JP2010017614A - Method and apparatus for treating organic wastewater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably maintain a membrane flux over a long period of time by preventing clogging of an RO membrane due to microorganisms or mucilage produced by microorganisms in organic wastewater treatment for solid-liquid separating biologically treated water and desalting the treated water with the RO membrane to recover water. <P>SOLUTION: When subjecting the organic wastewater to methane fermentation treatment in an anaerobic digestion tank 1 for solid-liquid separating the treated water by a UF membrane separator 2 to get the separated water desalted by an RO membrane separator 3, the concentrated water of the UF membrane separator 2 is returned to the anaerobic digestion tank 1. High molecular components adhering to the surface of the RO membrane to cause clogging are separated by the UF membrane, circulated to the anaerobic digestion tank 1 and kept for a long period of holding time under an anaerobic condition to be decomposed away by anaerobic microorganisms. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for anaerobic digestion treatment of organic wastewater, and more particularly to an organic wastewater treatment method and apparatus for anaerobic digestion treatment of wastewater to be used as a raw material for producing pure water.

  In equipment that uses pure water and discharges its waste water, such as in the electronics industry factories such as semiconductor manufacturing and liquid crystal manufacturing, monoethanolamine, tetramethylammonium hydroxide, etc., as cleaning agents, release agents, etc. Water recovery is progressing by biologically treating wastewater containing organic substances to be used and using the treated water as a raw material for producing pure water. In the case of reusing biologically treated water for pure water production, the treated water is subjected to a solid-liquid separation process to separate microorganisms, and then desalted with a reverse osmosis (RO) membrane separator (for example, Patent Document 1).

  However, when the solid-liquid separation water of biologically treated water is subjected to RO membrane separation treatment, the microorganism itself and mucilage produced from the microorganism tend to adhere to the membrane surface, and the RO membrane tends to be clogged. There is a problem of decrease in the flux (permeation flux) of the membrane due to. It is said that the mucilage produced by this microorganism is a non-biodegradable component mainly composed of high molecular organic substances.

In Patent Document 2, it is described that the filtrate obtained by filtering the anaerobic digestion treatment liquid with an ultrafiltration (UF) device is sent to the secondary treatment step. Usually, this secondary treatment step and Refers to aerobic biological treatment. For example, in Patent Document 3, an aerobic biological treatment is performed on separated water obtained by solid-liquid separation of an anaerobic biological treatment liquid. In Patent Document 1, the aerobic biological treatment liquid is filtered by a filtration device and then desalted by an RO membrane separation device. An anaerobic biological treatment and an aerobic biological treatment are performed before the RO membrane separation device. Therefore, it is described that the decrease in the membrane flux of the RO membrane can be suppressed.
JP 2007-175582 A Japanese Patent Publication No. 3-18955 Japanese Patent Laid-Open No. 11-156392

  In the treatment of organic wastewater which collects water by recovering water by solid-liquid separation of biologically treated water and desalting the separated water with the RO membrane, the RO membrane of the microorganism itself and the viscous material produced by the microorganism is used. It aims at providing the processing method and apparatus of the organic waste water which prevents clogging and maintains a membrane flux stably over a long period of time.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have adhered to the membrane surface of the RO membrane and clogged when the separation water obtained by subjecting the biologically treated water to the UF membrane separation treatment is RO membrane separation treatment. The macromolecular components that cause stagnation remain in the biological treatment tank by solid-liquid separation using a UF membrane, and are degraded by anaerobic microorganisms by maintaining a long residence time (for example, 50 days or more) under anaerobic conditions. Therefore, the UF membrane concentrated water is returned to the anaerobic digestion process and circulated, thereby decomposing this polymer component and reducing its concentration in the system. It was found that clogging can be prevented.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] An anaerobic digestion step of subjecting organic wastewater to methane fermentation, a solid-liquid separation step of treating the treated water of the anaerobic digestion step with an ultrafiltration membrane, and separated water separated in the solid-liquid separation step In the organic wastewater treatment method having a desalting step of performing reverse osmosis membrane separation treatment without aerobic biological treatment, a return step of returning the concentrated water separated in the solid-liquid separation step to the anaerobic digestion step An organic wastewater treatment method characterized by comprising:

[2] The method for treating organic wastewater according to [1], wherein the organic wastewater contains monoethanolamine and / or tetramethylammonium hydroxide.

