JP2013212497A - Water treating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treating method which can improve filtration efficiency economically and to the maximum by optimal chemical washing when being optimal.SOLUTION: A water treating method is configured by alternately and repeatedly performing a filtration process and a backwashing process. In the filtration process, filtered water can be obtained by infiltration of raw water through a membrane by using a membrane module using a hollow fiber membrane made of a single main component material having an independent structure in which an outer diameter is 3.6 to 10 mm and an SDR value expressed by a ratio of the outer diameter to wall thickness is 5.8 to 34. In the backwashing process, a part of the filtered water is supplied to wash the membrane. The water treating method is characterized in that washing by a chemical is performed: when filtration pressure rises above predetermined pressure or when a filtration flow rate falls below a predetermined flow rate at the filtration process; or when backwashing pressure rises above predetermined backwashing pressure or when a backwashing flow rate falls below a predetermined backwashing flow rate at the backwashing process.

Description

  The present invention relates to a water treatment method, and more particularly, to a water treatment method with controlled maintenance timing.

Conventionally, hollow fiber membranes have been used for water purification, for example, clarification of river water and groundwater, clarification of industrial water, drainage and sewage treatment, pretreatment for seawater desalination, and the like. In a situation where it is required to constantly supply a large amount of safe water, various components contained in the water to be treated are separated by a membrane in a more efficient and more economical manner. It is necessary to supply water.
For this purpose, for example, a membrane module made of a hollow fiber membrane is subjected to washing by performing a backwashing process in which filtered water flows back during the filtration process and / or washing with a chemical solution at predetermined intervals (for example, Patent Documents 1 and 2).

However, even if an appropriate filtration step and backwashing step are repeated, dirt that cannot be peeled off accumulates due to adsorption on the membrane surface and inside the membrane. Therefore, filtration performance will fall by accumulation of dirt in filtration for a long time.
In such a case, chemical cleaning with a chemical solution is performed. However, since the degree of progress of contamination of the hollow fiber membrane varies depending on the type or state of the water to be treated, the temperature, etc., the chemical solution on the surface of the hollow fiber membrane is used. The cleaning by may not be performed at an appropriate timing in the control by time. As a result, there is a problem that the filtration efficiency cannot be sufficiently secured, and the membrane may be broken beyond the use range pressure of the membrane module before washing with the chemical solution.

  Furthermore, there are methods for immersing the membrane module with the chemical solution, such as a method of immersing the membrane module in the chemical solution and a method of circulating the chemical solution in the membrane module at a high speed. Or the water treatment operation is forced to stop during the chemical cleaning. Therefore, in order to efficiently perform cleaning with chemicals, the optimal chemical cleaning timing that can maximize the filtration efficiency in water treatment is managed, the cost of chemicals used for chemical cleaning, and the processing cost of waste chemicals Therefore, it is required to reduce the operating cost.

JP 2006-102634 A JP-A-10-192665

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a water treatment method capable of economically and maximally improving the filtration efficiency by performing an optimal chemical cleaning at an optimal time. To do.

The water treatment method of the present invention comprises:
A membrane module using a hollow fiber membrane made of a single main constituent material having a self-standing structure having an outer diameter of 3.6 mm to 10 mm and an SDR value of 5.8 to 34 which is a ratio of the outer diameter to the wall thickness, or an outer diameter is A hollow fiber membrane having a self-supporting structure of 3.6 mm to 10 mm, an SDR value that is a ratio of outer diameter to wall thickness of 5.8 to 34, and an inner diameter of 3.2 mm or more, and having a separation function on both sides was used. A filtration step of obtaining filtered water by permeating raw water through the membrane using a membrane module;
A water treatment method for alternately and repeatedly performing a backwashing step of washing a membrane by supplying a part of the filtered water,
When the filtration pressure rises above a predetermined pressure in the filtration step or when the filtration flow rate falls below a predetermined flow rate, or when the backwash pressure in the backwash step rises above a predetermined backwash pressure, or the backwash flow rate When the flow rate drops below a predetermined backwash flow rate, cleaning with a chemical solution is performed.
In such a water treatment method, it is preferable to further include one or more of the following.
The hollow fiber membrane is formed of a single main constituent material of vinyl chloride resin.
In the backwashing step, water selected from the group consisting of treated water treated with activated carbon, ultrafiltration membrane or reverse osmosis membrane, filtered water, tap water and industrial water is supplied at a constant flow rate.
When the filtration pressure rises above the predetermined pressure in the filtration step or when the filtration flow rate falls below the predetermined flow rate, after performing a backwashing step of washing the membrane by supplying a part of the filtered water at a constant flow rate, Wash with chemicals.
The chemical cleaning is performed using water selected from the group consisting of activated water, treated water treated with an ultrafiltration membrane or a reverse osmosis membrane, filtered water, tap water, and industrial water.
The chemical cleaning is performed using an organic or inorganic acid or alkali aqueous solution, an oxidizing agent, a detergent, a surfactant, an organic solvent, or a combination thereof.
The back washing step or the chemical solution washing is performed using warm water.

