JPH10244295A - Nitrogen removal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrogen removal device in which microorganisms stuck to a fluidized carrier are certainly released. SOLUTION: In the device for biologically removing BOD and nitrogen in organic drainage containing ammonia nitrogen such as sewage, a biomembrane peeling device 28 is provided with a suction port 29a for sucking a carrier stuck with microorganisms in the lower part, an air lift pipe 29 having an air supply part 30 in the vicinity of the suction port, a separation part which is provided in the upper part of the air lift pipe and separates peeled organisms discharged from the air lift pipe and the carrier and a water level controlling weir 35 provided in the separation part. Further, the biomember peeling device 28 is operated so that the suction port of the air lift pipe is arranged in the part slightly lower than the interface of a fluidized bed and the fluidized interface ascending according to multiplication of the films of microorganisms sticking on the surface of the carrier is maintained and controlled to a constant height by peeling the films of microorganisms while raising the carrier stuck with microorganisms through the air lift pipe from the anaerobically fluidized bed near to the fluidized interface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological treatment apparatus for removing BOD and nitrogen in organic wastewater containing ammonia nitrogen such as sewage.

[0002]

2. Description of the Related Art As seen in the eutrophication of lakes and marshes and enclosed waters, the removal of nutrients (nitrogen and phosphorus) has become important from the viewpoint of water environment conservation. Conventionally, there have been considered several types of biological methods for removing BOD and nitrogen from wastewater such as sewage, which are based on the activated sludge method. There is a modified activated sludge circulation method of the nitrification liquid circulation type.

[0003] A modified method of circulating activated sludge of the nitrification liquid circulation type is as follows.
As shown in FIG. 3, the first stage is an anaerobic tank (complete mixing tank) 2 for denitrification, and the second stage is an aerobic tank (complete mixing tank) 3 for BOD oxidation and nitrification of ammonia nitrogen. The effluent from the tank 3, that is, a part of the nitrification liquid is circulated to the preceding anaerobic tank 2 by the nitrification liquid circulation pump 4.

In FIG. 3, raw water is supplied to a first settling basin 1.
, Flows into the anaerobic tank 2, passes through the aerobic tank 3, and flows into the second sedimentation basin 5. However, the activated sludge circulation method requires a significantly long treatment time and requires a large site area. Further, in the activated sludge circulation method, the treated water and the sludge are separated by using the second sedimentation basin 5, so that an obstacle in operation management such as bulking may occur, and maintenance is not easy. Requires professional skills.

Therefore, recently, a filler (carrier) for water treatment has been used.
Due to the development of the filter bed method utilizing anaerobic filter, as shown in FIG. 4, the first stage is an anaerobic filter bed 8 for denitrification, and the second stage is an aerobic filter bed 10 for BOD oxidation and nitrification of ammonia nitrogen. The so-called anaerobic filter / aerobic filter method of circulating a part of the effluent from the aerobic filter bed, that is, a part of the nitrification liquid, to the anaerobic tank 8 at the preceding stage by the nitrification liquid circulation pump 9 is being studied.

In FIG. 4, raw water is supplied to the first sedimentation basin 6.
From the anaerobic filter bed 8 by the supply pump 7. The advantages of using the filter bed method instead of the activated sludge method are as follows. The aerobic filter bed has better nitrification performance than the activated sludge method (it has a nitrification rate about three times that of activated sludge), so that high-speed treatment is possible. The reason that the nitrification performance of the aerobic filter is excellent is that nitrifying bacteria grow slower than BOD oxidizing bacteria, but in the aerobic filter, the nitrifying bacteria form a biofilm on the surface of the carrier and are retained. Therefore, the nitrifying bacteria can be maintained at a higher concentration than the nitrifying bacteria concentration in the complete mixing tank.

