JP2014168729A - Water treatment method and water treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method capable of obtaining, even if the flocculant injection ratio is decreased, a body of purified water having low contents of chromaticity components or organic components and also capable of enhancing the raw water recovery ratio.SOLUTION: The provided water treatment method includes a flocculant injection step of injecting a flocculant into a body of raw water, a mixing step of obtaining, by mixing the injected flocculant with the raw water so as to form a floc, a body of treatment target water including the floc, and a membrane filtering step of obtaining, by filtering the treatment target water through a membrane so as to realize a raw water recovery ratio of 90% or above, a body of purified water where the floc has been at least partially removed from the treatment target water and a sludge including the concentrated floc.

Description

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

In recent years, membrane filtration devices have attracted attention as new water treatment devices. This is a device for turbidity, and replaces a conventional sand clarifier and a quick sand filter. Since the membrane filtration device is a device for turbidity, it has been frequently used when relatively clear water that requires 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 treated water, the membrane filtration device will be introduced not only into clean raw water but also into raw water that requires treatment other than turbidity. There is a lot of movement to do.

  Examples of substances that need to be removed in addition to turbidity include chromaticity and organic substances. Since these substances are colloidal components (soluble substances), it is difficult to remove them with a normal membrane filtration apparatus. As a method for removing these substances with a membrane filtration apparatus, a coagulation facility for injecting a flocculant and mixing with raw water is provided in the previous stage. In this coagulation facility, chromaticity components and organic components are aggregated to a size that can be removed by membrane filtration, and removed as turbidity components by membrane filtration to obtain clear treated water.

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

  In Patent Document 1, powdered activated carbon mixed water in which powdered activated carbon is added to raw water in advance is allowed to flow into the membrane filtration tank, or raw water is flowed into the membrane filtration tank to add powdered activated carbon to obtain powdered activated carbon mixed water, Substances to be treated, such as trace organic substances in raw water, are adsorbed to powdered activated carbon, and the powdered activated carbon mixed water in the membrane filtration tank is solid-liquid separated by an immersion membrane filtration apparatus installed in the tank, and the immersion membrane filtration apparatus When taking out the membrane filtered water that has passed through the membrane surface from the tank, the amount of the membrane filtered water with respect to the amount of water flowing into the membrane filtration tank is set to 99% or more, and the powdered activated carbon is kept at a high concentration in the membrane filtration tank. Describes a method for operating a water treatment facility using a submerged membrane filtration device characterized by promoting adsorption of a substance to be treated. Powdered activated carbon can remove organic chlorine compounds such as trihalomethane or precursors thereof, trace harmful substances such as pesticides, off-flavor causing substances such as musty odors, and trace organic substances such as anionic surfactants, and membranes. Ammonia nitrogen and organic substances can be removed by microorganisms such as nitrifying bacteria that are naturally generated and retained in the filtration tank. It is described 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 filtered and separated by a membrane filtration device. Furthermore, at this time, the amount of membrane filtrate 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 kept at a high concentration in the membrane filtration tank, and the ability of the powdered activated carbon is utilized to the maximum. By doing so, it is possible to promote the adsorption of the object to be treated, and as a result, the amount of powdered activated carbon can be reduced, and since it can respond widely to fluctuations in raw water quality, It is described that it is possible to obtain a filtered water having a treated water quality.

  In Patent Document 2, the solid content concentration in the tank is subjected to membrane filtration of the solid content water until the solid content concentration becomes 0.1 Ct to Ct as the limit solid concentration (Ct). Membrane filtration process including the implementation of cleansing, drainage process of draining all or part of the solid-containing water in the tank after the membrane filtration process, supplying raw water into the tank after the drainage process and containing solids A water purification treatment method is described that 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 treatment method, it is possible to prevent the cake from adhering to the membrane surface while maintaining a high recovery rate of the treated water by periodically draining the entire volume or partially draining under certain conditions. In addition, it is described that the adsorption effect by activated carbon can be maintained high.

JP-A-9-28579 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 (such as a rapid filtration method and a slow filtration method). In order to remove a chromaticity component and an organic component by adopting a membrane filtration method, injection of a flocculant or the like is indispensable, which increases operating costs. In adopting the membrane filtration method, it is an urgent issue to reduce the operation cost, and particularly in the case of the membrane filtration method having an additional process such as injecting a flocculant, it becomes an especially important issue.

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

  In addition, as the 21st century is said to be the century of water, there are abundant water resources if you look at the situation in Japan alone, but if you look at the world, water demand is expected to tighten as the population increases. . In view of such future trends, it is obvious that a process that can be treated as purified water as much as possible without wasting the taken water will become indispensable in the future.

