JP2024036939A - Water treatment method and apparatus - Google Patents

Abstract

To provide a water treatment method and apparatus, capable of stably membrane-filtering treatment water containing a high molecular weight biopolymer, without causing clogging in a filter membrane.SOLUTION: A water treatment method that clarifies treatment water using a water treatment apparatus, implements, by a water treatment apparatus provided with a separation membrane facility, the following steps (1) to (4): (1) a filtration step of passing and filtering the treatment water through a porous separation membrane module; (2) a cleaning step of cleaning the porous separation membrane module; (3) a chemical cleaning step of cleaning the porous separation membrane module with a chemical; and (4) a discharging step of discharging a cleaning liquid remaining on an outside surface of and inside the porous separation membrane module. The water treatment method determines an operation condition of the water treatment apparatus according to a concentration of a high molecular weight biopolymer contained in the treatment water, the biopolymer having a peak in molecular weights of 1,000,000 or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a water treatment method and apparatus for clarifying treated water containing high molecular weight biopolymers.

Filtration membranes, which are used to filter various types of raw water, are used in various separation membrane devices because they have excellent filtration accuracy, require less installation space, and are easy to manage.

However, in separation membrane devices using such filtration membranes, as filtration continues, the substances to be removed in the raw water adhere to the membrane surface and clog the pores, resulting in a gradual decline in filtration performance. The problem is that it eventually becomes impossible to filter.

Therefore, in order to maintain filtration performance, gas cleaning such as air is introduced as bubbles into the raw water side of the filtration membrane, and backwashing media such as filtered water or clear water is introduced from the filtrate side in the opposite direction to the filtration direction. Back-pressure water cleaning (hereinafter referred to as backwashing), which removes deposits from the filtration surface of a membrane by ejecting water, is generally performed.

Japanese Unexamined Patent Publication No. 6-182355 International Publication No. 2009/020157 International Publication No. 2018/105569

In order to remove deposits on the membrane surface and maintain a high membrane filtration flux, it is effective to increase the flow rate during gas cleaning and lengthen the gas cleaning time. However, these methods increase the vibration of the filtration membrane during gas cleaning, which places a load on the filtration membrane, resulting in a problem that the life of the filtration membrane is shortened. In addition, backwashing methods using oxidizing agents such as sodium hypochlorite or ozonated water, and methods in which air or ozonized air is introduced as bubbles into the raw water side of the filtration membrane are effective in increasing the cleaning effect. Depending on conditions such as turbidity of raw water, a sufficiently stable filtration flux may not always be obtained. Another possible method for cleaning the separation membrane device is to fill a membrane dipping tank with a chemical solution, but this method has problems in that it requires a large amount of chemical solution and is complicated to operate.

Furthermore, it has been said that humic substances, mainly humic acid and fulvic acid, are the main cause of fouling when filtering natural water such as river water and seawater.

A method of removing humic substances from the water to be treated and then subjecting it to membrane filtration treatment is disclosed in Patent Document 1 and Patent Document 2, but since humic substances are unlikely to interfere with membrane filtration in the first place, the effectiveness is limited. It was a target. Furthermore, a method of measuring the biopolymer concentration, removing humic substances, adding a flocculant, and performing membrane filtration treatment is disclosed in Patent Document 3.
However, the method of adding a flocculant after removing humic substances is also not a practical method because it takes time and effort to remove humic substances.

Through studies conducted by the present inventors, it has become clear that the fouling substance that induces clogging of filtration membranes is a biopolymer composed of polysaccharides and proteins derived from microorganisms. In particular, seawater has a higher concentration of biopolymers than river water, making it difficult to filter.

The present invention has been made to solve such problems. The present inventors have discovered that the membrane fouling properties of substances commonly referred to as biopolymers vary greatly depending on their molecular weight, and that those with a molecular weight of 1,000,000 or more are particularly correlated with membrane fouling properties. Water that can be stably membrane-filtered by detecting in advance the water to be treated that contains high-molecular-weight biopolymers that have a peak and taking countermeasures to prevent clogging before the filtration membrane becomes clogged. A processing method and apparatus are provided.

