Wastewater treatment apparatus and wastewater treatment method

Abstract

To provide a wastewater treatment system and a wastewater treatment method that can reduce the cost required for dewatering treatment of digested sludge and secure the amount of activated sludge required for biosorption.SOLUTION: Inflowing sewage is separated from coarse solids in a sedimentation basin and a screen unit 1, and the separated coarse solids are treated in a methane fermentation unit 2 to produce digested sludge. The digested sludge is transferred to a dewatering unit 4 and a digested sludge conditioning apparatus 5, and the digested sludge is brought into contact in the digested sludge conditioning unit 5 with surplus sludge from a water treatment apparatus 8 and is conditioned. The conditioned sludge is then contacted in a contacting / mixing unit 6 with treated water from the sedimentation basin and the screen unit 1, and the organic matters contained in the treated water are adsorbed by the conditioned sludge. Sludge with adsorbed organic matters is separated in a separation and concentration unit 7, and the concentrated sludge is transferred to the methane fermentation unit 2. Separated water from the separation / concentration unit 7 is supplied to the water treatment unit 8, and organic matters contained in the wastewater are decomposed in the water treatment unit 8.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a wastewater treatment apparatus and a wastewater treatment method.

Background Art

[0002] Conventionally, water treatment of wastewater such as sewage containing contaminants, organic matter, and moisture has been performed by the standard activated sludge method. For example, sewage discharged from homes, factories, etc. is transferred to a biological reaction tank containing activated sludge through a grit chamber and a primary sedimentation tank, and in the biological reaction tank, organic matter in the sewage is decomposed and removed by the activated sludge.

[0003] FIG. 4 is a diagram schematically showing a wastewater treatment apparatus by the standard activated sludge method generally implemented in medium and large-scale sewage treatment facilities.

[0004] The wastewater treatment apparatus of FIG. 4 includes a grit chamber and a pump well 41, a methane fermentation facility 42, an energy recovery facility 43, a dehydration facility 44, a primary sedimentation tank 47, a biological reaction tank (aeration tank) 48, and a final sedimentation tank 49. First, sewage discharged from homes, factories, etc. is transferred to the primary sedimentation tank 47 after coarse solids (grit and scum) are removed in the grit chamber and the pump well 41, and in the primary sedimentation tank 47, it is separated into solids (primary sludge) and treated water. Next, the primary sludge is transferred to the methane fermentation facility 42 for methane fermentation treatment. Through the methane fermentation treatment of this primary sludge, digested gas (methane gas) and digested sludge are generated. The digested gas is transferred to the energy recovery facility 43, and the digested sludge is transferred to the dehydration facility 44. Thereafter, the digested sludge is dehydrated in the dehydration facility 44 to generate dehydrated cake and dehydrated filtrate.

[0005] Meanwhile, the treated water from the primary sedimentation tank 47 is transferred to the biological reaction tank 48, where organic matter in the treated water is aerobically decomposed by activated sludge. Next, the separated water discharged from the biological reaction tank 48 is transferred to the final sedimentation tank 49, where it is separated into sludge and treated water. Of the sludge separated in the final sedimentation tank 49, some is returned to the biological reaction tank 48 (returned sludge), and the remainder is transferred to the methane fermentation facility 42 together with the primary sedimentation sludge separated in the primary sedimentation tank 47 (excess sludge). The treated water discharged from the final sedimentation tank 49 is sterilized in a sterilization tank before being discharged or put to good use.

[0006] Incidentally, it has been known for some time that activated sludge, which has undergone aerobic oxidative decomposition, adsorbs organic matter from influent sewage, a process known as biosorption. For example, Patent Document 1 discloses a method for efficiently recovering methane by transferring excess sludge separated from an aerobic treatment tank to an adsorption tank into which raw water flows, separating the excess sludge that has adsorbed organic matter from the raw water into a solid-liquid separation tank, and then introducing the separated sludge into an anaerobic digester. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2003-190997 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, digested sludge produced by methane fermentation contains many very fine particles, making it more difficult to dewater compared to raw sludge (primary sedimentation sludge and excess sludge). As a result, the dewatered cake obtained from the dewatering treatment of digested sludge has a high water content, leading to a large amount of dewatered cake generated and significant disposal costs. Furthermore, while coagulants are added during the dewatering treatment, digested sludge contains many cationic low-molecular-weight substances and has many charged sites on its surface, thus consuming many ion sites of the coagulant. Consequently, digested sludge requires a higher coagulant addition rate compared to raw sludge, leading to increased dewatering costs. Furthermore, in the case of a method that uses biosorption of excess sludge (activated sludge) to adsorb organic matter in wastewater (Patent Document 1), the amount of excess sludge generated in the aerobic treatment tank decreases, which presents a problem in that it becomes difficult to secure the amount of activated sludge necessary for biosorption as wastewater treatment progresses. Therefore, there was a need for wastewater treatment that could reduce the cost of dewatering digested sludge while also securing the amount of activated sludge necessary for biosorption.

