JP4911730B2 - Organic wastewater treatment method - Google Patents

Description

  The present invention relates to a method for discharging organic sludge, for example, organic wastewater containing organic sludge discharged from a sewage treatment process such as a sewage treatment plant and a manure treatment plant, a manufacturing process such as a food factory and a chemical factory. The present invention relates to a method for treating biotin by biological reaction.

  Conventionally, an aerobic biological treatment method called an activated sludge method has been most commonly performed as a method for treating such organic wastewater. In this method, as shown in FIG. 2, for example, organic wastewater such as sewage introduced from the organic wastewater storage tank 1 to the biological reaction tank 3 is oxidatively decomposed by microorganisms in the biological reaction tank 3 under aerobic conditions. It is a method in which it is decomposed into inorganic substances such as carbon dioxide or water by biological oxidation as a reaction. The organic wastewater treated in the biological reaction tank 3 is solid-liquid separated into the treated water 301 and sludge 302 in the solid-liquid separation tank 5, and a part of the sludge 302 is returned to the biological reaction tank 3 as a microorganism source. In addition, the remaining sludge is generally disposed of as surplus sludge 303.

  For this reason, as a treatment method that does not discharge as much surplus sludge as possible, in recent years, a method has been proposed in which surplus sludge is solubilized in a solubilization reaction treatment tank, the solubilized sludge is returned to the bioreaction tank, and biological treatment is performed again. . For example, a technique for reducing excess sludge in an activated sludge method by solubilizing sludge with thermophilic bacteria in a solubilization reaction treatment tank in a high-temperature aerobic state and returning the liquid to the biological reaction tank has been disclosed. (For example, Patent Document 1). A technique is disclosed in which the size of a solubilization reaction treatment tank can be reduced by making sludge to be introduced into a solubilization reaction treatment tank part into a moisture content of 99% or less by using a concentrator or the like (for example, Patent Document 2). ).

  However, in the sludge solubilization method as in Patent Document 1, a substance that does not completely dissolve is accumulated as a hardly decomposable substance in the biological reaction tank. This accumulated substance is one of the causes of deterioration of water quality such as chemical oxygen demand of so-called COD and transparency of treated water after solid-liquid separation in the method of returning solubilized sludge to the biological reaction tank. In patent document 2, in order to make a solubilization reaction reaction tank small, the concentrator is put before the solubilization reaction treatment tank. In this case, in order to facilitate dehydration, a flocculant such as a polymer flocculant may be added. In such a case, since the polymer flocculant itself is an organic substance, a load for biological treatment is increased. Sometimes it was high.

  In addition, since a solution in which a solute is dissolved in a solvent generally has a high viscosity, even when sludge is solubilized, bacteria and the like can be dissolved in the solution, which increases the viscosity of the solution and is high for filtration through a membrane. It has been considered unsuitable due to viscosity.

JP-A-9-10791 JP 11-235598 A

  The present invention eliminates the problems of the prior art as described above, and a novel organic wastewater treatment method capable of significantly reducing the amount of surplus sludge generated with biological treatment of organic wastewater. The purpose is to provide.

  The present inventor has solubilized sludge generated by biological treatment of organic wastewater in a solubilization reaction treatment tank, membrane-filtered the solubilized liquid with a membrane filtration device, and biological treatment of the membrane filtrate with a biological reaction tank. The membrane concentrate was found to be able to significantly reduce the amount of excess sludge generated by the method of concentrating in the solubilization reaction treatment tank, and the present invention was completed.

