JPH07115032B2 - 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 wastewater containing nitrate nitrogen and / or nitrite nitrogen in the presence of organic matter. 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 (N ₃ ^-1 ) in water.
O 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 property), NO ₃ ^-1 or NO ₂ ^-1 is used instead 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 nitrogen gasified with the reaction shown by the following formula.

^{_{2NO 3 -1 +10 (H) →}} N 2 + 2OH - + 4H 2 O 2NO 2 -1 +6 (H) → N 2 + 2OH - + 2H 2 O ·· hydrogen in the formula (H) is given by the decomposition reaction 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 used, In many cases, the organic matter necessary for the denitrification reaction is insufficient in the sewage, and usually an appropriate amount of the organic matter such as methanol is 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 bacteria concentration (typically represented by sludge concentration) K : Expressed by denitrification rate constant.

According to this formula, in order to increase the denitrification rate dN / dt,
It is understood that the operation for 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 the 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 that it is 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 so-called fixed that can keep the sludge concentration (the amount of microorganisms) in the inside higher than that of the conventional floating denitrification device (sludge concentration is usually 2,000 to 5,000 mg / l, maximum 7,000 to 8,000 mg / l) Although a so-called floor type (biofilm type) denitrification device is also put into practical use, the sludge concentration in the tank is about 1.5 to 2 times that of the floating type at most, and the space between the carriers is also in use. If the gap is too small, it causes a problem of clogging due to sludge and the like, so that regular cleaning is required, which requires consideration for maintenance.

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 called sludge granules) in which denitrifying bacteria are aggregated in a high concentration inside the denitrification tank. The original sludge is made to flow through the granulated sludge bed in an upward flow for denitrification. Other configurations are similar to 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 passing a proper amount of sewage containing nitrate nitrogen and organic matter in an upward flow for a predetermined period (usually 1 to
It will be held for 2 weeks.

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.

Also the acclimatization is important to perform Always passed through the wastewater containing nitrate nitrogen (NO ₃ ^-1 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 / l, 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. Also, there is a risk of blockage in a fixed bed type device provided with a microbial carrier, and the binding of granule sludge particles to each other is N ₂ gas produced by decomposition of NO ₃ ^-1 N and / or NO ₂ ^-1 N in the water to be treated. There is also a feature that it is not necessary to consider because it is loosened by the ascending flow of.

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

Also, in a high-concentration sludge bed type denitrification device, if the particle size of granule sludge particles becomes too large, the denitrification reaction will be carried out only on the sludge particle surface, 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 excessive enlargement of granule sludge particles and maintain the diameter at a preferable particle size (1 to 2 mm). As a means therefor, NO ₃ ^-
N, NO ₂ ^- and a method of controlling the nitrogen volume loading of N.
That is, the nitrogen concentration C (NO ₃ ^-1 N
And NO ₂ ^- if the sum of the N) is in excess of ^{0.2kg · N / m 3 (200mg} / l), to control the nitrogen volume load L in the range of 6~16kg · N / m ³ · day, nitrogen When the concentration C is 0.2 kg ・ N / 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 conventional processing apparatus will be described with reference to FIG.

Figure 3 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. 3 ^- 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 substances, and generally, the amount of organic substances 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 granular sludge bed 7 formed in the denitrification tank 1 in an upward flow, and the nitrate nitrogen is gasified into N ₂ to be diffused and denitrified. Sewage is passed through the overflow pipe 8 to the latter oxidation tank 2
Be led to.

In the denitrification tank 1, the organic substances injected into the raw sewage are also consumed in an amount corresponding to the amount of denitrified nitrate nitrogen,
As described above, since the excess amount of organic matter was injected into the raw sewage, the surplus organic matter that was not consumed by the denitrification reaction remained in the denitrified sewage, and BOD and COD
However, 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 8, and the residual organic matter is biologically oxidatively decomposed in the tank 2 and then discharged. That is, the third
The oxidation tank 2 shown in the figure represents a normal floating type activated sludge device, and the sewage introduced through an overflow pipe 8 is supplied from an air diffuser 10 through an air pipe 9 in the presence of activated sludge. By aeration with the air, the organic matter in the wastewater is oxidatively decomposed, and the mixed solution in the tank is guided to the subsequent settling tank 3 to be decomposed into treated water and sludge.
On the other hand, a part of the settled sludge is returned to the oxidation tank 2 via the sludge return line 12 to the treated water system not shown via 11 and the other is sent to the sludge treatment system not shown to be treated. Also in the denitrification tank 1, excess sludge is appropriately extracted from the sludge extraction line 13 provided at the bottom of the tank, and the extracted sludge is similarly sent to the sludge treatment for treatment.

