JPH0478426A - Membrane separating method and device for liquid - Google Patents

Abstract

PURPOSE:To maintain a high permeation flux over a long period of time and to allow efficient sepn. with good efficiency by providing flow rate sensors in two lines among the liquid inflow, concd. liquid and permeated liquid line of a rotary flat membrane module and controlling the discharge rate of a liquid supply pump via a controller so as to maintain a constant flow rate ratio. CONSTITUTION:The flow rate sensors 5 and 6 are installed respectively in the concd. liquid line 8 and permeated water line of the rotary flat membrane module 3. The signals from the flow rate sensors are taken into a controller 4 and a signal is sent from the controller 4 to a liquid supply pump 2 to vary the discharge rate of the pump. The sludge concn. in the rotary flat membrane module 3 is controlled by the ratio (concn. ratio Qi/Qo) of the discharge rate (Qi) of the pump and the concd. liquid volume (Qo) from the module. The sharp drop of the permeation flux is prevented by controlling the flow rate ratio constant in such a manner. The relatively high permeation flux is thereby maintained over a long period of time.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a liquid membrane separation method and apparatus.

[Conventional technology]

In order to obtain reclaimed water by separating and removing components in various liquids,
In recent years, membrane separation technology has attracted attention. Recently, sewage,
It has been proposed to obtain recycled water by combining biological treatment of liquids containing organic matter such as human waste with membrane separation. The conventional equipment used in this method consists of a biological treatment tank containing a group of microorganisms called activated sludge, and a membrane separation device that separates treated water and activated sludge.

This membrane separation apparatus is composed of a supply pump and a membrane module, and a fixed flat membrane module is mainly used as the membrane module. To perform membrane separation, a biological treatment liquid containing activated sludge is supplied to the membrane module and the treated water is separated, but separation requires pressure, several kg, f
Operate at pressures below /c4. On the other hand, in order to increase the reaction rate in the biological treatment tank, it is efficient to operate the activated sludge at a high concentration. It is known that the value decreases as the value increases.

Furthermore, it is known that suspensions such as activated sludge have a constant permeation flux above a certain pressure, that is, there is a so-called critical flux. Therefore, in such a system, it is inevitable that the permeation flux gradually decreases, and the only way to maintain the permeation flux above a certain level is to perform periodic chemical washing. Moreover, the sludge concentration in the biological treatment tank gradually increases due to growth, so either drain the sludge in the biological treatment tank periodically to lower the sludge concentration at the inlet of the membrane module, or increase the discharge rate of the supply pump. Therefore, it is necessary to control the operation to prevent sludge concentration within the membrane module from proceeding, and all of these methods have problems such as increased labor and power.

[Problems to be Solved by the Invention] The object of the present invention is to provide a membrane separation method for liquids that can eliminate the drawbacks of the prior art, maintain a high permeation flux over a long period of time, and perform efficient separation with low power. The goal is to provide equipment.

[Means for Solving the Problems] The present invention is based on the knowledge that by moving the membrane of a membrane module, the flow velocity on the membrane surface can be obtained, and that the membrane module can be operated with low power. In addition to completing the flat membrane module, we investigated the relationship between the permeation flux of the rotating flat membrane module and the concentration of solutes and suspended solids, and confirmed through experiments that a high permeation flow rate could be obtained within a certain concentration range. the membrane module's liquid inlet line as a means of controlling the concentration of solutes and suspended solids within the membrane module;
Flow rate sensors are provided in two of the concentrated liquid line and the permeated liquid line, and the rotation speed of the supply pump is controlled by a controller so that the flow rate ratio is constant.

That is, the liquid membrane separation method according to the present invention uses a rotating flat membrane module in which a plurality of disc-shaped membrane disks are provided on a hollow rotating shaft as a membrane separation module, and the liquid inflow line and concentrated liquid line of the module are The present invention is characterized in that flow rate sensors are provided in two of the permeate lines and the liquid supply pump discharge amount is controlled via a controller so that the flow rate ratio is constant.

