JPH02214596A - Method and device for removing nitrogen from sewage - Google Patents

Abstract

PURPOSE:To enhance the rate of removal of nitrogen at small volume by bringing a carrier with nitrifier immobilized thereon by bringing it into contact with the mixed liquid of activated sludge introduced from a denitrifying stage in the aerobic conditions in the respective nitrifying stages of a multistage circulation type nitrifying and denitrifying method. CONSTITUTION:Sewage wherein solid is firstly removed in a sedimentation basin 1 is split and introduced into the nitrification tanks 13, 15 of respective stages. Activated sludge is returned to the denitrification tank 13 from the final sedimentation tank 5. Nitrifying liquid circulated from the respective nitrification tanks 24, 26 adjacently provided on the tanks 13, 15 is mixed and agitated in the respective denitrification tanks 13, 15 and denitrification is performed by BOD in sewage and the mixed liquid is introduced into the nitrification tanks 24, 26. A carrier such as porous ceramics with nitrifier immobilized thereon is housed in the respective tanks 24, 26 and brought into contact with the mixed liquid introduced from the denitrification tanks 13, 15 in the aerobic conditions and nitrifying treatment is performed. Therefore the nitrification tanks 24, 26 can be miniaturized and the rate of removal of nitrogen is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for biologically removing nitrogen components from wastewater such as sewage, human waste or industrial wastewater.

[Conventional technology]

Conventional methods for biologically removing nitrogen components from wastewater include installing a denitrification tank after the nitrification tank and adding methanol or the like as a hydrogen donor to the denitrification tank; A nitrification/endogenous denitrification method was known in which the volume of the denitrification tank was increased without feeding anything.

However, in order to achieve a nitrogen removal rate of about 80%, the method of adding methanol, etc. to the denitrification tank requires the cost of chemicals, and the nitrification/endogenous denitrification method requires a very large volume of the denitrification tank, which makes urban areas It was not suitable for large-scale sewage treatment plants.

In addition, a nitrification tank is installed following the denitrification tank, and a part of the nitrified liquid is circulated from the nitrification tank to the denitrification tank, and organic matter in the wastewater is used as a hydrogen donor. Methods A and O were also known, in which an anaerobic tank was installed before the denitrification tank to simultaneously remove nitrogen and phosphorus components.
These methods require significantly larger volumes and installation areas than standard activated sludge aeration tanks, and the nitrogen removal rate is only 6.
It remained at about 0-70%.

In order to further reduce the installation space, as shown in Fig. 2, a part of the nitrification liquid is circulated from the anaerobic tank 2 to which activated sludge is returned from the initial settling tank 1 and the final settling tank 5, and the nitrifying tank 4. Denitrification tank 3, nitrification tank 4, and final settling tank 5 were arranged in series.
A hybrid biological treatment method in which a rotating disk 6 is provided in the nitrification tank 4 of the 20 method, and a large number of nitrifying bacteria are attached to the rotating disk 6 (
Activated sludge method with rotating disk) was also developed.

Recently, as shown in Fig. 3, a part of the wastewater is led to the first stage denitrification tank 13, and the activated sludge returned from the final settling tank 5 is recycled from the first stage nitrification tank 14. After the nitrified solution is mixed and subjected to denitrification treatment, it is led to the first-stage nitrification tank 14 for BOD oxidation and nitrification treatment, and a part of the obtained nitrification solution is transferred to the first-stage denitrification tank 14. While being circulated to the nitrification tank 13, the remaining nitrification liquid is led to the second-stage denitrification tank 15, where part of the wastewater is mixed with the nitrification liquid circulated from the second-stage nitrification tank 16 for denitrification treatment. After that, it is led to the second stage nitrification tank 16 to perform BOD oxidation and nitrification treatment, and a part of the obtained nitrified solution is circulated to the second stage denitrification tank 15, while the remaining nitrified solution is Solid-liquid separation is performed in the final settling tank 5, or
After repeating the same denitrification and nitrification processes as in the first stage,
The remaining nitrified liquid obtained in the final stage nitrification process is subjected to solid-liquid separation in the final settling tank 5, and a part of the separated activated sludge is returned to the first stage denitrification tank 13. A circulating nitrification-denitrification method was also developed.

[Problem to be solved by the invention]

However, in the conventional hybrid biological treatment method shown in FIG. 2, although the volume required is about the same as that of the aeration tank of the standard activated sludge method, the nitrogen removal rate was only 60 to 70%. Furthermore, since a rotating disk is used, it requires space to support the weight of the rotating disk, installation space for a drive motor, and a drive source, and it is also necessary to provide space at the top of the tank to take out the disk, so sewage treatment facilities There were problems such as the need to make the sewage treatment facility very deep if the top of the sewage treatment facility was to be covered and used effectively.

