JP4544583B2 - Waste water treatment apparatus and method - Google Patents

Description

  The present invention relates to a wastewater treatment apparatus and method, and more particularly to a technique for improving the flow characteristics of a carrier and improving the treatment characteristics when wastewater is purified using a carrier holding microorganisms.

Examples of the wastewater treatment for purifying wastewater under anaerobic conditions using a carrier holding microorganisms include denitrification treatment of wastewater containing nitric acid or nitrous acid, and methane fermentation treatment of organic wastewater. As a conventional technique, Patent Document 1 proposes a means for rotating a draft tube obtained by bending a lower end portion of a vertical pipe horizontally and forming a water flow from the upper part to the lower part of the draft tube by centrifugal force. . Patent Document 2 proposes a means for installing a perforated plate under the upper surface of the tank while stirring the inside of the tank with a stirring blade while preventing the carrier from floating. Furthermore, Patent Document 3 uses a stirring blade (impeller device) to form a downward flow in a draft tube arranged vertically in the tank and an upward flow between the draft tube and the inner wall surface of the tank. Means have been proposed.
Japanese Patent No. 2798007 JP 2000-254682 A JP 2000-288568 A

  In a wastewater treatment apparatus using a carrier holding microorganisms as described above, the carrier is likely to deposit on the bottom due to an increase in apparent specific gravity due to adhesion and retention of microorganisms. In the methane fermentation treatment, methane gas is generated inside the carrier and the apparent specific gravity is lowered, so there is a concern that the gas may float and stay on the liquid surface. That is, it can be said that the change in the apparent specific gravity of the carrier is large and is substantially unpredictable.

Examples of functions required for the means for flowing the carrier against such a change in the apparent specific gravity of the carrier include the following.
(1) In order to increase the chance of contact with the wastewater to be treated and the carrier holding the microorganisms as much as possible, a flow means capable of eliminating both accumulation at the bottom of the tank and floating on the liquid surface is required. .
(2) The energy required for flow is required to be small.
(3) In order to separate the gas generated inside the carrier from the carrier, it is effective to apply a physical shearing force. However, if an excessive shearing force is applied, the carrier wears quickly, so that excessive shearing is applied. It is required to avoid applying force.
(4) Further, if the flow velocity at the liquid surface is increased in order to prevent the surface from rising to the liquid surface, the dissolution rate of oxygen from the liquid surface increases. For example, the anaerobic conditions in the liquid cannot be maintained, and the processing efficiency May be drastically reduced, so it is required to prevent this situation.

  Regarding the above-mentioned Patent Document 1, although the above (1) and (3) are effective means, it is necessary because of the characteristic that a large draft tube with its lower end bent sideways is rotated and a water flow is formed by centrifugal force. Energy increases and does not conform to (2) above. Regarding the above-mentioned Patent Document 2, although it is an effective means especially for the above (4), the installation of the porous plate is complicated, the flow velocity in the vicinity of the porous plate is difficult to obtain, and the porous plate is clogged by the floated carrier. Great concern. With respect to Patent Document 3, the above (1) and (2) are effective means, but the main point is to uniformly disperse the carrier in the liquid, and the above (3) and (4) Is not considered at all.

  Therefore, an object of the present invention is to provide a flow means that can satisfy all of the functions as described above, and to provide a wastewater treatment apparatus and method capable of efficiently performing a desired treatment.

In order to solve the above problems, a wastewater treatment apparatus according to the present invention is a wastewater treatment apparatus for purifying wastewater under anaerobic conditions using a carrier holding microorganisms,
A reaction tank for storing the carrier;
A draft tube installed vertically inside the reaction vessel and having upper and lower openings;
An impeller device that forms a downward flow in the draft tube and forms an upward flow between the draft tube and the inner wall surface of the reaction vessel;
Rotational speed change of the impeller device provided as output adjusting means for adjusting the impeller device output to suppress the region where the carrier rising with the upward flow by the impeller device is substantially below the upper end of the draft tube Inverter for
Have
When the carrier carrying bubbles rises to the upper part of the reaction vessel, the carrier carrying the bubbles raised to the upper part of the reaction vessel is sucked from the upper end of the draft tube and defoamed by the shearing force when passing through the impeller device. It consists of what is characterized by letting.

