WO2013129111A1

WO2013129111A1 - Water production method

Info

Publication number: WO2013129111A1
Application number: PCT/JP2013/053395
Authority: WO
Inventors: 千智勲; 花田茂久; 高畠寛生
Original assignee: 東レ株式会社
Priority date: 2012-02-29
Filing date: 2013-02-13
Publication date: 2013-09-06
Also published as: JPWO2013129111A1

Abstract

This water production method involves processing water to be processed using a semi-permeable membrane and separating said water into a permeate and a concentrate, and is characterized in that, when cleaning the semi-permeable membrane and/or infusing the water to be processed with a chemical agent, the concentrate is periodically filtered using a filter that is able to capture solids, and after filtering has been carried out, when an operating reference index, derived from at least one index selected from a group comprising a filter performance index, the amount of adhesion on the filter and the filter color, has reached a preset prescribed reference value, the semi-permeable membrane is cleaned, or conditions for cleaning the semi-permeable membrane and/or conditions for infusing the chemical agent are strengthened. When a membrane is used to obtain fresh water by desalinating seawater or brine, etc. using a membrane, or when reclaimed water is obtained by purifying treated sewage water or industrial wastewater, etc., this water production method allows the progression of fouling at the membrane surface to be easily grasped before operating data for the membrane appears.

Description

Fresh water generation method

The present invention relates to a fresh water generation method for obtaining fresh water by performing desalination of seawater, brine, or the like using a membrane, or purifying sewage wastewater treated water or industrial wastewater to obtain reused water. .

A desalination system using a semipermeable membrane is applied in many industries and water treatment fields, including seawater desalination, and has advantages in terms of separation performance and energy efficiency compared to other separation methods. Has been demonstrated. On the other hand, in the fresh water generation system, microorganism growth on the membrane surface, biofilm adhesion on the membrane surface, inorganic scale adhesion on the membrane surface, or organic matter adhesion on the membrane surface, that is, fouling. Therefore, there is a problem that the membrane differential pressure rises rapidly and the permeability and separation of the membrane are lowered.

When membrane differential pressure increases due to fouling or membrane permeability and separability decrease, it is common to perform chemical cleaning in which the membrane is cleaned using a cleaning agent. Examples of the detergent include chelating agents such as citric acid, sodium hydroxide, ethylenediamine-4-acetic acid (EDTA), and surfactants, and these are used alone or in combination.

However, once fouling has progressed, even if chemical cleaning is performed, the membrane differential pressure, permeability, and separation properties are not completely recovered, and the frequency of chemical cleaning gradually increases, eventually becoming inoperable. Membrane exchange is required. Therefore, it is important to clean the membrane at an appropriate stage before fouling progresses to suppress the progress of fouling.

As a means for suppressing the progress of fouling, when the fouling substance is an inorganic scale, there is a method of adding a scale inhibitor such as sodium hexametaphosphate (SHMP) to the water to be treated. In the case where the fouling substance is a biofilm, many techniques for adding an agent (hereinafter referred to as “bactericidal agent”) that suppresses the growth of the biofilm to the water to be treated have been proposed as effective techniques. For example, a bactericidal agent containing 2-methyl-4-isothiazolin-3-one or 5-chloro-2-methyl-4-isothiazolin-3-one and a salt thereof as an active ingredient is added to the water to be treated. A method for suppressing the growth of biofilm (Patent Document 1) and a method for adding acid or silver ion as a bactericide to water to be treated are disclosed (Patent Documents 2 and 3). If the concentration, frequency, time, and the like at the time of adding these scale inhibitor and bactericidal agent are too small, the progress of fouling cannot be suppressed. On the other hand, if the concentration, frequency, time, and the like of the drug are too high, the progress of fouling can be suppressed, but the drug cost increases. Therefore, it is important to grasp the proper concentration, frequency, and time when adding a drug for suppressing the progress of fouling.

For this purpose, there is a technology for determining the conditions for membrane cleaning or chemical addition by grasping the progress of fouling on the membrane surface before it appears in the membrane operation data such as membrane differential pressure, permeability and separation. is necessary. As such a technique, in Patent Document 4, reverse osmosis membrane supply water and / or reverse osmosis membrane non-permeate water is flowed at a linear velocity equivalent to the non-permeate water linear velocity in the reverse osmosis membrane module of the reverse osmosis membrane filtration unit. A biofilm-forming substrate is placed under the conditions, and the amount of biofilm on the biofilm-forming substrate is measured by the ATP measurement method once a day to 6 months, There is disclosed a technique for determining a film cleaning condition and a disinfectant addition condition so that an ATP amount per unit surface of a material is 200 pg / cm ² or less.

JP-A-8-229363 JP-A-12-354744 Japanese Patent Laid-Open No. 10-463 International Publication WO2008 / 038575 Pamphlet

However, the technology of Patent Document 4 can basically deal only with fouling by biofilm (biofouling), and adhesion of inorganic scale to the membrane surface (inorganic fouling), other than biofilm to the membrane surface It is not possible to cope with the adhesion of organic matter (organic matter fouling). In addition, the reverse osmosis membrane supply water and / or the reverse osmosis membrane non-permeate water must always be run at a linear velocity equal to the non-permeate water linear velocity in the reverse osmosis membrane module. If the linear velocity deviates greatly, there is a risk that a valid evaluation cannot be performed.

The present invention provides a means by which the progress of fouling on the membrane surface can be easily grasped before it appears in membrane operation data such as membrane differential pressure, permeability, and separability.

In order to solve the above problems, the fresh water generation method of the present invention has any one of the following configurations.

