JP3095620B2 - Biological nitrogen removal equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological nitrogen removing apparatus for treating raw water containing organic matter such as sewage and industrial wastewater.

[0002]

2. Description of the Related Art In a conventional biological nitrogen removing apparatus,
Raw water containing organic matter is first introduced into a denitrification tank, and then introduced into a nitrification tank. Further, a part of the nitrification tank mixture flowing out of the nitrification tank is circulated and returned to the denitrification tank as a nitrification liquid, and the remaining is discharged to a final sedimentation tank for separating excess sludge. The denitrification tank uses the BOD component contained in the incoming raw water as a hydrogen donor for the denitrification reaction to denitrify the oxidized nitrogen brought into the denitrification tank along with the nitrification liquid circulation. In the nitrification tank, oxidative decomposition of residual BOD components not removed in the denitrification tank and nitrification of ammonia nitrogen are performed. In this process, nitrogen is removed by nitrification and denitrification using suspended activated sludge, and this method is a conventional general nitrogen removal method. In order to accelerate the denitrification treatment, a fixed-bed type denitrification tank filled with a contact material may be used.

[0003]

As described above, in the nitrification tank, oxidative decomposition of residual BOD components not removed in the denitrification tank and nitrification of ammoniacal nitrogen are performed. But,
Of the energy required to biologically denitrify raw water such as sewage, the energy required for aeration is high, and from the viewpoint of energy saving, it is required to reduce the amount of air blown into a nitrification tank. For this reason, in the nitrification tank, only nitrification of ammonia nitrogen is performed, and the BOD component is prevented from flowing into the nitrification tank from the denitrification tank.
It is required that the energy required for the oxidation of the BOD component be made unnecessary and the amount of air blown be reduced.

On the other hand, the amount of soluble BOD contained in raw water such as sewage is small compared to the amount of oxidized nitrogen flowing from a nitrification tank, and there are many cases where a sufficient denitrification treatment cannot be performed.
For this reason, it is required to supply a soluble BOD such as methanol to the denitrification tank as a hydrogen donor which is easily used for the denitrification reaction.

The present invention has been made to solve the above-mentioned problems, and the BOD is reduced by flowing only BOD in a denitrification tank in an amount corresponding to the denitrification treatment of oxidized nitrogen such as nitrate nitrogen and nitrite nitrogen. Sufficiently denitrification treatment by making it almost completely consumed in the denitrification reaction so that it is not brought in.Also, acid fermentation of suspended substances is performed in the denitrification tank, and the generated hydrogen donor is used for denitrification treatment. It is an object of the present invention to provide a biological nitrogen removing apparatus capable of performing the above.

[0006]

In order to solve the above-mentioned problems, a biological nitrogen removing apparatus according to the present invention comprises a denitrification tank into which raw water containing organic substances flows, and a mixed liquid from the denitrification tank of the denitrification tank. In a biological nitrogen removal device comprising a nitrification tank, a nitrification liquid circulation flow path for circulating the nitrification liquid in the nitrification tank to the denitrification tank, and a nitrification tank diffuser disposed in the nitrification tank, a denitrifying bacteria-immobilized carrier. The denitrification tank is provided with a denitrifying bacterium-immobilized carrier filling zone that captures and removes suspended substances in raw water flowing into the denitrification tank. A sludge hopper is provided at the bottom of the denitrification tank to communicate with the lower position of the immobilization carrier filling zone, and a sludge hopper for depositing suspended matter trapped and removed in the denitrification bacteria immobilization carrier filling zone is provided at the bottom of the denitrification tank. Is provided.

[0007] Further, the denitrification tank is provided with a denitrification tank air diffuser below the denitrification bacteria-immobilized carrier filling zone. Further, a solid-liquid separator for guiding the separated liquid after the raw water is subjected to the solid-liquid separation to the denitrification tank is provided as an upstream process of the denitrification tank.

[0008]

According to the above configuration, in the denitrification tank, the raw water flowing into the denitrification tank from the raw water introduction passage reaches the upper region of the denitrification tank through the denitrifying bacteria-immobilized carrier filling zone, and then flows out to the nitrification tank. Meanwhile, nitrification liquid containing nitrate nitrogen or nitrite nitrogen is circulated and returned from the nitrification tank through the nitrification liquid circulation flow path.

