JPS60244397A - Biological denitrification of waste water - Google Patents

Abstract

PURPOSE:To simply and economically hold the amount of denitrification bacteria as the whole of a waste water treatment process to a predetermined one, by reducing denitrification bacteria propagated upon the digestion of BOD substances in a denitrification process by internal respiration in the other denitrification process. CONSTITUTION:Waste water 1 containing NH3 and BOD is introduced into a denitrification process A along with recycled nitrated water 2 to perform the denitrification of NOx in the recycled water 2 by the BOD component of the waste water 1 and the treated solution is introduced into a nitration process under an aerobic condition not only to nitrate NH3 in the solution but also to perform the oxidative decomposition of the remaining BOD while a part of the nitrated solution is recycled to the denitrification process. The remainder is denitrified by the internal respiration of denitrification bacteria in a denitrification process and taken out as treated water 4. At this time, denitrification bacteria are propagated upon the digestion of BOD substances in the denitrification process A and denitrification bacteria adhered consuming the org. substance in denitrification bacteria cells are gradually reduced by the internal respiration in the denitrification process B. Therefore, if the amounts of denitrification bacteria in the processes A, B are same, about 80-90% of NOx-N formed in the nitration process 3 is recycled to the process A and the remainder may be removed in the process B.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a biological denitrification method for effectively denitrifying wastewater such as sewage, human waste, and other industrial wastewater using a denitrification process.

Conventional technology Generally, biological denitrification methods include activated sludge method and granular denitrification method.

It is broadly divided into biological fixed bed methods, in which microorganisms are attached to media in the form of blocks, plates, nets, rods, fibers, and tubes. A fixed bed method has been put into practical use that allows bacteria to be kept pure and at a high concentration and allows for downsizing of equipment.

This conventional fixed bed denitrification treatment usually converts nitrogen (hereinafter referred to as N) compounds in wastewater, such as NH4, into NO during the nitrification process.
After nitrification to No.2 or No.3 (hereinafter referred to as NOx), NOx is reduced and decomposed to NO2 gas (denitrification) in a denitrification process in which a fixed bed or fluidized bed is formed by a medium to which desorbing bacteria are attached. to do, to be something.

Problems that the invention is trying to solve In order to reuse the medium, the surplus bacteria generated by this method is treated through a denitrification process. The cells are returned to the denitrification process, while the cells are dehydrated, dried, and incinerated. However, this method requires a large amount of energy to remove the cells because they adhere strongly to the medium, and the removed cells are Since it is a pure culture, it has the disadvantage of extremely poor dehydration properties.

There is also a method that uses anaerobic digestion to solubilize all the bacterial cells on the medium and separate them from the medium, but this also requires a long time to solubilize the bacterial cells, and the digestion solution is It has the disadvantage of requiring reprocessing.

° All of these conventional methods for treating surplus bacteria are complicated in operation and are prone to the above-mentioned drawbacks, which are problems that are of concern to the industry. Improving the treatment method for surplus denitrifying bacteria has become a major issue, but this is because the growth rate of the nitrifying bacteria used is 0.1 growth bacteria/NH4-N (
g/g), whereas the growth rate of denitrifying bacteria is 0.4 t/N03N (g/g), even for methanol-assimilating denitrifying bacteria, which has a small bacterial cell yield, per nitrogen removed. This is because the number of nitrifying bacteria reaches four times that of nitrifying bacteria. In addition, with conventional media-based methods, it was impossible to denitrify through the internal respiration of denitrifying bacteria, so it was necessary to add a reducing agent such as methanol during denitrification, which increased the cost of wastewater treatment. There was a drawback.

Means for Solving the Problems The present invention attempts to eliminate the various drawbacks of these conventional methods.In the biological denitrification method, by controlling the amount of denitrifying bacteria on the medium, it is easy and economical. The purpose of this invention is to provide a biological denitrification method for wastewater that enables the treatment and disposal of excess denitrifying bacteria and does not require the addition of valuable denitrifying reducing agents such as methanol from outside the system. .

