JP2020018986A - Method for cleaning membrane filtration device and water treatment method - Google Patents

Abstract

To provide a method for cleaning a membrane filtration device which can sufficiently remove iron or manganese from a filtration membrane when cleaning the membrane filtration device for subjecting treated water containing at least one type of iron and manganese and ions or colloids thereof to membrane treatment using a precise filtration membrane or ultrafiltration membrane.SOLUTION: A method for cleaning a membrane filtration device for filtrating treated water containing at least one type of iron and manganese and ions or colloids thereof with a filtration membrane to obtain treatment water includes: a first acid cleaning step of supplying a sulfuric acid to the filtration membrane; and a second acid cleaning step of supplying a mixed acid of a hydrochloric acid and an organic acid to the filtration membrane, in which the filtration membrane is a precise filtration membrane or ultrafiltration membrane.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for cleaning a membrane filtration device and a method for treating water.

  Industrial water sources in Southeast Asia (Vietnam, Thailand, Myanmar, etc.) include industrial effluents, green algae, salinity, metal ions or colloids, and inorganic substances, especially iron or manganese. I have. When industrial water is obtained from an industrial water source, filtration is performed using a microfiltration membrane or an ultrafiltration membrane (UF membrane) as a pretreatment for water treatment using a reverse osmosis membrane. When filtration is performed, there is a problem that the filtration membrane is easily clogged. In order to solve this problem, there is known a method in which a filtration membrane that has filtered water to be treated containing iron or manganese is efficiently washed to recover filtration performance (see Patent Documents 1 and 2).

  Patent Literature 1 describes a method for cleaning a membrane module in which a liquid containing hydrochloric acid and an organic acid is circulated in a porous membrane module.

  In Patent Document 2, as a study of a method for cleaning a chemical solution of a hollow fiber membrane clogged with manganese, when the solubility of manganese dioxide powder was evaluated, it was found that the dissolved amount of a chemical solution mixed with hydrochloric acid based on oxalic acid was large. Has been described. In addition, Patent Document 2 evaluates a chemical cleaning method based on the water permeability of a membrane closed with manganese, and confirms the cleaning effect of a method of cleaning with a mixed acid (oxalic acid, hydrochloric acid) and sodium hypochlorite. Has been described.

JP-A-10-118471

Proceedings of the Sanitary Engineering Symposium. 5, 1997, 252-255

  However, when the cleaning methods of Patent Literature 1 and Patent Literature 2 were examined using water to be treated containing at least one of iron, manganese and their ions or colloids, iron or manganese was still sufficiently removed from the filtration membrane. Could not be removed.

  The problem to be solved by the present invention is to provide a membrane filtration device for subjecting treated water containing at least one of iron, manganese and their ions or colloids to membrane treatment using a microfiltration membrane or an ultrafiltration membrane. An object of the present invention is to provide a method for cleaning a membrane filtration device capable of sufficiently removing iron or manganese from a filtration membrane when cleaning.

  In the present invention, by performing a first acid washing step of supplying sulfuric acid to the filtration membrane and a second acid washing step of supplying a mixed acid of hydrochloric acid and an organic acid to the filtration membrane, iron is removed from the filtration membrane. Alternatively, they have found that manganese can be sufficiently removed, and have solved the above problem.

The configuration of the present invention, which is a specific means for solving the above problems, and a preferred configuration of the present invention will be described below.
[1] A method for washing a membrane filtration device for filtering treated water containing at least one of iron, manganese and ions or colloids thereof through a filtration membrane to obtain treated water;
A first acid washing step of supplying sulfuric acid to the filtration membrane;
A second acid washing step of supplying a mixed acid of hydrochloric acid and an organic acid to the filtration membrane,
A method for cleaning a membrane filtration device, wherein the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.
[2] The method for cleaning a membrane filtration device according to [1], wherein the filtration membrane after the second acid cleaning step does not contain iron, manganese, or ions or colloids thereof as a residue.
[3] The method for washing a membrane filtration device according to [1] or [2], wherein the organic acid is oxalic acid or citric acid.
[4] The first acid washing step is a step of circulating sulfuric acid inside the membrane filtration device,
The method for cleaning a membrane filtration device according to any one of [1] to [3], wherein the second acid cleaning step is a step of circulating a mixed acid inside the membrane filtration device.
[5] Any one of [1] to [4] including, after the first acid washing step and after the second acid washing step, a step of discharging discharged water from the membrane filtration device and a neutralizing step, respectively. The method for cleaning a membrane filtration device according to any one of the first to third aspects.
[6] After the second acid washing step, a washing step with a detergent containing at least one of hypochlorous acid or a salt thereof, sodium hydroxide, and hydrogen peroxide solution is included [1] to [5]. The method for cleaning a membrane filtration device according to any one of the above.
[7] The method for cleaning a membrane filtration device according to any one of [1] to [6], wherein the filtration membrane is a hollow fiber membrane.
[8] The method for cleaning a membrane filtration device according to any one of [1] to [7], wherein the water to be treated is water to be treated with a coagulant added.
[9] Any one of [1] to [8], wherein the water to be treated contains iron or its ions or colloids, manganese or its ions or colloids, calcium or its ions or colloids, and aluminum or its ions or colloids. The method for cleaning a membrane filtration device according to any one of the first to third aspects.
[10] A membrane treatment step of filtering treated water containing at least one of iron, manganese and their ions or colloids with a filtration membrane provided in a membrane filtration device to obtain treated water,
A water treatment method, comprising: the method for cleaning a membrane filtration device according to any one of [1] to [9].
[11] The water treatment method according to [10], wherein the method of cleaning the membrane filtration device is performed at a frequency of 6 times or less per year.
[12] including a step of adding flocculants to the water to be treated to form flocs, and
The water treatment method according to [10] or [11], which does not include a step of solid-liquid separation of flocs before the membrane treatment step.
[13] The water treatment method according to any one of [10] to [12], including a step of permeating the treated water through a reverse osmosis membrane to obtain a permeated water after the membrane treatment step.

