JP6662558B2 - Water treatment method and water treatment device - Google Patents

Description

  The present invention relates to a water treatment method and a water treatment device.

In recent years, a membrane filtration device has been receiving attention as a new water treatment device. This is a device for turbidity, and replaces the conventional sand clarifiers, rapid sand filter and slow sand filter. Since the membrane filtration device is a device for turbidity, it has been often used when relatively clear water requiring only turbidity is used as raw water.
However, due to the ease of operation management of the membrane filtration device and the certainty of the quality of the resulting treated water, it is important to introduce the membrane filtration device not only to clear raw water, but also to raw water that requires treatment other than turbidity. Movements are increasing.

  Substances that need to be removed in addition to turbidity include chromaticity and organic substances. Since these substances are colloid components (soluble substances), it is difficult to remove them with a normal membrane filtration device. As a method for removing these substances with a membrane filtration device, a flocculant is injected at the former stage, and a flocculation facility for mixing with raw water is provided. In this coagulation facility, the chromaticity component and the organic component are coagulated to a size that can be removed by membrane filtration, and removed as turbidity components by membrane filtration to obtain clear treated water.

  Conventionally, as such a membrane filtration method, for example, the methods described in Patent Documents 1 and 2 have been proposed.

  In Patent Document 1, powdered activated carbon mixed water obtained by adding powdered activated carbon to raw water in advance flows into the membrane filtration tank, or raw water flows into the membrane filtration tank and powdered activated carbon is added to form powdered activated carbon mixed water, A substance to be treated such as trace organic matter in raw water is adsorbed on the powdered activated carbon, and the powdered activated carbon mixed water in the membrane filtration tank is solid-liquid separated by an immersion type membrane filtration device installed in the tank. When taking out the membrane filtered water permeated through the membrane surface out of the tank, the amount of the membrane filtered water taken out with respect to the amount of water flowing into the membrane filtration tank is set to 99% or more, and the activated carbon powder is kept at a high concentration in the membrane filtration tank. Describes a method of operating a water treatment facility using a submerged membrane filtration device, which promotes adsorption of a substance to be treated. The powdered activated carbon removes organic chlorine compounds such as trihalomethane or its precursors, trace harmful substances such as pesticides, off-flavor-causing substances such as mold odor, and trace organic substances such as anionic surfactants. Microorganisms such as nitrifying bacteria that are naturally generated and retained in the filtration tank can remove ammonia nitrogen and organic substances. It states that iron can be removed. Further, it is described that bacteria and turbid substances contained in raw water, added powdered activated carbon, naturally occurring microorganisms, and the like can be separated by filtration using a membrane filtration device. In addition, at this time, the extraction amount of the membrane filtration water with respect to the amount of water flowing into the membrane filtration tank is set to 99% or more, and the added powdered activated carbon is maintained at a high concentration in the membrane filtration tank to maximize the capacity of the powdered activated carbon. As a result, the adsorption of the object to be treated can be promoted, and as a result, the amount of powdered activated carbon added can be reduced. It is described that it is possible to obtain a membrane filtered water having a treated water quality.

  Patent Document 2 discloses that the solid-containing water in the tank is subjected to membrane filtration while the solid-containing water is subjected to membrane filtration until the solid concentration of the solid-containing water reaches a critical solid concentration (Ct) of 0.1 Ct to Ct. Membrane washing step including performing a proper washing, a draining step of draining all or a part of the solid-containing water in the tank after the membrane filtering step, supplying raw water into the tank after the draining step, A water purification method is described, which includes a water filling step of controlling the concentration of powdered activated carbon in water to be a target value of 50 mg / L or more. And, by such a water purification method, the recovery rate of treated water is maintained at a high level by periodically draining the entire amount or partial drainage under certain conditions, and the adhesion of cake to the membrane surface is prevented. And that the adsorption effect of activated carbon can be maintained at a high level.

JP-A-9-285779 JP 2012-223697 A

  The membrane filtration method can obtain high-quality treated water, but has a disadvantage that the operation cost is higher than conventional methods (rapid filtration method, slow filtration method, etc.). In order to remove the chromaticity component and the organic component by adopting the membrane filtration method, it is necessary to inject a coagulant or the like, which causes an increase in operating cost. In adopting the membrane filtration method, it is an urgent task to reduce the operation cost, and particularly in the case of a membrane filtration method having an additional process such as injection of a flocculant, it is particularly important.

  In the coagulation / membrane filtration method in which a coagulant is injected, a reduction in the coagulant injection rate is an effective means for reducing the operation cost. If the coagulant injection rate is reduced, it is possible to reduce operating costs.

  Also, as the 21st century is said to be the century of water, the situation in Japan alone has abundant water resources, but globally, water demand is expected to tighten with population growth. . In view of such future trends, it is obvious that a process that can treat treated water as purified as possible without wasting water will become essential in the future.

  Therefore, what is required for the membrane filtration method in the future is that it is possible to operate at a low running cost for relatively unclear raw water, and to achieve a high recovery rate without wasting the raw water. It is.

  However, in order to obtain purified water having a low concentration of the chromaticity component or the organic component in the conventional membrane filtration device or membrane filtration treatment, it is necessary to increase the coagulant injection rate. A high coagulant injection rate is not preferable because the running cost increases. In addition, when the injection rate of the flocculant is high, the turbid components tend to adhere to the membrane in the membrane filtration device, and it becomes necessary to frequently perform an operation of removing the adhered turbid components by performing back washing and the like. The filtration time per unit time is undesirably reduced.

An object of the present invention is to solve the above problems.
That is, the present invention provides a water treatment method and a water treatment apparatus which can obtain purified water having a low content of the chromaticity component and the organic component even when the coagulant injection rate is reduced, and can further increase the raw water recovery rate. It is in.

