JPH10128084A - Operation of membrane separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently restrain an increase in a load to stably perform operation and to enable stable operation over a long time by detecting a change in water quality of original liquid and to adjust a filtration flux according to the water quality to restrain contamination of the membrane surface. SOLUTION: After sewage such as night soil is once stored in a storage tank, the sewage is fed to an original liquid treating tank 1 by a liquid transfer pump 52, and air is jetted from a diffusing pipe 3 by the drive of a blower 32. At the same time, membrane elements 2,... are evacuated on the filtrate flow passage side by the drive of a vacuum pump 41 to apply a prescribed inter-membrane differential pressure, and under contact with jetted air, organic matter in the sewage is adsorbed and decomposed metabolically by aerobic microorganisms while the aerobic microorganisms are propagated, water is made to permeate the membrane of the membrane elements 2,..., and the filtrate is taken out to a filtrate storage tank 42 through a filtrate takeoff piping 4. Therefore, in a membrane separating method, particularly a membrane separation active sludge treating method, operating conditions are adjusted according to water quality to restrain membrane contamination and enable long-term stable operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a membrane separation apparatus used for treating sewage such as human waste, sewage, domestic wastewater, and industrial wastewater.

[0002]

2. Description of the Related Art Recently, a gravity separation activated sludge treatment method, which is a traditional treatment method for human waste, sewage, domestic wastewater, and industrial wastewater (hereinafter referred to as sewage) (microbial decomposition treatment in an aeration tank,
A membrane separation activated sludge treatment method is attracting attention as an alternative to the method of introducing the treated wastewater into a sedimentation separation chamber, separating the activated sludge by gravity separation, and returning a part of the separated sludge to an aeration tank. . In this treatment method, solid-liquid separation is performed by filtration using a membrane module, the filtrate is taken out, and excess sludge is directly drawn out of the aeration tank.
(Floating solids in the liquid mixture) can be significantly higher than in the gravity separation method, so that the aeration tank can be considerably reduced in comparison with the gravity separation method. Since the MLSS concentration in the aeration tank can be maintained at a high level, there are advantages that, unlike the gravity separation method, there is no need for dehydration at the time of treating excess sludge, and it is possible to save operating energy. .

[0003] In the present applicant, a sewage treatment apparatus using a membrane separation method is described as "a membrane module having an air diffuser and having a vertical passage along the membrane surface is disposed immediately above the air diffuser. And a diffuser-type aeration tank provided with means for reducing the pressure on the membrane filtration side of the membrane device ”(Japanese Patent Publication No. 4-70).
958, Patent No. 1874881). The membrane module of this device uses flat membrane elements stacked so as to maintain a vertical passage between each other.

To treat sewage using this aeration type aeration tank, the undiluted solution in the tank is swirled by the air-lift effect of the air ejected from the aeration device, and the organic matter in the sewage is brought into contact with air. Adsorbed, metabolized and decomposed by aerobic microorganisms to reduce organic matter and proliferate aerobic microorganisms, and to suppress the generation of sludge gel layer on the membrane surface by gas-liquid mixed upflow along the membrane surface of the membrane element The filtrate side of the element is depressurized to generate a transmembrane pressure, and water is separated from the activated sludge by filtration under the transmembrane pressure.

[0005] In this membrane separation, the depressurizing force on the membrane element filtrate side, ie, the transmembrane pressure difference is ΔP, the filtration resistance of the membrane itself is R, the increase in filtration resistance due to membrane surface contamination is ΔR, and the filtration flux is I. Then, the relationship ΔP = I (R + ΔR) holds.

Conventionally, as a method of operating a membrane separation apparatus, in order to keep ΔP constant under an increase ΔR in filtration resistance, ΔR
The filtration flux I is reduced in accordance with the following. When the filtration flux I reaches the lower limit, the operation is interrupted, the membrane is washed to recover the filtration flux, and then the operation is resumed (constant pressure method); In order to keep the filtration flux I constant under the increase ΔR of the filtration resistance,
A method is known in which ΔP is increased in accordance with ΔR, and when ΔP reaches an upper limit value, the operation is interrupted, the membrane is washed to recover the filtration flux, and then the operation is restarted (constant flow rate method). .
Therefore, the rate of contamination of the membrane surface, and thus the rate of increase of the filtration resistance, is higher as the water quality of the undiluted solution is worse, and slower as the water quality is better.
It is known to set the decreasing rate of the filtration flux I in the constant pressure method or the increasing rate of ΔP in the constant flow rate method according to the water quality.