In addition, in the conventional multi-stage circulation nitrification-denitrification method shown in FIG. 3, energy is saved because the nitrification solution is normally circulated by the air lift effect in the nitrification process, and the nitrogen removal rate is about 80%. This required a considerably larger volume and installation area than the aeration tank used in the standard activated sludge method.

Therefore, conventional methods and equipment for biologically removing nitrogen components from sewage have been developed that achieve a nitrogen removal rate of about 80% without using chemicals, and that the equipment volume is about the same as the aeration tank of the standard activated sludge method. There was no biological nitrogen removal process.

The present invention solves the above-mentioned conventional problems, achieves a nitrogen removal rate of about 80% without using chemicals, and has a smaller volume and relatively smaller installation area than conventional ones, comparable to the aeration tank of the standard activated sludge method. The purpose of this invention is to provide a biological nitrogen removal process that can be easily performed, as well as a device that solves the above problems by relatively easily modifying an existing activated sludge treatment device.

[Means to solve the problem]

In the present invention, a biological nitrogen removal process in which a denitrification process is followed by a nitrification process is installed in multiple stages in series, wastewater is distributed to each denitrification process, and the wastewater is distributed to the first denitrification process. The activated sludge returned to the wastewater and the nitrification liquid circulated from the nitrification process in the stage are mixed and subjected to denitrification treatment, and then led to the nitrification process in the stage to undergo BOD oxidation and nitrification treatment. A part of the nitrified liquid is circulated to the denitrification process of the previous stage, while the remaining nitrified liquid is flowed out, and in each denitrification process from the next stage onward, the nitrified liquid discharged from the previous stage nitrification process is added to the distributed tη water. After denitrification treatment is performed by mixing the nitrification liquid circulated from the nitrification process of the stage, the mixture is led to the nitrification process of the stage, where BOD oxidation and nitrification treatment are performed, and a part of the obtained nitrification liquid is While circulating to the denitrification process in this stage, the remaining nitrification liquid is flowed out, the nitrification liquid flowing out from the final stage nitrification process is separated into solid and liquid, and a part of the separated activated sludge is sent to the first stage denitrification process. In the multi-stage circulation nitrification-denitrification method with return, in each stage of the nitrification process, the carrier on which nitrifying bacteria are immobilized is brought into contact with the activated sludge mixture derived from the denitrification process of the stage under aerobic conditions. This is a method for removing nitrogen from sewage, and in an activated sludge treatment device that mainly consists of an aeration tank and a subsequent settling tank, the aeration tank is replaced with a denitrification section that only performs stirring from the sewage inlet side. The nitrification section containing carriers immobilized with nitrifying bacteria is alternately divided into multiple stages and communicated with each other, and a path is provided for four people to distribute wastewater to each denitrification section, and the nitrification solution from each subsequent nitrification section is This is a device for removing nitrogen from wastewater, which is characterized by having a circulation path, and furthermore, the carrier on which each of the nitrifying bacteria is immobilized adheres the nitrifying bacteria to the surface of solid particles or inside the pores of porous solid particles. It is also characterized by being immobilized or comprehensively immobilized with nitrifying bacteria.

[For production]

The operation of the present invention will be explained with reference to FIG. 1 showing embodiment B.

First, the sewage to be treated is led to the initial settling tank 1 to separate coarse solids, and then distributed and led to the denitrification tanks 13 and 15 at each stage. Activated sludge is returned from 5, but in the denitrification tanks 13 and 15 of each stage, the nitrification liquid circulated from the adjacent nitrification tanks 24 and 25 is stirred and mixed, and the BOD in the wastewater is denitrified. Denitrification is performed using the activated sludge as a hydrogen donor, and the mixed liquid (activated sludge mixed liquid) is immediately led to the respective adjacent nitrification tanks 24 and 26. Each nitrification tank 24, 26 is equipped with a carrier on which nitrifying bacteria are immobilized, such as sand, anthracite, granular activated carbon, plastic particles, or carriers with nitrifying bacteria attached and immobilized on the surface, or nitrifying bacteria not only on the surface but also inside the pores. solid particles such as porous plastics and porous ceramics, or carriers in which nitrifying bacteria are entrappingly immobilized with polymer gel, etc. Nitrification treatment is performed by contacting the liquid mixture drawn from the denitrification tank 13.15 under aerobic conditions, but a large amount of nitrifying bacteria is retained in solid particles with a large surface area, or a large amount of nitrifying bacteria is is comprehensively immobilized, so nitrification treatment can be carried out extremely efficiently even in a small tank.

The carrier layer in each nitrification tank 24, 25 may be a fixed bed, but since clogging tends to occur during water flow, it is preferable to fluidize the carrier to form a fluidized bed. It is most preferable to use a solid-liquid-gas three-phase fluidized bed system in which fluidization is performed by flowing water and aeration from below.

