Processing system and processing method of organic wastewater using aquatic earthworm

Abstract

To provide an energy-saving sludge volume reduction technique utilizing sludge predation by aquatic earthworm which stands in the upper class of the food chain and autoxidation of active sludges.SOLUTION: A processing system of organic wastewater includes: active sludge aeration means 1 for biological treatments of organic wastewater; sludge treatment means 2 having a treatment tank 12 for retaining aquatic earthworm preying sludges in an aerated liquid obtained by biological treatment; solid-liquid separation treatment means 3 for solid-liquid separation treatment of a treated aerated liquid obtained by the active sludge aeration means 1 and the sludge treatment means 2; and an excess sludge return line 4 for returning excess sludges obtained by the solid-liquid separation treatment to the sludge treatment means 2 or the active sludge an aeration means 1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a treatment system and method for organic wastewater, and particularly to a sludge volume reduction technology by sludge predation of aquatic earthworms.

Background Art

[0002] The activated sludge method is generally used as a method for treating organic wastewater, but the excess sludge generated during the treatment has been a problem since long ago. As a method for reducing the volume of this excess sludge, research and development using chemical treatment methods (bactericides, chemicals, acids / alkalis, ozone) and physical treatment methods (hydrothermal reaction, pressurization, wet bead mill, ultrasonic waves) have been carried out for a long time. Although these technologies have achieved certain results, they require a large amount of energy and chemicals, and thus do not meet the current needs required for the conversion from a mass consumption type society to a resource recycling type society and a decarbonized society.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 discloses a method for growing aquatic organisms using excess sludge generated in the treatment of waste liquid as a method for culturing aquatic feed organisms by activated sludge. However, this method focuses on the cultivation of aquatic organisms and does not consider an appropriate load in terms of treated water quality and sludge volume reduction of excess sludge. Although the technology of this Patent Document 1 may lead to sludge volume reduction, when excessive organic matter is input, the sludge predation of aquatic organisms becomes limited. In addition, since the device has a peripheral circuit structure, the device capacity is excessive.

[0005] Patent Document 2 discloses a method for reducing excess sludge volume using predator animals as a sludge treatment apparatus and a sludge treatment method. However, the technology of this Patent Document 2 mainly focuses on the control of software aspects such as pH and water temperature, and does not disclose the detailed structure of the apparatus. In addition, this technology requires three or more tanks, and the apparatus capacity is excessive. Also, when the supply amount of organic matter becomes excessive, the sludge predation behavior by metazoans becomes limited, and the properties of the treated water quality obtained are also unknown.

[0006] Therefore, an object of the present invention is to provide an energy-saving sludge volume reduction technology that utilizes sludge predation by aquatic earthworms, which are at the upper level of the food chain, and autoxidation of activated sludge.

Means for Solving the Problems

[0007] In one aspect, there is provided a treatment system for organic wastewater, comprising activated sludge aeration means for biologically treating organic wastewater, sludge treatment means having a treatment tank for holding aquatic earthworms that prey on the sludge in the aerated liquid obtained by the biological treatment, solid-liquid separation treatment means for subjecting the treated aerated liquid obtained by the activated sludge aeration means and the sludge treatment means to solid-liquid separation treatment, and an excess sludge return line for returning the excess sludge obtained by the solid-liquid separation treatment to the sludge treatment means or the activated sludge aeration means.

[0008] In one aspect, the sludge treatment means is characterized by comprising a surface aeration device. In one aspect, the treatment tank has a rectangular horizontal cross-section, and the ratio of the short side to the long side of the rectangular horizontal cross-section is 1:1.5 to 1:3.0. In one aspect, the sludge treatment means includes a sampling port in which an aquatic earthworm-containing sludge sampling passage is formed, and port opening / closing means attached to the sampling port, and the sampling port is connected to the bottom of the treatment tank. In one aspect, the bottom of the treatment tank is inclined downward toward the aquatic earthworm-containing sludge sampling passage. In one aspect, it is characterized in that the sludge concentration in the treatment tank is adjusted to 1,000 to 5,000 mg / L using the excess sludge. In one aspect, the surface aeration device adjusts the dissolved oxygen concentration in the aeration liquid existing at a position lower than 10% of the height from the bottom of the treatment tank to 0.1 to 1 mg / L, adjusts the dissolved oxygen concentration in the aeration liquid existing within the range of 10 to 30% of the height from the bottom of the treatment tank to 1 to 3 mg / L, and adjusts the dissolved oxygen concentration in the aeration liquid existing at a position higher than 30% of the height from the bottom of the treatment tank to 3 mg / L or more. In one aspect, the introduction amount of the aeration liquid introduced from the activated sludge aeration means to the sludge treatment means is adjusted to 50 to 150% with respect to the inflow amount of the organic wastewater to the activated sludge aeration means, and the return amount of the secondary aeration liquid returned from the sludge treatment means to the activated sludge aeration means is made the same as the introduction amount of the aeration liquid introduced from the activated sludge aeration means to the sludge treatment means.

