JP2540150B2 - Biological denitrification equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a biological denitrification device for wastewater, and more particularly to a biological denitrification apparatus in the presence of organic matter in wastewater containing nitrate nitrogen and / or nitrite nitrogen. The present invention relates to a device for performing denitrification treatment.

<Prior art> The biological denitrification method utilizes the nitric acid respiration ability of denitrifying bacteria to utilize nitrate nitrogen (NO ₃ ^-1 ) and nitrite nitrogen (NO ₂
^-1 ) is reduced to N ₂ gas to remove nitrogen in water.

Under the normal environment, the denitrifying bacteria utilize energy obtained by oxidizing organic matter in the presence of molecular oxygen (O ₂ ) for its growth and living body maintenance. Further, under the anaerobic condition without molecular oxygen (hereinafter referred to as facultative anaerobic), NO ₃ ^-1 or NO ₂ ^-1 is used in place of the molecular oxygen molecule to decompose an organic substance to obtain energy, The biological denitrification method utilizes this fact.

In the above, NO ₃ ^-1 and NO ₂ ^-1 are gasified with nitrogen along with the reaction represented by the following formula.

^{_{2NO 3 - +10 (H) →}} N 2 + 2OH - + 4H 2 O 2NO 2 - +6 (H) → N 2 + 2OH - + 2H 2 O ·· hydrogen in the formula (H) are those given by the decomposition of organic matter Therefore, in order to carry out the denitrification reaction, an organic substance is required, and when this organic substance is contained in the wastewater in a biodegradable form, it is generally used. In many cases, the organic matter necessary for the denitrification reaction is insufficient in the sewage, and an appropriate amount of organic matter such as methanol is usually added from the outside.

The denitrification reaction is also a reaction rate equation of the following equation dN / dt = K ・ M ・ ・ ・ where N: NO ₃ ^-1 or NO ₂ ^-1 concentration M: Denitrifying bacterium concentration (typically represented by sludge concentration) K : Expressed by denitrification rate constant.

According to this equation, it can be seen that in order to increase the denitrification rate dN / dt, an operation of increasing the K value or the M value may be performed.

The K value varies depending on factors such as the amount of organic substances required for denitrification, water temperature and pH, or the type of denitrifying bacteria, and is generally a value of about 0.2 kgN / kg · ss days. It is not directly related to the type of equipment, operation method, etc.

On the other hand, the M value is a value that directly changes with respect to the type of denitrification device, the operating method, etc., and is usually represented by the sludge concentration as described above.

By the way, in performing denitrification treatment on an industrial scale, it is needless to say that it is desirable that the reaction rate dN / dt be as high as possible in terms of downsizing of the apparatus, therefore, the reaction rate dN / dt. In denitrification equipment, the development of equipment in which the M value (represented by sludge concentration as described above) that is the value that controls dt and is related to the equipment type (structure, volume, etc.) is as large as possible It can be said to be one of the major issues.

Therefore, in order to increase the M value (hereinafter, M value = sludge concentration) in the above equation, for example, a microbial carrier (sand, stone, carbon, honeycomb tube, etc.) in which denitrifying bacteria can grow is placed in the tank. The sludge concentration (the amount of microorganisms) in the conventional floating denitrification equipment (sludge concentration is usually 2,000-5,000 mg /
, The maximum is 7,000-8,000 mg /), which is higher than that, so-called fixed bed type (biofilm type)
Although a so-called denitrification device is also put into practical use, the sludge concentration in the tank is at most that of the floating type in this device.
It is about 1.5 to 2 times, and if the gap between the carriers is too small, it causes a problem of clogging due to sludge and the like, so that it is necessary to take into consideration maintenance such that periodic cleaning is required.

On the other hand, in recent years, a denitrification device capable of keeping the sludge concentration in the tank much higher than before, tentatively a high concentration sludge bed type (or sludge blanket type), has been developed. . The high-concentration sludge bed type denitrification device forms a sludge bed (hereinafter referred to as a granule sludge bed), which is composed of granular materials (generally known as granules of sludge particles) in which a high concentration of denitrifying bacteria has aggregated inside the denitrification tank The raw sludge is passed through the granulated sludge bed in an upward flow for denitrification, and other configurations are the same as those of the conventional floating type.

