JP5120106B2 - Method and apparatus for treating organic alkaline wastewater - Google Patents

Description

  The present invention relates to a membrane separation biological treatment method and treatment apparatus for biologically treating wastewater containing organic alkali as raw water and separating the biological treatment liquid using a separation membrane, and in particular, for solid-liquid separation of biological treatment liquid. The present invention relates to a method and apparatus for treating organic alkali waste water that stably maintains membrane flux (permeated water amount) by washing the used separation membrane with raw water.

  Conventionally, a biological treatment method has been widely adopted as a method for treating organic wastewater, and in order to remove contaminants mainly composed of suspended solids (SS) in a treatment liquid obtained by biological treatment, In order to recover water from sewage, a membrane separation biological treatment method is used in which the biological treatment liquid is separated into solid and liquid by a membrane separation process in which the solid-liquid separation performance is not affected by sludge sedimentation and SS can be removed to a high degree. (Patent Document 1). For example, in equipment that uses pure water and discharges the wastewater, such as semiconductor manufacturing, liquid crystal manufacturing and other electronic industrial factories, the wastewater containing organic matter is biologically treated, and the treatment liquid is used as a raw material for the production of pure water. Although the recovery is progressing, membrane separation biological treatment methods that can obtain good treated water quality are widely used in biological treatment of organic wastewater that performs such water recovery.

  In the membrane separation biological treatment method, it is necessary to periodically clean the separation membrane with chemicals in order to prevent clogging of the membrane and maintain a stable flux. In this case, alkali is effective as a chemical against biological membrane contamination, and a sodium hypochlorite solution or the like is generally used. In addition, the proposal which uses organic alkalis, such as tetramethylammonium hydroxide, for the washing | cleaning removal of the biofilm in the system in an ultrapure water manufacturing system is also made | formed (patent document 2).

  In membrane chemical cleaning, the membrane unit is taken out of the tank and transferred into the chemical tank, where it is cleaned, and after the sludge in the water tank of the membrane separator is drawn out, the chemical is filled and the separation membrane is placed in the chemical. Although there is a method of immersion cleaning to be immersed, a method of injecting a cleaning chemical solution from the piping for taking out membrane separation water (secondary side of the membrane) and allowing the membrane to permeate can be easily performed, and is often used (for example, Patent Document 3).

  However, in chemical cleaning, there is a problem in that the cost of the chemical is high and the chemical solution flows into the biological treatment tank, which has an adverse effect on the biological treatment and the biological treatment efficiency is lowered. In other words, in the membrane separation biological treatment method, the separated water obtained by solid-liquid separation by the separation membrane is taken out as treated water, while the concentrated water is returned to the biological treatment tank to maintain the amount of sludge in the biological treatment tank. To be done. In this case, the cleaning chemical solution flowing from the secondary side of the membrane flows into the biological treatment tank through the concentrated water return pipe. Moreover, in the submerged membrane separation apparatus in which the separation membrane is immersed in the biological treatment tank, the cleaning chemical solution injected from the secondary side of the membrane flows into the biological treatment tank as it is. By switching the flow path, the cleaning chemical liquid that has permeated the membrane can be discharged out of the system so as not to flow into the biological treatment tank, but in this case, the processing of the discharged chemical liquid becomes a problem.

  Although it has been proposed to wash the separation membrane used for water treatment and wastewater treatment with raw water (Patent Document 4), this raw water does not contain alkali, and this washing with raw water Physical water is washed by spraying raw water on the raw water side (primary side).

In addition, it has been proposed to wash the ultrafiltration membrane with a solution containing tetramethylammonium hydroxide, but this method is to supply and wash from the raw water side (primary side) of the membrane. The effect is inferior (Patent Documents 5 and 6).
JP 2007-38107 A JP 2002-52324 A JP 2007-209964 A JP 2005-342609 A JP-A 64-43306 JP-A 64-70187

  The present invention solves the above-mentioned conventional problems, performs biological treatment using wastewater containing organic alkali as raw water, and efficiently separates the separation membrane in the membrane separation biological treatment in which the biological treatment liquid is separated into solid and liquid using the separation membrane. It aims at providing the processing method and processing apparatus of the organic alkali waste water which wash | cleans and maintains a film | membrane flux stably.

  The method for treating organic alkali waste water of the present invention (Claim 1) includes a biological treatment step for biologically treating wastewater containing organic alkali as raw water, and a membrane separation step for solid-liquid separation of the treatment liquid of the biological treatment step with a separation membrane. And a membrane washing step of washing the separation membrane by supplying the raw water from the secondary side of the separation membrane. It is characterized by having.