That is, the present invention is as follows.
1) Organic wastewater is biologically treated in a biological reaction tank, and the generated sludge is subjected to medium-to-high temperature microbial treatment in a solubilization reaction treatment tank, and at least a part of the liquid in the solubilization reaction treatment tank is removed from the liquid. While the gas is mixed in, the membrane is sent to a membrane filtration device having a hollow fiber membrane shape. The membrane filtration device separates the membrane filtrate into a membrane filtrate, and the membrane filtrate is returned to the biological reaction tank. A method for treating organic wastewater, wherein the concentrate is returned to the solubilization reaction treatment tank and backwashed when necessary. 2) The method for treating organic wastewater according to 1), wherein the membrane filtration device has a pump for sucking the membrane filtrate. 3) The method for treating organic wastewater according to 1) or 2), wherein the filtration membrane comprises an ultrafiltration membrane. 4) The method for treating organic wastewater according to 1) or 2), wherein the filtration membrane comprises a microfiltration membrane.

  Biological treatment is treatment that decomposes and stabilizes pollutants in wastewater such as sewage by biological action, and is classified into aerobic treatment and anaerobic treatment. In general, organic matter is decomposed by biological treatment through oxygen respiration, nitric acid respiration, fermentation process, etc., and gasified or taken into the body of microorganisms and removed as sludge. Nitrogen (nitrification denitrification method) and phosphorus (biological phosphorus removal method) can also be removed. A tank that performs such biological treatment is called a biological reaction tank.

  Solubilization means that an organic substance that has been insoluble in water undergoes biodegradation by microorganisms, thermal decomposition by heat treatment, and the like, and as a result of changes such as low molecular weight, it becomes soluble in water. The medium-high temperature microbial treatment in the solubilization reaction processing tank means that the above-mentioned solubilization is caused by an enzyme reaction by microorganisms in a state where a medium-high temperature is applied. The temperature is preferably 40 to 70 ° C.

The membrane filtration device refers to a device that is configured to filter by combining a filtration membrane, piping, a pump, and the like. The pump here includes a pump for sending liquid and an air pump for sending air.
An ultrafiltration membrane refers to a filtration membrane having a pore size of about 500 to 1,000,000 in the molecular weight cut-off. The microfiltration membrane refers to a filtration membrane having an average membrane pore diameter of about 0.01 to 10 micrometers.

Sludge generated during biological treatment of organic wastewater is solubilized in a solubilization reaction treatment tank, the solubilized liquid is membrane filtered with a membrane filtration device, the membrane filtrate is biologically treated in the biological reaction tank, and the membrane concentrate Can significantly reduce the amount of excess sludge generated by the method of concentrating in the solubilization reaction treatment tank.
In addition, the quality of the treated water after the solid-liquid separation can be kept at a water quality that can be discharged.

  Hereinafter, the present invention will be specifically described focusing on its preferred form.

  The bioreactor used in the present invention can employ either aerobic biological treatment or anaerobic biological treatment. In general, an aerobic biological treatment method called an activated sludge method is most commonly implemented as a method for treating such organic wastewater.

  The present invention is illustrated in FIG. Organic wastewater such as sewage introduced from the organic wastewater storage tank 1 into the biological reaction tank 3 is subjected to an oxidative degradation reaction by microorganisms in the biological reaction tank 3 under aerobic conditions.

It is a method of decomposing into inorganic substances such as carbon dioxide or water by some biological oxidation. The wastewater treated in the biological reaction tank 3 is solid-liquid separated into the treated water 301 and sludge 302 in the solid-liquid separation tank 5, and a part of the sludge 302 is returned to the biological reaction tank 3 as a microorganism source. .

