JP2548561B2 - Wastewater treatment method and apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a circulating fluidized bed type wastewater treatment method, and more particularly to a wastewater treatment method capable of saving energy required for aeration and maintaining high treatment efficiency, and a method thereof. Regarding the device.

“Prior art and its problems” Conventionally, as one method of treating wastewater, for example, wastewater in which a microbial carrier is suspended is circulated and fluidized by turbidity, and the wastewater is removed by microorganisms carried on the microbial carrier. Clean aerobically. There is a so-called circulating fluidized bed type wastewater treatment method.

This circulating flow type wastewater treatment method can support many microorganisms on the surface of the microorganism carrier having a large specific surface area and can increase the chances of contact with the microorganism carrier by aeration, thus enhancing the treatment capacity per unit volume of the treatment tank. Since it is obtained, it is excellent in that the processing tank can be made compact.

By the way, in such a wastewater treatment method, the aeration amount required to fluidize the microbial carrier (hereinafter referred to as the fluidizing aeration amount) is the same for the production of the treatment tank, the type and the diameter of the microbial carrier, and the like. If so, the larger the rate of addition of the microbial carrier to the wastewater, the larger. Further, the aeration amount that can satisfy the oxygen demand amount in the wastewater (hereinafter referred to as the oxygen supply aeration amount).
If the type of organic matter (substrate) in the wastewater is the same,
D It increases as the volumetric load increases. Then, the magnitude relationship between the fluidized aeration amount and the oxygen supply aeration amount may be reversed at a predetermined value of the BOD volumetric load.

Therefore, the aeration amount required for wastewater treatment is premised on satisfying the above fluidization aeration amount and oxygen supply aeration amount at the same time, and it is necessary to decide on the basis of the larger of these aeration amounts. .

However, in the conventional wastewater treatment method, aeration gas (air, oxygen-enriched gas, etc.) to the wastewater is treated throughout the treatment.
In many cases, the amount was determined based on either the fluidization aeration amount or the oxygen supply aeration amount. That is, when the amount of aeration gas is determined based on the above fluidization aeration amount, when the BOD volumetric load of the wastewater is smaller than a predetermined value, the oxygen supply aeration amount is smaller than the fluidization aeration amount, and the oxygen in the wastewater is reduced. Wastewater can be purified because the required amount is small, but when concentrated wastewater flows into the treatment tank and the BOD volume load increases, the oxygen demand of the wastewater increases,
Since the oxygen supply aeration amount is larger than the fluidization aeration amount, the aeration amount based on the fluidization aeration amount is too small,
There was a problem that the amount of dissolved oxygen in the wastewater was insufficient and the decomposition of organic substances in the wastewater did not proceed, resulting in insufficient purification of the wastewater.

In addition, the aeration amount control by the dissolved oxygen (hereinafter,
It is called DO control. ), When the BOD volume load is smaller than the specified value, the fluidization aeration amount becomes larger than the oxygen supply aeration amount, so the aeration amount becomes insufficient and some of the microbial carriers in the wastewater are fluidized. However, there is a drawback that the amount of microbial carriers that are deposited on the bottom of the treatment tank and are effectively involved in wastewater treatment is reduced, resulting in a reduction in treatment capacity. Especially, when the inflow of wastewater is stopped, aeration is performed only in a very small amount, most of the microbial carriers are deposited on the bottom of the treatment tank, and then the inflow of wastewater is restarted and the wastewater increases. However, there was a fatal drawback that the circulation flow (restart) of the microbial carrier could not be performed.

Therefore, conventionally, it has been necessary to sequentially control the aeration amount during the wastewater treatment to be appropriate in response to changes in various conditions such as circulation and fluidization of wastewater and oxygen demand.

"Means for solving the problem" Therefore, the wastewater treatment method of the present invention, based on this dissolved oxygen concentration, while grasping the flow state of the microbial carrier in the wastewater and measuring the dissolved oxygen concentration in the wastewater. The BOD volumetric load of the wastewater at that time is estimated, and when the BOD volumetric load of this wastewater is smaller than a predetermined value, the fluidization of the microbial carrier is used as a criterion, and when the BOD volumetric load is larger than the predetermined value, the wastewater is discharged. By controlling the amount of aeration to wastewater using the oxygen demand as a criterion, it is possible to respond to the oxygen demand necessary for wastewater treatment (organic matter decomposition and internal respiration of microorganisms) and to enable the mobilization of microbial carriers. The minimum amount of aeration required was blown into the wastewater to solve the above problems.