  ADVANTAGE OF THE INVENTION According to this invention, optimal chemical | medical solution washing | cleaning can be performed at the optimal time, and it becomes possible to improve filtration efficiency economically and to the maximum.

It is a conceptual diagram of the water treatment system of this invention. It is a schematic sectional drawing of the membrane module used with the water treatment method by this invention.

  The water treatment method of the present invention is usually performed using a system that can alternately perform a filtration step and a backwashing step.

(Water treatment system)
Although the water treatment system used with the water treatment method of this invention is not specifically limited, For example, the water treatment system shown in FIG. 1 can be utilized. Such a water treatment system includes a raw water tank 1, a membrane module 2, a permeated water tank 3, a chemical solution injection unit 4, and the like.

  Here, any membrane module 2 may be used as long as it is generally used in water treatment and can be filtered by a membrane. Such membrane modules themselves are conventionally known. For example, JP-A-62-2140607, JP-A-6-319961, JP-A-2009-183822, International Publications 2011 / 004786A1, 2011 / 108579A1, etc. Various things described in the above can be used.

Specifically, as shown in FIG. 2, at least a case 10 and a plurality of hollow fiber membranes 12 accommodated therein are included.
Examples of the case 10 include a cylindrical one, and various materials such as metals and plastics can be used. However, the case is generally easy to mold and ensure mechanical strength. Plastic that can be used is used.
The hollow fiber membrane 12 can be appropriately adjusted with respect to the outer diameter, length, number, etc. of the hollow fiber membrane according to the characteristics of the membrane module to be obtained. It is preferable that a predetermined number of hollow fiber membranes 12 are bundled into a hollow fiber membrane bundle, the hollow fiber membrane bundle is cut into a predetermined length according to the cylindrical case 10, and inserted into the case in a straight shape. .

  The plurality of hollow fiber membranes 12 are sealed with a sealing material 11 at both end surfaces 10 a and 10 b in the case 10. On the surface of the case between the sealing materials 11 (for example, the end surfaces (one end surface or both end surfaces) 10a, 10b side), supply / discharge of raw water communicating with the inner (hollow) space of the plurality of hollow fiber membranes 12 described above. A raw water supply port 2a and a drain port 2b to which a pipe (not shown) is connected are provided. Of the raw water supply port 2a and the drain port 2b, the drain port 2b is closed when performing dead-end filtration, and is used when performing so-called flushing, draining, or the like. A filtered water outlet 2c to which a permeate side pipe (not shown) communicating with the outer space of the hollow fiber membrane 2 is connected is disposed at another part (for example, a side surface) of the case between the seals 11. Two or more filtered water outlets 2c may be arranged.

  In particular, in the present invention, the hollow fiber membrane 12 used in the membrane module 2 has a free-standing structure having an outer diameter of 3.6 mm to 10 mm and an SDR value that is a ratio of the outer diameter to the wall thickness of 5.8 to 34. The film | membrane which has is mentioned. The inner diameter is preferably 3.2 mm or more. Furthermore, what consists of a polymer and has a separation function in both surfaces is more preferable. The separation function here means a separation function more than microfiltration.

  As long as the hollow fiber membrane has a separation function on both sides, the method known in the art, for example, coating method, multilayer or single layer extrusion method, lamination method, thermally induced phase separation method (TIPS), non-solvent It can be produced using an induced phase separation method (NIPS), a stretching method, or the like. As a specific method, a method described in International Publication 2011/108579 can be used. Especially, it is preferable to manufacture by the NIPS method and TIPS method which shape | mold from 1 or more types of polymers melt | dissolved with the heat | fever or the solvent.