  The organic alkaline waste water treatment method according to claim 2 is characterized in that, in claim 1, the raw water contains semiconductor production waste water or liquid crystal production waste water containing monoethanolamine and / or tetramethylammonium hydroxide.

  The treatment apparatus for organic alkali waste water of the present invention (Claim 3) has a biological reaction tank for biological treatment using waste water containing organic alkali as raw water, and a membrane separation apparatus for solid-liquid separation of the treatment liquid in the biological reaction tank. Then, in the treatment apparatus for organic alkaline drainage that takes out the separation water of the membrane separation device as treated water, the raw water is supplied from the secondary side of the separation membrane of the membrane separation device to wash the separation membrane of the membrane separation device It has a film cleaning means.

  According to a fourth aspect of the present invention, there is provided an apparatus for treating organic alkali wastewater according to the third aspect, wherein the raw water includes semiconductor production wastewater or liquid crystal production wastewater containing monoethanolamine and / or tetramethylammonium hydroxide.

  According to the present invention, since raw water containing organic alkali is supplied from the secondary side of the separation membrane, the separation membrane can be effectively washed with the organic alkali contained in the raw water.

  This eliminates the need for chemicals for membrane chemical cleaning, and the raw water used for cleaning does not adversely affect biological treatment even if it is directly introduced into the biological treatment system. There is no need to switch the flow path for discharging out of the system, and there is no problem with the treatment of the cleaning waste liquid.

  Therefore, the cleaning frequency can be increased, and as a result, a high film flux can be stably maintained.

  In the present invention, the separation membrane can be washed with raw water by supplying raw water from the secondary side of the separation membrane to permeate the membrane, and the water that has permeated the membrane can be directly returned to the biological treatment system.

  The present invention is particularly effective for biological treatment of membrane separation using raw water for semiconductor production or liquid crystal production containing monoethanolamine and / or tetramethylammonium hydroxide (claims 2 and 4). That is, alkaline organic substances and surfactants such as monoethanolamine and tetramethylammonium hydroxide contained in semiconductor manufacturing wastewater and liquid crystal manufacturing wastewater are used as release agents and cleaning agents in the manufacturing process. Also has a high effect. Therefore, the separation membrane can be efficiently washed with the raw water containing these components.

  Embodiments of the method and apparatus for treating organic alkali waste water of the present invention will be described in detail below.

[Raw water]
The raw water to be treated in the present invention is wastewater containing organic alkali and is not particularly limited, and examples thereof include electronic industry wastewater, chemical factory wastewater, and food factory wastewater. Preferably, it is semiconductor manufacturing wastewater or liquid crystal manufacturing wastewater containing monoethanolamine and / or tetramethylammonium hydroxide, and it is based on alkaline organic substances such as monoethanolamine and tetramethylammonium hydroxide and surfactants contained in these wastewaters. Efficient membrane cleaning.

  In the present invention, a portion of such raw water is separated and membrane cleaning is performed. However, when SS or the like that causes clogging of the membrane is contained in the raw water, cleaning is performed during membrane cleaning. It is preferable that the raw water stream is subjected to solid-liquid separation with a filter or the like in advance to remove SS.

  In addition, when the raw water used for washing is wastewater mixed with wastewater containing organic alkali and wastewater from other systems, the wastewater containing organic alkali before being mixed is separated into a membrane. It is preferable to use for washing. In addition, regarding wastewater containing organic alkali, it is preferable to separate high-concentration wastewater and use it for membrane cleaning if it is a system that discharges high-concentration wastewater and low-concentration wastewater of organic alkali.

  If the concentration of the organic alkali in the raw water used for the membrane cleaning is excessively low, a sufficient membrane cleaning effect cannot be obtained. Therefore, although it varies depending on the type of organic alkali contained in the raw water, it is preferably 100 mg / L or more.

  The upper limit of the organic alkali concentration of the raw water used for the membrane cleaning is not particularly defined, but the organic alkali concentration of the organic alkali-containing water discharged as wastewater is usually about 5,000 mg / L or less.

  From a semiconductor manufacturing process or a liquid crystal manufacturing process, wastewater having a TOC concentration of about 50 to 1,000 mg / L, which generally contains about 100 to 2,000 mg / L of organic alkali such as monoethanolamine and tetramethylammonium hydroxide, in general. Since it is discharged, it is suitable as membrane cleaning water.

[Biological treatment]
The type of biological treatment to which the present invention is applied is not particularly limited, and examples include aerobic biological treatment, anaerobic biological treatment, nitrification denitrification treatment, and combinations of two or more thereof.