[0007] Also, since the aerobic filter bed has a filtration function,
The second sedimentation basin 5 in the activated sludge method is unnecessary, and there is no trouble peculiar to the activated sludge method such as bulking. Further, for example, “Experimental research on fluidized bed denitrification” (Proceedings of the 15th Sewage Works Research Conference, Vol.15 No.165 1978/2)
Studies have been made to use a fluidized bed as a reaction tank for denitrification.

[0008]

However, an anaerobic filter
The aerobic filter method has the disadvantage that the sludge concentration in the anaerobic filter is low and the treatment time is long. When the treatment time is prolonged, a putrefactive gas such as hydrogen sulfide is generated, so that it is necessary to take measures against deodorization and consideration for corrosion prevention of equipment.

[0009] In addition, studies have been made to use a fluidized bed as a denitrification reaction tank. In this case, however, the wastewater after nitrification is intended to be denitrified using methanol, and the circulation after nitrification is performed. It is not a type flow. By the way, from the results shown in "Experimental research on fluidized bed denitrification",
It is clear that the fluidized bed method has a higher concentration of microorganisms, and requires a shorter treatment time than the floating method (activated sludge method) and the fixed bed method (anaerobic filter bed), so that the apparatus can be made more compact.

However, in order for the fluidized bed to function stably and continuously, it is indispensable to maintain the fluid interface of the carrier, which rises with the treatment, at a constant height and to stably maintain the amount of microorganisms. It is. Despite the fact that the fluidized bed is an excellent reaction vessel, one of the biggest causes that has not been sufficiently commercialized so far is this interface control mechanism, in other words, peeling off excess microorganisms from the carrier. This is because practical use of a biological exfoliation apparatus for maintaining the interface at a constant height by discharging the liquid to the outside of the reaction tank has not been achieved.

"Experimental research on fluidized bed denitrification"
As this mechanism, there is shown a sand returning device including an air lift, a degassing tower, a cyclone, a sand separator, and a sand returning cylinder (FIG. 2 on page 38). This sand returning device has a problem that the mechanism is complicated, troubles in the operation are expected, and the sand (carrier) is taken out of the tower, so that a space is required.

As a cleaning apparatus using an air lift tube, for example, a moving bed type denitrification apparatus disclosed in Japanese Patent Application Laid-Open No. 2-184398 is known. However, in this washing device, since the tip of the air lift pipe for sucking the carrier, that is, the suction port is set at the bottom of the tower, the thickened carrier having a small density that has been classified in the fluidized bed and ascended to the top is removed. Cleaning (biofilm removal) cannot be performed preferentially.

In Japanese Patent Application Laid-Open No. 2-184398, "the sludge concentration of the carrier 3 and thus of the packed bed 4 can be maintained at a high concentration" (page 10, upper right, lines 10 to 11).
However, whether or not the concentration is high requires a judgment index, and without this index, the cleaning cannot be optimized. By the way, as a judgment index,
Pressure loss in the tower, that is, water level change is considered,
In order to keep the water level constant, it is impossible to optimize the cleaning unless a mechanism for detecting this change and performing cleaning or adjusting the backwash water discharge amount is added.

Therefore, the conventional cleaning device using an air lift tube cannot clean the carrier with a simple structure. The present invention has been made in order to solve such conventional problems, the purpose of which is to use an anaerobic fluidized bed instead of an anaerobic filter bed in the first stage to further reduce the denitrification time, By using the nitrifying solution of the aerobic filter bed for fluidization of the fluidized bed carrier, the power can be reduced to a level comparable to that of the conventional method, and the surplus amount of microorganisms adhering to the fluidized carrier can be reliably reduced. It is an object of the present invention to provide a nitrogen removing device which is combined with a simple biofilm removing device capable of always stably maintaining a necessary and sufficient amount of microorganisms so as to be detached from a carrier and capable of performing treatment.

