JP2003094058A - Method for treating water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method requiring only a low power and enabling to suppress membrane fouling in spite of applying dead-end filtration. SOLUTION: In the water treatment method carried out filtration by supplying a liquid to be treated from a storage tank to an internal pressure type hollow fiber membrane module, the water treatment method is carried out by filtration of the liquid to be treated by the dead-end filtration through supplying the liquid to be treated from the lower end side of a membrane of the internal pressure type hollow fiber membrane module disposed longitudinally, and operated by a transmembrane pressure difference in filtration in the range of 1 to 20 kPa and further at a constant transmembrane pressure difference.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water treatment method using an internal pressure type hollow fiber membrane module.

[0002]

2. Description of the Related Art Filtration methods using a hollow fiber membrane module are roughly classified into cross-flow filtration and dead end (total volume) filtration.
Cross-flow filtration gives the same linear velocity as the liquid to be treated from the supply side of the liquid to be treated of the membrane module to the concentration side, and circulates the liquid while removing the fouling substances accumulated on the membrane surface or inside the membrane by the liquid linear velocity. This is a partial filtration method in which filtration is performed. The dead end filtration is a method in which the concentrated liquid outlet side of the membrane module is closed and all the liquid to be treated that has entered the membrane module is filtered without circulating the liquid.

Generally, the cross-flow filtration has an advantage that the fouling of the membrane is suppressed by the liquid linear velocity, but on the other hand, it has a disadvantage that the power required for the filtration is large because the liquid is circulated. On the contrary, the dead-end filtration is While it has the advantage of requiring less power, it has the drawback of significantly fouling the membrane. Fouling is a phenomenon in which the structure of the film itself does not change, but the function of the film deteriorates due to clogging or the formation of an adhesion layer.

The present invention is a water treatment method using a hollow fiber membrane, which can be operated at low cost and with low power and can reduce membrane fouling, so that high membrane separation performance can be maintained for a long period of time. The challenge is to provide the law.

[0005]

The present inventor has found that the above problems can be solved by applying dead end filtration to water treatment by an internal pressure type hollow fiber membrane and performing filtration operation at low pressure and constant pressure. Completed the invention.

That is, the present invention is, as a means for solving the above problems, a water treatment method in which a liquid to be treated is sent from a storage tank to an internal pressure type hollow fiber membrane module for filtration, and the liquid to be treated is vertically filtered. The internal pressure type hollow fiber membrane module installed in the above is fed from the lower end side of the membrane to perform dead end filtration, and the transmembrane pressure difference during filtration is in the range of 1 to 20 kPa, and the operation is performed at a constant transmembrane pressure difference. A water treatment method is provided.

[0007]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram showing a treatment flow for explaining the water treatment method of the present invention. The present invention is shown in FIG.
It is not limited to the processing flow shown in (1), and other processing steps usually performed by those skilled in the art can be added if necessary.

The liquid to be treated which has been sent from the raw water supply line 10 to the storage tank 1 is agglomerated with the aggregating agent as it is or according to the concentration of suspended solids (SS) in the liquid to be treated and the size of SS. After that, the liquid is fed to the lower end side of the membrane of the internal pressure type hollow fiber membrane module 2 installed vertically through the liquid to be treated supply line 11. At this time, it is desirable that the liquid transfer from the storage tank 1 to the hollow fiber membrane module 2 uses the head difference because the filtration operation is performed at a low pressure and a constant pressure. 7
Is an on-off valve (flow control valve).

As the aggregating agent, an inorganic aggregating agent, an organic aggregating agent or a combination of these may be used.

Examples of the inorganic flocculant include polyaluminum chloride, polyiron chloride, ferric sulfate, aluminum sulfate, bentonite and the like.

Examples of the organic coagulant include polyacrylamide, cationic polyacrylamide, cationic poly (meth) acrylic acid ester, polyamine, polydicyandiamide, low molecular organic amine, sodium polyacrylate, anionic polyamine. Examples thereof include nonionic, cationic, anionic polymers such as (meth) acrylic acid ester-based and anionic polyacrylamide-based or low-molecular aggregating agents.

Examples of the hollow fiber membrane 5 used in the internal pressure type hollow fiber membrane module 2 include cellulose acetate type hollow fiber membranes, polysulfone type hollow fiber membranes, polyacrylonitrile type hollow fiber membranes, and the like. From the viewpoint that it is easy to suppress fouling, the cellulose acetate-based hollow fiber membrane is preferable, and those having a smaller pore size on the inner surface side than the pores on the outer surface side are suitable as the internal pressure type.