[0009] In one aspect, an organic wastewater treatment method is provided, which comprises flowing the organic wastewater into the activated sludge aeration means, biologically treating the organic wastewater by the activated sludge aeration means, introducing the aeration liquid obtained by the biological treatment into the treatment tank of the sludge treatment means, allowing the sludge in the aeration liquid to be preyed on by the aquatic earthworms in the treatment tank, guiding the treated aeration liquid obtained by the activated sludge aeration means and the sludge treatment means to the solid-liquid separation treatment means for solid-liquid separation treatment, and returning the excess sludge obtained by the solid-liquid separation treatment to the sludge treatment means or the activated sludge aeration means.

[0010] In one aspect, the treatment method further comprises aerating the aeration liquid in the treatment tank by a surface aeration device. In one aspect, the treatment tank has a rectangular horizontal cross-section, and the ratio of the short side to the long side of the rectangular horizontal cross-section is 1:1.5 to 1:3.0. In one aspect, it is characterized in that the sludge concentration in the treatment tank is adjusted to 1,000 to 5,000 mg / L using the excess sludge. In one aspect, the dissolved oxygen concentration in the aerated liquid present at a position lower than 10% of the height from the bottom of the treatment tank is adjusted to 0.1 to 1 mg / L, the dissolved oxygen concentration in the aerated liquid present within the range of 10 to 30% of the height from the bottom of the treatment tank is adjusted to 1 to 3 mg / L, and the dissolved oxygen concentration in the aerated liquid present at a position higher than 30% of the height from the bottom of the treatment tank is adjusted to 3 mg / L or more. In one aspect, the introduction amount of the aerated liquid introduced from the activated sludge aeration means to the sludge treatment means is adjusted to 50 to 150% with respect to the inflow amount of the organic wastewater to the activated sludge aeration means, and the return amount of the secondary aerated liquid returned from the sludge treatment means to the activated sludge aeration means is made the same as the introduction amount of the aerated liquid introduced from the activated sludge aeration means to the sludge treatment means.

Advantages of the Invention

[0011] According to the present invention according to claims 1 to 12, the following effects can be obtained.

[0012] The sludge treatment apparatus using aquatic earthworms according to the present invention can reduce the volume of sludge with energy savings and remove nitrogen in organic wastewater by culturing and using aquatic earthworms.

[0013] According to the present invention, an energy-saving sludge volume reduction technology utilizing the food chain can be realized. Conventional sludge volume reduction technologies often require a large amount of energy. However, since the present invention mainly utilizes the predation of activated sludge and bacteria by aquatic earthworms and the autoxidation action of activated sludge, it has the advantage of being more energy-saving compared to conventional sludge volume reduction technologies.

[0014] According to the present invention, aquatic earthworms can be cultured without a fixed bed. That is, the present invention defines the aspect ratio of the bottom structure of the sludge treatment apparatus and adopts a surface aeration method to retain sludge at the bottom of the sludge treatment apparatus, so that aquatic earthworms can be cultured without a fixed bed.