The hollow fiber membrane used in the present invention includes an integral laminated membrane obtained by coextrusion or lamination of polymers having different compositions. In particular, a hollow fiber membrane made of a single main constituent material such as a vinyl chloride resin is preferable.
Here, the hollow fiber membrane made of a single main constituent material means that the main constituent material is a single material, and a self-supporting structure is formed on the site functioning as a hollow fiber membrane without using a support member made of other materials. It means what can be taken. That is, it is a support-free film, which is different from a film obtained by coating on a support having a self-supporting structure.
Specifically, it is preferable to use those described in International Publications 2011 / 004786A1 and 2011 / 108579A1. In particular, the outer diameter is preferably about 4 mm or more, about 4.2 mm or more, about 4.5 mm or more, about 5 mm or more, and the SDR value is about 6.0 or more, about 6.2 or more, or about 6.5. The above is more preferable. However, in these cases, the inner diameter is preferably 3.2 mm or more.

  Examples of the vinyl chloride resin include those having 50% by mass or more of vinyl chloride (including chlorinated vinyl chloride) with respect to all monomers constituting the hollow fiber membrane. Moreover, what contains 50 mass% or more of vinyl chloride-type resin with respect to all the resin which comprises a hollow fiber membrane, Preferably it is 60 mass% or more, More preferably, 70 mass% or more is mentioned. In addition to vinyl chloride resin, polysulfone (PS), polyvinylidene fluoride (PVDF), polyolefins such as polyethylene (PE), cellulose acetate (CA), polyacrylonitrile (PAN), polyether sulfone, Various polymer materials such as polyvinyl alcohol (PVA) and polyimide (PI) may be used.

In such a hollow fiber membrane, the amount of pure water permeated at a transmembrane pressure difference of 100 kPa is suitably about 100 L / (m ² · h) or more, about 200 L / (m ² · h) or more, and 600 L / (M ² · h) or higher, preferably 800 L / (m ² · h) or higher, more preferably 1000 L / (m ² · h) or higher.

  In the water treatment system, between the raw water tank 1 and the raw water supply port 2a of the membrane module 2, between the filtered water outlet 2c of the membrane module 2 and the chemical solution unit 4, and through the filtered water outlet 2c of the membrane module 2. The water tank 3 is connected to each other by piping. These pipes are provided with a raw water pump 5, a chemical liquid injection pump 6, and a backwash pump 7, respectively. In addition, piping which comprises the channel | path in which the backwash pump 7 is not arrange | positioned is connected between the filtrate outlet 2c of the membrane module 2, and the permeated water tank 3. FIG. The drainage port 2b of the membrane module 2 is connected to the raw water tank 1 by piping.

Automatic valves 8 and 9 are disposed between the drain outlet 2b of the membrane module 2 and the raw water tank 1 and between the membrane module 2 and the permeated water tank 3, respectively.
Also, between the raw water tank 1 and the raw water supply port 2a of the membrane module 2; between the drain port 2b of the membrane module 2 and the raw water tank 1, and on the membrane module 2 side of the automatic valve 8; Pressure gauges PI-1, PI-2, and PI-3 are respectively connected between the water outlet 2c, the permeated water tank 3, and the chemical solution injection unit 4 and on the membrane module 2 side of the automatic valve 9. It is preferable that it is disposed.
Further, between the drain outlet 2b of the membrane module 2 and the raw water tank 1 and on the raw water tank 1 side of the automatic valve 8; between the filtrate outlet 2c of the membrane module 2 and the permeate tank 3, and automatically The flowmeters FI-1, FI-2, and the permeate tank 3 side of the valve 9; between the permeate tank 3 and the membrane module 2 and between the backwash pump 7 and the pressure gauge PI-3; FI-3 is preferably provided.

  The raw water pump 5 is not particularly limited as long as the raw water can be fed to the membrane module. For example, a centrifugal pump, a diffuser pump, a spiral mixed flow pump, a mixed flow pump, a piston pump, a plunger pump Various pumps such as a diaphragm pump, a gear pump, a screw pump, a vane pump, a cascade pump, and a jet pump can be used. Note that the raw water pump can be used as a pump for absorbing, pumping, pumping, or the like the raw water or the permeated water either downstream or upstream of the membrane module 2 regardless of the position shown in FIG. it can.

Only one membrane module 2 may be used, or two or more membrane modules 2 may be connected in series, in parallel, or a combination of series and parallel.
The backwash pump 7 is a pump used for supplying permeated water to the membrane module at the time of backwashing, and the same pump as exemplified in the raw water supply pump 5 described above can be used.
The chemical solution injection pump 6 may be the same as that illustrated in the raw water supply pump 5 described above. When supplying a chemical solution to the membrane module 2, it is preferable to operate the chemical solution injection pump 6 and simultaneously operate the backwash pump 7 so that the chemical solution is injected into the permeated water at a predetermined concentration. .