  Therefore, what is required for the future membrane filtration method is that it can be operated at a low running cost with respect to raw water that is relatively unclear, and the raw water is not wasted and a high recovery rate can be achieved. It is.

  However, in order to obtain purified water having low concentrations of chromaticity components and organic components in conventional membrane filtration devices and membrane filtration treatments, it is necessary to increase the injection rate of the flocculant. If the injection rate of the flocculant is high, the running cost increases, which is not preferable. Moreover, if the injection rate of the flocculant is high, turbid components tend to adhere to the membrane in the membrane filtration device, and it is necessary to frequently perform an operation for removing the adhering turbid components by performing backwashing and the like. The filtration time per unit time is undesirably lowered.

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 capable of obtaining purified water having a low content of chromaticity components and organic components even when the flocculant injection rate is lowered and further increasing the raw water recovery rate. There is.

The present inventor has intensively studied to solve the above-described problems and completed the present invention.
The present invention includes the following (1) to (5).
(1) a flocculant injection step of injecting the flocculant into raw water;
A mixing step of mixing the injected flocculant and the raw water to form a floc and obtaining water to be treated containing the floc;
A membrane that obtains sludge containing purified water obtained by removing at least a part of the floc from the water to be treated and the concentrated floc by subjecting the water to be treated to membrane filtration so that the raw water recovery rate is 90% or more. A filtration process;
A water treatment method.
(2) The water treatment method according to (1), wherein in the membrane filtration step, the treatment target water is subjected to membrane filtration treatment after blowing gas or while blowing gas.
(3) The water treatment method according to (2), wherein in the membrane filtration step, the treatment target water is stirred by blowing a gas at intervals of 1 to 60 minutes for 1 to 10 minutes.
(4) In the membrane filtration step, when the membrane to be treated is subjected to membrane filtration, the membrane to be treated is always adjusted so that the floc is contained in the membrane to be treated, which is retained in an immersion tank in which the membrane is immersed. The water treatment method according to any one of 1) to (3).
(5) a flocculant injection means for injecting the flocculant into the raw water;
Mixing means for mixing the injected flocculant and the raw water to form a floc, and obtaining water to be treated containing the floc;
A membrane that obtains sludge containing purified water obtained by removing at least a part of the floc from the water to be treated and the concentrated floc by subjecting the water to be treated to membrane filtration so that the raw water recovery rate is 90% or more. Filtration means;
Having a water treatment device.

  According to the present invention, there is provided a water treatment method and a water treatment apparatus capable of obtaining purified water having a low content of chromaticity components and organic matter components even when the flocculant injection rate is lowered by increasing the raw water recovery rate. Can do.

It is the schematic which shows the outline of the apparatus of this invention. It is the schematic which shows the preferable aspect of the apparatus of this invention. It is the schematic which shows another preferable aspect of the apparatus of this invention. It is the schematic which shows another preferable aspect of the apparatus of this invention. It is the schematic which shows another preferable aspect of the apparatus of this invention. It is a graph which shows the relationship between a raw water collection | recovery rate and the ratio of the removal rate of a chromaticity component and an organic substance component. It is a graph which shows the relationship between the residual rate of process target water, and the ratio of the removal rate of a chromaticity component and an organic substance component. It is a graph which shows the relationship between the time which blows air from a diffuser, and turbidity ratio. It is the schematic which expanded a part of immersion type membrane filtration apparatus used in order to demonstrate turbidity ratio.

The present invention will be described in detail.
The present invention includes a flocculant injection step of injecting a flocculant into raw water, a mixing step of mixing the injected flocculant and the raw water to form a floc, and obtaining water to be treated containing the floc, and raw water Membrane filtration is performed so that the water to be treated is subjected to membrane filtration so that the recovery rate is 90% or more, and at least a part of the floc is removed from the water to be treated, and the sludge containing the concentrated floc is obtained. A water treatment method comprising: a step.
Hereinafter, such a water treatment method is also referred to as “the method of the present invention”.

The present invention also includes a flocculant injecting means for injecting a flocculant into raw water, a mixing means for mixing the injected flocculant and the raw water to form a floc, and obtaining water to be treated containing the floc. Then, the water to be treated is subjected to membrane filtration so that the raw water recovery rate is 90% or more, and purified water from which at least a part of the floc is removed from the water to be treated and sludge containing the concentrated floc are obtained. 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 carried out using the apparatus of the present invention.

  Hereinafter, the simple description of “the present invention” means both the method of the present invention and the apparatus of the present invention.

