JP2008221190A - Wastewater treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively prevent membrane clogging to enhance the treatment efficiency. <P>SOLUTION: An EPS (extracellular polymeric substance) filter 25 is installed in a circular line 19 which draws activated sludge from an activated sludge tank 3 and returns it thereto. The EPS filter 25 denudes aerobic microorganisms X of the EPS P in the activated sludge and then the EPS P becomes a soluble organic substance and is reduced via the activated sludge decomposition. Hence, the membrane clogging is essentially prevented. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wastewater treatment apparatus for biologically treating organic wastewater such as sewage and industrial wastewater.

While biologically treating organic wastewater using activated sludge, the treated water is membrane separated by reverse osmosis (RO) membrane, ultrafiltration (UF) membrane, microfiltration (MF) membrane, hollow fiber (HF) membrane, etc. The method is known. As an apparatus applied to this method, for example, an apparatus in which an immersion film is installed in an aeration tank is disclosed in Patent Document 1. In this apparatus, it is possible to prevent the outflow of suspended substances (also referred to as “SS”) and to stabilize the quality of the treated water. However, since the treated water and the activated sludge are separated by the submerged membrane, the activated sludge and its secretions adhere to the membrane surface, causing a problem of membrane clogging. Therefore, in this apparatus, a reverse cleaning apparatus is provided to prevent the membrane from being blocked.
JP 2002-253935 A

  However, in the above apparatus, it is difficult to essentially improve the membrane blockage, and if it is attempted to keep the permeated water amount above a certain level, frequent backwashing is required, and it is difficult to improve the processing efficiency.

  The object of the present invention is to provide a wastewater treatment apparatus that can effectively prevent membrane clogging and improve treatment efficiency.

  If the extracellular polymeric substances (EPS) that induce membrane occlusion can be reduced, membrane occlusion is eliminated. The inventor who has focused on this has made extensive studies in order to achieve the above object. As a result, the extracellular polymer peeled from the aerobic microorganism becomes a soluble organic substance, and the soluble organic substance becomes a substrate (nutrient) for activated sludge. It was found that it can be easily reduced. The present invention has been made based on the above findings.

  The present invention provides a wastewater treatment apparatus for biologically treating organic wastewater by using activated sludge, wherein organic wastewater is introduced, a treatment tank for storing activated sludge, and a treatment tank for storing activated sludge. A membrane separation means for separating sludge and an extracellular polymer removal means for separating the extracellular polymer in the activated sludge from the aerobic microorganisms are provided.

  In the wastewater treatment apparatus according to the present invention, organic matter is decomposed into the organic wastewater introduced into the treatment tank by activated sludge. Treated water obtained by decomposing organic matter is separated from activated sludge by membrane separation means. The aerobic microorganisms in the activated sludge produce extracellular polymers in the course of the decomposition process and become highly viscous flocs. The extracellular polymer in the activated sludge is peeled from the aerobic microorganism by the extracellular polymer removing means. Then, the extracellular polymer becomes a soluble organic substance and decreases due to the decomposition action of the activated sludge. Therefore, according to the present invention, the extracellular polymer in the activated sludge can be reduced, and membrane clogging can be essentially prevented. As a result, it is possible to reduce time loss associated with membrane cleaning and replacement, and improve processing efficiency. Furthermore, the running cost can be reduced as compared with a device that uses a flocculant or the like to prevent membrane clogging.

  Furthermore, it is preferable that the extracellular polymer removal means is provided on a circulation line that extracts a part of the activated sludge in the treatment tank and returns it to the treatment tank. Because it is possible to treat the activated sludge while circulating a part of it, the extracellular polymer can be reduced while the organic matter is decomposed in the treatment tank, and the aerobic microorganisms after removing the extracellular polymer are decomposed into the organic matter. Can be used effectively.

