JPH08243587A - Method for circulating nitrified solution and carrier - Google Patents

Abstract

PURPOSE: To provide a method for circulating nitrified soln. and carrier by which a power for circulating the nitrified soln. is reduced, DO is not brought into a denitrification tank, and the carrier concn. in the denitrification tank and nitrification tank is maintained constant at all times. CONSTITUTION: Baffle walls 5 and 6 are formed respectively close to the outlet end of a nitrification tank 2 and close to the inlet end of a settling tank 3. A hopper 8 is furnished on the bottom of the nitrification tank 2 between the baffle wall 5 and a partition wall 7 to settle a polymer gel carrier therein. The carrier settled in the hopper 8 is sucked by an air-lift pipe 9 and returned to the inlet end of a denitrification tank 1. Meanwhile, a part of a nitrified soln. is sucked by a suction pipe 12 formed between the baffle wall 6 of the settling tank 3 and the partition wall 7 and returned to the inlet end of the denitrification tank 1.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a nitrification solution and a carrier used when treating a nitrogen-containing wastewater such as sewage or leachate of wastes by a nitrification solution circulation method in a nitrification tank and a denitrification tank to which a polymer gel carrier is added. It is about the circulation method of.

[0002]

2. Description of the Related Art In order to treat nitrogen-containing wastewater by a nitrification solution circulation method in a denitrification tank and a nitrification tank to which a carrier is added, conventionally, a nitrification solution and carrier circulation method as shown in FIG. 7 has been used. . In this method, an air lift pipe 4 is provided near the outflow end of the nitrification tank 2, and a nitrification solution containing a polymer gel carrier is circulated to the inflow end of the denitrification tank 1 through the air lift pipe 4. This makes it possible to perform nitrification / denitrification of nitrogen in the nitrogen-containing wastewater, and to accelerate these reactions by the microorganisms attached to the carrier.

However, this conventional method is a method in which the carrier and the nitrification solution are circulated in a single system and at a carrier concentration substantially the same as the carrier concentration in the tank, so if the circulation amount is small, the outflow end of the nitrification tank At the same time as the carrier accumulates in the vicinity, the carrier concentration in the denitrification tank and the nitrification tank gradually decreases. Moreover, if the circulation amount is increased to maintain the carrier concentration constant, not only the power for circulation increases, but also the DO (dissolved oxygen concentration) increases due to the dissolution of air during the air lift, and the denitrification performance of the denitrification tank 1 is increased. There was a drawback that it decreased. Further, at this time, there is a problem that it is difficult to control the circulation amount of the nitrification liquid because the carrier circulation is limited.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and can reduce the power for circulating the nitrifying solution without deteriorating the denitrification performance of the denitrification tank. What was made to provide a method for circulating a nitrification solution and a carrier, which makes it possible to always maintain a uniform carrier concentration in the denitrification tank and the nitrification tank without accumulating the carrier near the outflow end of the nitrification tank. Is.

[0005]

DISCLOSURE OF THE INVENTION The present invention, which has been made to solve the above-mentioned problems, provides a blocking wall in the vicinity of the outflow end of a nitrification tank and in the vicinity of the inflow end of a subsequent settling tank. While the polymer gel carrier is settled inside the hopper provided at the bottom between the baffle wall and the partition wall, the polymer gel carrier settled in the hopper is sucked by the air lift pipe and returned to the inflow end of the denitrification tank. The nitrification solution suction pipe provided between the baffle wall and the partition wall of the precipitation tank sucks a part of the nitrification solution flowing from the nitrification tank into the precipitation tank and returns it to the inflow end of the denitrification tank. To do.

[0006]

According to the present invention, since the nitrification solution and the carrier are circulated by independent circulation means, it is not necessary to circulate an excessive amount of nitrification solution for carrier circulation as in the conventional case, and the nitrification solution is circulated. Power for circulation can be reduced. Further, since the carrier that has been settled and concentrated is circulated inside the hopper, the carrier is not accumulated near the outflow end of the nitrification tank, and the carrier concentration in the denitrification tank and the nitrification tank can be always kept uniform. Moreover, since the high-concentration carrier is circulated, it is possible to reduce the carry-in amount of the melted DO into the denitrification tank at the time of the air lift and prevent the denitrification performance of the denitrification tank from being deteriorated.

[0007]

The present invention will be described below in more detail with reference to the illustrated embodiments. FIG. 1 is a flow sheet of an embodiment of the present invention, in which 1 is a denitrification tank, 2 is a nitrification tank, and 3 is a subsequent settling tank. A polymer gel carrier to which microorganisms are attached is added to the treatment liquid inside the denitrification tank 1 and the nitrification tank 2. Barrier walls 5 and 6 are provided near the outflow end of the nitrification tank 2 and near the inflow end of the precipitation tank 3, respectively. 2 and 3
As shown in, a plurality of hoppers 8 are provided at the bottom of the nitrification tank 2 between the baffle wall 5 and the partition wall 7.

