JP2000005566A - Treatment of sewage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the treating quantity of sewage without decreasing the purifying ability for water by treating the sewage after biologically treated in 2 stages with membranes each having a specific average pore diameter to suppress the construction and operation cost. SOLUTION: The 1st stage treatment is carried out by sending the sewage treated with aerobic microorganism in a biologically treating tank 10 to the membrane 11 using a flat membrane, a hollow fiber membrane or a ceramic membrane and having >=0.5 μm average pore diameter with a pump 20 operated. The filtrate after flocculation treatment in a flocculation treatment tank 12 is sent to the membrane 13 using a hollow fiber membrane, a cylindrical membrane or the like and having <0.5 μm average pore diameter to be treated in the 2nd stage. The filtrate treated with the membrane 13 is discharged to the outside or reutilized and the concentrated liquid is returned to the flocculation treatment tank 12. As a result, the treating rate is acceleated by reducing the load on and after next process without filtering no large solid material in the 1st stage treatment to increase the treating quantity without lowering the level of the treated water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater suitable for using a biological treatment method such as a human waste treatment plant or a sewage treatment plant.

[0002]

2. Description of the Related Art
A membrane is known as a means of solid-liquid separation after biological treatment of sewage. For example, Japanese Patent Application Laid-Open No. 4-16300 discloses a method using an ultrafiltration membrane.
No. 372 discloses a method combining two membranes, a microfiltration membrane and a reverse osmosis membrane.

[0003] The solid-liquid separation method using such a membrane is excellent in that it has a high water purification ability and does not require a space as in the case of using a sedimentation tank, but has a small throughput per day. There is room for improvement in this respect. As a method of increasing the throughput, it is conceivable to greatly increase the number of membranes, but this is not a practical method in consideration of construction costs and operation costs.

[0004] It is an object of the present invention to provide a sewage treatment method capable of suppressing construction costs and operation costs and increasing the throughput of sewage without lowering the water purification capacity.

[0005]

Means for Solving the Problems The present inventor paid attention to a two-stage film processing method, and as a result of study, found an optimal combination of the first and second stage films, and completed the present invention. .

[0006] The present invention relates to a biologically treated sewage,
Provided is a method for treating sewage, comprising performing a first-stage treatment with a membrane having an average pore size of 0.5 μm or more, and then performing a second-stage treatment with a membrane having an average pore size of less than 0.5 μm.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for treating wastewater of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram for explaining one embodiment of the present invention, and FIG. 2 is a conceptual diagram for explaining another embodiment of the present invention.

First, an embodiment shown in FIG. 1 will be described.
As shown in FIG. 1, sewage is treated by aerobic microorganisms (sludge) in a biological treatment tank 10. This biological treatment tank 10
Contains treated water and sludge in a suspended state. In the wastewater treatment method of the present invention, for example, the biological treatment tank 1
The liquid in 0 becomes “sewage that has undergone biological treatment”.

The biologically treated sewage is sent to the membrane 11 by driving the pump 20 to perform the first stage treatment. In this case, instead of directly extracting the liquid from the biological treatment tank 10 with a pump, a raw water tank for membrane treatment is once provided, and a pump 2 is provided therefrom.
0 may be supplied to the film 11. The membrane 11 used in the first-stage treatment has an average pore diameter of 0.5 μm or more.
The type of the membrane 11 is not particularly limited as long as it has the above average pore diameter, and a flat membrane, an asymmetric nonwoven fabric, a hollow fiber membrane, a ceramic membrane, or the like can be used. Conditions such as the pressure and the flow rate during the treatment can be appropriately determined according to the type of the film and the like.

In the first stage processing of such a membrane 11, large solids are not filtered and are not sent to the next processing step, so that the load on the subsequent steps is reduced and the subsequent processing speed is reduced. Can be increased. Further, since the fine suspension passes through the membrane 11, the amount of solids in the concentrated liquid returned to the biological treatment tank 10 is reduced, and the burden required for the operation of adjusting the amount of excess sludge in the biological treatment tank 10 is reduced. You.

After performing the first stage processing on the film 11,
The filtrate (primary treatment liquid) is subjected to a membrane 13 for performing the second stage treatment.
Before that, the coagulation treatment can be performed in the coagulation treatment tank 12.

Next, the filtrate subjected to the coagulation treatment in the coagulation treatment tank 12 is sent to the membrane 13 by driving the pump 21,
Perform the processing of the column. In this case, instead of directly extracting the liquid from the coagulation treatment 12 with a pump, a raw water tank for membrane treatment may be once provided, and then supplied to the membrane 13 by the pump 21 from here. The membrane 13 used in the second stage treatment has an average pore diameter of 0.5 μm.
less than m. The type of the membrane 13 is not particularly limited as long as it has the above-mentioned average pore diameter.
Those having a molecular weight of 000 daltons or less, preferably 200,000 daltons or less can be used. Conditions such as the pressure and the flow rate during the treatment can be appropriately determined according to the type of the film and the like.

