JPH04193399A - Operating method of aeration stirrer of single tank type anaerobic and aerobic activated sludge method - Google Patents

Abstract

PURPOSE:To effectively progress the oxidation under an aerobic condition and the denitrification and dephosphorization under an anaerobic condition by operating a stirring mechanism in such a manner that the rotating speed of the stirring mechanism at the time of aeration and the rotating speed of the stirring mechanism at the time of the stop of the aeration vary. CONSTITUTION:The rotating speed of stirring vanes is varied by a controller 5 in the case of using a submersible aerator 3 or a propeller. An inverter or VS motor is adequately used to change the rotating speed. Sewage flows through an inflow pipe 8 into an aeration tank 1 and the oxidation decomposition by aeration or denitrification or the taking in of org. matter under the anaerobic condition is executed. The liquid mixture of an aeration tank 1 is sent via a piping 14 to a settling basin 2 and is subjected to a solid-liquid sepn. to treated water and sludge in this settling basin 2. The supernatant, thereafter, flows as the treated water 9 to the outside of the system and the separated and concentrated sludge is returned as return sludge via a return piping 10 to the aeration tank 1 by a pump 11. A part of the return sludge is properly discharged as excess sludge via an excess sludge withdrawing pipe 16 by a pump 15.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for biologically treating organic wastewater such as sewage and industrial wastewater containing organic pollutants using a single-tank anaerobic and aerobic activated sludge method. The present invention relates to a method for operating and controlling an aeration agitation device.

[Prior art] Intermittent aeration using an aeration agitation device has conventionally been used in the batch activated sludge method and the single tank anaerobic method (Japanese Patent Application Laid-Open No.
310798) etc. In this case, there are systems in which the aeration function and stirring function are provided separately, and systems in which the aeration function and the stirring function are combined in one device.

Examples of systems that have separate aeration and agitation functions include an aeration pipe with an external blower and an agitation fitting above the aeration pipe. In addition, as a device that has both stirring and aeration functions, there is an underwater machine that sends compressed air before or after the impeller in the casing, and uses the shearing action of the water flow or the rotational action of the impeller to atomize air bubbles and disperse them into the liquid. type equipment, or
There is a circulating pump mixing type device in which pressurized water from a pump is passed through a liquid nozzle to form a shet flow, and at the same time, compressed air sent from a blower is mixed to form a gas-liquid multiphase flow.

In the batch activated sludge method and the single tank anaerobic and aerobic method, an external blower and a stirrer are operated simultaneously during aeration to perform aeration and stirring, and the inflow organic matter that comes into contact with the activated sludge under aerobic conditions is is oxidized to C02 and H2O, and NH4
-N becomes N0x-N. On the other hand, when aeration is stopped, the operation of the blower is stopped and the supply of air or gas containing oxygen is stopped, but the agitator or pump is kept running to mix and stir the inflowing sewage and activated sludge. As a result, the dissolved oxygen in the aeration tank is rapidly consumed, resulting in anaerobic conditions, and the organic matter that has flowed into the tank is either decomposed by denitrification or taken up by dephosphorizing bacteria. Further, NOx-N is reduced to N2 and dissipated into the atmosphere.

By performing this type of operation, advanced treatment such as not only BOD and SS removal but also nitrogen and phosphorous removal can be performed in a single aeration tank, so aeration and stirring can be carried out by combining an aeration function and a stirring mechanism in such an aeration tank. The use of devices is becoming popular.

[Problems to be Solved by the Invention] In this way, in the aeration stirring device, compressed gas is atomized by the flow rate of the shet flow generated when pressurized water pressurized by the stirrer or pump is ejected from the liquid nozzle. Therefore, the oxygen dissolution efficiency is higher than that of the diffuser plate method alone, and as a result, the amount of aeration air can be reduced, which has the advantage of reducing the power of the blower. However, since power is also required for stirring, the overall energy consumption has not been reduced much.

Furthermore, during aeration, power from agitation is applied in addition to aeration, which increases the shearing force on activated sludge flocs, causing deterioration in the properties of activated sludge, especially in sedimentation properties due to finer flocs, and clouding and floating of treated water. Problems such as an increase in sludge were recognized.

In particular, this tendency is high in the single-tank anaerobic and aerobic activated sludge method, which targets small-scale sewage and is based on continuous inflow consisting of a single aeration tank and settling tank, and improvements are needed.