  That is, the prior art, particularly the technique described in Patent Document 3 is intended to uniformly disperse the carrier in the tank, but since the carrier always flows to the vicinity of the liquid surface, There is a disadvantage that the carrier is likely to be affected by oxygen dissolution, the carrier frequently passes through the impeller device, and is easily worn.

  On the other hand, in the present invention, the output of the impeller device is set so that most of the carrier flows and expands to the middle position of the tank (below the upper end of the draft tube) (that is, it is not uniformly dispersed or flowed over the entire area of the tank). Adjust and set. That is, most of the carrier is kept in a state where it does not flow up to the vicinity of the liquid level of the tank, and is kept in a state where it does not accumulate at the bottom of the tank. In other words, most of the carrier is present in a predetermined region between the draft tube and the inner wall surface of the reaction vessel (a region suppressed below the upper end of the draft tube), and flows in that region. It will come into contact with the water to be treated. Therefore, while maintaining the opportunity of contact between the carrier holding the microorganisms and the wastewater to be treated, it is kept in a state where it is hardly affected by the dissolution of oxygen from the liquid surface, and extremely efficient treatment is possible. Then, only a part of the carrier with bubbles (only the carrier with a reduced apparent specific gravity) rises (floats) to the top of the tank, is sucked from the upper end of the draft tube, and defoamed by the shearing force when passing through the impeller device The That is, only a part of the carrier desired to be defoamed is sucked from the upper end of the draft tube and efficiently defoamed by the shearing force when passing through the impeller device. Therefore, when viewed from the total amount of the carrier, it is possible to prevent the frequency of the carrier passing through the impeller device from becoming too high, and to suppress wear of the carrier.

  Further, the treated water is usually taken out from the upper part of the tank, and a carrier separation screen is provided in the treated water take-out part to prevent the carrier from being discharged as it is. In particular, by restraining it below the upper end of the draft tube, it is possible to reduce the abundance of the carrier in the vicinity of the carrier separation screen, and to reduce clogging of the screen by the carrier.

Such waste water treatment apparatus according to the present invention, that apply to the purification process of the waste water under anaerobic conditions.

The impeller device output to be adjusted can be obtained in advance by a test and adjusted based on the result. Alternatively, means (for example, an interface meter) capable of detecting the substantial upper end of the region where the carrier exists can be provided, and the output of the impeller device can be adjusted based on the signal from the detection means. . The case based on the signal of this detection means is easier to respond to changes in the properties of the water to be treated and changes in various conditions. As a method of obtaining the impeller device output to be adjusted in advance by a test, for example, a water sampler (for example, various commercial water samplers manufactured by TechJam Co., Ltd. A type that can be opened and closed is preferable, and is poured into the water from the top of the reaction vessel, submerged in water, measured (eg, observed) for the abundance of the above-mentioned carrier, The output of the inverter of the impeller device of the water sampler is adjusted, the carrier existing rate at the upper end position of the draft tube is 0% to very little, and the carrier is sufficient up to the middle position of the tank Look for output with conditions that exist and can flow. If such an output is obtained in advance and grasped or set as a reference value, the actual output of the impeller device can be accurately adjusted to the desired output based on the above reference value without performing a test again. Is possible.

  The impeller device can be operated either continuously or intermittently. Even in the case of intermittent operation, by setting the operation cycle and each operation time appropriately, a state in which the carrier simply flows in the specific area without sinking or floating in the specific area. Appearance is possible.

  In addition to the output adjustment of the impeller device, it is also possible to perform a forced intermittent operation of the impeller device for defoaming from the carrier. In other words, for the purpose of defoaming, the impeller device is periodically operated in a relatively large output state, and the majority of the carrier is kept in a state where no bubbles are always held, thereby improving the processing efficiency.

  In order to accurately adjust the output of the impeller device, for example, an inverter for changing the rotation speed of the impeller device is preferably provided.

