Sludge flotation inhibitor, treatment method for organic wastewater, and treatment apparatus for organic wastewater

Abstract

To provide a sludge flotation inhibitor capable of efficiently suppressing sludge flotation in a treatment tank that may occur during a biological treatment process of organic wastewater with a simple configuration, as well as a treatment method and a treatment apparatus for organic wastewater.SOLUTION: A sludge flotation inhibitor 100 is composed of a fiber compact 10 including recycled fibers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sludge floating inhibitor, a method for treating organic wastewater, and an apparatus for treating organic wastewater, and in particular to a sludge floating inhibitor for preventing sludge from floating up in a settling tank in the biological treatment of organic wastewater, and a method for treating organic wastewater and an apparatus for treating organic wastewater using the same. [Background technology]

[0002] Organic wastewater containing organic matter and nitrogen, such as sewage, human waste, and industrial wastewater, is mixed with return sludge returned from a settling tank in a biological treatment tank, and the BOD in the organic wastewater is removed by aerobic biodegradation using air supplied from the bottom of the biological treatment tank. The biologically treated water flowing out of the biological treatment tank is separated into sludge and treated water in the settling tank, with some sludge being used as return sludge and the remaining sludge being treated as excess sludge. The treated water is either discharged into public waters or further treated for reuse.

[0003] In biological treatment of organic wastewater that does not include a nitrification / denitrification process, for example, when the organic wastewater contains ammonia nitrogen and organic nitrogen along with BOD, nitrification can occur if the BOD sludge load in the biological treatment tank becomes low. This nitrification produces nitrate ions (hereinafter also referred to as "nitrate nitrogen") and nitrite ions (hereinafter also referred to as "nitrite nitrogen") from the ammonia nitrogen and organic nitrogen in the organic wastewater.

[0004] When biologically treated water containing such nitrate and nitrite nitrogen is subjected to solid-liquid separation in a solid-liquid separation tank such as a settling tank, if the sludge in the settling tank becomes anoxic, nitrogen gas bubbles are generated, and the generated nitrogen gas adheres to the sludge, causing the sludge to float to the surface.If the sludge that has floated to the surface in the settling tank flows out of the tank, treated water containing SS caused by the floating sludge will be discharged from the settling tank, which may result in the discharge standard values for suspended solids (SS) and chemical oxygen demand (COD) not being met.

[0005] One method for suppressing sludge floating is to add a nitrification inhibitor to a biological treatment tank to suppress nitrification, which causes denitrification. For example, Japanese Patent Laid-Open Publication No. 5-337489 (Patent Document 1) describes a method in which a chemical such as thiourea or allylthiourea is added to an activated sludge treatment device having a settling tank to suppress the nitrification reaction of nitrogen compounds, thereby preventing activated sludge from floating up due to nitrification and denitrification in the settling tank. Other methods for suppressing sludge floating include denitrifying nitrate nitrogen and nitrite nitrogen produced by nitrification by adding a hydrogen donor such as methanol, and suppressing nitrification through operational management such as adjusting the aeration air volume and SRT. For example, Japanese Patent Laid-Open Publication No. 2000-334492 (Patent Document 2) describes the use of a denitrification promoter in which a linear saturated monocarboxylic acid having six or more carbon atoms is supported on a support. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-337489 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-334492 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the method of suppressing nitrification by adding chemicals such as thiourea or allylthiourea as described in Patent Document 1, the nitrification inhibitor is decomposed in activated sludge, so the nitrification inhibitor effect may not last long. To maintain a certain level of nitrification inhibitor effect, it is necessary to continuously add the chemicals, but this poses problems such as the complexity of chemical management and increased chemical costs.

[0008] As described in Patent Document 2, a denitrification accelerator containing granules containing a denitrification accelerator in a bag-shaped nonwoven fabric uses granules with a diameter of about 2 mm, but when a denitrification accelerator with such small particle diameter is used, the water may not be sufficiently passed through the granules, resulting in uneven flow where only some of the granules come into contact with the water to be treated, or clogging may occur between the granules in activated sludge, etc. If the particle diameter of the granules is large, the surface area is correspondingly smaller, resulting in a decrease in denitrification performance and insufficient effect of suppressing sludge floating.

[0009] In view of the above problems, the present invention provides a sludge floating inhibitor that can efficiently suppress the floating of sludge in a treatment tank, which can occur during the biological treatment of organic wastewater, with a simple configuration, a method for treating organic wastewater, and an apparatus for treating organic wastewater. [Means for solving the problem]

[0010] As a result of intensive research into solving the above problems, the inventors discovered that it would be useful to use a sludge floating inhibitor composed of a fibrous material, i.e., a fiber molded body made by molding recycled fibers into a certain shape.

[0011] In order to solve the above problems, one aspect of the present invention is a sludge floating inhibitor comprising a fibrous molded body containing recycled fibers.

[0012] In one embodiment of the sludge floating inhibitor according to the present invention, the recycled fibers contain rayon fibers having a fiber diameter of 100 μm or less.

[0013] In another embodiment of the sludge floating inhibitor according to the present invention, the fibrous molded article comprises a support for supporting the recycled fibers.

[0014] In yet another embodiment of the sludge floating inhibitor of the present invention, the fiber molding has any one of the following shapes: rectangular, cubic, cylindrical, columnar, block, plate, membrane, lattice, or string-like shape formed by bundling both ends of recycled fibers.

[0015] In another aspect, the present invention provides a method for treating organic wastewater, comprising subjecting organic wastewater to activated sludge treatment in a biological treatment tank containing a sludge floatation inhibitor composed of a fibrous molded body containing recycled fibers, agitating the organic wastewater in the biological treatment tank to bring it into contact with the sludge floatation inhibitor, and then performing solid-liquid separation of the biologically treated water obtained by the activated sludge treatment.

[0016] In one embodiment of the method for treating organic wastewater according to the present invention, a nitrification inhibitor for inhibiting nitrification of the organic wastewater is further added to the biological treatment tank.

