JP2015047591A - Seawater desalination system and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desalination system which can effectively prevent the generation of biofouling of a reverse osmosis membrane module, and to provide a control method of the desalination system.SOLUTION: A desalination system includes: a flocculation device 3 which injects a flocculant into water 1 to be treated, which is seawater or saline water, to subject the water 1 to be treated to flocculation treatment; a reverse osmosis membrane module 6 which separates the water 1 to be treated after the flocculation treatment into salt-removed fresh water 21 and salt-concentrated water 22; and a control device 10 which controls the flocculation device 3 and the reverse osmosis membrane module 6. The control device 10 controls the injection rate of the flocculant based on the concentrations of dissolved low molecular polysaccharides of 20 kDa or less and organic nitrogen components contained in the water 1 to be treated.

Description

  The present invention relates to a desalination system and a desalination treatment control method for obtaining fresh water from seawater or brine using a reverse osmosis membrane.

  In recent years, with the emergence of increased water demand due to global population growth and the emergence of emerging countries, reverse osmosis membrane (Reverse Osmosis Membrane; hereinafter referred to as “RO membrane”) is used to obtain fresh water from seawater. The tendency for the system to increase is remarkable. The RO membrane is made of materials such as cellulose and polyamide. By applying a pressure of at least twice the osmotic pressure of seawater to this RO membrane, water is passed through the micropores of the RO membrane, and the salinity (mainly NaCl) permeation is suppressed and fresh water is obtained. In a desalination system using an RO membrane, biofouling is known as a phenomenon that reduces the permeation performance of the RO membrane.

  For biofouling, TEP (Transparent Expolymer Particles: Transparent extracellular particles (transparent particulate organic matter)), which includes phytoplankton-derived biopolymers and carbon-containing organic substances, especially polysaccharides with adhesive properties Is known to contribute greatly.

  In Patent Document 1, a plurality of water quality items such as MFI (Modified Fouling Index) and SDI (Silt Density Index), which are indexes indicating how much fouling is caused in the TEP and filtration membrane, are measured and stored in advance. The flocculant injection rate is determined based on the relationship between each water quality item and the flocculant injection rate.

  Patent Document 2 proposes a method of installing an aggregation monitoring device, measuring the turbidity or chromaticity of a collected sample, and controlling the injection amount of the flocculant according to the measured value.

JP 2012-170848 A JP-A-5-146608

  In Patent Document 1 and Patent Document 2, in order to suppress biofouling, the injection rate of the flocculant added to the water to be treated is determined based on the water quality items of TEP, MFI, and SDI, or turbidity and chromaticity. Aggregation is performed before the RO membrane.

  However, in the method of determining the flocculant injection rate based on the above water quality items, it is difficult to suppress the occurrence of fouling of the RO membrane, and the flocculant injection rate is based on a component that has a high correlation with the factor causing fouling. It is necessary to ask.

  Therefore, the present invention provides a desalination system that can effectively prevent the occurrence of biofouling in a reverse osmosis membrane module and a control method thereof.

  In order to solve the above-mentioned problems, the desalination system of the present invention has a coagulation treatment device that injects a coagulant into seawater or brine to be treated and performs coagulation treatment, and salt is removed from the water to be treated after coagulation treatment. A reverse osmosis membrane module that separates fresh water and salt-enriched concentrated water, and a control device that controls the coagulation treatment device and the reverse osmosis membrane module, wherein the control device is at least 20 kDa contained in the treated water The injection rate of the flocculant is controlled based on the concentration of the following dissolved low molecular weight polysaccharide and organic nitrogen component.