  The manifestation mechanism of the effect of the present invention estimated by the present inventor will be described using a specific example. 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, the flocs produced are fine because slow stirring is not performed. When solid-liquid separation is performed using a conventional precipitation method, fine flocs are not preferable because the flocs sedimentation rate is slow and the separation efficiency in the sedimentation tank deteriorates. However, in the case of the membrane filtration method, if the fine floc diameter is larger than the pores on the membrane surface, solid-liquid separation is possible.
The present inventor discovered that there is room for improvement in the coagulation / membrane filtration process in the following two points while carrying out diligent research.
[1] With rapid mixing alone, there are ultrafine flocs that could not be larger than the pores on the membrane surface, and chromaticity or organic matter components that could not become flocs.
[2] The nominal pore diameter indicating the size of the pores 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. Therefore, ultrafine flocs may escape from the pores.
Despite these rapid mixing, in order to solid-liquid separate the components that escape the membrane, it is possible to inject more flocculant or add a slow mixing process. , Both are unfavorable because they increase the operating cost.

Accordingly, the inventor has devised an apparatus and method for increasing the removal rate of colloidal components such as chromaticity components and organic components without adding a process while keeping the injection rate of the flocculant low.
That is, the membrane filtration device is operated with an increased raw water recovery rate.

About this reason, this inventor estimates 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 film 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 fine flocs, but also between fine flocs and chrominance components or organic matter components that could not become flocs or flocs smaller than the pores of the membrane. It is possible to make it larger than the hole. As a result, the removal rate of chromaticity components and organic components can be increased. In order to make the most of this phenomenon, the contact probability between the chrominance component or organic component that could not be converted into ultrafine flocs or flocs smaller than the membrane pores and the floc already existing in the membrane immersion bath The present inventor has thought that it is effective to increase the value. Furthermore, for this purpose, the present inventor considered that it is effective to drive the raw water recovery rate high and increase the concentration of floc.
It is considered that the floc diameter existing in the film immersion tank increases because the number of collisions between flocs increases as the floc concentration increases. Since the present invention has a very high degree of concentration, even if the floc has an increased floc diameter, the number of collisions with the chromaticity component or organic component that could not be converted into an ultrafine floc or floc does not decrease, and a larger floc 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 an apparatus of the present invention. In FIG. 1, the 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. The mixing means 14 for obtaining the target water 5, the 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 and And 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 water such as turbid components, chromaticity components, and organic components.
Examples of such raw water 1 include tap water (river water, groundwater, lake water, etc.), sewage, seawater, brackish water, and the like.
In addition, the above-mentioned raw water for water, sewage, seawater, brackish water, biological contact filtration, sand filtration, micro flock method, coagulation sedimentation filtration, biofilm treatment, ozone treatment, activated carbon treatment, ion exchange treatment, UV oxidation treatment, acceleration The water obtained after performing a conventionally known treatment such as an oxidation treatment can also 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, turbidity, chromaticity, and TOC are values obtained by measurement by a method defined by 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 the Minister of Health, Labor and Welfare based on the provisions of the Ministerial Ordinance on Water Quality Standards after filtering the target water (raw water here) with a membrane filter having a pore size of 0.1 μm. It shall mean the value obtained by measurement based on the method stipulated (Juluary 22, 2003, Ministry of Health, Labor and Welfare Notification No. 261 (final revision, Ministry of Health, Labor and Welfare Notification No. 290, 2012)).

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

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

The Al-based flocculant means a flocculant mainly composed of an aluminum compound. Here, the “main component” means that the content in components other than the solvent is 50% by mass or more, preferably 80% by mass or more, more preferably 95% by mass or more, and further preferably 100% by mass (substantially other It does not contain the component. Hereinafter, unless otherwise specified, “main component” is used in this sense.
An aluminum compound means a compound containing Al atoms. Examples of the aluminum compound include polyaluminum chloride and sulfuric acid clay (aluminum sulfate).

The Fe-based flocculant means a flocculant mainly composed of an iron-based compound.
An iron-based compound means a compound containing Fe atoms. Examples of iron-based compounds include ferric chloride, polyferric sulfate, and iron-silica inorganic polymer flocculants.

  Examples of organic flocculants include polyacrylamide, polyamine, polyacrylic ester, and polyethyleneimine.

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

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

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

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

  In the flocculant injection step, before the flocculant 3 is injected into the raw water 1, a pH adjusting agent is added to the raw water 1 to adjust the pH of the raw water 1 to a pH that can enhance the flocculating ability of the flocculant 3. preferable. The pH at which the aggregating ability of the flocculant 3 is increased depends on the type of the flocculant 3 and the like. A conventionally known acid or alkali can be used as the pH adjuster. The pH adjusting agent may be added after injecting the flocculant 3 into the raw water 1 or may be added simultaneously while injecting the flocculant 3 into the raw water 1.

  The apparatus of the present invention preferably further includes 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 flocculant 3 and the raw water 1 to form a floc and obtaining the water 5 to be treated containing the floc.

