JPH07232192A - Sewage treatment method - Google Patents

Abstract

(57) [Summary] [Structure] Raw water is biologically nitrified and denitrified in the anaerobic tank 17 and the aerobic tank 18, and the biologically treated water is subjected to solid-liquid separation by a membrane separator 28 immersed in the tank. To do. R permeated water
It is passed through a membrane filtration device 19 provided with an O membrane to separate it into a concentrated liquid in which phosphorus or the like is concentrated and demineralized water. An aggregating agent is added to the concentrated liquid to agglomerate phosphorus and the like in the concentrated liquid, and the aggregate is settled and separated and then withdrawn. [Effects] Nitrogen is preferentially removed in the biological reaction tank and phosphorus is separated by the RO membrane, so that nitrogen and phosphorus in the raw water are stably removed, and highly treated water is obtained. At this time, suspended matter such as activated sludge is separated in advance by the membrane separation device in the biological reaction tank, so that it can be applied to the RO membrane.

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, and more particularly to a denitrification / dephosphorization device, an advanced sewage treatment device,
The present invention relates to a method for treating sewage performed in a hydrophilic water production device or the like.

[0002]

2. Description of the Related Art Denitrification / Phosphorus removal equipment, advanced sewage treatment equipment,
A conventional sewage treatment flow performed in a landscape / hydrophilic water production device is, for example, as shown in FIG. In FIG. 3, reference numeral 1 denotes a biological reaction tank, which is composed of an absolute anaerobic tank 2, an anaerobic tank 3 and an aerobic tank 4, and water to be treated 5 containing nitrogen and phosphorus is introduced into the absolute anaerobic tank 2. The treated water 5 is biologically treated by the activated sludge in the anaerobic tank 3 and the aerobic tank 4 sequentially.

In the absolute anaerobic tank 2 and the anaerobic tank 3, the water 5 to be treated is agitated and mixed with activated sludge mainly composed of denitrifying bacteria in the tanks by agitators 6 and 7, and under anaerobic conditions, nitric acid of the denitrifying bacteria is mixed. By breathing, nitrate nitrogen and nitrite nitrogen contained in the treated water 5 are reduced to nitrogen gas and BO
D is decomposed. At this time, the phosphorus taken into the body of the activated sludge is released under anaerobic conditions in the tank.

The treated water 5 sent to the aerobic tank 4
Is mixed with activated sludge mainly composed of nitrifying bacteria in the tank in a state where air is supplied from the blower 8 through the air diffuser 9, and organic nitrogen and ammonia nitrogen contained in the treated water 5 are: Under aerobic conditions, nitrifying bacteria oxidize to nitrate nitrogen. A part of the nitrification solution 10 in the aerobic tank 4 containing this nitrate nitrogen is circulated back to the anaerobic tank 3 by the circulation pump 11, and the remaining nitrification solution 1 in the aerobic tank 4 is returned.
0 is sent to the settling tank 12. At this time, phosphorus contained in the water to be treated 5 is taken into the body of activated sludge under aerobic conditions in the aerobic tank 4.

Then, the nitrification liquid 1 sent from the aerobic tank 4
0 is settled and separated in the settling tank 12, and the supernatant is treated water 1
While being taken out as 3, the part of the sludge containing the settled phosphorus is returned to the absolute anaerobic tank 2 as the returning sludge 14, and the remaining sludge containing the phosphorus is withdrawn as an excess sludge 15.

As described above, the nitrogen contained in the treated water 5 is removed by the nitrifying denitrification action of the activated sludge, and the phosphorus contained in the treated water 5 is taken into the activated sludge and drawn out of the system. Be done.

[0007]

As described above, it is known that activated sludge releases phosphorus in the body when anaerobic and takes in excess phosphorus in the body when aerobic. Therefore,
Dephosphorization can be effectively performed by extracting sludge as much as possible under aerobic conditions. On the other hand, it is known that nitrifying bacteria that nitrify organic nitrogen or ammonia nitrogen to nitrate nitrogen under aerobic conditions have a low growth rate. Therefore, in order to perform sufficient nitrification and denitrification, it is necessary to pull out the sludge so much and prolong the sludge age.
In this way, it is preferable to pull out the sludge as often as possible for dephosphorization, and it is desirable to lengthen the sludge age for nitrifying denitrification. It is difficult to perform dephosphorization and nitrification denitrification.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a method for treating sewage, which is capable of stably performing both dephosphorization and nitrification / denitrification to obtain excellent treated water. To do.