  ADVANTAGE OF THE INVENTION According to this invention, the desalination system which can prevent effectively generation | occurrence | production of the biofouling of a reverse osmosis membrane module, and its control method can be provided.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a whole block diagram of the desalination system which concerns on one Example of this invention. It is a conceptual diagram which shows the coagulant | flocculant injection | pouring control procedure in the desalination system shown in FIG. It is an aggregation pattern characteristic figure which shows the relationship between the coagulant | flocculant injection rate and the dissolved low molecular polysaccharide density | concentration of 20 kDa or less after an aggregation process. It is an aggregation pattern characteristic figure which shows the relationship between the coagulant | flocculant injection rate and E260 value of the supernatant liquid after an aggregation process. It is a figure which shows the relationship between a coagulant injection rate, pH, and a humic acid removal rate.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a desalination system according to an embodiment of the present invention. In FIG. 1, the flow of water is indicated by a solid arrow, and the signal line is indicated by a dotted arrow. As shown in FIG. 1, a desalination system 100 includes a water intake tank 2 that stores water to be treated 1 that is seawater or brine, and a flocculant added to the water 1 to be treated that is fed from the water intake tank 2 through a pipe 12. A coagulation treatment apparatus 3 for adding and coagulating, a multi-media filter 4 (hereinafter referred to as MMF membrane) for separating the treated water 1 after the coagulation treatment, an ultrafiltration membrane 5 (hereinafter referred to as UF membrane), a reverse osmosis membrane (RO) (Membrane: Reverse Osmosis Membrane) module 6. The agglomeration apparatus 3 adds an inorganic flocculant or a polymer flocculant to the water 1 to be treated, and traps impurities such as organic substances contained in the water 1 to be treated to form flocs. Below, the case where ferric chloride is used as an inorganic type flocculant is demonstrated to an example. The agglomeration processing apparatus 3 has a stirrer (not shown), and controls the rotation speed of a motor that drives the stirrer blades of the stirrer to control the stirring strength and promote floc formation and growth. The treated water 1 after the coagulation treatment is sent to the MMF membrane 4 and the UF membrane 5 through the pipes 13 and 14, and is separated into solid and liquid according to the filter pore diameter. The treated water 1 after the solid-liquid separation is sent to the reverse osmosis membrane module 6 through the pipe 15 and separated into fresh water 21 from which salt content has been removed and concentrated water 22 which is high-concentration salt water. The reverse osmosis membrane module 6 has, for example, a structure in which elements of a reverse osmosis membrane (RO membrane) are connected in multiple stages.

  The coagulation treatment apparatus 3, the MMF membrane 4, and the UF membrane 5 constitute a pretreatment unit, and impurities such as organic substances are removed from the water 1 to be treated before the reverse osmosis membrane module 6. In addition, the structure of a pre-processing part is not limited to these, For example, instead of the MMF membrane 4 and the UF membrane 5, you may use a microfiltration membrane (MF membrane), a sand filtration apparatus, etc.

  The analyzer 7 takes in the treated water 1 sent from the water intake tank 2 to the flocculation treatment device 3 via the branch pipe 16 branched from the pipe 12 and branches the treated water after the flocculation treatment from the pipe 13. Take in via the branch pipe 17. And the analyzer 7 performs the analysis process corresponding to the analysis item mentioned later with respect to the taken in to-be-processed water. In the present embodiment, the case where the water to be treated from the water intake tank 2 and the water to be treated after being agglomerated by the aggregating treatment device 3 will be described. However, the present invention is not limited to this. You may comprise so that the to-be-processed water after liquid separation or the to-be-processed water after solid-liquid separation by the UF membrane 5 may also be taken in.

  The analysis result 18 by the analysis device 7 is stored in the storage device 11 provided in the control device 10. Based on the analysis result stored in the storage device 11, the control device 10 obtains the injection rate of the flocculant injected from the flocculant storage tank 8 into the water to be treated in the flocculant treatment device 3. In addition, you may make it obtain | require collectively the injection amount of the pH adjuster inject | poured into the intake water tank 2 from the pH adjuster storage tank 23. FIG. In this case, instead of injecting the pH adjusting agent into the water to be treated 1 in the intake water tank 2, the pH adjusting agent is injected into the pipe 12 connecting the intake water tank 2 and the aggregation treatment device 3 or the aggregation treatment device 3. It may be configured. Below, the case where seawater is taken in as treated water 1 is explained.

  Further, the agglomeration test apparatus 9 realized by, for example, a jar tester uses the water to be treated supplied to the analyzer 7 or a material obtained by adding an artificial component to the water to be agglomerated to change the coagulant injection rate. Processing is performed, and the water to be treated after the coagulation treatment is analyzed with respect to analysis items similar to those of the analysis device 7 and stored in the storage device 11 as test results. At this time, by storing information representing the correlation between each analysis item and the coagulant injection rate in the storage device 11, the control device 10 can treat the raw water obtained from the analysis device 7 and the coagulation treatment device 3. It becomes possible to obtain the coagulant injection rate corresponding to the analysis result of the water to be treated after the coagulation treatment. Generally, a jar tester includes a plurality of beakers and a stirring mechanism, and is configured to be able to perform an agglomeration test under the same conditions as the agglomeration processing apparatus 3.

