JPS5923878B2 - Nitrogen-containing wastewater treatment method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for treating nitrogen-containing wastewater, and more particularly to a method and apparatus for nitrification and denitrification treatment by passing wastewater through a fluidized bed using solid granular carriers to which microorganisms are attached.

Conventionally, known biological treatment methods for nitrogen-containing wastewater include a fluidized bed method, a suspended sludge method, and a contact circulation method.

Among these, the fluidized bed method has a much better ability to retain microorganisms per unit volume than other methods.

Therefore, the fluidized bed system is being put into practical use because it can increase the nitrogen treatment capacity per unit volume (hereinafter referred to as nitrogen load).

A nitrogen-containing wastewater treatment device using a fluidized bed system mainly includes a nitrification tank and a denitrification tank.

In the nitrification tank, the above wastewater is passed through a fluidized bed of solid granular carriers (hereinafter referred to as an aerobic fluidized bed) on which nitrifying bacteria are attached and grown, and a nitrification reaction is carried out.

In the denitrification tank, the denitrification reaction is performed by passing the wastewater after the nitrification process through a fluidized bed of solid granular carriers (hereinafter referred to as an anaerobic fluidized bed) on which denitrifying bacteria are attached and grown.

However, in such a configuration, since the nitrification tank and the denitrification tank are operated functionally independently, the nitrification tank and the denitrification tank have a processing capacity only within a predetermined range.

For this reason, changes in the properties of wastewater cannot be easily followed.If the form of nitrogen compounds in wastewater changes significantly, either the nitrification tank or denitrification tank will be overloaded and sufficient treatment performance will not be maintained. become unable.

In other words, in the conventional technology in which the nitrification tank and the denitrification tank are operated independently, it is difficult to follow changes in the form of nitrogen compounds in wastewater, and the treatment capacity of each tank cannot be fully utilized. There were drawbacks.

In addition, from the perspective of equipment management, since there are two independent tanks, a nitrification tank and a denitrification tank, twice as much effort is required as in the case of one tank, such as adjusting the flow rate in the tank and the upper interface of the carrier with attached organisms. Become.

Furthermore, if you try to reduce the amount of neutralizer by passing circulating water alternately from the nitrification tank to the denitrification tank and from the denitrification tank to the nitrification tank,
Balancing the flow rate becomes difficult.

In terms of equipment costs, pumps, flow meters, nitrification tanks, denitrification tanks,
Since it requires many components such as the circulating water balance device, it cannot help but be expensive.

Previously, the present inventors proposed a treatment method in which the nitrification step and the denitrification step are sequentially performed in a continuous fluidized bed in the same tank.

However, with this method, the processing capacity of the denitrification layer decreases due to the inflow of dissolved oxygen from the nitrification tank, and conversely, dissolved oxygen is limited when introduced into the nitrification layer, suppressing its outflow to the denitrification layer. Otherwise, the ability of the nitrification layer decreases.

In addition, since water is passed to the nitrification layer after dissolving oxygen in the pre-aeration tank, nitrification must be carried out using only the oxygen present at the time of inflow. As a result, the height of the nitrification layer is limited and the width is wide. The drawback was that the equipment had to be changed and the circulation flow rate had to be very high.

Furthermore, there is an intermediate layer between the nitrification layer and the denitrification layer, where there is too little dissolved oxygen for nitrification and a dead space where dissolved oxygen causes processing inhibition for denitrification. become.

Furthermore, because the apparent specific gravity of the carriers with bacteria attached is smaller in the nitrification layer than in the denitrification layer, the carriers with nitrifying bacteria in the nitrification layer flow into and mix with the upper denitrification layer, which tends to cause a decrease in the performance of each process. .

Generally, the larger the surface area of the carrier, the more microorganisms will adhere to it, so the smaller the particle size of the carrier, the better.However, since the nitrification layer is at the bottom, carrier particles that are larger than the denitrification layer at the top must be used. First, there is a limit to the amount of nitrifying bacteria that can adhere, and it takes quite a long time for them to acclimate.

In addition, a single treatment tank is filled with solid particles, treated water and circulating water are introduced from the bottom, and oxygen-containing gas is introduced only into the top of the treatment tank, making the top part an aerobic part and the bottom part an anaerobic part. There are also known methods of processing.

However, this method has the problem that the water introduced from the lower part contains oxygen gas, which tends to make the anaerobic section incomplete, and that it is not possible to change the treatment conditions in response to changes in the quality of the treated water.

