JPH0466195A - Nitrogen removal method of sewage - Google Patents

Abstract

PURPOSE:To efficiently carry out denitrification and BOD removal in one aeration treatment tank by using an aerobic region formed in the cut layer part of a porous carrier having specified physical properties and an anaerobic region formed in its inner layer functionally. CONSTITUTION:A main treatment tank 2 having a gas blowing pipe 8 is filled at 10-35% filling ratio with a porous carrier B whose outer layer part becomes an aerobic region and at the same time inner layer part becomes an anaerobic region and which has a tetragonal pillar shape with 10-15mm length of one side and contains activated sludge inside. While sewage which comes in the main treatment tank 2 is circulated in the tank by an air flow sprayed from the gas blowing pipe 8, about 90% of BOD in the sewage is removed by biological treatment with activated sludge. Also, nitrification treatment of ammonia- nitrogen, etc. is carried out by bringing the sewage into contact with the aerobic region of the outer layer part of the porous carrier B and nitrification bacteria in floating sludge. Further, the nitrified nitric acid-nitrogen in the sludge is brought into contact with denitrification bacteria in sludge in the anaerobic region of the inner layer part, so that denitrification is carried out and about >=70% of the total nitrogen is removed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to improving a method for removing nitrogen from wastewater, and enables efficient BOD removal and denitrification by combining a carrier flow type aeration tank and a settling tank. This invention relates to a method for 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, -N, No, -N) through the nitrification process and (b) the action of denitrifying bacteria.
The basic method is a combination with a denitrification process in which nitrogen gas is converted into nitrogen gas in the presence of a carbon source (organic matter) in an anaerobic environment. - 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 treatment tank and managing the sludge concentration in the denitrification treatment tank is time-consuming, making it difficult to perform stable sewage treatment.

On the other hand, in order to solve these problems, the denitrification treatment tank is filled with a porous filling (small pieces of sponge) on which microorganisms, mainly denitrifying bacteria, are cultured and attached, and a gas flow containing no oxygen is used to A technique has been developed that eliminates the need for sludge recovery and replenishment by forcibly stirring the filler, sewage after nitrification treatment, added methanol, etc. (Japanese Patent Laid-Open Publication No. 150870/1987, 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 have BOD
It is intended for nitrogen removal and cannot be applied to nitrogen removal (Japanese Patent Application Laid-open No. 49-39949, Japanese Patent Publication No. 55
-51639 etc.).

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems in conventional wastewater nitrogen removal methods, namely (a) the nitrification process and denitrification process are required separately, so the treatment equipment is small. The aim is to solve the problem of not being able to simplify the processing and processing operations, and by using porous fillers with specific physical properties,
- Provides a method for removing nitrogen from wastewater that allows both the nitrification process and the denitrification process to be performed in parallel in the main treatment tank, thereby making it possible to significantly downsize treatment equipment and reduce treatment costs. It is.

(Means for Solving the Problem) By the way, the present inventor discovered that in the process of performance testing of a fluidized aeration treatment equipment using a porous carrier to which activated sludge was attached, If you use BOD
Not only that, but the total nitrogen in the wastewater was also significantly reduced.

Table 1 shows the results of the above tests, and in Test 2 (Sample D) and Test 4 (Sample C), the carrier was a small piece of nonwoven fabric NO2 (15WX 15WX IQ am) and a small piece of polyurethane NOI (12+mX 12WX 12
-), it has been shown that approximately 40% of the total nitrogen TN is removed by aeration treatment for 120 minutes.

In addition, the results in Table 1 were obtained when the filling rate of the porous carrier was 30% (30 VOL% of the carrier was filled with respect to the internal volume of the aeration tank) and the aeration intensity was 5.5 Nm"/m・Hr. This is the value of the case.

As is clear from the results in Table 1 above, when certain porous carriers are used, nitrogen is removed even in the aeration 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.

Although the processing mechanism in which nitrification and denitrification proceed simultaneously as described above has not yet been fully analyzed, BOD removal and nitrification of nitrate nitrogen in an aerobic environment are mainly caused by denitrification is carried out in the outer layer region (i.e. aerobic region) of the porous carrier, and denitrification in an anaerobic environment is mainly carried out in the inner shoulder region (i.e. anaerobic region) of the porous carrier. It is assumed that there are.