(1) In a fresh water generation method of treating water to be treated with a semipermeable membrane and separating it into permeated water and concentrated water, when cleaning the semipermeable membrane and / or injecting a chemical into the water to be treated, The concentrated water is periodically filtered with a filter capable of trapping solid matter, and is derived from at least one index selected from the group consisting of the performance index of the filter, the amount of deposit on the filter, and the color of the filter when filtered. When the operation standard index reaches a predetermined reference value set in advance, the semipermeable membrane is washed or the semipermeable membrane washing condition and / or the chemical injection condition are strengthened Method.
(2) The fresh water generation method according to (1), wherein the performance index of the filter is at least one selected from the group consisting of a pressure value during constant flow filtration and a filtration resistance value during constant flow filtration.
(3) The performance index of the filter is the reciprocal value of the filtration flow rate value when a constant pressure is applied, the reciprocal value of the amount of water filtered during a predetermined time when the constant pressure is applied, and the constant pressure value The fresh water generation method according to (1), which is at least one selected from the group consisting of a time required for filtering a predetermined amount of water and a filtration resistance value of the filter when a constant pressure is applied.
(4) The fresh water generation method according to (1), wherein the performance index of the filter is an SDI value defined by ASTM D4189-95.
(5) A group in which the deposit amount index on the filter is composed of a microorganism amount, an inorganic solid amount, an organic matter amount, a ratio between an inorganic solid matter amount and an organic matter amount, a ratio between an inorganic solid matter amount and a microorganism amount, and a ratio between a microorganism amount and an organic matter amount. The fresh water generation method according to (1), which is at least one selected from:
(6) The fresh water generation method according to (5), wherein the amount of the microorganism is a value obtained by an ATP measurement method.
(7) The color index of the filter is a color difference defined in JIS Z 8730: 2009 between the filter before filtration and the filter after filtration, and the filter after filtration The fresh water generation method according to (1), which is at least one index selected from the group consisting of reciprocal values of whiteness defined in JIS P 8148: 2001.
(8) Further, the semipermeable membrane feed water supplied to the semipermeable membrane is regularly filtered with a filter capable of capturing solid matter, and the performance index of the filter, the amount of deposits on the filter, and the filter when filtered Y is at least one index selected from the group consisting of the following colors: at least one index selected from the group consisting of the performance index of the filter, the amount of deposits on the filter, and the color of the filter when the concentrated water is filtered A value calculated from X and Y when X is used as an operation reference index, and when the predetermined reference value is reached, the semipermeable membrane is cleaned, or the semipermeable membrane cleaning conditions And / or the fresh water generation method according to any one of (1) to (7), wherein the drug injection conditions are strengthened.
(9) When the concentrated water is filtered, the value of at least one index selected from the group consisting of the performance index of the filter, the amount of deposits on the filter and the color of the filter is X, and the semipermeable membrane feed water is filtered XY, where Y is the value of at least one index selected from the group consisting of the performance index of the filter, the amount of deposits on the filter, and the color of the filter, and Re is the recovery rate of the treatment with the semipermeable membrane / The calculation value obtained from the formula of (1-Re) is used as an operation reference index, and when it reaches a predetermined reference value, the semipermeable membrane is cleaned, or the semipermeable membrane cleaning conditions and (5) The method for producing fresh water according to (8).

According to the present invention, it is not limited to the types of fouling such as bio-fouling, inorganic fouling, and organic fouling, and the fouling progress state on the membrane surface is determined by the operation of the membrane such as membrane differential pressure, permeability and separation. It is possible to grasp before appearing in the data. Moreover, since the operation | work which filters concentrated water with a filter is main, operation is also easy.

It is the schematic which shows an example of the fresh water generation method of this invention. It is the schematic which shows another example of the fresh water generation method of this invention. It is the schematic of the SDI measuring apparatus used in the Example. It is a figure in the comparative example 1 which shows the time-dependent change of the SDI of semipermeable membrane feed water, SDI of concentrated water, and the operation | movement differential pressure of a semipermeable membrane. It is a figure which shows the time-dependent change of the operation | movement differential pressure | voltage of SDI of concentrated water and a semipermeable membrane in Example 1. FIG. It is a figure which shows the time-dependent change of the operation | movement differential pressure | voltage of SDI of concentrated water and a semipermeable membrane in Example 2. FIG.

Hereinafter, the present invention will be described in detail with reference to FIG. 1, but the content of the present invention is not limited to the embodiment shown in this figure.

The fresh water generation method of the present invention is carried out in a fresh water generation system in which treated water 1 is treated by a semipermeable membrane 3 and separated into permeated water 4 and concentrated water 5.

Examples of the treated water 1 include seawater, river water, lake water, ground water, sewage, sewage secondary treated water, and the like. Normally, the water 1 to be treated contains solid components such as turbidity, so when the water 1 to be treated is directly filtered through the semipermeable membrane 3, the solid components adhering to the membrane surface increase, and the differential pressure is increased. It soars and it becomes impossible to drive. Therefore, it is common to pre-process the for-treatment water 1 beforehand. The most commonly used pretreatment method is a flocculating sand filtration method in which a flocculant is added to the water 1 to be treated, the solid components are flocked, and filtered with sand or anthracite. However, since this method is easily affected by fluctuations in raw water and the quality of treated water is unstable, a membrane pretreatment for treating the water to be treated 1 with a microfiltration membrane or an ultrafiltration membrane can also be employed as a pretreatment. . Moreover, when the to-be-processed water 1 is organic wastewaters, such as a sewage, the pretreatment which performs solid-liquid separation in order to isolate | separate activated sludge after performing activated sludge treatment in order to reduce the organic matter contained in wastewater Can also be implemented. The solid-liquid separation method may be precipitation separation using a conventionally used sedimentation basin, or a solid-liquid separation method using a separation membrane such as a microfiltration membrane or an ultrafiltration membrane may be employed.

The pretreated water to be treated is supplied to the semipermeable membrane 3 by a high pressure pump 2 at a pressure required for filtration, and separated into permeated water 4 and concentrated water 5. In addition, after pre-processing, the to-be-processed water before supplying to the semipermeable membrane 3 may be called semipermeable membrane supply water.

As the semipermeable membrane 3, any material may be used as long as the salt concentration can be lowered so that the treated water 1 can be used for drinking water, industrial water, city water, etc. For example, a cellulose acetate type semipermeable membrane and a polyamide type semipermeable membrane are mentioned. Among these, a polyamide-based semipermeable membrane is particularly effective in the method of the present invention. Polyamide-based membranes are less resistant to chlorine, the most commonly used disinfectant to prevent biofilm growth, and even at low concentrations of chlorine, membrane degradation occurs significantly, preventing biofouling Difficult to do. Therefore, the effect by implementing this invention appears notably.

When injecting the chemical | medical agent 10 into the to-be-processed water 1 in order to suppress advancing of the fouling in the semipermeable membrane 3, the chemical | medical agent 10 is added from the middle of supply piping, as FIG. 1 shows. The apparatus for adding the drug 10 preferably includes a control mechanism having a valve and a pump that can control the addition amount, the addition time, the addition frequency, and the like in order to control the addition conditions of the drug.

Similarly, in order to suppress the progress of fouling in the semipermeable membrane 3, when the semipermeable membrane 3 is chemically washed, the cleaning agent 11 is introduced from a pipe line provided upstream of the semipermeable membrane 3. Thus, chemical cleaning is performed. Although the point which introduce | transduces the cleaning agent 11 is not specifically limited, Since there exists a possibility of corroding the high pressure pump 2 depending on the kind of the cleaning agent 11, the downstream is preferable. Usually, the cleaning agent 11 is led out from the middle of the pipe of the concentrated water 5 and circulated.

In order to determine the conditions for membrane cleaning or chemical addition, it is necessary to know the fouling progress on the membrane surface before it appears in the membrane operation data such as membrane differential pressure, permeability, and separation. . When fouling effects appear in membrane operation data, fouling has already progressed excessively, and even if membrane cleaning or chemical addition is performed, fouling cannot be completely removed. This will adversely affect the operation of the membrane, such as an increase in the operating pressure of the membrane. On the other hand, when the membrane is excessively washed or the drug is added excessively, the progress of fouling can be suppressed, but not only the cost is increased but also the membrane is deteriorated.

Fouling is microbial growth on the membrane surface, biofilm adhesion on the membrane surface, inorganic scale adhesion on the membrane surface, or organic matter adhesion on the membrane surface. Therefore, when the fouling progresses to some extent, the biofilm, inorganic scale, or organic matter adhering to the membrane surface is peeled off by the flow of water on the membrane surface, and these solid matters are mixed into the concentrated water. .