[0009]

In order to solve the above problems, in the method for treating wastewater of the present invention, the biological reaction tank is composed of an anaerobic tank and an aerobic tank, and raw water containing nitrogen and phosphorus is anaerobic tank. Sewage treated by the activated sludge in the tank and denitrified under anaerobic conditions, and this denitrified water is introduced into the aerobic tank and nitrified by the activated sludge in the tank under aerobic conditions. In the treatment method, the nitrification treated water in the aerobic tank is solid-liquid separated by a membrane separation device immersed in the tank to take out the membrane permeated water, and the membrane permeated water is introduced into a membrane filtration device provided with an RO membrane. Separation into concentrated liquid containing concentrated phosphorus and demineralized water that has passed through the RO membrane,
It is characterized in that a flocculant is added to the concentrated liquid to coagulate phosphorus or the like contained in the concentrated liquid and the aggregate is sedimented and separated.

Further, in the method for treating wastewater of the present invention, the concentrated liquid containing the agglomerates aggregated by the addition of the aggregating agent is returned to the biological reaction tank, and the agglomerates are collected together with the excess sludge generated in the activated sludge treatment. Characterized by pulling out.

[0011]

With the above structure, the raw water containing nitrogen and phosphorus is biologically nitrified and denitrified in the biological reaction tank, and the nitrogen content is removed, but phosphorus is sent to the membrane filtration device in a state where it remains. At this time, since the activated sludge is separated by the membrane separation device in the aerobic tank, in the membrane filtration device,
It becomes possible to apply it to an RO film that does not like fine particles. Then, the RO membrane separates the demineralized water from which phosphorus and the like have been removed into a concentrated liquid in which phosphorus and the like have been concentrated, and the phosphorus left in the concentrated liquid is made into an aggregate by the aggregating agent, and the system is separated by sedimentation. Pulled out. As a result, nitrogen and phosphorus in the raw water are stably removed, and very good treated water as demineralized water is obtained.

Further, the concentrated liquid containing the agglomerates is returned to the biological reaction tank, and the agglomerates are extracted together with the excess sludge in the tank, so that the agglomerates containing phosphorus can be separated without providing a device for sedimentation separation. it can. Also by this method, nitrogen and phosphorus in the raw water are stably removed, and very good treated water is obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a sewage treatment apparatus in which a sewage treatment method according to an embodiment of the present invention is performed. In FIG. 1, 16 is a biological reaction tank composed of an anaerobic tank 17 and an aerobic tank 18, and 19 is Membrane filtration device with RO membrane (reverse osmosis membrane), 2
Reference numeral 0 is a coagulation and mixing tank, and 21 is a sedimentation tank.

The anaerobic tank 17 is provided with a raw water supply pipe 22 opened above the tank, and is composed of microorganisms mainly composed of denitrifying bacteria mixed with the raw water supplied from the raw water supply pipe 22 inside the tank. A stirrer 23 is arranged to stir and mix the mixed liquid in the tank while maintaining the activated sludge. Above the anaerobic tank 17, a nitrification-treated water circulation pipe 24 led from the aerobic tank 18 is provided.
And a coagulation treatment liquid return pipe 25 led from the coagulation / mixing tank 20.
And are open. The denitrification-treated water denitrified in the anaerobic tank 17 flows out to the aerobic tank 18 from the upper part of the tank.

The aerobic tank 18 mixes with the denitrification-treated water flowing from the anaerobic tank 17 inside the tank to maintain the activated sludge composed of microorganisms mainly composed of nitrifying bacteria, and at the top of the tank 18. A nitrification-treated water circulation pipe 24 that circulates and returns the nitrification-treated water that has been nitrified in the tank to the anaerobic tank 17 is provided with a circulation pump 26, and a sludge extraction pipe 27 that draws excess sludge in the tank at the bottom of the tank 18. Is provided.

