JPH05329477A - Membrane separation - Google Patents

Abstract

PURPOSE:To improve the membrane filtration efficiency of the membrane sepn. device in the membrane sepn. method for treating biologically treated water with the membrane sepn. device and to improve the treatment efficiency. CONSTITUTION:A chlorine agent 13 is added to the biologically treated water from an aerobic membrane treatment device 10 to adjust the free chlorine concn. thereof to 0.3 to 1.5mg/l and thereafter, this water is supplied to the membrane sepn. device 17. The filterability of the bacteria contained in the outflow water of the aerobic membrane treatment device is improved and the membrane sepn. efficiency is improved. This method is particularly effective for the treatment of the recovered water from washing of the ultrapure water of a semiconductor production process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane separation method, and more particularly to a membrane separation method in which raw water is treated by an aerobic biomembrane treatment apparatus and then treated by the membrane separation apparatus. The present invention relates to a membrane separation method for improving the treatment efficiency.

[0002]

2. Description of the Related Art Ultrapure water used in a semiconductor manufacturing process is used for cleaning semiconductors, then recovered, and then reprocessed for recycling. That is, an organic solvent such as isopropyl alcohol is mixed in the wash and recovered water, and TOC of 1 to 5 mg / l is detected. For this reason, conventionally, this cleaning / recovered water is subjected to UV (ultraviolet) oxidation, then subjected to RO (reverse osmosis) membrane treatment or the like to be reprocessed, and is recycled and used as recovery system ultrapure water.

On the other hand, in the above treatment method, a method has been proposed in which, instead of UV oxidation, a fluidized bed of activated carbon is used, and TOC in washing and recovery water is separated by oligotrophic bacteria adhering to the surface of activated carbon. This activated carbon fluidized bed method is
It is possible to perform TOC decomposition at a lower cost than UV oxidation.

[0004]

However, if the activated carbon fluidized bed is simply used instead of UV oxidation, there is a problem that the RO spiral membrane module in the subsequent RO membrane treatment is clogged with cells. In order to solve such a problem, it is an effective method to incorporate a step of blocking the outflow of bacterial cells to a subsequent step using a UF (ultrafiltration) membrane separator or the like. Therefore, in such a membrane separation apparatus for separating bacterial cells, if a high filtration rate can be secured, a practically extremely effective method is provided as a method for treating washing and collecting water in the semiconductor manufacturing process.

It is known that chlorine is added as an oxidant to the outflow water from the floating activated sludge process, which is supplied to the membrane separator. However, these conventional methods do not target the treatment in the ultrapure water recovery system,
Therefore, sufficient effects cannot be obtained with the amounts of chlorine suggested or disclosed. That is, conventionally, the amount of chlorine generally added for cell fouling is 1 / l as a chlorine agent.
It is on the order of 10 ppm, and a sufficient effect cannot be obtained with such an addition amount.

The present invention has been made in view of the above conventional circumstances, and in a membrane separation method for treating biologically treated water with a membrane separation apparatus, the membrane filtration efficiency in the membrane separation apparatus is improved and the treatment efficiency is improved. It is an object of the present invention to provide a membrane separation method for achieving the above.

[0007]

Means for Solving the Problems The membrane separation method of the present invention comprises:
In the membrane separation method for subjecting the biologically treated water from the aerobic biofilm treatment device to membrane separation, after adding a chlorine agent to the biologically treated water to adjust the free chlorine concentration to 0.3 to 1.5 mg / l,
It is characterized in that it is supplied to the membrane separation device.

[0008] Conventionally, sterilization and sterilization treatments have been carried out by adding chlorine. For example, in waterworks, the free residual chlorine concentration at a water tap is 0.1 mg / l (combined chlorine is 0.4 mg / l).
l) It is stipulated by the Waterworks Law Construction Regulations to maintain the above. The amount of chlorine required for sterilization is generally said to be 0.1 to 0.5 mg / l as free chlorine. As described above, many cases have been reported so far regarding the chlorine treatment and the bactericidal effect, but no case has been examined regarding the effect on the membrane filtration. The present inventor has conducted studies on chlorine treatment and filterability, and has clarified that there is an optimum chlorine treatment region that improves filterability, and completed the present invention.

The present invention will be described in detail below. In the present invention, the chlorine agent is added to the biologically treated water obtained by supplying the raw water to the aerobic biofilm treatment device so that the free chlorine concentration in the outflow water is 0.3 to 1.5 mg / l. Supply to the post-membrane separation device.

In the present invention, the amount of chlorine agent added is such that the concentration of free chlorine in the effluent of the biofilm treatment apparatus is 0.3 mg /
When the amount is less than 1, the effect of improving the filterability of the microbial cells cannot be sufficiently obtained. On the contrary, when the amount exceeds 1.5 mg / l, a phenomenon that seems to destroy the cell membrane of the microbial cells occurs. However, it is not preferable because the filtration resistivity increases. In this case,
The viscous substance flowing out from the destroyed cells adheres to the membrane surface of the membrane separation device, resulting in long-term membrane contamination. Also,
Excessive addition of such a chlorine agent is unfavorable since it adversely affects the RO membrane when there is a RO membrane separation step using a polymer composite membrane having no chlorine resistance in the subsequent step.