  There are no particular restrictions on these biological treatment conditions.

[Membrane separator]
There is no particular limitation on the membrane separation apparatus used for the solid-liquid separation of the biological treatment liquid, and a general membrane separation apparatus can be adopted. This membrane separation device may have a means for aeration of the primary side (raw water side), or may be an immersion type membrane separation device in which the separation membrane is immersed in a water tank. In the case of a submerged membrane separator, the membrane immersion tank may also serve as a biological reaction tank.

  The type of separation membrane is not particularly limited, and UF (ultrafiltration) membrane, MF (microfiltration) membrane, RO (reverse osmosis) membrane or the like is used. The membrane type may be any of a flat membrane type, a hollow fiber membrane type, a tubular membrane type and the like.

  The separation water of this membrane separator is taken out as treated water, and the concentrated water is usually returned to the biological treatment system.

[Membrane cleaning]
In the present invention, a part of the raw water used for biological treatment is separated to wash the separation membrane as described above.

  Specifically, in this membrane cleaning, raw water is supplied from the secondary side of the membrane, and the raw water that has permeated the membrane is supplied to the biological treatment system as it is. By doing so, not only the chemical in the case of conventional chemical cleaning can be made unnecessary, but also the problem of a decrease in biological treatment efficiency due to the introduction of the cleaning chemical into the biological treatment system is solved, It also eliminates the need for cleaning wastewater treatment.

Note that such membrane cleaning with raw water may be performed periodically, or may be performed irregularly when the membrane flux decreases. The frequency of membrane cleaning is appropriately determined according to the water quality of the treatment system, the degree of increase in membrane flux, etc. For example, the raw water is used per unit membrane area for about 30 to 180 minutes once every half day to 10 days. It is preferable to pass the liquid at a flow rate of about 3 to ²⁰ L / m ² .

  In addition, after performing membrane cleaning with such raw water, it is preferable to perform finish cleaning in which treated water (membrane permeated water) is supplied from the secondary side of the membrane, thereby performing membrane separation operation after membrane cleaning. It is possible to prevent the raw water from being mixed into the treated water side when resuming.

  In addition, when mixing of raw water on the treated water side is not preferable, at the time of restarting the membrane separation operation after membrane cleaning, the treated water (membrane permeated water) at the initial stage of operation restart is returned to the biological reaction system, The treated water may be collected after sufficiently clear treated water is obtained.

[Organic alkaline wastewater treatment equipment]
Next, with reference to FIG. 1, embodiment of the processing apparatus of the organic alkaline waste water of this invention is shown. FIG. 1 shows an example of an embodiment of the apparatus for treating organic alkaline waste water of the present invention, and the present invention is not limited to the illustrated one.

  The apparatus of FIG. 1 employs a circulatory nitrification denitrification method as a biological treatment. The biological reaction tank is composed of a denitrification tank 1 and a nitrification tank 2, and the nitrification tank 2 is provided with an aeration pipe 2A. Yes.

  3 is a membrane separation apparatus, and includes a separation membrane 3M. This membrane separation device 3 is also provided with an air diffuser 3A for aeration of the primary side (raw water side).

The raw water is introduced into the denitrification tank ₁ through the raw water introduction pipe 11 by the raw water pump P ₁ , and the denitrification treatment liquid is introduced into the nitrification tank 2 through the pipe 12.

Nitrification denitrification treatment liquid from the nitrification tank 2, part of which is returned from the pipe 13 to the denitrification tank 1, the balance is being membrane separation process is introduced into the membrane separation device 3 from the pipe 14, separated water suction pump P ₂ Is taken out from the pipe 15. On the other hand, the concentrated water is returned to the nitrification tank 2 through the pipe 16.

In the processing apparatus of this organic alkali waste water, when to clean the separation membrane 3M membrane separation device 3 stops the aeration from aeration tube 3A, stops the suction pump P _2, the raw water pump P ₁ The raw water is supplied to the secondary side of the separation membrane 3M from the secondary side pipe (treated water extraction pipe) 15 of the membrane separation device 3 through the cleaning raw water pipe 17 branched from the raw water introduction pipe 11. The washing effluent that has passed through the separation membrane 3M is introduced into the nitrification tank 2 through the pipe 16. At this time, the washing waste liquid introduced into the nitrification tank 2 is raw water used for biological treatment, and even if this is introduced into the nitrification tank 2, the sludge activity in the tank is not hindered. Processing efficiency is not reduced.

After such raw water by membrane cleaning predetermined time, it operates the suction pump P _2, and restart the aeration from aeration tube 3A, restarts the operation of the membrane separation device 3.