The water treatment method of the present invention is as follows.
<Aspect 1>
A water treatment method for clarifying water to be treated using a water treatment device, the method comprising:
The method includes the following steps (1) to (4) using the water treatment apparatus equipped with separation membrane equipment:
(1) A filtration step in which the water to be treated is passed through a porous separation membrane module and filtered;
(2) a cleaning step of cleaning the porous separation membrane module;
(3) a chemical cleaning step of cleaning the porous separation membrane module with a chemical;
(4) a discharge step of discharging the cleaning liquid remaining on the outer surface and inside of the porous separation membrane module;
A method of implementing
A water treatment method in which operating conditions of the water treatment device are determined according to a concentration of a high molecular weight biopolymer having a peak at a molecular weight of 1,000,000 or more contained in the water to be treated.
<Aspect 2>
The water treatment method according to aspect 1, wherein the washing step includes one or more treatments selected from the group consisting of the following treatments.
a backwashing process of passing the filtrate through the porous separation membrane module from the inner surface of the separation membrane module to the outside;
an air scrubbing process of cleaning the outer surface of the porous separation membrane module by discharging compressed air and shaking the separation membrane with the air passing outside the separation membrane;
a flushing process of washing the outer surface of the separation membrane by passing the liquid to be filtered outside the porous separation membrane module;
<Aspect 3>
The operating conditions of the water treatment equipment include at least one selected from the group consisting of filtration time, filtration flux, backwash air cleaning time, backwash flux, air flow rate, flushing time, flushing flow rate, chemical concentration, and chemical cleaning interval. The water treatment method according to aspect 1 or 2, wherein one of the following is changed.
<Aspect 4>
In the water treatment method, at least one pretreatment facility selected from the group consisting of coagulation sedimentation treatment facility, pressure flotation treatment facility, flocculant addition treatment facility, and oxidizing agent addition treatment facility is installed before the filtration step. The water treatment method according to any one of aspects 1 to 3.
<Aspect 5>
According to aspect 4, at least one selected from the group consisting of the type of chemical introduced, the residence time of the chemical and the water to be treated, and the amount of the chemical added is changed as a setting condition of the pretreatment equipment. Water treatment methods.
<Aspect 6>
The water treatment device includes the pretreatment equipment and the separation membrane equipment, and the setting conditions of the pretreatment equipment or the filtration step are determined depending on the concentration of the high molecular weight biopolymer contained in the water to be treated. , the water treatment method according to any one of aspects 3 to 5, wherein one or more operating conditions of the washing step, the chemical washing step, and the discharge step are determined.
<Aspect 7>
The water treatment method according to any one of aspects 1 to 6, wherein the water to be treated is natural water.
<Aspect 8>
A water treatment device that processes water to be treated including the natural water,
The water treatment device includes a high molecular weight biopolymer measuring device that measures the high molecular weight biopolymer concentration in the water to be treated;
The pretreatment equipment provided for the water to be treated before membrane filtration;
A water treatment device comprising a separation membrane facility that performs a filtration step of filtering the water to be treated treated with the pretreatment facility using a separation membrane module.
<Aspect 9>
The water treatment device according to aspect 8, wherein the high molecular weight biopolymer measuring device is an LC-OCD (Liquid Chromatography-Organic Carbon Detection).
<Aspect 10>
The water according to aspect 8 or 9, wherein the measurement of the high molecular weight biopolymer concentration is carried out by removing the low molecular weight substances, separating the high molecular weight biopolymer using a molecular sieve, and measuring the concentration. Processing equipment.

According to the water treatment method and apparatus of the present invention, it is possible to detect in advance high molecular weight biopolymers that have a molecular weight of 1,000,000 or more and have an extremely high correlation with clogging of filtration membranes, which are contained in the water to be treated. Before clogging occurs, membrane filtration can be stably performed by controlling the operating conditions of the filtration process, cleaning process, etc. and the setting conditions of the pretreatment equipment. Alternatively, if it is foreseeable that clogging will not occur, the filtration flux can be increased during operation.

1 is a diagram showing a schematic configuration of an embodiment of a water treatment device of the present invention.

EMBODIMENT OF THE INVENTION Below, the suitable embodiment of the water treatment apparatus based on this invention is described with reference to drawings.

FIG. 1 is a block diagram showing an example of a water treatment apparatus according to an embodiment of the present invention.

The water treatment device 1 of this embodiment is equipped with a pretreatment facility 2 which is a coagulation sedimentation treatment facility or a pressure flotation treatment facility, or a flocculant addition treatment facility or an oxidizing agent addition treatment facility, which performs pretreatment before the filtration step. At least one pretreatment facility selected from the group consisting of a certain pretreatment facility 3 is installed, and includes a separation membrane facility 4 and a high molecular weight biopolymer measuring device 9.
In the water treatment device 1 of this embodiment, first, water to be treated (natural water) containing a high molecular weight biopolymer is continuously or intermittently introduced into the high molecular weight biopolymer measuring device 9, and the water to be treated is After measuring the concentration of the high molecular weight biopolymer, a flocculant or an oxidizing agent is continuously or intermittently applied to the water to be treated by the pre-treatment equipment 2 and/or the pre-treatment equipment 3 provided before membrane filtration. It is then sent to the separation membrane equipment 4. A filtration step is performed in which the water to be treated treated by the pretreatment equipment 2 and/or the pretreatment equipment 3 is filtered by the separation membrane equipment 4 in which the separation membrane module is incorporated, and filtrate water is obtained from the separation membrane equipment 4. It is configured as follows.

Here, the natural water to be treated contains humic substances, which are decomposition products of plants etc. by microorganisms, and biopolymers, which are metabolites of microorganisms, and as mentioned above, only humic substances are removed. Also, the biopolymer causes clogging of the filtration membrane, and the subsequent separation membrane equipment 4 does not operate stably.
Furthermore, although biopolymers are substances with relatively high molecular weights, the fraction that causes clogging of filtration membranes is the fraction with a molecular weight of 1,000,000 or more (high molecular weight biopolymers). ).

