JP2002191942A - Method for waste water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for waste water treatment by which waste water treatment can be stably performed for a long time. SOLUTION: The present invention is characterized by using a flocculating agent containing at most 0.1 wt.% manganese as an iron type flocculating agent in the method for waste water treatment comprising a flocculating treatment process for performing flocculating treatment by adding the iron type flocculating agent into a liquid to be treated containing an activated sludge and a membrane separating treatment process for performing membrane separating treatment of the liquid to be treated in which the activated sludge obtained by flocculating treatment in the flocculating treatment process and a flocculated sludge are mixed. By this invention, even when the flocculating treatment is performed by adding the iron type flocculating agent into the liquid to be treated containing the activated sludge and the liquid to be treated in which the activated sludge obtained by flocculating treatment and the flocculated sludge are mixed is treated by means of membrane separation, formation of manganese oxide is enough suppressed on the surface of the membrane and it is possible to prevent fouling of the membrane from occurring for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wastewater treatment method, and more particularly, to a wastewater treatment method in which an iron-based flocculant is added to a liquid to be treated containing activated sludge to perform a membrane separation treatment.

[0002]

2. Description of the Related Art A membrane separation process for solid-liquid separation of a liquid to be treated containing activated sludge by means of a membrane has advantages such as no need for a sedimentation basin and an increased sludge concentration in an aeration tank. ing. Among them, a wastewater treatment method in which an iron-based coagulant is added prior to membrane separation has been frequently used in order to efficiently remove COD components and to suppress fouling of the membrane (for example, see Japanese Patent Application Laid-Open No. HEI 9-163572). 9-1
9700, JP-A-10-128393).

[0003]

However, in the wastewater treatment methods described in the above-mentioned conventional gazettes, it cannot be said that membrane fouling is sufficiently suppressed, and it is difficult to perform stable operation for a long period of time. This has made it possible to frequently perform chemical cleaning of the membrane.

[0004] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wastewater treatment method capable of performing wastewater treatment stably for a long period of time.

[0005]

Means for Solving the Problems In order to achieve the above object, the present inventors have studied the causes of the above-mentioned problems in the prior art. First, the present inventors noticed that the surface of the film after film fouling was black, tried analysis of this black substance, and found that this black substance was manganese oxide. As a result of further study on the source of manganese oxide, the present inventors have found that the source is manganese (generally 1.2 to 1.7) contained as an impurity in an iron-based coagulant usually used for wastewater treatment. % By weight), thereby completing the present invention.

That is, the present invention provides a coagulation treatment step in which an iron-based coagulant is added to a liquid to be treated containing activated sludge, coagulation treatment, and activated sludge and coagulation sludge obtained by coagulation treatment in the coagulation treatment step. And a membrane separation treatment step of subjecting the treatment liquid to a membrane separation treatment step, wherein a manganese-containing coagulant containing 0.1% by weight or less of manganese is used.

According to the present invention, an iron-based coagulant is added to a liquid to be treated containing activated sludge to perform coagulation treatment, and a treatment liquid in which activated sludge obtained by coagulation treatment and coagulated sludge are mixed is subjected to membrane separation. Even if the treatment is performed, generation of manganese oxide on the film surface is sufficiently suppressed, and film fouling can be prevented for a long period of time.

According to the present invention, the pH of the processing solution is adjusted to 5.2 to 5.8.
It is preferable that the method further includes a step of adjusting the temperature.

By adjusting the pH of the treatment solution to the above range, the membrane separation treatment can be performed more stably for a longer period of time as compared with the case where the pH is out of the above range.

In the coagulation treatment step, the ratio of iron hydroxide (Fe (OH) ₃ ) to activated sludge is 0.1 to 0.5.
It is preferable to add an iron-based flocculant so that

In this case, the membrane separation treatment can be performed more stably for a longer period of time than when the ratio of iron hydroxide to activated sludge is out of the above range.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail.