The present invention has been proposed in view of the problems of the prior art, and aims to provide a novel sewage treatment method that can effectively treat sewage.

[Means for Solving the Problems] As a result of intensive studies to improve the above-mentioned problems, the inventors decided to appropriately change the rotational speed of stirring during aeration and when stopping aeration, and to improve the optimum speed even during aeration. It was discovered that good processing results could be obtained by operating at a high rotational speed, and the present invention was created.

In the present invention, an aeration device and an agitation device or an aeration and agitation device that integrates aeration and agitation are installed in the aeration tank of a single-tank anaerobic and aerobic activated sludge treatment equipment, and the aeration and agitation are performed while continuously flowing wastewater. Aeration is performed intermittently using a device, and the rotation speed of the stirring mechanism during aeration is different from the rotation speed of the stirring mechanism when aeration is stopped.

In the present invention, the rotation speed of the stirring device during aeration, the aeration air volume, or both are changed according to the load amount of inflow water, that is, according to at least one of the BOD load, Do concentration, and 0RPO of wastewater. You can also do that.

Further, the rotation speed of the stirring device during aeration, the aeration air volume, or both may be configured to be changed according to a preset time sequence.

When carrying out the present invention, it is preferable to install a Do meter and an ORP meter in the aeration tank and control the Do value within the range of 1 to 4 ■/l during aeration, or the ORP value to be controlled within the range of +50 to +1.
It is preferable to control the voltage within a range of 00 mV (measured with a gold-silver chloride electrode). Here, when the Do value or the ORP value is high, the rotation speed of the stirring device and/or the aeration air volume is controlled to be lowered, and when it is low, it is controlled to be increased.

Further, various known techniques can be applied to control the rotation speed of the aeration stirring device, but in particular, the use of an inverter can significantly reduce power consumption, which is advantageous in terms of energy.

When the aeration is stopped, the rotational speed of the aeration stirring device becomes low. Specifically, the circumferential speed of the stirring blade of the stirring device is 5 m/'
The rotation speed is controlled so that it is within seconds. In other words, in the present invention, the control may be performed based on the rotational speed of the stirring device or the peripheral speed of the stirring blade.

[Function] According to the method of the present invention having the above-described configuration, by operating the stirring device at different rotational speeds during aeration and at different rotational speeds when the aeration is stopped, oxidation and Effectively promotes denitrification and dephosphorization under anaerobic conditions. As a result, the properties of the activated sludge are made good, and in particular, it is possible to suppress the deterioration of sedimentation properties due to finer flocs, the cloudiness of treated water, and the increase in floating sludge, thereby achieving efficient sewage treatment.

[Example] The present invention will be described in detail below with reference to the accompanying drawings and tables.

The apparatus shown in FIG. 1 is used in an example for investigating the effects on sludge properties and treated water quality when an aeration tank is provided with an aeration agitator and an agitator.

This apparatus, designated as a whole by the reference numeral 20, has an aeration tank 22 and 37! having an actual volume of 101! The aeration tank 22 is provided with an aeration pipe 26 connected to an air pump (not shown) and an agitator 28 above the aeration pipe 26. Here, the air pump was configured to perform aeration by intermittent operation using a timer (not shown), and the agitator 28 used was one whose rotational speed could be changed arbitrarily.

The experiment used activated sludge that had been previously acclimatized with artificial sewage using peptone and acetic acid as organic carbon sources, and a portion of the activated sludge was put into the experimental apparatus, and the same artificial sewage was continuously added while the activated sludge was heated using a preset agitator 28. The treatment was carried out for 24 hours under the rotational speed and aeration conditions, and the properties of the sludge and the quality of the treated water were examined. After data collection, the sludge was replaced, the same operation was performed under different conditions, and data was collected.

FIG. 2 shows the results of Do, SV, ..., and treated water transparency of the aeration tank 22 when aeration is performed continuously and the number of revolutions of the stirrer 280 is varied.

The sludge properties and treated water transparency are determined when the rotation speed of the agitator 28 is 110.
It started to get worse when it exceeded 0 orp and reached 1600 rpm.
Above that, it became quite cloudy. On the other hand, it was observed that Do in the aeration tank 22 tended to increase as the rotation speed increased.

From the above results, it is clear that although oxygen dissolution efficiency increases by providing the agitator 28, when the rotation speed of the agitator 28 increases beyond a certain level, it has a negative effect on the sludge properties and the quality of the treated water. .

