JP3285754B2 - Sewage treatment apparatus and operation method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sewage treatment apparatus for denitrifying sewage such as domestic wastewater and a method of operating the same.

[0002]

2. Description of the Related Art As a sewage treatment apparatus for denitrifying sewage such as domestic wastewater, such as a merger treatment septic tank, a membrane separation system in which a plurality of membrane cartridges 2 are arranged at appropriate intervals inside a casing 1 as shown in FIG. An apparatus utilizing the apparatus 3 has been put into practical use, and a processing flow when such a membrane separation apparatus 3 is incorporated is as follows, for example.

In the treatment flow shown in FIG. 4, the wastewater 4 is introduced into a pretreatment facility 5 to perform a pretreatment such as removal of contaminants, and the pretreated wastewater 4a is introduced into a flow control tank 6 to be appropriately treated. Adjust to flow rate. Then, the sewage 4b having the appropriate flow rate
Is sequentially introduced into the denitrification tank 7 and the nitrification tank 8 into which the activated sludge has been introduced, and a part 9 of the activated sludge mixed liquid in the nitrification tank 8 is denitrated in the denitrification tank 8.
The nitrogen in the sewage 4b is removed by the action of activated sludge, and at this time, the remaining activated sludge mixed liquid in the nitrification tank 8 is solid-liquid separated by a membrane separation device immersed and installed in the tank. . Membrane permeated water 1 that has passed through the membrane surface of the membrane separator
0 is sent to a disinfection tank 11 for disinfection, and then discharged as treated water 12.

The nitrogen removal by activated sludge will be described in detail. In the denitrification tank 7, nitrate nitrogen contained in the wastewater 4b and the activated sludge mixture 9 circulated and returned from the nitrification tank 8 is activated under anaerobic conditions. In the nitrification tank 8, the ammonia nitrogen contained in the activated sludge mixture 13 transferred from the denitrification tank 7 is oxidized under the aerobic condition by the action of the activated sludge. To nitrate nitrogen. Such a method is called a circulating denitrification method. Usually, the amount of circulation of the activated sludge mixture 9 circulated and returned from the nitrification tank 8 to the denitrification tank 7 is set to about four times the daily average amount of sewage. , 80%.

However, when the nitrogen removal rate is set to 90% or more, the intermittent aeration method is generally employed because the above-described circulating denitrification method is inefficient. In the intermittent aeration method, as shown in FIG. 5, the sewage 4b adjusted to an appropriate flow rate in the flow rate adjustment tank 6 is guided to an aeration tank 14 in which a membrane separation device is immersed. At that time, the inflow of the sewage 4b is stopped, and a nitrification step of nitrifying ammonia nitrogen in the sewage 4b under an aerobic atmosphere for aeration while solid-liquid separation is performed by a membrane separation device; And a denitrification step of reducing and denitrifying nitrate nitrogen in the sewage water 4b under an anaerobic atmosphere in which the process has been stopped is alternately performed for an appropriate time.

In order to further increase the nitrogen removal rate, (9)
0% or more), it is difficult to increase the nitrogen removal rate only by biological treatment except for employing the two-stage denitrification method employed in human waste treatment. In the two-stage denitrification method, as shown in FIG. 6, a part of the activated sludge mixed liquid in the nitrification tank 8 is introduced while sequentially introducing an appropriate flow of sewage 4 b into the denitrification tank 7 and the nitrification tank 8 into which activated sludge has been introduced. By circulating and returning 9 to the denitrification tank 8, nitrogen in the wastewater 4b is removed by the action of activated sludge. Then, the remaining activated sludge mixed solution 15 in the nitrification tank 8
Is introduced into a second denitrification tank 16 and further denitrified while adding an organic substance 17 such as methanol as a respiration substrate for denitrifying bacteria and a cell synthesis substrate. Then, the activated sludge mixed solution 18 in the second denitrification tank 16 is introduced into the re-aeration tank 19 to remove the excess of the organic substances 17 added in the second denitrification tank 16, and the membrane separation immersed and installed in the tank. Solid-liquid separation is performed by the device. The sludge deposited in the re-aeration tank 19 is appropriately returned to the denitrification tank 7 as return sludge 20.

[0007]

However, when the immersion type membrane separation device is installed in the re-aeration tank as described above,
It is necessary to have a tank capacity of a certain degree or more to be able to install the immersion type membrane separation device.
It has been around 9 hours.

