JP2002143849A - Method for producing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method hardly causing the deposition of microorganisms or their metabolic products on a separation membrane and the reduction of the amount of produced water in the method for producing water by using a separation membrane. SOLUTION: In the process of adding a sterilizer to the raw water and supplying the water to the separation membrane, at least one condition selected from the group of the concentration of the sterilizer added, time of addition and frequency of addition is controlled based on the following factors. The factors are the viable cell count in the raw water and the concentration of assimilable organic carbon, or the volume of bacteria in the raw water and the concentration of assimilable organic carbon, or the viable cell count in the raw water and the biofilm formation rate, or the volume of bacteria in the raw water and the biofilm formation rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for desalinating seawater or brine using a separation membrane such as a reverse osmosis membrane to obtain fresh water, or purifying industrial wastewater to obtain clean water. The present invention relates to a desalination method that can be suitably used for water.

[0002]

2. Description of the Related Art Separation techniques using membranes are widely used for desalination of seawater and brackish water, and for treatment of industrial water and wastewater. In these treatments, the permeation performance and separation performance of the membrane are reduced due to the attachment and growth of microorganisms to the membrane and the attachment of their metabolites, and various solutions have been sought. Among them, a method of adding a chlorine-based disinfectant, a method of adding a reducing agent after adding a disinfectant, and a method of adding sodium bisulfite in addition to them have been used as effective. .

[0003] However, since all of these methods are carried out at a certain addition concentration, addition time, and addition frequency, an excess bactericide is added depending on the number of microorganisms contained in the raw water and the water quality. To be done,
In addition, there has been a problem that a bactericide is insufficient and microorganisms rapidly grow and deposit on a film.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a fresh water producing method in which the accumulation of microorganisms and their metabolites on a membrane is small and a decrease in the amount of fresh water is small. It is in.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for adding a bactericide to raw water and supplying it to a separation membrane, wherein the number of viable bacteria contained in the raw water, the assimilable organic carbon concentration, the raw water The amount of bacteria and assimilable organic carbon concentration contained in, the number of viable bacteria and biofilm formation rate contained in the raw water, or, based on the amount of bacteria contained in the raw water and the biofilm formation rate, the concentration of the fungicide added, At least one selected from the group consisting of addition time and addition frequency
It features a desalination method that controls two conditions. Here, it is preferable to control the pH of the raw water to 4 or less, and it is also preferable to use sulfuric acid as a bactericide.

It is also preferable to use a reverse osmosis membrane as the separation membrane, and it is also preferable to use seawater or brine as raw water.

[0007] Further, the above-mentioned fresh water producing method in which an oxidizing agent is added to raw water, a reducing agent is added, and then a bactericide is added is also preferable.

In addition, the number of viable bacteria and the concentration of assimilable organic carbon contained in the raw water, the amount of cells contained in the raw water and the concentration of assimilable organic carbon, the number of viable bacteria and the biofilm formation rate contained in the raw water, or It is also preferable to control at least one condition selected from the group consisting of the concentration of the oxidizing agent or the reducing agent, the time of addition, and the frequency of addition, based on the amount of cells contained and the rate of biofilm formation. Is also preferred.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION
Not only the number of microorganisms present in the raw feed water, but also the organic carbon contained in the raw feed water, particularly assimilable organic carbon that can be taken as nutrients of the microorganism [hereinafter referred to as AOC (Assimirable
Organic Carbon) is determined by the amount of microorganisms in the raw water, and when the concentration of AOC is low, the addition conditions (addition concentration and addition time) of the bactericide to be supplied to the membrane separation device are considered. , Frequency of addition)
Conversely, when the number of viable bacteria and the AOC concentration are high, the conditions for adding the bactericide are strengthened, for example, by controlling the conditions for adding the bactericide according to the number of viable bacteria and the AOC concentration of the microorganisms in the raw water. And an optimum bactericidal effect can be obtained.

[0010] In addition, regarding the sterilization in the pretreatment prior to the treatment with the separation membrane, by adding an oxidizing agent such as a chlorine-based germicide in the pretreatment, the organic carbon present in the feed solution is oxidized and decomposed, and microorganisms are removed. The theory that it is converted to AOC, which is easily taken as a nutrient (ABHamida and I. Moch,
Jr., Desalination & Water Reuse, 6/3, 40-45, (199
6).)), As in the sterilization of the membrane separation device, to create excess AOC by changing the addition conditions of the oxidizing agent and the reducing agent according to the number of viable microorganisms in the raw water and the AOC concentration. In addition, the present inventors have found that by combining with the above-described method for sterilizing a membrane separation device, it is possible to more effectively suppress the growth of microorganisms in the membrane separation device, and have reached the present invention.

Now, the fresh water producing method of the present invention will be described using a fresh water producing apparatus shown in FIG.

In FIG. 1, a fresh water generator 50 includes an intake pipe 1, an intake pump 2, a coagulation filtration device 4a, a polishing filtration device 4b, an intermediate tank 5, a security filter 7, and a high-pressure pump from the upstream side with respect to the flowing direction of raw water. 8, a separation membrane module 9, a permeated water flow path 10, a decarbonation device 11a, and a calcium addition device 11b are connected and configured in this order. Also,
A concentrated water neutralization device 13 is provided on the concentrated water side of the separation membrane module 9.
And a concentrated water flow path 14, and a chemical injection device 3 is provided in a path between the water intake pump 2 and the coagulation filtration device 4 a.
However, chemical injection devices 6a and 6b are connected to a path between the intermediate tank 5 and the security filter 7, and a chlorine injection device 12 is connected to a path downstream of the calcium addition device 11b.

