Organic wastewater treatment apparatus and organic wastewater treatment method

Abstract

[Problem] To provide an organic wastewater treatment apparatus and an organic wastewater treatment method. [Solution] The present invention is provided with: a main stream line L1 that introduces organic wastewater W1 that includes suspended solids, organic matter, and nitrogen constituents; a membrane separation methane fermentation tank 20 which is disposed on the main stream line L1 and in which the organic matter in the organic wastewater W1 is subjected to methane fermentation under anaerobic conditions and membrane filtration is performed to obtain membrane-filtered water W2; an after-treatment device 40 that subjects the membrane-filtered water W2 from the membrane separation methane fermentation tank 20 to an after-treatment; a sludge concentration device 201 which is disposed on a side stream line L11 that extracts excess sludge 20a rfom the membrane separation methane fermentation tank 20, and which concentrates the excess sludge 20a to form concentrated sludge 20b; and a digestion tank 203 that subjects the concentrated sludge 20b concentrated by the sludge concentration device 201 to digestion treatment.

Description

Organic wastewater treatment apparatus and organic wastewater treatment method

[0001] The present invention relates to an organic wastewater treatment apparatus and an organic wastewater treatment method that highly treat organic wastewater and increase the amount of biogas recovered.

[0002] Currently, organic wastewater containing organic matter and nitrogen components, such as domestic wastewater, industrial wastewater, sewage, or wastewater mixed with at least one of these (hereinafter collectively referred to simply as "organic wastewater"), is often treated using aerobic microorganisms, typified by the activated sludge process. The activated sludge process is a method that uses microorganisms suspended in water. Activated sludge is formed when air is blown into organic wastewater and agitated, allowing various microorganisms to proliferate using the organic matter in the wastewater and form flocculent structures. In addition to microorganisms such as bacteria, protozoa, and metazoans, activated sludge contains abiotic inorganic and organic matter.

[0003] Here, the activated sludge method for sewage treatment (organic wastewater treatment) has been in practical use for about 100 years, and various methods such as the standard activated sludge method and the recirculating nitrification-denitrification method have been developed. The standard activated sludge method is a technology that treats sewage by combining an aeration tank (aeration tank) for oxidative decomposition of organic matter in sewage using activated sludge and a sedimentation tank for gravity separation of the activated sludge. The recirculating nitrification-denitrification method is a technology that removes nitrogen biologically by arranging a biological reaction tank in the order of an anoxic tank (denitrification tank) and an aerobic tank (nitrification tank), and circulating a portion of the nitrification mixture from the aerobic tank to the anoxic tank for treatment.

[0004] Conventional activated sludge methods, such as the aforementioned circulating nitrification-denitrification method, require aeration using a large amount of air and power in an aerobic tank (nitrification tank), which has the problem of requiring a great deal of energy. To solve this problem, an organic wastewater treatment system equipped with a single-tank anammox treatment system has been proposed, which can reduce energy consumption and the amount of excess activated sludge generated (Patent Document 1).

[0005] Japanese Patent Publication No. 2019-25438

[0006] However, in the technology described in Patent Document 1, as the water temperature of the sewage flowing into the membrane bioreactor (anaerobic MBR) decreases, the conversion rate of organic matter in the sewage to methane gas decreases, and the proportion of organic matter in the sewage that is not decomposed and accumulates in the membrane bioreactor (anaerobic MBR) as excess sludge increases. In particular, when the water temperature drops below 20°C, the proportion of organic matter that accumulates in the anaerobic MBR without being decomposed becomes significant. As a result, there is a problem in that methane gas cannot be recovered efficiently.

[0007] The present invention aims to provide an organic wastewater treatment apparatus and an organic wastewater treatment method that can recover methane gas from undegraded organic matter contained in excess sludge of a membrane separation methane fermentation tank (anaerobic MBR) when the organic wastewater is at a low temperature (for example, 20°C or below), thereby improving the overall organic matter recovery rate and methane recovery rate of the system, as well as reducing the amount of excess sludge generated.

[0008] An organic wastewater treatment apparatus according to a first aspect of the present invention is characterized by comprising: a main stream line for introducing organic wastewater containing suspended solids, organic matter and nitrogen components; a membrane separation methane fermentation tank provided in the main stream line for methane fermentation of the organic matter in the organic wastewater under anaerobic conditions and for membrane filtration to obtain membrane filtered water; a post-treatment apparatus for post-treatment of the membrane filtered water from the membrane separation methane fermentation tank; a side stream line for extracting excess sludge from the membrane separation methane fermentation tank; a sludge thickening apparatus provided in the side stream line for concentrating the excess sludge to obtain concentrated sludge; and a digester for methane fermentation of the organic matter in the concentrated sludge.

[0009] A second aspect of the present invention relates to an organic wastewater treatment method comprising: a membrane separation methane fermentation step provided in a main stream line for introducing organic wastewater containing suspended solids, organic matter and nitrogen components, in which organic matter in the organic wastewater is methane fermented under anaerobic conditions and membrane filtration is performed to obtain membrane filtered water; a post-treatment step for post-treatment of the membrane filtered water from the membrane separation methane fermentation step; a sludge concentration step or sludge dewatering step in a side stream line for extracting excess sludge in the membrane separation methane fermentation step, in which the excess sludge is concentrated or dewatered to obtain concentrated sludge or dewatered sludge; and a digestion step for methane fermentation of organic matter in the concentrated sludge or dewatered sludge.

[0010] According to the present invention, when the water temperature of organic wastewater in a membrane separation methane fermentation tank is low (for example, 20°C or lower), methane gas can be recovered from undecomposed organic matter contained in excess sludge. This improves the recovery rate of organic matter and methane as a whole system, and reduces the amount of excess sludge generated.

[0011] This is a schematic diagram of the organic wastewater treatment device according to the first embodiment. This is a schematic diagram of a modified example of the organic wastewater treatment device according to the first embodiment. This is a schematic diagram of the side streamline portion of the organic wastewater treatment device according to the first embodiment. This is another schematic diagram of the side streamline portion of the organic wastewater treatment device according to the first embodiment. This is another schematic diagram of the side streamline portion of the organic wastewater treatment device according to the first embodiment. This is another schematic diagram of the side streamline portion of the organic wastewater treatment device according to the first embodiment. This is a schematic diagram of the configuration of the water temperature acclimatization tank according to the first embodiment. This is a schematic diagram illustrating the configuration of the organic wastewater treatment device according to the second embodiment. This is a schematic diagram illustrating the configuration of the main streamline of the organic wastewater treatment device according to the second embodiment. This shows a schematic diagram of the configuration of the vacuum degassing device. This is a perspective view of the carrier.

[0012] Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the following modes for carrying out the invention (hereinafter referred to as embodiments). In addition, constituent elements in the following embodiments include those that can be easily conceived by those skilled in the art, those that are substantially the same, that is, those within the scope of equivalents. Furthermore, the constituent elements disclosed in the following embodiments can be appropriately combined.

[0013] [First Embodiment] FIG. 1A is a schematic configuration diagram illustrating the configuration of an organic wastewater treatment apparatus 100A-1 according to the first embodiment. FIG. 1B is a schematic configuration diagram illustrating the configuration of an organic wastewater treatment apparatus 100A-2, which is a modified example of the organic wastewater treatment apparatus 100A-1. [Organic Wastewater Treatment Apparatus] The organic wastewater treatment apparatus 100A-1 according to the present embodiment is an apparatus that highly treats organic wastewater (water to be treated) W₁ containing organic matter and nitrogen components, such as domestic wastewater, industrial wastewater, sewage, or wastewater mixed using at least one of these, for example.

