JPH0768294A - Sewage treatment method - Google Patents

Abstract

(57) [Summary] [Structure] The amount of circulating liquid is maintained at an appropriate ratio to the amount of treated water, and aeration in the nitrification tank 6 is performed intermittently. Nitrate nitrogen in the mixed liquid in the nitrification tank 6 during non-aeration Or, the nitrite nitrogen is denitrified, and at the time of aeration, the mixed solution is suction-filtered by the membrane separation device 7 to take out the treated water. [Effect] When the nitrification tank 6 is made anaerobic during intermittent non-aeration by performing intermittent aeration in the nitrification tank 6, nitrate nitrogen or nitrite nitrogen remaining in the mixed solution in the nitrification tank 6 is endogenously respired by denitrifying bacteria. The nitrogen removal rate is 9
It can be improved to 0% or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sewage treatment method for denitrifying organic wastewater in the living system by a membrane separation activated sludge method.

[0002]

2. Description of the Related Art Conventionally, as a nitrogen removing method, intermittent aeration is performed in a single aeration tank to intermittently aerate nitrification and denitrification, and a denitrification tank that performs anoxic anaerobic treatment. There is a circulation denitrification method in which a nitrification tank that performs aerobic treatment is used, and a mixed solution of several times the amount of treated water to be denitrified is circulated from the nitrification tank to the denitrification tank.

On the other hand, in the membrane separation activated sludge method in which the membrane separation device is immersed in the aeration tank and the mixed liquid in the aeration tank is separated into activated sludge and treated water by the membrane separation device, air for aeration stirring is used. Since the membrane surface is cleaned by utilizing it, suction filtration of the treated water is performed only during aeration.

When performing denitrification treatment by this membrane separation activated sludge method, if intermittent aeration is carried out, there is a problem that the operating rate of the membrane separation device is lowered because the treated water is taken out only during aeration. In order to increase the operating rate of the membrane separation device and reduce the membrane area, the membrane separation device is installed in the nitrification tank in the circulation denitrification method and the membrane separation device is continuously operated.

[0005]

However, in the above-mentioned conventional structure, the nitrogen removal rate in the circulating denitrification method is practically determined because it is almost determined by the circulating liquid amount of the mixed liquid from the nitrification tank to the denitrification tank. 80% is a general nitrogen removal rate. Therefore, when a nitrogen removal rate of 90% or more is required, it is necessary to separately install an advanced processing device.

The present invention solves the above problems, and provides a sewage treatment method capable of achieving a nitrogen removal rate of 90% or more in the membrane separation activated sludge method without separately providing an advanced treatment device or the like. The purpose is to

[0007]

In order to solve the above-mentioned problems, the sewage treatment method of the present invention is an oxygen-free state of the treated water in the denitrification tank of the first stage and the mixed liquid which is circulated and returned from the nitrification tank of the second stage. While stirring and mixing, denitrifying nitrate nitrogen or nitrite nitrogen in the mixed liquid, and stirring and mixing the mixed liquid supplied from the denitrification tank in the subsequent nitrification tank by aeration, and at the same time, in the mixed liquid in an aerobic state. In a sewage treatment method in which ammonia nitrogen is nitrified into nitrate nitrogen or nitrite nitrogen, and a mixed solution is suction-filtered by a membrane separator immersed in a nitrification tank to obtain treated water, the amount of circulating liquid relative to the amount of treated water Maintain an appropriate ratio, intermittently perform aeration in the nitrification tank, denitrify nitrate nitrogen or nitrite nitrogen in the mixture in the nitrification tank during non-aeration, and aspirate the mixture with a membrane separator during aeration Filter It is obtained by a configuration in which take out the physical water.

Also, the circulating liquid amount of the mixed liquid from the nitrification tank to the denitrification tank is set to 3 times or more the treated water amount, and the aeration time in the intermittent aeration cycle of the nitrification tank is set to 2 hours or less.
The non-aeration time ratio is set to 0.5 or less.