Raw water taken from the sea or a water storage tank through a water intake pipe 1 by a water intake pump is added with a coagulant or a bactericide by a chemical injection device 3 and then supplied to a coagulation filtration device 4a or a polishing filtration device 4b. It is processed by the pretreatment device and temporarily stored in the intermediate tank 5. Next, a reducing agent or a bactericide is added by the chemical injection devices 6a and 6b, passes through the security filter 7, and is supplied to the separation membrane module 9 by the high-pressure pump 8.
Supplied to The supplied raw water is separated into permeated water and concentrated water, of which the concentrated water is adjusted to near neutral pH by the concentrated water neutralization device 13 and passes through the concentrated water passage 14 to the original sea or reservoir. Will be returned. On the other hand, the permeated water passes through the permeated water path 10 and is treated by the decarbonation device 11a, the calcium addition device 11a, and the chlorine injection device 12, for example,
It is removed from the freshwater generator as fresh water that meets the drinking water standards.

The present invention is based on the number of viable bacteria contained in the seawater (raw water) withdrawn by the above-mentioned water intake pipe 1 and the concentration of assimilable organic carbon. Conditions such as concentration, addition time, and addition frequency are controlled to obtain permeated water while preventing microorganisms from propagating in each pipe, separation membrane module 9 and the like.

In the above, water may be taken directly from the surface of the sea or so-called deep water may be extracted. In addition, water may be collected by a permeation water intake method using a seabed sand layer or the like as a filter, and it is preferable that the extracted seawater is once separated into particles such as sand in a sedimentation tank or the like. Next, a germicide or a coagulant is added by the chemical injection device 3, and the germicide to be used may be an oxidizing germicide, for example, a chemical that can generate free chlorine. And sterilization is performed by adding sodium hypochlorite or the like. Further, as a coagulant, ferric chloride, polyaluminum chloride, or the like can be used. Thereafter, pretreatment is performed by the coagulation filtration device 4a and the polishing filtration device 4b. This may be performed by sand filtration, etc., or an ultrafiltration membrane, a microfiltration membrane,
Processing using a film such as a loose RO film may be performed.
This pretreatment does not impose a load on each downstream step,
The process has the purpose of purifying the raw water to a necessary degree and is appropriately selected depending on the degree of contamination of the raw water, and may be performed by appropriately combining the above-described respective processes. Next, the raw water after the pretreatment is stored in the intermediate tank 5, which provides a water volume adjusting function and a water quality buffering function, and is provided as necessary. Next, a reducing agent such as sodium bisulfite is added by the chemical injection device 6a. This is performed when an oxidizing germicide is added in an upstream process, and is for preventing residual chlorine and the like from deteriorating the separation membrane. Next, a bactericide such as sulfuric acid is added by the chemical injection device 6b and passed through the security filter 7. The security filter removes solids in the raw water supplied to the separation membrane module,
It has the effect of preventing performance degradation of pumps and membranes.

[0016] The above-mentioned chemical injection device, in particular, 3 and 6b to which a disinfectant is added, as will be described later, automatically controls the amount of the disinfectant added in order to control the addition conditions of the disinfectant according to the properties of the raw water. It is preferable to provide a control mechanism having a valve or a pump capable of controlling the addition time, the addition frequency, and the like. This can be performed, for example, by installing a pH meter, a timer, and the like, and controlling the opening of a valve, a pump, and the like based on information obtained from the pH meter and the timer.

Of course, the timing of adding a chemical such as a bactericide may be arbitrarily determined, but is preferably immediately after water withdrawal, before or during pretreatment, or before and after passing through a security filter.

The separation membrane module 9 can be, for example, a module using a reverse osmosis membrane, a module using an ultrafiltration membrane, a microfiltration membrane, or the like. It is preferable to use a reverse osmosis membrane module using an osmosis membrane.

Here, the reverse osmosis membrane refers to a semipermeable membrane which permeates some components in the feed water, for example, a solvent and does not allow other components to permeate, such as a so-called nanofiltration membrane. A loose RO film is also included. As a material, it is preferable to use a polymer material such as a cellulose acetate polymer, polyamide, polyester, polyimide, and pinyl polymer. In addition, the membrane structure may be an asymmetric structure having a dense layer on at least one side and gradually having fine pores with a large pore diameter from the dense layer toward the inside of the membrane or the other surface, or a dense layer of the asymmetric membrane. A composite membrane structure having a separation function layer formed of another material on the layer can also be used. As the membrane form, a hollow fiber membrane or a flat membrane can be used. The thickness of the hollow fiber membrane and the flat membrane is preferably in the range of 10 μm to 1 mm. When a hollow fiber membrane is used, the outer diameter thereof is 50 μm to 4 m.
m is preferably within the range. The flat membrane preferably has an asymmetric structure, and the composite membrane is preferably supported by a substrate such as a woven fabric, a knitted fabric, or a nonwoven fabric. Representative reverse osmosis membranes include, for example, a cellulose acetate-based or polyamide-based asymmetric membrane and a composite membrane having a polyamide-based or polyurea-based separation function layer. Among them, in the present invention, cellulose acetate-based membranes are used. The use of an asymmetric membrane or a polyamide composite membrane is highly effective. In particular, JP-A-6
Use of an aromatic polyamide composite film described in JP-A-2-121603, JP-A-8-138658, and U.S. Pat. No. 4,277,344 has a large effect.

The separation membrane module is one in which the above-mentioned reverse osmosis membrane or the like is incorporated in a casing for actual use. When a flat membrane type membrane is used, a spiral type module or a tubular type module is used. Mold module, plate
When a hollow fiber membrane is used as the and frame type module, it is preferable to bundle the module and incorporate it into a U-shaped or I-shaped casing to form a module. Of the above, a spiral type module is disclosed in, for example,
No. 0 and Japanese Patent Application Laid-Open No. 9-141067 incorporate members such as a supply water flow path material and a permeate flow path material, and use seawater having a high solute concentration as raw water, or operate the apparatus at high pressure. It is highly effective when driving.

The permeated water obtained by the above separation membrane module is treated by a decarbonation device 11a, a calcium addition device 11b, and a chlorine injection device 12, and is used for purposes such as drinking water.

