JPH0423598B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a wastewater treatment method for biologically removing nitrogen contained in organic wastewater such as domestic wastewater, industrial wastewater, and human waste.

"Prior Art and its Problems" A cyclic denitrification method has recently attracted attention as a wastewater treatment method for biologically removing nitrogen contained in wastewater. This cyclic denitrification method is
This is a method in which a denitrification process is provided before the nitrification process, and the wastewater nitrified in the latter nitrification process is circulated back to the previous denitrification process for denitrification. This cyclic denitrification method can use BOD components (organic pollutants) in raw wastewater as an organic nutrient source necessary for denitrification treatment, and also reduces the PH of wastewater during the nitrification process.
This is prevented by the inflow of wastewater with increased PH from the denitrification process, which has the advantage of reducing the amount of chemicals required for wastewater treatment, such as organic nutrients and PH regulators.

On the other hand, in the cyclic denitrification method, a part of the nitrified wastewater is circulated back to the denitrification process for denitrification, so nitrate nitrogen and nitrite in the wastewater that is not returned is nitrogen (hereinafter referred to as
NOx-N (abbreviated as NOx-N) flows out untreated, which has the disadvantage that the efficiency of nitrogen removal (total nitrogen removal rate) is slightly reduced. As one means of compensating for such shortcomings of the cyclic denitrification method, a method is generally considered to increase the amount of waste water that is recycled and returned to increase the ratio of waste water that is denitrified.

However, in this cyclic denitrification method, when the amount of wastewater that is actually recycled is increased, that is, when the ratio of the amount of wastewater that is recycled to the amount of inflowing raw wastewater (circulation ratio) is increased, contrary to expectations, the total nitrogen There was a problem that the removal rate decreased.

The reason for this is thought to be as follows. That is,
Since the nitrification process is carried out under aerobic conditions, the nitrified wastewater enters the denitrification process with a high dissolved oxygen concentration (DO), resulting in an organic nutrient source that should be used for denitrification. (BOD component) is consumed by dissolved oxygen in the recycled wastewater. Therefore, when the wastewater circulation ratio is increased, the amount of BOD components consumed by dissolved oxygen in the recycled wastewater increases and the BOD components that can be used for denitrification treatment decrease, thereby increasing the total nitrogen removal rate. A decrease occurs.

As a processing method that can deal with this problem,
No. 45964 proposes a biological denitrification method in which a portion of the liquid flowing out from the denitrification process is mixed into the circulated nitrification liquid.

In this denitrification method, microorganisms such as nitrifying bacteria and BOD assimilating bacteria present in the circulating nitrification solution nitrify when they assimilate NH ₄ -N and BOD components in the denitrification process effluent. Since dissolved oxygen in the liquid is used, it is possible to reduce the dissolved oxygen in the nitrification liquid that is circulated and returned. As a result, even if the amount of nitrification liquid to be circulated and returned is increased, the anaerobic state of the denitrification tank can be prevented from being impaired. In other words, the denitrification tank
BOD components can be avoided from being consumed by dissolved oxygen. In addition, it is possible to avoid a decrease in the total nitrogen removal rate due to an increase in the amount of nitrifying solution circulated.

However, when trying to adopt the denitrification method proposed here using the fixed contact method in which the group of organisms is fixed, the above prerequisites cannot be met because in the fixed contact method, the microorganisms are fixed and are hardly present in the nitrification solution. is not satisfied.

Therefore, even if this denitrification method is adopted as a treatment method using a fixed contact method, it is difficult to remove dissolved oxygen in the nitrification liquid that is returned to the denitrification tank.

Furthermore, in this denitrification method, when the effluent from the denitrification process is mixed into the nitrification solution to be returned, it is necessary to ensure time for the dissolved oxygen in the nitrification solution to be consumed, so a retention tank is required. For this reason, this denitrification method has the problem of complicating the processing equipment, increasing equipment space, and increasing construction costs.

