JP2007245002A - Driving method of membrane separation type biological treatment tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the driving method of membrane separation type biological treatment tank for performing stable driving by preventing the deterioration of separation performance due to inflow of scum pieces. <P>SOLUTION: In the driving method of membrane separation type biological treatment tank, tank water in a biological treatment tank 1 is circulated and filtered by a separation membrane 2 and is taken out as treated water, wherein MLSS of the biological treatment tank 1 is maintained at high concentration of 5,000 to 20,000 mg/L. Further, scum 5 accumulated on water surface of the biological treatment tank 1 is removed by a scum removal device and the clogging of the separation membrane 2 due to the inflow of the scum pieces into the separation membrane 2 is prevented. As the scum removal device, a scum suction device, a scum scraper, a scum stirrer, etc. can be used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of operating a membrane separation type biological treatment tank used for wastewater treatment.

  Biological treatment is widely used for the treatment of organic wastewater such as sewage, return water, factory wastewater, waste leachate, human waste, agricultural wastewater, livestock wastewater and aquaculture wastewater. Biological treatment is a treatment method that decomposes organic components in wastewater by the action of microorganisms in the water. Conventionally, the biological treatment tank is combined with a sedimentation basin, and the water in the biological treatment tank is guided to the sedimentation basin and solidified by gravity sedimentation. Liquid separation was performed, and the supernatant water was taken out as treated water.

  However, these conventional methods require a large sedimentation basin and, depending on the sludge properties, bulking may occur, making sedimentation impossible. Membrane-separated biological treatment tanks that perform solid-liquid separation using separation membranes are spreading around the sewage treatment plant. Two types of membrane separation type biological treatment tanks are known: an immersion type in which the separation membrane is immersed in the tank, and an outside tank type (Patent Document 1) in which the separation membrane is installed outside the tank to perform circulation filtration. ing.

  In a biological treatment tank combined with a conventional sedimentation tank, the MLSS in the tank is generally controlled to about 1000 to 3000 mg / L. On the other hand, the membrane separation type biological treatment tank is often operated by maintaining the MLSS in the biological treatment tank at a high concentration of 5000 to 20000 mg / L because the membrane surface is easily clogged when the MLSS is low. However, when the biological treatment tank is an anaerobic tank or an oxygen-free tank, scum accumulates on the water surface when MLSS is set to a high concentration, and if part of it breaks, it may obstruct liquid feeding to the separation membrane. It was.

In particular, in the case of the outside installation type in which the in-vessel water of the biological treatment tank is circulated and filtered through a separation membrane installed outside the tank and taken out as treated water, this problem is remarkable. In addition, when the separation membrane has a narrow flow path such as a monolith type or a tubular type, the inlet pressure of the separation membrane is remarkably increased due to the inflow of scum fragments, and filtration may become impossible. In Patent Document 1, the separation membrane is backwashed when the inlet pressure of the membrane module rises due to the inflow of residue, but if the amount of scum is large, the backwashing must be performed frequently, There was a risk that the rate would decrease.
Japanese Patent Laid-Open No. 2005-246307

  An object of the present invention is to solve the above-mentioned conventional problems, and to provide a method for operating a membrane separation biological treatment tank capable of preventing a decrease in separation performance due to inflow of scum fragments and capable of stable operation. is there.

  The present invention made to solve the above problems is a method of operating a membrane separation biological treatment tank in which the water in the tank of the biological treatment tank is circulated and filtered through the separation membrane and taken out as treated water, and the MLSS of the biological treatment tank Is maintained at a high concentration of 5000 to 20000 mg / L, while scum accumulated on the water surface of the biological treatment tank is removed by a scum removing device to prevent clogging of the separation membrane.

  As the scum removing device, any of a scum suction device, a scum scraping device, and a scum stirring device can be used, and a monolith type, tubular type, or honeycomb type membrane is used as a separation membrane. Can do.

  According to the present invention, since the MLSS of the biological treatment tank is operated while maintaining a high concentration of 5000 to 20000 mg / L, the membrane surface of the separation membrane is hardly clogged, and the treatment capacity per unit volume of the biological treatment tank is increased. Can be maintained. Moreover, since the scum that tends to be generated by increasing the MLSS of the biological treatment tank is removed from the biological treatment tank by the scum removing device, the scum fragment does not flow into the separation membrane and increase the inlet pressure of the separation membrane. , Stable operation becomes possible.

Preferred embodiments of the present invention are shown below.
FIG. 1 is a view showing a first embodiment of the present invention, wherein 1 is a biological treatment tank, and 2 is a separation membrane installed outside the tank. The biological treatment tank 1 is a treatment tank for the nitrification liquid circulation method, the AO method, the A ₂ O method, the nitrification + endogenous denitrification method, the activated sludge method, etc., and includes sewage, return water, industrial wastewater, waste leachate, Biological treatment is performed using organic wastewater such as manure, agricultural wastewater, livestock wastewater, and aquaculture wastewater as raw water.