[0015]

SUMMARY OF THE INVENTION An apparatus for biologically removing BOD and nitrogen in an organic wastewater containing ammonia nitrogen, such as sewage, is provided. An anaerobic fluidized bed, an aerobic filter for BOD oxidation and nitrification of ammoniacal nitrogen, a first pipe for transferring the overflow from the anaerobic fluidized bed to the aerobic filter, and an aerobic filter. A second pipe for returning the nitrifying liquid from the bed to the anaerobic fluidized bed, and a circulation pump provided in the second pipe, the biofilm stripping apparatus has a suction port for sucking the carrier to which the microorganisms are attached at the bottom, and this An air lift pipe having an air supply section in the vicinity of the suction port, a separation section provided at an upper portion of the air lift pipe, for separating exfoliated organisms and carriers that have exited the air lift pipe, and a water level control weir provided at the separation section; The biofilm stripping device has The suction port of the lift tube was placed slightly below the fluidized bed interface, and the microorganisms attached from the anaerobic fluidized bed near the fluidized interface to the rising fluidized interface with the growth of the microbial membrane attached to the surface of the carrier. The method is characterized in that the carrier is maintained and controlled at a constant height by removing the microbial membrane while raising the carrier with an air lift tube.

(Action) In the first aspect, an organic wastewater (raw water) containing ammonia nitrogen such as sewage is introduced into an anaerobic fluidized bed, where the raw water and a return liquid from a downstream aerobic filter bed are used to carry the carrier. Is denitrified while flowing. Next, the overflow water from the anaerobic fluidized bed is sent to an aerobic filter bed, where BOD and SS contained in the overflow water are removed, and nitrification of ammonia nitrogen is performed. Thereafter, a part of the nitrification liquid from the aerobic filter bed is returned to the anaerobic fluidized bed, and the concentration of microorganisms adhering to the carrier is increased while the carrier in the anaerobic fluidized bed is fluidized together with raw water.

The microbial membrane is separated from the anaerobic fluidized bed in the vicinity of the flow interface by raising the microbeads with the microbes attached thereto by an air lift tube. By doing so, it is possible to maintain and control at a constant height.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

An embodiment of the nitrogen removing apparatus according to claim 1 will be described with reference to FIGS. In the figure,
Reference numeral 20 denotes a first settling basin, which is in communication with an anaerobic fluidized bed 23 via a raw water supply pipe 21. The raw water supply pipe 21 is provided with a raw water supply pump 22.

The anaerobic fluidized bed 23 has a first pipe 32 for carrying the overflow liquid into the aerobic filter bed 36 and a second pipe 37 for returning the nitrified liquid from the aerobic filter bed 36 to the anaerobic fluidized bed 23. Is attached. In the second pipe 37, the nitrification liquid circulation pump 3
8 are provided. The carrier 2 is contained in the anaerobic fluidized bed 23.
Granules (sand, activated carbon, plastic media, etc.) as 4
Is filled and fluidized by the upward flow.

The anaerobic fluidized bed 23 is provided with a raw water supply pipe 21.
And a supply unit 25 connected to the second pipe 37, and the supply unit 2
5 has a dispersion nozzle 26, a fluidized bed 27 filled with a carrier 24, and a biofilm stripping device 28 provided on the upper part. The biofilm stripping device 28 has an air lift pipe 29 having a suction port 29a at a lower portion for sucking the carrier 24 to which microorganisms are attached and an air supply section 30 near the suction port 29a, and a discharge port at an upper portion of the air lift pipe 29. 29b
And a separation unit 31 provided on the side, for separating exfoliated organisms and carriers from the air lift pipe 29. The separation section 31 is provided with a water level control weir 35. Further, as shown in FIG. 2, the suction port 29a at the lower part of the air lift pipe 29 is
It is disposed so as to be located slightly below the fluid interface of the fluidized bed 27 to be controlled.