  Part of the sludge returned to the biological reaction tank is sent to the solubilization reaction processing tank by the medium and high temperature microorganism treatment. The microorganism treatment at a medium high temperature of the present invention is preferably 40 to 70 ° C. This method can be applied to any of a medium to high temperature anaerobic treatment and aerobic treatment. In order to make it aerobic, anything can be used as long as air can be introduced into the solubilization reaction treatment tank and the solution in the solubilization reaction treatment tank can be aerated. For example, air may be introduced by a tube into a solubilization reaction processing tank using a blower. The filtration membrane used in the present invention may be anything such as a hollow fiber membrane shape or a flat membrane shape, but a hollow fiber membrane shape is preferred because clogging substances can be easily washed by backwashing. Various materials such as polyethylene-based, polyacrylonitrile-based, polysulfone-based, polyvinylidene fluoride-based, and cellulose acetate-based materials can be applied, but it is effective to use different materials depending on the temperature and liquid. Polysulfone and polyvinylidene fluoride are particularly preferred from the viewpoint of heat resistance and chemical washing resistance. The filtration membrane is used in such a form that the membranes are bundled or wound in a roll shape, or the ends are sealed with an adhesive and the primary side and the secondary side of the membrane are called membrane modules. The shape of the membrane module is preferably a hollow fiber membrane type for the reason described above. The membrane filtration device used in the present invention means a device having means for providing a differential pressure between the primary side and the secondary side, comprising a filtration membrane primary side inlet pipe, outlet pipe, and secondary side outlet pipe. .

  For example, the membrane filtration apparatus in the present embodiment uses a hollow fiber membrane type module using a polysulfone-based membrane material, and includes a primary side inlet pipe, an outlet pipe, and a secondary side outlet pipe of the hollow fiber membrane module. The primary side inlet pipe is equipped with a pump for sending liquid to the membrane module, and the primary side outlet pipe is equipped with a valve, and has a means to provide differential pressure between the primary side and the secondary side. . Furthermore, the method of mixing the gas when sending the liquid to the membrane module on the primary side includes an air pump between the pump that sends the liquid to the primary side of the membrane filtration device and the membrane module, Mix gas. For example, FIG. In 1, the air pump 10 of piping is put in the middle of the 9th line. By mixing the gas, sludge and the like are hardly clogged at the entrance of the membrane module, and the membrane clogging substance can be prevented from adhering to the membrane surface and the membrane filtration rate can be kept high. It is preferable from the viewpoint of biological treatment that gas is mixed in the liquid in the solubilization reaction treatment tank even when the liquid is in the membrane filtration device. In the case of an aerobic reaction, aerobic conditions are used even in the membrane filtration apparatus, and a long time for biological reaction can be taken. Moreover, in the case of an anaerobic reaction, if the gas generated in the solubilization tank is used or a gas other than oxygen is used, an anaerobic state can be constantly maintained, and the anaerobic reaction proceeds. Moreover, if the gas generated in the solubilization tank is used, it is not necessary to provide a device for generating gas again, which contributes to cost reduction.

  In the treatment method of the present invention, it is better to apply backwashing in order to keep the filtration rate high. Backwashing is a method for washing a membrane to suppress a decrease in filtration rate as much as possible, and this method applies a filtration pressure opposite to that during filtration to the filtrate side of the membrane, so that the membrane filtrate side to the membrane side. This is a method of removing clogging substances adhering to the membrane surface on the membrane concentrate side by flowing the solution to the concentrate side. In addition, a chemical for cleaning clogging on the membrane may be added during backwashing. It is preferable to add a backwashing pump and a device that can add a chemical during backwashing so that pressure can be applied from the filtrate side of the membrane module to the membrane filtration device. The membrane filtrate in the membrane filtration device is returned to the biological reaction tank, and the membrane concentrate is returned to the solubilization reaction treatment tank. The membrane concentrate contains thermophilic bacteria and enzymes that cannot permeate the membrane and is reused in the solubilization reaction treatment tank. In the present invention, as shown in FIG. 3, it is the same as in FIG. 1 until a part of the liquid returned to the biological reaction tank is sent to an apparatus capable of solubilizing reaction by a medium-high temperature microbial treatment. As described above, the filtrate is preferably sucked from the filtrate side by the suction pump 16 or the like. A membrane filtrate is obtained, and the obtained membrane filtrate is returned to the biological reaction tank. The concentrate that does not permeate the filtration membrane is returned to the solubilization reaction treatment tank.

