JP6699681B2 - Reverse osmosis membrane device operation management method and reverse osmosis membrane treatment system - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention provides a reverse osmosis membrane device operation management method and reverse osmosis membrane treatment capable of stably operating for a long time even under a low water temperature condition (for example, a water temperature of 5 to 10° C.). Regarding the system.
In the present invention, the “reverse osmosis membrane” means a “reverse osmosis membrane” in a broad sense including “reverse osmosis membrane” and “nanofiltration membrane”.

  A reverse osmosis membrane consisting of a dense surface layer and a porous support layer, which allows solvent molecules but not solute molecules, has made possible a further step in desalination of seawater. After that, the field of application of reverse osmosis membranes expanded, and low-pressure reverse osmosis membranes that could be operated at low pressure were developed. Permeable membranes have come into use.

Since the reverse osmosis membrane has a high solute rejection rate, the permeated water obtained by the reverse osmosis membrane treatment has good water quality, so it can be effectively used for various purposes. Therefore, it is important to properly control the water quality and operating method of the reverse osmosis membrane device. In particular, under a low water temperature condition, there is a high possibility that a scale mainly composed of silica is generated, and there is a problem of a decrease in flux due to the silica scale on the film surface.
For example, when tap water is raw water, the silica concentration of the feed water is about 10 to 20 mg/L, whereas the solubility of silica (at equilibrium) is low at 20 mg/L at low water temperature, especially at a water temperature of 5°C. Therefore, it becomes difficult to concentrate the reverse osmosis membrane.
On the other hand, in the reverse osmosis membrane device, silica scale may be generated on the membrane surface and the flux may be reduced, even though the reverse osmosis membrane apparatus is operated under the condition that the saturated solubility of silica is not more than the condition.

Conventionally, these problems are generally dealt with by adjusting the pH of the feed water or using a scale dispersant. For example, a method of adding a scale dispersant and adjusting the pH of the feed water to about 5.5 is adopted (Patent Document 1).
Further, a method has been adopted in which a scale dispersant is added to operate so that the Langeria index of the concentrated water is 0.3 or less and the silica concentration of the concentrated water is 150 mg/L or less (Patent Documents 2 to 4). ).

However, if an excessive amount of acid is added to adjust the pH, the hydrogen carbonate ions and carbonate ions of the feed water become dissolved carbon dioxide, which penetrates the reverse osmosis membrane, which may deteriorate the quality of treated water.
In addition, the method using a scale dispersant has a risk of scale generation when the chemical addition is defective, and the chemical cost becomes an economical load.

  Patent Document 5 describes a reverse osmosis membrane separation device that changes the circulation ratio in a reverse osmosis membrane permeation module according to the water quality of either the feed water or the concentrated water, and measures and detects the silica concentration Cs in the feed water. It is described that the target drainage flow rate Qd' is determined by comparing the silica solubility Ss determined from the temperature value with Cs, and the precipitation of silica-based scale is suppressed by adjusting to this flow rate. However, there is no description suggesting that the operation management is performed based on the concentration of aluminum ions and/or iron ions in the feed water and concentrated water of the reverse osmosis membrane device.

  In Patent Document 6, the scale adjustment of the reverse osmosis membrane element is performed by controlling the pH adjusting means and the permeated water recovery rate adjusting means so that the Langerian index and silica concentration of the concentrated water are maintained within a certain numerical range. Although the suppression method is described, there is also no description in Patent Document 6 suggesting that the operation management is performed based on the concentration of aluminum ions and/or iron ions in the feed water and concentrated water of the reverse osmosis membrane device.

  Further, in Patent Document 7, the allowable concentration ratio of silica in the concentrated water is calculated based on the silica concentration determined from the silica concentration of the feed water and the temperature value of the permeated water or the concentrated water, and the calculated value of the allowable concentration ratio is calculated. And by calculating the first drainage flow rate value from the target flow rate value of permeate and controlling the drainage valve so that the actual drainage volume becomes the first drainage volume value, without using chemicals, Although a method for suppressing scale precipitation and fouling is described, this Patent Document 7 also manages operation based on the concentration of aluminum ions and/or iron ions in the feed water and concentrated water of the reverse osmosis membrane device. There is no suggestion to do so.