The present invention was developed based on the above-mentioned knowledge, and by specifying the physical properties, dimensions, filling rate, etc. of the porous carrier used, it is possible to realize -based carrier fluidized aeration. Both BOD removal and nitrogen removal can be performed simultaneously using a treatment tank and a sedimentation tank (or one carrier flow type aeration treatment tank with a sedimentation unit).

That is, 1. The present invention provides a main treatment tank equipped with an air diffuser, in which the outer layer becomes an aerobic region, the outer layer becomes an anaerobic region, and the length of one side is 10 to 15 square meters. The columnar porous carriers are filled at a filling rate of 10 to 35%, and the sewage and porous carriers are circulated and flowed by the air ejected from the aeration device, and the treated sewage is transferred from the main treatment tank to the settling tank. The basic structure of the invention is to perform sedimentation separation of the sludge by advection to the main treatment tank, and to return a part of the separated sludge to the main treatment tank.

(Function) Ammonia nitrogen and organic nitrogen in sewage undergo nitrification by coming into contact with nitrifying bacteria in the sludge that adheres to the outer layer of the porous carrier in an aerobic environment. ,
Converted to nitrate nitrogen, etc.

The converted nitrate nitrogen, etc., continues to undergo denitrification in the inner layer of the porous carrier under an anaerobic environment by coming into contact with the denitrifying particles in the sludge adhering to it, and is converted into nitrogen. Removal takes place.

The treated sewage is advected to a settling tank through a screen, where the sludge is separated by sedimentation, and then subjected to disinfection and other treatments before being discharged to the outside.

A portion of the sludge that has been precipitated and separated is returned to the main treatment tank and adsorbed onto the flowing porous carrier. As a result, the amount of sludge in the main treatment tank is always maintained at a predetermined value.

(Example) The present invention will be described in detail below based on one drawing.

FIG. 1 shows the treatment process of the present invention. In the figure, 1a is running wastewater, 1b is discharged water, 2 is a carrier flow type main treatment tank, 3 is a settling tank, and 4 is a disinfection tank.

5 is a discharge pump tank, 6a is a metering device, 6 is a sludge return path,
7 is a sludge thickening storage tank.

Further, FIGS. 2 to 5 show the main parts of the processing apparatus used to implement the present invention. The main treatment tank 2, disinfection tank 4, discharge pump tank 5, etc. are integrally formed within the tank body A, and the sedimentation tank 3 (not shown) is provided separately.

In addition, in FIGS. 2 to 5, 8 is a diffuser pipe, 9 is a diffuser pipe fixing base, 10 is a detachable union, 11 is an air supply valve, 1
2 is a piping support plate, 13 is an air relief pipe, 15 is an advection pipe,
16 is a screen part, 17 is a discharge pump stand, 18 is a discharge pump, 19 is a disinfection device, 20 is a partition wall, 21 is an advection wall, 22 is a drug barrel, 23, 24 is an advection pipe, and 25 is a partition wall.

Further, in this embodiment, the settling tank 3 is separate from the main processing tank 2, but it is also possible to form them integrally.

An aeration pipe 8 is provided at the bottom of the main treatment tank 2, and air supplied from a compressor (not shown) is blown out, thereby discharging the sewage in the tank as well as the porous carrier B.
circulates in the direction of the arrow.

In addition, the main treatment tank 2 has external dimensions of 12m x 12rm.
A polyurethane porous carrier B having a cubic shape of X l 2 m is filled so that the volume occupancy is about 30%.

The porous carrier B is preferably a prismatic body with a specific gravity of approximately 1 and a side length of about 10 to 15 mm, because the specific gravity is far away from 1, or the length of a side is 15 mm.
If it becomes more than that, the fluidity due to aeration will deteriorate,
Moreover, when the dimension of the - side becomes 10 - or less, the anaerobic region of the porous carrier B described later decreases, and the denitrification ability decreases.

Further, the porous carrier B must have wear resistance, and in the case of the porous carrier B made of polyurethane, ether-based open-cell polyurethane is preferable.