[0017] In yet another aspect, the present invention provides an organic wastewater treatment device comprising: a biological treatment means for treating organic wastewater with activated sludge; a sludge floating prevention means disposed within the biological treatment means and made of a fiber molding containing recycled fibers; an agitation means for agitating the activated sludge mixed liquid within the biological treatment means and bringing the activated sludge mixed liquid into contact with the sludge floating prevention means; and a settling means for separating the biologically treated water treated in the biological treatment means into solid and liquid.

[0018] In one embodiment, the organic wastewater treatment device according to the present invention further comprises a nitrification inhibitor adding means for adding a nitrification inhibitor that inhibits nitrification of the organic wastewater into the biological treatment means.

[0019] In another embodiment of the organic wastewater treatment device according to the present invention, the biological treatment means includes a first biological treatment means that performs a first biological treatment on the organic wastewater, and a second biological treatment means that biologically treats the organic wastewater treated by the first biological treatment means with a lower BOD sludge load than the first biological treatment, and the sludge floating prevention means is disposed in the second biological treatment means.

[0020] In yet another embodiment, the organic wastewater treatment device according to the present invention is a device for treating organic wastewater, wherein the biological treatment means is composed of a plurality of biological treatment means or a biological treatment means obtained by dividing one biological treatment means into a plurality of biological treatment means, and the sludge floating prevention means is disposed at least in the rear half of the biological treatment means. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a sludge floating inhibitor, a method for treating organic wastewater, and an apparatus for treating organic wastewater that can efficiently suppress the floating of sludge in a settling tank with a simple configuration, which can occur during the biological treatment of organic wastewater. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an explanatory diagram showing one embodiment of a sludge floating inhibitor according to an embodiment of the present invention. [Figure 2] 1 is a photograph showing an example of a regenerated fiber according to an embodiment of the present invention. [Figure 3] 1 is an explanatory diagram showing one embodiment of a sludge floating inhibitor according to an embodiment of the present invention. [Figure 4] 1 is a schematic diagram showing an example of an organic wastewater treatment method and an organic wastewater treatment device according to an embodiment of the present invention. [Figure 5] 1 is a schematic diagram showing an example of the configuration of a biological treatment tank according to an embodiment of the present invention. [Figure 6] FIG. 10 is a schematic diagram showing an example of a method for treating organic wastewater and an apparatus for treating organic wastewater according to a modified example of an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. Note that the embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of component parts to those described below.

[0024] (Sludge floating inhibitor) The sludge floating inhibitor according to the embodiment of the present invention can be suitably used to inhibit sludge floating in a settling tank in a biological treatment process for organic wastewater, which is composed of a biological treatment tank and a settling tank, and can particularly inhibit the floating of sludge that adheres to nitrogen gas, etc., generated in the biological treatment process for organic wastewater. The organic wastewater to which the sludge floating inhibitor can be applied is not particularly limited as long as it contains at least organic matter and nitrogen, and can be applied to various types of wastewater, such as sewage, human waste, industrial wastewater, river water, and groundwater.

[0025] Suitable organic wastewater has an SS of 10 to 500 mg / L, more typically 150 to 500 mg / L, and a nitrogen concentration of typically 5 to 50 mg / L, more typically 10 to 50 mg / L, and even more typically 20 to 50 mg / L. The nitrogen concentration of organic wastewater refers to the total concentration of ammoniacal nitrogen, nitrate nitrogen, and nitrite nitrogen, which cause nitrogen gas to be generated in the organic wastewater.

[0026] The sludge floating inhibitor 100 is composed of a fiber molding containing recycled fibers. Because recycled fibers are biodegradable, they can reduce the burden on the external environment compared to when chemicals are used. In addition, because recycled fibers are hydrophilic, they easily blend with organic wastewater and sludge, and can adsorb sludge floating in organic wastewater for a long period of time. Therefore, the sludge floating inhibitor 100 using recycled fibers can maintain its sludge floating inhibition effect for a longer period of time compared to when chemicals are used.

[0027] Suitable regenerated fibers include regenerated cellulose fibers such as rayon, polynosic, cupra, lyocell, etc. Examples of regenerated cellulose fibers include regenerated artificial fibers such as viscose rayon fiber and cupra rayon fiber, which have cellulose as the base polymer, and semi-synthetic regenerated fibers such as cellulose diacetate fiber and cellulose triacetate fiber.

[0028] Among these, viscose rayon fibers have multiple striae in the fiber direction and an irregular petal-like cross-sectional outline, which gives them a larger surface area than fibers with a smooth surface. Viscose rayon fibers are also particularly preferable as the regenerated fibers 11 used in this embodiment because they drain water easily and are easy to handle.

[0029] Recycled fibers are preferably fine fibers with a fiber diameter of 100 μm or less, which allows them to flow more easily in liquid than granular simple substances and increases contact efficiency. The fiber diameter is more preferably 80 μm or less, and even more preferably 50 μm or less. There is no particular lower limit for the fiber diameter, but from the viewpoint of handleability, 0.1 μm or more is preferred, and 1 μm or more is more preferred. There is no limit to the fiber length of the recycled fibers, but typically, short recycled fibers with a fiber length of 30 mm or less, or even 10 mm or less, can be used. Note that, as will be described later, depending on the shape of the fiber molded product, recycled fibers with a fiber length of more than 30 mm, or even more than 100 mm, or even more than 500 mm can also be used.

[0030] The fiber length of the recycled fibers refers to the average value of the maximum lengths of five fibers extracted from any position of the fiber molding that constitutes the sludge floating inhibitor 100. Similarly, the fiber diameter of the recycled fibers 11 refers to the average value of the maximum cross-sectional diameters of five fibers extracted from any position of the fiber molding that constitutes the sludge floating inhibitor 100. The fiber length and fiber diameter of the recycled fibers 11 can be measured, for example, by observing the fibers using a tabletop scanning electron microscope (Miniscope (registered trademark) TM3000, manufactured by Hitachi High-Technologies Corporation).