Further, the wastewater treatment apparatus of the present invention, a flow sensor for grasping the flow state of the microbial carrier in the wastewater in the treatment tank,
Dissolved oxygen meter to measure the dissolved oxygen concentration in the wastewater, and to estimate the BOD volume load of the wastewater at that time based on the dissolved oxygen concentration measured by this dissolved oxygen meter, the BOD volume load of this wastewater and the microorganisms The above-mentioned wastewater treatment method is carried out by providing a control device for controlling the amount of aeration of wastewater using the fluidization data of the carrier as a criterion.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of the wastewater treatment apparatus of the present invention, in which reference numeral 1 is a treatment tank. In this processing tank 1, a draft tube 2 is erected in the center of the inside thereof, an overflow weir 3 is provided in the upper part thereof, and a solid-liquid separation column 4 is provided between the overflow weir 3 and the tube 2. It will be. And
An air diffuser 6 connected to the electric blower 5 is arranged at the bottom of the processing tank 1 below the draft tube 2. Further, a detection end of a flow sensor 7 for grasping the flow state of the microorganism carrier in the wastewater is provided in the vicinity of the bottom of the treatment tank 1 in a suspended state, and is provided above the treatment tank 1 and in the draft tube 2. A detection end of a dissolved oxygen meter 8 for detecting the dissolved oxygen concentration in the wastewater is also provided in the outer portion of the in a suspended state.

As the flow sensor 7, a photocoupler that optically detects the position of the deposition interface of the microbial carrier deposited on the bottom of the treatment tank 1 is preferably used in terms of sensitivity, but other than this, for example, treatment of wastewater It is also possible to use a densitometer for detecting the density of the microbial carrier at the bottom of the tank 1 or a velocity meter for measuring the flow rate of the microbial carrier by the Doppler effect or the like.

An ordinary diaphragm type DO meter is preferably used as the dissolved oxygen meter 8. In addition to this, for example, an enzyme electrode capable of quantifying the dissolved oxygen amount by reacting dissolved oxygen in waste water with various enzymes such as oxidase. And the like are used. Further, in order to measure the dissolved oxygen concentration in wastewater, for example, a small amount of wastewater is sampled, a predetermined voltage is applied to the sampled wastewater, and the dissolved oxygen in the wastewater is determined from the magnitude of the current flowing at that time. Polarographic techniques that measure density can also be used.

Then, the flow sensor 7 and the dissolved oxygen meter 8 are
This connection device 9 is electrically connected to the control device 9.
Is electrically connected to the electric blower 5 via an inverter 10.

The control device 9 sends data (output signal) indicating the flow status of the microbial carrier in the wastewater sent from the flow sensor 7 (for example, the position change of the deposition interface of the microbial carrier) and the dissolved oxygen meter 8 from the dissolved oxygen meter 8. The dissolved oxygen concentration data (output signal) in the generated waste water is analyzed, and the amount of aeration from the air diffuser 6 into the processing tank 1 is controlled based on these output signals. As such a control device 9, for example, a device having a controlled saturation logic circuit (CSL), a sequencer, a computer, etc. may be used alone or in combination of two or more thereof.

Next, an example of a wastewater treatment method using such a wastewater treatment device will be described. First, waste water (raw water) is supplied from the upper opening of the treatment tank 1 into the treatment tank 1 filled with a predetermined amount of microbial carriers by a pump or the like (not shown). Next, this wastewater is aerated by a predetermined amount of air or oxygen-enriched gas blown into the wastewater from the air diffuser 6,
Due to the ascending action of the aeration gas, the gas is circulated in the direction of the arrow in FIG. Then, along with the circulation flow of the waste water, the microbial carrier is also circulated and flowed to increase the chances of contact with the waste water, thereby purifying the waste water. Here, examples of the microbial carrier used in this method include diatomaceous earth, sand, anthracite, activated carbon, microbial entrapment carriers having a specific gravity of greater than 1, and the microorganisms are adhered or contained on the surface of the microbial carrier. ing.

During the aeration process, the flow sensor 7 always detects a change in the position of the deposition interface of the microbial carrier deposited on the bottom of the processing tank 1, and the output signal of this detection data is sent to the control device 9. In this control device 9, the minimum amount of fluidized aeration amount is immediately calculated from the above output signal.