The granulated sludge bed is formed by placing so-called activated sludge as a seed sludge in a denitrification tank and allowing an appropriate amount of sewage containing nitrate nitrogen and organic matter to flow in an upward flow for a predetermined period (usually 1
~ 2 weeks) Let's get accustomed.

At this time, the rising streamline velocity (LV) of the sewage should be set to 2 m / day or more, and if the rising LV is less than this, the formation of granule sludge cannot be performed well.

Further, the acclimatization always nitrate nitrogen ^- it is important to carry out by passed through the wastewater containing (NO ₃ N), for example, nitrite nitrogen (NO ₂ ^- N) substantially nitrate nitrogen contained only Granule sludge particles are not formed by passing sewage that does not contain water. However, after forming a sludge bed consisting of granule sludge particles in the denitrification tank by acclimatization, even if the wastewater contains only nitrite nitrogen, denitrification treatment can be performed while maintaining the granule sludge bed. It is possible.

The formed granule sludge particles become sand particles of about 0.5 to 3 mm, although it depends on the operating conditions. In this granule sludge bed, even if raw sewage flows from the lower part of the denitrification tank and is passed through in an upward flow, the settling LV of the granule sludge is higher than the sludge washout force (increase LV). No outflow will occur.

The sludge concentration in the denitrification tank having such a granule sludge bed reaches 20,000 to 100,000 mg /, which is more than 10 times that in the floating denitrification tank, and a large M value can be obtained. In other words, in the simple calculation, if the same nitrogen load is used, the denitrification tank with a capacity less than 1/10 of the floating denitrification tank can be used for treatment. The risk of obstruction in the fixed bed type apparatus in which a microbial carrier also, the coupling of the granular sludge grains in the water to be treated NO ₃ ^- rise of the N ₂ gas generated by the decomposition of N ^- N and or NO ₂ Another feature is that it does not need to be considered because it is loosened in the flow.

In order to form and maintain such a granule sludge bed, it is important to allow Ca ²⁺ ions to exist in the sewage flowing in an upward flow, and usually, the Ca ²⁺ concentration should be 1 mg / or more. It is good to do so.

Also, in the high-concentration sludge bed type denitrification device, if the particle size of granule sludge particles becomes too large, the denitrification reaction will be performed only on the surface of the sludge particles, and the denitrifying bacteria inside the particles will react. It is not preferable because the reaction rate of the whole denitrification tank becomes small as a result. Therefore, in the device, it is important to prevent the granule sludge particles from being excessively enlarged and to maintain the diameter at a preferable particle size (1 to 2 mm). One way to do that is
NO ₃ ^- N, NO ₂ ^- and a method of controlling the nitrogen volume loading of N. That is, nitrogen in the raw sewage to be treated concentration C (NO ₃ ^-
N and NO ₂ ^- if the sum of the N) is in excess of ^{0.2kg · N / m 3 (200mg} /), to control the nitrogen volume load L in the range of 6~16kgN / m ³ · day, the nitrogen concentration C Is 0.2 kgN / m ³ or less,
The above target can be achieved by setting the volume load L calculated by the following equation.

a × C ≦ L ≦ b × C where a: constant, 30 [1 / day] b: constant, 80 [1 / day] A high-concentration sludge bed type denitrification device having such excellent characteristics was used. An example of the flow outline of the processing device will be described with reference to FIG.

Figure 2 shows a denitrification tank 1 with a bed of granulated sludge.
And a floating type oxidation tank 2 and a precipitation tank 3 are combined, and the oxidation tank 2 oxidizes and decomposes the organic substances remaining in the wastewater denitrified in the denitrification tank 1 as described later. It is intended to be installed.

NO ₃ by the apparatus of the flow shown in FIG. 2 ^- N, NO ₂ ^- N
In order to treat the raw sewage containing (hereinafter collectively referred to as nitrate nitrogen), the raw sewage is supplied from the lower part of the denitrification tank 1 into the tank through the sewage inflow line 4, and at this time, Organic matter (usually methanol) necessary for the nitrification reaction is injected into the raw sewage through the organic matter injection line 5. In order to complete the denitrification reaction promptly, it is necessary to inject more than the theoretically required amount of organic substance, and generally, the amount of organic substance is about 1.2 times the theoretical amount. Also, if necessary, adjust the pH of the raw sewage.
The adjusting agent is injected through the pH adjusting agent injection line 6.