  Patent Documents 8 and 9 and Non-Patent Document 1 describe that in a reverse osmosis membrane module, the precipitation of silica scale is promoted by the presence of aluminum ions and iron ions in the water to be treated. It only mentions the effect of aluminum and iron ions as "coexisting ions" of silica, and aluminum and iron ions in the concentrated water of the reverse osmosis membrane device are independent indicators that have nothing to do with silica. However, it does not suggest the technical idea of the present invention that it affects the reduction of the flux of the reverse osmosis membrane.

JP-A-9-206749 Patent No. 5287908 Japanese Patent No. 5757109 Japanese Patent No. 5757110 JP, 2014-188439, A JP 2012-183473 A JP, 2013-154274, A JP, 10-128075, A JP, 2003-326259, A

S. Salvador Cob et al., "Silica and silicate precipitation as limiting factors in high-recovery reverse osmosis operations", Journal of Membrane Science, July 23, 2012, Vol.423-424, pp.1-10.

  When scale occurs on the surface of the reverse osmosis membrane, the amount of treated water decreases extremely.Therefore, it is necessary to properly set the feed water concentration and operation method to achieve long-term stable operation. Satisfactory technology is not provided.

  The present invention solves the above-mentioned conventional problems, and does not require pH adjustment or addition of a scale dispersant, and even under low water temperature conditions such as a water temperature of 5 to 10° C. An object of the present invention is to provide an operation management method for a reverse osmosis membrane device and a reverse osmosis membrane treatment system that can suppress the occurrence of the gas and can continue stable operation for a long time.

As a result of repeated studies on the mechanism of the decrease in the flux of the reverse osmosis membrane, the inventors have found that the decrease in the flux of the reverse osmosis membrane is significantly affected not only by the silica scale but also by the aluminum ion or iron ion itself in water. I found that That is, in order to stabilize the operation of the reverse osmosis membrane device for a long period of time, along with the silica concentration in the feed water and/or the concentrated water, the aluminum ion and/or iron ion concentration should be appropriately adjusted as an index independent of silica. It was revealed that management is important.
The present invention has been achieved based on such findings, and the gist is as follows.

[1] When treating raw water with a reverse osmosis membrane device, water introduced into the reverse osmosis membrane device (hereinafter referred to as “water supply”) and/or aluminum ions of concentrated water of the reverse osmosis membrane device and/or An operation management method for a reverse osmosis membrane device, characterized by managing the operation of the reverse osmosis membrane device based on an iron ion concentration.

[2] In [1], based on the aluminum ion and/or iron ion concentration of the feed water and/or the concentrated water, the suitability of the raw water as the feed water, the water temperature of the feed water, the concentration ratio (recovery rate), the pressure (reverse osmosis). It is characterized by managing any one or more of the membrane feed water supply pressure, concentrated water pressure, treated water pressure), concentrated water amount, continuous operation period, cleaning time, cleaning frequency, and reverse osmosis membrane replacement time. Operation management method for reverse osmosis membrane device.

[3] The operation management method for a reverse osmosis membrane device according to [1] or [2], wherein the management is performed based on the total concentration of aluminum ions and iron ions in the feed water and/or concentrated water.

[4] In any one of [1] to [3], the aluminum ion and/or iron ion concentration is an index of any one or more of a desired continuous operation period, a cleaning time, a concentration ratio, and a quality of water to be supplied. A method for managing operation of a reverse osmosis membrane device, characterized by being set as.

[5] In any one of [1] to [4], the aluminum ion concentration of the concentrated water is 0.2 mg/L or less, the iron ion concentration is 0.2 mg/L or less, or the total concentration of aluminum ion and iron ion. Is controlled to be 0.2 mg/L or less.

[6] In any one of [1] to [5], the control is performed based on the concentration of aluminum ions and/or iron ions in the feed water and/or the concentrated water and the saturation solubility of silica alone. Operation management method for reverse osmosis membrane device.

[7] The operation management method for a reverse osmosis membrane device according to [6], wherein the management is performed such that the silica concentration of the concentrated water is 80 mg/L or less.