A wastewater treatment method according to the present invention is a wastewater treatment method for purifying wastewater under anaerobic conditions using a carrier holding microorganisms, and storing the carrier in a reaction tank, and in the reaction tank A draft tube having an open top and bottom is installed vertically, and an impeller device forms a downward flow in the draft tube, and an upward flow is formed between the draft tube and the inner wall surface of the reaction vessel, and the impeller The impeller device output is adjusted by an inverter for changing the rotation speed of the impeller device in order to suppress the region where the carrier rising with the upward flow by the device is present substantially below the upper end of the draft tube,
When the carrier carrying bubbles rises to the upper part of the reaction vessel, the carrier carrying the bubbles raised to the upper part of the reaction vessel is sucked from the upper end of the draft tube and defoamed by the shearing force when passing through the impeller device. It consists of the method characterized by making it carry out.

The waste water treatment method also that apply to the purification process of the waste water under anaerobic conditions.

  Further, the output of the impeller device to be adjusted can be obtained in advance by a test. Alternatively, the substantial upper end of the region where the carrier exists may be detected, and the impeller device output may be adjusted based on the detection result.

  The impeller device can be operated continuously or intermittently.

  In addition to the output adjustment of the impeller device, a forced intermittent operation of the impeller device can also be performed for defoaming from the carrier.

Output adjustment of the impeller device, is performed by the rotational speed change inverter impeller device can output adjustment with high accuracy.

  According to the wastewater treatment apparatus and method according to the present invention, the carrier holding the microorganisms does not flow uniformly throughout the reaction tank, but exists in a predetermined specific region between the draft tube and the inner wall surface of the reaction tank. In addition, since it is maintained in an appropriate flowable state within the specific region, it is possible to satisfy all the required characteristics (1) to (4) for the impeller device described above at the same time. It is possible to perform efficient and desirable treatment while achieving suppression of wear and suppression of oxygen dissolution from the liquid surface portion.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
First, the flow state of the carrier in the present invention will be described in comparison with the flow state of the carrier according to the conventional method.

  FIG. 1 shows a wastewater treatment apparatus 1 according to an embodiment of the present invention and a carrier flow state during operation of the apparatus 1. FIG. 2 shows a conventional waste water treatment apparatus 11 and the flow state of the carrier during operation of the apparatus 11. 1 and 2, reference numerals 2 and 12 denote reaction tanks, and carriers 3 and 13 holding microorganisms are stored in the reaction tanks 2 and 12, respectively. The treated water 4 and 14 is introduced into the reaction tanks 2 and 12, and the treated water after the treatment is discharged through the carrier separation screens 5 and 15. The reaction vessels 2 and 12 are provided with draft tubes 6 and 16 that are vertically installed and open at the top and bottom, and a downward flow is formed in the draft tubes 6 and 16 in the draft tubes 6 and 16. In addition, impeller devices 7 and 17 that form an upward flow between the draft tubes 6 and 16 and the inner wall surfaces of the reaction vessels 2 and 12 are provided.

  In the conventional apparatus, for example, the apparatus described in Patent Document 3 described above, the object is to uniformly disperse and flow the carrier 13 over the entire region of the reaction tank 12 as shown in FIG. It was operated at a relatively high output compared to the invention, whereby the carrier 13 was allowed to flow and circulate throughout the reaction tank 12. Therefore, as described above, a large amount of energy is required for flow, there are many opportunities for contact between the impeller device 17 and the carrier 13, wear of the carrier 13 proceeds due to shearing force, and the carrier 13 always passes through or near the liquid surface. Thus, the rate of dissolution of oxygen from the liquid surface increases, and in the case of treatment under anaerobic conditions, the anaerobic conditions in the liquid cannot be maintained, and the treatment efficiency decreases.