When a membrane separation device is used in a sewage treatment device for denitrifying sewage such as domestic wastewater, the average daily amount is usually taken into consideration in an emergency when a large amount of sewage including unknown water such as rainwater flows in. It is necessary to set a membrane area capable of treating about three times the amount of wastewater. However, when three times the amount of wastewater flows in, the membrane is often operated with the permeation flux of the membrane separation device being twice the amount of normal operation.
The membrane area is set to be about 1.5 times the average daily sewage volume. As described above, as a measure for an emergency in which a large amount of sewage flows, a membrane area of 1.5 times the membrane area required for processing the normal inflow sewage is required,
The re-aeration tank also needs to be set to 1.5 times the tank capacity.

On the other hand, when the activated sludge such as denitrifying bacteria in the re-aeration tank lacks an organic substance corresponding to a substrate, the activated sludge decomposes the organic substance taken into the body and performs internal respiration to obtain energy. More nitrogen is exhausted. Nitrification bacteria in the activated sludge nitrify this nitrogen, so that nitrate nitrogen is newly generated in the tank.When the residence time of the mixed solution in the re-aeration tank increases, The residual amount of nitrogen is increased.

As described above, when the immersion type membrane separation device is installed in the re-aeration tank, the capacity of the tank is increased and the residence time in the tank is prolonged, so that the organic matter corresponding to the activated sludge substrate tends to be insufficient. In such a case, nitrogen is released from the body of the activated sludge to be nitrate nitrogen, so that even in the two-stage denitrification method, the nitrate nitrogen in the treated water can be stably reduced to 5 mg / ml.
It could not be less than L.

An object of the present invention is to provide a sewage treatment apparatus capable of suppressing the generation of nitrate nitrogen in a re-aeration tank provided with an immersion type membrane separation apparatus, and an operation method thereof. Things.

[0012]

In order to solve the above-mentioned problems, a sewage treatment apparatus according to the present invention comprises a denitrification tank, a nitrification tank, a second denitrification tank, and a re-aeration tank arranged in this order, and supplies waste water and the like. A first, second, and third liquid feeder for opening a sewage introduction means for introducing sewage into a denitrification tank, and sending an activated sludge mixed liquid in the denitrification tank, the nitrification tank, and the second denitrification tank to a subsequent tank, respectively. Means, and a circulating means for circulating and returning a part of the activated sludge mixed solution in the nitrification tank to the denitrification tank, and in a sewage treatment apparatus in which a immersion type membrane separation device is installed inside the re-aeration tank, A separate immersion type membrane separation device used in an emergency is installed inside, and the re-aeration tank is configured to have a tank volume capable of accommodating a immersion type membrane separation device capable of treating an amount of sewage equivalent to a normal inflow amount.

In the sewage treatment apparatus of the present invention, the ratio of the membrane area of the immersion type membrane separation device installed in each of the re-aeration tank and the nitrification tank is about 2: 1 in the above configuration.

[0014] The method for operating the sewage treatment apparatus of the present invention includes:
Sewage such as domestic wastewater is sequentially introduced into the denitrification tank and the nitrification tank by the sewage introduction means and the first liquid sending means, and a part of the activated sludge mixture in the nitrification tank is circulated to the denitrification tank by the circulation means. And the remaining activated sludge mixture in the nitrification tank
During the denitrification by sequentially introducing the activated sludge mixture into the second denitrification tank and the re-aeration tank by the liquid sending means, the activated sludge mixed liquid is usually solidified by the immersion type membrane separation device installed in the tank in the re-aeration tank. Separates the liquid, sends the permeated water to the next treatment system such as a disinfection tank, and in an emergency where a large amount of sewage flows, even in the nitrification tank, the activated sludge mixed liquid is immersed by the immersion type membrane separation device installed in the tank. Solid-liquid separation is performed, and the membrane permeated water is directly sent to the next processing system such as the above-mentioned disinfection tank.

According to the above-described sewage treatment apparatus and its operation method, in the event of an emergency when a large amount of sewage flows, the immersion type membrane separation device installed in the nitrification tank responds to the emergency and the membrane installed in the re-aeration tank. Since the area, the membrane separation device, and the tank capacity of the re-aeration tank were set to be large enough to treat the inflowing amount of sewage, the residence time in the tank in the re-aeration tank can be shortened, and the generation of nitrate nitrogen can be suppressed.