[8] In any one of [1] to [6], there is a period in which the water temperature of the supply water is 5 to 10° C. and a period in which the water temperature exceeds 10° C. An operation control method for a reverse osmosis membrane device, characterized in that the operation control according to the operation control method for the osmosis membrane device and the operation control according to the silica concentration and/or the Langerian index are performed together.

[9] A reverse osmosis membrane device for treating raw water with a reverse osmosis membrane, water introduced into the reverse osmosis membrane device (hereinafter referred to as “water supply”) and/or aluminum ions of concentrated water of the reverse osmosis membrane device, And/or a measuring means for measuring the iron ion concentration, and a reverse osmosis membrane treatment system.

[10] In [9], based on the aluminum ion and/or iron ion concentration measured by the measuring means, suitability of the raw water as feed water, water temperature of feed water, concentration ratio (recovery rate), pressure (reverse osmosis) A control means for managing any one or more of membrane supply water supply pressure, concentrated water pressure, treated water pressure), concentrated water volume, continuous operation period, cleaning time, cleaning frequency, and reverse osmosis membrane replacement time. A reverse osmosis membrane treatment system characterized in that

[11] In [10], the control means performs the management based on the total concentration of aluminum ions and iron ions of the feed water and/or the concentrated water measured by the measuring means. Membrane processing system.

[12] In [10] or [11], the control means has an aluminum ion concentration of 0.2 mg/L or less, an iron ion concentration of 0.2 mg/L or less, or an aluminum ion and iron ion concentration of the concentrated water. A reverse osmosis membrane treatment system, wherein the above-mentioned control is performed so that the total concentration becomes 0.2 mg/L or less.

[13] In any one of [10] to [12], further has a means for measuring the silica concentration of the feed water and/or the concentrated water, and the control means measures the concentration of the aluminum ion and/or the iron ion. A reverse osmosis membrane treatment system, wherein the above-mentioned control is performed based on a value and a measured value of concentration based on the saturated solubility of the silica alone.

[14] In the reverse osmosis membrane treatment system according to [13], the control means performs the management so that the silica concentration of the concentrated water is 80 mg/L or less.

According to the present invention, in the reverse osmosis membrane device, it is possible to continue operation with a stable flux for a long period of time by operation management based on water quality without requiring pH adjustment or addition of a scale dispersant, and water supply is possible. Even at a low temperature (for example, 5 to 10°C), it is possible to suppress scale deposition and perform stable operation with a high flux.
For example, it is possible to continuously operate without cleaning for at least 3 months or more as a period in which the converted flux becomes 70% of the initial value.
When a scale dispersant is used as in the conventional method, there is a risk of scale at the time of poor chemical addition, but since the present invention can cope without using the scale dispersant, such a problem is solved.

It is a typical flow figure showing an embodiment of the reverse osmosis membrane treatment system of the present invention. 9 is a graph showing the results of Experimental Example 3. 9 is a graph showing the results of Experimental Example 4.

  Embodiments of the present invention will be described in detail below.

[water supply]
In the present invention, the raw water to be treated with the reverse osmosis membrane includes tap water, clarified industrial water, well water and the like, but is not limited thereto.
Regarding the water quality of the water supply of the reverse osmosis membrane, conventionally, in order to perform long-term continuous operation, the water supply is defined as a fouling index (FI) defined in JIS K3802 or a silt density index (SDI) defined in ASTM D4189. , MF value (Desalination, vol.20, p.353-364, 1977) proposed by Taniguchi as a simpler evaluation method, and the FI value or SDI value, for example, is set so that this value becomes equal to or less than a predetermined value. If necessary, the raw water is pretreated so that the water supply is clarified to some extent, so that the water content becomes 3 to 4 or less. It is preferable that the FI value of the feed water is set to 4 or less by performing pretreatment such as.

[Reverse osmosis membrane treatment system configuration]
FIG. 1 is a schematic flow chart showing an example of an embodiment of a reverse osmosis membrane treatment system of the present invention, in which raw water from a raw water tank (not shown) is supplied by a feed water pump (not shown) and a high pressure for reverse osmosis membrane device. By the pump 2, the permeated water introduced into the reverse osmosis membrane device 4 through the water supply pipe 3 and permeating the reverse osmosis membrane is discharged from the treated water pipe 6, while the concentrated water is discharged from the concentrated water pipe 5.

