JP6833645B2 - Water treatment method and water treatment equipment - Google Patents

Description

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

In recent years, a membrane filtration device has been attracting attention as a new water treatment device. This is a device for decontamination and replaces the conventional decontamination device, a rapid sand filtration device and a slow speed sand filtration device. Since the membrane filtration device is a device for sterilization, it has been often used when relatively clear water that requires only sterilization 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 obtained, we are trying to introduce the membrane filtration device not only to clear raw water but also to raw water that requires treatment other than turbidity. There are more movements to do.

Substances that need to be removed in addition to turbidity include chromaticity and organic substances. Since these substances are colloidal components (soluble substances), they are difficult to remove with a normal membrane filtration device. As a method for removing these substances with a membrane filtration device, a coagulation facility for injecting a coagulant and mixing with raw water may be provided in the preceding stage. In this coagulation facility, the chromaticity component and the organic substance component are agglomerated to a size that can be removed by membrane filtration, and removed as a turbidity component by membrane filtration to obtain clear treated water.

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

In Patent Document 1, powdered activated charcoal mixed water in which powdered activated charcoal is previously added to raw water is made to flow into a membrane filter tank, or raw water is made to flow into a membrane filtration tank and powdered activated charcoal is added to obtain powdered activated charcoal mixed water. The substance to be treated such as trace organic substances in the raw water is adsorbed on the powdered activated charcoal, and the powdered activated charcoal mixed water in the membrane filtration tank is solid-liquid separated by the immersion type membrane filtration device installed in the tank, and the immersion type membrane filtration device When the membrane-filtered water that has permeated the membrane surface is taken out of the tank, the amount of the membrane-filtered water taken out with respect to the amount of water flowing into the membrane-filtered tank should be 99% or more, and the powdered activated charcoal should be maintained at a high concentration in the membrane-filtered tank. Describes a method of operating a water treatment facility using an immersion type membrane filtration device, which is characterized by promoting the adsorption of a substance to be treated. Then, the powdered activated charcoal can remove organic chlorine compounds such as trihalomethane or precursors thereof, trace harmful substances such as pesticides, offensive odor-causing substances such as musty odor, and trace organic substances such as anionic surfactants, and a film. Ammonia nitrogen and organic substances can be removed by microorganisms such as nitrifying bacteria that naturally occur and are retained in the filtration tank, and soluble manganese and soluble manganese and organic substances can be taken into the turbid substances that are concentrated and retained in the membrane filtration tank. It is stated that iron can be removed. In addition, it is stated that bacteria and turbid substances contained in raw water, added powdered activated carbon, naturally occurring microorganisms, etc. can be filtered and separated by a membrane filtration device. Further, at this time, the amount of the powdered activated carbon taken out with respect to the amount of water flowing into the membrane filter tank is set to 99% or more, and the added powdered activated carbon is maintained at a high concentration in the membrane filter tank to maximize the capacity of the powdered activated carbon. 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 added can be reduced, and since it is possible to respond widely to fluctuations in raw water quality, it can be operated at a constant amount and is stable. It is stated that membrane-filtered water of the treated water quality can be obtained.

In Patent Document 2, the microfiltration of the solid-containing water is carried out periodically until the solid-state concentration of the solid-containing water in the tank reaches 0.1 Ct to Ct as the limit solid-containing concentration (Ct). A membrane filtration step including the implementation of a thorough cleaning, a drainage step of draining all or part of the solid-containing water in the tank after the membrane filtration step, and a drainage step of supplying raw water into the tank after the drainage step and containing solids. A water purification method including a water filling step of controlling the concentration of powdered activated carbon in water to a target value of 50 mg / L or more is described. Then, by such a water purification treatment method, the recovery rate of the treated water is maintained high by periodically draining the entire amount or partial drainage under certain conditions, and the cake is prevented from adhering to the membrane surface. It is stated that the adsorption effect of activated carbon can be maintained high.

Japanese Unexamined Patent Publication No. 9-285779 Japanese Unexamined Patent Publication No. 2012-223697

While the membrane filtration method can obtain high-quality treated water, it has the disadvantage of higher operating costs than conventional methods (rapid filtration method, slow sand filtration, etc.). In order to remove chromaticity components and organic substances by adopting the membrane filtration method, it is essential to inject a coagulant or the like, which is a factor that pushes up operating costs. In adopting the membrane filtration method, it is an urgent issue to reduce the operating cost, and particularly in the case of the membrane filtration method having an additional process such as injecting a coagulant, it becomes a particularly important issue.

In the coagulation / membrane filtration method in which a coagulant is injected, a reduction in the coagulant injection rate can be mentioned as an effective means for reducing the operating cost. If the coagulant injection rate is reduced, the operating cost can be reduced.