[0014] As shown in FIG. 1A, the organic wastewater treatment apparatus 100A-1 according to the present embodiment receives organic wastewater W containing suspended solids, organic matter, and nitrogen components １ , which is introduced into a main water treatment process (hereinafter also referred to as "mainstream line" or "mainstream") L １ (L １－１ , L １－２ , L １－３ , L １－４ ), and a membrane separation methane fermentation tank 20 which is provided in the mainstream line (main water treatment process) L １－２ and subjects organic matter in the organic wastewater W １ to methane fermentation under anaerobic conditions and performs membrane filtration to obtain membrane filtered water W ２ , a post-treatment apparatus 40 that post-treats the membrane filtered water W ２ from the membrane separation methane fermentation tank 20, a side stream treatment process (hereinafter also referred to as "sidestream line" or "sidestream") L １１ (L １１－１ , L １１－２ , L １１－３ ), that extracts excess sludge 20a from the membrane separation methane fermentation tank 20, and the sidestream line L １１－１The facility includes a sludge thickening device 201 that concentrates the excess sludge 20a to produce concentrated sludge 20b, a concentrated sludge storage tank 202 for storing the concentrated sludge 20b concentrated by the sludge thickening device 201, and a digester 203 (medium-temperature digestion at 30°C to 37°C or high-temperature digestion at 50°C to 55°C) for digesting (methane fermentation) the organic matter in the concentrated sludge 20b from the concentrated sludge storage tank 202.

[0015] The membrane separation methane fermentation tank 20 contains the generated biogas (methane, etc.) G １ Biogas discharge line L that emits biogas ５－１ A digester tank 203 is provided, and digester gas (methane, etc.) G ２ Digestive gas discharge line L that discharges ５－２ A biogas storage tank, which is a gas holder (not shown), is provided and stores the biogas.

[0016] Furthermore, in this embodiment, the main streamline L １ The excess sludge 20a containing undecomposed organic matter in the membrane separation methane fermentation tank 20 is channeled to the side stream line L １１ Extracted from this side streamline L １１ The sludge is concentrated in a sludge thickening device 201 installed in the building, and then digested in a digester 203.

[0017] Here, the sludge concentration rate in the sludge thickening device 201 is such that the solid matter concentration of the excess sludge 20a before concentration was, for example, 1 to 1.5 wt%, and the sludge thickening device 201 concentrates it to a concentrated sludge 20b with a solid matter concentration of, for example, 4 to 10 wt%.

[0018] In this invention, "domestic wastewater" refers to water generated and discharged as a result of general human activities such as cooking, washing, and bathing. Domestic wastewater may include human waste and rainwater. "Industrial wastewater" refers to wastewater from agriculture, forestry, and fisheries (primary industries), manufacturing, construction, mining (secondary industries), and industries other than primary and secondary industries (tertiary industries such as real estate and food service). "Sewage" refers to wastewater mainly composed of domestic wastewater, sometimes with industrial wastewater and, in some cases, rainwater added. In this specification, leachate from landfills can also be treated as organic wastewater. "Organic matter" is also called an organic compound and refers to a compound that is composed primarily of covalent bonds between carbon atoms. Nitrogen components include proteins, free ammonia (NH3), and ammonium ions (NH4). + Examples include ammonia nitrogen (NH4-N), nitrite nitrogen (NO2-N), and nitrate nitrogen (NO3-N). "Ammonia nitrogen" refers to nitrogen in the form of ammonia, "nitrite nitrogen" refers to nitrogen in the form of nitrite, and "nitrate nitrogen" refers to nitrogen in the form of nitrate. "Advanced treatment" means removing the aforementioned organic matter, removing the aforementioned nitrogen components (denitrification), and generating biogas as digester gas from the aforementioned organic matter and excess sludge.

[0019] (Flow rate adjustment tank 10) The organic wastewater treatment device 100A-1 may be equipped with a flow rate adjustment tank 10 in front of the membrane separation methane fermentation tank 20 to adjust the amount of organic wastewater W1 flowing into the membrane separation methane fermentation tank 20. The flow rate adjustment tank 10 may be provided as needed, but it is not required to be provided.

[0020] The amount of organic wastewater flowing from the flow rate adjustment tank 10 to the membrane separation methane fermentation tank 20 can be adjusted, for example, by adjusting the output of the flow rate adjustment tank pump P1 installed between the flow rate adjustment tank 10 and the membrane separation methane fermentation tank 20. The inflow of organic wastewater into the flow rate adjustment tank 10 can be performed by a pump (not shown) installed between the organic wastewater generation site and the organic wastewater treatment plant facility. The flow rate adjustment tank 10 may be equipped with a stirrer (not shown) for stirring the organic wastewater W1.

[0021] (Membrane separation methane fermentation tank 20) ​​The membrane separation methane fermentation tank (membrane separation tank) 20 performs methane fermentation on the aforementioned organic wastewater W1 under anaerobic conditions and performs membrane filtration to produce membrane filtered water W ２ This is a device that obtains organic wastewater W by the membrane separation methane fermentation tank 20. １ It can decompose most of the organic matter contained within, and produces biogas G, methane (CH4). ４ ) can be produced. Here, methane fermentation is a reaction in which various microorganisms decompose organic matter, and methane-producing archaea ultimately produce methane (CH₂). ４ This is a general term for methane production reactions that produce methane.

[0022] The methane produced in this membrane-separated methane fermentation tank 20 is (CH4) ４ ) is biogas G (G １ ) as biogas discharge line L ５－１ It is recovered separately via [a certain method]. The recovered methane is stored in a gas holder (not shown), and electricity and heat are generated by using the obtained biogas G for power generation and combustion. In addition, membrane filtration is performed, so membrane filtered water W is produced. ２ It does not contain suspended solids. If organic matter or suspended solids flow into the post-treatment device 40, they become a source of activated sludge in the post-treatment device 40. In other words, if denitrifying bacteria are present in the post-treatment device 40, activated sludge is more likely to be generated. Therefore, it is preferable to decompose or remove as much organic matter and suspended solids as possible in this membrane separation methane fermentation tank 20. Methane is produced by the action of methanogenic archaea.

[0023] The membrane separation methane fermentation tank 20 preferably includes a membrane module 22 for membrane filtration, as shown in Figure 2A, which will be described later. With this configuration, the organic wastewater treatment device 100A-1 can be made more compact compared to conventional activated sludge methods, and construction costs can be reduced. In addition, since there is no need to aerate with a large amount of oxygen (air) as in the activated sludge method, energy consumption can be reduced and running costs can be lowered. The membrane separation methane fermentation tank 20 can be a methane fermentation tank that holds suspended anaerobic bacteria (including methane-producing archaea), a methane fermentation tank that holds anaerobic granular sludge, a methane fermentation tank that holds anaerobic bacteria attached to a carrier, etc. Suspended anaerobic bacteria refer to anaerobic bacteria that do not form granules, anaerobic bacteria that are not attached to a carrier, etc.

[0024] For membrane filtration, at least one of the following can be used: a microfiltration (MF) membrane, an ultrafiltration (UF) membrane, a nanofiltration (NF) membrane, or a reverse osmosis (RO) membrane. In this way, organic matter of a predetermined size cannot pass through, thus reducing the amount of activated sludge generated in the post-treatment device 40 described later.

[0025] In this embodiment, it is preferable to use an MF membrane or a UF membrane among those described above. When filtering with an MF membrane or a UF membrane, organic wastewater (membrane-filtered water) that does not contain not only solid organic matter but also microorganisms such as methane-producing archaea can be supplied to the post-treatment device 40 described later. In other words, by using an MF membrane or a UF membrane, the organic wastewater treatment device 100A-1 can prevent the outflow of methane-producing archaea from the membrane separation methane fermentation tank 20 and maintain a high number of viable methane-producing archaea in the membrane separation methane fermentation tank 20. In this embodiment, it is more preferable to use an MF membrane with a pore size of, for example, 1 μm or less. In this case, the power of the membrane filtration pump P used for filtration can be reduced compared to when an NF membrane or RO membrane is used.

[0026] The membrane used for membrane filtration can be made of chlorinated vinyl resin (CPVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or the like. The membrane used for membrane filtration can be in the form of a flat membrane, a tubular membrane, or a hollow fiber membrane (a tubular membrane with an inner diameter of, for example, 5 mm or less, preferably 3 mm or less).

[0027] As described above, membrane separation methane fermentation tanks (anaerobic MBRs) can be, for example, cross-flow type anaerobic membrane bioreactors (MBRs), immersion type anaerobic MBRs (separate tank type), or immersion type anaerobic MBRs (integrated type). Figure 2A, which will be described later, shows an example of this immersion type anaerobic MBR (integrated type) 20A.

[0028] A cross-flow anaerobic MBR (Membrane Broker) is a system in which a methane fermentation tank for methane fermentation and a membrane separation unit for separating sludge with a membrane are installed independently. High pressure is applied inside the membrane module of the membrane separation unit to flow the sludge and perform membrane filtration.

[0029] The immersion-type anaerobic MBR (separate tank type) and the immersion-type anaerobic MBR (integrated type) 20A perform membrane separation, i.e., membrane filtration, by suction using a membrane filtration pump P2. The immersion-type anaerobic MBR (separate tank type) has the methane fermentation tank and membrane separation device installed independently, while the immersion-type anaerobic MBR (integrated type) 20A has the membrane separation device installed inside the methane fermentation tank.

[0030] In this embodiment, any of the membrane separation methane fermentation tanks described above can be used, but it is preferable to use the immersion type anaerobic MBR (integrated type) 20A, as shown in Figure 2A, which will be described later. This is because, by using the immersion type anaerobic MBR (integrated type) 20A, the membrane module 22 is housed inside the methane fermentation tank, which reduces the installation area and makes the device more compact. In addition, by using the immersion type anaerobic MBR (integrated type) 20A, the pump (membrane filtration pump P ２This reduces the number of units that need to be installed. As a result, organic wastewater treatment systems can reduce construction and running costs, and also save energy. Furthermore, when using an immersion-type anaerobic MBR (separate tank type), membrane cleaning becomes easier compared to an immersion-type anaerobic MBR (integrated type).

[0031] When considering the methane fermentation tank of the membrane separation methane fermentation tank (anaerobic MBR) 20 in terms of biological reactor type, for wastewater with a small amount of suspended solids contained in organic wastewater, the complete mixing method, fluidized bed method, anaerobic contact method, anaerobic filter bed method, etc., can be mentioned. Furthermore, when dealing with wastewater with a large amount of suspended solids (solid waste), for example, the complete mixing method, anaerobic contact method, anaerobic baffled reactor (ABR) method, etc., can be mentioned, but the present invention is not limited to these.

[0032] The membrane separation methane fermentation tank 20 may be equipped with a device (not shown) for adding inorganic salts (metals) such as calcium, magnesium, iron, nickel, cobalt, potassium, sodium, zinc, selenium, tungsten, molybdenum, copper, manganese, and aluminum, for the purpose of maintaining the activity of methanogenic archaea. The membrane separation methane fermentation tank 20 may also be equipped with a heating device (not shown) for adjusting the water temperature. This heating device can utilize heat or electricity obtained by burning the methane gas produced in the membrane separation methane fermentation tank 20. The membrane separation methane fermentation tank 20 may be equipped with sensors such as a pH meter, a dissolved carbon dioxide meter, and a thermometer. The sensors are provided individually for each measurement target.

[0033] (Post-treatment device 40) As shown in Figure 1A, the post-treatment device 40 is used to process the membrane filtered water W ２ The effluent W is in a state suitable for discharge regulations in the treatment area. ４ This is a post-treatment device, for example, membrane filtered water W ２Examples include an Anammox treatment device that denitrifies nitrogen components contained in by an anaerobic ammonia oxidation reaction, an aeration treatment device that raises the oxidation-reduction potential and oxidizes the treated water by aeration treatment and removes residual BOD components, and a biofilm filtration treatment device. In this embodiment, the membrane filtered water W of the membrane separation methane fermentation tank 20 is used. ２ It is preferable to install an anammox processing device as a post-processing device 40 that performs anammox processing for advanced processing.

[0034] Here, the Anammox treatment device uses membrane filtered water W. ２ The nitrogen components contained in are denitrified by the anaerobic ammonium oxidation (Anammox) reaction. The Anammox reaction is carried out under anaerobic conditions when Anammox bacteria oxidize NH ４ -N and NO ２ -N as a substrate ２ This is a reaction that produces [the substance], and the following reaction equation (1) is shown.

[0035] 1.0NH ４ ＋ +1.32NO ２ － +0.066HCO ３ － +0.13H ＋ → 1.02N ２ +0.26NO ３ － +0.066CH ２ O ０．５ N ０．１５ +2.03H ２ O... (1)

[0036] Anammox bacteria can be any bacteria belonging to the order Brocadiales, phylum Plantomycetes, kingdom Bacteria. Currently, pure culture of Anammox bacteria has not been established, so all are classified as "Candidatus". Specifically, Anammox bacteria that can be used in this embodiment include Candidatus Brocadia, Candidatus Kuenenia, Candidatus Jettenia, Candidatus Anammoxoglobus, Candidatus Scalindua, and Candidatus Anammoximicrobium. In this embodiment, however, any bacteria capable of performing the Anammox reaction can be used, without being limited by classification or scientific name. Anammox bacteria can be obtained by using activated sludge or excess activated sludge collected from existing wastewater treatment equipment as seed sludge and culturing it for a long period in a medium containing ammoniacal nitrogen and nitrite nitrogen or in organic wastewater such as sewage. Alternatively, Anammox bacteria can also be obtained by culturing the aforementioned seed sludge in a known Anammox medium.

[0037] [Composition of Anammox medium] ・NaNO ２ :0~300mg / L ・KHCO ３ :500mg / L ・(NH ４ ) ２ SO ４ :0~300mg / L・KH ２ PO ４ : 27 mg / L • Trace mineral solution (Fe, Ni, Co, EDTA, etc.): 1 mL / L

[0038] As shown in the reaction equation (1) above, the molar ratio of NH4-N to NO2-N contained in the methane fermentation treated water used for the Anammox reaction is preferably about 1:1 to 1:1.5, and more preferably about 1:1.32. However, depending on the state of the raw water, such as organic wastewater or membrane filtered water, the NH4-N content of the membrane filtered water is often high while the NO2-N content is low, and the molar ratio is often not as described above. Therefore, it is preferable to oxidize a portion of the NH4-N contained in the methane fermentation treated water with nitrifying bacteria (ammonia-oxidizing bacteria) to produce NO2-N. ４ - Part of N is NO ２ Since it is converted to -N, it is called "partial nitrite," etc. In other words, in this embodiment, an "anaerobic" ammonia oxidation reaction (anammox reaction) is carried out, but it is not necessary to make the methane fermentation treated water completely oxygen-free. In this embodiment, NH contained in the membrane filtered water ４ - Ammonia-oxidizing bacteria convert a portion of N into NO ２ It is possible to keep the amount of oxygen necessary for conversion to -N. In other words, the aforementioned "anaerobic" does not mean that the post-treatment device 40 is made completely anaerobic, but simply that the conditions under which the anammox reaction takes place (i.e., a limited range in which the anammox reaction takes place) must be anaerobic. Accordingly, treated water W from the membrane separation methane fermentation tank in the post-treatment device 40 ２ If the solution does not contain enough oxygen to perform partial nitrite formation, aeration can be performed using a blower, for example. The oxygen concentration of the liquid in the tank of the post-treatment device 40 can be measured with a dissolved oxygen meter DOS (not shown).

[0039] Partial nitrite is, in principle, NH ４ - Approximately half of N is NO ２ Since it only needs to be converted to -N, the conventional activated sludge process NH ４ - The entire amount of N is NO ２ Compared to the nitrification reaction to -N, the amount of air required for contact can be reduced by about half. Therefore, in this embodiment, NH ４ -N to NO ２When aeration power is used for nitrification to -N, the required aeration power can be reduced by half compared to the conventional activated sludge method. Therefore, energy consumption, such as electricity, can also be reduced by about half in such cases.

[0040] Examples of ammonia-oxidizing bacteria that can be used include bacteria belonging to the genera Nitrosomonas, Nitrosococcus, Nitrosospira, Nitrosolobus, and Nitrosovibrio, but are not limited to these.

[0041] NO ２ The generation of -N may be carried out in the same vessel in which the anammox reaction is performed, or in a separate vessel. ２ A system in which the generation of -N and the anammox reaction are carried out in the same tank is called a "single-tank system," while a system in which they are carried out in separate tanks is called a "double-tank system." In this embodiment, it is preferable to use a single-tank system. This is because using a single-tank anammox tank allows for space savings and lower construction costs compared to a double-tank system (not shown). Furthermore, using a double-tank system allows for the management of anammox bacteria and ammonia-oxidizing bacteria in separate tanks, making it easier to manage each bacterium and control the reaction. In addition, using a double-tank system allows for the management of NO produced by ammonia-oxidizing bacteria. ２ NO in membrane filtered water containing -N ２ -N concentration and flow rate can be adjusted and introduced into the tank where the anammox reaction is performed, so NH ４ -N and NO ２ -The molar ratio with N is easily set to the one described above.