[0009] The object of the present invention is to provide a wastewater treatment apparatus and wastewater treatment method that can reduce the cost required for dewatering digested sludge and secure the amount of activated sludge necessary for biosorption. [Means for solving the problem]

[0010] To achieve the above objective, the wastewater treatment apparatus of the present invention is a wastewater treatment apparatus for treating wastewater containing impurities, organic matter and moisture, comprising: impurity separation means for separating impurities, organic matter and moisture; methane fermentation treatment means for methane fermentation treatment of impurities separated by the impurity separation means; and water treatment means for water treatment of treated water containing organic matter and moisture obtained by the impurity separation means, wherein at least a portion of the digested sludge obtained by the methane fermentation treatment means is treated by contacting it with activated sludge in the presence of oxygen. The system includes a contact means for contacting and mixing the treated sludge obtained by the digested sludge conditioning means with the treated water obtained by the impurities separation means, and a separation and concentration means for separating the mixture obtained by the contact means into concentrated sludge and separated water. It is characterized by having the following features.

[0011] In order to achieve the above object, the wastewater treatment method of the present invention is a wastewater treatment method using the wastewater treatment apparatus of the present invention, and includes a foreign matter separation step of separating the foreign matter, the organic matter, and moisture, a methane fermentation treatment step of subjecting the foreign matter separated in the foreign matter separation step to methane fermentation treatment, a water treatment step of treating the treated water containing the organic matter and moisture obtained by the foreign matter separation step, and a digestion sludge conditioning step of conditioning at least a part of the digested sludge obtained by the methane fermentation treatment step by contacting it with activated sludge in the presence of oxygen. A contact step in which the treated sludge obtained in the digested sludge treatment step is brought into contact and mixed with the treated water obtained in the impurity separation step; a separation and concentration step in which the mixture obtained in the contact step is separated into concentrated sludge and separated water; and a concentrated sludge supply step in which the concentrated sludge separated in the separation and concentration step is supplied to the methane fermentation treatment step. It is characterized by having the above.

Effect of the Invention

[0012] According to the present invention, it is possible to reduce the cost required for the dehydration treatment of digested sludge and ensure the amount of activated sludge required for biosorption to perform stable wastewater treatment.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram schematically showing a wastewater treatment apparatus according to an embodiment of the present invention. [Figure 2] It is a diagram showing a modified example of the wastewater treatment apparatus of FIG. 1. [Figure 3] It is a diagram showing a modified example of the wastewater treatment apparatus of FIG. 2. [Figure 4] It is a diagram schematically showing a wastewater treatment apparatus by the standard activated sludge method.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0015] FIG. 1 is a diagram schematically showing a wastewater treatment apparatus 10 according to an embodiment of the present invention.

[0016] The wastewater treatment apparatus 10 shown in Fig. 1 includes equipment 1 composed of a grit chamber and a screen, a methane fermentation facility 2, an energy recovery facility 3, a dewatering facility 4, a digestion sludge conditioning facility 5, a contact mixing facility 6, a separation and concentration facility 7, and a water treatment facility 8. First, the sewage discharged from households, factories, etc. is transferred to equipment 1 (entrapped matter separation means), and in equipment 1, the coarse solids (entrapped matter) in the sewage are removed as grit and screenings. For the screen, in order to remove coarse solids that are difficult to be adsorbed by the activated sludge in the contact mixing facility 6 described later, it is preferable to use a fine-mesh screen facility with a mesh size of 20 to 300 μm, preferably 50 to 200 μm. Equipment 1 is not particularly limited as long as it can remove the coarse solids (entrapped matter) in the sewage. Since the grit separated in the grit chamber contains sand, after the sand is removed by a grit washing device or the like, a part of it is transferred to the methane fermentation facility 2, and the rest is disposed of or effectively utilized. On the other hand, since the screenings separated by the screen contain a large amount of organic matter and little sand, after being crushed by a crusher, a part of it is transferred to the methane fermentation facility 2, and the rest is disposed of or effectively utilized.

[0017] The methane fermentation facility 2 (methane fermentation treatment means) performs methane fermentation treatment on the grit after sand removal, the screenings after crushing, and the separation and concentration sludge described later. The methane fermentation treatment is a treatment using a digestion reaction in which methanogenic bacteria (anaerobic bacteria) decompose organic matter to generate digestion gas mainly composed of methane and digestion sludge. Specifically, first, methanogenic bacteria hydrolyze organic matter to generate soluble amino acids and the like. Next, the generated amino acids and the like are taken into the cells of anaerobic bacteria and metabolically decomposed to generate acetic acid, hydrogen, carbon dioxide, etc. Thereafter, methane as biogas is generated from acetic acid, hydrogen, and carbon dioxide. Digestion sludge is the sludge remaining after the organic matter in the sludge is decomposed by the action of methanogenic bacteria and digestion gas is generated, and it contains methanogenic bacteria. Since this digestion sludge contains a large amount of very fine particles, it has the property of being more difficult to dewater than raw sludge (primary sedimentation sludge and excess sludge).

