JPH03181394A - Denitrifying method of sewage - Google Patents

Abstract

PURPOSE:To sufficiently remove nitrogen contained in sewage and to simultaneously remove BOD by continuously performing aerating work wherein air is introduced from a draft tube for 3 hours or 8 hours and stopping the aerating work for at least 6 hours or more and introducing sewage into a filter tank during stoppage of aeration. CONSTITUTION:Liquid discharged from a preliminary filter tank 8 is passed through a flow rate regulator 11 and an advection pipe 12 and introduced into the lower part of a first aeration tank 13. Draft tubes D are provided to the central part of the first aeration tank 13 and air can be introduced thereinto. In relation to COD, the longer an aeration time is, the better lowering of COD is enhanced. In relation to Kjeldahl nitrogen, it is better that the aeration time does not exceed 8 hours. In relation to BOD, this is not much changed at >=3 hours but the aeration time is made utmost at about 4 to 5 hours. In the first and second aeration tanks, BOD is generally made small in the upper part thereof and it is made large in the lower part. In the meantime, sewage is not aerated and therefore aerobic organisms absorb oxygen and the inside of the aeration tank is made anaerobic.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to the treatment of sewage in which air is injected into the sewage by inserting a draft tube for feeding air into the bottom of a filtration tank using a large number of cylindrical bodies as filter media. Regarding denitrification methods.

[Prior Art] In order to purify sewage, such as domestic wastewater, if a large number of cylindrical bodies from which the bottoms of containers of the brand name Yakult have been removed are placed in a filter tank as filter media, suspended solids (SS) are significantly reduced. is known.

It is also known that the BOD treatment efficiency can be improved by injecting air into wastewater or stirring it for wastewater treatment.

However, according to the prior art, although it is relatively easy to remove BOD and solid content (particles), it is especially difficult to remove nitrogen content, such as ammonia called Kjeldahl nitrogen, organic nitrogen, nitrite nitrogen, and nitric acid. It was difficult to remove nitrogen.

[Problems to be Solved] Therefore, an object of the present invention is to provide a method for denitrifying wastewater that can quickly denitrify wastewater and, as a result, also remove BOD.

[Principle of the Invention] Generally, nitrogen contained in wastewater exists mainly in the form of ammonia. This ammonia is oxidized to nitrite nitrogen and nitrate nitrogen by the action of nitrifying bacteria (water containing a large amount of nitrite and nitric acid is called nitrified water). They have also found that in an anaerobic state, the presence of denitrifying bacteria, nitrified water, and BOD (hydrogen donor) has a denitrifying effect. On the other hand, aeration is effective for oxidizing nitrogen. To this end, we have found that repeating aerobic conditions with aeration and anaerobic conditions without aeration is effective for denitrification.

[Means for Solving the Problems] According to the present invention, a method for denitrifying wastewater includes inserting a draft tube for sending air below an aeration tank using a large number of cylindrical bodies as filter media, and injecting air into the wastewater. In the process, aeration work is carried out by injecting air through the draft tube for 3 to 8 hours continuously, and then the aeration work is stopped for at least 6 hours, and sewage is allowed to flow into the filtration tank while the aeration is stopped. .

[Operations] Therefore, the cylindrical filter medium sufficiently retains and traps biofilm on its surface. Therefore, the residence time of the sludge in the aeration tank becomes longer, and aerobic nitrifying bacteria with a low specific growth rate are sufficiently present, and nitrification progresses.

As a result, ammonia is relatively quickly converted into nitrite nitrogen and nitrate nitrogen, producing nitrified water.

At that time, since there is no inflow of sewage, untreated aeration liquid is not discharged.

The aeration time is preferably continuous for about 4 to 5 hours as described below; if it is less than 3 hours, the oxidation of ammonia will be insufficient and the growth of nitrifying bacteria will be insufficient. As a result, nitrogen removal is reduced.

In addition, if the heating time is longer than 8 hours, the Kjeldahl nitrogen removal rate decreases as will be described later, and the nitrogen removal rate also decreases.

If the aeration stop time is less than 6 hours, the anaerobic state will not be sufficient for denitrifying bacteria, which are anaerobic organisms, to denitrify, and sufficient time must be given for aerobic organisms to absorb enough oxygen and become anaerobic. No.

In particular, domestic wastewater undergoes repeated depletion 24 hours a day, so it is possible to perform cycle operation that fully satisfies the above conditions.

[Examples and Experimental Examples] FIG. 1 shows an outline of an apparatus for implementing the present invention, and in the figure, muddy water, such as domestic wastewater, flows into a first septic tank 2 from an inlet 1. A second septic tank 3 provided adjacent to the first septic tank 2 is separated by a wall 4, and the liquid from the first septic tank 2 is distributed between the partition plate 5 and the wall 4. It passes through the passage 6 and flows into the second septic tank 3 from the inflow lower. A preliminary filtration tank 8 provided adjacent to the second septic tank 3 is separated from the second septic tank 3 by a partition wall 10 whose lower part 9 is open. The liquid flows into the preliminary filtration tank 8.

