JPS5959297A - Biological denitrification of organic waste water - Google Patents

Abstract

PURPOSE:To curtail the amount of an organic carbon source to be used without lowering the efficiency of denitrification, by performing the biological denitrification to denitrify said organic waste water while injecting an organic carbon source in it, after dissolved oxygen in the inflow organic waste water has been reduced. CONSTITUTION:The interior of a denitrification tank 2 is maintained under an anaerobic condition by intercepting the contact of oxygen with it, and gentle agitation for inhibiting the precipitation of microbes, etc. is performed all over the tank. A nitrified liquid 5 containing NOX-N and microbes is let flow into a diffusion zone A, to diffuse dissolved oxygen in the nitrified liquid 5. Just after the nitrified liquid spontaneously falling down passes through a partition plate 13, an organic carbon source 9 is supplied to reduce NOX-N into nitrogen gas. Since the inflow organic waste water is fluctuated in a day as one cycle reflecting human life, a time for diffusion is changed. Hence, the diffusion of dissolved oxygen is not sufficient, and the organic carbon source is consumed by residual dissolved oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a biological denitrification method for organic wastewater in which denitrification treatment is performed by supplying an organic carbon source as a reducing agent to organic wastewater.

[Prior art]

Organic nitrogen or ammonia nitrogen, which is found in organic wastewater such as water, is a nutrient-rich substance.

If water is released containing eutrophic substances, it will seriously pollute rivers and lakes. Biological denitrification using activated sludge is said to be the most effective method for removing nitrogen contained in organic wastewater.

The biological denitrification method has a structure as shown in FIG. 1, for example.

The organic wastewater 4 flows into the nitrification tank 1 and is mixed with return sludge 8 returned from the settling tank 3. The inside of the nitrification tank 1 is aerated by an aeration means (not shown) to make it aerobic. Organic or ammonia nitrogen (NH) contained in organic wastewater 4
s-N) is converted into nitrate nitrogen (NO3-N) or nitrite nitrogen (NO2-N) by the action of nitrifying bacteria in the returned sludge 8.
) is oxidized to

Hereinafter, N05-N and N02-N will be simply referred to as nitrogen.

The nitrified liquid 5 flowing out from the nitrification tank 1 flows into the denitrification tank 2.

N03-N of nitrification liquid 5 in denitrification tank 2.

N02-N is reduced to nitrogen gas by denitrifying bacteria.

The denitrification tank 2 is anaerobic, and an organic carbon source 9 such as methanol is injected as a reducing agent. Sedimentation pond 3
The denitrifying bacteria and denitrifying bacteria in the denitrifying liquid 6 are separated by sedimentation, and the resulting liquid is discharged into a river as treated water 7.

On the other hand, most of the settled activated sludge containing nitrifying bacteria and denitrifying bacteria is returned to the nitrification tank 1, and the remainder is discharged outside the system.

In this way, the room is removed, and the biological reactions in the nitrification tank 1 and the denitrification tank 2 can be expressed by the following chemical formula.

Nitrification tank N) (4”+1.50.→N02-HJ20+2
H" ・(1) NO□-+〇, 502→NO,-・・
・(2) Denitrification tank 2NO□-+3(ru) → N2 +20H
-+ 2) L! 0...(3) 2NO3'-+5 (几)→N2+20pressure+4H20・
(4) When performing denitrification through such a chemical reaction, it is necessary to inject an organic carbon source into the denitrification tank 2 as a reducing agent. However, organic carbon sources are consumed not only by reduction of NO and -H but also by dissolved oxygen (DO).

When methanol is used as an organic carbon source, methanol consumption fi Cm is expressed by the following equation.

Cm-2,47(NOsN)+1.53(NO2N
)+0.87(DO)...
- (5) Since the nitrification efficiency in the nitrification tank 1 deteriorates when the dissolved oxygen concentration is low, a certain level of dissolved oxygen concentration must be maintained in order to obtain stable efficiency.

In general, it is said that it is necessary to maintain the oxygen level in the bath on the 3rd to 41st floors/7. Therefore, the nitrification liquid flowing into the denitrification tank 2 contains the dissolved oxygen maintained in the nitrification tank 1. Most of the NO and -N in the nitrification solution are NO and -N, but the concentration of NO and -N in the nitrification solution in a typical sewage treatment plant is 1.
It is about 0 to 20 g/. Therefore, the proportion of methanol consumed by dissolved oxygen is 7 to 13% of the total supply amount.

Since the 1M organic carbon source is thus consumed by dissolved oxygen in the nitrifying solution, the denitrification efficiency will decrease even if an appropriate amount of organic carbon source is injected as a reducing agent. Furthermore, injecting an organic carbon source in consideration of the consumption of dissolved oxygen results in the unnecessary use of an expensive organic carbon source, which is not economically advisable.

