JPH0583320B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to improving a method for removing nitrogen from sewage, and uses a combination of a carrier flow type aeration tank and a hollow filtration membrane installed in the tank to achieve both BOD removal and denitrification. This invention relates to a new method for efficiently removing nitrogen from wastewater. (Prior Art) Nitrogen components present in sewage mainly exist as organic nitrogen (amines, etc.) produced by decomposition of proteins, and ammonia nitrogen produced by further decomposition. Therefore, conventional biological denitrification methods generally involve (a) converting organic nitrogen or ammonia nitrogen into nitrate nitrogen or nitrite nitrogen in an aerobic environment through the action of nitrifying bacteria; nitrified nitrogen (NO ₂ -N, NO ₃ -N) is converted into nitrogen gas in the presence of a carbon source (organic matter) in an anaerobic environment through the nitrification process and (b) the action of denitrifying bacteria. The basic method is a combination with a denitrification process, including a three-stage activated sludge method (methanol addition method), a nitrification liquid circulation method, an anaerobic
Various denitrification methods called aerobic circulation methods have been developed. However, in the conventional denitrification method, the nitrification process in an aerobic environment and the denitrification process in an anaerobic environment are performed separately, so the processing equipment becomes large and the denitrification process There are disadvantages in that returning the sludge to the tank and managing the sludge concentration in the denitrification tank is time-consuming, making it difficult to perform stable sewage treatment. On the other hand, in order to solve these problems, a porous filler (small pieces of sponge) on which microorganisms, mainly denitrifying bacteria, have been cultured and attached is filled into the denitrification treatment tank, and a gas flow that does not contain oxygen is used. Therefore, a technology has been developed that eliminates the need for sludge recovery and replenishment by forcibly stirring sewage after nitrification treatment, methanol, etc.
−150870, etc.) However, even with these treatment technologies that use porous fillers (sponge pieces), a nitrification process is required in addition to the denitrification tank process, so it is said that it is not possible to significantly downsize the treatment equipment. Problems remain. In addition, various types of carrier fluidized aeration treatment tanks that use porous carriers have been developed, but all of these are aimed at BOD removal and cannot be applied to nitrogen removal. (Japanese Unexamined Patent Application Publication No. 1973-1999)
39949, Special Publication No. 55-51639, etc.). Furthermore, in a normal aeration treatment tank, a membrane filtration device is installed inside the aeration treatment tank, and the treated water is suction-separated using the excellent sludge separation ability of the membrane filtration device. has been developed, which prevents the filtration capacity of the membrane filtration device from deteriorating by washing the biofilm that forms and adheres to the outer surface of the membrane filtration device with circulating wastewater due to the filtration action ( (Japanese Patent Publication No. 129094/1983). However, simply cleaning the outer surface of the filtration membrane by circulating sewage does not actually completely remove the biofilm that gradually grows on the membrane surface, even when the flow rate of sewage is increased to a considerably high speed. It is difficult to remove, and as a result, the filtration capacity of the membrane filtration device decreases over time, making it impossible to perform stable aeration treatment of wastewater. (Problems to be Solved by the Invention) The present invention solves the above-mentioned problems in the conventional method for removing nitrogen from wastewater, namely (a) the nitrification process and denitrification process are required separately, so the size of the treatment equipment is small. (b) If a hollow membrane filtration device is installed in the treatment tank, the filtration capacity cannot be maintained at a specified value for a long period of time. By using an air permeable packing with specific physical properties, both the nitrification and denitrification processes can be performed in parallel in one main treatment tank, and the main treatment In addition to suctioning and separating the treated water through a hollow filtration membrane installed in the tank, the circulating aeration packing is brought into repeated contact with the filtration membrane to clean the outer surface of the filtration membrane, thereby significantly reducing the amount of waste in the treatment equipment. The object of the present invention is to provide a method for removing nitrogen from sewage that enables miniaturization, improved aeration management ability, and reduced processing costs. (Means for Solving the Problem) By the way, the inventor of the present invention discovered that in the process of performance testing of a fluidized aeration treatment equipment using a permeable carrier to which activated sludge was attached, It was found that not only the BOD but also the total nitrogen in wastewater was significantly reduced when using this method. Table 1 shows the results of the above tests, and in Test 2 (Sample D) and Test 4 (Sample C),
By using nonwoven fabric piece No. 2 (15 mm x 15 mm x 10 mm) and polyurethane piece No. 1 (12 mm x 12 mm x 12 mm) as carriers, the total nitrogen T-N can be reduced to approximately 40% by aeration treatment for 120 minutes. It has been shown that the problem can be removed. The results in Table 1 are based on the filling rate of the breathable carrier being 30%.
