JPH03186322A - Reverse washing of membrane separation apparatus - Google Patents

Abstract

PURPOSE:To improve reverse washing efficiency by making a tank airtight and taking out raw water from the inside of the tank to the outside and at the same time making air flowing in by keeping an inner plane of a separation membrane of a membrane set open to air at the time of reverse washing. CONSTITUTION:At the time of reverse washing, supply of raw water 4 through a flowing-in pipe 2 is stopped, a valve 22 is shut, and while a valve 23 of flowing-out pipe 3 is opened, a valve 24 of a branched pipe 27 is opened to air. A valve 25 of a gas discharging pipe 5 is opened, a wastewater pump 26 is started, and raw water in a separation tank 1 is discharged. In this way, the pressure of the separation tank 1 becomes lower than atmospheric pressure and the inside of flowing-out pipe 3 has atmospheric pressure and thus pressure difference is generated between the inside plane and outside planes of a separation membrane 12 and air flows in a flowing route 13 through the branched pipe and flowing-out pipe 3 and passes the separation membrane 12 to the outer plane. By this method, deposit are scaled off and driving cost is lessened.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a flat membrane type water treatment system suitable for water treatment such as sewage recycling, gray water supply, water purification, advanced water treatment, and rainwater utilization. This invention relates to a method for backwashing a membrane separator.

[Conventional technology]

As an advanced treatment method for removing impurities from wastewater, a membrane separation system is often used due to its advantageous manufacturing cost. There are many types of membranes of this type, such as hollow fiber membranes, flat membranes, and tubular membranes, but all of them have the following problems.

That is, when performing separation using a membrane, as filtration progresses, the concentration of separated deposits removed on the membrane surface increases, and filtration resistance increases. Furthermore, if deposits are allowed to remain deposited on the membrane surface, the membrane separation performance will deteriorate.

Therefore, regular backwashing of such separation membranes becomes necessary.For example, in the case of tubular membranes, methods such as inserting a sponge-like ball inside the tube and using the ball to remove dirt adhering to the inner surface of the tube are recommended. For membranes, there are relatively effective methods such as backwashing with air. On the other hand, conventionally, a so-called cross-flow method as shown in FIG. 3 has been adopted as a backwashing method for a flat membrane.
[Problem to be solved by the invention] However, the sludge adhering to the flat membrane is Although there are layers that can be removed relatively easily, there are other layers that are relatively firmly attached to the surface of the membrane and are difficult to remove. This latter layer is difficult to backwash using the conventional cross-flow method, and it is necessary to use an amount of water several times the amount of water that permeates during filtration as backwash water.
There are drawbacks such as high operating costs. Furthermore, if too much water is allowed to flow in during backwashing, there is a risk that the membrane itself or the membrane unit will be deformed by the water pressure.

SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a method for backwashing a separation membrane, which has a high backwashing effect and reduces operating costs during backwashing.

[Means to solve the problem]

The above-mentioned problem is a membrane set including a membrane separation tank, at least one membrane disposed inside the membrane separation tank, a support and a filtrate separation membrane on at least one side of the tank, and a flow path for the filtrate formed between them. and an inflow means for flowing raw water into the membrane separation tank, and an outflow means for filtering the raw water reaching the outer surface of the separation membrane and flowing the filtrate out of the membrane separation tank through the flow path. In a separator: At least during backwashing, the inside of the tank is made airtight, the raw water is forcibly drawn out from the tank, the inside of the tank is brought into a negative pressure state, and the inner surface of the separation membrane of the membrane set is communicated with the outside air. This problem can be solved by causing air to flow from the inner surface to the outer surface of the separation membrane using negative pressure to peel off the deposits.

In addition, it is particularly preferable to repeat the above-mentioned negative pressure action and return pressure in one backwashing process.

[Effect]

In the above membrane separator, according to the present invention, the inside of the tank is made airtight at least during backwashing, the raw water is forcibly drawn out from the tank to the outside of the tank, the inside of the tank is brought into a negative pressure state, and the inner surface of the separation membrane of the membrane set is When the separation membrane is communicated with outside air and the negative pressure causes air to flow from the inner surface to the outer surface of the separation membrane, the deposits are peeled off by this air flow.

On the other hand, a method of flowing clean water from the inner surface to the outer surface of the separation membrane can be considered, but the inventors have found that in this case, the backwashing effect is not as high as that of the method of the present invention. .

[Specific structure of the invention]

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows an overall example of a membrane separator, and FIG. 2 shows a longitudinal section of the jl# set.

The membrane separator includes a membrane separation tank 1, at least one membrane separation membrane 12 disposed inside the membrane separation tank 1, a support 11, a filtration separation membrane 12 on at least one side of the support 11, and a flow path 13 formed between them through which a filtrate passes. A membrane set 10 having a membrane set 10, an inflow means 2 for flowing raw water into the membrane separation tank I, and a flow means 2 for filtering the raw water reaching the outer surface of the separation membrane 12 and causing the filtrate to flow out of the membrane separation tank 1 through a flow path 13. Outflow means 3 are provided.

The membrane separation tank l has a lid IA, which makes it possible to air-tightly seal the inside. In the embodiment, an inflow pipe 2 for raw water 4 is provided on the lid IA, and an outflow pipe 3 for filtrate is provided on the side wall. Backwash drain pipes 5 are attached to the bottom wall so as to communicate with each other inside.

On the other hand, the membrane set IO wraps around the support 11,
A filtration separation membrane 12 made of plastic net, porous fabric, nonwoven fabric, etc. is provided. In the embodiment, two unit separation membranes are arranged on both sides of the support 11, and the periphery is joined by heat sealing using ultrasonic waves or an adhesive.