The operating pressure of the high-pressure pump of the fresh water generator can be set as appropriate according to the type of raw water, the operating method, and the like. At a relatively low pressure of about 3.0 MPa, 2.5 to 1 in the case of seawater desalination, wastewater treatment, recovery of useful materials, etc.
It is preferable to use at a relatively high pressure of about 5.0 MPa because energy such as electric power is not wasted and good quality of permeated water can be obtained. In addition, a pump can be installed in an arbitrary route in the fresh water generator in order to obtain appropriate supply pressure and operating pressure.

When the operating temperature of the fresh water generator is lower than 0 ° C., the supplied water is frozen and cannot be used. When the operating temperature is higher than 100 ° C., the supplied water is evaporated and cannot be used.
The temperature is appropriately set within the range of -100 ° C, but is preferably in the range of 5-50 ° C in order to maintain good performance of the apparatus and the reverse osmosis membrane.

The recovery rate of the fresh water generator can be appropriately set within a range of 5 to 98%. However, it is necessary to consider pretreatment conditions, operating pressure, and the like in accordance with the properties, concentration, and osmotic pressure of the raw feed water and concentrated water (Japanese Patent Laid-Open No. 8-108048). For example, in the case of seawater desalination, usually 10 to 10
A recovery rate of 40% to 70% is set for a device with a high efficiency of 40%. In addition, in the case of desalination or ultrapure water production, the operation can be performed at a recovery rate of 70% or more, further, 90 to 95%.

Further, the separation membrane module 9 in the fresh water generator may be provided in one stage or in multiple stages, and may be arranged in series or in parallel with the supply water. When arranged in series, a booster pump may be installed between the modules. In the case of seawater desalination, in the case of employing a reverse osmosis membrane module and employing a serial arrangement, from the viewpoint of equipment cost and efficiency, etc., in particular, the two-stage concentrated water in which the concentrated water in the preceding stage is used as the supply water in the subsequent stage. It is preferable to arrange the booster pump between the modules arranged in series to increase the pressure of the supply water within a range of 1 to 5 MPa and supply it to the subsequent module (Japanese Patent Laid-Open No. 8-108).
048). When the separation membrane modules are arranged in series with the supply water, the time of contact between the separation membrane module and the supply water is long, so that the effect of the method of the present invention is large. Further, an arrangement of two stages of permeated water in which the permeated water in the first stage is the supply water in the second stage is also a preferable method when the quality of the permeated water in the first stage is insufficient or when it is desired to recover solute components in the permeated water.
In this case, a pump can be installed between the modules to pressurize the permeated water again, or extra pressure can be applied in the previous stage to apply back pressure to perform membrane separation. Further, a disinfectant addition device may be provided between the membrane modules in order to sterilize the subsequent membrane module portion.

In the above fresh water generator, a portion of the feed water that has not passed through the membrane is taken out of the membrane module as concentrated water. The concentrated water can be treated and discarded according to the intended use, or can be further concentrated by another method. Also, part or all of the concentrated water can be circulated to the feed water. The permeated water that has passed through the membrane may be discarded or used as it is, or a part or all of the permeated water may be circulated to the supply water.

The concentrated water of the fresh water generator using the reverse osmosis membrane has pressure energy, and it is preferable to recover this energy in order to reduce operating costs. As a method of energy recovery, it can also be recovered by an energy recovery device attached to a high pressure pump of any part,
It is preferable to use a dedicated turbine type energy recovery pump attached before and after the high-pressure pump or between the modules. Further, the processing capacity of the fresh water generator can be in the range of 0.5 to 1,000,000 m ³ in terms of the amount of water per day.

Further, it is preferable that the piping of the fresh water generator has a structure having as few stagnation portions as possible. Further, as described later, since the pH of raw water is preferably 4 or less, pipes, valves and other members through which such acidic water flows have acid resistance such as stainless steel and duplex stainless steel. It is preferable to use a material.

In the present invention, the bactericide includes the viable cell count of microorganisms contained in the raw water supplied to the separation membrane and the AOC.
, The addition concentration, the addition time, and the addition frequency are controlled. This is very effective for efficiently and surely sterilizing the separation membrane.

For example, when the salt concentration is 0.1 to 4.5% by weight.
In the case where seawater or brackish water is used as raw water, the viable cell count in the raw water is less than 1.0 × 10 ³ cfu / ml (hereinafter, the unit of the viable cell count used in the present invention is the number of colonies found in 1 ml of raw water. Number [cfu / ml: colony form
ing unit). And in microbiologically relatively clean raw water having an AOC concentration of less than 10 μg / l, the concentration of the fungicide added is 50 to 150 mg / l.
It is preferable that the addition time is selected within the range of 1 to 1, 0.5 to 1 hour, and the addition frequency within the range of 1 time / 2 months to 1 time / 6 months. In addition, the number of viable bacteria in raw water is 1.0 × 10
Within the range of ^{3 to} 1.0 × 10 ⁵ cfu / ml and AO
In the case of raw water in which the C concentration is in the range of 10 to 50 μg / l, the concentration of the fungicide to be added is 150 to 200 mg / l.
, The addition time is preferably in the range of 1 to 2 hours, and the addition frequency is preferably in the range of 1 time / week to 1 time / 2 months. × 10 ⁵ cfu
/ Ml and AOC concentration exceeding 50 µg / l in raw water with a large amount of microorganisms, the disinfectant concentration should be within the range of 200 to 250 mg / l and the addition time should be 2 hours.
It is preferable to select the addition frequency within a range of 1 to 4 hours and a frequency of once / day to once / week. As described above, by controlling all three conditions of the addition concentration, addition time and addition frequency of the bactericide based on the number of viable bacteria contained in the raw water and the AOC concentration, the propagation of microorganisms on the separation membrane can be performed more efficiently. And a decrease in the amount of fresh water produced by the separation membrane can be prevented.

In the above, an example has been described in which all of the concentration, time and frequency of addition of a bactericide are controlled as control items. However, it is needless to say that controlling only one or two of them is also possible. The effect can be sufficiently exhibited.