Therefore, the present inventors first measured the concentration of the fraction with a molecular weight of 1,000,000 or more (high molecular weight biopolymer) in the water to be treated and estimated the ease of fouling. We decided to take measures to ensure stable operation of Facility 4.
This embodiment is a water treatment method in which water to be treated is clarified by a water treatment device 1, comprising:
This water treatment method determines the operating conditions of the water treatment device 1 according to the concentration of a high molecular weight biopolymer having a peak molecular weight of 1,000,000 or more contained in the water to be treated.
The water treatment method of this embodiment uses a water treatment apparatus 1 equipped with a separation membrane facility 4, and the following steps (1) to (4) are performed:
(1) A filtration step in which the water to be treated is passed through a porous separation membrane module and filtered;
(2) Cleaning step of cleaning the porous separation membrane module;
(3) Chemical cleaning step of cleaning the porous separation membrane module with chemicals;
(4) a discharge step of discharging the cleaning liquid remaining on the outer surface and inside of the porous separation membrane module;
This is a method of implementing

The concentration of the high molecular weight biopolymer in the water to be treated can be measured using a biopolymer measuring device LC-OCD (Liquid Chromatography-Organic Carbon Detection) or by a membrane concentration method.
The concentration of high molecular weight biopolymer in the water to be treated, as measured by LC-OCD, may in one embodiment be between 10 and 100 μg/L, or between 10 and 40 μg/L, or between 20 and 40 μg/L.
In one embodiment, the concentration of the high molecular weight biopolymer in the water to be treated measured by the membrane concentration method may be 10 to 100 μg/L, 12 to 50 μg/L, or 25 to 50 μg/L.

The setting conditions for the pretreatment equipment of this embodiment include the type of chemical (oxidizing agent, flocculant, etc.) to be introduced, the residence time of the chemical and the water to be treated in the buffer tank 7, and the amount of the chemical added. By changing at least one selected from the following, stable operation can be performed.

When the concentration of high molecular weight biopolymer is high, setting the conditions of pretreatment equipment 2 or 3 to be stronger or increasing the amount of chemicals such as flocculants or oxidizing agents added in the pretreatment equipment can be used in the subsequent separation membrane equipment 4. It was revealed that the system can operate stably. For example, as a setting condition for the coagulation-sedimentation treatment, pressure flotation treatment, flocculant addition treatment, or oxidation agent addition treatment carried out in the pretreatment equipment 2 or 3, the concentration of the chemical introduced in each treatment is set to 10 to 100 mg/L. The amount is preferably 20 to 50 mg/L, more preferably 20 to 50 mg/L, and particularly preferably 40 to 50 mg/L.
On the other hand, when the concentration of high molecular weight biopolymers is low, stable operation can be achieved at low cost by loosening the setting conditions of the pretreatment equipment or reducing the amount of chemicals such as flocculants added. .
The determination of whether the high molecular weight biopolymer concentration is "high" or "low" may be performed according to a threshold concentration arbitrarily set as desired; for example, a concentration above the threshold value is considered "high" and a concentration below the threshold is considered "low". It may be defined as concentration. The threshold concentration may be set at, but not limited to, 25 μg/L, or 30 μg/L, or 35 μg/L for LC-OCD, and 30 μg/L for membrane concentration method. , or 35 μg/L, or 40 μg/L, or 45 μg/L.

More specifically, the water treatment device 1 of this embodiment includes a raw water supply pump 6, a buffer tank 7, and a filtration pump 8 in addition to the above-mentioned pretreatment equipment 2, pretreatment equipment 3, and separation membrane equipment 4. ing.
The water treatment device 1 includes a pretreatment facility 2 and/or a pretreatment facility 3, and a separation membrane facility 4, and includes a high molecular weight biopolymer having a peak molecular weight of 1,000,000 or more contained in the water to be treated. Stable operation can be achieved by determining the setting conditions of the pretreatment equipment 2 or 3 or the operating conditions of one or more of the filtration process, cleaning process, chemical cleaning process, and discharge process described below, depending on the concentration. can be executed.

First, after the water to be treated is sampled online or in-line, the water to be treated is supplied to the high molecular weight biopolymer measuring device 9 . In the high molecular weight biopolymer measuring device 9, after the humic substances are removed, the biopolymers in the high molecular weight band are separated by the fractionation device, and the concentration thereof is quantified. In addition, the water to be treated by the raw water supply pump 6 is continuously or intermittently treated by the pretreatment equipment 2 and/or 3, and in the pretreatment equipment 2, biopolymers are removed from the water to be treated, and biopolymer reduction is reduced. water is produced. In the pretreatment facility 3, the high molecular weight biopolymer is converted into a form that is less likely to clog the membrane.
Moreover, the pretreatment equipment 2 may be installed together with the pretreatment equipment 3, or may be installed independently.

Next, the water to be treated from which the biopolymer has been removed by the pretreatment equipment 2 is stored in the buffer tank 7. Alternatively, if the pre-treatment equipment 3 is installed, the water to be treated to which a coagulant or oxidizing agent has been added is temporarily stored in the buffer tank 7, but in this case also, the water to be treated is , a flocculant or an oxidizing agent is added continuously or intermittently by the pretreatment equipment 3.

Then, in the buffer tank 7, the polymer substances (biopolymers) in the water to be treated are aggregated or decomposed, and aggregate-containing water or low-molecular-weight water is produced.

Next, the aggregate-containing water or low-molecular water generated in the buffer tank 7 is supplied to the separation membrane equipment 4 by the filtration pump 8, and the water to be treated (aggregate-containing water or low-molecular water) treated with the pretreatment equipment is A filtration process is performed in which water) is filtered using a separation membrane module, and clear filtered water is obtained.