The inventors of the present invention have made intensive studies to solve the above-described problems, and have completed the present invention.
The present invention is the following (1) to (5).
(1) a coagulant injection step of injecting a coagulant into raw water;
Mixing the injected coagulant and the raw water to form a floc, a mixing step of obtaining a treatment target water containing the floc,
A membrane for subjecting the water to be treated to membrane filtration so that the raw water recovery rate is 90% or more, and obtaining purified water obtained by removing at least a part of the flocs from the water to be treated and sludge containing the concentrated flocs. A filtration step;
A water treatment method comprising:
(2) The water treatment method according to (1), wherein in the membrane filtration step, the water to be treated is subjected to membrane filtration after or while blowing gas.
(3) The water treatment method according to (2), wherein, in the membrane filtration step, a gas is blown at an interval of 1 to 60 minutes for 1 second to 10 minutes to stir the water to be treated.
(4) In the membrane filtration step, when the water to be treated is subjected to the membrane filtration treatment, the floc is always adjusted to be contained in the water to be treated held in the immersion tank in which the membrane is immersed. The water treatment method according to any one of (1) to (3).
(5) a coagulant injection means for injecting a coagulant into raw water;
Mixing means for mixing the injected coagulant and the raw water to form flocs, and obtaining a water to be treated containing the flocs,
A membrane for subjecting the water to be treated to membrane filtration so that the raw water recovery rate is 90% or more, and obtaining purified water obtained by removing at least a part of the flocs from the water to be treated and sludge containing the concentrated flocs. Filtration means;
, A water treatment device.

  According to the present invention, it is possible to provide a water treatment method and a water treatment apparatus that can obtain purified water having a low content of a chromaticity component and an organic substance component even when a coagulant injection rate is reduced by increasing a raw water recovery rate. Can be.

It is a schematic diagram showing the outline of the device of the present invention. FIG. 2 is a schematic view showing a preferred embodiment of the device of the present invention. FIG. 2 is a schematic diagram showing another preferred embodiment of the device of the present invention. FIG. 4 is a schematic view showing still another preferred embodiment of the device of the present invention. FIG. 4 is a schematic view showing still another preferred embodiment of the device of the present invention. 4 is a graph showing a relationship between a raw water recovery rate and a ratio of a chromaticity component and an organic matter component removal rate. It is a graph which shows the relationship between the residual ratio of the water to be treated and the ratio of the removal ratio of the chromaticity component and the organic component. It is a graph which shows the relationship between the time which blows air from an air diffuser, and a turbidity ratio. It is the schematic which expanded a part of immersion type membrane filtration apparatus used for explaining a turbidity ratio.

The present invention will be described in detail.
The present invention relates to a coagulant injection step of injecting a coagulant into raw water, a mixing step of mixing the injected coagulant and the raw water to form a floc, and obtaining a treatment target water containing the floc, Membrane filtration of the water to be treated so that the recovery rate is 90% or more, and membrane filtration to obtain purified water obtained by removing at least a part of the flocs from the water to be treated and sludge containing the concentrated flocs. And a water treatment method.
Hereinafter, such a water treatment method is also referred to as “method of the present invention”.

Further, the present invention also provides a flocculant injecting means for injecting a flocculant into raw water, a floc formed by mixing the injected flocculant and the raw water, and a mixing means for obtaining a water to be treated containing the floc. And subjecting the water to be treated to membrane filtration so that the raw water recovery rate is 90% or more, to obtain purified water obtained by removing at least a part of the flocs from the water to be treated and sludge containing the concentrated flocs. And a membrane filtration means.
Hereinafter, such a water treatment apparatus is also referred to as “the apparatus of the present invention”.

  The method of the present invention is preferably performed using the device of the present invention.

  Hereinafter, the term "the present invention" means both the method of the present invention and the device of the present invention.

  The mechanism of realizing the effect of the present invention estimated by the present inventors will be described using specific examples. The present invention is not limited to the specific examples in the following description.

When a flocculant is added to raw water and only rapid mixing is performed, floc generated is fine because slow stirring is not performed. When solid-liquid separation is performed using a conventional sedimentation method, fine flocs are not preferable because the sedimentation speed of the flocs is slow, and the separation efficiency in the sedimentation basin deteriorates. However, in the case of the membrane filtration method, if the fine floc diameter is larger than the pores on the surface of the membrane, solid-liquid separation can be performed.
The present inventor has found that there is room for improvement in the agglomeration / membrane filtration process in the following two points during the intensive research.
[1] Only by rapid mixing, there are ultrafine flocs that could not be larger than the pores on the film surface or chromaticity or organic components that could not be flocs.
[2] The nominal pore size indicating the pore size of the membrane does not indicate the size of all pores on the membrane surface, but is a representative value, and there are pores larger than the nominal pore size. For this reason, the ultrafine flocs may come out of the pores.
In order to perform solid-liquid separation of components that escape through the membrane despite the rapid mixing, it is conceivable to inject more coagulant or to add a slow mixing step. However, these methods are not preferable because they cause an increase in operating costs.

Therefore, the inventor has devised an apparatus and a method for increasing the removal rate of a colloid component such as a chromaticity component or an organic component without adding a process while keeping the injection rate of the coagulant low.
That is, in the membrane filtration device, an operation in which the raw water recovery rate is increased is performed.

For this reason, the present inventors presume as follows.
In the membrane immersion tank, fine flocs generated by rapid mixing are solid-liquid separated by the membrane and concentrated. The fine flocs collide with each other in the membrane immersion tank and are captured by the flow of water flowing into the immersion tank and the flow of water generated by membrane filtration. This phenomenon occurs not only between the fine flocs but also between the fine flocs and the ultrafine flocs smaller than the pores of the membrane or the chromaticity components or organic components that could not be formed into flocs. It is possible to make it larger than the hole. As a result, the removal rate of chromaticity components, organic components, and the like can be increased. To make the most of this phenomenon, the probability of contact between the ultrafine flocs smaller than the pores of the membrane and the chromaticity components or organic components that could not become flocs and the flocs already present in the membrane immersion tank The present inventor considered that it was effective to increase the Further, for this purpose, the present inventor considered that it is effective to increase the raw water recovery rate and increase the concentration of floc.
As the concentration of flocs is increased, the number of collisions between flocs increases, and it is considered that the diameter of flocs existing in the membrane immersion tank increases. Since the present invention has a very high concentration, the number of collisions with a chromaticity component or an organic component which could not become a very fine floc or a floc does not decrease even with a floc having an increased floc diameter. Therefore, it is considered that the removal rate by membrane separation can be increased.

