JP2014133206A - Waste water treatment apparatus, and update/modification method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treatment apparatus in which, when facilities of an activated sludge process are updated or reconstructed, the surface of a membrane can be cleaned stably and water treatment using activated sludge can be stabilized even in the case that a membrane separation unit is installed in a precipitation tank, and to provide an update/modification method of the waste water treatment apparatus.SOLUTION: The waste water treatment apparatus is characterized in that organic sewage and activated sludge are aerated and mixed with each other in an aeration tank, an obtained liquid mixture is subjected to solid-liquid separation in the precipitation tank, the concentrated sludge obtained by the solid-liquid separation is returned to the aeration tank as return sludge, and the membrane separation unit, in the lower part of which an aeration device for cleaning the surface of the membrane is arranged, is installed in the precipitation tank so that flow rate of the return sludge is made higher than that of the return sludge of the existing activated sludge process. The update/modification method of the waste water treatment apparatus is also provided.

Description

  The present invention provides an aeration tank for aeration mixing of organic sewage and activated sludge and a method for updating a wastewater treatment apparatus equipped with a sedimentation tank for solid-liquid separation of the mixed liquid, thereby improving the treatment efficiency of the existing wastewater treatment apparatus. It relates to an update / improvement method that can be implemented.

  A standard activated sludge method is known as a general method for treating sewage using microorganisms. In the standard activated sludge method, organic sewage is introduced into an aeration tank containing activated sludge and aerated and stirred. Thereafter, the water treated with the microorganisms is solid-liquid separated in a sedimentation tank, and the supernatant is discharged as treated water. The separated concentrated sludge is returned to the aeration tank as return sludge, and a part thereof is drawn out of the activated sludge system as surplus sludge.

  In the membrane separation activated sludge method (hereinafter referred to as MBR), inflowing organic sewage is introduced into an aeration tank after contaminants such as residue are removed by a fine screen. A membrane separation module is installed in the aeration tank, whereby solid-liquid separation is performed and treated water can be obtained. In order to make the concentration of activated sludge suspended matter (hereinafter referred to as MLSS) in the aeration tank constant, an excess amount of excess sludge is extracted by a sludge extraction pump.

  For example, in Patent Document 1, a filtration membrane is installed in a biological reaction tank that treats sewage by mixing and aeration of sewage and activated sludge. Thus, an invention is disclosed in which solid-liquid separation is simultaneously performed, and the final sedimentation tank that is no longer used is used as the initial sedimentation tank. Patent Document 2 discloses an invention characterized in that in an oxidation ditch in which organic sewage is biologically treated by sludge microorganisms in a reaction tank, a membrane separation device is installed so as to be immersed in a settling tank. ing.

JP 2004-321862 A JP 2004-188255 A

  In order to apply the membrane separation activated sludge method to the renewal of the standard activated sludge method, which is a general existing wastewater treatment method, the layout is considered so that the membrane module is properly washed, and the MLSS concentration in the aeration tank (The unit of MLSS concentration is generally expressed in mg / L) needs to be set to an appropriate range. However, none of the patent documents fully discloses a technique that can provide a solution to these problems.

  The purpose of the present invention is to perform stable membrane cleaning and to stabilize water treatment with activated sludge when a membrane separation device is loaded in a settling tank when the activated sludge process equipment is updated or remodeled. The present invention provides a wastewater treatment apparatus and a method for updating and remodeling the wastewater treatment apparatus.