  According to the present invention, when cleaning the membrane filtration device for treating the water to be treated containing at least one of iron, manganese and their ions or colloids using a microfiltration membrane or an ultrafiltration membrane, In addition, it is possible to provide a method for cleaning a membrane filtration device capable of sufficiently removing iron or manganese from a filtration membrane.

FIG. 1 is a schematic view of an example of a water treatment apparatus when performing a first acid cleaning step and a second acid cleaning step. FIG. 2 is a schematic view of an example of a water treatment device when performing a step of discharging discharged water from a membrane filtration device. FIG. 3 is a schematic diagram of an example of a water treatment device used in the water treatment method of the present invention. FIG. 4 is a flowchart of a method for cleaning the membrane filtration device according to the first embodiment. FIG. 5 is a flowchart of a method for cleaning the membrane filtration devices of Comparative Examples 1 to 6.

  Hereinafter, the present invention will be described in detail. The description of the components described below may be made based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In addition, in this specification, the numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit and an upper limit.

[Washing method for membrane filtration device]
The method for cleaning a membrane filtration device of the present invention is a method for cleaning a membrane filtration device for obtaining treated water by filtering water to be treated containing at least one of iron, manganese and ions or colloids thereof through a filtration membrane. A first acid washing step of supplying sulfuric acid to the filtration membrane, and a second acid washing step of supplying a mixed acid of hydrochloric acid and an organic acid to the filtration membrane, wherein the filtration membrane is a microfiltration membrane or It is an ultrafiltration membrane.
According to the present invention, when cleaning the membrane filtration device for treating the water to be treated containing at least one of iron, manganese and their ions or colloids using a microfiltration membrane or an ultrafiltration membrane, In addition, iron or manganese can be sufficiently removed from the filtration membrane.
By performing the first acid cleaning step using sulfuric acid as a pre-cleaning treatment in the second acid cleaning step using a mixed acid of hydrochloric acid and an organic acid, iron or manganese adhering to the surface of the filtration membrane can be effectively cleaned. Presumed. Furthermore, it is presumed that iron or manganese permeating the inside of the filtration membrane can be effectively washed by the subsequent washing using a mixed acid of hydrochloric acid and an organic acid, and a synergistic effect is exhibited.
Hereinafter, preferred embodiments of the method for cleaning a membrane filtration device of the present invention will be described.

<Overall configuration of cleaning method for membrane filtration device>
The overall configuration of the method for cleaning a membrane filtration device of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of an example of a water treatment apparatus when performing a first acid cleaning step and a second acid cleaning step.
The water treatment device 51 shown in FIG. 1 includes a membrane filtration device 22a for filtering treated water through a filtration membrane 22 to obtain treated water.
When performing the first acid cleaning step and the second acid cleaning step, a flow path between the membrane filtration device 22a and the chemical cleaning tank 25 is opened, and the acid in the chemical cleaning tank 25 is supplied to the flow path by the circulation pump 41. It is preferable to circulate and wash the filtration membrane 22.
The water treatment apparatus 51 includes a water tank 21 that can store water to be treated, a reverse osmosis membrane 23 installed downstream of the filtration membrane, and a water tank 24 that can store discharged water. However, when performing the first acid washing step and the second acid washing step, the flow path between these members and the membrane filtration device 22a is preferably closed.
In the water treatment apparatus 51 shown in FIG. 1, the valves 42a, 42b, and 42c are controlled to open and close so as to be in a state of a flow path when performing the first acid cleaning step and the second acid cleaning step. I do.

FIG. 2 is a schematic view of an example of a water treatment device when performing a step of discharging discharged water from a membrane filtration device.
When performing the step of discharging the discharged water from the membrane filtration device, it is preferable to open a flow path between the membrane filtration device 22a and the discharge water tank 24, and discharge the discharged water 15 to this flow path. When performing the step of discharging the discharged water from the membrane filtration device, a flow path between the water tank 21 to be treated and the membrane filtration device 22a, a flow channel between the reverse osmosis membrane 23 and the membrane filtration device 22a, and a membrane filtration device The flow path from 22a to the chemical cleaning tank 25 is preferably closed.
In the water treatment apparatus 51 shown in FIG. 2, the valves 42a, 42b, and 42c are controlled to open and close so as to be in a state of a flow path when performing a step of discharging the discharged water from the membrane filtration device.
A mode in which the neutralization step is further performed after the step of discharging the discharged water from the membrane filtration device is shown by a broken line in FIG. It is preferable that the neutralized washing waste liquid 16 obtained in the neutralization step be discharged out of the system without being circulated to the membrane filtration device 22a. For example, after performing a neutralization step of adding a neutralizing agent from the neutralizing agent adding means 33 provided in the discharge water tank 24 to neutralize the acid, the neutralized washing waste liquid 16 is provided outside the water treatment apparatus 51. It is preferable to discharge.
After the first acid cleaning step and the second acid cleaning step, a part of the circulated acid (cleaning waste liquid) stored in the chemical cleaning tank 25 is drained (not shown in FIG. 2). ) May be discharged outside the system. In this case, the flow path from the chemical cleaning tank 25 to the membrane filtration device 22a is closed (not shown in FIG. 2), and the neutralizing agent adding means 33 provided in the chemical cleaning tank 25 neutralizes alkali or the like. After performing a neutralization step of adding an agent to neutralize the acid, it is preferable to discharge discharged water (not shown in FIG. 2) as a neutralized washing waste liquid 16 outside the water treatment apparatus 51.