In the second stage processing of the membrane 13, fine suspended matter that has passed through the membrane 11 is also removed. The filtrate (secondary treatment solution) that has been subjected to the second stage treatment in the membrane 13 is discharged or reused, and the concentrated solution is collected in the coagulation treatment tank 12.
Return to.

Next, another embodiment shown in FIG. 2 will be described. As shown in FIG. 2, sewage is treated by aerobic microorganisms (sludge) in a biological treatment tank 50. The biological treatment tank 50 contains treated water and sludge in a suspended state.

The biologically treated sewage is sent to the flat membrane 51 by driving the pump 60 to perform the first-stage treatment. In this case, instead of directly extracting the liquid from the biological treatment tank 50 with a pump, a raw water tank for membrane treatment is once provided, and a pump 6 is provided therefrom.
0 may be supplied to the film 51. The flat membrane 51 used in the first-stage treatment preferably has an average pore diameter of 0.5 μm or more. As such a flat membrane 51, a flat membrane, a combination of two or more flat membranes, an asymmetric nonwoven fabric, a combination of two or more asymmetric nonwoven fabrics, a combination of a flat membrane and an asymmetric nonwoven fabric, or the like is used. Can be.

The conditions such as the pressure and the flow rate during the treatment can be appropriately determined according to the type of the film and the like.

In the first stage processing of such a flat membrane 51, a large solid is not filtered and is not sent to the next processing step, so that the load in the subsequent steps is reduced, and the subsequent processing is performed. Speed can be increased. Also,
Since the fine suspension passes through the flat membrane 51, the biological treatment tank 5
The amount of solids in the concentrate returned to 0 is reduced, and the burden required for the operation of adjusting the amount of excess sludge in the biological treatment tank 50 is reduced.

Next, after the first treatment in the flat membrane 51, the filtrate (primary treatment liquid) is sent to the hollow fiber membrane or the cylindrical membrane 52 for the second treatment. At this time, the filtrate can be sent by a pump (not shown), but the driving force for sending the activated sludge to the flat membrane 51 by the pump 60 can be used as it is as the driving force for sending the filtrate to the membrane 52. . In this way, by passing the liquid through the two membranes with the driving force of one pump, the amount of energy consumption can be reduced.

The hollow fiber membrane or cylindrical membrane 52 used in the second stage treatment preferably has an average pore diameter of less than 0.5 μm. As the hollow fiber membrane or the cylindrical membrane 52, the molecular weight cut off is 500,000 daltons or less, preferably 200,000 daltons.
Those having a value of 00 dalton or less can be used.

The conditions such as the pressure and the flow rate during the treatment can be appropriately determined according to the type of the film.

In the second stage treatment of such a hollow fiber membrane or cylindrical membrane 52, fine suspended matter that has passed through the flat membrane 51 is also removed. The filtrate (secondary treatment liquid) that has been subjected to the second-stage treatment in the hollow fiber membrane or the cylindrical membrane 52 is discharged or reused, and the concentrated liquid is returned to the biological treatment tank 50.

In the method as shown in FIG. 2, since coarse filtration is performed by a flat membrane in the first stage treatment, a hollow fiber membrane having a high treatment capacity can be used in the second stage treatment, and the throughput is increased. Can be greatly improved.

[0023]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 Sewage treatment was performed according to the flow shown in FIG. First, M
The activated sludge having an LSS of 7000 ppm was passed under pressure through a flat membrane (FM-300; manufactured by Fuji Photo Film Co., Ltd.) having an average pore diameter of 3 μm, and was filtered until the amount of the activated sludge became 70%.
The average filtration speed was 1.0 m / day. Next, after adding ferric chloride as a coagulant to the primary treatment liquid to cause coagulation,
The aggregated solution was pressurized and passed through a flat membrane (FM-22; manufactured by Fuji Photo Film Co., Ltd.) having an average pore size of 0.22 μm, and was filtered until the amount of the primary treatment solution became 70%. Average filtration speed is 0.4m
/ Day. The resulting secondary treatment liquid had a turbidity of 1 degree or less and a COD of 55 mg / L.

Example 2 In the first stage treatment, the average pore size of the separation surface was 15 μm.
asymmetric non-woven fabric (F
C3105; manufactured by Japan Vilene Co., Ltd., and in the second step, a cylindrical membrane having a cut-off molecular weight of 40,000 daltons and an inner diameter of 14 mm (DUYL010; manufactured by Daisen Membrane Systems Co., Ltd.) was used. Treated sewage in the same manner as in Example 1. As a result, the average filtration speed in the first stage treatment was 1.5 m / day, and the average filtration speed in the second stage treatment was 1.2 m / day. The resulting secondary treatment liquid had a turbidity of 1 degree or less and a COD of 26 mg / L.