In addition, as the oxidation tank 2, there is a case where a fixed bed type (biofilm type) oxidation tank capable of maintaining the concentration of sludge in the tank to a certain degree higher than that of the floating type is used. As the tank, one having the same structure as the fixed bed type 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 apparatus 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 apparatus. 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 / l, as in the case of the floating denitrification tank described above, and the sludge concentration in the tank must be kept higher than in the floating type. Even in the case of a fixed-bed type oxidation tank that can be operated, the sludge concentration is at most about 1.5 to 2 times that of the floating type, and the denitrification tank that is installed in the preceding stage of the oxidation tank and that forms a granule sludge bed It can be said that there is a significant difference compared with the sludge concentration of 20,000 to 100,000 mg / l as described above.

That is, as the denitrification tank, even if a high-concentration sludge bed type that can make the tank capacity extremely small is adopted, the capacity of the oxidation tank installed in the subsequent stage is still large as before. 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 considered from the above viewpoints, and its maximum purpose is to make a high-concentration sludge not only in the denitrification tank but also in the denitrification tank for oxidative decomposition of the residual organic matter in the denitrification apparatus of industrial scale. 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 Problems> The characteristics of the biological denitrification device of the present invention made to solve the above problems are intended for wastewater containing nitrate nitrogen and / or nitrite nitrogen, For denitrification in the presence of organic matter, a denitrification tank having a sludge bed formed of granular material in which denitrifying bacteria are aggregated at a high concentration and an organic matter remaining in the outflow water from the denitrification tank are biologically treated. A device equipped with an oxidation tank for oxidative decomposition, which is a sludge feed for sending high-concentration sludge particles (hereinafter referred to as granule sludge particles) formed in the denitrification tank in the first stage to the oxidation tank in the second stage. The configuration has a supply line.

In the denitrification device of the present invention having such a configuration, a part of the granule sludge particles formed in the denitrification tank of the previous stage,
By sending the sludge through the sludge feed line to the subsequent oxidation tank, the sludge concentration in the oxidation tank is kept dramatically higher than that of the conventional oxidation tank, and the oxidation tank required for oxidative decomposition of residual organic matter The aim is to reduce the capacity as much as possible.

The present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of a flow showing an example of an embodiment of the present invention. In FIG. 1, 1 is a denitrification tank having a granule sludge bed 7 in the tank, 51 is an oxidation tank installed in the subsequent stage, and the feature of the present invention is that the granular sludge formed in the denitrification tank 1 in the previous stage. The point is that the sludge feed line 52 for feeding the particles to the subsequent oxidation tank 51 (hereinafter referred to as high-concentration sludge type oxidation tank 51) is provided. The high-concentration sludge oxidation tank 51 used in the present invention has, for example, an air diffuser 54 connected to an air pipe 53 in the tank, and may be structurally similar to a conventional floating oxidation tank.

In FIG. 1, 3 is a sedimentation tank, 4 is a wastewater inflow line, 5 is an organic substance injection line, 6 is a pH adjusting agent injection line,
Although 8 is an overflow pipe and 11 is a treated water line, these are the same as in the case of the conventional apparatus, but in the present invention, the sludge in the settling tank is oxidized as in the conventional apparatus (FIG. 3). Denitrification tank for settling sludge, instead of returning it to the tank 1
The sludge return line 55 from the settling tank 3 to the denitrification tank 1 is provided for that purpose.
In addition, in the middle of the sludge feeding line 52, a sludge feeding line
A branch line 56 for branching off excess sludge is provided branching from 52. With such a configuration, more effective processing can be performed, which will be described later.

<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 part of the denitrification tank 1 through the sewage injection line 4. If necessary, the pH adjuster injection line 6 is used to inject the pH adjuster into the raw wastewater.