  Next, analysis items analyzed by the analyzer 7 will be described. Analyzes the three components of (1) minute dissolved polysaccharides with a molecular weight of 20 kDa or less, (2) organic nitrogen components, and (3) humic substances contained in the treated water that is raw seawater and the treated water after the coagulation treatment. . In the following, the case where the three components are analyzed to determine the injection rate of the flocculant to be injected into the water to be treated will be described as an example. However, the present invention is not limited to this, and at least (1) a minute dissolved polysaccharide having a molecular weight of 20 kDa or less and (2) If two components of the organic nitrogen component are analyzed, the flocculant injection rate can be determined.

  Here, the minute dissolved polysaccharide is a sugar component that is fractionated to 0.45 μm or less among the sugar components dissolved in the seawater, and the concentration in the seawater is generally determined by an analysis method such as the phenol-sulfuric acid method. Quantified. On the other hand, a low molecular weight dissolved polysaccharide of 20 kDa or less, which is of interest in the present invention, is difficult to measure with the phenol-sulfuric acid method, and therefore employs a phosphate-phenylhydrazine sugar analysis system by high performance liquid chromatography (HPLC). And quantify. The particle size with a molecular weight of 20 kDa is about 70 nm.

  In addition, the organic nitrogen component corresponds to a component constituting protein, and each component of total nitrogen (TN), ammonia nitrogen (NH4-N) and nitrate nitrogen (NO3-N) in the water to be treated is included. It is obtained by analyzing each and obtaining the difference by the following equation.

Organic nitrogen = (TN)-(NH4-N)-(NO3-N)
Moreover, E260 value is used for the analysis of humic substances. The E260 value indicates the ultraviolet absorbance, which is an absorbance value when the water to be treated is irradiated with ultraviolet rays having a wavelength of 260 nm, and is an index indicating the abundance of an organic substance having a double bond. Specifically, the E260 value increases as the concentration of humic acid or fulvic acid increases.

  Hereinafter, the low molecular weight dissolved polysaccharide having a molecular weight of 20 kDa or less obtained by the aggregation test apparatus 9 and information representing the correlation between the concentration of humic substance obtained as the E260 value and the flocculant injection rate will be described.

  FIG. 3 is an aggregation pattern characteristic diagram showing the relationship between the flocculant injection rate and the concentration of dissolved low molecular polysaccharides of 20 kDa or less after the aggregation treatment. In FIG. 3, the vertical axis represents the concentration of dissolved low molecular polysaccharides of 20 kDa or less, and the horizontal axis represents the injection amount of ferric chloride, which is an inorganic flocculant. The aggregation pattern characteristics shown in FIG. 3 are prepared by preparing test water (seawater) having different dissolved low-molecular-weight polysaccharide concentrations of 20 kDa or less in advance using the aggregation test device 9, and changing the addition amount of ferric chloride to 20 kDa or less. The concentration of dissolved low-molecular polysaccharides was obtained.

  In FIG. 3, the horizontal axis Fe (ferric chloride) addition amount “0” is the concentration of dissolved low-molecular polysaccharides of 20 kDa or less in the raw seawater, the seawater with the concentration C1 is round, the seawater with the concentration C2 is triangular, Seawater with concentration C3 is plotted as a square. When the analysis is performed without adding the pH adjuster (pH = 8), the results are shown in black, and when the raw seawater is adjusted to pH “6” (acidic) by adding the pH adjuster, the white square And a triangle. When the addition amount of the flocculant is increased without adjusting the pH, the concentration of dissolved low-molecular polysaccharides of 20 kDa or less decreases in any concentration of seawater, and the concentration of dissolved low-molecular polysaccharides increases when a certain addition amount is exceeded. ing. Moreover, when a pH adjuster is added and the pH is reduced to “6” in advance, the effect of reducing the dissolved low-molecular polysaccharide concentration of 20 kDa or less is further increased. That is, by increasing the amount of the flocculant added to the value (optimum value) when the concentration of the dissolved low-molecular polysaccharide is switched from a decrease to an increase, the concentration of the dissolved low-molecular polysaccharide can be reduced, and the pH is adjusted in advance. The effect of reducing the concentration of dissolved low-molecular-weight polysaccharides can be increased by adjusting to a low level.