In order to achieve the above object, the wastewater treatment apparatus of the present invention and the update / modification method of the existing wastewater treatment apparatus have the following characteristics.
(1) An aeration tank for aeration mixing organic sludge and activated sludge, a precipitation tank for solid-liquid separation of the mixed liquid mixed in the aeration tank, and a sludge for returning concentrated sludge obtained by the solid-liquid separation And a return pipe for transferring to the aeration tank, a membrane separation device having an aeration device for washing the membrane surface in the lower part is loaded in the settling tank, and a return sludge pump is provided in the return pipe. A wastewater treatment apparatus characterized by that.
(2) The wastewater treatment apparatus according to (1), wherein the sedimentation tank includes a rail-like instrument for maintaining the level of the membrane separation device.
(3) Organic sewage and activated sludge are aerated and mixed in an aeration tank, the mixed liquid mixed in the aeration tank is solid-liquid separated in a precipitation tank, and the solid-liquid separated concentrated sludge is returned to the aeration tank as return sludge. A method for renewing and remodeling a wastewater treatment apparatus, wherein a membrane separation device having an aeration device for washing a membrane surface is loaded in the settling tank, and the flow rate of the return sludge is changed to the organic wastewater. A method for renewing or remodeling a wastewater treatment apparatus, characterized in that the inflow amount is in the range of 100% to 500%.
(4) The method for updating and remodeling a wastewater treatment apparatus according to (3), wherein an air lift pump is provided in a pipe for transferring the return sludge, and the flow rate of the return sludge is adjusted by the air lift pump.
(5) The update of the wastewater treatment apparatus according to (3) or (4) above, wherein the inclination of the center line of the membrane separation device in the settling tank is suppressed to within 5% with respect to the vertical direction. -Remodeling method.
(6) The method for updating and remodeling a wastewater treatment apparatus according to (5) above, wherein a rail-like instrument for maintaining the level of the membrane separation device is installed in the sedimentation tank.

  According to the present invention, the MLSS concentration staying in the aeration tank and the precipitation tank can be stabilized. In addition, by suppressing the bias of aeration accompanying the installation in the settling tank, it becomes possible to perform aeration cleaning of the membrane surface of the membrane separation device uniformly and effectively. In addition, since the membrane separation activated sludge method can be applied, operation at a higher volume load is possible compared to existing activated sludge treatment, and solid-liquid separation is performed with a separation membrane, so compared with precipitation separation. Clean treated water can be obtained.

It is a figure which shows the flow of a standard activated sludge method. It is a flowchart which shows embodiment of the update / remodeling method of the wastewater treatment apparatus which concerns on this invention. It is a figure which shows the ratio of the MLSS density | concentration in an activated sludge processing tank with respect to the MLSS density | concentration in a sedimentation tank in each sludge return rate. It is a figure which shows embodiment of this invention, (a) is the figure which installed the membrane separator 10 in the precipitation tank 5 as it is, (b) is a precipitation tank using the rail member 15 for the membrane separator 10 FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart of the standard activated sludge method before renewal / modification. Waste water containing organic pollutants such as sewage and factory waste water, that is, organic sludge 1 is introduced into the activated sludge treatment tank 2 and activated sludge treatment in the activated sludge treatment tank 2. The residence time of the organic sewage 1 in the activated sludge treatment tank 2 is usually about 1 to 24 hours, but an optimum time is selected according to the concentration of the organic sewage 1 and the like. Moreover, the MLSS concentration in the activated sludge treatment tank 2 is approximately 1,500 mg / L to 4,000 mg / L. When the MLSS concentration is increased, the processing efficiency per volume of the activated sludge treatment tank is improved. However, since separation becomes difficult in the subsequent solid-liquid separation step, it is important to maintain an appropriate MLSS concentration.

  In the activated sludge treatment tank 2, an air diffusion unit 3 for diffusing air supplied from the blower 4 is attached. The air diffused from the air diffusion unit 3 is supplied to the activated sludge mixed liquid and used for the decomposition of the organic matter. The activated sludge mixed solution after the treatment is introduced into the settling tank 5.

In the settling tank 5, activated sludge (microorganisms) and treated water are separated by precipitation, and the settling tank overflow water is discharged into the environment as treated water 9 in the activated sludge method. The settling tank 5 is designed with a water area load suitable for the properties of the activated sludge, and the activated sludge is stored at the bottom of the settling tank 5. The sludge accumulated in the sedimentation tank is returned to the activated sludge treatment tank 2 via the return sludge pump 7 as the return sludge 6. A part of the returned sludge 6 is appropriately extracted out of the system as surplus sludge 8. The sludge return rate in the standard activated sludge method is approximately 30%. The sludge return rate is calculated as follows.
Sludge return rate = (Return sludge volume / day) ÷ (Organic sewage inflow sewage volume / day) x 100

  The wastewater treatment facility of the present invention is characterized in that a membrane separator is loaded in the sedimentation tank 5 and the amount of the returned sludge 6 from the sedimentation tank 5 to the activated sludge treatment tank 2 is increased.

