JPH09201598A - Treatment of sewage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove phosphorus in a biologically effective manner without adding a flocculant and to prevent the lowering of a removal ratio of nitrogen. SOLUTION: Absolute unaerobic operation stopping the circulation of a nitrified mixed liquid 9 to a denitrifying tank 5 to hold the denitrifying tank 5 to an absolute unaerobic atmosphere and a facultative unaerobic operation circulating the nitrified mixed liquid 9 to the denitrifying tank 5 to hold the denitrifying tank 5 to a faculative unaerobic atmosphere are alternately performed by a predetermined time. At a time of absolute unaerobic operation, phosphorus in sewage is effectively removed as environment suitable for activated sludge participated in dephosphorization and, at a time of facultative unaerobic operation, nitrogen in sewage can be effectively removed as environment suitable for activated sludge participated in denitrification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method, and more particularly to a wastewater treatment method performed in a combined treatment septic tank or the like.

[0002]

2. Description of the Related Art Conventionally, in a domestic wastewater treatment equipment such as a combined treatment septic tank, a treatment flow as shown in FIG. 3, for example, has been carried out.

Sewage is introduced into a pretreatment facility 3 equipped with a rough screen 1 and a flow rate adjusting tank 2 to remove sand and large contaminants contained in the wastewater, and to adjust the flow rate to mitigate inflow fluctuations. Then, the sewage 4 at an appropriate flow rate is sent to the biological treatment tank 7 including the denitrification tank 5 and the nitrification tank 6 in which the membrane separation device 6a is immersed.

In the biological treatment tank 7, the sewage 4 is introduced into the denitrification tank 5 and treated with activated sludge under anaerobic conditions, and the denitrification mixture 8 containing the activated sludge in the denitrification tank 5 is introduced into the nitrification tank 6. While transferring and treating with activated sludge under aerobic conditions, a part of the nitrification mixture 9 containing activated sludge in the tank is circulated back to the denitrification tank 5 to remove nitrogen contained in the wastewater 4. The organic substances are biologically removed using the hydrogen supply source, and the remaining nitrification mixture 9 in the nitrification tank 6 is subjected to solid-liquid separation by the membrane separation device 6a.

At this time, an inorganic coagulant is added to the nitrification tank 6 so that phosphorus contained in the wastewater 4 and reaching the nitrification tank 6 is combined with the metal ions in the coagulant to insolubilize it. Then, the membrane permeated water 10 separated by the membrane separation device 6a is sent to the disinfection tank 11 to be disinfected and then discharged as treated water 12, and the activated sludge 13 containing the insolubilized phosphorus remaining in the nitrification tank 6 is appropriately taken out. It is sent to the slag sludge storage tank 14 and carried out as slag sludge 15 for disposal.

[0006]

However, although the above-mentioned conventional method can reliably remove phosphorus, it requires a coagulant storage facility and an injection facility, and disposes in proportion to the coagulant injection amount. It has drawbacks such as increased sludge volume.

Although biological dephosphorization is possible with activated sludge, in the above-mentioned conventional method, the nitrification mixture 9 is circulated and returned to the denitrification tank 5, so that it is constantly converted into nitrate nitrogen as nitric nitrogen. Oxygen and dissolved oxygen are supplied, and the denitrification tank 5 has a facultative anaerobic atmosphere. Such a facultative anaerobic atmosphere is suitable for activated sludge involved in denitrification, but is not desirable for activated sludge (polyphosphoric acid accumulating bacteria etc.) that exerts a dephosphorization action in an absolutely anaerobic environment. The phosphorus removal effect by sludge was small, and the phosphorus removal rate was about 50% at maximum.