[0018] The digester gas discharged from the methane fermentation plant 2 is transferred to the energy recovery plant 3, where it is either used directly as fuel or transferred to a power generation device for use as electricity. Additionally, some of the digested sludge discharged from the methane fermentation plant 2 is transferred to the digested sludge conditioning plant 5, and the remainder is transferred to the dewatering plant 4. In the dewatering plant 4, a coagulant is added to the digested sludge for dewatering treatment. Examples of coagulants added to the digested sludge include organic polymer-based coagulants, often referred to as polymers. Because digested sludge contains many cations and has high alkalinity, anionic polymers, amphoteric polymers, or a combination of anionic and cationic polymers are used as coagulants.

[0019] By transferring a portion of the digested sludge to the digested sludge conditioning equipment 5 in this manner, the amount of digested sludge supplied to the dewatering equipment 4 can be reduced. This reduces the amount of coagulant added to the dewatering treatment and the amount of dewatered cake generated, thereby significantly reducing the cost required for the dewatering treatment of digested sludge.

[0020] Furthermore, by transferring a portion of the digested sludge to the digested sludge conditioning equipment 5, as described later, the amount of conditioning sludge (activated sludge) supplied to the contact mixing equipment 6 along with the treated water from equipment 1 can be increased. As a result, the amount of organic matter adsorbed on the conditioning sludge increases, and the amount of digester gas generated by methane fermentation treatment can be increased. If the amount of energy recovered from the digester gas increases, it is possible to provide a wastewater treatment device that can be energy-sufficient if used for power generation, etc.

[0021] Furthermore, by transferring a portion of the digested sludge to the digested sludge conditioning facility 5, the digested sludge is conditioned and converted into aerobic activated sludge, as will be described later, thus ensuring the amount of activated sludge necessary for biosorption.

[0022] The digested sludge conditioning equipment 5 (digested sludge conditioning means) performs conditioning treatment on digested sludge. Conditioning treatment is a process in which digested sludge is brought into contact with activated sludge in the presence of oxygen. As a result, the activated sludge (aerobic microorganisms) decomposes and preys on the digested sludge (methanogenic bacteria, anaerobic bacteria, etc.) and self-replicates, converting the digested sludge into aerobic activated sludge (conditioned sludge) with a biosorption effect, and increasing the oxygen dissolution efficiency. The activated sludge functions as seed sludge for conditioning treatment, enabling conditioning in a short time. Digested sludge contains reducing substances such as organic acids (propionic acid, butyric acid, valeric acid, etc.), ammonia, hydrogen sulfide, and sulfides, but these reducing substances in the digested sludge are also oxidized by the conditioning treatment.

[0023] In this embodiment, the activated sludge supplied to the digested sludge conditioning plant 5 is surplus sludge discharged from the water treatment plant 8, which will be described later. In order to efficiently carry out the conditioning treatment, it is necessary to have a sufficient amount of activated sludge relative to the digested sludge in the digested sludge conditioning plant 5. The weight ratio of digested sludge to surplus sludge supplied to the digested sludge conditioning plant 5 should be in the range of 1:0.5 to 1:10. This is thought to allow the conversion of digested sludge to activated sludge to proceed efficiently. In order to reduce the capacity of the digested sludge conditioning plant 5, it is desirable to increase the ratio of surplus sludge to digested sludge. Also, if the amount of surplus sludge supplied to the digested sludge conditioning plant 5 is small and the supply ratio of surplus sludge to digested sludge is small, it is effective to install carriers or contact materials for maintaining aerobic microorganisms in the digested sludge conditioning plant 5. The concentration of digested sludge supplied to the digested sludge conditioning plant 5 is usually 1-2% by weight, and the concentration of activated sludge supplied to the digested sludge conditioning plant 5 is usually 0.2-0.5% by weight. From the viewpoint of ease of conditioning, the concentration of mixed sludge (digested sludge and activated sludge) in the mixed sludge digested sludge conditioning plant 5 should be maintained at 1% by weight or less, preferably 0.4-0.6% by weight. If the concentration of mixed sludge exceeds 1% by weight, the viscosity of the sludge tends to increase and the oxygen dissolution efficiency tends to decrease. The concentration of mixed sludge can be adjusted, for example, by adding dewatered filtrate from the dewatering plant 4 to the digested sludge conditioning plant 5.

[0024] Contact between digested sludge and activated sludge can be achieved, for example, by aeration stirring, where an aeration device is placed within the digested sludge conditioning facility 5 and the digested sludge and activated sludge are mixed while aerating air. In addition to aeration stirring, contact between digested sludge and activated sludge can also be achieved by line mixing using a static mixer (line mixer), for example. It is preferable to provide a sludge flow rate adjustment means within the digested sludge conditioning facility 5, and the residence time of the mixed sludge (digested sludge and activated sludge) within the digested sludge conditioning facility 5 varies depending on the mixing ratio of digested sludge and activated sludge, the capacity of the aeration device, the presence or absence of contact material, etc., but is usually 3 to 12 days. The sludge that flows out of the digested sludge conditioning facility 5 is mostly activated sludge and is transferred to the contact mixing facility 6. When converting a standard activated sludge process facility to a membrane bioreactor (MBR) process, a portion of the existing aeration tank (biological reaction tank) can be used as a digested sludge conditioning facility 5.