The present invention utilizes denitrification bacteria grown on a medium through a denitrification reaction (external breathing type denitrification reaction) caused by organic carbon compounds in wastewater. The process utilizes multiple denitrification processes to completely reduce excess denitrifying bacteria that have grown on the medium through a denitrification reaction (denitrification reaction), and then grows the denitrification bacteria again through a denitrification reaction using organic carbon compounds in the wastewater. This is a biological denitrification method in which the total amount of denitrifying bacteria is suppressed.

Next, one embodiment of the present invention will be described with reference to FIG.

The wastewater containing NH3 and BOD' flows into the denitrification process (A) together with the circulating nitrified water 2, and after the NOx in the circulating water 2 is denitrified by the BOD components of the wastewater 1, it is under aerobic conditions. The NHs in the liquid flows into the nitrification process 3 and becomes NOx.
The remaining BOD is oxidized and decomposed. For the nitrification step 3, either a method using a biological medium or an activated sludge method can be applied. Part of the nitrifying solution is used in the denitrification process (A)
is circulated.

The remainder is denitrified by internal respiration of denitrifying bacteria in the denitrification step (B) and flows out as treated water 4. Denitrifying bacteria perform the denitrifying process (A)
In the denitrification process (B), the organic matter inside the denitrifying bacteria is consumed by internal respiration, so the number of attached denitrifying bacteria gradually decreases. The denitrification rate due to internal respiration is usually approximately 1/1 to 1/1 degree of the denitrification rate in the presence of BOD material. Therefore, the denitrification process (A)
, If the amount of denitrifying bacteria in (B) is the same, 80 to 90% of the NOx-N produced in nitrification process 3 will be recycled to denitrification process (A), and the remaining 10 to 20% will be recycled to denitrification process ( It is best to remove it using B).

Before the denitrifying bacteria in the denitrifying process (A) and (B) excessively increase and decrease, respectively, the medium in the denitrifying process (A) is transferred to the transfer line 5.
, the medium of the denitrification process (B) is transferred and returned to the denitrification process (B) and (A) via the return line 6, respectively, manually or automatically, simultaneously or separately, to the denitrification process (A). ) and (B) can be maintained at appropriate predetermined levels. Denitrifying bacteria proliferate through denitrification reactions in the presence of BOD, even though they decrease due to internal respiration, so the denitrification process (A).

If (B) has the same volume, the amount of growth of denitrifying bacteria in the entire denitrification process is significantly reduced by the present invention compared to the conventional method.
Even so, they will continue to proliferate, so any excess must be disposed of.

However, if the volume of the denitrification process (B)' is increased by increasing the volume by using one or more bacteria, increasing the amount of denitrifying bacteria held in the same process (B), and increasing the amount of NOx -N flowing into the denitrification process, denitrification can be achieved. It is possible to suppress the growth of denitrifying bacteria throughout steps (A) and (B). Denitrification step (A) of NOx-N amount,
(B) The distribution of water can be easily achieved by adjusting the amounts of the two circulating fluids. When applying the fluidized bed method to the denitrification process, if the denitrification process does not allow the circulating fluid 2 to flow, and the water volume is small and the medium does not flow, a pump may be attached and the treated water 4 may be circulated for the purpose of media flow. However, since denitrification is unlikely to be impaired even without fluidization, the fourth circulation of treated water is not essential. As a medium for denitrifying bacteria, use materials such as sand, activated carbon, anthracite, zeolite, ore slag, etc., or materials made of porcelain, glass, or plastic that are granular or flaky in size and easy to transport through piping using a pump, etc. Although sand and activated carbon are preferred.

Further, as the denitrification reactor for the denitrification steps (A) and (B), a bucket-type or base-type device can be used, but a base-type device is particularly preferable, and it is possible to control the return and transfer of the medium as described below. It can be done easily and economically.