At this time, if the ratio of the membrane area of the immersion type membrane separator installed in each of the re-aeration tank and the nitrification tank is set to about 2: 1, the inflow of the sewage is equal to the daily average amount of sewage. At about 1 time, the membrane separation device in the re-aeration tank is operated at the design permeate flux calculated from the daily average sewage volume, and the inflow of sewage is 1 to 1.5 times the daily average sewage volume. At the time, each membrane separation device inside the re-aeration tank and the nitrification tank is operated at the design permeation flux. This can be handled by operating with a permeation flux larger than the designed permeation flux. If each membrane separation device is operated at a permeation flux about twice as large as the designed permeation flux, it is possible to cope with sewage three times the daily average sewage expected in an emergency.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. In the sewage treatment apparatus shown in FIG. 1, a denitrification tank 21, a nitrification tank 22, a second denitrification tank 23, and a re-aeration tank 24 are arranged in this order, and sewage from a flow rate adjustment tank (not shown) is introduced. Sewage introduction pipe 25 is denitrification tank 2
1, denitrification tank 21, nitrification tank 22, second denitrification tank 2
A liquid sending means 29, 30, 31 for sending the activated sludge mixed liquid 26, 27, 28 inside the tank 3 respectively to a subsequent tank;
A circulation pipe 33 provided with a circulation pump 32 for circulating and returning a part of the activated sludge mixed liquid 27 in 2 to the denitrification tank 21 is provided. Inside the nitrification tank 22 and the re-aeration tank 24, immersion type membrane separation devices 34 and 35 are installed, respectively. An organic substance supply pipe 37 for supplying an organic substance such as methanol is opened in the second denitrification tank 23. A sludge return pipe 39 for returning sludge deposited from the activated sludge mixture liquid 38 in the tank to the denitrification tank 21 is led to the bottom of the re-aeration tank 24, and a pump 40 is connected to the sludge return pipe 39. Is equipped.

The membrane separators 34 and 35 have substantially the same construction as those described with reference to FIG. 3, and are respectively provided with a permeated water pipe 34b provided with a suction pump 34a or a membrane provided with a suction pump 35a. A permeate pipe 35b is provided at the upper part, and a diffuser pipe 34d communicating with the blower 34c or a diffuser pipe 35d communicating with the blower 35c is provided at the lower part. The membrane separation device 35 in the re-aeration tank 24 has a membrane area of a size almost corresponding to the daily average amount of sewage, and the membrane separation device 34 in the nitrification tank 22 has a membrane area of about a half thereof. Have.

The treatment flow using this sewage treatment apparatus is as follows:
The flow of the two-stage denitrification method described with reference to FIG. 6 is almost the same. Sewage is introduced into the denitrification tank 21 by the sewage introduction pipe 25, and the activated sludge mixed liquid 26 in the denitrification tank 21 is sent to the liquid sending means 2.
9, the mixture is introduced into the nitrification tank 22, and a part of the activated sludge mixture liquid 27 in the nitrification tank 22 is circulated to the denitrification tank 21 by the circulation pipe 33 to denitrify. The remaining activated sludge mixture 27 in the nitrification tank 22 is introduced into the second denitrification tank 23 by the liquid sending means 30, and further denitrified while adding an organic substance through the organic substance supply pipe 37. The activated sludge mixture 28 is introduced into the re-aeration tank 24 to remove excess organic matter.

However, under normal conditions, the activated sludge mixture 38 in the tank is separated into solid and liquid only by the membrane separator 35 in the re-aeration tank 24, and the membrane permeated water is disinfected by the membrane permeation pipe 35b (not shown). And release it as appropriate.

In an emergency where a large amount of wastewater flows, the nitrification tank 2
2 also, the activated sludge mixed liquid 27 in the tank is separated into the membrane separation device 3
The liquid is separated into solid and liquid by 4 and the permeated water is directly sent to a disinfection tank (not shown) by a permeated water pipe 34b.

Specifically, when the amount of inflow of sewage is about one time the daily average amount of sewage, the membrane separation device 35 in the re-aeration tank 24 is operated at the designed permeation flux calculated from the average amount of sewage daily. I do.
When the inflow of the sewage 4b is 1 to 1.5 times the daily average sewage, the membrane separation device 3 inside the re-aeration tank 24 and the nitrification tank 22 is used.
5 and 34 are operated at the designed permeation flux, respectively, and when the inflow sewage is larger than that, the membrane separation devices 35 and 34 inside the re-aeration tank 24 and the nitrification tank 22 are each operated at a permeation flux larger than the designed permeation flux. Operate with flux. When three times the amount of sewage flows in daily average sewage assumed in an emergency, the membrane separation devices 35 and 34 are operated at a permeation flux approximately twice as large as the designed permeation flux.

In the above-described sewage treatment apparatus and treatment flow, in case of emergency when a large amount of sewage flows, the membrane area and the membrane installed in the re-aeration tank 24 are handled by the membrane separator 34 installed in the nitrification tank 22. Since the size of the separator 35 is set to be approximately equal to the daily average amount of sewage, and the tank capacity of the re-aeration tank 24 is made smaller than before, the residence time in the tank in the re-aeration tank 24 becomes shorter, and internal respiration such as denitrification bacteria occurs. The generation of nitrate nitrogen is suppressed.