In addition, as the 21st century is said to be the century of water, although there are abundant water resources in Japan alone, it is expected that water demand will become tight as the population grows globally. .. In view of such future trends, it is obvious that a process that can treat the taken water as purified water without wasting it will become indispensable in the future.

Therefore, what is required for future membrane filtration methods is that it is possible to operate raw water that is not relatively clear at a low running cost, and that the raw water is not wasted and a high recovery rate can be achieved. Is.

However, in order to obtain purified water having a low concentration of chromaticity component and organic component in the conventional membrane filtration apparatus and membrane filtration treatment, it is necessary to increase the injection rate of the flocculant. A high injection rate of the flocculant is not preferable because the running cost is high. In addition, 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 operations such as backwashing to remove the adhered turbid components. , It is not preferable because the filtration time per arbitrary unit time is 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 capable of obtaining purified water having a low chromaticity component and organic component content even if the coagulant injection rate is lowered, and further increasing the raw water recovery rate. There is.

The present inventor has completed the present invention by diligently studying in order to solve the above problems.
The present invention is the following (1) to (5).
(1) A flocculant injection step of injecting a flocculant into raw water,
A mixing step of mixing the injected coagulant with the raw water to form flocs and obtaining water to be treated containing the flocs.
The water to be treated is membrane-filtered so that the recovery rate of raw water is 90% or more, and a membrane obtained by removing at least a part of the flocs from the water to be treated to obtain purified water and concentrated sludge containing the flocs. Filtration process and
A water treatment method that comprises.
(2) The water treatment method according to (1) above, wherein in the membrane filtration step, after injecting gas, the water to be treated is subjected to membrane filtration treatment.
(3) The water treatment method according to (2) above, wherein in the membrane filtration step, gas is blown at intervals 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 membrane filtration treatment is performed, the water to be treated is always adjusted so as to contain the flocs in the 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 a flocculant into raw water,
A mixing means that mixes the injected coagulant with the raw water to form flocs and obtains water to be treated containing the flocs.
The water to be treated is membrane-filtered so that the recovery rate of raw water is 90% or more, and a membrane obtained by removing at least a part of the flocs from the water to be treated to obtain purified water and concentrated sludge containing the flocs. Filtration means and
Has 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 component and organic component even if the coagulant injection rate is lowered by increasing the raw water recovery rate. Can be done.

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 a schematic diagram which shows another preferable aspect of the apparatus of this invention. It is a schematic diagram which shows still another preferable aspect of the apparatus of this invention. It is a schematic diagram which shows still another preferable aspect of the apparatus of this invention. It is a graph which shows the relationship between the raw water recovery rate and the ratio of the chromaticity component and the removal rate of an organic substance component. It is a graph which shows the relationship between the residual rate of the water to be treated, 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 to blow air from an air diffuser, and the turbidity ratio. It is an enlarged schematic view of a part of the immersion type membrane filtration apparatus used for explaining a turbidity ratio.

The present invention will be described in detail.
The present invention includes a coagulant injection step of injecting a coagulant into raw water, a mixing step of mixing the injected coagulant with the raw water to form flocs, and obtaining water to be treated containing the flocs, and raw water. The water to be treated is membrane-filtered so that the recovery rate is 90% or more, and purified water obtained by removing at least a part of the flocs from the water to be treated and membrane filtration to obtain concentrated sludge containing the flocs. It is a water treatment method including a step.
Such a water treatment method is also referred to as "the method of the present invention" below.

Further, the present invention comprises a coagulant injecting means for injecting a coagulant into raw water and a mixing means for mixing the injected coagulant with the raw water to form flocs to obtain water to be treated containing the flocs. The water to be treated is membrane-filtered so that the recovery rate of raw water is 90% or more, and purified water obtained by removing at least a part of the flocs from the water to be treated and sludge containing the flocs concentrated are obtained. It is a water treatment apparatus having a membrane filtration means.
Such a water treatment device is also referred to as "the device of the present invention" below.

The method of the present invention is preferably carried out using the apparatus of the present invention.

Hereinafter, when the term "invention" is simply used, it means both the method of the present invention and the apparatus of the present invention.

The mechanism of expression of the effect of the present invention estimated by the present inventor will be described with reference to specific examples. The present invention is not limited to the specific examples in the following description.

