JP2019141779A - Operation method of aerobic biological treatment apparatus - Google Patents

Abstract

To provide an operation method of an aerobic biological treatment apparatus capable of efficiently discharging excess sludge adhered to a carrier.SOLUTION: There is provided an aerobic biological treatment apparatus 1 which comprises: a reaction tank (tank body) 2; a water permeation plate 3 installed horizontally on the lower part of the reaction tank 2; a large diameter particle layer 4 formed on the upper side of the water permeation plate 3; a small diameter particle layer 5 formed on the upper side of the large diameter particle layer 4; an oxygen dissolution membrane module 6 disposed on the upper side of the small diameter particle layer 5; a reception chamber 7 formed on the lower side of the water permeation plate 3; a raw water spray pipe 8 for supplying raw water into the reception chamber 7; an aeration pipe 9 installed so as to perform aeration in the reception chamber 7 and the like. A part of a biological membrane adhered to a carrier is peeled off by intermittently aerating the reaction tank 2, followed by passing water with LV higher than during normal operation to discharge the peeled-off sludge to the outside of the reaction tank.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for operating an aerobic biological treatment apparatus for organic wastewater.

  Since the aerobic biological treatment method is inexpensive, it is widely used as a treatment method for organic wastewater. In this method, it is necessary to dissolve oxygen in the water to be treated, and aeration with a diffuser is usually performed.

  Aeration with an air diffuser has a low dissolution efficiency of about 5 to 20%. In addition, it is necessary to aerate at a pressure higher than the water pressure applied to the water depth where the diffuser pipe is installed, and a large amount of air is blown at a high pressure, so that the power cost of the blower is high. Usually, more than 2/3 of the power cost in aerobic biological treatment is used for oxygen dissolution.

  A membrane aeration bioreactor (MABR) using a hollow fiber membrane can dissolve oxygen without generating bubbles. In MABR, it is only necessary to ventilate air having a pressure lower than the water pressure applied to the water depth, so that the required pressure of the blower is low and the oxygen dissolution efficiency is high.

JP 200687310 A

  When aerobic biological treatment is carried out in a fluidized bed reaction tank, the biofilm attached to the carrier becomes thick, resulting in reduced biological treatment efficiency, outflow of the carrier, or drift in the reaction tank. May be blocked.

  An object of this invention is to provide the operating method of the aerobic biological treatment apparatus which can discharge | emit the excess sludge adhering to a support | carrier efficiently.

  An operation method of an aerobic biological treatment apparatus according to one embodiment of the present invention includes a reaction tank, an oxygen-dissolving membrane module installed in the reaction tank, and an oxygen-containing gas supply that supplies an oxygen-containing gas to the oxygen-dissolving membrane module. And a part of a biofilm adhering to the carrier by intermittently aeration of the inside of the reaction tank, comprising a means and a fluidized bed of the carrier formed in the reaction tank Then, water is passed at a higher LV than during normal operation, and the separated sludge is discharged out of the reaction tank.

  In one aspect of the present invention, the upper part of the reaction tank is a widened part having a larger horizontal cross-sectional area than the middle part and the lower part, and the upper surface of the carrier fluidized bed is positioned in the widened part when the high LV water flows. .

  In one embodiment of the present invention, the oxygen-dissolving membrane module includes a non-porous oxygen-dissolving membrane.

  In one embodiment of the present invention, the oxygen-dissolving membrane is hydrophobic.

  In the operation method of the aerobic biological treatment apparatus of the present invention, the reaction tank is intermittently aerated to remove excess sludge from the carrier. Thereafter, the water flows upward at a high LV, and the separated sludge is discharged out of the reaction tank. In this way, excess sludge adhering to the carrier can be efficiently discharged.

It is a longitudinal cross-sectional view of the biological treatment apparatus which concerns on embodiment. (A) is a side view of an oxygen-dissolved membrane unit, and (b) is a perspective view of the oxygen-dissolved membrane unit.