The structure of the hollow fiber membrane module 2 is not particularly limited as long as it has at least one liquid feed port for the liquid to be treated at the lower end side of the hollow fiber membrane module installed vertically. The discharge port can be provided if necessary.
Preferably, the hollow fiber membrane has a one-end sealing structure in which the upper end side is sealed, and at least one permeate outlet may be provided in the body.

In the internal pressure type hollow fiber membrane module 2,
Dead-end filtration is performed under a predetermined condition, and the permeated liquid is sent from the permeated liquid line 12 to the permeated liquid tank 3 and stored therein.

In the dead end filtration, the concentrated liquid is not discharged, and the one-way discharge of the permeated liquid to the permeated liquid line 12 is carried out within the range of the transmembrane pressure difference of 1 to 20 kPa and constant.

The transmembrane pressure difference is determined by the height difference (Δh) between the liquid level of the storage tank 1 and the outlet of the permeate line 12 from the hollow fiber membrane module 2 and the internal liquid pressure loss of the hollow fiber membrane module 2. As described above, it is desirable to send the liquid to be treated by utilizing the head difference between the storage tank 1 and the hollow fiber membrane module 2. However, when the viscosity of the liquid to be treated is high or when the inner diameter of the hollow fiber membrane that constitutes the hollow fiber membrane module is small, the pressure loss inside the hollow fiber membrane becomes too high, and therefore the liquid feed pump 6 is used. Then, the transmembrane pressure can be adjusted by sending the liquid.

The transmembrane pressure difference is 1 to 20 kPa, preferably 1
It is ~ 15 kPa. When the transmembrane pressure difference is 1 kPa or more, the water permeation rate required for practical use can be maintained,
When it is 20 kPa or less, clogging of the membrane can be prevented, and a stable water permeation rate can be obtained for a long period of time.

Further, when the transmembrane pressure difference is not constant, the filtration performance becomes unstable and the permeation rate varies, which makes it difficult to control the filtration operation, and the turbidity and COD of the permeate also vary. Will be difficult to reuse.

It is desirable that the transmembrane pressure be kept constant in the same case. However, considering the actual condition of the filtration operation, the range which does not impair the object of the present invention is ± 20%.
It also includes the case where there is an error of about ± 10%.

The method for maintaining the transmembrane pressure difference constant is not particularly limited, and the method of providing the pressure reducing valve 9 in the permeate line 12 is simple, and when the liquid feed pump 6 is used, the inverter system is used. The method of changing the number of rotations according to the pressure fluctuation is applied by using the pump.

In this way, the low pressure (transmembrane pressure difference is 1-2
By operating the filtration at 0 kPa) and at a constant pressure (the transmembrane pressure difference is constant), low power operation can be performed.
Since it is not necessary to consider the pressure resistance of the device as compared with the case of high pressure operation, the cost required for the device can be reduced. Further, by performing the constant pressure operation, it is possible to suppress the fouling of the membrane, which was conspicuous in the dead end filtration, as compared with the case where the fixed amount operation is applied.

In the course of the filtration operation, it is desirable to carry out back pressure washing with water or air periodically in order to maintain the filtration capacity.

When water is used as the back pressure cleaning medium, the permeate tank 3 is activated by operating the back pressure pump 16.
The permeated liquid in the back pressure cleaning line 15 and the permeated liquid line 12
After that, the hollow fiber membrane module 2 is press-fitted from the permeated liquid outlet (permeated liquid line 12) side. Then, the hollow fiber membrane is back-pressure washed and the on-off valve 18 is operated to discharge the concentrate from the concentrate discharge line 13 to the outside of the system, or to return the concentrate from the concentrate return line 13 to the storage tank 1. .

At the time of back pressure cleaning, it is desirable to operate the pump 17 to mix the chemical liquid in the chemical liquid tank 4 with the permeated liquid in order to enhance the cleaning power. Examples of the chemical solution include an aqueous solution of sodium hypochlorite, and the addition amount of the chemical solution is
When a sodium hypochlorite aqueous solution is used, the residual chlorine concentration in the hollow fiber membrane after back pressure washing is 5 to 100 mg.
Adjust to become / L.

The water treatment method of the present invention is a treatment of wastewater containing activated sludge, etc. in wastewater treatment plants, wastewater of various facilities and domestic wastewater, wastewater containing other suspended solids, and further purification treatment of rivers, lakes and marshes. Etc. can be applied.

[0026]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by these examples.

