JPS63291698A - Biological denitrification of waste water - Google Patents

Abstract

PURPOSE:To effectively remove a BOD component and nitrogen in waste water by maintaining the concentration of sludge in an aerobic tank at high level and also keeping the high concentration of dissolved oxygen in the aerobic tank by means of high concentration oxygen aeration. CONSTITUTION:Raw water 3 is permitted to flow into an anaerobic tank 1 and concentrated sludge solution containing nitric acid and nitrogen nitrite is introduced from an aerobic tank 2 to the anaerobic tank 1 so that said solution may be stirred and mixed with raw water, and this mixture be denitrified with adsorption of a BOC component into sludge. Next, the mixture in the anaerobic tank 1 is introduced into a precipitation tank 4 to be precipitated and separated into treated water 5 and concentrated sludge, and to permit treated water to flow out. In the meantime, the concentrated sludge is returned to the aerobic tank 2 and its is aerated with high-concentration oxygen 8 at high sludge concentration to decompose the BOD component adsorbed in said sludge and the nitrogen component of the mixed liquid into nitric acid and nitrogen nitrite through oxidation. Then the mixed liquid is again permitted into the anaerobic tank 1. Subsequently, the activity of nitration bacteria is increased and thereby effective waste water treatment is achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for treating wastewater containing BOD and nitrogen components;
More specifically, the present invention relates to a method for treating urban sewage, housing complex wastewater, factory wastewater, and the like.

Prior Art and Problems Activated sludge methods have been widely used to purify various wastewaters, and have also been used to treat BOD and nitrogen components. However, the treatment using the conventional activated sludge method has problems such as a low removal rate of nitrogen from wastewater and the need for a hydrogen donor during nitrification and denitrification, and is not necessarily satisfactory.

As an improvement of this activated sludge method,
No. 58 utilizes the nitrification and denitrification effects of bacteria in activated sludge,
Disclosed is a wastewater treatment method that can continuously and efficiently remove nitrogen from wastewater without requiring the addition of an organic compound as a hydrogen donor.

The present inventors applied the contact stabilization method in the activated sludge method to maintain the sludge concentration in the aerobic tank at a high concentration, and to maintain the dissolved oxygen concentration in the aerobic tank at a high concentration by high-concentration oxygen aeration. The present inventors have discovered that nitrogen can be removed even more effectively in wastewater treatment, and have completed the present invention.

Means for Solving the Problems The present invention provides a biological denitrification method for removing BOD components and nitrogen from wastewater using activated sludge. The concentrated sludge liquid containing nitric acid and nitrite nitrogen is introduced from the aerobic tank into the anaerobic tank and mixed with the raw water to denitrify and BOD.
The components are adsorbed into the sludge, and then the mixed liquid in the anaerobic tank is introduced into the settling tank where it is sedimented and separated into treated water and thickened sludge, and while the treated water is discharged, the thickened sludge is returned to the aerobic tank. The sludge is then aerated with high-concentration oxygen while the sludge remains at a high agricultural concentration to oxidize and decompose the BOD components adsorbed to the sludge and the nitrogen components in the mixed solution into nitric acid and nitrite nitrogen, which are then allowed to flow into the anaerobic tank again. The present invention provides a biological denitrification method for wastewater characterized by the following.

According to the method of the present invention, a reaeration tank may be provided between the anaerobic tank and the settling tank, or an oxygen consumption tank may be provided between the aerobic tank and the anaerobic tank, After the dissolved oxygen in the liquid is completely consumed in the consumption tank, the sludge flows into the anaerobic tank, and the sludge flowing out from the anaerobic tank may be brought into an aerobic state in the reaeration tank and then subjected to sedimentation separation.

In the method of the present invention, N/B OD is 1/20 or more.
Contains an OD component and a nitrogen component and has a pH of 6 to 8, or
It is suitable for treating urban sewage, housing complex wastewater, and factory wastewater adjusted to this range, for example, BOD component 250
Suitable for urban sewage treatment with R9/(l or less, nitrogen content of 6019/(l or less). Adjustment of pg (of the treated raw water)
For example, an adjustment tank is provided, and p) [adjustment is carried out using an acid or an alkali in a conventional manner.

