JPH02139094A - Method and equipment for removing nitrogen from sewage - Google Patents

Abstract

PURPOSE:To make installation area comparatively small and also to obtain a preferable biological denitrifying process at small volume without lowering denitrification efficiency by mixing sewage with both the circulated nitrification liquid and the returned activated sludge to perform denitrification and thereafter performing oxidations of BOD and then performing nitrification treatment. CONSTITUTION:Raw water is agitated and mixed with both the nitrification liquid circulated from a nitrification tank 12 and the activated sludge returned from a final sedimentation basin 4 in a denitrification tank 2 to perform denitrification. The discharged water is introduced into a BOD oxidation tank 11 and aeration is performed in the existence of activated sludge and BOD remaining in water is chiefly oxidized. The solid particle group with nitrification bacterial stuck thereon is housed in a nitrification vessel 12 and this solid particle is brought into contact with the discharged water sent from the BOD oxidation tank 11 under the aerobic conditions to perform nitrification treatment. Since large amounts of nitrification bacteria are held on the solid particle group having the large surface area, nitrification treatment is extremely efficiently performed even in a miniature vessel.

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 is known in which the capacity of the denitrification tank is increased without feeding anything.

An improved version of these denitrification methods is the cyclic nitrification and denitrification method, which uses organic matter in wastewater as a hydrogen donor.
In this method, as shown in Figure 2, a primary sedimentation tank 1, a denitrification tank 2, a BOD oxidation/nitrification tank 3, and a final sedimentation tank 4 are arranged in series, and coarse solids in raw water are removed in the primary sedimentation tank 1. The activated sludge is returned to the denitrification tank 2 from the final settling tank 4, and a part of the nitrification liquid flowing out from the BOD oxidation/nitrification tank 3 is circulated to remove the raw material flowing into the denitrification tank 2. Denitrification is performed using organic matter in water as a hydrogen donor. Furthermore, the Barnard method is widely known in which a second denitrification tank for adding methanol or the like is provided after the BOD oxidation/nitrification tank 3 in this circulating nitrification/denitrification method.

In addition, as shown in FIG. 3, an anaerobic tank 5 is provided before the denitrification [2] of the circulating nitrification and denitrification method to biologically remove the phosphorus component as well as the nitrogen component in the wastewater. ,0
In addition, there is also a hybrid biological treatment method (activated sludge method with rotating disk) in which a rotating disk is installed in the BOD oxidation/nitrification tank 3 in this ^80 method, and a large number of nitrifying bacteria are attached to the rotating disk. Are known.

[Problem to be solved by the invention]

However, methods that add methanol, etc. to the denitrification tank, including the conventional Pernat method, require high chemical costs, and the nitrification/endogenous denitrification method requires a very large denitrification tank capacity, making it difficult to use in large-scale urban areas. It was not suitable for sewage treatment plants.

In addition, the circulating nitrification-denitrification method (see Figure 2) and the IhO method (
(see Figure 3), the capacity of the BOD oxidation/nitrification tank 3 was large, requiring a considerably larger capacity and installation area than the aeration tank of the standard activated sludge method. This is because the growth rate of nitrifying bacteria is extremely slow, and in order to retain nitrifying bacteria in activated sludge even in winter, it becomes necessary to lengthen the sludge retention time, and as a result, a large amount of capacity and site area is required. This is what it was supposed to be.

Furthermore, since the above-mentioned hybrid biological treatment method also uses a rotating disk, it requires space to support the weight of the rotating disk, installation space for a drive motor, and a drive source, and there is also a need to provide space at the top of the tank to take out the disk. Therefore, when covering the top of a sewage treatment facility and using the upper part of the cover effectively, there was a problem that the sewage treatment facility had to be made very deep.

The present invention solves the above-mentioned conventional problems, has a smaller capacity than the conventional one, has a relatively small installation area, does not reduce denitrification efficiency, and is suitable for use in covered sewage treatment facilities. The present invention aims to provide a denitrification process and a device that is a simple modification of an existing standard activated sludge treatment device.