  At this time, prior to restarting the operation, the secondary side of the membrane separation device 3 may be washed by flowing back the treated water from the secondary side pipe 15 as described above, and is indicated by a wavy line in FIG. The treated water return pipe 18 may be provided, and the treated water may be returned to the nitrification tank 2 for a predetermined time after the operation is resumed, and then the treated water sampling may be resumed.

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

[Example 1]
The raw water treatment and separation membrane cleaning were performed by the organic alkaline waste water treatment apparatus of the present invention shown in FIG.

  The specification of each part of the used apparatus is as follows.

<Biological reaction tank (circulation nitrification denitrification tank)>
Hydrological residence time: 6 hr
MLSS in the tank: 12,000 mg / L (sludge was pulled out so as to maintain this MLSS)
Circulation ratio (circulation water volume / raw water volume): 2
Denitrification tank capacity: 0.5m ³
Nitrification tank capacity: 1m ³
Nitrification tank DO concentration: 2 mg / L (aeration was performed so that the DO (dissolved oxygen) concentration in the tank was 2 mg / L or more)

<Membrane separator>
104 tubular UF membranes (made of PVDF, pore size 0.03 μm) with a diameter of 0.52 cm (membrane area 5 m ² ) are arranged, and the treatment liquid from the nitrification tank flows in along with the aerated air, and the concentrated water and gas are in the nitrification tank Returned to.

The raw water quality was as follows, and the treatment was performed at a raw water flow rate of 0.25 m ³ / hr.
<Raw water quality>
TOC: 200 mg / L
TN: 70 mg / L
TP: 1.0 mg / L
Organic alkali composition:
Tetramethylammonium hydroxide: 100 mg / L
Monoethanolamine: 250 mg / L
Diethylene glycol monobutyl ether: 100 mg / L

A suction pump P ₂ and aeration of the membrane separation apparatus 3 stops at a frequency of once a day, from the secondary pipe 15 of the separation membrane 3M, through the washing raw water pipe 17 branched from the raw water inlet pipe 11, the raw water For 30 minutes, the membrane was washed at a flow rate of 10 L / m ² per unit membrane area, and the operation was resumed.

  Table 1 shows the membrane flux, water flow resistance, and treated water (membrane filtered water) quality of the membrane separation device 3 after such treatment was continued for 30 days.

[Comparative Example 1]
The raw water similar to that treated in Example 1 was treated in the same manner using the apparatus shown in FIG.

  The apparatus of FIG. 2 is provided with a cleaning pipe 20 for injecting a cleaning chemical into the secondary pipe 15 of the separation membrane instead of the cleaning pipe for feeding raw water to the secondary side of the membrane separation apparatus 3. Unlike the apparatus shown in FIG. 1, other configurations have the same specifications as the apparatus shown in FIG.

This device, wash liquor at once a suction pump P ₂ and aeration of the membrane separation device 3 stops at a frequency, not shown through the cleaning pipe 20 from the secondary pipe 15 of the separation membrane 3M liquid chemical pump in one day Injected. A 3,000 mg / L sodium hypochlorite aqueous solution was used as the cleaning chemical, and 2.0 L / m ² per unit membrane area was passed through for 30 minutes to perform membrane cleaning, and then the operation was resumed.

  Table 1 shows the membrane flux, water flow resistance, and treated water (membrane filtered water) quality of the membrane separation device 3 after such treatment was continued for 30 days.

  From the results of Table 1, Example 1 and Comparative Example 1 obtained the same results as the membrane cleaning effect, but in Comparative Example 1 in which chemical cleaning was performed using a sodium hypochlorite aqueous solution, chemical cleaning was performed. Sometimes the activity of sludge decreased due to the influence of sodium hypochlorite that flowed into the biological reaction tank, and the quality of treated water decreased. On the other hand, in Example 1 which washed with raw | natural water, there was no problem of such sludge activity fall and the treated water of favorable water quality was obtained.

[Comparative Example 2]
In Comparative Example 1, the treatment was performed in the same manner except that the frequency of the membrane chemical cleaning was set to once every 10 days.

As a result, the average TOC of the treated water was 5.1 mg / L (removal rate 97%) and NO ₃ -N was 20.5 mg / L (removal rate 71%). After washing, the water resistance tends to increase gradually, reaches 70 kPa at the maximum, decreases the membrane flux by 20%, and maintains the hydraulic retention time of 6 hours in the biological treatment tank (circulating nitrification denitrification tank). In some cases, raw water could not be treated.