The anaerobic tank in the present invention is usually one tank, and it is sufficient if the liquid in the tank can be maintained in an anaerobic state containing no dissolved oxygen, but in order to perform oxygen aeration in the aerobic tank, If the dissolved oxygen concentration in the circulating fluid introduced is high, dissolved oxygen will rise in the anaerobic tank and the denitrification reaction will be suppressed and will not be carried out effectively. In such cases, two or more anaerobic tanks or two
It is also possible to divide the tank into more than one stage and completely consume the dissolved oxygen in the liquid in the first anaerobic tank.

The anaerobic tank contains BOD components and ammonia nitrogen (NH;-
Treated raw water containing nitrogen (N) and nitric acid, nitrite nitrogen (N
A concentrated activated sludge containing s N -N O; -N flows in. The anaerobic tank is stirred using normal mechanical agitation so that the sludge concentration in the tank is uniform, and there is no oxygen in the gas phase at the top of the tank. As mentioned above, in the anaerobic tank, dissolved oxygen brought in by the mixed liquid and raw water from the aerobic tank is consumed, and nitrate and nitrite nitrogen are reduced to nitrogen (Nt), and BOD components in the raw water are converted to sludge. It is adsorbed and removed from the liquid.

The residence time in the anaerobic tank varies depending on the nitrogen concentration in the raw water, water temperature, circulation amount of returned sludge, pH, etc., but in the case of general sewage, it is usually at a water temperature of 15°C (in winter when the nitrification reaction is the lowest). , within 3 hours based on raw water.

The sludge concentration (MLSS) of the anaerobic tank is usually 4.000 to 1.
5,000H/Q, preferably 5,000 to 10.00
(It is about IMg/ρ.

Normally, the mixed liquid that flows out of the anaerobic tank is directly flowed into the settling tank, but in cases where the activated sludge that has absorbed BOD components is likely to rot in the settling tank, or when soluble BOD among the BOD components in the raw water is If the proportion of sludge is high and the sludge cannot be adsorbed sufficiently in the anaerobic tank, install a reaeration tank between the anaerobic tank and the aerobic tank and pass the sludge through the reaeration tank 1. It is preferable to promote decomposition and its adsorption to sludge.

The reaeration tank is a closed type, with an oxygen concentration of 4 in the gas phase at the top of the tank.
By supplying high concentration oxygen gas of 0% or more, the oxygen concentration inside the tank is 3.
Aerate with 5% or more gas to reduce the soluble concentration to 2 mgI
It is preferable to maintain it at or above Q.

Note that the reaeration tank may be an air aeration tank.

For aeration, commonly used aeration means such as surface aeration and gas circulation aeration can be used.

The residence time in the reaeration tank (as aeration time) is usually 15 minutes or more and preferably 1 hour or less.

Next, the liquid flows into a settling tank, where solid-liquid separation is performed by gravity settling, the supernatant water is discharged as treated water, and the settled sludge is returned to the aerobic tank via the sludge return line. The amount of returned sludge is 1 to 5 times, preferably 1 to 3 times, the amount of inflow raw water, but if the amount of sludge becomes excessive, it is preferable to discharge it to the outside of the system as surplus sludge.

The aerobic tank is usually a 1 tank, but in order to increase oxygen utilization efficiency, an aerobic tank is used in the same way as the anaerobic tank 2)! or more or 2
It may be divided into more than one stage. The upper gas phase of an aerobic tank is sealed, and the nitrogen components in the mixed liquid are oxidized and decomposed by supplying oxygen and stirring the liquid through circulating aeration of high-concentration oxygen in the gas phase and mechanical surface aeration. do. In the method of the present invention, exhaust gas containing carbon dioxide and nitrogen in addition to oxygen is appropriately discharged to the outside of the system.

The a degree of oxygen introduced into the aerobic tank is preferably 90% or more, and the direction of the oxygen gas flow relative to the flow of the liquid in the aerobic tank may be either cocurrent or countercurrent.

The sludge concentration (MLSS) in the aerobic tank is s, o o o~2
0.000x9/121 preferably IO,000~1
It is 5.00019/+2.

In addition, the dissolved oxygen concentration in the aerobic tank solution is an important operating factor for the nitrification reaction, and is 2J + 97σ or more, preferably 4 to 1
0119/I2.