When the flocculant is added to the raw water and only rapid mixing is performed, the flocs produced are fine because slow sand stirring is not performed. When solid-liquid separation is performed using the conventional sedimentation method, it is not preferable to use fine flocs because the floc sedimentation rate 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 membrane surface, solid-liquid separation is possible, and it is considered that there is no problem only with rapid mixing.
The present inventor has found that there is room for improvement in the aggregation / membrane filtration process in the following two points while proceeding with diligent research.
[1] There are ultrafine flocs that cannot be made larger than the pores on the film surface by rapid mixing alone, and chromaticity or organic components that cannot become flocs.
[2] The nominal pore size indicating the size of the pores of the film does not indicate the size of all the pores on the film surface, but is a representative value, and there are pores larger than the nominal pore size. Therefore, ultrafine flocs may escape from the pores.
In order to separate the components that escape from the membrane by the membrane in spite of these rapid mixing, it is conceivable to inject more coagulant or add a slow mixing step. , Both of which lead to an increase in operating cost, which is not preferable.

Therefore, the inventor has devised a device and a method for increasing the removal rate of colloidal components such as chromaticity components and organic substances while keeping the injection rate of the flocculant low without adding steps.
That is, in the membrane filtration apparatus, the operation with a high raw water recovery rate is performed.

The present inventor presumes the reason for this as follows.
In the membrane immersion tank, microflocs generated by rapid mixing are solid-liquid separated by the membrane and concentrated. The microflocs collide with each other in the membrane immersion tank and capture each other due to 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 ultrafine flocs smaller than the membrane pores or chromaticity components or organic components that could not become flocs, and their size is reduced to film fineness. Allows it to be larger than the hole. As a result, the removal rate of the chromaticity component and the organic substance component can be increased. In order to make the best use of this phenomenon, the contact probability between the chromaticity component or organic component that could not become ultrafine flocs or flocs smaller than the membrane pores and the flocs that already exist in the membrane immersion tank. The present inventor thought that it would be effective to increase. Further, for that purpose, the present inventor considered that it is effective to operate with a high raw water recovery rate and increase the concentration of flocs.
As the concentration of flocs increases, the number of collisions between flocs increases, so it is considered that the flocks diameter existing in the membrane immersion tank increases. Since the present invention has a very high concentration, even a floc with an increased floc diameter does not reduce the number of collisions with an ultrafine floc or a chromaticity component or an organic component that could not become a floc, and a larger floc. Therefore, it is considered possible to increase the removal rate by membrane separation.

The present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing the apparatus of the present invention. In FIG. 1, the apparatus 10 of the present invention mixes the flocculant injecting means 12 for injecting the flocculant 3 into the raw water 1 and the injected flocculant 3 and the raw water 1 to form flocs, and performs a treatment containing the flocs. The mixing means 14 for obtaining the target water 5, the purified water 7 obtained by membrane-filtering the treated water 5 so that the raw water recovery rate is 90% or more, and removing at least a part of the flocs from the treated water 5 and It has a membrane filtration means 16 for obtaining sludge 9 containing the concentrated flocs.

<Raw water>
In the present invention, the raw water 1 is not particularly limited as long as it is water containing impurities such as a turbidity component, a chromaticity component, and an organic substance component.
Examples of such raw water 1 include tap raw water (river water, groundwater, lake water, etc.), sewage drainage, seawater, brackish water, and the like.
In addition, for the above raw tap water, sewage, seawater, steam water, etc., biological contact filtration, sand filtration, microflock method, coagulation sedimentation filtration, biological film treatment, ozone treatment, activated carbon treatment, ion exchange treatment, UV oxidation treatment, promotion The water obtained after performing a conventionally known treatment such as an oxidation treatment can also be referred to as 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)
-Saturation: 0 to 100 degrees (preferably 0 to 20 degrees, more preferably 0 to 10 degrees)
TOC: 0-10 mg / L (preferably 0-5 mg / L, more preferably 0-3 mg / L)

In the present invention, the turbidity, chromaticity and TOC are values obtained by measuring by the method specified by the clean water 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 water to be measured (raw water in this case) with a membrane filter having a pore size of 0.1 μm. It shall mean the value obtained by measuring based on the specified method (July 22, 2003, Ministry of Health, Labor and Welfare Notification No. 261 (final revision, March 30, 2012, Ministry of Health, Labor and Welfare Notification No. 290)).

<Coagulant injection means, coagulant injection process>
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 flocculant injecting means 12 is a means for injecting the flocculant 3 into the raw water 1.

The coagulant 3 is not particularly limited as long as it can coagulate impurities such as turbidity component, chromaticity component, and organic component contained in the raw water 1, and for example, conventionally known ones can be used. For example, an inorganic flocculant (specifically, for example, an Al-based and / or Fe-based flocculant) can be used. In addition, an organic flocculant can also be used. Further, a plurality of types of coagulants may be used at the same time, for example.