An object of the present invention is to eliminate the drawbacks of the prior art described above, to be able to easily follow changes in the form of nitrogen compounds in wastewater, and to be able to easily follow changes in the form of nitrogen compounds in wastewater, and to reduce the processing capacity of the denitrification process due to the inflow of dissolved oxygen or the lack of dissolved oxygen. It eliminates the reduction in processing capacity of the nitrification process, the height of the nitrification layer is not limited, there is no dead space in the middle layer, and the reduction in nitrification capacity due to the outflow of nitrifying bacteria is eliminated.
To provide a method for treating nitrogen-containing wastewater that facilitates the acclimatization of nitrifying bacteria, and a compact device with a small installation area, easy maintenance, and low cost for implementing this method.

According to the invention, this object is achieved by making the lower layer of the tank an anaerobic fluidized bed for denitrification treatment and the upper layer of the tank an aerobic fluidized bed for nitrification treatment.

In order to form an aerobic fluidized bed in the upper layer of the tank, an aeration device is installed, but the location of the aeration device is arranged so that it can be changed. It is advantageous to vary the proportion of the aerobic fluidized bed section to accommodate variations in the quality of the raw wastewater.

In addition, in order to introduce treated liquid that contains almost no dissolved oxygen into the anaerobic fluidized bed section, a deoxidizing tank is installed, and when raw wastewater and circulating water contain excess oxygen, they are passed through the deoxidizing tank in advance. is advantageous.

The carrier used to form the fluidized bed preferably has a relatively wide fluidization tendency.

For example, when filtered river sand with the same specific gravity is used as a carrier,
Use one with a wide particle size distribution.

That is, due to the difference in particle size, in a fluidized bed, large particle size carriers form an anaerobic fluidized bed in the lower part of the tank due to the classification effect, and small particle size carriers form an aerobic fluidized bed in the upper part of the tank. Each forms in a stable state.

In this case, if the particle size of the carrier is composed of two types of carriers, for example, 0.8 to 0.6 mm and 0.4 to 2 mm, the anaerobic and aerobic fluidized beds can be separated. The interface can be made even clearer.

As the carrier, not only those with the same specific gravity and different diameters as described above, but also carriers with different specific gravity and the same diameter, or carriers with different specific gravity and different diameters may be used.

The material of the carrier may be R-applied sand, activated carbon, coal particles, volcanic ash, various granular plastics, etc.

Next, the present invention will be explained in detail based on the drawings.

The drawing is a system diagram showing an embodiment of the loading method of the present invention.

In the drawing, nitrogen-containing wastewater is introduced into the upper part of a deoxidizing tank 1 through a pipe 2, and circulating treated water is introduced through a pipe 3.

In the lower part of the deoxidizing tank, the flow rate of a gas that contains almost no oxygen and is harmless to the human body, such as nitrogen, is controlled by a flow control valve 5 provided in the pipe 4, and then deoxidized via an aeration device 6. Diffusion of air into the tank as fine bubbles.

The nitrogen-containing wastewater and circulating treated water introduced into the deoxidizing tank 1 are allowed to remain in the deoxidizing tank 1 while descending in the deoxidizing tank while being given sufficient residence time. removes oxygen.

The deoxidizing tank 1 is required only when there is an excess of oxygen in the mixed water, and is not normally required.

The mixed water drawn out from the bottom of the deoxidizing tank 1 by the circulation pump 7 is introduced into the bottom of the biological treatment tank 10 via a pipe 8.

Note that a flow meter 9 and a flow rate regulating valve 9a are provided in the middle of the pipe line 8, and the amount of mixed water is adjusted so as to be suitable for fluidizing the carrier in the biological treatment tank 10.

The mixed water introduced into the biological treatment tank fluidizes the carrier supported by the porous partition plate 11 to form a fluidized bed.

As mentioned above, a carrier with a relatively wide fluidization tendency is used as the carrier filled in the biological treatment tank, and an anaerobic fluidized bed 12 is formed in the lower part of the tank, and an aerobic bed 12 is formed in the upper part of the tank. A fluidized bed 13 is formed.

In the region of the anaerobic fluidized bed 12, nitrate nitrogen contained in the mixed water adheres to the surface of the carrier, and denitrification processing is performed in which it becomes nitrogen gas through the biological reduction action of the grown denitrifying bacteria.

In the area of the aerobic fluidized bed 13, oxygen is supplied by an oxygen or air diffuser 14, and ammonia nitrogen is attached to the surface of the carrier, and the nitrification process is carried out to become nitrate nitrogen due to the oxidizing action of the grown nitrifying bacteria. It will be done.