  In the above-described system, a gas supply device can be used during backwashing or chemical cleaning. This gas supply device is a device for supplying gas (preferably compressed air) to the membrane module 2, and generally includes a blower, a compressor, a microbubble generating blower, and the like. Usually, air, ozone, nitrogen gas, or inert gas is supplied as the gas. The gas is supplied to the membrane module as bubbles, and the bubbles can effectively wash the hollow fiber membrane in the membrane module. The size of the bubble is not particularly limited as long as it is useful for cleaning the hollow fiber membrane, and an air discharge hole of about 1 mm to several tens of mm is formed in stainless steel, ceramic, plastic, rubber or the like. It is preferable to adjust appropriately using an air diffuser or the like. Further, a means for generating so-called microbubbles (for example, about several tens μm to several hundreds μm) may be used. The gas supply device may be connected to either the upstream side (water treatment tank side) and / or the downstream side (permeate tank side) of the membrane module, but is preferably connected to the upstream side, It is more preferable that the raw water supply pump 5 and the membrane module 2 are connected to each other.

(Water treatment method)
A water treatment method in the case of using such a water treatment system is usually as follows.
First, the raw water in the raw water tank 1 is supplied to the raw water supply port 2 a of the membrane module 2 by the raw water supply pump 5, flows inside the hollow portion of the membrane module 2, flows out of the drain port 2 b, and returns to the raw water tank 1 again. Circulate the returning raw water circuit.
On the other hand, the raw water supplied to the raw water supply port 2 a of the membrane module 2 is filtered by the membrane module 2. This filtrate is taken out from the filtrate outlet 2c of the membrane module 2, and is sent to the filtrate tank 3 by opening the automatic valve 9 provided in the pipe connecting the membrane module 2 and the permeate tank 3. .
The raw water may be subjected to cross-flow filtration as described above, or may be subjected to dead-end filtration using a water treatment system that closes the drain port 2b and omits or closes the raw water circulation path. .

A part of the permeated water sent to the permeate tank 3 can be fed back to the membrane module 2 by the backwash pump 7 in order to supply it as water for backwashing the membrane constituting the membrane module 2.
Further, when a part of the permeated water sent to the permeate tank 3 is sent back to the membrane module 2, the chemical solution is injected into the backwash water from the chemical solution injection unit 4 by the chemical solution injection pump 6, and the chemical solution is washed. The water is sent back to the membrane module 2.
However, the water used for backwashing and chemical cleaning is not only filtered water but also clean water such as tap water, industrial water, and treated water (for example, water treated with activated carbon, UF membrane, RO membrane, etc.). That's fine.

When using filtered water for chemical cleaning, for example, it is preferable to continue adding a bactericide such as sodium hypochlorite to the filtrate tank so as to have a constant concentration and keep the filtrate clean.
It is also effective to place activated carbon in a filtered water tank or to arrange activated carbon in the backwash pipe.

  The permeated water and the chemical cleaning water that have been sent back to the membrane module 2 are backwashed from the membrane module 2, and then discharged from the system through a drainage port 2 b of the membrane module 2 to the outside of the system.

  In the water treatment method of the present invention, the filtration step for obtaining filtered water can be performed by methods and conditions known in the art. As described above, the filtration method may be either dead-end filtration or crossflow filtration. Moreover, any of constant pressure filtration, constant flow filtration, these combinations, etc. may be sufficient. Among these, either constant pressure filtration or constant flow filtration is preferable. The degree of pressure and the degree of flow can be appropriately adjusted depending on the scale of the water treatment system to be used, the type / characteristics of the equipment (for example, the physical strength of the membrane module, etc.), the amount of treated water, and the like. For example, the pressure method in the membrane module may be either an internal pressure type or an external pressure type. In particular, the internal pressure type, that is, water to be treated is supplied to the inside of the hollow fiber membrane and permeated to the outside of the hollow fiber membrane. A method of taking out water is preferred. In this case, the transmembrane pressure difference between the inside and the outside is, for example, about 10 to 300 kPa in terms of permeation pressure, and preferably about 200 kPa or less. By setting the transmembrane pressure difference within this range, the water permeation performance required in practice can be maintained, and a stable water permeation rate can be obtained for a long period of time. In particular, when the hollow fiber membrane used in the membrane module has a large diameter (for example, about 4 mm or more), water with high turbidity can be treated without clogging the membrane pores.

