JP6761245B2 - How to treat organic wastewater - Google Patents

Description

The present invention relates to a technique for treating organic wastewater by biologically treating organic wastewater in a fluidized bed type reaction tank under anaerobic conditions.

The anaerobic fluidized bed wastewater treatment is a treatment method in which anaerobic microorganisms are attached to the carrier and flowed in the reaction vessel to improve the contact efficiency between the wastewater and the carrier and enable stable and highly efficient treatment. is there. However, such a method has a problem that it takes time for the anaerobic microorganisms to adhere to the carrier and it takes a long time to start up the biological treatment.

For example, in Patent Document 1, an anaerobic microorganism mother liquor and a carrier are placed in a centrifuge device, and the anaerobic microorganism is attached to the carrier by centrifuging the mother liquor and the carrier, and the carrier to which the anaerobic microorganism is attached is attached. A method for treating organic wastewater using the above as a fixed bed is disclosed.

Further, for example, in Patent Documents 2 and 3, when the reaction tank holding the carrier is started up, the carrier and the anaerobic granule coexist in the reaction tank to start the flow of organic waste water, and then. Disclosed is a method for treating organic wastewater, which disassembles and disperses a part of granules in a reaction vessel by continuing the flow of organic wastewater.

Japanese Unexamined Patent Publication No. 2003-190985 Japanese Unexamined Patent Publication No. 2012-110821 Japanese Unexamined Patent Publication No. 2014-100680

However, in the centrifugal treatment of Patent Document 1, anaerobic microorganisms are easily peeled off from the carrier. In particular, when used in the fluidized bed type, the fluidity of the carrier is higher than that in the fixed bed type, so that the exfoliation of anaerobic microorganisms may proceed more. If the exfoliated anaerobic microorganisms flow out together with the treated water, the amount of microorganisms in the reaction vessel fluctuates. For example, in the case of overload, the growth of anaerobic microorganisms is inhibited, resulting in biological treatment. It may take a lot of time to start up.

Further, in the methods of Patent Documents 2 and 3, since the anaerobic granules are disassembled and dispersed, if the anaerobic granules flow out together with the treated water, as described above, it takes a lot of time to start the biological treatment. It may take.

INDUSTRIAL APPLICABILITY The present invention is a method for treating organic wastewater in which organic wastewater is biologically treated in a fluidized bed type reaction tank under anaerobic conditions, and it is possible to suppress a long start-up period of biological treatment. The purpose is to provide.

The present invention is a method for treating organic wastewater by biologically treating organic wastewater in a fluidized bed type reaction tank under anaerobic conditions. When the biological treatment is started, denitrifying microorganisms and denitrifying microorganisms are contained in the reaction tank. This is a method for treating organic wastewater in which a carrier to which a sticky product produced by the denitrifying microorganism is attached as a biofilm is charged .

Further, in the method for treating organic wastewater, it is preferable that the reaction tank is a stirring type reaction tank.

Further, in the method for treating organic wastewater, the carrier to be charged into the reaction vessel is preferably a gel-like carrier.

According to the present invention, in a method for treating organic wastewater by biologically treating organic wastewater in a fluidized bed type reaction tank under anaerobic conditions, it is possible to suppress a long start-up period of biological treatment. A processing method can be provided.

It is a schematic diagram which shows an example of the structure of the wastewater treatment apparatus used in the organic wastewater treatment method of this embodiment. It is a schematic diagram which shows another example of the structure of the wastewater treatment apparatus used for the organic wastewater treatment method of this embodiment.

Hereinafter, embodiments of the present invention will be described. It should be noted that the present embodiment is an example of carrying out the present invention, and the present invention is not limited to the present embodiment.

FIG. 1 is a schematic view showing an example of the configuration of a wastewater treatment apparatus used in the organic wastewater treatment method of the present embodiment. The wastewater treatment apparatus 1 shown in FIG. 1 includes a fluidized bed type reaction tank 10, and a carrier 12 is charged in the fluidized bed type reaction tank 10. A drainage inflow line 14 is installed at the inlet of the fluidized bed type reaction tank 10, and a treated water discharge line 16 is installed at the outlet of the fluidized bed type reaction tank 10.