Further, the liquid membrane separation apparatus according to the present invention includes a liquid supply pump, a rotary flat membrane module in which a plurality of disc-shaped membrane disks are provided on a hollow rotating shaft, a liquid inflow line of the module, a fi condensed liquid The present invention is characterized by being provided with a flow rate sensor provided in two of the line and the permeate line, and a controller that controls the discharge amount of the liquid supply pump so that the flow rate ratio is constant based on the signal from the flow rate sensor. .

It is particularly preferable to carry out the method of the present invention in combination with biological treatment of a liquid. In this case, a biological treatment liquid containing activated sludge is supplied from a biological treatment tank to a rotary flat membrane module using a liquid supply pump, and then treated. It can be separated into water and thickened sludge.

The rotating flat membrane module differs from conventional commercially available membrane modules in that it has a structure in which the membrane is moved to obtain a flow velocity on the membrane surface. Therefore, it is possible to operate with lower power than conventional modules. In addition, unlike conventional membrane modules, there is no need to narrow the flow path of the liquid to be treated to create turbulence on the membrane surface, so the rotating flat membrane module used in the present invention can handle highly concentrated suspensions. A feature of this method is that membrane treatment can be performed without pretreatment using a strainer or the like. In conventional membrane modules, for example, fixed flat membrane modules, the flow path for the liquid to be treated is as narrow as 1.5 m.
A strainer of 60 to 100 mesh is required. Moreover, in a liquid containing activated sludge, when the concentration exceeds 60001 g, '42, the liquid viscosity rapidly increases, resulting in a phenomenon in which the permeation flux decreases as the sludge concentration increases. This is shown in FIG. 1 as a conventional fixed flat membrane module. FIG. 1 is a graph showing the relationship between the permeation flux of the membrane module and the sludge concentration.

In order to eliminate the phenomenon of the above-mentioned decrease in permeation flow rate, it is necessary to perform operations such as pulling out sludge and increasing the discharge amount of the supply pump to prevent the sludge concentration from increasing, and to perform periodic chemical cleaning to improve performance. It was necessary to strive for recovery.

On the other hand, as shown in Figure 1, the rotating flat membrane module has a sludge concentration of about 100,001 g/l to 20,000 g/l.
, #! It has been found through experiments that the permeation flux significantly increases when This indicates that the shear stress between the membrane surface and the sludge acts in a manner different from that of conventional modules, and is a major feature of the rotating flat membrane module. In particular, the ability to obtain a high permeation flux even with highly concentrated sludge is not only economical for membrane separation equipment, but also reduces the sludge concentration in the biological treatment tank to 6,000 μm in a system using a conventional module. In contrast, in a system using a rotating flat membrane module, the sludge concentration in the biological treatment tank must be kept at around 600%.
0■/! This brings about the advantage that the sludge concentration in the rotary flat membrane module can be increased to 1000 to 20000+ g/f, leading to more efficient and more compact biological treatment.

In the method of the present invention, activated sludge proliferates in the biological treatment tank, and if left as it is, the sludge concentration will increase.
It is preferable to periodically draw the sludge out of the tank and maintain the sludge concentration almost constant.

〔Example〕

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

FIG. 2 is a system diagram of a membrane separation device showing an embodiment of the present invention, and this device includes a biological treatment tank 1 and a liquid supply pump 2.
, a rotating flat membrane module 3, a controller 4, and flow rate sensors 5 and 6.

The biological treatment tank 1 is provided with a raw water inflow pipe 7, a sludge concentrate return pipe 8, and an air introduction pipe 9. A rotating flat membrane module 3 is supplied from the bottom of the biological treatment tank 1 via a liquid supply pump 2.
0-rotation flat membrane module 3 to which activated sludge-containing liquid is supplied to
is a system in which multiple disk-shaped membrane disks are set on a hollow rotating shaft, and the water that permeates through the membrane is collected within the hollow rotating shaft.
Zero rotation flat membrane module 3 discharged as treated water outside the system
may be uniaxial, but it is more preferable to have biaxial structure in which the membrane disks are interlocked.