The chlorine agent used in the present invention is not particularly limited, but examples thereof include chlorine gas and sodium hypochlorite.

In the present invention, examples of the biological treatment apparatus include an activated carbon fluidized bed (aerobic biofilter), particularly an activated carbon fluidized bed using oligotrophic bacteria. The membrane module of the membrane separation device preferably has a structure that is difficult to be blocked by bacterial cells, for example, a spiral membrane module having a corrugated spacer inserted. Hollow fiber membrane module with an inner diameter of 1 mm or more, with internal pressure cross flow type. External pressure cross-flow hollow fiber membrane module. Etc. are preferable because the filling rate of the film is high and the film area is large. The type of membrane is selected from MF (microfiltration), UF, RO, etc. according to the subsequent treatment process, but it is important that the material has a high durability against chlorine.

The method of the present invention as described above is particularly effective for treating cleaning and recovery water of ultrapure water having a low TOC concentration in the semiconductor manufacturing process, and is also applicable to treatment of tap water having a low TOC concentration. Is.

In particular, the method of the present invention is extremely effective as a TOC removal step in place of UV oxidation in the treatment step of washing and recovering ultrapure water in the semiconductor manufacturing process, and is a biological material of the RO film in the RO treatment in the latter stage. The failure is effectively prevented without causing deterioration of the RO film, and good processing is possible.

[0015]

[Operation] Like cleaning and recovery water in the semiconductor manufacturing process, T
When raw water having a very low OC concentration (for example, 1 to 10 mg / l) is treated with an activated carbon fluidized bed (aerobic biofilter) using oligotrophic bacteria, flocs are formed in the outflow water from the activated carbon fluidized bed. It contains a lot of non-bacillus (Pseudomonas spp.).

As described above, in the effluent containing a large amount of Bacteria, even if chlorine of 1/10 ppm order is added as in the conventional case, a sufficient effect of improving the filterability cannot be obtained.

On the other hand, according to the method of the present invention, when a chlorine agent is added in an amount of 0.3 to 1.5 mg / l as the amount of free chlorine in the effluent, which is larger than in the conventional case, the filterability of the cells is high. In addition, the bacterial cells are prevented from accumulating on the membrane surface, and the permeation flux and filtration rate of the latter membrane separation device are significantly improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The membrane separation method of the present invention will be specifically described below with reference to the drawings. In addition, in the following, the case of treating the cleaning and recovery water of ultrapure water in the semiconductor manufacturing process as raw water will be described, but the present invention is not limited to the illustrated method.

FIG. 1 is a system diagram showing an embodiment of the present invention.

In FIG. 1, reference numeral 1 is an inlet pipe for raw water (here, cleaning / recovered water in the semiconductor manufacturing process), which is introduced into the raw water tank 2 and temporarily stored therein. 3 is a pH adjusting unit, 4 is an N (nitrogen), P (phosphorus) injection unit, and a pipe 5 equipped with a pump 5A from the raw water tank 2
Acid or alkali is added to the raw water sent from the pipe 6 to adjust the pH, and nitrogen and / or phosphorus is added to the pH-adjusted water in the pipe 7 from the pipe 8 to show the raw water below. Adjust to conditions that allow the reproduction of oligotrophic bacteria. pH = 5-9 TOC: N: P = 100: 5: 1 9 and 10 are an aeration tank and an aerobic biological treatment apparatus in which a fluidized bed of activated carbon is formed, respectively, and the aeration tank 9 supplies oxygen to oligotrophic bacteria. Is provided in the circulation line of the activated carbon fluidized bed 10.

The circulation line includes an introduction pipe 11 having a pump 11A and an extraction pipe 12 having an ejector 12A.
Composed of and.

In the activated carbon fluidized bed of the aerobic biological treatment apparatus 10, the fluidized bed expansion rate is 3 in order to achieve good contact with raw water.
The TOC in the raw water is decomposed by the oligotrophic bacteria adhering to the surface of the activated carbon by making it flow in the range of 0 to 50%. The activated carbon used is 10 to 40 mesh as a standard.

Reference numeral 13 is a chlorine injection unit, and a pipe 14
According to the present invention, the effluent of the aerobic biotreatment device therein,
A chlorine agent is injected through the pipe 15.

In the present embodiment, the chlorine injecting unit 13 is used to adjust the concentration of free chlorine in the effluent containing microbial cells to 0.3 to 1.5 mg / l in the effluent. Add the chlorine agent.

Reference numeral 16 is an intermediate water tank for temporarily storing the outflow water, and also serves as a raw water tank of the membrane separation device 17 in the subsequent stage.