Therefore, the inventors examined whether or not the concentrated water 5 in the fresh water generation system used in the present invention can be regularly used as an index for determining the conditions for membrane cleaning or chemical addition. However, the concentrated water contains impurities. Especially when the water to be treated is seawater, the concentrated water contains a large amount of salinity. Could not do. As a result of further studies, the inventors do not directly measure the concentrated water, but once filter the concentrated water with a filter and measure the characteristics of the filtered filter or the substance collected on the filter. Thus, the inventors have found that a highly reliable index can be measured for the progress of fouling by eliminating the influence of impurities in the concentrated water, and the present invention has been achieved.

In the fresh water generation system used in the present invention, the concentrated water 5 is periodically filtered by a filtering means 6 equipped with a filter capable of capturing solid matter. When the filter is filtered, an operation standard index derived from at least one index selected from the group consisting of the performance index of the filter, the amount of deposits on the filter, and the color change value of the filter reaches a predetermined standard value set in advance. At this time, the semipermeable membrane 3 is cleaned, or the cleaning conditions for the semipermeable membrane and / or the injection conditions for the drug 10 are strengthened. By filtering the concentrated water 5 through a filter, it is possible to grasp the progress of fouling by detecting the presence of solids contained in the concentrated water.

Components in water are divided into suspended components, colloidal components and dissolved components according to their dimensions. Among these, the solid substance in the present invention represents a suspended component and a colloid component. Therefore, the pore size of the filter provided in the filtering means 6 is not particularly limited as long as the solid matter can be captured, but in consideration of the dimensions of the suspended component and the colloidal component, 0.01 to It is preferably 5 μm. If a filter with a large pore size is used, the filtration speed is increased and the working time is shortened. However, there is a possibility that the solid matter that cannot be captured increases and the detection of fouling is delayed. On the other hand, if a filter with a small pore diameter is used, solid matter that cannot be captured is reduced and the fouling detection reliability is increased, but the filtration speed is slowed down and the working time is lengthened. Which hole diameter should be selected may be appropriately determined by those skilled in the art according to the purpose and allowable work.

The material of the filter is not particularly limited. For example, when the amount of deposit on the filter is evaluated by the amount of inorganic solid or organic matter, the filter is heated to about 600 ° C. to volatilize the organic matter. In this case, a filter that can withstand a temperature of about 600 ° C., for example, a glass fiber filter is desirable.

In the present invention, when the concentrated water is filtered with such a filter, (a) the performance index of the filter, (b) the amount of deposit on the filter, and (c) the operation standard index derived from the index selected from the color of the filter , Grasp the progress of fouling. The indices (a) to (c) will be described below.

First, (a) the performance index of the filter refers to an index selected from various measured values representing the performance of the filter, such as a flow rate value, a pressure value, and a resistance value when concentrated water passes through the filter. The performance index includes pressure value during constant flow filtration, filtration resistance value during constant flow filtration, filtration flow value when constant pressure is applied, amount of water filtered during a predetermined time when constant pressure is applied, constant An index selected from the group consisting of the time required to filter a predetermined amount of water when pressure is applied and the filtration resistance value of the filter when constant pressure is applied is preferred. As long as it shows the performance of passing through. In addition, as a driving | operation reference parameter | index, the said value may be used directly and the value (for example, change speed etc.) calculated using the said value may be used.

The performance index of the filter is measured as follows, for example. As shown in FIG. 1, after the concentrated water 5 separated by the semipermeable membrane 3 is adjusted to a constant flow rate or pressure by a flow rate adjusting means (or pressure adjusting means) 7, it is applied to a filtering means 6 equipped with a filter. Introduce. The pressure value or flow rate value of the concentrated water when being filtered by the filtering means 6 is measured by the pressure measuring means 8 or the flow rate measuring means 9. Also, prepare a measuring device connected by piping in the order of water tank, pump, valve, pressure gauge and filter, put concentrated water into the water tank, supply it to the filter using the pump, and between the pump and filter Using a certain pressure gauge, it is possible to measure the pressure value or flow rate value of the concentrated water by performing filtration while adjusting the valve so that the concentrated water can be filtered at a constant pressure or a constant flow rate.
The filtration resistance value can be obtained from the pressure difference, the viscosity coefficient, and the flow rate by the following equation.
R = ΔP / (μ × (Q / A))
here,
R: Filtration resistance value [1 / m]
ΔP: Concentrated water pressure difference [Pa]
μ: viscosity coefficient of concentrated water [Pa · s]
Q: Flow rate of concentrated water [m ³ / s]
A: The filter area [m ² ].

Also, to filter the reciprocal value of the filtration flow value when a constant pressure is applied, the reciprocal value of the amount of water filtered during a predetermined time when a constant pressure is applied, and the predetermined water amount when a constant pressure is applied The time required, the filter filtration resistance value when a constant pressure is applied, and the like can also be used as indicators.

(A) It is particularly preferable to use the SDI value defined by ASTM D4189-95 as the performance index of the filter. SDI is an abbreviation of Silt Density Index, and is one of values calculated based on the time required to filter a predetermined amount of water when a certain pressure is applied. SDI is specified by ASTM D4189-95 (Standard Test Method for Silt Density Index of Water D4189-95) as a semi-permeable membrane feedwater monitoring index.

SDI is calculated by the following calculation formula.
SDI = (1−T ₀ / T ₁₅ ) × 100/15
here,
T ₀ : Time (seconds) required for filtering a sample at a pressure of 206 kPa using a membrane filter having a pore diameter of 0.45 μm and a diameter of 47 mm and filtering an initial sample of 500 ml
T ₁₅ : Time (seconds) required to continue filtering for 15 minutes after T ₀ and filter 500 ml of sample from that point.

The SDI value is a value from 0 to 6.66, and the larger the value, the greater the degree of contamination of the sample. In general, after pretreatment of raw water such as seawater and sewage, the SDI of the water to be treated supplied to the semipermeable membrane is preferably 4 or less. SDI is an index that is generally measured in the operation of a semipermeable membrane, and is an operation that is easy for an operator to learn. Therefore, when SDI is used as an index, the progress of fouling can be easily grasped. It becomes possible. The SDI value can be used as an operation reference index as it is, or the SDI change rate can be calculated and used.

Next, (b) the amount of deposits on the filter is the amount of substances deposited on the filter after filtering the concentrated water. For example, the filter after filtering concentrated water is dried, a weight is measured, and the amount of adhering matter can be calculated | required from the difference with the weight of the filter before filtration. Moreover, the filter after filtering can be immersed in pure water etc., and the method of measuring the turbidity, transparency, light absorbency, etc. of the immersed solution can also be used.

The index of the amount of deposit is preferably at least one selected from the group consisting of the amount of microorganisms, the amount of inorganic solids, and the amount of organic matter. Biofouling can be grasped by measuring the amount of microorganisms, inorganic fouling can be grasped by measuring the amount of inorganic solid matter, and organic fouling can be grasped by measuring the amount of organic matter.

