JP2748041B2 - Uniform mixing method of aeration tank in activated sludge treatment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for uniformly mixing activated sludge and an immobilized carrier in an aeration tank used for treating activated sludge in wastewater or the like. .

(Prior art) Wastewater such as sewage is generally treated in a treatment plant first by a sand basin,
First, after removing most of the sediment and coarse suspended solids in the sedimentation basin, etc., the activated sludge treatment is performed in the aeration tank to decompose and remove the pollutants, and the activated sludge is settled and separated in the final sedimentation basin. It is treated by releasing clear water after chlorination.

In recent years, as a trend of technology development for activated sludge treatment of sewage,
Treatment technology for maintaining the activated sludge in the bioreactor at a high concentration using the activated sludge immobilization carrier to improve the treatment efficiency, treated water quality, etc., and dividing the reactor with activated sludge into an anaerobic zone and an aerobic zone Phosphorus compounds, nitrogen compounds,
Processing technology for simultaneous removal of BOD has been developed.

There are many issues to be solved in the development of these new processing technologies. For example, an inorganic fixed carrier such as furnace water granulation, zeolite, silica sand, cristobalite, and incinerated ash of coal is added to an aeration tank for uniformly mixed activated sludge treatment, and the activated sludge is fixed to the carrier and sedimentation of the activated sludge is performed. There is a method for improving the performance and maintaining the concentration of activated sludge in the reactor at a concentration. Japanese Patent Application Laid-Open No. 63-42796 describes a method in which furnace granulation is added to an aeration tank for treatment. This is to increase the efficiency of decomposing and removing pollutants by increasing the concentration of activated sludge in the aeration tank, etc., by adding furnace water granulation to use as a carrier for immobilizing activated sludge. In this new treatment technology, if the oxidation-reduction potential (ORP), which is closely related to the decomposability of pollutants such as sewage, is controlled, activated sludge immobilized on the inorganic immobilization carrier will pass through the aeration tank. It does not flow uniformly, which may lead to a decrease in treatment efficiency and a deterioration in treated water quality. That is, the activated sludge immobilized on the inorganic immobilization carrier has a higher specific gravity than the activated sludge that is not immobilized. Therefore, a large amount of aeration is required to uniformly flow the activated sludge. For this reason, when sewage with a low concentration of pollutants flows in due to rainfall or the like, the ORP of the aeration tank reaches a predetermined ORP value with a small amount of aeration, and the activated sludge fixed on the inorganic immobilization carrier has the bottom of the aeration tank. It accumulates in a dead space or the like, and the accumulating portion becomes anaerobic, which causes many problems. In particular, the conventional flat-bottom type aeration tank tends to cause such a problem, and therefore uses a very fine inorganic fixed carrier, for example, 20 μm or less. However, when such a fine immobilized carrier is used, a large amount of the immobilized carrier flows into the treated water, so that a predetermined performance cannot be obtained. For this reason, ship bottom type aeration tanks have been developed to prevent the accumulation of inorganic immobilized carriers.

In addition, the bioreactor where activated sludge is present is divided into an anaerobic zone and an aerobic zone, and phosphorus compounds, nitrogen compounds,
In the method of removing BOD at the same time, it is necessary to control and control the anaerobic degree of the aeration tank, mix the activated sludge uniformly in the aeration tank, and ensure sufficient contact between the wastewater and the activated sludge. When it is insufficient, the efficiency of decomposing and removing pollutants decreases.

For example, Japanese Patent Application Laid-Open No. 63-126599 describes a continuous activated sludge treatment method. Regarding anaerobic control, the ORP of an aeration tank is measured, and the ORP is measured by mechanical stirring or aeration.
Is to be controlled.

In this case, the aerobic tank sets the ORP at +100 to +150 mV (gold-silver /
(A silver chloride electrode), the aeration is sufficiently performed, and the activated sludge flows almost uniformly in the aerobic tank. However, the anaerobic tank makes the activated sludge flow by mechanical stirring, but when vigorously stirred so that the activated sludge does not settle, air is entrained, and the ORP of the anaerobic tank rises above the set value, making it impossible to remove phosphorus compounds and nitrogen compounds. May be enough.