Note that there is still a lot of ammonia nitrogen in the treated water after nitrification (
If it remains, it is considered that the nitrification process is insufficient, so the position of the aeration device 14 is moved downward to expand the area of the aerobic fluidized bed.

In other words, by moving the position of the aeration device 14 according to the properties of the raw wastewater, the ratio of the denitrification main part to the nitrification main part can be adjusted to the optimum state, and the biological treatment tank of the present invention is extremely effective. It has flexible functions.

In addition, in the nitrification treatment in the aerobic fluidized bed,
The pH of the mixed water shifts to the acidic side due to biological oxidation.

For this reason, a pH meter electrode 15 is attached to the top of the fluidized bed so that the pH of the mixed water at this point is at least 6.
An alkaline solution is injected into the middle of the pipe line 8.

Furthermore, when there are few organic substances coexisting in the raw wastewater, a hydrogen donor such as methanol, which is necessary for the biological reduction action of denitrifying bacteria, is injected into the pipe line 8.

・Gas such as nitrogen generated by the denitrification process in the anaerobic fluidized bed 12 is collected in bubbles at the top of the tank along with the remaining air or oxygen gas diffused in the aerobic fluidized bed 13 and generated gas. It is collected by the cylinder 16 and released into the atmosphere through the gas vent pipe 17.

Most of the treated water that has reached the top of the biological treatment tank 10 is returned to the upper part of the deoxidizing tank 1 via the pipe 3 as circulating treated water.

The remaining treated water, which is approximately equal to the introduced amount of nitrogen-containing wastewater to be treated, is discharged out of the apparatus via line 18.

The amount of circulating treatment water is determined by taking into account the amount of nitrogen-containing wastewater to be treated, the number of circulations required based on its properties, and the flow rate necessary to properly form a fluidized bed in the biological treatment tank.
The optimum flow rate is selected.

In addition, since the treated water discharged outside the apparatus contains bacterial cells detached from the carrier as surplus sludge, after separating this surplus sludge, the treated water is discharged or used for other purposes.

As mentioned above, the present invention has an anaerobic fluidized bed for denitrification in the lower layer of the biological treatment tank, an aerobic fluidized bed for nitrification in the upper layer of the tank, and a movable air diffuser for oxygen supply. This makes it possible to easily follow changes in the form of nitrogen compounds in wastewater, and it also has the effect of simplifying and downsizing the equipment, contributing to environmental conservation technology. It is something.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

Example Using the apparatus shown in the drawings, the particle size of the carrier was 0, 8 to 0.
．． A treatment experiment was conducted under the following conditions using 6 mm and 0.4 to 0.2 mm sands.

Ammonia nitrogen 200% as nitrogen-containing wastewater to be treated
ammonium sulfate solution containing ppm, using oxygen gas as the oxygen supply gas and methanol as the hydrogen donor,
Nitrogen load 4.0kg-N/m”・d (4.0kg-N/m”・d in the denitrification treatment section
．． 0kg-N/rtl-d, 4.0kg- in the nitrification processing section
N/m'·d), the ammonia nitrogen in the treated water was 2 ppm or less, the nitrate nitrogen was 3 ppm or less, and a total nitrogen removal rate of 97% or more was obtained.

[Brief explanation of drawings]

The drawing is a system diagram showing one embodiment of the device of the present invention. Explanation of symbols, 1... Oxygen removal tank, 10...
・Biological treatment tank, 12... Anaerobic fluidized bed, 13.
...Aerobic fluidized bed, 14...Aeration device.

Claims (1)

[Scope of Claims] 1. A process in which nitrogen-containing wastewater is introduced from the bottom of a tank, the lower layer of this tank is treated as an anaerobic fluidized bed for denitrification, and the upper layer of the tank is treated as an aerobic fluidized bed for nitrification. In the method, the nitrogen-containing wastewater is a deoxygenated wastewater of raw nitrogen-containing wastewater and nitrification-treated water, and the fluidized bed portions of the anaerobic fluidized bed and the aerobic fluidized bed are divided according to the water quality of the wastewater. A method for treating nitrogen-containing wastewater, characterized by changing the ratio. 2. A biological treatment tank containing solid granular fluidized carriers with attached microorganisms, an oxygen-containing gas diffuser installed in the tank so as to be able to move up and down, and wastewater introduced from the bottom of the treatment tank. A nitrogen-containing wastewater treatment device consisting of a deoxidizing tank that removes dissolved oxygen.