The following methods can be used to transport or return the medium. First, during the transfer from the denitrification process (A) to the denitrification process (B), the layer height of the medium in the denitrification process (A) is monitored, and the layer height increases and the medium is just before entrainment or begins to be entrained. However, it is preferable to start the transfer when the layer height of the medium in the denitrification step (A) increases to a predetermined height.

On the other hand, the return from the denitrification process (B) to the denitrification process (A) is carried out in the same way, when the layer height of the medium in the denitrification process (B) decreases to a predetermined height or when the amount of denitrifying bacteria on the medium is returned. It is desirable to start sending back when the amount decreases to a predetermined state.

In addition to the manual transfer using the naked eye as described above, if unmanned operation is to be performed for a long period of time, it is recommended to perform automatic transfer and return as described below. For example, the denitrification step (A).

(B) A method of detecting the increase or decrease in the layer height (solid-liquid interface) of the medium using a surface meter based on light transmittance or other means, and transferring and returning the medium, or using a timer to determine the time for transferring (returning) the medium. For example, a method is used to set up and transfer data intermittently.

In the latter method, it is sufficient to empirically set the optimum transfer time by knowing the change in the layer height of the winter medium with respect to the set time. Although the total amount of denitrifying bacteria in the denitrifying processes (A) and (B) is greatly suppressed by the present invention, they still continue to proliferate gradually, so that the total amount of denitrifying bacteria in the denitrifying processes (A) and (B) is When there is an excess, the excess denitrifying bacteria must be removed and disposed of.

The extraction 7 of surplus denitrifying bacteria and the return 8 of the medium from which the denitrifying bacteria have been removed are preferably performed in the denitrification process A.

Example As an apparatus for denitrification steps (A) and (B), two cylindrical columns (φ200 mm, height 31
80 mm), and an activated carbon sludge type nitrification tank (200 t) was used as the equipment for the nitrification process. Sand was used as the denitrification tower fluidized bed medium.

30 m of NH3N in the above equipment? / l, BOD 8
Artificial wastewater of 0"i/1 was treated by flowing water at 2000 t/day so that the amount of circulating fluid was 6000 to 800017 days.

Regarding the amount of denitrifying bacteria in the fluidized bed, the height of the fluidized bed was visually monitored to determine whether it increased or decreased, and the timing and amount of media transfer and return between the two units was adjusted to ensure smooth denitrification. .

At the beginning of water flow, the medium to which denitrifying bacteria have adhered (denitrifying bacteria concentration: 18,000 μ/1) is first added. I entered the second tower.

The results obtained from the above experimental equipment and conditions are shown in Table 1.

Table 1 Note: The arrow (→) at the height of the fluidized bed indicates that the medium was transferred from the first column to the second column, and from the second column to the first column and returned.

As shown in Table 1, a good processing bottom volume was stored in the second column without adding methanol, and the amount of denitrifying bacteria in the entire device, that is, the height of the fluidized bed, remained unchanged even after 30 days. It has not reached the point where it is necessary to discharge denitrifying bacteria.

Effects of the Invention As described above, according to the present invention, denitrifying bacteria grown on a medium by a denitrification reaction using an organic carbon source (exo-breathing denitrification reaction) are treated without the addition of an organic carbon source, that is, by removing the constituent components of the denitrifying bacteria themselves. After reducing excess denitrifying bacteria that have grown on the medium through a denitrification reaction (internal respiration type denitrification reaction) using carbon as a reducing agent, the denitrifying bacteria are grown again through a denitrification reaction using an organic carbon source. By using the denitrification process to maintain the amount of denitrifying bacteria in the entire process at an appropriate predetermined amount, the amount of denitrifying bacteria in the entire wastewater treatment process can be easily and economically maintained at an appropriate predetermined amount. Since the surplus denitrifying bacteria are retained, the frequency of discharging the surplus denitrifying bacteria outside the system of the wastewater treatment process is reduced, and the surplus denitrifying bacteria can be treated and disposed of more easily and economically than in the conventional method. Since endorespiration type denitrification reaction is used as a means to maintain an appropriate predetermined amount, an amount of organic carbon source equivalent to the amount of denitrifying bacteria required for this reaction can be saved, making extremely economical wastewater treatment possible. In addition, it is possible to simultaneously and rationally control the amount of denitrifying bacteria and limit the amount of organic carbon source used, and the operation management is simple and the biological treatment of wastewater can be carried out with high efficiency. be.