  In the present invention, as shown in FIG. 5, it is preferable that a microfiltration membrane is installed in the first stage and an ultrafiltration membrane is installed in the second stage as a membrane filtration device. The membrane concentrates generated from each were collectively returned to the solubilization reaction treatment tank as the membrane concentrate of the membrane filtration device. The membrane filtrate of the second ultrafiltration is returned to the biological reaction tank as the membrane filtrate of the filtration membrane device.

  In the case of an ultrafiltration membrane, the pore size of the filtration membrane indicates a pore size of about 500 to 1,000,000, and in the case of a microfiltration membrane, the average membrane pore size is about 0.01 to 10 micrometers. Point to. The fractional molecular weight means the minimum molecular weight that the membrane can block at a specific blocking rate. In the present invention, 90% was used as the specific rejection rate. Polyethylene glycol, dextran, globular protein and the like are used as standard substances for measuring the molecular weight cut off.

In the present invention, the ultrafiltration membrane is effectively used for the concentration of the enzyme in the solubilization reaction treatment tank. In general, enzymes have molecular weights of thousands to hundreds of thousands. Therefore, it is preferable that the ultrafiltration membrane has a molecular weight cut-off of about 1,000 to 100,000 capable of blocking the enzyme. More preferably, the molecular weight cut off is about 5,000 to 50,000. More preferably, it is 6,000-10,000. If it is too small, the filtration rate tends to decrease, and if it is too large, the enzyme is easily removed. If the enzyme can be concentrated, the solubilization reaction by the enzyme proceeds in the solubilization reaction tank. The microfiltration membrane can concentrate bacterial cells. In general, since the size of the bacterial cells is 0.2 to several micrometers, the average membrane pore diameter of the microfiltration membrane is preferably 0.1 to 1 micrometer. If it is too small, the filtration rate tends to be low, and if it is too large, the bacterial cells are easily removed. If the bacterial cells can be concentrated in the solubilization treatment reaction tank, solubilization by the bacterial cells is effective. The average membrane pore size of the microfiltration membrane is defined by the fine pressure determined from the pressure of the pores at the average flow rate in ASTM F316-86 “Measurement by a specific standard test method of the membrane filter pore size by the bubble point test and the average flow pore test”. It refers to the pore size.
Examples of the present invention will be described below.

[Example 1]
A schematic diagram of the apparatus used in Example 1 is shown in FIG. In FIG. 1, 3 is a biological reaction tank, 5 is a solid-liquid separation tank, and 6 is a return sludge line. The liquid is branched from the return sludge line 6 and sent to the solubilization reaction treatment tank through the liquid feed line 7. 8 is a solubilization reaction processing tank, 81 is an air piping from an aeration apparatus, and this is a solubilization reaction apparatus. 10 is an air pump and 11 is a membrane filtration device. In this example, the organic wastewater flowing into the biological reaction tank 3 had a BOD concentration of 200 mg / L. The organic waste water used was a model solution in which inorganic extract was added so that meat extract: peptone = 1: 1 (weight ratio) and BOD concentration: nitrogen concentration: phosphorus concentration = 100: 5: 1. BOD concentration is the amount of oxygen consumed when organic matter in 1 liter (L) of water is decomposed by the action of microorganisms, and is a representative index for measuring organic pollution in rivers. Measured by the drainage test method K0102.21. The organic wastewater was supplied to the biological reaction tank 3 at an inflow rate of 70 L / day. The capacity of the bioreactor was 20L. The liquid flowing out from the biological reaction tank 3 is sent to the solid-liquid separation tank 5. Here, a solid-liquid separation tank by a sedimentation separation method was used as the solid-liquid separation tank, and it was divided into a supernatant and sludge. The sludge settled and separated in the solid-liquid separation tank 5 is returned to the biological reaction tank 3 as a partially returned sludge. Part of the sludge passes through the liquid feed line 7 and is sent to the solubilization reaction treatment tank 8 at a flow rate of 0.8 L / day with 1% by weight of suspended solids (SS). The jacket of the solubilization reaction treatment tank 8 is used for heat retention so that 0.05 L / min of air is sent to the solubilization reaction treatment tank 8 through the air pipe 81 from the aeration apparatus and the temperature of 60 ° C. can be maintained. I put warm water in the room. The liquid that passed through the solubilization reaction treatment tank 8 was sent to the membrane filtration device 11 while sending a 10 L / min air from the air pump by installing a pump (not shown) on the route of the liquid feeding line 9. . The sludge separated in the solid-liquid separation tank 5 was appropriately sent to the solubilization reaction treatment tank 8 by a pump. The membrane concentrate in the membrane filtration device 11 is sent to the solubilization reaction treatment tank 8 through the membrane filtration device concentrate line 12. The membrane filtrate was sent to the biological reaction tank 3 through the membrane filtrate line 13. As for the continuous operation condition of the membrane separator, the amount of the membrane filtrate was 0.8 L / day. Backwashing was performed as appropriate. It was sent to the solubilization reaction treatment tank 8 at a membrane concentration of 3 L / hr. The filtration membrane module used in the membrane filtration device was SLP-1053 (membrane area 0.1 m ² ) manufactured by Asahi Kasei Corporation, which is a hollow fiber type ultrafiltration membrane made of polysulfone. The molecular weight cut-off is 10,000. In this state, continuous operation for 10 days was performed.