[0031] Although not limited to the following, the recycled fibers preferably have a moisture content of 30 to 80% by weight, more preferably 40 to 70% by weight. If the moisture content is 30% by weight or less, the hydrophilicity to sludge decreases, and it may take time for the recycled fibers to become familiar with the sludge. If the moisture content exceeds 80% by weight, the amount of moisture becomes too high, and the fiber content of the recycled fibers may not contribute to adsorption to the sludge, so it is necessary to add a larger amount of recycled fibers.

[0032] Known methods can be used to adjust the moisture content of the regenerated fibers. For example, the moisture content may be adjusted by spraying water onto the regenerated fibers. When the regenerated fibers are produced by a wet spinning method, the moisture content may be adjusted by washing with a solvent, forming the fibers into a fiber molded product of a predetermined shape, and then squeezing or drying the fibers.

[0033] If recycled fibers are directly introduced into a biological treatment tank and used as a sludge floating inhibitor 100, there is a risk that they will be mixed into the treated water flowing out of the biological treatment tank. Furthermore, in the treatment tank that further treats the biologically treated water containing recycled fibers, the recycled fibers may adhere to various devices, causing blockage of the devices. The sludge floating inhibitor 100 of this embodiment is composed of a fiber molded body 10 formed from recycled fibers into a specific shape. Therefore, it is possible to efficiently suppress the floating of sludge in the biological treatment tank for a long period of time with a simple configuration while suppressing the outflow of recycled fibers from the biological treatment tank.

[0034] There are no particular limitations on the specific shape of the fiber molded product 10. For example, the fiber molded product 10 may be in a variety of shapes, such as a rectangular parallelepiped, cube, cylinder, column, block (meaning an irregular mass), plate, film (including nonwoven fabric, felt, etc.), lattice, or string-like shape formed by bundling both ends of recycled fibers.

[0035] For example, as shown in Figures 1(a) to 1(d), a fiber molded product 10 preferably includes recycled fibers 11a, 11b, 11c, and 11d, and supports 12a, 12b, 12c, 12d, 13a, and 13d that support the recycled fibers 11a, 11b, 11c, and 11d.

[0036] The example shown in Figure 1(a) shows a sludge floating inhibitor 100 in which bulky recycled fibers 11a (see Figure 2) having a fiber length of 30 mm or less, more preferably 10 mm or less, are sandwiched between opposing first and second supports 12a and 13a to form a fibrous molded product 10. The first and second supports 12a and 13a can be, for example, wire mesh or porous plates made of synthetic resin or ceramic. The materials of the first and second supports 12a and 13a may be the same or different.

[0037] For example, in a biological treatment tank, the side on which the regenerated fiber 11a is most likely to be loaded, such as the side on which the first support 12a is disposed, is made of a relatively strong material, while the other side on which the second support 13a is disposed is made of an inexpensive material that is weaker in strength than the first support 12a. This makes it possible to provide a sludge floating inhibitor 100 that is strong and can withstand long-term use.

[0038] To improve contact between the fibrous molded body 10 and the organic wastewater, it is preferable that the top and bottom of the fibrous molded body 10 have an open structure. However, to more effectively prevent the regenerated fibers 11a from flowing out of the biological treatment tank, supports (not shown) may also be placed at the bottom and top of the fibrous molded body 10.

[0039] Bulk recycled fibers 11a (see Figure 2) made of short fibers with a fiber length of 30 mm or less, more preferably 10 mm or less, disperse and float within the biological treatment tank when introduced directly into the biological treatment tank, potentially resulting in outflow of treated water or clogging of equipment in the treatment tank downstream of the biological treatment tank. On the other hand, if the recycled fibers are placed in a bag such as a nonwoven fabric, they may clog the bag. As shown in Figure 1(a), the sludge floating inhibitor 100 of the present invention is composed of a fibrous molded body 10 having supports 12a and 13a supporting the recycled fibers 11a. This prevents the recycled fibers 11a from leaking out of the biological treatment tank, increases contact between the recycled fibers 11a and the organic wastewater, and allows them to adsorb nitrogen gas generated within the biological treatment tank, enabling stable denitrification treatment to continue for a long period of time.

[0040] The example shown in Figure 1(b) shows an example of a fiber molded product 10 having a configuration in which a molded body of recycled fiber 11b, which has been previously formed into a membrane (nonwoven fabric or felt), is stacked in the thickness direction and supported by a support body 12b consisting of a wire mesh, a perforated plate, a support pillar, etc.

[0041] In the configuration shown in FIG. 1(b), the recycled fibers 11b are formed into a predetermined shape and then fixed to the support 12b. Therefore, compared to the configuration shown in FIG. 1(a), the amount of bulk recycled fibers 11a (short fibers) that flow out of the biological treatment tank is reduced, and handling is also improved. In the configuration shown in FIG. 1(b), the supports 12b are arranged parallel to each other in the longitudinal direction, but this configuration is not limited to this. Furthermore, the recycled fibers 11b can be formed into any shape, such as a membrane, plate, rectangular parallelepiped, or columnar, and stacked in the thickness direction to obtain the sludge floating inhibitor 100 shown in FIG. 1(b). To further enhance contact between the recycled fibers 11b and the organic wastewater, the recycled fibers 11b may be wrapped around the support 12b in the longitudinal direction.

[0042] The example shown in Figure 1(c) shows a fiber molded product 10 having a structure in which a columnar support 12c is fixed to the inner surface of recycled fiber 11c, which is obtained by forming a nonwoven fabric or felt-like material into multiple layers and then laminating them into a cylindrical shape. The radial thickness of recycled fiber 11c is not particularly limited, but can be, for example, 1 to 50 mm, or even 10 to 50 mm. In the example of Figure 1(c), a structure in which recycled fiber 11c is wound around the outer surface of support 12c is shown, but recycled fiber 11c may also be fixed to the inner surface of support 12c.