The Al-based coagulant means a coagulant containing an aluminum compound as a main component. Here, the "main component" has a content of 50% by mass or more, preferably 80% by mass or more, more preferably 95% by mass or more, still more preferably 100% by mass in a component other than the solvent (substantially other than that). It shall mean that it does not contain the components of. Hereinafter, unless otherwise specified, "main component" shall be used in this sense.
The aluminum compound means a compound containing an Al atom. Examples of the aluminum compound include polyaluminum chloride and sulfated soil (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 compound include ferric chloride, ferric polysulfate, and iron-silica inorganic polymer flocculant.

Examples of the organic flocculant include polyacrylamide-based, polyamine-based, polyacrylic ester-based, and polyethyleneimine-based.

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

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

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

The flocculant injection step in the method of the present invention can be performed by the flocculant 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 injecting the coagulant 3 into the raw water 1 to adjust the pH of the raw water 1 to a pH capable of enhancing the coagulation ability of the coagulant 3. preferable. The pH at which the aggregating ability of the aggregating agent 3 is enhanced differs depending on the type of the aggregating agent 3 and the like. Conventionally known acids or alkalis can be used as the pH adjuster. Further, the pH adjuster may be added after injecting the flocculant 3 into the raw water 1, or may be added at the same time 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 a means for mixing the injected flocculant 3 and the raw water 1 to form flocs to obtain the treated water 5 containing the flocs.

The mixing means 14 agglomerates impurities contained in the raw water 1 by the action of the aggregating agent 3 by mixing the aggregating agent 3 and the raw water 1 (that is, by flowing the raw water 1 into which the aggregating agent 3 is injected). However, it is not particularly limited as long as it is a means capable of forming flocs.

As the mixing means 14, for example, a coagulation tank (reaction tank) provided with a stirring device such as a stirring blade can be used. In this case, the raw water 1 in which the coagulant 3 is injected is flowed into the coagulation tank and stirred by a stirrer to form flocs in which impurities are aggregated, and the treated water 5 containing the formed flocs is aggregated. It can be discharged from the tank. Mixing by such means is also referred to as rapid mixing or rapid stirring. In the present invention, rapid mixing is preferably performed as a mixing means or a mixing step. However, slow mixing (or flock formation) may be performed, or both rapid mixing and slow mixing may be performed.

Further, if the raw water 1 into which the coagulant 3 is injected flows in the coagulation tank to form flocs without stirring using a stirrer or the like, a coagulation tank (reaction tank) without a stirrer is provided. Can also be used as the mixing means 14.
Further, as the mixing means 14, a static mixer which is a pipe connection type and causes turbulent flow in the pipe to perform mixing can be used.
Further, piping can be used as the mixing means 14. When the length of the pipe is longer than a certain level, the water to be treated 5 containing the flock can be obtained only by flowing the raw water 1 in which the coagulant 3 is injected 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 the raw water 1 to form flocs to obtain the water to be treated 5 containing the flocs.

<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 water to be treated 5 so that the recovery rate of raw water is 90% or more, and the purified water 7 obtained by removing at least a part of the flocs from the water 5 to be treated. And a means to obtain sludge 9 containing concentrated flocs.

Although there may be some loss due to evaporation or the like, it can 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. That is, it can be considered that the volume of the water to be treated 5 supplied to the membrane filtration means 16 is 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 a means for separating at least a part (usually almost all) of flocs contained in the water to be treated 5 from the water to be treated 5 using, for example, a conventionally known separation membrane and removing it.

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

The immersion type membrane filtration device can be exemplified as having a tank, a membrane module and a suction pump. Further, here, it is preferable that the tank is provided with a sludge draining portion for discharging sludge 9 below the tank. Further, the membrane module includes, for example, a macaroni-shaped separation membrane called a hollow fiber, and may be used by immersing it in water 5 to be treated stored in a tank. Further, the suction pump is connected to the membrane module by a pipe or the like, and by sucking with the suction pump, a part of the water to be treated 5 can pass through the separation membrane to obtain purified water 7.

In such an immersion type membrane filtration device, the water to be treated 5 is continuously or intermittently supplied into the tank, and a part of the water to be treated 5 is passed through a separation membrane by the action of a suction pump to purify the water 7. Is obtained continuously or intermittently. In addition, sludge 9 is usually discharged from the mud draining portion intermittently. Since the sludge is concentrated with flocs, it is discharged from the tank.

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

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

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

As the separation membrane in the membrane filtration means 16 represented by the immersion type membrane filtration device and the casing type membrane filtration device, for example, a microfiltration membrane (MF membrane) having a pore size of about 0.01 to 0.2 μm is used. Can be done. Further, an ultrafiltration membrane (UF membrane), a reverse osmosis membrane (RO membrane), and a nanofiltration membrane (NF membrane) can also be used.
The nominal pore size of the separation membrane is preferably 0.001 μm to 0.2 μm.