  On the other hand, in the waste water treatment apparatus 1 according to the present invention, the region where the carrier 3 that rises with the upward flow generated by the operation of the impeller device 7 is present is substantially suppressed below the upper end of the draft tube 6. Since the output of the impeller device is adjusted, as shown in FIG. 1, most of the carrier 3 is kept in a state where it does not flow up to the vicinity of the liquid level of the tank 2 and is not deposited on the bottom of the tank 2. Kept. Most of the carrier 3 exists in a predetermined region between the draft tube 6 and the inner wall surface of the reaction vessel 2 (that is, a region suppressed below the upper end of the draft tube 6). It flows and comes into contact with water to be treated. Therefore, while maintaining a sufficiently high opportunity for contact between the carrier holding the microorganisms and the wastewater to be treated, it is kept in a state that is hardly affected by the dissolution of oxygen from the liquid surface, and extremely efficient treatment is possible.

  Then, only a part of the carrier carrying bubbles (only the carrier having a reduced apparent specific gravity) rises (floats) to the upper part of the tank, is sucked from the upper end of the draft tube 6 and circulated, and the shear when passing through the impeller device 7 Defoamed by force. That is, most of the carrier 3 is flowed only in the specific region, and only a part of the carrier 3 that is desired to be defoamed is sucked from the upper end of the draft tube 6 and efficiently by the shearing force when passing through the impeller device 7. Defoamed. Therefore, when viewed from the total amount of the carrier, the frequency at which the carrier 3 passes through the impeller device 7 does not become too high, and the carrier 3 is reliably prevented from being worn excessively.

  The carrier in the wastewater treatment apparatus and method according to the present invention is not particularly limited, but is a porous body made of cellulose, polyethylene, polypropylene, polyurethane, etc., a gel-like body made of polyvinyl alcohol, polyethylene glycol, or the like. Is mentioned. The larger the pore size, the more easily the oxidized nitrogen and hydrogen donating state in the water to be treated diffuses into the inside of the carrier, and gas is easily generated inside the carrier (easily floats and hardly defoams). Those having a small pore diameter (several μm to several tens μm) are preferable.

  Also, the shape of the carrier is not particularly limited, but a spherical or cube shape of about 0.5 to 10 mm is preferable. Further, in order to form a fluid state as shown in FIG. 1, the specific gravity of the carrier is at least greater than 1.0, and the true specific gravity is 1.1 or more, or the apparent specific gravity is 1.01 or more. preferable.

  The filling rate of the carrier stored in the reaction tank may be about 5 to 40%. The shape of the reaction vessel may be rectangular or cylindrical, and is not particularly limited. In order to prevent accumulation at the bottom corner of the tank, it is preferable that the bottom corner of the tank is tapered as shown in FIG. 1, and it is particularly preferable that the taper be 45 degrees or more. Moreover, in order to suppress the oxygen dissolution from the liquid surface as much as possible, it is preferable that a lid is installed on the top of the tank.

  The concrete form, especially the form used in the below-mentioned Example is shown in FIG. 3, FIG. 4 about the waste water treatment equipment 1 which concerns on this invention shown in the said FIG. In the reaction tank 2, a draft tube 6 having an open top and bottom is installed vertically. The shape of the draft tube 6 may be a square shape or a cylindrical shape, and is not particularly limited. However, the cylindrical shape is preferable because the downward flow velocity inside tends to be uniform. In order to prevent the carrier 3 from staying on the liquid surface, the cross-sectional area of the draft tube 6 is set so that the average downward flow velocity in the draft tube 6 is 20 cm / s or more from the amount of water discharged from the impeller device 7. Is preferred.

  The draft tube 6 is preferably installed diagonally in the case of a square tank and at the center position if it is a cylindrical tank. The number of draft tubes 6 may not necessarily be one for one tank, and a plurality of draft tubes 6 may be installed according to the shape of the tank.

  If the distance from the liquid surface to the upper end of the draft tube 6 (liquid fog) is small, the liquid surface flow velocity becomes high, and there is a concern that the penetration of oxygen becomes large. On the other hand, if the liquid fog is large, the liquid surface flow velocity becomes small, and there is a concern that the floated carrier cannot be sucked. The liquid fog is preferably about 300 to 1000 mm. Moreover, it is good also as a structure which can adjust the height of the draft tube 6. FIG.