<Water to be treated>
The water to be treated used in the present invention contains at least one of iron, manganese, and ions or colloids thereof.
Others are not particularly limited, and various types of raw water such as groundwater, well water, river water, lake water, sewage, and factory drainage can be used as the water to be treated. In particular, water from industrial water sources in Southeast Asia (Vietnam, Thailand, Myanmar, etc.) can be mentioned.
It is preferable to use, as the water to be treated, water which has been appropriately pretreated as needed with respect to the raw water. Examples of the pretreatment include biological treatment, coagulant addition treatment, solid-liquid separation treatment, and other general neutralization treatments and mixing treatments. In particular, the water to be treated is preferably water to which a coagulant has been added, and more preferably water to which a coagulant containing iron, aluminum, or their ions or colloids has been added. The water to be treated to which the coagulant has been added can be confirmed, for example, from an SS concentration of 5 mg / L or more.
In the present invention, the water to be treated preferably contains iron or its ions or colloids, manganese or its ions or colloids, calcium or its ions or colloids, and aluminum or its ions or colloids. Further, the water to be treated may contain silicon or its ions or colloids, and may contain green algae.
The water to be treated preferably contains manganese or its ion or colloid in an amount of 0.01 mg / L or more, more preferably 0.01 to 0.1 mg / L.
The water to be treated preferably contains iron or its ions or colloids in an amount of 0.01 mg / L or more, more preferably 0.01 to 0.1 mg / L.
The water to be treated preferably contains calcium or its ions or colloids in an amount of 50 mg / L or more, more preferably 50 to 200 mg / L.
The water to be treated preferably contains aluminum or its ion or colloid in an amount of 1 mg / L or more, more preferably 1 to 5 mg / L.
It is particularly effective to apply the method for cleaning a membrane filtration device of the present invention to a filtration membrane obtained by filtering the water to be treated, and iron or manganese can be sufficiently removed from the filtration membrane. In particular, before and after performing the coagulant addition treatment, even when filtering the water to be treated that has not been subjected to solid-liquid separation treatment such as precipitation, the filtration method according to the membrane filtration device cleaning method of the present invention removes water from the filtration membrane. Iron or manganese can be sufficiently removed.

<Filtration membrane>
In the present invention, the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.
The opening diameter of the microfiltration membrane is not particularly limited, and is preferably 0.1 to 0.5 μm, and more preferably 0.1 to 0.2 μm. The opening diameter of the ultrafiltration membrane is not particularly limited, but is preferably 0.01 to 0.05 μm, and more preferably 0.01 to 0.02 μm.
The shape of the filtration membrane is not particularly limited, and examples thereof include a hollow fiber membrane, a spiral membrane, a pleated membrane, and a flat membrane. In the present invention, the filtration membrane is preferably a hollow fiber membrane.

<First acid washing step>
The method for cleaning a membrane filtration device of the present invention includes a first acid cleaning step of supplying sulfuric acid to a filtration membrane.
The concentration of sulfuric acid is preferably 1% or more, more preferably 1 to 2%, and particularly preferably 1.5 to 2.0%.

  In the present invention, the first acid washing step is preferably a step of circulating sulfuric acid inside the membrane filtration device. The method of circulation is not particularly limited. Any circulation pump may be used. Here, the term “circulation” refers to repeatedly passing a chemical such as an acid through a filtration membrane twice or more. In the circulation, the chemical solution may be permeated in a normal filtration direction for washing or back washing. The circulation time is not particularly limited, but may be, for example, 1 to 5 hours.