The fluidized bed type reaction tank 10 shown in FIG. 1 biologically treats organic waste water under anaerobic conditions while flowing the carrier 12 in the tank. The fluidized bed type reaction tank 10 shown in FIG. 1 is a stirring type reaction tank, and includes a draft tube 18 which is installed substantially vertically in the tank and has an open top and bottom, and a stirring device 20 which stirs the carrier 12 in the tank. .. The stirring device 20 shown in FIG. 1 includes a motor 22, a stirring blade 24, and a shaft 26 connecting the motor 22 and the stirring blade 24, and the stirring blade 24 is arranged in the draft tube 18. The stirring device 20 is not limited to the above configuration as long as it has a device configuration capable of stirring the carrier 12 in the fluidized bed type reaction tank 10. Further, it is preferable to install the draft tube 18 from the viewpoint of improving the fluidity of the carrier 12, but it is not always necessary to install the draft tube 18.

The carrier 12 contains a carrier to which non-anaerobic microorganisms are attached as a biofilm. Here, the biofilm is a membrane-like structure in which non-anaerobic microorganisms and products such as exopolysaccharide produced by non-anaerobic microorganisms are aggregated, and has a film thickness of at least 10 μm or more, preferably. It has a film thickness of 20 μm or more. The film thickness is the thickness from the surface of the carrier 12, and is an average value of 10 to 20 carriers 12. For products such as exopolysaccharides, polysaccharides can be extracted from the biofilm using alkali, and the sugar concentration in the extract can be measured by the Anthrone method. Products such as exopolysaccharides have adhesiveness and are considered to affect the adhesion of biofilms. For example, 20 ppm or more is preferably present in the biofilm, and 50 ppm or more is present. It is more preferable to do so.

The anaerobic condition or anaerobic means a state in which dissolved oxygen, bound oxygen such as nitrate nitrogen, etc. are not present in the wastewater. The non-anaerobic microorganism means a microorganism that can survive in a state where dissolved oxygen and bound oxygen such as nitrate nitrogen are present in the wastewater. In other words, a non-anaerobic microorganism means a microorganism that cannot survive (kill) under anaerobic conditions.

The wastewater treatment device 1 of the present embodiment preferably includes, for example, a screen (not shown) installed so as to surround the discharge port of the fluidized bed type reaction tank 10. The screen makes it possible to prevent the carrier 12 from flowing out of the fluidized bed type reaction vessel 10. Examples of the screen include a wedge wire screen, a wire mesh, a punching metal, and the like.

The method for treating organic wastewater according to the present embodiment will be described using the wastewater treatment apparatus 1 shown in FIG.

The organic wastewater to be treated in the present embodiment is, for example, wastewater containing organic substances discharged from a food manufacturing factory, an electronic industry factory, a pulp manufacturing factory, a chemical factory, or the like. The organic substance is a biodegradable organic substance, and examples thereof include soluble proteins, sugars, amino acids, alcohols, organic acids, fatty acids and the like.

At the start-up of biological treatment, organic wastewater is introduced into the fluidized bed type reaction tank 10 from the wastewater inflow line 14. The carrier 12 is charged into the fluidized bed type reaction tank 10 before or after the start of water flow of the organic waste water. Further, it is preferable to add sludge containing anaerobic microorganisms (including granule sludge) as seed sludge before or after the start of water flow of organic wastewater. Then, in the fluidized bed type reaction tank 10, the biological treatment is performed under anaerobic conditions while the carrier 12 and the organic waste water are agitated by the stirring device 20. In the present embodiment, since the stirring blade 24 is stirred in the draft tube 18, a downward flow is formed in the draft tube 18, and the outer wall surface of the draft tube 18 and the inner wall surface of the fluidized bed type reaction tank 10 are formed. An upward flow is formed between the two. The treated water biologically treated in the fluidized bed type reaction tank 10 is discharged from the treated water discharge line 16 to the outside of the system. When such processing is continued and a preset load is reached, the start-up of biological processing is completed. After the start-up of the biological treatment is completed, for example, the biological treatment (main treatment) of the organic wastewater is executed while maintaining the load reached during the start-up period of the biological treatment. The reached load during the biological treatment start-up period is preferably set to 2 kg / m ³ / day or more, and more preferably 10 kg / m ³ / day or more, for example, with a CODcr volume load.