  In the water treatment method of the present invention, the backwashing step may be constant pressure backwashing in which the backwashing pressure is supplied at a constant pressure, but is preferably performed by supplying a part of the filtered water at a constant flow rate. The duration and interval of backwashing are not particularly limited, and can be appropriately adjusted depending on the type of water to be treated, turbidity, and the like.

Therefore, in the water treatment method of the present invention, usually, a series of steps of filtration and backwashing are:
(A) repeated quantitative filtration-quantitative backwashing,
(B) repeated quantitative filtration-constant pressure backwashing,
(C) Repeating constant pressure filtration-quantitative backwashing, or (d) Repeating constant pressure filtration-constant pressure backwashing. However, you may combine these 2 or more types arbitrarily.

In general, the cause of the decrease in the water permeability of the membrane in the membrane module is mainly (i) generation of a cake layer, (ii) generation of a gel layer, (iii) adsorption of the cake layer and / or gel layer, and the like. The stain due to (i) and (ii) is a reversible stain that can be removed by physical washing such as backwashing, flushing or air scrubbing described later. On the other hand, if the generated cake layer grows and closes the film surface, the soil cannot be removed by simple physical cleaning or the like. Further, (iii) correlates with irreversible dirt that cannot be removed by physical cleaning alone. Thus, these soils and / or soil growth can be fatal to membrane maintenance.
That is, in the water treatment, as described above, even if filtration and backwashing are repeatedly performed, dirt that cannot be removed / removed accumulates even if the backwashing process is performed.

  In the water treatment method of the present invention, in order to reliably prevent / reduce the growth of such dirt, the degree of accumulation is determined by a decrease in flow rate or an increase in pressure during filtration or backwashing, and filtration or reverse By performing the chemical cleaning at the timing when the washing flow rate or pressure reaches the predetermined flow rate or the predetermined pressure, it is possible to always obtain a predetermined filtering effect and a constant backwashing effect. In addition, it is possible to reduce the rapid cleaning effect due to a decrease in the backwash flow rate and to prevent the progressive progress of the film surface blockage. Furthermore, it is possible to avoid the execution of chemical cleaning at an early timing, and to further reduce the chemical cost and the operating cost.

As a method for obtaining a constant flow rate in the filtration and backwashing steps, a method known in the art can be used. For example, PID control of a pump using an inverter can be mentioned.
Specifically, the constant flow filtration is performed by operating the raw water supply pump 5 with the automatic valve 8 closed and the automatic valve 9 open. As a result, raw water can be supplied from the raw water tank 1 into the membrane module 2, and the filtrate can be discharged in a certain amount to the filtrate water tank 3 through the piping from the filtrate outlet 2 c of the membrane module 2.
Similarly, constant flow backwashing is performed by operating the backwash pump 7 with the automatic valve 9 closed and the automatic valve 8 open. As a result, a certain amount of backwash water (part of filtered water) is ejected from the filtrate water tank 3 to the inside of the membrane module 2 and discharged from the drainage port 2b of the membrane module 2 to outside the system. it can.

  Here, the constant flow rate means that a predetermined flow rate value is indicated, but slight fluctuation is allowed. The constant flow rate here can be appropriately adjusted according to the scale of the water treatment system to be used, the type / characteristics of the equipment, the amount of treated water, and the like.

During constant flow filtration performed once during the backwashing process, the filtration pressure is maintained substantially constant over time from the beginning of filtration, or as time passes from the beginning of filtration, Filtration pressure (value represented by {[(PI-1) + (PI-2)] / 2)}-(PI-3)) gradually increases due to clogging or surface blockage of the membrane module due to filtration. It is assumed that The increase in the filtration pressure occurs not only during continuous filtration but also due to the progress of irreversible contamination in a series of steps repeated with backwashing.
In addition, in the case of one continuous constant flow backwash performed between the filtration steps, the effect of backwashing is exhibited as time passes from the initial backwashing by keeping the backwash flow rate constant. Thus, it is assumed that the backwash pressure (value represented by (PI-3)-{[(PI-1) + (PI-2)] / 2}) gradually decreases. However, the backwash pressure increases due to the progress of irreversible dirt in the long term.

