JP5339054B2 - Water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method which enables an efficiently stable operation without requiring large-scale equipment for sand filtration and the like when performing water purification treatment of water to be treated, such as groundwater, containing metal ions and insoluble materials. <P>SOLUTION: The water to be treated containing metal ions and insoluble materials is subjected to filtration treatment by a filtration membrane supporting a precoating agent to remove the insoluble materials, and then subjected to desalting treatment. The membrane filtration treatment and the desalting treatment are performed in a state of inhibiting oxidative precipitation of the metal ions by adding a reducing agent to the water to substantially remove dissolved oxygen in the water. The reducing agent is added before the membrane filtration treatment so that dissolved oxygen is not substantially contained in concentrate and/or permeate accompanying the desalting treatment. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a water treatment method used for water purification, industrial water production and the like.

  Conventionally, as one of the water treatment methods, in order to decompose organic matter, disinfect bacteria, remove metals, etc., water to be treated is treated with a chlorine-based oxidizing agent such as sodium hypochlorite or an oxidizing agent such as ozone. An oxidation treatment method is used.

For example, in groundwater treatment, it is usual to add an oxidizer to oxidize and precipitate dissolved metal, and after rapid filtration, treat with a microfiltration membrane or ultrafiltration membrane. In particular, when the water to be treated is a deep well as a water source, rapid filtration is essential in the previous stage when the water source is oxygen-free and there are many dissolved metals and a microfiltration membrane or ultrafiltration membrane is used. For this reason, the water treatment apparatus becomes larger and a large space is required for installation. Moreover, since it is necessary to carry out back washing of the sand filtration tower and the membrane, there is a drawback that a large amount of waste water is generated from these treatment facilities.
Furthermore, when drinking water is treated with a microfiltration membrane or ultrafiltration membrane using a deep well as a water source, the hardness components in the raw water and silica remain mostly in the treated water, which may cause problems due to scale. The

  As an example of dealing with the above-mentioned problems, Patent Document 1 discloses that the primary treated water obtained is obtained by oxidizing part of the polyvalent metal ions in the previous stage of the treatment process and removing the precipitated solid content. A high-level treatment method using a nanofiltration membrane or a reverse osmosis membrane is disclosed. In this case, since the nanofiltration membrane or reverse osmosis membrane for fresh water treatment does not have resistance to an oxidizing agent, it is essential to inject a reducing agent in advance and remove the remaining oxidizing agent when supplying raw water. In addition, when this treated water is used as drinking water, sodium hypochlorite, which is an oxidizing agent, is added again after water treatment with a nanofiltration membrane or reverse osmosis membrane, and residual chlorine in the drinking water is 0.1 mg / It is necessary to inject and manage it so that it is maintained at L or more. Therefore, many kinds of chemicals must be repeatedly added a plurality of times, the amount of chemicals increases, the cost increases, and the process becomes complicated.

Depending on the quality of the raw water, when a microfiltration membrane or ultrafiltration membrane is used to remove the solid content, the amount of wastewater increases because reverse water is usually applied after about 1 hour of water treatment. In addition, the treated water recovery rate is reduced.
As described above, the conventional water treatment method based on the oxidation treatment has many inefficient aspects such as necessary space, amount of chemical solution used, and a large amount of drainage, and there is room for improvement.

On the other hand, Patent Document 2 discloses a method in which groundwater pumped up is directly solid-liquid separated and then treated with a nanofiltration membrane or a reverse osmosis membrane. This method is remarkable in that the chemical solution is reduced. However, even with this method, it is difficult to completely block oxygen contamination because it is treated in the atmosphere in the treatment process. As a result, metal ions such as iron in raw water are oxidized, and metal such as iron oxide is oxidized. It precipitates as oxide fine particles.
Iron oxide is known to have a wide distribution with a particle size of 10 nm to 5000 nm, but if a microfiltration membrane or ultrafiltration membrane is used for pretreatment to remove iron oxide, The microfiltration membrane or ultrafiltration membrane is blocked in a very short time. In addition, once membrane clogging occurs, these insoluble substances have a very small particle size, so even if reverse water flow, which is a physical cleaning of the membrane, is performed, the membrane differential pressure does not recover and the treatment process is The result will be a hindrance. Moreover, if the frequency of reverse water flow is increased, the recovery rate of treated water will decrease.