Further, the organic substance is added to the nitrification tank as an organic carbon source during non-aeration. Further, the configuration is such that the circulation and return of the mixed liquid from the nitrification tank to the denitrification tank is stopped during non-aeration of the intermittent aeration cycle of the nitrification tank.

[0010]

With the above structure, the mixture and the denitrifying bacteria and nitrifying bacteria in the mixture circulate in the denitrification tank and the nitrification tank, and denitrify nitrate nitrogen or nitrite nitrogen in the mixture in the denitrification tank, In the nitrification tank, ammonium nitrogen in the mixed solution is nitrified to nitrate nitrogen or nitrite nitrogen, so the amount of the mixed solution circulating from the nitrification tank to the denitrification tank is appropriate for the amount of treated water taken out from the nitrification tank. If the retention time in the denitrification tank and the nitrification tank is properly secured by maintaining the magnification,
The mixed liquid in the nitrification tank has an extremely low concentration of ammonia nitrogen and is in a state in which nitrate nitrogen or nitrite nitrogen remains.

Therefore, if intermittent aeration is performed in the nitrification tank and the nitrification tank is made anaerobic during non-aeration, the nitrate nitrogen or nitrite nitrogen remaining in the mixed solution in the nitrification tank causes endogenous respiration of denitrifying bacteria. Since it is denitrified by nitrogen, the concentration of nitrogen in the treated water taken out through the membrane separator during aeration is small, and the nitrogen removal rate is improved.

Further, when the water to be treated is organic waste water of a living system having a relatively low nitrogen concentration, the amount of circulating liquid is set to 3 to 4 times the amount of treated water so that the mixed liquid in the nitrification tank contains The concentration of nitrate nitrogen or nitrite nitrogen is about 6 to 9 mg / l. Under this condition, the aeration time is 1 hour and the non-aeration time is 20 hours.
When intermittent aeration for a short cycle of ~ 30 minutes is performed, the nitrification tank is in a non-aerated anaerobic state before the concentration of nitrate nitrogen or nitrite nitrogen in the nitrification tank reaches the standard value in the conventional circulating denitrification method. Then, denitrification begins and the concentration of nitrate nitrogen or nitrite nitrogen in the mixture in the nitrification tank is 0-5.
It changes in the range of mg / l.

Therefore, at the start of aeration, that is, when the treated water begins to be taken out through the membrane separation device, there is almost no nitrate nitrogen or nitrite nitrogen in the treated water, and at the end of the aeration, nitric acid in the treated water is removed. The concentration of neutral nitrogen or nitrite nitrogen rises to near 5 mg / l, but the average nitrogen concentration in the treated water is small, and a nitrogen removal rate of 90% or more can be achieved. In addition, high-concentration nitrogen-containing wastewater such as human waste has the same effect by maintaining the circulating fluid amount 10 times or more.

Further, by adding an organic substance as an organic carbon source to the nitrification tank, the denitrifying bacteria change from endogenous respiration to extrinsic respiration, the denitrification rate at the time of non-aeration is increased, and the nitric acid remaining in the nitrification tank is increased. Denitrifying nitrogen or nitrite nitrogen in a shorter time.

Further, by stopping the circulation and return of the mixed liquid from the nitrification tank to the denitrification tank during non-aeration in the intermittent aeration cycle of the nitrification tank, it is possible to perform better denitrification in the nitrification tank during non-aeration.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the water to be treated 1 is a domestic organic wastewater containing nitrogen such as ammonia. This treated water 1
After passing through the coarse screen 2 to remove impurities, it is guided to the sand settling tank 3, and the supernatant water of the sand settling tank 3 is stored in the flow rate adjusting tank 4. Subsequently, the water to be treated 1 is put into the denitrification tank 5 from the flow rate adjusting tank 4.

In the denitrification tank 5, the water to be treated 1 and the mixed solution which is circulated and returned from the nitrification tank 6 in the subsequent stage are stirred and mixed in an oxygen-free state, and nitrate nitrogen or nitrite nitrogen in the mixed solution is mixed. Denitrify. Then, the mixed liquid of the denitrification tank 5 is supplied to the nitrification tank 6.

