JPH0321397A - Method and apparatus for denitrification of sewage - Google Patents

Abstract

PURPOSE:To make installation of a nitrification tank unnecessary and carry out denitrification very simply by returning a part of treated water after passing an anaerobic tank and an aerobic tank to the aerobic tank. CONSTITUTION:A part of treated water cleaned in degree of 90% BOD removal by passing an anaerobic tank 1 and an aerobic tank 2 is returned to the aerobic tank 2 again and treated in the aerobic tank repeatedly. BOD is lessened to 100ppm level at which nitrification bacterial e.g. ammonia oxidation bacteria and nitrous acid bacterial can be active. The nitrification bacteria thus decomposes organic-N to NH4-N, and then oxidized quickly to NO2-N and NO3-N. By this method, the nitrification tank is made unnecesary and the side of an aerobic tank is made small and denitrification is carried out efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a denitrification method and an apparatus therefor that can exhibit a denitrification function of removing nitrogen from wastewater during wastewater treatment.

[Conventional technology]

By performing primary treatment of sewage in an anaerobic filter bed tank (anaerobic tank), and then performing secondary treatment in a contact aeration tank, both anaerobic and aerobic microorganisms are effectively utilized, making sewage treatment more efficient. An energy-saving type processing device that can be carried out efficiently and economically has already been developed by the applicant and others.
This sewage treatment equipment has the problem of not being able to effectively remove nitrogen contained in the sewage.

Conventionally, as shown in Figure 3, a nitrification tank 3 is installed between the aeration tank 2 and the settling tank 4 to oxidize the nitrogen N in the wastewater into nitric acid.
By using a denitrification device which is provided with a return path 5 downstream of the settling tank 4 for returning part of the treated water to the anaerobic tank 1 for primary treatment via the pump 6, The nitrogen inside was removed.

That is, in order to oxidize nitrogen N in sewage to nitrate, it is necessary to lower the BOD of sewage to about 10 ppm in order to effectively activate nitrifying bacteria such as ammonia oxidizing bacteria and nitrite oxidizing bacteria. However, the BOD removal rate using the conventional anaerobic tank 1 and aeration tank 2 is around 90%. For example, if the BOD of wastewater (J!
It can only descend to about m. Therefore, in conventional denitrification equipment, the BOD is lowered to an effective value of around 10 ppm using the nitrification tank 3 connected after the aeration tank 2, thereby effectively nitrifying nitrogen N. After that, this is precipitated in a sedimentation tank 4, and further passed through a reduction route 5 to an anaerobic tank 1.
As a result, the anaerobic microorganisms in the anaerobic tank 1 convert it into nitrogen gas N2, which is then released into the air. [Problem to be solved by the invention] However, in the conventional denitrification equipment, as described above, the aeration tank 2
Since it is necessary to install a nitrification tank 3 of the same size as the aeration tank 2 at the subsequent stage, there is a problem in that the cost of the entire equipment increases. Therefore, the technical problem of the present invention is to provide a denitrification method for sewage that does not require the installation of a nitrification tank, does not require increasing the size of the aeration tank, and can exhibit excellent denitrification effects with an extremely simple configuration. and to provide the equipment.

[Means for solving Problem B]

In order to solve the above-mentioned technical problem, the measures taken in the present invention are as follows.

In a sewage treatment system that purifies wastewater by passing it through an anaerobic tank, an aeration tank, and a settling tank in that order, (1) A part of the treated water that has been aerated to the rear of the aeration tank is returned to the front of the aeration tank. A return route must be established to send the item back. (2) A reduction path is provided at the rear of the sedimentation tank to direct a portion of the treated water that has undergone sedimentation treatment back to the anaerobic tank. (3) Set the return rate of treated water returned to the aeration tank through the return route to approximately half the amount of inflow water. However, in this case, the term anaerobic tank refers to a septic tank equipped with anaerobic conditions in which anaerobic organisms that decompose and purify suspended matter and soluble organic matter in sewage can effectively grow. Also,
An aeration tank is a septic tank that receives air from an aeration blower, etc. to aerate wastewater through contact, and is equipped with aerobic conditions that allow aerobic microorganisms to grow effectively. [Operation] The above means operates as follows.

■The factors mentioned in (1) above are because part of the treated water that has been purified to a BOD removal rate of about 90% through the anaerobic tank and aeration tank is returned to the aeration tank and the aeration process is repeated. BOD
can be reduced to a level of IQppm at which aerobic nitrifying bacteria such as ammonia oxidizing bacteria and nitrite oxidizing bacteria can be actively activated. Therefore, these nitrifying bacteria decompose organic mu element N in wastewater into ammonia nitrogen NH4. Furthermore, it is possible to quickly oxidize this into nitrite NO and nitrate NO. ■The element mentioned in (2) above is that the nitrogen No2, NO, in the wastewater that has been oxidized to nitric acid by being returned to the aeration tank is converted into nitrogen gas N2 by the anaerobic microorganisms in the anaerobic tank and released into the air. Since it is released, nitrogen can be removed from wastewater and the quality of treated water can be improved. ■The factors mentioned in (3) above mean that if the return rate of treated water returned to the aeration tank is, for example, 50%, the BOD will be reduced to 10pp.
2 m, compared to conventional denitrification equipment that supplies all the treated water to the nitrification tank and performs nitrification.
The time required for nitrification can be reduced to about half. As described above, the above-mentioned technical problem can be solved by the above-mentioned means, and the problems of the conventional technology can be solved.