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

  FIG. 1 is a longitudinal sectional view of an aerobic biological treatment apparatus 1 according to an embodiment. This aerobic biological treatment apparatus 1 includes a reaction tank (tank body) 2, a perforated plate such as a punching plate installed horizontally below the reaction tank 2, and a plurality of dispersion nozzles uniformly provided on a flat plate A large-diameter particle layer 4 formed above the water-permeable plate 3, a small-diameter particle layer 5 formed above the large-diameter particle layer 4, and a powder above the small-diameter particle layer 5. A fluidized bed F formed by filling a bioadhesive carrier such as granular activated carbon, an oxygen-dissolving membrane module 6 at least partially disposed in the fluidized bed F, and a receiving chamber formed below the water-permeable plate 3. 7, a raw water spray pipe 8 for supplying raw water into the receiving chamber 7, a diffuser pipe 9 installed in the receiving chamber 7, and the like. Air is supplied to the air diffuser 9 from a compressor (or blower) 13.

  The upper part of the reaction tank 2 is a widened part 2W having a larger horizontal cross-sectional area than the middle part to the lower part. Between the widened part 2W and the middle part of the reaction tank 2, there is a tapered part 2T whose horizontal cross-sectional area increases toward the upper side. The horizontal cross-sectional area of the widened portion 2W is preferably about 150 to 300%, particularly about 175 to 225% of the horizontal cross-sectional area of the middle part or the lower part.

  A trough 10 and an outlet 11 for allowing the treated water to flow out are provided above the widened portion 2W. The trough 10 forms an annular flow path along the inner wall of the tank.

  FIG. 1 shows that the reaction vessel is filled with a fluidized bed carrier, and the biofilm adheres to the surface of the oxygen-dissolved membrane by the shearing force caused by the flow of the carrier so that most of the biofilm adheres to the fluidized bed carrier. The oxygen-dissolved film is used only for the purpose of supplying oxygen.

  In FIG. 1, a non-porous oxygen-dissolving film is used as the oxygen-dissolving film, and an oxygen-containing gas is vented from the outside of the tank to the primary side of the oxygen-dissolving film through the pipe, and the exhaust is discharged outside the tank through the pipe. It is configured to do. Therefore, an oxygen-containing gas is passed through the oxygen-dissolving film at a low pressure, passes oxygen as oxygen molecules between constituent atoms of the oxygen-dissolving film (dissolves in the film), and is brought into contact with the water to be treated as oxygen molecules (water In other words, since the process is performed using a molecular diffusion mechanism based on a concentration gradient, it is not necessary to diffuse using a diffusion tube.

  In addition, it is preferable to use a hydrophobic material as the oxygen-dissolving film, because it is difficult to infiltrate the film, but even if it is hydrophobic, a small amount of water vapor is inevitable.

  FIG. 2 shows an example of the oxygen-dissolving membrane module 6. This oxygen dissolution membrane module 6 uses a non-porous hollow fiber membrane 22 as an oxygen dissolution membrane. In this embodiment, the hollow fiber membranes 22 are arranged in the vertical direction, and the upper end of each hollow fiber membrane 22 is connected to the upper header 20 and the lower end is connected to the lower header 21. The interior of the hollow fiber membrane 22 communicates with the upper header 20 and the lower header 21, respectively. Each header 20, 21 is a hollow tube. Even when a flat membrane or a spiral membrane is used, it is desirable to arrange the ventilation direction to be the vertical direction.

  As shown in FIG. 2B, a plurality of units composed of a pair of headers 20 and 21 and a hollow fiber membrane 22 are arranged in parallel. As shown in FIG. 2A, one end or both ends of each upper header 20 are preferably connected to the upper manifold 23, and one end or both ends of each lower header 21 are preferably connected to the lower manifold 24. An oxygen-containing gas is supplied to the upper part of the oxygen-dissolving membrane module 6 and discharged from the lower part of the oxygen-dissolving membrane module 6 through the discharge pipe 29 to the outside of the tank. Oxygen-containing gas such as air flows from the upper header 20 through the hollow fiber membrane 22 to the lower header 21, during which oxygen passes through the hollow fiber membrane 22 and dissolves in the water in the reaction vessel 2.

  Each header 20, 21 and each manifold 23, 24 may be provided to have a running water gradient. The oxygen-dissolving membrane module 6 may be installed in multiple stages up and down.