[0025] The contact mixing equipment 6 (contact means) is a means for aerobic contact mixing of treated water from equipment 1 and treated sludge transferred from digested sludge conditioning equipment 5. Contact mixing can be carried out by aeration and stirring by placing an aeration device inside the contact mixing equipment 6. Mechanical stirring can also be added, for example, line mixing can be performed using a stationary mixer (line mixer) such as a static mixer. Through this contact mixing, dissolved organic matter in the treated water transferred from equipment 1 is adsorbed onto the treated sludge.

[0026] In the contact mixing equipment 6, it is preferable to maintain a weight ratio of approximately the same amount of dissolved organic matter in the treated water transferred from equipment 1 and the amount of treated sludge transferred from the digested sludge treatment equipment 5, such as 1:0.5 to 1:1.5, preferably 1:0.6 to 1:1.3. This ensures that dissolved organic matter and fine solids in the treated water transferred from equipment 1 are efficiently adsorbed onto the treated sludge within the contact mixing equipment 6.

[0027] The mixed liquid discharged from the contact mixing equipment 6 contains tempered sludge with adsorbed dissolved organic matter and fine solids. Most of this mixed liquid is transferred to the separation and concentration equipment 7, but a portion is transferred to the water treatment equipment 8 via a bypass route without passing through the separation and concentration equipment 7. By providing such a bypass route, it is possible to easily control the amount of mixed liquid supplied to the separation and concentration equipment 7 and the amount of mixed liquid that moves to the bypass route without passing through the separation and concentration equipment 7, thereby controlling the amount of activated sludge supplied to the water treatment equipment 8. By installing such a bypass route, the MLSS (activated sludge suspended solids) concentration in the water treatment facility 8 can be quickly adjusted to an optimal range, enabling stable operation even with daily load fluctuations. Furthermore, when modifying equipment for the standard activated sludge method, a portion of the primary sedimentation tank can be used as the contact mixing equipment 6.

[0028] The separation and concentration equipment 7 (separation and concentration means) is a means for separating and concentrating tempered sludge, which has adsorbed dissolved organic matter and fine solids, from the mixed liquid transferred from the contact mixing equipment 6, and has a higher organic matter separation efficiency than conventional primary sedimentation tanks. In the separation and concentration process, it is possible to increase the separation efficiency of organic matter by adding iron-based or aluminum-based inorganic coagulants or organic coagulants, but the separation efficiency can be further increased by using a pressurized flotation separator or a centrifuge. In particular, a pressurized flotation separator is preferable because it can efficiently separate and concentrate solids of 20-50 μm or larger in a short time of about 15-30 minutes without using a coagulant, but by using a coagulant, it becomes possible to separate sludge in the colloidal region, further improving the separation efficiency of organic matter. In addition, phosphorus can be removed by using inorganic coagulants containing aluminum or iron in the separation and concentration process. When modifying equipment for the standard activated sludge process, a part of the primary sedimentation tank can be used as the separation and concentration equipment 7.

[0029] Through this separation and concentration process, most of the organic matter in the mixed liquid supplied to the separation and concentration equipment 7, both solid and soluble, is separated as concentrated sludge. Furthermore, the resulting separated water has a significantly reduced organic matter content compared to the water flowing into the conventional water treatment equipment. By transferring this separated water to the water treatment equipment 8 along with the mixed water via a bypass route, the amount of organic matter in the water treatment equipment 8 is reduced, thereby significantly reducing the power consumption used by the water treatment equipment 8.

[0030] The concentrated sludge, which contains a large amount of organic matter and is separated in the separation and concentration facility 7, is transferred to the methane fermentation facility 2, where it undergoes methane fermentation treatment together with the sand-removed sediment and crushed residue transferred from facility 1. The concentration of concentrated sludge in the wastewater transferred from the separation and concentration facility 7 to the methane fermentation facility 2 is usually 3-5% by weight, depending on the separation and concentration method. The digestion rate of concentrated sludge in the methane fermentation facility 2 (the percentage that is converted into methane or carbon dioxide and gasified) is 60-90% by weight, so the percentage of separated concentrated sludge that changes into digested sludge is 10-40% by weight. Therefore, the concentration of digested sludge in the wastewater discharged from the methane fermentation facility 2 is usually 0.3-2.0% by weight.

[0031] The water treatment facility 8 performs water treatment to decompose dissolved organic matter in wastewater transferred from the separation and concentration facility 7 and the bypass route. As the water treatment facility 8, for example, a standard activated sludge method or an MBR method apparatus is used, in which organic matter in the wastewater is oxidatively decomposed by activated sludge under aeration. Activated sludge is sludge mainly composed of microorganisms that have proliferated through the aerobic oxidative decomposition of organic matter. In the present invention, it is preferable to use an MBR method apparatus, which is compact, has high nitrogen removal performance and can be operated in an energy-saving manner, and in particular an MBR method apparatus with a partition plate insertion type (hereinafter referred to as the "B-MBR method"). In the MBR method and the B-MBR method, a nitrification reaction proceeds in which nitrifying bacteria convert ammonia contained in the wastewater into nitrite and nitrate in the presence of oxygen, and a denitrification reaction proceeds in which denitrifying bacteria convert nitrite and nitrate into nitrogen in an oxygen-free state. The B-MBR method apparatus is a wastewater treatment apparatus having a partitioning means that separates a nitrification reaction area in which the nitrification reaction is carried out and a denitrification reaction area in which the denitrification reaction is carried out, and a membrane separation means installed in the nitrification reaction area for separating and removing solid matter contained in the wastewater. In the water treatment facility 8, it is necessary to maintain the MLSS concentration at a predetermined level, and it is preferable to maintain it at 4500 to 5500 mg / L, taking into consideration aeration efficiency and BOD-MLSS load. After the water treatment is completed, the activated sludge is discharged from the water treatment facility 8 as excess sludge and transferred to the digested sludge conditioning facility 5.