  The mixing means 14 mixes the flocculant 3 and the raw water 1 (that is, by flowing the raw water 1 into which the flocculant 3 has been injected), thereby aggregating impurities contained in the raw water 1 by the action of the flocculant 3. However, there is no particular limitation as long as it is a means capable of forming a floc.

  As the mixing means 14, for example, a coagulation tank (reaction tank) including a stirring device such as a stirring blade can be used. In this case, the raw water 1 into which the flocculant 3 has been injected flows into the flocculation tank and is stirred by a stirrer to form a floc formed by agglomeration of impurities, and the water 5 to be treated including the formed floc is flocculated. It can be discharged from the tank. Mixing by such means is also called rapid mixing or rapid stirring. In the present invention, it is preferable to perform rapid mixing as the mixing means or mixing step. However, slow mixing (or flock formation) may be performed, or both rapid mixing and slow mixing may be performed.

Moreover, even if it does not stir using a stirring apparatus etc., when the raw | natural water 1 in which the coagulant | flocculant 3 was poured flows in a coagulation tank and a flock is formed, the coagulation tank (reaction tank) which is not equipped with a stirring apparatus Can also be used as the mixing means 14.
Further, as the mixing means 14, a static mixer which is of a pipe connection type and causes mixing by causing turbulent flow in the pipe can be used.
Furthermore, piping can be used as the mixing means 14. If the length of the pipe is equal to or greater than a certain value, the treatment target water 5 including floc can be obtained simply by flowing the raw water 1 injected with the flocculant 3 into the pipe.

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 flocculant 3 and raw water 1 to form a floc, and obtaining the water 5 to be treated containing the floc.

<Membrane filtration means, membrane filtration process>
The membrane filtration means 16 in the apparatus 10 of the present invention will be described.
In the apparatus 10 of the present invention, the membrane filtration means 16 performs membrane filtration treatment of the treatment target water 5 so that the raw water recovery rate is 90% or higher, and at least a part of the floc is removed from the treatment target water 5. And means for obtaining sludge 9 containing concentrated floc.

  Although there may be some loss due to evaporation or the like, it may be considered that the water 5 to be treated is roughly separated into the purified water 7 and the sludge 9 by the membrane filtration means 16. That is, the volume of the water 5 to be treated supplied to the membrane filtration means 16 may be considered to be the same as the total volume of the purified water 7 and the sludge 9 discharged from the membrane filtration means 16.

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

  Examples of the membrane filtration means 16 include an immersion membrane filtration device and a casing type membrane filtration device that can make the raw water recovery rate 90% or more.

  Examples of the submerged membrane filtration device include a tank, a membrane module, and a suction pump. Moreover, it is preferable that a tank is an aspect provided with the sludge part for discharging the sludge 9 in the downward direction here. Moreover, a membrane module is provided with the macaroni-like separation membrane called a hollow fiber, for example, and what is immersed and used for the process target water 5 stored in the tank is mentioned. Moreover, the suction pump is connected with the membrane module by piping or the like, and the purified water 7 can be obtained by passing the separation membrane through a part of the water 5 to be treated by suctioning with the suction pump.

  In such a submerged membrane filtration apparatus, the water 5 to be treated is supplied into the tank continuously or intermittently, and the purified water 7 is passed through the separation membrane for a part of the water 5 to be treated by the action of the suction pump. Is obtained continuously or intermittently. Moreover, the sludge 9 is normally discharged | emitted from a waste mud part intermittently. 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 membrane filtration device as the membrane filtration means 16.

  The casing-type membrane filtration apparatus is a unit in which a membrane module is housed in a pressure vessel (casing). Usually, the water to be treated 5 is filtered by press-fitting the casing 5 into the casing by the action of a pump, and the purified water 7 and sludge are filtered. 9 is obtained.

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

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

  It is preferable that the membrane filtration means 16 has a means which can further stir the to-be-processed water 5 using gas. A diffuser is illustrated as such means. For example, when an air diffuser is installed in the lower part of the tank provided in the submerged membrane filtration apparatus, gas (air or the like) is blown into the process target water 5 stored in the tank using this, and the process target water 5 is preferable because it can be stirred.

  In the membrane filtration step in the method of the present invention, it is preferable to subject the water to be treated 5 to membrane filtration after blowing gas. Moreover, in the membrane filtration step in the method of the present invention, it is preferable to subject the treatment target water 5 to membrane filtration treatment while blowing gas.