Thus, in each nitrification tank 24, 26, ammonia nitrogen in the mixed liquid led from each denitrification tank 13, 15 immediately adjacent to it is converted to nitrite nitrogen by the action of nitrifying bacteria on or in the carrier. and is nitrified to nitrate nitrogen and flows out.

A part of this outflowing nitrification liquid is circulated to each denitrification tank 13.14 immediately adjacent as described above, and the nitrite nitrogen and nitrate nitrogen in the liquid are absorbed by BOD in the raw water as a hydrogen donor. It is then reduced to nitrogen gas and removed by denitrifying bacteria.

The higher the circulation rate of the nitrifying solution, the higher the nitrogen removal rate. General circulating nitrification and denitrification method, A! In the zero method and the hybrid biological treatment method, the nitrification solution is usually circulated by a pump, which requires a considerable amount of energy and power, and the nitrogen removal rate is only about 60 to 70%.However, the conventional multistage circulation method In the nitrification-denitrification method, the liquid level of the nitrification liquid is raised by the air lift effect of each nitrification tank, and the liquid level can be circulated by gravity to the immediately adjacent denitrification tank, which saves energy and can increase the nitrogen removal rate to around 80%. .

In the present invention, the liquid level is raised by the air lift effect of the nitrification tank, and the nitrified liquid can be circulated under natural flow, which not only saves energy but also reduces the nitrogen removal rate (which is the same as the conventional multi-stage circulation nitrification-denitrification method). A high denitrification effect can be obtained.

Therefore, in the present invention, a carrier with a specific gravity larger than 1 is housed in the nitrification tank. However, in order to give the nitrification tank an air lift effect, it is necessary to adjust the specific gravity of the carrier, activated sludge mixture, and aeration air. ×tank volume ratio] must be smaller than the specific gravity of the activated sludge mixture, and the carrier should be a carrier with as low a specific gravity as possible, such as anthracite or activated carbon, or a porous carrier even if the specific gravity is high. Therefore, it is more desirable to use a carrier that can support a large amount of nitrifying bacteria and achieve the desired purpose of the present invention even if the tank internal volume ratio, ie, the filling amount is small, such as a ceramic porous carrier.

In addition, a part of the nitrified liquid obtained in the second stage nitrification tank 26 is circulated to the immediately preceding denitrification tank 15 as described above, but the remainder is separated into solid and liquid in the final settling tank 5. A part of the activated sludge is returned to the first stage denitrification tank 13 as described above, and the separated water is led out of the system as treated water.

In addition, when the denitrification tank and nitrification tank are arranged in three or more stages alternately, the same treatment with the denitrification tank and nitrification tank as in the second stage is repeated in the third stage and thereafter, and then the process in the final stage is performed. The remaining nitrified liquid after removing the circulating amount from the nitrification tank is separated into solid and liquid in the final settling tank 5, and a part of the separated activated sludge is transferred to the first stage denitrification tank 13.
send it back to

Conventionally, in the circulating nitrification-denitrification method, the Ago method, and the multi-stage circulation nitrification-denitrification method, it is necessary to retain nitrifying bacteria in activated sludge. However, in the above-mentioned nitrification treatment of the present invention, the nitrifying bacteria are immobilized on or in the carrier, so they are not drawn out of the system and are not removed during the winter. Stable nitrification is also carried out in each nitrification tank. Therefore, the tank volume from the first settling tank 1 to the final settling tank 5 may be about the same as the tank volume of the standard activated sludge method, and the conventional circulating nitrification-denitrification method, ^! It requires less volume and installation area than the zero method and multi-stage circulation nitrification-denitrification method.

As described above, the present invention increases the nitrogen removal rate to about 80% with a small-volume device without using chemicals. In addition, the aeration tanks of the existing activated sludge treatment equipment are installed in order from the sewage inlet side: the first stage denitrification tank 13, the first stage nitrification tank 24, the second stage denitrification tank 15, and the second stage denitrification tank 15. Nitrification tank 2
Alternatively, the denitrification tank and the nitrification tank can be divided into 6 sections, or the denitrification tank and the nitrification tank can be divided into multiple stages and communicated with each other, and each denitrification tank is equipped with an agitator and no aeration is performed, and each nitrification tank is equipped with a nitrification tank. A path for accommodating carriers with immobilized bacteria and distributing and introducing wastewater into each of the denitrification tanks, and a path for circulating nitrification solution from the nitrification tank immediately adjacent to each of the denitrification tanks to the denitrification tank are provided. This allows for relatively simple modification of existing activated sludge treatment equipment, without changing the overall volume or installation area.
A high nitrogen removal effect with a nitrogen removal rate of about 80% can be obtained.