For example, when only one condition is changed, regardless of the number of viable bacteria contained in the raw water and the AOC concentration,
The addition time of the fungicide is fixed at 1 hour, the addition frequency is once / day, etc., and the number of viable bacteria in the raw water is 1.
Less than 0 × 10 ³ cfu / ml and AOC concentration of 1
When the concentration is less than 0 μg / l, the addition concentration is 50 to 15
0 mg / l, and the viable cell count is 1.0 × 10 ^3-
Within the range of 1.0 × 10 ⁵ cfu / ml and AOC
When the concentration is in the range of 10 to 50 μg / l, the addition concentration is in the range of 150 to 200 mg / l, the viable cell count exceeds 1.0 × 10 ⁵ cfu / ml, and the AOC concentration is When the concentration exceeds 50 μg / l, the addition concentration is 200
It is preferable to control the amount within the range of 250 mg / l.

Further, for example, when the addition concentration is 150 mg /
1, the addition frequency is fixed at once / day, etc., and the number of viable bacteria in the raw water is 1.0 × 10 ³ cfu / ml.
When the AOC concentration is less than 10 μg / l, the addition time is set within the range of 0.5 to 1 hour, and the number of viable bacteria is 1.0 × 10 ^{3 to} 1.0 × 10 ⁵ cfu / l. When the AOC concentration is within the range of 10 to 50 μg / l and the addition time is within the range of 1 to 2 hours, the viable cell count is 1.0 × 10 ⁵ cfu / ml. And AO
If the C concentration exceeds 50 μg / l, the addition time should be 2
It is also preferable to control it within the range of 4 hours.

Further, for example, when the addition concentration is 150 mg
/ L, the addition time is fixed at 1 hour, etc., and the number of viable bacteria in the raw water is 1.0 × 10 ³ cfu / ml.
When the AOC concentration is less than 10 μg / l, the addition frequency is set within the range of once / two months to one time / 6 months, and the number of viable bacteria is 1.0 × 10 ³ -1. 0 × 10 ⁵ cfu
/ Ml and the AOC concentration is 10 to 50 μg
/ L, the addition frequency is once / week to 1
Times / two months, and the number of viable bacteria is 1.0 × 10 ⁵ cf
When the concentration exceeds u / ml and the AOC concentration exceeds 50 μg / l, the addition frequency may be controlled within the range of once / day to once / week.

It is also possible to keep one of the conditions of the concentration, time and frequency of addition of the germicide constant and control the remaining two conditions. For example, the addition concentration of the fungicide may be kept constant regardless of the number of viable bacteria and the AOC concentration, and the two conditions of the addition time and the addition frequency may be controlled according to the number of viable bacteria in the raw water and the AOC concentration. The addition time may be kept constant, and the two conditions of the addition concentration and the addition frequency may be controlled. Alternatively, the addition frequency may be kept constant, and the two conditions of the addition concentration and the addition time may be controlled. May be.

The number of viable bacteria in raw water and the level of AOC concentration
Classification is always classified into the three levels as described above.
It is not necessary, for example, if the number of viable bacteria is 1.0 × 10^Fourcfu /
ml and the AOC concentration is less than 30 μg / l
When the number of viable bacteria is 1.0 × 10 ^Fourmore than cfu / ml
When the AOC concentration is 30 μg / l or more
And the number of viable bacteria is 1.0 × 10
^Threeless than cfu / ml and an AOC concentration of 10 μg /
l, the viable cell count is 1.0 × 10^Three~ 1.0 × 10^Four
cfu / ml and AOC concentration of 10-3
When it is within the range of 0 μg / l, the viable cell count is 1.0 × 10
^Four~ 1.0 × 10^Fivewithin the range of cfu / ml and AO
When the C concentration is in the range of 30 to 50 μg / l,
The number is 1.0 × 10^FiveExceeds cfu / ml and AOC
Four levels, such as when the concentration exceeds 50 μg / l
May be. In addition, it can be classified into more levels.
No, but even if the number of levels is increased unnecessarily, the sterilization effect is large.
Since it is not expected that a difference appears, the number of classifications is 2
Classify the number of viable bacteria and the level of AOC concentration within the range of ~ 5
Is preferred.

As described above, by changing the sterilization conditions based on the number of viable bacteria in the raw water and the AOC concentration, it is possible to sterilize the membrane reliably and without waste.

If the sterilization conditions are always constant irrespective of the nature of the raw water, the sterilization of the separation membrane can be performed reliably when the number of viable bacteria or AOC is small, but unnecessary sterilization is repeated, which is wasteful. Become. In addition, when the number of viable bacteria or AOC is large, sterilization of the separation membrane cannot be carried out reliably, and microorganisms tend to adhere or accumulate on the membrane surface, resulting in a decrease in membrane performance such as a decrease in water production.

When the properties of the raw water are judged only by the viable cell count of the microorganism, for example, the viable cell count is 1.0 × 10 ³ cfu /
Even when the amount of AOC is small or large,
Because the degree of growth of microorganisms is different, it is difficult to select the optimum sterilization conditions. On the other hand, if the number of viable bacteria cannot be grasped naturally, even if judging only by the AOC concentration, the optimum sterilization conditions should be selected. Will be difficult.

In the present invention, the addition of the bactericide is preferably performed intermittently. Continuous addition of fungicide
Not only will a large amount of the drug be consumed and waste will increase, but also microbiologically, the same environment will always be created, and abnormal growth of microorganisms that are resistant to bactericides is likely to occur.
By intermittently adding fungicides, waste of drug consumption can be eliminated, and microbiologically, the environment will be changed, thus preventing abnormal growth of specific microorganisms such as resistant bacteria. be able to.

In the present invention, the viable cell count and AO
The C concentration refers to a value measured by the method described below.

Viable cell count: 100 μl of a seawater sample was spread on an agar medium for marine bacteria adjusted to pH 7.0,
After culturing at 3 ° C. for 3 days, the number of colonies formed in the medium was counted, and the value obtained by multiplying the number by 10 was counted as the viable cell count (unit: cf).
u / ml).

AOC concentration: A sulfuric acid was added to a seawater sample so as to have a concentration of 300 mg / l, and a seawater sample to which sulfuric acid had been added was added to a previously sterilized flat-bottomed test tube.
Neutralize to around pH 8 with N sodium hydroxide.