The results are shown in Table 1.
Table 1 lists the averaged values for the 5th to 10th days, with the experiment start date as the first day and the fifth and subsequent days as a steady state.
The SS of the liquid entering the solubilization reaction treatment tank 8 in the steady state was 12,000 mg / L, but the SS of the membrane filtrate was 0 mg / L. The BOD of the membrane filtrate was 30 mg / L.

The transparency of treated water after solid-liquid separation is 30 degrees.
The chemical oxygen demand COD of the treated water after the solid-liquid separation was 8 mg / L.
Suspended matter (SS) was measured by Japanese Industrial Standards, factory drainage test method K102.14.1.
The COD was measured according to Japanese Industrial Standard, factory drainage test method K102.14.1.
BOD was measured according to Japanese Industrial Standards, factory wastewater test method K0102.17.
The degree of transparency was measured by Japanese Industrial Standard, factory drainage test method K102.9.

[Comparative Example 1]
A schematic diagram of the apparatus used in Comparative Example 1 is shown in FIG. In FIG. 2, 3 is a biological reaction tank, 5 is a solid-liquid separation tank, and 6 is a return sludge line, which is a general biological treatment apparatus.
The organic wastewater flowing into the biological reaction tank 3 has a BOD concentration of 200 mg / L. The organic waste water having the same composition as in Example 1 was used. Organic wastewater was supplied to the bioreactor at 70 L / day. The capacity of the biological reaction tank 3 was 20L. The liquid flowing out from the biological reaction tank 3 is sent to the solid-liquid separation tank 5. The sludge settled and separated in the solid-liquid separation tank 5 is returned to the biological reaction tank 3 as a partially returned sludge.

  The result of Table 1 was obtained as the data of the continuous operation. As shown in Table 1, the water quality of the treated water after solid-liquid separation is as good as 30 ° C. and COD of 6 mg / L. 8 g / day was generated.