The present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing the apparatus of the present invention. In FIG. 1, an apparatus 10 of the present invention includes a flocculant injecting means 12 for injecting a flocculant 3 into raw water 1, a floc formed by mixing the injected flocculant 3 and raw water 1, and a process including the floc. A mixing means 14 for obtaining the target water 5, a purified water 7 obtained by subjecting the target water 5 to membrane filtration so that the raw water recovery rate is 90% or more, and removing at least a part of the floc from the target water 5; Membrane filtration means 16 for obtaining sludge 9 containing the concentrated floc.

<Raw water>
In the present invention, the raw water 1 is not particularly limited as long as it contains impurities such as a turbid component, a chromatic component, and an organic component.
Examples of such raw water 1 include raw tap water (river water, groundwater, lake water, etc.), sewage, seawater, brackish water, and the like.
In addition, biological contact filtration, sand filtration, micro-floc method, coagulation sedimentation filtration, biofilm treatment, ozone treatment, activated carbon treatment, ion exchange treatment, UV oxidation treatment, and promotion of the above tap water, sewage, seawater, brackish water, etc. Water obtained after performing a conventionally known treatment such as an oxidation treatment can be used as the raw water 1.

Examples of the raw water 1 include those having the following turbidity, chromaticity, or TOC (total organic carbon).
-Turbidity: 0 to 500 degrees (preferably 0 to 50 degrees, more preferably 0 to 20 degrees)
Chromaticity: 0 to 100 degrees (preferably 0 to 20 degrees, more preferably 0 to 10 degrees)
-TOC: 0 to 10 mg / L (preferably 0 to 5 mg / L, more preferably 0 to 3 mg / L)

  In the present invention, the turbidity, chromaticity, and TOC are values obtained by measuring according to the method specified in the water supply test method (2011 version).

  The raw water 1 may contain soluble manganese. Specifically, the raw water 1 may contain soluble manganese at a concentration of about 0.005 to 1 mg / L.

  In the present invention, the concentration of soluble manganese is determined by filtering the water to be measured (raw water in this case) through a membrane filter having a pore size of 0.1 μm, and filtering the filtered water based on the regulations of the Ministry of Health, Labor and Welfare based on the water quality standards. It shall mean the value obtained by measurement based on the prescribed method (Ministry of Health, Labor and Welfare Notification No. 261 on July 22, 2003 (final revision Notification of Ministry of Health, Labor and Welfare No. 290 on March 30, 2012)).

<Coagulant injection means, coagulant injection step>
The coagulant injection means 12 in the apparatus 10 of the present invention will be described.
In the apparatus 10 of the present invention, the coagulant injection means 12 is a means for injecting the coagulant 3 into the raw water 1.

  The coagulant 3 is not particularly limited as long as it can coagulate impurities such as a turbid component, a chromatic component, and an organic component contained in the raw water 1. For example, a conventionally known coagulant can be used. For example, an inorganic coagulant (specifically, for example, an Al-based and / or Fe-based coagulant) can be used. Further, an organic coagulant can be used. Further, a plurality of types of flocculants may be used, for example, simultaneously.

The Al-based flocculant means a flocculant containing an aluminum compound as a main component. Here, the “main component” means that the content of the component other than the solvent is 50% by mass or more, preferably 80% by mass or more, more preferably 95% by mass or more, and still more preferably 100% by mass (substantially other ). Hereinafter, “main component” is used in such a meaning unless otherwise specified.
The aluminum compound means a compound containing an Al atom. Examples of the aluminum compound include polyaluminum chloride and sodium sulfate (aluminum sulfate).

The Fe-based flocculant means a flocculant containing an iron-based compound as a main component.
The iron-based compound means a compound containing an Fe atom. Examples of the iron-based compound include ferric chloride, ferric polysulfate, and an iron-silica inorganic polymer flocculant.

  Examples of the organic coagulant include polyacrylamide, polyamine, polyacrylester, and polyethyleneimine.

  The injection amount of the flocculant 3 into the raw water 1 is not particularly limited, but is preferably 0 to 100 mg / L, more preferably 0 to 30 mg / L, as an addition amount to 1 L of the raw water.

  The flocculant 3 may be in a powder form. Further, for example, an embodiment in which a powdery inorganic coagulant (for example, an Al coagulant and / or an Fe coagulant) is dispersed in a liquid may be used.

  The coagulant injection means 12 is not particularly limited as long as it can inject the coagulant 3 into the raw water 1. For example, a conventionally known coagulant injection pump capable of storing the coagulant 3 and discharging the coagulant 3 continuously or intermittently can be used as the coagulant injection means.

The coagulant injection step in the method of the present invention can be performed by the coagulant injection means 12.
The coagulant injection step in the method of the present invention is a step of injecting the coagulant 3 into the raw water 1.

  In the coagulant injection step, a pH adjuster may be added to the raw water 1 before the coagulant 3 is injected into the raw water 1 to adjust the pH of the raw water 1 to a pH that can enhance the coagulability of the coagulant 3. preferable. The pH that enhances the aggregating ability of the flocculant 3 differs depending on the type of the flocculant 3 and the like. As the pH adjuster, a conventionally known acid or alkali can be used. Further, the pH adjuster may be added after the coagulant 3 is injected into the raw water 1, or may be added simultaneously while the coagulant 3 is injected into the raw water 1.

  The apparatus of the present invention preferably further comprises a means for adding such a pH adjuster to the raw water 1.

<Mixing means, mixing process>
The mixing means 14 in the apparatus 10 of the present invention will be described.
In the apparatus 10 of the present invention, the mixing means 14 is means for mixing the injected coagulant 3 and the raw water 1 to form flocs, and obtaining the water 5 to be treated containing the flocs.

  The mixing means 14 mixes the coagulant 3 and the raw water 1 (that is, by flowing the raw water 1 into which the coagulant 3 is injected), thereby coagulating impurities contained in the raw water 1 by the action of the coagulant 3. However, there is no particular limitation as long as the means can form a floc.

