Method for producing organic concentrated sludge and organic concentrated sludge

Abstract

To provide a method for more efficiently recovering organic matter from organic wastewater such as sewage. [Solution] A method for producing concentrated organic sludge from organic wastewater using at least a reaction tank 3 and a solid-liquid separator 4, wherein the reaction tank 3 comprises an anaerobic tank 30 and an aerobic tank 31, phosphorus-accumulating bacteria are present inside the anaerobic tank 30, and organic wastewater is passed through the anaerobic tank 30, the aerobic tank 31, and the solid-liquid separator 4 in that order, with a hydraulic residence time in the anaerobic tank 30 of 1.0 hour or more and less than 2.0 hours.

Description

Technical Field

[0001] The present invention relates to a method for producing organic matter-concentrated sludge.

Background Art

[0002] Currently, most of the water treatment methods in sewerage facilities adopt biological treatment systems using microorganisms, for the reason that high stability of treated water quality can be ensured. However, biological treatment systems have two problems. The first problem is that since aerobic microorganisms are used, aeration for oxygen supply must be continued, which increases power consumption and leads to a large amount of carbon dioxide being emitted for power generation. The second problem is that a large amount of sludge is generated in the reaction tank, most of which is incinerated, resulting in the emission of large amounts of greenhouse gases such as carbon dioxide and nitrous oxide.

[0003] In recent years, in response to the progressing global warming, various initiatives have been implemented in various countries aiming for a carbon-neutral society, and water treatment technology is no exception, with various research and development efforts being carried out.

[0004] As one of such initiatives, research is being advanced to realize carbon neutrality by focusing on the fact that a large amount of organic matter is contained in sewage, efficiently recovering the organic matter from sewage and using it as a new energy source. A treatment method for recovering organic matter from sewage is disclosed, for example, in Non-Patent Document 1 below.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technology disclosed in the above non-patent document is called the high-load anaerobic-aerobic method (high-load AO method), and is carried out using an anaerobic tank and an aerobic tank as reaction vessels in the presence of phosphate-accumulating bacteria. In the high-load anaerobic-aerobic method, when phosphate-accumulating bacteria are placed under anaerobic conditions in the anaerobic tank, they hydrolyze polyphosphate within their cells to release soluble phosphorus outside the cells, while simultaneously taking in and storing organic matter within their cells. Then, when placed under aerobic conditions in the aerobic tank, they decompose the organic matter within their cells, and use the energy obtained in the process to take in soluble phosphorus into their cells and resynthesize polyphosphate. In addition, BOD-degrading bacteria are also present in the aerobic tank, so the environment is one in which organic matter is decomposed.

[0007] However, the high-load anaerobic-aerobic method disclosed in Non-Patent Document 1 does not consider the operating conditions necessary for efficiently recovering organic matter, and the operating parameters that maximize the amount of organic matter recovered have not yet been identified.

[0008] The object of the present invention is to provide a method for more efficiently recovering organic matter from organic wastewater such as sewage. [Means for solving the problem]

[0009] The characteristics of the method for producing organic concentrated sludge according to the present invention are: A method for producing concentrated organic sludge from organic wastewater using at least a reaction tank and a solid-liquid separator, The reaction tank comprises an anaerobic tank and an aerobic tank. Phosphate-accumulating bacteria are present inside the anaerobic tank. The organic wastewater is passed through the anaerobic tank, the aerobic tank, and the solid-liquid separator in that order. The key feature is that the hydraulic residence time in the anaerobic tank is set to be between one hour and less than two hours.

[0010] The inventors focused on the correlation between the amount of phosphorus released by phosphorus-accumulating bacteria and the amount of organic matter taken up, and investigated the optimal hydrological residence time for phosphorus-accumulating bacteria to more efficiently take up organic matter in an anaerobic tank. Therefore, according to the present invention, organic matter contained in organic wastewater can be efficiently recovered via phosphorus-accumulating bacteria.

[0011] In the method for producing organic concentrated sludge according to the present invention, it is preferable that the total hydraulic residence time in the anaerobic tank and the aerobic tank be 2 hours or more and 5 hours or less.

