JP2012210635A - Water treatment method and water treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method in which when a flocculant is used to improve the flux of a membrane separation, the adsorption of the flocculant and a membrane is controlled to minimum, and the flux in an MBR apparatus is more efficiently improved, in the membrane separation activated sludge process in which an organic sewage is subjected to an activated sludge process in a biological treatment tank, and an activated sludge mixed liquid is subjected to a solid-liquid separation by an immersion type membrane separator that is set up to be immersed in the biological treatment tank.SOLUTION: The water treatment method is characterized as follows. In the membrane separation activated sludge process, an organic sewage is subjected to an activated sludge process in a biological treatment tank 3, and an activated sludge mixed liquid is subjected to a solid-liquid separation by an immersion type membrane separator 4 which is set up to be immersed in the biological treatment tank 3; a flocculant 13 and a portion of an activated sludge in the biological treatment tank 3 are mixed beforehand while preventing the organic sewage from contacting with the flocculant 13, then a composition after the mixing is supplied into the immersion type membrane separator 4 in the biological treatment tank 3.

Description

  The present invention is a membrane separation activated sludge method in which organic sludge is treated with activated sludge in a biological treatment tank, and the activated sludge mixed liquid is solid-liquid separated by an immersion type membrane separation apparatus immersed in the biological treatment tank. The present invention relates to a method and apparatus for using a flocculant when the flocculant is used to improve the flux.

  Membrane separation activated sludge process (MBR) is a process in which organic sludge such as sewage is treated with activated sludge in a biological treatment tank, and the activated sludge mixed liquid is solid-liquid separated with an immersion type membrane separator installed in the biological treatment tank. It is a method, and since the treated water quality is stable and the activated sludge concentration can be increased, it is becoming widespread.

  On the other hand, there is a problem of clogging of the membrane due to the use of the separation membrane. That is, since filtration is continued for a long period of time, dirt components are gradually deposited on the membrane surface and inside the membrane, and the transmembrane pressure rises. In addition, during the cold season of winter and when the raw water quality changes, the components in the treated water are not temporarily decomposed, the amount of microbial extracellular metabolites (EPS) increases, or dispersible microorganisms. As a result, the separation inhibiting component of the separation membrane remains and the transmembrane pressure increases.

  As a method for resolving these cloggings, the separation membrane is usually washed with chemicals such as hypochlorite aqueous solution, but especially when the clogging of the membrane occurs due to fluctuations in the raw water quality in the winter season, Since there is a problem with the properties of the activated sludge itself, it is necessary to frequently perform cleaning operations.

  As a method for improving the clogging of the separation membrane in such an MBR apparatus, there is known a method in which an adsorbent such as powdered activated carbon is added to raw water to adsorb and remove filterability-inhibiting components (Patent Document 1). However, since the activated carbon and the membrane are in direct contact with each other, there is a problem that the surface of the membrane is scratched and the life of the membrane is shortened.

  Other known methods for improving flux in MBR devices include adding an effective amount of one or more cationic polymers, amphoteric polymers, zwitterionic polymers, or a combination thereof to the MBR device. (Patent Document 2). The flux improvement by the flocculant is that the components in the treated water are not temporarily decomposed or the amount of microbial extracellular metabolites (EPS) increases in the cold season of winter and when the raw water quality changes. When the number of dispersible microorganisms increases, these membrane-inhibiting components can be aggregated to facilitate membrane filtration, which is an effective countermeasure. However, if a high-concentration flocculant is put into a membrane separation tank as it is, activated sludge and unreacted flocculant may be adsorbed on the filtration membrane, and conversely, the membrane may be clogged.

JP-A-10-309567 JP 2006-334487 A

  Therefore, the present invention provides a membrane separation activated sludge method in which organic sludge is treated with activated sludge in a biological treatment tank, and the activated sludge mixed liquid is solid-liquid separated by a submerged membrane separation apparatus immersed in the biological treatment tank. In using a flocculant to improve the separation flux, a method is provided that minimizes flocculant and membrane adsorption and more efficiently improves the flux in an MBR apparatus.