Further, 2.8 mg / l of sodium nitrate
(0.5 mg / l as nitrogen atom), 0.3 mg / l dipotassium phosphate (0.05 mg / l as phosphorus element)
l), TES (Trace Element Solu)
Tion: Tetrasodium ethylenediaminetetraacetate, iron sulfate, boric acid, cobalt chloride, zinc chloride, manganese chloride, sodium molybdate, nickel chloride, copper chloride, selenious acid as a solute) is 0.032 as a solute concentration.
mg / l, sodium acetate 50 μg / l, 100 μg
/ L and 150 μg / l to seawater sample, and simultaneously added seawater without sulfuric acid added thereto so as to have a concentration of 1%, and capped with polypropylene. Incubate in the dark in an incubator adjusted to the seawater temperature at the time of collection.

[0045] Every 24 hours from the start of the culture, a sample was taken from a seawater sample cultured statically in the dark and sterilized.
Dilute to 4 levels of 10 times, 100 times, 1000 times and 10000 times with 5% saline, spread 3 plates at each dilution on an agar medium for marine bacteria, and culture at the same temperature as the seawater sample. I do.

With respect to the above-mentioned medium sample, the number of colonies after culturing was 30
The dilutions within the range of 300 were selected, the average number of colonies was measured, and the maximum growth number of each colony was calculated from this value, and the correlation between the sodium acetate concentration and the maximum growth number was calculated and regression analysis was performed. , The following equation is obtained with respect to the viable cell count and the AOC concentration, and the AOC contained in the supplied seawater is calculated from this equation.
Calculate the concentration.

(AOC concentration: μg / l) = [(viable cell count:
cfu / ml) -A] / B (However, since the values of the coefficients A and B in the above equation differ depending on the type of growing bacteria, they do not always have the same value in seawater at different locations.) Then, instead of using the viable cell count as a reference as described above, the amount of cells contained in the raw water can also be used.

As a method for measuring the amount of bacterial cells, it is preferable to use an ATP measurement method because accurate, simple and rapid measurement can be performed. The ATP assay involves adding an acid or a surfactant as an extraction reagent to a sample containing bacteria, dissolving the cell wall,
A method of extracting TP (adenosine-5'-triphosphate), further adding an enzyme such as luciferase as a luminescent reagent to cause luminescence, and quantifying the amount of ATP by the amount of luminescence to measure the amount of bacterial cells. The amount of cells thus determined is usually indicated by the amount of ATP contained per liter of sample, and the unit is usually (ng-ATP / l).

Further, in the present invention, a biofilm formation rate of raw water (hereinafter referred to as BFR (Biofilm Formation Rate)) may be used instead of the assimilable organic carbon concentration. BFR indicates the amount of microbial membrane adhered to the carrier surface per unit area and per unit time.

As a method of measuring the BFR, for example, a flat plate such as glass is immersed in raw water, taken out after a certain period of time, the microorganisms adhering to the surface of the glass plate are scraped, and the adhering amount is measured. The measurement of the amount of microorganisms attached is performed by the above-mentioned A
It is preferable to use a TP measurement method or the like because it is accurate.
When the ATP measurement method is used, the unit of BFR is per day,
It is indicated by the amount of cells adhering per 1 cm ² , and the unit is usually (pg-ATP / cm ² / d).

In the present invention, instead of controlling the disinfection based on the number of viable bacteria in the raw water and the AOC concentration as described above, the disinfection may be controlled based on the combination of the amount of the cells and the AOC concentration. Good, and the sterilization may be controlled based on the combination of the viable cell count and the BFR.
Sterilization may be controlled based on a combination of the above. The combination is either the viable cell count or the bacterial mass, AOC concentration and B
What is necessary is just to select from the combination with either one of FR.

For example, if the sterilization is controlled based on the combination of the amount of cells and the AOC concentration, the above-mentioned viable cell count and AOC
As in the case of the concentration, when seawater or brackish water having a salt concentration of 0.1 to 4.5% by weight is used as raw water, the amount of cells in the raw water is less than 1.0 ng-ATP / l and the AOC concentration Is 1
In microbiologically relatively clean raw water, such as less than 0 μg / l, the concentration of fungicide added is 50-150 mg / l.
, The addition time is preferably selected within the range of 0.5 to 1 hour, and the addition frequency is preferably selected within the range of 1 time / 2 months to 1 time / 6 months. The number of viable bacteria in raw water is 1-100ng
-Within the range of ATP / l and an AOC concentration of 10 to 5
In the case of raw water in the range of 0 μg / l, the concentration of the fungicide is in the range of 150 to 200 mg / l, the addition time is in the range of 1 to 2 hours, and the addition frequency is 1 time / week to 1 time. Times /
It is preferable to select within a range of 2 months, and furthermore, the amount of cells in raw water exceeds 50 ng-ATP / l, and A
In raw water having a very large number of microorganisms such as an OC concentration exceeding 50 μg / l, the concentration of the fungicide to be added is 200 to 250 m
It is preferable to select the addition time within the range of g / l, the addition time within the range of 2 to 4 hours, and the addition frequency within the range of once / day to once / week.

Further, if the sterilization is controlled based on the combination of the viable cell count and the BFR, the viable cell count in the raw water is also reduced to 1.0.
× less than 103 cfu / ml and BFR of 10 pg
-In microbiologically relatively clean raw water, such as less than ATP / cm < ² > / d, the concentration of the fungicide added should be between 50 and 15
It is preferable that the addition time is selected in the range of 0 mg / l, the addition time is in the range of 0.5 to 1 hour, and the addition frequency is in the range of 1 time / 2 months to 1 time / 6 months. In addition, the number of viable bacteria in raw water is 1.
Within the range of 0 × 103 to 1.0 × 105 cfu / ml,
In the case of raw water having a BFR in the range of 10 to 50 pg-ATP / cm ² / d, the concentration of the disinfectant is in the range of 150 to 200 mg / l, and the addition time is in the range of 1 to 2 hours. Of these, the addition frequency is preferably selected within the range of once / week to once / two months. Furthermore, the number of viable bacteria in raw water exceeds 1.0 × 10 5 cfu / ml, and the BFR is 50 pg-. In raw water having a large number of microorganisms such as exceeding ATP / cm ² / d, the concentration of the fungicide added is 200 to 2
It is preferable to select the addition time within the range of 50 mg / l, the addition time within the range of 2 to 4 hours, and the addition frequency within the range of once / day to once / week.