[0015] According to the present invention, while obtaining the sludge volume reduction effect by aquatic earthworms, nitrogen in the organic wastewater to be treated can be removed by nitrification and denitrification. The aerated liquid introduced into the sludge treatment apparatus of the present invention is primarily treated in an activated sludge aeration tank, with little residue of organic substances and an environment where autotrophic bacteria such as Nitrosomonas and Nitrobacter coexist. Therefore, nitrification of nitrite nitrogen and ammonia nitrogen proceeds to form nitrate nitrogen. Further, since the sludge treatment apparatus of the present invention employs surface aeration, in addition to the fact that activated sludge tends to accumulate at the bottom of the apparatus, the influence of the metabolites of aquatic earthworms makes it even easier for the activated sludge to accumulate, and the bottom of the apparatus becomes an anaerobic condition where denitrification reactions are likely to occur. Furthermore, the metabolites of aquatic earthworms not only contribute to the retention of bacteria involved in denitrification but also serve as substrates (electron donors). Therefore, the nitrate nitrogen is removed by denitrification reactions. From the above, the sludge treatment apparatus of the present invention also serves as a one-tank nitrification and denitrification tank.

[0016] According to the present invention, it is easy to collect aquatic earthworms with high market value. Although aquatic earthworms are often avoided due to physiological aversion, they are used as raw materials for feed and pharmaceuticals for cultured fish and ornamental fish, etc., so their market value is high and their evaluation is still in development. Since the sludge treatment apparatus of the present invention cultivates aquatic earthworms without a fixed bed, by installing pipes for collection, aquatic earthworms with high market value can be easily obtained.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a treatment system for organic wastewater using aquatic earthworms. The treatment system includes an activated sludge aeration tank 1 as an activated sludge aeration means for biologically treating organic wastewater, and a sludge treatment device 2 as a sludge treatment means having a treatment tank 12 for holding aquatic earthworms that prey on the sludge in the aeration liquid obtained by the biological treatment in the activated sludge aeration tank 1, a sedimentation tank 3 as a solid-liquid separation treatment means for performing solid-liquid separation treatment on the treated aeration liquid obtained in the activated sludge aeration tank 1 and the sludge treatment device 2, and an excess sludge return line 4 for returning the excess sludge obtained by the solid-liquid separation treatment in the sedimentation tank 3 to the sludge treatment device 2 or the activated sludge aeration tank 1.

[0019] The organic wastewater to be treated is introduced into the activated sludge aeration tank 1. The activated sludge aeration tank 1 and the sludge treatment device 2 are connected by an aeration liquid transfer line 7 and a secondary aeration liquid transfer line 8, and the activated sludge aeration tank 1 and the sedimentation tank 3 are connected by a treated aeration liquid transfer line 9. The excess sludge return line 4 extends from the sedimentation tank 3 to both the activated sludge aeration tank 1 and the sludge treatment device 2.

[0020] First, the organic wastewater to be treated is introduced into the activated sludge aeration tank 1, and biological treatment is performed in the activated sludge aeration tank 1. The activated sludge aeration tank 1 has an aeration device (not shown) and is configured to aerate the organic wastewater. More specifically, the activated sludge aeration tank 1 performs nitrification of ammonia nitrogen and treatment of organic components under conditions controlled to a dissolved oxygen concentration of 4 mg / L or more and a sludge concentration of 2,000 to 3,000 mg / L.

[0021] The aerated liquid obtained from the biological treatment in the activated sludge aeration tank 1 is introduced into the sludge treatment device 2 having aquatic earthworms through the aerated liquid transfer line 7. The type of aquatic earthworms may be any one belonging to either Oligochaeta of Annelida or Polychaeta of Annelida. Specifically, species classified into the subfamily Eiseniinae, the order Eiseniida, or the subfamily Perionyxinae are desirable, and in particular, species such as Eisenia fetida, Drawida willsi, and Drawida japonica that are widely growing in the country are desirable.

[0022] Figure 2 is a cross-sectional view showing an embodiment of the sludge treatment device 2. The sludge treatment device 2 includes a treatment tank 12 that stores the aerated liquid transferred from the activated sludge aeration tank 1 and holds aquatic earthworms, and an air diffuser 15 disposed in the treatment tank 12. The air diffuser 15, which is an air diffusing means for surface aeration, is disposed at the upper part of the treatment tank 12. The air diffuser 15 injects air into the aerated liquid in the treatment tank 12 to generate an upward flow of bubbles in the treatment tank 12, and forms a circulating flow of the aerated liquid as shown by the arrow in Figure 2 in the upper layer of the treatment tank 12.