This invention was made in view of the above circumstances,
We provide a treatment method for nitrogen-containing wastewater that can be applied to a fixed contact method using a nitrification tank and a denitrification tank in which biological groups are fixed, and can also be easily introduced with existing treatment equipment. The purpose is to

"Specific Structure of the Invention" The present invention will be described in detail below with reference to the drawings.

The figure shows an example of a treatment apparatus used in an embodiment of the method for treating nitrogen-containing wastewater of the present invention. This treatment equipment performs a so-called two-stage cyclic denitrification method, with a first denitrification tank 1 and a first nitrification tank 2.
A second denitrification tank 3 and a second nitrification tank 4 are connected in sequence, and the raw wastewater is allowed to flow into the first denitrification tank 1 and the second denitrification tank 3 at a predetermined ratio. A portion of the wastewater nitrified in the nitrification tank 4 is circulated and returned to the first denitrification tank 1 via the sludge thickening tank 5. Filling materials 6, 7, 8, and 9 to which activated sludge is attached are housed in each tank 1 to 4 of this treatment equipment, and the first and second denitrification tanks 1 and 3 are filled with activated sludge. , an in-tank waste water circulation device 10, 10 for circulating waste water in the tank is provided, and a first,
In the two nitrification tanks 2 and 4, air diffusers 11 and 11 are provided, respectively, for circulating the waste water in the tanks and supplying oxygen to the waste water in the tanks.

Next, the wastewater treatment performed by this treatment device will be explained step by step.

First, in the first denitrification tank 1, NOx-N in the waste water (nitrified water) that has been treated in the second nitrification tank 4 and is returned is removed (denitrification).
Raw wastewater and wastewater that is circulated and returned from the second nitrification tank 4 flow into the first denitrification tank 1.
The wastewater in the tank 1 is removed by a drain pipe 10a provided at the bottom of the tank 1, a discharge pipe 10b extending to the top and opened, and a pump 10c interposed between the drain pipe 10a and the discharge pipe 10b. The wastewater is circulated in the tank by an in-tank wastewater circulation device 10 consisting of the following, and is brought into circulation contact with the sludge (fixed sludge) adhered to the surface of the filler 6. Denitrifying bacteria are present in this fixed sludge, and these denitrifying bacteria convert the BOD components (organic nutrients) in the raw wastewater into NOx- Since N is assimilated using oxygen, NOx-N is reduced and released into the atmosphere as nitrogen gas to be removed (denitrogenization). During this denitrification, if dissolved oxygen exists in the wastewater, denitrifying bacteria first utilize this dissolved oxygen to assimilate organic nutrient sources, which reduces the efficiency of denitrification. For this reason, it is necessary that the first denitrification tank 1 be in an anaerobic state as much as possible. The wastewater that has been denitrified in this first denitrification tank 1 is
It is sent to nitrification tank 2.

In the first nitrification tank 2, organic nitrogen and ammonia nitrogen (hereinafter referred to as total Kjeldahl nitrogen,
(abbreviated as TK-N) is nitrified. The wastewater in the first nitrification tank 2 is circulated by air sent from the blower 12 to the diffuser 11 via the valve 11a and blown in as bubbles, and is brought into circulation contact with the fixed sludge of the filler 7. This fixed sludge contains nitrifying bacteria and nitrite-oxidizing bacteria, and these nitrifying bacteria and nitrite-oxidizing bacteria are sent untreated from the first denitrification tank 1 under aerobic conditions. TK in raw wastewater
-N is oxidized and decomposed into NOx-N (nitrification). The wastewater nitrified in this way is sent to the second denitrification tank 3.

In the second denitrification tank 3, similarly to the first denitrification tank 1, denitrification treatment of wastewater is performed. In this treatment method, raw wastewater is also sent to this second denitrification tank 3, and in this tank 3, denitrifying bacteria remove BOD components from this raw wastewater from the first nitrification tank 2. Since NOx-N in the wastewater that is sent is used and assimilated, the nitrogen content is removed. The wastewater treated in this way is sent to the second nitrification tank 4.