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

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

For example, in the case of an immersion type membrane filtration device, the flocs existing inside the tank provided therein may gradually settle if the stirring force in the tank is derived only from the raw water flow input or the like. In this case, the area where the flocs are present may shrink downward in the tank. Then, the contact efficiency between the floc and the chromaticity component or the organic component may decrease. Therefore, in order to make the flocs exist in the tank as uniformly as possible, it is preferable to stir the water 5 to be treated in the tank using an air diffuser or the like. This air diffuser or the like does not have to be used only for agitating the water to be treated, and a device that diffuses air for cleaning the membrane may be used, and the air diffuser for cleaning is the water to be treated. It may be responsible for stirring.
When powdered activated carbon is used as in the method described in Patent Document 1, since the settling speed is lower than that of aggregated flocs, it does not settle significantly in a short time without stirring. However, since flocs aggregated by adding a flocculant for sedimentation have a significantly higher sedimentation property than powdered activated carbon, it is preferable to appropriately stir in order to improve contact efficiency. Therefore, in the case of powdered activated carbon alone, it is not necessary to pay attention to stirring to improve the contact efficiency, but in the case of flocs, it is important.

Here, the time for blowing the gas into the water to be treated 5 is preferably 1 second to 10 minutes, and more preferably 10 seconds to 5 minutes.
Further, the interval between blowing the gas into the water to be treated 5 and then blowing the gas again is preferably 1 to 60 minutes, more preferably 10 to 50 minutes.
With such a blowing time and / or blowing interval, the flocs are likely to collide with the chromaticity component or the organic component, and the chromaticity component or the organic component is taken into the floc, and as a result, the chromaticity component and the organic component are incorporated. This is because purified water 7 having a lower content can be obtained.

In the apparatus 10 of the present invention, the membrane filtration means 16 performs membrane filtration treatment of the water to be treated 5 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. Further, it may be 99.999% or less.

The raw water recovery rate is defined as the ratio (percentage) of the volume of purified water 7 discharged from the membrane filtration means 16 to the volume of the water to be treated 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, and therefore the raw water. The recovery rate is expressed by the following equation.

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

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

The raw water recovery rate represents the concentration of the water to be treated 5. For example, it represents the concentration of the water to be treated 5 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 to be treated 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 large flocs are likely to be formed, so that it is considered that the removal rate of the chromaticity component or the organic substance component is increased.

When the membrane filtration means 16 performs the membrane filtration treatment of the water 5 to be treated, it is preferable to always adjust so that the water 5 to be treated held in the immersion tank in which the membrane is immersed contains flocs. For example, when an immersion type membrane filtration device is used as the membrane filtration means 16, sludge 9 is normally discharged intermittently from the sludge portion as described above, but not all sludge 9 is discharged, but a tank. By discharging the sludge 9 so that it remains inside, when the treatment target water 5 is subjected 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 contain flocs. can do. Further, for example, by adding a part of the sludge 9 discharged from the sludge portion to the tank in which the water to be treated 5 is stored again, the water to be treated is always held in the immersion tank in which the membrane is immersed. It can also be adjusted so that flock is included in 5.

For example, when an immersion type membrane filtration device is used as the membrane filtration means 16, if the entire amount of sludge 9 is discharged from the mud drainage portion, when the membrane filtration treatment is restarted, the chromaticity component in the water to be treated 5 and the like. Flocks for capturing organic components may be reduced. Then, the flocs derived from the raw water 1 may reduce the removal rates of the chromaticity component and the organic matter component by the time the concentration of the flocs in the water 5 to be treated increases again. Therefore, for example, it is preferable to discharge the sludge 9 so as to leave 0.01% by volume or more of the water to be treated 5 stored in the tank. 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 to be treated 5 stored in the tank may remain.

The membrane permeation flow velocity 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 in equilibrium 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 device is used as the membrane filtration means 16, it is not necessary to add activated carbon to the tank. Impurities can be separated and removed from the water to be treated 5 without adding activated carbon.
Similarly, activated carbon does not have to 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 membrane-filtered so that the recovery rate of raw water is 90% or more, and at least a part of the flocs is removed from the water 5 to be treated. This is a step of obtaining the sludge 9 containing the concentrated flocs.

Next, the flow of the treatment when the raw water 1 is treated 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 flocculant 3 is injected into the raw water 1 by the flocculant injection means 12 (coagulant injection step). Then, the infused flocculant 3 and the raw water 1 are mixed by the mixing means 14 to form flocs. Then, the water to be treated 5 containing the flocs is obtained (mixing step).
Next, the membrane treatment means 16 performs membrane filtration treatment of the water to be treated 5 so that the raw water recovery rate is 90% or more. Then, purified water 7 and sludge 9 are obtained (membrane filtration step).