For example, in the case of a submerged membrane filtration apparatus, flocs existing inside the tank provided therein may gradually settle if the stirring force in the tank is derived only from the input of the raw water flow. In this case, there is a possibility that the area where the floc exists is shrinking downward in the tank. If it does so, the contact efficiency of a floc and a chromaticity component or an organic substance component may fall. Therefore, in order to make the floc exist as uniformly as possible in the tank, it is preferable to stir the processing target water 5 in the tank using an air diffuser or the like. This air diffuser need not be used only for agitation of water to be treated, and a device for performing air diffuser for cleaning a membrane may be used. It may be responsible for stirring.
In addition, when using powdered activated carbon like the method of patent document 1, since a sedimentation speed is smaller than an aggregation floc, it does not settle notably in a short time even if it does not stir. However, flocs obtained by adding a flocculant to cause sedimentation have a significantly higher sedimentation property than powdered activated carbon. Therefore, in order to increase contact efficiency, it is preferable to appropriately stir. Therefore, in the case of powdered activated carbon alone, it is not necessary to pay attention to stirring for increasing 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.
Moreover, it is preferable to set it as 1 to 60 minutes, and it is more preferable to set it as 10 minutes to 50 minutes after blowing gas in the process target water 5 next until it blows gas again.
With such blowing time and / or blowing interval, the floc easily collides with the chromaticity component or organic component, and the chromaticity component or organic component is taken into the floc. As a result, the chromaticity component and organic component It is because the purified water 7 with a lower content rate is obtained.

  In the apparatus 10 of the present invention, the membrane filtration means 16 performs membrane filtration treatment of 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 further preferably 98% or more. Moreover, it may be 99.999% or less.

  The raw water recovery rate is defined as the ratio (percentage) of the volume of the purified water 7 discharged from the membrane filtration means 16 to the volume of the processing target water 5 supplied to the membrane filtration means 16. Further, as described above, the volume of the water to be treated 5 supplied to the membrane filtration means 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 means 16. The recovery rate is expressed as follows:

Raw water recovery rate (%) = volume of purified water 7 discharged / volume of treated water 5 supplied × 100
= (Volume of supplied treatment target water 5 -volume of discharged sludge 9) / Volume of supplied treatment target water 5 × 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 represents the degree of concentration of the water 5 to be treated. For example, the concentration of the water to be treated 5 in the tank of the submerged membrane filtration device is represented. When the raw water recovery rate is increased to 90% or more, the concentration of the processing target water 5 in the tank increases, so that the floc concentration increases. Then, the contact efficiency between the existing flocs and the ultrafine flocs is increased, and a large floc is likely to be formed. Therefore, it is considered that the removal rate of the chromaticity component or the organic component increases.

  When subjecting the treatment target water 5 to the membrane filtration treatment by the membrane filtration means 16, it is preferable to always adjust so that the treatment subject water 5 held in the immersion tank in which the membrane is immersed contains flocks. For example, when a submerged membrane filtration device is used as the membrane filtration means 16, as described above, the sludge 9 is usually discharged intermittently from the sludge section, but not all the sludge 9 is discharged. By discharging so that the sludge 9 remains in the inside, when subjecting the treatment target water 5 to the membrane filtration treatment, the treatment target water 5 held in the immersion tank in which the membrane is immersed is always adjusted to include flocks. can do. Further, for example, by adding a part of the sludge 9 discharged from the sludge section again into the tank in which the processing target water 5 is stored, the processing target water that is always held in the immersion tank in which the membrane is immersed. It can also be adjusted so that 5 includes a flock.

  For example, when a submerged membrane filtration device is used as the membrane filtration means 16, if the entire amount of sludge 9 is discharged from the drainage part, when the membrane filtration process is restarted, There is a possibility that flocs for capturing organic components are reduced. Then, the removal rate of the chromaticity component and the organic component may be lowered by the floc derived from the raw water 1 before the floc concentration in the treatment target water 5 is increased again. Therefore, for example, it is preferable to discharge the sludge 9 so that 0.01% by volume or more of the processing target water 5 stored in the tank remains. You may leave 99 volume% or less of the process target water 5 stored in the tank, preferably 95 volume% or less, more preferably 30 volume% or less, and still more preferably 10 volume% or less.

Although the membrane permeation | transmission flow rate in the membrane filtration means 16 is not specifically limited, It is preferable to set it as 0.4-10 m / d.
The amount of water supplied to the membrane in the membrane filtration means 16 is not particularly limited, but it is preferable that it is balanced with the amount of membrane filtration water.
The amount of air diffused 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 apparatus 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 apparatus is used as the membrane filtration means 16, it is not necessary to add activated carbon into the tank. Impurities can be separated and removed from the water 5 to be treated without adding activated carbon.
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 to be treated 5 is subjected to membrane filtration so that the raw water recovery rate is 90% or more, and at least a part of the floc is removed from the water to be treated 5 This is a step of obtaining the sludge 9 containing the concentrated floc.