In the second nitrification tank 4, like the first nitrification tank 2, TK-N in the wastewater is oxidized and decomposed into NOx-N.

A part of the wastewater thus treated in the second nitrification tank 4 is recycled back to the first denitrification tank 1 as circulating wastewater, and the remainder is treated as treated water and discharged after undergoing treatments such as sterilization and dilution. be done.

The above-mentioned circulating wastewater is first processed by the nitrification liquid circulation pump 13.
The sludge is sent to the sludge thickening tank 5. This sludge concentration tank 5 is a tank for storing and concentrating surplus sludge generated in the process of treating wastewater by this treatment device, and is in an extremely anaerobic state. In this sludge thickening tank 5, dissolved oxygen in the circulating wastewater is consumed by the breathing of the sludge in the tank 5.

The wastewater whose oxygen has been consumed in this sludge thickening tank 5 is
Next, it is sent to the DO concentration measurement tank 14, where the DO concentration is checked, and then returned to the first denitrification tank 1. At this time, if the DO concentration of the circulating wastewater exceeds a predetermined value, the measuring device 15 of the DO concentration measuring tank 14
The discharge amount of the nitrification liquid circulation pump 13 is limited by a control signal sent from the controller 16 through the control device 16.
The residence time of the circulating wastewater in the sludge storage tank 5 is extended. Thereby, the DO concentration of the wastewater returned to the first denitrification tank 1 is always maintained below a predetermined value.

"Specific effects of the invention" In this method of treating nitrogen-containing wastewater,
The circulating wastewater from the second nitrification tank 4 is temporarily transferred to the sludge thickening tank 5.
Since the dissolved oxygen is digested by the sludge stored in this tank 5 and then returned to the first denitrification tank 1, the wastewater aerobically treated in the second nitrification tank 4 has a high The DO concentration is not returned to the first denitrification tank 1 with the same DO concentration, and the anaerobic state of the first denitrification tank 1 is not impaired. Therefore, in the first denitrification tank 1, the assimilation of BOD components in the raw wastewater to be used for denitrification does not proceed due to dissolved oxygen in the circulating wastewater, and the assimilation of BOD components in the raw wastewater does not proceed. The process mainly uses NOx-N oxygen, so
This wastewater treatment method has excellent denitrification efficiency.

Moreover, in this method of treating nitrogen-containing wastewater, the existing sludge thickening tank 5 is used to reduce the dissolved oxygen concentration of the returned wastewater, so there is no need to install new equipment and the processing equipment is complicated. It is possible to avoid problems such as increased size, increased space, and soaring construction costs. Therefore, this treatment method also has the advantage of being a very practical and easy-to-implement treatment method.

In addition, in this nitrogen-containing wastewater treatment method, a denitrification tank and a nitrification tank are provided in two stages in series, and a part of the wastewater after being treated in the second nitrification tank 4 is passed through a sludge thickening tank 5. Since it is returned to the first denitrification tank 1, the
NOx-N generated in the nitrification tank 2 is decomposed into nitrogen in the second denitrification tank 3, and NOx-N generated in the second nitrification tank 4 is decomposed into nitrogen.
N is decomposed into nitrogen in the first denitrification tank 1 and NOx-
N is highly removed. Therefore, this treatment method can further improve the nitrogen removal rate.

Furthermore, in this method for treating nitrogen-containing wastewater, the raw wastewater is allowed to flow into each of the two denitrification tanks 1 and 3, so that the denitrification treatment in these denitrification tanks 1 and 3 can be performed efficiently.

In the above embodiment, after the dissolved oxygen was digested in the sludge thickening tank 5, the DO concentration was checked and the wastewater was returned to the first denitrification tank 1. This may be performed while the wastewater is being sent to the tank 5, thereby managing the DO of the circulating wastewater and controlling the amount of circulating wastewater.