[0023] The air diffuser 15 is a surface aeration device disposed near the liquid surface of the aerated liquid in the treatment tank 12. Since the air diffuser 15 generates bubbles in the upper layer of the aerated liquid in the treatment tank 12, it does not stir the bottom of the treatment tank 12. As a result, the aquatic earthworms inhabiting the lower layer of the treatment tank 12 do not rise due to the bubbles and settle in the lower layer of the treatment tank 12. Also, it is possible to prevent the aquatic earthworms from flowing out from the overflow weir 17 together with the secondary aerated liquid.

[0024] As shown in Figure 2, the installation location of the air diffuser 15 is preferably near the vertical wall 18 on the side opposite to the overflow weir 17 of the treatment tank 12 from which the secondary aerated liquid flows out. By installing the air diffuser 15 on the vertical wall 18, a swirling flow is generated in the sludge treatment device 2, and a situation is created in which aquatic earthworms easily stay at the bottom 20 of the treatment tank 12. The configuration of the air diffuser 15 is not particularly limited, and examples include a porous air diffuser plate made of magnetic material or synthetic resin, and a membrane-type round diffuser.

[0025] The sludge treatment device 2 not only obtains the sludge volume reduction effect by the sludge predation of aquatic earthworms but also serves as a water treatment device using the activated sludge method. Therefore, the MLSS (Mixed Liquor Suspended Solids) concentration in the treatment tank 12 of the sludge treatment device 2 is preferably maintained at 3,000 to 5,000 mg / L using the returned sludge, more preferably maintained at 2,000 to 3,000 mg / L, and even more preferably maintained at 1,000 to 2,000 mg / L. When the MLSS concentration increases, it becomes difficult to control the dissolved oxygen concentration, and in addition, the sludge predation behavior of aquatic earthworms is suppressed. Therefore, it is desirable that the upper limit of the MLSS concentration be 5,000 mg / L. When the MLSS concentration in the sludge treatment device 2 reaches a predetermined concentration, it is desirable to stop adjusting the MLSS concentration by returning excess sludge and circulate the aerated liquid in the activated sludge aeration tank 1.

[0026] The return amount of excess sludge from the sedimentation tank 3 to the treatment tank 12 via the excess sludge return line 4 can be adjusted by the excess sludge flow rate control device 23 shown in FIG. 2. Also, the introduction amount of the aerated liquid from the activated sludge aeration tank 1 to the treatment tank 12 of the sludge treatment device 2 via the aerated liquid transfer line 7 can be adjusted by the aerated liquid flow rate control device 24 shown in FIG. 2. The specific configurations of the excess sludge flow rate control device 23 and the aerated liquid flow rate control device 24 are not particularly limited, and for example, a variable speed pump, a flow control valve, or a combination thereof can be used.

[0027] When the concentration of dissolved organic matter remaining in the aerated liquid in the treatment tank 12 increases, the sludge predation behavior of aquatic earthworms is suppressed, which also affects the survival of aquatic earthworms. Therefore, it is necessary to manage an appropriate BOD (Biochemical Oxygen Demand) volume load and BOD-SS (Biochemical Oxygen Demand - Suspended Solids) load. Also, since the sludge treatment device 2 also serves as a secondary treatment of organic wastewater, it is preferable to adjust the organic matter load based on the total capacity of the two tanks, namely the sludge treatment device 2 and the activated sludge aeration tank 1. The specific BOD volume load of the total of the two tanks is preferably controlled to be 0.8 to 1.2 [kg / (m 3 ·d)], and more preferably 0.5 to 0.8 [kg / (m3 It is more preferable to set it as ·d)], and it is even more preferable to adjust it to 0.1 to 0.5 [kg / (m 3 ·d)].

[0028] Furthermore, the organic matter load with respect to the total amount of activated sludge in the two tanks of the sludge treatment device 2 and the activated sludge aeration tank 1 is preferably 0.4 to 0.7 [kg / (kg·d)] as the BOD-SS load, more preferably 0.2 to 0.4 [kg / (kg·d)], and even more preferably 0.1 to 0.2 [kg / (kg·d)].

[0029] The purpose of returning the excess sludge to the sludge treatment device 2 is to contribute to the concentration adjustment in the sludge treatment device 2 and the inoculum supply of the bacteria for denitrification. However, the excessive supply of the excess sludge compacted by sedimentation in the sedimentation tank 3 and made anaerobic limits the sludge predation of aquatic earthworms. Therefore, the concentration adjustment by the return of the excess sludge should be kept to the minimum necessary, and it is preferable to mainly introduce and circulate the aeration liquid.