<Second acid cleaning step>
The cleaning method of the membrane filtration device of the present invention includes a second acid cleaning step of supplying a mixed acid of hydrochloric acid and an organic acid to the filtration membrane.
The concentration of hydrochloric acid is preferably 0.5% or more, and more preferably 0.5 to 1.0%.
The organic acid is not particularly limited, and examples thereof include acetic acid, citric acid, oxalic acid, ethylenediaminetetraacetic acid (EDTA), phthalic acid, and fumaric acid. In the present invention, the organic acid is preferably oxalic acid or citric acid. Only one type of organic acid may be used, or two or more types may be used. The concentration of the organic acid is preferably 0.5% by mass or more, more preferably 0.5 to 1.0% by mass, based on the whole mixed acid.
By using a mixed acid of hydrochloric acid and an organic acid, hydrochloric acid dissolves inorganic substances such as iron, calcium, aluminum, and silicon, and exhibits a synergistic effect with an organic acid. For example, water-soluble salts such as aluminum chloride and calcium chloride can be formed to easily dissolve inorganic substances, and calcium silicate and the like can be dissolved with hydrochloric acid. Further, iron oxide and manganese oxide can be washed with an organic acid.
In the present invention, it is preferable that the second acid washing step is a step of circulating a mixed acid inside the membrane filtration device. The circulation time is not particularly limited, but may be, for example, 1 to 5 hours. Other preferable embodiments of the circulation method in the second acid washing step are the same as the preferable embodiments of the circulation method in the first acid washing step.
In the present invention, it is preferred that the filtration membrane after the second acid washing step does not contain iron, manganese and their ions or colloids as residues. The filtration membrane after the second acid washing step should not contain iron or its ions or colloids, manganese or its ions or colloids, calcium or its ions or colloids, and aluminum or its ions or colloids as residues. More preferred. Note that “not included as a residue” can be confirmed from the fact that the concentration of each element is, for example, 1 ppm or less when the surface of the filtration membrane is analyzed by secondary ion mass spectrometry (SIMS). More simply, it may be confirmed from the naked eye that the colored components have been removed and the transmembrane pressure has recovered.

<Process of discharging discharged water from membrane filtration device>
The method for washing the membrane filtration device preferably includes a step of discharging the discharged water from the membrane filtration device after the first acid washing step and after the second acid washing step. In particular, in the present invention, it is more preferable to include a step of discharging discharged water from the membrane filtration device after each of the first acid cleaning step and the second acid cleaning step.

<Neutralization step>
The method for washing the membrane filtration device preferably includes a neutralization step after the first acid washing step and / or after the second acid washing step. In particular, in the present invention, it is more preferable to include a neutralization step after the first acid washing step and after the second acid washing step, respectively.
In the neutralization step after the second acid washing step, sodium hydroxide, sodium hydrogen carbonate, and other general neutralizing agents serving as alkali sources can be used to neutralize sulfuric acid. Among them, sodium hydroxide is preferable from the viewpoint of cost reduction.
In the neutralization step after the second acid washing step, it is preferable to use sodium hydroxide to neutralize a mixed acid of hydrochloric acid and an organic acid. Can be exhausted.

<Rinse process>
The washing method of the membrane filtration device is such that an aqueous solution such as membrane filtered water (processed water obtained by filtering water to be treated, which is obtained by filtration with a filtration membrane) is used between the second acid washing step and the washing step with a detergent. It is preferable to include a rinsing step from the viewpoint of extending the life of the film and reducing the cost.

<Washing process with detergent>
The method of cleaning the membrane filtration device may include a cleaning step with a cleaning agent after the second acid cleaning step, which further cleans inorganic substances such as iron or manganese, and has an acid-resistant substance (for example, organic substances such as green algae). Is preferred from the viewpoint of cleaning. The cleaning agent is preferably a cleaning agent having resistance to an alkali or an ultrafiltration membrane. Examples of the detergent having resistance to the alkali and the ultrafiltration membrane include a chlorine-containing alkali such as hypochlorous acid or a salt thereof, sodium hydroxide, and hydrogen peroxide. In the present invention, a detergent containing at least one of hypochlorous acid or a salt thereof (sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, etc.), sodium hydroxide, and hydrogen peroxide solution It is preferable to include a washing step. Among them, hypochlorous acid and sodium hypochlorite are more preferred.

[Water treatment method]
The water treatment method of the present invention comprises a membrane treatment step of filtering treated water containing at least one of iron, manganese and their ions or colloids with a filtration membrane provided in a membrane filtration device to obtain treated water, And a method for cleaning a membrane filtration device of the invention.

Here, to reduce the frequency of CIP (cleaning-in-place cleaning) cleaning using chemicals, which is performed when stable operation cannot be maintained by physical cleaning (for example, backwashing or bubbling cleaning) of the microfiltration membrane or ultrafiltration membrane. Is preferred. Since the CIP cleaning using chemicals stops the water treatment and circulates the chemicals in the system of the water treatment apparatus, the efficiency of the water treatment is reduced, and the chemical cost, electricity cost, labor cost and the like are required. In contrast, in a preferred embodiment of the present invention, as a result of sufficiently removing iron or manganese from the filtration membrane, it is possible to extend the time until the filtration membrane is clogged after chemical cleaning, and to suppress the frequency of chemical cleaning. preferable.
In the water treatment method of the present invention, the cleaning method of the membrane filtration device of the present invention is preferably performed at a frequency of 6 times or less per year, more preferably at a frequency of 4 times or less per year, and more preferably per year. It is particularly preferable to carry out the treatment three times or less.
Further, since the frequency of chemical cleaning can be suppressed in the water treatment method of the present invention, the amount of treated water or permeated water obtained can be made larger than before.