Here, in the pretreatment equipment 2, a flocculating sedimentation process or a pressure flotation process is performed, and the flocculant added (introduced) includes an inorganic flocculant, a polymer flocculant, and the like. In the case of inorganic flocculants, ferric chloride, polyferric sulfate, polyaluminum chloride (PAC), and aluminum sulfate (aluminum sulfate) are used, but polyaluminum chloride is It is preferable because it is highly effective. In the case of polymer flocculants, polyacrylamide and the like are preferably used, but inorganic flocculants are more preferred.
When the pretreatment equipment 3 is a flocculant addition treatment equipment, by adding the flocculant, the biopolymer is flocculated and the filtration membrane becomes less likely to be clogged. In the case of an oxidizing agent addition treatment facility, by adding an oxidizing agent, the high molecular weight biopolymer is reduced in molecular weight, and this also becomes a form that is less likely to clog the filtration membrane. Although the total amount of biopolymers remains the same, these have a shape that is sufficiently larger than the pores of the filtration membrane, or a shape that is small enough to pass through the pores of the filtration membrane as is.
In the pretreatment equipment 3, in the case of a flocculant addition treatment equipment, an inorganic flocculant is preferable. As the inorganic flocculant, ferric chloride, polyferric sulfate, polyaluminum chloride, aluminum sulfate, etc. are used as described above, but polyaluminum chloride is preferred because it has a high effect relative to the amount introduced. In the case of oxidizing agent addition treatment equipment, chlorine-based oxidizing agents such as sodium hypochlorite (NaClO) and chlorine dioxide, and peroxides such as hydrogen peroxide, sodium persulfate, and ozone are used. Sodium chlorate (NaClO) is preferred.
It is preferable that the residence (contact) time of the agent such as a flocculant or oxidizing agent and the water to be treated in the buffer tank 7 is about 1 to 5 minutes, and as in the buffer tank 7 of this embodiment, a short circuit flow may occur. It is preferable to use equipment that does not have
Further, the amount of the chemical (concentration of flocculant, oxidizing agent, etc.) added to the water to be treated is preferably 10 to 100 mg/L, more preferably 20 to 50 mg/L, and particularly preferably 40 to 50 mg/L.

The addition method in the pretreatment equipment 3 is not particularly limited, but a method that allows quantitatively controlled injection is preferable, and for example, it is preferable to use a gravity flow method, an injection method, a pump pressure feeding method, or the like. Moreover, it is preferable to also use pH adjusters such as acids and alkalis, if necessary.

(How to operate hollow fiber membrane module)
The separation membrane equipment 4 of this embodiment includes a hollow fiber membrane module 4-1 which is a porous separation membrane module, and can be incorporated into an appropriate filtration system and applied to the filtration process of this embodiment.
FIG. 1 shows a block diagram of an example of a filtration system for performing a filtration process, a cleaning process, a chemical cleaning process, and a discharge process using the hollow fiber membrane module of this embodiment.

The separation membrane equipment 4 in FIG. 1 has a configuration in which the hollow fiber membrane module 4-1 of this embodiment, the filtrate tank 5, and the compressor 4-2 are connected by piping in which valves are appropriately arranged. In FIG. 1, pumps for liquid feeding, drain piping normally installed in each tank, chemical liquid tanks for chemical cleaning and associated piping, sensors for checking operating conditions, and the like are omitted.
In the water treatment method of this embodiment, the operating conditions of the water treatment device 1 including steps (1) to (4) include filtration time, filtration flux, backwash air cleaning time, backwash flux, air flow rate, and flushing. Stable operation of the water treatment device 1 can be performed by changing at least one selected from the group consisting of time, flushing flow rate, chemical concentration, and chemical cleaning interval.
The filtration time is preferably 20 to 38.5 minutes, more preferably 20 to 28.5 minutes.
The filtration flux is preferably 50 to 100 LМH, more preferably 80 to 100 LМH.
The backwash air cleaning time is preferably 0.1 to 2 minutes, more preferably 0.5 to 1 minute.
The backwash flux is preferably 30 to 240 LМH, more preferably 50 to 100 LМH, and particularly preferably 80 to 100 LМH.
The air flow rate is preferably 3 to 10 Nm ³ /h, more preferably 5 to 8 Nm ³ /h.
The flushing time is preferably 0.3 to 1 minute, more preferably 0.5 to 1 minute.
The flushing flow rate is preferably 1 to 5 m ³ /h, more preferably 3 to 5 m ³ /h.
The concentration of the chemical is preferably 100 to 5,000 mg/L, more preferably 500 to 1,000 mg/L.
The chemical cleaning interval is preferably 0.5 to 7 days, more preferably 1 to 2 days.
Note that the chemical cleaning interval refers to the time between the timing when the hollow fiber membrane module is cleaned with a chemical and the timing when the hollow fiber membrane module is cleaned again with a chemical.

Using the separation membrane equipment 4 shown in FIG. 1, the steps of this embodiment, including predetermined filtration steps, washing steps, chemical washing steps, and discharge steps: steps (1) to (4), include, for example, the following steps. It can be done as follows.