[0030] The dissolved oxygen concentration in the treatment tank 12 of the sludge treatment device 2 controlled by the aeration device 15 adopting the surface aeration method is adjusted so that the dissolved oxygen concentration in the aeration liquid existing at a position lower than 10% of the height from the bottom 20 of the treatment tank 12 is 0.1 to 1 mg / L, the dissolved oxygen concentration in the aeration liquid existing within the range of 10 to 30% of the height from the bottom 20 of the treatment tank 12 is adjusted to 1 to 3 mg / L, and the dissolved oxygen concentration in the aeration liquid existing at a position higher than 30% of the height from the bottom 20 of the treatment tank 12 is adjusted to 3 mg / L or more. Such control of the dissolved oxygen concentration is possible by adopting the surface aeration method, and by providing a difference in the dissolved oxygen concentration in the height direction of the treatment tank 12, not only the nitrification of ammonia nitrogen remaining in the aeration liquid and the treatment of organic matter components but also nitrogen removal by denitrification can be achieved.

[0031] The nitrate nitrogen nitrified by the activated sludge aeration tank 1 and the sludge treatment device 2 is denitrified by the bacteria retained under anaerobic conditions at the bottom of the sludge, so nitrogen treatment is possible without providing a denitrification tank. It can be confirmed by the continuous water flow type treatment test described later that the denitrification by this anaerobic part favorably affects the retention of the bacteria contributing to denitrification due to the influence of the metabolites generated from the aquatic earthworms.

[0032] As an example of single-tank nitrification and denitrification, the oxidation ditch method is well-known, but it has drawbacks such as the need for a long reaction time and a large device capacity. Therefore, by adopting the aspect ratio of the bottom surface of the sludge treatment device 2 and the surface aeration method, the reaction capacity can be reduced to a small scale.

[0033] FIG. 3 is a front view of the sludge treatment device 2 shown in FIG. 2, and FIG. 4 is a cross-sectional view taken along line A-A of FIG. 3. The treatment tank 12 of the sludge treatment device 2 has a rectangular horizontal cross-section. The ratio of the short side D1 to the long side D2 of the horizontal cross-section of the treatment tank 12 is preferably 1:1.5 to 1:3.0, and more preferably 1:1.5 to 1:2.0.

[0034] The introduction amount of the aeration liquid introduced from the activated sludge aeration tank 1 into the treatment tank 12 of the sludge treatment device 2 is preferably 100 to 150% with respect to the inflow amount of the organic wastewater into the activated sludge aeration tank 1, and more preferably 50 to 100%. The return amount of the secondary aeration liquid returned from the treatment tank 12 of the sludge treatment device 2 to the activated sludge aeration tank 1 is preferably the same as the introduction amount of the aeration liquid introduced from the activated sludge aeration tank 1 into the treatment tank 12 of the sludge treatment device 2. Here, "the same" includes not only being completely the same, but also being substantially the same in consideration of minute fluctuations in the flow rate.

[0035] The HRT (hydraulic retention time) as the organic wastewater is preferably controlled by the total of the two tanks of the sludge treatment device 2 and the activated sludge aeration tank 1. In one embodiment, by setting the total HRT of the two tanks of the sludge treatment device 2 and the activated sludge aeration tank 1 to 25 to 40 hours, the culture of the aquatic earthworms is stabilized, and not only the sludge volume reduction effect due to the sludge predation of the aquatic earthworms but also the sludge volume reduction effect due to the autoxidation of the activated sludge can be obtained.

[0036] By observing the amount of aeration liquid introduced into the sludge treatment device 2, the HRT of the organic wastewater, and the ratio of the short side D1 to the long side D2 of the horizontal cross section of the treatment tank 12 of the sludge treatment device 2, and by adopting a surface aeration method in the sludge treatment device 2, aquatic earthworms can be cultured under a non-fixed bed without flowing out of the sludge treatment device 2, and nitrification and denitrification can be performed in a single treatment tank 12 with a small capacity.

[0037] The bottom 20 of the treatment tank 12 is in an anaerobic condition, and so there are concerns about the survival of aquatic earthworms, which are generally aerobic animals. However, it has been confirmed through testing that aquatic earthworms can survive even with a small concentration of dissolved oxygen, and can ingest the oxygen necessary for survival by moving to the top of the stagnant sludge as needed.