FIG. 1 is a flowchart showing one example of a wastewater treatment apparatus to which the wastewater treatment method of the present invention is applied. As shown in FIG. 1, the wastewater treatment apparatus includes an aeration tank 1 for storing activated sludge, and the aeration tank 1 includes a raw water introduction line L1.
Raw water is introduced through the process. An air diffuser 2 is provided in the aeration tank 1, and the air diffuser 2 is connected to an air supply blower 3 via an air supply line L2. Therefore, air can be supplied from the air supply blower 3 to the activated sludge from the air diffuser 2 via the air supply line L2. In the aeration tank 1, the nitrification and denitrification treatment can be performed in one tank by intermittently introducing air from the air diffuser 2.

The aeration treatment liquid discharged from the aeration tank 1 is introduced into the coagulation tank 4 via the line L3. The liquid in the coagulation tank 4 can be stirred by the stirrer 5. Further, a pH meter 6 is installed in the coagulation tank 4 so that the pH value of the liquid in the tank can be monitored.

The coagulation treatment liquid discharged from the coagulation tank 4 is introduced into the membrane separation tank 7 via the line L4. In the membrane separation tank 7, a membrane unit 8 for solid-liquid separation of the liquid in the tank is provided. In the membrane unit 8, a rotary flat membrane, a hollow fiber membrane, an immersion flat membrane, or the like can be used. As the type of the membrane, for example, any of an ultrafiltration membrane and a microfiltration membrane can be used. A diffuser 9 is provided below the membrane unit 8. The air diffuser 9 is connected to the air supply blower 3 via an air supply line L9. The membrane unit 8 is connected to a membrane separation treatment liquid discharge line L5, and the membrane separation treatment liquid discharge line L5 is connected to a suction pump 10. Then, when the suction pump 10 is operated, the liquid in the tank is sucked through the membrane unit 8 and solid-liquid separation of the liquid in the tank is performed.

The membrane separation tank 7 and the aeration tank 1 are connected by a return line L6, and a return pump 11 is installed in the return line L6. Therefore, the liquid in the membrane separation tank 7 is returned to the aeration tank 1 via the return line L6.

Next, a wastewater treatment method using the wastewater treatment apparatus having the above-described configuration will be described.

Raw water is introduced into the aeration tank 1 through a raw water introduction line L1. On the other hand, the air supply blower 3 is operated, and the air supply blower 3 is
More air is supplied to the liquid in the aeration tank 1 to continuously aerate the liquid in the tank.

An aeration treatment liquid containing activated sludge is introduced into the flocculation tank 4 via a line L3. An iron-based coagulant is added to the liquid in the coagulation tank 4 to perform coagulation treatment (coagulation treatment step). Here, as the iron-based coagulant, manganese is added at 0.1%.
% Or less, preferably 0.05% by weight or less. When the content of manganese is set to 0.1% by weight, if it exceeds 0.1% by weight, manganese oxide is easily generated on the surface of the membrane in the subsequent membrane separation tank 7, and membrane fouling occurs in a short period of time. Because. The iron-based flocculant may be any one containing manganese at the above content, and one containing mainly ferric chloride or polysulfate is used. The amount of the iron-based coagulant added is such that the weight ratio of iron hydroxide (Fe (OH) ₃ ) to activated sludge is 0.
It is preferable to set it to 1 to 0.5. In this case, the membrane fouling can be sufficiently suppressed as compared with the case where the value is out of the above range, and the wastewater treatment device can be stably operated for a longer period of time. Further, in the coagulation tank 4, the addition of the iron-based coagulant generates coagulated sludge in the coagulation tank 4, thereby removing the COD component in the liquid to be treated. At this time, when the liquid in the tank is stirred by the stirrer 5, coagulated sludge is easily generated.