The raw sewage injected with the organic matter is denitrified while passing through the granule sludge bed 7 formed in the denitrification tank 16> in an upward flow, and the nitrate nitrogen is gasified with N ₂ . Sewage containing N ₂ gas and fine sludge further rises in the denitrification tank 1,
It reaches the gas / liquid / solid separation section 8 in the upper part and is separated into denitrified sewage, N ₂ gas and sludge, and the denitrified sewage flows out of the tank through an overflow pipe 9, N ₂ gas is released into the atmosphere. On the other hand, sludge is granulated sludge bed 7
Settle inside. Reference numeral 10 is a partition wall provided in the gas / liquid / solid separation portion 8 and formed of, for example, an inner cylinder.

In the denitrification tank 1, the organic substances injected into the raw sewage are also consumed in an amount commensurate with the amount of denitrified nitrate nitrogen, but as described above, the organic substances in excess of the theoretical amount are injected into the raw sewage. Therefore, the surplus organic matter that was not consumed in the denitrification reaction remains in the denitrified wastewater.
D and COD are high, and the water cannot be discharged as it is. Therefore, the denitrification-treated sewage is guided to the subsequent oxidation tank 2 through the overflow pipe 9, and the residual organic matter is biologically oxidatively decomposed in the tank 2 and then discharged. That is,
The oxidation tank 2 shown in FIG. 2 represents a normal floating type activated sludge device, and the wastewater introduced through the overflow pipe 9 is diffused through an air pipe 11 in the presence of activated sludge. The organic matter in the wastewater is oxidatively decomposed by aeration with the air supplied from the tank, and the mixed solution in the tank is guided to the subsequent settling tank 3 to separate the treated water and the sludge. Through the sludge return line 14, a part of the settled sludge is returned to the oxidation tank 2 through the sludge return line 14, and the other is sent to the sludge treatment system (not shown) for treatment. In addition,
Also in the denitrification tank 1, excess sludge is appropriately extracted from the sludge extraction line 15 provided at the lower part of the tank, if necessary, and the extracted sludge is similarly sent to the sludge treatment system for treatment.

Further, as the oxidation tank 2, there is a case where a fixed bed type (biofilm type) oxidation tank capable of maintaining the sludge concentration in the tank as high as possible is used, which is the case in this case. As the oxidation tank, one having the same structure as the fixed bed denitrification tank described above and having a structure in which a microorganism carrier capable of growing microorganisms is filled is used.

<Problems to be Solved by the Invention> As described above, in the denitrification device having the granule sludge bed, the sludge concentration in the denitrification tank, in other words, the M value can be dramatically increased as compared with the conventional device. As a result, the denitrification rate dN / dt in the above formula can be remarkably increased, so that high-load treatment of nitrogen components can be performed, and the capacity of the denitrification tank can be made extremely small.

However, in the conventional treatment device including the denitrification tank having such excellent characteristics, although the denitrification tank itself is downsized, the so-called post-treatment device installed in the latter stage of the denitrification tank for removing the residual organic matter is used. The capacity of the oxidation tank is still the same as the conventional one, and requires a larger capacity than the denitrification tank. That is, even in the biological oxidation treatment of organic substances, just as in the case of denitrification treatment, increasing the sludge concentration in the oxidation tank is a condition for reducing the tank capacity. The sludge concentration in the (activated sludge treatment device) is generally about 2,000 to 5,000 mg / similar to the case of the floating denitrification tank described above, and it is possible to keep the sludge concentration in the tank higher than that of the floating type. Even in the case of a fixed bed type oxidation layer, the sludge concentration is at most about 1.5 to 2 times that of the floating type, and the sludge in the denitrification tank, which is installed in the preceding stage of the oxidation tank and forms the granule sludge bed, is installed. It can be said that there is a significant difference when the concentration is 20,000 to 100,000 mg / as described above.

That is, even if a high-concentration sludge bed type that can make the tank capacity extremely small is adopted as the denitrification tank, the capacity of the oxidation tank to be installed in the subsequent stage is still large as before. However, there is a problem that the size of the entire processing apparatus including the oxidation processing of the residual organic matter is not so small.