[0042] In the anammox reaction, a small amount of NO3-N is produced. Therefore, it is preferable that the post-treatment device 40 contains denitrifying bacteria that reduce the produced NO3-N to N2. In this way, the anammox bacteria and denitrifying bacteria ultimately remove the NH4 contained in the organic wastewater. ＋ NH ４ - Most of the N is environmentally harmless N ２ It can be converted to [this].

[0043] Examples of denitrifying bacteria that can be used include, but are not limited to, Pseudomonas denitrificans, Pseudomonas aeruginosa, Pseudomonas stutzeri, Pseudomonas mendocina, Comamonas testosteroni, Paracoccus denitrificans, and Alcaligenes faecalis. Treatment with denitrifying bacteria may be carried out in a separate device (tank) from the post-treatment device 40.

[0044] Furthermore, ammonia-oxidizing bacteria and denitrifying bacteria can be easily obtained from activated sludge or excess activated sludge collected from existing wastewater treatment equipment. Since Anammox bacteria and ammonia-oxidizing bacteria are autotrophic bacteria that do not utilize organic matter for growth, they will not proliferate in large quantities even if the methane fermentation treated water contains dissolved organic matter. Therefore, in this embodiment, the amount of activated sludge produced from Anammox bacteria and ammonia-oxidizing bacteria can be reduced. On the other hand, denitrifying bacteria use organic matter as electron donors to produce NO ３ -N to N ２ It converts to methane, but it is a heterotrophic bacterium that proliferates by utilizing organic matter. Therefore, in this embodiment, although activated sludge derived from denitrifying bacteria is produced, most of the organic matter has already been decomposed into methane in the membrane separation methane fermentation tank 20 mentioned above, and the treated water (membrane filtered water) from the membrane separation methane fermentation tank W ２ The concentration of residual organic matter is low. Therefore, in this embodiment, the amount of activated sludge produced by the proliferation of denitrifying bacteria can be reduced compared to the conventional activated sludge method. Furthermore, in this embodiment, since the proliferation of heterotrophic bacteria, including denitrifying bacteria, is suppressed in the post-treatment device 40, it is possible to promote the dominance of Anammox bacteria. Therefore, it is possible to increase the concentration of Anammox bacteria and perform an efficient Anammox reaction. In this embodiment, NO by denitrifying bacteria ３ － From N ２ To ensure sufficient conversion to methanol, organic substances other than methanol can be added.

[0045] The single-tank anammox tank preferably includes a carrier 42 which is a hollow cylinder with an inner diameter of, for example, 3 to 30 mm and a length of, for example, 3 to 30 mm, and which has open ends.

[0046] Figure 6 shows a perspective view of the carrier 42. By using such a carrier 42, ammonia-oxidizing bacteria are retained on the outer surface 42a of the carrier 42, and dissolved oxygen originating from the air supplied to the single-tank anammox tank is consumed. Therefore, the inner surface 42b of the carrier 42 tends to become anaerobic. Consequently, anammox bacteria can easily grow and be retained on the inner surface 42b of the carrier 42. Furthermore, the anaerobic ammonia oxidation reaction by anammox bacteria can be suitably carried out on the inner surface 42b of the carrier 42. In this embodiment, from the viewpoint of more favorable growth and retention of anammox bacteria and anaerobic ammonia oxidation reaction by anammox bacteria, the inner diameter of the hollow cylindrical carrier 42 is preferably 5 to 15 mm, and the length is preferably 5 to 15 mm. The hollow cylinder is preferably cylindrical, but can be any shape such as triangular prism or square prism. The carrier 42 can be made of any resin, such as polypropylene (PP) resin, polyethylene terephthalate (PET) resin, or polyvinyl chloride (PVC) resin. The outer diameter of the carrier 42 is not particularly limited. The amount of carrier 42 administered can be, for example, 10 to 30% of the volume of the single-chamber anammox tank 41, preferably 20%, but is not limited to this.

[0047] Furthermore, in the single-tank Anammox tank into which the carrier 42 is introduced, it is preferable to agitate the tank liquid supplied with membrane-filtered water using at least one of the following devices: air blowing and mechanical stirring, thereby controlling the dissolved oxygen concentration of the tank liquid to, for example, 0.5 mg / L or less. In this way, the ammonia-oxidizing bacteria retained on the outside of the carrier 42 are exposed to an oxygen concentration ranging from the minimum necessary to an appropriate level. ２ It is possible to supply and carry out partial nitrite. Furthermore, as described above, in this embodiment, the ammonia-oxidizing bacteria held on the surface of the carrier 42 can carry out O ２is consumed. Therefore, in the present embodiment, anaerobic conditions can be maintained for the anammox bacteria retained on the inner side 42b of the carrier 42, and the anammox reaction can be caused to proceed. In other words, when the dissolved oxygen concentration is controlled as described above, partial nitritation by ammonia-oxidizing bacteria can be performed without significantly affecting the anammox reaction by anammox bacteria. In order to more reliably obtain the aforementioned effect, it is more preferable to control the dissolved oxygen concentration of the liquid in the tank to 0.3 mg / L or less.

[0048] The post-treatment device 40 may be provided with a device (not shown) for adding inorganic salts (metals) such as calcium, magnesium, iron, nickel, cobalt, potassium, sodium, zinc, selenium, tungsten, molybdenum, copper, manganese, and aluminum, for the purpose of maintaining the activities of anammox bacteria, ammonia-oxidizing bacteria, denitrifying bacteria, and the like.

[0049] Further, the post-treatment device 40 may be provided with a heating device (not shown) for adjusting the water temperature. The heating device can utilize heat or electricity obtained by burning biogas (methane) G obtained in the membrane separation methane fermentation tank 20. The post-treatment device 40 may be provided with various sensors such as a pH meter, a dissolved oxygen meter, an ammonia sensor, a nitrate sensor, and a thermometer, for example.

[0050] A final sedimentation tank 50 is installed on the downstream side of the post-treatment device 40 to allow final sedimentation, and the discharged water W ４ is discharged to the outside as

[0051] Although an anammox treatment device is exemplified as the nitrogen removal device of the post-treatment device 40, the present invention is not limited thereto. Examples of other sewage treatment methods include a standard activated sludge process, a circulating nitrification denitrification process, a circulating nitrification denitrification type membrane separation activated sludge process, an anaerobic-aerobic activated sludge process, and an anaerobic anoxic aerobic process, but the present invention is not limited thereto.

[0052] (Side stream line (side stream treatment step) L １１ (L １１－１ , L １１－２ , L １１－３)) As shown in FIG. 1A, the organic wastewater treatment apparatus 100A-1 is provided with a sidestream line L １１－１ comprising: a sludge thickener 201 that thickens excess sludge 20a discharged from a membrane separation methane fermenter 20 to obtain thickened sludge 20b; a thickened sludge storage tank 202 that stores the thickened sludge 20b thickened by the sludge thickener 201; and a digestion tank 203 (for mesophilic digestion at 30°C to 37°C, or thermophilic digestion at 50°C to 55°C) that subjects organic matters in the thickened sludge 20b from the thickened sludge storage tank 202 to methane fermentation.

[0053] The sludge thickener 201 is configured to thicken the excess sludge 20a, and for example, a known sludge thickener such as a belt-type thickener or a centrifugal thickener can be used.

[0054] The thickened sludge storage tank 202 is configured to temporarily store the thickened sludge 20b that has been thickened.

[0055] The digestion tank 203 is configured to digest the thickened sludge 20b, and generates digestion gas (methane) G that is biogas containing methane through methane fermentation ２ . The generated digestion gas G containing methane ２ is discharged from the digestion tank 203 through the digestion gas G ２ discharge digestion gas line L ５－２ is provided, and the digestion gas discharge line L ５－２ passes therethrough and joins the biogas discharge line L containing methane ５－１ .

[0056] The digestion tank 203 is heated and maintained at a water temperature of 30 to 37°C, and digestion treatment is performed in this mesophilic temperature range (water temperature of 30 to 37°C). As shown in Test Example 1 described below, for sewage (influent water quality of a treatment plant; BOD ５ : 200 mg / L, CODcr: 440 mg / L, SS: 200 mg / L, VSS: 180 mg / L, total nitrogen: 33 mg / L), when a treatment amount of 4,000 m ３ / day is treated in the membrane separation methane fermenter 20A, when the temperature of the sewage (water temperature of the membrane separation methane fermenter) is 17°C, the amount of thickened sludge with a solid content concentration of 4 wt% is 11.8 m ３ / day, at 20°C it is 6.6 m ３ / day, and at 25°C it is 6.2 m ３Since this occurs daily, the effective capacity of the sidestream digester 203 should be, for example, 236 m³. ３ In this case, the organic matter decomposition rate in the sidestream digester 203 is approximately 40%, as shown in the test example described later, and a by-gas with a methane concentration of 60-65% can be generated.

[0057] Here, the digestion temperature of the digester 203 is not limited to the medium temperature range (water temperature 30-37°C), but may be set to, for example, the so-called high temperature range (50-55°C).

[0058] In this digester 203, methane fermentation is also performed during the digestion process, and the subsequent digested sludge 203a is sent to line L ２０ The sludge is dewatered in the digested sludge dewatering unit 204, and the total nitrogen concentration of the dewatered separated liquid (*1: see Figure 1A) is 1,000 to 3,000 mg / L, and ammoniacal nitrogen (NH ４ -N) The concentration is high, around 500 to 1,500 mg / L, and denitrification treatment is performed in the post-treatment device 40 using methods such as the anammox treatment method. Also, since the dewatered separated liquid (*1) has a high nitrogen concentration and a relatively high water temperature of around 30°C, nitrogen removal treatment may be performed by a device that performs the anammox treatment method or the like before it flows into the post-treatment device 40 installed in the main stream. Dewatered sludge 204a is treated separately. As shown in Figure 1A, before the dewatered separated liquid (*1) flows into the post-treatment device 40 installed in the main stream, a treatment device such as a denitrification treatment device may be installed to perform treatment on the dewatered separated liquid (*1), for example, denitrification treatment (shown by a dashed line in the figure).

[0059] Furthermore, Figure 1B shows a modified example of the organic wastewater treatment apparatus 100A-1. In this organic wastewater treatment apparatus 100A-2, a return line L returns the digestate 203b, which has been digested in the digester 203, to the membrane separation methane fermentation tank 20 on the mainstream side. ２２This is installed so that the digestate 203b is returned to the membrane separation methane fermentation tank 20, where it is processed again, thereby improving processing efficiency. In addition, since the dewatered separated liquid (*1) has a high nitrogen concentration and a relatively high water temperature of around 30°C, it may be possible to remove the nitrogen using a denitrification device such as an Anammox treatment device before it flows into the post-treatment device 40 installed in the mainstream line. Furthermore, by performing methane fermentation on the sludge withdrawn from the membrane separation methane fermentation tank in a medium temperature range suitable for methane fermentation, more active methane-producing bacteria are returned to the membrane separation methane fermentation tank 20, thereby maintaining highly active methane-producing bacteria within the methane fermentation tank (membrane separation methane fermentation tank) 20.

[0060] Next, using Figures 2A to 2D, the side stream line L １１ Further explanation will be given regarding the processing. Figures 2A to 2D are schematic diagrams of the sidestreamline portion of the organic wastewater treatment device according to this embodiment.

[0061] As shown in Figure 2A, the organic wastewater treatment device 100A-2 according to the first embodiment has a belt-type sludge thickening device 201 installed between the membrane separation methane fermentation tank 20A and the thickened sludge storage tank 202, and a side stream line L １１－１ via pump P ４ The sludge is transported by the belt. This belt-type sludge thickening device 201 is preferable to the centrifugal separation method because it is energy-efficient and produces concentrated sludge 20b with a high concentration rate. The filtrate (sludge thickening device separation liquid) 20c from the belt-type sludge thickening device 201 is temporarily stored in a separate storage tank 209. After that, it is transported to the post-treatment device 40 and treated in this post-treatment device 40 (*2: see Figure 2A). The concentrated sludge 20b is then transported to the side stream line L １１－３ via pump P ５ The digester gas G is then sent to the digester tank 203. ２ (*3: See Figure 2A) is the digester gas discharge line L ５－２ From methane recovery line L ５－１ It will be sent to [location].

[0062] Furthermore, the organic wastewater treatment device 100A-3 according to the first embodiment shown in Figure 2B is provided between the concentrated sludge storage tank 202 and the digestion tank 203 and includes a sludge solubilization device 210 that solubilizes the concentrated sludge 20b to produce solubilized sludge 20d.

[0063] The solubilization apparatus 210 can be either a high-temperature solubilization apparatus or an ultra-high-temperature solubilization apparatus. The high-temperature solubilization apparatus processes the material at a solubilization temperature of, for example, 50 to 70°C for about two days. The ultra-high-temperature solubilization apparatus processes the material at a solubilization temperature of 70 to 90°C for about two days. These two types of apparatus perform biological treatment using high-temperature solubilizing bacteria and ultra-high-temperature solubilizing bacteria, and the apparatus is in the form of a complete mixing tank.

[0064] Furthermore, instead of solubilization treatment using only temperature, a hydrothermal solubilization device can also be used. In the organic wastewater treatment device 100A-4 shown in Figure 2C, the sludge thickening device 201 consists of two types of thickening devices installed in series: a first sludge thickening device 201A and a second sludge thickening device (thickened sludge dewatering device) 201B. In addition, a coagulation reaction tank 220 is installed between the membrane separation methane fermentation tank 20A and the first sludge thickening device 201A, and a coagulant is added to improve the concentration and dewatering efficiency.

[0065] Furthermore, the organic wastewater treatment device 100A-4 according to the first embodiment shown in Figure 2C is equipped with a cylindrical hydrothermal solubilization device (solubilization device) 210.

[0066] In this hydrothermal solubilization device 210, excess sludge (sludge concentration MLSS: 10,000 to 15,000 mg / L, solids concentration approximately 1 to 1.5%) 20a withdrawn from the membrane separation methane fermentation tank 20A is concentrated in the sludge thickening device 201A, and then the entire amount of concentrated sludge is dewatered in the concentrated sludge dewatering device 201B (Figure 2C), or a portion of the concentrated sludge is dewatered in the concentrated sludge dewatering device 201B (Figure 2D), or (or), all or part of the excess sludge 20a withdrawn from the membrane separation methane fermentation tank 20A is introduced into the coagulation reaction tank 220 for coagulation, and then, without passing through the sludge thickening device 201A, is directly dewatered in the sludge dewatering device 201B (not shown), resulting in a dewatered cake (solids concentration approximately 15 to 20%) 20b ２The mixture is continuously injected. Then, it is mixed and stirred in a hydrothermal solubilization device 210 where superheated steam is introduced, at 120 to 180°C for 10 to 30 minutes. The resulting hydrothermal solubilized sludge 20e is flowed into a digester 203 for medium-temperature methane fermentation treatment or high-temperature methane fermentation treatment. The amount of dewatered cake injected into the hydrothermal solubilization device 210 is set to an amount that can control the temperature of the digester 203 to a medium temperature (30 to 37°C) or a high temperature (50 to 55°C).

[0067] By solubilizing the concentrated dewatered sludge using such a solubilization device 210, the amount of biogas generated from the digester (medium-temperature digester) 203 increases by approximately 30% to 300% compared to when the sludge is not solubilized, although this varies depending on the properties of the organic wastewater treated in the membrane separation methane fermentation tank 20 and the sludge retention time in the membrane separation methane fermentation tank 20, making it a more preferable method.

[0068] On the other hand, when hydrothermally solubilized sludge 20e is subjected to mesothermally methane fermentation treatment in digester 203, and the digested sludge 203a withdrawn from digester 203 is dewatered, the dewatered separated liquid (*1) has a total nitrogen concentration of about 3,000 to 9,000 mg / L and an ammoniacal nitrogen concentration of about 1,000 to 3,500 g / L, which is a high concentration. Therefore, denitrification treatment such as the anammox treatment method is required in the post-treatment device 40 (see Figure 3).

[0069] Furthermore, since the dewatered separated liquid has a high nitrogen concentration and a relatively high water temperature of around 30°C, nitrogen removal treatment may be performed by a device that performs the Anammox treatment method or the like (denitrification device) before it flows into the post-treatment device 40 installed in the main stream.

[0070] Furthermore, as shown in Figures 2A to 2D, in the organic wastewater treatment apparatus 100A-2 to 100A-5 according to this embodiment, a return line L returns the digested liquid 203b from the digester 203. ２２ A water temperature acclimatization tank 205 may be provided. This water temperature acclimatization tank 205 consists of at least two or more acclimatization tanks (205a, 205b, etc.).

[0071] By providing this water temperature acclimatization tank 205, the temperature of the digestate 203b is gradually lowered when it is returned to the low-temperature (20°C) membrane separation methane fermentation tank 20 (for example, an immersion-type anaerobic MBR (integrated type) 20A). The purpose of providing this water temperature acclimatization tank 205 is to allow the bacteria involved in methane fermentation in the digestate to gradually adapt to the rapid change in temperature.

[0072] Figure 2E shows an example of the configuration of the water temperature acclimatization tank 205. As shown in Figure 2E, the water temperature acclimatization tank 205 is equipped with a first acclimatization tank 205a to a third acclimatization tank 205c. For example, if the digestion treatment temperature in the digester is 35°C, the temperature is first lowered to 30°C in the first acclimatization tank 205a, then to 25°C in the second acclimatization tank 205b, and then to 20°C in the third acclimatization tank 205c. In this way, by gradually lowering the temperature of the digestate 203b that is returned, the bacteria involved in methane fermentation in the digestate are gradually allowed to adapt to the rapid temperature change.

[0073] Furthermore, if the digestion temperature in the digester 203 is high (high-temperature digestion treatment), the number of acclimatization tanks is increased to address this. It is generally known that when the water temperature changes by 5°C / day or more, the methane production activity of methane-producing bacteria contained in digested sludge decreases rapidly, and the methane fermentation reaction stops. For this reason, in this invention, when returning the digested liquid 203b from the sidestream digester 203, where medium-temperature digestion treatment is performed, to the membrane separation methane fermentation tank 20, which operates at the water temperature of organic wastewater such as sewage, acclimatization tanks are installed to gradually lower the return temperature of the digested liquid 203b so that the activity of methane-producing bacteria contained in the returned sludge does not decrease significantly.

[0074] [Second Embodiment] Figure 3 is a schematic diagram illustrating the configuration of the organic wastewater treatment device 100B according to the second embodiment. Note that components identical to those in the first embodiment are denoted by the same reference numerals, and redundant explanations are omitted. Figure 4 is a schematic diagram illustrating the configuration of the mainstream line of the organic wastewater treatment device 100B according to the second embodiment. Figure 5 shows a schematic diagram of the vacuum degassing device 32. Note that components identical to those in the first embodiment are denoted by the same reference numerals, and redundant explanations are omitted. As shown in Figures 3 and 4, the organic wastewater treatment device 100B is provided downstream of the membrane separation methane fermentation tank 20, and membrane filtered water W ２ or W ２Ａ The methane recovery apparatus 60 includes a vacuum degassing device 32 that removes and recovers a portion of the dissolved methane inside. As shown in Figure 4, this methane recovery apparatus 60 is equipped with membrane filtered water W. ２Ａ It consists of a processing tank 31 into which the waste flows, and a vacuum degassing device 32.

[0075] This vacuum degassing device 32 includes a sealing section 31a that closes the top of the processing tank 31 to create a sealed state, a degassing outer cylinder (hereinafter referred to as "outer cylinder") 33 erected vertically in the direction of the axis above the sealing section 31a, and one end 34a of the membrane filtered water W in the processing tank 31 inside the degassing outer cylinder 33. ２ An inner cylinder 34 is positioned inside, with its other end 34b positioned within the upper gas reservoir S inside the degassing outer cylinder 33, and a methane recovery line L is connected to the top of the outer cylinder 33 and equipped with a vacuum pump VP. ５－３ It is composed of the above. Furthermore, methane-removed treated water W is present on the lower side surface of the outer cylinder 33. ２Ｂ Discharge line L transfers to post-processing device 40 for post-processing. １－４ It is connected.

[0076] By using such a vacuum degassing device 32 to drive the vacuum pump VP and maintain a predetermined vacuum level (X) in the gas reservoir S, the membrane filtered water W in the processing tank 31 is released. ２ The water is sucked up and rises inside the inner cylinder 34, overflows from the other end 34b of the inner cylinder 34, and falls between the outer cylinder 33 and the inner cylinder 34. At this time, the membrane filtered water W is subjected to a reduced pressure treatment by the vacuum pump VP. ２The dissolved methane is separated into gas and liquid as a gas, and the methane-removed treated water W3 is dropped. ３ The discharge line L is provided on the side of the outer cylinder 33. １－４ From, methane removal treated water W ２Ｂ It is then sent to the post-treatment device 40. Here, in this invention, degassing treatment refers to using a vacuum pump VP to degass the liquid (membrane filtered water W). ２ This refers to reducing the pressure applied to the system, thereby separating dissolved gases (such as methane) into liquid and releasing them. The vacuum pump VP is, for example, a water-sealed type, and the motor is explosion-proof.

[0077] Subsequently, biogas G, which is the recovered methane gas that has been separated and recovered. ３ This is the methane recovery line L ５－３ Removed via the methane discharge line L ５－１ Biogas G from １ and digester gas discharge line L ５－２ Biogas (digestive gas) from G ２ It merges with (G = G1 + G2 + G3).

[0078] In this embodiment, sewage (influent water quality: BOD 200 mg / L, COD Cr The target is membrane-filtered water obtained by methane fermentation treatment of 440 mg / L, SS 200 mg / L, VSS 180 mg / L, total nitrogen 33 mg / L) at a water temperature of 20°C in an immersed anaerobic MBR (integrated type) as a membrane separation methane fermentation tank, and under conditions of a vacuum degree (VD) of 30 kPa (≒0.3 atm) in the vacuum degassing device 32, the membrane-filtered water W ２ The degassing and recovery rate of dissolved methane is approximately 75%. Also, under vacuum conditions of, for example, 20 kPa (≒0.2 atmospheres), membrane filtered water W ２ The degassing and recovery rate of dissolved methane is approximately 85%.

[0079] Also, the membrane filtration liquid W in the processing tank 31 ２Assuming the specific gravity of the gas is 1.0 and the vacuum level in the vacuum degassing device 32 is, for example, 30 kPa, when the upper gas phase pressure of the processing tank 31 is atmospheric pressure, as shown in Figure 5, 75% of the dissolved methane can be recovered by setting the height (H1) from the water surface (WL) of the processing tank 31 to the other end 34b of the inner cylinder 34 to approximately 7.3 m. In this case, the height (H2) of the free board section of the upper gas reservoir S is set to approximately 2 m, taking into consideration space for defoaming, etc. Furthermore, when the upper gas phase pressure of the processing tank 31 is, for example, 4 kPa, the height (H1) from the water surface (WL) of the processing tank 31 to the other end 34b of the inner cylinder 34 is approximately 7.3 m. １ By setting the height to approximately 7.7m, 75% of the dissolved methane can be recovered. In this case, the height (H2) of the free board section of the upper gas reservoir S is set to approximately 2m.

[0080] Furthermore, when the vacuum level in the vacuum degassing device 32 is 20 kPa (≒0.2 atmospheres), and the upper gas phase pressure of the processing tank 31 is set to atmospheric pressure, 85% of the dissolved methane can be recovered by setting the height (H1) from the water level (WL) of the processing tank 31 to the other end 34b of the inner cylinder 34 to approximately 8.3 m. Moreover, when the upper gas phase pressure of the processing tank 31 is set to, for example, 4 kPa, the height (H1) from the water level (WL) of the processing tank 31 to the other end 34b of the inner cylinder 34 can be recovered. １ By setting the length to approximately 8.7m, 85% of the dissolved methane can be recovered. The pressure (or vacuum) of the vacuum pump VP is controlled by the upper gas phase section S of the outer cylinder 33 or the methane recovery line L ５－３ It is adjusted using a pressure indicator regulator (PIC) installed there.