According to the present invention, purified water having a low content of chromaticity component and organic component can be obtained even if the coagulant injection rate is lowered. Specifically, for example, when the amount of the flocculant 3 injected into the raw water 1 is 0 to 100 mg / L (preferably 0 to 30 mg / L) as the amount added to the raw water 1 L, the purified water 7 having a low chromaticity is obtained. 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 1/1000 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)
-Saturation: 1 degree or less (preferably 0.1 degrees or less, more preferably 0.01 degrees 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 for explaining one of the preferred embodiments of the apparatus of the present invention.
In FIG. 2, the apparatus 20 mixes the flocculant injection pump 22 that injects the flocculant 3 into the raw water 1 and the injected flocculant 3 and the raw water 1 to form flocs, and the water to be treated 5 containing the flocs. The rapid mixing tank 24 for discharging water and the water to be treated 5 are membrane-filtered so that the recovery rate of raw water is 90% or more, and at least a part of the flocs is removed from the water 5 to be treated. It has an immersion type membrane filtration device 26 for obtaining the sludge 9 containing the flocs.

The device 20 further has a pH adjusting means for adding a pH adjusting agent to the raw water 1 before injecting the flocculant 3. By this pH adjusting means, a pH adjusting agent 8 (acid and / or alkali) can be added to the raw water 1 to adjust the pH of the raw water 1 to a pH capable of enhancing the agglutinating ability of the aggregating agent 3.
The device 20 further has a water purification pond 28 for storing the purified water 7.
The device 20 further has a backwash pump 281 and a pipe 282 used for backwashing the separation membrane 261a of the immersion type membrane filtration device 26 using the purified water 7 stored in the water purification ground 28.

The coagulant injection pump 22 has a tank and a pump, and 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 after the pH adjuster stored in the rapid mixing tank 24 has been added.

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

The rapid mixing tank 24 has a two-stage tank (first tank 241 and second tank 242). Then, in the first tank 241, the flocculant 3 and the raw water 1 to which the pH adjuster 8 is added can be accepted and mixed. Then, it is mixed again in the second tank 242, and the water to be treated 5 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 coagulant 3 is injected is stirred by the stirrer to mix the coagulant 3 and the raw water 1. By doing so, it is possible to form a floc formed by aggregating impurities contained in the raw water 1.

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 a mode having a one-stage tank, or a tank having three or more stages. It may be the aspect which has.

The immersion type membrane filtration device 26 includes a membrane module 261, a tank 262, a suction pump 263, a pipe 264, and a mud drain valve 265. The membrane module 261 has a separation membrane 261a, a water collecting portion 261b, and a lower support 261c. Then, the water collecting portion 261b and the water purification ground 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 Purified water 7 can be obtained. Further, the obtained purified water 7 reaches the purified water pond 28 through the pipe 264 and is configured to be stored there. Further, by opening the sludge valve 265, a part of the water to be treated 5 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 to be treated 5 is stored inside the tank 262. The membrane module 261 is used by being immersed in the water to be treated 5 stored inside the tank 262. Then, when the suction pump 263 is operated, a part of the water to be treated 5 passes through the separation membrane 261a to become purified water 7, and reaches the purified water area 28 through the pipe 264 and is stored there. Further, since the flocs contained in the water to be treated 5 cannot pass through the separation membrane 261a, they stay in the tank 262.

The sludge 9 containing flock is discharged from the sludge portion at the lower part of the tank 262. The frequency with which the sludge 9 is discharged from the sludge portion of the tank 262 is not particularly limited. For example, once every few days, the sludge valve 265 can be opened to discharge the sludge 9 from the inside of the tank 262. However, it 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 the treatment when the raw water 1 is treated by the device 20 as described above will be described. This description is also a description of preferred embodiments of the method of the invention.

