JPH0550093A - Treatment of sewage - Google Patents

Abstract

PURPOSE:To control increase in the DO value under low-load conditions and to efficiently remove nitrogen at the time of treating sewage in a single tank. CONSTITUTION:An underwater aerator 3 and a DO meter 5 are set in a single reaction tank 1. The ratio of the anaerobic operation time A when air is not supplied to the aerobic operation time B is specified in one intermittent aeration cycle, and operation is conducted. When the DO in the tank exceeds a specified value during the aerobic operation time B, the supply of air and/or the rotating speed of an agitator are reduced to control the aerobic treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single tank method for treating wastewater, which is suitable for nitrification-denitrification treatment of small-scale wastewater such as sewage and industrial wastewater, and particularly an effective control method for intermittent aeration. It is about.

[0002]

2. Description of the Related Art Conventionally, as a method for nitrifying and denitrifying sewage, a batch method or an oxidation ditch method (OD method)
It has been known.

However, since the batch method requires a plurality of reaction tanks, not only the installation area becomes large, but also adjustment of fluctuations in the inflow amount is troublesome. In addition, the OD method has a disadvantage that an intermediate boundary portion which is neither aerobic nor anaerobic is formed in the reaction tank, resulting in a wasteful space and is uneconomical.

Therefore, it is possible to efficiently nitrify and denitrify sewage in a single reaction tank without requiring a large installation area, and it is easy to operate, especially for small-scale nitrification-denitrification of sewage. As an effective sewage treatment method when applied, JP-A-1-31
The method described in Japanese Patent No. 0798 has been proposed, and its superiority to other methods has been confirmed by experiments. In this method, a stirrer and an aerator are installed inside the reaction tank, and while continuously agitating the wastewater in the reaction tank by the stirrer, the aerator intermittently aerates the same reaction at the required time. By alternately switching the inside of the tank to an anaerobic state and an aerobic state, sewage is treated with nitrification-denitrification, until now, anaerobic and aerobic, according to the time preset by the timer,
It went cyclically by repeating the operation stop and operation of the blower.

[0005]

However, in actual sewage treatment, the substantial aerobic time and anaerobic time may differ greatly from the set time of the timer due to load fluctuations. For example, at night, when the inflow water is small and the load is small, the DO becomes too high, and it takes a long time until the inside of the aeration tank becomes anoxic even if the blower is stopped, resulting in a short anaerobic time. As a result, the effect of removing nitrogen decreases, and during that time, the blower or the stirring device is wastefully operated.

The present invention has been made in order to solve the problems in the above-mentioned conventional method, and in particular, when the load is small, the increase in the DO value is suppressed to prevent the nitrogen removal effect from being lowered, and the power is wasted. It is intended to provide a wastewater treatment method capable of preventing the consumption of water.

[0007]

As a result of intensive studies to solve the above problems, the present inventor has found that the amount of air supply or the agitation during the aerobic time zone in one cycle of intermittent aeration are controlled. It has been found that good processing results can be obtained by controlling, and the present invention has been completed.

That is, in the wastewater treatment method of the present invention, the wastewater is intermittently aerated in a single reaction tank while continuously stirring it, and the inside of the tank is alternately switched between an anaerobic state and an aerobic state. Thus, in the method for treating sewage, the anaerobic time zone in which no air is supplied and the aerobic time zone in which air is supplied in the intermittent 1 cycle are set at a predetermined ratio for operation, and in the tank during the aerobic time zone. When DO exceeds a predetermined value, the supply amount of air and / or the rotation speed of the agitator are reduced.

In the present invention, an apparatus for performing mixing and stirring and oxygen supply, such as an underwater aerator, is installed in the intermittent aeration tank, and air (oxygen) is supplied and stopped from the compressor by turning the timer on and off. When the supply is stopped, only mixing and stirring can be performed so that the required aerobic state and anaerobic state can be alternately formed in each tank.

By the intermittent aeration method described above, organic matter and S
S removal and nitrogen removal are performed, but in order to promote particularly effective nitrogen removal, the aeration cycle is used to properly maintain the reaction time in the anoxic state (anaerobic state) and the aerobic state, and It is important to repeat. The more time anaerobic nitrification are controlled, will be Kje-N removal rate is gradually lowered, denitrification and time of anaerobic conditions is shortened inhibited Conversely, in the treated water NO _x -N Higher concentration. From the results of many experiments conducted so far, the ratio A / B between the aerobic operating time B for supplying air and the anaerobic operating time A for stopping the air supply in the aeration cycle is 0.6 to 1.
A range of 0 is suitable.

Looking at the change over time in the DO in the tank due to the aeration cycle described above, the DO in the tank began to rise sharply due to the start of aeration (air supply) in the aeration cycle, and due to the consumption of oxygen accompanying the sludge breathing when the aeration was stopped. DO decreases gradually. In this case, the time when the DO becomes zero depends on the maximum value of DO and the oxygen consumption rate of the mixed liquid. In the intermittent aeration process, the state of anaerobic treatment and the state of aerobic treatment are alternately repeated in time by this aeration cycle. The above aeration cycle was tested for general raw sewage with various long and short times.
20 minutes is appropriate.

By the way, in the actual wastewater treatment, the substantial aerobic time and anaerobic time may differ greatly from the set time of the timer due to load fluctuation. Especially at night, when the inflow water is small and the load is small, the DO becomes too high, and it takes a long time until the inside of the aeration tank becomes anoxic even if the blower is stopped, resulting in a short anaerobic time. Therefore, the effect of nitrogen removal is reduced.