There are 16 known types of iron oxides, including iron hydroxide and iron oxyhydroxide, but Fe ₂ O ₃ represented by Bengala has very low solubility in chemicals, When such insoluble iron oxide is contained and the microfiltration membrane or ultrafiltration membrane is clogged, recovery to the initial state is very difficult even if chemical cleaning is performed.

  As described above, the methods currently disclosed have not been adequately addressed, and more effective solutions are being sought.

  JP 11-192482 A   JP 2007-38052 A

  The present invention provides a water treatment method capable of efficient and stable operation without requiring large facilities such as sand filtration when water to be treated (eg, groundwater) containing metal ions and insoluble substances is purified. The purpose is that.

  As a result of diligent research to achieve the above object, the present inventors have continuously reduced this series of water treatment steps when subjecting water to be treated containing metal ions and insoluble substances to solid-liquid separation by membrane filtration and desalting. It was found that the amount of drainage was reduced and stable operation was possible by carrying out under an atmosphere (a state in which dissolved oxygen was substantially removed), and the present invention was completed.

That is, the water treatment method of the present invention removes insoluble substances by subjecting water to be treated containing metal ions and insoluble substances to membrane filtration with a microfiltration membrane or ultrafiltration membrane holding a precoat agent (filter aid). Thereafter, a desalting process using a reverse osmosis membrane, adding sodium bisulfite to the raw water pumped up from the well as the treated water, substantially removing dissolved oxygen in the treated water, The membrane filtration treatment and the desalting treatment are performed in a state where oxidation precipitation of metal ions is suppressed.

The sodium bisulfite is preferably added so that dissolved oxygen is not substantially contained in the concentrated water and / or permeated water accompanying the desalting treatment.
Specifically, the sodium bisulfite is added so that the concentration of dissolved oxygen in the concentrated water and / or permeated water accompanying the desalting treatment is maintained at, for example, 0.1 mg / L or less.
The sodium bisulfite is preferably added in excess of the theoretical amount necessary for the reaction with dissolved oxygen in the water to be treated and oxygen newly dissolved before the desalting treatment, preferably in excess of the theoretical amount. Here, the amount of sodium bisulfite to be injected may be 1 to 50 mg / L in excess of the theoretical amount necessary for oxygen removal, for example.

  The target insoluble substances here are not particularly limited, but when groundwater is used as the water to be treated, for example, metal oxides such as iron oxide and manganese oxide, calcium compounds, soil components, organic substances, microorganisms, etc. Can be mentioned. In addition, examples of metal ions include ions of metals such as iron, manganese, calcium, and magnesium.

The microfiltration membrane or ultrafiltration membrane is used to perform the removal of insoluble material (solids) as pretreatment desalting.
Here, any microfiltration membrane or ultrafiltration membrane can be used regardless of the water flow method (internal pressure type, external pressure type, etc.), membrane material (organic, inorganic, etc.), membrane shape, etc. In order to prevent membrane clogging of the reverse osmosis membrane employed in the process, it is preferable to use a membrane having a membrane pore diameter of 0.1 μm or less.
As the filtration method, the dead end method is preferable because it can reduce the dissolution of oxygen, and the frequency of reverse water flow is appropriately determined from the ability of the microfiltration membrane or ultrafiltration membrane used mainly as prefiltration and the state of the water to be treated. .

The desalting treatment is a treatment for removing metal ions in the water to be treated. In the present invention, the treatment is performed using a reverse osmosis membrane, but the shape of the membrane is not limited, and any of spiral type, hollow fiber type, etc. It is preferable to determine in consideration of the removal rate, the recovery rate, the circulation rate, and the properties of the water to be treated.