[0043] The example shown in FIG. 1(d) is a string-like fiber molding 10 in which both ends of recycled fibers 11d are bundled. This fiber molding 10 is made by fixing both ends of recycled fibers 11d, which have a fiber length of more than 500 mm, with supports 12d and 13d made of fixing devices such as metal plates or cable ties. The fixing devices 12d and 13d function to prevent the recycled fibers 11d from dispersing in the biological treatment tank, and the material and fixing method are optional. The number of recycled fibers 11d can also be determined arbitrarily. Of course, the fiber length of the recycled fibers 11d can also be adjusted appropriately to suit the dimensions and treatment capacity of the biological treatment tank in which they are to be housed.

[0044] When placed in a biological treatment tank containing organic wastewater, the ratio of the longitudinal length (vertical direction in the plane of the drawing) of the fiber molding 10 shown in FIG. 1(d) to the maximum lateral length (horizontal direction in the plane of the drawing) can be any ratio, but it is preferable that the longitudinal length is greater than the lateral length and that the longitudinal length / lateral length ratio is 2 to 5. If the longitudinal length / lateral length ratio is less than 2, sludge may accumulate in the recycled fibers 11d with use, resulting in a decrease in treatment performance. If the longitudinal length / lateral length ratio is more than 5, the contact efficiency between the recycled fibers 11d and the organic wastewater may decrease.

[0045] As shown in Figure 3(a), it is more preferable that the sludge floating inhibitor 100 is fixed to a stand 15 for installing the fiber molding 10 in the biological treatment tank. After use of the sludge floating inhibitor 100 has been completed, the stand 15 containing the sludge floating inhibitor 100 can be lifted from the biological treatment tank to the water surface for replacement, facilitating replacement. There is no limit to the number of stands 15, and two stands 15 may be used as long as replacement work is not hindered, and the stand 15 may be rod-shaped or rail-shaped.

[0046] The stand 15 allows the fiber moldings 10 to withstand water currents caused by aeration and other factors in the biological treatment tank and allows for easy replacement from the top of the tank; installation of the stand 15 within the biological treatment tank is optional. By further fixing the stand 15 to the fiber moldings 10, the fiber moldings 10 can be stably positioned in the biological treatment tank so that they are always approximately perpendicular to the direction of the wastewater flow. There is no limit to the number of fiber moldings 10 that can be fixed to the stand 15. For example, as shown in Figure 3(b), multiple fiber moldings 10 can be fixed to the stand 15 at regular intervals.

[0047] The filling rate of the sludge floatation inhibitor 100 in the biological treatment tank is preferably 5% by volume or more and less than 40% by volume per effective water volume of the biological treatment tank. A filling rate of less than 5% by volume may result in insufficient denitrification performance due to low contact efficiency between the sludge floatation inhibitor 100 and the organic wastewater. A filling rate of more than 40% by volume may result in uneven flow of the organic wastewater or increased clogging of the sludge floatation inhibitor 100. The filling rate of the sludge floatation inhibitor 100 in this embodiment refers to the effective area of the biological treatment tank (the amount of water held in the biological treatment tank) relative to the volume of the fiber molded body 10 containing recycled fibers (excluding the stand 15). This can be expressed as [filling rate of the sludge floatation inhibitor 100 (fiber molded body 10)] = [volume of the fiber molded body 10 including fiber spaces] ÷ [effective volume of the biological treatment tank (the amount of water held in the biological treatment tank)] × 100. The filling rate of the sludge floating inhibitor 100 is preferably 7 to 35% by volume, more preferably 10 to 30% by volume, per available water volume of the biological treatment tank.

[0048] Furthermore, if the volume of recycled fibers filled in the fibrous molding 10 used as the sludge floating inhibitor 100 is too small, the area occupied by the fiber spaces in the fibrous molding 10 will be small, and denitrification performance may not be significantly improved. Although not limited to the following, the volume of recycled fibers contained in the fibrous molding 10 can be, for example, 30 to 100% by volume, more preferably 50 to 95% by volume, of the volume of the fibrous molding 10.

[0049] In addition to its denitrification properties, the fibrous molded article 10 can also be used as a microbial carrier. While supplying return sludge to the biological treatment tank is generally necessary during initial startup, once biological treatment has stabilized and steady-state operation is achieved, stable treatment can be achieved over a long period of time while maintaining a low MLSS concentration (activated sludge concentration) in the biological treatment tank, even if the return sludge flow rate is reduced compared to conventional methods. Furthermore, by keeping the MLSS concentration low in the biological treatment tank, the BOD sludge load in the biological treatment tank is increased to above 0.1 kg / kg-MLSS-day, which also has the effect of suppressing nitrification in the biological treatment tank.

[0050] The sludge floating inhibitor 100 according to the embodiment of the present invention includes a fibrous molding 10 containing recycled fibers 11, and therefore can increase contact with organic wastewater while preventing the fibrous molding 10 from flowing out of the biological treatment tank. This allows for efficient suppression of sludge floating, which is a problem in solid-liquid separation tanks such as settling tanks downstream of the biological treatment tank, with a simple configuration.

[0051] (Organic wastewater treatment method) An example of a treatment flow for organic wastewater that can use a sludge floatation inhibitor according to an embodiment of the present invention is shown in Figure 4. In the method for treating organic wastewater according to an embodiment of the present invention, the organic wastewater is subjected to activated sludge treatment in a biological treatment tank 1 that contains a sludge floatation inhibitor 100 composed of a fibrous molded body 10 containing recycled fibers, and the organic wastewater in the biological treatment tank 1 is agitated to contact the sludge floatation inhibitor 100. After that, the biologically treated water obtained by biological treatment such as activated sludge treatment is subjected to solid-liquid separation. A portion of the separated sludge obtained by solid-liquid separation is returned to the biological treatment tank 1 via return line 3 as returned sludge, and the remaining separated sludge is subjected to sludge treatment.