[0038] Oligochaeta of the phylum Annelida are small and have the habit of burrowing into crevices and settling. When culturing aquatic earthworms, this habit is often exploited by using fixed beds made of fibers or other materials. However, when collecting aquatic earthworms, it is difficult to separate them, which is an issue.

[0039] The sludge treatment device 2 of the present invention is characterized in that since aquatic earthworms can be cultured without a fixed bed, by providing a collection port 30 for collecting aquatic earthworms at the bottom 20 of the treatment tank 12 as shown in Figures 2 and 3, aquatic earthworms with high market value can be easily collected. An aquatic earthworm-containing sludge collection passage 31 is formed in the collection port 30. A port opening / closing valve 32 is attached to the collection port 30 as a port opening / closing means. When the port opening / closing valve 32 is opened, the aquatic earthworms in the treatment tank 12 are discharged outside the treatment tank 12 through the aquatic earthworm-containing sludge collection passage 31, and the cultured aquatic earthworms can be collected.

[0040] The extraction port 30 is connected to the bottom 20 of the treatment tank 12. The bottom 20 of the treatment tank 12 slopes downward toward the sludge extraction passage 31 containing aquatic earthworms. In order to efficiently extract the sludge containing aquatic earthworms, it is preferable to lower the bottom 20 at an angle of 10 to 20 degrees with respect to the horizontal plane. The installation location of the extraction port 30 is preferably below the air diffuser 15 which is the end point of the swirling flow of the aerated liquid.

[0041] The pH of the activated sludge aeration tank 1 and the sludge treatment device 2 is preferably maintained at 6.5 to 8.5, and more preferably maintained at 7.0 to 8.0. The temperature of the organic wastewater in the activated sludge aeration tank 1 is more preferably maintained at 20 to 25°C, and even more preferably maintained at 25 to 30°C. The temperature of the aerated liquid in the treatment tank 12 of the sludge treatment device 2 is preferably maintained at a temperature suitable for the survival and growth of aquatic earthworms. Specifically, it is preferably maintained at 22 to 25°C, and more preferably maintained at 20 to 22°C. By appropriately maintaining the temperature of the aerated liquid in the treatment tank 12, the spawning of aquatic earthworms is promoted and contributes to growth.

[0042] The secondary aerated liquid obtained by sludge treatment in the sludge treatment device 2 overflows from the treatment tank 12 over the overflow weir 17 and is returned to the activated sludge aeration tank 1 as shown in FIG. 2. The treated aerated liquid that has overflowed from the overflow weir (not shown) of the activated sludge aeration tank 1 is sent to the sedimentation tank 3 as a solid-liquid separation means. In the sedimentation tank 3, the activated sludge and water contained in the treated aerated liquid are separated. The separated water is discharged from the sedimentation tank 3 as treated water, and the separated activated sludge is returned to the sludge treatment device 2 and / or the activated sludge aeration tank 1 through the excess sludge return line 4 as excess sludge.

[0043] Next, the test results obtained using the treatment system will be described. Test Conditions (1) Continuous water flow type treatment test FIG. 5 shows the test conditions of the examples and comparative examples. As an example, using the treatment system of FIG. 1 equipped with the sludge treatment device 2 shown in FIG. 2, continuous water flow was carried out with organic wastewater from the beverage system as a test water, and the volume reduction effect of excess sludge by aquatic earthworms and the quality of the treated water were examined. As the aquatic earthworms, the easily handled Itoh earthworms were used. The same kind of Yuri earthworms or Era earthworms may also be used. The introduced amount of the aquatic earthworms introduced into the treatment tank 12 of the sludge treatment device 2 with a volume of 2.6 L was 15 ml in bulk volume.

[0044] In the comparative example, a continuous water flow treatment test was carried out without introducing aquatic earthworms under the same operating conditions as in the example. The device part corresponding to the sludge treatment device 2 adopted the surface aeration method as in the example, and the test was carried out with an equivalent capacity, but a device with a different shape from the sludge treatment device 2 of the present invention was used. The conditions of the total tank BOD volume load, the total tank BOD-SS load, the introduced amount of the aerated liquid, and the return amount of the excess sludge in the comparative example were the same as those in the example. In addition, in both the example and the comparative example, the test period was divided into Tests 1 to 4 for the test.