(Filled with 30VOL% carrier based on the internal volume of the aeration tank)
This is the value when the aeration intensity is 5.5Nm ³ /m ³ ·Hr. As is clear from the results in Table 1 above, when a certain type of air permeable carrier is used, nitrogen is removed even in the aeration treatment tank under an aerobic environment. In the aeration treatment tank, in addition to BOD removal and nitrification under an aerobic environment, denitrification under an anaerobic environment is simultaneously proceeding. The processing mechanism in which nitrification and denitrification proceed simultaneously as described above has not yet been fully analyzed, but BOD removal and nitrification of nitrate nitrogen in an aerobic environment are mainly caused by aeration. Denitrification is carried out in the outer region of the carrier (i.e., aerobic region) and in an anaerobic environment.
It is assumed that this is mainly carried out in the inner layer region (ie, anaerobic region) of the breathable carrier. This invention was developed based on the above knowledge.

[Table] By specifying the physical properties, dimensions, filling rate, etc. of the permeable carrier to be used, it is possible to create a carrier fluidized aeration system with a hollow filtration membrane in the tank. The treatment tank enables both BOD removal and nitrogen removal at the same time. In the present invention, in the main treatment tank equipped with an aeration device,
The outer layer becomes an aerobic region and the inner layer becomes an anaerobic region, and is a prismatic air permeable carrier with a side length of 10 to 15 mm or an outer diameter and height of 10 to 15 mm.
The cylindrical air permeable carrier is filled at a filling rate of 20 to 35%, and the sewage and the air permeable carrier are circulated and flowed by the air ejected from the aeration device, and are made to flow along the circulating flow channel. A hollow filtration membrane is disposed over the entire waterway or a part thereof, and only the treated water is suctioned and separated from the mixed liquid in the main treatment tank through the hollow filtration membrane, and the air-permeable carrier that circulates and flows is The basic structure of the invention is to prevent clogging of the filtration membrane by repeatedly contacting the surface of the hollow filtration membrane disposed in the fluid waterway. (Function) Ammonia nitrogen and organic nitrogen in wastewater are released in the outer layer of the breathable carrier under an aerobic environment.
When it comes into contact with nitrifying bacteria in the sludge that adheres to it, it undergoes nitrification and is converted into nitrate nitrogen and the like. The converted nitrate nitrogen, etc. continues to contact denitrifying bacteria in the sludge that adheres to the inner layer of the breathable carrier under an anaerobic environment.
Nitrogen is removed by denitrification. The treated wastewater is separated through a hollow filtration membrane disposed within the tank, and is discharged to the outside through a hollow passage inside the membrane. Further, the outer surface of the hollow filtration membrane is forcefully cleaned by repeated contact with the air-permeable carrier circulating in the tank, thereby preventing clogging of the filtration membrane. (Example) Hereinafter, an example of the present invention will be described based on FIGS. 1 to 4. Figure 1 is a cross-sectional schematic diagram of the sewage treatment equipment according to the present invention, in which 1 is the main treatment tank, 2 is the hollow filtration membrane, 3 is the air diffuser, 4 is the suction pump, and 5 is the inflow of sewage. 6 is an air pipe, and 7 is an air permeable carrier. The main treatment tank 1 is made of concrete or plastic, and is provided with a sewage inlet, an overflow hole, a manhole, etc., respectively. The hollow filtration membrane 2 has a blocked particle size of 0.05~
It is formed from a filtration membrane of about 0.5 μm, and has a hollow passage 2a inside. This hollow filtration membrane 2 is made up of an air permeable carrier 7 which will be described later.