[0052] The biological treatment tank 1 is a treatment tank in which organic wastewater is biologically treated under aerobic conditions. In the biological treatment tank 1, biological treatment using, for example, the activated sludge method is preferably carried out. The organic wastewater introduced into the biological treatment tank 1 is mixed with returned sludge returned from the settling tank 2 in the biological treatment tank 1, producing an activated sludge mixed liquor. The dissolved oxygen (DO) from the air supplied from the bottom of the biological treatment tank 1 preferably biodegrades the BOD in the activated sludge mixed liquor, and the BOD is removed.

[0053] As shown in Figure 5, the biological treatment tank 1 is connected to an agitation means 20 that agitates the activated sludge mixed liquor in the biological treatment tank 1. The agitation means 20 is provided for the purposes of agitating the biological treatment tank 1 and improving contact between the activated sludge mixed liquor and the sludge floating inhibitor 100. A mechanical agitator such as an agitator blade or a pump agitator is used as the agitation means 20, but from the perspective of simplifying the equipment, it is preferable to use an agitation device that is equipped with an aeration tube and a blower that sends air to the aeration tube, which is capable of simultaneously agitating the biological treatment tank 1 and supplying air to the biological treatment tank 1.

[0054] A DO meter 30 is disposed in the biological treatment tank 1 to measure the DO of the activated sludge mixed liquor in the biological treatment tank 1. The DO meter 30 may be a commercially available diaphragm type or a fluorescent type. Multiple DO meters 30 may be installed in the biological treatment tank 1 horizontally or in the water depth direction. The DO of the activated sludge mixed liquor in the biological treatment tank 1 may be measured sequentially by removing the activated sludge mixed liquor from the biological treatment tank 1 using a pump or the like. In the case of an agitation means 20 that supplies air, it is preferable that the amount of air supplied is controlled based on the measurement results of the DO meter 30 so that the biological treatment tank 1 maintains a predetermined DO concentration.

[0055] A sludge floating inhibitor 100 equipped with a fiber molding 10 is disposed above the agitation means 20. By disposing the sludge floating inhibitor 100 directly above the agitation means 20 and supplying air from the agitation means 20, contact between the fiber molding 10 provided in the sludge floating inhibitor 100 and the activated sludge mixed liquid can be improved, further improving denitrification performance. In addition, by introducing air from the bottom of the fiber molding 10 to generate an upward airflow toward the fiber molding 10 and causing contact, clogging of the fiber molding 10 with sludge can be suppressed. As a result, stable denitrification performance can be achieved over a long period of time.

[0056] Although not limited to the following, it is preferable to adjust the amount of air introduced into the biological treatment tank 1 so that the DO concentration in the biological treatment tank 1 is, for example, 0.2 to 1.0 mg / L.

[0057] There are no particular limitations on the number or location of the fiber moldings 10. For example, by arranging the fiber moldings 10 so that the spacing (shortest distance) between each other is about 20 to 200 mm, more preferably about 30 to 100 mm, the contact between each fiber molding 10 and the activated sludge mixed liquid can be improved while maintaining the desired denitrification performance and improving the effect of preventing the sludge from floating up.

[0058] When the BOD sludge load in the biological treatment tank 1 exceeds 0.1 kg / kg-MLSS-day, the problem of sludge floating due to nitrification is not a major issue. However, when the BOD sludge load is 0.1 kg / kg-MLSS-day or less, nitrification may occur in the biological treatment tank 1. When nitrification occurs, nitrate nitrogen and nitrite nitrogen are generated from the organic nitrogen contained in the organic wastewater. When the biologically treated water containing this nitrate nitrogen and nitrite nitrogen is supplied to the settling tank 2 described below and an anoxic state is created in the settling tank 2, denitrification occurs, generating nitrogen gas bubbles. The generated nitrogen gas can cause sludge to adhere to the sludge and float up. Therefore, the sludge floating inhibitor according to the embodiment of the present invention is particularly suitable for a biological treatment tank 1 with a BOD sludge load of 0.1 kg / kg-MLSS-day or less.

[0059] The nitrogen concentration of the organic wastewater introduced into the biological treatment tank 1 is not particularly limited. However, for example, in a treatment apparatus equipped with a biological treatment tank 1 and a settling tank 2, as shown in FIG. 4, it is preferable to use organic wastewater with a nitrogen concentration of, for example, 5 to 50 mg / L, preferably 10 to 50 mg / L, or even 20 to 50 mg / L. This is because even if the nitrogen concentration is 50 mg / L or less, if the BOD sludge load in the biological treatment tank 1 is low, the activated sludge may be broken down, producing ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen, which may then be nitrified. According to the organic wastewater treatment method of the embodiment of the present invention, in an organic wastewater treatment apparatus equipped with a biological treatment tank 1 and a settling tank 2, organic wastewater with a nitrogen concentration of 50 mg / L or less is introduced into the biological treatment tank 1, and a fibrous molded body 10 is placed therein to perform biological treatment, thereby efficiently preventing sludge floating in the settling tank 2 for a long period of time.

[0060] As shown in Figure 4, a settling tank 2 is connected downstream of the biological treatment tank 1. The biologically treated water in the biological treatment tank 1 is separated into solids and liquids by gravitational settling or the like in the settling tank 2, yielding separated sludge and treated water. According to this embodiment, by using the sludge floating inhibitor 100 according to this embodiment in the biological treatment tank 1, sufficient denitrification treatment is performed in advance in the biological treatment tank 1, making it difficult for nitrogen gas to be generated in the settling tank 2 and for sludge adhering to the generated nitrogen gas to float up. This improves the quality of the treated water.