<Overall configuration of water treatment device>
The overall configuration of the water treatment apparatus used in the water treatment method of the present invention will be described with reference to the drawings. FIG. 3 is a schematic diagram of an example of a water treatment device used in the water treatment method of the present invention.
The water treatment apparatus 51 shown in FIG. 3 includes a treated water tank 21 that can store the raw water 11, a coagulant adding unit 31, and a bactericide adding unit 32, and can prepare the treated water 12. The water treatment device 51 shown in FIG. 3 further includes a membrane filtration device 22 a including the filtration membrane 22, a reverse osmosis membrane, and a discharge water tank 24.
In the water treatment method of the present invention, in the membrane treatment step, the water to be treated 12 is filtered by the filtration membrane 22 of the membrane filtration device 22a to obtain the treated water 13. When the water to be treated 12 containing at least one of iron, manganese, and their ions or colloids is subjected to membrane treatment by the water treatment device 51, iron, manganese, ions, or colloids contained in the water to be treated 12 are filtered. The film 22 can be effectively removed. Further, a floc (a flocculant derived from the flocculant) is formed by adding a flocculant, and the treated water 12 in which the flocs are not subjected to solid-liquid separation is subjected to membrane treatment by the water treatment device 51, and is included in the treated water 12. Flock and the like can be effectively removed by the filtration membrane 22. However, inorganic substances such as iron and manganese and turbid substances derived from the coagulant adhere to or impregnate the filtration membrane 22. Then, the suspended matter derived from an inorganic substance such as iron or manganese or a coagulant that has adhered or impregnated to the filtration membrane 22 is washed by the above-described washing method of the membrane filtration device of the present invention. As a result, the frequency of CIP cleaning using chemicals can be dramatically reduced, and water treatment can be performed at low cost.
In the water treatment method of the present invention, it is preferable that the treated water 13 obtained as necessary is passed through the reverse osmosis membrane 23 to obtain the permeated water 14.
On the other hand, if necessary, a part of the water to be treated 12 that has not passed through the filtration membrane 22 of the membrane filtration device 22a can be discharged to the discharge water tank 24 as the discharge water 15.

<Film treatment step>
The water treatment method of the present invention includes a membrane treatment step of filtering treated water containing at least one of iron, manganese and their ions or colloids with a filtration membrane provided in a membrane filtration device to obtain treated water.

<Adding flocculant>
The water treatment method preferably includes a step of forming a floc by adding a flocculant to the water to be treated. The addition of the flocculant is preferably upstream of the filtration membrane.
Examples of the flocculant include an inorganic flocculant and a polymer flocculant. Examples of the inorganic coagulant include aluminum sulfate (sulfuric acid band), polyaluminum chloride (PAC), ferric chloride, ferrous sulfate, polyiron sulfate, and polysilica iron. Among these, a sulfate band and PAC are preferable, and PAC is more preferable from the viewpoint of being used without pH adjustment. Examples of the polymer flocculant include an amphoteric polymer flocculant, a nonionic polymer flocculant, an anionic polymer flocculant, and a cationic polymer flocculant. Among these, an amphoteric polymer flocculant or an anionic polymer flocculant is preferable.
The amount of the flocculant to be added is not particularly limited, but is preferably adjusted appropriately so that flocs having a particle diameter capable of removing the flocs without using a solid-liquid separating means such as a sedimentation tank can be formed.

The water treatment apparatus may be provided with a solid-liquid separation means such as a sedimentation tank, a floating tank, a centrifuge, and a sand filtration device upstream or downstream of the filtration membrane. Conventionally, these large-scale devices (coagulation settling tank, sand filtration device, etc.) have been installed.
However, in the water treatment method of the present invention, upstream or downstream of the filtration membrane, since it can be continuously operated without performing solid-liquid separation treatment, from the viewpoint of reducing the cost that the water treatment apparatus does not include the solid-liquid separation means. preferable. That is, the water treatment method of the present invention preferably includes a step of adding flocculants to the water to be treated to form flocs, and does not include a step of solid-liquid separating flocs prior to the membrane treatment step. In particular, it is more preferable that no solid-liquid separation means is provided upstream of the filtration membrane, and it is particularly preferable that no settling tank and sand filtration device are provided upstream of the filtration membrane. By controlling flocculation by controlling the appropriate type and amount of the flocculant and combining the microfiltration membrane or the ultrafiltration membrane, a water treatment apparatus which is more compact and lower in cost than before can be obtained.
Here, in the case where the step of adding flocculant to the water to be treated includes a step of forming flocs and does not include the step of solid-liquid separation of flocs prior to the membrane treatment step, the components derived from flocs are subjected to conventional chemical washing. The method did not allow sufficient washing from the filtration membrane. For this reason, the period from the chemical cleaning to the film blockage is short, and the frequency of chemical cleaning may increase the cost of chemicals. However, even in this case, according to the method for cleaning a membrane filtration device of the present invention, the components derived from flocs can be sufficiently washed from the filtration membrane, and the period from membrane cleaning to membrane blockage can be extended, and chemical cleaning can be performed. And the cost of chemicals can be reduced.