Therefore, if the transmembrane pressure difference (that is, the filtration pressure or the backwash pressure) during the filtration or backwashing is monitored, the filtration pressure or the backwash pressure may continue to increase suddenly or gradually. The increase in the filtration pressure or the backwash pressure is an index representing the degree of progress of the membrane contamination. Therefore, the timing at which the filtration pressure or backwash pressure reaches a predetermined pressure set in advance (becomes a predetermined pressure or higher) can be set as the timing at which chemical cleaning is performed.
Here, the fact that the filtration pressure has reached a predetermined pressure in the filtration step is, for example, on the permeate outlet 2c side of the membrane module, the pressure installed in the connecting pipe without pressure fluctuation, for example, in FIG. It can be determined by the filtration pressure (value represented by {[(PI-1) + (PI-2)] / 2)}-(PI-3)). In the backwashing process, the fact that the backwashing pressure has reached the predetermined backwashing pressure is represented by (PI-3)-{[(PI-1) + (PI-2)] / 2}. Can be judged by. The predetermined pressure or the predetermined backwash pressure can be set to an optimum value in consideration of various factors such as the type of water treatment system to be used, drainage properties, etc., preferably 0.3 MPa or less, more preferably 0. 2 MPa or less, more preferably 0.1 MPa or less.

As a method of setting a constant pressure in the filtration and backwashing steps, methods known in the art can be used. For example, PID control of a pump using an inverter can be mentioned.
Specifically, in the constant pressure filtration, the automatic valve 8 is closed, the automatic valve 9 is opened, and the filtration pressure ({[(PI-1) + (PI-2)] / 2)} -The value represented by (PI-3)) is monitored and the raw water supply pump 5 is operated. As a result, the raw water can be supplied from the raw water tank 1 into the membrane module 2, and the filtrate can be discharged to the filtrate water tank 3 at a constant pressure through the piping from the filtrate outlet 2 c of the membrane module 2.
Similarly, in the constant pressure backwash, the automatic valve 9 is closed and the automatic valve 8 is opened, so that (PI-3)-{[(PI-1) + (PI-2)] / 2. }, By operating the backwash pump 7 while monitoring the pressure represented by. As a result, backwash water (part of filtered water) can be ejected from the filtrate water tank 3 to the inside of the membrane module 2 at a constant pressure, and the backwash water is piped from the drain port 2b of the membrane module 2. After that, it can be discharged out of the system.

  Here, the constant pressure means that a predetermined pressure value is indicated, but a slight fluctuation is allowed. The constant pressure here can be appropriately adjusted depending on the scale of the water treatment system used, the type / characteristics of the equipment, the amount of treated water, and the like.

In the case of one continuous constant pressure filtration performed during the backwashing process, by keeping the filtration pressure constant, the membrane module is clogged or clogged by filtration even after a long time from the beginning of filtration. If not, it is assumed that the filtration flow rate is gradually reduced due to the clogging of the membrane module or surface clogging due to slight filtration as the filtration flow rate is maintained substantially constant or as time passes from the beginning of filtration. The
On the other hand, in the case of one constant pressure backwashing performed continuously during the filtration step, the effect of backwashing is exhibited as time passes from the initial backwashing by keeping the backwashing pressure constant. Therefore, it is assumed that the backwash flow rate gradually increases. However, the backwash flow rate decreases due to the progress of irreversible dirt in the long term.

Therefore, if the filtration flow or backwash flow at the time of filtration or backwashing is monitored, the filtration flow or backwash flow may continue to decrease suddenly or gradually. This decrease in the filtration flow rate or backwash flow rate serves as an index indicating the degree of progress of membrane contamination, and chemical cleaning is performed at the timing when the flow rate reaches a predetermined flow rate that is set in advance (below the predetermined flow rate). Can be set with timing.
Here, the fact that the filtration flow rate has reached the predetermined pressure flow rate in the filtration step is, for example, a flow meter provided in the connecting pipe on the permeate outlet 2c side of the membrane module, for example, the flow meter FI- in FIG. 2 can be determined. Moreover, in the backwashing process, it can be judged according to the filtration process that the backwashing flow rate has reached the predetermined backwashing pressure flow rate. The predetermined flow rate or the predetermined backwash flow rate may be set to an optimum value in consideration of various factors such as the type and scale of the water treatment system to be used, individual equipment, particularly the configuration, size, and performance of the membrane module. it can.

In the present invention, as described above, when the filtration pressure rises above the predetermined pressure in the filtration step or when the filtration flow rate falls below the predetermined flow rate, cleaning with a chemical solution is performed. After the interruption of the filtration process cycle when the filtration pressure is increased or the filtration flow rate is lowered, washing with a chemical solution may be performed, or such a filtration process is interrupted, or the filtration pressure rises or the filtration flow rate. After the cycle of the filtration step in which has been lowered, the normal backwashing step may be performed and then the cleaning with the chemical solution may be performed.
However, when the backwash pressure rises above a predetermined pressure or when the backwash flow rate falls below a predetermined flow rate in the backwash process, such backwash process is interrupted, or the backwash pressure rises or reverses. After the cycle of the backwashing process in which the washing flow rate is lowered, it is preferable to perform the cleaning with the chemical solution without performing the filtration process.