In the present embodiment, at the start-up of the biological treatment, a carrier to which non-anaerobic microorganisms are attached as a biological membrane is added (carrier 12 is added), and the biological treatment is performed under anaerobic conditions. The non-anaerobic microorganisms inside are gradually killed. However, since exopolysaccharide and other sticky products remain on the carrier, it is considered that the anaerobic microorganisms in the wastewater adhere to the carrier so as to replace the dead non-anaerobic microorganisms. Therefore, it is possible to improve the adhesion of anaerobic microorganisms to the carrier and suppress the outflow of anaerobic microorganisms into the treated water, as compared with the case where a carrier to which no microorganisms are attached is added. As a result, fluctuations in the amount of anaerobic microorganisms in the fluidized bed type reaction tank are suppressed, so that overload is less likely to occur and growth of anaerobic microorganisms is more likely than when a carrier to which no microorganisms are attached is added. It is thought that it will be less likely to be inhibited, and it will be possible to suppress the prolongation of the start-up period of biological treatment. Since the products such as exopolysaccharide contained in the biofilm have adhesiveness, peeling from the flowing carrier can be suppressed.

In the present embodiment, it is desirable to add sludge containing anaerobic microorganisms (including granule sludge) as the main sludge from the viewpoint that a large amount of anaerobic microorganisms can be retained in the reaction tank immediately after the start of water flow. The amount of main sludge to be charged is preferably in the range of 1 to 30%, more preferably 5 to 20% with respect to the volume of the reaction vessel, for example. If the amount of main sludge input is less than 1%, the advantage of adding main sludge may not be obtained, and if it exceeds 30%, the quality of treated water may deteriorate.

In the present embodiment, in addition to the carrier to which non-anaerobic microorganisms are attached as a biofilm, for example, a carrier to which anaerobic microorganisms are attached as a biofilm, a carrier to which no microorganisms are attached, etc. However, the loading rate of the carrier to which the non-anaerobic microorganisms are attached as a biofilm is in the range of 20% to 95% with respect to the total amount of the carriers charged into the fluidized bed type reaction tank 10. Is preferable, and the range of 20% to 70% is more preferable. When the input rate of the carrier to which the non-anaerobic microorganisms are attached as a biofilm exceeds 95%, the dead non-anaerobic microorganisms flow out into the treated water and are treated as compared with the case where the above range is satisfied. The quality of water may deteriorate. In addition, a carrier to which non-anaerobic microorganisms are attached as a biofilm generally has a high production cost, and as a result, the cost for biological treatment may also be high. On the other hand, when the input rate of the carrier to which the non-anaerobic microorganisms are attached as a biofilm is less than 20%, the prolongation of the start-up period of the biological treatment is suppressed as compared with the case where the above range is satisfied. The effect may be reduced.

The carrier to which the non-anaerobic microorganisms are attached as a biofilm is secured from, for example, an acclimatization device in which the carrier to which the microorganisms are not attached is immersed in organic wastewater or nitrogen-containing wastewater and acclimatized for a long period of time. Will be done. Further, for example, it is secured from another treatment apparatus that biologically treats organic wastewater and nitrogen-containing wastewater for a long period of time using a carrier.

Non-anaerobic microorganisms include, for example, aerobic microorganisms that survive (preferably grow) in the presence of dissolved oxygen in wastewater, denitrifying microorganisms that survive (preferably grow) in the presence of bound oxygen such as nitrate nitrogen, and the like. Can be mentioned. Comparing aerobic microorganisms and denitrifying microorganisms, it is considered that the denitrifying microorganisms have higher resistance under anaerobic conditions and can maintain the effect of adhering the anaerobic microorganisms to the carrier for a long time. Therefore, as the non-anaerobic microorganism, a denitrifying microorganism is preferable to an aerobic microorganism in terms of the effect of adhering the anaerobic microorganism to the carrier. On the other hand, aerobic microorganisms have a higher growth rate and a higher cell yield than denitrifying microorganisms. Therefore, it is preferable to utilize aerobic microorganisms because it is easy to secure a carrier to which non-anaerobic microorganisms are attached as a biofilm.

The total amount of the carriers 12 charged into the fluidized bed type reaction tank 10 is preferably in the range of 10 to 50% with respect to the tank volume. If the total amount of the carrier 12 is less than 10% of the tank volume, the reaction rate may decrease, and if it exceeds 50%, the fluidity of the carrier 12 decreases, and organic wastewater is discharged due to sludge clogging during long-term operation. May cause a short pass and the quality of treated water may deteriorate.