The raw sewage injected into the denitrification tank 1 is the granule sludge bed 7
As it passes through the interior in an upward flow, it is denitrified and nitrate nitrogen
The N ₂ gasified, diffused, and denitrified sewage is guided to the high-concentration sludge oxidation tank 51 in the subsequent stage through the overflow pipe 8. In the present invention, at this time, the sludge feed line 52
A part of the granule sludge particles formed in the denitrification tank 1 is fed to the high-concentration sludge oxidation tank 51 via the. In the present invention, the granulated sludge particles having a very high sludge concentration (as described above, the sludge concentration is 20,000 to 100,000 mg / l) formed in the denitrification tank 1 in this manner is used in the high-concentration sludge oxidation tank 5
Since it is sent to 1, the sludge concentration in the oxidation tank 51 can be kept dramatically higher than that in the conventional oxidation tank.

In the high-concentration sludge type oxidation tank 51, by supplying air from the air diffuser 54 through the air pipe 53 under such a high tank sludge concentration, residual organic matter in the outflow water from the denitrification tank 1 Oxidize and decompose. Therefore, in the high-concentration sludge type oxidation tank 51, compared with the conventional oxidation tank, organic substances can be treated with a very high load, and the capacity of the oxidation tank 51 can be remarkably downsized.

In the present invention, as described above, a part of the granule sludge particles formed in the denitrification tank 1 and having a high concentration of denitrifying bacteria are fed to the high-concentration sludge type oxidation tank 51, and the sludge particles are preferably discharged. It is used for the oxidative decomposition of organic matter under vaporous conditions, and the reason why it is possible is as follows.

That is, as described above, the denitrifying bacterium uses NO ₃ ⁻ or NO ₂ ⁻ instead of the molecular oxygen molecule under the facultative anaerobic state without the molecular oxygen (that is, the state without the dissolved oxygen) to use the organic substance. Is decomposed and the energy obtained is used for its growth and biological maintenance. However, under the aerobic condition in which molecular oxygen exists, the molecular oxygen is used just like ordinary aerobic bacteria (so-called activated sludge). This is because it has the ability to decompose organic substances and obtain energy.

The mixture of sewage and sludge in which the residual organic matter has been decomposed in the high-concentration sludge type oxidation tank 51 is then guided to the settling tank 3 and separated into treated water and sludge, and the treated water is processed through the treated water line 11. The sludge is discharged to the outside, while the settled sludge is returned to the denitrification tank 1 via the sludge return line 55. In the conventional floating oxidation tank, the sludge returned from the settling tank is returned to the oxidation tank.
In the present invention, as described above, the returned sludge may be returned to the denitrification tank 1 and the sludge may be used again for the denitrification reaction. With such a configuration, the denitrification reaction in the denitrification tank 1 is further improved. It can be done effectively. In the high-concentration sludge denitrification tank 1, as described above, if the particle size of the granule sludge becomes too large, the reaction rate of the entire tank becomes small, which is not preferable, but high-concentration sludge The denitrification tank 1 is returned to the denitrification tank 1 again by returning sludge that has been subdivided to some extent by aeration in the oxidation oxidation tank 51.
This is because it is possible to prevent the granule sludge particles from growing inside. In addition, in the apparatus of the present invention having such a configuration, when the excess sludge in the system is drawn out, the sludge in the settling tank 3 is not drawn out as in the conventional case, but is granulated in the denitrification tank 1. It is advisable to pull out the sludge particles. In FIG. 1, excess sludge is removed through a sludge drawing line 56 that is branched from the sludge feed line 52 from the denitrification tank 1 to the high concentration sludge oxidation tank 51. It is better to pull it out. This is because it is difficult to directly dehydrate the sludge present in the settling tank 3 because it is subdivided to some extent by aeration as described above, but the granulated sludge in the denitrification tank 1 is not This is because the dehydration property is very good, and it is possible to directly dehydrate without adding a dehydration auxiliary such as a polymer flocculant. Needless to say, the sludge drawing line 56 may be directly connected to the denitrification tank 1.

FIG. 2 is an explanatory view of a flow showing another embodiment of the present invention, which is a high-concentration sludge type oxidation tank installed in the latter stage of the denitrification tank 1.
As 51, a structure in which a gas / liquid / solid separation section 57 is integrally provided above the 51 is used, and the entire apparatus is made more compact. 58 is a gas / liquid / solid separation part
It is a partition wall provided inside 57, for example, an inner cylinder.

In the denitrification apparatus, treated water, air, and sludge are separated by a gas / liquid / solid separation section 57 that is integrally provided above the high-concentration sludge oxidation tank 51, and sludge in the denitrification tank 1 is separated. The high-concentration sludge oxidation tank 51 is directly returned via the sludge return line 55. The other parts are the same as those of the apparatus shown in FIG.