  As shown in FIG. 2, in the wastewater treatment apparatus of the present invention, the membrane separation device 10 is immersed in the precipitation tank 5. A membrane surface cleaning aeration unit 12 as an aeration device is installed at the lower part of the membrane separation device 10, and the air supplied from the membrane surface cleaning air blower 11 is diffused from the membrane surface cleaning aeration unit 12 to perform membrane separation. The film surface of the apparatus 10 is cleaned. A membrane filtration suction pump 13 is connected to the membrane separation device 10, and the water subjected to membrane filtration is discharged as membrane filtrate 14.

  Similar to the existing activated sludge method, the concentrated sludge (return sludge 6) separated in the solid-liquid separation in the settling tank 5 is returned to the activated sludge treatment tank 2 via the return sludge pump 7. In the present invention, the flow rate of the return sludge pump 7 is desirably operated in the range of about 100% to 500% of the inflow amount of the organic sewage 1, and more preferably in the range of 200% to 400%. Since the return rate in the normal activated sludge method is about 30% as described above, it is necessary to increase the rate from about 3 times to 16 times by introducing the membrane separation device 10. As a method of augmentation, there is a method of replacing the return sludge pump with a large pump or adding a new pump while diverting the return sludge pump of the existing equipment to enhance the equipment. In particular, an air lift pump that is advantageous in running cost may be used.

Here, the influence which the difference in the sludge return rate has on the MLSS concentration in the activated sludge treatment tank and the sedimentation tank will be described. FIG. 3 shows the ratio of the MLSS concentration in the activated sludge treatment tank to the MLSS concentration in the sedimentation tank at each sludge return rate (MLSS concentration (activated sludge treatment tank) / MLSS concentration (precipitation tank)). If this value is low, the MLSS concentration difference between the activated sludge treatment tank and the sedimentation tank becomes large.
For example, as in the conventional activated sludge method, if the sludge return rate is 30%, the MLSS concentration (activated sludge treatment tank) / MLSS concentration (precipitation tank) value is 0.23. If the MLSS concentration in the sedimentation tank during operation is 10,000 mg / L, the MLSS in the activated sludge treatment tank is 2,300 mg / L. With this, the MLSS concentration in the activated sludge treatment tank is too low, and the merit in the membrane separation activated sludge method that can increase the treatment efficiency per unit volume cannot be found. On the other hand, if the sludge return rate is increased, the value of MLSS concentration (activated sludge treatment tank) / MLSS concentration (precipitation tank) also increases. Here, as shown in FIG. 3, since the increase curve is asymptotic, it is desirable to set the sludge return rate to about 100 to 500% in consideration of economy. Therefore, if the sludge return rate is within the above range, the merit of processing by MBR can be brought out.

  Here, in order to improve the handleability and physical durability of the filtration membrane, the membrane separation device 10 has, for example, a flat membrane element structure in which a filtration membrane is bonded to both sides of a frame and a filtration membrane is bonded. A hollow fiber structure in which hollow fiber membranes are bundled is included, and refers to a submerged membrane unit used in a membrane separation activated sludge method. Examples of the membrane structure of the filtration membrane include, but are not limited to, a porous membrane and a composite membrane in which a functional layer is combined with the porous membrane.

  Specific examples of these membranes include polyacrylonitrile porous membrane, polyimide porous membrane, polyethersulfone porous membrane, polyphenylene sulfide sulfone porous membrane, polytetrafluoroethylene porous membrane, polyvinylidene fluoride porous membrane, polypropylene Examples of the porous film include a porous film and a porous film such as a polyethylene porous film, and a polyvinylidene fluoride porous film and a polytetrafluoroethylene porous film are particularly preferable because of high chemical resistance. Furthermore, a composite membrane in which a rubbery polymer such as cross-linked silicone, polybutadiene, polyacrylonitrile butadiene, ethylene propylene rubber, or neoprene rubber is combined as a functional layer with these porous membranes can also be used in the membrane separation apparatus 10. The filtration membrane here refers to one having a pore size of about 0.01 μm to 10 μm, generally coarser than an ultrafiltration membrane in which separation by molecular sieve is performed, and a normal operating pressure is 200 kPa or less from a reduced pressure state. Driven.