This phenomenon is due to a change in the state of the ferric chloride flocculant depending on the pH in the seawater. The pH of ordinary raw seawater is about “8”, and the ferric chloride injected into the seawater at this time is in an iron hydroxide state and efficiently captures dissolved low-molecular polysaccharides of 20 kDa or less in the seawater. A flock is formed. The iron hydroxide ^{Fe (OH) 2+, Fe (} OH) 2 +, or Fe (OH) ₄ ^-, and the like. In the case of seawater (pH = 8), it is considered that Fe (OH) ₂ ⁺ and Fe (OH) ₄ ⁻ coexist. In order to promote the agglomeration phenomenon, it is important that Fe (OH) ₂ ⁺ exists stably. For that purpose, it is effective to adjust the pH to about “8” to “6”. Lowering the more acidic side than "6" to pH ^{Conversely, Fe (OH) 2+, Fe} (OH) 2+, change state Fe (OH) ₂ ⁺ or Fe ³⁺ coexist, Fe (OH) ₂ ^The efficiency of capturing low-molecular polysaccharides dissolved in seawater is reduced by becoming a state in which ⁺ is hardly generated.

  In the storage device 11 in the control device 10, as the information representing the correlation between the flocculant injection rate and the dissolved low molecular polysaccharide concentration of 20 kDa or less, the aggregation pattern shown in FIG. 3 or the function obtained from the aggregation pattern shown in FIG. Store. The information representing the correlation between the organic nitrogen component concentration and the flocculant injection rate is also obtained by the coagulation test apparatus 9 in the same manner.

  FIG. 4 is an agglomeration pattern characteristic diagram showing the relationship between the flocculant injection rate and the E260 value of the supernatant after the agglomeration treatment. The vertical axis indicates the E260 value, and the horizontal axis indicates the amount of Fe (ferric chloride) added. The E260 value is expressed as the transmittance (Absorbance) with respect to the optical path length (cm) of the solution in the cell of the measuring apparatus. Similar to FIG. 3, test water (seawater) having different humic concentrations in seawater is prepared, and the amount of ferric chloride flocculant added is changed in the coagulation test apparatus 9 to change the E260 value of the supernatant after the coagulation treatment. Is obtained.

  In FIG. 4, seawater having a humic substance concentration C1 is indicated by a circle, seawater having a humic substance concentration C2 is indicated by a triangle, and seawater having a humic substance concentration C3 is indicated by a square. When the analysis is performed without adding the pH adjuster (pH = 8), the results are shown in black, and when the pH adjuster is added to adjust the pH to “6”, the open squares and circles are shown. . In any case, when the addition amount of the ferric chloride flocculant is increased, the E260 value decreases, and when it exceeds a certain addition amount, the E260 value increases again. Therefore, the storage device 11 in the control device 10 stores the aggregation pattern shown in FIG. 4 or a function obtained from the aggregation pattern shown in FIG. 4 as information indicating the correlation between the coagulant injection rate and the E260 value.

  Furthermore, the removal performance of humic acid, which is a humic substance, will be described. FIG. 5 is a graph showing the relationship between the flocculant injection rate, pH, and humic acid removal rate. In FIG. 5, the horizontal axis represents pH, and the vertical axis represents the concentration of ferric chloride flocculant added to the test water (seawater) in terms of the amount of Fe (ferric chloride). The pH and Fe (ferric chloride) The humic acid removal rate is plotted from the humic acid concentrations before and after the aggregation treatment obtained by changing the addition concentration as the E260 value. That is, for seawater containing humic acid, the E260 value before flocculation treatment (E260-before) is measured, and thereafter, the ferric chloride flocculant is added to obtain the E260 value after flocculation treatment (after E260-after). Measure the humic acid removal rate by the following formula.

