JPS62225296A - Biological nitrification and denitrification device - Google Patents

Abstract

PURPOSE:To efficiently realize a biological nitrification and denitrification method by combining a nitrification vessel of a fixed bed type and a denitrification vessel having a sludge be consisting of a granular material in which denitrifying bacteria are concentrated to a high concn. CONSTITUTION:The biological nitrification stage of a device which is designed to treat sewage 1 contg. ammonia nitrogen and is provided with the biological nitrification stage and biological denitrification stage is constituted of the vessel 20 of the fixed bed type packed therein with a microorganism carrier, and the biological denitrification stage is constituted of the vessel 71 having the sludge bed consisting of the granular material in which the denitrifying bacteria are concentrated to a high concn. As a result, the nitrifying and denitrifying bacteria are maintained at the high concn. in optimum environment, by which the exertion of high nitrogen load to both the nitrification vessel and the denitrification vessel is made possible and the device is made more compact than the device of the conventional method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a biological nitrification and denitrification device for wastewater, and more particularly to a device for biologically treating wastewater containing ammonia nitrogen, NO, and NO8. .

[Prior art and background]

The principle of the biological nitrification and denitrification method is to convert nitrogen compounds (ammonia nitrogen) in wastewater into N2 gas by the microbial action of nitrifying bacteria and A-Douga, and the treatment process is divided into a nitrification process and a denitrification process. It will be done.

In the nitrification process, nitrifying bacteria (nitrate bacteria and nitrite bacteria) extract ammonium ions (NH4) from wastewater under aerobic conditions.
is oxidized to nitrous acid (NO2-) or nitric acid (NO3-) as shown in the following formulas (1) and (2).

Nitrite bacteria Nitrate bacteria Also, in the denitrification process, denitrifying bacteria remove NO2-,
Under anaerobic conditions, NO3- is converted to nitrogen gas (
N2).

6N03-”5G)1.OH→3N2”5C02+71
(20"60H-...■In addition, methanol (C1
hOH) contributes to the reaction either by being pre-existing in the wastewater or by being added separately.

Figure 3 shows a conventional example of a nitrification-denitrification device that applies the above principle.
This will be explained with reference to FIGS. 4 and 5.

The example in Figure 3 shows the flow outline of the floating biological nitrification-denitrification method. First, ammonia nitrogen (NH4) is converted into nitrate nitrogen or nitrite nitrogen (NO2-
, NOx-: hereinafter collectively referred to as nitrate nitrogen).

Since the nitrification reaction is an acid production reaction, alkali injection for neutralization (the alkali injection line is indicated by reference numeral 12) may be performed in order to maintain the optimum pH for nitrifying bacteria (the same applies in the following examples).

Next, in the denitrification tank 4, nitrate nitrogen is removed with N2 in the presence of organic matter.
Gasify. At this time, if necessary, an organic substance (usually methanol) may be added from the external addition line 13 (the same applies in the following examples), and since this organic substance is usually added in excess of the required amount, the remaining In some cases, an oxidation tank 6 is provided after the denitrification tank 4 for the purpose of oxidizing and decomposing organic matter, and the organic matter is usually decomposed aerobically (hereinafter referred to as each tank 2).
, 4.6 is called a reaction tank).

In this method, the nitrifying bacteria, denitrifying bacteria, and organic matter oxidizing bacteria in each reaction tank 492, 4.6 are placed in a settling tank 3, 5.7 between each reaction tank.
Therefore, it has the advantage of being able to culture each fraction under its own optimal conditions, and has the characteristic of maximizing the abilities of bacteria with different properties.

The example in FIG. 4 shows an apparatus of the type shown in FIG. 3 in which the sedimentation tank between each reaction tank is omitted, and in this case, the size of the entire apparatus can be reduced.

Figure 5 shows a fixed-bed type (biofilm type) tank in which microbial carriers that allow nitrifying bacteria, denitrifying bacteria, and oxidizing bacteria to adhere and grow are placed in reaction tanks 2 and 4.6, rather than a floating type. An example of the device is shown. In this example, each image can be fixed in the reaction tank, so even if the sedimentation tank shown in the example in Figure 3 is omitted, the independence of each image is guaranteed. This has the advantage of solving problems such as those shown in the example.

