JPS61200812A - Membrane separation apparatus - Google Patents

Abstract

PURPOSE:To reduce membrane cost by enabling the reutilization of a membrane having become impossible in the recovery of a transmitted water amount even if washing is performed, in a multistage type membrane separation apparatus, by using a membrane, of which the transmitted water amount after washing reached a reference value set so as to be lower than an initial transmitted water amount or less, as the membrane of a post-stage side. CONSTITUTION:The ultrafiltration membranes of ultrafiltration membrane separation apparatuses 1, 2 of respective stages are respectively same in a fractional MW at the time of a new article and the second stage apparatus 2 uses a membrane advance in clogging. The second stage apparatus 2 uses the membrane which was used in the first stage apparatus 1 to generate clogging and of which the transmitted water amount was not recovered up to a preset transmitted water amount as the membrane of the first stage even if washing is performed. By this method, treatment can be performed in the same way as an apparatus wherein membranes gradually reduced in a fractional MW apparently are arranged in a multistage fashion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a membrane separation device, and particularly to a membrane separation device in which multiple membranes are provided for membrane separation treatment of water to be treated.

[Conventional technology]

As a device for obtaining advanced membrane separation treated water.

Devices in which membranes are provided in multiple stages are known.

For example, there is a device in which ultrafiltration membranes with different molecular weight fractions are installed in order of increasing molecular weight fraction, and water is passed through in this order, or reverse osmosis membranes are installed in order of decreasing salt removal rate, and water to be treated is passed in order of decreasing salt removal rate. Devices in which water is passed from a low salt removal rate side to a high salt removal rate side, and devices in which different membranes such as an ultrafiltration membrane and a reverse osmosis membrane are combined are known.

[Problem that the invention seeks to solve]

Maintenance and management of the above-mentioned known devices is extremely complicated because: (1) Multiple membranes or different types of membranes with different removal rates must be prepared; (2) Different types of membranes require different cleaning methods; etc. .

In addition, in general, in membrane separation equipment, when the amount of permeated water in the membrane decreases, it is cleaned and the permeated mercury is recovered and reused, but even after cleaning, the amount of permeated water does not recover to a predetermined value or higher. Sometimes it is necessary to discard it, i.e.
In the above-mentioned known apparatus, there is also the problem that (1) a membrane whose permeated water amount has not recovered cannot be reused, so that the membrane cost becomes correspondingly high.

[Means for solving problems]

The present invention is a multi-stage membrane separation device in which membranes are provided in multiple stages and the liquid that has permeated through the membrane on the front stage is supplied to the membrane on the rear stage. This method uses a membrane that has not fully recovered.

[Effect]

In the present invention, membranes whose permeated water volume is no longer fully recovered even after cleaning can be reused, and thus the membrane cost is reduced.

Moreover, according to the apparatus of the present invention, it is possible to improve the quality of treated water. That is, the present inventors conducted various studies on water treatment devices using membranes and found the following points.

When water to be treated is subjected to membrane separation treatment, the membrane becomes clogged over time, and the amount of permeated water gradually decreases. On the other hand, as the clogging progresses, the removal rate of the membrane increases. Compared to a filtration membrane, it appears better in appearance and behaves with a lower molecular weight cutoff.

In addition, a reverse osmosis membrane that has become clogged similarly exhibits behavior in which the salt removal rate is increased, although it appears to be better.

Therefore, as in the present invention, if a membrane is used in the latter stage where the amount of permeated water does not recover sufficiently even after cleaning and the membrane is clogged, the membranes are installed in order of decreasing removal rate. It is possible to perform multi-stage membrane treatment similar to an apparatus in which water to be treated is sequentially passed through and subjected to membrane separation treatment, and the quality of the treated water is improved.

In addition, when using a membrane that has become clogged in this way, it is not necessary to use one type of membrane or membranes with different removal rates, and it is sufficient to prepare only one type of membrane.