  In order to supply air to the oxygen-dissolving membrane module 6, a blower 26 and an air supply pipe 27 are provided (constituting oxygen-containing gas supply means), and the air supply pipe 27 is connected to the upper manifold 23. Yes. A relay pipe 28 for exhaust gas is connected to the lower manifold 24. The relay pipe 28 is connected to a discharge pipe 29. The discharge pipe 29 is provided so as to have a downward slope (including a vertically downward direction), and extends to the outside of the reaction tank 2. In FIG. 1, the discharge pipe 29 is drawn to the side of the reaction tank 2, but may be drawn downward from the bottom of the reaction tank 2.

  As shown in FIG. 1, the remainder of the oxygen-containing gas that did not dissolve in the oxygen-dissolving membrane is exhausted out of the tank through the discharge pipe 29, and its end is the lower end of the oxygen-dissolving membrane module. Therefore, when the exhaust gas contains condensed water, the condensed water flows out to the tank 32 installed below the discharge pipe 29. The water in the tank 32 can also be sent to the reaction tank 2 by the pump 33 and the pipe 34.

  In addition, you may provide separately the waste gas piping 30 which branches the discharge piping 29 inside or out of a tank, and exhausts exhaust_gas | exhaustion out of a tank. In this case, since the condensed water is discharged through the discharge pipe 29, the exhaust gas pipe 30 provided separately by branching can be arranged at a position where the exhaust part at the end is higher than the lower end of the oxygen-dissolving membrane module. It is preferable that the pipe has only a downward slope or a vertically upward direction so that the pipe cannot be accumulated. At this time, a valve may be provided on the downstream side of the branch point of the discharge pipe 29 with the exhaust gas pipe 30, and the condensed water may flow out into the tank 32 by opening the valve.

  The valve may be either an automatic valve or a manual valve. The valve for discharging the condensed water may be opened continuously or intermittently. In the case of the intermittent type, the temperature changes due to changes in temperature and humidity, but in normal operation, once a day to once every 30 days (at most once a day, at most, once a month about 10 times a month) Seconds), preferably once a day to once every 15 days by draining the valve.

  In the aerobic biological treatment apparatus 1 configured as described above, raw water is introduced into the receiving chamber 7 through the spray pipe 8, and is circulated upward through the water permeable plate 3 and the large and small diameter particle layers 4 and 5, and SS is generated. Then, in the fluidized bed F of the granular activated carbon adhered to the biofilm, the water is flowed upward in a transient manner, undergoes a biological reaction, and is taken out as treated water from the upper clarified region through the trough 10 and the outlet 11. At this time, the height of the upper surface of the fluidized bed F is lower than the tapered portion 2T.

  In a normal biological treatment operation, the oxygen-containing gas such as air supplied from the air supply pipe 27 flows downward through the oxygen-dissolving membrane module 6 and then the lower header 21 and the lower part from the lower end position of the oxygen-dissolving module 6. It flows out through the manifold 24, and the exhaust air is exhausted from the exhaust pipe 29 (or from the exhaust gas pipe 30 when the exhaust gas pipe 30 is provided) to the atmosphere. The condensed water flows out to the tank 32 through the discharge pipe 29.

  If the biological treatment operation is continued, the biofilm on the surface of the carrier gradually becomes thicker. When this biofilm becomes excessively thick, the carrier flows out and the biological treatment efficiency decreases. (The aerobic biological treatment is not performed in the deep part of the biofilm, that is, on the side close to the carrier, because oxygen does not reach.) Processing efficiency may decrease.

  Therefore, the compressor 13 is operated regularly or based on the observation result of the flow state in the reaction tank 2, the air is caused to flow out from the air diffuser 9, and the inside of the reaction tank 2 is aerated. By this aeration, the excess sludge on the surface of the carrier is peeled off by the shearing force of the water flow.

  After this air aeration, the raw water is circulated in the reaction tank 2 at a higher LV than the LV during normal processing. Thereby, the sludge which peeled and existed in the reaction tank 2 flows out from the outflow port 11. The discharged water at this time is not treated but treated separately as washing wastewater or sent to the raw water tank. In this way, sticking of the carriers can be suppressed, and drift and blockage in the reaction tank 2 can be prevented.