Flow rate sensors 5 and 6 are installed in the I-liquid liquid line 8 and the permeated water line of the rotating flat membrane module 3, respectively. Signals from these flow rate sensors are input to the controller 4, and signals are sent from the controller 4 to the liquid supply pump 2 to change the discharge amount of the pump.

The sludge concentration in the rotary flat membrane module 3 is controlled by the ratio (concentration ratio Qi/Q) between the discharge amount of the pump (Q8) and the amount of concentrated liquid (Qo) from the module. If the permeate flow rate (Q,), that is, the permeate flux of the membrane decreases due to contamination or pressure drop, Q is constant, so Qo
increases, and as a result, Qi/Q decreases, that is, the sludge concentration within the rotating flat membrane module 3 decreases.
Below arrow A in FIG. 1, a phenomenon occurs in which the permeation flux further decreases. When it is above arrow A, Q decreases, and even if the sludge concentration decreases, the permeation flux recovers, but the operation becomes unstable. In order to solve this problem, even if Q decreases, Q
It is necessary to control Ql so that i/Q is constant, and by reading this from the flow rate sensor and the signal, the rotation speed of the liquid supply pump 2 is changed to adjust the discharge amount to Q,
control. It is also possible to measure Q and Q and control the pump discharge amount Q1.

In addition, since the discharge amount Q of the pump is Qp + Qo, (
Qp+Q, )/Q, = Qp/Q, +1, and the flow rate of permeated water and the amount of concentrated liquid may be measured by flow rate sensors 5 and 6, and the flow rate ratio may be controlled via the controller 4 based on the signals. . By controlling the flow rate ratio to be constant in this manner, a sudden drop in permeation flux can be prevented, and a relatively high permeation flux can be maintained for a long period of time.

The discharge amount of the liquid supply pump 2 is kept at a concentration ratio of about 1.1 or less, since in conventional modules, the permeation flux decreases as the concentration increases, and the sludge concentration is 600.
Operation management is in place to ensure that the temperature does not exceed 0g#. On the other hand, in the rotating flat membrane module, as mentioned above, the
0011g/I! , In operation at high concentrations,
Because it has the characteristic of high permeation flux, the sludge concentration in the biological treatment tank when using conventional modules is
The concentration ratio can be increased to about twice or more, and operation can be performed in which the discharge lid of the liquid supply pump 2 is closed to 115, leading to a large reduction in power. Moreover, higher permeation flux can be obtained than in conventional modules.

FIG. 3 shows another embodiment of the present invention, which differs from the previous embodiment in that a treated water withdrawal pump is installed in the treated water line.
By providing 0, according to this embodiment, the amount of permeated water can be drawn out at a constant rate without being affected by fluctuations in water temperature.

FIG. 4 shows another embodiment of the present invention, which differs from the previous embodiment in that the biological treatment tank is replaced with an anaerobic tank 11 and an aerobic tank. !
It is divided into 12 parts, and is configured to be able to process not only BOD components but also nitrogen bone. When using a conventional membrane module, the amount of concentrated liquid returned was too large and the anaerobic degree in the anaerobic tank could not be maintained sufficiently. However, in the example shown in Fig. 4, fIA Because the amount of liquid condensate is small and the concentrated sludge is returned, a higher degree of anaerobicity is maintained, making it possible to remove nitrogen at a higher level with less power.

Although the drawings show an embodiment in which the membrane separation device of the present invention is applied to separation of biological treatment liquids, the membrane separation method and device of the present invention can also be suitably applied to membrane separation of other liquids.