Furthermore, the ratio between the amount of inorganic solids and the amount of organic matter, the ratio between the amount of inorganic solids and the amount of microorganisms, or the ratio between the amount of microorganisms and the amount of organic matter can be used as an indicator of the amount of deposits. Thereby, when a plurality of fouling selected from bio fouling, inorganic fouling, and organic fouling occur at the same time, it is possible to determine mainly what kind of fouling has occurred.

These values can also be used as driving standard indicators as they are, and the rate of change can be calculated and used.

The microbial amount represents the amount of bacteria, its metabolite polysaccharides and proteins, its dead bodies, and its constituent nucleic acids. Therefore, various methods for measuring the amount of microorganisms are conceivable, and examples include quantification using protein, sugar, nucleic acid, total bacterial count, viable count, ATP, and the like. Among these, the ATP measurement method is particularly preferable because it is excellent in sensitivity, simplicity, and rapidity, and portable kits and reagents are commercially available.

Quantification of proteins, sugars, and nucleic acids requires equipment such as an absorptiometer and a fluorescence analyzer, and uses a strongly alkaline, strongly acidic, or mutagenic reagent. It's hard to say. In addition, there is an agar culture method in which deposits on a filter are suspended in a liquid, and culturable microorganisms are counted as colonies using the suspension. However, only culturable microorganisms can be cultured and counted. Therefore, there is a problem that the total number of microorganisms cannot be evaluated. Moreover, in order to evaluate the amount of microorganisms by this method, many equipments and facilities are required, and further, there are problems that it takes a number of days to culture and cannot be evaluated quickly. Although a method of directly counting the number of bacteria using a microscope is also conceivable, it is difficult to disperse the bacteria, and counting is also a laborious operation.

The ATP measurement method, on the other hand, extracts ATP (adenosine-5'-triphosphate), which is an energy substance of life activity of all living organisms, from microbial cells and emits light using luciferase, a firefly luminescent enzyme. The light emission amount (RLU: Relative Light Unit) is measured. Since the amount of luminescence is proportional to the amount of ATP, the amount of microorganisms can be evaluated by measuring the amount of luminescence. The reaction proceeds in the presence of the substrates ATP, luciferin, oxygen, luciferase and coenzyme magnesium ions, and light is generated. The measurement time is as short as a few minutes, and kits for measuring reagents are commercially available. Also, a luminescence photometer device is commercially available that has high detection sensitivity and is portable while being detectable at a concentration of 1 pg / cm ³ .

The method for measuring the amount of ATP from the deposit on the filter is not particularly limited as long as it is a quantitative method. For example, the deposit on the filter is collected with a cotton swab and suspended in pure water. In addition, there is a method of measuring using a commercially available ATP measuring reagent and a luminescence photometer device.

As a method of measuring the amount of inorganic solid matter, for example, a method of measuring the weight of a filter after volatilizing organic matter by heating the filter after filtration to about 600 ° C., and obtaining from the difference from the weight of the filter before filtration There is. It can also be measured by immersing the filter in an acid such as hydrochloric acid or nitric acid or pure water, and analyzing the amount of the inorganic substance in the immersion liquid by ICP or the like. In the analysis by ICP or the like, since it is possible to obtain information on which substances occupy most of the inorganic substances, it is possible to select a drug corresponding to each substance.

As a method for measuring the amount of organic matter, for example, the filtered filter is dried and weighed, and then the filter is heated to about 600 ° C. to volatilize the organic matter, and then the weight of the filter is measured. There is a method for obtaining the difference by calculating the difference from the weight of the filter before heating to 600 ° C. Also, immerse the filter in sodium hypochlorite, sodium hydroxide or pure water, and analyze the total organic carbon content in the immersion liquid with a TOC meter, or analyze the amount of sugar and protein in the immersion liquid. Can also be measured.

Next, (c) the color difference of the filter before and after the filtration of the concentrated water, the whiteness of the filter after the filtration of the concentrated water, etc. can be used as the color index of the filter.

As the color difference, a chromaticity difference defined in the L ^* a ^* b ^* color system or the L ^* u ^* v ^* color system defined by JIS Z 8730: 2009 can be used. The calculation formula of these color differences is shown below.
ΔE ^* _ab = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ] ^1/2
ΔE ^* _uv = [(ΔL ^* ) ² + (Δu ^* ) ² + (Δv ^* ) ² ] ^1/2
here,
ΔE ^* _ab : L ^* a ^* b ^* Color difference based on the color system ΔL ^* : Difference of L ^* of two filters Δa ^* : Difference of a ^* of two filters Δb ^* : Difference of b ^* of two filters ΔE ^{_{^{^{^{* uv: L * u * v}}}}} * color difference based on the color system Δu ^*: 2 one filter of ^{u *} of the difference Δv ^*: which is the difference between the ^{v *} of the two filters. The color difference can be measured with a commercially available color difference meter.

As the whiteness, the whiteness specified in JIS P 8148: 2001 can be used. Also, it is possible to use the whiteness specified by the international standard ISO 2470-1: 2009 or the international standard ISO 2470-2: 2008 corresponding to JIS P 8148. The whiteness is an index indicating the degree of whiteness of the surface color of pulp or paper, and the test piece is irradiated with diffuse illumination using a diffuse reflectance meter having an integrating sphere (diameter 150 mm), and the degree of whiteness is 0 degrees. The reflected light is received at an angle, and the obtained reflectance (percentage) is expressed numerically. The whiteness can be measured with a commercially available whiteness meter. At this time, the filter before filtration is preferably white. Thereby, whiteness can be used as a more effective index.

In the present invention, the progress state of fouling is grasped by an operation standard index derived from an index selected from the above three indices (a) to (c), and a predetermined standard set in advance by the operation standard index is set. When the value is reached, semi-permeable membrane cleaning is performed or semi-permeable membrane cleaning conditions and / or drug infusion conditions are enhanced. Here, the operation reference index includes a case where an index selected from the above (a) to (c) is directly used and a case where a value obtained from a value of the index using a predetermined calculation formula is used. When the indicator and the fouling progress have a negative correlation, the reciprocal of the value obtained by the measurement is used as the driving reference indicator so that the driving reference indicator and the fouling progress have a positive correlation. This is preferable.

As a result, measures to suppress the progress of fouling can be executed before the influence of fouling appears in the operation data of the membrane, such as membrane differential pressure, permeability and separation. It is possible to maintain the film in a stable state, and as a result, it is possible to make the film last longer.

As a method for cleaning the semipermeable membrane, for example, as described above, chemical cleaning is performed by introducing the cleaning agent 11 from the pipe provided upstream of the semipermeable membrane 3 shown in FIG. Is mentioned. The cleaning agent is usually placed in a cleaning tank or the like, introduced into the piping from the downstream side of the high-pressure pump 2 by a pump, led out from the middle of the piping of the concentrated water 5 and circulated. The cleaning condition depends on the degree of fouling. For example, the cleaning agent is circulated for about 1 hour for cleaning, the circulation is stopped, the semipermeable membrane is immersed in the cleaning agent for 2 to 24 hours, and finally rinsed. To complete the cleaning. In some cases, this operation is repeated 2-3 times.