In addition, the dissolved oxygen concentration in the wastewater is measured by the dissolved oxygen meter 8, and the output signal of this measurement data is also sent to the control device 9. In this control device 9, the BOD volumetric load of the wastewater at that time is immediately estimated from the above output signal, the oxygen demand amount of the wastewater corresponding to this load is determined, and the oxygen supply aeration amount corresponding to this oxygen demand amount is determined. The minimum amount of is determined.

Next, in the control device 9 described above, in order to simultaneously satisfy the two conditions of fluidization of the microbial carrier in the wastewater and the oxygen demand of the wastewater, the larger one of the two minimum aeration amounts is selected, and this is selected. The amount of aeration for wastewater is determined as a criterion. That is, when the minimum amount of oxygen supply aeration is smaller than the minimum amount of fluidization aeration (the BOD volume load is smaller than a predetermined value), the treatment tank 1 uses the larger amount of fluidization aeration as a reference. Determine the amount of aeration for the wastewater inside. On the contrary, when the minimum oxygen supply aeration amount is larger than the fluidization aeration amount minimum, the aeration amount for the wastewater is determined based on the larger oxygen supply aeration amount.
Then, when the magnitude of the fluidized aeration amount and the magnitude of the oxygen supply aeration amount are reversed, a predetermined value of the BOD volume load (hereinafter, the limit B
It is called OD volume load. ) Is a substrate (for example, the type and content ratio of organic waste) in the wastewater to be treated, the addition amount of the microbial carrier to the volume of the treatment tank, the treatment temperature during the treatment of the wastewater, the specific gravity and diameter of the microbial carrier, etc. Although varying depending on the conditions, these various conditions can be set in advance before the wastewater treatment, and the above-mentioned limit BOD volume load can be roughly grasped. For example, specific gravity 2.2-2.3, diameter 0.4-0.6
When the microbial carrier of mm (average 0.5 mm) is used in the range of 7 to 20 V / V%, the limit BOD volume load is 1 to 4 kg BOD / m ³ /
Determined in the range of days. And BO of wastewater at the time of wastewater treatment
When the D volume load changes through the above-mentioned limit BOD volume load, the controller 9 switches the criterion for determining the aeration amount for wastewater before and after the limit BOD volume load. By this switching, the amount of aeration for wastewater can be always maintained at an appropriate amount without excess or deficiency.

The appropriate amount of aeration gas determined in this way is controlled from the electric blower 5 by controlling the rotation speed of the blower part of the electric blower 5 by using the inverter 10 which operates by a command from the control device 9 described above. It is blown into the wastewater in the treatment tank 1 via the air diffuser 6. Here, as a method for controlling the aeration amount, the electric blower 5 by the inverter 10 is used.
In addition to the method of controlling the number of revolutions of the blower part, a method of controlling the number of electric blowers 5, a method of providing a plurality of air diffusers 6 and increasing or decreasing the operating number of the plurality of air diffusers 6, an air diffuser A method of changing the opening of the aeration gas injection valve of No. 6 and the like can also be used.

By aeration in this way, the dissolved oxygen concentration in the wastewater is increased, and thus the growth environment of the microorganisms supported on the microorganism carrier is maintained in a good state, the decomposition of organic matter in the wastewater is promoted, and aerobic Wastewater is purified.

Next, in the wastewater that has been sufficiently aerated by the above aeration amount, the microbial carrier is separated and removed in the solid-liquid separation column 4 in the treatment tank 1 and then passed over the overflow weir 3 to be treated water as treatment water 1
Is discharged to the outside.

According to this method, the flow sensor 7 grasps the flow state of the microbial carrier in the wastewater, the dissolved oxygen meter 8 measures the dissolved oxygen concentration, and the controller 9 controls the dissolved oxygen concentration based on the dissolved oxygen concentration. The BOD volume load in the wastewater at that time was estimated, and the aeration amount controlled so that both the mobilization of the microbial carrier and the oxygen demand of the wastewater could be satisfied was blown into the wastewater. There is always a proper amount of aeration to blow in, so that the energy required for aeration can be saved, and the treatment tank 1 can always be kept in a highly efficient state, causing problems such as circulatory flow of microbial carriers being stopped. The effect that it does not occur can be obtained.