The support body 11 is made of plastic or the like, and consists of an upper hanging part 11A and a lower net part 11B, and the net part 11B has a grid shape, for example. In addition, the hanging part 1
A through hole 11a is formed in 1A, and this through hole 11a
Discharge guide grooves 11b are formed radially from the thick portion of the hanging portion 11A and communicate with the gap 13 between the support 11 and the separation membrane 12.

Note that the support body 11 does not have to be in the form of a net, and may simply be a plate having no through holes.

On the other hand, the outflow pipe 3 extends horizontally within the membrane separation tank 1, is held by a holder 6 on the side wall, and has a plurality of drainage slits 3a formed at required locations. A plurality of membrane sets 1O11O... are suspended in the outflow pipe 3 in a relatively penetrating state. Each membrane set 10.10
A spacer 7 is interposed between them. Moreover, when the membrane set 10 is suspended on the outflow pipe 3, the above-mentioned discharge guide groove 1
1b communicates with the drainage slit 3a.

In the membrane separator configured in this way, the raw water (water to be treated) 4 is fed by the supply pump 20 through the inflow pipe 2 so that at least the raw water 4 fills the entire membrane set 10 in the membrane separation tank 1. While flowing in, the filtrate is sucked from the outflow pipe 3 by the suction pump 21. As a result, the inside of the outflow pipe 3 is communicated with the flow path 13 via the drainage sleeve 3a and the discharge guide groove 11b, so the pressure on the inner surface of the separation membrane 12 becomes lower than that on the outer surface, creating a pressure difference, and the separation A filtration operation is performed on the membrane 12 surface. The filtrate is led out from the outflow pipe 3 through the channel 13, the discharge guide groove 11b, and the slit 3a.

If such filtration is continued, deposits such as sludge will continue to adhere to the outer surface of the separation membrane 12. Therefore, it is necessary to perform backwashing at an appropriate time.

During this backwashing, the supply of raw water 4 from the inflow pipe 2 is stopped, the valve 22 is closed, the valve 23 of the outflow pipe 3 is left open, and the valve 24 of the branch pipe 27 is opened to release it to the atmosphere. Then, the valve 25 of the drain pipe 5 is opened, the drain pump 26 is started, and the raw water 4 in the separation tank 1 is discharged. As a result, the pressure inside the separation tank 1 becomes lower than atmospheric pressure, and the inside of the outflow pipe 3 is at atmospheric pressure, so a pressure difference is created between the inner and outer surfaces of the separation membrane 12, and air is discharged from the branch pipe and the outflow pipe 3. The air flows into the flow path 13 and escapes to the outer surface of the separation membrane 12. At this time, the deposits adhering to the outer surface of the separation membrane 12 are peeled off and discharged from the drain pipe 5 together with the raw water. Also,
As the raw water 4 is drained, the liquid in the separation tank 1 is fluidized, and this liquid flow also has the effect of peeling off deposits.

On the other hand, as a modified example, in the middle of the - times backwashing process,
Drainage can also be stopped. By this stop, the expanded separation membrane 12 returns to its original position.
During this restoration, the separation membrane 12 moves in a direction perpendicular to its surface, so that the deposits peel off. Thus, by repeating negative pressure and pressure recovery in the separation tank 1 by draining, the -layer peeling effect increases.

If necessary, a compressor (not shown) is installed in the branch pipe 27.
Connect it and let the compressor supply the air,
It is also possible to promote the peeling off of deposits. A specific example of the pressure of this compressed air is atmospheric pressure + 0.3 to 1 kg/c.
Air with a pressure of - degree can be used.

In addition, instead of separately providing the above-mentioned drainage pump 26,
As shown by the phantom line in FIG. 1, the suction pump 21 can be used as a drainage pump.

〔Example〕

Next, to clarify the effect of the present invention through an example, when the backwashing method of the first example was adopted and the membrane separator was continued to operate, it was found that in the conventional example, the membrane set was replaced with a new one in about 10 days. However, it was found that continuous operation can be performed for more than 180 days.

〔Effect of the invention〕

As described above, according to the present invention, effects such as an enhanced backwashing effect and a reduction in operating costs during backwashing are brought about.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing a membrane separator, FIG. 2 is a longitudinal cross-sectional view of an arrangement example of a membrane set group, and FIG. 3 is an explanatory diagram of a conventional backwashing method. l... Membrane separation tank, 2... Inflow pipe (inflow means), 3.
...Outflow pipe (outflow means), 3a...Slit, 5...
- Backwash drain pipe, 10... Membrane set, 11... Support, llb... Discharge guide groove, 12... Separation membrane, 13
...Filtrate channel (interval II), 26...Drainage pump.

Claims (2)

[Claims] (1) A membrane set including a membrane separation tank, at least one membrane set disposed inside the tank, and comprising a support and a filtrate separation membrane on at least one side of the tank, and a flow path for the filtrate to be formed between them. , a membrane separation comprising an inflow means for flowing raw water into the membrane separation tank, and an outflow means for filtering the raw water reaching the outer surface of the separation membrane and flowing the filtrate out of the membrane separation tank through the flow path. In the machine: At least during backwashing, the inside of the tank is made airtight, the raw water is forcibly drawn out from the tank to the outside of the tank, the inside of the tank is brought into a negative pressure state, and the inner surface of the separation membrane of the membrane set is communicated with outside air. A method for backwashing a membrane separator, characterized by causing air to flow from the inner surface to the outer surface of the separation membrane under pressure to remove deposits. (2) The method according to claim 1, wherein the action of negative pressure and the return pressure are repeated in one backwashing process.