JPH10249344A - Membrane separator, its operation, activated-sludge treating device and water treating equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the lowering of performance in the initial stage of operation in the case where a separation membrane is dipped in a raw water tank to separate the component in the raw water supplied from a raw water supply means by providing a water supply means for dipping the membrane in a liq. lower in concn. than the raw water. SOLUTION: The raw water is supplied to a raw water tank 1 by a raw water supply means 3, and water is supplied by a water supply means 4. A separation membrane 2 is dipped in the raw water tank 1 so that an intermembrane differential pressure necessary for the separation is obtained by the difference between the liq. level in the tank and the level of the outlet 5 of the water permeated through the membrane 2. Since the raw water to be separated is high in concn., a cleaning means 7 is preferably furnished. Water is supplied to the raw water tank 1 by the water supply means 4 to make the liq. concn. in the tank lower than the concn. of the raw water supplied by the means 3, the membrane 2 is dipped in the raw water tank 1 kept at a low concn. or in the water to obtain a permeated water, then the separator is started, and the lowering of performance is suppressed in the initial stage of operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane separation device used for wastewater treatment and the like, an operation method thereof, an activated sludge treatment device, and a treatment facility.

[0002]

2. Description of the Related Art Regardless of purpose, such as at home, industry, etc., the amount of water used is increasing year by year, and the amount of wastewater is steadily increasing. From the viewpoint of preventing water pollution, wastewater treatment equipment always has a high treatment capacity. Has been requested.

[0003] As a method for treating wastewater, the activated sludge method is currently most widely adopted. Problems associated with the current activated sludge method include difficulty in sludge management and the necessity of a large sedimentation tank for solid-liquid separation of treated water and sludge.

[0004] By using membrane separation for the solid-liquid separation, the sedimentation basin, which has been enlarged as the processing amount increases, can be reduced or reduced. In addition, the activated sludge tank can be downsized and maintained by increasing the concentration of sludge. There are demands for a technology of wastewater treatment using membrane separation because it can be expected to have merits such as improvement in water quality and stability of treated water quality.

[0005] Regarding wastewater treatment, there is a demand for a technique capable of performing a large amount of treatment irrespective of membrane separation, being resistant to fluctuations in inflow wastewater, capable of operating stably for a long period of time, and having a low treatment cost. First, when treating high concentration activated sludge treated water by membrane separation,
At the time of separation, the sludge is deposited on the membrane surface, and the performance tends to deteriorate.

Therefore, a technique of performing solid-liquid separation of the activated sludge treated water by cross-flow operation using a tubular separation membrane has been put to practical use in human waste treatment and the like. In this method, activated sludge treatment water is supplied to a pipe having a separation membrane on the inner wall, pressure is applied between the membranes by narrowing the outlet pressure from the inlet pressure of the pipe, and a predetermined flow rate is applied to the separation membrane surface of the inner wall. Sludge separation is performed while sludge that is applied and accumulates on the membrane surface is washed away. However, in this method, it is necessary to circulate and supply the activated sludge treatment water to the separation membrane, and since the high-concentration activated sludge treatment water has a high viscosity, a large amount of power is required for the circulation and the treatment cost is high. However, it has been a problem that strength is required for the separation membrane.

Recently, a method has been studied in which a separation membrane is immersed in an activated sludge treatment tank, and the permeate side of the separation membrane is depressurized or the permeate outlet is set lower than the liquid level in the tank to separate sludge by a difference in water level. . This technology can be operated while flowing sludge accumulated on the membrane surface by effectively applying an aeration flow for biological treatment to the membrane surface in the activated sludge treatment tank. Technology.

However, since it is used under high-concentration raw water, sludge easily adheres and deposits on the membrane surface, and when a heavy load is applied to the membrane, sludge that has firmly accumulated on the membrane surface can be removed. Disappears. Therefore, when the operation pressure increases due to the operation with a small burden on the membrane, the decrease in the obtained water amount cannot be denied. Therefore, it is important that technology to minimize the adhesion and deposition of sludge on the membrane surface becomes important.

Therefore, if the accumulation of sludge on the membrane surface can be suppressed from the early stage of operation, the operating life of the membrane will be prolonged.
As disclosed in Japanese Patent Publication No. 1141, there is also a technique for suppressing a decrease in membrane performance at the time of starting by gradually increasing the obtained water amount and maintaining the obtained water amount at a constant value when performing a fixed amount operation.