In addition, the conventional fixed bed type oxidation tank can reduce the capacity of the oxidation tank to some extent compared to the floating type, but on the other hand, periodic cleaning is performed to prevent clogging of the packing material layer made of biological carrier. There is also a maintenance problem that it must be maintained.

The present invention has been made from the above viewpoints, and its main purpose is to improve not only the denitrification reaction but also the oxidation reaction of residual organic matter in a highly concentrated sludge in an industrial-scale denitrification apparatus. The object is to improve the efficiency and further reduce the size of the entire processing apparatus as compared with the conventional one, and to provide an apparatus free from problems such as blockage.

<Means for Solving the Problems> The feature of the biological denitrification apparatus of the present invention made to solve the above-mentioned problems is that a sludge bed in which denitrifying bacteria are aggregated in a high concentration to form a granular material ( In a biological denitrification device equipped with a wastewater supply means for passing a wastewater containing nitrate nitrogen and / or nitrite nitrogen in an upward flow in the presence of organic matter in a tank having a granule sludge bed), An oxygen-containing gas supply means is provided at an intermediate position in the vertical direction of the sludge bed. In the denitrification device of the present invention having such a configuration, one tank is divided into an upper part and a lower part with the installation position of the supply means as a boundary, and the sludge bed below the supply means is used as an original denitrification section. The sludge bed above the supply means is caused to react and the organic matter is oxidized, and an oxygen-containing gas such as air is supplied from the supply means for aeration, whereby the denitrification section is operated under aerobic conditions. Allows oxidative decomposition of unconsumed residual organic matter. Instead of supplying the oxygen-containing gas for aeration, water in which oxygen is dissolved at a high concentration may be supplied into the sludge bed from a supply means such as a sprinkling pipe.

The present invention will be described based on FIG. 1 (longitudinal cross-sectional explanatory view), which is an example of an embodiment, and the feature of the denitrification device of the present invention is that the granulated sludge formed in a tank 51 (hereinafter referred to as a reaction tank). A means for supplying an oxygen-containing gas, for example, an air diffuser 53 (air diffuser plate, air diffuser, etc.) connected to the air pipe 52 is provided at an intermediate position of the floor 7, and the sludge bed below the air diffuser 53 is denitrified. 54, the upper sludge bed is the oxidizing part 55, and the other parts are the same as the conventional high-concentration sludge bed type denitrification device, and therefore detailed description will be omitted.

Incidentally, the device of the present invention is of a type in which an oxidizing unit is integrally provided above the conventional high-concentration sludge bed type denitrification tank,
Needless to say, the size of the device itself must be made larger than that of the conventional high-concentration sludge bed type denitrification device that performs only the denitrification reaction.

<Operation> Using the denitrification device configured as described above, the wastewater containing nitrate nitrogen is treated as follows.

That is, the raw sewage in which a predetermined amount of organic matter necessary for the denitrification reaction is injected through the organic matter injection line 5 is supplied to the lower portion of the reaction tank 51 through the sewage inflow line 4 and is formed in the reaction tank 51. Further, air is introduced as fine bubbles from the air diffuser 53 into the intermediate position of the granule sludge bed 7 to supply oxygen to the granule sludge bed 7 above the air diffuser. If necessary, the pH adjusting agent is injected into the raw wastewater through the pH adjusting agent injection line 6.

In the apparatus of the present invention, during the so-called acclimatization period until the granule sludge bed 7 is formed in the reaction tank 51, air is not introduced from the air diffuser 53, and the entire reaction tank 51 is As a permeable anaerobic, only denitrification reaction is performed, and
It is advisable to form the granulated sludge bed 7 in the inside of 51, and then supply air from the air diffuser 53 to start the treatment of the raw sewage.