[0032] Figure 2 shows a modified example of the wastewater treatment apparatus shown in Figure 1.

[0033] The wastewater treatment system in Figure 2 is identical in configuration and function to the wastewater treatment system in Figure 1, except that it transfers all of the digested sludge discharged from the methane fermentation plant 2 to the digested sludge conditioning plant 5, and transfers a portion of the conditioned sludge discharged from the digested sludge conditioning plant 5 to the dewatering plant 4, instead of the digested sludge itself. The differences from the wastewater treatment system in Figure 1 are explained below.

[0034] In Figure 2, the entire amount of digested sludge discharged from the methane fermentation plant 2 is transferred to the digested sludge conditioning plant 5. Compared to the wastewater treatment device in Figure 1, the amount of digested sludge transferred to the digested sludge conditioning plant 5 increases, and consequently, the amount of conditioned sludge (activated sludge) discharged from the digested sludge conditioning plant 5 and transferred to the contact mixing plant 6 also increases. As a result, the amount of organic matter adsorbed onto the activated sludge in the contact mixing plant 6 also increases. Therefore, the wastewater treatment device in Figure 2 generates a larger amount of digester gas (methane gas) in the methane fermentation plant 2 and has higher energy recovery efficiency compared to the wastewater treatment device in Figure 1.

[0035] Furthermore, most of the treated sludge (activated sludge) discharged from the digested sludge treatment facility 5 is transferred to the contact mixing facility 6, but a portion of this treated sludge is supplied to the dewatering facility 4. In this way, by supplying activated sludge, which has a low coagulant addition rate and produces less dewatered cake, to the dewatering facility 4 instead of digested sludge, which has a high coagulant addition rate and produces a large amount of dewatered cake, the costs required for dewatering and subsequent treatment can be significantly reduced.

[0036] Figure 3 shows a modified example of the wastewater treatment apparatus shown in Figure 2.

[0037] The wastewater treatment system in Figure 3 is identical in configuration and function to the wastewater treatment system in Figure 2, except that the water treatment equipment 8 also functions as the digested sludge conditioning equipment 5, supplying digested sludge to the water treatment equipment 8, and transferring some of the excess sludge discharged from the water treatment equipment 8 to the dewatering equipment 4 and the remainder to the contact mixing equipment 6. The differences from the wastewater treatment system in Figure 2 will be explained below.

[0038] In the wastewater treatment system shown in Figure 3, the digested sludge conditioning equipment 5 is not provided separately. Instead, the water treatment equipment 8 functionally combines the functions of the digested sludge conditioning equipment 5, and both water treatment and digested sludge conditioning are performed within the water treatment equipment 8. That is, because activated sludge is present in the water treatment equipment 8, organic matter in the wastewater transferred from the separation and concentration equipment 7 and the bypass route is aerobically decomposed by the activated sludge within the water treatment equipment 8. At the same time, the digested sludge supplied to the water treatment equipment 8 is conditioned by contact with the activated sludge under aeration (in the presence of oxygen), and the digested sludge is converted into aerobic activated sludge with a biosorption effect. The amount of digested sludge supplied to the water treatment equipment 8 per day is 1 / 40 to 1 / 30 of the amount of activated sludge in the water treatment equipment 8, and since there is a sufficient amount of activated sludge relative to the digested sludge, the conditioning of the digested sludge proceeds easily. The capacity of the water treatment equipment 8 should be larger than that of the water treatment equipment in Figure 2 in order to perform the digested sludge conditioning treatment.

[0039] In the case of the B-MBR water treatment device 8, a nitrification reaction occurs in which nitrifying bacteria convert ammonia contained in wastewater into nitrite and nitrate in the presence of oxygen, and a denitrification reaction occurs in which denitrifying bacteria convert nitrite and nitrate into nitrogen in an oxygen-free state. The denitrification reaction requires organic matter as a hydrogen donor, but by supplying digested sludge to the water treatment device 8 as shown in Figure 3, the organic matter in the digested sludge is utilized in the denitrification reaction. With this device configuration, the device in Figure 3 has a simpler overall structure compared to the device in Figure 2, and a wastewater treatment device can be easily constructed by modifying the equipment of the standard activated sludge method.

[0040] Furthermore, treated excess sludge (treated sludge) is discharged from the water treatment facility 8. A portion of the discharged excess sludge (treated sludge) is transferred to the dewatering facility 4, and the remainder is transferred to the contact mixing facility 6. As a result, the dewatering facility 4 is supplied with treated sludge (activated sludge) with a low coagulant addition rate and a low amount of dewatered cake, rather than digested sludge with a high coagulant addition rate and a large amount of dewatered cake. This significantly reduces the costs required for dewatering and subsequent processing of the dewatered cake.

