JPH0741260B2 - How to remove nitrogen from sewage - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an improvement of a method for removing nitrogen from wastewater, which can efficiently perform BOD removal and denitrification by combining a carrier flow type aeration tank and a precipitation tank. The present invention relates to a method for removing nitrogen from wastewater.

(Prior Art) Nitrogen components existing in wastewater mainly exist as organic nitrogen (amines and the like) produced by decomposition of proteins and ammonia nitrogen further decomposed.

Therefore, in all of the conventional biological denitrification methods, (a) the action of nitrifying bacteria converts organic nitrogen or ammonia nitrogen into nitrate nitrogen or nitrite nitrogen in an aerobic environment. converting the nitrification step of converting, by the action of denitrifying bacteria (b) nitrifying nitrogen _{(NO 2 -N, NO 3 -N} ) to a nitrogen gas in the presence of a carbon source under anaerobic environment (organic matter) Basically, it is combined with the denitrification process, and various denitrification methods called three-stage activated sludge method (methanol addition method), nitrification solution circulation method, anaerobic / aerobic circulation method, etc. have been developed.

However, in the conventional denitrification method, the nitrification step in an aerobic environment and the denitrification step in an anaerobic environment are separately performed, so that the treatment equipment becomes large and the denitrification treatment is performed. There is an inherent drawback that it takes time to return sludge to the tank and control the sludge concentration in the denitrification tank, making it difficult to perform stable wastewater treatment.

On the other hand, in order to solve these problems, a porous packing (small pieces of sponge), in which microorganisms mainly composed of denitrifying bacteria are cultured and adhered, is filled in the denitrification treatment tank, and a gas flow containing no oxygen is used. A technique has been developed in which the packing and the nitrification-treated sewage, added methanol, and the like are forcibly agitated to eliminate the need for sludge recovery and supplementation (JP-A-51-150870).

However, even in the processing technology using such porous packing (small pieces of sponge), a nitrification step is additionally required in addition to the denitrification tank step, so it can be said that the size of the processing equipment cannot be significantly reduced. The problem remains.

In addition, various types of carrier fluidization type aeration treatment tanks using porous carriers have been developed, but these are all intended for BOD removal and are not applicable 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 has the above-mentioned problems in the conventional nitrogen removal method for wastewater, that is, (a) the nitrification step and the denitrification step are separately required, and therefore the size of the treatment facility is small. It is intended to solve the problem that simplification and simplification of treatment operation cannot be achieved, and by using a porous packing having specific physical properties,
A method for removing nitrogen from sewage that allows the nitrification process and the denitrification process to be performed in parallel in a single main processing tank, thereby significantly reducing the size of the processing equipment and reducing the processing cost. Is.

(Means for Solving the Problem) By the way, in the process of performance test of a fluidized aeration treatment apparatus using a porous carrier to which activated sludge is adhered, the present inventor It was found that not only BOD but also total nitrogen in the sewage was significantly reduced when using.

Table 1 shows the results of the above test. In Test 2 (Sample D) and Test 4 (Sample C), the carrier was a nonwoven fabric piece NO2 (15 mm × 15 mm × 10 mm) and a polyurethane piece NO1.
(12mm × 12mm × 12mm) makes the total nitrogen T-N
Has been shown to be removed by about 40% by aeration treatment for 120 minutes.

The results in Table 1 show that the filling rate of the porous carrier was 30% (30 VOL% of the carrier was filled in the aeration tank volume) and the aeration strength was 5.5 Nm ³ / m ³ · Hr. This is the case value.

As is clear from the results in Table 1 above, certain types When the porous carrier is used, nitrogen is removed even in the aeration treatment tank under aerobic environment. Therefore, in the aeration treatment tank, BOD removal and nitrification under aerobic environment are performed. In addition to the action, the denitrification action under the anaerobic environment is also proceeding at the same time.

Although the mechanism of the treatment that the nitrification action and the denitrification action simultaneously proceed as described above has not been sufficiently analyzed, the BOD removal action in an aerobic environment and the nitrification action such as nitrate nitrogen are mainly porous. The denitrification action is performed in the outer layer region (ie, aerobic region) of the porous carrier and in the anaerobic environment, is mainly performed in the inner layer region (ie, anaerobic region) of the porous carrier. Assumed to be.