Further, based on the combination of the amount of cells and BFR
If sterilization is controlled, the amount of cells in raw water is 1.0 ng-
Less than ATP / l and BFR of 10 pg-ATP /
cm ^TwoMicrobiologically relatively clean, less than / d
In raw water, the concentration of the fungicide added is 50 to 150 mg / l.
, The addition time is in the range of 0.5 to 1 hour,
The degree can be selected from once / two months to once / six months.
Is preferred. In addition, the amount of cells in raw water is 1.0 to 100.
ng-ATP / l and BFR of 10-5
0pg-ATP / cm^TwoRaw water that is in the range of / d
In the case of, the addition concentration of the bactericide is 150-200 mg / l.
Within the range of 1 to 2 hours, the frequency of addition
It is preferable to select within the range of once / week to once / two months.
And the amount of cells in raw water is 100 ng-ATP /
1 and the BFR is 50 pg-ATP / cm^Two/
In raw water that is very rich in microorganisms, such as exceeding d,
Add the concentration of the agent within the range of 200-250mg / l
The time is in the range of 2 to 4 hours, and the addition frequency is once / day to once
/ Week is preferred. In the present invention
The pH of raw water at the time of disinfectant addition should be 4 or less
However, it is preferable because it can exert a high sterilizing effect on the separation membrane.
New This is especially true when using seawater as feedwater.
The fruits are remarkable. The pH at which microorganisms die is determined by the individual microorganism
For example, in the case of E. coli,
Is pH 4.6, but kills at pH 3.4 or less.
You. On the other hand, a wide variety of microorganisms also exist in seawater,
The pH at which they die is different. However, in the present invention
Maintains seawater containing various live bacteria at pH 4 or lower for a certain period of time
Then 50 to 100% can be killed.
You. Further, the pH is set to 3.9 or less, and the pH is further set to 3.
It is also said that killing bacteria derived from seawater will be less than 7
It is preferable from a viewpoint. By controlling the pH in this way,
Not only high sterilization effect is obtained, but also accumulated on pipes
The effect of removing even scales can be expected.

As a disinfectant, for example, chlorine gas, sodium hypochlorite, sulfuric acid, hydrochloric acid, nitric acid, citric acid and the like can be used. Above all, it is preferable to use an acid as a bactericide, since the above-mentioned pH control is easily performed at the same time. As the acid, either an organic acid or an inorganic acid may be used, but from the viewpoint of economy, it is preferable to use sulfuric acid. The addition amount of sulfuric acid necessary to control the pH to 4 or less is proportional to the salt concentration of the feed solution. For example, in raw water having a salt concentration of about 1% by weight, 50 mg /
1 to make the pH fall to 3.2, but 120 mg / l in seawater (salt concentration of about 3.5% by weight).
It is preferable to add the above. The maximum addition amount is 400 mg / l, more preferably 300 mg / l, in consideration of the economy and the effect on facilities such as piping. In addition, assuming that the concentration of sulfuric acid added to seawater is 150 mg / l and 200 mg / l,
The pH ranges are 3.2-3.0, 2.8-2.2, respectively.
9, and the pH fluctuation decreases as the added concentration increases.

By the way, in the past, various sterilization techniques have been adopted in the separation apparatus using the membrane, but the oxidizing agent such as chlorine is continuously added. According to this method, the feed water can be almost completely sterilized unless resistant bacteria appear, but since the oxidizing agent usually causes chemical degradation of the reverse osmosis membrane, sodium hydrogen sulfite is represented before the membrane separation device. Add a reducing agent. However, the supply water after removing the excess oxidizing agent with the reducing agent is in a state where microorganisms can easily propagate. Moreover, rather than various microorganisms as in the raw seawater before the addition of the fungicide, a considerably selected group of microorganisms exists there, and many acid-resistant bacteria are also contained therein. If the addition of the reducing agent is insufficient, the oxidizing agent may not be completely eliminated and may cause the deterioration of the film. On the other hand, the excessive addition may cause the propagation of certain bacteria. Therefore, when the sterilizing method is performed by adding an acid such as sulfuric acid to the raw water supplied to the membrane separation device of the present invention, it is preferable not to add an oxidizing agent. Creatures will breed.

To cope with this problem, an oxidizing agent is added intermittently in the pretreatment step, and a reducing agent is added before the supply to the membrane separation device, so that the pipe of the pretreatment step, the filtration water tank, etc. The problem is solved by disinfecting organisms that have adhered to and deposited on the surface. According to this method, it is also effective to prevent the deterioration of the film at the same time.

At this time, the addition concentration, the addition time, or the addition frequency of the oxidizing agent and the reducing agent were determined in the same manner as in the case of sterilization of the membrane separation device, such as the number of viable bacteria in the raw water and the AOC concentration, the amount of the bacterial cells and the AO
It is preferable to appropriately change the C concentration, the number of viable cells and BFR, or the value obtained from the combination of the amount of cells and BFR. For example, in the case of a combination of the viable cell count and the AOC concentration, the viable cell count in the raw water is less than 1.0 × 10 ³ cfu / ml, and
In microbiologically relatively clean raw water, where the AOC concentration is less than 10 μg / l, the concentration of oxidizing agent added is 0.1.
~ 1.0 mg / l, addition time is 0.1 ~ 1.0
Within the range of time, the addition frequency is preferably within a range of once a year to once a month. Conversely, the number of viable bacteria in raw water is 1.0 ×
10 ⁵ cfu / ml or more, and AOC concentration is 50μ
g / l or more of raw water that is very rich in microorganisms,
For example, the addition concentration of the fungicide is in the range of 1.0 to 5.0 mg / l, the addition time is in the range of 1.0 to 5 hours, and the addition frequency is in the range of once a week to once a day. Should be sterilized. Even in the case of other combinations, it is preferable to perform sterilization by the same method as described above. Regarding the addition of the reducing agent, in any case, it is preferable to add a considerable amount necessary to completely eliminate the oxidizing agent in accordance with the time and frequency of adding the oxidizing agent.