Humic acid removal rate = 100 × [(E260−before) − (E260−after)] / (E260−before)
In the coagulation test apparatus 9, a humic acid reagent is added to seawater as test water, a ferric chloride coagulant and a pH adjuster are added, and the humic acid removal rate is obtained. As shown in FIG. 5, the humic acid removal rate is improved by increasing the addition concentration of the ferric chloride flocculant. Moreover, the humic acid removal rate can be improved with the same amount of ferric chloride flocculant by adding a pH adjuster and adjusting the pH of the seawater to lower the pH from “8” to “6”. That is, the same humic acid removal rate can be obtained with a small addition amount of the ferric chloride flocculant. Accordingly, when sulfuric acid is used as the pH adjuster, for example, the chemical cost due to the addition of sulfuric acid increases, but the amount of ferric chloride flocculant added can be reduced, and the chemical cost can be reduced accordingly. Thus, the desalination system which can suppress biofouling can be optimally operated by using a pH adjuster and an iron chloride flocculant together.

  In addition to the test water used in the agglutination test apparatus 9, in addition to the humic acid reagent added to seawater, a monosaccharide (glucose, fructose, mannose, etc.) may be added as an alternative to a dissolved low molecular polysaccharide of 20 kDa or less. It is also possible to use a medium for marine bacteria as an alternative to the organic nitrogen component.

  Next, the control device 10 includes (1) a minute dissolved polysaccharide having a molecular weight of 20 kDa or less, and (2) an organic material, which is contained in the treated water that is the raw seawater obtained from the separating device 7 and the treated water after the aggregation treatment. The calculation of the flocculant injection rate to be fed from the flocculant reservoir 8 to the flocculant processing device 3 based on the concentration of the state nitrogen component will be described. As described above, information indicating the correlation between the concentration of a minute dissolved polysaccharide having a molecular weight of 20 kDa or less and the coagulant injection rate, and information indicating the correlation between the concentration of the organic nitrogen component and the coagulant injection rate are stored in the control device 10. Are stored in the storage device 11.

The control device 10 receives the analysis result 18 by the analyzer 7 for the treated water 1 taken from the intake tank 2 and taken in via the branch pipe 16. Here, the analysis result 18 includes the concentration of a minute dissolved polysaccharide (analytical component A) having a molecular weight of 20 kDa or less contained in the water 1 to be treated and the organic nitrogen component (analytical component B) contained in the water 1 to be treated. Concentration is included. When obtaining the optimum coagulant injection rate Y from the two concentrations of the analysis component A and the analysis component B, first, the optimum value of the coagulant injection rate corresponding to each analysis component is determined. That is, for analysis component A, the optimum aggregation injection rate is obtained from the aggregation pattern shown in FIG. The agglomeration pattern shown in FIG. 3 shows the characteristics of the analysis component A by increasing the addition amount of the flocculant by a predetermined interval n times with respect to the test water having different concentrations of the analysis component A contained in the seawater before adding the flocculant. It is stored in the storage device 11 as a curve f (Y _A ). At f (Y _A ) at that time, the flocculant injection rate at which dX / dY _A = 0 is calculated. The condition that dX / dY _A = 0 means that the aggregation removal rate of the analysis component A does not increase even if the injection amount of the flocculant is further increased, and the optimum addition amount of the flocculant described in FIG. It corresponds to the value. If the concentration of the analysis component A continues to decrease even if the flocculant injection rate is continuously increased, the flocculant injection rate at the time when the threshold value of the concentration of the analysis component A set in advance is reached. Use the optimum value. Similarly, for the analysis component B, the optimum value of the flocculant injection rate is obtained.

  Subsequently, after the optimum values of the respective coagulant injection rates are defined as YA (analytical component A) and YB (analytical component B), for example, a new Yc is obtained from the relationship such as the following equation (1). become.

Yc = a · YA + b · YB (1)
a: Weighting factor of component A, b: Weighting factor of component B, where a + b = 1
The weighting factors a and b are set based on the importance of the analysis component A and the analysis component B. In this embodiment, the importance of the analysis component A is higher than the importance of the analysis component B.