(Problems to be Solved by the Invention) A method for improving the treatment efficiency and treated water quality by adding an inorganic immobilized carrier to an activated sludge treatment aeration tank, for example,
In the method described in JP-A-63-42796, aeration is
It plays the role of decomposing pollutants indicated by BOD and uniformly flowing the activated sludge immobilized on the inorganic immobilization carrier into the aeration tank. However, if aeration is performed using the ORP in the aeration tank as an index to decompose the BOD, the BOD will be sufficiently decomposed. Since the activated sludge having a high specific gravity is not suitable for the BOD, it is necessary to uniformly flow the activated sludge without adversely affecting the ORP closely related to the degradability of BOD.

Similarly, in a process in which a reactor in which activated sludge is present is divided into an anaerobic tank and an aerobic tank to simultaneously remove phosphorus compounds, nitrogen compounds and BOD, the sludge in the anaerobic tank is discharged as activated sludge, which is indispensable for removing phosphorus. It is necessary to make the fluid flow evenly while maintaining an appropriate ORP for the denitrification reaction.

Therefore, for example, when the aeration amount is increased as in the aerobic tank in the continuous activated sludge treatment or the aerobic step in the batch activated sludge treatment, the activated sludge and the immobilized carrier are also mixed to some extent. If the amount of aeration is reduced to reduce ORP as in the process, or if aeration is not performed at all, the uniform mixing means becomes insufficient. However, it goes without saying that even in an anaerobic state, the activated sludge and the immobilized carrier need to be uniformly mixed and sufficiently contacted with the wastewater. In addition, even in aerobic tanks and aerobic processes, uniform mixing is only an incidental matter, so a large amount of aeration may only result in uniform mixing, and aeration is insufficient due to insufficient uniform mixing. Further increase in the amount is often not allowed in relation to ORP, and no consideration was given to controlling the homogenous mixture itself on its own criteria.

The present invention provides a method capable of uniformly mixing activated sludge and immobilized carrier independently of ORP control in an aeration tank in which activated sludge is present.

(Means for Solving the Problems) The present invention measures the ORP of an aeration tank, controls the amount of aeration based on the measured ORP, measures the turbidity of the aeration tank, and measures the turbidity based on the measured turbidity. This is a method for uniformly mixing an aeration tank in activated sludge treatment, characterized by controlling the amount of mechanical stirring.

(Action) The present invention relates to a reactor ORP in which activated sludge is present,
The aerobic tank controls the aeration amount so that it can maintain the appropriate value for the oxidative decomposition of BOD, nitrification reaction, intake of phosphorus by activated sludge, etc., and the anaerobic tank maintains the appropriate value for the release of phosphorus from activated sludge and the denitrification reaction. Manage and control by At the same time, the activated sludge immobilized on the inorganic immobilization carrier and the activated sludge in the anaerobic tank are flowed to a concentration suitable for oxidative decomposition of BOD, nitrification, denitrification, release of phosphorus by activated sludge, ingestion, etc. Then, the stirring intensity of the underwater stirrer installed at the bottom of the reactor is controlled by the activated sludge concentration meter installed in the reactor, and the flow state of the activated sludge in the reactor is appropriately maintained.

First, the ORP control method of the reactor will be described. O
The RP control includes an ORP center 7 (gold-silver / silver chloride electrode) immersed in the reactor 1 as shown in FIG. 1, an ORP controller 8 and a roots blower 9. The aeration is always performed, and when the ORP falls below the set value, the rotation speed of the roots blower 9 is increased to increase the aeration amount, and when the ORP is restored to the set value, the rotation speed is decreased to reduce the aeration amount. On the other hand, in the anaerobic tank, the activated sludge is normally flown by the below-mentioned agitator 5 without performing aeration, but when the ORP falls below the set value, the aeration is performed from the bottom of the reactor 1 and when the ORP is restored to the set value, the aeration is started. Control is performed by an on-off method in which the motor stops.