  As the mixing means 14, for example, a flocculation tank (reaction tank) having a stirring device such as a stirring blade can be used. In this case, the raw water 1 into which the coagulant 3 has been injected flows into the coagulation tank and is stirred by the stirrer to form a floc in which impurities are coagulated, and the water 5 to be treated containing the formed floc is coagulated. Can be discharged from the tank. Mixing by such means is also called rapid mixing or rapid stirring. In the present invention, rapid mixing is preferably performed as the mixing means or the mixing step. However, slow mixing (or floc formation) may be performed, or both rapid mixing and slow mixing may be performed.

Also, in the case where the raw water 1 into which the coagulant 3 has been injected flows and flocs are formed even without stirring using a stirrer or the like, a coagulation tank (reaction tank) without a stirrer is provided. Can be used as the mixing means 14.
Further, as the mixing means 14, a pipe-connected type static mixer which causes turbulence in the pipe to perform mixing can be used.
Further, a pipe can be used as the mixing means 14. When the length of the pipe is equal to or more than a certain length, the raw water 1 into which the coagulant 3 has been injected is simply flown into the pipe, so that the water 5 to be treated including flocs can be obtained.

The mixing step in the method of the present invention can be performed by the mixing means 14.
The mixing step in the method of the present invention is a step of mixing the injected coagulant 3 and the raw water 1 to form flocs and obtaining the water 5 to be treated containing the flocs.

<Membrane filtration means, membrane filtration process>
The membrane filtration means 16 in the device 10 of the present invention will be described.
In the apparatus 10 of the present invention, the membrane filtration means 16 performs the membrane filtration treatment of the water 5 to be treated so that the raw water recovery rate is 90% or more, and the purified water 7 obtained by removing at least a part of the floc from the water 5 to be treated. And sludge 9 containing concentrated floc.

  Although there may be some loss due to evaporation or the like, it may be generally considered that the water to be treated 5 is separated into purified water 7 and sludge 9 by the membrane filtration means 16. In other words, it may be considered that the volume of the treatment target water 5 supplied to the membrane filtration unit 16 is equal to the total volume of the purified water 7 and the sludge 9 discharged from the membrane filtration unit 16.

  The membrane filtration unit 16 is a unit that separates and removes at least a part (usually, almost all) of flocs contained in the water 5 to be treated from the water 5 to be treated using, for example, a conventionally known separation membrane.

  Examples of the membrane filtration unit 16 include an immersion type membrane filtration device and a casing type membrane filtration device capable of setting the raw water recovery rate to 90% or more.

  As the immersion type membrane filtration device, an embodiment having a tank, a membrane module and a suction pump can be exemplified. Here, it is preferable that the tank has a mode in which a sludge discharging section for discharging the sludge 9 is provided below the tank. The membrane module includes, for example, a macaroni-like separation membrane called a hollow fiber, and is used by being immersed in the treatment target water 5 stored in a tank. In addition, a suction pump is connected to the membrane module by a pipe or the like, and a part of the water 5 to be treated can be passed through the separation membrane to obtain purified water 7 by suction by the suction pump.

  In such an immersion type membrane filtration device, the water 5 to be treated is continuously or intermittently supplied into the tank, and a part of the water 5 to be treated is passed through the separation membrane by the action of the suction pump to purify the water 7. Are obtained continuously or intermittently. Moreover, the sludge 9 is discharged | emitted intermittently from a sludge part normally. Since floc is concentrated in the sludge, it is discharged from the tank.

  In the device 10 of the present invention, it is preferable to use an immersion type membrane filtration device as the membrane filtration means 16.

  The casing-type membrane filtration device is a device in which a membrane module is housed in a pressure-resistant container (casing). Usually, the water to be treated 5 is press-fitted into the casing by the action of a pump, whereby the water is filtered to purify the purified water 7 and the sludge. 9 is obtained.

  In the membrane filtration means 16 typified by an immersion type membrane filtration device or a casing type membrane filtration device, the separation membrane can be backwashed and washed using the purified water 7 obtained.

For example, a membrane having a pore size of about 0.01 to 0.2 μm called a microfiltration membrane (MF membrane) is used as a separation membrane in the membrane filtration unit 16 typified by a submerged membrane filtration device or a casing type membrane filtration device. Can be. Further, an ultrafiltration membrane (UF membrane), a reverse osmosis membrane (RO membrane), or a nanofiltration membrane (NF membrane) can also be used.
The nominal pore size of the separation membrane is preferably from 0.001 μm to 0.2 μm.

  It is preferable that the membrane filtration unit 16 further includes a unit capable of stirring the water 5 to be treated using gas. A diffuser is exemplified as such means. For example, if an air diffuser is installed below the tank provided in the immersion type membrane filtration device, a gas (air or the like) is blown into the water 5 to be treated stored in the tank by using this, and the water to be treated is 5 is preferred because it can be stirred.

  In the membrane filtration step in the method of the present invention, it is preferable that the water 5 to be treated is subjected to membrane filtration after gas is blown. Further, in the membrane filtration step in the method of the present invention, it is preferable that the water 5 to be treated is subjected to membrane filtration while blowing gas.

For example, in the case of the immersion type membrane filtration device, the floc existing inside the tank provided therein may gradually settle if the stirring power in the tank is derived only from the raw water flow input or the like. In this case, there is a possibility that the area where the floc is present is reduced downward in the tank. Then, the contact efficiency between the floc and the chromaticity component or the organic component may decrease. Therefore, it is preferable to stir the water 5 to be treated in the tank using an air diffuser or the like in order to make the floc exist in the tank as uniformly as possible. The air diffuser does not need to be used only for stirring the water to be treated, and may use a device for diffusing air for cleaning the membrane. Stirring may be performed.
In addition, when powdered activated carbon is used as in the method described in Patent Document 1, the sedimentation speed is lower than that of the flocculated floc. Therefore, the sedimentation does not significantly occur in a short time without stirring. However, the floc that has been flocculated by adding a flocculant for sedimentation has remarkably higher sedimentation property than powdered activated carbon. Therefore, in order to increase the contact efficiency, it is preferable to perform appropriate stirring. Therefore, in the case of powdered activated carbon alone, it is not necessary to pay attention to stirring to enhance the contact efficiency, but it is important in the case of floc.