[3] The method for treating organic waste water according to [1] or [2], wherein the ultrafiltration membrane has a molecular weight cut-off of 200,000 daltons or less.

[4] Anaerobic digester for methane fermentation treatment of organic wastewater, ultrafiltration membrane separator for solid-liquid separation of treated water in the anaerobic digester, and separation separated by the ultrafiltration membrane separator In an organic wastewater treatment device having a reverse osmosis membrane separation device that desalinates water without aerobic biological treatment, the concentrated water separated by the ultrafiltration membrane separation device is returned to the anaerobic digester An organic wastewater treatment apparatus characterized by having a return means.

[5] The treatment apparatus for organic wastewater according to [4], wherein the organic wastewater contains monoethanolamine and / or tetramethylammonium hydroxide.

[6] The organic wastewater treatment apparatus according to [4] or [5], wherein the ultrafiltration membrane has a molecular weight cut-off of 200,000 daltons or less.

  According to the present invention, in the treatment of organic wastewater that recovers water by solid-liquid separation of biologically treated water and desalting the separated water with the RO membrane, the microorganism itself that causes clogging of the RO membrane and The anaerobic digestion process (by separating the polymer components such as mucilage produced by microorganisms with a UF membrane and returning the concentrated water containing the polymer components to the anaerobic digestion process (tank) The residence time in the tank can be made extremely long. Thereby, in the anaerobic digestion process (tank), microorganisms capable of degrading such a slow biodegradable polymer component are acclimatized, and the slow biodegradable polymer component is anaerobic digestion process (tank). Thus, the RO membrane is prevented from being clogged, and the membrane flux of the RO membrane can be maintained stably over a long period of time.

  The polymer component that causes clogging of the RO membrane is easily generated when wastewater containing monoethanolamine or tetramethylammonium hydroxide, such as factory wastewater in the electronics industry, is used as raw water. For this reason, this invention is effective in the process of the organic waste water containing a monoethanolamine and / or tetramethylammonium hydroxide (Claims 2 and 5).

  In addition, the polymer component that causes clogging of the RO membrane is presumed to be a high molecular organic substance having a molecular weight of 300 to 1,000,000 daltons. Therefore, by using a UF membrane having a fractional molecular weight of 200,000 dalton or less, these The polymer component can be reliably separated and concentrated by the UF membrane.

  According to the present invention, in an electronic industry factory such as semiconductor manufacturing, liquid crystal manufacturing, etc., in a facility that discharges the waste water using pure water, the waste water containing the discharged organic matter is biologically treated, and the treated water is Water can be efficiently recovered and used as a raw material for producing pure water.

  Embodiments of an organic wastewater treatment method and apparatus according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of an organic wastewater treatment apparatus of the present invention.
In the present invention, as shown in FIG. 1, organic wastewater is used as raw water, raw water is subjected to methane fermentation treatment in an anaerobic digestion tank 1, the treated water is subjected to solid-liquid separation using a UF membrane separation device 2, and the separated water is supplied to an RO membrane. In the treatment of the organic waste water which is desalted by the separator and takes out the permeate as the treated water, a part or all of the concentrated water of the UF membrane separator 2 is returned to the anaerobic digester 1 and circulated.

  In the present invention, the nature of the organic wastewater treated as raw water is not particularly limited, but as described above, the polymer component that causes clogging of the RO membrane is monoethanolamine or tetramethylammonium hydroxide. It is easy to produce when the wastewater it contains is used as raw water. For this reason, the present invention provides wastewater containing organic substances used as cleaning agents, stripping agents, etc. in process steps such as monoethanolamine and tetramethylammonium hydroxide discharged in electronic industry factories such as semiconductor manufacturing and liquid crystal manufacturing. Effective when treated as raw water. For example, it is effective for the treatment of organic wastewater having a TOC of about 30 to 500 mg / L containing about 50 to 1,000 mg / L of monoethanolamine and / or tetramethylammonium hydroxide.

  Such raw water is subjected to methane fermentation treatment in the anaerobic digester 1 by an anaerobic biological treatment mainly composed of methanogenic bacteria to remove organic substances. If the methane fermentation treatment in the anaerobic digestion tank 1 is performed under such conditions that the temperature of the liquid in the tank is 15 ° C. or higher and 40 ° C. or lower, about 90% of the microorganism is decomposed even when the microorganism produces a high molecular organic substance. Therefore, it is preferable. Further, it is preferable to adjust the pH of the liquid in the tank to 6 or more and 9 or less because about 90% of the high-molecular organic matter produced by the microorganism is decomposed.