Sodium sulfite used in the present invention, Ru der which can remove dissolved oxygen. When the water treatment method of the present invention is used for the production of drinking water, the one that meets the standards for chemicals for water supply is used .

As the precoat agent (hereinafter also referred to as a protective agent) used in the present invention, fine particles having an average particle size of 0.4 to 50 μm are preferable, and when supplied to a microfiltration membrane or an ultrafiltration membrane, the differential pressure of the membrane It is preferable to select a particle size distribution and an injection amount that do not deteriorate the flow rate characteristics. The precoat agent may be either organic or inorganic, and examples thereof include kaolin, zeolite, alumina, silica sand, activated carbon, ion exchange resin, chelate resin, and polymer beads. Such a precoat agent can be used alone or in combination of two or more.
Moreover, it is preferable to select a precoat agent suitably according to raw | natural water state. At this time, it is preferable to determine the selection of precoat agent fine particles and the mixing ratio thereof in consideration of properties such as affinity for water, particle shape, adsorption ability of organic substances, and the like.
As a method of pre-coating such a pre-coating agent on the filtration membrane surface, a conventionally known method is used.

As a method for recovering the differential pressure of the microfiltration membrane or ultrafiltration membrane , it is preferable to reduce the frequency of reverse water flow from the conventional frequency and increase the frequency of chemical cleaning from the conventional frequency. Here, reverse water flow means that water is passed from the primary side of the filtration membrane to the secondary side during normal membrane filtration operation, but treated water or the like is passed from the secondary side of the filtration membrane to the primary side. Say.

When a microfiltration membrane or an ultrafiltration membrane is used as a filtration membrane, reverse water flow is performed once every hour, and chemical cleaning is generally performed once every several weeks to several months. By the way, according to the present invention, as described above, the load on the microfiltration membrane or the ultrafiltration membrane can be remarkably reduced, so that the frequency of reverse water flow can be reduced. On the other hand, even if the number of times of chemical cleaning is increased, for example, if the same sodium bisulfite used for removing dissolved oxygen is used as a cleaning chemical solution, it is possible to resume water flow without performing a rinsing step. , No chemical operation is caused by chemical cleaning. Therefore, by optimizing the frequency of reverse water flow and chemical cleaning, it becomes possible to reduce the amount of drainage, improve the treated water recovery rate, and reduce the number of maintenance. Longer stable operation is possible.

The reverse flow of a microfiltration membrane or ultrafiltration membrane is based on determining the water flow conditions in consideration of the properties of the water to be treated, but under conditions where dissolved oxygen in the water to be treated has been substantially removed. The filtration is preferably performed once every 3 to 24 hours.
In addition, the chemical cleaning is preferably determined from the differential pressure recoverability by the reverse water flow and the initial differential pressure, but is performed about once every 1 to 7 days, for example.

A cleaning chemical solution containing an acid and a reducing agent is used for the chemical cleaning, and the cleaning chemical solution is supplied to the primary side of the microfiltration membrane or ultrafiltration membrane and held or circulated for a predetermined time, and then the cleaning chemical solution is recovered. However, it is preferable to reuse after adjusting the concentration of the acid and the reducing agent.
The cleaning chemical used for the chemical cleaning can be appropriately selected depending on the plugging material, but when there are many metal-based plugging materials, a combination of a reducing agent and an acid is preferable. Especially as a reducing agent, 1 type, or 2 or more types of sulfite or bisulfite can be used conveniently. In addition, it is preferable in terms of chemical management to use the same sodium bisulfite as the reducing agent for removing dissolved oxygen.
Further, the concentration and holding time of various cleaning chemicals are appropriately determined from the type of chemicals, the cleaning effect to be obtained, and the like, and are not particularly limited. In addition, it is necessary to consider the chemical resistance of the microfiltration membrane used as a filtration membrane or an ultrafiltration membrane for determination of a density | concentration and holding time.