First, the pH adjuster 8 (acid or alkali) is added to the raw water 1, and then it 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), mixed by the action of the stirrer 243, and then the second tank 242. In the second tank 242, the water is mixed again by the action of the stirrer 244, and then discharged as the water to be treated 5 (mixing step). The water to be treated 5 contains flocs in which impurities contained in the raw water 1 are aggregated by the action of the flocculant 3.
After that, 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 to be treated 5, 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. It reaches the water purification site 28 through the pipe 264 and is stored there. Further, since the flocs contained in the water to be treated 5 cannot pass through the separation membrane 261a, they stay in the tank 262. Here, it is preferable to install a flow meter for measuring the flow rate of the water to be treated 5 flowing into the tank 262 and a flow meter for measuring the flow rate of the discharged purified water 7 in the immersion type membrane filtration device 26. Then, it is preferable to operate so that the flow rates indicated by these flow meters are substantially the same. Further, it is preferable to monitor the value of each flow meter and adjust the water level of the water to be treated 5 in the tank 262 to be within a specific range for operation.
Next, the sludge 9 containing flocs is discharged from the sludge portion at the lower part 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 can be opened to discharge the sludge 9 from the sludge section of the tank 262. However, it is discharged so that the raw water recovery rate is 90% or more.
Further, by operating the backwash pump 281, the separation membrane 261a included in 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 backwashing is not particularly limited. For example, it is preferable to perform backwashing once every 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 another preferred embodiments of the apparatus of the present invention.
In FIG. 3, the same components as those shown in FIG. 2 are designated by the same reference numerals. Hereinafter, the points different from the embodiment shown in FIG. 2 will be mainly described.

In FIG. 3, the apparatus 30 has a coagulant injection pump 22 similar to the embodiment shown in FIG. 2, a rapid mixing tank 24, a pH adjusting means, a water purification pond 28, a backwash pump 281 and a pipe 282. ing.
The immersion type membrane filtration device 36 is an embodiment in which the immersion type membrane filtration device 26 shown in FIG. 2 is further provided with an electrode 37 and an interface meter 38. It is preferable to monitor the water level at the time of drainage of the water to be treated 5 in the tank 262 by the electrode 37 and / or the interface meter 38. Then, when the water level falls below 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 sludge valve 265 and adjust the amount of sludge 9 discharged from the tank 262. Is preferable.

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

Next, another preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 4 is a schematic diagram for explaining one of another preferred embodiments of the apparatus of the present invention.
In FIG. 4, the same components as those shown in FIG. 2 are designated by the same reference numerals. Hereinafter, the points different from the embodiment shown in FIG. 2 will be mainly described.

In FIG. 4, the apparatus 40 has a coagulant injection pump 22 similar to the embodiment shown in FIG. 2, a rapid mixing tank 24, a pH adjusting means, a water purification pond 28, a backwash pump 281 and a pipe 282. ing.
The immersion type membrane filtration device 46 is an embodiment in which the immersion type membrane filtration device 26 shown in FIG. 2 is further provided with an air diffuser 47 and a blower 48. By operating the blower 48, air is sent from the air diffuser 47 to the inside of the tank 262, and the water to be treated 5 stored therein can be agitated. By sending an appropriate amount of air into the tank 262 and stirring the water 5 to be treated, the flocs can be more uniformly present inside the tank 262, so that the contact efficiency between the flocs and the chromaticity component or the organic component can be improved. It is preferable to be able to do it. Then, purified water 7 having a lower content of chromaticity component and organic component can be obtained, which is preferable.

Next, another preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 5 is a schematic diagram for explaining one of another preferable aspects of the apparatus of the present invention.
In FIG. 5, the same components as those shown in FIG. 2 are designated by the same reference numerals. Hereinafter, the points different from the embodiment shown in FIG. 2 will be mainly described.

In FIG. 5, the device 50 includes a coagulant injection pump 22, a rapid mixing tank 24, an immersion type membrane filtration device 26, a pH adjusting means, a water purification pond 28, and a backwash pump similar to those shown in FIG. It has 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 inside, and when the raw water 1 contains soluble manganese, it can be removed from the raw water 1, which is preferable. By operating the pump 513, the raw water 1 flows in from the lower part of the soluble manganese filtration tower 51 and is moved toward the upper part. In the process, the soluble manganese contained in the raw water 1 is removed from the raw water 1 by the action of manganese sand. It is separated and at least part of it is removed. After that, 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. After that, 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, experiments relating to the present invention will be described.

<Experiment 1>
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 component component by treating the raw water 1 using the device (device 20) of the present invention of the embodiment shown in FIG. Is measured to obtain the graph shown in FIG. In FIG. 6, the ratio of the removal rate of the chromaticity component or the organic substance on the Y-axis is shown as a value when the removal rate of the chromaticity component or the organic substance 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 substance component is high.