  Furthermore, the extracellular polymer removal means includes a sludge retention tank to which activated sludge is supplied, a shaft portion disposed in the sludge retention tank, a porous plate fixed to the shaft portion, and the shaft portion along the axial direction. And a drive unit that reciprocates. The perforated plate reciprocates by the reciprocating motion of the shaft portion, and the activated sludge undergoes a crushing action when passing through the holes of the perforated plate. As a result, the extracellular polymer in the activated sludge is effectively peeled off from the aerobic microorganisms.

  Further, the extracellular polymer removal means includes a sludge retention tank to which activated sludge is supplied, a shaft portion disposed in the sludge retention tank, a plurality of perforated plates fixed to the shaft portion, and the shaft portion in the axial direction. And a drive section that reciprocates along the line. The perforated plate reciprocates by the reciprocating motion of the shaft portion, and the activated sludge undergoes a crushing action when passing through the holes of the perforated plate. In particular, since the plurality of perforated plates are reciprocated, the activated sludge is crushed by the interaction between the perforated plates. As a result, the extracellular polymer in the activated sludge is effectively peeled off from the aerobic microorganisms.

  Furthermore, it is preferable that at least one of the plurality of holes formed in the porous plate is arranged non-coaxially with the holes formed in other porous plates adjacent to each other. In such a configuration, the activated sludge meanders when flowing between the holes of the two perforated plates, so that vortex flow and turbulent flow are generated and stirring is promoted, and the exfoliating action of the extracellular polymer is improved. .

  Further, it is preferable that the extracellular polymer removal means further has a heating means for heating the inside of the sludge retention tank. The exfoliation of the extracellular polymer is greatly facilitated by heating the activated sludge. Therefore, the reciprocating motion of the shaft portion can be reduced, and the operation efficiency in the drive portion can be improved.

  Further, it is preferable that the extracellular polymer removal means further has an aeration means for supplying gas to the activated sludge staying in the sludge retention tank. By supplying the gas, the inside of the sludge retention tank is agitated, and the extracellular polymer is easily separated from the aerobic bacteria, and the removal efficiency of the extracellular polymer is improved.

  The wastewater treatment apparatus according to the present invention can effectively prevent membrane clogging and improve treatment efficiency.

  Hereinafter, preferred embodiments of a wastewater treatment apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a wastewater treatment apparatus 1 according to the present invention. The waste water treatment apparatus 1 is used for biological treatment that decomposes organic matter using activated sludge. The wastewater treatment apparatus 1 includes an activated sludge tank (treatment tank) 3 that holds activated sludge. The activated sludge tank 3 is connected with a raw water line 5 for introducing the organic waste water W and an aeration line 7 for introducing an aeration gas made of air or oxygen gas. An aeration pump 7 a is provided on the aeration line 7.

  In the activated sludge tank 3, an immersion membrane unit (membrane separation means) 9 having a separation membrane is disposed, and an aeration device 11 connected to the aeration line 7 is disposed below the immersion membrane unit 9. ing. The aeration apparatus 11 supplies aeration gas into the activated sludge tank 3. Then, the aerobic microorganism X (see FIG. 3) in the activated sludge decomposes the organic matter in the organic wastewater W. The aerobic microorganism X generates an extracellular polymer P in the course of the decomposition treatment, and is combined with other aerobic microorganisms X via the extracellular polymer P to form a flock. The submerged membrane unit 9 selectively filters the treated water Ws from the floc-like activated sludge. The aerated gas released from the aeration apparatus 11 comes into contact with the separation membrane of the submerged membrane unit 9 and also has an effect of cleaning the deposits on the membrane surface. As the separation membrane, a reverse osmosis (RO) membrane, an ultrafiltration (UF) membrane, a microfiltration (MF) membrane, a hollow fiber (HF) membrane, or the like can be used as appropriate.

  A treated water transfer pipe 15 connected to the treated water storage tank 13 is connected to the immersion membrane unit 9. The treated water Ws filtered by the immersion membrane unit 9 is transferred to the treated water storage tank 13 through the treated water transfer pipe 15. A water discharge pipe 17 is connected to the treated water storage tank 13, and the treated water Ws temporarily stored in the treated water storage tank 13 is discharged through the water discharge pipe 17.