[0081] Furthermore, the height (H1) from the water level (WL) of the treatment tank 31 to the other end 34b of the inner cylinder 34 is equal to the membrane filtered water W inside the treatment tank 31. ２ The specific gravity, resistance to the upward flow on the inner surface of the inner cylinder 34, etc., are adjusted as appropriate.

[0082] In this way, by maintaining a predetermined vacuum level (for example, 30 kPa) using the vacuum pump VP, the membrane filtered water W in the treatment tank 31 is maintained. ２ The water is sucked up under vacuum, rises inside the inner cylinder 34, overflows from the other end 34b of the inner cylinder 34, and falls between the outer cylinder 33 and the inner cylinder 34. Membrane filtered water W ２The dissolved methane gas is removed by gas-liquid separation under reduced pressure inside this cylinder. The resulting methane-removed water W is then obtained. ２Ｂ The discharge line L is connected to the post-treatment device 40. １－４ It is sent via [a specific method / platform].

[0083] In this embodiment, preferred vacuum levels of 20 kPa and 30 kPa were given as examples, but the vacuum level in the present invention is not limited to these, and can be, for example, 10 kPa to 50 kPa.

[0084] Furthermore, membrane filtered water W rises up the inner cylinder 34. ２ The flow velocity (F) in the rising section １ The flow velocity (F) of the descending section of the methane removal treated water W3 between the inner cylinder 34 and the outer cylinder 33 shall be, for example, 0.3 m / sec or less (preferably 0.2 m / sec), and ２ The speed of the descending section (F) is preferably 0.1 m / sec or less (preferably 0.07 m / sec). ２ If the upward flow velocity (F) is too fast, the methane gas that has been separated into gas and liquid will be drawn into the downward flow and sent to the downstream post-treatment device 40, resulting in a loss of recovered methane. To prevent this, the upward flow velocity (F) is set to prevent this. １ It is preferable to set the diameter of the outer cylinder, the diameter of the inner cylinder, and the gap diameter between the inner cylinder and the outer cylinder so that the flow velocity (F2) is, for example, 0.3 m / s or less and 0.15 m / s or more, and the flow velocity (F2) of the descending section is 0.1 m / s or less and 0.05 m / s or more.

[0085] [Test Examples] The following describes test examples demonstrating the effects of the present invention, but the present invention is not limited to these test examples.

[0086] Test Example 1: Sewage as organic wastewater (water quality at treatment plant; BOD) ５ For a total nitrogen concentration of 200 mg / L (CODcr: 440 mg / L, SS: 200 mg / L, VSS: 180 mg / L, total nitrogen: 33 mg / L), the processing volume was 4,000 m³. ３ The water was treated at water temperatures of 17°C, 20°C, and 25°C using the membrane separation methane fermentation tank 20A of the first embodiment (hereinafter referred to as the "membrane separation tank").

[0087] The membrane separation tank has an effective capacity of 1,333 m³, capable of maintaining a hydraulic retention time (HRT) of 8 hours. ３ And 4,000m ３ The membrane separation tank contains a hollow fiber MF membrane necessary for membrane filtration. The inside of the membrane separation tank is completely mixed by methods such as circulating gas from the gas phase of the membrane separation tank for membrane cleaning. Some of the organic pollutants contained in the influent wastewater are decomposed by anaerobic microorganisms such as methane-producing bacteria during the 8-hour HRT to become biogas containing methane. The remaining organic pollutants consist of proliferated anaerobic microbial cells and parts that remain in a state where decomposition has not progressed, and these remain as sludge.

[0088] The sludge concentration (MLSS concentration) in the membrane separation tank is maintained at approximately 10,000 mg / L at all water temperatures of 17°C, 20°C, and 25°C. The excess sludge in the tank is withdrawn, concentrated to a sludge concentration (MLSS concentration) of 4% in a belt-type sludge thickening device, and then fed into the sidestream digester 203, which is maintained at a water temperature of 35°C, for digestion treatment. The sludge conversion rate in the membrane separation methane fermentation tank is shown in "Table 1" below.

[0089] Furthermore, BOD in sewage ５ The CODcr, SS, VSS, and total nitrogen are shown in Table 2 below.

[0090]

[0091]

[0092] The sludge conversion rate is 5 m³ of effective capacity. ３ In the membrane separation methane fermentation tank, 15 m of sewage was used. ３ The results are obtained by treating the water at 17°C, 20°C, and 25°C per day. Here, the sludge conversion rate (%) refers to the proportion of suspended solids (SS) contained in the sewage flowing into the membrane separation methane fermentation tank that are converted into sludge in the tank.

[0093] The sludge conversion rate was very high at 59% at 17°C, which is below 20°C. This is because decomposition by methane fermentation decreases when the water temperature drops below 20°C.

[0094] When sewage (4,000 m³ / day) is treated in a membrane separation methane fermentation tank (effective capacity 1,333 m³), ​​the amount of excess sludge with a sludge concentration of 1% withdrawn from the membrane separation methane fermentation tank is 47.2 m³ / day (472 kg / day as solids), 26.4 m³ / day (264 kg / day as solids), and 24.8 m³ / day (248 kg / day as solids) at 17°C, 20°C, and 25°C, respectively. After adding a suitable amount of a flocculant such as polymer and mixing and stirring, the sludge is concentrated to a sludge concentration of 4% using a belt-type sludge thickening device.

[0095] The amount of concentrated sludge treated in this process was 11.8 m³ each. ３ / day, 6.6m ３ / day, 6.2m ３ This amount is per day. This concentrated sludge with a sludge concentration of 4% is digested in the sidestream digester 203, which is heated and maintained at a water temperature of 35-38°C. The effective capacity of the sidestream digester 203 is 236 m³. ３ Therefore, the HRT (hydraulic residence time of supplied concentrated sludge) when treating concentrated sludge at each water temperature is 20 days, 36 days, and 38 days, respectively.

[0096] The organic matter decomposition rate in the sidestream digester 203 is approximately 40%, and by-gas with a methane concentration of 60-65% is generated.

[0097] <First Embodiment (System consisting of a membrane separation methane fermentation tank 20 + post-treatment device 40 + side-stream digester 203)> In the configuration of the first embodiment (system consisting of a membrane separation methane fermentation tank + post-treatment device + side-stream digester 203), the amount of methane recovered and the amount of sludge generated (amount of dewatered cake) when sewage is treated at each water temperature are shown in "Table 3".

[0098]

[0099] For comparison, Table 4 shows the amount of methane recovered and the amount of sludge generated (dewatered cake) in a system without the sidestream digester 203.

[0100]

[0101] Furthermore, the ratio of the amount of methane recovered and the amount of sludge generated for the sidestream system with a digester to the case without a digester is shown in Table 3.

[0102] These results show that the amount of recovered methane increases by approximately 15-40% by installing the sidestream digester 203. In particular, at low water temperatures of 17°C, the decomposition of organic matter in the membrane separation methane fermentation tank decreases, so the increase in methane recovery by installing the sidestream digester 203 becomes more pronounced.

[0103] Furthermore, it was confirmed that the amount of dewatered cake was reduced by 30% by installing the sidestream digester 203, and reduced to approximately 70% of the amount in the case without the sidestream digester 203. In addition, as can be seen from "Table 3" of this Test Example 1, it was found that in Test Example 1, the amount of recovered methane was approximately 1.4 to 2 times greater, and the amount of dewatered cake was approximately 30 to 70%, compared to the conventionally implemented standard activated sludge method and circulating nitrification-denitrification method.

[0104] Test Example 2 <Second Embodiment (System consisting of membrane separation methane fermentation tank 20 + vacuum degassing device (methane recovery device) 60 + post-treatment device 40 + side stream digester 203)> In the second embodiment (system consisting of membrane separation methane fermentation tank 20 + vacuum degassing device (methane recovery device) 60 + post-treatment device 40 + side stream digester 203), sewage (4,000 m ３ Table 6 shows the amount of methane recovered and the amount of sludge generated (amount of dewatered cake) at each water temperature when the sample (per day) was treated at 17°C, 20°C, and 25°C.

[0105] For comparison, Table 5 shows the amount of methane recovered and the amount of sludge generated (dewatered cake) in a system without a sidestream digester.

[0106]

[0107]

[0108] Similar to Test Example 1, as can be seen from "Table 6" in Test Example 2, it was found that the amount of recovered methane increased by 10-30% by installing the sidestream digester 203. Furthermore, it was found that the amount of dewatered cake was reduced by 30% by installing the sidestream digester 203, and reduced to 70% compared to when the sidestream digester 203 was not installed. Also, as can be seen from "Table 6" in Test Example 2, it was found that in Test Example 2, the amount of recovered methane was approximately doubled and the amount of dewatered cake was reduced by approximately 30-70% compared to the conventionally implemented standard activated sludge method and circulating nitrification-denitrification method.

[0109] Although the embodiments described above were explained using a configuration that includes a concentrated sludge storage tank, configurations without a concentrated sludge storage tank are also possible, and the design can be modified as appropriate within the scope of the present invention.

[0110] Next, the process of the organic wastewater treatment method of the present invention will be described. The method includes: a membrane separation methane fermentation step provided in the main stream line into which organic wastewater containing suspended solids, organic matter and nitrogen components is introduced, in which organic matter in the organic wastewater is methane fermented under anaerobic conditions and membrane filtration is performed to obtain membrane filtered water; a post-treatment step for post-treatment of the membrane filtered water from the membrane separation methane fermentation step; a sludge concentration step or sludge dewatering step in the side stream line from which excess sludge in the membrane separation methane fermentation step is extracted, in which excess sludge is concentrated or dewatered to obtain concentrated sludge or dewatered sludge; and a digestion step in which organic matter in the concentrated sludge or dewatered sludge is methane fermented.

[0111] Furthermore, it includes a sludge solubilization step for solubilizing concentrated sludge. It also includes a digestion step in which dewatered sludge obtained by dewatering a portion or all of the concentrated sludge after concentrating excess sludge, or dewatered sludge obtained by directly dewatering a portion or all of the excess sludge without concentrating it, is hydrothermally solubilized, and organic matter in the hydrothermally solubilized sludge is methane fermented. Between the membrane separation methane fermentation step and the sludge concentration step, there is a coagulation reaction step for coagulating excess sludge.

[0112] Furthermore, the following processes are carried out at each stage: The biogas obtained from the membrane separation methane fermentation stage and the digestion stage is recovered. The digestate from the digestion stage is returned to the membrane separation methane fermentation tank. The temperature of the digestate from the digestion stage that is returned to the low-temperature membrane separation methane fermentation stage is gradually lowered.

[0113] Furthermore, between the membrane separation methane fermentation process and the post-treatment process, there is a vacuum degassing process to remove and recover a portion of the dissolved methane in the membrane filtration water. The post-treatment process is either a re-aeration process or a nitrogen removal process. The dewatered sludge generated from the dewatering device for digested sludge withdrawn from the digester is denitrified before being introduced into the post-treatment device.

[0114] The present invention is applicable to organic wastewater treatment equipment and organic wastewater treatment methods in general.

[0115] 100A-1 to 100B Organic wastewater treatment equipment 20 Membrane separation methane fermentation tank 201 Sludge thickening equipment 203 Digestion tank 210 Sludge solubilization equipment 40 Post-treatment equipment 50 Final sedimentation tank 60 Methane recovery equipment 20a Excess sludge 20b Concentrated sludge 20c Filtrate (separated liquid from sludge thickening equipment) 20d Solubilized sludge 20e Hydrothermally solubilized sludge 32 Vacuum degassing equipment L １ Mainstreamline L １１ Sidestream line *1 Dewatered separated liquid *2 Sludge thickening unit separated liquid *3 Digester gas (methane, etc.) G ２

Claims

1. An organic wastewater treatment apparatus comprising: a main stream line for introducing organic wastewater containing suspended solids, organic matter and nitrogen components; a membrane separation methane fermentation tank provided in the main stream line for methane fermentation of the organic matter in the organic wastewater under anaerobic conditions and for membrane filtration to obtain membrane filtered water; a post-treatment device for post-treatment of the membrane filtered water from the membrane separation methane fermentation tank; a side stream line for extracting excess sludge from the membrane separation methane fermentation tank; a sludge thickening device provided in the side stream line for concentrating the excess sludge to obtain concentrated sludge; and a digester for methane fermentation of the organic matter in the concentrated sludge.

2. The organic wastewater treatment apparatus according to claim 1, further comprising a sludge solubilizer for solubilizing the concentrated sludge, located downstream of the sludge thickening apparatus and upstream of the digester.

3. The organic wastewater treatment apparatus according to claim 1, further comprising a concentrated sludge storage tank for storing concentrated sludge from the sludge thickening apparatus between the sludge thickening apparatus and the digestion tank.

4. The organic wastewater treatment apparatus according to claim 2, further comprising a concentrated sludge storage tank for storing concentrated sludge from the sludge thickening apparatus, between the sludge thickening apparatus and the sludge solubilizing apparatus.

5. The organic wastewater treatment apparatus according to claim 1 or 2, characterized by providing a hydrothermal solubilization device for hydrothermally solubilizing dehydrated sludge obtained by dewatering a portion or all of the concentrated sludge obtained by concentrating excess sludge withdrawn from the membrane separation methane fermentation tank, or dehydrated sludge obtained by directly dewatering a portion or all of the excess sludge withdrawn from the membrane separation methane fermentation tank without concentrating it.

6. The organic wastewater treatment apparatus according to claim 1 or 2, characterized in that a coagulation reaction tank for coagulating the excess sludge is provided between the membrane separation methane fermentation tank and the sludge thickening device or sludge dewatering device.

7. The organic wastewater treatment apparatus according to claim 1 or 2, characterized in that it is provided with a return line for returning the digestate from the digester to the membrane separation methane fermentation tank.

8. The organic wastewater treatment apparatus according to claim 1 or 2, further comprising a vacuum degasser provided between the membrane separation methane fermentation tank and the post-treatment apparatus, for removing and recovering a portion of the dissolved methane in the membrane filtered water.

9. The organic wastewater treatment apparatus according to claim 1 or 2, characterized in that it is equipped with a denitrification apparatus that denitrifies the dewatered separated liquid generated from a dewatering apparatus for digested sludge withdrawn from the digester tank before introducing it into the post-treatment apparatus.

10. A method for treating organic wastewater, comprising: a membrane separation methane fermentation step provided in a main stream line for introducing organic wastewater containing suspended solids, organic matter and nitrogen components, in which organic matter in the organic wastewater is methane fermented under anaerobic conditions and membrane filtration is performed to obtain membrane filtered water; a post-treatment step for post-treatment of the membrane filtered water from the membrane separation methane fermentation step; a sludge concentration step or sludge dewatering step in a side stream line for extracting excess sludge in the membrane separation methane fermentation step, in which the excess sludge is concentrated or dewatered to obtain concentrated sludge or dewatered sludge; and a digestion step for methane fermentation of organic matter in the concentrated sludge or dewatered sludge.

11. The method for treating organic wastewater according to claim 10, characterized by having a sludge solubilization step for solubilizing the concentrated sludge.

12. The organic wastewater treatment method according to 10, characterized by comprising a digestion step of hydrothermally solubilizing dewatered sludge obtained by dewatering a portion or all of the concentrated sludge after the excess sludge has been concentrated, or dewatered sludge obtained by directly dewatering a portion or all of the excess sludge without concentration, and methane fermentation of organic matter in the hydrothermally solubilized sludge.

13. The method for treating organic wastewater according to claim 10 or 11, characterized in that it includes a coagulation reaction step for coagulating the excess sludge between the membrane separation methane fermentation step and the sludge concentration step or sludge dewatering step.

14. The method for treating organic wastewater according to claim 10 or 11, characterized in that the temperature of the digestate in the digestion step, which is returned to the membrane separation methane fermentation step on the low-temperature side, is gradually lowered.

15. The method for treating organic wastewater according to claim 10 or 11, characterized in that it includes a vacuum degassing step between the membrane separation methane fermentation step and the post-treatment step, for removing and recovering a portion of the dissolved methane in the membrane filtration treated water.

16. The method for treating organic wastewater according to claim 10 or 11, characterized in that the dewatered separated liquid generated from the dewatering device for digested sludge withdrawn from the digester is subjected to denitrification treatment before being introduced into the post-treatment device.

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