The water supply pipe 3 is provided with a management instrument 1, which measures the concentration of aluminum ions and/or iron ions in the supply water, and the operation management of the reverse osmosis membrane device is performed based on the measurement result.
The management instrument 1 may be provided in the concentrated water pipe 5 or may be provided in both the concentrated water pipe 5 and the water supply pipe 3. Further, the water supply pipe 3 and/or the concentrated water pipe 5 may be provided with a control instrument for measuring the silica concentration or the Langerian index and performing operation control based on this value. It may also serve as both measurement and control of the concentration and/or the Langerian index.

The basic operating conditions of the reverse osmosis membrane device are not particularly limited, but if the concentrated water amount is 3.6 m ³ /hr or more and the ultra low pressure reverse osmosis membrane is used, the standard pressure is 0.735 MPa and the membrane area is 35 to 35. 41 m ² , initial pure water flux of 1.0 m/day (25° C.) or higher, and initial desalination rate of 98% or higher. However, the reverse osmosis membrane does not change the exclusion rate of aluminum ions and iron ions, so the type of membrane does not depend on it.

[Operation management of reverse osmosis membrane device]
In the present invention, the concentration of aluminum ions and/or iron ions in feed water and/or concentrated water is measured, and the reverse osmosis membrane is based on this measurement value (hereinafter sometimes referred to as “Al/Fe measurement value”). Manage the operation of the equipment. This operation management item includes suitability as raw water supply, supply water temperature, concentration ratio (recovery rate), pressure (reverse osmosis membrane supply water supply pressure, concentrated water pressure, treated water pressure), concentrated water volume, continuous operation Any one or more of the period, the cleaning time, the cleaning frequency, and the reverse osmosis membrane replacement time may be mentioned, and specifically, the following operation management method may be mentioned.

(1) When the measured Al/Fe value is less than or equal to a predetermined value, it is directly introduced into the reverse osmosis membrane device, and when the measured Al/Fe value is higher than the predetermined value, it is determined that the raw water is unsuitable as water supply, Treatment for stopping the supply of raw water to the reverse osmosis membrane or reducing the concentration of aluminum ions and/or iron ions in the raw water to reduce the Al/Fe measured value to a predetermined value or less, for example, iron removal/manganese removal treatment Or after ion exchange treatment, it is introduced into the reverse osmosis membrane device. In addition, when the PAC or iron salt is used for the aggregating treatment on the upstream side, the washing cycle is affected, so it is preferable to appropriately change the aggregating conditions.
(2) If the measured Al/Fe value is less than or equal to the predetermined value, continue the operation as it is, and if the measured Al/Fe value is higher than the predetermined value, raise the water temperature of the feed water.
(3) When the measured Al/Fe value is higher than a predetermined value, the flux, pressure, and concentration rate (recovery rate) are lowered, and when the measured value is lower than the predetermined value, flux, pressure, and concentration rate (recovery rate) are increased.
(4) When the measured Al/Fe value is higher than a predetermined value, the continuous operation period is set to be short, the cleaning time is long, the cleaning frequency is high, and the reverse osmosis membrane replacement time is short (replacement frequency is low). On the contrary, when the measured Al/Fe value is lower than the predetermined value, the continuous operation period is set to be long, the cleaning time is short, the cleaning frequency is low, and the reverse osmosis membrane replacement time is long (the replacement frequency is high).

  The predetermined value of the above Al/Fe measured value is appropriately set based on the specifications of the reverse osmosis membrane device and other operating conditions so that desired stable operation can be performed. 5 to 10° C.) and 10° C. or higher, the concentration of aluminum ion is 0.01 to 0.2 mg/L and the concentration of iron ion is 0.01 to 0.2 mg/L as Al/Fe measurement value of concentrated water. It is appropriately determined within the range of L and the range of the total concentration of aluminum ion and iron ion of 0.02 to 0.2 mg/L.