The present invention has been developed based on the above-mentioned knowledge, and by specifying the physical properties, dimensions, filling rate, etc. of the porous carrier to be used, a single carrier fluidized aeration process can be performed. Both the BOD removal and nitrogen removal are possible at the same time by the tank and the settling tank (or a single carrier fluidized aeration processing tank with a settling section).

The present invention has a thickness of 10 mm in the main processing tank equipped with an air diffuser.
And the gas filtration resistance is 5-12 under the condition of wind speed 2m / sec.
The specific gravity formed by cutting a polyurethane or polyethylene sheet of mmH ₂ O is almost 1, and the length of one side is 10
mm ~ 15 mm prismatic, and in the wastewater is filled with a porous carrier in which the outer layer part becomes an aerobic region and the inner layer part becomes an anaerobic region at a filling rate of 20 to 35%, While circulating and circulating sewage and porous carrier by the air blown from the air diffuser, only the treated sewage is admitted to the settling tank through the screen from the main treatment tank to perform sludge sedimentation separation, and the separated sludge The basic constitution of the present invention is to return a part of it to the main processing tank while controlling the measurement by a measuring device.

(Function) Ammonia nitrogen and organic nitrogen in sewage undergo nitrification by contacting nitrifying bacteria in sludge attached to the outer layer of the porous carrier under aerobic environment. ,
Converted to nitrate nitrogen, etc.

The converted nitrate nitrogen, etc. continues to undergo denitrification by contacting the denitrifying bacteria in the sludge adhering to it in the inner layer of the porous carrier under anaerobic environment to remove nitrogen. Is performed.

The treated sewage is transferred to a settling tank through a screen, where sludge is separated and settled and then discharged to the outside through treatment such as disinfection.

Part of the sludge that has been separated by settling is returned to the main treatment tank and adsorbed on the flowing porous carrier. As a result, the amount of sludge in the main treatment tank is always maintained at a predetermined value.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 shows the treatment process of the present invention. In the figure, 1a is running water sewage, 1b is discharged water, 2 is a carrier-fluid-type main treatment tank, 3 is a sedimentation tank, 4 is a disinfection tank, 5 is a discharge pump tank, 6a is a metering device, 6 is a sludge return passage, and 7 is a sludge concentration storage tank.

Further, FIGS. 2 to 5 show the essential parts of a processing apparatus used for carrying out the present invention. The main treatment tank 2, the disinfection tank 4, the discharge pump tank 5 and the like are integrally formed in the tank body A, and the precipitation tank 3 (not shown) is provided as a separate body.

In FIGS. 2 to 5, 8 is an air diffuser, 9 is an air diffuser fixing base, 10 is a detachable union, 11 is an air supply valve, 12 is a pipe support plate, 13 is an air escape pipe, and 15 is Advection pipe, 16 screen part, 17 discharge pump mount, 18 discharge pump, 19 disinfection device, 20 partition wall, 21 advection wall, 22 chemical tube, 23, 24
Is an advection pipe and 25 is a partition wall.

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

An air diffuser 8 is provided at the bottom of the main treatment tank 2 so that the air supplied from a compressor (not shown) is jetted out so that the sewage in the tank and the porous carrier B move in the arrow direction. Circulate.

Further, in the main treatment tank 2, a porous carrier B made of polyurethane having a cubic shape with external dimensions of 12 mm × 12 mm × 12 mm,
It is filled so that the volume occupancy rate is about 30%.

The porous carrier B is preferably a prism having a specific gravity of about 1 and a length of one side of about 10 to 15 mm. The reason is that if the specific gravity deviates greatly from 1, or the dimension of one side becomes 15 mm or more, the fluidity due to aeration deteriorates, and if the dimension of one side becomes 10 mm or less, the anaerobic region of the porous carrier B described later And the denitrification capacity will decrease.

Further, the porous carrier B needs to have abrasion resistance, and in the case of the polyurethane porous carrier B, an ether-based open-cell polyurethane is desirable.

Further, the filling rate of the porous carrier B is optimally about 20 to 35%. When the filling rate is 20% or less, the denitrification effect drops sharply, and when the filling rate is 35% or more, it becomes difficult to flow due to erration, and if the amount of air is increased to increase the fluidity. This is because the denitrification effect is offset on the contrary, and all of these have been confirmed by the denitrification test.