  Next, the process flow when the raw water 1 is processed by the apparatus 10 of the present invention as described above 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). And the flocculant 3 and raw | natural water 1 which were inject | poured are mixed by the mixing means 14, and a flock is formed. And the process target water 5 containing a floc is obtained (mixing process).
Next, the membrane treatment means 16 subjects the treatment target water 5 to membrane filtration so that the raw water recovery rate is 90% or more. And purified water 7 and sludge 9 are obtained (membrane filtration process).

  According to the present invention, purified water having a low content of chromaticity components and organic components can be obtained even if the flocculant injection rate is lowered. 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 the addition amount with respect to 1 L of the raw water, the purified water 7 with low chromaticity is used. 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 view for explaining one of the preferred embodiments of the apparatus of the present invention.
In FIG. 2, the apparatus 20 forms a floc by mixing the flocculant injection pump 22 for injecting the flocculant 3 into the raw water 1, and the injected flocculant 3 and the raw water 1, and the water 5 to be treated containing the floc. , A rapid mixing tank 24 that discharges water, a membrane filtration treatment of the treatment target water 5 so that the raw water recovery rate is 90% or more, and purified water 7 in which at least a part of the floc is removed from the treatment target water 5 and concentration And a submerged membrane filtration device 26 for obtaining the sludge 9 containing the floc.

The apparatus 20 further has a pH adjusting means for adding a pH adjusting agent to the raw water 1 before the flocculant 3 is injected. By this pH adjusting means, the pH adjusting agent 8 (acid and / or alkali) is added to the raw water 1, so that the pH of the raw water 1 can be adjusted to a pH at which the coagulating ability of the flocculant 3 can be enhanced.
The device 20 further has a purified water pond 28 for storing the purified water 7.
The device 20 further includes a backwash pump 281 and a pipe 282 used for backwashing the separation membrane 261a of the submerged membrane filtration device 26 using the purified water 7 stored in the water purification plant 28.

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

  The flocculant injection pump 22 corresponds to the flocculant injection means in the apparatus of the present invention.

  The rapid mixing tank 24 has a two-stage tank (a first tank 241 and a second tank 242). And in the 1st tank 241, the flocculant 3 and the raw | natural water 1 to which the pH adjuster 8 was added can be received and these can be mixed. Then, it mixes again in the 2nd tank 242, and the process target water 5 is discharged | emitted. The first tank 241 and the second tank 242 each have a stirrer (243, 244). The raw water 1 into which the flocculant 3 is injected is stirred by this stirrer to mix the flocculant 3 and the raw water 1. By doing so, flocs formed by aggregation of impurities contained in the raw water 1 can be formed.

  The rapid mixing tank 24 corresponds to the 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 a two-stage tank as shown in FIG. 2, but may be an embodiment having a single-stage tank, or a tank having three or more stages. It may be that of having an aspect.

  The submerged membrane filtration device 26 includes a membrane module 261, a tank 262, a suction pump 263, a pipe 264, and a waste mud valve 265. The membrane module 261 has a separation membrane 261a, a water collection part 261b, and a lower support 261c. And the water collection part 261b and the purified water 28 are connected by the piping 264, and the suction pump 263 is arrange | positioned in the middle, From the process target water 5 in the tank 262 by operating the suction pump 263, it is. Purified water 7 can be obtained. Moreover, the obtained purified water 7 reaches the purified water pond 28 through the piping 264, and is comprised so that it can be stored here. Moreover, it is comprised so that a part of process target water 5 in the tank 262 can be discharged as the sludge 9 from the lower part of the tank 262 by opening the drainage valve 265.

  In the submerged membrane filtration device 26, the treatment target water 5 is stored inside the tank 262. The membrane module 261 is used by being immersed in the water to be treated 5 stored in the tank 262. When the suction pump 263 is operated, a part of the water 5 to be treated passes through the separation membrane 261a to become purified water 7 by the action, reaches the purified water 28 through the pipe 264, and is stored therein. In addition, the floc contained in the water to be treated 5 stays in the tank 262 because it cannot pass through the separation membrane 261a.

  The sludge 9 containing flocks is discharged from the lower part of the tank 262. The frequency with which the sludge 9 is discharged from the drainage portion of the tank 262 is not particularly limited. For example, the sludge 9 can be discharged from the inside of the tank 262 by opening the sludge valve 265 once every few days. However, it is discharged so that the raw water recovery rate is 90% or more.