The carrier 24 from which the biofilm has been stripped by the biofilm stripping device 28 sinks to the upper part of the fluidized bed 27, and the separated sludge is returned to the first settling basin 20 via the sludge discharge pipe 33. Further, a pipe 34 communicating with the aeration blower 39 is attached to the air supply section 30 of the air lift pipe 29. The first pipe 32 communicates with the upper part of the aerobic filter bed 36,
A nitrification liquid reservoir 41 is provided at the lower part. A filter medium filling tank 43 is formed inside the filter medium filling tank 43, and a diffuser pipe 44 communicating with the aeration blower 39 via a pipe 40 is formed in the filter medium filling tank 43.
Is arranged.

The nitrification liquid flows from the filter medium filling layer 43 into the lower nitrification liquid reservoir 41. further,
A second pipe 37 and a treated water discharge pipe 45 are attached to the nitrification liquid reservoir 41. A valve 46 is attached to the treated water discharge pipe 45. In addition, the treated water discharge pipe 45
Communicates with the treatment water tank 47.

The treated water tank 47 is connected to a nitrification liquid reservoir 41 through a backwash pipe 48. In this backwash tube 48,
A backwash pump 49 and a valve 50 are provided. A backwash blower pipe 51 is attached to the nitrification liquid reservoir 41. The backwash blower pipe 51 is provided with a backwash blower 52 and a valve 53. The backwash water sent from the backwash pump 49 and the air sent from the backwash blower 52 are jetted through the nozzle 42 to the filter medium filling layer 43.

Next, a method for removing nitrogen will be described using the apparatus according to the present embodiment configured as described above. Organic wastewater (raw water) containing ammonia nitrogen such as sewage is stored in the first sedimentation basin 20, and sent from the raw water supply pump 22 to the supply section 25 of the anaerobic fluidized bed 23 via the raw water supply pipe 21. Then, it is introduced into the fluidized bed 27 by the dispersion nozzle 26. Here, raw water and the aerobic filter bed 36
The carrier 24 is denitrified while flowing with the return liquid from the carrier.

When the flow interface rises as the biofilm grows on the surface of the carrier 24, the air-lift type biofilm stripping device 28 is operated to control the flow interface of the carrier 24, and the flow interface is maintained at a certain height. Is maintained and controlled. In the air lift type biofilm stripping device 28, the air lift pipe 2
By blowing air into 9, the carrier 24 to which microorganisms adhere is sucked from the lower portion 29a of the air lift tube 29,
Carrier 2 which rises in air lift pipe 29 by the turbulence of air
The biofilm adhering to 4 is peeled off, and the separated organisms and carrier 24 that have exited air lift tube 29 are separated by ascending flow in anaerobic fluidized bed 23 using the difference in specific gravity in separation section 31.

The exfoliated organisms extruded by the ascending flow may be discharged to the first sedimentation basin 20 as shown in the figure, or may be separately taken out and treated.
2 to allow it to flow into the subsequent aerobic filter bed 36,
It may be discharged by washing the filter bed. Further, the air lift type biofilm peeling device 28 may be activated by detecting a flow interface, or may be activated continuously or intermittently without detecting the interface.

Next, the overflow water from the anaerobic fluidized bed 23 is sent to the aerobic filter bed 36 through the first pipe 32, where BOD and SS contained in the overflow water are removed, and nitrification of ammonia nitrogen is performed. I do. The nitrification liquid flowing into the nitrification liquid reservoir 41 of the aerobic filter bed 36 is supplied to the nitrification liquid circulation pump 38.
Thus, the concentration of microorganisms adhering to the carrier 24 is increased while the carrier 24 in the anaerobic fluidized bed 23 flows together with the raw water while returning the carrier 24 in the anaerobic fluidized bed 23 through the second pipe 37.

By this flow, the carrier 24 in the fluidized bed 27
Is provided as a place where microorganisms adhere, and the carrier 2 is compared with that before flowing (that is, in a fixed bed state).
Since the specific surface area of No. 4 increases dramatically and the denitrifying bacteria accumulate on the surface of the carrier 24 in the form of a microbial membrane, a high concentration is achieved.