Here, the time for blowing the gas into the water 5 to be treated is preferably 1 second to 10 minutes, and more preferably 10 seconds to 5 minutes.
Further, the interval between the time when the gas is blown into the water 5 to be treated and the time when the gas is blown again is preferably 1 to 60 minutes, more preferably 10 to 50 minutes.
With such a blowing time and / or a blowing interval, the floc easily collides with the chromaticity component or the organic substance component, and the chromaticity component or the organic substance component is taken into the floc. As a result, the chromaticity component and the organic substance component This is because purified water 7 having a lower content is obtained.

  In the apparatus 10 of the present invention, the membrane filtration means 16 performs the membrane filtration treatment on the water 5 to be treated so that the raw water recovery rate is 90% or more. The raw water recovery rate is preferably 94% or more, more preferably 97% or more, and even more preferably 98% or more. Also, it may be 99.999% or less.

  The raw water recovery rate is defined as a ratio (percentage) of the volume of the purified water 7 discharged from the membrane filtration unit 16 to the volume of the treatment target water 5 supplied to the membrane filtration unit 16. In addition, as described above, the volume of the treatment target water 5 supplied to the membrane filtration unit 16 may be considered to be substantially the same as the total volume of the purified water 7 and the sludge 9 discharged from the membrane filtration unit 16. The recovery is represented by the following equation.

Raw water recovery rate (%) = volume of purified water 7 discharged / volume of supplied water 5 to be treated × 100
= (Volume of supplied treatment target water 5-volume of discharged sludge 9) / volume of supplied treatment target water 5 x 100

  The raw water recovery rate can be adjusted to 90% or more by adjusting the discharge amount of the sludge 9 discharged from the membrane filtration means 16.

  The raw water recovery rate indicates the degree of concentration of the water 5 to be treated. For example, it indicates the degree of concentration of the water 5 to be treated in the tank of the immersion type membrane filtration device. When the raw water recovery rate is increased to 90% or more, the concentration of the water 5 to be treated in the tank increases, so that the floc concentration increases. Then, the contact efficiency between the existing floc and the ultrafine floc is increased, and the floc is likely to be large, so that the removal rate of the chromaticity component or the organic component is considered to increase.

  When the water 5 to be treated is subjected to the membrane filtration treatment by the membrane filtration means 16, it is preferable to always adjust so that the floc is contained in the water 5 to be treated held in the immersion tank in which the membrane is immersed. For example, when the immersion type membrane filtration device is used as the membrane filtration means 16, as described above, the sludge 9 is usually intermittently discharged from the sludge discharge section, but not all the sludge 9 is discharged. The sludge 9 is discharged so as to remain therein, so that when the water 5 to be treated is subjected to membrane filtration, the floc is always contained in the water 5 to be treated held in the immersion tank in which the membrane is immersed. can do. Further, for example, by adding a part of the sludge 9 discharged from the sludge discharge section again to the tank in which the water 5 to be treated is stored, the water to be treated always kept in the immersion tank in which the membrane is immersed. 5 can also be adjusted to include flock.

  For example, when the immersion type membrane filtration device is used as the membrane filtration means 16 and the entire amount of sludge 9 is discharged from the drainage section, the chromaticity component in the water 5 to be treated and There is a possibility that flocs for trapping organic components are reduced. Then, the removal rate of the chromaticity component and the organic substance component may be reduced by the floc derived from the raw water 1 before the concentration of the floc in the water 5 to be treated increases again. Therefore, for example, it is preferable to discharge the sludge 9 so that 0.01% by volume or more of the treatment target water 5 stored in the tank remains. 99% by volume or less, preferably 95% by volume or less, more preferably 30% by volume or less, still more preferably 10% by volume or less of the water 5 to be treated stored in the tank may be left.

The membrane permeation flow rate in the membrane filtration means 16 is not particularly limited, but is preferably 0.4 to 10 m / d.
The amount of water supplied to the membrane in the membrane filtration means 16 is not particularly limited, but is preferably a level that balances the amount of water supplied to the membrane.
The amount of diffused air in the membrane filtration means 16 is preferably 1 to 350 m ³ / h per 1 m ² of the membrane installation area.

In the device 10 of the present invention, activated carbon may not be used in the membrane filtration means 16. For example, when an immersion type membrane filtration device is used as the membrane filtration means 16, there is no need to add activated carbon into the tank. Even without adding activated carbon, impurities can be separated and removed from the water 5 to be treated.
Similarly, activated carbon may not be used in the membrane filtration step in the method of the present invention.

The membrane filtration step in the method of the present invention can be performed by the membrane filtration means 16.
In the membrane filtration step in the method of the present invention, the water 5 to be treated is subjected to membrane filtration so that the raw water recovery rate is 90% or more, and purified water 7 obtained by removing at least a part of the floc from the water 5 to be treated. This is a step of obtaining sludge 9 containing the concentrated flocs.

  Next, the flow of processing when the raw water 1 is processed by the above-described apparatus 10 of the present invention will be described. This description is also a description of the method of the present invention.

First, the coagulant 3 is injected into the raw water 1 by the coagulant injection means 12 (coagulant injection step). The mixing means 14 mixes the injected coagulant 3 and the raw water 1 to form flocs. And the water 5 for a process containing a floc is obtained (mixing process).
Next, the water 5 to be treated is subjected to membrane filtration by the membrane treatment means 16 so that the raw water recovery rate is 90% or more. Then, purified water 7 and sludge 9 are obtained (membrane filtration step).

  ADVANTAGE OF THE INVENTION According to this invention, even if the coagulant injection | pouring rate is made low, the purified water with low content of a chromaticity component and an organic substance component is obtained. Specifically, for example, when the injection amount of the flocculant 3 into the raw water 1 is set to 0 to 100 mg / L (preferably 0 to 30 mg / L) as an addition amount to 1 L of the raw water, the purified water 7 having a low chromaticity is purified. can get. Specifically, the ratio of the chromaticity of the purified water 7 to the chromaticity of the raw water 1 can be, for example, 1/10000 to 1/2 (preferably, for example, 1/10000 to 1/10).