After the chemical cleaning, it is preferable to resume the liquid flow without performing the rinsing step.
That is, by supplying the rinsing liquid to the next step, it is possible to reduce the rinsing waste water and improve the water treatment recovery rate. Furthermore, because the reverse osmosis membrane used in the desalination process, it becomes possible to perform the primary sterilization and washing by Rigyaku osmosis membrane in the rinsing liquid at the same time stable operation possible desalting process It becomes.
Here , when the rinsing liquid is fed to the reverse osmosis membrane, the conductivity of the treated water of the reverse osmosis membrane is monitored, and when the conductivity reaches a predetermined value or more, the treated water is preferably returned to the intermediate water tank. .

Another aspect of the present invention is a reducing agent injection means for injecting sodium bisulfite into water to be treated containing metal ions and insoluble substances, and a solid-liquid separation device for separating insoluble substances from the water to be treated after sodium bisulfite injection. And a desalinator equipped with a reverse osmosis membrane for separating metal ions from primary treated water obtained from the solid-liquid separator, and a dissolved oxygen concentration of concentrated water and / or permeate obtained from the desalter A water treatment system that controls the amount of sodium bisulfite injected according to the dissolved oxygen concentration measured by the dissolved oxygen meter.

According to the water treatment method of the present invention, sodium bisulfite is added to the water to be treated, and dissolved oxygen in the water to be treated is substantially removed, so that oxidation precipitation of metal ions contained in the water to be treated is suppressed. However, membrane filtration and desalting can be performed. Accordingly, microfiltration membranes or adhere to the ultrafiltration membrane, it is possible minimizing the amount of insoluble material which also causes removal difficult film closed by chemical cleaning or the like, microfiltration membranes or ultrafiltration membranes The number of maintenance operations can be reduced, and the amount of drainage can be reduced. In addition, by holding a precoat agent on the membrane surface, it is possible to suppress an increase in membrane differential pressure, and it is possible to easily remove insoluble substances attached to the microfiltration membrane or ultrafiltration membrane. It becomes. Therefore, it is possible to provide a water treatment method capable of stable operation and improving the water treatment recovery rate.

  In addition, the conventional method based on oxidation treatment requires large equipment such as sand filtration in the treatment process, and when a nanofiltration membrane or a reverse osmosis membrane is used, it is supplied to the nanofiltration membrane or the reverse osmosis membrane. The process was complicated and the cost of the chemical solution was high, such as removing the oxidant before and re-adding the oxidant after the treatment. However, according to the present invention, it is possible to save space because a large facility is not required, and since the reduction process is the basis, the amount of the chemical solution is reduced and the processing process is simplified. Is possible. Therefore, according to the method of the present invention, it is convinced that the industrial utility is remarkable in that it is possible to stably obtain drinking water with good water quality at a very low cost.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a flowchart for explaining the entire flow of a water treatment system suitably used in a water treatment method according to an embodiment of the present invention.

As shown in FIG. 1, this water treatment system includes a reducing agent injection means for injecting sodium bisulfite as a reducing agent to remove dissolved oxygen from raw water pumped from a well 1, and an insoluble metal component (eg, insoluble metal). Membrane separation device (MS) 2 (hereinafter also referred to as solid-liquid separation device) for solid-liquid separation of insoluble substances such as oxide) and reverse osmosis membrane for desalting primary treated water from membrane separation device 2 ( RO) 3.

  Here, the reducing agent injection means mainly comprises a reducing agent tank T2 and a first reducing agent pump P4. The injection amount of the reducing agent is adjusted so that the measured value measured by the dissolved oxygen meter (DO) 4 provided in the concentrated drainage line L7 for draining the concentrated water of the reverse osmosis membrane 3 is always around 0 mg / L. . Although the management method of the reducing agent injection amount is not particularly limited, for example, the measurement data of the DO meter 4 is sent to a control unit (not shown), and the measurement value is a predetermined value (for example, 0.1 mg / L) for a certain time (for example, If it exceeds 120 seconds), the first reducing agent pump P4 may be instructed to increase the injection amount of the reducing agent. At this time, the amount of increase of the reducing agent is, for example, an amount corresponding to the increased amount of oxygen (reaction equivalent) or a value exceeding it, and when the dissolved oxygen concentration returns to a predetermined value, the injection amount of the reducing agent is initially set. You may comprise so that it may return to injection amount. In addition, data such as the amount of dissolved oxygen contained in the water to be treated, the amount of oxygen mixed in the main water treatment process, the consumption of reducing agent consumed in addition to the reaction with oxygen, etc. are collected and required based on the data. It is good also as calculating the quantity of the reducing agent to be injected and injecting the reducing agent more than the said calculation value.