Here, the concentration of the microorganism is expressed per unit volume.
From 10,000 mg / l to 50,000 mg / l, denitrification in a very short time (substantially several minutes to several tens of minutes) becomes possible. In contrast, the concentration of microorganisms in the complete mixing tank (suspension organism method) is 1500 mg / l to 3000 mg / l per unit volume, and the concentration of microorganisms in the anaerobic filter is 5000 mg / l to 7000 mg / l per unit volume. there were.

In the anaerobic fluidized bed 23, as described above, in addition to the high concentration of microorganisms, the fluidized bed 27 has good contact between the liquid and the microbial membrane, as in the anaerobic filter bed. No phenomenon such as deterioration of the uniform dispersion of water due to partial blockage occurs. The carrier 24 in the anaerobic fluidized bed 23 of the former stage may be any material that flows according to the flow rate of the sum of the circulating amount of the nitrification liquid and the supply amount of raw water from the aerobic filter bed 23 of the latter stage, and has a high specific gravity. Generally, those having a small particle diameter may be used if they have a small particle diameter, and those having a large particle diameter may be generally used if they have a small specific gravity.

The downstream aerobic filter bed 36 transfers the effluent (overflow liquid) from the upstream anaerobic fluidized bed 23 to the first pipe 32.
For removing BOD and SS contained in this solution and nitrification of ammoniacal nitrogen, and may be any of a fixed-bed type or a moving-bed type filled with a granular carrier. -The function is usually the same as the aerobic filter bed used in organic wastewater treatment.

As described above, according to the present embodiment, in the method of biologically removing BOD and nitrogen in organic wastewater containing ammoniacal nitrogen such as sewage, the anaerobic filter is replaced by an anaerobic filter in the first stage. Using fluidized bed 23, Table 1
As shown in the figure, the denitrification time could be further reduced. In addition, by using the liquid to be treated (raw water) and the circulating liquid from the aerobic filter bed 36 for the flow of the carrier 24 in the anaerobic fluidized bed 23, the flow required for maintaining the fluidity of the fluidized bed is conventionally required. By eliminating the need for circulation (a part of the effluent of the fluidized bed is supplied to the fluidized bed again) and reducing the circulating power of the fluid for fluidization, the power can be reduced to a level comparable to the conventional method. did it.

Furthermore, in the method for biologically removing BOD and nitrogen in organic wastewater containing ammoniacal nitrogen such as sewage, the expansion interface of the anaerobic fluidized bed 23 is automatically controlled by an airlift type biofilm stripping device 28. It became possible to control. Further, as described above, the air lift-type biofilm peeling device 28 in the present embodiment includes the carrier 24.
The feature is that the tip of the air lift pipe 29 (that is, the suction port 29a) for sucking air is set slightly below the carrier flow interface. On the other hand, in a conventional cleaning device using an air lift tube, for example, as shown in Japanese Patent Application Laid-Open No. 2-184398, the cleaning device is installed at the bottom of the tower, which is clearly different.

This difference is very important. This is because, in the present embodiment, as a device combined with the anaerobic fluidized bed 23, the thickened carrier 24 having a small density that has been classified and has risen upward in the anaerobic fluidized bed 23 is preferentially washed (biofilm removal). (Peeling).
Therefore, unlike the cleaning device using a conventional air lift tube, the air lift type biofilm stripping device 28 in this embodiment can be said to be a device unique to a fluidized bed that functions integrally with the anaerobic fluidized bed 23.

Further, as described above, the air-lift type biofilm stripping device 28 in the present embodiment is configured such that the tip of the air-lift tube 29 for sucking the carrier 24 (ie, the suction port 29).
By setting a) slightly below the predetermined carrier flow interface, the carrier 24 expanded above the suction port 29a can be automatically sucked into the air lift pipe 29. Also,
The washing wastewater (exfoliated biological effluent) moves out toward the water level control weir 35, so the washing wastewater is reliably discharged only by adjusting the weir height and setting the water level in the separation unit below the overflow water level. .