Examples of the purified water 7 obtained by the present invention include those having the following turbidity, chromaticity, or TOC (total organic carbon).
-Turbidity: 0.1 degrees or less (preferably 0.01 degrees or less, more preferably 0.0001 degrees or less)
Chromaticity: 1 degree or less (preferably 0.1 degree or less, more preferably 0.01 degree or less)
-TOC: 3 mg / L or less (preferably 0.5 mg / L or less, more preferably 0.1 mg / L or less)

Next, a preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic diagram illustrating one preferred embodiment of the device of the present invention.
In FIG. 2, the apparatus 20 includes a coagulant injection pump 22 for injecting the coagulant 3 into the raw water 1, a floc formed by mixing the injected coagulant 3 and the raw water 1, and a treatment target water 5 containing the floc. Tank 24 that discharges water, membrane water treatment of the water 5 to be treated so that the raw water recovery rate is 90% or more, purified water 7 obtained by removing at least a part of the floc from the water 5 to be treated, and concentration And a submerged membrane filtration device 26 that obtains the sludge 9 containing the flocs.

The apparatus 20 further has a pH adjusting means for adding a pH adjusting agent to the raw water 1 before the coagulant 3 is injected. By adding the pH adjuster 8 (acid and / or alkali) to the raw water 1 by this pH adjusting means, the pH of the raw water 1 can be adjusted to a pH at which the coagulability of the coagulant 3 can be increased.
The device 20 further has a water purification reservoir 28 for storing the purified water 7.
The apparatus 20 further includes a backwash pump 281 and a pipe 282 used for backwashing and cleaning the separation membrane 261a of the immersion type membrane filtration device 26 using the purified water 7 stored in the water purification area 28.

  The coagulant injection pump 22 has a tank and a pump. The coagulant can be stored in the tank, and a desired amount of the coagulant 3 can be discharged from the tank by the action of the pump. is there. The coagulant injection pump 22 can inject a desired amount of the coagulant 3 into the raw water 1 to which the pH adjuster stored in the rapid mixing tank 24 has been added.

  The coagulant injection pump 22 corresponds to a coagulant injection unit in the apparatus of the present invention.

  The rapid mixing tank 24 has two tanks (a first tank 241 and a second tank 242). Then, in the first tank 241, the coagulant 3 and the raw water 1 to which the pH adjuster 8 has been added can be received and mixed. Thereafter, the water is mixed again in the second tank 242, and the water 5 to be treated is discharged. Each of the first tank 241 and the second tank 242 has a stirrer (243, 244), and the raw water 1 into which the flocculant 3 is injected is stirred by the stirrer to mix the flocculant 3 with the raw water 1. By doing so, it is possible to form a floc in which impurities contained in the raw water 1 are aggregated.

  The rapid mixing tank 24 corresponds to a mixing means in the apparatus of the present invention.

  The mixing means in the apparatus of the present invention may be a rapid mixing tank having two tanks as shown in FIG. 2, but may be an embodiment having one tank, or three or more tanks. It may be an embodiment having

  The immersion type membrane filtration device 26 has a membrane module 261, a tank 262, a suction pump 263, a pipe 264, and a drain valve 265. The membrane module 261 has a separation membrane 261a, a water collecting part 261b, and a lower support 261c. Then, the water collecting part 261b and the water purification area 28 are connected by a pipe 264, and a suction pump 263 is arranged in the middle thereof. By operating the suction pump 263, the water to be treated 5 in the tank 262 is removed. Purified water 7 can be obtained. The obtained purified water 7 reaches the water purification reservoir 28 through the pipe 264 and is configured to be stored therein. Also, by opening the sludge valve 265, a part of the water 5 to be treated in the tank 262 can be discharged as sludge 9 from the lower part of the tank 262.

  In the immersion type membrane filtration device 26, the water 5 to be treated is stored inside the tank 262. The membrane module 261 is used by being immersed in the water 5 to be treated stored in the tank 262. Then, when the suction pump 263 is operated, a part of the treatment target water 5 passes through the separation membrane 261a to become the purified water 7 by the action thereof, reaches the purified water place 28 through the pipe 264, and is stored therein. Further, flocs contained in the water 5 to be treated cannot pass through the separation membrane 261a, and thus stay in the tank 262.

  The sludge 9 containing the flocs is discharged from a sludge discharging section below the tank 262. The frequency of discharging the sludge 9 from the sludge discharging section of the tank 262 is not particularly limited. For example, once every few days, the sludge 9 can be discharged from the inside of the tank 262 by opening the sludge valve 265. However, the water is discharged so that the raw water recovery rate is 90% or more.

  The immersion type membrane filtration device 26 corresponds to the membrane filtration means in the device of the present invention.

  Next, the flow of processing when the raw water 1 is processed by the above-described apparatus 20 will be described. This description is also a description of a preferred embodiment of the method of the present invention.

First, the pH adjuster 8 (acid or alkali) is added to the raw water 1, and then the raw water 1 flows into the first tank 241 in the rapid mixing tank 24. Then, in the first tank 241, the coagulant 3 is added from the coagulant injection pump 22 to the raw water 1 stored therein (coagulant injection step), and after being mixed by the action of the stirrer 243, the second tank 242. After being mixed again by the action of the stirrer 244 in the second tank 242, it is discharged as the water 5 to be treated (mixing step). The water 5 to be treated includes flocs formed by aggregation of impurities contained in the raw water 1 by the action of the coagulant 3.
Thereafter, the water 5 to be treated is stored in the tank 262 of the immersion type membrane filtration device 26. The membrane module 261 is installed so as to be immersed in the stored water 5 to be treated, and by operating the suction pump 263, a part of the water 5 to be treated passes through the separation membrane 261a to become purified water 7, The water reaches the water purification plant 28 through the pipe 264 and is stored therein. Further, flocs contained in the water 5 to be treated cannot pass through the separation membrane 261a, and thus stay in the tank 262. Here, it is preferable to install a flow meter for measuring the flow rate of the treatment target water 5 flowing into the tank 262 and a flow meter for measuring the flow rate of the purified water 7 discharged into the immersion type membrane filtration device 26. It is preferable that the operation is performed so that the flow rates indicated by these flow meters are substantially the same. Further, it is preferable to monitor the values of the respective flow meters and adjust the operation so that the water level of the water 5 to be treated in the tank 262 falls within a specific range.
Next, the sludge 9 containing the flocs is discharged from a sludge discharging section below the tank 262. The frequency of discharging the sludge 9 from the tank 262 is not particularly limited. For example, once every few days, the sludge 9 can be discharged from the sludge section of the tank 262 by opening the sludge valve 265. However, it is discharged so that the raw water recovery rate is 90% or more.
In addition, by operating the backwash pump 281, the separation membrane 261 a of the immersion type membrane filtration device 26 can be backwashed and washed using the purified water 7 stored in the water purification area 28. The frequency of the backwashing is not particularly limited. For example, it is preferable to perform backwashing once for several tens of minutes.