Example 3 In the second stage treatment, the molecular weight cut off was 150,000.
Hollow fiber membrane (FUY15E) with a diameter of 1.4 mm in Dalton
1; wastewater was treated in the same manner as in Example 1 except that Daisen Membrane Systems Co., Ltd. was used. As a result, the average filtration speed in the first stage treatment was 1.0 m
/ Day, and the average filtration rate in the second-stage treatment was 0.7 m / day. The obtained secondary treatment liquid had a turbidity of 1 degree or less and a COD of 32 mg / L.

Comparative Example 1 Wastewater was treated in the same manner as in Example 1 except that a flat membrane (FM-22; manufactured by Fuji Photo Film Co., Ltd.) having an average pore diameter of 0.22 μm was used in the first stage treatment. did. as a result,
The average filtration speed in the first-stage treatment was 0.3 m / day, and the average filtration speed in the second-stage treatment was 0.5 m / day.
/ Day. The resulting secondary treatment liquid had a turbidity of 1 degree or less and a COD of 37 mg / L.

As is clear from the comparison between Examples 1 to 3 and Comparative Example 1, when the method for treating sewage of the present invention is applied, the amount of treatment per day can be reduced without reducing the purification capacity of sewage. Can be significantly increased.

Example 4 Sewage treatment was performed according to the flow shown in FIG. First, M
The activated sludge liquid having an LSS of 7000 mg / L was pressurized and passed through an asymmetric nonwoven fabric (FC3105; manufactured by Japan Vilene Co., Ltd.) having an average pore size of 15 μm on the separation surface and an average pore size of about 40 μm on the support portion. Next, the primary treatment liquid was subjected to a fractionation molecular weight of 15
A hollow fiber membrane (FU) having a diameter of 1,000 mm and an inner diameter of 1.4 mm
Y15E1; Daisen Membrane Systems Co., Ltd.
(Independent pressurization), and the activated sludge amount is 70
%. The average filtration speed was 0.9 m / day. The obtained secondary treatment liquid has a turbidity of 1 degree or less and CO
D was 95 mg / L.

Comparative Example 2 A treatment was performed in the same manner as in Example 4 except that the first-stage treatment with an asymmetric nonwoven fabric was not performed. The average filtration speed is 0.5m /
It was a day. The resulting secondary treatment liquid has a turbidity of 1 degree or less,
COD was 97 mg / L.

As is clear from the comparison between Example 4 and Comparative Example 2, when the method for treating sewage of the present invention is applied, the amount of treatment per day is greatly increased without lowering the purification capacity of sewage. be able to.

[0032]

By applying the wastewater treatment method of the present invention, the amount of treatment can be greatly increased without lowering the purification level of treated water.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram for explaining an embodiment of the present invention.

FIG. 2 is a conceptual diagram for explaining another embodiment of the present invention.

[Procedure amendment]

[Submission date] November 20, 1998 (1998.11.
20)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006] The present invention relates to a biologically treated sewage,
Provided is a method for treating sewage, comprising performing a first- stage treatment with a membrane having an average pore size of 0.5 μm or more, and then performing a second-stage treatment with a membrane having an average pore size of less than 0.5 μm.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B01D 63/08 B01D 63/08 69/04 69/04 69/06 69/06 69/08 69/08 C02F 1/44 C02F 1/44 K 1/52 1/52 Z

Claims (8)

[Claims] 1. A method comprising: performing a first-stage treatment on a biologically treated sewage with a membrane having an average pore size of 0.5 μm or more, followed by a second-stage treatment with a membrane having an average pore size of less than 0.5 μm. A method for treating wastewater. 2. The method for treating sewage according to claim 1, wherein a coagulation treatment is performed between the first-stage treatment and the second-stage treatment. 3. The method for treating sewage according to claim 1, wherein the membrane used in the second stage treatment is an ultrafiltration membrane having a molecular weight cut-off of 500,000 daltons or less. 4. A method for treating sewage, comprising subjecting sewage subjected to biological treatment to a first-stage treatment using a flat membrane, followed by a second-stage treatment using a hollow fiber membrane or a cylindrical membrane. . 5. The method according to claim 4, wherein the flat membrane has an average pore diameter of 0.5 μm or more, and the hollow fiber membrane or the cylindrical membrane has an average pore diameter of less than 0.5 μm. 6. A hollow fiber membrane or a cylindrical membrane having a molecular weight cut off of 5
5. An ultrafiltration membrane having a molecular weight of 000 daltons or less.
Or the method for treating sewage according to 5. 7. The method according to claim 4, wherein the pressure is applied only in the first-stage processing, and the second-stage processing is performed using the pressure.
The method for treating sewage described in the above. 8. The method for treating sewage according to claim 1, wherein the membrane used in the first-stage treatment is an asymmetric nonwoven fabric.