  Since the treated water from the anaerobic digestion tank 1 contains microorganisms, water (separated water) from which the solid content has been removed after the solid-liquid separation by the UF membrane separator 2 is desalted by the RO membrane separator 3. The treated water (RO membrane permeated water) is taken out as a pure water raw material or the like.

  In the present invention, it is preferable to use a UF membrane of the UF membrane separation device 2 having a molecular weight cut off of 200,000 daltons or less. That is, the polymer component that causes clogging of the RO membrane is presumed to be a high molecular weight organic substance having a molecular weight of 300 to 1,000,000 daltons. Therefore, by using a UF membrane having a fractional molecular weight of 200,000 dalton or less, The polymer component can be reliably separated and concentrated by the UF membrane. If the molecular weight cut off of the UF membrane is excessively small, the amount of separated water is remarkably reduced, the required membrane area is increased, and energy consumption in membrane separation such as a suction pump is increased, which is not economical. The molecular weight cutoff of the membrane is preferably 3,000 to 200,000 daltons.

  The module type of the UF membrane separation device 2 is not particularly limited, but it is preferable that the sludge fed from the anaerobic digester 1 is configured to be less likely to block or stay inside the UF membrane separation device 2, for example, Tubular type or flat membrane type can be preferably used. Moreover, if the UF membrane which separates the liquid content and the solid content in the treated water of the anaerobic digestion tank 1 is provided outside the anaerobic digestion tank 1 as in this embodiment, the so-called outside tank type has a membrane surface flow velocity. Since control is easy, it is preferable from the viewpoint of preventing contamination of the film surface.

  Note that a gas exhaust pipe (not shown) is connected to the UF membrane separation device 2, and the generated gas is sent to the UF membrane separation device 2 together with the treated water from the anaerobic digestion tank 1. This gas aerates and cleans the separation membrane while moving along the treated water flow path in the UF membrane separation device 2.

  In the present invention, the concentrated water separated by the UF membrane separation device 1 is returned to the anaerobic digester 1.

  The methanogen group in the anaerobic digestion tank 1 has a slower growth rate than the aerobic microorganisms, but the concentrated water is returned in this way so that the sludge (MLSS) concentration in the anaerobic digestion tank 1 is 6, The same level as when aerobic biological treatment with aerobic activated sludge is carried out by maintaining it at about 000 to 15,000 mg / L and setting the hydraulic residence time of the anaerobic digester 1 to about 2 to 8 hours. It is possible to obtain a decomposition rate of the polymer, and it is also possible to decompose and remove a slow biodegradable polymer component that causes clogging of the RO membrane. From this anaerobic digester 1, the sludge concentration in the anaerobic digester 1 is adjusted by drawing out excess sludge as appropriate through a sludge pipe (not shown).

  There is no particular limitation on the separation membrane of the RO membrane separation device 3 for desalting the separation water of the UF membrane separation device 2, and any membrane type such as a flat membrane, tubular, spiral, etc. can be used.

  The permeated water that has been treated by the RO membrane separation device 3 and from which salts have been removed is taken out as treated water. This treated water can be used as raw water for producing pure water. Specifically, equipment constituting a pure water production apparatus such as a decarboxylation apparatus, an ion exchange apparatus, and an ultraviolet sterilization apparatus is arranged at the subsequent stage of the RO membrane separation apparatus 3, and the RO membrane separation apparatus 3 is used by using these equipments. Pure water can be produced by treating the permeated water taken out from the water.

  Concentrated water enriched with salts discharged from the RO membrane separation device 3 is discharged out of the system.

  In the present invention, the methane fermentation treated water is subjected to solid-liquid separation in the UF membrane separation apparatus, and the separated concentrated water is circulated, whereby the polymer component that causes the clogging of the RO membrane is supplied to the RO membrane separation apparatus. Inflow is blocked by a UF membrane, and this is decomposed and removed in an anaerobic digester to prevent the accumulation of this polymer component in the system. Thereby, the membrane flux of the RO membrane can be maintained high and stable and efficient treatment can be performed over a long period of time.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Example 1]
In the following, water was treated with the organic wastewater treatment apparatus of the present invention shown in FIG.