[0010]

However, even if the method of obtaining permeated water at the time of starting is reduced, the method of immersing the separation membrane in the tank is difficult in the method of immersing the separation membrane in a high-concentration activated sludge tank. , Or when supplying high-concentration activated sludge treatment water to the raw water tank containing the separation membrane, the sludge already adhered to the membrane surface when the membrane was immersed in the raw water in the tank. Performance is reduced.

This is because when a high-concentration liquid is supplied to the raw water tank with the permeation side of the separation membrane open at the start of operation, the high-concentration liquid permeates through the membrane surface due to a difference in water level, and sludge starts to adhere to the membrane surface. . If the permeate side of the separation membrane is kept closed, there is no liquid permeation, but when the operation is started (opening of the permeate side or depressurization), the liquid permeates the membrane surface rapidly and sludge starts to deposit and accumulate.

If the separation membrane is immersed while applying an aeration flow, the effect of removing adhering substances can be expected. However, if the permeability and removal performance of the separation membrane are high, the adhesion to the membrane surface under high-concentration raw water is high. Many become strong.

Further, if permeated water is obtained at the start of operation from a separation membrane immersed in high-concentration raw water, adhesion and deposition on the membrane surface is promoted, and the performance is greatly reduced at the beginning of operation.

[0014] Therefore, since high-concentration activated sludge treated water is treated using a separation membrane, sludge adheres to the membrane surface immediately before and immediately after the start of operation, resulting in a deterioration in performance. It is undeniable that the performance decreases with use.However, it is necessary to operate with as little burden on the membrane as possible because the use conditions are severe and the performance of the membrane will be greatly affected even if the performance is very small even if the amount is large. was there.

[0015]

The present invention is basically achieved by the following constitutions in order to solve the above-mentioned problems.

That is, "a membrane separation apparatus for immersing a separation membrane in a raw water tank and separating components in raw water supplied from the raw water supply means has a water supply means for immersion with a liquid having a lower concentration than the raw water. Or a membrane separation device that immerses a separation membrane in a raw water tank and separates components in raw water supplied from raw water supply means when the separation membrane is immersed in raw water. Then, the raw water in the tank is adjusted to a low concentration using a water supply means and immersed, and after obtaining the membrane permeated water, the concentration of the raw water in the tank is increased using the raw water supply means. Method of operating the device. "

By adjusting the concentration of the raw water in the raw water tank or the raw water to be low by using the water supply means provided in the membrane separation apparatus according to the present invention, the separation membrane is immersed in the raw water tank, or the separation in the raw water tank is performed. Occurs when raw water is supplied to the membrane,
Adhesion and deposition of the separation object on the film surface can be suppressed, and performance degradation that occurs at the beginning of operation can be suppressed.

The present invention will be described with reference to the drawings, but is not particularly limited to the drawings. FIG. 1 shows an example of the membrane separation device of the present invention. The size and shape of the raw water tank 1 are not particularly limited as long as the raw water tank 1 can store the separation membrane 2 and can store raw water by the raw water supply means 3 or water by the water supply means 4. As shown in FIG. 2, the separation membrane may be immersed in the existing raw water tank 1, and a water supply means 4 may be provided therein. Further, the bottom of the raw water tank 1 is tapered toward the discharge port, and it is preferable that the raw water tank 1 has a shape capable of easily discharging the raw water, since the work is shortened.

In the membrane separation apparatus, the separation membrane 2 is immersed in a raw water tank 1, and as shown in FIG. 1, the separation between the membranes required for separation is performed based on the difference between the liquid level in the tank and the outlet 5 of the permeated water of the separation membrane. It is preferable to obtain a differential pressure, or to obtain the transmembrane pressure by reducing the pressure by simply connecting the permeate side of the separation membrane to the suction side of the pump 6 or the like as shown in FIG. The combined use of a water level difference and a pump is more preferable because the burden on the pump is small and the treated water can be stably obtained. However, the method is not particularly limited. Since the raw water to be separated has a high concentration, it is more preferable to provide a washing means.