"Example" Wastewater treatment was performed using the treatment apparatus shown in FIG. Then, six air diffusers were arranged at the bottom of the processing tank of this processing apparatus, a flow sensor was arranged near the bottom of the inverted cone, and a dissolved oxygen meter was arranged at the upper part of the processing tank. Moreover, diatomaceous earth having a specific gravity of 2.2 to 2.3 and a diameter of 0.4 to 0.6 mm (average 0.5 mm) was used as a microorganism carrier, and this was added to the wastewater in the treatment tank at an addition rate of 12 V / V%.

Next, the waste water in the treatment tank is aerated while changing the aeration amount, and the change of the deposition interface of the microbial carrier deposited on the bottom of the treatment tank is measured using a flow sensor, and the result is shown in the glass of FIG. Indicated. In the above flow sensor, the ends of two optical fibers are arranged at the detection end so as to be parallel to each other, and a light emitting element (LED) is connected to the rear end of one optical fiber (light emitting portion), and the other end is connected. Is a photocoupler in which a light receiving element (APD) is connected to the rear end of the optical fiber (light receiving portion). According to this photocoupler, the light emitted from the tip (light emitting end) of the optical fiber of the light emitting section is reflected at the sedimentation interface of the microorganism carrier, and the reflected light is connected to the rear end of the optical fiber of the light receiving section by the light receiving element. Light is received, and the change in the distance between the detection end and the deposition interface can be detected from the change in the amount of received light. In the graph of FIG. 2, the horizontal axis represents the distance of the deposition interface from the detection end of the flow sensor, and the vertical axis represents the output signal voltage indicating the change in the deposition interface optically detected by the flow sensor. It was Set the maximum scale of output signal voltage to 0
It was set to 3V.

As is clear from this graph, the separation dimension between the accumulation interface of the microbial carrier and the detection end of the flow sensor corresponds to the logarithmic value of the output signal voltage of the flow sensor almost linearly up to a certain value. It can be seen that by reading the signal voltage, it is possible to easily grasp the above-mentioned change in the separation dimension, that is, the flow state of the microorganism carrier.

In addition, in the state where the wastewater is continuously supplied, the addition rate (V / V%) of the microbial carrier and the BOD volume load (1 to 6 kg · BOD / m ³ /
The required aeration intensity (per unit time, aeration amount per unit volume of the treatment tank) was measured in relation to (day), and the results are shown in the graph of FIG.

In this example, the critical BOD volume load at which the size of the fluidized aeration amount and the size of the oxygen supply aeration amount are reversed is 1.6 kgBOD / m ³ / day when the addition rate of the microbial carrier is 10 V / V%. ((A) in FIG. 3). And this 1.6kg ・ B
If it is less than OD / m ³ / day, the oxygen demand for wastewater treatment is small and largely depends on the fluidization aeration amount, and 1.6 kg ・ BOD / m ³ /
Over a day, the oxygen demand for wastewater treatment increased, depending on the oxygen supply aeration amount.

Next, increase the microbial carrier addition rate to 15V / V% and
The wastewater was continuously treated by continuously changing the concentration of the supplied wastewater over a day until the OD volume load changed from 4 kg · BOD / m ³ / day to 0 kg · BOD / m ³ / day. Here, from the graph of FIG. 3, the limit BOD volume load when the addition rate of the microbial carrier is 15 V / V% is 2.2 kg · BOD / m ³ / day.

Then, by taking the means of the method of the present invention, the aeration intensity was automatically controlled in the following manner during the wastewater treatment. That is, for wastewater with a BOD volume load of 4 kgBOD / m ³ / day, first, the aeration intensity is set to about 96.5 m ³ / m ³ / day based on the oxygen supply aeration amount. But
The aeration intensity gradually weakens in response to the decrease to 2.2 kg ・ BOD / m ³ / day, and the BOD volumetric load of wastewater is 2.2 kg ・ BO.
After falling below D / m ³ / day, it was controlled to about 62 m ³ / m ³ / day based on the fluidized aeration rate until it reached 0 kg BOD / m ³ / day. In such wastewater treatment, the total aeration amount per day was about 70 m ³ / m ³ .

On the other hand, the wastewater was continuously treated by the conventional treatment method of adjusting the aeration amount to the maximum load amount. That is, the maximum BOD volume load of the waste water (4kg · BOD / m ³ / day) aeration intensity relative to the oxygen supply aeration amount corresponding to (approximately 96.5m ³ / m ³ / day)
Then, when the wastewater treatment was continuously performed from the beginning to the end, the total aeration amount per day was about 96.5 m ³ / m ³ .