The sedimentation rate of the carrier 12 charged into the fluidized bed type reaction vessel 10 is preferably 100 to 200 m / hr. If the settling speed is less than 100 m / hr, the carrier 12 charged into the tank floats and easily flows out from the tank, and if it exceeds 200 m / hr, the flow state deteriorates and the organic wastewater is short-passed. In some cases, the energy of stirring may increase.

The specific gravity of the carrier 12 to be charged into the fluidized bed type reaction tank 10 is, for example, greater than 1.0, the true specific gravity of 1.1 or more, or the apparent specific gravity of 1. in order to form a fluidized state inside the tank. Those of 01 or more are preferable.

The carrier before attaching the biological membrane (hereinafter, may be referred to as a plain carrier) is not particularly limited as long as it is a carrier conventionally used in anaerobic biological treatment, and is, for example, a plastic carrier or a sponge-like carrier. Examples thereof include carriers and gel-like carriers. Among these, a gel-like carrier is preferable because, for example, the adhesiveness of the biofilm, the fluidity of the carrier, and the like, and the high load treatment is possible. The gel-like carrier is not particularly limited, and examples thereof include a water-absorbent polymer gel-like carrier containing polyvinyl alcohol, polyethylene glycol, polyurethane, and the like.

The shape of the raw carrier is not particularly limited, but a spherical or cubic (cube-shaped), rectangular parallelepiped, cylindrical or the like having a diameter of about 0.5 mm to 20 mm is preferable. In particular, a spherical or cylindrical gel-like carrier having a diameter of about 3 to 8 mm is preferable.

In the present embodiment, when the organic wastewater is biologically treated, the pH of the wastewater is preferably in the range of 6.0 to 8.0, more preferably in the range of 7.0 to 8.0. The pH of wastewater is adjusted, for example, by supplying a pH adjuster from a pH adjuster supply line (not shown) to a raw water tank (not shown) storing organic wastewater. If the pH of the organic wastewater is out of the above range, the decomposition reaction rate of organic matter by biological treatment may decrease.

The pH adjusting agent is not particularly limited, such as an acid agent such as hydrochloric acid and an alkaline agent such as sodium hydroxide. Further, the pH adjusting agent may be, for example, sodium bicarbonate having a buffering action, a phosphate buffer solution or the like.

In the present embodiment, it is preferable to add a nutrient to the organic wastewater, for example, from the viewpoint of maintaining good decomposition activity of anaerobic microorganisms when biologically treating the organic wastewater. The nutritional supplement is not particularly limited, and examples thereof include a carbon source, a nitrogen source, and other inorganic salts (Ni, Co, Fe, etc.).

In the present embodiment, it is preferable to adjust the temperature of the water in the fluidized bed type reaction vessel 10 so as to be 20 ° C. or higher. Usually, when the temperature is lower than 20 ° C., the decomposition reaction rate tends to decrease. The method for adjusting the temperature of the water temperature in the fluidized bed type reaction tank 10 is not particularly limited. For example, a heating device such as a heater is installed in the fluidized bed type reaction tank 10 and the fluidized bed is heated by the heat of the heater or the like. A method of adjusting the water temperature in the formula reaction tank 10 and the like can be mentioned.

FIG. 2 is a schematic view showing another example of the configuration of the wastewater treatment apparatus used in the organic wastewater treatment method of the present embodiment. In the wastewater treatment apparatus 2 shown in FIG. 2, the same reference numerals are given to the same configurations as those of the wastewater treatment apparatus 1 shown in FIG. 1, and the description thereof will be omitted. The wastewater treatment apparatus 2 shown in FIG. 2 includes an upward flow type fluidized bed type reaction tank 38, and the carrier 12 described above is charged in the fluidized bed type reaction tank 38. The fluidized bed type reaction tank 38 shown in FIG. 2 is provided with a drainage supply unit 40 provided near the bottom of the tank, and a wastewater inflow line 14 is connected to the wastewater supply unit 40. Organic wastewater is passed through the tank through the section 40. Further, the fluidized bed type reaction tank 38 shown in FIG. 2 includes an overflow type treated water take-out section 42 provided in the upper part of the tank, and the treated water discharge line 16 is connected to the treated water take-out section 42. The treated water obtained by anaerobically treating the wastewater is discharged to the outside of the system through the treated water take-out unit 42 and the treated water discharge line 16. Further, the fluidized bed type reaction tank 38 shown in FIG. 2 includes a circulation line 44 and a circulation pump 46. One end of the circulation line 44 is connected to the fluidized bed type reaction tank 38, and the other end is connected to the drainage inflow line 14, so that the organic wastewater in the tank is circulated through the circulation line 44. Has been done. The upward flow type fluidized bed type reaction tank is not limited to the device configuration of the fluidized bed type reaction tank 38 shown in FIG. 2 as long as it has an apparatus configuration for anaerobically treating organic wastewater by an upward flow. Absent.