The cleaning means 7 may be a means for generating a circulating flow in the raw water tank 1 by bubbling as shown in FIG. 1 to wash away the deposits on the membrane surface, or as shown in FIG. May be used. A liquid such as a spray may be applied to the surface of the membrane to remove the adhering substance, or the adhering substance may be removed by shaking the membrane by vibrating means such as bubbling provided on the separation membrane. However, it is not particularly limited. The cleaning means 7 may be operated constantly or intermittently, or may be operated when the performance is deteriorated. The driving method is not particularly limited.

The raw water supply means 3 is not particularly limited in form and method as long as it can supply a liquid having a component to be separated into the raw water tank 1. As shown in FIG. 1, a pump may be connected to be communicable with an adjacent liquid tank as shown in FIG. 2, or may be a liquid that flows down from an adjacent liquid tank as shown in FIG. Not something. It is preferable to provide a valve or a valve or the like in the raw water supply means 3 as shown in FIGS. It is more preferable that the raw water tank 1 is provided with an overflow port, or a raw water supply means 3 in conjunction with a ball tap or a level sensor so that the raw water does not overflow from the tank, so that the raw water is not excessively supplied.

The water supply means 4 is only required to supply water into the raw water tank 1 and lower the concentration of the raw water in the tank than the concentration of the raw water supplied from the raw water supply means 3. It is not limited. The present invention can be practiced if it is provided separately from the raw water supply means 3 as shown in FIG. More preferably, as shown in FIG. 4, the connection with the raw water supply means 3 is switchably connected so that the concentration of the raw water supply means 3 and the water supply means 4 can be changed by switching the valves or the valves or adjusting the opening degree. Raw water adjusted to a low level can be supplied directly into the tank.

There are various types of raw water supplied by the raw water supply means 3 depending on the use, and one of the uses is a flocculation treatment solution of wastewater or separation of cells. The higher the concentration of the raw water used, the greater the effect of the present invention, but if the operation is performed with less load on the membrane, it is also preferable to use the raw water with a low concentration. Any raw water containing solids is applicable.
The applications are not particularly limited.

The liquid supplied by the water supply means may be tap water, river water, seawater, or the like. It is also possible to use a liquid obtained by temporarily separating raw water, and there is no particular limitation as long as the concentration of the solid content is lower than that of the raw water. The lower the concentration of the raw water adjusted by the water supply means 4 is, the lower the load on the membrane surface is, and the more preferable, but the concentration is not particularly limited.

It is also possible to use the activated sludge treated water as raw water for an activated sludge treatment apparatus for separating sludge or its equipment. The activated sludge treatment device is provided with an aeration device and performs aerobic microbial treatment to generate activated sludge by using wastewater such as BOD, COD or nitrogen such as domestic wastewater, industrial wastewater, or human waste as a treatment target water. It comprises a tank and a raw water tank for separating the generated activated sludge from the liquid component, and membrane separation is applied to this raw water tank. As means for transferring the water to be treated from the activated sludge tank to the raw water tank, a pipe that naturally flows in may be used, or a pump may be used, but the former is preferable from the viewpoint of energy cost and maintenance.
Further, the sludge that has accumulated in the raw water tank can be taken out from the discharge port and disposed of after further removing water, or can be returned to the conditioning tank or the activated sludge tank for reprocessing. In addition, it is preferable that the activated sludge apparatus is provided as an activated sludge apparatus provided with a process facility for removing dust such as hair and an adjusting tank for keeping the flow rate constant before the activated sludge device.

In the activated sludge apparatus, when the operation is started for the first time, after the membrane is temporarily out of the immersion state due to replacement of the separation membrane module, washing, or other maintenance, etc., the water supply means is used to supply water to the tank. It is preferable to adjust the sludge concentration to 3000 mg / L or less,
More preferably, it is 1000 mg / L or less. The one with the least burden on the membrane is preferable, regardless of whether it is separate or integral with the raw water supply means 3.
Is stopped, and the separation membrane 2 is immersed in water using only the water supply means 4. This is preferable because the sludge (solid content) concentration in the tank can be reduced to almost zero.

If the permeated water is obtained and the operation is started in a state where the separation membrane 2 is immersed in the raw water tank 1 or the water adjusted to a low concentration, the load on the membrane is higher than when the operation is started under the high concentration of the raw water. Is preferred.