[Problem that the invention attempts to solve]

However, in the floating nitrification and denitrification equipment shown in Fig. 3,
Since each reaction tank 2, 4.6 has an individual settling tank 3, 5.7 in the latter stage, there are disadvantages in that the entire device becomes large, and it also requires the addition of chemicals such as alkaline agents, resulting in high running costs. There are also difficulties.

In addition, in the example shown in Fig. 4, the sludge tends to become a single-phase sludge in which nitrifying bacteria, denitrifying bacteria, and oxidizing bacteria in each reaction tank 2° 4.6 are mixed.
Since it is not possible to cultivate each fraction under the optimal conditions (for example, nitrifying bacteria that grow under aerobic conditions are temporarily exposed to anaerobic conditions during the denitrification process), there is a problem in that the stability of the treatment is poor.

Furthermore, in the equipment shown in Figure 5, which has a fixed bed type reaction tank, there is a risk that the fixed bed in the denitrification tank, where the amount of bacterial growth is large, may become clogged with sludge, suspended solids in the sewage, etc. Large-scale equipment requires careful management to ensure stable operation.

[Means for Solving the Problems] The object of the present invention is to provide an apparatus that eliminates the drawbacks of the conventional biological nitrification-denitrification apparatus as described above and can realize the biological nitrification-denitrification method more efficiently. It was made for the purpose of The biological nitrification-denitrification device of the present invention, which has been made to achieve this purpose, is characterized by being targeted at wastewater containing ammonia nitrogen, and which includes a biological nitrification process and a biological denitrification process. The biological nitrification step is comprised of a fixed-bed oak filled with microbial carriers, and the biological denitrification step is comprised of a granular material in which denitrifying bacteria have aggregated at a high concentration. It consists of a tank with a sludge bed formed by.

In the above configuration, the fixed bed type tank that constitutes the nitrification process is
It has a structure in which a microorganism support 8 made of sand, carbon, plastic, honeycomb tube, etc. is fixedly installed inside, and the microorganism support is as large as possible in order to retain the microorganisms that are nitrifying bacteria. Those with a specific surface area are preferable,
Compared to the floating type, the sludge concentration (microbial concentration) in the tank can be considerably higher. In addition, in this fixed bed type nitrification tank, it is not actually necessary to consider clogging.

In addition, the tank constituting the denitrification process has a sludge bed (hereinafter referred to as granule sludge bed) consisting of granular materials (sludge grains commonly known as granules) in which denitrifying bacteria have aggregated at a high concentration.
The sewage is passed through this granule sludge bed in an upward flow.

The formation of the granule sludge bed is generally carried out by placing so-called activated sludge as seed sludge in a denitrification tank for a predetermined period (usually 1 to 2 hours) while passing an appropriate amount of sewage containing nitrate nitrogen and organic matter.
(weeks) for acclimatization. The granule sludge bed formed is 0.5 to 1 mm, although it varies depending on operating conditions etc.
It becomes sand grain-like. Even if this granule sludge bed Ct sewage flows in from the lower part of the denitrification tank and is passed through in an upward flow, the sludge particles will not flow out because the settling LV of the granule sludge is higher than the force to wash out the sludge (rise LV). It won't happen.

The sludge concentration in a denitrification tank with such a granule sludge bed reaches 20,000 to 100,000 mg/U, which is more than 10 times that in the floating type denitrification tank. Another feature is that there is no need to consider the possibility of clogging in the device because the bonds between granule sludge particles are loosened by the upward flow of nitrogen and gas.

In order to form and maintain such a granule sludge bed, Ca'' ions must be present in the sewage flowing upward (normal concentration Lmg/l, preferably 10n+g/, Q or more), or the granule sludge bed Preferably, a system is adopted in which sewage is distributed and passed through the sludge bed from the bottom position in the vertical direction of the sludge bed and from at least one position in the middle of the sludge bed in the vertical direction on the upper side. Ru.

According to the above, the ratio of distribution of sewage water from the pipes connected to the bottom and at least one other point above it may be fixed at a fixed ratio for both. The timing of sewage water conveyance between the pipe and the pipe located above it is alternated every predetermined period (for example, - days), in response to changes in nitrogen load (including changes in the amount of sewage, etc.), etc. It is also possible to perform various distribution controls such as changing the distribution ratio, normally sending wastewater only from the bottom pipe, and temporarily sending wastewater from the upper pipe as necessary.