Table 1 below shows the nitrate nitrogen concentration in the permeated water taken out of the re-aeration tank. In the conventional sewage treatment apparatus shown in Table 1 and the sewage treatment apparatus of the present invention, the membrane area immersed and installed in the re-aeration tank is smaller in the sewage treatment apparatus of the present invention, Each of the capacitors has a size proportional to the film area.

[0025]

[Table 1]

FIG. 2 shows the change over time in the concentration of nitrate nitrogen in the permeated water taken out of the re-aeration tank. From FIG. 2, it can be seen that the concentration of nitrate nitrogen in the membrane permeated water increases as the aeration time in the re-aeration tank, that is, the residence time in the tank, increases. From Table 1, it can be seen that the sewage treatment apparatus of the present invention is a conventional sewage treatment apparatus. It can be seen that the residence time in the re-aeration tank is shorter than that of the apparatus, and the concentration of nitrate nitrogen in the permeated water is reduced.

[0027]

As described above, according to the present invention, a membrane separation device having a membrane area sufficient to treat almost daily average sewage is installed in the re-aeration tank, and unknown water such as rainwater flows in. As an emergency measure, by installing a membrane separation device in the nitrification tank, the tank capacity of the re-aeration tank can be made smaller than before, and as a result, the residence time in the tank in the re-aeration tank can be shortened. In addition, the generation of nitrate nitrogen due to endogenous respiration such as denitrifying bacteria can be suppressed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of a sewage treatment apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the concentration of nitrate nitrogen in the permeated water taken out of the re-aeration tank and the aeration time in the re-aeration tank.

FIG. 3 is a partially broken perspective view showing the entire configuration of a conventional membrane separation device used in the sewage treatment apparatus shown in FIG.

FIG. 4 is a flowchart illustrating a conventional circulation denitrification method.

FIG. 5 is a flowchart for explaining a conventional intermittent aeration method.

FIG. 6 is a flowchart illustrating a conventional two-stage denitrification method.

[Explanation of symbols]

 21 Denitrification tank 22 Nitrification tank 23 Second denitrification tank 24 Reaeration tank 25 Sewage inlet pipe 27 Activated sludge mixture 29,30,31 Liquid supply means 33 Circulation pipe 34,35 Membrane separator 34b, 35b Membrane permeate pipe 38 Activated sludge Mixture

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-232597 (JP, A) JP-A-3-77699 (JP, A) JP-A-60-94196 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) C02F 3/30-3/34

Claims (3)

(57) [Claims] 1. A denitrification tank, a nitrification tank, a second denitrification tank, and a re-aeration tank are arranged in this order, and a sewage introduction means for introducing sewage such as domestic wastewater is opened in the denitrification tank. First, second, and third liquid feeding means for sending the activated sludge mixed liquid in the second and third denitrification tanks to the subsequent tank, respectively, and circulating and returning a part of the activated sludge mixed liquid in the nitrification tank to the denitrification tank In the sewage treatment apparatus provided with a circulating means to perform, the immersion type membrane separation device is installed inside the re-aeration tank, in the case of an emergency separately inside the nitrification tank
A sewage treatment apparatus, wherein a immersion type membrane separation device to be used is installed, and the re-aeration tank is configured to have a tank capacity capable of accommodating an immersion type membrane separation device capable of treating a sewage amount corresponding to a normal inflow amount. 2. The sewage treatment apparatus according to claim 1, wherein the ratio of the membrane area of the immersion type membrane separation device installed in each of the re-aeration tank and the nitrification tank is about 2: 1. 3. The method for operating a sewage treatment apparatus according to claim 1 or 2, wherein sewage such as domestic wastewater is supplied to a denitrification tank and a nitrification tank by a sewage introduction means and a first liquid supply means. In addition, the activated sludge mixture in the nitrification tank is partly circulated to the denitrification tank by the circulation means, and the remaining activated sludge mixture in the nitrification tank is subjected to the second dehydration by the second and third liquid sending means. At the time of introducing nitrogen into the nitrification tank and the re-aeration tank in order to perform denitrification, usually, in the re-aeration tank, the activated sludge mixed liquid is solid-liquid separated by the immersion type membrane separation device installed in the tank, and the membrane permeated water is discharged. To the next treatment system such as a disinfection tank, and in the event of a large amount of wastewater flowing into the tank, even in the nitrification tank, the activated sludge mixture is separated into solid and liquid by the immersion type membrane separation device installed in the tank, Operation of a sewage treatment apparatus characterized in that the wastewater is directly sent to the next treatment system such as the disinfection tank. Method.