Further, various experiments have shown that contaminants adhering to the second stage (or later) membranes are easier to remove than the first stage membranes, and that they can be washed and used repeatedly.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a system diagram of a membrane separation device according to an embodiment of the present invention. In FIG. Water is pipe 1a
The water is supplied to the second stage ultrafiltration membrane separation device 2 through the filter. The permeated water from the second-stage ultrafiltration membrane separation device is taken out from pipe 2a and sent to a discharge process, reuse process, etc. 4 in the figure is a wastewater tank for receiving wastewater, which is the water to be treated. It is connected to the $1st stage membrane separator l via piping 4a. Further, pipes 1b and 2b for taking out concentrated water from the ultrafiltration membrane separation devices 1 to 3 are connected to this wastewater tank 4.

Therefore, the ultrafiltration membranes used in each stage of the ultrafiltration membrane separation device (hereinafter sometimes simply referred to as the device) 1.2 have the same molecular weight cutoff when new. , second
The membrane of the device 2 in the second stage is said to have become increasingly clogged.

Specifically, the membrane of the second-stage device 2 becomes clogged when used in the first-stage device 1, and even after cleaning, the membrane does not reach the preset standard permeate amount for the first stage. Membranes that no longer recover are being used.

In this way, by using a highly clogged membrane as the membrane in the second-stage device 2, the process is similar in appearance to a device in which multiple membranes with progressively smaller molecular weight cut-offs are installed. This will improve the quality of treated water.

In addition, the amount of permeated water used in the first stage device 1 does not recover to the standard value required for the first stage device 1,
It is possible to reuse membranes that conventionally had to be discarded, and it is possible to reduce membrane costs accordingly.

In the embodiment shown in FIG. 1, two stages of ultrafiltration membrane separation devices are installed, but there may be three or more stages.

Furthermore, since the amount of permeated water decreases in the second and subsequent stages compared to the first stage, the second and subsequent stages may be configured to have a plurality of systems so as to maintain the overall amount of permeated water.

In the above embodiment, a waste water tank 4 is provided, but instead of this waste water tank 4, a biological treatment tank or a physicochemical treatment tank may be provided.

Further, the pipe 2b may be connected to the pipe 1a so that the concentrated water from the second stage device 2 is returned to the liquid supply side of the device 2.

Furthermore, the concentrated water in the apparatuses 1.2 at each stage may be evaporated and incinerated.

In the present invention, the reference value for determining whether the amount of permeated water has been sufficiently recovered by washing is 20 to 80%.
It is particularly preferable to set the value to about 40 to 60%, for example 50%. This reference value is the value obtained by dividing the amount of permeated water after cleaning by the amount of permeated water when new, and multiplying by 100.

Although each of the above embodiments shows an apparatus using an ultrafiltration membrane as the membrane, the present invention may also be an apparatus using a reverse osmosis membrane or a microfiltration membrane. The membranes used in each stage are preferably of the same type (for example, only ultrafiltration membranes, only microfiltration membranes, or only reverse osmosis membranes).

It is also preferable to use the same removal rate for each stage when new. For example, in the case of ultrafiltration membranes, use membranes with the same molecular weight cutoff, and in the case of reverse osmosis membranes, If available, use one with the same salt removal rate. In this way, only one type of membrane can be used for the entire device, making maintenance and management of the device easier.

Note that the deposits on the second and subsequent stages can be easily removed and cleaning is simple.

In the above embodiment, the film used in the first stage is used as the second stage film. However, in the present invention, membranes used in other membrane separation apparatuses may be used as the membranes of the second stage apparatus 2.

Membranes that are used in the second stage (or the most recent stage) are no longer sufficient for the amount of water permeated in the second stage (or the most recent stage).

Discard this.