  The submerged 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 apparatus 20 as described above 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 flows into the first tank 241 in the rapid mixing tank 24. Then, in the first tank 241, after the flocculant 3 is added from the flocculant injection pump 22 to the raw water 1 stored here (flocculating agent injection step) and mixed by the action of the stirrer 243, the second tank 242 is added. After being mixed in the second tank 242 again by the action of the stirrer 244, it is discharged as the water 5 to be treated (mixing step). The treatment target water 5 includes flocs formed by aggregation of impurities contained in the raw water 1 by the action of the flocculant 3.
Thereafter, the water 5 to be treated is stored in a tank 262 in the submerged membrane filtration device 26. It is installed so that the membrane module 261 is immersed in the stored processing target water 5, and by operating the suction pump 263, a part of the processing target water 5 passes through the separation membrane 261a to become purified water 7, It reaches the water purification plant 28 through the pipe 264 and is stored here. In addition, the floc contained in the water to be treated 5 stays in the tank 262 because it cannot pass through the separation membrane 261a. Here, it is preferable to install a flow meter for measuring the flow rate of the processing target water 5 flowing into the tank 262 and a flow meter for measuring the flow rate of the discharged purified water 7 in the submerged membrane filtration device 26. And it is preferable to operate so that the flow rates indicated by these flow meters are substantially the same. Moreover, it is preferable to operate by monitoring the value of each flow meter and adjusting the water level of the water 5 to be treated in the tank 262 to be within a specific range.
Next, the sludge 9 containing flocks is discharged from the lower portion of the tank 262. The frequency with which the sludge 9 is discharged from the tank 262 is not particularly limited. For example, once every few days, the sludge valve 265 is opened, and the sludge 9 can be discharged from the drainage portion of the tank 262. 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 submerged membrane filtration device 26 can be backwashed and cleaned using the purified water 7 stored in the water purification plant 28. The frequency of 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 another preferred embodiment of the apparatus of the present invention.
In FIG. 3, the same components as those shown in FIG. Below, it demonstrates centering on a different point from the aspect shown in FIG.

In FIG. 3, the apparatus 30 has the same flocculant injection pump 22, the quick mixing tank 24, the pH adjusting means, the water purification pond 28, the backwash pump 281 and the pipe 282 as in the embodiment shown in FIG. ing.
The submerged membrane filtration device 36 is an embodiment in which the submerged membrane filtration device 26 shown in FIG. It is preferable to monitor the water level during drainage of the water 5 to be treated in the tank 262 by the electrode 37 and / or the interface meter 38. When the water level falls below a specific level during drainage, an electrical signal is transmitted from the electrode 37 and / or interface meter 38 to close the drainage valve 265 and adjust the amount of sludge 9 discharged from the tank 262. It is preferable.

  As the electrode 37 and the interface meter 38, for example, conventionally known ones can be used. The operation similar to that of the electrode 37 and the interface meter 38 can also 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 diagram for explaining another preferred embodiment of the apparatus of the present invention.
In FIG. 4, the same components as those shown in FIG. Below, it demonstrates centering on a different point from the aspect shown in FIG.

In FIG. 4, the apparatus 40 has the same flocculant injection pump 22, the quick mixing tank 24, the pH adjusting means, the water purification pond 28, the backwash pump 281 and the pipe 282 as in the embodiment shown in FIG. ing.
The submerged membrane filtration device 46 is an embodiment having an aeration device 47 and a blower 48 in addition to the submerged 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 and the water 5 to be treated is agitated, flocs can be more uniformly present in the tank 262, so that the contact efficiency between the floc and the chromaticity component or organic component is increased. Is preferable. And since the purified water 7 with lower content rate of a chromaticity component and an organic substance component can be obtained, it is preferable.

Next, another preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 5 is a schematic view for explaining one of other preferred embodiments of the apparatus of the present invention.
In FIG. 5, the same components as those shown in FIG. Below, it demonstrates centering on a different point from the aspect shown in FIG.

In FIG. 5, an apparatus 50 includes a flocculant injection pump 22, a rapid mixing tank 24, a submerged membrane filtration device 26, a pH adjusting unit, a water purification pond 28, and a backwash pump similar to the embodiment shown in FIG. 2. 281 and a pipe 282.
The apparatus 50 further includes a soluble manganese filter tower 51. The soluble manganese filtration tower 51 has a layer 511 made of manganese sand and a support layer 512 inside, and 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 is caused to flow from the lower part of the soluble manganese filter tower 51 by operating the pump 513 and moved upward, the soluble manganese contained in the raw water 1 is moved from the raw water 1 by the action of manganese sand in the process. Separated and at least part of it 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 filter tower 51 toward the rapid mixing tank 24. The subsequent processing is the same as in the case of the embodiment shown in FIG.
As the soluble manganese filter tower 51, for example, a conventionally known one can be used.

  Hereinafter, experiments related to the present invention will be described.