<Add fungicide>
The water treatment method preferably includes a step of adding a disinfectant upstream of the reverse osmosis membrane, and more preferably includes a step of adding a disinfectant that is an oxidizing agent. The order of adding the germicide and the flocculant is not particularly limited, and any one may be added first, and the bactericide and the flocculant may be added substantially simultaneously.
The fungicide is not particularly limited, and includes an oxidizing agent, a slime control agent, and an alkali agent.
Examples of the oxidizing agent include a chlorine-based oxidizing agent, a bromine-based oxidizing agent, and ozone. In particular, by sterilizing the water to be treated with a chlorine-based oxidizing agent to suppress biofouling on the reverse osmosis membrane surface, a viewpoint of further reducing the frequency of chemical cleaning of the filtration membrane and / or the reverse osmosis membrane. Is preferred. However, an optimum bactericide can be selected according to the conditions of the water treatment.
Examples of the chlorine-based oxidizing agent include chlorine dioxide, hypochlorous acid, and sodium hypochlorite, and sodium hypochlorite is more preferable. Further, an additive described in [0036] of JP-A-2015-174018 may be used.
The amount of the fungicide to be added is not particularly limited, but the water to be treated should contain the fungicide in an amount of 0.1 to 10 mg / L (more preferably 0.5 to 5 mg / L, particularly preferably 2 to 5 mg / L). It is preferable to add a bactericide to the mixture. The water treatment apparatus preferably includes a means for measuring the residual chlorine in the water to be treated and a means for controlling the amount of the chlorine-based oxidizing agent to be added according to the data obtained from the means for measuring the residual chlorine. It is preferable to add a chlorine-based oxidizing agent until the residual chlorine of the water to be treated becomes 0.1 mg / L or more, and it is more preferable to add the chlorine-based oxidizing agent until the residual chlorine becomes 0.2 mg / L or more.

<Step of obtaining permeated water>
The water treatment method of the present invention preferably includes, after the membrane treatment step, a step of permeating treated water through a reverse osmosis membrane to obtain permeated water.
The opening diameter of the reverse osmosis membrane is not particularly limited, and is preferably 0.001 to 0.005 μm, and more preferably 0.001 to 0.002 μm.
The material of the reverse osmosis membrane is not particularly limited, and for example, a polyamide membrane or the like can be used.

<Permeated water>
According to the water treatment method of the present invention, treated water can be subjected to reverse osmosis membrane treatment, recovered as permeated water (also referred to as recovered water), and reused. For example, wastewater from a factory can be collected as permeated water having a quality similar to that of industrial water, and can be reused as service water (industrial water). The permeated water can be reused as sterile water.

<Other devices>
The water treatment device may include a portion having another function. For example, a pH adjusting means may be provided.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. Materials, usage amounts, ratios, processing contents, processing procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples described below.

[Example 1]
<Addition of flocculant>
The water treatment apparatus shown in FIG. 3 was prepared, and water treatment was performed.
Water from industrial water sources in Southeast Asia (Vietnam, Thailand, Myanmar), including industrial wastewater, green algae, salinity, metal ions or colloids, and inorganic substances, was stored in the treated water tank as raw water.
A process of adding a sulfuric acid band and polyaluminum chloride (PAC) as an inorganic coagulant to a water tank to be treated and forming flocs was performed to prepare water to be treated. Qualitative analysis of the water to be treated by ICP emission spectrometry and atomic absorption spectrometry revealed that the water contained at least each of iron, manganese, calcium and aluminum. The water to be treated contains 0.05 mg / L of iron or its ion or colloid, 0.05 mg / L of manganese or its ion or colloid, 100 mg / L of calcium or its ion or colloid, aluminum or its ion or colloid. 3 mg / L was contained.
The flocs in the water to be treated were used for membrane treatment without solid-liquid separation. The fact that the flocculant was added to the water to be treated was visually confirmed to contain floc, and also confirmed that the SS concentration was 5 mg / L or more.

<Film treatment>
The water to be treated was passed through the ultrafiltration membrane with a pump from the water tank to be treated to perform a membrane treatment step, and treated water was obtained.
Further, a step of applying pressure to the treated water to permeate the polyamide-based reverse osmosis membrane to obtain permeated water was performed.
Then, water for back washing was supplied from the downstream side of the filtration membrane from a water supply unit for back washing not shown in FIG. 3, and back washing and bubbling washing of the filtration membrane were performed several times per hour. .
The above process is repeated until the differential pressure recovery effect by the back washing and the bubbling cleaning is reduced. (Even if the differential pressure temporarily drops, it immediately rises during the membrane processing step, and the differential pressure increase width during the membrane processing converges. Until it disappeared and the pressure difference recovery effect was substantially lost).

<Washing method of membrane filtration device>
(First acid wash, discharge and neutralization)
Then, the washing method of the membrane filtration device of Example 1 was performed by the following method. The flow path was switched by opening and closing a valve (not shown) of the water treatment apparatus shown in FIG. 3, and the washing method of the membrane filtration device was performed as the flow path shown in FIGS. 1 and 2. FIG. 4 shows a flowchart of a method for cleaning the membrane filtration device of Example 1 and Example 2 described later.
First, the first acid cleaning was performed as the flow channel shown in FIG. In the flow path, the valve 42a was opened, the valve 42b was closed, and the valve 42c was opened in the flow path from the filtration membrane 22 to the chemical cleaning tank 25. Then, sulfuric acid 9 having a concentration of 1% was supplied from the chemical cleaning tank to the filtration membrane 22 using the circulation pump 41, and circulated from the filtration membrane 22 to the chemical cleaning tank 25. The circulation time was 1 hour.
After the first acid cleaning, the flow path shown in FIG. 2 was set, and the discharged water was discharged. In the flow path, the valve 42a is closed (not shown in FIG. 2), the valve 42b is open, the valve 42c is open, the flow path from the filtration membrane 22 to the valve 42b is open, 15 was discharged to a discharge water tank 24.
Thereafter, while the valve 42a is kept closed, an alkali (specifically, sodium hydroxide) is added from the neutralizing agent adding means 33 to the discharge water tank 24 and the chemical cleaning tank 25 to perform neutralization. The neutralized washing waste liquid 16 was discharged out of the system of the device 51.