〔Example〕

Hereinafter, preferred embodiments of the wastewater denitrification apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

In Figure 1, 1 is an anaerobic tank, 2 is an aeration tank, 4 is a settling tank, 7 is a return route (pipe) connecting both the water channels at the rear and front of the aeration tank 2, and 8 is this route. A return pump installed in the middle of 7 is shown, and 5 is a return path (pipe) connecting the rear water channel of the settling tank 4 and the front water channel of the anaerobic tank 1, both of which are shown in Figure 3. Components that are the same as those in conventional denitrification equipment are given the same symbols. FIG. 2 shows the amount of treated water returned to the front of the aeration tank 2 through the return path 7 (Q=inflow water amount bo/d), and 13
This is a diagram showing the relationship between 0D (■/Q), and from this diagram, when the return rate is approximately half (0.5Q) of the inflow water volume, B
It can be understood that it is possible to purify the OD to around 10 ppm, which is suitable for nitrification. Therefore, in the present invention, the return rate of the treated water is set at about half, specifically between 45% and 60%. However, the above-mentioned return rate shall be adjusted as appropriate depending on the required nitrification rate.

The amount of treated water returned to the front part of the anaerobic tank 1 through the above-mentioned reduction path 5 is 0.6 to 2Q (60 to 200%).
It is. Since the present invention has the structure as described above, a portion (approximately 50%) of the treated water that has passed through the anaerobic tank 1 and the aeration tank 2 and has been purified to a BOD of about 20 ppm is passed through the return route 7 again. Since it is returned to the aeration tank 2 and aerated, the BOD of the treated water in the aeration tank 2 is reduced to 10 ppm, which is suitable for the activity of nitrifying bacteria.
Therefore, the ammonia nitrogen NH4 contained in the treated water is oxidized by the nitrifying bacteria and decomposed into nitrates such as nitrite nitrogen NOt and nitrate nitrogen NO. Furthermore, the nitrogen N in the treated water that is returned to the middle of the anaerobic tank 1 (for example, the second tank in the case of a two-tank anaerobic tank) through the reduction path 5 is converted to nitrate nitrogen No., No., as described above. As they are decomposed, these nitrates are attacked by anaerobic microorganisms living in the anaerobic tank and converted into nitrogen gas N2, which is released into the air through the soil cover layer. Ru.

〔effect〕

Since the sewage denitrification method and its device according to the present invention are as described above, it is possible to remove the rear and front parts of the aeration tank without using a nitrification tank with a complicated structure or making the aeration tank unnecessarily large. By simply connecting a return route between the two and sending a portion of the aerated treated water back to the aeration tank, the nitrogen contained in the wastewater can be oxidized to nitrate, producing an excellent denitrification effect. Therefore, compared to conventional denitrification equipment, the structure is simpler and the equipment can be made smaller and lower in cost. Since denitrification function can be provided extremely easily by simply providing a path, it can be implemented at low cost and has the economical advantage of reducing nitrification time to approximately half of the conventional method, resulting in energy savings. Coupled with the fact that it can be used to reduce wastewater pollution, it is useful for implementing it in various types of sewage septic tanks.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a preferred embodiment of the wastewater denitrification device according to the present invention, Figure 2 is a diagram illustrating the relationship between the amount of treated water returned to the aeration tank and the BOD value, and Figure 3 is a diagram illustrating the relationship between the amount of treated water returned to the aeration tank and the BOD value. The figure is a block diagram showing a conventional example of denitrification equipment for wastewater. 1 is an anaerobic tank, 2 is an aeration tank, 4 is a settling tank, 5 is a reduction route,
7 is the return route. Figure 1 Figure 3

Claims (3)

[Claims] (1) A wastewater denitrification method characterized by oxidizing nitrogen in the treated water to nitric acid by returning a portion of the treated water that has been purified through an anaerobic tank and an aeration tank to the aeration tank. . (2) In a sewage treatment device that purifies wastewater by passing it through an anaerobic tank, an aeration tank, and a settling tank in that order, a portion of the treated water that has been aerated to the rear of the aeration tank is returned to the front of the aeration tank. A wastewater denitrification device characterized in that a return route is provided for returning the water, and a reduction route is provided at the rear of the settling tank to return a part of the treated water that has been subjected to sedimentation treatment to the anaerobic tank. . (3) The sewage denitrification device according to claim (2), wherein the return rate of the treated water returned to the aeration tank through the return route is set to approximately half the amount of inflow water.