By reducing the pressure inside the hollow passage 2a through the suction pipe 8 with the pump 4, the treated water flows through the filtration membrane into the hollow passage 2a. It is advected and sucked out to the outside. In FIG. 1, the hollow filtration membrane 2 is disposed above the circulating flow passage of the air-permeable carrier 7 (i.e., above the tank), but in FIGS. As shown in the figure, it may be arranged at the side part (side part of the tank) or the lower part (bottom part of the tank) of the circulating flow passage, so that the flowing air permeable carrier 7 can effectively contact the outer surface of the filtration membrane. It may be any location as long as it is possible. Further, the hollow filtration membrane 2 may be of any type or structure; for example, the filtration membrane 2 may be a bundle of hollow membranes as shown in FIG. The air diffuser 3 is installed at the lower side of the main treatment tank 1, and blows out air supplied from a compressor (not shown) through an air pipe 9, thereby discharging sewage and air-permeable carriers in the tank. 7 circulates in the direction of the arrow. In addition, the external dimensions of the main treatment tank 1 are 12mm x 12mm.
A polyurethane air-permeable carrier 7 having a cubic shape of 12 mm is filled so that the volume occupancy is about 30%. The air permeable carrier 7 is desirably a prismatic body with a specific gravity of approximately 1 and a side length of about 10 to 15 mm, or a cylindrical body with an outer diameter and a height of 10 to 15 mm. This is because if the specific gravity greatly deviates from 1, or if the length or height dimensions exceed 15 mm, the fluidity due to air ration will deteriorate, and if the dimensions become 10 mm or less, the anaerobic properties of the air permeable carrier 7, which will be described later, will deteriorate. The area will be reduced and the denitrification capacity will be reduced. Further, the air-permeable carrier 7 must have abrasion resistance, and in the case of the polyurethane carrier 7, ether-based open-cell polyurethane is preferable. Furthermore, the filling rate of the breathable carrier 7 is optimally about 20 to 35%. This is because the denitrification effect decreases rapidly when the filling rate is less than 20%, and when the filling rate is 35% or less, the denitrification effect decreases rapidly.
% or more, it becomes difficult to flow by air ration, and if the amount of air is increased to improve fluidity, the denitrification effect will be canceled out. Confirmed by denitrification test. As mentioned above, the air-permeable carrier 7 needs to have an outer layer that acts as an aerobic region and an inner layer that acts as an anaerobic region, and from this point of view, it is necessary that the air-permeable carrier 7 is simply open-cell, or has a low cell rate. Even if it is possible to remove BOD, it is impossible to achieve an excellent nitrogen removal effect if the That is, if the air bubbles in the air-permeable carrier are large and most of the bubbles are open, the air bubbles will easily pass through the carrier together with water, and the anaerobic region will become almost zero. Denitrification effect cannot be obtained. Conversely, no matter how large the porosity is, if the cells are not open-celled, the anaerobic region will increase but the water permeability will be poor and no denitrification effect will be obtained. Therefore, the air-permeable carrier 7 should have an appropriate pore size and an appropriate open cell ratio (preferably a relatively large open cell ratio in the outer layer region and a relatively small open cell ratio in the inner layer region). The PPI value (number of cells per 1 inch width), cell ratio (cell volume/total volume), and open cell ratio (open cell ratio), which are generally used to indicate the characteristics of this type of foam, are essential requirements. It is impossible to express the physical properties of the breathable carrier that are optimal when nitrogen removal is performed using a single carrier flow type aeration tank as in the present invention using only the number of foamy bubbles/total number of bubbles. Therefore, in the present invention, we focused on the filtration performance of the air permeable carrier 7, and used the Japan Air Cleaning Association (JACA No. The filtration resistance of the plate material C for the breathable carrier was measured using the first performance test method described in 10).That is, first, the thickness corresponding to the length of one side (10 mm) of the prismatic breathable carrier 7 was measured. Breathable board material C with length L = 10mm
were arranged as shown in Fig. 5, and the filtration resistance P was measured under a wind speed of 2 m/sec. In addition, FIG. 5 shows the vertical performance test device used in the first performance test method, and in the figure, C
is the test object, D is the manometer, E is the rectifying grid, F is the air volume adjustment plate, G is the fan, H is the sight glass, I is the tester body, J is the orifice, and the anemometer is omitted. Next, the filtration resistance P under the aforementioned wind speed of 2 m/sec
The porous carrier 7 is formed by cutting the permeable plate material C after the measurement of (mmH ₂ O) into cubes of predetermined dimensions.