The present invention solves the above problems, and an object thereof is to provide a method for treating sewage which can be biologically dephosphorized without adding a coagulant and which does not reduce the removal rate of nitrogen. It is what

[0009]

In order to solve the above-mentioned problems, the method for treating sewage according to claim 1 of the present invention is such that sewage is made to flow from a flow rate adjusting tank to a denitrification tank and treated with activated sludge to remove the sewage. The denitrification mixed solution containing activated sludge in the nitrification tank is transferred to the nitrification tank and treated by the activated sludge, and the nitrification mixed solution containing the activated sludge in the nitrification tank is immersed in the tank to form a solid-liquid Separating the membrane-permeated water to the outside of the tank, and part of the nitrification mixture is circulated to the denitrification tank.In the treatment method of sewage, the circulation of the nitrification mixture to the denitrification tank is stopped to make the denitrification tank anaerobic. The absolute anaerobic operation for maintaining the atmosphere and the facultative anaerobic operation for circulating the nitrification mixture to the denitrification tank to maintain the denitrifying tank in the permeable anaerobic atmosphere are alternately performed for a predetermined time, and nitrogen in the wastewater is discharged. And phosphorus are biologically removed.

The method for treating sewage according to claim 2 is:
A process of performing absolute anaerobic operation and facultative anaerobic operation for a predetermined time is defined as one operation cycle, and during absolute anaerobic operation, the amount of sewage obtained by dividing the daily average sewage treatment amount by the number of operation cycles per day is a denitrification tank. The flow of sewage from the flow control tank to the denitrification tank is stopped during facultative anaerobic operation.

In the method for treating sewage according to the third aspect, the absolute anaerobic operation is 0.5 to 1 hour, and the facultative anaerobic operation is 1 to 1.
The cycle operation is carried out 8 to 16 times per day for 2 hours.

According to the above-mentioned constitution of claim 1, during the absolutely anaerobic operation, since the nitrification mixed solution containing nitrate nitrogen is not circulated, the denitrification tank is maintained in the absolutely anaerobic atmosphere and in the denitrification tank. In an absolutely anaerobic atmosphere, polyphosphate-accumulating bacteria etc. in activated sludge discharge the phosphorus taken up in the body into water and ingest organic matter in the water, and the discharged phosphorus and polyphosphate-accumulating bacteria etc. Transferred to nitrification tank. In the nitrification tank, polyphosphoric acid-accumulating bacteria decompose the organic substances in the body while taking in phosphorus using the energy generated by the decomposition in an aerobic atmosphere, and nitric acid bacteria in the activated sludge generate ammonia nitrogen in the water. Is oxidized to nitrate nitrogen.

During a facultative anaerobic operation, the denitrification tank is maintained in a facultative anaerobic atmosphere because the nitrification mixed solution containing nitrate nitrogen is circulated, and in the denitrification tank, in a facultative anaerobic atmosphere, Denitrifying bacteria etc. in the activated sludge reduce nitrate nitrogen while decomposing organic matter in water to denitrify, and in the nitrification tank under the aerobic atmosphere, polyphosphoric acid accumulating bacteria etc. In addition to taking in, nitric acid bacteria oxidize ammoniacal nitrogen in water to nitrate nitrogen.

Therefore, if the activated sludge in the nitrification tank such as polyphosphoric acid-accumulating bacteria that has taken up phosphorus is appropriately discharged, both nitrogen and phosphorus in the wastewater can be effectively removed by the above-mentioned method. .

According to the second aspect of the present invention, the amount of daytime air treatment is the same as that of the conventional one, and the sewage flows in intensively during the absolute anaerobic operation. Therefore, the denitrification tank during the absolute anaerobic operation is absolutely anaerobic. In addition to maintaining a sexual atmosphere, a large amount of organic matter is supplied, and a more desirable environment for polyphosphate-accumulating bacteria and the like is secured.

According to the third aspect, the residence time in the denitrification tank and the nitrification tank such as the septic tank is 8 to 12
In a general membrane-separation biological treatment tank, the appropriate absolute anaerobic operating time, facultative anaerobic operating time, and the number of operating cycles can be secured. As a result, it is possible to suitably dephosphorize by sufficiently discharging phosphorus in an absolutely anaerobic atmosphere with a proper treatment amount per one operation cycle, and to perform suitable denitrification in a facultative anaerobic atmosphere. Even when sewage is allowed to flow in only during absolute anaerobic operation as described in claim 2, sewage can be received without particularly increasing the size of the denitrification tank, and the sewage can be removed during facultative anaerobic operation without any inflow of sewage. The denitrification can be suitably performed in a state where a sufficient amount of BOD exists in the nitrification tank.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method for treating sewage of the present invention will be described below. Since the basic processing flow in this embodiment is the same as the conventional processing flow described with reference to FIG. 3, it will be described with reference to FIG. That is, the sewage 4 is made to flow from the flow rate adjusting tank 3 to the denitrification tank 5 and treated with activated sludge, and the denitrification mixture 8 containing the activated sludge in the denitrification tank 5 is transferred to the nitrification tank 6 and treated with activated sludge. Then, the nitrification mixed solution containing the activated sludge in the nitrification tank 6 is subjected to solid-liquid separation by the membrane separation device 6a installed in the tank, and the membrane permeated water 10 is sent to the outside of the tank. Circulate to the denitrification tank 5.