Example 1 Water treatment was carried out by the following method according to the treatment flow shown in FIG. Activated sludge treated water was used as water to be treated. The water to be treated was sent from the storage tank 1 to the hollow fiber membrane module 2 with a water head difference (Δh = about 1 m), and dead end filtration was performed with the hollow fiber membrane module having a membrane area of 0.5 m ² . As the hollow fiber membrane, a cellulose acetate hollow fiber membrane (FUC1582, manufactured by Daicel Chemical Industries, Ltd.) is used, and dead end filtration is
A constant pressure filtration was performed at a transmembrane pressure difference of 10 kPa. In addition,
In the operating time range shown in FIGS. 2 to 4, the storage tank 1
Ferric polysulfate was added therein in an amount of 100 mg / L for aggregation treatment. In addition, once every 30 minutes, by the sodium hypochlorite aqueous solution diluted by being injected into the permeate,
Back pressure washing was performed at 10 m / day for 1 minute.

The actual permeation rate (20
℃, 10kPa conversion value, m / day), turbidity (NTU) in the water to be treated and permeate was measured, and COD in the water to be treated and permeate was measured once every several weeks (mg / day). L) measured, total nitrogen (TN) concentration (mg / L), total phosphorus (T-
P) Concentration (mg / L) for portable analyzer (DR / 201
0, manufactured by HACH). The results are shown in FIGS.

As is apparent from FIGS. 2 to 4, 2000 were measured in all measurement items in both the liquid to be treated and the permeate.
Stability over time was confirmed over a long period of time.

Example 2 As a hollow fiber membrane, a polyether sulfone hollow fiber membrane (FUS
1582, manufactured by Daicel Chemical Industries, Ltd. was used, and filtration operation was performed in the same manner as in Example 1 except that the coagulant treatment was not performed. FIG. 5 shows the change over time in the actual water permeability (m / day).

Example 3 A polyacrylonitrile hollow fiber membrane (FUY) was used as the hollow fiber membrane.
1581, manufactured by Daicel Chemical Industries, Ltd., and filtration operation was performed in the same manner as in Example 1 except that the flocculant treatment was not performed. FIG. 5 shows the change over time in the actual water permeability (m / day).

Comparative Example 1 A filtration operation was performed in the same manner as in Example 1 except that the transmembrane pressure difference was set to 10 kPa and no coagulant treatment was performed. FIG. 5 shows the change over time in the actual water permeability (m / day).

As is clear from FIG. 5, compared with Examples 2 and 3, the water permeability of Comparative Example 1 was low, even though the membrane was operated at a large transmembrane pressure difference.

[0034]

By applying the water treatment method of the present invention, filtration treatment can be performed with low power and low operating cost. Furthermore, while applying dead end filtration,
Since fouling of the membrane can be suppressed, stable filtration capacity can be maintained for a long period of time.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a treatment flow for explaining a water treatment method of the present invention.

FIG. 2 is a diagram showing a measurement result of an actual water permeation rate in Example 1.

FIG. 3 is a view showing a measurement result of turbidity of Example 1.

FIG. 4 is a diagram showing measurement results of COD, TN, and TP in Example 1.

FIG. 5 is a diagram showing measurement results of Examples 2 and 3 and Comparative Example 1.

[Explanation of symbols]

1 Storage tank 2 Internal pressure type hollow fiber membrane module 3 Permeate tank 4 Chemical liquid tank

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shuji Nakatsuka             1239 Daicel New House, Aboshi Ward, Himeji City, Hyogo Prefecture             Chemical Industry Co., Ltd. F-term (reference) 4D006 GA02 HA03 HA95 KA01 KA03                       KB13 KC03 KC13 KC16 KD08                       KD24 KE06R KE22Q KE23Q                       MA01 MC18X MC39X MC62                       MC63X PA01 PB08                 4D015 BA22 BB05 BB08 CA01 CA14                       DA04 DA06 DA13 DA16 DA32                       DB02 DB03 DB12 DB14 DB23                       DB24 DC06 DC07 DC08 EA37

Claims (5)

[Claims] 1. A water treatment method for feeding a liquid to be treated from a storage tank to an internal pressure type hollow fiber membrane module for filtration.
The liquid to be treated is filtered from the lower end side of the internal pressure type hollow fiber membrane module installed vertically by dead end filtration, and the transmembrane pressure difference during filtration is within a range of 1 to 20 kPa and is constant. Water treatment method operating by transmembrane pressure difference. 2. The water treatment method according to claim 1, wherein the liquid transfer from the storage tank to the internal pressure type hollow fiber membrane module utilizes a head difference between the storage tank and the membrane module. 3. The water treatment method according to claim 1, wherein the liquid to be treated is treated with a coagulant as a pretreatment. 4. The water treatment method according to any one of claims 1 to 3, wherein backwashing is periodically performed from the permeate outlet side to discharge the washing wastewater from the lower end side of the internal pressure type hollow fiber membrane module. . 5. The hollow fiber membrane used in the internal pressure type hollow fiber membrane module is a cellulose acetate-based hollow fiber membrane.
The water treatment method according to any one of 1.