As described above, according to the air-lift type biofilm stripping apparatus 28 of this embodiment, there is no need to detect the water level, etc., and the flow interface is kept constant with a very simple structure.
As a result, it is possible to secure a sufficient amount of microorganisms necessary for the treatment. Table 1 shows the processing time (standard) of each processing method for reference.

[Table 1] In Table 1, Conventional Method 1 represents an anaerobic / aerobic filter bed,
Conventional method 2 represents a modified activated sludge method.

EXPERIMENTAL EXAMPLE Primary effluent from a sewage treatment plant (first settling pond effluent) was used as the target water. The apparatus shown in FIG. 1 was used. The size of the anaerobic fluidized bed was 120φ × 4650H, and silica bed having a diameter of 0.5 mm was filled as a carrier 24 into the fluidized bed 27 at a height of 700 mm.
Further, the size of the aerobic filter bed was set to 500φ × 4000H, and an anthracite having a diameter of 3 to 6 mm was filled into the filter medium filling layer 43 at a height of 2000 mm as a carrier.

The operating conditions were as shown in Table 2.

[Table 2] The treatment results were as shown in Table 3 below.

[Table 3] However, in Table 3, raw water is primary treated water.

[0040]

As described above, according to the present invention,
The expansion interface of the anaerobic fluidized bed can be easily performed by using an airlift type biofilm stripper, which is an easy maintenance process.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a nitrogen removing device according to the present invention.

FIG. 2 is an enlarged sectional view showing a main part of the anaerobic fluidized bed in FIG.

FIG. 3 is an explanatory diagram showing a modified nitrification liquid circulation type activated sludge circulation method.

FIG. 4 is an explanatory view showing a conventional anaerobic filter / aerobic filter method.

[Explanation of symbols]

 Reference Signs List 23 Anaerobic fluidized bed 24 Carrier 28 Biofilm stripping device 29 Air lift pipe 29a Suction port 29b Discharge port 30 Air supply unit 31 Separation unit 32 First pipe 35 Water level control weir 36 Aerobic filter bed 37 Second pipe 38 Nitrification liquid circulation pump

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshio Oshima 2-3-13 Toranomon, Minato-ku, Tokyo Inside the Japan Sewerage Corporation (72) Inventor Fumio Sanpin 1-185-15, Drilling Imabari City, Ehime Prefecture In Japan Sewerage Corporation Ehime Construction Office (72) Inventor Norio Muroya 1-4-1, Yurakucho, Chiyoda-ku, Tokyo

Claims (1)

[Claims] 1. An apparatus for biologically removing BOD and nitrogen in an organic wastewater containing ammonia nitrogen such as sewage, comprising: an anaerobic fluidized bed for denitrification equipped with a biofilm stripping apparatus; Aerobic filter bed for nitrification of ammonia and ammonia nitrogen, first pipe to transfer overflow from anaerobic fluid bed to aerobic filter bed, and anaerobic flow of nitrifying solution from aerobic filter bed A second pipe returning to the floor, and a circulation pump provided in the second pipe, the biofilm stripping apparatus has a suction port for sucking a carrier to which microorganisms are attached at a lower portion, and an air supply unit near the suction port. An air lift pipe, a separation unit provided above the air lift pipe and separating the exfoliated organisms and the carrier that have exited the air lift pipe, and a water level regulating weir provided at the separation unit. , The suction port of the air lift pipe, The fluid interface, which is located slightly below the moving bed interface and rises with the growth of the microbial film attached to the surface of the carrier, is raised by an airlift tube from the anaerobic fluid bed near the fluid interface to the carrier with microorganisms attached. A nitrogen removing device, which is operated to maintain and control a constant height by peeling a microbial membrane while removing the microorganism film.