  In FIG. 1, the water treatment line is indicated by a broken line, and the chemical washing line is indicated by a one-dot chain line. The water treatment line is a line for desalting metal ions remaining in the water to be treated after solid-liquid separation of insoluble substances in the water to be treated by membrane filtration. Specifically, as shown in FIG. 1, the groundwater (treated water) pumped from the well 1 is transferred to the membrane separation device 2, and the primary treated water obtained after membrane separation is reverse osmosis through the intermediate tank T3. This refers to the line from the transfer to the membrane 3 to the transfer of the desalted permeated water to the treated water tank T4.

  The chemical washing line is a line for cleaning the membrane separation device 2, and specifically, as shown in FIG. 1, the chemical solution stored in the chemical solution tank T5 is subjected to membrane separation via the chemical supply line L10. This is a circulation line that is transferred to the apparatus 2 and returns the cleaned chemical liquid to the chemical liquid tank T5 again via the chemical recovery line L11.

In the above embodiment, is provided with the D O meter concentration drain line L7, not particularly limited, the path of the permeate and / or retentate is separated by a reverse osmosis membrane 3 (for example, L5, L6 , L12, etc.). The reducing agent is added before membrane filtration, but may be replenished in the subsequent process. Although the present invention has been described above, the present invention is not construed as being limited to these and the examples described below, and various modifications and changes can be made based on the knowledge of those skilled in the art without departing from the scope of the present invention. It is possible to make corrections and improvements.

  In this example, sodium metasilicate pentahydrate, kaolin, ferrous chloride tetrahydrate, manganese (II) chloride tetrahydrate, silica dispersant (GE MSI300) in the ground water (well water). , Name sugar apple tea (powdered black tea) manufactured by Meisho Sangyo Co., Ltd. is added as an organic substance, pH = 6.7-7.3, silica concentration 50 mg / L, kaolin concentration 50 mg / L, iron concentration 1 mg / L Simulated raw water prepared to have a manganese concentration of 50 mg / L, a TOC concentration of 3 mg / L, and a silica dispersant concentration of 3 mg / L was used as the feed raw water.

  In this example, drinking water for groundwater was formed under the following conditions according to the flow shown in FIG.

  First, when water flow is started, as a preparatory operation, tap water is supplied and stored in the intermediate tank T3 from a supply line (not shown), and then the pretreatment pump P1 is operated, and membrane separation is performed from the protective agent supply line L1. The liquid was sent to the primary side of the apparatus 2, and the primary treated water of the obtained MS was collected in the intermediate tank T3 so that tap water could circulate between the intermediate tank T3 and the MS. During the circulation process, the protective agent was set so that the protective agent was supplied from the protective agent tank T1 to the protective agent supply line L1 by the protective agent pump P2 as necessary.

  Here, the membrane separator 2 was an ultrafiltration membrane “Well Pure S” manufactured by Welsey. In addition, the protective agent was 80 g / L of hydrous kaolin ASP200 (average particle size 0.4 μm) manufactured by Hayashi Kasei Co., Ltd., and the protective agent was injected in a state where the membrane separator 2 was circulated and passed through. A protective layer was provided on the primary side, and it was confirmed that the flow rate and differential pressure did not change and were used for the experiment.