This inconvenience can be solved by constructing a structure in which the denitrification tank 2 is located before the nitrification tank 1, and the nitrification liquid io, which is about 403 times the amount of organic wastewater, is circulated from the nitrification tank 1 to the desaturation tank 2, as shown in Figure 2. If you choose to do so, you will be at a significant disadvantage. That is, since the nitrifying solution 1o has a dilution effect with low NO and -Na degrees, the methanol consumption rate due to dissolved oxygen is 22 to 36 times the total supply amount.

As described above, the conventional biological denitrification method has the problem of being economically disadvantageous because the organic carbon source injected as a reducing agent is wasted by dissolved oxygen in the nitrifying solution.

[Purpose of the invention]

The present invention was developed in response to the above-mentioned problems, and its purpose is to provide a biological denitrification method for organic wastewater that can reduce the amount of organic carbon source used without reducing the denitrification efficiency. Our goal is to provide the following.

Another object of the present invention is to provide a biological denitrification device for organic wastewater that can be easily realized without changing the basic structure of the biological denitrification device.

[Summary of the invention]

The present invention is characterized in that dissolved oxygen in the nitrification solution is diffused into the gas phase, and the organic carbon source is completely injected after waiting for the dissolved oxygen to be reduced.

Another feature of the present invention is that dissolved oxygen in the nitrifying solution is diffused within the desorption ellipse. The dispersion time of dissolved oxygen may be about 30 minutes, the residence time in the denitrification tank is 2 to 3 hours, and the dispersion area in the denitrification tank is about 1/4 or less of the whole. Further, the denitrification region is also in an anaerobic state, and the denitrification reaction proceeds using the nitrification solution or organic matter contained in the inflowing organic wastewater as a reducing agent, so there is no shortage of denitrification volume.

Other features of the invention will become apparent from the description below.

[Embodiments of the invention]

FIG. 3 shows an embodiment of the present invention, in which only the denitrification tank 2 is shown.

In FIG. 3, the same reference numerals as in FIGS. 1 and 2 indicate equivalent parts. The denitrification tank 2 is divided into a dispersion area A and a denitrification area B, and a porous partition plate 13 having a large number of holes 13a is arranged at the boundary thereof. The dissolved oxygen concentration (DO) in the diffusion area A is measured by a DO meter 21 and manually inputted to the stirring control device 22.

The stirring control device 22 controls the DO measurement value DOo and the DO target value DO.
The electric motor 23 rotates according to the deviation. The stirring blades 24 are driven by the electric motor 23. Nitrogen gas generated in the air section C of the denitrification tank 2 is drawn out by a drawing pipe 10. The other end of the drawing pipe 11 is connected to the suction pipe 14. Gas flows through the suction pipe 14 at a relatively high flow rate.

Next, its operation will be explained.

The inside of the denitrification tank 2 is maintained in an anaerobic state by cutting off contact with oxygen, and gentle stirring is performed throughout the tank to prevent microorganisms from settling. The nitrifying solution 5 containing NO□-N and microorganisms is caused to flow into the dispersion area A, and the dissolved oxygen in the nitrifying solution 5 is dissipated. Immediately after the naturally flowing nitrification liquid passes through the partition plate 13, an organic carbon source 9 is supplied to reduce No and -N to nitrogen gas.

Dissolved oxygen in the dispersion area A is dissipated as follows.

Equation (6) shows gas-liquid equilibrium.

x,=P. /K...(6)(
From equation 6), it can be seen that the oxygen melt KXo in the liquid is proportional to the oxygen partial pressure Po in the gas phase. FIG. 4 shows the results of determining the amount of oxygen dissolved in water (dissolved oxygen concentration) at 20C using equation (6). In FIG. 4, it can be seen that dissolved oxygen can be reduced by lowering the oxygen partial pressure in the gas phase. Generally, the CO gas atmosphere in the gas phase of the denitrification tank 2 is dominated by hydrogen gas generated as a result of the denitrification reaction, and the oxygen concentration is about 1%. Equilibrium dissolved oxygen concentration is 0.5 mt/
is as follows. Therefore, by providing the dispersion region A, the dissolved dolphins are naturally dissipated and reduced, so that the amount of wasteful consumption of the organic carbon source can be reduced.

On the other hand, the dissipation time of the inflowing morphological wastewater changes over the course of a day, reflecting human life, and the dispersion of dissolved oxygen is insufficient, resulting in the organic carbon source being consumed by the residual dissolved oxygen. It turns out.

For this reason, it is desirable to manipulate oxygen dissipation in the dissipation region A.

Dissolved QHccD diffusion rate in liquid e-d/dt (DO)
f! It is shown in equation c(7).

Here, DOo: dissolved oxygen concentration, 1) On: equilibrium dissolved oxygen concentration with respect to gas phase oxygen partial pressure* K ta: oxygen transfer coefficient, Kr: oxygen consumption rate period, S: microorganism concentration.