In the coagulation tank 4, it is preferable to adjust the pH of the solution (treatment liquid) in the tank after the addition of the iron-based coagulant to 5.2 to 5.8. When the pH is less than 5.2, biological treatment with activated sludge becomes unstable due to too strong acidity,
The removal efficiency of OD components and the like tends to decrease. When the pH exceeds 5.8, the effect of removing soluble organic substances by the iron-based flocculant decreases, and the removal efficiency in the subsequent membrane separation tank 7 is relatively short. Membrane fouling tends to occur. In addition, pH adjustment,
It can be performed by adding an acid or an alkali to the coagulation tank 4.

The coagulation treatment liquid in which activated sludge and coagulated sludge are mixed is introduced into the membrane separation tank 7 via the line L4. Then, the suction pump 10 is operated to suck the liquid in the tank of the membrane separation tank 7 through the membrane unit 8 to perform solid-liquid separation of the liquid in the tank (membrane separation step). On the other hand, the air supply blower 3 is operated to supply air to the liquid in the tank via the air supply line L9 and the air diffuser 9. This cleans the membrane surface and places the activated sludge under aerobic conditions. Even if the liquid in the tank is subjected to solid-liquid separation, the iron-based flocculant added in the flocculation tank 4 contains manganese at 0.1% by weight or less and contains only a trace amount of manganese. For a long period of time, generation of manganese oxide on the film surface is sufficiently suppressed, and film fouling can be sufficiently suppressed. Therefore, the wastewater treatment device can be stably operated for a long period of time.

The clear membrane separation processing liquid separated through the membrane unit 8 is discharged through a membrane separation processing liquid discharge line L5, and a part of the liquid in the tank is operated by the return pump 11 to return the return line L6. After that, it is returned to the aeration tank 1. Thereby, the activated sludge is returned to the aeration tank 1, so that the activated sludge can be effectively used.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, continuous aeration is performed in the aeration tank 1. However, when the raw water contains a large amount of nitrogen compounds, the air supply blower 3 is operated intermittently to allow the aeration tank 1 to operate. Perform nitrification denitrification treatment,
Nitrogen compounds may be sufficiently removed.

Next, the contents of the present invention will be specifically described using examples.

[0025]

EXAMPLES (Example 1) Synthetic sewage having the composition shown in Table 1 was diluted 300 times with tap water and used as inflow raw water.
This inflow raw water was introduced into the aeration tank, and the aeration tank was operated under the conditions shown in Table 2. The liquid containing the activated sludge discharged from the aeration tank was designated as No. Filter with 5C filter paper, and add F
Manganese is added in an amount of 0.1% so that the eCl ₃ concentration becomes 2% by weight.
An iron-based coagulant (ferric chloride solution (low manganese) manufactured by Nippon Steel Corporation) containing 02% by weight was added to perform coagulation treatment. After the addition of the iron-based flocculant, the pH was adjusted using 0.1 N NaOH or 0.1 N HCl. And
The liquid in which the activated sludge and the coagulated sludge were mixed was filtered using a micro module (manufactured by Mitsubishi Rayon Co., Ltd.), and the increase in the differential pressure with respect to the pH value was measured, and the increase in the differential pressure was compared for each pH. Table 3 shows the results. Note that a capillary module was used as the micro module. Further, in Table 3, the differential pressure value was a value obtained by converting the pressure difference from 10 L of the liquid to 1 L, that is, the pressure difference when 9 L of the liquid was sucked, at 25 ° C. Table 3 also shows the water quality of the liquid before suction by the micromodule. Further, air scrubbing was performed during the membrane separation. The type, material, pore size, permeation flux and air scrubbing conditions of the membrane were as shown in Table 2.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

As shown in Table 3, when the coagulation treatment is performed in the range of pH 4.5 to 7.0, the TOC and COD _(cr) concentrations before suction by the micro module are sufficiently reduced, and
It was found that the differential pressure during L filtration was sufficiently small. In particular, when the coagulation treatment was performed at pH 5.2 to 5.8, it was found that the differential pressure during 9 L filtration was significantly reduced.