The method for operating the membrane separation apparatus of the present invention is to prevent the contamination of the membrane surface which occurs at the beginning of the operation. If the membrane permeated water can be obtained with low-concentration raw water, water supply means 4
May be stopped or closed, and the raw water supply means 3 may be used to increase the concentration in the raw water tank. The acquisition of the membrane permeated water can be performed in a few seconds by using automatic control such as inverter control in the case of quantitative operation. When a water level difference or the like is used, membrane permeated water can be obtained immediately after immersion in the tank. The longer the operation in low concentration raw water or water, the less the burden on the membrane surface. It is also preferable to operate for a long time to check the state, such as checking the operating pressure at the time of acquisition. However, the shorter the time from the start of operation until the input of raw water is more efficient,
If normal operation can be performed, the time is preferably within 10 seconds, but these times are not particularly limited. If a large amount of permeated water is obtained, the adhesion of dirt to the membrane surface is large.
It is preferable to obtain the operating pressure so as to be 50 kPa or less. More preferably, it is 30 kPa, and most preferably, it is 10 kPa or less. Although the amount to be obtained is not particularly limited, the concentration in the tank is 3000 mg.
/ L or less, the amount obtained per membrane area is 0.05 to
1.2 m ³ / m ² is preferred, and 0.2 to 0.5 m ³ / m ² is more preferred.

When the raw water supply means 3 is used to increase the concentration in the tank, it is preferable to supply the raw water at a high concentration suddenly because the concentration in the tank increases rapidly. However, there is no particular limitation as long as the concentration in the tank is increased after obtaining the permeated water.

By using the membrane separation apparatus or its operation method of the present invention, not only when starting a new separation membrane, but also when simply discharging the raw water in the tank or when the function of the separation membrane is restored by a chemical solution. It is also preferred to use.

If the separation membrane 2 is a flat membrane, it has a simple structure, and it is easy to scrape off dirt adhering by a diffused flow. If it is a tubular membrane, it is resistant to pressure, and a hollow fiber membrane can have a large membrane area per unit volume. Good for each. However, the type of film is not particularly limited. However, it is immersed in raw water to obtain permeate, so that the membrane surface with the separation function is in contact with raw water, and the raw water side and the membrane permeate side are sealed in a liquid-tight manner. preferable.
As the separation function, a microfiltration membrane or an ultrafiltration membrane is suitable and most preferable. The microfiltration membrane is a porous membrane having many pores on the membrane surface, and has a pore diameter of 1 to 0.1 μm. The ultrafiltration membrane is also a porous membrane having a large number of pores on the membrane surface, and has a pore diameter of 0.1 to 0.01 μm.

If the driving power is small, a reverse osmosis membrane may be used.
It is preferable to select according to the raw water, but this is not particularly limited. The separation membrane material may be inexpensive as long as it is an organic material. Cellulose acetate, polycarbonate, nitrocellulose as organic materials
, Cellulose, polysulfone, polyethersulfone, polyacrylonitrile, cross-linked polyvinyl alcohol
And polyfluoroethylene, but are not limited thereto. The film structure can also be exemplified by an asymmetric film having a dense layer on at least one surface of the film and gradually having fine pores with a large diameter from the dense layer toward the inside of the film or the other surface. Alternatively, an organic material may be coated on a supporting substrate such as a fiber or a porous body. If it is an inorganic material, it can be semi-permanently maintained in various raw waters which are hardly affected by a chemical solution or the like. It is also preferable to divide the used material into a part expected to be replaced and a part used semi-permanently. However, the material is not particularly limited as long as it has a separation function.

(Embodiment 1) Raw water supply means of the apparatus was treated water (MLSS about 12000 mg / ml) from an activated sludge treatment tank of factory wastewater.
L) using a submersible pump in a raw water tank (1.2 x 0.5 x 1.8 = 1.1
m ³ ) was pumped through a screen (1 mm). The raw water supply means is provided above the raw water tank, the water supply means is provided above the raw water tank separately from the raw water supply means, and a lake water line in a factory is used as the water supply means. The raw water tank is 1.
An overflow port was provided at 6m so that the liquid level could be kept constant. As the separation membrane, a 750 mm long hollow fiber membrane module (membrane area of about 6.5 m ² ) in which 5000 polyacrylonitrile external pressure porous hollow fiber membranes (nominal pore diameter: 0.01 μm, outer diameter: 680 μm, inner diameter: 400 μm) are bundled is used. The hollow fiber membrane module is immersed in the raw water tank, and the permeated side is suctioned by a magnet pump to obtain the permeated water. In addition, a gas is constantly ejected by a diffuser provided in the hollow fiber membrane module to swing the hollow fiber membrane and clean the membrane surface.