An impeller device 7 is provided to form a downward flow in the draft tube 6. As the impeller device 7, for example, an underwater aerator “SJ type” manufactured by Shin Meiwa Kogyo Co., Ltd. is suitable as an underwater throwing type device. For example, as shown in FIG. 4, such an underwater aerator is installed at the bottom of the tank as an underwater agitator 7 a, and the draft tube 6 may be joined to the suction surface of the underwater agitator 7 a. The impeller device 7 of this type has the advantage that it can be easily installed and can be easily prevented from depositing on the tank bottom. It is also possible to connect a pipe to the impeller 7. However, the impeller device 7 may be configured to be completely accommodated in the draft tube 6 as shown in FIG. For example, as described in the above-mentioned Patent Document 3, a configuration including a motor at the top of the tank, a rotating shaft, and an impeller (stirring blade) in a draft tube may be used.

  If the clearance between the impeller of the impeller device 7 and the surrounding wall surface is small, the carrier may be broken. If the clearance is large, the shearing force is not sufficiently applied and it is difficult to defoam. Therefore, the clearance is preferably in the range of 1.2 times to 10 times the long side of the carrier 3.

The output of the impeller device 7 can be adjusted by the output adjusting means, whereby the flow state of the carrier 3 whose apparent specific gravity changes can be controlled to the flow state and flow region targeted by the present invention. The output adjusting means of the impeller device 7 is not particularly limited. For example, as shown in FIG. 3, if an inverter 8 for changing the rotational speed of the drive motor of the impeller device 7 is provided as the output adjusting means, It is possible to adjust the output with high accuracy. Although the output which will be in a fluid state as shown in FIG. 1, FIG. 3 changes with the support | carriers 3, it is about 20-60 W / m < ³ > (vs. tank capacity) grade.

Furthermore, it is also effective to vary the output of the impeller device 7 at a constant cycle, for example. For example,
Normal output: 30 W / m ³
Forced stirring output: 60 W / m ³
Cycle: 110 minutes (normal output operation + 10 minutes, forced stirring output operation)
By doing so, regular degassing from the carrier 3 can be sufficiently performed, and the flow state of the carrier can be stabilized.

Using the apparatus shown in FIG. 3, the relationship between the flow state of the carrier in the reaction tank and the treatment capacity was examined as follows.
(Denitrification test conditions)
・ Reaction tank capacity: Square water tank 1m ³
・ Carrier: Polyvinyl alcohol gel carrier ・ Carrier filling rate: 10% (bulk volume / tank volume)
・ Test wastewater: NO ₃ -N 100mg-N / L, PO ₄ -P 1.0mg-P / L
-Nitrogen volume load: The maximum load at which a removal rate of 95% or more was obtained was confirmed by gradually increasing the amount of water. -Stirrer (impeller device) output adjustment: The output of the stirrer was adjusted stepwise by an inverter, and the behavior of the carrier and the treatment performance of the water to be treated (raw water) were confirmed in two different flow conditions.
-Methanol addition amount: 3 times the amount of inflow NO ₃ -N load-The output of the stirrer is adjusted by an inverter. The behavior and processing performance were confirmed.

〔result〕
Condition 1: The carrier flowed and expanded to about 50-60% of the water depth (below the upper end of the draft tube). At this time, the maximum allowable load was 1.2 kg-N / m ³ / d, and no retention of the floated carrier near the water surface was confirmed.
Condition 2: The carrier flowed and developed throughout the tank. At this time, the maximum allowable load was 1.0 kg-N / m ³ / d.

  That is, it was found that it is most preferable to flow and expand the carrier to the middle part of the water depth as in Condition 1. Under condition 2, it is considered that the treatment performance has been lowered by the dissolution of oxygen from the water surface, and the carrier is constantly exposed to the shearing force of the stirring blade, so that there is a risk of wear. In condition 1, only the lifted carrier is sucked into the draft tube, and a shearing force is applied, and the defoaming is appropriately performed while suppressing wear on the whole carrier.