The residence time in an aerobic tank varies depending on various factors, as in the case of an anaerobic tank, but in the case of general sewage, the water temperature is 15℃ (
(winter season, when the nitrification reaction is the lowest), it is usually within 4 hours based on raw water, and preferably about 6 hours at maximum at a nitrogen concentration of 60 x g/Q and a water temperature of 15°C based on raw water.

The effluent from the aerobic tank is normally sent as is to the anaerobic tank, but it may contain a dissolved oxygen concentration of up to 10o/Q. Since the oxidative decomposition occurs and the BOD component is consumed, the OD acid component required for the denitrification reaction becomes depleted, resulting in a problem that the reaction is delayed. In order to prevent such problems, an oxygen consumption tank is installed between the aerobic tank and the anaerobic tank, and after the dissolved oxygen in the liquid is completely consumed by the breathing action of the sludge and the temperature reaches 9/Q, the anaerobic tank is opened. to flow into.

The oxygen consumption tank may have no gas phase, or may have a gas phase but no oxygen. Furthermore, although the nuclide does not require a particular stirring device, the structure is designed to prevent sludge from accumulating in the tank. The residence time in this oxygen consumption tank is preferably 15 minutes or less.

As mentioned above, in the present invention, it is not necessary to provide a reaeration tank and an oxygen consumption tank, and either one of them,
Or both may be provided.

Hereinafter, the method of the present invention will be specifically explained using the accompanying drawings.

In the drawings, FIG. 1 is a flow chart of one specific example of the method of the present invention. In this specific example, an anaerobic tank 11, an aerobic tank 2, and a sedimentation tank 4 are provided.
' and the second anaerobic tank 2, and the aerobic tank 2 is divided into the first aerobic tank 2' and the second aerobic tank 2''.The raw water 3 is pH% adjusted tank 9. The sludge is introduced into the first anaerobic tank 1', where it is mixed with the concentrated sludge liquid containing nitric acid and nitrite nitrogen from the second aerobic tank 2'', and denitrification and BOD adsorption to the sludge are performed. Denitrification and adsorption of BOD to the sludge are completed in the second anaerobic tank 1''.Then, the mixed liquid in the anaerobic tank 1 is separated into sludge and treated water in the sedimentation tank 4, and the treated water 5 flows out of the system. On the other hand, the settled sludge is returned to the first aerobic tank 2' via the sludge return line 6, and excess sludge is returned to the first aerobic tank 2' via the sludge return line 6.
is discharged from the system via the In the first aerobic tank 2', highly concentrated oxygen is supplied from line 8 to the gas phase in the upper part of the closed tank, nitrification is performed by circulating aeration, and the generated exhaust gas is discharged from line 7 to the outside of the yarn. The mixed liquid that has been nitrified in the second aerobic tank is introduced into the first anaerobic tank 1', mixed with the treated raw water 3, and the treatment proceeds in the same manner.

FIG. 2 is a flow sheet of another specific example of the method of the present invention, in which an oxygen consumption tank 1O1 is provided between the aerobic tank 2 and the anaerobic tank 1, and a reaeration tank 11 is provided between the anaerobic tank 1 and the sedimentation tank 4. The flow differs from the flow shown in FIG. 1 in that the oxygen in the aerobic tank is introduced into the reaeration tank, and the air is exhausted from the reaeration tank. As described above, dissolved oxygen is consumed in the oxygen consumption tank 10 to prevent a delay in the escape reaction.

Further, in the reaeration tank, decomposition of soluble BOD components and adsorption to sludge are promoted.

Figure 3 is a flow sheet showing an example of the conventional activated sludge method for comparison.
The flow is fundamentally different from that of the method of the present invention in that a circulation line 6' for the sludge mixture is provided, and oxidation is carried out using air in the aerobic tank.

For this reason, it is not possible to increase the dissolved enzyme concentration in the aerobic tank, and the nitrification rate becomes slow.

Figure 4 is a flow sheet showing an example of another conventional activated sludge method, in which an aerobic tank 2 is provided between an anaerobic tank 1 and a sedimentation tank 4, and a circulation line for the wastewater-sludge mixture is installed. 6' is provided between the anaerobic tank 1 and the aerobic tank 2, which is fundamentally different from the flow of the method of the present invention, and similar to the flow of FIG. 3, it is difficult to effectively remove nitrogen.

cold nose carp The present invention will be explained in more detail with reference to Examples below.