Immediately above each hopper 8 is an air lift pipe 9
Is provided. Air is supplied to the inside of the air lift pipe 9 from the air diffuser 10 provided at the lower end of the air lift pipe 9, and the buoyant force sucks the polymer gel carrier in the hopper 8 to flow into the denitrification tank 1 through the carrier channel 11. Send it back to the end. Further, a nitrification solution suction pipe 12 is provided near the water surface between the baffle wall 6 and the partition wall 7 of the settling tank 3 and sucks a part of the nitrification solution flowing from the nitrification tank 2 into the settling tank 3. And returns it to the inflow end of the denitrification tank 1. The circulation amount of nitrification liquid is preferably controlled by a pump 13 having an inverter control mechanism.

Next, the steps of the present invention will be sequentially described. First, the nitrogen-containing wastewater is supplied to the inflow end of the denitrification tank 1 together with the returned sludge from the settling tank 3, the nitrification liquid from the nitrification tank 2 and the polymer gel carrier. Here, nitrite nitrogen (NO ₂ -N) and nitrate nitrogen (NO ₃ -N) contained in the nitrification solution convert organic matter (BOD) in nitrogen-containing wastewater into nitrogen gas as a hydrogen donor. And denitrified. This reaction is also carried out by the denitrifying bacteria in the activated sludge, but is rapidly carried out by the denitrifying bacteria which inhabit the surface or the inside of the polymer gel carrier at a high density.

The mixed liquid leaving the denitrification tank 1 enters the nitrification tank 2 together with the polymer gel carrier. In the nitrification tank 2, the residual organic matter (BOD) used in the denitrification tank 1 is oxidatively decomposed, and ammonia nitrogen (NH ₄ -N) and organic nitrogen are converted into nitrite nitrogen.
It is oxidized to (NO ₂ -N) and nitrate nitrogen (NO ₃ -N). Again, the reaction proceeds with nitrite bacteria or nitric acid bacteria in the activated sludge,
The reaction is promoted by the Nitrous bacterium and the nitric acid bacterium which inhabit the surface or the inside of the polymer gel carrier with high density.

The mixed liquid reaching the outflow end of the nitrification tank 2 passes through the baffle wall 5 of the nitrification tank 2. Then, the activated sludge and water rise toward the overflow weir at the upper part of the partition 7 between the nitrification tank 2 and the precipitation tank 3, but the polymer gel carrier settles down and the hopper 8 of the hopper 8 provided at the bottom thereof. Collect inside. The hopper 8 is in the shape of an inverted quadrangular pyramid or an inverted cone, and preferably has a slope greater than the repose angle of the polymer gel carrier to prevent bridge formation. FIG. 4 is a graph showing the relationship between the inclination angle of the hopper 8 and the concentration of the returned polymer gel carrier. Further, it is preferable to coat the inner surface of the hopper 8 with a copper plate to prevent the generation of biofilm.

The distance between the baffle wall 5 and the partition wall 7 is selected so that the rising velocity of the mixed solution is 5 to 80 cm / min and each hopper 8 is a substantially square or a perfect circle. For example,
When the tank width is 10 m ³ / min and the tank width is 10 m, the distance is 2 m with 5 hoppers 8 or the distance is 3 with 3 hoppers 8.
It should be 3.3 m. The rising velocity of the mixed solution is 5 cm / m.
If it is less than in, the activated sludge tends to settle, and if it exceeds 80 cm / min, the polymer gel carrier may float, which is not preferable.

The polymer gel carrier accumulated in the hopper 8 is lifted above the water surface of the nitrification tank 2 through the air lift tube 9 by the buoyancy of air blown out from the air diffusing means 10 provided at the lower end of the air lift tube 9. And is returned to the inflow end of the denitrification tank 1 through the carrier flow path 11. Also, nitrification tank 2
A part of the nitrification solution that has entered the precipitation tank 3 from the above is sucked by a nitrification solution suction pipe 12 provided between the baffle wall 6 and the partition wall 7 of the precipitation tank 3, and is returned to the inflow end of the denitrification tank 1. .

In the present invention, the circulation amount of the carrier-containing liquid containing the polymer gel carrier is controlled by adjusting the amount of air from the air diffusing means 10. As shown in FIG. 5, the discharge amount of the carrier-containing liquid increases as the air amount increases,
From a certain point in time, even if the air amount is increased, the discharge amount does not increase. Also, the carrier concentration is lower than the carrier concentration in the reaction tank (denitrification tank 1 and nitrification tank 2) in the stage where the amount of air is small, but the carrier concentration increases as the amount of air increases, and is 2 to 3 times higher than the carrier concentration in the reaction tank. It is possible to circulate in a double concentrated state. However, the carrier concentration decreases contrary to the increase in the discharge amount at a certain concentration, which is because the discharge speed becomes higher than the carrier concentration speed in the hopper 8.