[0045] For the examination of the sludge volume reduction effect by aquatic earthworms, in Tests 1 to 3, the return of excess sludge was only to the activated sludge aeration tank 1, and only the aerated liquid was introduced into the sludge treatment device 2. The total tank BOD volume load in Test 1, which is the startup period, started from 0.52 kg / (m 3 ·d), and the load was increased step by step. In Test 3, which is the maximum load, the load was increased to 1.30 kg / (m 3 ·d) to examine the sludge volume reduction effect by aquatic earthworms and the quality of the treated water. The total tank BOD-SS load was 0.22 - 0.26 kg / (kg·d) in Tests 1 and 2, and 0.33 kg / (kg·d) in Test 3 due to the high load.

[0046] In Test 4, for the purpose of examining the denitrification effect, after appropriately adjusting the sludge concentration of the sludge treatment device 2 by returning the excess sludge, the aerated liquid in the activated sludge aeration tank 1 was returned to the sludge treatment device 2. The total tank BOD volume load in Test 4 was 0.5 kg / (m 3 ·d), which is almost the same as that in Test 1. The total tank BOD-SS load was 0.25 kg / (BOD-SS·d).

[0047] Since the organic wastewater did not contain nitrogen (N) and phosphorus (P) as nutrients required for biological treatment, NH4Cl reagent and KH2PO4 reagent were used to appropriately adjust the weight ratio to BOD:N:P = 100:5:1. The evaluation of each item of the treated water was carried out in accordance with the sewage test method.

[0048] The evaluation of sludge volume reduction was carried out by the BOD sludge conversion rate, which is the ratio of excess sludge generated to the removal amount of BOD input during each test period. The BOD sludge conversion rate of the general standard activated sludge method is said to be 0.3 - 0.7.

[0049] Continuous water flow type treatment test results The test results are shown in Figs. 6 and 7. Also, the examination results of the sludge volume reduction effect are shown in Fig. 8. The SS in the treated water of Test 1 and Test 2 generally ranged from about 5 to 26 mg / L in both the examples and the comparative examples. Due to the increase in load, the soluble CODcr in the comparative example increased to 112 mg / L, but as the test progressed, the treatment became stable and ranged from 21 to 50 mg / L. On the other hand, in the examples, no deterioration of treatment due to the increase in load was observed, and the soluble CODcr ranged from 26 to 55 mg / L. The soluble BOD was 1 - 8 mg / L in the comparative example and 3 - 6 mg / L in the examples, indicating good BOD removal by biological treatment. The BOD sludge conversion rate of Test 1 was 0.37 in the comparative example and 0.16 in the examples.

[0050] The BOD sludge conversion rate of Test 2 was 0.44 in the comparative example and 0.32 in the examples. Although the sludge volume reduction effect was reduced compared to Test 1, the sludge volume reduction effect due to sludge predation by aquatic earthworms was recognized. In Test 3, which was the maximum load, an increase was observed in the SS in the treated water. The SS in the treated water of the examples increased to a maximum of 43 mg / L, and in the comparative example, it increased to 29 mg / L. Similar trends were also observed for soluble CODcr and soluble BOD. The soluble CODcr in the comparative example increased to 92 mg / L, and the soluble BOD increased to 26 mg / L. The soluble CODcr in the examples increased to 128 mg / L, and the soluble BOD increased to 24 mg / L.

[0051] In Test 3, the BOD sludge conversion rate was 0.30 in the comparative example and 0.31 in the example. In addition to the fact that the sludge volume reduction effect by the aquatic earthworms was not obtained, the water quality of the treated water also deteriorated. Therefore, it is considered that operation with an appropriate organic load is necessary. In Test 4, due to the influence of the load reduction, the SS in the treated water of both the comparative example and the example decreased. Also, the dissolved CODcr of the treated water ranged from 16 to 24 mg / L in both the comparative example and the example, and an improvement in the water quality of the treated water was observed. The dissolved BOD of the treated water ranged from 1 to 4 mg / L in both the comparative example and the example, and the stability of biological treatment was confirmed.