  In this example, the case where the optimum value Yc of the flocculant injection rate is determined based on the concentrations of two components of a minute dissolved polysaccharide (analytical component A) having a molecular weight of 20 kDa or less and an organic nitrogen component (analytical component B) is described. did. When the optimum value of the flocculant injection rate is obtained based on the concentration of the three components of humic substance (analytical component C) in addition to the above two components, the optimum value of the flocculant injection rate obtained from the aggregation pattern shown in FIG. It ’s fine. Therefore, when n analysis components are used, the optimum value of the flocculant injection rate may be obtained by the following equation (2).

Y = n1 / Y1 + n2 / Y2 + ... + nn / Yn (2)
The weighting coefficient of the component Yi (i = 1, 2,..., Nn) may be set according to the importance of the analysis component as in the equation (1), and the aggregation pattern for each analysis component is determined by the aggregation test device 9. Set by getting.

  FIG. 2 is a conceptual diagram showing a coagulant injection control procedure in the desalination system shown in FIG. In FIG. 2, the analysis device 7 and the control device 10 shown in FIG. 1 are each provided as two figures, but this is for easy understanding and is processed through the branch pipe 16 and the branch pipe 17. The analyzer 7 for taking in water is the same.

  In FIG. 2, the water to be treated 1 is taken into the analyzer 7 via the on-off valve 40 and the branch pipe 16 and analyzed for the above-described analysis items. The analysis device 7 transmits the analysis result for the treated water 1 to the control device 10. In addition, a predetermined amount of ferric chloride flocculant is injected from the flocculant storage tank 8 through the control valve 43 into the water to be treated 1 sent to the flocculation treatment apparatus 3 via the pipe 12, and the rapid stirring tank 31. In the slow stirring tank 32 and the precipitation tank 33, the stirring is performed. In the rapid stirring tank 31, the water to be treated 1 and the ferric chloride flocculant are stirred by a stirrer (not shown), and flocs are formed by agglomeration reaction. Thereafter, the water to be treated after the coagulation treatment in the rapid stirring tank 31 is sent to the slow stirring tank 32 and stirred, and then sent to the precipitation tank 33, and the formed floc is removed. The rapid stirring tank 31 and the slow stirring tank 32 are provided with a stirrer (not shown) including a stirring blade and a motor for driving the stirring blade, and the rotational speed of the motor for driving the stirring blade in the rapid stirring tank 31 is set. The rotation speed of the motor that drives the stirring blade in the slow stirring tank 32 is set higher. This is because the impurities such as organic matter in the water 1 to be treated are trapped in the ferric chloride flocculant by rapid stirring to form a floc, and then slowly trapped by the ferric chloride flocculant. This is for growing flocs while preventing the separation of impurities.

  The water to be treated that has been subjected to the agglomeration treatment in the rapid stirring tank 31, the slow stirring tank 32, and the settling tank 33 is taken into the analyzer 7 through the on-off valve 40 and the branch pipe 17, respectively, and analyzed for the above-described analysis items. . Further, the control device 10 injects the flocculant based on the analysis result of the water to be treated transmitted from the analysis device 7 and the aggregation patterns shown in FIGS. 3 and 4 obtained in advance by the aggregation test device 9 and stored in the storage device 11. The optimum value 51 of the rate is obtained. The optimum value 51 of the obtained flocculant injection rate, the concentration of minute dissolved polysaccharides having a molecular weight of 20 kDa or less, and the concentration of organic nitrogen component 52 included in the analysis result of the water to be treated after the aggregation treatment by the aggregation treatment device 3 Based on this, the flocculant injection rate is determined.

  Subsequently, the coagulant to be injected from the coagulant storage tank 8 to the coagulation treatment device 3 based on the flow rate of the water to be treated 1 fed from the intake tank 2 measured by the flow meter 41 and the determined coagulant injection rate. And the opening degree of the control valve 43 is set so that the set injection amount is obtained. As a result, the flocculant is injected from the flocculant reservoir 8 through the control valve 43 into the flocculant processing device 3. Here, a flow meter 42 is provided between the flocculant storage tank 8 and the control valve 43. If the injection amount of the flocculant is changed in a state where the flocculant is injected from the flocculant storage tank 8 to the flocculant treatment device 3, the flow rate measured by the flow meter 42 and the set injection amount are set. The opening degree of the control valve 43 can be corrected according to the difference.