In addition, as a means for strengthening the cleaning conditions of the semipermeable membrane, in the case of periodically cleaning the semipermeable membrane, a method of increasing the frequency of cleaning and the concentration of the cleaning agent than the preset steady conditions The method of increasing the number is mentioned.

As a method for injecting the medicine, for example, the medicine 10 is added from the middle of the supply pipe shown in FIG. As an injection method, it may be added continuously or intermittently at a frequency such as once a day, but it is usually added continuously. Examples of means for strengthening the drug injection condition include a method of increasing the concentration of the drug added and a method of increasing the frequency of addition, compared to a preset steady condition.

Moreover, by measuring the same index not only for concentrated water but also for semipermeable membrane supply water, and analyzing the relationship between the concentrated water index and the semipermeable membrane supply water index, it becomes clearer about the fouling situation. It is possible to present a driving standard index. For example, when the concentrated water is filtered through a filter, (a) the performance index of the filter, (b) the amount of deposit on the filter, and (c) the value of the index selected from the filter color is X, and the filter is a semipermeable membrane X and Y, where Y is the value of the index selected from (a ′) the performance index of the filter when the feed water is filtered, (b ′) the amount of deposit on the filter, and (c ′) the color of the filter A value calculated from (for example, a calculated value obtained from the formula XY) is used as an operation reference index, and when the predetermined reference value is reached, the semipermeable membrane is cleaned, or the semipermeable membrane Membrane cleaning conditions and / or drug injection conditions can be enhanced.

Also, the progress of fouling can be grasped using the above-mentioned index and a calculated value using the recovery rate of the treatment with the semipermeable membrane as an operation standard index. For example, when the concentrated water is filtered with a filter, (a) the performance index of the filter, (b) the amount of deposit on the filter, and (c) the value of the index selected from the filter color is X, and the filter is a semipermeable membrane Y is the value of the index selected from (a ′) the performance index of the filter when the feed water is filtered, (b ′) the amount of deposits on the filter, and (c ′) the color of the filter. When the recovery rate is Re, the calculated value obtained from the formula XY / (1-Re) is used as an operation standard index, and when the predetermined standard value is reached, the semipermeable membrane is cleaned. Or cleaning conditions and / or drug injection conditions for the semipermeable membrane can be enhanced. As a result, the concentration rate generated by the semi-permeable membrane operation recovery rate can be added to the operation standard index, and the difference between the index obtained from the concentrated water and the index obtained from the semi-permeable membrane feed water can be calculated. By taking into account, it is possible to provide a more accurate operating reference index for fouling.

Also, when (b) the amount of deposit on the filter is used as an index, it is possible to select an appropriate drug or cleaning agent based on the type of deposit on the filter. For example, when a large amount of microorganisms is detected among the deposits on the filter, biofouling is a concern, so it is preferable to select a bactericidal agent as an agent to be injected. As the fungicide, for example, an ingredient selected from 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, salts thereof and mixtures thereof is used as an active ingredient. And bactericides such as 2,2-dibromo-3-nitrilopropionamide (DBNPA) and sulfuric acid.

Of the deposits on the filter, if the amount of inorganic solids is large, select a scale inhibitor as the agent to be injected, or wash the semipermeable membrane with acid as a cleaning agent to remove the inorganic matter. This is preferable because accumulation can be prevented. Examples of the scale inhibitor include sodium hexametaphosphate (SHMP). Examples of the acid used for the membrane cleaning include 2% citric acid and 0.2% hydrochloric acid.

When the amount of organic matter among the deposits on the filter is large, accumulation of organic matter can be prevented by washing the semipermeable membrane using alkali as a cleaning agent. Examples of the alkali used for the membrane cleaning include a 0.1% sodium hydroxide solution.

That is, in the present invention, not only grasping of the fouling itself but also the type of fouling can be detected, so that an appropriate drug or cleaning agent can be selected according to the form of each fouling.

Hereinafter, the present invention will be specifically described. However, the present invention is not limited to the embodiment.

(Comparative Example 1)
Seawater 12 was processed by the processing method as shown in FIG. First, seawater 12 was taken and stored in a seawater storage tank 14. At the water intake point, a maximum of 15 mg / L sodium hypochlorite 13 was added for 30 minutes once every two days in order to suppress microbial growth in the water intake pipe. In addition, the addition concentration of sodium hypochlorite was adjusted so that the free residual chlorine concentration in the semipermeable membrane feed water storage tank 17 to be described later was about 1 mg / L. Next, seawater is pressurized by the supply pump 15 and supplied from the seawater storage tank 14 to the ultrafiltration membrane 16 (polyvinylidene fluoride hollow fiber ultrafiltration membrane, Toray HFU-1010, membrane area: 28 m ² ). Pretreatment of seawater was performed by performing filtration. The filtration flux was 2 m / day.

Seawater pretreated using the ultrafiltration membrane 16 is once stored in the semipermeable membrane feed water storage tank 17, then sent to the high pressure pump 21 by the water pump 18, and pressurized by the high pressure pump 21. It was filtered through a semipermeable membrane 24 and separated into permeated water 25 and concentrated water 26. Since free residual chlorine was contained in the water to be treated between the water pump 18 and the high-pressure pump 21, about 3 mg / L of sodium bisulfite (SBS) 19 was added to remove chlorine. The purpose of adding SBS is to prevent chlorine degradation of the semipermeable membrane due to free chlorine remaining in the water to be treated. As the semipermeable membrane, a spiral type reverse osmosis membrane (TM810C manufactured by Toray) having a membrane material of polyamide, a desalination rate of 99.75%, and a membrane area of 7.8 m ² was operated in series. The operation was set to a membrane filtration flux of 14 L / m ² / hr and a recovery rate of 37%. Here, the recovery rate is calculated by the flow rate of the permeated water 25 / (flow rate of the permeated water 25 + flow rate of the concentrated water 26). Further, during the operation of the semipermeable membrane 24, the pressure difference between the semipermeable membrane supply water 22 and the concentrated water 26 (hereinafter referred to as operation differential pressure) was constantly monitored, and changes in the operation differential pressure were observed. Further, between the high-pressure pump 21 and the semipermeable membrane 24, a conduit for introducing a cleaning agent 23 described later is provided so that chemical cleaning can be performed. A conduit for leading the cleaning agent 23 is provided in the middle of the piping of the concentrated water 26 so that the circulation cleaning can be performed.