First, without operating the submersible pump, the lake water line was opened and the lake water was supplied into the tank. Next, while supplying gas to the air diffuser, the lake was supplied and overflowed from the tank.
The operation was started at a constant value of 5 L / min. Since the permeated water was obtained stably, the submersible pump was operated and the supply of lake water was stopped. After 0.5, 2, 6, and 12 hours, the concentration in the raw water tank and the operating pressure from the pressure gauge before the pump were recorded. The operating pressure after 12 hours was 6.2 kPa.

[0035]

[Table 1] (Example 2) In the same manner as in Example 1, the membrane module was replaced with a new one, the air diffuser was started, the lake water was supplied into the tank, and the raw water was supplied from the point 40 cm up to the overflow port. Both raw waters were supplied. Separation was started at the same flow rate from the time of overflow. About 5 minutes after the start of separation, the supply of lake water was stopped. 0.5,2,
After 6 and 12 hours, the concentration in the raw water tank and the operating pressure from the pressure gauge before the pump were recorded. Operating pressure after 12 hours is 6.2kPa
Met.

[0036]

[Table 2] (Comparative Example 1) A new membrane module was used, the air diffuser was started, raw water was supplied, and after overflow, separation was started at the same flow rate. The operating pressure after 12 hours was 8.8 kPa.

[0037]

[Table 3]

[0038]

According to the present invention, it is possible to provide a membrane separation apparatus and an operation method in which the components of raw water are prevented from adhering to the membrane and the burden on the membrane is reduced.

[Brief description of the drawings]

FIG. 1 shows a membrane separation apparatus of the present invention using a diffuser as a washing means.

FIG. 2 is a membrane separation apparatus of the present invention using stirring as a washing means.

FIG. 3 shows a membrane separation device of the present invention having a structure in which a stock solution flows down from a liquid tank next to the device.

FIG. 4 shows a membrane separation device according to the invention which is switched and connected.

[Explanation of symbols]

 1: Raw water tank 2: Separation membrane 3: Raw water supply means 4: Water supply means 5: Permeated water outlet 6: Pump 7: Cleaning means

Claims (11)

[Claims] 1. A membrane separation apparatus for immersing a separation membrane in a raw water tank and separating components in raw water supplied from the raw water supply means, comprising a water supply means for immersing in a liquid having a lower concentration than the raw water. A membrane separation device characterized by the above-mentioned. 2. The membrane separation apparatus according to claim 1, further comprising a washing means in the separation membrane or the raw water tank. 3. The membrane separation apparatus according to claim 1, further comprising a water supply means separately from the raw water supply means to the raw water tank. 4. The membrane separation device according to claim 1, wherein the raw water supply means and the water supply means for the raw water tank are integrated and switchable. 5. A membrane separation device for immersing a separation membrane in a raw water tank and separating components in raw water supplied from raw water supply means by previously immersing the separation membrane in a liquid having a lower concentration than raw water using water supply means. A method of operating a membrane separation apparatus, wherein the concentration of raw water in a tank is increased using the raw water supply means after obtaining the membrane permeated water. 6. The method for operating a membrane separation device according to claim 5, wherein the raw water is treated activated sludge water. 7. The concentration of a liquid having a concentration lower than that of the raw water is 300.
The method for operating a membrane separation device according to claim 5, wherein the amount is 0 mg / L or less. 8. The method according to claim 1, wherein the separation membrane is immersed in water using only the water supply means, and the concentration of the raw water in the tank is raised using the raw water supply means after obtaining the membrane permeated water. 6. The method for operating the membrane separation device according to 5. 9. The membrane separation method according to claim 5, wherein the water permeated through the membrane is obtained by a difference in water level or a reduced pressure on the permeation side. 10. An activated sludge treatment apparatus using the membrane separation apparatus according to claim 1. 11. A water treatment facility using the membrane separation device according to claim 1.