[0061] (Organic wastewater treatment equipment) As shown in Fig. 4, an organic wastewater treatment apparatus according to an embodiment of the present invention includes a biological treatment tank 1 (biological treatment means) for treating organic wastewater with activated sludge, a sludge floatation prevention means (sludge floatation inhibitor) 100 disposed in the biological treatment tank 1 and comprising a fibrous molded body 10 containing recycled fibers, an agitation means 20 for agitating the activated sludge mixed liquid in the biological treatment tank 1 and bringing the activated sludge mixed liquid into contact with the sludge floatation prevention means 100, and a settling tank 2 (settling means) for performing solid-liquid separation of the biologically treated water treated in the biological treatment tank 1. A return line 3 is connected between the settling tank 2 and the biological treatment tank 1. A portion of the separated sludge obtained in the settling tank 2 is returned to the biological treatment tank 1 via the return line 3 as returned sludge, and the remaining separated sludge is discharged outside the treatment system for sludge treatment.

[0062] The sludge floating prevention means 100 can be composed of a fiber molding 10 as shown in Figures 1(a) to 1(d). Furthermore, by providing the sludge floating prevention means 100 with a stand 15 as shown in Figures 3(a) and 3(b), it can be stably placed in a predetermined position in the biological treatment tank 1. Furthermore, by placing agitation means 20 that can supply air to the sludge floating prevention means 100 below the sludge floating prevention means 100 as shown in Figure 5, it is possible to agitate the contents of the biological treatment tank 1 while preventing clogging of the sludge floating prevention means 100.

[0063] (Variation) Figure 6 shows an example of a method and apparatus for treating organic wastewater according to a modified embodiment of the present invention. As shown in Figure 6, biological treatment tank 1 includes a first biological treatment tank 1a (first biological treatment means) that performs a first biological treatment on organic wastewater, and a second biological treatment tank 1b (second biological treatment means) that performs biological treatment on the organic wastewater treated in first biological treatment tank 1a with a lower BOD sludge load than in the first biological treatment, and sludge floating prevention means 100 is arranged in second biological treatment tank 1b.

[0064] For example, by performing nitrification and denitrification of organic wastewater in the first biological treatment tank 1a and the second biological treatment tank 1b, respectively, the nitrogen contained in the organic wastewater can be treated more efficiently. For example, in the first biological treatment tank 1a, nitrifying bacteria oxidize ammonia nitrogen in the organic wastewater to nitrate nitrogen or nitrite nitrogen under aerobic conditions, and the first biological treatment water containing nitrate nitrogen or nitrite nitrogen that has been biologically treated in the first biological treatment tank 1a is supplied to the second biological treatment tank 1b. In the second biological treatment tank 1b, the biological treatment water containing nitrate nitrogen or nitrite nitrogen is denitrified in the presence of denitrifying bacteria.

[0065] The sludge floating prevention means 100 disposed in the second biological treatment tank 1b can be the sludge floating prevention agent shown in Figures 1(a) to 1(d) and 3(a) to 3(b). In the second biological treatment tank 1b, the sludge floating prevention means 100 functions as a hydrogen donor. The second biological treatment tank 1b further includes a nitrification inhibitor addition means 4 that adds a nitrification inhibitor to the second biological treatment tank 1b to inhibit nitrification of organic wastewater.

[0066] In this way, by placing sludge floating prevention means 100 in biological treatment tank 1 in consideration of fluctuations in the water quality of organic wastewater and further adding a nitrification inhibitor from nitrification inhibitor adding means 4, nitrification in second biological treatment tank 1b can be suppressed and denitrification treatment in second biological treatment tank 1b can be sufficiently carried out. This makes it difficult for nitrogen gas to be generated in settling tank 2, which separates the biologically treated water from second biological treatment tank 1b into solids and liquids, and prevents sludge floating in settling tank 2.

[0067] The nitrification inhibitor may be added at one or more locations via the nitrification inhibitor adding means 4. As the nitrification inhibitor, for example, thiourea, allylthiourea, dithiocarbamate, or a combination thereof may be used.

[0068] The amount of nitrification inhibitor to be added is appropriately determined based on the BOD sludge load in the second biological treatment tank 1b, etc. The amount of nitrification inhibitor to be added varies depending on the filling rate of the fibrous extrusions, etc. For example, in a biological treatment tank where biological treatment with a BOD sludge load of 0.1 kg / kg-MLSS-day or less can occur, when thiourea is added as a nitrification inhibitor, the amount of thiourea is 1 to 100 mg / L, preferably 10 to 60 mg / L, and more preferably 40 to 60 mg / L. When allylthiourea is added as a nitrification inhibitor, the amount of allylthiourea is 1 to 50 mg / L, preferably 1 to 10 mg / L, and more preferably 5 to 10 mg / L.

[0069] According to a modified embodiment of the present invention, a sludge floating prevention means 100 is provided in the second biological treatment tank 1b, which has a low BOD sludge load and is prone to nitrification. A nitrification inhibitor is then added to the second biological treatment tank 1b via the nitrification inhibitor addition means 4. This allows denitrification to be performed while suppressing nitrification in the second biological treatment tank 1b, resulting in lower nitrate and nitrite concentrations in the biologically treated water in the second biological treatment tank 1b. As a result, the amount of nitrogen gas generated in the settling tank 2 can be reduced compared to the conventional example without the sludge floating prevention means 100. Furthermore, the provision of the sludge floating prevention means 100 in the second biological treatment tank 1b allows for a smaller amount of nitrification inhibitor to be added via the nitrification inhibitor addition means 4, thereby saving on chemical costs.

[0070] Furthermore, according to the organic wastewater treatment method and treatment device of the modified embodiment of the present invention, stable and high denitrification performance is exhibited even for organic wastewater with a higher nitrogen concentration than the organic wastewater treatment method and treatment device shown in FIG. 4, for example, organic wastewater with a nitrogen concentration exceeding 50 mg / L, so that floating of sludge in the downstream settling tank 2 is prevented and treated water of good quality is obtained.

[0071] As described above, the present invention has been described with reference to the above-mentioned embodiments, but the descriptions and drawings forming part of this disclosure should not be understood as limiting the present invention. The present disclosure is not limited to the above-mentioned embodiments, and components can be combined and modified to be embodied within the scope of the gist of the present disclosure.