《Filtration step (1)》
In the filtration step, the water to be treated is passed through the hollow fiber membrane in the hollow fiber membrane module 4-1, which is a porous separation membrane module, and filtered to obtain a filtrate. Filtration can be carried out by external pressure filtration or internal pressure filtration, but external pressure filtration reduces the load per unit membrane area and is suitable for removing turbidity from large amounts of water through physical cleaning such as air scrubbing. It is preferable to carry out by. In the water treatment apparatus 1 of FIG. 1, the water to be treated in the buffer tank 7 is transferred from the inlet (4-1-2) to the hollow fiber membrane module 4-1 via the filtrate sending valve (V1). The liquid is introduced from the outside of the hollow fiber membrane, passes through the thick part of the hollow fiber membrane, is filtered, and oozes into the inner space of the hollow fiber membrane as a filtrate. The filtrate seeped into the inner space of the hollow fiber membrane is stored in the filtrate tank 5 via the filtrate port 4-1-1 and the filtrate feed valve (V2).

《Cleaning step (2)》
In the cleaning step, the porous separation membrane module is cleaned. Further, the cleaning step preferably includes one or more treatments selected from the group consisting of backwashing (BW) treatment, flushing (FL) treatment, and air scrubbing (AS) treatment. Furthermore, backwashing (BW) processing or flushing (FL) processing and air scrubbing (AS) processing may be performed in combination, or ASBW or ASFL may be performed in which AS and BW or FL are performed simultaneously.
BW or FL may be performed prior to ASBW or ASFL, or FL may be performed after ASBW or ASFL.
Moreover, you may implement a filtration process before a washing process.
When the separation membrane equipment 4 of FIG. 1 is used, the BW, FL, and AS, the ASBW and ASFL, the chemical cleaning process, and the discharge process can be performed as follows, respectively.

<Backwash (BW) treatment>
In BW, the filtrate is passed from the inner surface of the hollow fiber membrane in the hollow fiber membrane module 4-1 to the outside.
In this case, the filtrate in the filtrate tank 5 is introduced into the hollow fiber membrane module 4-1 from the filtrate port 4-1-1 via the backwash valve (V3), and from the inside of the hollow fiber membrane. It passes through the thick part of the hollow fiber membrane and seeps out onto the outer surface of the hollow fiber membrane. In this process, the suspended substances deposited in the pores of the thick part of the hollow fiber membrane are pushed out to the outside of the hollow fiber membrane, thereby cleaning the hollow fiber membrane.
The filtrate seeped out onto the outer surface of the hollow fiber membrane is discharged to the outside of the system via the inlet 4-1-2 and the cleaning drain valve (V4).
BW may be performed after the chemical cleaning step described below.

<Flushing (FL)>
In FL, the liquid to be filtered is passed through the outside of the hollow fiber membrane module 4-1, and suspended substances adhering to the outside surface of the hollow fiber membrane module 4-1 are washed away by being washed outside the hollow fiber membrane. .
In the FL, the filtrate in the filtrate tank (buffer tank) 7 was introduced into the hollow fiber membrane module 4-1 from the inlet 4-1-2 via the filtrate sending valve (V1). Thereafter, it passes through the outer space of the hollow fiber membrane and is discharged to the outside of the system via the cleaning discharge port 4-1-3 and the cleaning drainage discharge valve (V5).
FL may be performed after the discharge step or chemical cleaning step described below.

<Air scrubbing (AS)>
In AS, compressed air is introduced from the inlet 4-1-2 and discharged from the cleaning outlet 4-1-3, and air (bubbles) passes through the outside of the hollow fiber membrane (separation membrane) module 4-1. By shaking the hollow fiber membrane, the outer surface of the hollow fiber membrane module 4-1 is cleaned.
In the AS, air compressed by the compressor 4-2 is introduced into the hollow fiber membrane module 4-1 from the inlet 4-1-2 via the AS valve (V6), and passes through the outer space of the hollow fiber membrane. Then, it is discharged to the outside of the system via the cleaning discharge port 4-1-3 and the cleaning waste liquid discharge valve (V5).

<Backwashing - Air scrubbing simultaneous cleaning (ASBW)>
In ASBW, the above-mentioned BW and AS are performed simultaneously. That is, the filtrate in the filtrate tank 5 is introduced into the hollow fiber membrane module 4-1 from the filtrate port 4-1-1 via the backwash valve (V3), and is then introduced into the hollow fiber membrane module 4-1 through the inlet port 4-1-2 and the washing port. The liquid is discharged to the outside of the system through the drain valve (V4), and the compressed air from the compressor 4-2 is supplied to the hollow fiber membrane module 4 from the inlet 4-1-2 through the AS valve (V6). -1, and is discharged outside the system via the cleaning discharge port 4-1-3 and the cleaning waste liquid discharge valve (V5).

<Simultaneous flushing-air scrubbing cleaning (ASFL)>
In ASFL, the above-mentioned FL and AS are performed simultaneously. That is, after the filtrate in the filtrate tank (buffer tank) 7 is introduced into the hollow fiber membrane module 4-1 from the inlet 4-1-2 via the filtrate sending valve (V1). , is discharged to the outside of the system through the cleaning discharge port 4-1-3 and the cleaning waste liquid discharge valve (V5), and compressed air from the compressor 4-2 is introduced through the AS valve (V6). It is introduced into the hollow fiber membrane module 4-1 through the port 4-1-2, and is discharged outside the system via the cleaning discharge port 4-1-3 and the cleaning drainage discharge valve (V5).