The raw sewage that has flowed into the reaction tank 51 is granulated sludge bed 7
In the apparatus of the present invention, the raw sewage first comes into contact with the granule sludge bed 7 existing in the denitrification section 54 below the air diffuser 53 to remove the dewatering inside the bed 7. It is denitrified by the action of nitrifying bacteria, and nitrate nitrogen in raw wastewater is converted to N ₂ gas. Up to this point, it is exactly the same as the conventional high-concentration sludge bed type denitrification device, but in the present invention, the denitrification-treated sewage is further granulated sludge bed existing in the oxidation part 55 above the aeration device 53. 7 and the air pipe 52 in the sludge bed 7
Under the aeration of the air introduced from the air diffuser 53 via the, the oxidative decomposition of the surplus organic matter not consumed in the denitrification reaction is performed. This is because the denitrifying bacterium, as described above, under the facultative anaerobic condition without molecular oxygen (that is, without dissolved oxygen), NO ₃ ^- or NO instead of molecular oxygen.
₂ ^- to decompose organic matter with, utilizes the resulting energy to the proliferation and biological maintained, under aerobic conditions the presence of molecular oxygen, ordinary aerobic bacteria (so-called activated sludge)
This is because it has the ability to obtain energy by decomposing organic substances using molecular oxygen in the same manner as in.

In the present invention, as described above, the granulated sludge in which the denitrifying bacteria are aggregated in a high concentration (as described above, the sludge concentration is 20,000 to
Since a part of 100,000 mg /) is used for the oxidative decomposition of organic matter, the sludge concentration involved in the oxidative decomposition in the oxidation part 55 is also high at about 20,000-100,000 mg /. Therefore, compared to the conventional floating oxidation tank (concentration of sludge is 2,000-5,000 mg /), the tank capacity required for high-load treatment of organic substances and the capacity required for oxidative decomposition (capacity equivalent to the oxidizing section 55 in Fig. 1) are To about 1/10, and fixed bed type oxidation tank (sludge concentration is about 5,
Compared with the capacity of 000 to 10,000 mg /), it can be about 1/5 and the tank capacity required for oxidative decomposition can be made much smaller than before.

The wastewater containing the gas and sludge that have undergone the oxidation of the residual organic matter reaches the upper gas / liquid / solid separation section 8 where treated water,
Separated into gas and sludge, treated water is overflow pipe 9
Is discharged to the outside of the system via the
On the other hand, the sludge settles in the reaction tank 51. In addition, the sludge drawing line installed at the bottom of the reaction tank 51
It is the same as in the conventional method to appropriately pull out from 15.

As the oxygen supply means in the device of the present invention, air was introduced from the air diffuser 53 in the above-described embodiment, but the portion immediately below the air diffuser 53 is agitated by the introduction, and oxygen is supplied to the immediately lower portion. Since there is a possibility that an aerobic atmosphere will be created, in order to prevent this, a baffle plate such as an eye plate may be provided laterally below the air diffuser 53.

Further, in the present invention, the denitrification section 54 below the air diffuser 53
The granulated sludge formed in step (5) is aerated relatively gently so as not to destroy it in the oxidation part 55 above the air diffuser 53 as much as possible, but the granulated sludge is divided into some extent by the aeration in the oxidation part 55. The liquefaction is unavoidable, and some of the subdivided sludge flows out of the tank along with the treated water. However, most sludge is again in the reactor
It settles in 51 and circulates in the denitrification section 54 below the air diffuser 53,
Granulated again. In the high-concentration sludge bed type denitrification equipment, if the particle size of the granulated sludge becomes too large, as described above, the reaction rate of the entire tank becomes small, which is not preferable. It can be said that the appropriate subdivision of is rather preferable.

Further, in the above-mentioned embodiment, the gas / liquid / solid separation section 8 is used as the reaction tank.
Although the structure is integrally provided above the 51, as a separating means, for example, a settling tank or the like may be provided separately from the reaction tank 51, and the sludge in the settling tank may be returned to the reaction tank 51. .