  In addition, when the analysis result of minute dissolved polysaccharides having a molecular weight of 20 kDa or less and organic nitrogen components contained in the water to be treated after the aggregation treatment, correction of the aggregation pattern shown in FIGS. 3 and 4 is necessary. , Stirring strength of a stirrer (not shown) provided in the agglomeration processing device 3 (property values such as the rotation speed of the stirring blade, the area of the stirring blade), water quality of the water to be treated, and each device constituting the desalination system 100 The agglomeration test apparatus 9 executes the above-described processing based on the data, newly creates an agglomeration pattern, and can be transmitted to the control apparatus 10.

  In this example, information indicating the correlation between the coagulant injection rate and the concentration of a minute dissolved polysaccharide having a molecular weight of 20 kDa or less, information indicating the correlation between the coagulant injection rate and the organic nitrogen component, the coagulant injection rate and humin The information representing the correlation with the quality concentration is determined in advance by the agglutination test apparatus 9, but the present invention is not limited to this. For example, the analysis apparatus 7 adds an artificial component 53 to the water 1 to be treated, a humic acid reagent, and a monosaccharide (glucose, fructose, mannose, etc.) as an alternative to a dissolved low-molecular polysaccharide of 20 kDa or less to seawater. A culture medium for marine bacteria may be used as an alternative to the state nitrogen component, and processing may be performed in the same manner as the aggregation test apparatus 9 so as to obtain the aggregation pattern shown in FIGS. 3 and 4 described above.

  In addition, the agglomeration processing apparatus 3 is configured such that the rapid stirring tank 31, the slow stirring tank 32, and the precipitation tank 33 are arranged in series. However, the present invention is not limited thereto, and the aggregation processing apparatus 3 is configured by one stirring tank. May be.

  To understand the basic properties of raw seawater other than the analysis of the above-mentioned specific components (1) minute dissolved polysaccharides with a molecular weight of 20 kDa or less, (2) organic nitrogen components, and (3) humic substances Items analyzed during normal operation (turbidity, pH, SDI value, etc.) may be measured at any time.

  According to the present example, the flocculant injection rate is determined according to the concentration of minute dissolved polysaccharides and organic nitrogen components having a molecular weight of 20 kDa or less in the water to be treated, which cause biofouling in the reverse osmosis membrane module 6. A desalination system that can be set optimally and can suppress bio-fouling can be realized.

  In addition, according to this example, the flocculant injection rate can be set based on the concentration of humic substances in addition to the concentration of minute dissolved polysaccharides and organic nitrogen components having a molecular weight of 20 kDa or less in the water to be treated. Biofouling can be suppressed.

  Moreover, according to the present Example, the desalination system which considered the chemical | medical agent cost can be operated by using a pH adjuster and a flocculant together.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace the configurations of other embodiments with respect to a part of the configurations of the embodiments.

DESCRIPTION OF SYMBOLS 1 Water to be treated 2 Intake tank 3 Aggregation treatment device 4 Milety media filter 5 Ultrafiltration membrane 6 Reverse osmosis membrane module 7 Analyzing device 8 Coagulant storage tank 9 Aggregation test device 10 Control device 11 Storage devices 12, 13, 14, 15 Pipe 16, 17 Branch pipe 18 Analysis result 19 Control command 20 Test result 21 Fresh water 22 Concentrated water 23 pH adjuster storage tank 31 Rapid stirring tank 32 Slow stirring tank 33 Precipitation tank 40 Valve 41, 42 Flow meter 43 Control valve 51 , 52 Signal line 53 Artificial component 100 Desalination system

Claims (11)