Example 1 Urban sewage (pH 7.5, BOD l 50xtt/σ,
Total nitrogen (1 degree 40s+s+/Q) was treated as wastewater using an apparatus as shown in FIG. 1 (however, without a pH adjustment tank).

The pilot Plato scale device made of hard vinyl chloride used had a first anaerobic tank 1' with a volume of 200Q, a second anaerobic tank with a volume of 400Q, a first aerobic tank 2' with a volume of 4009°, and a second aerobic tank 2 with a volume of 400Q. '' was 400Q, and sedimentation tank 4 was 1.200Q.

The processing conditions were as follows.

Water temperature = 15℃ Sludge concentration: Aerobic tank to, 0OOON? #! 1st anaerobic tank 6.67QR9/12 2nd anaerobic tank 6. ? 0O19#! Returned sludge concentration: to, 000ff9#! Raw water flow M
: 20Of/hr return sludge amount:
400g/hr Dissolved oxygen concentration: 1st aerobic tank 3.5u#! (Aerated with an oxygen-containing gas with an oxygen concentration of 40% by volume) 2nd aerobic tank 6.5 mg # (Aerated with an oxygen-containing gas with an oxygen concentration of 70% by volume) Residence time: Total of 4 hours in the 1st and 2nd aerobic tanks ( Inflow raw water base l1l) 1st
Anaerobic tank 1 hour (〃) Second anaerobic tank 2 hours (〃) During the treatment operation, the pH of the liquid in the second aerobic tank was maintained at 6.5 using a 48% NaOH solution. In addition, pi-1 of the liquid in the first aerobic tank was 7.0.

Oxygen used for aeration was supplied to the second aerobic tank by an oxygen cylinder, and was discharged as exhaust gas through the first aerobic tank.

During the above operations, the pH of the first anaerobic tank was 7.0.0RP (redox potential) was -50a+V, and the dissolved enzyme concentration was θ19/
The pi (pi) in I2 and the second anaerobic tank was 7.7, the ORP was -150 mV, and the dissolved oxygen concentration was Omg/Q.

In addition, the pH of the final treated water is 1!7.5, and the BOD is 19x9.
/(!, SS is l 019/12. Ammonia nitrogen is 13, 811F/Q.

Nitric acid N1g was 0.519IQ.

Example 2 Urban sewage (pH 7.6, BOD 120*9/Q, ammonia nitrogen 35 my/(1) was treated with a device as shown in Fig. 2.The device used was the first anaerobic tank 1. The volume of ' is 30012.The volume of the second anaerobic tank 1'' is 30012
, the first aerobic tank 2' is 40 (021 the second aerobic tank 2'' is 40
012, oxygen consumption tank lO is 80Q, reaeration tank 11 is to
oQ, sedimentation tank 4 was 1,200Q.

The processing conditions were as follows.

Water temperature = 15℃ Sludge concentration; Aerobic tank L2.00019/Q Oxygen consumption tank 12,000R9/(1 anaerobic tank
8.00019/+2 Return sludge agricultural rate: 12,0OOu/Q raw water flow rate +
250C/hr return sludge amount: 500
(!/hr Dissolved oxygen concentration: 1st aerobic tank 419/Q (Aeration with oxygen-containing gas with oxygen concentration of 85% by volume) 2nd aerobic IIF 1.5 mg/QC Aeration with oxygen-containing gas with oxygen concentration of 65% by volume) Oxygen consumption tank 0 shoulder 9/Q Reaeration tank 3 J! 1? /12 (oxygen concentration 40
Residence time: 1st and 2nd aerobic tank total 3.2 hours (based on inflow raw water) Oxygen consumption tank 9.6 minutes 1st and 2nd anaerobic tank total 2.4 hours ( Inflow raw water standard) Re-aeration tank During the 12-minute treatment operation, oxygen gas used for aeration was supplied to the first aerobic tank from an oxygen cylinder and sent to the reaeration tank via the second aerobic tank.