Further, the aerobic tank 18 is immersed in the mixed solution in the tank, and a membrane separation apparatus 28, for example, a membrane separation type activated sludge treatment apparatus (BIOREM) in which a plurality of ceramic tubes having a membrane pore diameter of about 0.1 μm are arranged. (Trademark) manufactured by Kubota Co., Ltd., and the permeated water extraction pipe 30 having a suction pump 29 is connected to the membrane separation device 28. Membrane separation device 28
Below the table, the air diffuser 32 connected to the blower 31 outside the tank
Is provided. The membrane permeated water extraction pipe 30 is connected to the pipe line,
A cartridge filter 33 for security and a driving pump 34 for sending the membrane permeated water under pressure to the membrane filtration device 19 are sequentially provided.

The membrane filtration device 19 is provided with an RO membrane, and R
The demineralized water that has permeated the O membrane is taken out by the demineralized water take-out pipe 35, and the concentrated liquid separated and concentrated by the RO membrane is sent to the coagulation and mixing tank 20 by the concentrated liquid return pipe 36. The aggregating and mixing tank 20 is provided with a coagulant supply pipe 37, and is provided with an aggregating treatment liquid returning pipe 25 for returning the aggregating treatment liquid aggregated in the tank to the anaerobic tank 17 through the sedimentation tank 21. An agglomerate withdrawing pipe 38 for withdrawing the agglomerated agglomerates is provided.

With the above structure, the nitrification-treated water circulation pipe 24 circulates and returns the nitrification-treated water, and the coagulation treatment liquid return pipe 25.
When the raw water containing nitrogen and phosphorus is supplied to the anaerobic tank 17 from the raw water supply pipe 22 in the state of returning the coagulation treatment liquid by means of the raw water, the raw water is activated sludge composed of microorganisms mainly denitrifying bacteria in the tank, and the nitrification treated water. , And the aggregating treatment liquid are stirred and mixed by the stirring device 23. Then, nitrate nitrogen and nitrite nitrogen contained in this mixed solution were reduced to nitrogen gas by nitric acid respiration of denitrifying bacteria under anaerobic conditions, and biodegradable organic matter was decomposed and denitrified in the tank. The denitrification treated water flows out to the aerobic tank 18.

The denitrification-treated water that has flowed into the aerobic tank 18 is activated sludge composed of microorganisms mainly composed of nitrifying bacteria in the tank under aerobic conditions in which air is supplied from the blower 31 through the air diffuser 32. The organic nitrogen and ammonia nitrogen contained in this mixed solution are nitrified into nitrite nitrogen and nitrate nitrogen by the oxidizing action of nitrifying bacteria. The nitrification-treated water nitrified in the tank is returned by the circulation pump 26 to the anaerobic tank 17 through the nitrification-treated water return pipe 24, and is again subjected to the denitrification action. Excess sludge accumulated in the aerobic tank 18 is drawn out by the sludge drawing pipe 27, but the sludge age is set to be long to sufficiently remove the nitrogen content in the anaerobic tank 17 and the aerobic tank 18.

At this time, when a negative suction pressure is applied to the membrane separation device 28 by the suction pump 29 through the membrane permeated water extraction pipe 30, the nitrification-treated water in the tank is subjected to solid-liquid separation by the membrane separation device 28, and nitrogen content is removed. The permeated water which has been removed but contains phosphorus in the form of phosphate ions is taken out to the permeated water extraction pipe 30. Aggregates and activated sludge contained in the aggregation treatment liquid returned by the aggregation treatment liquid return pipe 25 remain in the tank. In the membrane separation device 28, the deposits on the membrane surface are separated by the rising liquid flow generated by the air supplied from the air diffuser 32, and the separation membrane is prevented from being clogged. The membrane permeated water taken out to the membrane permeated water take-out pipe 30 passes through the RO membrane protection cartridge filter 33 and is pressure-fed to the membrane filtration device 19 by the driving pump 34.