Next, the prepared raw water is transferred from the well pump P3 to the membrane separation device 2 via the raw water supply line L2, and at that time, the reducing agent is supplied to the raw water supply line L2 from the reducing agent tank T2 using the first reducing agent pump P4. Injected. Concentrated waste water after desalting by the reverse osmosis membrane 3 was measured with a dissolved oxygen meter 4 and the amount of reducing agent injected was controlled according to the measured value obtained. Here, the dissolved oxygen meter 4 is an industrial dissolved oxygen meter manufactured by HORIBA Advanced Techno Co., Ltd. (model name: HD-480, measurement method: galvanic cell method, resolution 0.01 mg / L, repeatability ± 0.5%) , Linearity ± 0.5%) was used.
The MS treated water obtained was stored in the intermediate tank T3 via the primary treated water feed line L3. Here, the membrane separation apparatus 2 was set so that water could be passed at a membrane filtration flow rate of 2.4 m / day.

  Next, this treated water is supplied from the intermediate tank T3 to the reverse osmosis membrane 3 through the primary treated water supply line L4 by the booster pump P5, and the obtained advanced treated water is measured by the conductivity meter (CD) 5. The water was stored in the treated water tank T4 via the treated water line L5 under the condition of 70 μS / cm or less, and returned to the intermediate tank T3 via the treated water circulation line L12 under the condition exceeding 70 μS / cm.

A part of the concentrated water was supplied to the booster pump P5 through the circulation line L6, and the rest was drained through the concentrated drain line L7.
Here, as the RO apparatus 3, BW30-4040 manufactured by Dow was used, and the recovery rate was set to be 75%.

  When the flow of the membrane separation device 2 reaches a predetermined time, the primary treated water is supplied from the intermediate tank T3 to the secondary side of the membrane separation device 2 via the reverse water flow line L8 by the booster pump P5. It was set so that it could be discharged from the drain line L9. The backwash conditions were set so that water flow could be resumed after backwashing at an arbitrary flow rate for 60 seconds.

Furthermore, it set so that a chemical | medical agent washing | cleaning could be implemented when the liquid flow of the membrane separator 2 reached | attained predetermined time. First, the raw water in the membrane separation device 2 is discharged from the drain line L9, and then the cleaning chemical solution is supplied from the chemical solution tank T5 to the primary side of the membrane separation device 2 through the chemical supply line L10 by the chemical solution supply pump P6. At that time, an arbitrary amount of acid can be injected into the chemical washing line from the acid tank T6 by the acid pump P7, and an arbitrary amount of reducing agent can be injected from the reducing agent tank T2 by the second reducing agent pump P8. Set to.
This chemical solution was recovered from the chemical recovery line L11 to the chemical solution tank T5 and set so that the chemical solution could be circulated for an arbitrary time.
Here, 20% sodium bisulfite was used as the reducing agent, and citric acid was used at 0.1% as the acid.

The amount of reducing agent injected into the raw feed water was controlled so that the dissolved oxygen concentration in the concentrated wastewater was kept almost stable at 0 mg / L, and water was supplied. In addition, although the actual concentration of dissolved oxygen instantaneously increased dissolved oxygen concentration exceeding 0.1 mg / L within 120 seconds due to the switching of the treatment process, the average calculated every hour was 0 in all cases. 0.02 mg / L (maximum value other than momentary increase was 0.08 mg / L). In addition, the reverse flow of the ultrafiltration membrane is evaluated under the conditions that the water flow time during normal operation (water treatment operation) is performed after 1, 3, 6, 12, 24 hours have passed, respectively. Washing was performed every day.
Here, the time-dependent change of the differential pressure in the various reverse water flow intervals implemented in Example 1 is shown in FIG.

From FIG. 2, it can be confirmed that the differential pressure of the ultrafiltration membrane increases as the water passage time becomes longer as 1, 3, 6, 12, 24 hours. It can be confirmed that the membrane differential pressure has recovered to about 0.02 MPa, which is the same level as in the initial stage of water flow.
From this, the amount of dissolved oxygen from the raw feed water to the concentrated drainage water after reverse water flow is controlled at 0 mg / L, and a protective layer is provided on the surface of the microfiltration membrane or ultrafiltration membrane, thereby reducing the membrane differential pressure. It was confirmed that it was possible to reduce the rise and reduce the frequency of reverse water flow. Furthermore, by carrying out chemical cleaning regularly, it was possible to recover the initial differential pressure, and this result proved the effect of the present invention. In this embodiment, chemical cleaning is performed once a day (every 24 hours), but it is possible to extend the cleaning interval in consideration of the well raw water state and the increase in membrane differential pressure.