[0052] In addition, the BOD sludge conversion rate was 0.20 in the comparative example and 0.09 in the example, and the sludge volume reduction effect by the aquatic earthworms was recognized. Also, while the NH4-N of the organic wastewater in Test 4 was 17.4 to 24.4 mg / L, the NH4-N of the sludge treatment apparatus 2 was 0.1 to 1.7 mg / L in the comparative example and 0.1 to 5.9 mg / L in the example. Although some residual NH4-N was observed, the nitrification reaction was confirmed. Also, on the 18th and 19th days from the start of Test 4, the NO X -N of the sludge treatment apparatus 2 remained at 13.3 to 17.4 mg / L in the comparative example, while it was 0.25 to 0.35 mg / L in the example, and almost no residual NO X -N was observed. From the above, it was confirmed that according to the present invention, while obtaining the sludge volume reduction effect by the sludge predation of the aquatic earthworms, nitrogen removal by nitrification and denitrification is possible.

[0053] The above-described embodiments are described for the purpose of enabling those with ordinary knowledge in the technical field to which the present invention pertains to implement the present invention. Various modifications of the above embodiments can be naturally made by those skilled in the art, and the technical idea of the present invention can also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is interpreted in the broadest range in accordance with the technical idea defined by the claims.

Explanation of Reference Numerals

[0054] 1 Activated sludge aeration tank 2 Sludge treatment apparatus 3 Shen Dianchi 4 Excess sludge return line 7 Aerated liquid transfer line 8 Secondary aerated liquid transfer line 9 Treated aerated liquid transfer line 12 Treatment tank 15 Diffuser 17 Overflow weir 18 Vertical wall 20 Bottom 23 Excess sludge flow control device 24 Aerated liquid flow control device 30 Sampling port 31 Aquatic earthworm-containing sludge sampling passage 32 Port opening and closing valve

Claims

1. A means of aerating activated sludge for biological treatment of organic wastewater, A sludge treatment means having a treatment tank for holding aquatic earthworms that feed on sludge in the aerated liquid obtained by the biological treatment, The activated sludge aeration means and the sludge treatment means provide a solid-liquid separation treatment means for performing solid-liquid separation on the treated aerated liquid obtained from the sludge treatment means, An organic wastewater treatment system characterized by comprising an excess sludge return line for returning excess sludge obtained in the solid-liquid separation treatment to the sludge treatment means or the activated sludge aeration means.

2. The organic wastewater treatment system according to claim 1, characterized in that the sludge treatment means includes a surface aeration device.

3. The treatment system for organic wastewater according to claim 1, characterized in that the treatment tank has a rectangular horizontal cross-section, and the ratio of the short side to the long side of the rectangular horizontal cross-section is 1:1.5 to 1:3.

0.

4. The sludge treatment means comprises a collection port in which a passage for collecting sludge containing aquatic earthworms is formed, and a port opening and closing means attached to the collection port. The organic wastewater treatment system according to claim 1, characterized in that the sampling port is connected to the bottom of the treatment tank.

5. The organic wastewater treatment system according to claim 1, characterized in that the sludge concentration in the treatment tank is adjusted to 1,000 to 5,000 mg / L using the excess sludge.

6. The organic wastewater treatment system according to claim 1, characterized in that the amount of aeration liquid introduced from the activated sludge aeration means to the sludge treatment means is adjusted to 50 to 150% of the amount of organic wastewater flowing into the activated sludge aeration means, and the amount of secondary aeration liquid returned from the sludge treatment means to the activated sludge aeration means is the same as the amount of aeration liquid introduced from the activated sludge aeration means to the sludge treatment means.

7. Organic wastewater is introduced into an activated sludge aeration means, and the organic wastewater is biologically treated by the activated sludge aeration means. The aerated liquid obtained by the biological treatment is introduced into the treatment tank of the sludge treatment means, and the sludge in the aerated liquid is consumed by aquatic earthworms in the treatment tank. The treated aerated liquid obtained from the activated sludge aeration means and the sludge treatment means is led to a solid-liquid separation treatment means for solid-liquid separation treatment. A method for treating organic wastewater, characterized in that the excess sludge obtained in the solid-liquid separation treatment is returned to the sludge treatment means or the activated sludge aeration means.

8. The method for treating organic wastewater according to claim 7, characterized in that the sludge concentration in the treatment tank is adjusted to 1,000 to 5,000 mg / L using the excess sludge.

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