[0009] At this time, the denitrifying bacteria-immobilized carrier filling zone functions as a filter bed, and suspended matter in the raw water flowing into the denitrification tank is filled with the denitrifying bacteria-immobilized carrier when passing through the denitrifying bacteria-immobilized carrier filling zone. After being trapped and removed by the biofilm on the surface, they settle in the sludge hopper. For this reason, the suspended matter hardly flows into the nitrification tank in the subsequent stage, and the amount of oxygen required for oxidizing the BOD derived from the suspended matter can be reduced in the nitrification tank.

In the denitrification tank, the denitrifying bacterium denitrifies nitrate nitrogen or nitrite nitrogen using the BOD in the raw water as a hydrogen donor, and the denitrifier is immobilized in the denitrifier immobilization carrier filling zone. Since it is immobilized on the carrier at a high concentration,
The denitrification reaction is performed at a higher speed than in the case of using suspended activated sludge. As a result, the size of the denitrification tank can be reduced, and the area required for the denitrification tank can be reduced.

Further, in the sludge hopper, the accumulated sediment undergoes acid fermentation in the absence of dissolved oxygen, and low-molecular-weight soluble BO easily used by denitrifying bacteria as a hydrogen donor.
Generate D. At this time, the denitrification tank is under an oxygen-deficient condition, and the acid fermentation proceeds in a state where the value of the oxidation-reduction potential becomes a negative value, but when the negative value of the oxidation-reduction potential further increases, the acid fermentation starts. A methanation reaction using the organic acid as the final product, hydrogen and carbon dioxide as intermediates as substrates occurs. For this reason, methane fermentation is performed by supplying air or an oxygen-containing gas to the sedimentary sludge from the hopper air diffuser, and reducing the negative value of the oxidation-reduction potential in the sedimentation sludge to a value suitable for acid fermentation. It suppresses and promotes the production of organic acids that are hydrogen donors in the denitrification reaction. Since the hydrogen donor generated by this acid fermentation contributes to the denitrification treatment in the denitrification tank, the BO which is soluble in raw water
Even when D is small, the denitrification treatment can be sufficiently performed.

Further, by periodically supplying air or an oxygen-containing gas to the denitrifying bacteria-immobilized carrier filling zone through a denitrification tank diffuser, the surface of the denitrifying bacteria-immobilized carrier or the denitrifying bacteria-immobilized carrier can be removed. In addition to being able to wash the space, the sludge excessively attached to the denitrifying bacteria-immobilized carrier is peeled off, deposited and stored in the sludge hopper at the bottom of the denitrification tank, and can be subjected to acid fermentation.

Further, in the solid-liquid separation apparatus, in the acid fermentation in the denitrification tank, organic matter other than an amount sufficient to generate a hydrogen donor necessary for the denitrification reaction is removed.
The load of suspended solids to be captured and removed at the biofilm portion on the surface of the denitrifying bacteria-immobilized carrier can be reduced, clogging in the denitrifying bacteria-immobilized carrier loading zone can be suppressed, and the denitrifying bacteria-immobilized carrier can be diffused. The number of times of cleaning can be reduced.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. Raw water 3 such as sewage flows into a solid-liquid separation device 2 installed as an upstream process of the denitrification tank 1, and the solid-liquid separation device 2 separates solid-liquid from the raw water 3 and then introduces raw water formed in a pipeline. The separation liquid is guided to the denitrification tank 1 through the flow path 4.

A denitrification tank-fixed carrier filling zone 5 is provided inside the denitrification tank 1 into which the separated liquid of the raw water 3 flows, and a raw water introduction flow path 4 is provided below the denitrification bacteria-fixed carrier filling zone 5 in the denitrification tank. It communicates with 1. The denitrifying bacteria-immobilized carrier filling zone 5 is filled with a denitrifying bacteria-immobilized carrier and captures and removes suspended substances in the raw water 3 flowing into the denitrification tank 1. When the denitrifying bacteria-immobilized carrier has a specific gravity larger than that of water, the denitrifying bacteria-immobilized carrier is supported by a mesh material or the like so that the denitrifying bacteria-immobilized carrier does not fall at the bottom of the filling zone 5. When the denitrifying bacteria-immobilized carrier having a low specific gravity is to be filled, the denitrifying bacteria-immobilized carrier is held above the denitrifying bacteria-immobilized carrier loading zone 5 by a mesh material or the like so as not to flow out of the denitrification tank 1.