[Means to solve the problem]

The present invention introduces wastewater into a denitrification process, mixes the recycled nitrification liquid and returned activated sludge to perform denitrification, and then performs BO
Leading to the Df12 conversion step, mainly oxidizing BOD,
Next, it is led to the nitrification process, where it is brought into contact with the solid particles to which nitrifying bacteria have adhered, under aerobic conditions, and nitrified. A part of the obtained nitrified liquid is circulated to the denitrification process, while the remainder is used as a solid liquid. This method of removing nitrogen from wastewater is characterized in that the activated sludge is separated and a part of the separated activated sludge is returned to the denitrification process.

In addition, the present invention provides a standard activated sludge treatment device mainly consisting of an aeration tank and a subsequent settling tank, in which the aeration tank is sequentially equipped with a denitrification tank that performs only agitation from the wastewater inlet, a BOD oxidation tank that performs aeration, and a nitrification tank. The nitrification tank is divided and communicated with a nitrification tank containing a group of solid particles to which bacteria are attached, and a circulation flow path circulates a part of the nitrification liquid flowing out into the nitrification tank to the denitrification tank, and the remainder of the nitrification liquid is connected to the sedimentation tank. This is a device for removing nitrogen from wastewater, which is characterized by being equipped with a flow path that leads to nitrogen.

[For production]

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

First, raw water is first led to a settling tank 1 to separate coarse solids in the raw water, and then led to a denitrification tank 2. In the denitrification tank 2, the raw water is stirred and mixed with a nitrification liquid circulated from the nitrification tank 12, which will be described later, and activated sludge returned from the final settling tank 4, and BOD in the raw water is used as a hydrogen donor necessary for denitrification. Then, denitrification is performed, and the effluent water is led to the BOD oxidation tank 11.

In the BOD oxidation tank 11, aeration is performed in the presence of activated sludge, and BOD mainly remaining in the water is oxidized and then introduced to the nitrification tank 12.

The nitrification tank 12 contains sand to which nitrifying bacteria have adhered, anthracite 1 granular activated carbon, plastic particles, and other solid particles, and the solid particles and the outflow water from the BOD oxidation tank 11 are aerobically heated. Nitrification is carried out by contacting the particles under certain conditions, and since large amounts of nitrifying bacteria are retained in solid particles with a large surface area, nitrification can be carried out extremely efficiently even in small tanks.

The solid particle group in the nitrification tank 12 may be a fixed layer, but
Since clogging is likely to occur during water flow, it is preferable to fluidize the solid particles to form a fluidized bed, and further fluidize the solid particles by upward flowing water and aeration from the bottom.
A solid-liquid-gas three-phase fluidized bed system is most preferable.

Thus, in the nitrification tank 12, ammonia nitrogen in the outflow water from the BOD oxidation tank 11 is nitrified into nitrite nitrogen and nitrate nitrogen by the action of the nitrifying bacteria on the solid particles, and then flows out. A part of this outflowing nitrification liquid is circulated to the denitrification tank 2 as described above, and the nitrite nitrogen and nitrate nitrogen in the liquid are converted into nitrogen gas by denitrifying bacteria, with BOD in the raw water being used as a hydrogen donor. is reduced to and removed. Also,
The remainder of the nitrified liquid flowing out from the nitrification tank 12 is led to the final settling tank 4 where it is separated into solid and liquid, and a part of the separated activated sludge is returned to the denitrification tank 2 as described above, and the separated water is used as treated water. be led outside the system.

Conventionally, in the circulating nitrification-denitrification method and the A,0 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 solid particles, so they are not drawn out of the system, and the nitrifying bacteria remain stable in the nitrification tank 12 even in winter. Nitrification takes place. Therefore, in BOD oxidation fff, 11, nitrification does not necessarily need to be performed, and oxidation of BOD alone is sufficient for treatment.