  In the present invention, the continuous operation period of concentrated water, the washing time, the concentrated water ratio, and the water temperature may be set from the measured value of Al/Fe, and the measured value of Al/Fe of concentrated water is equal to or less than a predetermined value. These may be managed so that

For example, the aluminum ion concentration of concentrated water is 0.2 mg/L or less, preferably 0.15 mg/L or less, the iron ion concentration is 0.2 mg/L or less, preferably 0.15 mg/L or less, aluminum ion and iron ion By controlling the operation so that the total concentration of water is 0.2 mg/L or less, preferably 0.15 mg/L or less, even if the water temperature of the feed water is a low temperature of 5 to 10° C. The operation can be continued by washing.
For example, as shown in Table 3 below, the concentration of aluminum ions in concentrated water is 0.2 mg/L or less, the concentration of iron ions is 0.2 mg/L or less, and the total concentration of aluminum ions and iron ions is 0.2 mg/L. By managing the following, operation can be continued without maintenance for 3 months or more. When managing the aluminum ion concentration and iron ion concentration in the concentrated water, a management sensor may be provided in the concentrated water pipe, or the concentration ratio may be adjusted based on the measurement value of the management sensor provided in the water supply pipe. It may be controlled so as to fall within the above range.

  In addition to the measured Al/Fe value, the silica concentration of the feed water and/or the concentrated water may be used as a management index. In this case, the silica concentration of the concentrated water is controlled to 80 mg/L or less, particularly 60 mg/L or less. Preferably.

  The operation control based on the above Al/Fe measurement value is effective in the entire water temperature range of the feed water, but when the water temperature of the feed water is lower than 10° C., other operation control, for example, the silica concentration of the concentrated water and/or It is preferable that the operation management based on the Langerian index is also performed.

As a specific operation management method, when the water temperature of the feed water is 5 to 10° C., the silica concentration and calcium hardness of the feed water or the concentrated water, or the aluminum ion concentration and the iron ion concentration of the concentrated water are recovered as follows. There is a method of determining the rate and selecting the lowest recovery rate among the recovery rates calculated based on the respective values.
That is, first, the recovery rate at which the concentration of concentrated water silica is 80 mg/L or less, preferably 60 mg/L or less is determined. For example, when the silica concentration of the feed water is 20 mg/L, the recovery rate is set to about 70% in consideration of the saturated solubility of silica alone.
Further, the recovery rate is determined so that the Langerian index of the concentrated water becomes 0 or less.
Furthermore, the recovery rate is determined so that the aluminum ion concentration of the concentrated water is 0.2 mg/L or less, the iron ion concentration is 0.2 mg/L or less, or the total concentration of these is 0.2 mg/L or less.
By performing the operation with the lowest recovery rate among the above three recovery rates, it is possible to suppress the decrease in the flux and perform stable operation for a long period of time. When the flux becomes 70% or less of the initial value, there is a high possibility that it cannot be recovered even by cleaning. However, by performing operation management based on the measured Al/Fe value, it is possible to operate without chemicals for 3 months until the flux drops to 70% or less of the initial value.

[About flushing]
In the present invention, it is preferable to perform low-pressure flushing as follows when the reverse osmosis membrane device is stopped.

That is, the equilibrium concentration of silica at a water temperature of 5° C. is 20 mg/L. Since the polymerization rate of silica is slow, concentrated water allows a silica concentration of up to 80 mg/L. However, if the operation of the device is stopped as it is, silica may precipitate on the concentrated water side, so low-pressure flushing is performed.
The low-pressure flushing stops the high-pressure pump for the reverse osmosis membrane device when the device is stopped, and operates only the water supply pump,
Pressure: about 0.1 to 0.3 MPa Water amount: It is carried out by flowing at least 3 times or more, for example, about 3 to 5 times the amount of water held in the reverse osmosis membrane vessel, and securing a time between them.
Further, it is preferable to perform the above-mentioned low pressure flushing when the operation is stopped, and then perform the low pressure flushing again when the operation stop state of the apparatus continues for 5 hours or more.