Furthermore, in this wastewater treatment method, an organic substance such as methanol may be added to each denitrification tank to obtain the maximum amount of denitrification, if necessary.

"Effects of the Invention" As explained above, the wastewater treatment method of the present invention is a method in which nitrified wastewater is sent to a denitrification tank via a tank for storing excess sludge such as a sludge thickening tank, so the nitrification treatment Wastewater with high DO value will not directly flow into the denitrification tank and inhibit the denitrification function of denitrifying bacteria. Therefore, this treatment method exhibits excellent denitrification efficiency.

That is, in the method for treating nitrogen-containing wastewater of the present invention,
Since the nitrified wastewater is returned to the denitrification tank via the tank for storing surplus sludge, the dissolved oxygen in the returned nitrification liquid is consumed by respiration by the sludge in the surplus sludge storage tank. Therefore, according to the method for treating nitrogen-containing wastewater of the present invention, even in the fixed contact method where there are almost no suspended microorganisms in the nitrification liquid that is circulated and returned, the DO concentration of the nitrification liquid that is sent to the denitrification tank is reduced. Therefore, it is possible to prevent the anaerobic state of the denitrification tank from being impaired due to an increase in the amount of nitrification liquid that is circulated and returned.

Therefore, according to the method for treating nitrogen-containing wastewater of the present invention, when the nitrogen content in wastewater is further treated by the fixed contact method, the amount of nitrification solution that is circulated back to the denitrification tank is increased to improve the denitrification efficiency. A special effect that can be realized is produced.

In addition, the method for treating nitrogen-containing wastewater of the present invention can be carried out using a surplus sludge storage tank that is generally provided in existing treatment equipment. This eliminates the need for complex processing equipment, increases in space, and increases in construction costs. Therefore, the method for treating nitrogen-containing wastewater of the present invention also has the advantage of being a very practical and easy-to-implement treatment method.

Furthermore, in the method for treating nitrogen-containing wastewater of the present invention,
A denitrification tank and a nitrification tank are installed in two stages in series.
A portion of the wastewater treated in the second stage nitrification tank is returned to the first stage denitrification tank via the excess sludge storage tank, so NOx-N generated in the first stage nitrification tank is transferred to the second stage denitrification tank. NOx is decomposed into nitrogen and generated in the second nitrification tank.
-N is decomposed into nitrogen in the first denitrification tank, NOx-
N is highly removed. Therefore, with the treatment method of the present invention, the nitrogen removal rate can be further improved.

Furthermore, in the method for treating nitrogen-containing wastewater of the present invention, 2
Since raw wastewater is allowed to flow into each of the two denitrification tanks provided, denitrification treatment can be carried out efficiently in each of the denitrification tanks.

[Brief explanation of drawings]

The figure is a schematic configuration diagram showing a processing device used in an embodiment of the processing method of the present invention. 1...First denitrification tank, 2...First nitrification tank, 3...
...Second denitrification tank, 4...Second nitrification tank, 5...Sludge thickening tank.

Claims (1)

[Claims] 1 Perform the first denitrification treatment in the first denitrification tank where the biological population is fixed, then send this wastewater to the first nitrification tank where the biological population is fixed, perform the first nitrification treatment, and then This wastewater is sent to the second denitrification tank where biological groups are immobilized to perform the second denitrification treatment, and then this wastewater is sent to the second nitrification tank where the biological groups are immobilized to undergo the second nitrification treatment. A biological nitrogen-containing wastewater treatment method using a fixed contact method for removing nitrogen content from wastewater by performing a second nitrification treatment in the second nitrification tank. is returned to the first denitrification tank via a tank for storing excess sludge such as a sludge thickening tank or a sludge storage tank, and the raw wastewater is allowed to flow into the first denitrification tank and the second denitrification tank, respectively. A method for treating nitrogen-containing wastewater, characterized by: