Organic matter recovery equipment, sewage treatment system, organic matter recovery method, and sewage treatment method

Abstract

Organic matter recovery equipment (1) comprises: a separation tank (2) that stores organic wastewater; a separation membrane (24) that separates permeated water; a separation membrane drive mechanism (34) that drives the separation membrane (24); and a control device (40) that controls the operating conditions of the separation tank such that the concentration of suspended matter (SS) is 50-4000 mg / L and the concentration of dissolved oxygen (DO) is 1.5 mg / L or lower.

Description

Organic Matter Recovery Equipment and Sewage Treatment System, as well as Organic Matter Recovery Method and Sewage Treatment Method

[0001] The present invention relates to organic matter recovery equipment for recovering organic matter from organic wastewater containing ammonia nitrogen, a sewage treatment system using the same, and an organic matter recovery method and a sewage treatment method. This application claims priority based on Japanese Patent Application No. 2024-169898 filed in Japan on September 30, 2024, and incorporates its content herein by reference.

[0002] As a generally practiced method for treating organic wastewater, the activated sludge method is known. The activated sludge method is a method in which wastewater containing organic matter is introduced into a biological reaction tank, and a large amount of air is aerated into the wastewater while aerobic microorganisms decompose the organic matter. However, there is a problem of consuming a large amount of electricity for aeration, and there is room for improvement in terms of energy cost.

[0003] Therefore, Patent Document 1 proposes a wastewater treatment method in which wastewater containing organic matter is first passed through a hollow fiber membrane module and separated into permeated water that has passed through the hollow fiber membrane and concentrated water containing organic matter. Then, the concentrated water containing organic matter is stored in an anaerobic biological treatment tank and biologically treated under anaerobic conditions to obtain digested gas. According to this method, the electricity for aeration can be reduced, and the organic matter in the wastewater can be used as a source of digested gas without losing much of it, and the generated digested gas can be used for power generation. It is also proposed in Patent Document 1 to vibrate the membrane surface of the hollow fiber membrane during membrane filtration.

[0004] Non-Patent Document 1 proposes a method in which the effluent from the primary sedimentation tank is introduced into a pretreatment tank, slightly aerated while floating a sponge carrier, and the soluble organic matter is decomposed and reduced by the microorganisms attached to the sponge carrier. Then, it is passed through a hollow fiber membrane module and separated into permeated water that has passed through the hollow fiber membrane and concentrated water containing suspended organic matter. According to this method, it is possible to selectively decompose the soluble organic matter and reduce the organic matter concentration in the membrane permeated water while suppressing the decomposition of suspended organic matter in order to prevent a decrease in the organic matter recovery rate in membrane concentration.

[0005] Patent No. 7105431

[0006] "Direct Membrane Filtration of Sewage Using a Simple Pretreatment Method with Biofilms," Transactions of the Japan Society of Civil Engineers, Series G (Environment), Vol. 76, No. 7, III_227-III_234, 2020.

[0007] As shown in Patent Document 1 and Non-Patent Document 1, when organic matter is recovered from wastewater using hollow fiber membranes, the electricity required for aeration is reduced compared to the activated sludge method, and the recovered organic matter can be effectively utilized in the production of digester gas, thereby reducing energy costs. However, according to the inventors' research, it has been found that there is room to further increase the amount of dissolved organic matter recovered by setting the operating conditions of the separation tank to an appropriate range different from the conventional range. The present invention is based on the above findings and aims to provide an organic matter recovery facility and wastewater treatment system that can reduce the energy costs of wastewater treatment.

[0008] [Aspect 1] Aspect 1 of the present invention is an organic matter recovery system for recovering organic matter from organic wastewater containing ammonia nitrogen, comprising: a separation tank for storing the organic wastewater supplied from a supply source; a separation membrane provided in the separation tank for separating permeate water from which the organic matter has been removed from the organic wastewater; a separation membrane driving mechanism for driving the separation membrane within the separation tank and removing deposits from the separation membrane; and a control device for controlling the operating conditions of the separation tank such that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank is 50 mg / L or more and 4000 mg / L or less, and the dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank is 1.5 mg / L or less.

[0009] According to the organic matter recovery equipment of Embodiment 1, by controlling the operating conditions of the separation tank so that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank is 50 mg / L or more and 4000 mg / L or less, and the dissolved oxygen (DO) concentration of the organic wastewater is 1.5 mg / L or less, the dissolved organic matter contained in the organic wastewater is adsorbed by microorganisms (biosorption) within the separation tank, while suppressing the decomposition of the dissolved organic matter by the microorganisms. As a result, the dissolved organic matter attached to the microorganisms can be separated together with the microorganisms by the separation membrane. This makes it possible to recover organic components that would have passed through the separation membrane as dissolved material under conventional operating conditions, together with the microorganisms and sludge, increasing the overall organic matter recovery rate to about 65-90%, and making it possible to use the digester gas obtained from the recovered organic matter for power generation, etc. Furthermore, under operating conditions that suppress the decomposition of organic matter as described above, organic matter, sludge, and microorganisms tend to adhere to and accumulate on the separation membrane, leading to clogging (fouling) of the separation membrane and making it difficult to continue operation. However, in this embodiment, the separation membrane drive mechanism membrane drives the separation membrane within the separation tank, effectively causing the attached material (foulant) to fall off the separation membrane, thereby preventing fouling and improving operating efficiency.

[0010] In Embodiment 1, the operating conditions may be changed as follows: The suspended solids (SS) concentration of the organic wastewater stored in the separation tank may more preferably be 300 mg / L or more and 2500 mg / L or less. The dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank may preferably be 0.1 mg / L or more and 1.0 mg / L or less, and more preferably 0.5 mg / L or more and 1.0 mg / L or less. Control may be performed by a control device directly controlling each part of the separation tank, pumps, blowers, etc., or by an operator manually based on instructions, displays, or signals from the control device.

[0011] The organic matter recovery equipment includes a suspended solids concentration measuring means for measuring the suspended solids (SS) concentration in the organic wastewater stored in the separation tank, and a dissolved oxygen concentration measuring means for measuring the dissolved oxygen (DO) concentration in the organic wastewater stored in the separation tank. The control device may control the operating conditions of the separation tank based on the outputs of the suspended solids concentration measuring means and the dissolved oxygen concentration measuring means, such that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank is 50 mg / L or more and 4000 mg / L or less, and the dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank is 1.5 mg / L or less.

[0012] [Aspect 2] Aspect 2 is an organic matter recovery facility of Aspect 1, comprising: an organic wastewater introduction means for introducing the organic wastewater from the inlet of the separation tank; a sludge recovery means for recovering sludge containing the organic matter from the sludge recovery port of the separation tank; and a permeate water discharge means for sucking and recovering permeate water that permeates through the separation membrane, wherein the control device controls at least one of the organic wastewater introduction means, the sludge recovery means, and the permeate water discharge means. The control device may control at least one of the organic wastewater introduction means, the sludge recovery means, and the permeate water discharge means based on the output of the suspended solids concentration measuring means and the dissolved oxygen concentration measuring means.

[0013] According to the organic matter recovery equipment of embodiment 2, the control device can easily automatically control the operating conditions of the separation tank by controlling at least one of the organic wastewater introduction means, the sludge recovery means, and the permeate discharge means.

[0014] [Aspect 3] In aspect 3, in the organic matter recovery facility of aspect 1 or 2, the control device controls the operating conditions such that the hydrological residence time (HRT) of the separation tank is 20 minutes or more and 3 hours or less, and the solid matter residence time (SRT) of the separation tank is 4 hours or more and 80 hours or less.

[0015] According to the organic matter recovery equipment of embodiment 3, by controlling the operating conditions such that the hydrological residence time (HRT) of the separation tank is 20 minutes or more and 3 hours or less, and the solid matter residence time (SRT) of the separation tank is 4 hours or more and 80 hours or less, it is easy to increase the organic matter recovery rate while suppressing the decomposition of organic matter in the separation tank.

[0016] In embodiment 3, the operating conditions may be changed as follows: The hydrological residence time (HRT) of the separation tank may preferably be 30 minutes or more and 2 hours or less, and more preferably 40 minutes or more and 1.5 hours or less. The solids residence time (SRT) of the separation tank may preferably be 6 hours or more and 70 hours or less, and more preferably 8 hours or more and 60 hours or less.

[0017] [Aspect 4] In aspect 4, in the organic matter recovery equipment described in any of aspects 1 to 3, the control device controls the operating conditions so that the ammonia nitrogen removal rate, defined by the following formula, is 24% or less. Ammonia nitrogen removal rate [%] = (Ammonia nitrogen concentration in the organic wastewater (mg / L) - Ammonia nitrogen concentration in the permeate (mg / L)) / (Ammonia nitrogen concentration in the organic wastewater (mg / L)) × 100

[0018] In the organic matter recovery equipment of embodiment 4, the operating conditions are controlled so that the ammonia nitrogen removal rate is 24% or less, making it easy to increase the recovery rate of organic matter while effectively suppressing the decomposition of organic matter in the separation tank. In addition, a large amount of N is discharged during the biological treatment of ammonia. ２ Because the amount of O generated can be reduced, N in the treatment facility ２ It can reduce greenhouse gases originating from oxygen. The ammonia nitrogen removal rate may be 0% or more and 15% or less.

[0019] [Aspect 5] In aspect 5, in the organic matter recovery equipment described in any of aspects 1 to 4, the control device controls the operating conditions such that the oxidation-reduction potential (ORP) of the organic wastewater stored in the separation tank is -150 mV or higher.

[0020] According to the organic matter recovery equipment of embodiment 5, the operating conditions are controlled so that the oxidation-reduction potential (ORP) of the organic wastewater stored in the separation tank is -150 mV or higher. Therefore, it is easy to increase the recovery rate of organic matter while effectively suppressing the decomposition of organic matter in the separation tank. The oxidation-reduction potential (ORP) of the organic wastewater may be -100 mV or higher, and may be between -50 mV and +100 mV.

[0021] [Aspect 6] Aspect 6 is an organic matter recovery apparatus according to any one of aspects 1 to 5, wherein the separation membrane driving mechanism comprises a movable frame that supports both ends of the separation membrane and an actuator that drives the movable frame within a certain range of motion.

[0022] According to the organic matter recovery equipment of embodiment 6, the actuator of the separation membrane drive mechanism makes it possible to vibrate, oscillate, or intermittently operate the movable frame supporting both ends of the separation membrane within a certain range of motion. Therefore, the separation membrane can be driven in accordance with the state of adhesion of foulants, causing the foulants to fall off the membrane, thereby effectively preventing fouling and improving operating efficiency. The separation membrane drive mechanism also requires a simple structure.

[0023] [Aspect 7] Aspect 7 is an organic matter recovery apparatus according to any one of aspects 1 to 6, wherein the separation membrane driving mechanism comprises a movable frame that supports both ends of the separation membrane and an actuator that drives the movable frame within a certain oscillation range, and the actuator oscillates the separation membrane at 0.01 to 0.90 Hz via the movable frame.

[0024] According to the organic matter recovery equipment of embodiment 7, the actuator oscillates the separation membrane at 0.01 to 0.90 Hz via the movable frame, thereby effectively preventing fouling and improving operating efficiency while maintaining a simple actuator structure and operation. The separation membrane may be oscillated at 0.3 to 0.7 Hz, or even further at 0.4 to 0.5 Hz.

[0025] [Aspect 8] Aspect 8 is an organic matter recovery facility described in any of aspects 1 to 7, in which 40 to 80 mass% of the total amount of organic matter contained in the organic wastewater is recovered.

[0026] According to the organic matter recovery equipment of embodiment 8, by recovering 40 to 80 mass% of the total amount of organic matter contained in the organic wastewater in the separation tank, it is possible to increase the recovery efficiency of organic matter per unit time and per unit volume. Alternatively, 50 to 75 mass% of the total amount of organic matter contained in the organic wastewater may be recovered, or even 60 to 70 mass% of the total amount of organic matter contained in the organic wastewater may be recovered.

[0027] [Aspect 9] Aspect 9 is an organic matter recovery facility according to any one of aspects 1 to 8, wherein the separation membrane is one or more selected from hollow fiber membrane modules, flat membrane modules, and tubular membrane modules, and is arranged vertically within the separation tank.

[0028] According to the organic matter recovery equipment of embodiment 9, one or more types selected from hollow fiber membrane modules, flat membrane modules, and tubular membrane modules are used as the separation membrane and are arranged vertically within the separation tank, resulting in high efficiency in recovering permeate and effective removal of foulants.

[0029] [Aspect 10] In aspect 10, in the organic matter recovery equipment described in any of aspects 1 to 9, the control device controls the operating conditions such that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank is 50 mg / L or more and 1200 mg / L or less, and the solid matter residence time (SRT) in the separation tank is 4 hours or more and 36 hours or less.

[0030] According to the organic matter recovery equipment of embodiment 10, compared to embodiment 11 described later, the solid matter residence time (SRT) is set to a relatively short range and the suspended solids (SS) concentration is controlled to a lower range, thereby relatively reducing the decomposition of dissolved organic matter by microorganisms and further increasing the recovery rate of dissolved organic matter.

[0031] In embodiment 10, the operating conditions may be changed as follows: The suspended solids (SS) concentration of the organic wastewater may preferably be 300 mg / L or more and 800 mg / L or less. The solids retention time (SRT) in the separation tank may preferably be 6 hours or more and 24 hours or less, and more preferably 8 hours or more and 16 hours or less.

[0032] [Aspect 11] In aspect 11, in an organic matter recovery facility according to any one of aspects 1 to 9, the control device controls the operating conditions such that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank is 500 mg / L or more and 4000 mg / L or less, and the solid matter residence time (SRT) in the separation tank is 36 hours or more and 80 hours or less.

[0033] According to the organic matter recovery equipment of embodiment 11, compared to embodiment 10 described above, by setting the solid matter residence time (SRT) to a relatively longer range and controlling the suspended solids (SS) concentration to a higher range, although the decomposition of organic matter proceeds to some extent, the microorganisms tend to adsorb substances that cause clogging of the separation membrane, making clogging (fouling) of the separation membrane less likely and increasing the effectiveness of suppressing fouling. This reduces the need for and frequency of processes to remove fouling, thereby increasing the operating efficiency of the recovery equipment.

[0034] In embodiment 11, the operating conditions may be changed as follows: The suspended solids (SS) concentration of the organic wastewater may preferably be 1500 mg / L or more and 2500 mg / L or less. The solids retention time (SRT) in the separation tank may preferably be 42 hours or more and 70 hours or less, and more preferably 48 hours or more and 60 hours or less. The hydraulic retention time (HRT) may preferably be 1 hour or more and 3 hours or less, and more preferably 1.5 hours or more and 2.5 hours or less.

[0035] [Aspect 12] The wastewater treatment system of aspect 12 comprises an organic matter recovery facility described in any of aspects 1 to 11, a digestion tank to which secondary sludge recovered from the organic matter recovery facility is supplied, a sludge digestion facility for methane fermentation of the secondary sludge in the digestion tank, and a power generation facility for generating electricity using digestion gas discharged from the sludge digestion facility, wherein the organic matter recovery facility recovers 40 to 80 mass% of the total amount of sludge contained in the organic wastewater as secondary sludge.

[0036] [Aspect 13] The wastewater treatment system of aspect 13 comprises an organic matter recovery facility described in any of aspects 1 to 11, a primary sludge recovery facility that recovers 20 to 50 mass% of the total amount of organic matter contained in the influent as primary sludge before the organic matter recovery facility, a digestion tank to which at least one of the primary sludge recovered from the primary sludge recovery facility and the secondary sludge recovered from the organic matter recovery facility is supplied, a sludge digestion facility that methane ferments at least one of the primary sludge and the secondary sludge in the digestion tank, and a power generation facility that generates electricity using the digestion gas discharged from the sludge digestion facility, wherein the organic matter recovery facility recovers 40 to 80 mass% of the total amount of sludge contained in the organic wastewater as secondary sludge.

[0037] According to the wastewater treatment system of embodiment 13, 20 to 50 mass% of the total amount of sludge contained in the influent water is recovered as primary sludge by the primary sludge recovery equipment, and further, 40 to 80 mass% of the total amount of sludge contained in the organic wastewater is recovered as secondary sludge by the organic matter recovery equipment. Then, the primary sludge and the secondary sludge are subjected to methane fermentation in the digestion tank by the sludge digestion equipment. As a result, organic matter corresponding to approximately 50 to 90% of the total amount of organic matter contained in the influent water is introduced into the digestion tank to obtain digester gas, which can then be used for power generation. Therefore, the generated electricity can be sold or used within the system to reduce power consumption, thereby increasing economic efficiency. Alternatively, 25 to 45 mass% of the total amount of sludge contained in the influent water may be recovered as primary sludge by the primary sludge recovery equipment, or 30 to 40 mass% of the total amount of primary sludge may be recovered by the primary sludge recovery equipment. 50 to 75 mass% of the total amount of sludge contained in the organic wastewater may be recovered as secondary sludge, or 60 to 70 mass% of the total amount of sludge contained in the organic wastewater may be recovered as secondary sludge.

[0038] [Aspect 14] The method for recovering organic matter according to aspect 14 is a method for recovering organic matter from organic wastewater containing ammonia nitrogen, comprising the steps of: storing the organic wastewater supplied from a source in a separation tank; separating the permeate obtained by removing the organic matter from the organic wastewater in the separation tank using a separation membrane; driving the separation membrane in the separation tank to remove deposits from the separation membrane; and setting the suspended solids (SS) concentration of the organic wastewater stored in the separation tank to 50 mg / L or more and 4000 mg / L or less, and setting the dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank to 1.5 mg / L or less. In aspect 14, the descriptions of various preferred configurations and operating conditions described in aspects 1 to 13 are incorporated herein by reference.

[0039] [Aspect 15] The wastewater treatment method according to aspect 15 includes the steps of: introducing influent water containing sludge into a primary sludge recovery facility, recovering 20 to 50 mass% of the total amount of sludge contained in the influent water as primary sludge, and obtaining the remainder as organic wastewater; storing the organic wastewater in a separation tank, separating the permeate obtained by removing the organic matter from the organic wastewater in the separation tank using a separation membrane; driving the separation membrane in the separation tank to remove deposits from the separation membrane; and setting the suspended solids (SS) concentration of the organic wastewater stored in the separation tank to 50 mg / L or more and 40 The apparatus comprises the steps of: setting the dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank to 1.5 mg / L or less, and recovering secondary sludge from the separation tank; methane fermentation of at least one of the primary sludge recovered from the primary sludge recovery equipment and the secondary sludge recovered from the separation tank in the digestion tank; and generating electricity using the digestion gas discharged from the digestion tank, wherein the separation tank recovers 40 to 80 mass% of the total amount of sludge contained in the organic wastewater as secondary sludge. In embodiment 15, the descriptions of various preferred configurations and operating conditions described in embodiments 1 to 13 are incorporated herein by reference.

[0040] According to the organic matter recovery equipment and wastewater treatment system of the present invention, by controlling the operating conditions as described above, dissolved organic matter contained in organic wastewater can be adsorbed by microorganisms in the separation tank, while suppressing the decomposition of the dissolved organic matter by the microorganisms. Dissolved organic matter taken up by the microorganisms can be separated together with the microorganisms by the separation membrane. As a result, organic components that would have passed through the separation membrane as dissolved matter under conventional operating conditions can be recovered as sludge together with the microorganisms, increasing the overall organic matter recovery rate to, for example, 65-90%, and the digester gas obtained from the recovered organic matter can be used for power generation, etc. Furthermore, under operating conditions in which the decomposition of organic matter is suppressed as described above, organic matter, sludge, and microorganisms tend to adhere to and accumulate on the separation membrane, causing clogging (fouling) of the separation membrane and making it difficult to continue operation. However, in this embodiment, the separation membrane driving mechanism membrane drives the separation membrane in the separation tank and can effectively remove adhering substances (foulants) from the separation membrane, thereby preventing fouling and improving operating efficiency.

[0041] It is a longitudinal sectional view showing an organic matter recovery facility according to an embodiment of the present invention. It is a block diagram showing a sewage treatment system according to an embodiment of the present invention. It is a schematic diagram for explaining the effects of the present invention. It is a longitudinal sectional view of the experimental apparatus used in Examples 1 and 2 of the present invention. It is a graph showing the measurement results of the organic matter recovery rate according to Example 1. It is a graph showing the measurement results of the organic matter recovery rate according to Example 1. It is a graph showing the measurement results of the ammonia nitrogen removal rate according to Example 2. It is a graph showing the measurement results of the ammonia nitrogen removal rate according to Example 2. It is a block diagram of the experimental apparatus used in Example 3 of the present invention. It is a graph showing the results of Example 3. It is a graph showing the change in the ammonia nitrogen removal rate [%] when the solid retention time (SRT) of the separation tank is changed from 20 to 100 hours in Example 4. It is a graph showing the change in the concentration of suspended solids (SS) [mg / L] when the solid retention time (SRT) of the separation tank is changed from 20 to 100 hours in Example 4.

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The organic wastewater that can be used in the embodiments of the present invention is not particularly limited. For example, in addition to the organic wastewater flowing in or generated in sewage treatment plants, manure treatment plants, various industrial wastewater treatment plants, etc., organic wastewater generated in various factories such as food manufacturing factories and fertilizer manufacturing factories can be used.

[0043] [Embodiment 1 of Organic Matter Recovery Facility] FIG. 1 shows an organic matter recovery facility 1 according to Embodiment 1. This organic matter recovery facility 1 is a facility for recovering organic matter from organic wastewater containing ammonia nitrogen, and has a separation tank 2 for storing the organic wastewater supplied from a supply source of the organic wastewater. The shape and dimensions of the separation tank 2 are not limited, but generally have a rectangular parallelepiped shape or a cylindrical shape, and have a capacity corresponding to the amount of organic wastewater to be treated. The separation tank 2 has an inlet 4 at one end (the left side in this example in the figure), and organic wastewater is supplied from the inlet 4 through an organic wastewater introduction pump 6 (organic wastewater introduction means) from a supply source not shown. The organic wastewater introduction pump 6 is connected to a control device 40 that controls the operating conditions of the separation tank 2.

[0044] As the organic drainage introduction means, the pump 6 may be used as described above, or a method of natural flow using a liquid level difference (liquid level difference water supply mechanism) may be adopted. Examples of the types of pumps include centrifugal pumps, gear pumps, rotary pumps, etc., but are not limited thereto, and any type of pump can be selected according to the purpose. The selection of the pump is appropriately determined based on conditions such as flow rate, pressure, installation environment, etc.

[0045] At the lower end of the separation tank 2, a sludge recovery port 12 is formed, from which the recovered sludge (secondary sludge described later) is recovered and sent to the next process through a sludge recovery pump 14 (sludge recovery means). The sludge recovery pump 14 is connected to the control device 40. Along the inner bottom of the separation tank 2, an air blowing portion 16 having a number of ejection holes is arranged, and an air blower 18 is connected to the air blowing portion 16, and fine air bubbles are blown into the organic drainage stored in the separation tank 2 from below, and the required amount of aeration is performed. The air blower 18 is connected to the control device 40. In this embodiment, the air blower 18 is provided, but in the case of controlling the dissolved oxygen by other means described later, the air blower 18 does not necessarily have to be provided.

[0046] Examples of the sludge recovery pump 14 include centrifugal pumps, gear pumps, rotary pumps, etc., but are not limited thereto, and any type of pump can be selected according to the purpose. Also, a pump may be used, or a method of natural flow using a liquid level difference (liquid level difference water supply mechanism) may be adopted. As the air blowing portion 16, a fine bubble diffusing type disk, tube, plate type diffusing device, etc. with high oxygen dissolution efficiency are used, but are not limited thereto, and a diffusing device with any shape or structure can be used. For the blower 18, a multistage turbo blower, roots blower, etc. are used, but as long as air can be supplied, a compressor, etc. may also be used, and the gas to be blown may not be normal air as long as it is a gas containing oxygen.

[0047] Inside the separation tank 2, a separation membrane 24 is arranged to separate the permeate water from which organic matter has been removed from organic wastewater. As the separation membrane 24, one or more types can be used, selected from, for example, a hollow fiber membrane module with a thin tubular hollow fiber membrane, a flat membrane module with a flat membrane, and a tubular membrane module with a tubular membrane, and are arranged vertically within the separation tank 2. When arranged vertically, it has the advantage that attached matter (foulant) can easily fall off. However, in the present invention, the orientation of the separation membrane 24 is not necessarily limited, and it may be oriented horizontally or inclined.

[0048] The fineness of the separation membrane 24 is not limited, but a pore size of 0.05 to 1.0 μm is preferable. The material of the separation membrane 24 can be PVDF or PTFE for organic membranes, or aluminum oxide or silicon carbide for inorganic membranes, but is not limited to these.

[0049] In this example, the separation membrane 24 is modularized by bundling many thin tubes with fine perforations, and the communication hole at the upper end of each module is connected to a manifold 26, forming one water passage in each manifold 26. The lower ends of each tube in the separation membrane 24 are closed, and the upper and lower ends of the separation membrane 24 are fixed to movable frames 20 which are horizontally arranged in the separation tank 2. The water passages of each manifold 26 are all connected to a water collection pipe 28, and the permeate that has passed through the separation membrane 24 is collected by a permeate suction pump 30 (permeate suction means) which sucks it from the water collection pipe 28. The permeate suction pump 30 is connected to a control device 40. A backwash water supply pump 32 is also connected to the water collection pipe 28, and when the backwash water supply pump 32 (backwash water supply means) is operated, backwash water from a backwash water supply source (not shown) is supplied to the separation membrane 24 through the water collection pipe 28, backwashing the separation membrane 24. The backwash water supply pump 32 is also connected to the control device 40.

[0050] A pump may be used as the means for drawing in permeate water, or a system that utilizes the difference in liquid level to allow water to flow naturally (a liquid level difference water supply mechanism) may be used. Examples of pump types include centrifugal pumps, gear pumps, and rotary pumps, but the system is not limited to these, and any type of pump can be selected depending on the purpose. The selection of the pump is determined appropriately based on conditions such as flow rate, pressure, and installation environment.

[0051] The upper and lower movable frames 20 are supported by slide rails (not shown) or the like so that they can reciprocate within a certain range in the horizontal direction, and are connected to a frame support 38, which is connected to a separation membrane drive mechanism 34 located outside the separation tank 2. The separation membrane drive mechanism 34 has an actuator 36 that drives the frame support 38 horizontally within a certain range, and the actuator 36 is connected to a control device 40.

[0052] Inside the separation tank 2 are a suspended solids (SS) concentration measuring means 42 for directly or indirectly measuring the suspended solids (SS) concentration in the organic wastewater stored in the separation tank, a dissolved oxygen (DO) concentration measuring means 46 for directly or indirectly measuring the dissolved oxygen (DO) concentration in the organic wastewater, and an oxidation-reduction potential measuring means 48 for directly or indirectly measuring the oxidation-reduction potential in the organic wastewater. All of these are connected to the control device 40. Although the suspended solids concentration measuring means 42, the dissolved oxygen concentration measuring means 46, and the oxidation-reduction potential measuring means 48 are shown as being located inside the separation tank 2, this embodiment is not limited to this. For example, these means may be provided outside the separation tank 2, as long as the suspended solids concentration, dissolved oxygen concentration, and oxidation-reduction potential in the organic wastewater in the separation tank 2 can be measured directly or indirectly, such as by sampling a portion of the organic wastewater in the separation tank 2 to measure the suspended solids concentration. With respect to the suspended solids concentration measuring means 42, the dissolved oxygen concentration measuring means 46, and the oxidation-reduction potential measuring means 48, the above-mentioned "direct measurement" includes all methods of measuring the measured indicator by sampling the liquid to be measured, and "indirect measurement" includes methods of determining the measured indicator from values ​​read by sensors, such as the transmittance or reflectance of electromagnetic waves such as infrared rays, and also includes inferring the measured indicator from measured values ​​of other indicators using an AI (artificial intelligence) inference device.

[0053] As the suspended solids concentration measuring means 42, for example, a continuous measuring device using the transmitted light measurement method or the forward scattered reflected light measurement method, or an intermittent measuring device using the glass fiber filter paper method or the centrifugal separation method can be used. As the dissolved oxygen concentration measuring means 46, for example, the diaphragm electrode method, which determines the dissolved oxygen concentration by measuring the diffusion current or reduction current generated in response to the dissolved oxygen concentration, can be used, and for example, a polaro-type oxygen measuring means or a galvanic-type oxygen measuring means may be used. As the oxidation-reduction potential measuring means 48, an oxidation-reduction potential meter can be used. Although not shown in the figure, an ammonia nitrogen concentration measuring means for continuously or intermittently measuring the ammonia nitrogen concentration (mg / L) in organic wastewater may also be provided in the separation tank 2. The ammonia nitrogen concentration measuring means is also connected to the control device 40.

[0054] The control device 40 controls the operating conditions of the separation tank 2, for example, based on the outputs of the suspended solids concentration measuring means 42 and the dissolved oxygen concentration measuring means 46, so that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank 2 is 50 mg / L or more and 4000 mg / L or less, and the dissolved oxygen (DO) concentration of the organic wastewater is 1.5 mg / L or less. This control allows dissolved organic matter contained in the organic wastewater to be adsorbed by microorganisms in the separation tank 2, while suppressing the decomposition of the dissolved organic matter by the microorganisms, and enabling the separation of dissolved organic matter attached to the microorganisms together with the microorganisms in the separation membrane 24. As a result, organic components that would have passed through the separation membrane as dissolved matter under conventional operating conditions can be recovered together with the microorganisms and sludge.

[0055] The control device 40 may be specifically implemented by hardware such as a computer, including a circuit section, executing a software program. The hardware may include, for example, a CPU (Central Processing Unit), an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit). The program described above is stored in a storage device equipped with a storage medium. The storage medium may include, for example, an HDD (Hard Disk Drive), flash memory, ROM (Read Only Memory), or DVD (Digital Versatile Disc). Furthermore, the program described above may be a differential program that implements some of the functions of the control device 40. The specific control method by the control device 40 is as follows.

[0056] [Control of Suspended Solids (SS) Concentration] Suspended solids (SS) are particulate matter with a diameter of approximately 1 μm to 2 mm that is suspended or floating in the organic wastewater in the separation tank 2. This includes fine particles of clay minerals, zooplankton and phytoplankton and their remains, and precipitates of organic matter and metals derived from sewage, factory wastewater, etc. The control device 40 sets a threshold or threshold range (upper and lower limits) for the suspended solids (SS) concentration that is included in the range of 50 mg / L or more and 4000 mg / L or less. If the suspended solids (SS) concentration in the separation tank 2 rises above the threshold or upper limit, at least one of the following operations is performed. The following operations may be performed by the control device 40 directly controlling each pump, or by an operator manually based on instructions, displays, or signals from the control device 40. (1) Reduce the amount of organic wastewater introduced into the separation tank 2 by the organic wastewater introduction pump 6. (2) Increase the amount of recovered sludge discharged by the sludge recovery pump 14. (3) Increase the amount of aeration in the separation tank 2 by the air blower 18 to promote the decomposition of suspended solids by aerobic microorganisms.

[0057] Conversely, if the suspended solids (SS) concentration in the separation tank 2 falls below the threshold or lower limit, at least one of the following operations is performed: (1) Increase the amount of organic wastewater introduced into the separation tank 2 by the organic wastewater introduction pump 6. (2) Decrease the amount of recovered sludge discharged by the sludge recovery pump 14. (3) Reduce the amount of aeration in the separation tank 2 by the air blower 18 to lower the rate of decomposition of suspended solids by aerobic microorganisms. By performing the above operations, the suspended solids concentration in the separation tank 2 is adjusted to be maintained at the threshold or within the threshold range. The operating conditions may be changed as follows: The suspended solids (SS) concentration of the organic wastewater stored in the separation tank is preferably 300 mg / L or more and 2500 mg / L or less.

[0058] [Control of Dissolved Oxygen (DO) Concentration] The dissolved oxygen (DO) concentration in organic wastewater represents the oxygen concentration dissolved in the organic wastewater in the separation tank 2, and is expressed as the weight of oxygen contained in 1 liter of water. The control device 40 sets a threshold or threshold range (upper and lower limits) that encompasses the dissolved oxygen (DO) concentration within the range of 1.5 mg / L or less (preferably 0.1 mg / L or more and 1.0 mg / L or less). If the dissolved oxygen (DO) concentration in the separation tank 2 rises above the threshold or upper limit, at least one of the following operations is performed: (1) Increase the amount of organic wastewater introduced into the separation tank 2 by the organic wastewater introduction pump 6. (2) Increase the amount of recovered sludge discharged by the sludge recovery pump 14. (3) Decrease the amount of aeration in the separation tank 2 by the air blower 18.

[0059] Conversely, if the dissolved oxygen (DO) concentration in the separation tank 2 falls below the threshold or lower limit, at least one of the following operations is performed: (1) Reduce the amount of organic wastewater introduced into the separation tank 2 by the organic wastewater introduction pump 6. (2) Increase the amount of recovered sludge discharged by the sludge recovery pump 14. (3) Increase the amount of aeration in the separation tank 2 by the air blower 18. By performing the above operations, the dissolved oxygen (DO) concentration in the separation tank 2 is adjusted to be maintained at the threshold or within the threshold range.

[0060] The above operating conditions may be changed as follows: The dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank 2 may preferably be 0.1 mg / L or more and 1.0 mg / L or less, and more preferably 0.5 mg / L or more and 1.0 mg / L or less.

[0061] According to the organic matter recovery equipment 1 of this embodiment, by controlling the operating conditions of the separation tank 2 so that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank 2 is 50 mg / L or more and 4000 mg / L or less, and the dissolved oxygen (DO) concentration of the organic wastewater is 1.5 mg / L or less, as shown in Figure 3, dissolved organic matter contained in the organic wastewater is adsorbed by microorganisms in the separation tank 2, while suppressing the decomposition of the dissolved organic matter by the microorganisms, and the dissolved organic matter that has been taken up by the microorganisms can be separated together with the microorganisms by the separation membrane 24. As a result, it becomes possible to recover organic components that would have passed through the separation membrane as dissolved matter under conventional operating conditions, together with the microorganisms and sludge, thereby increasing the overall organic matter recovery rate to, for example, 65 to 90%, and making it possible to effectively utilize the increased amount of digester gas obtained from the recovered organic matter for power generation, etc. Furthermore, under operating conditions that suppress the decomposition of organic matter as described above, organic matter, sludge, and microorganisms tend to adhere to and accumulate on the separation membrane, leading to clogging (fouling) of the separation membrane and making it difficult to continue operation. However, in this embodiment, the separation membrane drive mechanism membrane drives the separation membrane within the separation tank, effectively causing the attached material (foulant) to fall off the separation membrane, thereby preventing fouling and improving operating efficiency.

[0062] Furthermore, the control device 40 can easily control the suspended solids (SS) concentration and dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank 2 to the threshold or threshold range by controlling at least one of the organic wastewater introduction pump 6, sludge recovery pump 14, air blower 18, and permeate suction pump 30 based on the outputs of the suspended solids concentration measuring means 42 and the dissolved oxygen concentration measuring means 46.

[0063] In this embodiment, it is preferable that the control device 40 controls the operating conditions such that the hydraulic residence time (HRT) of the separation tank 2 is 20 minutes or more and 3 hours or less, and the solids residence time (SRT) of the separation tank 2 is 4 hours or more and 80 hours or less. However, the present invention is not limited to this range.

[0064] [Control of Hydraulic Residence Time (HRT)] Hydraulic residence time (HRT) refers to the time from when organic wastewater flows into the separation tank 2 until it flows out, and can be calculated by dividing the effective capacity of the separation tank 2 by the amount of water flowing in per unit time. To control the hydraulic residence time (HRT) of the separation tank 2, a threshold or threshold range (upper and lower limits) encompassing a range of 20 minutes or more and 3 hours or less is set in the control device 40, and if the hydraulic residence time (HRT) of the separation tank 2 rises above the threshold or upper limit, at least one of the following operations is performed. The following operations may be performed manually by an operator based on instructions or signals from the control device 40. (1) Increase the amount of organic wastewater introduced into the separation tank 2 by the organic wastewater introduction pump 6. (2) Increase the amount of permeate pumped out by the permeate suction pump 30. (3) Increase the amount of recovered sludge discharged by the sludge recovery pump 14.

[0065] If the hydrological residence time (HRT) of the separation tank 2 falls below the threshold or lower limit, at least one of the following operations shall be performed. The following operations may be performed manually by an operator based on instructions or signals from the control device 40. (1) Reduce the amount of organic wastewater introduced into the separation tank 2 by the organic wastewater introduction pump 6. (2) Reduce the amount of permeate pumped out by the permeate suction pump 30. (3) Reduce the amount of recovered sludge discharged by the sludge recovery pump 14. By performing the above operations, the hydrological residence time (HRT) in the separation tank 2 shall be adjusted to be maintained at the threshold or within the threshold range. The above operating conditions may be changed as follows. The hydrological residence time (HRT) of the separation tank 2 may preferably be 30 minutes or more and 2 hours or less, and more preferably 40 minutes or more and 1.5 hours or less.

[0066] [Control of Solid Matter Residence Time (SRT)] The solid matter residence time (SRT) in the separation tank 2 is a value obtained by dividing the amount of suspended solids in the separation tank 2 by the amount of suspended solids flowing out of the separation tank 2 per unit time (amount of suspended solids in the permeate water and amount of recovered sludge). A threshold or threshold range (upper and lower limits) encompassing a range of 4 hours or more and 80 hours or less is set in the control device 40. If the solid matter residence time (SRT) in the separation tank 2 rises above the threshold or upper limit, at least one of the following operations is performed. The following operations may be performed manually by an operator based on instructions or signals from the control device 40. (1) Reduce the amount of organic wastewater introduced into the separation tank 2 by the organic wastewater introduction pump 6. (2) Increase the amount of recovered sludge discharged by the sludge recovery pump 14. (3) Increase the amount of aeration in the separation tank 2 by the air blower 18 to promote the decomposition of suspended solids by aerobic microorganisms.

[0067] If the solids retention time (SRT) in the separation tank 2 falls below the threshold or lower limit, at least one of the following operations shall be performed. The following operations may be performed manually by an operator based on instructions or signals from the control device 40. (1) Increase the amount of organic wastewater introduced into the separation tank 2 by the organic wastewater introduction pump 6. (2) Decrease the amount of recovered sludge discharged by the sludge recovery pump 14. (3) Reduce the amount of aeration in the separation tank 2 by the air blower 18 to slow down the decomposition of suspended solids by aerobic microorganisms.

[0068] In the organic matter recovery equipment 1 of this embodiment, by controlling the operating conditions so that the hydrological residence time (HRT) of the separation tank 2 is 20 minutes or more and 3 hours or less, and the solid matter residence time (SRT) is 4 hours or more and 80 hours or less, it is possible to adsorb dissolved organic matter contained in organic wastewater into microorganisms in the separation tank 2, while suppressing the decomposition of the dissolved organic matter by the microorganisms, thereby enhancing the effect of separating the dissolved organic matter attached to the microorganisms together with the microorganisms in the separation membrane 24.

[0069] The above operating conditions may be changed as follows: The solids retention time (SRT) in the separation tank may preferably be 6 hours or more and 70 hours or less, and more preferably 8 hours or more and 60 hours or less.

[0070] [Control of Ammonia Nitrogen Removal Rate] In the organic matter recovery equipment 1 of this embodiment, the operating conditions may be controlled so that the ammonia nitrogen removal rate, defined by the following formula, is 24% or less. Ammonia Nitrogen Removal Rate [%] = (Ammonia nitrogen concentration in organic wastewater (mg / L) - Ammonia nitrogen concentration in permeate (mg / L)) / (Ammonia nitrogen concentration in organic wastewater (mg / L)) × 100

[0071] When the operating conditions are controlled so that the ammonia nitrogen removal rate is 24% or less, it is easy to increase the recovery rate of organic matter while effectively suppressing the decomposition of organic matter in the separation tank 2.

[0072] The ammonia nitrogen concentration (mg / L) in the organic wastewater may be measured on the organic wastewater before it is introduced into the separation tank 2, or it may be measured continuously or intermittently by an ammonia nitrogen concentration measuring means installed in the separation tank 2. An upper limit is set in the control device 40 that is included in the range of 24% or less, and if the ammonia nitrogen removal rate in the separation tank 2 rises above the upper limit, at least one of the following operations is performed. The following operations may be performed by the control device 40 directly controlling each pump, or by an operator manually based on instructions, displays, or signals from the control device 40. (1) Increase the amount of recovered sludge discharged by the sludge recovery pump 14. (2) Reduce the amount of aeration in the separation tank 2 by the air blower 18 to slow down the oxidation of ammonia nitrogen by aerobic microorganisms. The above operating conditions may be changed as follows. The ammonia nitrogen removal rate may preferably be 0% or more and 15% or less, and more preferably 0% or more and 4% or less.

[0073] [Control of Oxidation-Reduction Potential (ORP)] In this embodiment, the operating conditions of the separation tank 2 may be controlled so that the oxidation-reduction potential (ORP) of the organic wastewater in the separation tank 2 is -150 mV or higher. -150 mV or higher means that it is on the positive side of -150 mV. When the operating conditions are controlled so that the oxidation-reduction potential (ORP) of the organic wastewater is -150 mV or higher, it is easy to maintain a reducing atmosphere inside the separation tank 2, effectively suppress the decomposition of organic matter, and increase the recovery rate of organic matter.

[0074] To control the operating conditions so that the oxidation-reduction potential (ORP) in organic wastewater is -150 mV or higher, the control device 40 is set to a lower limit within the range of -150 mV or higher, and if the oxidation-reduction potential (ORP) falls below the lower limit, at least one of the following operations is performed. The following operations may be performed by the control device 40 directly controlling each pump, or by an operator manually based on instructions, displays, or signals from the control device 40. (1) Increase the amount of recovered sludge discharged by the sludge recovery pump 14. (2) Increase the amount of aeration in the separation tank 2 by the air blower 18 to weaken the reducing atmosphere. The above operating conditions may be changed as follows. The oxidation-reduction potential (ORP) in organic wastewater may be -100 mV or higher, and may also be -50 mV or higher and +100 mV or lower. However, if it is higher than +100 mV, the rate of decomposition by microorganisms may become too high.

[0075] In this embodiment, the separation membrane drive mechanism 34 is controlled by the control device 40. When treating organic wastewater, the separation membrane drive mechanism 34 is always operated to drive the separation membrane 24 horizontally within a certain range. The separation membrane 24 may be driven by oscillating it at a constant period, intermittently driving it in the forward and reverse directions, or vibrating it at a constant or variable frequency. If necessary, the separation membrane drive mechanism 34 may also cause the separation membrane 24 to move in a circular motion.

[0076] The actuator 36 may oscillate the separation membrane 24 at 0.05 to 0.9 Hz. By oscillating the separation membrane 24 at 0.05 to 0.9 Hz, the actuator's structure and operation can be kept simple while effectively preventing fouling and improving operating efficiency. The separation membrane may also be oscillated at 0.3 to 0.7 Hz, or even further at 0.4 to 0.5 Hz.

[0077] In this embodiment, 40 to 80 mass% of the total amount of organic matter contained in the organic wastewater may be recovered. By recovering 40 to 80 mass% of the total amount of organic matter contained in the organic wastewater, it is possible to increase the recovery efficiency of organic matter per unit time and per unit volume. 50 to 75 mass% of the total amount of organic matter contained in the organic wastewater may also be recovered, or even 60 to 70 mass% of the total amount of organic matter contained in the organic wastewater may be recovered.

[0078] [Embodiment 2 of the Organic Matter Recovery Equipment] Next, Embodiment 2 of the organic matter recovery equipment will be described. Embodiment 2 differs from Embodiment 1 in some aspects of the operating conditions, with a relatively shorter solids retention time (SRT) range and a lower suspended solids (SS) concentration range. This reduces the decomposition of dissolved organic matter by microorganisms, and relatively enhances the effect of increasing the recovery rate of dissolved organic matter.

[0079] In Embodiment 2, in the organic matter recovery equipment described above, the control device 40 controls the operating conditions so that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank 2 is 50 mg / L or more and 1200 mg / L or less, and the solid matter residence time (SRT) in the separation tank 2 is 4 hours or more and 36 hours or less. The configuration of the recovery equipment and the control method will be described in reference to Embodiment 1.

[0080] According to the organic matter recovery equipment of Embodiment 2, compared to Embodiment 3 described later, the solid matter residence time (SRT) is set to a relatively short range and the suspended solids (SS) concentration is controlled to a lower range, thereby relatively reducing the decomposition of dissolved organic matter by microorganisms and further increasing the recovery rate of dissolved organic matter.

[0081] In Embodiment 2, the suspended solids (SS) concentration of the organic wastewater may preferably be 300 mg / L or more and 800 mg / L or less. The solids retention time (SRT) in the separation tank may preferably be 6 hours or more and 24 hours or less, and more preferably 8 hours or more and 16 hours or less.

[0082] [Embodiment 3 of the Organic Matter Recovery Equipment] Next, Embodiment 3 of the organic matter recovery equipment will be described. Embodiment 3 differs from Embodiments 1 and 2 in some aspects of the operating conditions, with a relatively long solids retention time (SRT) and a higher suspended solids (SS) concentration. This makes clogging (fouling) of the separation membrane less likely to occur, and enhances the effect of suppressing fouling.

[0083] In Embodiment 3, in the organic matter recovery equipment described above, the control device 40 controls the operating conditions so that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank 2 is 500 mg / L or more and 4000 mg / L or less, and the solid matter residence time (SRT) in the separation tank 2 is 36 hours or more and 80 hours or less. The configuration of the recovery equipment and the control method will be described in reference to Embodiment 1.

[0084] According to the organic matter recovery equipment of Embodiment 3, compared to Embodiment 2 described above, by setting the solid matter residence time (SRT) to a relatively longer range and controlling the suspended solids (SS) concentration to a higher range, although the decomposition of organic matter proceeds to some extent, the microorganisms tend to adsorb substances that cause clogging of the separation membrane, making clogging (fouling) of the separation membrane less likely, thus increasing the effect of suppressing fouling, and reducing the need to perform processes to remove fouling, thereby increasing the operating efficiency of the recovery equipment. Processes to remove fouling include decomposition and washing of the separation membrane 24 and dissolution and removal of fouling with chemical solutions.

[0085] In Embodiment 3, the suspended solids (SS) concentration of the organic wastewater may more preferably be 1500 mg / L or more and 2500 mg / L or less. The solids retention time (SRT) in the separation tank 2 may preferably be 42 hours or more and 70 hours or less, and more preferably 48 hours or more and 60 hours or less. The hydraulic retention time (HRT) may preferably be 1 hour or more and 3 hours or less, and more preferably 1.5 hours or more and 2.5 hours or less.

[0086] [Embodiment of the Wastewater Treatment System] Next, Figure 2 shows an embodiment of a wastewater treatment system 50 using the organic matter recovery equipment 1 shown in Figure 1. This wastewater treatment system 50 comprises the organic matter recovery equipment 1 of embodiments 1 to 3 shown in Figure 1, a primary sedimentation tank 52 (primary sludge recovery equipment) that supplies organic wastewater to the organic matter recovery equipment 1, a sludge digestion equipment 71 equipped with a digestion tank 70 to which at least one of the secondary sludge recovered from the organic matter recovery equipment 1 and the primary sludge recovered from the primary sedimentation tank 52 is supplied, and a power generation equipment 80 that generates electricity using digestion gas discharged from the sludge digestion equipment. In this embodiment, the primary sedimentation tank 52 is provided as the primary sludge recovery equipment, but it is not limited to this as long as it is equipment that can recover sludge. For example, a filtration device, a flotation separator, a centrifugal separator, etc. may be used. Hereinafter, an embodiment in which the primary sedimentation tank 52 is used as the primary sludge recovery equipment will be described.

[0087] The primary sedimentation tank 52 has an inlet 60 at one end and an organic wastewater outlet 64 at the other end, and inflow water is introduced from the inlet 60 via an inflow water introduction pump 62 (inflow water introduction means). The inflow water introduction pump 62 is connected to a control device 40. The inflow water is, for example, water (sewage) entering the sewage treatment plant or various organic wastewater. In the case of sewage, the inflow water settles easily settled dirt and organic matter contained in the sewage within the primary sedimentation tank 52. A sludge discharge port 66 is formed at the lower end of the primary sedimentation tank 52 on the inlet 60 side, and downstream of the sludge discharge port 66, a gently sloping bottom 58 is formed that rises toward the organic wastewater outlet 64. An endless chain 54 is installed along the sloping bottom 58 and is slowly rotated in the direction of the arrow in the figure by multiple sprockets 55. Numerous scraping plates (not shown) are fixed to the outer surface of the endless chain 54, and as the scraping plates move along the inclined bottom 58, dirt and organic matter that have settled in the primary sedimentation tank 52 are scraped towards the primary sludge discharge port 66. The organic wastewater, from which dirt and organic matter have been settled and removed, is discharged from the organic wastewater outlet 64 and sent to the organic matter recovery facility 1 by gravity flow or by the organic wastewater introduction pump 6.

[0088] The primary sedimentation tank sludge (primary sludge) flowing out from the sludge discharge port 66 is sent to the digestion tank 70 by the primary sludge pump 68. At the same time, recovered sludge (secondary sludge) from the sludge recovery port 12 of the organic matter recovery equipment 1 is also sent to the digestion tank 70 by the sludge recovery pump 14, and the primary and secondary sludge are mixed. The primary sludge pump 68 is also connected to the control device 40. The digestion tank 70 is equipped with a digester gas discharge port 72 and a digested sludge discharge port 74 for discharging digester gas, and also has a heating device for warming the sludge inside the digestion tank 70. The primary and secondary sludge stored inside the digestion tank 70 are digested by anaerobic microorganisms and, after a certain period of time, are transformed into reduced-volume digested sludge and discharged from the digested sludge discharge port 74. The digested sludge discharged from the digested sludge pump 78 is sent to the next process dewatering and incineration equipment by the digested sludge pump 78, where it is dewatered and incinerated.

[0089] The digester gas discharged from the digester gas outlet 72 is sent to the power generation equipment 80 by the digester gas blower 76, and is burned by, for example, a gas combustion generator 82 to generate electricity. The gas combustion generator 82 is connected to and controlled by a control device 40. The electricity generated may be used to power the wastewater treatment system 50, or any excess electricity may be supplied to an external source. As an example of a power generation equipment 80 that uses digester gas to generate electricity, the example of digester gas combustion power generation, which generates electricity by burning digester gas, has been given, but it is not limited to this, and for example, it may also be a digester gas fuel cell power generation that generates electricity using a chemical reaction.

[0090] In this wastewater treatment system 50, it is preferable to settle and recover 20 to 50 mass% of the total amount of sludge contained in the influent water as primary sludge in the primary sedimentation tank 52. In this case, as described above, it is preferable to recover 40 to 80 mass% of the total amount of sludge contained in the organic wastewater as secondary sludge in the organic matter recovery equipment 1.

[0091] According to this wastewater treatment system 50, 20 to 50 mass% of the total amount of sludge contained in the influent water is settled and recovered in the primary sedimentation tank 52, and further, 40 to 80 mass% of the total amount of sludge contained in the organic wastewater can be recovered as recovered sludge (secondary sludge) in the organic matter recovery equipment 1. Then, the primary and secondary sludge are subjected to methane fermentation in the digestion tank 70 in the sludge digestion equipment 71, thereby obtaining digester gas corresponding to approximately 50% of the total organic matter contained in the sludge supplied to the digestion tank, which can be used for power generation. Therefore, the power consumption of the entire system can be reduced, and economic efficiency can be improved.

[0092] In this wastewater treatment system 50, 25 to 45 mass% of the total amount of sludge contained in the influent water may be recovered as primary sludge in the primary sedimentation tank 52, or more preferably, 30 to 40 mass% of the total amount of primary sludge may be recovered in the primary sedimentation tank 52. Alternatively, 50 to 75 mass% of the total amount of sludge contained in the organic wastewater may be recovered as secondary sludge, or 60 to 70 mass% of the total amount of sludge contained in the organic wastewater may be recovered as secondary sludge.

[0093] Although the above description has focused on a configuration with a primary recovery facility, a system without a primary recovery facility is also possible. In the case of a wastewater treatment system 50 without a primary recovery facility, the system comprises an organic matter recovery facility 1 as shown in Figure 1, a sludge digestion facility 71 equipped with a digestion tank 70 to which the secondary sludge recovered from the recovery facility 1 is supplied, and a power generation facility 80 that generates electricity using the digester gas discharged from the sludge digestion facility. Inflow water (organic wastewater) is introduced into the organic matter recovery facility 1 by an inflow water introduction means, and the sludge in the inflow water is recovered. In this case, it is preferable that the recovery facility recovers 40 to 80 mass% of the total amount of sludge contained in the inflow water as the secondary sludge. As a result, the secondary sludge is subjected to methane fermentation in the digestion tank 70 in the sludge digestion facility 71, and digester gas corresponding to approximately 50% of the total amount of organic matter contained in the sludge supplied to the digestion tank is obtained and can be used for power generation. Therefore, the power consumption of the entire system can be reduced, and economic efficiency can be improved.

[0094] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0095] [Example 1] An experimental apparatus shown in Figure 4 was created as an embodiment of the apparatus shown in Figure 1. The capacity of the separation tank 2 was 7.3 L, the separation membrane 24 was a ceramic flat membrane with a pore size of 0.1 μm, and the membrane permeation flux was 16 L / m ２ The sludge retention time (SRT) was set to 12-36 hours, the hydrological retention time (HRT) to 1-3 hours. Overflow water from the primary sedimentation tank was supplied to the separation membrane 24 as organic wastewater, and the relationship between organic matter recovery rate and HRT and SRT was investigated under conditions of aeration rate of 3-4 L / min. The results are shown in Figures 5, 6 and Table 1. As in Examples 1-2 and 1-3, a tendency was observed for the organic matter recovery rate to be higher under conditions of short HRT and SRT. In particular, it was found that the organic matter recovery rate was relatively higher and preferable under conditions where HRT was 1 hour or more and 2 hours or less, and SRT was 12 hours or more and 24 hours or less.

[0096]

[0097] [Example 2] Using the same apparatus as in Example 1, the relationship between the ammonia nitrogen removal rate and HRT and SRT was investigated. The results are shown in Figures 7 and 8 and Table 2. Under all conditions of Examples 2-1, 2-2, and 2-3, the ammonia nitrogen removal rate was kept low, ranging from 3.7% to 24%. Furthermore, in Examples 2-1 and 2-2, where HRT and SRT were shorter, the ammonia nitrogen removal rate was lower than in Example 2-3. From this, it was found that the ammonia nitrogen removal rate can be kept below 24% with an HRT of 1 to 3 hours and an SRT of 12 to 36 hours, and that it is preferable to have an HRT of 1 to 2 hours or an SRT of 12 to 24 hours to further reduce the ammonia nitrogen removal rate.

[0098]

[0099] [Example 3] In organic matter recovery using the high-speed membrane separation activated sludge method, it is known that high dissolved oxygen (DO) concentration in the liquid increases microbial activity and decomposes organic matter. Therefore, in order to determine the appropriate range of DO concentration, the relationship between the amount of decomposition by microorganisms and DO concentration was investigated.

[0100] An experimental apparatus was constructed as shown in Figure 9. In this experimental apparatus, in order to confirm the effects of biodegradation, the experiment was conducted without installing a separation membrane in the bioadsorption tank corresponding to separation tank 2. Therefore, the sludge withdrawn from the bioadsorption tank was sent to the sedimentation tank, and a portion of the sludge from the sedimentation tank was returned to the bioadsorption tank as return sludge. The operating conditions were as follows: inflow water supply rate of 3.0 L / h, bioadsorption tank capacity of 1.5 L (HRT 0.5 h), sedimentation tank capacity of 6.0 L (HRT 2 h), and DO concentration in the bioadsorption tank of 0.1 to 1.0 mg / L.

[0101] The results are shown in Figure 10. Regarding the organic matter recovery rate, decomposition of organic matter was observed under conditions where the DO concentration was 0.75 mg / L or higher. The higher the DO concentration, the lower the organic matter recovery rate, and the lower the DO concentration, the higher the organic matter recovery rate. In addition, under conditions of high DO concentration, the COD (chemical oxygen demand), an indicator of the amount of organic matter in the treated water, decreased, and under conditions of low DO concentration, the COD in the treated water increased. When the COD in the treated water is high, the COD of the effluent after membrane separation will also be high, which may affect subsequent treatment.

[0102] Furthermore, even when the DO concentration is 0 mg / L, the COD in the treated water is expected to be high, similar to the case of 0.1 mg / L, and the organic matter recovery rate is also presumed to be high. On the other hand, it was found that when the DO concentration exceeds 1.5 mg / L, the decomposition of organic matter progresses as described above, and the organic matter recovery rate decreases significantly. From these findings, it was determined that it is best to keep the DO concentration below 1.5 mg / L.

[0103] [Example 4] An organic matter recovery system as shown in Figure 1 was constructed, and the changes in the ammonia nitrogen removal rate [%] and suspended solids (SS) concentration [mg / L] were investigated when the solid matter residence time (SRT) in the separation tank 2 was varied from 20 to 100 hours.

[0104] The conditions of the apparatus used were as follows: Liquid volume in separation tank 2: 570 L, Air injection volume by air blowing section 16: 30-50 L / min, Liquid temperature in separation tank 2: 18-24°C, Separation membrane 24: Hollow fiber membrane module (average pore size: 0.1 μm), Dissolved oxygen (DO) concentration of organic wastewater: 0.3-1.5 mg / L, Hydrological residence time (HRT) of separation tank 2: 1.6-3.0 hours, Redox potential (ORP) of organic wastewater in separation tank 2: -100-40 mV.

[0105] Figure 11 is a graph showing the change in the ammonia nitrogen removal rate [%] when the solids retention time (SRT) in the separation tank 2 is changed from 20 to 100 hours in Example 4, and Figure 12 is a graph showing the change in the suspended solids (SS) concentration [mg / L] in the same case.

[0106] The following points were revealed from the graphs in Figures 11 and 12. As shown in Figure 11, when the SRT was varied from 20 to 100 hours, data was obtained showing a sharp increase in the ammonia nitrogen removal rate [%] when the SRT exceeded 80 hours. In other words, it is inferred that when the SRT exceeds 80 hours, the amount of ammonia oxidized in organic wastewater increases due to the nitrification reaction, and the oxygen demand increases accordingly. It was found that supplying the oxygen corresponding to the increased oxygen demand by aeration may impair energy efficiency.

[0107] Furthermore, when the SRT was varied from 20 to 100 hours, it was found that the suspended solids (SS) concentration [mg / L] increased linearly, as shown in Figure 12. At an SRT of 80 hours, which is the upper limit where nitrification reactions do not occur significantly, the suspended solids (SS) concentration was found to be approximately 4000 mg / L at most, even considering variability. Therefore, it was found that by controlling the operating conditions so that the suspended solids (SS) concentration of the organic wastewater is between 500 mg / L and 4000 mg / L, and the solids residence time (SRT) in the separation tank is between 36 hours and 80 hours, it is possible to operate within a range that offers excellent energy efficiency.

[0108] [Examples 5 and 6] Next, the experiments of Examples 5 and 6 were carried out using the same experimental apparatus as in Example 4. In Example 5, the solids residence time (SRT) was set to 12.0 hours, and the suspended solids (SS) concentration was 600 [mg / L]. In Example 6, the solids residence time (SRT) was set to 72.0 hours, and the suspended solids (SS) concentration was 2400 [mg / L]. While maintaining the same conditions as in Example 4, continuous operation was performed in each case, and the differential pressure inside and outside the separation membrane 24 was measured from the pump pressure after 5 days (120 hours) and 10 days (240 hours), and the rate of increase of the differential pressure relative to the initial value (differential pressure increase rate: %) was measured.

[0109] Table 3 shows the results. Although cleaning was performed by oscillation using the separation membrane driving mechanism 34, in Example 5, the differential pressure inside and outside the separation membrane 24 increased by 74.1% from the initial value after 5 days, and fouling occurred before 10 days had passed, so the experiment was stopped. On the other hand, in Example 6, the rate of increase in the differential pressure of the separation membrane 24 was limited to 31.5% after 5 days and 29.5% after 10 days, indicating that fouling could be suppressed for a long period of time.

[0110]

[0111] As in Example 6, the reason why fouling can be suppressed by increasing the solids retention time (SRT) and setting a higher suspended solids (SS) concentration is not clear, but it is thought that this is because microorganisms tend to adsorb substances that cause clogging of the separation membrane 24. This phenomenon is not publicly known and has been found to be beneficial in improving the operating efficiency of the organic matter recovery equipment.