Next, a method for maintaining the flow of the reactor in a state suitable for wastewater treatment will be described. Flow control of activated sludge
As shown in FIG. 1, the apparatus comprises an activated sludge concentration meter 4 installed in the reactor 1, an underwater stirrer 5 installed at the bottom, and a rotation speed control device 6 of the stirrer 5. The activated sludge concentration is controlled by measuring the activated sludge concentration with the activated sludge concentration meter 4 and, when the concentration is lower than the set value, increasing the number of revolutions of the underwater agitator 5 by the control device 6 so that the activated sludge flow is actively performed. When the speed has recovered, the rotation speed is reduced.

In addition, it is good to use the thing of a structure which does not entrap air on the surface of a water as an underwater stirrer. This is because when air is entrained by the underwater stirrer, the ORP rises above the set value and ORP control becomes impossible, and many problems occur. For example,
In the case of aerobic activated sludge treatment, a nitrification reaction occurs in addition to the oxidative decomposition of BOD, and the nitrate and nitrite nitrogen compounds are denitrified in the sludge sedimentation tank. It may cause a decrease in the quality of treated water. In the case of an anaerobic tank, when the ORP rises, the release of phosphorus from the activated sludge and the denitrification reaction are inhibited, so that the performance of removing these pollutants decreases.

The activated sludge densitometer is most suitable for the ultrasonic method, and should be installed at 1/3 to 1/4 from the water surface of the reactor.

As explained above, ORP control of the reactor is indispensable for oxidative decomposition of BOD, nitrification / denitrification reaction, and phosphorus removal in the reactor where activated sludge exists. Further, in order to carry out these reactions efficiently and obtain good treatment performance, it is necessary to maintain the activated sludge at an appropriate concentration. For this reason, if the flow of the activated sludge relies on aeration or a general stirring method, the ORP cannot be maintained at an appropriate value. Therefore, it is difficult to maintain an appropriate ORP value and a flow state of activated sludge in the reactor by the conventional technology. The present invention can maintain ORP properly regardless of anaerobic state or aerobic state by using both the aeration amount control based on the ORP measurement value of the reactor and the control of the intensity of stirring based on the activated sludge concentration measurement. Activated sludge can be maintained at an appropriate concentration.

(Example) An example of the present invention will be described.

Example 1 Reactor 1 having activated sludge as shown in FIG.
In the activated sludge treatment facility consisting of a sludge sedimentation tank and a sludge sedimentation tank, an aeration diffuser 10 and an impeller type underwater stirrer 5 are installed at the bottom of the reactor 1, the amount of aeration is indicated by the ORP of the reactor 1, and the impeller The number of revolutions, that is, the stirring intensity was controlled and controlled by the activated sludge concentration detected by the ultrasonic activated sludge concentration meter 4 installed at about 1/4 from the upper part of the reactor 1 to perform the activated sludge treatment of sewage.

Specifically, the reactor (1.5 x 1.5m x 4m depth, capacity 9
m ³ ) is charged with the activated sludge mixed solution (concentration: 1000-1500 mg / l) taken from the reactor of the homogeneous mixing type activated sludge treatment, and the fine powder of the furnace water granulation (particle size distribution 20-200 μm, 50% average particle size) : 60 μm) as an initial charge, and about 270 kg (3% by weight based on the reactor capacity) was added.
The treatment time was set to 3 hours to carry out sewage treatment. The sludge settling tank of this device has a capacity of about 2 m ³ (diameter 2 m, depth 1.5 m),
The experiment was performed with a sludge return rate of 25%.

To control the amount of aeration, set the ORP of the aeration tank to +50 mV (using a gold-silver / silver chloride ORP sensor), and when the ORP falls below the set value, increase the rotation speed of the roots blower 9 by the ORP controller 8 to perform aeration. The amount was increased, and when the ORP recovered to the set value, the PID method was used in which the number of revolutions of the blower 9 was reduced to reduce the amount of aeration. This allows the reactor ORP to be set to ± 10m
V was maintained with accuracy.