A filter medium area A1 is formed in the middle of this preliminary filtration tank 8,
A large number of cylindrical bodies are densely gathered and arranged at random. A flow rate regulator 11 is installed at the top of the preliminary filtration tank 8.
An advection pipe 12 is provided via the . In the figure, WL indicates the liquid level of the first and second septic tanks 2.3 and the preliminary filtration tank 8.

The liquid from the preliminary filtration tank 8 is passed through the flow rate regulator 11 and the advection pipe 1.
2, and flows into the lower part of the first aeration tank (3).A draft tube D is provided in the center of the first aeration tank 13, so that air can be injected, and it also flows in the vertical direction. A filter medium area A2 is provided in the middle.

A liquid flows into a second aeration tank provided adjacent to the first aeration tank 16 from an outlet 15 connected to the advection pipe 14. This second aeration tank 16 is substantially the same as the first aeration tank 16.
It has the same structure as the aeration tank 3, and is equipped with a draft tube D and a filter medium area A. The liquid from the second aeration tank 16 is then discharged from the outlet 17. In the figure, WL2 indicates the liquid level of the first and second aeration tanks.

As experimental plants, various containers described above with CrrO and surface areas (-) as shown below were made.

Capacity d Surface area d No. 1 septic tank 2 1.16 0.77 2nd septic tank 3 0.57 0.38 Pre-filtration tank 8 0
．． 57 0.38 First aeration tank 13 1. 04
0. 72 Second aeration tank 16 1. 03 2
．． 97 Experiments A to J were conducted with various aeration times as described below.

In Table 1, the horizontal solid line indicates the aeration time, and the treatment BOD
is mg/ls nitrogen removal rate is shown in %.

In addition, experiments were conducted to determine the nitrogen removal rate by varying the aeration time, and the results shown in Figure 2 were obtained.

Therefore, continuous operation for about 5 hours is preferred for nitrogen removal.

However, when it comes to water quality treatment, other
We also have to consider BOD.

The relationship between the COD and Kjeldahl nitrogen removal rates and the aeration time was similarly tested. The results are shown in Figure 3.
In the figure, the solid line B is the removal rate of BOD, and the dashed line e is the removal rate of COD.
The removal rate of Kjeldahl nitrogen is shown by the - dotted chain line.

As can be seen from Table 1 and Figures 2 and 3, the aeration time was 3.
If the time is less than 1 hour, nitrogen, Kjeldahl nitrogen, BOD, and COD cannot be removed sufficiently.

For COD, the longer the aeration time, the better, but for Kjeldahl nitrogen, it is better not to exceed 8 hours. Regarding BOD, it doesn't change much after 3 hours or more, but it reaches its maximum when it is around 4 or 5 hours.

Considering the above points, in the present invention, the aeration time is continuously set to 3.
8 hours.

Now, the aeration stop time will be considered as follows.

In the present invention, since sewage flows in during the aeration stop, the liquid in the preliminary filtration tank 8 passes through the flow regulator 11 and gradually flows into the lower part of the first aeration tank 13, and then upwards through the filter medium area A2. During the flow, the wastewater and aeration liquid are gradually mixed.

That is, in the initial state, an interface between the lower wastewater and the upper aeration liquid occurs at the position indicated by the symbol X in FIG. Next, mixing is gradually performed between ff1Y and X above and below this interface X, and after 6 hours, for example, the mixture is mixed throughout the aeration tank 13. Therefore, in both the first and second aeration tanks, the BOD is generally small in the upper part and large in the lower part.

During this time, there is no aeration, so aerobic organisms absorb oxygen and the inside of the aeration tank becomes anaerobic.

In this way, the conditions for denitrification are prepared, the nitrogen removal rate can be improved, and the BOD can also be brought to around ippm.

[Effects of the Invention] As described above, according to the present invention, since nitrogen is nitrified when aeration is stopped and nitrogen is oxidized during aeration, the nitrogen content in wastewater can be sufficiently removed, and BOD can also be removed at the same time.

Since domestic wastewater normally increases and decreases in a 24-hour cycle, the present invention can be suitably implemented. Furthermore, oxygen from aeration is generally used for oxidizing BOD and nitrogen, but in reality it is mainly used for oxidizing nitrogen, so less energy is required, and BOD is consumed for denitrification, resulting in energy saving. This is a great method. In particular, in the present invention, since BOD is consumed during denitrification, the processing BOD can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of an apparatus for carrying out the present invention, and FIG. 2 is a diagram showing the relationship between aeration time and nitrogen removal rate according to the present invention.
FIG. 3 is a diagram showing the relationship between the aeration time and the removal rate of BOD5C0D and Kjeldahl nitrogen. 8...Preliminary filtration tank 13...No.■ aeration tank A
,A, ,A2... Filter medium area 11... Flow rate regulator 12.14... Advection pipe 16... Second aeration tank

Claims (1)

[Claims] In a wastewater denitrification method in which air is injected into wastewater by inserting a draft tube that sends air below a filtration tank that uses many cylindrical bodies as filter media, the aeration work of injecting air from the draft tube is performed continuously. A method for denitrifying wastewater, which comprises carrying out the aeration operation for 3 to 8 hours, stopping the aeration operation for at least 6 hours or more, and allowing the wastewater to flow into a filter tank during the aeration stoppage.