Comparative Example 1

In Comparative Example 1, the amount of the reducing agent injected is an amount corresponding to the dissolved oxygen concentration in the feed raw water, and the dissolved oxygen concentration including the state where the dissolved oxygen concentration in the RO concentrated waste water continues to be 0.2 mg / L or more. Water was passed and regenerated under conditions where removal could not be sufficient, and the conditions were the same as in Example 1 except that the frequency of reverse water passing through the ultrafiltration membrane was set as follows.
In Comparative Example 1, the ultrafiltration membrane holds the protective agent and allows water to pass therethrough.
Moreover, the reverse water flow of the ultrafiltration membrane was evaluated under the condition that the water flow time was 6 hours later, and the chemical cleaning was performed every day.
Here, FIG. 3 shows the change with time of the differential pressure of the ultrafiltration membrane carried out in Comparative Example 1, and FIG. 4 shows the change with time of the dissolved oxygen in the concentrated waste water.

  As shown in FIGS. 3 and 4, when the dissolved oxygen concentration in the concentrated effluent of the reverse osmosis membrane 3 once rises continuously, the ultrafiltration membrane can be removed even if reverse flow is performed thereafter. The pressure difference could hardly be recovered. Further, when the operation was continued without eliminating the differential pressure even by reverse water flow, it was confirmed that the differential pressure of the ultrafiltration membrane increased by 0.12 MPa relative to the initial differential pressure after 24 hours. Thus, since the differential pressure rises in a very short time, it is necessary to perform chemical cleaning several times a day, and the apparatus must be stopped during that time. In addition, it can be seen that stable operation cannot be achieved, for example, the blockage proceeds at a speed higher than expected.

Comparative Example 2

In Comparative Example 2, the operation was carried out under the condition that the protective agent was not retained in the ultrafiltration membrane, and the reverse water flow frequency of the ultrafiltration membrane was changed to the following, similarly to the conditions in Example 1. Carried out.
Moreover, the reverse water flow of the ultrafiltration membrane was evaluated under the condition that the water flow time of normal operation was performed after 6 hours passed, and the chemical cleaning was performed every day.
Here, the time-dependent change in the differential pressure of the ultrafiltration membrane carried out in Comparative Example 2 is shown in FIG.

From FIG. 5, when operating under the condition that the dissolved oxygen concentration in the concentrated effluent of the reverse osmosis membrane 3 is maintained at around 0 mg / L (maximum 0.62 mg / L), the ultrafiltration membrane differential pressure is 24 hours later. The initial differential pressure increased by 0.04 MPa, and even after chemical cleaning, it recovered only to 0.04 MPa. Subsequently, when water flow was carried out, the membrane differential pressure exceeded 0.2 MPa after 37 hours.
It was confirmed that this ultrafiltration membrane did not recover to the initial differential pressure after passing the chemical for the first time and did not recover at all after the chemical cleaning for 10 days. did.

In Example 2, evaluation was performed under the same conditions as in Example 1 except that the frequency of reverse water flow was once every 6 hours.
Here, the time-dependent change in pressure difference of the ultrafiltration membrane carried out in Example 2 is shown in FIG. 6, the time-dependent change in dissolved oxygen in the concentrated effluent of the reverse osmosis membrane is shown in FIG. 8 shows the change over time in the conductivity of the reverse osmosis membrane treated water, and FIG. 9 shows the quality of the feed raw water, ultrafiltration membrane treated water, and reverse osmosis membrane treated water, respectively. The water quality was measured in accordance with Ministry of Health, Labor and Welfare Notification No. 261.