  When the above-mentioned high LV water flow, the expansion rate of the fluidized bed F increases, and the interface of the fluidized bed F rises to the widened portion 2W. Since the horizontal cross-sectional area of the widened portion 2W is large, the rising flow velocity in the widened portion 2W is smaller than that in the middle portion to the lower portion, so that the carrier is prevented from being lost. After performing the high LV operation for a predetermined time, the LV is returned to the normal LV, and the normal biological treatment operation is resumed.

  This aeration also has the effect that the inside of the reaction tank 2 is decarboxylated, the pH is increased, and the carbonic acid accumulated between the carriers (activated carbon) is decarboxylated.

  In the present invention, since the amount of supplied oxygen is increased by installing a non-porous oxygen-dissolving membrane in a fluidized bed of a biological carrier such as activated carbon, there is no upper limit to the concentration of organic wastewater in the target raw water.

  In addition, since the biological carrier is operated in a fluidized bed, it is not exposed to severe disturbance. Therefore, since a large amount of organisms can be stably maintained, the load can be increased.

  In addition, since an oxygen-dissolving membrane is used in the present invention, the dissolution power of oxygen is small compared to preaeration and direct aeration.

  From these facts, according to the present invention, the pH in the reaction tank 2 is maintained in the vicinity of neutrality with little or no use of a neutralizing agent, and organic wastewater from a low concentration to a high concentration is heavily loaded. In addition, it is possible to stably process at a low cost.

<Biological carrier>
Activated carbon is suitable as the biological carrier.

  The packed amount of the fluidized bed carrier is preferably about 30 to 70%, particularly about 40 to 60% of the volume of the reaction vessel. The larger the filling amount, the more the biomass and the higher the activity. However, if the amount is too large, the carrier may flow out. Therefore, it is preferable to pass water at an LV (for example, 7 to 30 m / hr, particularly 8 to 15 m / hr) where the fluidized bed develops about 20 to 50%. As the fluidized bed carrier, a gel material other than activated carbon, a porous material, a non-porous material, etc. can be used under the same conditions. For example, polyvinyl alcohol gel, polyacrylamide gel, polyurethane foam, calcium alginate gel, zeolite, plastic and the like can also be used. However, when activated carbon is used as the carrier, it is possible to remove a wide range of pollutants by the interaction between the activated carbon adsorption and biodegradation.

  The average particle diameter of the activated carbon is preferably 0.2 to 1.2 mm, particularly preferably about 0.3 to 0.6 mm. When the average particle size is large, it is possible to increase the LV, and when a part of the treated water is circulated to the reaction tank, the amount of circulation can be increased, so that a high load is possible. However, since the specific surface area is small, the biomass is reduced. If the average particle size is small, the pump power can be reduced because it can flow at a low LV. And since the specific surface area is large, the amount of attached organisms increases.

  The expansion ratio of the activated carbon during normal operation is preferably about 20 to 50%. If the expansion rate is lower than 20%, there is a possibility of clogging and short circuit. If the development rate is higher than 50%, there is a risk of carrier outflow, and the pump power cost increases.

  In normal biological activated carbon, the expansion rate of the activated carbon fluidized bed is about 10 to 20%, but in this case, the activated carbon is in a non-uniform flow state and flows vertically and horizontally. As a result, the membrane installed at the same time is rubbed by activated carbon and worn out. In order to prevent this, in the present invention, the fluidized bed carrier such as activated carbon needs to be sufficiently fluidized, and the development rate is desirably 20% or more. For this reason, the particle size of the carrier is preferably smaller than that of normal biological activated carbon. In addition, in the case of activated carbon, it is not specifically limited, such as coconut charcoal, coal, charcoal. The shape is preferably spherical charcoal, but may be ordinary granular charcoal or crushed charcoal.

  At the time of high LV operation for discharging excess surplus sludge after aeration, as described above, the upper surface of the fluidized bed is located in the widened portion 2W and sufficiently higher than the overflow level of the trough 10 (preferably 50 to 500 mm, in particular 100 to 200 mm) to prevent the carrier from being lost.

<Oxygen-containing gas>
The oxygen-containing gas may be a gas containing oxygen, such as air, oxygen-enriched air, or pure oxygen. It is desirable that the gas to be vented passes through a filter to remove fine particles in advance.