A sludge hopper 6 is provided at the bottom of the denitrification tank 1. The sludge hopper 6 is for depositing sediment in the denitrification tank 1 and suspended matter trapped and removed in the denitrifying bacteria immobilization carrier filling zone 5. It is. At the bottom of the sludge hopper 6, a sludge withdrawing flow path 6a composed of a pipeline is opened, and a sludge opening / closing valve 6b is interposed in the middle of the sludge withdrawing flow path 6a. A denitrification tank diffuser 7 is disposed below the denitrifying bacteria immobilization carrier filling zone 5, and a sludge hopper 6
Is provided with a hopper air diffuser 8. The sludge hopper section 6 is provided with an oxidation-reduction potentiometer (ORP) 9.

A nitrification tank 10 is provided downstream of the denitrification tank 1, and a mixed liquid of the denitrification tank 1 flows into the nitrification tank 10 through the communication flow path 1 a. A nitrifying bacteria-immobilized carrier 11 for supporting nitrifying bacteria is put in the nitrification tank 10, and a screen is arranged as a carrier separating device 10 a on one side of the nitrification tank 10. A downstream end of the carrier separation device 10a communicates with a base end of a nitrification liquid circulation flow path 12 which forms a conduit for circulating the nitrification liquid in the nitrification tank 10 to the denitrification tank 1. Below the denitrifying bacteria immobilization carrier filling zone 5, it communicates with the denitrification tank 1. Nitrification liquid circulation channel 12
A circulation pump 13 is interposed midway. In addition, a nitrification tank diffuser 14 is arranged inside the nitrification tank 10,
The denitrification tank diffuser 7, the hopper diffuser 8, and the nitrification tank diffuser 14 are connected to the blower 16 through air supply pipes 15a, 15b, 15c, respectively. Opening / closing valves 17a and 17b are interposed in the air supply pipes 15a and 15b, respectively. Further, an outflow channel 18 is opened in the nitrification tank 10 on the downstream side of the carrier separation device 11, and the outflow channel 18 communicates with the next system.

The operation of the above configuration will be described below. First, the acid fermentation described below refers to the process of converting high-molecular organic matter into low-molecular organic matter and the step of generating volatile organic acids (acetic acid, propionic acid, etc.) from low-molecular-weight organic matter. I do.

In this case, methane fermentation refers to a methane production reaction in which acetic acid, which is the final product of acid fermentation, is used as a substrate, or hydrogen and carbon dioxide, which are intermediate metabolites in acid fermentation, are used as substrates. Methane production reaction. (A) Solid-Liquid Separation Step In the solid-liquid separation device 2, the solid-liquid of the raw water 3 is settled and separated, and an appropriate amount of organic substances required for acid fermentation in the denitrification tank 1 to be described later is removed to remove the raw water 3. The separated liquid is guided to the denitrification tank 1 via the raw water introduction flow path 4. The appropriate amount of the organic matter is an amount sufficient to generate an amount of hydrogen donor necessary for the denitrification reaction in the denitrification tank 1 by acid fermentation. This is performed by controlling the amount of raw water 3 flowing into the solid-liquid separator 2 or controlling the amount of coagulant added when coagulating and settling in the solid-liquid separator 2.

As described above, the solid-liquid separator 2 removes the hydrogen donor necessary for the denitrification reaction in the denitrification tank 1 except for the organic matter in an amount sufficient to generate in the acid fermentation. It is possible to reduce the load of suspended solids to be captured and removed at the biofilm portion on the surface of the denitrifying bacteria-immobilized carrier in the denitrifying bacteria-immobilized carrier loading zone 5, prevent clogging, and reduce the amount of denitrifying bacteria-immobilized carrier by aeration. The number of times of washing can be reduced.