Further, it is preferable that the sterilization in the pretreatment and the sterilization of the membrane separation device, which is the subsequent step, be performed at the same time, that is, in synchronization with each other, since the sterilization efficiency is increased. Such an intermittent oxidizing agent (chlorine disinfectant) adding method in the pretreatment step has a remarkable effect of reducing the processing cost such as the cost of chemicals with respect to the continuous addition of the oxidizing agent. This is remarkable in the fresh water producing method described above, and it has been difficult to carry out the conventional sterilizing method by adding a high concentration of sodium bisulfite.

The method for producing fresh water of the present invention can be suitably applied to separation and concentration of liquids and solids using a microfiltration membrane, and separation and concentration of turbid components using an ultrafiltration membrane. However, it is particularly suitable for separating or concentrating dissolved components using a reverse osmosis membrane. Above all, it is highly effective in desalination of seawater and brackish water, production of industrial water, production of pure water or ultrapure water, production of medicinal water, concentration of fruit juice, turbidity of tap water, advanced treatment in tap water, etc. . In addition, in the case of producing drinking water, according to the present invention, it is difficult to generate excessive free chlorine, so that generation of trihalomethane and the like can be suppressed low. The method of the present invention is a particularly effective method for killing bacteria and microorganisms contained in seawater.

[0061]

(Example 1) A pretreatment device for performing coagulated sand filtration and polishing filtration using surface seawater of Matsumae Port, Ehime Prefecture as a feedwater, and a cross-linked aromatic polyamide-based reverse osmosis membrane module with a diameter of 4 inches are provided. A seawater desalination apparatus as shown in FIG. 2 having three lines of membrane separation devices was operated to perform reverse osmosis separation for desalinating seawater. In FIG. 2, the same devices are denoted by the same reference numerals as those in FIG. The operation of each device is the same as that shown in FIG. The measurement of the viable cell count and the AOC concentration in the supplied seawater was performed as follows.

Viable cell count: 100 μl of the supplied seawater sample was spread on an agar medium for marine bacteria adjusted to pH 7, and the temperature was adjusted to 20 ° C.
For 3 days, the number of colonies was counted, and the number of viable cells was measured.

AOC concentration: 3% sulfuric acid was added to the supplied seawater sample.
The above seawater sample to which sulfuric acid had been added was placed in a flat-bottomed test tube which had been added to a concentration of 00 mg / l and sterilized in advance, and neutralized to a pH of about 8 with 1N sodium hydroxide. Further, 2.8 mg / l of sodium nitrate (0.5 mg / l as a nitrogen atom) and 0.3 mg / l of dipotassium phosphate were used.
l (0.05 mg / l as a phosphorus element), TES (Tr
ace Element Solution: Tetrasodium ethylenediaminetetraacetate, iron sulfate, boric acid, cobalt chloride, zinc chloride, manganese chloride, sodium molybdate, nickel chloride, copper chloride, and selenite are contained as the solute in a concentration of 0.032 mg. / L, 50 μg / l, 100 μg / l, 150 μg /
l, and 1% of the seawater without sulfuric acid added at the same time was added so as to have a concentration of 1%, and a cap made of polypropylene was added. Then, in a dark place in an incubator adjusted to the seawater temperature at the time of sample collection. 1. Stationary culture, and sampled and sterilized every 24 hours from the start of culture
10, 100, 1000 and 10000 in 5% saline
After dilution to four times the standard, three plates were spread on an agar medium for marine bacteria at each dilution level and cultured at the same temperature as the seawater sample. For medium samples sampled and cultured every 24 hours, select a dilution at which the number of colonies after culturing is in the range of 30 to 300 per plate for each sampling time. The number of proliferation was counted, the correlation between the sodium acetate concentration and the maximum number of proliferation was determined and regression analysis was performed.

(AOC concentration: μg / l) = [(viable cell count:
cfu / ml) -774,000] / 3,080 The above operation was carried out every month, and the number of viable bacteria and AOC concentration in the supplied seawater were measured each time. As shown in FIG.
Of the first series of the seawater desalination plant was operated for one year. (Example 2) The same supply seawater and the same apparatus were used in the same place as in Example 1, and the amount of the viable cells was measured by the ATP measurement method instead of the viable cell count, and the BFR was measured as follows instead of the AOC concentration.

Cell quantity: A 1 ml sample of the supplied seawater was placed in a test tube, an ATP extraction reagent was added thereto, and an ATP luminescence reagent (a mixture of luciferase, luciferin, etc.) was added. Made by science,
ATP concentration is measured in a compact Lumi VS501), and the numerical value is defined as the bacterial cell amount.

BFR: A slide glass having a surface area of 20 cm ^{2 on} one side is immersed in the vicinity of an intake pipe of raw seawater, pulled up after about three weeks, scraped off the attached matter on the surface of the slide glass, and weighed. Next, this attached sample 1
0 mg was put into a test tube for ATP measurement, diluted and dispersed in pure water of sterile water, and the ATP concentration of the sample was measured in the same manner as in the measurement of the amount of cells, and the adhesion rate per day per cm ² was measured. The BFR value is obtained.