[Other processing]
An electric deionization device or an ion exchange device may be provided in the subsequent stage of the reverse osmosis membrane device in the present invention to further process the reverse osmosis membrane permeate water. Further, a safety filter may be provided in the preceding stage of the reverse osmosis membrane device, and when the residual chlorine concentration of the raw water is high, a residual chlorine remover such as an activated carbon tower may be provided in the preceding stage of the reverse osmosis membrane device.

  The present invention will be described more specifically below with reference to experimental examples instead of the examples.

[Experimental Example 1]
The reverse osmosis membrane device was operated under the following conditions.

<Test conditions>
Raw water: Nogicho Water Treatment amount: 0.6-0.8m/day
Reverse osmosis membrane: Ultra low pressure reverse osmosis membrane “ES-20” manufactured by Nitto Denko Corporation
Recovery rate: 75%
Water supply (reverse osmosis membrane inlet) Water temperature: 5-8°C
Water supply silica concentration: About 16 mg/L

  Run 1 was carried out in Nogi-machi water without adding any chemicals. In Run 2, magnesium chloride, ferric chloride, and aluminum chloride were added to Nogi-cho water as Mg source, Fe source, and Al source, respectively, so as to have predetermined concentrations.

The concentrations of each component of the feed water and concentrated water of the reverse osmosis membrane device in Runs 1 and 2 were examined, and the concentration ratio of each component and the concentration ratio of the amount of water were obtained.
Further, the differential pressure increase rate was examined from the differential pressure before and after the operation for 4 days.
The results are shown in Table 1.

  As is clear from Table 1, in Run2, a tendency for an increase in the differential pressure was observed, and since the material balance of Fe was not matched, it is estimated that the reverse osmosis membrane was clogged with the Fe component. .. Also, Al has a larger error than other coexisting ions, and it is considered that Al is attached to the film surface.

  Elemental analysis of the film surface deposit of the reverse osmosis membrane after the operation in Run2 was performed, and the results are shown in Table 2. From Table 2, it can be seen that, of the coexisting ions, particularly Al and Fe are attached in large amounts.

[Experimental Example 2]
Tap water from which residual chlorine was removed at a water temperature of 5° C. and silica of 20 mg/L was used as the feed water for the reverse osmosis membrane device, aluminum chloride and ferric chloride were added as Al sources and Fe sources, respectively, to obtain a predetermined Al concentration, Fe. The concentration was adjusted, and the solution was concentrated three times using an ultra-low pressure reverse osmosis membrane "ES-20" manufactured by Nitto Denko Corporation (concentrated water silica 60 mg/L).
The Al concentration and the Fe concentration of this feed water were variously changed, and the concentration of the concentrated water obtained by the reverse osmosis membrane treatment was calculated, and the concentration of Fe and the total concentration of Fe and Al and the rate of flux decrease were calculated. Graph showing the relationship with the operating period until the converted flux drops to 70% of the initial value (hereinafter, may be referred to as "70% continuous operation days" (indicated in months in Table 3)) And the results are summarized in Table 3.

  From Table 3, it can be seen that the number of days that the 70% operation can be continued depends on the Al concentration, the Fe concentration, and the total concentration of Al and Fe of the concentrated water. Further, it can be seen from the conditions 1 and 2, the conditions 3 and 4, and the conditions 6 and 7 of the example that the Al concentration affects the number of days during which the operation can be continued more than the Fe concentration.

  Further, from the conditions 1 to 6 of the example, the conditions 1 to 3 of the comparative example, and the condition 7 of the example, the Al concentration (calculated value) in the concentrated water is 0.2 mg/L or less, and the Fe concentration (calculated value) is 0. By setting the total concentration of Al and Fe (calculated value) to 0.2 mg/L or less and to 0.2 mg/L or less, it is apparent that the reverse osmosis membrane can be stably operated for a long period of time. ..