  The amount of aeration is preferably about twice the amount of oxygen required for biological reactions. If it is less than this, BOD and ammonia will remain in the treated water due to insufficient oxygen, and if it is greater, the air flow will be unnecessarily increased and the pressure loss will be increased, so the economy will be impaired.

  The aeration pressure is desirably slightly higher than the pressure loss of the hollow fiber generated at a predetermined aeration amount.

<Flow rate of treated water>
In low-concentration wastewater with a LV concentration of LV 7 m / hr or more and a TOC concentration of 20 mg / L or less, the treatment water in the reaction tank during normal operation can be treated in one pass without circulating the treatment water. Pumping power can be reduced by a one-time process.

  When the LV is increased, the oxygen dissolution rate is proportionally increased. When LV is high, it is preferable to use activated carbon having a large particle size so that the expansion rate is not so large. From the biomass and oxygen dissolution rate, the optimum LV range is about 7 to 30 m / hr, particularly about 8 to 15 m / hr.

<Residence time>
It is preferable to set the residence time so that the tank load is 0.5 to 4 kg-TOC / m ³ / day.

<Blower>
The blower 26 is sufficient if the discharge wind pressure is equal to or lower than the water pressure coming from the water depth. However, it is necessary to be more than the pressure loss of piping. Usually, the pipe resistance is about 1 to 2 kPa.

  In the case of a water depth of 5 m, a general-purpose blower with an output of up to about 0.55 MPa is usually used, and a high-pressure blower has been used at a water depth higher than that.

  In the present invention, a general purpose blower having a pressure of 0.5 MPa or less can be used even at a water depth of 5 m or more, and a low pressure blower of 0.1 MPa or less is preferably used.

  The supply pressure of the oxygen-containing gas is higher than the pressure loss of the hollow fiber membrane, and the membrane is not crushed by water pressure. Since the pressure loss of the flat membrane and the spiral membrane is negligible compared to the water pressure, the pressure is extremely low, about 5 kPa or more, water depth pressure or less, desirably 20 kPa or less.

In the case of a hollow fiber membrane, the pressure loss varies depending on the inner diameter and length. Since the amount of air to be vented is 50 to 200 mL / day per 1 m ² of membrane, the amount of air doubles when the membrane length is doubled, and the amount of air is only doubled even when the membrane diameter is doubled. Don't be. Therefore, the pressure loss of the membrane is directly proportional to the membrane length and inversely proportional to the diameter.

  The value of pressure loss is about 3 to 20 kPa for hollow fibers having an inner diameter of 50 μm and a length of 2 m.

  In the above embodiment, air is allowed to flow downward through the oxygen-dissolving membrane module 6, but it may be allowed to flow upward.

DESCRIPTION OF SYMBOLS 1 Aerobic biological treatment apparatus 2 Reaction tank 6 Oxygen melt | dissolution membrane module 9 Air diffuser pipe 20,21 Header 22 Hollow fiber membrane 27 Air supply piping 29 Exhaust piping 30 Exhaust gas piping 32 Tank

Claims (4)

A reaction vessel;
An oxygen-dissolving membrane module installed in the reaction vessel;
Oxygen-containing gas supply means for supplying an oxygen-containing gas to the oxygen-dissolving membrane module;
A method for operating an aerobic biological treatment apparatus comprising a fluidized bed of a carrier formed in a reaction tank,
Aerobic organisms that intermittently aerate the inside of the reaction tank to peel off part of the biofilm adhering to the carrier, then pass water at a higher LV than during normal operation, and discharge the peeled sludge out of the reaction tank Operation method of the processing apparatus.   The upper part of the reaction tank is a widened part having a larger horizontal cross-sectional area than the middle part and the lower part, and the upper surface of the carrier fluidized bed is positioned in the widened part when the high LV water flows. The operation method of 1 aerobic biological treatment apparatus.   The method for operating an aerobic biological treatment apparatus according to claim 1 or 2, wherein the oxygen-dissolving membrane module comprises a non-porous oxygen-dissolving membrane.   The method for operating an aerobic biological treatment apparatus according to claim 3, wherein the oxygen-dissolving membrane is hydrophobic.

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