  The activated sludge tank 3 is provided with a circulation line 19 for extracting a part of the activated sludge and returning it to the activated sludge tank 3. The circulation line 19 has a sludge water extraction pipe 21 connected to the bottom of the activated sludge tank 3 and a sludge water return pipe 23 connected to the upper part of the activated sludge tank 3. Between the sludge water extraction pipe 21 and the sludge water return pipe 23, an EPS removing device (extracellular polymer removal means) 25 is provided.

  The EPS removing device 25 has a substantially cylindrical sludge retention tank 27 that stores sludge water containing activated sludge. A sludge water extraction pipe 21 is connected to the lower part of the sludge retention tank 27, and a sludge water return pipe 23 is connected to the upper part of the sludge retention tank 27. A shaft portion 29 is arranged in the sludge retention tank 27 along the longitudinal direction of the sludge retention tank 27. A drive motor (drive unit) 31 is connected to the upper portion of the shaft portion 29, and the shaft portion 29 reciprocates up and down along the axis L direction by driving of the drive motor 31.

As shown in FIG. 2, a plurality of disk-shaped perforated plates 33 are fixed to the shaft portion 29. In FIG. 2, among the plurality of perforated plates 33, the perforated plate 33 1 of the _uppermost, the second stage perforated plate 33 _2, it shows a perforated plate 33 ₃ of the third stage. The plurality of perforated plates 33 are all arranged at equal intervals and arranged so as to be orthogonal to the axis L. The activated sludge supplied from the sludge water extraction pipe 21 to the sludge retention tank 27 is stirred by the perforated plate 33 that reciprocates. Then, the extracellular polymer P peels from the aerobic microorganism X (see FIG. 3) in the activated sludge. The exfoliated extracellular polymer P becomes a soluble organic substance and is decomposed by aerobic microorganisms. As a result, the extracellular polymer P decreases. The arrangement of the plurality of perforated plates 33 is not limited to the arrangement orthogonal to the axis L, and may be arranged so as to be inclined with respect to the axis L and parallel to each other.

Furthermore, a plurality of holes H are formed in each of the plurality of perforated plates 33. The plurality of holes H formed in one porous plate 33 is non-coaxial with respect to the plurality of holes H formed in the other adjacent porous plate 33. For example, of the hole H ₂ formed in the perforated plate 33 ₂ of the second stage, there is one hole Ha is formed on the uppermost perforated plate 33 ₁ and the third stage of the porous plate 33 ₃ adjacent to each other The holes H1 and H3 are non-coaxial. As described above, the activated sludge is adjacent to each other by disposing at least one hole H out of the plurality of holes H formed in the porous plate 33 so as to be non-coaxial with the hole H of the adjacent porous plate 33. When the fluid flows between the holes H formed in the two perforated plates 33, meandering occurs, whirling or turbulent flow is generated, stirring is promoted, and the exfoliating action of the extracellular polymer P is improved.

  In addition, an aeration pump (aeration means) 35 is connected to the lower portion of the sludge retention tank 27, and gas is supplied into the sludge retention tank 27 by driving of the aeration pump 35. By supplying the gas, the inside of the sludge retention tank 27 is agitated, and the extracellular polymer P is easily separated from the aerobic bacteria X. Furthermore, when the supplied gas is an oxygen-containing gas, the decomposition treatment of the soluble organic matter by the aerobic microorganism X is promoted, and the removal efficiency of the extracellular polymer P is improved. Furthermore, supplying a gas with an increased oxygen concentration by an apparatus using a pressure swing adsorption system (PSA) or the like is more effective in terms of decomposition of soluble organic matter.

  In addition, a steam generator (heating means) 37 is connected to the sludge retention tank 27, and the inside of the sludge retention tank 27 is heated by steam from the steam generator 37. The exfoliation of the extracellular polymer P is greatly facilitated by heating the activated sludge. Therefore, by heating the sludge retention tank 27, the reciprocating motion of the shaft portion 29 can be reduced, the load on the drive motor 31 can be reduced, and the operation efficiency can be improved. Instead of the steam generator 37, a jacket heater surrounding the sludge retention tank 27 may be attached to heat the sludge retention tank 27.