In such a semipermeable membrane operation, the SDI of the semipermeable membrane feed water 22 and the SDI of the concentrated water 26 were continuously measured twice a week. The SDI measurement was performed using the SDI measurement apparatus shown in FIG. The SDI measuring device 27 includes a filter holder 28 as a membrane separation means, a holder valve 29, a sample tank 30 (18L × 2 pieces), a compressor 31 as a pressurization means, a pressure adjustment valve 32, a pressure gauge 33, and a filter. It consists of a graduated cylinder 34 for measuring the amount of liquid, a flow meter 35 and the like. The flow meter 35 may or may not be provided as necessary. The filter holder 28 was loaded with a membrane filter (MF-Millipore, HAWP04700F1 manufactured by Millipore) having a pore diameter of 0.45 μm and a diameter of 47 mm. The sample tank 30 was filled with semipermeable membrane feed water 22 or concentrated water 26, pressurized with a compressor 31, adjusted with a pressure control valve 32 to a filtration pressure of 206 kPa, filtered, and measured for SDI. The SDI calculation method is as described above. In Comparative Example 1, the semipermeable membrane was cleaned when the operating differential pressure of the semipermeable membrane reached 150 kPa or more.

FIG. 4 shows changes over time in the SDI of the semipermeable membrane feed water 22, the SDI of the concentrated water 26, and the operation differential pressure of the semipermeable membrane. First, the SDI of the semipermeable membrane feed water 22 hardly changed between 3 and 3.5 during the operation period. Next, the SDI of the concentrated water 26 was about 4 at the beginning, but gradually increased, and after 2 months from the start of operation, almost no filtered water was produced during the SDI measurement, and T ₁₅ could not be measured. (Ie, SDI = 6.66). On the other hand, the operating differential pressure of the semipermeable membrane hardly changed during the initial 2.5 months, but after 2.5 months, the operating differential pressure increased rapidly, and after that, the operating upper limit differential pressure was reached in 0.5 months. (150 kPa) was reached. Therefore, after the cleaning agent 23 (sodium hydroxide aqueous solution, pH = 12) was passed through the semipermeable membrane 24 and cleaned in the order of 1 hour circulation cleaning / 2 hours immersion / 1 hour circulation cleaning, the operation was resumed. The operating differential pressure recovered only to 120 kPa, and then reached the operating upper limit differential pressure again in 0.5 months. This forced replacement of the semipermeable membrane.

(Example 1)
After the experiment of Comparative Example 1 was completed and the semipermeable membrane was replaced, the operation was resumed, and the operation of Example 1 was performed under the same conditions as in Comparative Example 1. However, in Example 1, the timing for performing the membrane cleaning was determined using the SDI measurement result of the concentrated water instead of the operation differential pressure. That is, the operation was performed with the operation standard index as SDI of concentrated water and the standard value as 150% of the initial SDI. As in Comparative Example 1, the SDI of the concentrated water 26 was measured twice a week, and the semipermeable membrane was washed when the SDI of the concentrated water reached 150% of the initial SDI. FIG. 5 shows changes over time in the SDI of concentrated water and the operation differential pressure of the semipermeable membrane. The SDI of concentrated water was initially 3.8, but then gradually increased and reached 150% of 3.8, that is, 5.7 in 1.5 months after the start of operation. The semipermeable membrane was washed. As a result, the SDI of the concentrated water 26 recovered to almost the same value (3.9) as the initial stage. After that, when the SDI of the concentrated water 26 reached 5.7, washing was performed, and the operation was continued for about 10 months. In the meantime, the operation differential pressure of the semipermeable membrane hardly changed and the operation was stable.

(Example 2)
After the operation of Example 1, the operation of Example 2 was performed in the same manner as in Example 1. However, in order to reduce the cleaning frequency of the semipermeable membrane, the addition of the drug 20 was started. As the medicine 20, a bactericide 2,2-dibromo-3-nitrilopropionamide (hereinafter DBNPA) is used, and 10 mg / L of DBNPA is provided 1 to 3 times a week between the water pump 18 and the high-pressure pump 21. Added for 1 hour. In Example 2, as in Example 1, when the SDI of the concentrated water reached 150% of the initial SDI, the semipermeable membrane was cleaned in the same manner as in Comparative Example 1. FIG. 6 shows the time-dependent changes in the SDI of concentrated water and the operation differential pressure of the semipermeable membrane. As the frequency of addition of DBNPA increased, the increase in the SDI of the concentrated water slowed, suggesting that the progress of biofouling is slowing down. This also reduced the frequency of cleaning the semipermeable membrane. Based on these operation results, the addition frequency of the bactericide was determined from cost conditions and the like. Thus, by monitoring the SDI of concentrated water, it was possible to optimize the addition conditions of the bactericide without taking the risk of an increase in the operating differential pressure of the semipermeable membrane.

(Example 3)
After the operation of Example 2, the addition of the drug 20 was stopped again, and the operation of Example 3 was performed in the same manner as in Example 1. In Example 3, when the SDI of the concentrated water was measured, the amount of ATP on the filter after the SDI measurement was continuously measured twice a week.

The ATP amount on the filter was measured according to the following procedure. Three tubes were prepared by dispensing distilled water (Otsuka Pharmaceutical, for injection, 20 mL / piece) into an ATP amount measuring tube ("Lumitube (registered trademark)", manufactured by Kikkoman Co., 3 mL). The adhering matter on the filter was wiped off with one sterilized swab, and the swab from which the adhering matter was wiped was immersed in the water in the first tube for 1-2 minutes, and stirred carefully to obtain a suspension. The swab was sequentially immersed and stirred in the water in the second and third tubes to prepare a three-stage suspension.

For each prepared suspension, 100 μl of the suspension is dispensed into another new “Lumitube (registered trademark)” for measurement, to which 100 μl of ATP extraction reagent is added, and light emission occurs after 20 seconds. After adding 100 μl of the reagent, the amount of luminescence was measured with a portable ATP analyzer “Lumitester (registered trademark)” manufactured by Kikkoman. As the ATP extraction reagent and the luminescent reagent, a dedicated reagent kit “Lucifer (registered trademark) 250 plus” manufactured by Kikkoman Corporation was used. And the amount of ATP was computed from the correlation formula of the amount of ATP and the light-emission amount previously calculated | required by evaluation of the liquid of known ATP density | concentration.

In the measurement, the amount of concentrated water filtered by the filter was calculated from the difference between the weight before filtration and the weight after filtration of the sample tank 30 used in the SDI measurement. Then, the ATP concentration in the concentrated water was determined by dividing the ATP amount by the filtered concentrated water amount.

In Example 3, the operation was performed with the ATP concentration in the concentrated water calculated from the ATP amount on the filter as the operation reference index and the reference value as 10 times the initial ATP concentration. When the ATP concentration in the concentrated water reached 10 times the initial ATP concentration, the semipermeable membrane was washed in the same manner as in Comparative Example 1, and such operation was continued for about 4 months. In the meantime, the operation differential pressure of the semipermeable membrane hardly changed and the operation was stable.