<Experiment 1>
The raw water 1 is treated using the apparatus of the present invention (apparatus 20) of the embodiment shown in FIG. 2, and the relationship between the raw water recovery rate in the submerged membrane filtration apparatus 26 and the ratio of the chromaticity component or organic component removal rate Is measured, the graph shown in FIG. 6 is obtained. In FIG. 6, the ratio of the removal rate of the chromaticity component or organic component on the Y axis is shown as a value when the removal rate of the chromaticity component or organic 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 rate of the chromaticity component and the organic component increases.

<Experiment 2>
The raw water 1 is treated using the apparatus (apparatus 20) of the present invention in the mode shown in FIG. And after sufficient time passes, the sludge valve 265 in the submerged membrane filtration device 26 is opened, and the sludge 9 is discharged from the bottom sludge portion of the tank 262. At this time, if the processing target water 5 stored in the tank 262 is not completely discharged and a part of the water is left in the tank 262, the membrane filtration process by the submerged membrane filtration device 26 is resumed. The removal rate of the chromaticity component or organic component after the elapse of a specific time tends to be improved. FIG. 7 is a graph showing this. That is, FIG. 7 shows the ratio of the residual rate (X-axis) of the water 5 to be treated left in the tank 262 and the removal rate of the chromaticity component or organic component after the lapse of a specific time after starting membrane filtration ( It is a graph showing the relationship with (Y-axis). In FIG. 7, the ratio of the removal rate of the chromaticity component or organic component after the passage of a specific time on the Y-axis is as a value when the residual rate of the treatment target water is 20%. Show.
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 organic component.

<Experiment 3>
Processing the raw water 1 by using an apparatus (40) of the present invention embodiment shown in FIG. 4, the time and interval for blowing air from the air diffuser 47 in an immersion type membrane filtering device 46, the turbidity ratio (T _A / T _B ), the graph shown in FIG. 8 is obtained. Here, the turbidity ratio (T _A / T _B ) is the ratio of the turbidity T _{A to} the 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 means the turbidity of the water 5 to be treated at the water level of the lower support 261c inside the tank 262 in the submerged membrane filtration device 46, as shown in FIG. When the turbidity inside the tank 262 is uniform, the turbidity ratio (T _A / T _B ) is 1, and the turbidity ratio (T _A / T _B ) decreases as the sedimentation of the solid content proceeds. _A turbidity ratio (T _A / T _B ) close to 1 is preferable because the turbidity of the water 5 to be treated inside the tank 262 is more uniform.
As shown in the graph of FIG. 8, the time for blowing air into the treatment target water 5 is 1 second to 10 minutes, and after blowing air into the treatment target water 5, the next time until the gas is blown again. When the interval is 1 to 60 minutes, the turbidity ratio (T _A / T _B ) becomes higher (approximately 0.8 or more), which is preferable.

DESCRIPTION OF SYMBOLS 1 Raw water 3 Flocculant 5 Processed water 7 Purified water 9 Sludge 10 Apparatus of the present invention 12 Flocculant injection means 14 Mixing means 16 Membrane filtration means 8 pH adjuster 20 Apparatus 22 Flocculant 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 Piping 265 Drain valve 28 Purifier 281 Backwash pump 282 Piping 30 Equipment 36 Immersion type membrane filtration device 37 Electrode 38 Interface meter 40 Device 46 Immersion type membrane filtration device 47 Aeration device 48 Blower 50 Device 51 Dissolvable manganese filtration tower 511 Layer made of manganese sand 512 Support layer 513 Pump

Claims (5)

A flocculant injection step of injecting the flocculant into the raw water;
A mixing step of mixing the injected flocculant and the raw water to form a floc and obtaining water to be treated containing the floc;
A membrane that obtains sludge containing purified water obtained by removing at least a part of the floc from the water to be treated and the concentrated floc by subjecting the water to be treated to membrane filtration so that the raw water recovery rate is 90% or more. A filtration process;
A water treatment method.   The water treatment method according to claim 1, wherein in the membrane filtration step, the treatment target water is subjected to membrane filtration treatment after blowing gas or while blowing gas.   The water treatment method according to claim 2, wherein in the membrane filtration step, the treatment target water is stirred by blowing a gas at intervals of 1 to 60 minutes for 1 second to 10 minutes.   In the said membrane filtration process, when carrying out the membrane filtration process of the said process target water, it always adjusts so that the said floc is contained in the said process target water hold | maintained in the immersion tank which immerses a film | membrane. The water treatment method according to any one of the above. A flocculant injection means for injecting the flocculant into the raw water;
Mixing means for mixing the injected flocculant and the raw water to form a floc, and obtaining water to be treated containing the floc;
A membrane that obtains sludge containing purified water obtained by removing at least a part of the floc from the water to be treated and the concentrated floc by subjecting the water to be treated to membrane filtration so that the raw water recovery rate is 90% or more. Filtration means;
Having a water treatment device.

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