The water in the intermediate water tank 16 is introduced into the membrane separation device 17 through a pipe 18 equipped with a pump 18A and subjected to membrane separation treatment. In this membrane separation treatment device, the effluent of the activated carbon fluidized bed is subjected to membrane filtration. At this time, since the filterability of the bacterial cells in the outflow water is significantly improved by the added chlorine agent, the bacterial cells and the like contained therein are efficiently removed. As described above, the membrane module configuration of the membrane separation device 17 is appropriately determined according to the subsequent treatment process and the like.

The permeated water of the membrane separation device 17 is the pipe 1
9, discharged through the treated water tank 20 and the pipe 21 to the outside of the system,
If necessary, after being subjected to a membrane separation treatment such as an RO membrane treatment, it is recycled for use in a semiconductor manufacturing process or the like.

The treated water tank 20 can also be used as a backwash water tank, and by using such a backwash unit, the filtration speed of the MF membrane, the UF membrane and the like of the membrane separation device 17 can be maintained high. Is possible.

The treated water thus obtained is TOC
Is highly purified, and the bacterial cells are also sufficiently removed by the membrane separation device, which is high-purity water.

The effects of the present invention will be more specifically shown below with reference to experimental examples. Experimental Example 1 The relationship between the free chlorine concentration and the filtration resistivity was examined under the following conditions.

As raw water, oligotrophic bacteria of the genus Pseudomonas were suspended in ultrapure water under the following conditions. Raw water bacteria count: 5 × 10 ⁶ cells / ml Concentration: 0.16 mg / l This raw water was subjected to constant pressure filtration using 0.45 μMF filter paper (manufactured by Millipore) to obtain a filtration curve to obtain a filtration resistivity. As a result, it was 4.4 × 10 ⁸ m / kg. Next, to this raw water, sodium hypochlorite was added by changing its addition amount, and similarly the filtration specific resistance was determined. The relationship between the free chlorine concentration and the filtration specific resistance is shown in FIG.

From FIG. 2, the following is clear. That is, the free chlorine concentration is 0.1 mg / l or more and 1.5 mg / l
Within the range of less than, the filtration resistivity becomes smaller and the filterability is improved as compared with the case where sodium hypochlorite is not added. Particularly, when the free chlorine concentration is 0.3 to 1.5 mg / l, a practical improvement effect is obtained. On the other hand, when the free chlorine concentration exceeds 1.5 mg / l and is added excessively,
On the contrary, the filtration resistivity is increasing compared to when it was not added,
It is clear that the filterability deteriorates when chlorine is added in excess.

Experimental Example 2 In order to verify the effect of the addition of a chlorine agent on the actual UF membrane filtration, a water flow comparison was carried out under the following conditions. Raw water: Simulated raw water in which isopropyl alcohol was added to ultrapure water so that TOC was 4 mg / l Activated carbon fluidized bed: Kuraray Coal KW (trademark of Kuraray Co., Ltd.) 20/40 mesh Flow rate of expansion 50% UF membrane separation Equipment: UF membrane = polysulfone membrane (molecular weight cut-off = 20,000), flat membrane Membrane module = thin-layer flat membrane cell with corrugated spacers Effective membrane area (0.0336m ² ) Backwash for 3 minutes in 30 minutes (Backwash pressure: 0.2 kg / c
m ² ) After treating the above raw water with a fluidized bed of activated carbon and then treating the effluent with a UF membrane separator, the effluent has a free chlorine concentration of 1.0.
When sodium hypochlorite was added so as to be mg / l (No. 1) and when not added at all (No. 2)
With respect to and, the filtration rate of the UF membrane separator at the time when it became steady after the start of water flow (after 10 to 20 days) was examined, and the results are shown in Table 1.

[0034]

[Table 1]

From the above results, it is clear that the filtration performance can be improved by adding a chlorine agent as free chlorine in the range of 0.3 to 1.5 mg / l to the effluent containing biological cells.

[0036]

As described in detail above, according to the membrane separation method of the present invention, the filtration efficiency of the membrane separation apparatus is improved by greatly improving the filterability of the cells contained in the biologically treated water.
It is possible to prevent clogging of the membrane and perform stable treatment with high treatment efficiency for a long period of time. The membrane separation method of the present invention is particularly applicable to the UV of the ultrapure water recovery treatment step in the semiconductor manufacturing process.
It is industrially extremely useful as a TOC removal step that replaces oxidation.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the membrane separation method of the present invention.

FIG. 2 is a graph showing the results of Experimental Example 1.

[Explanation of symbols]

 2 Raw water tank 3 pH adjustment unit 4 N, P injection unit 9 Aeration tank 10 Aerobic biological treatment device 13 Chlorine injection unit 16 Intermediate water tank 17 Membrane separation device 20 Treated water tank

Claims (1)

[Claims] 1. A membrane separation method for subjecting biologically treated water from an aerobic biological membrane treatment device to a membrane separation treatment, wherein a chlorine agent is added to the biologically treated water to give a free chlorine concentration of 0.3 to 1.5 mg.
/ L, and then supplying to the membrane separation device.