[0041] Next, the wastewater treatment method of this embodiment will be described according to the wastewater treatment apparatus shown in Figure 1.

[0042] The wastewater treatment apparatus 10 shown in Figure 1 comprises equipment 1 consisting of a grit tank and screen equipment, methane fermentation equipment 2, energy recovery equipment 3, dewatering equipment 4, digested sludge conditioning equipment 5, contact mixing equipment 6, separation and concentration equipment 7, and water treatment equipment 8.

[0043] First, wastewater discharged from homes, factories, etc., is continuously supplied to facility 1, and coarse solids (sediment and debris) are separated by a grit chamber and a screen (impurity separation step). The sediment separated in the grit chamber is transferred to methane fermentation facility 2 after the sand content is removed by a sediment washing device, etc. Meanwhile, the debris separated by the screen is transferred to methane fermentation facility 2 after being crushed by a crusher. In methane fermentation facility 2, methane fermentation treatment is performed on the sediment after sand removal, the debris after crushing, and the aforementioned separated and concentrated sludge transferred from separation and concentration facility 7 (methane fermentation treatment step). This methane fermentation treatment produces digester gas and digested sludge. The digester gas is transferred to energy recovery facility 3, and part of the digested sludge is transferred to digested sludge conditioning facility 5, and the remainder to dewatering facility 4. The treated water separated from the coarse solids in facility 1 is transferred to contact mixing facility 6.

[0044] In the digested sludge conditioning facility 5, a conditioning treatment is performed in which the digested sludge comes into contact with excess sludge (activated sludge) transferred from the water treatment facility 8 in the presence of oxygen. This converts the digested sludge into aerobic activated sludge (conditioned sludge) with a biosorption effect (digested sludge conditioning step). Next, the conditioned sludge discharged from the digested sludge conditioning facility 5 is transferred to the contact mixing facility 6, where it comes into contact and mixes with the treated water from facility 1 under aeration (contact step). This causes dissolved organic matter and fine solids contained in the treated water to be adsorbed onto the conditioned sludge. Subsequently, part of the mixed liquid containing the conditioned sludge with adsorbed dissolved organic matter and fine solids is transferred to a bypass route, and the remainder is transferred to the separation and concentration facility 7.

[0045] The separation and concentration equipment 7 uses a pressurized flotation separator to concentrate the treated sludge, which has adsorbed dissolved organic matter and fine solids, and separate it into concentrated sludge and separated water (separation and concentration step). The separated concentrated sludge is transferred to the methane fermentation equipment 2 (concentrated sludge supply step), where it is subjected to methane fermentation treatment together with the coarse solids transferred from equipment 1 (methane fermentation treatment step).

[0046] The separated water discharged from the separation and concentration plant 7 is supplied to the water treatment plant 8 along with the mixed liquid from the contact mixing plant 6, which passes through a bypass route. The water treatment plant 8 contains activated sludge, which decomposes dissolved organic matter in the wastewater transferred from the separation and concentration plant 7 and the bypass route under aeration (water treatment step). Subsequently, the excess sludge (activated sludge) discharged from the water treatment plant 8 is transferred to the digested sludge conditioning plant 5.

[0047] Meanwhile, an organic polymer-based flocculant is added to the digested sludge discharged from methane fermentation facility 2 and transferred to dewatering facility 4, and dewatering treatment is carried out. Dewatering treatment produces dewatered cake and dewatered filtrate, and the dewatered filtrate is transferred to facility 1.

[0048] As described above, by transferring a portion of the digested sludge discharged from the methane fermentation plant 2 to the digested sludge conditioning plant 5, the amount of digested sludge supplied to the dewatering plant 4 can be reduced. As a result, the amount of coagulant added and the amount of dewatered cake produced in the dewatering plant 4 can be reduced, making it possible to significantly reduce the cost required for dewatering treatment.

[0049] Furthermore, by transferring a portion of the digested sludge to the digested sludge conditioning facility 5 and converting it into activated sludge (conditioned sludge), the amount of activated sludge supplied to the contact mixing facility 6 can be increased. As a result, the amount of organic matter adsorbed onto the conditioned sludge and transferred to the methane fermentation facility 2 after separation and concentration increases, thereby increasing the amount of digester gas generated by methane fermentation treatment in the methane fermentation facility 2.

[0050] Furthermore, by transferring a portion of the digested sludge to the digested sludge conditioning facility 5, the digested sludge is conditioned and converted into aerobic activated sludge, making it possible to secure a sufficient amount of activated sludge necessary for biosorption. [Examples]

[0051] Next, embodiments of the present invention will be described.

[0052] Sewage treatment was performed using the wastewater treatment device 20 shown in Figure 2. However, equipment 1 used a fine mesh screen (mesh size: 15 mm) and a micro-mesh screen (mesh size: 250 μm). First, the maximum daily wastewater volume was 100,000 m³. 3 / day, average daily wastewater volume: 75,000 m³ 3 Daily inflow sewage was continuously supplied to facility 1, where coarse solids were separated by a screen. Next, the coarse solids separated in facility 1 were crushed by a crusher and then transferred to methane fermentation facility 2 for methane fermentation treatment. This methane fermentation treatment produced digester gas and digested sludge. The digester gas was transferred to energy recovery facility 3, and the entire amount of digested sludge was transferred to digested sludge conditioning facility 5. The treated water separated from the coarse solids in facility 1 was transferred to contact mixing facility 6.