However, the absolute anaerobic operation for maintaining the denitrification tank 5 in the absolutely anaerobic atmosphere by stopping the circulation of the nitrification mixture 9 to the denitrification tank 5 as shown in FIG. 1 and shown in FIG. Such a nitrification mixed solution 9 is circulated to the denitrification tank 5 and a facultative anaerobic operation of maintaining the denitrification tank 5 in a facultative anaerobic atmosphere is alternately performed for a predetermined time, and the activated sludge 13 in the nitrification tank 6 is Eject appropriately.

When performing the absolute anaerobic operation shown in FIG. 1, a predetermined amount of dirty water 4 is supplied from the flow rate adjusting tank 3 to the denitrification tank 5 in a state where the circulation of the nitrification mixture 9 to the denitrification tank 5 is stopped. The membrane separator 6a is caused to flow in, the membrane permeate 10 is sent to the outside of the tank, and the denitrification mixed solution 8 having an amount substantially equal to the amount of the membrane permeate sent to the outside of the tank is transferred to the nitrification tank 6 for a predetermined time. To do.
Here, the predetermined amount of sewage 4 is the amount of sewage 4 obtained by dividing the daily average sewage treatment amount by the value of the number of operation cycles of (absolute anaerobic operation + facultative anaerobic operation) per day.

When the facultative anaerobic operation shown in FIG. 2 is performed, the membrane separation device 6a is operated while the inflow of the dirty water 4 from the flow rate adjusting tank 3 to the denitrification tank 5 is stopped. 10 is sent to the outside of the tank, an appropriate amount of nitrification mixed solution 9 is circulated to the denitrification tank 5 to secure the required treated water quality, and an amount of the denitrification mixed solution 8 corresponding to the circulation amount of the nitrification mixed solution 9 is circulated. Is transferred to the nitrification tank 6 for a predetermined time.

As a result, during the absolutely anaerobic operation, the denitrification tank 5 is maintained in an absolutely anaerobic atmosphere because the nitrification mixed solution 9 containing nitrate nitrogen is not circulated, and at the same time, the sewage 4 which flows in intensively. Depending on the amount of organic matter (B
OD) is supplied to form a desirable environment for the polyphosphate-accumulating bacteria in the activated sludge and the nitrification tank 6 is maintained in an aerobic atmosphere.

As a result, in the denitrification tank 5, in an absolutely anaerobic atmosphere, the phosphorus taken up by the polyphosphate-accumulating bacteria and the like is discharged into the water and the organic matter in the water is ingested to discharge the discharged phosphorus. The polyphosphate-accumulating bacteria and the like are transferred to the nitrification tank 6.

In the nitrification tank 6, polyphosphoric acid-accumulating bacteria and the like decompose phosphorus in the body by using energy generated by decomposing organic substances in the body under aerobic atmosphere, and nitric acid bacteria in the activated sludge in water. To oxidize the ammonia nitrogen of to the nitrate nitrogen.

During the facultative anaerobic operation, the denitrification tank 5
Is maintained in a facultative anaerobic atmosphere by circulating the nitrification mixture 9 containing nitrate nitrogen, and the nitrification tank 6 is maintained in an aerobic atmosphere.