《Chemical cleaning process (3)》
In the chemical cleaning step, the porous separation membrane module is cleaned with chemicals. In the chemical cleaning process, the chemical injection unit 4-3 and the backwash pump 10 (not shown) operate simultaneously to inject chemicals into the hollow fiber membrane module 4-1. After filling the hollow fiber membrane module with chemicals, the chemicals decompose or dissolve membrane contaminants by leaving the module for several minutes to several hours. After the chemical cleaning is completed, the cleaning liquid is drained out of the system via the cleaning drain valve (V4). Furthermore, the inside of the hollow fiber membrane module may be made neutral by performing a flushing process or a backwashing process. When the membrane contaminant is an organic substance, an alkali or an oxidizing agent is preferably used as the chemical. If the membrane contaminants are inorganic, acids are preferably used.
For example, the chemicals used include oxidizing agents such as sodium hypochlorite (NaClO) and chlorine dioxide, and peroxides such as hydrogen peroxide, sodium persulfate, and ozone. is preferred.

《Discharge process (4)》
In the discharge step, the cleaning liquid remaining on the outer surface and inside of the hollow fiber membrane module 4-1 is discharged.
The discharge step may be performed after the cleaning step or the chemical cleaning step.
In this discharge process, compressed air introduced from the cleaning discharge port 4-1-3 of the hollow fiber membrane module 4-1 is applied to the outer surface of the hollow fiber membrane module through the discharge process compressed air valve (V7). This can be done by discharging the cleaning liquid remaining inside the system to the outside of the system through the inlet 4-1-2 and the cleaning drain valve (V4).

<Measurement of biopolymer concentration by LC-OCD (Liquid Chromatography-Organic Carbon Detection)>
The biopolymer concentration is measured by the high molecular weight biopolymer measuring device 9 in treated water that has not been subjected to pretreatment or membrane filtration. As the high molecular weight biopolymer measuring device 9, it is preferable to use LC-OCD (Liquid Chromatography-Organic Carbon Detection).
High molecular weight biopolymers contained in natural water (water to be treated) usually have a molecular weight of more than 1,000,000, so they cannot be measured with a normal column configuration. As columns, one Tosoh size exclusion chromatography column Toyopearl HW-65s and two Toyopearl HW-50s are connected in series in this order to fractionate the molecular weight, resulting in a retention time of 40 minutes. If there is a peak with a molecular weight of less than 1,000,000, it can be measured as a high molecular weight biopolymer having a peak with a molecular weight of 1,000,000 or more.

<Measurement of biopolymer concentration using membrane concentration method>
Furthermore, regarding the high molecular weight biopolymer measuring device 9, the following membrane concentration method may be implemented instead of LC-OCD. That is, by first removing low molecular weight substances from the water to be treated, and then concentrating the removed water using a filter membrane with an average pore size of 0.1 μm, the soluble total organic carbon concentration (Total The concentration of the biopolymer can be determined by measuring the organic carbon. In this case, the removal of low molecular weight substances is achieved by, for example, circulating filtration while adding water through a molecular sieve such as an ultrafiltration membrane with a molecular weight cutoff of about 13,000, thereby filtering out substances with a molecular weight of 13,000 or less. The biopolymer having a molecular weight of 13,000 or more is separated from the system. The material of the ultrafiltration membrane is preferably hydrophilic polyacrylonitrile or the like because non-specific adsorption of the biopolymer to the membrane can be suppressed. If circulation filtration is performed for a long time, even biopolymers with a molecular weight larger than the molecular weight cutoff may slip through the filtration membrane and be discharged depending on the molecular shape, so the molecular weight cutoff of the ultrafiltration membrane used may be , preferably about 5,000 to 100,000, more preferably 10,000 to 50,000. Furthermore, it is preferable to adjust the ionic strength so that there is no change when adding water, since this makes it difficult for the high molecular weight biopolymer to be filtered and discharged. Once low molecular weight substances have been sufficiently removed, a high molecular weight biopolymer can be obtained by circulating and concentrating the liquid through a filter membrane with an average pore size of 0.1 μm. When the molecular weight of the residue thus obtained was measured using the LC-OCD described above, the molecular weight was 1,000,000 or more.

Although the separation membrane equipment 4 is not particularly limited, a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, or the like can be used. Among these, it is particularly preferable to use microfiltration membranes and ultrafiltration membranes, and membrane filtration treatment can be performed stably. Further, as the filtration membrane, it is preferable to use a filtration membrane having an average pore diameter of 0.2 μm or less. More preferably, it is 50 nm or less. Note that the average pore diameter is measured as follows.

First, the filtration membrane is cut in a cross section perpendicular to its length. The cross section is photographed using a scanning electron microscope at a magnification that allows the shapes of as many pores as possible to be clearly confirmed. Next, place a transparent sheet on top of the copy of the electron microscope image, fill in the pores with black using a black pen, etc., and copy the transparent sheet onto white paper, so that the pores are black and the non-pores are black. Clearly differentiated from white. Thereafter, the pore diameters of 100 arbitrarily selected pores are determined using commercially available image analysis software, and the average pore diameter is calculated by calculating the arithmetic average value. As the image analysis software, for example, software "WinRoof" sold by Mitani Shoji Co., Ltd. can be used. Note that the pore diameter refers to the distance between an arbitrary point on the circumference of the pore and a point on the circumference of the pore located at a position opposite to the arbitrary point.

Hereinafter, this embodiment will be described in more detail with reference to Examples and Comparative Examples, but this embodiment is not limited to these Examples.