Next, we will discuss various treatment performances when the rotation speed of the agitator 28 is set high during aeration to increase oxygen dissolution efficiency, and when the aeration is stopped, the rotation speed of the agitator 28 is set low enough to prevent sludge from settling. The results of the study are summarized in Table 1. Here, in Run 5 of Table 1, the rotation speed during aeration or when aeration was stopped was changed depending on the time period. In this experiment, sewage was continuously flowed, and the time cycle of aeration and aeration stop was 30 minutes intermittently.

As a result of experiments using the apparatus 20 shown in FIG. 1, it became clear that the quality of treated water and the properties of sludge could be sufficiently improved by lowering the rotational speed of the agitator when aeration was stopped.

The configuration and operation of an apparatus created based on the above experimental results and suitable for carrying out the present invention will be described with reference to FIG. 3.

In FIG. 3, the apparatus suitable for carrying out the present invention consists of an aeration tank 1 and a sedimentation tank 2 connected to it. ) is installed, and air is supplied to the aerator 3 from a blower 4 via an air pipe 12.

Note that the aeration and stirring device is an underwater mechanical aeration and stirring device (
Instead of a submersible aerator, a circulating pump mixed type aeration device may be used (or, an aeration pipe or a diffuser plate may be installed as an aeration and agitation device, and an agitator such as a propeller may be provided above the aeration device, as shown in Fig. 1). The configuration may be similar to that of the device.

When using the underwater aerator 3 or a propeller, the rotation speed of the stirring blade, and when using the circulation pump mixed diffuser, the rotation speed of the impeller within the pump are made variable via the controller 5. The rotation speed is preferably changed using an inverter or a VS motor, and is controlled by the controller 5. The blower 4 is one that can be operated intermittently by a timer or controller 6. Sewage flows into the aeration tank 1 through an inflow pipe 8, and is subjected to oxidative decomposition by aeration or denitrification, or organic matter is taken in under anaerobic conditions.

The mixed liquid in the aeration tank 1 is sent to the sedimentation tank 2 via a pipe 14, where it is separated into solid and liquid into treated water and sludge. Thereafter, the supernatant liquid flows out of the system as treated water 9, and the separated and concentrated sludge is sent to the pump 1 as return sludge via return piping 10.
1 is returned to the aeration tank 1. Here, a part of the returned sludge is appropriately discharged as surplus sludge by the pump 15 via the surplus sludge extraction pipe 16.

In this apparatus implementing the present invention, the rotational speed of the submersible aerator 3 (or agitator) is operated at a low speed when aeration is stopped. Specifically, a stirring blade (not shown)
It is good if the circumferential speed is 5 m/sec or less.

In addition, during aeration, the quality and amount of inflow water fluctuate over time, and if the BOD load fluctuates, it is preferable to change the amount of oxygen supplied depending on the load conditions. In particular, in order to improve denitrification and dephosphorization performance, it is necessary to avoid blowing in excess oxygen during aeration. Therefore, when the BOD load is low, the rotation speed of the stirrer is lowered to lower the oxygen dissolution efficiency, or at the same time, the aeration air volume is also reduced to reduce the oxygen supply amount. In this case, the rotation speed of the submersible aerator 3 (or agitator) and the amount of air supplied from the blower 4 can be controlled through the controller 5.6 in conjunction with the Do meter or ORP meter 17 installed in the aeration tank 1. can. here,
Beams during aeration.

It is preferable to control the value within the range of 1 to 4 /l, and OR
The P value is preferably controlled within the range of +50 to 100 mV (measured with a gold-silver chloride electrode). If either value is high, reduce the rotation speed and/or aeration air volume, and if low, increase it.

Note that the controllers 5 and 6 may be connected to each other,
Alternatively, it may be controlled by one controller. In addition, when the time fluctuation of BOD load is almost constant as in the case of domestic sewage, it is possible to operate by controlling the rotation speed and aeration air volume according to a preset time sequence in conjunction with a timer.

In this way, by changing the rotation speed of the stirring mechanism or changing the aeration air volume of the blower depending on the operating conditions, it is possible to improve the sludge properties of activated sludge and the quality of treated water.

Also, can various known techniques be applied to rotation speed control?
In particular, by using an inverter, power consumption can be significantly reduced, which is advantageous in terms of energy.

Next, a more specific example will be explained.