Next, the stirring intensity of the underwater stirrer 5 which is effective for the flow of the activated sludge adhering to the furnace water granulation is set at about 2 m from the water surface of the aeration tank. Was connected to the underwater stirrer rotation speed controller 6, and the controller 6 controlled the rotation speed of the impeller of the stirrer 5. That is, in the case of this experiment, the control value of the densitometer 4 was set to 20,000 mg / l, and when the sludge concentration was lower than this set value, the rotation of the impeller was accelerated, and when the sludge concentration was restored to the set value, the rotation was slowed down. The flow of the activated sludge in the tank was made uniform.

As a result of performing activated sludge treatment of sewage in such a method,
Activated sludge in reactor 1 can be uniformly mixed with an accuracy of 20,000mg / l ± 3,000mg / l, and activated sludge treatment of sewage can be performed in a short time of 3 hours. As shown in Table 2, good treated water quality was obtained.

Example 2 In a treatment system for simultaneously removing BOD, nitrogen compounds, and phosphorus compounds in sewage, one anaerobic tank, one aerobic tank, two anaerobic tanks, and two aerobic tanks from the inlet side to which sewage and returned sludge are supplied. It consists of a reactor (50 width x 3000 length x 1500 mm depth, 3.5 m ³ capacity) and a sludge sedimentation tank where the divided activated sludge exists, and manages and controls the aerobic and anaerobic degree of each tank using ORP as an index. An ORP controller was installed in each tank, and an anaerobic tank was equipped with an ultrasonic activated sludge densitometer, a rotational speed controller connected to it, and a submersible stirrer.

The ORP of each tank is -250mV for one anaerobic tank and +12 for one aerobic tank.
The two anaerobic tanks were controlled at -150 mV and the two anaerobic tanks were controlled at +150 mV by the above-described method. The activated sludge concentration control systems were installed in one anaerobic tank and two anaerobic tanks, respectively, and the activated sludge concentration was controlled and controlled at 2500 ± 500 mg / l by the method described above. the apparatus of aqueous ferric chloride solution can approximately 5ml added per sewer 1 m ³ is provided, the chloride 2
The aqueous iron solution was added to the treated water at the outlet of the aerobic two tanks in the ratio described above.

The treatment conditions were as follows: treatment time: about 8 hours, sludge return rate: 25
%, The sewage dispensing ratio to the anaerobic 1 tank and the anaerobic 2 tank was 4: 3.

As a result of pilot plant experiments on the method of simultaneously removing BOD, nitrogen compounds and phosphorus compounds in sewage, the ORP of each tank was set to ± 20 mV, and the activated sludge concentration was accurate to 2500 ± 500 mg / l. Each managed and controlled. Table 2 shows an example of the processing performance.

(Effect of the Invention) According to the present invention, the anaerobic degree and aerobic degree of the reactor can be controlled and controlled accurately under appropriate conditions, and the activated sludge concentration of the reactor can be kept substantially uniform. As a result, the activated sludge using the inorganic immobilized carrier can be made to flow almost uniformly without adversely affecting the ORP, thereby improving the treatment efficiency and the quality of the treated water. Energy can be minimized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an apparatus for carrying out the present invention. DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Sewage supply pump, 3 ... Return sludge pump, 4 ... Activated sludge concentration meter, 5 ... Underwater stirrer, 6 ... Underwater stirrer rotation speed control device, 7 ... ORP sensor, 8 …… ORP controller, 9 …… Roots blower, 10
…… a diffuser, 11 …… to a sludge settling tank.

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroshi Kamori 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation 3rd Technical Research Institute (56) References JP-A-49-23946 (JP, A) JP-A-61-57295 (JP, A)

Claims (1)

(57) [Claims] 1. A method for measuring the ORP of an aeration tank, controlling the amount of aeration based on the measured ORP, measuring the turbidity of the aeration tank, and controlling the amount of mechanical stirring based on the measured turbidity. A method for uniformly mixing an aeration tank in activated sludge treatment.