<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 tank, and one of the high-concentration sludge particles formed in the denitrification tank is used. By configuring the parts to be fed to the subsequent oxidation tank, the concentration of sludge in the oxidation tank can be maintained dramatically higher than before, thereby making the capacity of the oxidation tank much smaller than before. Therefore, there is an advantage that the entire denitrification apparatus including the denitrification tank and the oxidation tank which should be called a post-treatment can be downsized.

Further, in the present invention, the reaction in the denitrification tank can be better performed by returning the sludge used for the oxidation of the residual organic matter to the denitrification tank again, and when the excess sludge in the device system is extracted, the sludge is removed. By extracting the sludge in the nitrification tank which is granulated and has a very good dehydration property, the subsequent sludge treatment can be significantly facilitated.

Moreover, in the present invention, there is no fear that the clogging and the like considered in the fixed bed type oxidation tank which has been conventionally used for the oxidation treatment of the residual organic matter will occur, and stable treated water can be obtained, so that industrial treatment is possible. There is an effect that it can be suitably implemented on a scale, and its usefulness is extremely large.

〔Example〕

 Hereinafter, examples of the present invention will be described together with comparative examples.

High-concentration sludge bed type denitrification tank with a capacity of 2 liters and high-concentration sludge type oxidation tank with integrated gas / liquid / solid separation unit (oxidation tank capacity excluding the separation unit
Table 1 shows the results of treating raw sewage containing 200 mg / l of nitrate nitrogen by using the denitrification apparatus of the present invention as shown in FIG. In addition, methanol was used as the organic substance and was injected so that the concentration of methanol in the raw sewage was 600 mg / l.

As a comparative example, a denitrification device (comparative example-1) comprising a denitrification tank with a capacity of 2 l (high-concentration sludge bed type) and a fixed bed type oxidation tank with a capacity of 1.5 l (microorganism carrier; made of plastic, the same applies below), or Denitrification device consisting of the same denitrification tank and fixed bed type oxidation tank with a capacity of 5 l (Comparative Example-2), and further denitrification device consisting of the denitrification tank and fixed bed type oxidation tank with a capacity of 10 l (Comparative Example- 3) 3
Table 1 also shows the result of treating the same raw sewage as in the example using a set of devices.

However, the water temperature was controlled at 20 ° C, and aeration was performed so that the dissolved oxygen in each oxidation tank was 2 mg / l or more.

As described above, in the present invention, the BOD load in the oxidation tank can be made extremely high, and as a result, the denitrification tank and the oxidation tank together have a total capacity of 3.5 l, and denitrification and BOD removal are well performed. . On the other hand, in the comparative example using the conventional fixed bed type oxidation tank (which can be made smaller than the floating type oxidation tank shown in FIG. 3) as the oxidation tank, in order to obtain the same level of treated water. , As shown in Comparative Example-3, as the total capacity
It requires 12 liters (2 liters of denitrification tank, 10 liters of oxidation tank), and it can be seen that the device of the present invention can be made much smaller than the conventional device.

[Brief description of drawings]

FIG. 1 is an explanatory view of a flow showing an example of an embodiment of the biological denitrification device of the present invention, FIG. 2 is an explanatory view of a flow showing another embodiment of the present invention, and FIG. It is explanatory drawing which shows the flow of an apparatus. 1 ... Denitrification tank, 2 ... Oxidation tank 3 ... Sedimentation tank, 4 ... Sewage inflow line 5 ... Organic substance injection line 6 ... pH adjusting agent injection line 7 ... Granule sludge bed 8 ... Overflow pipe 9 , 53 …… Air pipe, 10, 54 …… Air diffuser 11 …… Treated water line 12, 55 …… Sludge return line 13, 56 …… Sludge drawing line 51 …… High-concentration sludge oxidation tank (oxidation tank) 52 …… Sludge feeding line 57 …… Gas / liquid / solid separation section 58 …… Partition wall

Claims (1)

[Claims] 1. A sludge bed for forming densification of denitrifying bacteria to a high concentration for denitrification in the presence of organic matter, targeting sewage containing nitrate nitrogen and / or nitrite nitrogen. A device provided with a denitrification tank having and an oxidation tank for biologically oxidatively decomposing organic matter remaining in the outflow water from the denitrification tank, wherein the high-concentration sludge particles formed in the denitrification tank in the previous stage are A biological denitrification device having a sludge feed line for feeding to a subsequent oxidation tank.