In the tanks constituting the nitrification step and the denitrification step in the present invention, either of these steps may be placed in the front stage and the other in the rear stage, and the treated water in the latter tank is appropriately circulated to the front tank by the circulating water system. be done. The circulation rate in this case is selected depending on the amount of treatment (amount of water passed), the amount of ammonia nitrogen loaded, and the discharge standard of treated water, but is generally 100 to 400%.

In the present invention, the nitrogen process is facultatively anaerobic (dissolved oxygen 0).
2 is absent, but NO2- and No3- are present), and if necessary, organic matter (usually methanol) is added as an energy source for denitrifying bacteria.

The nitrification process is kept under aerobic conditions and is generally aerated for this purpose. Further, a pH adjuster may be added as appropriate.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2 showing flow outlines.

Example 1 In this example shown in FIG. 1, wastewater 1 containing ammonia nitrogen is nitrified through a fixed bed nitrification tank 20, a granule sludge bed denitrification tank 71, and then a fixed bed oxidation tank 60. After denitrification treatment, a part of the treated water 8 is returned to the nitrification tank 20 via the circulating water line 72, and the rest is appropriately sent to a subsequent treatment system as treated water.

An appropriate amount of alkali was added as a pH adjuster to the nitrification tank 20, and aeration was performed with air. Further, a predetermined amount of methanol was added to the degassing tank 71 as an organic source.

Tests were conducted under the following conditions using the apparatus shown in the flow above, and the results are shown in Table 1.

Test conditions Nitrification tank Niblastic microbial support Denitrification tank Sludge bed oxidation tank Niblastic microbial support Circulation rate 3
00% Example 2 In Example 2 shown in FIG. 2, a denitrification tank 71 having a granule sludge bed, followed by a fixed bed nitrification tank 20
A portion of the treated water 8 is returned to the denitrification tank 71 via a circulating water line 72.

In this example, by installing a nitrification tank after the denitrification tank, the alkali produced during denitrification is used as a neutralizer for the acid produced during nitrification, reducing the amount of alkali added to the nitrification tank. That's what I do. Further, in this example, since the nitrification tank is provided after the denitrification tank, it is possible in some cases to eliminate the need for an oxidation tank for treating residual organic matter flowing out from the denitrification tank.

The treatment in this example was carried out under the same conditions as in Example 1, and the results are shown in Table 2.

〔Effect of the invention〕

According to the device of the present invention, by combining a fixed bed type nitrification tank and a denitrification tank with a granule sludge bed, nitrifying bacteria,
Denitrifying bacteria can be maintained at a high concentration in separate tanks under optimal conditions, making it possible to apply a high nitrogen load to both the nitrification tank and denitrification tank, making the equipment more compact than conventional methods. The advantage is that In addition, there is no risk of blockages that occur in fixed bed denitrification equipment, and stable treated water can be obtained.
It has the advantage that it can be suitably implemented on an industrial scale, and its exclusive use is extremely great.

[Brief explanation of drawings]

Figure 1 is a diagram showing an outline of the flow of Embodiment 1 of the present invention;
FIG. 2 is a diagram showing an outline of the flow of the second embodiment, and FIGS. 3 to 5 are diagrams showing an outline of the flow of the conventional example. 1... Sewage 2... Nitrification tank 3.5.7
... Sedimentation tank 4 ... Denitrification tank 6 ... Oxidation tank
8... Treated water 9, 10.11.14... Return sludge 12... Alkali addition line 13... Organic matter addition line 20... Fixed bed nitrification tank 40... Fixed bed denitrification tank 60... Fixed bed type oxidation tank 71... Granule sludge bed type denitrification tank 72...
・Circulating water line Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. An apparatus intended for wastewater containing ammonia nitrogen and comprising a biological nitrification process and a biological denitrification process, wherein the biological nitrification process is performed using a microorganism carrier. The biological denitrification process consists of a fixed bed tank filled with
Biological nitrification-denitrification device 2, characterized in that it is constituted by a tank having a sludge bed in which granular substances in which denitrifying bacteria aggregate at a high concentration are formed.The denitrification step is arranged before the nitrification step, Biological nitrification-denitrification device 3 according to claim 1, characterized in that it has a circulation system for supplying the treated water from the nitrification process to the denitrification process.The denitrification process is arranged after the nitrification process, The biological nitrification-denitrification device according to claim 1, characterized in that it has a circulation system for supplying the treated water in the denitrification step to the nitrification step.