Further, the optimum filling rate of the porous carrier B is about 20 to 35%. This is because when the filling rate is less than 20%, the denitrification effect decreases rapidly, and when the filling rate is more than 35%, it becomes difficult to flow by aeration, and the amount of air is increased to improve fluidity. This is because the denitrification effect is counterbalanced, and both of the above have been confirmed by denitrification tests.

As mentioned above, the porous carrier B needs to have an outer layer that acts as an aerobic region and an inner layer that acts as an anaerobic region.
Alternatively, if the bubble rate is only high, even if BOD removal is possible, it is impossible to exhibit an excellent nitrogen removal effect.

That is, if the air bubbles in the porous carrier are large and most of the bubbles are open cells, 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 porous carrier B has 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). This is an essential requirement, and the P, P, I values (number of cells per 11 width), cell ratio (cell volume/total volume), and open cell ratio are commonly used to indicate the characteristics of this type of foam. (
It is not possible to express the physical properties of the porous 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 open cells/total number of bubbles. It is possible.

Therefore, in the present invention, we focused on the filtration performance of porous carriers, and developed the Japan Air Cleaning Association's (JACANOIO) 1, which is a highly reliable evaluation test method for filtration performance, which is the basic characteristic of plastic ventilators. The filtration resistance of plate material C for porous carrier was measured using a performance test method.

That is, first, the length of one side of the prismatic porous carrier B (iol
A porous plate C having a thickness L of 10 cm corresponding to
The filter was installed as shown in the figure, and the filtration resistance P was measured under a wind speed of 2m756c.

FIG. 6 shows the vertical performance test device used in the first performance test method, in which C is the test object, D is the manometer, E is the rectifying grid, F is the air volume adjustment plate, and G is the test piece. is a fan, H is a peephole, G is the main body of the tester, J is an orifice, and the anemometer is omitted.

Next, the filtration resistance P (
After measuring ma+H20), the porous plate material C is cut into cubes of predetermined dimensions to form porous carriers B, which are filled into aeration treatment tanks at a filling rate of 30% and denitrified for a certain period of time. The treatment was carried out, and the total nitrogen TN removal rate Q 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 porous carrier B.

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 2 Table 2 shows the filtration resistance P measured by the test shown in Figure 6 above.
This shows an example, where the filtration resistance P is the wind speed 2
The filtration resistance (■H20) is expressed under m/see.

Furthermore, Fig. 7 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 coarseness of the mesh and the filtration resistance P expressed by .

Comparing the results in Tables 1 and 2 above, it can be seen that the porous carrier of sample code C can achieve a nitrogen removal rate of about 40%. In this way, the nitrogen removal rate Q and air filtration resistance P were measured for a large number of porous carriers, and from the comparison of the two, it was found that when the thickness L of the porous plate material is within the range of 10 to 15 m, In the present invention, a porous carrier having a sample thickness of 10 Wm and a filtration resistance of 5 to 121111H20 at a wind speed of 2 m/sec is formed into a rectangular prism shape with a side length of 10 to 15 mm. It turned out to be the most suitable porous carrier.

Next, a method for removing nitrogen from wastewater according to the present invention will be explained.

Referring to FIGS. 1 to 5, the water to be treated is first transferred to the advection pipe 1.
5 into the main treatment tank 2, and the activated sludge is circulated in the tank 2 together with the porous carrier B holding the activated sludge therein and the floating activated sludge by the air flow from the aeration pipe 8.

Approximately 90% of the BOD in the wastewater is removed by biological treatment using activated sludge while circulating in the tank 2.

Furthermore, when the wastewater comes into contact with the aerobic region of the outer layer of the porous carrier and the nitrifying bacteria in the suspended sludge, ammonia nitrogen and the like are nitrified. Furthermore, in the anaerobic region of the inner layer of the porous carrier, nitrified nitrate nitrogen comes into contact with denitrifying bacteria in the sludge, thereby denitrifying the sludge.
About 70% or more of the total nitrogen is removed.

In addition, in this example, the BOD load is 0.8 to 3 kg.
BoD/m'・day, activated sludge amount 5.0 dazzle/m or more, El
, average inflow total nitrogen 0.04 kg/kg (activated sludge) and 0.2 kg or less/rn' (tank volume), aeration intensity 9, O
rr['/m·Hr, respectively.