(Example 4)
In the same manner as in Comparative Example 1, permeated water 25 and concentrated water 26 were obtained from seawater 12. During operation, the amount of deposits on the filter after measuring SDI and SDI of concentrated water was measured twice a week. As the amount of deposits on the filter, the amount of ATP, the amount of inorganic solids, and the amount of organic matter were measured. The SDI of concentrated water and the amount of ATP on the filter were measured by the method described above. The amount of inorganic solid and organic matter on the filter was measured by the following procedure. First, the weight (M ₀ ) of the filter before filtration was measured, the filter after filtration was dried, and the weight (M ₁ ) was measured. Thereafter, the weight of the filter (M ₂ ) after the filter was heated to about 600 ° C. to volatilize the organic matter was measured. Inorganic solid content was determined by subtracting the M ₀ from M _2. The amount of organic matter was determined by subtracting M ₂ from M ₁ . Further, in the same manner as in Example 3, in the SDI measurement, the amount of concentrated water filtered through a filter is obtained, and the amount of inorganic solid matter and the amount of organic matter are divided by the amount of filtered concentrated water, respectively. Solid concentration and organic concentration were calculated.

As a result, the SDI of concentrated water reached 150% of the initial value in about one month after the start of operation. At that time, regarding the amount of deposits on the filter, the amount of ATP and the amount of organic matter were almost the same as the initial values, but the amount of inorganic solids increased to a value exceeding 10 times the initial value. In order to analyze the components of the inorganic solid matter on the filter, separately filter the concentrated water with a filter, soak the filter in 2.0% citric acid overnight, and measure the components of the soaked liquid by ICP emission spectrometry. As a result, it was found that iron accounted for the majority. From the above knowledge, it is judged that inorganic fouling mainly composed of iron has occurred, and a 2.0% citric acid aqueous solution is passed through the semipermeable membrane 24 as a cleaning agent, circulating for 1 hour / 2 hours for immersion / 1 hour. Washing was performed in the order of circulation washing. When the operation was restarted and the SDI of the concentrated water and the amount of inorganic solid matter on the filter were measured again, both returned to the initial values. Based on the obtained results, the addition of sodium hexametaphosphate (SHMP), which is a scale inhibitor, was then started as the drug 20. The operation was performed by continuously adding sodium hexametaphosphate to the concentrated water so as to be 2 mg / L.

Further operation was continued, and after about 3 months, the amount of ATP on the filter increased until it reached 10 times the initial value. The SDI of concentrated water also increased until reaching the initial 150%. On the other hand, the amount of inorganic solids on the filter was almost the same as the initial value. From the above findings, it was judged that biofouling occurred this time, and the membrane was washed in the same manner as in Comparative Example 1 using a sodium hydroxide aqueous solution (pH = 12) as a cleaning agent, and the operation was resumed. The SDI of concentrated water and the amount of ATP on the filter returned to their initial values.

After that, the ATP amount on the filter increased to 10 times the initial value and the SDI of the concentrated water rose to 150% of the initial value about every three months. Each time, using a sodium hydroxide aqueous solution (pH = 12) as a cleaning agent, the operation was continued while performing membrane cleaning in the same manner as described above. The operation differential pressure of the semipermeable membrane hardly changed after about one and a half years of operation, and the operation was stable. That is, in Example 4, SDI is the first operation reference index, the reference value is 150% of the initial SDI, the ATP amount on the filter through which the concentrated water is filtered is the second operation reference index, and the reference value Was operated 10 times the initial value. Furthermore, by analyzing the amount of microorganisms, the amount of inorganic solids, and the amount of organic matter on the filter through which concentrated water was filtered, it was possible to determine the conditions for drug addition and membrane cleaning.

(Example 5)
In the same manner as in Comparative Example 1, permeated water 25 and concentrated water 26 were obtained from seawater 12. Twice a week, 20L of concentrated water is filtered through a membrane filter (MF-Millipore manufactured by Millipore, HAWP04700F1). The color difference (ΔE ^* _ab ) between the filter before filtration and the filter after filtration (Nippon Denshoku Industries Co., Ltd., spectral color difference meter SE 6000).

In Example 5, the color difference (ΔE ^* _ab ) between the filter before filtration and the filter after filtration was used as an operation reference index, and the operation was performed with a reference value of 3.0. When ΔE ^* _ab reached 3.0, the semipermeable membrane was washed in the same manner as in Comparative Example 1, and such operation was continued for about 6 months. In the meantime, the operation differential pressure of the semipermeable membrane hardly changed and the operation was stable.

(Example 6)
In the same manner as in Comparative Example 1, permeated water 25 and concentrated water 26 were obtained from seawater 12. Twice a week, 20 L of concentrated water was filtered through a membrane filter (MF-Millipore, HAWP04700F1 manufactured by Millipore). PF-10R). The whiteness of the filter before filtration is 90%, the whiteness of the filter after filtering the concentrated water immediately after the start of operation is 85%, and the reciprocals thereof are 1 ÷ 0.9 = 1.11 and 1 ÷ 0. 85 = 1.18.

In Example 6, the reciprocal of the whiteness of the filter was used as the operation reference index, and when it was 1.3 times the initial value, that is, 1.33 was set as the reference value, the operation was performed. When the whiteness of the filter through which the concentrated water was filtered reached 75%, the reciprocal was 1 ÷ 0.75 = 1.33, which was 1.3 times the initial value of the reciprocal of the whiteness of the filter. The semipermeable membrane was washed in the same manner as in Example 1. Such operation continued for about 4 months. In the meantime, the operation differential pressure of the semipermeable membrane hardly changed and the operation was stable.

(Example 7)
In the same manner as in Comparative Example 1, permeated water 25 and concentrated water 26 were obtained from seawater 12. As in Example 3, the amount of ATP on the filter on which the SDI was measured was measured twice a week for each of the semipermeable membrane feed water and the concentrated water. Further, X is the ATP amount on the filter where the SDI of concentrated water is measured, Y is the ATP amount on the filter where the SDI of semipermeable membrane feed water is measured, and Re is the recovery rate of the semipermeable membrane. The value obtained from the equation 1-Re) was used as the operation standard index.

As a result, about 3 months after the start of operation, the operation standard index calculated by the above formula increased to 10 times compared with the initial operation. Thus, it was determined that fouling occurred and the addition of the drug 20 was started. As the medicine 20, DBNPA as a bactericidal agent was used, and 10 mg / L DBNPA was added between the water pump 18 and the high-pressure pump 21 1 to 3 times a week for 1 hour. Further, the operation was continued, and after about one month, the operation standard index was reduced to the same level as in the initial operation, so the addition of DBNPA as a disinfectant was stopped.

The operation was further continued, and after about 3 months, the operation standard index increased rapidly and increased to 20 times the initial operation. As a result, it was determined that fouling occurred, the membrane was washed with an aqueous sodium hydroxide solution (pH = 12) in the same manner as in Comparative Example 1, and the operation was resumed. Returned to value.

After that, the operation was performed with 10 times the initial value of the operation reference index as the first reference value and 20 times the initial value as the second reference value. When the operation standard index is increased by 10 times compared to the initial operation, DBNPA is added 1 to 3 times a week for 1 hour, and when it is increased to 20 times or more, the membrane is washed with an aqueous sodium hydroxide solution (pH = 12). went. By this method, the operation differential pressure of the semipermeable membrane hardly changed after about one and a half years of operation, and stable operation was possible.