FIG. 6 is a graph showing the relationship between the carrier transfer amount of the results of FIG. 5 and the carrier wear rate and the air amount. In the case of this example, the carrier transfer amount increases with the increase of the air amount, but the air blowing rate is 3 m ³ / m ³ · min.
Even if the amount of air is increased from around the point where the amount exceeds, the amount of carrier transfer does not increase. Further, the carrier wear rate at this time rapidly increases when the air blowing rate exceeds 3 m ³ / m ³ · min, but this is due to the fact that the holdup rate of bubbles does not increase due to the increase of the air amount, This is because the energy due to the increase in the amount of air acts on the formation of a turbulent flow in the air lift pipe 9 to increase the contact of the carrier pipes and to increase the carrier wear rate. Therefore there is a proper value in the air blowing rate of the air-lift pipe 9, but in the case of this example is ^{1.5 ~3.0m 3 / m 3 · min} , this value will vary the tube diameter, the tube length and the like.

In the present invention, the circulation of the nitrification solution is controlled in the same manner as the normal circulation of the nitrification solution without the polymer gel carrier, and the circulation rate of the nitrification solution at this time is calculated by the following equation. R = [(1-α) Qg + αβQg + Qn] / Qs

Here, R is the nitrification liquid circulation rate (%), Qs is the sewage treatment amount (m ³ / Hr), Qg is the carrier-containing liquid amount (m ³ / Hr), and Qn.
Is the circulating amount of mixed solution (nitrification liquid) (m ³ / Hr), α is the carrier volume standard concentration (−), and β is the carrier porosity (−).

As described above, the reaction tank (denitrification tank 1 and nitrification tank 2) can be obtained by properly selecting the air blowing rate of the air lift pipe 9.
The circulation rate of the carrier-containing liquid required to keep the carrier concentration in the reaction tank constant is 2 to 3 times as high as the polymer gel concentration of the nitrification liquid (mixed liquid). Circulation rate
Taking 100% as an example, 67-100% is sufficient. If the carrier porosity is neglected in this carrier-containing liquid, 48-80%
There is a mixed solution of, and the difference with respect to the set nitrification solution circulation rate is 52 ~
Only 20% needs to be circulated by the pump 13. The mixed liquid that has entered the settling tank 3 is subjected to solid-liquid separation, the supernatant water is discharged as a treatment liquid, and a part of the sludge is withdrawn as excess sludge, but the rest is returned to the denitrification tank 1 as return sludge. Next, Table 1 shows specific numerical values in Examples.

[0019]

[Table 1]

[0020]

As shown in the above embodiments, according to the present invention, the total circulation rate of the carrier-containing liquid (carrier + mixed liquid) and the circulation ratio of the mixed liquid are 100%, and the nitrogen (TN) equivalent to that in the conventional method is obtained. The treated water quality can be obtained. Therefore, compared with the conventional method in which the circulation rate is 350%, the power required for circulation can be 30%. Further, according to the present invention, the wear rate of the polymer gel carrier can be reduced to about 1 / 4.5 of that of the conventional one. Further, according to the present invention, since the DO in the denitrification tank can be made almost zero, many excellent effects such as stable denitrification can be obtained.

[Brief description of drawings]

FIG. 1 is a flow sheet of the present invention.

FIG. 2 is a plan view of a main part.

FIG. 3 is a vertical sectional view of a main part.

FIG. 4 is a graph showing the relationship between the inclination angle of the hopper and the carrier concentration in the carrier-containing liquid.

FIG. 5 is a graph showing the relationship between the air blowing rate of the air lift tube and the carrier concentration and discharge amount.

FIG. 6 is a graph showing a relationship between an air blowing rate of an air lift pipe, a carrier transfer amount, and a carrier wear rate.

FIG. 7 is a flow sheet of a conventional method (carrier addition nitrification solution circulation method).

[Explanation of symbols]

1 denitrification tank, 2 nitrification tank, 3 precipitation tank, 4 conventional air lift pipe, 5 nitrification tank side baffle wall, 6 precipitation tank side baffle wall, 7 partition wall, 8 hopper, 9 air lift pipe, 10
Air diffuser, 11 carrier channels, 12 nitrification liquid suction tube, 13 pump with inverter control mechanism

Claims (5)

[Claims] 1. A baffle wall is provided in the vicinity of the outflow end of the nitrification tank and in the vicinity of the inflow end of the subsequent settling tank respectively, and a high level is provided inside a hopper provided at the bottom between the baffle wall and the partition wall of the nitrification tank. The molecular gel carrier is allowed to settle, and the polymer gel carrier that has settled in the hopper is sucked by an air lift pipe and returned to the inflow end of the denitrification tank. A method for circulating a nitrification liquid and a carrier, wherein a part of the nitrification liquid flowing from the nitrification tank to the precipitation tank is sucked by a pipe and returned to the inflow end of the denitrification tank. 2. The method for circulating a nitrification solution and a carrier according to claim 1, wherein a hopper having an inclination equal to or more than the repose angle of the polymer gel carrier is used. 3. The method for circulating a nitrification solution and a carrier according to claim 1, wherein a hopper having an inner surface coated with a copper plate is used. 4. The method for circulating the nitrification liquid and the carrier according to claim 1, wherein the circulation amount of the polymer gel carrier is controlled by the amount of air blown into the air lift pipe. 5. A pump having an inverter control mechanism controls the amount of circulation of the nitrification liquid through the nitrification liquid suction pipe.
The method for circulating the nitrification liquid and the carrier according to item 1.