The membrane permeated water sent from the aerobic tank 18 is applied to the RO membrane in the membrane filtration device 19, and the demineralized water permeating the RO membrane is taken out by the demineralized water take-out pipe 35. On the other hand, phosphate ions and other ions and organic substances contained in the permeated water of the membrane are separated by the RO membrane and remain in the membrane filtration device 19, and the remaining concentrated liquid is sent to the coagulation and mixing tank 20 by the concentrated liquid return pipe 36. To be Then, it is mixed with a flocculant such as a sulfuric acid band, polyaluminum chloride, ferric chloride, and ferric polysulfate supplied from the flocculant supply pipe 37 in the tank 20, and phosphate ions in the concentrate and other Ions and organic substances are aggregated. The aggregating treatment liquid containing the agglomerates is sent to the settling tank 21 by the aggregating treatment liquid return pipe 25,
Aggregate withdrawal tube 38
The supernatant is returned to the anaerobic tank 17 by the coagulation treatment liquid return pipe 25 while being appropriately withdrawn by.

As described above, the raw water containing nitrogen and phosphorus is treated in the biological reaction tank with priority given to the removal of nitrogen,
After the activated sludge is separated by the membrane separation device immersed in the tank, nitrogen and phosphorus are stably removed from the raw water by separating the phosphorus and organic substances by the RO membrane, and it is treated as highly as possible for drinking water. Demineralized water can be obtained.

FIG. 2 shows a sewage treatment apparatus in which the sewage treatment method of another embodiment of the present invention is performed. This sewage treatment apparatus differs from the sewage treatment apparatus shown in FIG. 1 in that no settling tank is provided. Therefore, the aggregates of phosphorus and other ions and organic substances that have aggregated in the aggregating and mixing tank 20 are returned to the anaerobic tank 17 by the aggregating treatment liquid return pipe 25, and the sludge drawing pipe together with the excess sludge in the aerobic tank 18 is sent. It is pulled out of the system from 27.

[0024]

As described above, according to the present invention, raw water containing nitrogen and phosphorus is biologically treated with priority given to the removal of nitrogen content, and activated sludge is removed by a membrane separator immersed in a biological tank. After the removal, the RO membrane is used to separate the phosphorus, so that nitrogen and phosphorus can be stably removed from the raw water to obtain highly treated water. The phosphorus separated by the RO membrane can be aggregated with a flocculant and drawn out of the system. At this time, the membrane separation device immersed in the biological tank acts as a pretreatment device for using a general hollow fiber type or spiral type RO membrane that dislikes fine particles.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a sewage treatment apparatus in which a sewage treatment method according to an embodiment of the present invention is performed.

FIG. 2 is an explanatory view showing a sewage treatment apparatus in which a sewage treatment method according to another embodiment of the present invention is performed.

FIG. 3 is an explanatory view showing a sewage treatment apparatus in which a conventional sewage treatment method is performed.

[Explanation of symbols]

 16 Biological reaction tank 17 Anaerobic tank 18 Aerobic tank 19 Membrane filtration device 28 Membrane separation device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiya Ozaki 2-6, Nishijima, Nishiyodogawa-ku, Osaka-shi, Osaka Kubota Shin-Yodogawa factory

Claims (2)

[Claims] 1. A biological reaction tank is composed of an anaerobic tank and an aerobic tank, raw water containing nitrogen and phosphorus is introduced into the anaerobic tank, and denitrification is carried out under the anaerobic condition by activated sludge in the tank. In a method for treating wastewater in which denitrification treated water is introduced into an aerobic tank and nitrification is carried out under the aerobic condition by activated sludge in the tank, a membrane separation device in which the nitrification treated water in the aerobic tank is immersed in the tank The solid permeated water is taken out by means of and the membrane permeated water is taken out, and this membrane permeated water is introduced into a membrane filtration device provided with an RO membrane to separate it into a concentrated liquid in which phosphorus or the like is concentrated and demineralized water permeated through the RO membrane, A method for treating sewage, which comprises adding a flocculant to the concentrated liquid to coagulate phosphorus or the like contained in the concentrated liquid, and sedimenting and separating the aggregate. 2. The method for treating wastewater according to claim 1, wherein the concentrated liquid containing the aggregates aggregated by the addition of the aggregating agent is returned to the biological reaction tank, and the aggregates are generated by the activated sludge treatment. A method for treating sewage, which is characterized in that it is drawn out together with sludge.