<Effects> As described above, the denitrification device of the present invention skillfully utilizes the high concentration property of sludge in the tank in the high-concentration sludge bed type denitrification device. An oxygen-containing gas supply means is provided at an intermediate position, and the original denitrification reaction is performed in the sludge bed below the supply means.
In the sludge bed above the supply means, the oxygen-containing gas is supplied from the supply means to oxidize and decompose the residual organic matter. In the apparatus of the present invention having such a configuration, the concentration of sludge involved in the oxidative decomposition of the residual organic matter above the supply means of the oxygen-containing gas is the same as that in the high-concentration sludge bed denitrification section below the supply means. Since the same high concentration can be maintained, oxidative decomposition of organic substances can be carried out under a higher load than in the past, and the tank capacity required for oxidation can be made extremely small. Therefore, there is an advantage that the entire denitrification treatment apparatus including the denitrification treatment and the subsequent oxidation treatment of the residual organic matter can be further downsized as compared with the conventional one. Moreover, it is possible to obtain a stable treated water without the possibility of clogging which is considered in the fixed bed type oxidation tank which has been conventionally used for the oxidation treatment of the residual organic matter, and therefore it is suitable to be carried out on an industrial scale. There is an effect that can be realized, and its usefulness is extremely large.

〔Example〕

 Examples of the present invention will be described below together with comparative examples.

Using the apparatus of the present invention as shown in FIG. 1 in which the capacity of the denitrification section is 3 and the capacity of the oxidation section is 2 (however, the capacity excluding the gas / liquid / solid separation section), nitrate nitrogen is used. Table 1 shows the results of treating the raw sewage containing 200 mgN / of. In addition, methanol was used as the organic substance, and was injected so that the concentration of methanol in the raw sewage was 600 mgN /.

As a comparative example, a high-concentration sludge bed denitrification tank with a tank capacity of 2 (capacity excluding gas, liquid, and solid separation parts) and a fixed bed oxidation tank with a capacity of 2 (microorganism carrier: plastic carrier, the same applies below) (Comparative example-1), a device combining the same denitrification tank as described above and a fixed bed type oxidation tank having a capacity of 5 (comparative example-2), and the same denitrification tank as above, and a capacity Table 1 also shows the results of treating the same raw sewage as in the example using three sets of devices (comparative example-3) in which 10 fixed bed oxidation tanks were combined.

However, all the water temperatures were controlled at 20 ° C., and aeration was performed so that the dissolved oxygen in the oxidation part of the device of the present invention and the fixed bed oxidation tank of each comparative example would be 2 mg / or more.

In the apparatus of the present invention, the capacity of the denitrification part is set to 3 and is set to be larger than the capacity (2) of the denitrification tank of Comparative Example-1 to Comparative Example-3. This is because some oxygen is supplied to the denitrification section directly below the supply means (air diffuser 53 in FIG. 1), which may not effectively affect the denitrification reaction.

As described above, in the present invention, denitrification and BOD removal are performed satisfactorily in a tank having a total volume of 5 including the denitrification section and the oxidization section, whereas the same quality of treated water can be obtained with the conventional apparatus. Therefore, as shown in Comparative Example-3, 12 (denitrification tank 2 and oxidation tank 10) are required as the total capacity, and it can be seen that the apparatus of the present invention can be made much smaller than the conventional apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectional explanatory view showing an example of an embodiment of a biological denitrification device of the present invention, and FIG. 2 is an explanatory view showing a flow outline of a conventional device. 1 ... Denitrification tank, 2 ... Oxidation tank, 3 ... Precipitation tank, 4 ... Sewage inflow line, 5 ... Organic substance injection line, 6 ... pH adjusting agent injection line, 7 ... Granule sludge bed, 8 ... Gas / liquid・ Solid separation part 9 ... Overflow pipe, 10 ... Partition wall 11,52 ... Air pipe 12,53 ... Air diffuser (supply means of oxygen-containing gas) 13 ... Treatment water line, 14 ... Sludge return line 15 …… Sludge removal line 51 …… Reaction tank, 54 …… Denitrification section 55 …… Oxidation section

Continuation of the front page (56) References JP-A-63-209792 (JP, A) JP-A-60-187396 (JP, A) JP-A-57-1496 (JP, A)

Claims (1)

(57) [Claims] 1. Sewage containing nitrate nitrogen and / or nitrite nitrogen is passed in an upward flow in the presence of organic matter through a tank having a sludge bed in which denitrifying bacteria are aggregated at a high concentration to form a sludge bed. In a biological denitrification device equipped with a sewage water supply means, an oxygen-containing gas supply means is provided at an intermediate position in the vertical direction of the sludge bed, and the sludge bed below the supply means serves as a denitrification section and the supply. A biological denitrification device, wherein the sludge bed above the means is used as an oxidation part of residual organic matter.