[0053] An aeration device was installed in the digested sludge conditioning facility 5, and excess sludge (activated sludge) discharged from the water treatment facility 8 was supplied to it. In the digested sludge conditioning facility 5, conditioning treatment was performed by mixing the digested sludge and the excess sludge (activated sludge) under aeration to bring them into contact. At this time, the weight ratio of digested sludge to excess sludge supplied to the digested sludge conditioning facility 5 was 1:0.66. Through this conditioning treatment, the digested sludge was converted into aerobic activated sludge (conditioned sludge). Next, a portion of the conditioned sludge (conditioned sludge concentration: 6,576 mg / L) discharged from the digested sludge conditioning facility 5 was transferred to the dewatering facility 4, and the remaining conditioned sludge was transferred to the contact mixing facility 6 (amount of conditioned sludge injected into the contact mixing facility 6: 570 m³). 3 / day).

[0054] An aeration device was installed in the contact mixing facility 6, and the treated water from facility 1 and the digested sludge were agitated and mixed under aeration, causing dissolved organic matter and fine solids contained in the treated water to be adsorbed onto the tempered sludge. In the contact mixing facility 6, the amount of dissolved organic matter in the treated water transferred from facility 1 was approximately the same as the amount of tempered sludge transferred from the digested sludge tempering facility 5. Subsequently, a portion of the mixed liquid containing the tempered sludge with adsorbed dissolved organic matter and fine solids was transferred to a bypass route, and the remainder was transferred to the separation and concentration facility 7.

[0055] Separation and concentration facility 7 used a pressurized flotation separator to concentrate the treated sludge, which had adsorbed dissolved organic matter and fine solids, and separated it into concentrated sludge and separated water. The separated concentrated sludge (13,350 kg / day, concentration: 4 wt%) was transferred to methane fermentation facility 2, where it underwent methane fermentation treatment together with the coarse solids transferred from facility 1 (sludge input to methane fermentation facility: 394 m³). 3 ( / day). The entire amount of digested sludge (3,270 kg / day) discharged from methane fermentation facility 2 was transferred to digested sludge conditioning facility 5.

[0056] The separated water discharged from the separation and concentration plant 7, along with the mixed liquid from the contact mixing plant 6 which had passed through a bypass route, was supplied to the water treatment plant 8. The water treatment plant 8 (BOD-MLSS load: 0.043 kg / kg / day, MSLL concentration: 5,000 mg / L) is a B-MBR system that contains activated sludge, and the activated sludge decomposed dissolved organic matter in the wastewater transferred from the separation and concentration plant 7 and the bypass route under aeration. Subsequently, the excess sludge (activated sludge) (2,160 kg / day) discharged from the water treatment plant 8 was transferred to the digested sludge conditioning plant 5.

[0057] Meanwhile, in the dewatering facility 4, to which the treated sludge was transferred from the digested sludge treatment facility 5, an organic polymer-based flocculant (17 kg / day) was added to the treated sludge (amount of dewatered sludge: 255 m³). 3 Dehydration was performed on the cake (7.6m²). 3 Dehydrated filtrate was generated (per day), the dehydrated filtrate was transferred to facility 1, and the dehydrated cake was discharged or effectively utilized.

[0058] Furthermore, if the influent sewage with the same maximum daily wastewater volume and daily average wastewater volume were treated using a conventional standard activated sludge method apparatus (Figure 4), the amount of coagulant added to the dewatering equipment 4 would be 87 kg / day, and the amount of dewatered cake produced would be 29.2 m³. 3 This is per day. By using the wastewater treatment device shown in Figure 2, the amount of coagulant used is reduced by 70 kg / day, and the amount of dewatered cake produced is reduced by 21.6 m³. 3 As this reduces the cost per day, we were able to significantly lower the expenses required for dewatering the digested sludge.

[0059] Table 1 below shows the capacity and residence time (HRT) of each piece of equipment used in this embodiment.

[0060] [Table 1]

[0061] Table 2 below shows the water quality of the influent sewage and the treated water from each facility.

[0062] [Table 2]

[0063] When the same maximum and average daily wastewater volume as in this example was treated using a standard activated sludge system (Figure 4), the BOD of the treated water after treatment was 14 mg / L, the D-BOD (soluble BOD) was 8 mg / L, and the SS (suspended solids) was 12 mg / L. Therefore, the wastewater treatment system in Figure 2 was able to produce treated water of better quality compared to a conventional standard activated sludge system.

[0064] Based on these results, by transferring the digested sludge discharged from the methane fermentation plant 2 to the digested sludge conditioning plant 5, bringing it into contact with excess sludge from the water treatment plant 8, and then transferring a portion of the conditioned sludge (activated sludge) to the dewatering plant 4, the amount of coagulant used and the amount of dewatered cake produced could be reduced, and the cost required for dewatering treatment could be significantly reduced.