Waste water treatment apparatus and method according to the present invention is basically suitable for the purification process of the waste water under anaerobic conditions to Ru with a carrier which holds microorganisms.

It is a schematic longitudinal cross-sectional view of the waste water treatment apparatus which concerns on one embodiment of this invention. It is a schematic longitudinal cross-sectional view of the conventional waste water treatment equipment. It is a longitudinal cross-sectional view which shows an example of a more concrete structure regarding the apparatus of FIG. FIG. 4 is a partially enlarged longitudinal sectional view of the apparatus of FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Waste water treatment apparatus 2 Reaction tank 3 Carrier | carrier which hold | maintained microorganisms 4 To-be-treated (raw water)
5 Carrier separation screen 6 Draft tube 7 Impeller device 7a Underwater stirrer as impeller device 8 Inverter as output adjusting means of impeller device

Claims (13)

A wastewater treatment apparatus for purifying wastewater under anaerobic conditions using a carrier holding microorganisms,
A reaction tank for storing the carrier;
A draft tube installed vertically inside the reaction vessel and having upper and lower openings;
An impeller device that forms a downward flow in the draft tube and forms an upward flow between the draft tube and the inner wall surface of the reaction vessel;
Rotational speed change of the impeller device provided as an output adjusting means for adjusting the impeller device output to suppress the region where the carrier rising with the upward flow by the impeller device is substantially below the upper end of the draft tube Inverter for
Have
When the carrier carrying bubbles rises to the top of the reaction vessel, the carrier carrying the bubbles that rises to the top of the reaction vessel is sucked from the upper end of the draft tube and defoamed by the shearing force when passing through the impeller device. A wastewater treatment apparatus characterized by causing   The waste water treatment apparatus according to claim 1, wherein a clearance between the impeller and the surrounding wall surface of the impeller apparatus is in a range of 1.2 times to 10 times with respect to a long side of the carrier.   The waste water treatment apparatus according to claim 1 or 2, wherein an impeller device output to be adjusted is obtained in advance by a test. The waste water treatment apparatus according to claim 1, wherein means capable of detecting a substantial upper end of the region where the carrier exists is provided, and the output of the impeller device is adjusted based on a signal from the detection means.   The waste water treatment apparatus according to any one of claims 1 to 4, wherein the impeller device is operated continuously.   The wastewater treatment apparatus according to any one of claims 1 to 4, wherein the impeller device is operated intermittently.   The wastewater treatment apparatus according to any one of claims 1 to 6, wherein a forced intermittent operation of the impeller device for defoaming from the carrier is performed separately from output adjustment of the impeller device. A wastewater treatment method for purifying wastewater under anaerobic conditions using a carrier holding microorganisms, wherein the carrier is stored in a reaction tank, and a draft tube whose top and bottom are opened vertically in the reaction tank. Installed to form a downward flow in the draft tube by the impeller device, to form an upward flow between the draft tube and the inner wall surface of the reaction tank, and accompanying the upward flow by the impeller device In order to suppress the region where the rising carrier is present substantially below the upper end of the draft tube, the output of the impeller device is adjusted by an inverter for changing the rotation speed of the impeller device ,
When the carrier carrying bubbles rises to the upper part of the reaction vessel, the carrier carrying the bubbles raised to the upper part of the reaction vessel is sucked from the upper end of the draft tube and defoamed by the shearing force when passing through the impeller device. A wastewater treatment method characterized in that The waste water treatment method according to claim 8, wherein an output of the impeller device to be adjusted is obtained in advance by a test. The wastewater treatment method according to claim 8 , wherein a substantial upper end of the region where the carrier exists is detected, and the output of the impeller device is adjusted based on the detection result. The waste water treatment method according to any one of claims 8 to 10 , wherein the impeller device is operated continuously. The waste water treatment method according to any one of claims 8 to 10 , wherein the impeller device is operated intermittently. The wastewater treatment method according to any one of claims 8 to 12 , wherein a forced intermittent operation of the impeller device is performed separately from the output adjustment of the impeller device for defoaming from the carrier.

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