From FIG. 6 and FIG. 7, even if the raw well water containing soluble and insoluble metal components is directly ultrafiltered, the dissolved oxygen is maintained at around 0 mg / L (maximum 0.02 mg / L), and the ultrafiltration membrane It can be seen that by performing the operation under the condition that the protective agent is retained on the surface, the ultrafiltration membrane differential pressure is suppressed and the stable operation can be achieved.
Even in this continuous operation, the differential pressure of the ultrafiltration membrane recovers to the initial differential pressure after water washing, and stable operation is possible for a water passage period of 3 months. It was confirmed that the initial differential pressure after the test was 0.02 MPa, which is similar to that immediately after the start of water flow.

  Further, from FIG. 8, FIG. 9 and Table 1, the membrane differential pressure of the reverse osmosis membrane 3 used in the subsequent treatment and the water quality of the RO treated water are constant, and various soluble ions and organic substances are removed. It was confirmed that it can be applied to drinking water treatment because it meets legal standards.

Furthermore, even if the rinse solution after chemical cleaning is supplied to the reverse osmosis membrane, the maximum conductivity of the RO treated water is confirmed to be 70 μS / cm, and the treated water with a minimum of 20 μS / cm and an average of 32 μS / cm is stable. It was confirmed that it was obtained.
These provide a system and an apparatus capable of directly ultrafiltration or microfiltration of well raw water and capable of stably treating the well water, and the results proved the effect of the present invention.

  FIG. 1 is a flowchart showing an embodiment of the water treatment method of the present invention.   FIG. 2 is a graph showing the change over time in the differential pressure of the ultrafiltration membrane in Example 1.   FIG. 3 is a graph showing the change over time in the differential pressure of the ultrafiltration membrane in Comparative Example 1.   FIG. 4 is a graph showing the change with time of dissolved oxygen in the concentrated water in Comparative Example 1.   FIG. 5 is a graph showing the change over time in the differential pressure of the ultrafiltration membrane in Comparative Example 2.   6 is a graph showing the change over time in the differential pressure of the ultrafiltration membrane in Example 2. FIG.   FIG. 7 is a graph showing the change with time of dissolved oxygen in the concentrated water in Example 2.   FIG. 8 is a graph showing the change over time in the differential pressure of the reverse osmosis membrane in Example 2.   FIG. 9 is a graph showing the change with time of the conductivity of the reverse osmosis membrane in Example 2.

Explanation of symbols

1 well 2 membrane separator (MS)
3 Reverse osmosis membrane (RO)
4 dissolved oxygen meter (DO)
5 Conductivity meter (CD)
L1 Protective agent supply line L2 Raw water supply line L3 Primary treated water feed line L4 Primary treated water supply line L5 Treated water line L6 Circulation line L7 Concentrated drainage line L8 Reverse drainage line L9 Drainage line L10 Chemical supply line L11 Chemical recovery Line L12 Treated water circulation line P1 Pretreatment pump P2 Protective agent pump P3 Well pump P4 First reducing agent pump P5 Booster pump P6 Chemical supply pump P7 Acid pump P8 Second reducing agent pump T1 Protecting agent tank T2 Reducing agent tank T3 Intermediate Tank T4 Treated water tank T5 Chemical tank T6 Acid tank

Claims (3)

A method in which water to be treated containing metal ions and insoluble substances is subjected to membrane filtration treatment with a microfiltration membrane or ultrafiltration membrane holding a precoat agent to remove insoluble substances, and then desalted using a reverse osmosis membrane. There,
Sodium bisulfite is added to the raw water pumped up from the well as the water to be treated, the dissolved oxygen in the water to be treated is substantially removed, and oxidation and precipitation of metal ions is suppressed, and the membrane filtration treatment and desorption are performed. The water treatment method characterized by performing salt treatment. The water treatment method according to claim 1, wherein the sodium bisulfite is added so that dissolved oxygen is not substantially contained in the concentrated water and / or permeated water accompanying the desalting treatment. The said sodium bisulfite is added more than the theoretical amount required for reaction with the dissolved oxygen in the said to-be-processed water, and the oxygen newly melt | dissolved by the said desalination process, The Claim 1 or Claim 2 characterized by the above-mentioned. Water treatment method described

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