[0007]

However, this means does not suppress the contamination of the membrane surface, that is, the adhesion of the suspended substance in the stock solution to the membrane surface. For example, even if the water quality of the undiluted solution becomes bad water quality after normal water quality, and then returns to normal water quality again, I cannot maintain the same filtration flux at the same reduced pressure value as the reduced pressure value just before the poor water quality (constant). In the case of the flow rate method), ΔP cannot be maintained at the same degree of reduced pressure with the same filtration flux as that immediately before the deterioration of the water quality (in the case of the constant pressure method). This is because, despite the fact that the rate of decrease of the filtration flux I in the above constant pressure method or the rate of increase of ΔP in the constant flow rate method is set according to the water quality, the adhesion of suspended substances in the undiluted solution to the membrane surface. Has progressed considerably, and a considerable increase in filtration resistance has occurred. Under the progress of such membrane contamination, long-term safe driving cannot be expected at all.

An object of the present invention is to provide a membrane separation method, in particular, a membrane separation activated sludge treatment method, in which operating conditions are adjusted according to water quality to suppress membrane contamination and enable long-term stable operation.

[0009]

A method of operating a membrane separation apparatus according to the present invention is characterized in that a membrane element having a filtrate side on the inside is immersed in a stock solution, and the membrane element is air-scrubbed by a diffuser. A method of operating a membrane separation device for filtering a stock solution by depressurizing the filtrate side of the element, wherein a change in water quality of the stock solution is detected, and a filtration flux is adjusted according to the water quality to suppress membrane surface contamination. The change in the water quality of the stock solution is preferably detected by the TOC concentration, and the filtration flux is set to 0.5 m ³ / m ² · day or more for a TOC concentration of less than 30 mg / liter and a TOC concentration of 30 to 50
0.3~0.5m against mg / liter ³ / m ² · day
0.3m for TOC concentration of 50mg / L or more
It is appropriate to adjust to ³ / m ² · day or less.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing a membrane separation device used in the present invention. In FIG. 1, reference numeral 1 denotes a stock solution treatment tank, which can use an aeration tank body of a conventional aeration-type aeration tank using an activated sludge method. Are membrane elements disposed at predetermined intervals in the undiluted solution treatment tank, and have a filtrate flow path therein. Reference numeral 20 denotes a filtrate collection pipe of the membrane element 2, which is connected to a filtrate flow path in the element, and the filtrate that has passed through the membrane is collected in the filtrate collection pipe via the filtrate flow path.

Numerals 3, 3,... Are air diffusers provided below the membrane elements 2,... Which are arranged in the gaps between the membrane elements 2, 2 so that the stock solution can be efficiently raised by the air-lift effect. It is. 31 is an air supply pipe connected to the air diffuser 3;
2 is a blower. Reference numeral 4 denotes a filtrate taking-out pipe connected to the filtrate collecting pipes 20, ... of the membrane elements 2, ..., 41 denotes a vacuum pump inserted into the pipe 4, and 42 denotes a filtrate storage tank. Reference numeral 51 denotes a stock solution supply pipe, and reference numeral 52 denotes a liquid feed pump inserted into the pipe 51.

Reference numeral 6 denotes an undiluted water quality measuring instrument, for example, TO
C concentration meter (combustion oxidation-infrared TOC analysis method described in JIS K 0101 Industrial Water Test Method, combustion oxidation-infrared TOC automatic measurement method, etc. In any case, acid is added to the test water After adjusting the pH to 3 or less, an inert gas containing no carbon dioxide is passed to remove inorganic carbon, and this sample is quantitatively injected into a gas-liquid mixed flow of carbon dioxide gas and an oxidizing agent, and irradiated with ultraviolet rays. Oxidized, and the amount of carbon dioxide generated by the oxidation is measured with an infrared spectrometer), BOD
A measuring instrument, a COD measuring instrument, or the like can be used. In particular, it is preferable to use a TOC concentration measuring instrument because it can measure in a short time and is hardly affected by raw water components.

FIG. 2 (a) and FIG. 2 (b) [a cross-sectional view taken along the roll line in FIG. 2 (a)]
And a filtrate flow path material 22 (for example, woven cloth, non-woven cloth, net, etc.) in a frame 20 having a filtrate collection pipe 21.
And a flat membrane 23 (microfiltration membrane, ultrafiltration membrane, etc.) is adhered to both sides of the frame with an adhesive 24. The flat membrane 23 is formed by laminating a membrane on a supporting substrate, Embedded with a woven fabric, a non-woven fabric or the like can be used. 3 (a) and 3 (b) [a cross-sectional view taken along a line in FIG. 3 (a)]
Another example of the above membrane element is shown. Filtrate passage grooves 201,... Are formed on both sides of the plate 20, and a filtrate outlet hole communicating with the filtrate passage grooves 201,. 202, a filtrate passage spacer 21 and a flat membrane 23 are sequentially laminated on each side of the plate 20, and the periphery of the flat membrane 23 is sealed on each side of the plate with an adhesive. is there. The dimensions of the membrane element 2 are generally 50 cm to 150 cm in height and 20 cm to 100 c in width when the dimensions of the treatment tank are made substantially equal to the dimensions of the aeration chamber of the conventional aeration type aeration tank.
m and a thickness of 3 mm to 6 mm.

As shown in FIG. 4, the module structure of the membrane elements 2,.
Can be alternately arranged side by side through a gap for a stock solution passage, and a group in which the side-by-side group is accommodated in a frame 200 can be used. The module is placed directly on the bottom surface of the stock solution treatment tank, mounted on a gantry installed on the bottom surface, or immersed in the stock solution treatment tank in a suspended manner.

In order to operate the above-mentioned membrane separation apparatus according to the present invention, sewage (human waste, sewage, domestic wastewater, factory wastewater, etc.) is temporarily stored in a storage tank, and the wastewater is fed by a liquid feed pump 52 in FIG. Is supplied to the undiluted solution processing tank 1, air is blown out from the air diffuser 3 by driving the blower 32, and at the same time, the filtrate flow path side of the membrane elements 2,. To cause organic matter in sewage to be adsorbed and metabolized and decomposed by aerobic microorganisms under the contact with the jet air, and to allow the aerobic microorganisms to grow while allowing water to permeate through the membranes of the membrane elements 2 and ... The liquid is taken out to the filtrate storage tank 42 via the liquid take-out pipe 4.

In this case, the swirling flow rate (average flow rate) by air scrubbing varies depending on the liquid quality and concentration of the stock solution, the processing speed, and the like, but is usually 0.01 to 2.0 m / sec.
Preferably, the air flow rate of the blower 38 is adjusted so as to be in the range of 0.02 to 1.0 m / sec. 0.01
At m / sec or less, it is difficult to satisfactorily perform the cleaning effect on the membrane surface by air-scrubbing, and it is difficult to precipitate activated sludge to promote microbial reaction. Fixing is difficult and air supply costs are too high.

The mutual spacing between the membrane elements 2, 2 is
Normally 5 to 15 mm
Degree. When the thickness is 5 mm or less, the resistance to the upward flow of the stock solution between the membrane elements due to air-scrubbing becomes too high, and the flow rate cannot be increased at a high speed, so that the membrane surface cleaning effect is reduced. The area becomes too small, which leads to an increase in the size of the membrane separation device.

T in FIG. 5 shows a temporal change in the water quality (TOC concentration) of the sewage sent to the stock solution treatment tank 1. In the operation method according to the present invention, the water quality of the supplied sewage is changed at a constant frequency. And is usually measured once every 6 hours to 14 days, preferably once every 1 to 10 days. If there is a variation of a predetermined range or more with respect to the previous measurement result, The operation filtration flux is changed to the one suitable for the water quality, and if the fluctuation is within a predetermined range with respect to the previous measurement result, the previous set operation filtration flux is held. I in Figure 5 shows the setting of the operating filtration flux, operation filtered set the initial good operating filtration flux in water quality period I to i _1, there is a change in water quality in the period II is also at good quality the flux was kept at i _1, the operating filtration flux since dropped to medium water in the period III set slightly lower i _2, the operating filtration flux since dropped to poor water quality in the period IV in extremely low i ₃ set, since the recovered medium quality in the period V returns the operating filtration flux prior to i _2, returning the operating filtration flux to the previous i ₁ so recovered to more good water quality in the period VI. During this time, the transmembrane pressure ΔP, that is, the degree of pressure reduction on the filtrate side, changes in accordance with the setting change of the operation filtration flux. However, even if time elapses, for example, between the period II and the period VI, If the water quality is the same, the transmembrane pressure is equal, i.e., the transmembrane pressure / filtration flux is equal and the filtration resistance is equal, i.e., even if time elapses, the filtration resistance increases. No, in other words, no film surface contamination is guaranteed. In the conventional operation method, for example, the conventional constant pressure operation method,
It is known to adjust the filtration flux according to the quality of the water, but a considerable increase in filtration resistance due to the progress of membrane fouling over time cannot be avoided. On the other hand, in the present invention, in order to effectively suppress the progress of membrane contamination with the passage of time, the low filtration flux which does not easily adhere during the poor water quality period in which the contamination is likely to adhere. , And a sufficiently high filtration flux is set for good water quality to which adhesion of contaminants hardly occurs, and 0.5 m ³ / m ² · day for a TOC concentration of less than 30 mg / liter (good water quality). above (preferred range ^{0.5m 3 / m 2 · day~0.8m 3} / m 2 · day), tO
C concentration of 30 to 50 mg / liter (medium water quality)
The ^{3~0.5m 3 / m 2 · day,} TOC concentration 50 mg / l or more (poor quality) to 0.3m ³ / m ² · day or less (preferred range 0.3m ³ / m ² · day~0 .2m ³ / m
By setting to ² · day), an increase in filtration resistance over time can be substantially eliminated, and safe operation can be performed for a long period of time.

[0019]

【Example】

Example 1 The membrane element shown in FIG. 2 was used, and the dimensions of the frame 20 were 570 mm in length and 450 mm in width (width).
mm, thickness 5 mm, and the membrane 23 has a nominal pore size of 0.4 μm.
m, a polyolefin-based ultrafiltration membrane having a membrane area of 0.3 m ² was used. The module shown in FIG. 4 was used, the number of the membrane elements 2 was 15, and the interval between the membrane elements was 15 mm. The membrane separation device shown in FIG. 1 was used. Initial MLSS concentration 14,2 in stock solution
An activated sludge solution having an initial TOC concentration of 4.5 mg / liter was used at 00 mg / liter, and the water quality change over time of the supplied activated sludge solution is as shown in FIG. The decompression pump was set to an intermittent operation in which the operation was repeated for 8 minutes and stopped for 2 minutes, and the amount of diffused air was set such that the sewage swirl velocity was approximately 0.5 m / sec. The TOC concentration was measured once every two days, and for a TOC concentration of 30 mg / liter or less, the operation filtration flux was set to 0.5 m ³ / m ² · day, and the TOC concentration was 30 mg / liter to 50 mg / liter. For the range, on the basis of setting the operation filtration flux to 0.3 m ³ / m ² · day, I in FIG.
As shown by, the operation filtration flux was adjusted. During this time, the degree of pressure reduction on the filtrate side of the membrane element is as shown by ΔP in FIG. 6, and the set operation filtration flux is both 0.5 m ³ / m ² · da.
Since there is substantially no difference in the degree of pressure reduction between the period I and the period III, which is y, it is clear that there is no increase in filtration resistance and no membrane contamination has progressed.