Comparative Example 1 Synthetic sewage treatment was carried out in the same manner as in Example 1 except that no iron-based coagulant was added to the aeration tank, and the differential pressure during 9 L filtration was measured. Table 3 shows the results together with the water quality before suction by the micromodule. As shown in Table 3, when the iron-based flocculant was not added, the TOC and COD _(cr) concentrations were not sufficiently reduced, and 9 L
It was found that the pressure difference during filtration also became considerably large.

Example 2 The pH and activated sludge concentration in the aeration tank were kept constant, and the amount of the iron-based coagulant added was determined according to the weight ratio of iron hydroxide (Fe (OH) ₃ ) to the activated sludge. And the BOD in the aeration tank.
Example 1 except that the load was 0.8 kg / m ³ · day and the permeation flux of the membrane in the micromodule was 1.0 m / day.
In the same manner as in the above, the treatment of synthetic sewage was performed. And 10
The differential pressure was measured at the time of operation for 00 hours. The measurement of the differential pressure was carried out using the iron hydroxide (Fe (O
H) was performed for each case of the weight ratio of ₃ ). Table 4 shows the results.

[0032]

[Table 4]

From the results shown in Table 4, it is found that F
It was found that when the weight ratio of e (OH) ₃ was in the range of 0.1 to 0.5, it was possible to suppress the increase in the differential pressure for a longer time.

Comparative Example 2 Synthetic sewage treatment was carried out in the same manner as in Example 2 except that no iron-based coagulant was added.
Then, the differential pressure was measured at the time of operation for 1000 hours.
Table 4 shows the results.

From the results shown in Table 4, it can be seen that when the iron-based coagulant was not added, the weight ratio of Fe (OH) ₃ to the activated sludge was relatively shorter than when the weight ratio was in the range of 0.1 to 0.5. It was found that the differential pressure increased with time.

(Example 3) FIG. 2 shows a membrane separation test of a liquid containing mixed sludge of activated sludge and flocculated sludge obtained by adding an iron-based flocculant to activated sludge cultured in synthetic sewage. The test was performed using a membrane cell test apparatus.

Here, the membrane cell test apparatus will be described. As shown in FIG. 2, the membrane cell test apparatus has an aeration tank 12 having a volume of 8 L, and a blower 13 is provided inside the aeration tank 12.
From the air through the air introduction line L7 and the air diffuser 14. The aeration tank 12 has a pH meter 18
Is installed, and the pH of the liquid in the aeration tank 12 can be monitored. Further, the membrane cell test apparatus is a box-shaped membrane cell 1
5, and the liquid in the tank of the aeration tank 12 is introduced from a position below the membrane cell 15, and is a flat membrane made of polyolefin fixed to the inner wall surface of the membrane cell 15 (nominal pore diameter 0.4 μm,
After passing through the surface of a size 2 cm × 25 cm) 16, it is discharged from a position above the membrane cell 15 and returned to the aeration tank 12. Further, the membrane cell 15 includes a blower 13
Then, air is introduced through an air introduction line L8, and the air is used to perform air scrubbing of the flat membrane 16 (1.5 Nm ³ / m ² · min per sectional area under the membrane (0.8 cm × 2 cm)). ing. The air introduction line L8
Is provided with a flow meter 19. Further, the membrane separation liquid separated by the membrane is sucked by the pump 17 and returned to the aeration tank 12.

In such a membrane cell test apparatus, a membrane separation test of a liquid containing mixed sludge of activated sludge and coagulated sludge generated in the aeration tank 12 was performed as follows. First, activated sludge cultured with synthetic sewage having the composition shown in Table 1 was introduced into the aeration tank 12, and the activated sludge concentration was 12,000 mg / L.
And For the activated sludge, an iron-based flocculant containing 0.02% by weight of manganese (a ferric chloride solution (a low manganese product) manufactured by Nippon Steel Corporation) was added to Fe (OH) for the activated sludge.
₃ was added so that the weight ratio became 0.1, and the pH of the solution in the aeration tank 12 after the addition of the flocculant was adjusted using 0.1 N NaOH or 1 N HCl. The permeation flux of the membrane 16 was adjusted to 1.5 m / day. During the membrane separation test, no organic substance load was applied, and the membrane separation test was performed under the condition of empty aeration. Then, the time when the suction differential pressure reached 10 kPa and 20 kPa was measured. Table 5 shows the results.