The first term on the right side of equation (7) is the dissipation due to vapor-liquid equilibrium, and the second term is the reduction due to microbial consumption.

FIG. 5 shows the calculation results of the dissolved oxygen concentration versus the dispersion time during mechanical agitation and aeration agitation using equation (7), assuming that the oxygen concentration in the gas phase C of the denitrification tank 2 is 1%.

From FIG. 5, it can be seen that there is a diffusion time to obtain a predetermined dissolved oxygen concentration. On the other hand, the relationship shown in FIG. 5 shows that the larger the oxygen transfer coefficient Kt,a, the lower the dissolved oxygen. Further, since the oxygen transfer coefficient K ta changes in accordance with the stirring intensity, it is understood that the stirring intensity can be adjusted to achieve a predetermined dissolved oxygen concentration within a given diffusion time. Furthermore, if the gas phase C of the denitrification tank 2 is made negative pressure (
7) The equilibrium dissolved oxygen concentration DOn decreases and the dissipation rate increases. Therefore, oxygen dissipation in the dispersion area A is promoted by manipulating the stirring intensity and the pressure of the gas phase C.

In the embodiment shown in FIG. 3, the stirring intensity is controlled by controlling the rotational speed of the stirring blade 24 so that the actual value D Oo measured by the dissolved oxygen concentration meter 21 in the dispersion area A is equal to or less than a predetermined value Do.

Note that a conventionally installed mechanical stirring device may be used without installing a new mechanical stirring device.

On the other hand, the drawing pipe lO is the suction pipe 14 with a relatively high gas flow rate.
The gas phase section C becomes a negative pressure. The gas in the suction pipe 14 may be fresh air, but by flowing the exhaust gas from the nitrification tank 1, negative pressure can be maintained without using new power. When denitrifying in this manner, the porous partition wall 13 acts to prevent back mixing between the dispersion region A and the denitrification region B, and to suppress organic carbon consumption in the dispersion region A.

Next, in the embodiment shown in FIG. 3, oxygen diffusion is promoted by mechanical stirring, but gas stirring can also be used. As shown in FIG. 5, gas agitation can increase the dispersion speed and reduce the volume of the dispersion area A compared to mechanical agitation.

FIG. 6 shows an embodiment of the present invention using gas stirring.

As the stirring gas, a denitrifying gas in which nitrogen gas is dominant can be used.

In FIG. 6, the same symbols as in FIG. 3 indicate equivalents. Denitrification gas (nitrogen gas) collected from the gas phase C of the denitrification tank 2 by the drawing pipe IO is added to the compressor 25 via the circulating gas pipe 11. Denitrification gas is aerated by the compressor 25 from the aeration pipe 15 installed at the bottom of the diffusion area A, stirring is performed, and the dissolved oxygen is circulated through gas-liquid contact. The exhaust gas from the dispersion area A mixes with the generated gas from the denitrification area B and is circulated again as denitrification gas, and a portion is extracted to the outside of the yarn as exhaust gas 12 by the action of the distributor 19.

The dissipation rate +X is the dissolved oxygen concentration meter 2 installed in the dissipation area A.
The compressor 25 is controlled by the W stirring control device 22 so that the actual measured value DOo of 1 is below the predetermined range Do.

In the embodiment shown in FIG. 6, the denitrification gas was used as the stirring gas, but the same effect of accelerating the dispersion rate can be obtained even if a new inert gas is used.

WJ77 shows another embodiment of the present invention, in which all gas lift stirring is performed.

The circulating gas pipe 11 is immersed from the top to the bottom of the dispersion area A, and the lift pipe 16 is arranged around the circulating gas pipe 11 up to the gas phase part C of the dispersion area A. Dissolved oxygen in the liquid lifted by the circulating gas is dissipated upon contact with the circulating gas and during dripping in the gas phase section C.

FIGS. 8 and 9 show an example in which dissolved oxygen is diffused by combining gas stirring and mechanical stirring.

Fig. 8 shows a configuration in which an aeration pipe 15 is disposed below the stirring blade 24. In the embodiment shown in Fig. 8, the grazing resistance of the dispersed liquid of the stirring liquid is reduced.

It is possible to lengthen the residence time of the aeration gas and to atomize the bubbles. FIG. 9 shows J″i, in which gas guided through the circulation gas pipe 11 is blown into the upper surface of the stirring blade 24. In FIG. 9, the same effect as in FIG. 8 can be obtained.

In the real side connection shown in FIG. 9, the gas suction action is activated by the rotational force of the stirring blade 24, and the gas blowing power can be reduced. In this way, by stirring using a combination of gas stirring and mechanical stirring, the contact area between the liquid and the gas can be increased, and the dispersion of dissolved elements can be promoted. The increase in dissipation rate is
Since the diffusion time for obtaining a predetermined dissolved oxygen concentration can be shortened, the ratio of the diffusion region A to the entire denitrification tank 2 can be reduced.