<Experiment 2>
Raw water 1 is treated using the apparatus (device 20) of the present invention according to the embodiment shown in FIG. Then, after a sufficient time has elapsed, the sludge valve 265 in the immersion type membrane filtration device 26 is opened, and the sludge 9 is discharged from the sludge portion at the lower part of the tank 262. At this time, if a part of the water to be treated 5 stored inside the tank 262 is left inside the tank 262 without being discharged, the membrane filtration treatment by the immersion type membrane filtration device 26 is restarted. , The removal rate of the chromaticity component or the organic component tends to improve after a lapse of a specific time. FIG. 7 is a graph showing this. That is, FIG. 7 shows the ratio of the residual rate (X-axis) of the water to be treated 5 left inside the tank 262 to the removal rate of the chromaticity component or the organic component after the lapse of a specific time after starting the membrane filtration (X-axis). It is a graph which shows the relationship with (Y axis). In FIG. 7, the ratio of the removal rate of the chromaticity component or the organic component after the start of membrane filtration on the Y-axis and the lapse of a specific time is set to 1 when the residual rate of the water to be treated is 20%. 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, the effect of maintaining the removal rate of the chromaticity component or the organic substance component is recognized.

<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 If / T _B) to measure the relationship between, 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. Turbidity ratio turbidity inside the tank 262 is uniform (T _A / T _B) is a turbidity ratio becomes 1, the settling of such solids proceeds (T _A / T _B) is reduced. When the turbidity ratio (T _A / T _B) is close to 1, since the turbidity of the interior of the processed water 5 of the vessel 262 be construed to more uniform preferable.
As shown in the graph of FIG. 8, the time for blowing air into the water to be treated 5 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. If the interval is 1 to 60 minutes, turbidity ratio (T _A / T _B) is higher (approximately 0.8 or higher), preferably.

1 Raw water
3 Coagulant 5 Water to be treated 7 Purified water 8 pH adjuster 9 Sludge 10 Equipment of the present invention 12 Coagulant injection means 14 Mixing means 16 Membrane filtration means 20 Equipment 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 Piping 265 Mud drain valve 28 Water purification pond 281 Backwash pump 282 Piping 30 Equipment 36 Immersion type Membrane filtration device 37 Electrode 38 Interface meter 40 Device 46 Immersion type film filtration device 47 Air diffuser 48 Blower 50 device 51 Soluble manganese filtration tower 511 Layer made of manganese sand 512 Support layer 513 Pump

Claims (4)

The coagulant injection process that injects the coagulant into the raw water,
A mixing step of mixing the injected coagulant with the raw water to form flocs and obtaining water to be treated containing the flocs.
The flocs in the water to be treated containing the flocs formed by mixing the flocculant and the raw water without using activated charcoal, and ultrafine flocs, chromaticity components and organic matter components smaller than the membrane pore size. After injecting gas for 1 second to 10 minutes at intervals of 1 to 60 minutes in order to improve contact efficiency , the following relational expression: Raw water recovery rate (%) = volume of discharged purified water / supplied The raw water recovery rate represented by the volume of water to be treated x 100 = (volume of water to be treated-volume of sludge discharged) / volume of water to be treated x 100 to be supplied is 90% or more. As described above, a membrane filtration step of performing a membrane filtration treatment on the water to be treated to obtain purified water obtained by removing at least a part of the flocs from the water to be treated and a concentrated sludge containing the flocs.
With
A water treatment method comprising discharging the sludge so as to leave 0.01% by volume or more of the water to be treated stored in the tank after the completion of the membrane filtration step. The first aspect of the invention, wherein in the membrane filtration step, when the water to be treated is filtered, the water to be treated is always adjusted so that the water to be treated is contained in the immersion tank in which the membrane is immersed. Water treatment method. After blowing the gas, turbidity ratio (T _A / T _B) is the water treatment method according to claim 1 or 2 comprising the membrane filtration process the water to be treated to be 0.8 or more. A flocculant injection means for injecting a flocculant into raw water,
A mixing means that mixes the injected coagulant with the raw water to form flocs and obtains water to be treated containing the flocs.
A stirring means for stirring the water to be treated using gas without using activated carbon,
A pipe for extracting purified water obtained by removing at least a part of the flocs from the water to be treated, a sludge valve for discharging the concentrated sludge containing the flocs, and a separation membrane in the tank are provided for the water collecting portion and the lower part. It is provided with a membrane module configured to be sandwiched between the body and the body, and has an immersion type membrane filtration means for membrane filtration treatment of the water to be treated.
The immersion type membrane filtration means
The turbidity T _A is the turbidity of the water to be treated at the water level of the catchment portion in the tank, and the turbidity T _B is the turbidity of the water to be treated at the water level of the lower support in the tank. , relative turbidity ratio (T _a / T _B) is processed water that has been adjusted to 0.8 or more, the relationship: raw water recovery (%) = discharge water purification / volume supplied processed The raw water recovery rate represented by water volume x 100 = (supplied treatment target water volume-discharged sludge volume) / supplied treatment target water volume x 100 is 90% or more. A water treatment apparatus characterized in that the mud drain valve is configured to discharge the sludge by leaving 0.01% by volume or more of the water to be treated stored in the immersion type membrane filtering means. ..

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