[0039]

[Table 5]

Example 4 Using the wastewater treatment apparatus shown in FIG. 1, the pH was 5.0 to 6.0 and the SS was 400 to 800 mg /
L, BOD 900 to 1300 mg / L brewery effluent was treated. This beer factory effluent is introduced into the aeration tank 1 as raw water, and the BOD volume load 1.
Biological treatment was performed at 0 kg · BOD / m ³ · day. The air scrubbing condition at this time is 1.5 Nm ³ per under-film sectional area.
/ M ² / min. This biological treatment liquid is introduced into the coagulation tank 4 with the activated sludge remaining, and the iron-based coagulant is
The concentration is 250 mg / l based on the inflowing raw water (1 L).
L, and the solution in the coagulation tank 4 was stirred by the stirrer 5. Here, as the iron-based coagulant, a ferric chloride solution (low manganese product) manufactured by Nippon Steel Corporation was used.
The pH of the solution in the coagulation tank 4 was adjusted to a predetermined value by adding 0.1 N NaOH or 0.1 N HCl while monitoring the pH meter 6. In the flocculation tank 4, the MLSS is measured once a week and the MLSS is measured.
The excess sludge was extracted so as to be 15,000 mg / L. The hollow fiber membrane shown in Table 2 was used as the membrane in the membrane separation tank 7, and the permeation flux of the membrane was 0.5 m for one month from the start of operation.
³ / m ² / day, and 1.0 m ³ / m ² / day after one month.

In this way, the wastewater from the beer factory is treated, and the pH of the liquid in the coagulation tank 4 is adjusted to 4.8, 5.5, 6.0, and 7.0.
The change with time of the transmembrane pressure when it was set to 0 was examined. Fig. 3 shows the results.
Shown in From the results shown in FIG. 3, the differential pressure is constant for a relatively long time at any pH, but the pH is 5.5.
In the case of (1), it was found that the time during which the differential pressure was constant was particularly long, and that membrane fouling could be more sufficiently suppressed.

Example 5 Using a membrane cell test apparatus shown in FIG. 2, domestic wastewater from a factory having the water quality shown in Table 6 was treated.

[0043]

[Table 6]

The domestic wastewater of the above factory is treated as follows.
did. First, the aeration tank 12 was cultivated with synthetic sewage shown in Table 1.
Nourish activated sludge and factory wastewater to introduce activated sludge
The degree was 12,000 mg / L. Load of aeration tank 12
The case is 0.8kg-BOD / m ^Three・ It was a day. Activated sludge
Uses iron-based flocculant containing manganese for activated sludge
Fe (OH)_ThreeAdded so that the weight ratio becomes 0.2
The pH of the liquid in the aeration tank 12 after the addition of the flocculant is 0.1
5.5 with NaOH or 1N HCl
I adjusted it. The permeation flux of the membrane was adjusted to 1.0 m / day.
It was adjusted.

The wastewater from the factory is treated in this manner, and once a week, the iron content in the sludge is analyzed.
An iron-based flocculant was added so that the ratio of e (OH) ₃ was maintained at 0.2. In order to investigate the effect of manganese on the differential pressure, two types of iron-based coagulants with different manganese contents (those having a manganese content of 0.05% by weight and 0.1% by weight, respectively) were used. ), The suction differential pressure (converted value at 25 ° C.) during the operation for 3 months was measured for each iron-based flocculant. The manganese content is 0.05% by weight,
0.1% by weight of iron-based flocculant is 0.02% by weight of manganese
It was obtained by adjusting the manganese content by mixing the content and the 1.6 wt% content. The results are indicated by “○” in FIG.

Comparative Example 3 As an iron-based coagulant, one having a manganese content of 0.3% by weight, 0.75% by weight, 1.0% by weight and 1.6% by weight (manganese 0.02% by weight) The wastewater from the factory was treated in the same manner as in Example 5 except that the manganese content was adjusted by mixing the content and the 1.6 wt% content.) Then, for each iron-based flocculant, the suction differential pressure during operation for 3 months (25 ° C.)
(Converted value) was measured. The results are indicated by “●” in FIG.

From the results shown in FIG. 4, in the case of the fifth embodiment,
The suction differential pressure is sufficiently low even during the three-month operation, and the treatment of domestic wastewater can be stably performed over a long period of time.
It was found that the size was about 2 to 3 times larger than that of the case, and membrane fouling occurred in a short period of time, so that it was not possible to stably treat domestic wastewater.

[0048]

As described above, according to the wastewater treatment method of the present invention, an iron-based coagulant is added to a liquid to be treated containing activated sludge to perform a coagulation treatment, and the treatment liquid obtained by the coagulation treatment is treated. Even with the membrane separation treatment, the production of manganese oxide on the membrane surface is sufficiently suppressed, and membrane fouling can be prevented for a long period of time. Therefore, according to the present invention, the wastewater treatment can be stably performed over a long period of time.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an example of a wastewater treatment apparatus that performs a wastewater treatment method of the present invention.

FIG. 2 is a flowchart showing a membrane cell test apparatus used in Examples 3 to 5 and Comparative Example 3.

FIG. 3 is a graph showing the relationship between the aggregation pH and the membrane pressure difference.

FIG. 4 is a graph showing the relationship between the manganese concentration in the flocculant and the magnitude of the suction differential pressure.

[Explanation of symbols]

1,12 ... aeration tank, 2,9,14 ... aeration tube, 3,13 ...
Blower, 4 ... flocculation tank, 7 ... membrane separation tank, 15 ... membrane cell, 1
6 ... flat membrane.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C02F 1/44 C02F 1/44 K 1/52 1/52 K 3/12 3/12 DS (72) Inventor Okanaba Ryoyasu 5-9-1, Kita-Shinagawa, Shinagawa-ku, Tokyo Sumitomo Heavy Industries, Ltd. F term (reference) 4D006 GA06 GA07 HA01 HA41 HA93 HA95 JA53A JA55A JA71 KA02 KA03 KA41 KA72 KB13 KB30 KD12 KD17 KE15P KE15Q MA01 MA03 PA01 PB08 PB24 PC64 4D015 BA04 BA11 BB06 BB13 CA02 DA13 DC04 EA04 EA06 EA13 EA17 EA37 FA25 4D028 AC01 AC09 BC01 BC17 BD08 BD11 BD17 BE02 CA09 CD01 4D062 BA04 BA11 BB06 BB13 CA02 DA13 DC04 EA04 EA13 EA13 EA17 EA13 EA17

Claims (3)

[Claims] 1. An agglomeration treatment step in which an iron-based coagulant is added to a liquid to be treated containing activated sludge, and an aggregation treatment is performed, and the activated sludge obtained by the aggregation treatment in the aggregation treatment step and the aggregation sludge are mixed. A wastewater treatment method comprising a membrane separation step of subjecting a treatment liquid to be subjected to membrane separation, wherein the iron-based coagulant contains manganese at 0.1% by weight or less. 2. The wastewater treatment method according to claim 1, further comprising a step of adjusting the pH of the treatment liquid to 5.2 to 5.8. 3. An iron-based coagulant is added in the coagulation treatment step so that a weight ratio of iron hydroxide to the activated sludge is 0.1 to 0.5. A wastewater treatment method according to item 1.