Next, in the above embodiments, the stirring intensity was controlled using dissolved oxygen, but it can also be controlled using indicators other than dissolved oxygen. In equation (6), since the dissolved oxygen concentration is defined by the oxygen concentration in the gas phase, the oxygen concentration in the exhaust gas in the diffusion region A can be used as an index of the stirring intensity.

In addition, since the retention time of the dust A, that is, the dispersion time, is determined by the inflow water decomposition, fJ+''t・iq
You can also manipulate the i degree.

No.iotΔ? -1: In this case, the amount of nitrified water is flowed i [F total 26? il:, l set. 4i7 Stirring control r11υ'A itf, 22' is the flow rate (rule>X+
Direct and release; Shioguri J or A's from itf] Calculate the time of attack or defeat (H), and at the time of success or defeat, 1ii9, Sosai acid search standard degree 3 + 21'
0) in the nitrifying solution measured at
Calculate the dissipation rate as J<, and dissipate (*; pod and 1
In relation to the stirring intensity, ilj 23 is operated according to +5. At this time, the γ valley i γ1 element concentration in success/failure distribution castle A is stirred 1ijlJ:nl device d22' (coffee d22') is punctured, and the correction of the j-crossing intensity is actually controlled.

Here, due to the nitrified water flowing into the de-A tank 2, (1~
It can be easily understood that when controlling the stirring intensity by +1ltl, the same effect can be achieved even if j is mechanically stirred.

FIG. 1-1 shows another version of the present invention, in which a dispersion tank 2' is provided at the front stage of the desorption tank d2.

In the embodiment shown in FIG. 11, the purpose is to prevent the gas atmosphere in the diffusion tank 2' from increasing by 1 degree of oxygen due to diffusion.

The dechambering gas generated in the denitrification tank 2 is taken into the diffusion tank 2' via a drawer 710. The denitrification gas can be simply passed through the gas phase portion of the diffusion tank 2', but if used for lf stirring, the effect of accelerating the diffusion rate can be increased. In FIG. 11, nitrified water 5' whose dissolved oxygen has been reduced in the diffusion tank 2' flows into the denitrification tank 2. Further, the generated gas and the vented gas in the diffusion tank 2' are extracted from the extraction pipe 10'. Note that it is also possible to use a new inert gas instead of the denitrifying gas.

〔Effect of the invention〕

As explained above, in the present invention, since the organic carbon source is injected after reducing the dissolved oxygen in the nitrification solution, it is possible to reduce the amount of organic carbon source wasted due to dissolved oxygen. Therefore, the organic carbon source can effectively act as a reducing agent, and the amount of organic carbon source used can be reduced without reducing the denitrification efficiency.

Furthermore, in the present invention, dissolved oxygen in the nitrification solution can be reduced in the denitrification tank, so that it can be easily realized without changing the basic configuration of the biological denitrification device.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams of a biological denitrification apparatus, respectively, and FIG. 3 is a diagram showing an embodiment of the present invention. Fig. 4 is a characteristic diagram showing the relationship between oxygen concentration in the gas phase and dissolved oxygen concentration, Fig. 5 is a characteristic diagram showing the temporal change in dissolved oxygen concentration due to stirring, and Fig. 6 shows another embodiment of the present invention. Diagram,
7 to 9 are main part configuration diagrams showing other examples of stirring means according to the present invention, and FIGS. 10 and 11 are configuration diagrams showing other embodiments of the present invention, respectively. ■... Nitrification tank, 2... Denitrification tank, 5... Nitrification liquid, 9
...Organic carbon source, lO...Gas extraction pipe, 13...
Porous partition wall, Meat t (21 薯2m, 4th meter, 4 strokes, 4 designs)

Claims (1)

[Scope of Claims] 1. A biological denitrification method having a denitrification step of injecting an organic carbon source into inflowing organic wastewater to denitrify it, after waiting for the reduction of dissolved oxygen in the organic wastewater. A method for biological denitrification of organic wastewater, characterized by the injection of an organic carbon source. 2. The organic wastewater according to claim 1, wherein the reduction of dissolved oxygen in the organic wastewater is carried out by stirring the organic wastewater and forcibly dissipating the dissolved oxygen into the gas phase. Biological denitrification methods. 3. A method for biological denitrification of organic wastewater according to claim 2, characterized in that stirring of the organic wastewater is performed mechanically. 4. A biological denitrification method for organic wastewater according to claim 2, characterized in that stirring of the organic wastewater is performed by aerating inert gas. 5. The biological denitrification method for organic wastewater according to claim 4, wherein the inert gas is nitrogen gas generated in the denitrification process.