  Next, the activated sludge treatment using the wastewater treatment apparatus 1 will be described. First, the organic waste water W is introduced into the activated sludge tank 3 through the raw water line 5, and the organic waste water W is mixed with the sludge water containing activated sludge. Then, the organic matter in the organic wastewater W is decomposed by the aerobic microorganism X. The aerobic microorganism X generates extracellular polymer P in the course of the decomposition treatment, and the aerobic microorganisms X are linked together in a floc form via the extracellular polymer P.

  The treated water Ws is selectively filtered from the activated sludge by the immersion membrane unit 9 and discharged through the treated water transfer pipe 15, the treated water storage tank 13 and the water discharge pipe 17. On the other hand, the activated sludge is maintained at a high concentration in the activated sludge tank 3, and wastewater treatment with high efficiency becomes possible. However, the extracellular polymer P in the activated sludge is very viscous and adheres to the membrane surface, causing the membrane to be blocked. Therefore, a part of the activated sludge is drawn out by the circulation line 19, the extracellular polymer P is removed by the EPS removing device 25, and then returned to the activated sludge tank 3 to prevent the submerged membrane unit 9 from being blocked.

  According to the wastewater treatment apparatus 1, the extracellular polymer P can be peeled from the aerobic microorganism X in the activated sludge. The exfoliated extracellular polymer P becomes a soluble organic substance and is decomposed by the aerobic microorganism X. Therefore, the extracellular polymer P can be easily reduced, and the membrane blockage of the submerged membrane unit 9 can be essentially prevented. As a result, it is possible to reduce time loss associated with membrane cleaning and replacement, and improve processing efficiency. Furthermore, the running cost can be reduced as compared with an apparatus that uses an expensive flocculant or the like to prevent membrane clogging.

  Furthermore, since the EPS removing device 25 is provided on the circulation line 19 for extracting a part of the activated sludge, the extracellular polymer P can be reduced while the organic matter is decomposed in the activated sludge tank 3. Furthermore, by returning the aerobic microorganisms X from which the extracellular polymer P has been peeled off to the activated sludge tank 3, the aerobic microorganisms X after the removal of the extracellular polymer P can be effectively used for the organic substance decomposition treatment.

  Furthermore, if the extracellular polymer P is removed by the wastewater treatment apparatus 1, it results in the reduction of excess sludge, and the treatment cost of excess sludge can be reduced. And if surplus sludge can be reduced, the sludge (excess sludge) processing equipment conventionally required for the reduction of surplus sludge will become small or unnecessary, and an equipment cost burden will be reduced.

  Next, the wastewater treatment apparatus according to the present invention will be specifically described with reference to examples and comparative examples.

In the wastewater treatment apparatus according to the example, food wastewater was used as organic wastewater. As the activated sludge tank, a tank having an effective volume of 5 (m ³ ) was used. The activated sludge tank was provided with a membrane unit of 40 submerged flat membranes having an effective membrane area of 0.4 (m ² ). Further, an aeration apparatus was disposed below the membrane unit in the activated sludge tank.

In this example, the membrane unit was washed with an aeration apparatus and stirred so that the dissolved oxygen (also referred to as “DO”) concentration was maintained at about 2 (mg / l). Furthermore, the sludge water sent from the activated sludge tank to the EPS removing device was set to about 20% of the introduction amount of the organic waste water. In the EPS removal apparatus, the perforated plate was reciprocated at 20 times per minute, and the inside of the sludge retention tank was maintained at 50 ° C. by steam heating. At this time, it operated so that the permeation | transmission flux of membrane treated water might be set to 1.0 (m < ³ > / m < ² > / day). The initial MLSS concentration was 10 (kg-MLSS / m ³ ). The elapsed days when the differential pressure at this time was 10 (kPa) and the MLSS concentration were measured. As a result, the elapsed days of 10 (kPa) was 20 days. Furthermore, the MLSS density | concentration at that time was less than 11 (kg-MLSS / m < ³ >), and it was able to drive | operate, without extracting excess sludge.