(Second acid wash, discharge and neutralization)
Next, a second acid cleaning was performed as the flow channel shown in FIG. In the second acid washing, the same as the first acid washing except that instead of sulfuric acid, a mixed acid which is an aqueous solution of 0.5% by mass citric acid with respect to the whole mixed acid was used instead of hydrochloric acid having a concentration of 0.5%. And
After the second acid washing, discharge and neutralization were performed in the same manner as after the first acid washing, using sodium hydroxide as an alkali.

(Rinse cleaning, cleaning liquid cleaning)
Next, rinse cleaning using treated water was performed as the flow path shown in FIG.
After the rinsing, a cleaning liquid cleaning using sodium hypochlorite as a cleaning agent was further performed.

(Frequency of cleaning method for membrane filtration device)
The membrane treatment process was performed again using the filtration membrane that had been washed with the washing liquid. Then, when the differential pressure recovery effect by the back washing and the bubbling washing was reduced, the method of washing the membrane filtration device was repeated.
When water treatment was performed for one year using the water treatment apparatus of Example 1 described above, the frequency of the method of cleaning the membrane filtration device (ie, the frequency of chemical cleaning of the ultrafiltration membrane) was twice per year. . Here, the chemical cleaning means CIP cleaning (cleaning-in-place cleaning) in which the water treatment is stopped and the chemical is circulated through a membrane filtration device provided with an ultrafiltration membrane.

[Example 2]
The cleaning method and water treatment of the membrane filtration device of Example 2 were performed in the same manner as in Example 1 except that a mixed acid of hydrochloric acid and oxalic acid was used in place of the mixed acid of hydrochloric acid and citric acid in the second acid washing. Was.
When the water treatment was performed for one year by the method of Example 2, the frequency of the cleaning method of the membrane filtration device was twice per year.

[Comparative Example 1]
A cleaning method and a water treatment of the membrane filtration device of Comparative Example 1 were performed in the same manner as in Example 1 except that the second acid cleaning was not performed. FIG. 5A shows a flowchart of a method for cleaning the membrane filtration device of Comparative Example 1.
When the water treatment was performed for one year by the method of Comparative Example 1, the frequency of the method of cleaning the membrane filtration device was 12 times per year.

[Comparative Example 2]
A cleaning method and a water treatment of the membrane filtration device of Comparative Example 2 were performed in the same manner as in Example 1 except that citric acid was used instead of sulfuric acid in the first acid cleaning, and the second acid cleaning was not performed. went. FIG. 5B shows a flowchart of a method for cleaning the membrane filtration device of Comparative Example 2.
When the water treatment was performed for one year by the method of Comparative Example 2, the frequency of the cleaning method of the membrane filtration device was 12 times per year.

[Comparative Example 3]
The membrane of Comparative Example 3 was prepared in the same manner as in Example 1 except that hydrochloric acid and citric acid were used as a mixed acid instead of sulfuric acid in the first acid washing, and sulfuric acid was used instead of the mixed acid in the second acid washing. The washing method of the filtration device and the water treatment were performed. FIG. 5C shows a flowchart of a method for cleaning the membrane filtration device of Comparative Example 3.
When the water treatment was performed for one year by the method of Comparative Example 3, the frequency of the cleaning method of the membrane filtration device was 12 times per year.

[Comparative Example 4]
A cleaning method and a water treatment of the membrane filtration device of Comparative Example 4 were performed in the same manner as in Example 1 except that the first acid cleaning and the second acid cleaning were not performed. FIG. 5D shows a flowchart of a method for cleaning the membrane filtration device of Comparative Example 4.
When the water treatment was performed for one year by the method of Comparative Example 4, the frequency of the cleaning method of the membrane filtration device was 12 times per year.

[Comparative Example 5]
A method for cleaning the membrane filtration device of Comparative Example 5 in the same manner as in Example 1 except that hydrochloric acid and citric acid were used as mixed acids instead of sulfuric acid in the first acid washing, and the second acid washing was not performed. And water treatment. FIG. 5E shows a flowchart of a method of cleaning the membrane filtration device of Comparative Example 5 and Comparative Example 6 described later.
When the water treatment was performed for one year by the method of Comparative Example 5, the frequency of the cleaning method of the membrane filtration device was 12 times per year.

[Comparative Example 6]
A method for cleaning the membrane filtration device of Comparative Example 6 in the same manner as in Example 1 except that hydrochloric acid and oxalic acid were used as a mixed acid instead of sulfuric acid in the first acid washing, and the second acid washing was not performed. And water treatment.
When the water treatment was performed for one year by the method of Comparative Example 6, the frequency of the cleaning method of the membrane filtration device was 12 times per year.