  The membrane surface cleaning air diffusion unit 12 is disposed at the bottom of the membrane separation device 10. Usually, the air is diffused by an air diffuser that generates coarse bubbles, but it is also possible to use a fine bubble type (for example, EPDM (ethylene-propylene-diene rubber)) membrane diffuser. A membrane surface cleaning blower 11 is connected to the membrane surface cleaning air diffusion unit 12. Aeration for cleaning the membrane surface can be performed continuously or intermittently. In addition, this air diffuser can clean the membrane surface and supply oxygen necessary for the activated sludge.

  The membrane surface cleaning diffuser unit 12 may be of any structure that diffuses toward the entire membrane separation apparatus 10, and may have a structure in which a hole is formed in a tube, a ceramic diffuser plate, or the like. There is no particular limitation. The membrane surface cleaning blower 11 is a blower that blows compressed air, and it is preferable to select an optimum blower according to the scale of the equipment, the water depth, and the like.

  Separation of activated sludge and treated water is performed by the membrane separation device 10. A membrane filtration suction pump 13 is used as the motive power for filtration, and the membrane filtrate is used for discharge or reuse. The membrane filtration suction pump 13 is not particularly limited as long as it can obtain treated water from the membrane separation device 10, and is a centrifugal pump, diffuser pump, spiral mixed flow pump, mixed flow pump, piston pump, plunger pump, Diaphragm pumps, gear pumps, screw pumps, vane pumps, cascade pumps, jet pumps, and the like are used.

  As described above, the return sludge 6 plays an important role in appropriately maintaining the concentration of the activated sludge that can be stored in the activated sludge treatment tank 2 and the settling tank 5. The return sludge pump 7 may have either a shape installed outside the tank or a shape installed inside the tank, and the type of the pump is not particularly limited as long as activated sludge can be fed. Note that an air lift pump can be used to reduce running costs. An air lift pump is a pump that blows compressed air into an underwater vertical pipe, creates a specific gravity difference between the liquid inside and outside the pipe, and pumps up sewage and filth with bubbles that rise at that time. It is possible to reduce the amount of electric power compared to.

  In the present invention, the membrane separator 10 preferably has an inclination of the center line of 5% or less with respect to the vertical direction. In the activated sludge treatment facility, the sedimentation tank 5 is provided with a gradient so that the concentrated sludge that has settled is accumulated at the center of the bottom (see FIGS. 2 and 4). Therefore, as shown in FIG. 4 (a), when the membrane separation device 10 and the membrane surface cleaning air diffuser unit 12 at the lower part thereof are installed as they are at the bottom of the settling tank 5, the membrane is combined with the gradient. Separation apparatus 10 and membrane surface cleaning air diffusion unit 12 are also installed obliquely, and cleaning for membrane surface cleaning may not be performed sufficiently. Since the air ejected from the membrane surface cleaning air diffusion unit 12 rises in the vertical direction, the cleaning is not sufficient on the tilted side of the tilted membrane separator (that is, the left side of the membrane separator shown in FIG. 4A). A part will be made. Furthermore, since the swirling flow flowing around the membrane separation device 10 is not symmetrical, the cleaning performance of the membrane surface is not uniform.

  For this reason, in the wastewater treatment apparatus of the present invention, it is desirable that the inclination of the center line of the membrane separation device 10 in the settling tank 5 is adjusted to be 5% or less with respect to the vertical direction. Means for suppressing the inclination of the membrane separator 10 include a method of forming an angle in the entire interior of the sedimentation tank 5 and a method of ensuring the levelness by replenishing the entire bottom with concrete or the like. There is no particular limitation as long as it is selected. However, in order to reduce the number of members to be used as much as possible and minimize the construction at the site, as shown in FIG. 4B, it is conceivable to install the rail member 15 at a location with a low gradient. . The installation of the rail member 15 is simple in construction and the membrane separation apparatus can be kept horizontal, so that the air diffuses uniformly over the entire membrane separation apparatus 10 and the membrane surface is kept clean. Contributes to stable operation. As the rail member 15, stainless steel or a resin member is assumed in consideration of corrosiveness, but is not particularly limited. Moreover, what is necessary is just to design and select the shape according to the shape of the membrane module and the gradient of a sedimentation tank as a shape.