[Measurement of high molecular weight biopolymer by LC-OCD]
The molecular weight distribution measurement of organic matter and the biopolymer concentration measurement in the water to be treated were carried out using LC-OCD (Model 8, Doclabor), using “Characterization of aquatic humic and non-humic matter with size-exclusion”. chromatography - organic carbon detection - organic nitrogen detection (LC-OCD-OND)” was measured according to the method of Huber et al., Water Research, 45, 879-885 (2011).
The columns used here were Toyopearl HW-50s (manufactured by Tosoh) ⇒ HW-50s ⇒ HW-65s. The measurement sample was pretreated by filtering the water to be treated using a filter with a pore size of 0.45 μm. Through this measurement, each molecular weight fraction is detected as DOC (Dissolved Organic Carbon).
A calibration curve was created using pullulan as a standard sample, and it was confirmed that the water to be treated after filtration contained a high molecular weight biopolymer having a peak with a molecular weight of 1,000,000 or more. The water to be treated after the filtration treatment had a peak at a retention time of less than 40 minutes on LC-OCD, and thus contained a high molecular weight biopolymer having a peak with a molecular weight of 1,000,000 or more. The biopolymer concentration means the carbon component concentration of the biopolymer.
Table 1 below shows the concentrations of high molecular weight biopolymers measured by LC-OCD.

[Measurement of high molecular weight biopolymers using membrane concentration method]
100 mL of the water to be treated was subjected to circulation filtration using an ultrafiltration membrane ACP-0013 (manufactured by Asahi Kasei, material: polyacrylonitrile, molecular weight cut off: 13,000), and 90 mL was filtered and drained. The same amount of ionized water was added. Ion-adjusted water is pure water that has been adjusted with CaCl ₂ to have the same ionic strength as the water to be treated. In this way, water from which low molecular weight substances have been removed is obtained, and this water is filtered through a membrane with a pore size of 0.1 μm (manufactured by Millipore, material: nitrocellulose). Concentrated water was obtained. The concentration of the high molecular weight biopolymer was determined by measuring the TOC (Total Organic Carbon) of this water using a combustion catalytic oxidation type total organic carbon meter (TOC-L, manufactured by Shimadzu Corporation).
Table 1 below shows the concentrations of high molecular weight biopolymers measured by the membrane concentration method.

(Reference examples and working examples)
The water treatment device 1 shown in FIG. 1 was operated for the purpose of obtaining clean water from river surface water. The high molecular weight biopolymer measuring device 9 measured by two methods: LC-OCD method and membrane concentration method. The pretreatment equipment 2 used coagulation sedimentation treatment or pressure flotation treatment, and the pretreatment equipment 3 used either flocculant addition treatment or oxidizing agent addition treatment.
For the coagulation and precipitation treatment, PD-2600 manufactured by Elepon Kakoki Co., Ltd. was used, and the residence time was set to 2 hours. For the pressure flotation treatment, PAL-053 manufactured by Elepon Kakoki Co., Ltd. was used, and the residence time was set to 45 minutes.
Both the coagulation-sedimentation treatment and the pressure flotation treatment used polyaluminum chloride (PAC) as a flocculant.
The pretreatment equipment 3 for carrying out the flocculant addition treatment or the oxidizing agent addition treatment was provided with a polyaluminum chloride addition device or a sodium hypochlorite (NaClO) addition device, respectively. Furthermore, a buffer tank 7 with a volume of 10 m ³ was provided at the subsequent stage. The hollow fiber membrane module 4-1 of the separation membrane equipment 4 is equipped with a hollow fiber MF membrane made of polyvinylidene fluoride (manufactured by Asahi Kasei), with an average pore diameter of 0.1 μm and an effective membrane area of 50 m ² . The external dimensions are 180 mm in diameter and 2000 mm in effective membrane length (cylindrical). The separation membrane equipment 4 is provided with a backwashing means, an air supply means for air scrubbing, and a flushing means. The biopolymer concentration in the water to be treated was 10 to 50 μg/L.

The operating membrane filtration flux is set to 80 to 100 LMH, the filtration time is set to 20 to 38.5 minutes, and the membrane filtration amount in one cycle of filtration at this time is 1.2 to 2.375 m ³ . Depending on the level of the buffer tank 7, treatment is performed by the pre-treatment equipment 2 using the raw water supply pump 6, or PAC or NaClO is supplied from the pre-treatment equipment 3 (flocculant addition treatment equipment or oxidizing agent addition treatment equipment) in front of the filtration membrane. and mixed with the water to be treated, and the buffer tank 7 was controlled so as not to become empty. In either case, the residence time with the water to be treated is set to 20 minutes, and the amount of flocculant or oxidizing agent added is such that the concentration of polyaluminum chloride or sodium hypochlorite in the water to be treated is 20 to 40 mg/L. The solution was added in the following manner, and the residence time in the buffer tank 7 was set to 2 minutes or more. At this time, as summarized in Table 1, filtration tests were conducted for 7 days each in Runs 1 to 14, the filtration operating conditions and pretreatment conditions were set, and the average transmembrane pressure (TMP) for the 7 days was determined. The rate of rise was evaluated.

(Comparative example)
As shown in Table 1, the filtration operating conditions and pretreatment conditions were set, a 7-day filtration test was conducted in Run 15, and the average rate of increase in transmembrane pressure (TMP) over 7 days was evaluated.