Therefore, the tank capacity from the initial settling tank 1 to the final settling tank 4 may be about the same as the tank capacity of the standard activated sludge method, and in the nitrifying tank 12, nitrifying bacteria are retained at a high concentration by the solid particles. As a result, the residence time is shortened, and the overall capacity and installation area are smaller than those of the conventional circulating nitrification and denitrification method and the A,0 method. Further, the nitrification tank 12 does not require a large space for maintenance at the top of the tank.

As described above, the present invention improves denitrification efficiency with a small-capacity device without requiring any special operations, and only agitates the aeration tank of an existing standard activated sludge treatment device from the inlet of sewage. a denitrification tank 2 that performs aeration, a BODM tank 1 that performs aeration, and a nitrification tank 12 that accommodates solid particles to which oxidized bacteria have adhered.
The existing standard activated sludge treatment equipment was secretly modified by connecting the nitrification tank 12 with a nitrified liquid circulation pipe 13 to the denitrification tank 2 and an outflow pipe 14 to the final settling tank 4. At least the same denitrification efficiency can be obtained without changing the overall capacity or footprint.

〔Example〕

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

In the nitrogen removal system shown in FIG. 1, the nitrification tank 12 is filled with silica sand with an effective diameter of 0.3fi and a uniformity coefficient of 1.5 or less,
Average total nitrogen concentration 30m+r/j! raw sewage was passed through. The circulation rate of the nitrifying solution was 150% of the amount of raw sewage water. Table 1 shows the nitrogen removal system (invention) shown in Figure 1.
The total nitrogen removal rate, various treatment times, and device volume ratios are shown for the conventional circulating nitrification-denitrification method (comparative example) shown in FIG. In addition, the treatment time is the value obtained by dividing the equipment volume by the raw sewage water volume, and the equipment volume ratio is the sum of the volumes of the initial settling tank, aeration tank, and final settling tank of the standard activated sludge method as 100. It is a ratio.

According to the present invention, due to the circulating principle, the total nitrogen removal rate was comparable to that of the conventional circulating nitrification-denitrification method, but the device volume was reduced.

The following margins are Table 1. Figure 1 is a system explanatory diagram showing one embodiment of the present invention.
3 and 3 are system explanatory diagrams showing conventional embodiments, respectively.

1... First sedimentation tank, 2... Denitrification tank, 3... BOD
Oxidation/nitrification tank, 4... Final sedimentation tank, 5... Anaerobic tank,
11... BOD oxidation tank, 12... Nitrification tank, 13...
・Nitrification liquid circulation piping, 14...Outflow piping.

〔Effect of the invention〕

As described above, according to the present invention, stable nitrogen removal is possible without significantly increasing the scale of the equipment.
Even in places where site area is limited, application to treatment facilities with covered structures, modification of existing standard activated sludge treatment equipment, etc.
This method has effects that cannot be expected with conventional methods.

[Brief explanation of the drawing]

Claims (2)

[Claims] (1) Sewage is led to the denitrification process, and denitrification is performed by mixing the recycled nitrification liquid and returned activated sludge, and then led to the BOD oxidation process to mainly oxidize BOD, and then to the nitrification process. A part of the obtained nitrified liquid is circulated to the denitrification process, while the remaining part is separated into solid and liquid. A method for removing nitrogen from wastewater, comprising returning a part of the activated sludge to the denitrification process. (2) In a standard activated sludge treatment system that mainly consists of an aeration tank and a subsequent settling tank, the aeration tank is sequentially moved from the inlet of sewage to a denitrification tank that only performs agitation, a BOD oxidation tank that performs aeration, and nitrifying bacteria. A circulation flow path which is divided and communicated with a nitrification tank containing a group of solid particles, and which circulates a part of the nitrification liquid flowing into the nitrification tank to the denitrification tank, and a flow path which leads the remainder of the nitrification liquid to the precipitation tank. A device for removing nitrogen from wastewater, characterized in that it is equipped with a.