As a result, in the denitrification tank 5, denitrifying bacteria and the like in the activated sludge decompose nitric acid nitrogen while decomposing organic matter in the water in a facultative anaerobic atmosphere to denitrify the nitrification tank 6. Then, in an aerobic atmosphere, polyphosphoric acid-accumulating bacteria and the like take up phosphorus in the same manner as described above, and nitric acid bacteria and the like oxidize ammonia nitrogen in water to nitrate nitrogen.

Since the activated sludge 13 such as polyphosphoric acid-accumulating bacteria which has taken up phosphorus is appropriately discharged, both nitrogen and phosphorus are effectively removed while the above steps are repeated.

In the above-mentioned method, when treating sewage, which is domestic wastewater, with an average daily treatment amount of 35 m ³ , absolute anaerobic operation was carried out for 1 hour, and facultative anaerobic operation was carried out for 2 hours. Shown in. With such an operation, an absolute anaerobic atmosphere and a facultative anaerobic atmosphere are secured for 8 cycles per day, so the amount of sewage that flows into the denitrification tank per cycle is set to 1/8 of the daily average throughput, The circulation of the nitrification mixture solution to the denitrification tank was set so that four times the average daily treatment amount was circulated and returned in 16 hours in order to secure a nitrogen removal rate of 80% or more.

[0028]

[Table 1]

As can be seen from Table 1, about 80% of phosphorus and nitrogen in the wastewater were removed, BOD and COD were also suitably reduced, and the water quality of the membrane permeate became good.

[0030]

As described above, according to the present invention, the absolute anaerobic operation for maintaining the denitrification tank in the absolutely anaerobic atmosphere and the facultative anaerobic operation for maintaining the denitrification tank in the permeable anaerobic atmosphere are performed. By alternately performing every predetermined time, phosphorus in wastewater is effectively removed as a preferable environment for activated sludge involved in dephosphorization during absolute anaerobic operation, and activity involved in denitrification during facultative anaerobic operation. Nitrogen in wastewater can be effectively removed as a preferable environment for sludge.

At this time, a large amount of BOD can be present in the denitrification tank by concentrating the sewage in the absolute anaerobic operation, and a more preferable environment can be secured for the activated sludge involved in dephosphorization.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating absolute anaerobic operation in a wastewater treatment method of the present invention.

FIG. 2 is a cross-sectional view illustrating facultative anaerobic operation in the method for treating sewage.

FIG. 3 is a flowchart illustrating a conventional wastewater treatment method.

[Explanation of symbols]

 3 Flow rate adjustment tank 4 Sewage 5 Denitrification tank 6 Nitrification tank 6a Membrane separation device 8 Denitrification mixture 9 Nitrification mixture 10 Membrane permeate

Claims (3)

[Claims] 1. A denitrification tank is caused to flow into a denitrification tank from a flow rate control tank and treated with activated sludge, and a denitrification mixture containing activated sludge in the denitrification tank is transferred to a nitrification tank and treated with activated sludge.
A nitrification mixed solution containing activated sludge in the nitrification tank is immersed in the tank to perform solid-liquid separation and the membrane permeate is sent to the outside of the tank, and part of the nitrification mixed solution is circulated to the denitrification tank. In the treatment method, the absolute anaerobic operation of stopping the circulation of the nitrification mixture to the denitrification tank and maintaining the denitrification tank in an absolutely anaerobic atmosphere, and circulating the nitrification mixture to the denitrification tank and passing the denitrification tank. A method for treating sewage, characterized in that nitrogen and phosphorus in sewage are biologically removed by alternately performing a facultative anaerobic operation for maintaining a sexual anaerobic atmosphere for a predetermined time. 2. An amount obtained by dividing the daily average sewage treatment amount by the number of operation cycles per day during absolute anaerobic operation, wherein one step is a step of performing absolute anaerobic operation and facultative anaerobic operation for a predetermined time. 2. The method for treating sewage according to claim 1, wherein the sewage of No. 1 is allowed to flow into the denitrification tank, and during the facultative anaerobic operation, the flow of sewage from the flow rate adjustment tank to the denitrification tank is stopped. 3. Absolute anaerobic driving is 0.5 to 1 hour,
8 to 1 per day with facultative and anaerobic driving for 1 to 2 hours
The method for treating wastewater according to claim 1 or 2, wherein the cycle operation is performed about 6 times.