In the case where the amount of buoyant organic matter is not contained in the inflowing sewage sufficient to generate the amount of hydrogen donor necessary for the denitrification reaction in the denitrification tank 1 in the acid fermentation,
It is not necessary to set up a solid-liquid separation step, and it is necessary to add a soluble hydrogen donor such as methanol. (B) Denitrification Step In the denitrification tank 1, the separated liquid of the raw water 3 flowing into the denitrification tank 1 from the raw water introduction flow path 4 reaches the upper region of the denitrification tank 1 through the denitrifying bacteria immobilization carrier filling zone 5. After that, it flows out to the nitrification tank 10 through the communication flow path 1a. On the other hand, nitrification liquid containing nitrate nitrogen or nitrite nitrogen is circulated from the nitrification tank 10 through the nitrification liquid circulation flow path 12 by the circulation pump 13.

At this time, the denitrifying bacteria-immobilized carrier filling zone 5
Performs a filter bed function, so that suspended matter in the raw water 3 that has flowed into the denitrification tank 1 is captured by the biofilm on the surface of the denitrifying bacteria-immobilized carrier when passing through the denitrifying bacteria-immobilized carrier loading zone 5.
It is removed and deposited on the sludge hopper 6. For this reason, almost no organic suspended matter flows into the nitrification tank 10 in the downstream process, and the amount of oxygen required for oxidation of BOD derived from the suspended matter can be reduced in the nitrification tank 10.

Further, since the denitrifying bacteria are fixed to the denitrifying bacteria-immobilized carrier in the denitrifying bacteria-immobilized carrier-filling zone 5 at a high concentration, the denitrification reaction is performed at a higher speed than in the case where floating activated sludge is used. . As a result, the size of the denitrification tank 1 can be reduced, and the area required for the denitrification tank can be reduced.

On the other hand, in the sludge hopper 6, the accumulated sludge undergoes acid fermentation under oxygen-deficient conditions, and generates low molecular weight soluble BOD which can be easily used as a hydrogen donor by denitrifying bacteria. At this time, the acid fermentation proceeds in a state in which the value of the oxidation-reduction potential in the sediment sludge is a negative value, but subsequently, when the negative value of the oxidation-reduction potential further increases, the acid fermentation ends up with a final product. A methanation reaction using a certain organic acid, an intermediate product of hydrogen and carbon dioxide as a substrate occurs. For this reason, air or oxygen-containing gas supplied from the blower 16 through the air supply pipe 15a is diffused from the hopper diffuser 8 with respect to the accumulated sludge, and based on the value of the oxidation-reduction potential measured by the oxidation-reduction potentiometer 9. The opening / closing operation of the opening / closing valve 17a is automatically controlled, and the value of the oxidation-reduction potential (−) in the accumulated sludge measured by the oxidation-reduction potentiometer 9 is set to 0 to −25.
It is maintained at an appropriate value of 0 mV, more preferably -50 to -200 mV. This suppresses methane fermentation and promotes the production of organic acids that are hydrogen donors. Since the hydrogen donor generated by the acid fermentation contributes to the denitrification treatment in the denitrification tank 1, the denitrification treatment can be sufficiently performed even when the raw water 3 has a low soluble BOD.

The opening / closing valve 17b is opened and closed at an appropriate interval or at an appropriate time, and air or oxygen-containing gas supplied from the blower 16 through the air supply pipe 15b is supplied to the denitrification tank diffuser 7.
From the denitrifying bacteria-immobilized carrier filling zone 5.
The upward flow generated by the aeration diffuses the sludge that has excessively adhered to the surface of the denitrifying bacteria-immobilized carrier and between the denitrifying bacteria-immobilized carriers, and separates the separated sludge into the sludge hopper at the bottom of the denitrification tank 1. 6 can be deposited and stored for acid fermentation.

Further, excess sludge is drawn out of the system through the sludge withdrawing flow path 6a by periodically opening the sludge opening / closing valve 6b. (C) Nitrification Step In the nitrification tank 10, an air supply pipe 15 c is provided by a blower 16.
Air or oxygen-containing gas supplied through the nitrification tank is diffused from the nitrification tank diffuser 14, and sufficient oxygen is supplied to the nitrification tank mixture in the nitrification tank 10, and the nitrifying bacteria immobilized carrier 11 is aerated inside the nitrification tank 10. Randomly flow in.