Example 2 Initial MLSS concentration of 10,5 in stock solution
FIG. 7 shows the change in water quality over time of the activated sludge solution supplied using an activated sludge solution having an initial TOC concentration of 38 mg / liter. The membrane separator used, the intermittent operation of the vacuum pump, the sewage swirling flow rate, and the like were the same as in Example 1. The TOC concentration was measured once every 7 days. For the same TOC concentration of 30 mg / L or less as in Example 1, the operation filtration flux was set to 0.5 m ³ / m ² · day, and the TOC concentration was set to 30 mg / L. The operation filtration flux was adjusted as shown by I in FIG. 7 on the basis of setting the operation filtration flux to 0.3 m ³ / m ² · day in the range of 1 to 50 mg / liter. . During this period, the degree of pressure reduction on the filtrate side of the membrane element is as shown by ΔP in FIG. Since there is no difference, it is clear that there is no increase in filtration resistance and no membrane contamination has progressed.

[Comparative Example 1] The activated sludge solution having a temporal change in water quality shown in FIG.
The intermittent operation of the pressure reducing pump, the sewage swirl flow rate, etc.
8 and as shown by I in FIG.
The operation was performed at a constant flow rate of 5 mg / liter. The time-dependent fluctuation of the degree of decompression is as shown by ΔP in FIG. 8, and it is clear that the filtration resistance is significantly increased with time and the progress of membrane contamination is remarkable.

Comparative Example 2 Example 2 was the same as Example 2 except that the setting of the operation filtration flux in period III was not changed. As shown by I in FIG. 9, the operation filtration flux was changed to 0.3 m ³ / m ² · day based on the above-mentioned standard in the period V. It is clear that the degree of pressure reduction could not be recovered and there was considerable membrane fouling, that is, an increase in filtration resistance.

[0023]

According to the method of operating a membrane separation apparatus according to the present invention, in the treatment of sewage, in particular, the membrane separation activated sludge method, the membrane separation apparatus can sufficiently suppress the membrane contamination and sufficiently increase the load. Stable operation is possible, and stable operation is possible for a long period of time.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a membrane separation device used in the present invention.

FIG. 2 is an explanatory diagram showing an example of a membrane element in the membrane separation device of FIG.

FIG. 3 is an explanatory view showing another example of the membrane element in the membrane separation device of FIG.

FIG. 4 is an explanatory diagram showing an example of a membrane module in the membrane separation device of FIG.

FIG. 5 is an explanatory diagram showing a general method of adjusting a filtration flux in the present invention.

FIG. 6 is an explanatory diagram illustrating a method of adjusting a filtration flux in the first embodiment.

FIG. 7 is an explanatory diagram showing a method of adjusting a filtration flux in the first embodiment.

FIG. 8 is an explanatory diagram showing a method of adjusting a filtration flux in Comparative Example 1.

FIG. 9 is an explanatory diagram showing a method of adjusting a filtration flux in Comparative Example 1.

[Explanation of symbols]

 Reference Signs List 1 stock solution treatment tank 2 membrane element 3 diffuser 6 water quality meter

Claims (3)

[Claims] 1. A membrane separation method comprising immersing a membrane element having a filtrate side on the inner side in a stock solution and filtering the stock solution by depressurizing the filtrate side of the membrane element while air-scrubbing the membrane element by a diffuser. A method for operating a membrane separation device, comprising detecting a change in water quality of a stock solution and adjusting a filtration flux according to the water quality to suppress membrane surface contamination. 2. The method for operating a membrane separation apparatus according to claim 1, wherein a change in water quality of the stock solution is detected by a TOC concentration. 3. The method according to claim 3, wherein the filtration flux is set to 0.5 m ³ / m ² · day or more for a TOC concentration of less than 30 mg / liter,
0.3 to 0.5 m ³ / m ² for 0 to 50 mg / l
^{3. The} method for operating a membrane separation device according to claim 2, wherein the TOC concentration is adjusted to not more than 0.3 m ³ / m ² · day for a TOC concentration of 50 mg / liter or more on day.