In addition, the porous carrier B has a 12×12×12× urethane porous body (air filtration resistance P=5.7) of about 17.2
00 pieces/rn" (filling rate 30%), and the flow rate near the inner peripheral surface of tank 2 is 60-100
am7sec, flow velocity in the center of tank 2 is 5-10
It is about ex/see.

The mixed liquid of activated sludge and carrier from the main treatment tank 2 is prevented from flowing out of the porous carrier B by the screen part 16, and only the mixed liquid of activated sludge is sent to the settling tank 3 through the advection pipe 23, where it is sent to the settling tank 3. Sedimentation and separation of sludge is carried out.

The treated water from which the sludge has been separated passes through the advection pipe 24 to the disinfection tank 4.
The disinfected treated water is discharged to the outside of the tank via the discharge pump tank 5 by the discharge pump 18.

The sludge separated in the settling tank 4 is automatically measured by a measuring device 6a, and the required amount is returned to the main treatment tank 2 through the sludge return pipe 6, and the amount of activated sludge in the main treatment tank is is adjusted to the set value.

(Effects of the Invention) In the present invention, the aerobic region formed in the outer layer part of the porous carrier B and the anaerobic region formed in the inner layer part are functionally utilized, and - group carrier Since nitrogen and BOD are removed using a fluid flow type aeration treatment tank, compared to the previous treatment method in which the nitrification process and denitrification process are separated, the size of the treatment equipment and treatment operations can be significantly reduced. It is possible to measure the simplification of

In addition, in the present invention, the external dimensions of the porous carrier B used, its air filtration Ex EP, and the filling rate of the carrier B are selected to optimal values, so that the nitrification effect in the aerobic region and the anaerobic region 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.

Furthermore, in the present invention, a part of the activated sludge separated in the settling tank is returned to the main treatment tank and adsorbed into the flowing porous carrier, thereby maintaining the amount of activated sludge in the main treatment tank at a predetermined value. As a result, a good treatment effect can be achieved over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a wastewater treatment process according to the present invention. FIG. 2 is a plan view showing the main parts of the processing apparatus used for carrying out the present invention, FIG. 3 is a cross-sectional view taken along line AA in FIG.
The figure is a sectional view taken along line B-B in figure 2, and figure 5 is a cross-sectional view taken along line B-B in figure 2.
It is a B' sectional view. FIG. 6 is an explanatory diagram of a method for measuring the air filtration resistance P of a porous carrier, and FIG. 7 shows the relationship between the air filtration resistance P and the roughness of the sample. A Main treatment tank body B Porous carrier 2 Main treatment tank 3 Sedimentation tank 4 Disinfection tank
6 Sludge conveyance path 6a Automatic metering device 8 Diffusion tube 16 Screen part P Air filtration resistance of porous carrier Figure 5 Figure 7 Person who amends the name of the invention indicated in the case Relationship with the case Address Name Continuation Amendment (Spontaneous) August 7, 1990 Patent Application No. 179840/1990 Method for removing nitrogen from sewage

Claims (3)

[Claims] (1) Inside the main treatment tank equipped with an aeration device, the outer layer becomes an aerobic region and the outer layer becomes an anaerobic region in the wastewater, and a prismatic porous hole with a side length of 10 to 15 mm is formed. The porous carrier is filled with a porous carrier at a filling rate of 20 to 35%, and the sewage and porous carrier are circulated and flowed by the air ejected from the aeration device, and the treated sewage is advected from the main treatment tank to the settling tank. 1. A method for removing nitrogen from sewage, which comprises performing sedimentation separation of sludge and returning a portion of the separated sludge to the main treatment tank. (2) The porous carrier is a porous body made of urethane, polyethylene, or nonwoven fabric having a gas filtration resistance of 5 to 12 mm H_2O (wind speed 2 m/sec) in the direction of its longest side. How to remove nitrogen from wastewater. (3) Claim 1 in which only the treated sewage is advected from the main treatment tank through the screen to the settling tank, and the sludge separated in the settling tank is returned to the main treatment tank while being controlled by a metering device. Method for removing nitrogen from wastewater as described in .