<Evaluation>
By the methods described below, the removals from the filtration membrane and the residues of the filtration membrane were qualitatively analyzed in the cleaning methods of the membrane filtration devices of the respective Examples and Comparative Examples.
The elements removed from the filtration membrane were confirmed by using ICP emission spectrometry and atomic absorption spectrometry with respect to the discharged water obtained in all the discharging steps.
As for the residue of the filtration membrane, the surface of the filtration membrane was analyzed by secondary ion mass spectrometry (SIMS), and elements remarkably recognized as impurities (elements substantially recognized as impurities of 1 ppm or more) were confirmed.
The obtained results are shown in Table 1 below.

From Table 1 above, according to the present invention, the membrane filtration device for treating the water to be treated containing at least one of iron, manganese, and these ions using a microfiltration membrane or an ultrafiltration membrane is washed. In this case, it was found that iron or manganese could be sufficiently removed from the filtration membrane. As a result, it was also found that according to the method for cleaning a membrane filtration device of the present invention, the frequency of chemical cleaning of a filtration membrane can be suppressed. Furthermore, in Examples 1 and 2, when the filtration membrane was visually inspected, the coloring matter was removed, and the transmembrane pressure was restored. It was confirmed that manganese or its ions or colloids, calcium or its ions or colloids, and aluminum or its ions or colloids were not contained as residues.
From Comparative Example 1, it was found that iron and manganese could not be sufficiently removed from the filtration membrane when the second acid cleaning was not performed even if the sulfuric acid cleaning was performed.
From Comparative Example 2, it was found that iron and manganese could not be sufficiently removed from the filtration membrane when only citric acid washing was performed.
From Comparative Example 3, it was found that when the mixed acid cleaning was performed first and then the sulfuric acid cleaning was performed, iron and manganese could not be sufficiently removed from the filtration membrane.
From Comparative Example 4, it was found that when neither the first acid washing nor the second acid washing was performed, iron and manganese could not be sufficiently removed from the filtration membrane.
From Comparative Examples 5 and 6, it was found that iron and manganese could not be sufficiently removed from the filtration membrane when only the mixed acid washing was performed.
In addition, in Comparative Examples 1 to 6, it was also confirmed by visual observation of the filtration membrane that the coloring matter was not removed.

1 Sulfuric acid cleaning 2 Discharge and neutralization 3 Mixed acid cleaning 4 Rinse cleaning 5 Detergent cleaning 6 Citric acid cleaning 11 Raw water 12 Treated water 13 Treated water 14 Permeated water 15 Drained water 16 Neutralized cleaning waste liquid 21 Treated water tank 22 Filtration membrane 22a Membrane filtration device 23 Reverse osmosis membrane 24 Discharge water tank 25 Chemical washing tank 31 Coagulant addition means 32 Disinfectant addition means 33 Neutralizer addition means 41 Circulation pump 42a Valve 42b Valve 42c Valve 51 Water treatment device

Claims (13)

A method for cleaning a membrane filtration device for filtering water to be treated containing at least one of iron, manganese and ions or colloids thereof through a filtration membrane to obtain treated water;
A first acid washing step of supplying sulfuric acid to the filtration membrane;
A second acid washing step of supplying a mixed acid of hydrochloric acid and an organic acid to the filtration membrane,
A method for cleaning a membrane filtration device, wherein the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.   The method for cleaning a membrane filtration device according to claim 1, wherein the filtration membrane after the second acid cleaning step does not contain iron, manganese, or ions or colloids thereof as a residue.   3. The method for cleaning a membrane filtration device according to claim 1, wherein the organic acid is oxalic acid or citric acid. The first acid washing step is a step of circulating the sulfuric acid inside the membrane filtration device,
The method for cleaning a membrane filtration device according to any one of claims 1 to 3, wherein the second acid cleaning step is a step of circulating the mixed acid inside the membrane filtration device.   5. The method according to claim 1, further comprising a step of discharging discharged water from the membrane filtration device after the first acid cleaning step and a step of discharging the discharged water from the membrane filtration device, and the neutralizing step after the second acid cleaning step. 6. A method for cleaning a membrane filtration device according to the above.   The cleaning method according to any one of claims 1 to 5, further comprising a cleaning step using a cleaning agent containing at least one of hypochlorous acid or a salt thereof, sodium hydroxide, and hydrogen peroxide solution after the second acid cleaning step. The method for cleaning a membrane filtration device according to claim 1.   The method for cleaning a membrane filtration device according to any one of claims 1 to 6, wherein the filtration membrane is a hollow fiber membrane.   The method for cleaning a membrane filtration device according to any one of claims 1 to 7, wherein the water to be treated is water to be treated with a coagulant added thereto.   The said to-be-processed water contains iron or its ion or colloid, manganese or its ion or colloid, calcium or its ion or colloid, and aluminum or its ion or colloid. Cleaning method of membrane filtration device. A membrane treatment step of filtering treated water containing at least one of iron, manganese and their ions or colloids with a filtration membrane provided in a membrane filtration device to obtain treated water,
A water treatment method, comprising: the method for cleaning a membrane filtration device according to any one of claims 1 to 9.   The water treatment method according to claim 10, wherein the method of cleaning the membrane filtration device is performed at a frequency of 6 times or less per year. Including a step of adding a flocculant to the water to be treated to form flocs, and
The water treatment method according to claim 10, wherein the method does not include a step of solid-liquid separating the floc before the membrane treatment step.   The water treatment method according to any one of claims 10 to 12, further comprising a step of permeating the treated water through a reverse osmosis membrane to obtain a permeated water after the membrane treatment step.