This was filled into an aeration treatment tank at a filling rate of 30%, and denitrification treatment was performed for a certain period of time, and the removal rate Q of total nitrogen TN was actually measured. It goes without saying that test conditions such as the type and amount of water to be treated, treatment time, and amount of aeration used in the denitrification test are set to be the same for each breathable carrier 7. Thereafter, the filtration resistance P and the total nitrogen removal rate Q were compared, and from this comparison, the range of the filtration resistance P that could achieve a high nitrogen removal rate Q was determined.

[Table] Table 2 shows an example of the filtration resistance P measured by the test shown in Fig. 5, where the filtration resistance P is the filtration resistance mmH ₂ at a wind speed of 2 m/sec.
It is represented by O. Furthermore, Figure 6 is a semi-logarithmic graph showing the relationship between the filtration resistance P in Table 2 and the roughness of the sample, and in the case of a urethane sample, the number of pores (cells) per 1'' There is a logarithmic linear relationship between the roughness of the mesh and the filtration resistance P. Comparing the results in Tables 1 and 2 above, the air permeable carrier of sample code C removed approximately 40% of nitrogen. In this way, we measured the nitrogen removal rate Q and air filtration resistance P for a large number of breathable carriers, and from the comparison of the two, we found that the thickness L of the breathable board material is 10 to 15 mm. Sample thickness 10 within the range of
mm, filtration resistance at a wind speed of 2m/sec is 5 to 12mm
The air permeable carrier formed of H ₂ O into a rectangular prism shape with a side length of 10 to 15 mm or a cylindrical shape with an outer diameter and height of 10 to 15 mm has the optimum air permeability in the present invention. It turned out to be a carrier. Next, a method for removing nitrogen from wastewater according to the present invention will be explained. Referring to FIGS. 1 to 4, sewage enters the main treatment tank 1 from the sewage inflow pipe 5, and flows from the air diffuser 3 together with the air permeable carrier 7 holding activated sludge therein and the floating activated sludge. The air is circulated within the tank 1 by the ejected air flow. Approximately 90% of the BOD in the wastewater is removed by biological treatment using activated sludge while circulating in tank 1. In addition, when the sewage comes into contact with the aerobic region of the outer layer of the breathable carrier 7 and the nitrifying bacteria in the suspended sludge,
Nitrification treatment of ammonia nitrogen, etc. is carried out. Furthermore, in the anaerobic region of the inner layer of the air permeable carrier 7, the nitrified nitrate nitrogen comes into contact with denitrifying bacteria in the sludge, resulting in denitrification treatment, reducing approximately 70% or more of the total nitrogen. is removed. In addition, in this example, the BOD load is 0.8 to 3.
KgBOD/ ^m3・day, activated sludge amount 5.0Kg or more/ ^m3 ,
per day, average inflow total nitrogen 0.04Kg/Kg (activated sludge) and
0.2Kg or less/ ^m3 (tank volume), aeration intensity ^9.0m3 / ^m3・
Each is set in Hr. In addition, the breathable carrier has a 12mm x 12mm x 12mm urethane ventilation body (air filtration resistance P = 5.7) with a resistance of approximately 17200 mm.
pcs/m ³ (filling rate 30%).