Further, the amount of water to be treated in the present invention needs to be approximately equal to the amount of inflow of raw water, but this condition can be met by appropriately designing the membrane area at the initial design stage. Operational fluctuation factors, such as changes in permeation flux due to changes in water temperature due to changes in outside air temperature, can be addressed by changing the operating pressure within the rotating flat membrane module.

As a specific means for this, the simplest method is to control the back pressure on the concentrate side. Therefore, a back pressure valve or the like can be provided.

Example 1 The sludge concentration in the biological treatment tank was set to 80,001 g/n, and membrane separation was performed using the apparatus shown in Fig. 2 using a rotating flat membrane module equipped with 24 polysulfone flat membranes with a membrane disk diameter of 500 pupils. . When I set the concentration ratio to 2.0 times, the pump discharged! 181/min, operating pressure 0.8kg, f/cd
At that time, the permeation flux was 1.6 ho/bo・d. In the conventional fixed flat membrane module, in order to increase the concentration ratio to 1.1 times, the pump discharge rate was 401/min and the operating pressure was 1.0 kg-
At f/Ci, the permeation flux was 0.95 Bo/dd.

Therefore, according to the embodiment of the present invention, the membrane area can be reduced by about 4, and not only the power but also the membrane initial cost can be reduced.

In addition, the permeation flux may change due to changes in the water temperature due to changes in the outside air temperature, and the sludge concentration within the rotating flat membrane module may change due to sludge growth, which may cause the permeation flux to decrease. When we operated the supply pump for a long period of time by changing the discharge rate of the supply pump according to the signal from the flow rate sensor so that the concentration ratio was within 2.0 ± 0.2, the permeation flux was 1 after about 3 months of no cleaning. .6d/n(・d could be maintained.

〔Effect of the invention〕

According to the present invention, even if the solute and suspended solid concentrations in the membrane module are increased, a stable permeation flux can be obtained with high permeation flux and low power. Therefore, membrane area can also be saved. Further, the present invention is particularly suitable for membrane separation of a liquid containing activated sludge in combination with biological treatment.

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between sludge concentration in the membrane module and permeation flux, Fig. 2 is a system diagram of a membrane separation device showing one embodiment of the present invention, and Fig. 3 is another embodiment of the present invention. FIG. 4 is a system diagram of a membrane separation apparatus showing yet another embodiment of the present invention. Explanation of symbols 1... Biological treatment tank, 2... 3... Rotating flat membrane module, 5.6... Flow rate sensor 1 Extraction pump, 11... Anaerobic tank, liquid supply pump, 4... Controller, 0...Treatment water puller 12...Aerobic tank

Claims (5)

[Claims] (1) As a membrane module, a rotating flat membrane module in which a plurality of disc-shaped membrane disks are installed on a hollow rotating shaft is used, and two lines of the module's liquid inflow line, concentrated liquid line, and permeated liquid line are used. 1. A method for membrane separation of liquids, characterized in that a flow rate sensor is provided in the membrane, and the discharge amount of a liquid supply pump is controlled via a controller so that the flow rate ratio is constant. (2) Claim 1 wherein the liquid is a biological treatment liquid containing activated sludge.
The membrane separation method for the described liquid. (3) The liquid membrane separation method according to claim 2, wherein the sludge concentration in the rotating flat membrane module is 10,000 to 20,000 mg/l. (4) A liquid supply pump, a rotating flat membrane module with a plurality of disc-shaped membrane disks mounted on a hollow rotating shaft, and two lines of the module's liquid inflow line, concentrated liquid line, and permeated liquid line. 1. A liquid membrane separation device comprising: a flow rate sensor provided in the flow rate sensor; and a controller configured to control the discharge amount of a liquid supply pump so that the flow rate ratio is constant based on a signal from the flow rate sensor. (5) Claim 4, wherein the liquid supply pump is connected to the biological treatment tank, and a sludge concentrate return pipe is provided in the concentrate line of the module.
Membrane separation device for the liquid described.