  Especially, in the process of backwashing at a constant flow rate after the filtration step (either constant pressure or constant flow rate), when the filtration pressure in the filtration step rises above a predetermined pressure, or the filtration flow rate falls below a predetermined flow rate In this case, it is suitable to monitor the backwashing pressure with the backwashing flow rate constant in the backwashing process, and monitor the increase in the backwashing pressure by a predetermined pressure, thereby timing the cleaning with the chemical solution. According to this method, it is possible to determine the optimum timing for irreversible dirt.

  As the chemical solution in the cleaning with the chemical solution, those usually used in the field can be used, for example, organic or inorganic acid or alkaline aqueous solution, oxidizing agent, detergent, surfactant, organic solvent, etc. or these The combination of is mentioned. Specifically, when the dirt adhering to the film surface is organic, an alkaline aqueous solution such as sodium hydroxide, an oxidizing agent such as sodium hypochlorite can be used, and an inorganic substance such as manganese or a metal salt can be used. In some cases, hydrochloric acid, sulfuric acid, oxalic acid, citric acid and the like can be used. Further, in a fine membrane such as an ultrafiltration membrane, an organic solvent such as ethanol is also effective because low molecular weight organic matter that is difficult to be decomposed by an oxidizing agent or the like is captured as a contaminant.

The effects of backwashing and chemical cleaning tend to be proportional to concentration, temperature, and time. Therefore, it is preferable to perform backwashing and chemical cleaning with warm water (for example, 20 to 80 ° C.). Therefore, means such as winding the backwash pipe with a heater and passing a heat exchanger through the backwash pipe can be used. Since the viscosity of the liquid can be lowered by heating, it is effective for increasing the backwash flux.
The concentration of the chemical solution in the cleaning with the chemical solution can be appropriately selected / adjusted depending on the type and amount of treated water, the degree of contamination, and the like. Further, the cleaning with the chemical solution may be an online method such as a constant flow rate or a constant pressure backwashing of the chemical solution, or an off-line method in which the chemical solution is immersed or allowed to stand in a chemical solution outside the system. The immersion time here can be appropriately adjusted depending on the type and amount of treated water, the degree of contamination, and the like.

  In the water treatment of the present invention, particularly when the filtration method is cross flow filtration, the pressure loss between the inlet (that is, the raw water supply port 2a) and the outlet (that is, the filtered water outlet 2c) in the membrane module is higher than a predetermined value. Even when it rises, it can be used as an index of the timing of cleaning with a chemical.

  The water treatment method of the present invention does not necessarily require a turbidity removal device such as sand filtration, a spool filter, or a strainer, which is necessary for conventional seawater desalination, and a turbidity removal device and similar devices are not provided. Is preferred. This is because when a seawater treatment is performed using a hollow fiber membrane having a relatively small diameter, the hollow fiber membrane is immediately clogged, and thus turbidity as a pretreatment was necessary. This is because such a blockage hardly occurs when a hollow fiber membrane having a relatively large diameter is used.

  The type of water that is the target of the water treatment method of the present invention is not particularly limited, drainage including activated sludge in a sewage treatment plant, etc., urban sewage such as domestic wastewater, drainage of various facilities such as factory wastewater, agricultural wastewater, Biologically treated water, wastewater containing suspended solids, seawater, well water, and water to be treated by membrane separation such as rivers and lakes may be used. From another viewpoint, for example, a liquid having an SS (floating substance) of about 50000 or less, about 20000 or less, or about 10 to 15000 can be given.

  As described above, in the water treatment method of the present invention, water treatment by filtration and backwashing are alternately performed. In particular, while having a relatively large diameter (large inside diameter), particularly with a single material, it has high strength. When using a hollow fiber membrane with a single layer structure, without damaging the membrane due to accumulation of dirt, etc., by performing appropriate and appropriate chemical cleaning, even with high turbidity wastewater, with low energy, It is possible to perform treatment over a long period of time without replacing equipment, particularly a membrane module, and to maximize the filtration efficiency in water treatment. Further, it is possible to reduce the cost of chemicals used for cleaning chemicals, the cost of treating waste chemicals, and the operating cost.