In this state, the nitrifying bacteria are immobilized on the nitrifying bacteria-immobilizing carrier 11 at a high concentration, so that the nitrification reaction proceeds at a high speed. Further, the nitrifying bacteria-immobilized carrier 11 is held by the carrier separating device 10a without flowing out of the nitrification tank 10, and a high nitrification rate is stably maintained. At this time, since excess BOD does not flow into the nitrification tank due to the removing action by the denitrifying bacteria immobilization carrier filling zone 5, oxygen consumption required for oxidation of the BOD component does not occur, and the blown air amount is reduced to drive the blower 16. The required energy can be reduced.

Then, a part of the nitrification liquid after passing through the carrier separation device 10a is circulated to the denitrification tank 1 through the nitrification liquid circulation flow path 12.

[0029]

As described above, according to the present invention, suspended solids can be captured and removed by the denitrifying bacteria-immobilized carrier filling zone of the denitrification tank, so that the suspended substances hardly flow into the subsequent nitrification tank. Therefore, in the nitrification tank, the amount of oxygen consumed for oxidizing the organic matter derived from the suspended matter can be reduced. In addition, the accumulated sludge is acid-fermented in the sludge hopper to generate soluble BOD as a hydrogen donor that can be easily used for denitrification treatment. Processing can be performed.

The surface of the denitrifying bacteria-immobilized carrier and the space between the denitrifying bacteria-immobilized carriers are cleaned by periodically supplying air or an oxygen-containing gas to the denitrifying bacteria-immobilized carrier filling zone from below. Excessly adhered sludge can be peeled off, deposited and stored in a sludge hopper at the bottom of the denitrification tank, and used for acid fermentation.

Further, the solid-liquid separation device can reduce the load of suspended solids on the denitrifying bacteria-immobilized carrier loading zone in the subsequent denitrification tank, and can prevent the denitrifying bacteria-immobilized carrier loading zone from being excessively blocked.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a biological nitrogen removing apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Denitrification tank 2 Solid-liquid separation apparatus 3 Raw water 4 Raw water introduction flow path 5 Denitrifying bacteria immobilization carrier filling zone 6 Sludge hopper section 7 Denitrification tank diffuser 8 Hopper diffuser 9 Redox potentiometer (ORP) 10 Nitrification tank 12 Nitrification liquid circulation channel

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-232590 (JP, A) JP-A-60-193596 (JP, A) JP-A-4-61993 (JP, A) JP-A-6-193 114388 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 3/28-3/34

Claims (3)

(57) [Claims] 1. A denitrification tank into which raw water containing organic matter flows,
A biological system comprising: a nitrification tank into which a mixture of a denitrification tank flows into a denitrification tank, a nitrification liquid circulation flow path for circulating the nitrification liquid from the nitrification tank to the denitrification tank, and a nitrification tank diffuser arranged in the nitrification tank. In the nitrogen removal device, a denitrifying bacteria-immobilized carrier filling zone, which is filled with a denitrifying bacteria-immobilized carrier and captures and removes suspended substances in raw water flowing into the denitrification tank, is provided in the denitrifying tank, and a raw water introduction flow path and nitrification are provided. The liquid circulation channel is communicated with the lower part of the denitrification tank immobilization carrier filling zone of the denitrification tank, and at the bottom of the denitrification tank a sludge hopper for accumulating suspended matter trapped and removed in the denitrification bacteria immobilization carrier filling zone is provided. A biological nitrogen removing apparatus, wherein a sludge hopper is provided with a hopper air diffuser. 2. The biological nitrogen removal apparatus according to claim 1, wherein a denitrification tank air diffuser is provided below the denitrification tank immobilization carrier filling zone of the denitrification tank. 3. The biological method according to claim 1, wherein a solid-liquid separation device for guiding the separated liquid after solid-liquid separation of the raw water to the denitrification tank is provided as an upstream step of the denitrification tank. Nitrogen removal equipment.