[0072] 6 shows an example in which the sludge floating prevention means 100 and the nitrification inhibitor adding means 4 are arranged in the second biological treatment tank 1b, but it goes without saying that these may also be arranged in the first biological treatment tank 1a. Furthermore, there is no particular limit to the number of tanks in the biological treatment tank 1, and it goes without saying that two or more tanks can be arranged depending on the conditions such as the properties of the organic wastewater or the installation area of the treatment facility.

[0073] Furthermore, while the modified example in Figure 6 shows an example in which the first biological treatment tank 1a and the second biological treatment tank 1b are separate treatment tanks, the first biological treatment tank 1a and the second biological treatment tank 1b may be configured as a single treatment tank. That is, the biological treatment tank 1 may be configured as multiple biological treatment tanks 1, or as a single biological treatment tank 1 divided into multiple sections. In this case, the sludge floating prevention means 100 and the nitrification inhibitor addition means 4 are preferably disposed at least at any location in the latter half of the biological treatment tank when the entire biological treatment tank is divided into a first half and a second half. Alternatively, the sludge floating prevention means 100 and the nitrification inhibitor addition means 4 are preferably disposed in a region of one or more biological treatment tanks 1 where the BOD sludge load is 0.1 kg / kg-MLSS-day or less. [Example]

[0074] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0075] Example 1 Nitrified sludge collected from the nitrification tank of the nitrification and denitrification treatment facility at the Sludge Reclamation Center was sieved through a 2mm mesh sieve to remove impurities, and the resulting sludge was used as seed sludge (SS 8,000mg / L). This seed sludge was introduced into biological treatment tank 1 of the simulated test equipment corresponding to the organic wastewater treatment equipment shown in Figure 4, and a biological treatment test was conducted using organic wastewater produced at a beverage manufacturing plant as simulated organic wastewater. Table 1 shows the specifications and treatment conditions of the test equipment.

[0076] [Table 1]

[0077] The biological treatment tank 1 was a treatment tank with a width of 0.5 m, a length of 0.5 m, and an effective depth of 0.6 m. The simulated organic wastewater had a pH of 6.3, SS of 35.0 mg / L, BOD of 300 mg / L, an ammonia nitrogen concentration of 15.5 mg / L, a nitrate nitrogen concentration of 0.1 mg / L or less, and a nitrite nitrogen concentration of 0.1 mg / L or less, and reagent phosphoric acid was added as a nutrient to bring the phosphorus concentration to 2.0 mg / L.

[0078] Treated water volume: 0.15m 3 The biological treatment tank 1 was adjusted to 4000 mg / L of MLSS per day by adding the above-mentioned seed sludge, the liquid temperature was 20-25°C, and the BOD sludge load was 0.075 kg-BOD / kg-MLSS·day. The recycled fibers constituting the sludge floatation inhibitor fiber molded body were short rayon fibers with a fiber diameter of 40 μm and a fiber length of 10 mm (Evagrose® U-710, manufactured by Suing Co., Ltd.). This recycled fiber (volume 2.0 L, weight 1.0 kg) was fixed to a stainless steel wire mesh with a mesh opening of 3 mm to produce a fibrous molded body. Ten of these fibrous molded bodies were fixed on a stand as shown in Figure 3(a) and placed in the center of the biological treatment tank. A continuous biological treatment experiment was conducted while air was supplied from the bottom of the biological treatment tank. The filling rate of the sludge floatation inhibitor (fibrous molded body) was 0-40% by volume of the effective volume of the biological treatment tank 1. The amount (volume) of the sludge floating inhibitor (fibrous molded material) filled in the biological treatment tank 1 was 0 to 60 L.

[0079] The SS, BOD, ammonia nitrogen, and nitrate nitrogen concentrations of the biologically treated water at the outlet of the settling tank were measured. Measurements were performed in accordance with JIS K0102:2016, Industrial Wastewater Testing Methods. SS was measured according to "14.1 Suspended Solids," BOD was measured according to "21. Biochemical Oxygen Demand," ammonia nitrogen was measured according to "42 Ammonium Ion," and nitrate nitrogen was measured according to "43.2 Nitrate Ion." The ammonia nitrogen concentration was converted to the nitrogen concentration of ammonia ions, and the nitrate nitrogen concentration was converted to the nitrogen concentration of nitrate ions. The results are shown in Table 2. The sludge flotation effect was evaluated by visual observation of the liquid level in the settling tank. A correlation was found between the SS concentration of the biologically treated water and the SS concentration. Therefore, a SS concentration of less than 4.0 mg / L was evaluated as "Good," a concentration of 4.0 mg / L to less than 6.5 mg / L was evaluated as "Good," and a concentration of 6.5 mg / L or greater was evaluated as "Poor."

[0080] [Table 2]

[0081] In Test No. 1, where the loading rate of the sludge floating inhibitor was 0% by volume, sludge floating was clearly visible. The biologically treated water had SS 23 mg / L, BOD less than 1 mg / L, ammonia nitrogen 0.2 mg / L, and nitrate nitrogen 8.3 mg / L. In Test No. 1, nitrification occurred in the biological treatment tank, and denitrification in the settling tank caused the sludge to float, which is thought to have led to sludge overflow from the settling tank, resulting in a high SS concentration in the treated water.

[0082] In Test No. 2, where the sludge floatation inhibitor loading rate was 5% by volume, visual observation of the liquid level in the settling tank confirmed the sludge floatation prevention effect, and the biologically treated water had SS 5.2 mg / L, BOD 1 mg / L or less, and nitrate nitrogen 0.5 mg / L. In Tests No. 3 to 5, where the sludge floatation inhibitor loading rate was 13 to 30% by volume, the biologically treated water had SS 2.8 to 3.0 mg / L, BOD 1 mg / L or less, and nitrate nitrogen 0.2 to 0.3 mg / L, and visual observation of the liquid level in the settling tank confirmed the sufficient sludge floatation prevention effect.