The flow velocity near the inner peripheral surface of tank 1 is 60 to 100 cm/
sec, the flow velocity at the center of tank 1 is 5 to 10 cm/
It is about sec. When the suction pump 4 is operated to operate the hollow filtration membrane 2, the treated wastewater passes through the filtration membrane and enters the hollow passage 2a side, and is discharged to the outside through the suction pipe 8. Sludge and the like filtered by the filtration membrane adhere to the outer surface of the filtration membrane, but are washed by the flowing sewage that rises due to the air ration action of the air diffuser 3, and are remixed into the sewage. In the present invention, the circulating air permeable carrier 7 repeatedly collides with the outer surface of the hollow filtration membrane 2 disposed therein along the circulating flow path, thereby rubbing the outer surface of the filtration membrane. As a result, even deposits that cannot be removed by flowing sewage alone can be removed extremely smoothly. The sludge removed from the hollow filtration membrane 2 continues to remain in the main treatment tank 1. As a result, the activated sludge concentration in the tank 1 gradually increases, and efficient sewage treatment is performed under a high active contaminant concentration. (Effects of the Invention) In the present invention, the aerobic region formed in the outer layer part of the breathable carrier 7 and the anaerobic region formed in the inner layer part are functionally utilized, and a single carrier Since the configuration uses a fluid flow type aeration treatment tank to remove nitrogen and BOD, the treatment equipment can be significantly downsized compared to the conventional treatment method that separates the nitrification and denitrification processes. Processing operations can be simplified. In addition, in the present invention, the external dimensions of the air-permeable carrier 7 used, its air filtration resistance P, and the filling rate of the carrier 7 are selected to optimal values, so that the nitrification effect in the aerobic region and the anaerobic region are reduced. The denitrification effect is achieved in a well-balanced manner, and an excellent denitrification effect can be exhibited compared to the conventional device filled with a porous carrier B such as simply foamed urethane. Further, in the present invention, the hollow filtration membrane 2 is arranged along the circulation flow path of the air permeable carrier 7, so that the outer surface of the filtration membrane is rubbed by the flowing air permeable carrier 7. . As a result, the biofilm attached to the outer surface of the filtration membrane is almost completely removed.
It is possible to perform high-performance operation for a longer period of time than in the conventional configuration in which cleaning is performed using a circulating wastewater flow. In addition, since the surface of the filtration membrane can be sufficiently cleaned without increasing the flow rate of circulating wastewater, energy consumption is significantly reduced compared to conventional equipment that requires high-speed flow, and the filtration membrane The sludge separated from the outer surface is mixed into the wastewater again, so
Efficient wastewater treatment can be performed under high activated sludge concentration. As mentioned above, the present invention has excellent practical effects.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a sewage treatment apparatus used for carrying out the present invention. FIG. 2, FIG. 3, and FIG. 4 are cross-sectional schematic diagrams showing other examples of sewage treatment equipment used for carrying out the present invention. FIG. 5 is an explanatory diagram of a method for measuring the air filtration resistance P of a breathable carrier, and FIG. 6 shows the relationship between the air filtration resistance P and the roughness of the sample. 1... Main treatment tank, 2... Hollow filtration membrane, 3...
Air diffuser, 4... Suction pump, 5... Sewage inflow pipe, 6... Air piping, 7... Breathable carrier, 8...
Suction tube, P...Air filtration resistance of the breathable carrier.

Claims (1)

[Claims] 1. In the main treatment tank equipped with an aeration device, the outer layer is an aerobic region, the inner layer is an anaerobic region, and a prismatic ventilation section with a side length of 10 to 15 mm is provided. A cylindrical air-permeable carrier with an outer diameter and a height of 10-15 mm is filled at a filling rate of 20-35%, and the sewage and air-permeable carrier are removed by the air ejected from the air diffuser. In addition to circulating the water, a hollow filtration membrane is disposed in the entire area or part of the waterway along the circulation waterway, and only the treated water is passed through the hollow filtration membrane from the mixed liquid in the main treatment tank. The wastewater is separated by suction, and the circulating and flowing air-permeable carrier is repeatedly brought into contact with the surface of a hollow filtration membrane disposed in a flow channel to prevent clogging of the filtration membrane. Nitrogen removal method. 2 Use a breathable carrier with a gas filtration resistance of 5 to 12 mmH ₂
2. The method for removing nitrogen from sewage according to claim 1, wherein the air-permeable carrier is made of urethane, polyethylene, or nonwoven fabric and has a wind speed of 2 m/sec and a thickness of 10 mm. 3. The diameter of the particles to be blocked by the hollow filtration membrane is 0.05 to 0.5 μm.
The method for removing nitrogen from wastewater according to claim 1.