Table 3 shows the results of calculating the number of days for which 70% operation can be continued from some graphed values. Using these results, operation management can be performed as follows. For example, a relational expression between the number of days for which operation can be continued and the measured Al/Fe value is obtained from the slope of the graphed result, and a predetermined number of days as the number of days for which operation can be continued is substituted into this relational expression to calculate the measured value of Al/Fe. Then, the concentration ratio (recovery rate) and the like are controlled so that the measured Al/Fe value in the concentrated water becomes the calculated value.
Alternatively, by substituting the measured Al/Fe value into the above relational expression and obtaining the number of days during which 70% operation can be continued, the time during which continuous operation is possible can be set, and the cleaning cycle can be predicted. It is also possible to calculate to what extent the feed water Al/Fe measurement value can be concentrated.

  In addition, in Table 3 above, the operation period until the formula flux is reduced to 70% was evaluated, but the decrease from the initial flux is not limited to 70%, and the cleaning frequency and the operation under desired operation conditions are not limited. It is decided as appropriate so that it can continue.

[Experimental Example 3]
An experiment was conducted to prove that aluminum ions and iron ions in concentrated water are factors that influence the decrease in the flux of the reverse osmosis membrane independently of silica, not as coexisting ions for depositing silica.
Ferric chloride and aluminum chloride were added to pure water so as to have Al concentration and Fe concentration shown in Table 4 below to prepare simulated water supply 1. Separately, ferric chloride, aluminum chloride and silica were added to pure water to prepare simulated water supply 2 having Al concentration, Fe concentration and SiO ₂ concentration shown in Table 4 below.

  Simulated water supplies 1 and 2 were each passed through the reverse osmosis membrane under the following test conditions, and the change with time of the flux was examined. The results are shown in FIG.

<Test conditions>
Reverse osmosis membrane: Ultra low pressure reverse osmosis membrane “ES-20” manufactured by Nitto Denko Corporation
Recovery rate: 80%
Water supply (reverse osmosis membrane inlet) Water temperature: 23°C
Initial flux: 1.0m/day

As is clear from FIG. 2, regardless of the presence or absence of silica in the feed water, if the Al concentration and the Fe concentration in the feed water are the same, the decreasing tendency of the flux is the same. From this result, the following can be understood.
If aluminum ions and iron ions influence as coexisting ions of silica, the simulated water supply 1 containing no silica and the simulated water supply 2 containing silica should not have the same flux lowering tendency. As is clear from the results of Example 3, the simulated water supply 2 containing silica and the simulated water supply 1 not containing silica show the same tendency of flux decrease. This means that aluminum ions and iron ions are indices that must be controlled and managed independently of silica.

[Experimental Example 4]
Silica is further added to the feed water to change the silica concentration, Al concentration and Fe concentration of the feed water, and the Al concentration, Fe concentration, total concentration of Fe and Al of the concentrated water obtained by the reverse osmosis membrane treatment obtained by calculation , And the silica concentration were set to the concentrations shown in Table 5, and the relationship with 70% continuous operation days at a water temperature of 5° C. or 25° C. was examined in the same manner as in Experimental Example 2, and the results are shown in Table 5.

  Similarly, the total concentration of Al and Fe in the concentrated water was variously changed, and the relationship between the calculated value of the concentration of Al+Fe in the concentrated water and the 70% continuous operation possible days was examined at 5° C. or 25° C., and the result is shown in FIG. Indicated.

It can be seen from Table 5 that the Al and Fe concentrations are the same if the Al and Fe concentrations are the same regardless of the water temperature, that is, that the Al concentration and the Fe concentration influence the 70% continuous operation days.
Further, from FIG. 3, the greater the total concentration of Al and Fe in the concentrated water, the shorter the number of days for which 70% operation can be continued. In order to set the number of days for which 70% operation can be continued for 3 months or more, the Al+Fe concentration is 0.20 mg. It can be seen that it is necessary to set it to /L or less.