(Example 8)
In the same manner as in Comparative Example 1, permeated water 25 and concentrated water 26 were obtained from seawater 12. In the operation of the semipermeable membrane, instead of measuring the SDI, the pressure during constant flow filtration was continuously measured twice a week for the semipermeable membrane feed water 22 and the concentrated water 26. The pressure at the time of constant flow filtration was performed by using the same apparatus of FIG. The filter holder 28 was loaded with a membrane filter (MF-Millipore, HAWP04700F1 manufactured by Millipore) having a pore diameter of 0.45 μm and a diameter of 47 mm. Put semipermeable membrane feed water 22 or concentrated water 26 as a sample in the sample tank 30, pressurize it with the compressor 31, adjust the holder valve 29 while watching the flow meter 35, and adjust the filtration flow rate to 300 mL / min. For 15 minutes. A pressure gauge 33 was used to measure the pressure at the start of filtration and the pressure 15 minutes after the start of filtration. A value obtained by subtracting the pressure value at the start of filtration from the pressure value at 15 minutes after the start of filtration was calculated. X is the value obtained by subtracting the pressure value at the start of filtration from the pressure value after 15 minutes from the start of filtration when filtering the concentrated water, and the pressure after 15 minutes from the start of filtration when the semipermeable membrane feed water is filtered. The value obtained by subtracting the pressure value at the start of filtration from the value is Y, the recovery rate of the semipermeable membrane is Re, and the value obtained from the formula of XY / (1-Re) is used as the operation standard index. Further, the amount of ATP on the filter after measuring the pressure during filtration of the concentrated water at a constant flow rate was measured by the same method as in Example 3.

As a result, about two months after the start of operation, the operation standard index value calculated by the above formula increased by 10 times compared to the initial operation. At this time, the amount of ATP on the filter also increased up to 10 times compared to the initial value. As a result, it was determined that fouling occurred, and the disinfectant DBNPA was added as a medicine 20 between the water pump 18 and the high-pressure pump 21 1 to 3 times a week for 1 hour so as to have a concentration of 10 mg / L. . Further, the operation was continued, and after about 1 month, the operation standard index was reduced to the same level as compared with the initial operation, so the addition of DBNPA as a disinfectant was stopped.

After that, when the operation standard index increased to 10 times compared with the initial operation, DBNPA was added 1 to 3 times a week for 1 hour. By this method, the operation differential pressure of the semipermeable membrane hardly changed after about two and a half years of operation, and stable operation was possible.

The present invention provides a means by which the progress of fouling on the membrane surface can be easily grasped before it appears in membrane operation data such as membrane differential pressure, permeability, and separation. Therefore, the present invention is suitable for obtaining fresh water by performing desalination of seawater, brine, etc. using a membrane, or purifying sewage treated water or industrial wastewater to obtain reused water. Can be used.

DESCRIPTION OF SYMBOLS 1 Water to be treated 2 High pressure pump 3 Semipermeable membrane 4 Permeated water 5 Concentrated water 6 Filtration means 7 Flow rate adjustment means (or pressure adjustment means)
8 Pressure measuring means 9 Flow measuring means 10 Drug 11 Cleaning agent 12 Seawater 13 Sodium hypochlorite 14 Seawater storage tank 15 Supply pump 16 Ultrafiltration membrane 17 Semipermeable membrane supply water storage tank 18 Water pump 19 Sodium bisulfite 20 Drug 21 High pressure Pump 22 Semipermeable membrane supply water 23 Cleaning agent 24 Semipermeable membrane 25 Permeated water 26 Concentrated water 27 SDI measuring device 28 Filter holder 29 Holder valve 30 Sample tank 31 Compressor 32 Pressure adjustment valve 33 Pressure gauge 34 Measuring cylinder 35 Flowmeter A B0 No DBNPA added B1 DBNPA added once a week B2 DBNPA added twice a week B3 DBNPA added three times a week

Claims

In the water production method of treating water to be treated with a semipermeable membrane and separating it into permeated water and concentrated water, when the semipermeable membrane is washed and / or the chemical is injected into the treated water, An operation standard index derived from at least one index selected from the group consisting of the performance index of the filter, the amount of deposits on the filter, and the color of the filter when the concentrated water is periodically filtered with a trappable filter. When the water reaches a predetermined reference value set in advance, the semipermeable membrane is washed, or the semipermeable membrane washing conditions and / or chemical injection conditions are strengthened.
The fresh water generation method according to claim 1, wherein the performance index of the filter is at least one selected from the group consisting of a pressure value at the time of constant flow filtration and a filtration resistance value at the time of constant flow filtration.
The performance index of the filter is the reciprocal value of the filtration flow value when a constant pressure is applied, the reciprocal value of the amount of water filtered during a predetermined time when a constant pressure is applied, and the predetermined water amount when a constant pressure is applied The fresh water generation method according to claim 1, which is at least one selected from the group consisting of the time required to filter the water and the filtration resistance value of the filter when a constant pressure is applied.
The fresh water generation method according to claim 1, wherein the performance index of the filter is an SDI value defined by ASTM D4189-95.
The amount of deposits on the filter is selected from the group consisting of the amount of microorganisms, the amount of inorganic solids, the amount of organics, the ratio of inorganic solids to the amount of organic matter, the ratio of inorganic solids to the amount of microorganisms, and the ratio of the amount of microorganisms to the amount of organic matter The fresh water generation method according to claim 1, wherein there is at least one.
The fresh water generation method according to claim 5, wherein the amount of the microorganism is a value obtained by an ATP measurement method.
The color index of the filter is the color difference defined in JIS Z 8730: 2009 between the filter before filtration and the filter after filtration, and the JIS P of the filter after filtration. The fresh water generation method according to claim 1, which is at least one index selected from the group consisting of reciprocal values of whiteness defined by 8148: 2001.
Furthermore, the semipermeable membrane feed water supplied to the semipermeable membrane is regularly filtered with a filter capable of capturing solids, and from the performance index of the filter, the amount of deposits on the filter, and the color of the filter when filtered. Y is at least one index selected from the group consisting of X, and X is at least one index selected from the group consisting of the performance index of the filter, the amount of deposit on the filter, and the color of the filter when the concentrated water is filtered. Sometimes, a value calculated from X and Y is used as an operation reference index, and when the predetermined reference value is reached, the semipermeable membrane is cleaned, or the semipermeable membrane cleaning conditions and / or The fresh water generation method according to any one of claims 1 to 7, wherein the drug injection conditions are strengthened.
When filtering the concentrated water, the value of at least one index selected from the group consisting of the performance index of the filter, the amount of deposits on the filter and the color of the filter is X, and when the semipermeable membrane feed water is filtered, When the value of at least one index selected from the group consisting of the performance index of the filter, the amount of deposits on the filter and the color of the filter is Y and the recovery rate of the treatment with the semipermeable membrane is Re, XY / (1 -Re) The calculated value obtained from the formula is used as an operation reference index, and when the predetermined reference value is reached, the semipermeable membrane is cleaned, or the semipermeable membrane cleaning conditions and / or chemicals The fresh water generation method according to claim 8 which strengthens injection conditions.