The following is an example of renewal and modification of standard activated sludge treatment equipment for treating organic sewage. Table 1 shows the processing conditions of the existing processing equipment. The raw water (treated water) is the waste water from the chemical factory (water volume: 4,000 m ³ / day, BOD = 200 mg / L). This is an example that became necessary.

  As Example 1, as shown in FIG. 2, a wastewater treatment apparatus in which a sedimentation tank 5 was loaded with a membrane separation device 10 (TMR-140-100s manufactured by Toray Industries, Inc.) was used. In Example 1, the sludge return rate was 300%. As Comparative Example 1, the wastewater treatment apparatus shown in FIG. 2 was also used, and the sludge return rate was set to 30%, equivalent to the current state of existing activated sludge treatment equipment. Table 2 shows the treatment performance of Example 1 and Comparative Example 1, and also shows the treatment performance by the existing activated sludge method using the wastewater treatment apparatus shown in FIG.

  From the results of Table 2, in the existing activated sludge method of Reference Example 1, only activated sludge stored in the activated sludge treatment tank contributes to biological treatment, but a membrane separation apparatus is introduced as in Example 1, and By increasing the flow rate of the returned sludge and increasing the sludge return rate, five times the amount of microorganisms was retained in the activated sludge treatment tank and the sedimentation tank, and both of these contributed to the biological treatment. For this reason, the raw water allowable BOD concentration increased significantly. In this way, by introducing a membrane separator and increasing the sludge return rate by increasing the return sludge flow rate, the BOD-SS load (daily sewage added per unit MLSS amount [kg] in the aeration tank) It was found that the amount of BOD [kg / day] can be improved. On the other hand, in Comparative Example 1 in which the return sludge rate is set to be equal to that of the existing equipment, the MLSS concentration of the mixed liquid in the activated sludge treatment tank and the mixed liquid in the sedimentation tank is greatly different. Low compared to 1. In this way, it has been shown that it is effective to increase the return sludge rate to an appropriate value in consideration of the stability of treatment and the BOD concentration of raw water.

  INDUSTRIAL APPLICATION This invention can utilize the existing activated sludge processing apparatus which processes organic sewage etc. to a membrane separation activated sludge processing apparatus for renewal and remodeling.

1. Organic wastewater2. 2. Activated sludge treatment tank Air diffuser unit4. Blower 5 5. Settling tank Return sludge Return sludge pump8. Surplus sludge9. Treated water (settling tank overflow water)
10. Membrane separator 11. 11. Membrane surface cleaning fan 12. Membrane surface cleaning aeration unit Membrane filtration suction pump 14. Treated water (membrane filtered water)
15. Rail member

Claims (6)

An aeration tank for aeration mixing organic sludge and activated sludge, a precipitation tank for solid-liquid separation of the mixed liquid mixed in the aeration tank, and the aeration using the concentrated sludge obtained by the solid-liquid separation as return sludge A return pipe for transfer to the tank,
A wastewater treatment apparatus, wherein a membrane separation device having an aeration device for cleaning the membrane surface is loaded in the sedimentation tank, and a return sludge pump is provided in the return pipe.   The wastewater treatment apparatus according to claim 1, wherein the sedimentation tank includes a rail-like instrument for maintaining the level of the membrane separation device. Wastewater treatment equipment that mixes organic sludge and activated sludge in an aeration tank, separates the liquid mixture mixed in the aeration tank into a solid-liquid separation in a sedimentation tank, and returns the solid-liquid separated concentrated sludge to the aeration tank as return sludge Renewal / remodeling method,
The sedimentation tank is loaded with a membrane separation device having an aeration device for washing the membrane surface at the bottom, and the flow rate of the return sludge is in the range of 100% to 500% of the inflow amount of the organic wastewater. A method for renewing or remodeling a wastewater treatment apparatus.   The method for updating and remodeling a wastewater treatment apparatus according to claim 3, wherein an air lift pump is provided in a pipe for transferring the return sludge, and the flow rate of the return sludge is adjusted by the air lift pump.   The method for renewing or remodeling a wastewater treatment apparatus according to claim 3 or 4, wherein an inclination of a center line of the membrane separation device in the sedimentation tank is suppressed within 5% with respect to a vertical direction.   The method for updating and remodeling a wastewater treatment apparatus according to claim 5, wherein a rail-like instrument for maintaining the level of the membrane separation apparatus is installed in the sedimentation tank.

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