langeria index of the concentrated water;
Water quality for controlling the first adjusting means and the second adjusting means so that the Langeria index is maintained at 0.3 or less and the silica concentration of the concentrated water is maintained at 150 mgSiO ₂ / L or less. Control means;
Water treatment device with   The water treatment apparatus according to claim 1, wherein the water quality control means controls the first adjustment means so that the Langeria index is maintained at 0 or more.   The water treatment device according to claim 1 or 2, wherein the first adjustment means is an injection device for injecting a pH adjusting agent into the raw water.   The water treatment apparatus according to claim 3, wherein the pH adjuster is at least one of an acidic chemical that lowers the pH of the raw water and an alkaline chemical that increases the pH of the raw water.   The water treatment apparatus according to any one of claims 1 to 4, wherein a material containing polycarboxylic acid and phosphonic acid is used as the scale dispersant. A water treatment method for filtering raw water containing silica and a hardness component using a reverse osmosis membrane device,
Supplying the raw water to which the scale dispersant has been added to the reverse osmosis membrane device, and separating it into permeated water and concentrated water;
Maintaining the Langeria index of the concentrated water at 0.3 or less and the silica concentration at 150 mg SiO ₂ / L or less,
Water treatment method.   The water treatment method according to claim 6, wherein the Langeria index is maintained at 0 or more.   8. The silica concentration is controlled by controlling the Langeria index by adjusting the pH of the raw water, and controlling the recovery rate of the permeated water in the reverse osmosis membrane device. Water treatment method.   The water treatment method according to claim 6, wherein the scale dispersant contains polycarboxylic acid and phosphonic acid.

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