To achieve the above object, the present onset bright are identified as follows.
(1) In the membrane separation activated sludge method in which organic sludge is treated with activated sludge in a biological treatment tank, and the activated sludge mixed solution is solid-liquid separated with a submerged membrane separation device installed in the biological treatment tank, the organic wastewater There while not in contact with the coagulant, after thoroughly mixed and part of the activated sludge in advance coagulant and biological treatment tank, the composition after mixing the submerged membrane separator in the biological treatment tank A water treatment method characterized by providing.
(2) The water treatment method according to (1), wherein the flocculant is a cationic flocculant.
(3) The water treatment method according to (1) or (2), characterized in that the material of the membrane used in the submerged membrane separator is polyvinylidene fluoride or polyethylene.
(4) The mixing time of the flocculant and a part of the activated sludge in the biological treatment tank and / or the organic wastewater as the raw water is 10 minutes or more (1) to (3) The water treatment method in any one of.
(5) The water treatment according to any one of (1) to (4), wherein the activated sludge concentration in the biological treatment tank during the water treatment operation is 2,000 mg / L or more and 25,000 mg / L or less. Method.
(6) Organic sludge is treated in an activated sludge in a biological treatment tank, and the organic sludge is agglomerated in a water treatment apparatus for solid-liquid separation of the activated sludge mixed liquid using an immersion membrane separator installed in the biological treatment tank. while not in contact with the agent, water treatment apparatus characterized by comprising a flocculation mixing tank for mixing the part of the sludge pre-coagulant and biological treatment tank.

  Improved membrane separation flux in the membrane-separated activated sludge method, in which organic sludge is treated with activated sludge in a biological treatment tank and the activated sludge mixed liquid is separated into solid and liquid using a submerged membrane separator installed in the biological treatment tank. Therefore, when the flocculant is used, the adsorption of the flocculant and the membrane can be suppressed to the minimum, and a method for improving the flux in the MBR apparatus more efficiently can be provided.

It is a figure which shows embodiment of this invention. It is a figure which shows the conditions 1 in an Example. It is a figure which shows the conditions 2 in an Example. It is a figure which shows the conditions 3 in an Example. It is a figure which shows the examination result of an Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In FIG. 1, raw water 1 that is a liquid to be treated is supplied to a biological treatment tank 3 by a raw water pump 2. A submerged membrane separation device 4 is immersed in the biological treatment tank 3, and air for cleaning the submerged membrane separation device and biological treatment is supplied from the lower portion through the air supply device 5 from the air supply device 5. Supplied. The membrane permeated water is taken out as membrane treated water 9 by the suction pump 7. Moreover, it is preferable that the excess sludge 10 generated with the activated sludge treatment is extracted by the excess sludge pump 8, and the MLSS concentration in the biological treatment tank 3 is kept constant at about 2,000 to 25,000 mg / L. This is because this concentration range has the highest concentration effect of the flocculant. Here, MLSS refers to activated sludge suspended matter, which represents the suspended matter concentration in the sample in mg / L, and is used as a management index of the biological treatment tank 3. As a measuring method, a centrifugal separation method and a glass fiber filter method are used (Japan Sewerage Association Sewerage Test Method (1997), P269-271).

  Here, in the present invention, a part of the activated sludge in the biological treatment tank 3 is extracted and mixed in the coagulation mixing tank 12 as the aggregated sludge 11. In the agglomeration mixing tank 12, a flocculant 13 is added and sufficiently stirred by the stirrer 14. Aggregated sludge 15 after stirring is returned to the biological treatment tank 3. In the biological treatment tank 3, since aeration is performed by air, the coagulated sludge 15 is further diluted with sludge and sufficiently mixed.

  The raw water 1 is treated water that is treated by a membrane separation activated sludge method such as municipal sewage or factory wastewater. The raw water pump 2 is not particularly limited as long as the raw water 1 can be fed to the biological treatment tank 3, and is a centrifugal pump, a diffuser pump, a spiral mixed flow pump, a mixed flow pump, a piston pump, Plunger pumps, diaphragm pumps, gear pumps, screw pumps, vane pumps, cascade pumps, jet pumps, and the like can be used. The biological reaction tank 3 is a tank for immersing the submerged membrane separation device 4 at the same time as storing activated sludge for biological treatment. It can be used for concrete, resin, metal, etc. There is no particular limitation as long as there is no structure.

  The submerged membrane separation device 4 is a device in which a solid-liquid separation membrane is disposed, and the separation membrane includes a hollow fiber membrane type and a flat membrane type. In order to improve the handleability and physical durability of the filtration membrane (separation membrane), for example, a flat membrane element having a structure in which a flat membrane is adhered to both sides of the frame with a filtrate channel material sandwiched between them is provided. desirable. The structure of the flat membrane element is not limited to the above. Examples of the membrane material include organic materials and inorganic materials such as ceramics. In particular, a membrane made of an organic material such as PVDF (polyvinylidene fluoride) or PE (polyethylene) can be expected to improve the filtration flow rate by using the present invention. Is preferred. This is because the initial adsorption of the flocculant is more likely to occur on PVDF and PE that are organic films than on inorganic films.