The alternate water treatment (filtration) and backwashing performed in the water treatment method of the present invention are not necessarily performed continuously, for example, after or during water treatment or backwashing, A drain and break process may be performed.
Flushing is a process performed mainly for removing floating / adherent matters, residual foreign matters, etc. in the tank, piping and / or the membrane module, etc., without applying pressure, for example, a membrane surface flow rate of 0.1 m / s. It is preferable to carry out the above. The water used for flushing is usually treated water. The water passed through the membrane module is returned to the raw water tank 1 again as flushing water.
Particles larger than the inner diameter of hollow fiber membranes, fiber masses, and rod-like substances may get caught at the end face of the membrane module and block the pipe line, but this blockage at the end face of the module may be flushed in the direction opposite to the supply direction of raw water. You may prevent it by doing.

Drain is a process that mainly removes / discharges floating, adhesion, residue, concentrated liquid, etc. remaining on the treated water side of the hollow fiber membrane when water treatment is performed in the membrane module by total filtration. For example, there is a method in which the concentrated liquid or the like is naturally dropped and recovered by opening the lower part or the upper part of the membrane module while all the pumps are stopped. Alternatively, it may be a method in which backwashing is performed with the lower part or the upper part of the membrane module open at the same time, and the backwash waste water is recovered at the lower part or the upper part of the module. The recovered concentrated water or backwash waste water may be stored in a drain water tank provided separately or may be returned to the upstream side in the processing flow.
The break process means that water treatment is temporarily stopped.

  Furthermore, in the above-described water treatment, backwashing, and flushing, ultrasonic waves may be applied using a method known in the art using an ultrasonic generator. The ultrasonic waves in this case may be those having a frequency of about a dozen kHz to a few GHz, for example. The ultrasonic wave is preferably applied only to the membrane module, and may be applied during water treatment, backwashing, flushing, etc. or between these treatments, as in the above-described bubbling. It may be performed or may be applied intermittently.

  The present invention is widely used as a water treatment apparatus used for water purification such as clarification of river water and groundwater, clarification of industrial water, drainage and sewage treatment, pretreatment for seawater desalination, etc. It is possible to carry out economical and efficient water treatment.

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Membrane module 2a Raw water supply port 2b Drain port 2c Filtration water outlet 3 Permeate tank 4 Chemical liquid injection unit 5 Raw water supply pump 6 Chemical liquid pump 7 Backwash pump 8, 9 Automatic valve 10 Case 10a, 10b End face 11 Seal Material 12 Hollow fiber

Claims (7)

Hollow fiber membrane having a self-standing structure with an outer diameter of 3.6 mm to 10 mm, an SDR value of 5.8 to 34 as a ratio of outer diameter to wall thickness, and an inner diameter of 3.2 mm or more, and having a separation function on both sides A filtration step of obtaining filtered water by permeating the raw water through the membrane using a membrane module using
A water treatment method for alternately and repeatedly performing a backwashing step of washing a membrane by supplying a part of the filtered water,
When the filtration pressure rises above a predetermined pressure in the filtration step or when the filtration flow rate falls below a predetermined flow rate, or when the backwash pressure in the backwash step rises above a predetermined backwash pressure, or the backwash flow rate A water treatment method characterized by performing cleaning with a chemical solution when the flow rate drops below a predetermined backwash flow rate.   The water treatment device according to claim 1, wherein the hollow fiber membrane is formed of a single main constituent material of vinyl chloride resin.   In the backwashing step, water selected from the group consisting of treated water treated with activated carbon, ultrafiltration membrane or reverse osmosis membrane, filtered water, tap water and industrial water is supplied at a constant flow rate. The water treatment method as described.   When the filtration pressure rises above the predetermined pressure in the filtration step or when the filtration flow rate falls below the predetermined flow rate, after performing a backwashing step of washing the membrane by supplying a part of the filtered water at a constant flow rate, The water treatment method according to claim 1, wherein cleaning with a chemical solution is performed.   The chemical cleaning is performed using water selected from the group consisting of activated water, treated water treated with an ultrafiltration membrane or a reverse osmosis membrane, filtered water, tap water, and industrial water. The water treatment method as described in one.   The water treatment method according to any one of claims 1 to 5, wherein the chemical cleaning is performed using an organic solvent such as an organic or inorganic acid or alkali aqueous solution, an oxidizing agent, a detergent, a surfactant, or the like, or a combination thereof.   The water treatment method according to any one of claims 1 to 6, wherein the backwashing step or the chemical solution washing is performed using warm water.

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