In Examples (Runs 5 to 12), when the concentration of high molecular weight biopolymer was high, the filtration operating conditions and pretreatment conditions were set appropriately according to the concentration as shown in Table 1. As a result, the TMP rise rate was 1 kPa/day, and stable operation was possible at low pressure.
In Examples (Runs 13 to 14), when the concentration of high molecular weight biopolymer is low, the setting conditions of filtration operation conditions and pretreatment conditions are changed depending on the concentration, respectively, to the conditions when the concentration of high molecular weight biopolymer is high. Because it was possible to set it loosely compared to the previous model, it was possible to operate at a low cost. Furthermore, as shown in Table 1, the TMP increase rate was 1 kPa/day, so stable operation was possible at low pressure. Furthermore, since it was predicted that the filtration membrane would not be clogged, it was possible to operate with increased filtration flux.
In the reference examples (Runs 1 to 4), when the concentration of high molecular weight biopolymer is low, the filtration operation conditions and pretreatment conditions are set appropriately according to the concentration as shown in Table 1. As a result, the TMP rise rate was 1 kPa/day, and stable operation was possible at low pressure.
On the other hand, in the comparative example (Run 15), unlike the examples (Runs 5 to 12), when the concentration of the high molecular weight biopolymer is high, the setting conditions of the filtration operation conditions and pretreatment conditions are changed depending on the concentration. Because it was not set appropriately, the TMP rise rate became as high as 5 kPa/day as shown in Table 1, and stable operation was not possible.

1 Water treatment equipment 2 Pre-treatment equipment (coagulation sedimentation treatment equipment or pressure flotation treatment equipment)
3 Pre-treatment equipment (flocculant addition treatment equipment or oxidizing agent addition treatment equipment)
4 Separation membrane equipment 4-1 Hollow fiber membrane module (porous separation membrane module)
4-1-1 Filtrate port 4-1-2 Inlet port 4-1-3 Cleaning outlet 4-2 Air supply unit (compressor)
4-3 Chemical injection unit 5 Filtration tank 6 Raw water supply pump 7 Buffer tank (filtrate tank)
8 Filtration pump 9 High molecular weight biopolymer measuring device 10 Backwash pump V1 Filtrate feed valve V2 Filtrate feed valve V3 Backwash valve V4 Washing drain valve V5 Washing drain valve V6 AS valve V7 Discharge Process compressed air valve

Claims (10)

A water treatment method for clarifying water to be treated using a water treatment device, the method comprising:
The method includes the following steps (1) to (4) using the water treatment apparatus equipped with separation membrane equipment:
(1) A filtration step in which the water to be treated is passed through a porous separation membrane module and filtered;
(2) a cleaning step of cleaning the porous separation membrane module;
(3) a chemical cleaning step of cleaning the porous separation membrane module with a chemical;
(4) a discharge step of discharging the cleaning liquid remaining on the outer surface and inside of the porous separation membrane module;
A method of implementing
A water treatment method in which operating conditions of the water treatment device are determined according to a concentration of a high molecular weight biopolymer having a peak at a molecular weight of 1,000,000 or more contained in the water to be treated. The water treatment method according to claim 1, wherein the washing step includes one or more treatments selected from the group consisting of the following treatments.
a backwashing process of passing the filtrate through the porous separation membrane module from the inner surface of the separation membrane module to the outside;
an air scrubbing process of cleaning the outer surface of the porous separation membrane module by discharging compressed air and shaking the separation membrane with the air passing outside the separation membrane;
a flushing process of washing the outer surface of the separation membrane by passing the liquid to be filtered outside the porous separation membrane module; The operating conditions of the water treatment equipment include at least one selected from the group consisting of filtration time, filtration flux, backwash air cleaning time, backwash flux, air flow rate, flushing time, flushing flow rate, chemical concentration, and chemical cleaning interval. The water treatment method according to claim 2, wherein one of the water treatment methods is changed. In the water treatment method, at least one pretreatment facility selected from the group consisting of coagulation sedimentation treatment facility, pressure flotation treatment facility, flocculant addition treatment facility, and oxidizing agent addition treatment facility is installed before the filtration step. The water treatment method according to claim 2. 5. As a setting condition of the pretreatment equipment, at least one selected from the group consisting of the type of chemical to be introduced, the residence time of the chemical and the water to be treated, and the amount of the chemical added is changed. water treatment methods. The water treatment device includes the pretreatment equipment and the separation membrane equipment, and the setting conditions of the pretreatment equipment or the filtration step are determined depending on the concentration of the high molecular weight biopolymer contained in the water to be treated. The water treatment method according to claim 3 or 5, wherein one or more operating conditions of the washing step, the chemical washing step, and the discharge step are determined. The water treatment method according to claim 1 or 2, wherein the water to be treated is natural water. A water treatment device that processes water to be treated including the natural water,
The water treatment device includes a high molecular weight biopolymer measuring device that measures the high molecular weight biopolymer concentration in the water to be treated;
The pretreatment equipment provided for the water to be treated before membrane filtration;
A water treatment device comprising a separation membrane facility that performs a filtration step of filtering the water to be treated treated with the pretreatment facility using a separation membrane module. The water treatment device according to claim 8, wherein the high molecular weight biopolymer measuring device is an LC-OCD (Liquid Chromatography-Organic Carbon Detection). 10. The high molecular weight biopolymer concentration is measured by removing low molecular weight substances, separating the high molecular weight biopolymer using a molecular sieve, and measuring the concentration thereof. Water treatment equipment.

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