  The air supply device 5 is a device that blows compressed air, and generally a blower, a compressor, or the like is used. The blown air is sent out as bubbles from the diffuser 6 into the tank, and the bubbles clean the separation membrane surface of the membrane separator, and oxygen necessary for biological treatment (aerobic treatment) in the liquid. Supplied. The air diffuser 6 is not particularly limited as long as the air diffuser can generate bubbles for cleaning the membrane surface, but air discharge holes of 1 mm to 9 mm are provided in PVC or stainless steel pipes. An open air diffuser is usually used. In addition, a porous rubber, ceramics, a diffuser tube using a membrane, and the like can also be used.

  The suction pump 7 is a pump that sucks the membrane-treated water 9 in order to give a suction force necessary for membrane filtration solid-liquid separation by the submerged membrane separation device 4, and the shape is not particularly limited. Normally, a pump that is operated at a pressure of 300 kPa or less from a reduced pressure state is used. Further, instead of the suction pump, it is also possible to perform membrane filtration using the natural water head difference as a driving force. The surplus sludge pump 8 is a pump for extracting the surplus sludge 10 generated by the treatment with activated sludge from the biological reaction tank 3, and is particularly limited as long as it is a pump capable of extracting the activated sludge having high viscosity. It is not a thing.

  The aggregated sludge 11 is extracted from the biological reaction tank 3. The amount to be withdrawn is determined from the addition concentration of the flocculant 13, the size of the biological reaction tank 3, and the like, but is usually about 10% to 90% of the sludge in the biological treatment tank 3. As a method of adding the flocculant 13, a method (batch method) in which a part of the aggregated sludge 11 is extracted, the flocculant 13 is added and stirred, and then the whole amount is returned to the biological treatment tank 3 (batch method), Either the method of extracting the sludge 11 and continuously returning it to the biological treatment tank 3 (continuous method) may be used.

  As the flocculant 13, inorganic PAC (polyaluminum chloride) and various organic polymer flocculants can be used. The activated sludge properties and the membrane used in the submerged membrane separator 4 used are used. Appropriate ones may be selected from the compatibility with the material. In addition, since activated sludge itself is negatively charged, if a cationic flocculant is used, a filtration improvement effect can be expected in many cases. The addition concentration of the flocculant 13 is determined by a jar test or the like. If the addition concentration is too low, the agglomeration effect becomes low. If the addition concentration is too high, the unreacted flocculant 13 remains, and these components are formed into a film. Adsorption to the material and conversely clogging the membrane, there is a problem that the concentration of addition needs to be determined in advance. Cationic flocculants are generally commercially available, and examples include dimethylamine and polyacrylamide.

The stirrer 14 is for sufficiently mixing the flocculant 13 and the aggregated sludge 11, and a propeller type, an immersion type, aeration type, or the like can be used. The stirring time is usually about 5 minutes to about 1 day, and it is important to sufficiently mix and make the unreacted flocculant 13 as low as possible. From this point of view, the time required for mixing is desirably 10 minutes or more. The activated sludge after the flocculation reaction is returned to the biological treatment tank 3 as the flocculated sludge 15 .

Contact name, immersing the submerged membrane separator in a single biological treatment tank in the present embodiment, although described general membrane separation activated sludge process, the present invention is often used in urban sewage treatment circulation It can be applied to all types of membrane separation activated sludge methods, such as a membrane separation activated sludge method of the type nitrification denitrification method and a membrane separation activated sludge method that separates biological treatment and membrane separation.

It present invention importantly, by stirring was added flocculant preactivated sludge and in a separate tank to ten minutes, by preventing the coagulant unreacted flows directly to the immersion type membrane separation apparatus is there. Thereby, only the property of activated sludge can be improved by adding a flocculant, and as a result, the flux of membrane separation can be effectively improved.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to the aspect as described in an Example.

  In this embodiment, a flocculant is used to improve the membrane separation flux in the membrane separation activated sludge method in which the activated sludge mixed liquid is solid-liquid separated by a submerged membrane separation apparatus immersed in the biological treatment tank. At that time, a comparative study was performed under the following three conditions. The raw water is agricultural village wastewater, the submerged membrane separator is a PVDF flat membrane module (manufactured by Toray Industries, Inc.), and the polymer flocculant for flux improvement is sludge modification for membrane separation activated sludge process. The material MPE-50 (cationic flocculant manufactured by Nalco) was used. Details of the conditions are shown in Table-1.

(Condition 1) Perform filtration without using a flocculant (Condition 2) Add flocculant directly to the biological treatment tank and perform filtration.
(Condition 3) A part of the biological reaction tank is pulled out and aggregated in the coagulation tank, and then returned to the biological treatment tank for filtration operation (method of the present invention).
Condition 1 is an operation in a so-called normal membrane separation activated sludge method without using a flocculant as shown in FIG. Raw water 1 that is agricultural settlement wastewater is supplied to a biological treatment tank 3 by a raw water pump 2. In the biological treatment tank 3, the activated sludge treatment is performed for 6 hours, and then filtered by the submerged membrane separation device 4. Filtration is performed at a constant speed of 0.64 m / day, and the pressure is constantly monitored by the pressure gauge 16 on the filtration side.