[Comparative Example 3]
Using the apparatus shown in FIG. 3, the same raw water as that treated in Example 1 was treated in the same manner.

  The apparatus of FIG. 3 is provided with a cleaning raw water pipe 19 for supplying raw water to the primary side of the membrane separation apparatus 3 instead of the cleaning raw water pipe 17 for feeding raw water to the secondary side of the membrane separation apparatus 3. The configuration is the same as that of the apparatus shown in FIG. 1 except for the configuration shown in FIG.

This device, a frequency of once a membrane suction pump P ₂ and aeration of the separating apparatus 3 a day during operation of the apparatus is stopped, the raw water through a washing raw water pipe 19, the primary side of the separation membrane 3M pipe 14 Then, the membrane was washed at a flow rate of 10 L / m ² per unit membrane area for 30 minutes, and then restarted.

As a result, the average TOC of the treated water was 4.9 mg / L (removal rate 97%) and NO ₃ -N was 19.5 mg / L (removal rate 72%), which was not significantly different from Example 1. The water flow resistance increases gradually, reaches 70 kPa on the 21st day from the start of operation, and the flux decreases by 20%, maintaining the hydraulic retention time of 6 hours in the biological treatment tank (circulation nitrification denitrification tank). The raw water can no longer be treated.

It is a systematic diagram which shows embodiment of the processing apparatus of the organic alkaline waste water of this invention. It is a systematic diagram which shows the apparatus used by the comparative examples 1 and 2. FIG. It is a systematic diagram which shows the apparatus used in the comparative example 3.

Explanation of symbols

1 Denitrification tank 2 Nitrification tank 3 Membrane separation device 3M separation membrane

Claims (10)

It has a biological treatment process that biologically treats wastewater containing organic alkali as raw water, and a membrane separation process that separates the treatment liquid of the biological treatment process with a separation membrane, and uses the separated water of the membrane separation process as treated water. In the processing method of the obtained organic alkali waste water,
An organic alkaline wastewater treatment method comprising a membrane cleaning step of supplying the raw water from a secondary side of the separation membrane and cleaning the separation membrane.   2. The method for treating organic alkali wastewater according to claim 1, wherein the raw water includes semiconductor production wastewater or liquid crystal production wastewater containing monoethanolamine and / or tetramethylammonium hydroxide. 3. The separation membrane according to claim 1 or 2, wherein the raw water is waste water obtained by mixing waste water containing organic alkali and waste water of another system, and separating the waste water containing organic alkali before being mixed to wash the separation membrane. A method for treating organic alkali wastewater, characterized by being used in the above. 3. The system according to claim 1, wherein, as the raw water, in a system in which organic alkali high-concentration wastewater and low-concentration wastewater are discharged, the high-concentration wastewater is separated and used for cleaning the separation membrane. Organic alkali wastewater treatment method. 5. The process according to any one of claims 1 to 4, wherein when the membrane separation operation is resumed after the membrane cleaning, the separated water at the initial stage of the operation restart is returned to the biological reaction step, and then sampling of treated water is resumed. A method for treating organic alkaline wastewater. An organic alkali having a biological reaction vessel for biologically treating wastewater containing organic alkali as raw water and a membrane separation device for solid-liquid separation of the treatment liquid of the biological reaction vessel, and taking out the separated water of the membrane separation device as treated water In wastewater treatment equipment,
An apparatus for treating organic alkaline wastewater, comprising a membrane cleaning means for supplying the raw water from the secondary side of the separation membrane of the membrane separation device and cleaning the separation membrane of the membrane separation device. 7. The apparatus for treating organic alkali waste water according to claim 6 , wherein the raw water contains semiconductor production waste water or liquid crystal production waste water containing monoethanolamine and / or tetramethylammonium hydroxide. 8. The separation membrane according to claim 6 or 7, wherein the raw water is waste water obtained by mixing waste water containing organic alkali and waste water of another system, and waste water containing organic alkali before being mixed is separated to wash the separation membrane. An organic alkaline wastewater treatment apparatus characterized by being used in the above. 8. The system according to claim 6 or 7, wherein, as the raw water, in a system in which organic alkali high-concentration wastewater and low-concentration wastewater are discharged, the high-concentration wastewater is collected and used for cleaning the separation membrane. Organic alkaline wastewater treatment equipment. In any 1 paragraph of Claims 6 thru / or 9, when the membrane separation operation after the membrane washing restarts, the separation water at the initial stage of operation resumption is returned to the biological reaction tank, and the sampling of treated water is resumed after that. An organic alkaline wastewater treatment apparatus characterized by that.

Images