<Raw water quality>
TOC: 200 mg / L
TN: 70 mg / L
TP: 1.0 mg / L
Organic composition:
Tetramethylammonium hydroxide: 100 mg / L
Monoethanolamine: 250 mg / L
Diethylene glycol monobutyl ether: 100 mg / L

The temperature of the anaerobic digester (actual volume 1 m ³ ) was 35 ° C., the pH was 7.5, and the hydraulic residence time was 6 hours. This anaerobic digester was acclimatized for 6 months using sewage sludge as seed sludge, and the sludge was pulled out so as to maintain the MLSS in the tank at 12,000 mg / L.

In the UF membrane separator, a flat membrane UF membrane (made of polyvinylidene fluoride, molecular weight cut off: 200,000 daltons, membrane area: 20 m ² ) is disposed, and the treated water from the anaerobic digestion tank is gas in the tank. The concentrated water and gas were returned to the anaerobic digester. The amount of circulating gas was 100 m ³ / day (5 m ³ / m ² · day), and the amount of permeated water (flux) was 0.3 m / day.

[Comparative Example 1]
The operation was performed under the same conditions as in Example 1, except that a flat membrane type MF membrane (made of polyvinylidene fluoride, pore size: 0.40 μm, membrane area: 20 m ² ) was placed in the UF membrane separation apparatus.

  When the treatment was performed for 30 days under the above conditions, the average TOC concentration of the separated water obtained from the UF membrane separator was 3.2 mg / L in Example 1 (removal rate 98%), and 5.7 mg in Comparative Example 1. / L (removal rate 97%).

  Moreover, when the separation water of each UF membrane separator was desalted at 750 kPa with an RO membrane separator (spiral type having a wholly aromatic polyamide ultra-low pressure membrane as the RO membrane), after 20 hours had elapsed The amount of permeated water was maintained at 90% at the start of water flow in Example 1, but decreased to 40% in Comparative Example 1.

  Moreover, when TOC was analyzed about the separated water of a UF membrane separation apparatus and the filtrate which filtered this separated water with the filter from which a hole diameter differs, as shown in Table 1, in Example 1, what was filtered and what was not filtered are also shown. Since the TOC concentration did not change, it was confirmed that the polymer component found in Comparative Example 1 was not present in Example 1.

  Moreover, the soluble TOC concentration in the anaerobic digestion tank in Example 1 is stable at 120 to 140 mg / L, and the polymer component that does not pass through the UF membrane is decomposed in the anaerobic digestion tank and accumulated in the tank. I never did.

  From the above results, according to the present invention, when desalting the biologically treated water with the RO membrane and recovering the water, the polymer component causing the clogging of the RO membrane is reduced, and the efficient water recovery is achieved. You can see that it can be done.

It is a systematic diagram which shows embodiment of the processing apparatus of the organic waste_water | drain of this invention.

Explanation of symbols

1 Anaerobic digester 2 UF membrane separator 3 RO membrane separator

Claims (6)

An anaerobic digestion process for methane fermentation of organic wastewater;
A solid-liquid separation step of subjecting the treated water of the anaerobic digestion step to ultrafiltration membrane separation;
In a method for treating organic wastewater, which comprises a desalting step of separating the separated water separated in the solid-liquid separation step without subjecting to aerobic biological treatment, reverse osmosis membrane separation treatment,
An organic wastewater treatment method comprising a return step of returning the concentrated water separated in the solid-liquid separation step to the anaerobic digestion step.   2. The method for treating organic waste water according to claim 1, wherein the organic waste water contains monoethanolamine and / or tetramethylammonium hydroxide.   The method for treating organic waste water according to claim 1 or 2, wherein the ultrafiltration membrane has a molecular weight cut-off of 200,000 daltons or less. An anaerobic digester for methane fermentation of organic wastewater;
An ultrafiltration membrane separation device for solid-liquid separation of the treated water in the anaerobic digester;
In an organic wastewater treatment apparatus having a reverse osmosis membrane separation apparatus for desalinating the separated water separated by the ultrafiltration membrane separation apparatus without subjecting to aerobic biological treatment,
An organic wastewater treatment apparatus comprising return means for returning the concentrated water separated by the ultrafiltration membrane separator to the anaerobic digester.   5. The organic wastewater treatment apparatus according to claim 4, wherein the organic wastewater contains monoethanolamine and / or tetramethylammonium hydroxide.   6. The organic wastewater treatment apparatus according to claim 4 or 5, wherein the ultrafiltration membrane has a molecular weight cut-off of 200,000 daltons or less.

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