In the wastewater treatment apparatus 2 shown in FIG. 2, organic wastewater is introduced from the wastewater supply unit 40 into the fluidized bed type reaction tank 38, and is circulated through the circulation line 44 by the operation of the circulation pump 46. Then, the carrier 12 is fluidized and the organic wastewater is anaerobically treated.

The fluidized bed type reaction tank used in the present embodiment has high contact efficiency between the organic wastewater and the carrier 12, and can treat organic wastewater having a high oil / fat concentration and SS concentration. A stirring type fluidized bed type reaction tank is preferable to a countercurrent type. Further, the fluidized bed type reaction tank is not limited to the upward flow type and the stirring type, and is not particularly limited as long as the carrier 12 is of a fluidized type.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

(Example 1)
The test was carried out using the wastewater treatment apparatus shown in FIG. In an acrylic reaction vessel having a volume of 600 mL, 30% of the carrier to which denitrifying microorganisms are attached as a biofilm is charged with respect to the volume of the reaction vessel, and anaerobic granule sludge is added to the volume of the reaction vessel by 10. % Was put in. As a carrier (elementary carrier) before attachment to the biofilm, a spherical polyvinyl alcohol-based gel-like carrier (pore diameter 4 to 20 μm, diameter 4 mm, specific gravity 1.025, sedimentation rate 4 cm / sec) was used. As the target wastewater for biological treatment, food factory wastewater (CODcr2,500-3000 mg / L) containing sucrose and bonito extract as main components was used, and water flow to the reaction tank was started.

(Comparison example)
Instead of adding a carrier to which denitrifying microorganisms are attached as a biofilm, 30% of the carrier (elementary carrier) to which the biofilm is not attached is added to the volume of the reaction vessel, and anaerobic granule sludge is added. The conditions were the same as those in Example 1 except that 10% of the volume of the reaction tank was charged.

<Results of biological treatment start-up period>
In Example 1, the load can be increased while maintaining the CODcr concentration of the treated water at a low level, and the CODcr load becomes the standard for stabilizing the operation at 2 kg / 40 days from the start of the flow of the organic waste water. It reached m ³ / day. Then, on the 76th day of operation, the pressure was 16 kg / m ³ / day. On the other hand, in the comparative example, the load was gradually increased from the start of the flow of the organic wastewater, but the CODcr concentration of the treated water did not decrease even after 30 to 40 days of operation, and the load was significantly listed. Was difficult. Then, on the 70th day of operation, the CODcr load reached 2 kg / m ³ / day, which is a standard for stabilizing the operation, and finally, on the 100th day of operation, the CODcr load reached 16 kg / m ³ / day. From the above, it can be said that Example 1 can complete the start-up of biological treatment in a shorter period of time than Comparative Example. That is, it can be said that Example 1 can suppress the prolongation of the start-up period of biological treatment.

1,2 Wastewater treatment equipment, 10,38 Flow bed type reaction tank, 12 Carrier, 14 Wastewater inflow line, 16 Treated water discharge line, 18 Draft tube, 20 Stirrer, 22 Motor, 24 Stirrer blade, 26 Shaft, 40 Wastewater Supply section, 42 treated water extraction section, 44 circulation line, 46 circulation pump.

Claims (3)

A method for treating organic wastewater by biologically treating organic wastewater in a fluidized bed reactor under anaerobic conditions.
When the biological treatment is started, a carrier to which the denitrifying microorganism and the sticky product produced by the denitrifying microorganism are attached as a biological membrane is put into the reaction vessel. How to treat organic wastewater. The method for treating organic wastewater according to claim 1, wherein the reaction tank is a stirring type reaction tank. The method for treating organic wastewater according to any one of claims 1 to 2 , wherein the carrier to be charged into the reaction vessel is a gel-like carrier.