Note that piping equipped with a circulation pump can be installed as a route for circulating the nitrification liquid from the nitrification tank to the denitrification tank, but as mentioned above, it is possible to install an air lift effect in the nitrification tank and use it under natural flow. When circulating, it is only necessary to provide a groove or the like in the partition between the denitrification tank and the nitrification tank.

〔Example〕

Next, an embodiment of the present invention will be described.

In a two-stage embodiment of the present invention, each nitrifying species is filled with anthracite with an effective diameter of 0.6 fi and a uniformity coefficient of 1.4 or less, and raw sewage with an average total nitrogen concentration of 30 μ/l is charged in one stage.
Water was passed through at 0%/d. Table 1 shows the total nitrogen removal rates of the present invention, the conventional high-print biological treatment method (Comparative Example 1) shown in Figure 2, and the conventional two-stage circulation nitrification-denitrification method (Comparative Example 2) shown in Figure 3. , various treatment times and equipment volume ratios are shown. The treatment time is the value obtained by dividing the equipment volume by the amount of raw sewage water, and the equipment volume ratio is the initial settling tank, aeration tank, and final settling tank of the standard activated sludge method. This is the ratio when the total volume of the settling tank is set to 100.

In Comparative Example 1, the device volume ratio is small, but the total nitrogen removal rate is low, and in Comparative Example 2, the total nitrogen removal rate is high, but
The device volume ratio has increased. However, according to the present invention, it was possible to simultaneously achieve both effects that were not available in the past: a high total nitrogen removal rate and a small device volume ratio.

Table 1 [Effects of the Invention] As described above, according to the present invention, it is possible to perform stable nitrogen removal with a high nitrogen removal rate without using chemicals, and the installation space is saved due to the small volume. Where space is limited,
It also has extremely significant effects when applied to treatment facilities with covered structures and when modifying existing activated sludge equipment.

[Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram showing one embodiment of the present invention, and the second
3 and 3 are system explanatory diagrams showing conventional embodiments, respectively. 1... First settling tank, 2... Anaerobic tank, 3,13.15
...Denitrification tank, 4,14.16,24.26...Nitrification tank, 5...Final sedimentation tank, 6...Rotating disk.

Claims (4)

[Claims] (1) A biological nitrogen removal process in which a denitrification process is followed by a nitrification process is installed in series, and wastewater is distributed to each denitrification process, and the wastewater is distributed in the first denitrification process. The activated sludge returned to the sludge and the nitrification liquid circulated from the nitrification process of the stage were mixed and subjected to denitrification treatment, and then led to the nitrification process of the stage to undergo BOD oxidation and nitrification treatment. A part of the nitrification liquid is circulated to the denitrification process in the previous stage, while the remaining nitrification liquid is flowed out, and in each subsequent denitrification process, the nitrification liquid flowing out from the previous stage nitrification process and the nitrification liquid discharged from the previous stage nitrification process are mixed with the distributed wastewater. After denitrification treatment is performed by mixing the nitrified liquid circulated from the nitrification process in the stage, it is led to the nitrification process in the stage where BOD oxidation and nitrification treatment are performed, and a part of the obtained nitrified liquid is transferred to the nitrification process in the stage. While circulating in the denitrification process,
In the multi-stage circulating nitrification-denitrification method, in which the remaining nitrification liquid is discharged, the nitrification liquid flowing out from the final stage nitrification process is separated into solid and liquid, and a part of the separated activated sludge is returned to the first stage denitrification process. A method for removing nitrogen from wastewater, characterized in that in each step of the nitrification step, a carrier on which nitrifying bacteria are immobilized is brought into contact with an activated sludge mixture derived from the denitrification step of the step under aerobic conditions. (2) The carrier on which the nitrifying bacteria are immobilized is one in which the nitrifying bacteria are adhered and immobilized to the surface of solid particles or inside the pores of a porous solid particle, or the carrier is one in which the nitrifying bacteria are comprehensively immobilized. method of removing nitrogen from wastewater. (3) In an activated sludge treatment device that mainly consists of an aeration tank and a subsequent settling tank, the aeration tank is sequentially moved from the inlet side of the sewage to a denitrification unit that only stirs the sewage, and a nitrification unit that contains a carrier with immobilized nitrifying bacteria. The sewage system is characterized in that the sections are alternately divided into a plurality of stages and communicated with each other, and a path is provided for distributing and introducing sewage into each of the denitrification sections, and a path is provided for circulating nitrified liquid from each subsequent nitrification section. A device that removes nitrogen from (4) The carrier on which the nitrifying bacteria are immobilized is one in which nitrifying bacteria are adhered and immobilized on the surface of a solid particle or inside the pores of a porous solid particle, or one in which nitrifying bacteria are comprehensively immobilized. A device that removes nitrogen from wastewater.