1 Management instrument 2 High pressure pump 3 Water supply pipe 4 Reverse osmosis membrane device 5 Concentrated water pipe 6 Treated water pipe

Claims (10)

When treating raw water with a reverse osmosis membrane device, the concentration of aluminum ions and/or iron ions introduced into the reverse osmosis membrane device (hereinafter referred to as "supply water") and/or concentrated water of the reverse osmosis membrane device A method for controlling the operation of the reverse osmosis membrane device for controlling the operation of the reverse osmosis membrane device under a low temperature condition in which the water temperature of the feed water is lower than 10° C. , based on the saturated solubility of silica alone .
Performing the management so that the measured value of the aluminum ion and/or iron ion concentration of the feed water and/or the concentrated water becomes a predetermined value or less and the silica concentration of the concentrated water becomes 80 mg/L or less. And a method for operating and controlling a reverse osmosis membrane device.   In Claim 1, based on the aluminum ion and/or iron ion concentration of the feed water and/or concentrated water, suitability as feed water for raw water, water temperature of feed water, concentration ratio (recovery rate), pressure (feed water for reverse osmosis membrane). Reverse osmosis characterized by managing any one or more of supply pressure, concentrated water pressure, treated water pressure), concentrated water volume, continuous operation period, cleaning time, cleaning frequency, and reverse osmosis membrane replacement time. Membrane device operation management method.   The operation management method for a reverse osmosis membrane device according to claim 1 or 2, wherein the management is performed based on a total concentration of aluminum ions and iron ions of the feed water and/or the concentrated water.   4. The aluminum ion and/or iron ion concentration according to any one of claims 1 to 3, wherein any one or more of a desired continuous operation period, a cleaning time, a concentration ratio, and a quality of water to be supplied is set as an index. A method for operation management of a reverse osmosis membrane device, which is characterized by the above.   The aluminum ion concentration of the concentrated water is 0.2 mg/L or less, the iron ion concentration is 0.2 mg/L or less, or the total concentration of the aluminum ion and the iron ion is 0. A method for operation management of a reverse osmosis membrane device, characterized in that the above-mentioned management is carried out so as to be 2 mg/L or less. The reverse osmosis membrane device according to any one of claims 1 to 5 , wherein the water temperature of the feed water has a period of 5 to 10°C and a period of more than 10°C, and the water temperature is 5 to 10°C. The operation management method of the reverse osmosis membrane device, which is characterized by performing the operation management according to the operation management method of 1. and the operation management based on the silica concentration and/or the Langerian index. Reverse osmosis membrane device for treating raw water with a reverse osmosis membrane, water introduced into the reverse osmosis membrane device (hereinafter referred to as "water supply") and/or aluminum ions and/or iron in concentrated water of the reverse osmosis membrane device Measuring means for measuring ion concentration, means for measuring silica concentration of the feed water and/or concentrated water, and aluminum ion and/or iron ion measured by the measuring means for measuring aluminum ion and/or iron ion concentration concentration and, based on the silica concentration measured by means for measuring the concentration of silica, reverse osmosis membranes and a control means for managing the operation of the reverse osmosis unit at low low temperature than the water supply is 10 ° C. A processing system,
When the water temperature of the feed water is lower than 10° C., the control means is based on the measured value of the aluminum ion and/or iron ion concentration and the measured value of the concentration based on the saturated solubility of the silica alone. The management is performed such that the measured value of the aluminum ion and/or iron ion concentration of the feed water and/or the concentrated water becomes a predetermined value or less and the silica concentration of the concentrated water becomes 80 mg/L or less. A reverse osmosis membrane treatment system characterized by the above. In Claim 7 , the said control means is based on the aluminum ion and/or iron ion density|concentration measured by the said measurement means, the adequacy of the said raw water as the water supply, the water temperature of the water supply, the concentration ratio (recovery rate), the pressure ( water supply pressure of the reverse osmosis membrane, concentrated water pressure, treated water pressure), concentrate water, continuous operation period, the washing time, the washing frequency, and Turkey to manage any one or more of the replacement timing of the reverse osmosis membrane And a reverse osmosis membrane treatment system. 9. The reverse osmosis membrane treatment system according to claim 8 , wherein the control means performs the management based on a total concentration of aluminum ions and iron ions of the feed water and/or the concentrated water measured by the measuring means. .. 10. The control means according to claim 7 , wherein the concentrated water has an aluminum ion concentration of 0.2 mg/L or less, an iron ion concentration of 0.2 mg/L or less, or an aluminum ion and an iron ion concentration. The reverse osmosis membrane treatment system, wherein the above-mentioned control is performed so that the total concentration becomes 0.2 mg/L or less.

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