[0012] This configuration allows for more reliable uptake of organic matter by phosphorus-accumulating bacteria by limiting the total hydrological residence time in the anaerobic and aerobic tanks.

[0013] In the method for producing organic concentrated sludge according to the present invention, it is preferable that the total sludge retention time in the anaerobic tank and the aerobic tank be 1.5 days or more and 4 days or less.

[0014] This configuration allows for the recovery rate of organic matter by minimizing the decomposition of organic matter taken up by phosphorus-accumulating bacteria in the aerobic tank, while also promoting the uptake of soluble phosphorus into the bacteria by utilizing the energy obtained from the decomposition of some of the organic matter within the bacteria.

[0015] In the method for producing concentrated organic sludge according to the present invention, the organic wastewater is sewage, and it is preferable that the organic wastewater is passed through the reaction tank and the solid-liquid separator in that order, without passing through the sedimentation tank before the anaerobic tank.

[0016] This configuration allows for the production of concentrated organic sludge using a simpler apparatus, thereby reducing costs. Furthermore, it enables phosphorus-accumulating bacteria to take up more organic matter from organic wastewater than when using a sedimentation tank.

[0017] A feature of the organic matter concentrated sludge according to the present invention resides in that it is produced using the above-described method for producing organic matter concentrated sludge.

[0018] Since the organic matter concentrated sludge according to the present invention contains organic matter at a high concentration, it can be suitably used for fertilizers, fuels and the like. [Brief Description of the Drawings]

[0019] [Figure 1] It is a diagram showing an example of an organic matter concentrated sludge production facility. [Figure 2] It is a diagram showing another example of the organic matter concentrated sludge production facility. [Modes for Carrying Out the Invention]

[0020] [Embodiment] Hereinafter, embodiments of the present invention will be described.

[0021] (Organic matter concentrated sludge production facility) FIG. 1 shows an example of a suitable organic matter concentrated sludge production facility capable of implementing the method for producing organic matter concentrated sludge according to the present invention.

[0022] The organic matter concentrated sludge production facility 1 in the present embodiment is a facility capable of treating organic wastewater such as sewage and industrial wastewater, and includes, from the upstream side in the direction where the organic wastewater is transferred, a grit chamber 2, a reaction tank 3, a solid-liquid separation device 4, and a sludge treatment device 5. In the present embodiment, the grit chamber 2 may be provided as necessary.

[0023] Further, in the present embodiment, unlike a water treatment apparatus for implementing the conventional anaerobic-aerobic process (AO process), there is no need to provide a sedimentation tank between the grit chamber 2 and the reaction tank 3. Thereby, the organic matter concentrated sludge can be produced with a simpler apparatus configuration, and cost reduction can be achieved. Furthermore, more organic matter in the organic wastewater can be taken up by phosphorus-accumulating bacteria than in the case where a sedimentation tank is used.

[0024] The sedimentation basin 2 is for settling and removing solid matter, sediment, etc. contained in organic wastewater, and can suitably use, for example, a known sedimentation basin used in sewage treatment facilities.

[0025] Reaction tank 3 is where organic wastewater is treated by microorganisms. In this embodiment, reaction tank 3 is equipped with an anaerobic tank 30 and an aerobic tank 31 in that order, starting from the upstream side in the direction in which the organic wastewater is transported. At least phosphorus-accumulating bacteria are present in the anaerobic tank 30. A suitable volume ratio of the anaerobic tank 30 to the aerobic tank 31 is, for example, anaerobic tank:aerobic tank = 1:2.

[0026] In this embodiment, phosphate-accumulating bacteria refer to a group of bacteria capable of accumulating large amounts of phosphorus within their cells. Examples of such phosphate-accumulating bacteria include polyphosphate-accumulating bacteria, such as those belonging to the genus Acinetobacter. Under anaerobic conditions, phosphate-accumulating bacteria can hydrolyze polyphosphate within their cells to release soluble phosphorus outside the cell while simultaneously taking in and storing organic matter. Under aerobic conditions, they decompose organic matter within their cells, using the energy obtained to take in soluble phosphorus and resynthesize polyphosphate.