[0083] In Test No. 6, where the sludge floatation inhibitor loading rate was 40% by volume, the treated water had SS 6.4 mg / L, BOD 15.3 mg / L, ammonia nitrogen 3.6 mg / L, and nitrate nitrogen 1.8 mg / L. The slightly high SS concentration in the biologically treated water was due to residual BOD in the treated water, which meant that biological treatment was somewhat insufficient. The residual ammonia nitrogen also indicated incomplete nitrification. In Test No. 6, the water quality of the biologically treated water was not as good as in Tests Nos. 2 to 5, but sludge floating from the settling tank was only slightly visible, indicating that the sludge floatation prevention effect was achieved. However, since the sludge floatation inhibitor loading rate in Test No. 6 was 40% by volume, it is thought that the contact between the simulated organic wastewater and activated sludge in the biological treatment tank and with the fibrous extrusions may have been somewhat poor in some cases.

[0084] Example 2 Using the test equipment for treating organic wastewater in Example 1, a treatment test was conducted in the same manner as in Example 1 using simulated organic wastewater similar to that in Example 1, using a nitrification inhibitor in addition to a sludge floating inhibitor. The loading rate of the sludge floating inhibitor was set to 0 to 30% by volume, and thiourea and allylthiourea were used as nitrification inhibitors and added to the biological treatment tank. The thiourea addition rate was set to 5 to 60 mg / L, and the allylthiourea addition rate was set to 1 to 10 mg / L. Table 3 shows the results of the denitrification treatment test.

[0085] [Table 3]

[0086] In the case of Tests No. 7 to 12, where the loading rate of the sludge flotation inhibitor was 0% by volume, the thiourea addition rate was 60 mg / L or more and the allylthiourea addition rate was 10 mg / L or more, which resulted in the inhibition of sludge flotation and improved water quality of the biologically treated water.

[0087] On the other hand, in tests No. 13 to 18, where the sludge floating inhibitor loading rate was 5% by volume, the thiourea addition rate was 20 mg / L or more and the allylthiourea addition rate was 2 mg / L or more, and the sludge floating inhibition effect and the water quality improvement effect of the biologically treated water were achieved with a smaller amount of nitrification inhibitor added.

[0088] Even in Tests No. 19 to 24, where the sludge flotation inhibitor was 13% by volume, the thiourea addition rate of 20 mg / L or more and the allylthiourea addition rate of 2 mg / L or more achieved the effect of inhibiting sludge flotation and improving the water quality of the biologically treated water. In Tests No. 19 to 24, the SS and nitrate nitrogen concentrations of the biologically treated water were even better than in Tests No. 13 to 18.

[0089] In Tests 25 and 26, where the sludge flotation inhibitor was 20% by volume, a thiourea addition rate of 15 mg / L or more was found to inhibit sludge flotation and improve the water quality of the biologically treated water. In Tests 27 and 28, where the sludge flotation inhibitor was 30% by volume, a thiourea addition rate of 5 mg / L or more was found to be more effective in preventing sludge flotation and improve the water quality of the biologically treated water. In this way, by adding a sludge flotation inhibitor to the biological treatment tank, the addition rate of the nitrification inhibitor can be lowered, thereby reducing the amount of chemical used. [Explanation of symbols]

[0090] 1 Biological treatment tank 1a First biological treatment tank 1b Second biological treatment tank 2 Settling tank 3 Return Line 4 Means for adding nitrification inhibitor 10 Fiber molding 11, 11a, 11b, 11c, 11d Regenerated fiber 12a, 12b, 12c, 12d, 13a, 13d Support 15 Mounting stand 20 Stirring means 30 DO meter 100 Sludge floating inhibitor (sludge floating prevention means)

Claims

1. A sludge floating inhibitor characterized by being composed of a fibrous molded body containing recycled fibers.

2. 2. The sludge floating inhibitor according to claim 1, wherein the recycled fibers include rayon fibers having a fiber diameter of 100 μm or less.

3. 3. The sludge floating inhibitor according to claim 1, wherein the fibrous molding comprises a support for supporting the recycled fibers.

4. A sludge floating inhibitor as described in claim 1 or 2, characterized in that the fiber molding has any of the following shapes: rectangular, cubic, cylindrical, columnar, block, plate, membrane, lattice, or string-like with both ends of the recycled fiber bundled together.

5. The organic wastewater is subjected to activated sludge treatment in a biological treatment tank containing a sludge floating inhibitor made of a fiber molded body containing recycled fibers, agitating the organic wastewater in the biological treatment tank to bring it into contact with the sludge floating inhibitor, and then separating the biologically treated water obtained by the activated sludge treatment into solid and liquid. A method for treating organic wastewater, comprising:

6. 6. The method for treating organic wastewater according to claim 5, further comprising adding a nitrification inhibitor to the biological treatment tank to inhibit nitrification of the organic wastewater.

7. a biological treatment means for treating organic wastewater with activated sludge; a sludge floating prevention means disposed within the biological treatment means and made of a fiber molding containing recycled fibers; a stirring means for stirring the activated sludge mixed liquid in the biological treatment means and bringing the activated sludge mixed liquid into contact with the sludge floating prevention means; a settling means for separating the biologically treated water treated by the biological treatment means into solid and liquid; An organic wastewater treatment device comprising:

8. 8. The organic wastewater treatment device according to claim 7, further comprising a nitrification inhibitor adding means for adding a nitrification inhibitor for suppressing nitrification of the organic wastewater into the biological treatment means.

9. The biological treatment means a first biological treatment means for performing a first biological treatment on the organic wastewater; a second biological treatment means for biologically treating the organic wastewater treated by the first biological treatment means with a lower BOD sludge load than that of the first biological treatment means; Including, 9. The organic wastewater treatment device according to claim 7, wherein the sludge floating prevention means is disposed in the second biological treatment means.

10. 9. The organic wastewater treatment device according to claim 7, wherein the biological treatment means is composed of a plurality of biological treatment means or a biological treatment means divided into a plurality of biological treatment means, and the sludge floating prevention means is disposed in at least the rear half of the biological treatment means.

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