As described above, in the porous carrier B, it is necessary that the outer layer portion acts as an aerobic region and the inner layer portion acts as an anaerobic region. From this point, it is simply continuous foaming,
Or, even if the BOD can be removed only by having a high bubble ratio, it is impossible to exert an excellent nitrogen removing action.

That is, when the bubbles of the porous carrier are large and most of the bubbles are continuous bubbles, the air bubbles easily pass through the inside of the carrier together with water, and the anaerobic region becomes almost zero. The denitrifying effect cannot be obtained. On the contrary, if the voids are not open cells, no matter how large the porosity is, the anaerobic region increases, but the water permeability becomes poor, and the denitrifying action cannot be obtained.

Therefore, the porous carrier B has an appropriate pore diameter and an appropriate open cell ratio (desirably, the open cell region has a relatively high open cell ratio and the inner layer region has a relatively low open cell ratio). Is an essential requirement, and the PPI value (the number of cells per 1 ″ width), the cell rate (cell volume / total volume), and the open cell rate (open cell) that are normally used to show the characteristics of this type of foam. It is not possible to express the optimum physical properties of the porous carrier when removing nitrogen with a single carrier fluidized aeration tank as in the present invention only by the number of bubbles in the shape / total number of bubbles). is there.

Therefore, in the present invention, attention is paid to the filtration performance of the porous carrier, and it is highly reliable as an evaluation test method of the filtration performance which is a basic characteristic of the plastic aeration body. The filtration resistance of the plate material C for porous carriers was measured using 1 performance test method.

That is, first, the length of one side of the prismatic porous carrier B (10 mm)
A porous plate material C having a thickness L = 10 mm corresponding to the above was arranged as shown in FIG. 6, and the filtration resistance P at a wind velocity of 2 m / sec was measured.

Incidentally, FIG. 6 shows a vertical type performance tester used in the first performance test method. In the figure, C is a test body, D is a manometer, E is a rectifying grid, F is an air flow adjusting plate, and G is Is a fan, H is a sight glass, I is a tester body, J is an orifice, and the anemometer is omitted.

Next, filtration resistance P (mmH ₂ O) at the wind speed of 2 m / sec
The porous plate material C, which has been subjected to the above measurement, is cut into a cube having a predetermined size to form a porous carrier B, which is then transferred to an aeration treatment tank, respectively.
Filling with a filling rate of 30% and denitrifying for a certain time,
The removal rate Q of the total nitrogen TN was measured. Needless to say, the test conditions such as the type and amount of water to be treated, the treatment time, and the amount of aeration used for the denitrification test are set to be the same for each porous carrier B.

Then, the filtration resistance P and the total nitrogen removal rate Q were compared, and the range of the filtration resistance P capable of achieving a high nitrogen removal rate Q was determined from this comparison.

Table 2 shows the filtration resistance P measured by the test of FIG.
An example is shown here, where the filtration resistance P is a wind speed of 2 m.
It is expressed in filtration resistance mmH ₂ O under / sec.

FIG. 7 is a semilogarithmic graph showing the relationship between the filtration resistance P and the roughness of the sample in Table 2 above. In the case of the urethane sample, the number of pores (cells) per 1 ″ is shown. There is a logarithmic straight line relationship between the coarseness of the mesh and the filtration resistance P.

By comparing the results of 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 the air filtration resistance P of a large number of porous carriers were measured, and from the comparison between the two, the thickness L of the porous plate material was within the range of 10 to 15 mm.
Sample thickness 10 mm, filtration resistance at wind speed 2 m / sec is 5/12 mmH ₂
It was found that the O-shaped porous carrier formed in the shape of a quadrangular prism having a side length of 10 to 15 mm is the most suitable porous carrier in the present invention.

Next, the nitrogen removal treatment method of sewage according to the present invention will be described.

Referring to FIGS. 1 to 5, the water to be treated is first advection pipe 15
To the main treatment tank 2 and is circulated and circulated in the tank 2 by the air flow ejected from the air diffusing pipe 8 together with the porous carrier B and the floating activated sludge in which the activated sludge is held.