[0112] However, if the solids residence time (SRT) is shortened and the suspended solids (SS) concentration is set lower, as in Example 5, the decomposition reaction of organic matter can be suppressed more than in Example 6, and therefore the recovery rate of organic matter itself can be increased compared to Example 6. Thus, even under conditions like those in Example 5, it is perfectly usable if appropriate fouling countermeasures are taken.

[0113] As described above, according to the organic matter recovery equipment and wastewater treatment system of the present invention, by controlling the operating conditions of the organic matter recovery equipment as described above, dissolved organic matter contained in organic wastewater can be adsorbed by microorganisms in the separation tank, while suppressing the decomposition of the dissolved organic matter by the microorganisms. Dissolved organic matter attached to the microorganisms can be separated together with the microorganisms by the separation membrane. As a result, organic components that would have passed through the separation membrane as dissolved matter under conventional operating conditions can be recovered together with the microorganisms and sludge, increasing the overall organic matter recovery rate to about 65-90%, which can then be used for power generation, etc. Furthermore, under operating conditions in which the decomposition of organic matter is suppressed as described above, organic matter, sludge, and microorganisms tend to adhere to and accumulate on the separation membrane, causing clogging (fouling) of the separation membrane and making it difficult to continue operation. However, in this embodiment, the separation membrane drive mechanism membrane drives the separation membrane in the separation tank, effectively causing the attached material (foulant) to fall from the separation membrane, preventing fouling and improving operating efficiency. Therefore, the present invention is applicable to industrial use.

[0114] 1 Organic matter recovery equipment 2 Separation tank 4 Inlet 8 Outlet 12 Sludge recovery port 14 Sludge recovery pump 16 Air blowing section 18 Air blower 20 Movable frame 24 Separation membrane 26 Manifold 28 Water collection pipe 30 Permeate suction pump 32 Backwash water supply pump 34 Separation membrane drive mechanism 36 Actuator 38 Frame support 40 Control device 42 Suspended solids concentration measuring means 46 Dissolved oxygen concentration measuring means 48 Oxidation-reduction potential measuring means 50 Wastewater treatment system 52 Primary sedimentation tank 54 Endless chain 58 Inclined bottom 60 Inlet 62 Inflow water introduction pump 64 Organic wastewater outlet 66 Primary sludge discharge port 68 Primary sludge pump 70 Digestion tank 72 Digestion gas discharge port 74 Digestion sludge discharge port 76 Digestive gas blower 78 Digestive sludge pump 80 Power generation equipment 82 Gas combustion generator

Claims

1. An organic matter recovery facility for recovering organic matter from organic wastewater containing ammonia nitrogen, comprising: a separation tank for storing the organic wastewater supplied from a source; a separation membrane provided in the separation tank for separating the permeate water from which the organic matter has been removed from the organic wastewater; a separation membrane driving mechanism for driving the separation membrane within the separation tank and removing deposits from the separation membrane; and a control device for controlling the operating conditions of the separation tank such that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank is 50 mg / L or more and 4000 mg / L or less, and the dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank is 1.5 mg / L or less.

2. The organic matter recovery equipment according to claim 1, comprising: an organic wastewater introduction means for introducing the organic wastewater from the inlet of the separation tank; a sludge recovery means for recovering the sludge containing the organic matter from the sludge recovery port of the separation tank; and a permeate discharge means for aspirating and recovering the permeate that permeates through the separation membrane, wherein the control device controls at least one of the organic wastewater introduction means, the sludge recovery means, and the permeate discharge means.

3. The organic matter recovery apparatus according to claim 1 or 2, characterized in that the control device controls the operating conditions such that the hydrological residence time (HRT) of the separation tank is 20 minutes or more and 3 hours or less, and the solids residence time (SRT) of the separation tank is 4 hours or more and 80 hours or less.

4. The organic matter recovery equipment according to claim 1 or 2, characterized in that the control device controls the operating conditions so that the ammonia nitrogen removal rate, defined by the following formula, is 24% or less. Ammonia nitrogen removal rate [%] = (Ammonia nitrogen concentration in the organic wastewater (mg / L) - Ammonia nitrogen concentration in the permeate (mg / L)) / (Ammonia nitrogen concentration in the organic wastewater (mg / L)) × 100 5. The organic matter recovery apparatus according to claim 1 or 2, characterized in that the control device controls the operating conditions so that the oxidation-reduction potential (ORP) of the organic wastewater stored in the separation tank is -150 mV or higher.

6. The organic matter recovery apparatus according to claim 1 or 2, characterized in that the separation membrane driving mechanism comprises a movable frame that supports both ends of the separation membrane and an actuator that drives the movable frame within a certain range of motion.

7. The organic matter recovery apparatus according to claim 1 or 2, wherein the separation membrane driving mechanism comprises a movable frame that supports both ends of the separation membrane and an actuator that drives the movable frame within a certain oscillation range, and the actuator oscillates the separation membrane at 0.01 to 0.90 Hz via the movable frame.

8. The organic matter recovery equipment according to claim 1 or 2, characterized in that the organic matter recovery equipment recovers 40 to 80 mass% of the total amount of organic matter contained in the organic wastewater.

9. The organic matter recovery apparatus according to claim 1 or 2, characterized in that the separation membrane is one or more selected from hollow fiber membrane modules, flat membrane modules, and tubular membrane modules, and is arranged vertically within the separation tank.

10. The organic matter recovery equipment according to claim 1 or 2, characterized in that the control device controls the operating conditions such that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank is 50 mg / L or more and 1200 mg / L or less, and the solids retention time (SRT) in the separation tank is 4 hours or more and 36 hours or less.

11. The organic matter recovery equipment according to claim 1 or 2, characterized in that the control device controls the operating conditions such that the suspended solids (SS) concentration of the organic wastewater stored in the separation tank is 500 mg / L or more and 4000 mg / L or less, and the solids retention time (SRT) in the separation tank is 36 hours or more and 80 hours or less.

12. A wastewater treatment system comprising: an organic matter recovery facility according to claim 1 or 2; a sludge digestion facility to which secondary sludge recovered from the organic matter recovery facility is supplied, wherein the secondary sludge is subjected to methane fermentation in the digestion tank; and a power generation facility to which power is generated using digester gas discharged from the sludge digestion facility, wherein the organic matter recovery facility recovers 40 to 80 mass% of the total amount of sludge contained in the organic wastewater as secondary sludge.

13. A wastewater treatment system comprising: an organic matter recovery facility according to claim 1 or 2; a primary sludge recovery facility that receives influent water containing sludge, recovers 20 to 50 mass% of the total amount of sludge contained in the influent water as primary sludge, and supplies the remainder to the organic matter recovery facility as organic wastewater; a sludge digestion facility comprising a digestion tank to which at least one of the secondary sludge recovered from the organic matter recovery facility and the primary sludge recovered from the primary sludge recovery facility is supplied, and which methane ferments at least one of the primary sludge and the secondary sludge in the digestion tank; and a power generation facility that generates electricity using digester gas discharged from the sludge digestion facility, wherein the organic matter recovery facility recovers 40 to 80 mass% of the total amount of sludge contained in the organic wastewater as secondary sludge.

14. A method for recovering organic matter from organic wastewater containing ammonia nitrogen, comprising the steps of: storing the organic wastewater supplied from a source in a separation tank; separating the permeate from which the organic matter has been removed from the organic wastewater in the separation tank using a separation membrane; driving the separation membrane in the separation tank to remove deposits from the separation membrane; and adjusting the suspended solids (SS) concentration of the organic wastewater stored in the separation tank to 50 mg / L or more and 4000 mg / L or less, and adjusting the dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank to 1.5 mg / L or less.

15. A step of introducing influent water containing sludge into a primary sludge recovery facility, recovering 20 to 50 mass% of the total amount of primary sludge contained in the influent water, and obtaining the remainder as organic wastewater; a step of storing the organic wastewater in a separation tank, separating the permeate obtained by removing the organic matter from the organic wastewater in the separation tank using a separation membrane; a step of driving the separation membrane in the separation tank to remove deposits from the separation membrane; a step of setting the suspended solids (SS) concentration of the organic wastewater stored in the separation tank to 50 mg / L or more and 4000 mg / L or less, and the dissolved oxygen (DO) concentration of the organic wastewater stored in the separation tank to 1.5 mg / L or less; a step of recovering secondary sludge from the separation tank; a step of methane fermentation of the primary sludge recovered from the primary sludge recovery facility and the secondary sludge recovered from the separation tank in the digestion tank. A wastewater treatment method comprising the step of generating electricity using digester gas discharged from the digester tank, characterized in that the separation tank recovers 40 to 80 mass% of the total amount of sludge contained in the organic wastewater as secondary sludge.

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