In the present invention, the intermittent aeration tank has a D
Install a DO meter that detects O so that when the DO in the tank exceeds a predetermined value, the amount of air supplied from the compressor can be reduced, or the rotation speed of the agitator can be reduced. Or both can be reduced. This control time is a time (aerobic control time) C from the time when the DO in the tank reaches a predetermined value to the time when the air supply is stopped in the time B during the air supply.
By doing so, it is possible to prevent the DO from becoming too high, and shorten the time until the inside of the tank becomes anoxic,
It becomes easy to maintain the anaerobic state where the DO becomes 0.2 mg / l or less, and the nitrogen removing effect can be kept good. In addition, this control reduces the amount of power used during that time, thereby reducing the running cost. The predetermined value of DO is suitably 1.2 to 2.0 mg / l, and generally preferably about 1.5 mg / l.

[0014]

In the method of the present invention having the above-mentioned structure, the sewage that has continuously flown into the reaction tank is intermittently aerated while being continuously agitated by the aeration / stirring device, so that a predetermined aerobic state and an anaerobic state are obtained. By repeating the above, nitrification, denitrification, and dephosphorization are effectively performed.

[0015]

EXAMPLE FIG. 1 shows a flow sheet of an apparatus used in an example of the present invention, 1 is an intermittent aeration tank used as a reaction tank, and 2 is a sedimentation tank. An underwater aerator 3 is installed in the intermittent aeration tank 1, and air from the compressor 4 is supplied and stopped every predetermined time, for example, every 60 minutes by turning ON / OFF a timer (not shown). At the same time, the agitator of the submersible aerator 3 is continuously operated. Further, a DO meter 5 for measuring the DO of the mixed liquid is provided in the intermittent aeration tank 1, and the DO in the tank is
When it exceeds 1.5 mg / l, the amount of air from the compressor 4 is decreased or the rotation speed of the agitator of the submersible aerator 3 is decreased. In the case of this embodiment, the rotation of the agitator is changed. I try to reduce the number.

The treated sewage discharged from the intermittent aeration tank 1 flows into the settling tank for solid-liquid separation, a part of the sludge is returned to the intermittent aeration tank 1 by the sludge pump P, and the remaining sludge is discharged to the outside of the system. Then, the treated water is taken out from the upper part of the settling tank 2.

Experiments with the above apparatus were carried out on the present invention and its contrasting control. In each of the aeration cycles, the air supply time B was 60 minutes, the air supply stop time A was 60 minutes, and the DO setting value was 1.5 mg / l. If these values were exceeded, the stirring device of the submersible aerator 3 Oxygen supply was controlled by reducing the number of revolutions by 20% from that of normal operation. Other conditions are shown in Table 1.

[0018]

[Table 1] processing conditions (the onset bright) (control) processing water amount 2m ³ / day 2m ³ / day during repeated stagnation reservoir of repeat 60 minutes ON-60 minutes OFF of aeration cycle 60 minutes ON-60 minutes OFF Between 24 hours 24 hours Average inflow BOD 175mg / l 172mg / l Average inflow SS 138mg / l 140mg / l Average inflow N 27mg / l 25mg / l Water temperature 18 ℃ 18.2 ℃ MLS S 3,200mg / l 3,300mg / l

Regarding the change with time of DO due to the aeration cycle in the intermittent aeration tank according to the above experiment, the state from 2:00 am to 4:00 am when the load is small, as shown in FIG. When it exceeded mg / l, the rotation speed of the stirring device was reduced by 20%, but this slowed down the increase in DO, and the maximum value of DO was 2.0 m even when the load at night was small.
It remains at g / l, and it can be seen that the anaerobic time can be secured even at night when the load is small, compared to the case of the conventional control example in which the oxygen supply is not controlled.

The results of the above experiment show that, as shown in Table 2, the treated water quality according to the present invention has a better nitrogen removal rate than the control. Further, the power consumption of the underwater aerator was 6.3 Kwh / day in the present invention, whereas it was 6.9 Kwh / day in the target example, and the power consumption was about
It has been reduced by 10%.

[0021]

[Table 2] Treated water quality Example of exposure control BOD 3.5 to 6.2 mg / l 3.9 to 6.5 mg / l SS 12 to 15 mg / l 10 to 16 mg / l T-N 3.3 to 4.5 mg / l 4.0 to 7.1 mg / l NH ₄ -N 0.9 to 2.9 mg / l 0.8 to 3.2 mg / l No _x -N 0.2 to 2.3 mg / l 0.3 to 4.1 mg / l

[0022]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the aerobic time zone and the anaerobic time zone are set when the wastewater is treated by alternating the aerobic and anaerobic atmospheres in the single reaction tank by intermittent aeration. The operation is performed at a predetermined ratio, and when the DO exceeds the predetermined value during the aerobic time zone, the aerobic treatment is controlled, so that the reaction time in the aerobic state and the anaerobic state is appropriate. In addition to being retained, the increase of the DO value is suppressed especially when the load is small, the nitrogen removal effect is good, and the removal rate of organic substances and SS is also good.
In addition, useless consumption of power can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus applied to an embodiment of a method of the present invention.

FIG. 2 is a comparison diagram of DO patterns of the method of the present invention and a target.

[Explanation of symbols]

 1 Intermittent aeration tank 2 Sedimentation basin 3 Underwater aerator 4 Compressor 5 DO meter A Anaerobic operating time B Aerobic operating time C Aerobic control time

Claims (1)

[Claims] In a method for treating sewage by intermittently aerating sewage in a single reaction tank while continuously stirring the sewage and alternately switching the inside of the tank to an anaerobic state and an aerobic state, in one intermittent cycle , The anaerobic time zone in which air is not supplied and the aerobic time zone in which air is supplied are set at a predetermined ratio, and when the DO in the tank exceeds a predetermined value during the aerobic time zone, air is supplied. A method for treating sewage, which comprises reducing the amount and / or the rotation speed of a stirrer.