In this nitrification tank 6, the mixed liquid supplied from the denitrification tank 5 is agitated and mixed by intermittent aeration, and the nitrification tank 6 is
The mixed solution of is circulated back to the denitrification tank 5. The circulating liquid amount of this mixed liquid is an appropriate double amount of the treated water, and is 3 to 4 times in this embodiment. The mixed solution may be circulated and returned at any time, but in this embodiment, it is only returned during aeration. In the intermittent aeration cycle, the aeration time is set to 2 hours or less and the non-aeration time ratio is set to 0.5 or less. In the present embodiment, the aeration time is 1 hr and the aeration time is 20 to 30. It is a relatively short cycle of minutes.

Under the above operating conditions, in the nitrification tank 6,
In the aerobic state during aeration, nitrification of ammoniacal nitrogen in the mixed solution into nitrate nitrogen or nitrite nitrogen, and in the anaerobic state during non-aeration, the residual nitrate nitrogen or nitrite nitrogen is removed. It denitrifies by endogenous respiration of denitrifying bacteria.

On the other hand, the membrane separator 7 immersed in the nitrification tank 6 suction-filters the mixed solution at the time of aeration, and the treated water taken out is stored in the disinfection tank 8 and then discharged. This membrane separation device 7
Has an ultrafiltration membrane or a microfiltration membrane, and solid-liquid separates the activated sludge and the treated water in the mixed liquid, and the membrane surface is washed by the rising stirring flow by aeration.

By the way, when the treated water 1 is an organic wastewater of a living system having a relatively low nitrogen concentration, when the conventional circulating denitrification method is carried out with the circulating liquid amount being 3 to 4 times the treated water amount, nitrification is performed. The concentration of nitrate nitrogen or nitrite nitrogen in the mixed liquid in the tank 6 becomes about 6 to 9 mg / l. This state is shown in FIG. As is clear from FIG. 2, it takes about 2 hours for the concentration of nitrate nitrogen or nitrite nitrogen in the nitrification tank 6 to reach a normal value when simply performing the cycle denitrification.

However, the aeration time is 1 under the above operating conditions.
When intermittent aeration with a short cycle of 20 to 30 minutes for 20 minutes is performed before nitrification before the concentration of nitrate nitrogen or nitrite nitrogen in the nitrification tank 6 reaches the standard value in the conventional circulating denitrification method. The tank 6 becomes a non-aerated anaerobic state, and denitrification by endogenous respiration of the denitrifying bacteria starts, and the concentration of nitrate nitrogen or nitrite nitrogen decreases. This state is shown in FIG.
As is clear from FIG. 3, the concentration of nitrate nitrogen or nitrite nitrogen in the mixed solution in the nitrification tank 6 changes in the range of 0 to 5 mg / l.

Therefore, at the start of aeration, that is, when the treated water starts to be taken out through the membrane separation device 7, there is almost no nitrate nitrogen or nitrite nitrogen in the treated water, and at the end of the aeration, The concentration of nitrate nitrogen or nitrite nitrogen rises to near 5 mg / l, but the average nitrogen concentration in the treated water is small, and a nitrogen removal rate of 90% or more can be achieved. In addition, high-concentration nitrogen-containing wastewater such as human waste produces the same effect by maintaining the circulating fluid amount 10 times or more.

The results of applying the sewage treatment method of the present invention to the combined treatment septic tank are shown in Table 1, and the results of applying it to the human waste treatment facility are shown in Table 2.

[0025]

[Table 1]

[0026]

[Table 2]

Since the denitrification rate of the denitrifying bacteria due to endogenous respiration is relatively slow, if necessary, an organic substance 9 such as methanol is added to the nitrification tank 6 as an organic carbon source during non-aeration. This changes the denitrifying bacteria from endogenous respiration to external respiration,
The denitrification rate in the anaerobic state at the time of non-aeration is increased, and the nitrate nitrogen or the nitrite nitrogen remaining in the nitrification tank 6 can be denitrified in a shorter time.