The above operation was carried out every two months to measure the amount of bacterial cells in the supplied seawater and the BFR each time, and the sterilization conditions were selected from the combinations of Example 2 shown in Table 1 below. Then, the first series of sterilization of the seawater desalination apparatus of FIG.
I ran for a year. (Example 3) The same supply seawater and the same apparatus were used in the same place as in Example 1, and the AOC concentration in the supply seawater and the amount of cells by the ATP measurement method were determined every two months by the same method as in Examples 1 and 2, respectively. The sterilization conditions according to this were selected from the combinations of Example 3 shown in Table 1, and the second series of sterilization of the seawater desalination apparatus shown in FIG. 2 was performed and operated for one year. (Example 4) The number of viable bacteria in the supplied seawater and the BFR were measured every two months by the same method as in Examples 1 and 2 using the same supplied seawater and the same device at the same place as in Example 1,
The sterilization conditions were selected from the combinations of Example 4 shown in Table 1, and the third series of sterilization of the seawater desalination apparatus shown in FIG. 2 was performed and operated for one year. (Comparative Example 1) At the start of operation, the number of viable bacteria in the supplied seawater was measured in the same manner as in the example.
Since it was ⁴ cfu / ml, conditions were selected as in Comparative Example 1 in Table 1, and the sterilization of the second series in FIG. 2 was performed without changing these conditions for one year (without controlling). The operation was performed in the same manner as in Example 1 while performing the operation. (Comparative Example 2) Regardless of the number of viable bacteria in the supplied seawater and the AOC concentration, the condition of Comparative Example 2 in Table 1 was used for one year without changing the conditions (without controlling), and the third series of FIG. The operation was carried out in the same manner as in the example, while performing the sterilization of.

FIG. 3 shows the change in the amount of fresh water produced by the reverse osmosis membrane module for one year in Examples 1 to 4 and Comparative Examples 1 and 2. In addition, one year later, each element in the reverse osmosis membrane module was extracted, disassembled, and the amount of organic matter in the attached matter on the membrane surface was measured. The results show that sodium hypochlorite, sodium bisulfite consumed in one year and Table 1 shows the amount of sulfuric acid.

As a result, in Examples 1 to 4, there was almost no change in the amount of fresh water produced by the reverse osmosis membrane module for one year.
The amount of organic matter attached to the disassembly film was very small.
On the other hand, in Comparative Example 1, although the amount of consumed chemicals was smaller than that of the example, the amount of water produced by the reverse osmosis membrane module was reduced, and the amount of organic substances attached to the disassembly membrane was larger than that of the example. became. Further, in Comparative Example 2, although the amount of the consumed chemical was the largest, the amount of water produced in the reverse osmosis membrane module was reduced, and the amount of the organic substances attached to the disassembly membrane was the largest.

[0070]

[Table 1]

[0071]

[Table 2]

[0072]

According to the present invention, when adding a bactericide to raw water and supplying it to the separation membrane, the number of viable bacteria and assimilable organic carbon concentration in raw water, the amount of cells contained in raw water and the amount of assimilable organic Based on the carbon concentration, the number of viable bacteria contained in the raw water and the biofilm formation rate, or the amount of cells contained in the raw water and the biofilm formation rate, selected from the group consisting of the addition concentration of the fungicide, the addition time and the addition frequency Since at least one condition is controlled, optimal sterilization conditions can be selected according to the properties of raw water,
Insufficient or excessive sterilizing agents are less likely to occur, and efficient sterilization can be performed. Therefore, accumulation of microorganisms and metabolites thereof on the piping and the separation membrane of the fresh water generator is suppressed, and the performance of the fresh water generator can be maintained at a high level without lowering the amount of fresh water.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a fresh water generator for performing a fresh water method according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a seawater desalination apparatus used in Examples and Comparative Examples.

FIG. 3 is a schematic diagram showing a change in the amount of fresh water in Examples and Comparative Examples.

[Explanation of symbols]

 1: intake pipe 2: intake pump 3: chemical injection device (coagulant, oxidizing germicide) 4a: coagulation filtration device 4b: polishing filtration device 5: intermediate tank 6a: chemical injection device (reducing agent) 6b: chemical injection device (Disinfectant) 7: Security filter 8: High pressure pump 9: Separation membrane module 10: Permeated water flow channel 11 a: Decarbonation device 11 b: Calcium addition device 12: Chlorine injection device 13: Concentrated water neutralization device 14: Concentrated water flow channel 16 a: 1st line 16b: 2nd line 16c: 3rd line 50: Fresh water generator (whole)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/50 510 C02F 1/50 510A 520 520F 531 531J 531M 531P 532 532B 540 540B 550 550H 560 560E 1/76 1/76 A F term (reference) 4D006 GA03 HA21 HA41 HA61 KA03 KA51 KD06 KD11 KD12 KD23 KD24 KE07R KE30Q MC54 PB03 4D050 AA06 AB06 BB05 BB06 BD06 CA09

Claims (8)

[Claims] 1. A method of adding a bactericide to raw water and supplying it to a separation membrane, wherein the number of viable bacteria and the concentration of assimilable organic carbon contained in the raw water, the amount of cells contained in the raw water and the concentration of assimilable organic carbon, At least one condition selected from the group consisting of the concentration, time and frequency of addition of a bactericide based on the number of viable bacteria and the rate of biofilm formation, or the amount of biomass and the rate of biofilm formation in the raw water. Controlling fresh water. 2. The fresh water producing method according to claim 1, wherein the pH of the raw water is controlled to 4 or less. 3. The fresh water producing method according to claim 1, wherein sulfuric acid is used as a bactericide. 4. The method for producing fresh water according to claim 1, wherein a reverse osmosis membrane is used as the separation membrane. 5. Use of seawater or brackish water as raw water,
The fresh water producing method according to claim 1. 6. The fresh water producing method according to claim 1, wherein an oxidizing agent is added to the raw water, a reducing agent is added, and then a bactericide is added. 7. The number of viable bacteria and assimilable organic carbon concentration in raw water, the amount of cells and assimilable organic carbon concentration in raw water, the viable bacterial count and biofilm formation rate in raw water, or The fresh water production according to claim 6, wherein at least one condition selected from the group consisting of an addition concentration, an addition time, and an addition frequency of the oxidizing agent or the reducing agent is controlled based on the amount of the contained bacterial cells and the biofilm formation rate. Method. 8. Water obtained by the method for producing fresh water according to claim 1.