(1) Initially, the underground water treatment facility (aeration tank volume: 250 m3) with long-term aeration with a treated water volume of 300 m3/d.
Because it was recognized that nitrification was progressing, the pH of the treated water was decreasing, and there were problems such as disassembly of activated sludge (Runl), the aeration agitation device was replaced with a submersible aeration agitation device (submersible aerator output 2.2k).
w), and intermittent aeration was performed every 30 minutes. As a result, a high nitrogen removal rate was obtained and the quality of the treated water improved (
In Run 2) of Table 2, the visibility was somewhat poor, and the floating of fine bubbles with sludge attached was also observed.

For this reason, an inverter is attached to the aerator, and the speed is 300 rpm (peripheral speed; 3 m/'s) during aeration and 1 m/'s when aeration is stopped.
It was operated at a circumferential speed of 0100 rpm; 2.7 m/s). As a result, as shown in the data for Run 3 in Table 2, the quality of the treated water was improved, and the settling properties of the sludge were also improved. It was also recognized that there was a considerable energy saving effect.

(2) An experiment was conducted to treat domestic sewage of 25 m'/d using a pilot plant system consisting of an aeration tank with a practical volume of B m 3 and an associated settling tank (practical volume: 4 m'). A model machine (output: 04 kW) of an underwater mechanical aeration and stirring device (underwater aerator) was installed as an aeration and stirring device.

Run 1 was subjected to continuous aeration (aerator rotation speed: i500 rpm, circumferential speed 10 m/s
). Run 2 was operated at 1500 rpm during aeration and 700 rpm when aeration was stopped (peripheral speed 4.7 m/'S). Run 3 is from 1:00 a.m. to 6:00 a.m. during aeration.
The average BOD volume load during this time period is 0. 26Kg/m
Since it is as low as 3.d, the rotation speed of the aerator during aeration is set to 10.
100 Orp peripheral speed was lowered to 6.7 m/s), and during other aeration operations, the operation was performed at 1500 rpm.

Further, when the aeration was stopped, the operation was performed at 700 rpm.

Intermittent aeration is performed in an hourly cycle, and from 3:00 am to 6:00 am, the BOD volume load during this time is 0.10.
Since it was less than Kg/'m'·d, the aeration air volume was also reduced by half. The results are summarized in Table 3.

Compared to Run 1, it was observed that SS1 nitrogen and phosphorus removal was improved in Run 2. In addition, Run 3 has an even greater nitrogen and phosphorus removal effect than Run 2, and has improved BOD, SS,
Good transparency values were also obtained.

[Effect of the invention] The effects of the present invention are listed below.

(King) By operating the stirring mechanism at different rotational speeds during aeration and when the aeration is stopped, oxidation under aerobic conditions and denitrification and dephosphorization under anaerobic conditions can be effectively achieved. It is possible to proceed to

(2) By improving the properties of activated sludge, it is possible to achieve efficient sewage treatment by suppressing deterioration of sedimentation properties due to finer flocs, clouding of treated water, and increase in floating sludge.

(3) Overall energy consumption can be kept low.

[Brief explanation of the drawing]

Fig. 1 is a side view showing a device to which one embodiment of the present invention is applied, Fig. 2 is a characteristic diagram showing the operation of the device in Fig. 1, and Fig. 3 is a device to which another embodiment of the present invention is applied. FIG. 1.22... Aeration tank 2.24... Sedimentation tank 3
...Underwater mechanical aeration stirring device (underwater aerator) 26
... Diffusion pipe 28 ... Stirring mechanism 1 Table 2 Table 3

Claims (3)

[Claims] (1) An aeration stirring device is installed inside, and while sewage is continuously flowing in, aeration is performed intermittently while giving a stirring action using the aeration stirring device, and the anaerobic state and aerobic state are changed at each required time. In a method for operating an aeration agitation device in a single-tank anaerobic and aerobic activated sludge method consisting of a single aeration tank and a settling tank that alternately repeat A method for operating an aeration agitation device in a single-tank anaerobic and aerobic activated sludge process, which is characterized by operating the aeration stirring device in different numbers. (2) The single-tank anaerobic and aerobic activated sludge method according to claim (1), wherein the aeration air volume and/or the rotation speed of the aeration stirring device during aeration are changed in accordance with the load amount of water flowing into the aeration tank. How to operate an aeration agitator in. (3) Operation of the aeration agitation device in the single-tank anaerobic and aerobic activated sludge method according to claim (1), wherein the aeration air volume and/or the rotation speed of the aeration agitation device during aeration are changed according to a preset time sequence. Method.