Further, by stopping the circulation and return of the mixed liquid from the nitrification tank 6 to the denitrification tank 5 during non-aeration of the intermittent aeration cycle in the nitrification tank 6, NH ₄ --N from the denitrification tank 5 is stopped.
The inflow of carbon dioxide is eliminated and the denitrification rate is improved.

[0029]

As described above, according to the present invention, the circulating liquid amount of the mixed liquid which is circulated and returned from the nitrification tank to the denitrification tank is maintained at an appropriate ratio with respect to the amount of treated water taken out from the nitrification tank. If the nitrification tank is made anaerobic during non-aeration by performing intermittent aeration in, the nitrate nitrogen or nitrite nitrogen remaining in the mixture of the nitrification tank can be denitrified by endogenous respiration of denitrifying bacteria, The nitrogen removal rate can be improved to 90% or more.

When intermittent aeration for a short cycle is performed in the nitrification tank, the nitrification tank becomes a non-aerated anaerobic state before denitrification before the concentration of nitrate nitrogen or nitrite nitrogen in the nitrification tank reaches a normal value. Starts and the concentration of nitrate nitrogen or nitrite nitrogen in the mixed solution in the nitrification tank decreases, so that on average, almost no nitrogen component remains in the treated water.

By adding an organic substance as an organic carbon source to the nitrification tank and changing the denitrifying bacteria from endogenous respiration to extrinsic respiration, the denitrification speed can be increased and denitrification can be performed in a shorter time. By stopping the circulation and return of the mixed solution from the nitrification tank to the denitrification tank during non-aeration in the intermittent aeration cycle of the nitrification tank, it is possible to perform better denitrification in the nitrification tank during non-aeration.

[Brief description of drawings]

FIG. 1 is a block diagram showing a wastewater treatment method according to an embodiment of the present invention.

FIG. 2 is a graph showing changes with time in nitrogen concentration in a nitrification tank in the circulation denitrification method.

FIG. 3 is a graph showing changes with time in nitrogen concentration in a nitrification tank when intermittent aeration is performed.

[Explanation of symbols]

 1 Water to be treated 5 Denitrification tank 6 Nitrification tank 7 Membrane separation device 9 Organic matter

Claims (4)

[Claims] 1. In the denitrification tank of the first stage, the water to be treated and the mixed solution which is circulated and returned from the nitrification tank of the latter stage are stirred and mixed in an oxygen-free state, and the nitrate nitrogen or nitrite nitrogen in the mixed solution is denitrified. Then, the mixed liquid supplied from the denitrification tank in the subsequent nitrification tank is stirred and mixed by aeration, and in the aerobic state, the ammonia nitrogen in the mixed solution is nitrified into nitrate nitrogen or nitrite nitrogen and immersed in the nitrification tank. In a sewage treatment method that obtains treated water by suction filtration of the mixed liquid with the membrane separator, the circulating liquid amount is maintained at an appropriate ratio to the treated water amount, and aeration in the nitrification tank is intermittently performed, and nitrification is performed during non-aeration. A method for treating sewage, which comprises denitrifying nitrate nitrogen or nitrite nitrogen in a mixed solution in a tank, and suction-filtering the mixed solution with a membrane separator during aeration to take out treated water. 2. The sewage treatment method according to claim 1,
The circulating fluid amount of the mixed liquid from the nitrification tank to the denitrification tank is 3
The aeration time in the intermittent aeration cycle of the nitrification tank is set to 2 hours or less, and the non-aeration time ratio is set to 0.
A sewage treatment method, which is 5 or less. 3. The sewage treatment method according to claim 1 or 2, wherein an organic substance is added to the nitrification tank as an organic carbon source during non-aeration. 4. The sewage treatment method according to claim 1, wherein the circulation and return of the mixed liquid from the nitrification tank to the denitrification tank is stopped during non-aeration of the intermittent aeration cycle of the nitrification tank. Sewage treatment method.