[Brief explanation of the drawing]

FIG. 1 shows the flow of the present invention. 1... Wastewater, 2... Circulating nitrified water, 3... Nitrification process,
4... Treated water, 5... Media transfer Lypero... Media return line, 7... Surplus denitrifying bacteria extraction line, 8...
Stripping medium return line, A... denitrification process (A), B...
・Denitrification process (B). Representative Patent Attorney Masahiro Shiozaki Figure 1

Claims (1)

[Claims] 1. When removing nitrogen from wastewater using denitrifying bacteria attached to a medium that can be transported in piping, the denitrification process is performed before and after the nitrification process (A), (B ), denitrification is performed using a mixture of the digestive fluid from the nitrification step, and the remaining nitrification fluid that is not circulated is treated in the denitrification step (B). The surplus denitrifying bacteria from the denitrification process (A) are transferred together with the medium to the denitrification process (B), and the denitrification process (A) is carried out.
A biological denitrification method for wastewater, which is characterized in that in B), after the denitrifying bacteria are reduced by an endorespiration-type nitrification reaction, the medium is returned to the denitrification step (A). 2. Biological treatment of wastewater according to claim 1, wherein at least one of the denitrification steps (A) and (B) is treated using a plurality of tanks or towers. Denitrification method. 3. Each of the denitrification steps (A) and (B) is carried out using a medium in the form of granules or flakes and of a size and strength that makes it easy to transport through piping. The biological denitrification method for wastewater according to paragraph 1 or 2. 4. The first aspect of the present invention is that the medium is transferred from the denitrification step (A) to the denitrification step (B) without accompanying the supernatant water from the denitrification step (A). The method for biological denitrification of wastewater according to paragraph 2 or 3. 5. Claim 1, wherein the transfer of the medium from the denitrification step (A) to the denitrification step (B) is carried out with supernatant water from the denitrification step (A). , the method for biological denitrification of wastewater according to paragraph 2 or paragraph 3. 6. A patent in which the transfer of the medium from the denitrification process (A) to the denitrification process (B) starts at the time when the medium starts to be entrained in the supernatant water from the denitrification process (A). A biological denitrification method for wastewater according to claim 1, 2, 3, or 5. 7 The transfer of the medium from the denitrification process (A) to the denitrification process CB) and the return of the medium from the denitrification process (B) to the denitrification process (A) are carried out by detecting the layer height of the medium. Claims 1, 2, 3, 4, or 5
Biological denitrification of wastewater as described in Section. 8. Transfer of the medium from the denitrification process (A) to the denitrification process (B) and return of the medium from the denitrification process (B) to the denitrification process (A) are performed intermittently for a certain period of time. Claims 1 and 2 are set by a timer.
Section, Section 3. Biological denitrification method for wastewater according to paragraph 4 or 5. 9. Claims 1, 2, 3, and 4, wherein each of the denitrification steps (A) and (B) is performed using sand as a medium. Section 5, Section 6,
Biological denitrification method for wastewater according to paragraph 7 or 8. 10 A patent in which the transfer of the medium from the denitrification step (A) to the denitrification step (B) is started when the layer height of the medium in the denitrification step (A) increases to a predetermined height. Claims 1 and 2. The method for biological denitrification of wastewater according to paragraph 3, paragraph 4, paragraph 5, paragraph 7 or paragraph 9. ]1 The return of the medium from the denitrification process (B) to the denitrification process (A) is started when the layer height of the medium in the denitrification process (B) has decreased to a predetermined height. Claims 1 and 2. The method for biological denitrification of wastewater according to paragraph 3, paragraph 4, paragraph 5, paragraph 7, paragraph 9 or paragraph 10.