  The water in the biological treatment tank 1 is sent to the separation membrane 2 by a circulation pump 3 and subjected to circulation filtration by a cross flow method. As the separation membrane 2, an MF membrane or a UF membrane is used. The film material may be a ceramic film or a polymer film, and the film shape is not particularly limited, but a monolith film, a tubular film or a honeycomb film capable of increasing the film area per unit volume is preferable. . The pressurization method may be either an external pressure type or an internal pressure type, but in this embodiment, an internal pressure type monolithic ceramic membrane having a large number of raw water circulation holes whose cross section is a circle or a polygon of a quadrangle or more is used. The filtered water of the separation membrane 2 is taken out as treated water, and the concentrated water that has passed through the separation membrane 2 is returned to the biological treatment tank 1 through the circulation line 4.

  The MLSS of the water in the biological treatment tank 1 is maintained at a high concentration of 5000 to 20000 mg / L. As described above, by setting the concentration to 5000 mg / L or higher in this way, the membrane surface of the separation membrane 2 is prevented from being blocked and the treatment capacity per unit volume of the biological treatment tank 1 is maintained high. . In addition, when MLSS exceeds 20000 mg / L, the viscosity of activated sludge becomes high and membrane filtration becomes difficult, which is not preferable.

  Thus, in the biological treatment tank 1 having a high MLSS, the scum 5 is likely to be generated, and when the inside of the tank is in an anaerobic state, a layer of the scum 5 is formed on the water surface. Therefore, in this embodiment, the scum 5 accumulated on the water surface of the biological treatment tank 1 is removed by the scum suction device 6 which is a scum removing device. The scum suction device 6 vacuum-sucks the scum 5 with a nozzle 7 near the water surface and discharges it to the scum treatment tank.

  By removing the scum 5 from the biological treatment tank 1 in this way, a fragment of the scum 5 does not flow into the separation membrane 2 to increase its inlet pressure, and stable operation is possible. In particular, since the monolithic ceramic membrane has a narrow flow path of 1 to 5 mm, the fragments of the scum 5 are likely to be clogged on the inlet side. However, according to the present invention, troubles that the scum 5 flows into the separation membrane 2 can be effectively prevented. can do.

  FIG. 2 shows a second embodiment of the present invention and shows an example in which a scum scraping device 8 is used as a scum removing device. This device is a device that scrapes the scum 5 to one side of the biological treatment tank 1 and collects it in the scum tank 10 by a scraper 9 installed slightly above the water surface. The scum in the scum tank 10 is discharged to the scum processing tank by the pump 11. Further, instead of the scum tank 10, a scum skimmer or a pipe skimmer that opens a hole in a cylindrical tube and collects the scum in the hole may be used.

  FIG. 3 shows a third embodiment of the present invention. An auxiliary tank 12 is provided outside the biological treatment tank 1, and water in the tank is introduced by the communication part 13, and the separation membrane 2 is introduced into the auxiliary tank 12. Is immersed. Near the water surface of the biological treatment tank 1, a scum agitating device 14 is provided as a scum removing device. The scum 5 is agitated by a motor and finely crushed. The scum agitation may be mechanically performed as in this embodiment, or may be a water flow type in which the scum 5 is finely crushed by jetting a high-speed water flow onto the water surface.

  If the communicating portion 13 is placed below the water surface of the biological treatment tank 1 as in the third embodiment, the inflow of the scum 5 can be prevented, which is more effective. Moreover, you may use a scum removal apparatus combining multiple types.

  Also in these second and third embodiments, by removing the scum 5 of the biological treatment tank 1, troubles that the scum 5 flows into the separation membrane 2 can be effectively prevented. In addition, since the MLSS in the biological treatment tank 1 is maintained at a high concentration of 5000 to 20000 mg / L, the membrane surface of the separation membrane 2 is prevented from being blocked and the treatment capacity per unit volume of the biological treatment tank 1 is maintained high. can do.

  When the scum removing device was installed in the biological treatment tank 1 and the scum was removed, the membrane filtration device was able to operate stably for more than one month. However, when a scum is generated without installing a scum removing device, the operation of the membrane filtration device may become unstable several times a month.

It is sectional drawing which shows the 1st Embodiment of this invention. It is sectional drawing which shows the 2nd Embodiment of this invention. It is sectional drawing which shows the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Biological treatment tank 2 Separation membrane 3 Circulation pump 4 Circulation line 5 Scum 6 Scum suction apparatus 7 Nozzle 8 Scum scraping apparatus 9 Scraper 10 Scum tank 11 Pump 12 Auxiliary tank 13 Communication part 14 Scum stirring apparatus

Claims (3)

  An operation method of a membrane separation biological treatment tank in which water in a biological treatment tank is circulated and filtered through a separation membrane to obtain treated water, while maintaining the MLSS of the biological treatment tank at a high concentration of 5000 to 20000 mg / L A method of operating a membrane separation type biological treatment tank, wherein scum accumulated on the water surface of the biological treatment tank is removed by a scum removing device to prevent the separation membrane from being blocked.   The method for operating a membrane separation type biological treatment tank according to claim 1, wherein any one of a scum suction device, a scum scraping device, and a scum agitating device is used as the scum removing device.   2. The method of operating a membrane separation type biological treatment tank according to claim 1, wherein a monolith type or tubular type membrane or a honeycomb type membrane is used as the separation membrane.

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