An aggregating treatment apparatus for injecting an aggregating agent into the water to be treated to agglomerate;
A reverse osmosis membrane module that separates the fresh water from which the salinity has been removed from the water to be treated after the flocculation treatment and the concentrated water in which the salinity is concentrated;
A controller for controlling the aggregating apparatus and the reverse osmosis membrane module;
The said control apparatus controls the injection rate of the said coagulant | flocculant based on the density | concentration of the dissolved low molecular polysaccharide and organic nitrogen component of at least 20 kDa or less contained in the said to-be-treated water. The desalination system according to claim 1,
The said control apparatus controls the injection rate of the said coagulant | flocculant based on the density | concentration of the humic substance contained in the said to-be-processed water, The desalination system characterized by the above-mentioned. The desalination system according to claim 1,
The control device stores information indicating the correlation between the flocculant injection rate and the dissolved low molecular polysaccharide concentration of 20 kDa or less, and information indicating the correlation between the flocculant injection rate and the concentration of the organic nitrogen component And controlling the injection rate of the flocculant based on the measured low-molecular polysaccharide concentration and organic nitrogen component concentration of 20 kDa or less contained in the treated water and the correlation information stored in the storage device A desalination system characterized by that. The desalination system according to claim 3,
A coagulation test device is provided to measure the concentration of dissolved low-molecular polysaccharides and organic nitrogen components of 20 kDa or less contained in the water to be treated after the coagulation treatment when flocculants having different injection rates are added to the water to be treated. Then, a change in the dissolved low-molecular-weight polysaccharide and organic nitrogen component concentration corresponding to the coagulant injection rate is obtained as an aggregation pattern, and the obtained aggregation pattern is stored in the storage device. The desalination system according to claim 4,
The humic acid reagent is added to the water to be treated, and the concentration of humic substances contained in the water to be treated after the flocculation treatment when flocculants having different injection rates are added to the water to be treated is measured. A desalination system characterized in that a change in the concentration of humic substances corresponding to the above is obtained as an aggregation pattern, and the obtained aggregation pattern is stored in the storage device. an aggregating treatment device for injecting an aggregating agent into the water to be treated to which a pH adjuster has been added,
A reverse osmosis membrane module that separates the fresh water from which the salinity has been removed from the water to be treated after the flocculation treatment and the concentrated water in which the salinity is concentrated;
A controller for controlling the aggregating apparatus and the reverse osmosis membrane module;
The said control apparatus controls the injection rate of the said pH adjuster and the said flocculant based on the density | concentration of the dissolved low molecular polysaccharide and organic nitrogen component of at least 20 kDa or less contained in the said to-be-processed water. Desalination system. The desalination system according to claim 6,
The said control apparatus controls the injection rate of a pH adjuster so that the pH of the said to-be-processed water may be in the range of 6-7. The desalination system according to claim 7,
The control device includes information indicating a correlation between the injection rate of the flocculant and the pH adjuster and the dissolved low molecular polysaccharide concentration of 20 kDa or less, the injection rate of the flocculant and the pH adjuster, and the organic nitrogen component. A storage device for storing information representing the correlation between the concentrations, the dissolved low molecular polysaccharide concentration of 20 kDa or less and the organic nitrogen component concentration contained in the measured water to be treated, and the correlation information stored in the storage device The desalination system characterized by controlling the injection rate of the flocculant and the pH adjuster based on the above. In the desalination system of Claim 1 or Claim 6,
The agglomeration apparatus comprises a rapid stirring tank, a slow stirring tank and a precipitation tank arranged in series,
The desalination system characterized in that the stirring intensity of the rapid stirring tank is set higher than the stirring intensity of the slow stirring tank. A control method for a desalination system, in which a flocculant is injected into water to be treated and the water to be treated is separated into fresh water from which salt has been removed by a reverse osmosis membrane module and concentrated water in which the salt has been concentrated. ,
Measure the concentration of dissolved low molecular polysaccharides and organic nitrogen components of 20 kDa or less contained in the water to be treated,
According to the measured concentrations of the dissolved low molecular weight polysaccharide and the organic nitrogen component, the injection rate of the flocculant to be injected into the water to be treated is obtained, and the flocculant having the obtained injection rate is added to the water to be treated. A control method for a desalination system, characterized in that a coagulation treatment is performed. In the control method of the desalination system of Claim 10,
A flocculant having a different injection rate is added to the water to be treated to perform a coagulation treatment, and the concentrations of the dissolved low-molecular polysaccharides and organic components of 20 kDa or less contained in the water to be treated after the coagulation treatment are measured,
Holding the obtained flocculant injection rate and the aggregation pattern representing the correlation between the dissolved low-molecular-weight polysaccharide of 20 kDa or less and the concentration of organic nitrogen component,
Control of a desalination system characterized in that the injection rate of a flocculant is determined based on the measured concentration of dissolved low molecular polysaccharides and organic nitrogen components of 20 kDa or less and the organic nitrogen component contained in the water to be treated. Method.

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