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

Further, 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, whereby nitrification treatment of ammonia nitrogen and the like is performed. Furthermore, in the anaerobic region of the inner layer portion of the porous carrier, nitrified nitrate nitrogen comes into contact with the denitrifying bacteria in the sludge, thereby performing denitrification treatment,
About 70% or more of total nitrogen is removed.

In this example, the BOD load was 0.8 to ³ kg BOD / m ³
Daily, activated sludge volume 5.0 kg / m ³ / day, average total nitrogen inflow 0.0
It is set to 4 kg / kg (activated sludge), 0.2 kg or less / m ³ (tank volume), and aeration strength 9.0 m ³ / m ³ · Hr, respectively.

Further, the porous carrier B is made of 12 mm × 12 mm × 12 mm urethane porous body (air filtration resistance P = 5.7) at a rate of about 17,200 pieces / m ³ (filling rate 30%). The flow velocity in the vicinity of the inner peripheral surface is 60 to 100 cm / sec, and the flow velocity in the center of the tank 2 is about 5 to 10 cm / sec.

In the mixed solution of activated sludge and carrier from the main treatment tank 2, the screen portion 16 prevents the outflow of the porous carrier B, and only the activated sludge mixed solution is sent to the settling tank 3 through the advection pipe 23. Sludge sedimentation is performed.

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

The sludge separated in the settling tank 4 is automatically weighed by the weighing device 6a, and the necessary amount is returned to the main treatment tank 2 through the sludge return pipe 6 to determine the amount of activated sludge in the main treatment tank. Is adjusted to the set value.

(Effects of the Invention) In the present invention, the aerobic region formed in the outer layer portion of the porous carrier B and the anaerobic region formed in the inner layer portion thereof are functionally utilized, and a single carrier is used. Since it is configured to remove nitrogen and BOD with a body fluidized aeration treatment layer, compared to the conventional treatment method of separating the nitrification process and the denitrification process, it is possible to significantly reduce the size of the treatment equipment and the treatment operation. Can be simplified.

Further, in the present invention, since the outer dimensions of the porous carrier B to be used, its air filtration resistance P, and the filling rate of the carrier B are selected as optimum values, nitrification action and anaerobic region in the aerobic region are selected. The denitrification effect in the above is well balanced, and an excellent denitrification effect can be exhibited as compared with the conventional device filled with the porous carrier B such as urethane foam.

Further, in the present invention, a part of the activated sludge separated in the settling tank is returned to the main treatment tank and is adsorbed into the flowing porous carrier so that the amount of activated sludge in the main treatment tank is maintained at a predetermined value. As a result, good processing action can be exerted over a long period of time.

[Brief description of drawings]

FIG. 1 is a process drawing of wastewater according to the present invention. FIG. 2 is a plan view showing a main part of a processing apparatus used for carrying out the present invention, FIG. 3 is a sectional view taken along line AA of FIG. 2, and FIG.
FIG. 5 is a sectional view taken along the line BB of FIG. 2, and FIG. 5 is a sectional view taken along the line B'- of FIG.
It is a B'view sectional drawing. FIG. 6 is an explanatory diagram of a method for measuring the air filtration resistance P of the porous carrier, and FIG. 7 shows the relationship between the air filtration resistance P and the coarseness of the sample. A: Main treatment tank body, B: Porous carrier 2 ... Main treatment tank, 3 ... Settling tank, 4 ... Disinfection tank, 6 ... Sludge side passage 6a ... Automatic weighing device, 8 ... Air diffuser 16 …… Screen part P …… Air filtration resistance of porous carrier

Claims (1)

[Claims] 1. A main processing tank equipped with an air diffuser, having a thickness of 10 mm
And the gas filtration resistance is 5-12 under the condition of wind speed 2m / sec.
The specific gravity formed by cutting a polyurethane or polyethylene sheet of mmH ₂ O is almost 1, and the length of one side is 10
mm ~ 15 mm prismatic, and in the wastewater, the outer layer part becomes an aerobic region and the inner layer part becomes an anaerobic region at a filling rate of 20 to 35%, and the dispersion is performed. The sewage and the porous carrier are circulated and flowed by the air blown from the air device, and only the treated sewage is admitted to the settling tank from the main treatment tank through the screen to separate the sludge from the sludge, and a part of the separated sludge is separated. A method for removing nitrogen from wastewater, which comprises returning the wastewater to the main treatment tank while controlling the quantity by a metering device.