Next, another preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 3 is a schematic diagram for explaining one of other preferred embodiments of the device of the present invention.
In FIG. 3, the same components as those in the embodiment shown in FIG. 2 are denoted by the same reference numerals. In the following, a description will be given mainly of points different from the embodiment shown in FIG.

In FIG. 3, the apparatus 30 includes a coagulant injection pump 22, a rapid mixing tank 24, a pH adjusting means, a water purification tank 28, a backwash pump 281 and a pipe 282 similar to the embodiment shown in FIG. ing.
The immersion type membrane filtration device 36 is a mode in which the immersion type membrane filtration device 26 shown in FIG. It is preferable to monitor the water level of the water 5 to be treated in the tank 262 at the time of drainage by the electrode 37 and / or the interface meter 38. Then, when the water level becomes lower than a specific level at the time of drainage, an electric signal is transmitted from the electrode 37 and / or the interface meter 38 to close the drainage valve 265 and adjust the amount of the sludge 9 discharged from the tank 262. Is preferred.

  As the electrode 37 and the interface meter 38, for example, conventionally known ones can be used. The same operation as the electrode 37 and the interface meter 38 can be performed by using a conventionally known drainage process timer.

Next, another preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 4 is a schematic view for explaining one of other preferred embodiments of the device of the present invention.
In FIG. 4, the same components as those in the embodiment shown in FIG. 2 are denoted by the same reference numerals. In the following, a description will be given mainly of points different from the embodiment shown in FIG.

In FIG. 4, the apparatus 40 includes a coagulant injection pump 22, a rapid mixing tank 24, a pH adjusting means, a water purification tank 28, a backwash pump 281 and a pipe 282 similar to the embodiment shown in FIG. ing.
The immersion type membrane filtration device 46 is an embodiment in which the air diffusion device 47 and the blower 48 are further provided in the immersion type membrane filtration device 26 shown in FIG. By operating the blower 48, air is sent from the air diffuser 47 to the inside of the tank 262, and the processing target water 5 stored therein can be stirred. When an appropriate amount of air is sent into the tank 262 to stir the water 5 to be treated, flocs can be more uniformly present in the tank 262, so that the contact efficiency between the flocs and the chromaticity component or the organic component can be increased. Is preferred. And it is preferable because the purified water 7 having a lower content of the chromaticity component and the organic component can be obtained.

Next, another preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 5 is a schematic view for explaining another preferred embodiment of the device of the present invention.
In FIG. 5, the same components as those in the embodiment shown in FIG. 2 are denoted by the same reference numerals. In the following, a description will be given mainly of points different from the embodiment shown in FIG.

In FIG. 5, the device 50 includes a coagulant injection pump 22, a rapid mixing tank 24, a submerged membrane filtration device 26, a pH adjusting means, a water purification tank 28, and a backwash pump similar to the embodiment shown in FIG. 281 and a pipe 282.
The device 50 further has a soluble manganese filtration tower 51. The soluble manganese filtration tower 51 has a layer 511 made of manganese sand and a support layer 512 therein. When the raw water 1 contains soluble manganese, it can be removed from the raw water 1, which is preferable. When the raw water 1 flows from the lower part of the soluble manganese filtration tower 51 by operating the pump 513 and moves toward the upper part, the soluble manganese contained in the raw water 1 is converted from the raw water 1 by the action of manganese sand in the process. It is separated and at least a part thereof is removed. Thereafter, the raw water 1 from which at least a part of the soluble manganese has been removed is sent from the upper part of the soluble manganese filtration tower 51 toward the rapid mixing tank 24. Thereafter, processing is performed in the same manner as in the case of the embodiment shown in FIG.
As the soluble manganese filtration tower 51, for example, a conventionally known one can be used.

  Hereinafter, an experiment related to the present invention will be described.

<Experiment 1>
Raw water 1 is treated using the apparatus (apparatus 20) of the present invention in the mode shown in FIG. 2, and the relationship between the raw water recovery rate in the immersion type membrane filtration device 26 and the ratio of the removal rate of the chromaticity component or the organic substance component. Is measured, a graph shown in FIG. 6 is obtained. In FIG. 6, the ratio of the removal rate of the chromaticity component or the organic substance component on the Y axis is shown as a value when the removal rate of the chromaticity component or the organic substance component is 1 when the raw water recovery rate is 80%.
As shown in the graph of FIG. 6, when the raw water recovery rate is as high as 90% or more, the removal rates of the chromaticity component and the organic component are increased.

<Experiment 2>
The raw water 1 is treated using the apparatus (apparatus 20) of the present invention in the mode shown in FIG. Then, after a sufficient time has elapsed, the sludge valve 265 of the submerged membrane filtration device 26 is opened, and the sludge 9 is discharged from the lower part of the tank 262. At this time, if a part of the water 5 to be treated stored in the tank 262 is not discharged but remains inside the tank 262, the membrane filtration processing by the immersion type membrane filtration device 26 is restarted. In addition, there is a tendency that the removal rate of the chromaticity component or the organic component after a specific time has elapsed is improved. FIG. 7 is a graph showing this. That is, FIG. 7 shows the ratio of the residual ratio (X-axis) of the water 5 to be treated left inside the tank 262 and the removal ratio of the chromaticity component or the organic component after the elapse of a specific time after membrane filtration is started ( 6 is a graph showing a relationship with the Y axis. In FIG. 7, the ratio of the removal rate of the chromaticity component or the organic matter component after the lapse of a specific time from the start of the membrane filtration on the Y-axis is a value when 1 when the residual rate of the water to be treated is 20%. Is shown.
As shown in the graph of FIG. 7, when the residual rate of the water to be treated is 0.01% by volume or more, an effect is observed in maintaining the removal rate of the chromaticity component or the organic component.