[Test example]

Tomori 1 As shown in Figure 1, the first stage and second stage ultrafiltration membrane separation devices 1 and 2 were connected in series. In addition, a biological treatment tank is installed in place of the waste water tank 4 on the upstream side of the first-stage device 1, and piping 1b and 2b are arranged so that the concentrated water from the devices 1 and 2 in each stage is returned to this biological treatment tank. connected.

The first stage equipment is equipped with an ultrafiltration membrane (molecular weight cut off: 2000).
0) was installed. In addition, the second stage device 2 includes:
The ultrafiltration membrane had the same removal rate as the first stage membrane when it was new, but it became clogged and even after washing, the amount of permeated water was 50% that of the new membrane.
I installed something that no longer recovered by more than %. (
In addition, the pressure is 2K g/cm", the pure water permeation port in each stage at 25°C, and the membrane of the second stage device 2 is 2.0 m".
/n'1'7 days. In addition, the amount of permeated water of the biological treatment liquid is 1.3 tn"/m" for 7 days for the membrane of the first stage device l.
The film of the second stage device 2 is 0.3 go/rrf per day.

The membrane of this second stage device 2 is about 1
．． It was worn for 5 months, during which time 0.5% NaO was applied every 3 days.
It was washed with H solution for 30 minutes. ) The results obtained when biological treatment liquid was treated using the apparatus configured as described above are shown below.

Conditions Biological treatment liquid MLSS 10000mg/ICODm
600 mg/! L Processing amount 42 cycles/Hr Circulation rate 1st stage device 600 cycles/Hr 2nd stage device 6
00 sentences/Hr Water quality of permeated water (COI) Plm) 1st stage device 350mg/application 2nd stage device 110mg/ac 2nd stage device permeated water amount at start of water flow 1.5rn”/ba 7 days 1.5 After injury 1,0m'/rr1'7 days (every 3 days, 0.5
In the above-mentioned example of the present invention, the membrane of the second stage device 2 was
A new membrane was used that had the same removal rate as the membrane of device 1 in the first stage. The processing conditions are the same as in the examples of the present invention.

The processing results at this time are as follows.

Water quality of permeated water (CODNa) 1st stage device 350 mg/1 2nd stage device 300 mg/apparent From the above results, even if the ultrafiltration membrane has the same molecular weight cutoff when new , membranes that have become so clogged that the amount of pure water permeation cannot be recovered sufficiently even after cleaning are treated as C0DN.
It was observed that the removal rate of a was improved, and the molecular weight cut off appeared to be better and the molecular weight cut off became smaller.

It is also recognized that due to this behavior, the quality of the water treated by the apparatus of the present invention is extremely excellent.

〔effect〕

As detailed above, the present invention is a membrane separation device in which membranes are installed in multiple stages, in which a membrane in the latter stage is clogged and the amount of permeated water cannot be recovered sufficiently even after cleaning. Yes, the membrane can be effectively reused. In addition, only one type of membrane can be used, and cleaning for regenerating the membrane is easy, making maintenance management of the apparatus extremely easy. In addition, the resulting treated water is of excellent quality, similar to that obtained when subjected to multi-stage membrane treatment in which the membranes are installed in descending order of removal rate.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a membrane separation apparatus according to an embodiment of the present invention. 1... First-stage ultrafiltration membrane separation device, 2... Second-stage ultrafiltration membrane separation device.

Claims (3)

[Claims] (1) In a membrane separation device that performs membrane separation treatment on water to be treated,
It consists of a front-stage membrane that treats the water to be treated and a rear-stage membrane that processes the permeated water from the front-stage membrane.As the latter-stage membrane, the amount of permeated water after cleaning the membrane is set to be smaller than the initial amount of permeated water. 1. A membrane separation device characterized in that a membrane whose concentration is below a standard value is used. (2) A membrane separation device according to claim 1, wherein the membranes in each stage have the same removal rate when new. (3) A membrane separation device according to claim 1 or 2, characterized in that the membrane provided at the front stage is used as the membrane at the rear stage.