Therefore, according to the method of the present invention, the energy required for aeration can be saved by about 27.5% as compared with the conventional method.

In the continuous treatment of the above wastewater, when the aeration intensity based on the fluidization aeration amount (about 62 m ³ / m ³ / day) was applied, the BOD volumetric load of the wastewater was 2.4 kg BOD / m ³ / More than a day, the dissolved oxygen in the wastewater was insufficient and the quality of the treated water deteriorated.

In addition, when wastewater treatment by conventional DO control was performed, when the critical BOD volume load fell below 2.2 kgBOD / m ³ / day, the flow of the microbial carrier deteriorated and the microbial carrier gradually deposited. Initially, the BOD volume load was 1.3 kgBOD / m ³
In a day, a thick microbial carrier deposition tank was formed at the bottom of the treatment tank, and this aeration tank could not be destroyed by aeration, making it impossible to restart the circulation flow of the microbial carrier.

"Effect of the invention" As described above, according to the wastewater treatment method of the present invention, the flow state of the microbial carrier in the wastewater is grasped and the dissolved oxygen concentration in the wastewater is measured, and based on the dissolved oxygen concentration, Estimate the BOD volumetric load of the wastewater at that time, when the BOD volumetric load of this wastewater is smaller than a predetermined value, the mobilization of the microbial carrier is used as a criterion, and when the BOD volumetric load is larger than the predetermined value, Since the aeration amount for wastewater is controlled based on the oxygen demand of wastewater, the proper aeration amount is always blown into the wastewater, so that the energy required for aeration can be saved and the treatment tank can be saved. You can always keep the processing efficiency high,
It is possible to obtain an excellent effect that troubles such as the stop of the microorganism carrier do not occur.

Further, the wastewater treatment apparatus of the present invention, in the treatment tank, a flow sensor for grasping the flow state of the microbial carrier in the wastewater, a dissolved oxygen meter for measuring the dissolved oxygen concentration in the wastewater, and this dissolved oxygen meter is measured. In addition to estimating the BOD volumetric load of the wastewater at that time based on the dissolved oxygen concentration, a control device was installed to control the aeration amount of the wastewater based on the BOD volumetric load of this wastewater and the fluidization of the microbial carrier. Therefore, the above wastewater treatment method can be reliably implemented.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a wastewater treatment apparatus of the present invention, and FIG. 2 is a detection end of a flow sensor arranged in the wastewater treatment apparatus of the present invention and a microorganism carrier deposited on the bottom of a treatment tank. FIG. 3 is a graph showing the change in the separation dimension from the deposition interface, and FIG. 3 is a graph showing the relationship between the aeration intensity and the BOD volume load for explaining the operation of the wastewater treatment method of the present invention. 1 ... Processing tank, 7 ... Flow sensor, 8 ... Dissolved oxygen meter,
9 ... Control device.

Claims (3)

(57) [Claims] 1. A circulating fluidized bed-type wastewater treatment method in which a microorganism carrier is circulated and fluidized in the wastewater by aeration, and the wastewater is aerobically purified by the microorganisms carried by the microorganism carrier. In addition to grasping the flow state of the microbial carrier in and measuring the dissolved oxygen concentration in the wastewater, the BOD volumetric load of the wastewater at that time is estimated based on this dissolved oxygen concentration, and the BOD volumetric load of this wastewater exceeds the specified value. When the BOD volume load is larger than the predetermined value, the oxygen demand of the wastewater is used as the criterion to control the aeration amount to the wastewater when the BOD volume load is larger than the predetermined value. . 2. A fluidized bed type wastewater treatment device comprising a treatment tank holding wastewater in which a microbial carrier is suspended, and an air diffuser arranged at the bottom of the treatment tank, wherein , A flow sensor for grasping the flow state of the microbial carrier in the wastewater, a dissolved oxygen meter for measuring the dissolved oxygen concentration in the wastewater, and the BOD of the wastewater at that time based on the dissolved oxygen concentration measured by the dissolved oxygen meter A wastewater treatment apparatus comprising a controller for estimating a volume load and controlling an aeration amount for the wastewater based on the BOD volume load of the wastewater and fluidization data of the microbial carrier as criteria. 3. The wastewater treatment device according to claim 2, wherein the flow sensor is a photocoupler.