  Condition 2 is an example in which the flocculant 13 is directly added to the biological treatment tank 3 and the filtration operation is performed as shown in FIG. The addition was performed so that the concentration was 2.0% by weight (per MLSS unit in the biological treatment tank) in the state of the flocculant stock solution.

Condition 3 is an example in which 1 m ³ is extracted from 4.5 m ³ of sludge in the biological treatment tank 3 and sufficiently mixed with the flocculant 13 in the flocculation mixing tank 12 as shown in FIG. . The flocculant concentration was added so as to be 2.0% by weight per MLSS unit in the biological treatment tank 3 as in Condition 2. The stirring rate was 150 rpm for 30 minutes, followed by slow stirring at 40 rpm for 1 hour 30 minutes. Thereafter, the coagulated sludge 15 was returned to the biological treatment tank 3, aerated for 30 minutes, and then the filtration operation was started.

  FIG. 5 shows the operation status in (Condition 1), (Condition 2), and (Condition 3). The vertical axis represents transmembrane pressure (TMP), and the vertical axis represents time. Generally, the TMP value indicates the degree of clogging. When this value increases, it indicates that clogging is progressing. When the value exceeds a certain value (for example, 20 kPa for the Toray immersion membrane module), chemical cleaning, etc. Necessary.

  Looking at the results, it can be seen that in the operation under Condition 1, the TMP value gradually increases with the passage of the operation days, and clogging progresses. Under condition 2, the TMP value rose rapidly immediately after the addition of the flocculant, and reached the upper limit of 20 kPa in the differential pressure after 3 days of operation. This is probably because MPE-50, a flocculant, was initially adsorbed on the membrane surface. On the other hand, in condition 3, the effect of adding the flocculant was observed by providing a sufficient stirring and mixing time. It is considered that the activated sludge was modified by the addition of the flocculant without the initial adsorption to the membrane, and the increase in the transmembrane pressure difference was suppressed.

  By carrying out the present invention as described above, the effect of the flocculant can be maximized, and the submerged membrane filtration apparatus can be operated with high flux and less frequent chemical cleaning.

  The present invention is a membrane separation activated sludge method in which organic sludge is treated with activated sludge in a biological treatment tank, and the activated sludge mixed liquid is solid-liquid separated by an immersion type membrane separation apparatus immersed in the biological treatment tank. When using a flocculant to improve the flux, it is possible to provide a method for improving the flux in the MBR apparatus more efficiently by minimizing the adsorption of the flocculant and the membrane.

1: Raw water 2: Raw water pump 3: Biological treatment tank 4: Submerged membrane separator 5: Air supply device 6: Air diffuser 7: Suction pump 8: Surplus sludge pump 9: Membrane treated water 10: Surplus sludge 11: Covered Aggregated sludge 12: Agglomerated mixing tank 13: Aggregating agent 14: Stirrer 15: Aggregated sludge 16: Pressure gauge

Claims (6)

In the membrane separation activated sludge method in which organic sludge is treated with activated sludge in a biological treatment tank and the activated sludge mixed solution is solid-liquid separated with a submerged membrane separation apparatus installed in the biological treatment tank, the organic waste water is a flocculant. while not in contact with, the after well mixed and part of the activated sludge in advance coagulant and biological treatment tank, subjecting the composition after mixing the submerged membrane separator in the biological treatment tank A water treatment method characterized.   The water treatment method according to claim 1, wherein the flocculant is a cationic flocculant.   The water treatment method according to claim 1 or 2, wherein the material of the membrane used in the submerged membrane separator is polyvinylidene fluoride or polyethylene.   The time which mixes a flocculant and a part of activated sludge in a biological treatment tank, and / or the organic waste water which is raw | natural water is 10 minutes or more, It is any one of Claims 1-3 characterized by the above-mentioned. Water treatment method.   The water treatment method according to any one of claims 1 to 4, wherein the activated sludge concentration in the biological treatment tank during the water treatment operation is 2,000 mg / L or more and 25,000 mg / L or less. In a water treatment apparatus that treats organic sludge in activated biological sludge in a biological treatment tank and separates the activated sludge mixed liquid in a solid-liquid separation with a submerged membrane separator installed in the biological treatment tank, the organic waste water contacts the flocculant. while lest the water treatment apparatus characterized by comprising a flocculation mixing tank for mixing the part of the sludge pre-coagulant and biological treatment tank.

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