During the above operations, the pH in the first anaerobic tank was 7.1, the ORP was -70 mV, and the dissolved oxygen level was OxlJ/gj;
The pH in the second anaerobic tank is 7.8, and the ORP is -180.
mV, and the dissolved oxygen concentration was Omg/Q. Also, pi-1 in the final treated water is 7.5.130D is 17 j! 9
IQ, ammonia nitrogen was 9.5 ytg/(1, nitrate nitrogen was 1, OR9/Q.

Comparative Example 1 As shown in Figure 4, the arrangement of the aerobic tank and anaerobic tank was different.
A circulation line 6' for the wastewater-sludge mixture is installed between both tanks.
Urban sewage was treated under the same conditions as in Example 1 except that the residence time in the aerobic tank 2 was 9.1 hours and the residence time in the anaerobic tank 1 was 3.4 hours. The results obtained are shown below.

BOD in final treated water: 17 x 9/Q ammonia nitrogen: 0, 7 mg/Q nitrate nitrogen
13.6x9/(2 Comparative Example 2 The above-mentioned except that aeration in the aerobic tank was performed using air and the residence time in the aerobic tank was 30.1 hours and the residence time in the anaerobic tank was 7.3 hours. Urban sewage was treated under the same conditions as Comparative Example 1.

The results obtained are shown below.

BOD in final treated water: 1 B, R9/Q ammonia nitrogen = 0.7 shoulder g/12 nitrate nitrogen
13.619/12 Effects of the Invention As described above, according to the present invention, the sludge concentration in the aerobic tank can be maintained at a high concentration, and the dissolved oxygen in the aerobic tank can be maintained at a high concentration by high-concentration oxygen aeration. The nitrifying bacteria have high activity, allowing for effective wastewater treatment.

Furthermore, since denitrification does not occur in the sedimentation tank, there is no floating of sludge or scum, and no secondary pollution due to the generation of large amounts of waste gas. Moreover, since the nitrification rate can be increased and sludge of high concentration can be used, there is also the advantage that the treatment equipment can be made more compact.

[Brief explanation of drawings]

1 and 2 are flow sheets showing one specific example of the method of the present invention, and FIGS. 3 and 4 are flow sheets showing a comparative example of the present invention. The main symbols in the drawings mean the following: 1...Anaerobic tank, 2...Aerobic tank, 3...Raw water, 4.
... Sedimentation tank, 5... Treated water, 8... High concentration oxygen, I
O...Oxygen consumption tank, 11...Reaeration tank.

Claims (4)

[Claims] (1) In a biological denitrification method that removes BOD components and nitrogen from wastewater using activated sludge, an aerobic tank, an anaerobic tank, and a sedimentation tank are provided, raw water flows into the anaerobic tank, and nitric acid and nitrogen are removed from the aerobic tank. The concentrated sludge liquid containing nitrite nitrogen is introduced into the anaerobic tank and stirred and mixed with the raw water to perform denitrification and adsorption of BOD components to the sludge, and then the mixed liquid in the anaerobic tank is introduced into the settling tank. The treated water is separated by sedimentation into treated water and thickened sludge, and while the treated water is discharged, the thickened sludge is returned to the aerobic tank and aerated with high concentration oxygen to remove the BOD components adsorbed to the sludge. and a biological denitrification method for wastewater, which comprises oxidatively decomposing nitrogen components in the mixed liquid into nitric acid and nitrite nitrogen, and causing the mixture to flow into the anaerobic tank again. (2) The method according to item (1) above, wherein a reaeration tank is provided between the anaerobic tank and the settling tank, and the sludge in the effluent from the anaerobic tank is brought into an aerobic state and then sedimented and separated. (3) providing an oxygen consumption tank between the aerobic tank and the anaerobic tank;
The method according to item (1) above, wherein the dissolved oxygen in the liquid from the aerobic tank is completely consumed and then flows into the anaerobic tank. (4) providing an oxygen consumption tank between the aerobic tank and the anaerobic tank;
After the dissolved oxygen in the liquid from the aerobic tank is completely consumed, it flows into the anaerobic tank, and a re-aeration tank is provided between the anaerobic tank and the settling tank to remove the sludge from the effluent from the anaerobic tank. The method according to item (1) above, in which sedimentation separation is performed after aerobic conditions.