[0065] Furthermore, by transferring the digested sludge to the digested sludge conditioning facility 5 and converting it into activated sludge (conditioned sludge), the amount of activated sludge supplied to the contact mixing facility 6 could be increased. As a result, the amount of organic matter adsorbed onto the conditioned sludge and transferred to the methane fermentation facility 2 after separation and concentration increased, and the amount of digester gas generated by methane fermentation treatment could be increased. In other words, by providing the digested sludge conditioning facility 5, which conditions the digested sludge by bringing it into contact with excess sludge, the amount of digester gas generated in the methane fermentation facility 2 could be increased, and a wastewater treatment device with a high energy recovery rate could be provided.

[0066] Furthermore, by transferring the digested sludge to the digested sludge conditioning facility 5, the digested sludge was conditioned and converted into aerobic activated sludge, thus securing a sufficient amount of activated sludge (excess sludge) necessary for biosorption.

[0067] The wastewater treatment apparatus 20 shown in Figure 2 used in this embodiment can be constructed by modifying an existing apparatus that uses the standard activated sludge method. For example, the contact mixing equipment 6 and the separation and concentration equipment 7 can be constructed by modifying the primary sedimentation tank, and the digested sludge conditioning equipment 5 and the water treatment equipment 8 (B-MBR method) can be constructed by modifying the biological reaction tank (aeration tank). Furthermore, by using the wastewater treatment apparatus of this embodiment, it is possible to construct an apparatus that does not have a primary sedimentation tank, which has low efficiency in removing organic matter.

[0068] Although the present invention has been described above using the embodiments described above, the present invention is not limited to the embodiments described above. [Explanation of symbols]

[0069] 1. Sedimentation basin and screen equipment 2. Methane fermentation equipment 3. Energy recovery equipment 4 Dehydration equipment 5 Digested sludge conditioning equipment 6 Contact mixing equipment 7 Separation and concentration equipment 8. Water treatment facilities 10, 20, 30, 40 Wastewater treatment equipment

Claims

1. A wastewater treatment apparatus for treating wastewater containing impurities, organic matter and moisture, A means for separating impurities, organic matter, and moisture, A methane fermentation treatment means for treating the impurities separated by the impurities separation means with methane fermentation, A wastewater treatment apparatus comprising a water treatment means for treating treated water containing organic matter and water obtained by the impurity separation means, A digested sludge conditioning means for conditioning at least a portion of the digested sludge obtained by the methane fermentation treatment means by contacting it with activated sludge in the presence of oxygen, A contact means for bringing into contact and mixing the treated sludge obtained by the digested sludge treatment means and the treated water obtained by the impurities separation means, A separation and concentration means for separating the mixed liquid obtained by the contact means into concentrated sludge and separated water, A wastewater treatment apparatus characterized by having

2. The wastewater treatment apparatus according to claim 1, characterized in that a bypass route is provided for supplying a portion of the mixed liquid obtained by the contact means to the water treatment means without passing through the separation and concentration means.

3. The wastewater treatment apparatus according to claim 1, characterized in that concentrated sludge separated by the separation and concentration means is supplied to a methane fermentation treatment means.

4. The wastewater treatment apparatus according to claim 1, characterized in that the impurity separation means is a sedimentation tank and / or a screen device.

5. The wastewater treatment apparatus according to claim 1, characterized in that the water treatment means is a means using an activated sludge treatment method, and the activated sludge that is brought into contact with the digested sludge in the digested sludge conditioning means is excess sludge discharged from the water treatment means.

6. The wastewater treatment apparatus according to claim 1, characterized in that the weight ratio of the digested sludge and the activated sludge supplied to the digested sludge conditioning means is 1:0.5 to 1:

10.

7. The wastewater treatment apparatus according to claim 1, characterized in that the separation and concentration means is a pressurized flotation separation device.

8. The wastewater treatment apparatus according to claim 1, characterized in that it does not have a primary sedimentation tank.

9. A wastewater treatment method using the wastewater treatment apparatus described in any one of claims 1 to 8, A step of separating the aforementioned impurities from the organic matter and water, The process includes a methane fermentation treatment step in which the impurities separated in the impurities separation step are subjected to methane fermentation treatment, A water treatment step involves treating the treated water containing organic matter and water obtained by the aforementioned impurity separation step, A digested sludge conditioning step is performed in which at least a portion of the digested sludge obtained in the methane fermentation treatment step is brought into contact with activated sludge in the presence of oxygen to condition it, A contact step in which the treated sludge obtained in the aforementioned digested sludge treatment step and the treated water obtained in the aforementioned impurity separation step are brought into contact and mixed, A separation and concentration step is performed to separate the mixed liquid obtained in the above contact step into concentrated sludge and separated water, A concentrated sludge supply step in which the concentrated sludge separated in the separation and concentration step is supplied to the methane fermentation treatment step, A wastewater treatment method characterized by having the following features.

10. The wastewater treatment method according to claim 9, characterized in that the water treatment step is a step using an activated sludge treatment method, and the activated sludge that comes into contact with the digested sludge in the digested sludge conditioning is excess sludge discharged from the water treatment step.

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