[Comparative Example 2]
A schematic diagram of the apparatus used is shown in FIG. In FIG. 4, 3 is a biological reaction tank, 5 is a solid-liquid separation tank, and 6 is a return sludge line, which is a general biological treatment apparatus. Branching from the return sludge line 6, the liquid is sent to the solubilization reaction treatment tank 8. 8 is a solubilization reaction processing tank, 81 is an air piping from the aeration apparatus, and corresponds to the solubilization reaction processing apparatus. In this comparative example, the organic waste water flowing into the biological reaction tank 3 has a BOD concentration of 200 mg / L. The organic wastewater having the same composition as in Example 1 was used, and the amount of inflow of 70 L / day into the biological reaction tank 3 was obtained. The capacity of the biological reaction tank 3 is 20L. The liquid flowing out from the biological reaction tank 3 is sent to the solid-liquid separation tank 5. The sludge settled and separated in the solid-liquid separation tank 5 is returned to the biological reaction tank 3 as a partially returned sludge. Moreover, a part of sludge is sent to the solubilization reaction treatment tank 8 at a flow rate of 2 L / day with an SS concentration of 1% by weight through a liquid feed line 7. The solubilization reaction treatment tank 8 is fed with 0.05 liter / min of air through the air pipe 81 from the aeration apparatus, and warm water is put in the jacket for heat insulation so that the temperature of 60 ° C. can be maintained. It was. The liquid that passed through the solubilization reaction treatment tank 8 was returned to the biological reaction tank 3 through the solubilization liquid return line 20.

  The result of Table 1 was obtained as the data of the continuous operation. As shown in Table 1, the water quality of the treated water after the solid-liquid separation is 15 ° C., and the chemical oxygen demand COD is 21 mg / L. The excess sludge was 0 g / day in terms of dry weight.

  In Comparative Example 1, surplus sludge is generated, and in Comparative Example 2, much COD of the treated water after solid-liquid separation remains, but in Example 1, the surplus sludge is 0 g / L, and the COD is 8 mg / L. And solubilization reaction treatment device and membrane treatment device are put in, and the amount of excess sludge is reduced and the quality of treated water after solid-liquid separation is maintained.

[Table 1]

  The present invention relates to an apparatus and a method for discharging organic sludge, for example, an organic material containing organic sludge discharged from a sewage treatment process such as a sewage treatment plant and a sewage treatment plant, a manufacturing process such as a food factory and a chemical factory. This is a method of treating wastewater with a biological reaction, and is suitable for reducing excess sludge.

FIG. 3 is a schematic diagram illustrating a processing method according to the first embodiment. The schematic diagram which shows the conventional activated sludge method. The schematic diagram which shows the example of the processing method of this invention. The schematic diagram which shows the processing method of the comparative example 2. FIG. The schematic diagram which shows the example of the processing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic waste water storage tank 2 Waste water feed line 3 Biological reaction tank 4 Liquid feed line 5 Solid-liquid separation tank 6 Return sludge line 7 Liquid feed line 8 Solubilization reaction treatment tank 9 Liquid feed line 10 Air pump 11 Membrane filtration device 12 Membrane filtration device concentrate line 13 Membrane filtrate line 14 Microfiltration membrane 15 Ultrafiltration membrane 16 Suction pump 20 Solubilized liquid return line 31 Air pipe 81 Air pipe 112 Ultrafiltration membrane concentrate line 121 Microfiltration membrane filtrate line 301 Treatment liquid 302 Sludge 303 Excess sludge

Claims (4)

  Organic wastewater is biologically treated in a biological reaction tank, and generated sludge is subjected to medium-to-high temperature microorganism treatment in a solubilization reaction treatment tank, and at least a part of the liquid in the solubilization reaction treatment tank is gasified into the liquid. The membrane is fed into a membrane filtration device having a hollow fiber membrane, and is separated into a membrane filtrate and a membrane concentrate by the membrane filtration device. The membrane filtrate is returned to the biological reaction tank, and the membrane concentrate Is a method for treating organic wastewater, which is returned to the solubilization reaction treatment tank and backwashed when necessary.   The method for treating organic wastewater according to claim 1, wherein the membrane filtration device has a pump for sucking the membrane filtrate.   The method for treating organic wastewater according to claim 1 or 2, wherein the filtration membrane comprises an ultrafiltration membrane.   The method for treating organic wastewater according to claim 1 or 2, wherein the filtration membrane comprises a microfiltration membrane.

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