<Experiment 3>
Raw water 1 is treated using the apparatus (apparatus 40) of the present invention in the mode shown in FIG. 4, and the time and interval for blowing air from the air diffuser 47 in the submerged membrane filtration apparatus 46, and the turbidity ratio (T _A) / T _B ), the graph shown in FIG. 8 is obtained. Here turbidity ratio (T _A / T _B) is the ratio of the turbidity T _A with respect to turbidity T _B. Further, the turbidity T _A, as shown in FIG. 9, it is meant the turbidity of the water being treated 5 at water level of the water collecting portion 261b inside the tank 262 in the immersion type membrane filtering device 46, turbidity T _B, as shown in FIG. 9, which means the turbidity of the water being treated 5 at water level of the lower support 261c in the interior of the vessel 262 in the immersion type membrane filtering device 46. When the turbidity inside the tank 262 is uniform, the turbidity ratio (T _A / T _B ) becomes 1, and as the sedimentation of solids and the like progresses, the turbidity ratio (T _A / T _B ) decreases. When the turbidity ratio (T _A / T _B ) is close to 1, it is understood that the turbidity of the water 5 to be treated in the tank 262 is more uniform, which is preferable.
As shown in the graph of FIG. 8, the time for blowing air into the water 5 to be treated is 1 second to 10 minutes, and after the air is blown into the water 5 to be treated, until the gas is blown again again. When the interval is 1 to 60 minutes, the turbidity ratio (T _A / T _B ) becomes higher (about 0.8 or more), which is preferable.

DESCRIPTION OF SYMBOLS 1 Raw water 3 Coagulant 5 Water to be treated 7 Purified water 9 Sludge 10 Device of the present invention 12 Coagulant injection means 14 Mixing means 16 Membrane filtration means 8 pH adjuster 20 Device 22 Coagulant injection pump 24 Rapid mixing tank 241 First tank 242 Second tank 243, 244 Stirrer 26 Immersion type membrane filtration device 261 Membrane module 261a Separation membrane 261b Water collecting part 261c Lower support 262 Tank 263 Suction pump 264 Pipe 265 Drainage valve 28 Water purifier 281 Backwash pump 282 Pipe 30 Device 36 Immersion type membrane filtration device 37 Electrode 38 Interface meter 40 device 46 Immersion type membrane filtration device 47 Air diffuser 48 Blower 50 Device 51 Soluble manganese filtration tower 511 Layer composed of manganese sand 512 Support layer 513 Pump

Claims (3)

A coagulant containing impurities including a turbidity component, a chromaticity component and an organic component, and a flocculant for coagulating the impurities in raw water having a turbidity of 500 ° or less, a chromaticity of 100 ° or less, and a TOC of 10 mg / L or less to form flocs. A coagulant injection step of injecting,
Mixing or flowing the injected coagulant and the raw water to form the flocs, a floc forming step of obtaining the water to be treated including the flocs,
The water to be treated is supplied, and the purified water contains turbidity of 0.1 degrees or less, chromaticity of 1 degree or less, TOC of 3 mg / L or less, and the concentrated flocs discharged from the water to be treated after removal of the flocs. A membrane filtration step including discharging the sludge so as to obtain not less than 0.01% by volume of the water to be treated stored in the immersion tank after completion of the membrane filtration treatment. And
The membrane filtration step has the following relationship:
Raw water recovery rate (%) = volume of purified water discharged / volume of supplied water to be treated × 100 = (volume of supplied water to be treated−volume of discharged sludge) / supplied water to be treated Volume x 100
The water to be treated is subjected to membrane filtration and no activated carbon is used so that the raw water recovery represented by is 90% or more. In the membrane filtration, 1 to 60 minutes are used. Between seconds and 10 minutes, by stirring the water to be treated by blowing gas, the chromaticity component or the organic component in the water to be treated is further contacted with the floc to perform the membrane filtration treatment. Water treatment method.   2. The method according to claim 1, wherein in the membrane filtration step, when the water to be treated is subjected to membrane filtration, the floc is always adjusted to be contained in the water to be treated held in an immersion tank in which a membrane is immersed. Water treatment method. A coagulant containing impurities including a turbidity component, a chromaticity component and an organic component , and a flocculant for coagulating the impurities in raw water having a turbidity of 500 ° or less, a chromaticity of 100 ° or less, and a TOC of 10 mg / L or less to form flocs. Coagulant injection means for injecting,
A mixing means for mixing the injected flocculant and the raw water to form the flocs, and obtaining a treatment target water containing the flocs;
An immersion tank for immersing the membrane in the water to be treated and a diffuser for blowing gas into the immersion tank are provided, and the floc is formed from the water to be treated by performing membrane filtration of the water to be treated. Membrane filtration means for obtaining purified water having a turbidity of 0.1 ° or less, a chromaticity of 1 ° or less, a TOC of 3 mg / L or less, and a concentrated sludge containing the floc;
A sludge discharging section for discharging the sludge while leaving the water to be treated in the immersion tank so that the water to be treated stored in the immersion tank remains at 0.01% by volume or more after the completion of the membrane filtration treatment; With
The membrane filtration means,
The following relation:
Raw water recovery rate (%) = volume of purified water discharged / volume of supplied water to be treated × 100 = (volume of supplied water to be treated−volume of discharged sludge) / supplied water to be treated Volume x 100
The target water is subjected to membrane filtration so as to have a raw water recovery rate of 90% or more, and no activated carbon is used. In addition, 1 to 60 minutes is used in the immersion tank during the membrane filtration. At intervals, between 1 second and 10 minutes, by stirring the water to be treated in the immersion tank by blowing gas, the chromaticity component or the organic component in the water to be treated in the immersion tank is further increased A water treatment device characterized by performing membrane filtration treatment by contacting with floc.

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