In the wastewater treatment apparatus according to the comparative example, no EPS removing apparatus was used. Other configurations are the same as those of the wastewater treatment apparatus according to the embodiment. In this apparatus, food waste water was used as the organic waste water as in the waste water treatment apparatus according to the example. Furthermore, in this apparatus, the operation | movement similar to the waste water treatment apparatus which concerns on an Example was performed except the driving | operation with an EPS removal apparatus. As a result, the elapsed days of 10 (kPa) was 3 days, and it was confirmed that the period until the membrane occlusion was significantly shortened compared to the example. Furthermore, it was confirmed that the MLSS concentration became 11 (kg-MLSS / m ³ ) or more in a short period of time, and it may be necessary to extract excess sludge.

  The present invention is not limited to the above embodiment. For example, the number of perforated plates fixed to the shaft portion of the extracellular polymer removal means is not plural, and only one may be used. Further, a stirring blade may be provided on the perforated plate, and the shaft portion may be rotated while moving up and down. Moreover, you may utilize the screw blade | wing provided along the axial part instead of the perforated plate, and you may form a some hole in the screw blade | wing further.

It is a block diagram of the wastewater treatment apparatus which concerns on embodiment of this invention. It is a perspective view of the microbial cell polymer removal means which concerns on this embodiment. It is a figure which expands and shows the aerobic microorganisms which form a floc with an extracellular polymer, (a) is a figure before extracellular polymer peeling, (b) is a figure after extracellular polymer peeling.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Waste water processing apparatus, 3 ... Activated sludge tank (treatment tank), 9 ... Submerged membrane unit (membrane separation means), 19 ... Circulation line, 25 ... PES removal apparatus (extracellular polymer removal means), 27 ... Sludge retention Tank, 29 ... shaft part, 31 ... drive motor (drive part), 33, 33 ₁ , 33 ₂ , 33 ₃ ... perforated plate, 35 ... diffuser pump (aeration means), 37 ... steam generator (heating means) , L ... axis, H, Ha, Hb, Hc, Hd ... pore, P ... extracellular polymer, X ... aerobic microorganism.

Claims (7)

In wastewater treatment equipment that biologically treats organic wastewater using activated sludge,
While the organic wastewater is introduced, a treatment tank for storing the activated sludge,
Membrane separation means for separating the treated water and the activated sludge while being provided in the treatment tank;
A wastewater treatment apparatus comprising: an extracellular polymer removal means that is connected to the treatment tank and separates the extracellular polymer in the activated sludge from an aerobic microorganism.   The waste water according to claim 1, wherein the extracellular polymer removal means is provided on a circulation line for extracting at least a part of the activated sludge in the treatment tank and returning it to the treatment tank. Processing equipment.   The extracellular polymer removal means includes a sludge retention tank to which the activated sludge is supplied, a shaft portion disposed in the sludge retention tank, a porous plate fixed to the shaft portion, and the shaft portion as an axis. The wastewater treatment apparatus according to claim 1, further comprising: a drive unit that reciprocates along a direction.   The extracellular polymer removal means includes a sludge retention tank to which the activated sludge is supplied, a shaft portion disposed in the sludge retention tank, a plurality of perforated plates fixed to the shaft portion, and the shaft portion. The waste water treatment apparatus according to claim 1, further comprising: a drive unit that reciprocates the shaft along the axial direction.   The at least one hole among the plurality of holes formed in the perforated plate is arranged non-coaxially with holes formed in other perforated plates adjacent to each other. Waste water treatment equipment.   The waste water treatment apparatus according to any one of claims 3 to 5, wherein the extracellular polymer removal means further includes a heating means for heating the sludge retention tank.   The waste water treatment according to any one of claims 3 to 6, wherein the extracellular polymer removal means further includes an aeration means for supplying a gas to the activated sludge staying in the sludge retention tank. apparatus.

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