[0027] The solid-liquid separator 4 is used to separate sludge (organic matter-concentrated sludge) from the organic wastewater treated in the reaction tank 3, and can suitably use a known sedimentation tank, such as those used in sewage treatment facilities. This sedimentation tank is sometimes referred to as a final sedimentation tank.

[0028] Examples of organic substances in this invention include proteins, carbohydrates, volatile organic acids, lipids, and surfactants, but do not include organisms (microorganisms).

[0029] As shown in Figure 2, a membrane unit for membrane separation may be used as the solid-liquid separation device 4. Preferably, an immersion membrane is used as the membrane unit. In this case, the solid-liquid separation device 4 is placed in the aerobic tank 31, and the concentrated organic sludge is sent from the aerobic tank 31 to the sludge treatment device 5. The effluent from the solid-liquid separation device 4 is membrane-filtered water filtered by the membrane unit. Furthermore, when membrane separation is used for solid-liquid separation, a relatively higher solid-liquid separation efficiency is achieved compared to a sedimentation tank, resulting in a higher organic matter recovery rate.

[0030] The sludge treatment device 5 is for reducing the water content of the organic matter concentrated sludge separated by the solid-liquid separation device 4, or for performing microbial fermentation that can be carried out using the organic matter concentrated sludge. For example, known sludge drying devices, sludge dewatering devices, fermentation devices, etc., can be used as appropriate depending on the purpose of use.

[0031] Organic wastewater, such as sewage and industrial wastewater, that is to be treated first flows into sedimentation basin 2. Here, impurities such as garbage, stones, and sand contained in the organic wastewater are removed.

[0032] The organic wastewater, from which impurities have been removed, flows into the anaerobic tank 30 in the reaction tank 3, where the organic wastewater is treated under anaerobic conditions. Here, the phosphorus-accumulating bacteria hydrolyze polyphosphate within their cells to release soluble phosphorus outside the cells, while simultaneously taking in and storing organic matter present in the organic wastewater.

[0033] Next, the organic wastewater flows into the aerobic tank 31 in the reaction tank 3. Inside the aerobic tank 31, air is supplied by a diffuser (not shown) and other means to perform aeration treatment, causing oxygen to dissolve into the organic wastewater. Phosphate-accumulating bacteria use this oxygen to decompose some of the organic matter within their cells, and use the energy obtained in the process to take in dissolved phosphorus into their cells, resynthesize polyphosphate, and further proliferate.

[0034] Organic matter that flows into the aerobic tank 31 without being taken up by phosphorus-accumulating bacteria adheres to extracellular polymers (EPS) present on the surface of bacteria such as BOD-degrading bacteria, is taken up into the bacterial cells and stored. If aeration continues in this state, the organic matter will be decomposed and carbon dioxide and water will be produced. However, in this invention, before excessive decomposition of organic matter progresses, the organic wastewater treated in the reaction tank 3 is sent to the solid-liquid separator 4, thereby efficiently recovering the organic matter adsorbed or taken up by bacteria.

[0035] Furthermore, return sludge is necessary for continuous operation, but the organic wastewater is sent to the solid-liquid separator 4 before excessive decomposition of organic matter occurs, while allowing the minimum bacterial growth necessary for continuous operation to proceed. Therefore, organic matter concentrated sludge can be obtained by separating the organic matter taken up by phosphorus-accumulating bacteria and the organic matter taken up by BOD-degrading bacteria in the solid-liquid separator 4 before they are excessively decomposed in the aerobic tank.

[0036] Next, the organic wastewater flows into the solid-liquid separator 4, where the concentrated organic sludge is separated by sedimentation, and the supernatant liquid (separated water) is disinfected before being discharged. The separated water from the solid-liquid separator 4 may be further treated to obtain the desired treated water quality. At this time, a portion of the concentrated organic sludge separated by sedimentation is returned to the anaerobic tank 30 as return sludge by the return means 6, and the remainder is withdrawn as excess sludge. The excess sludge obtained in this embodiment contains a large amount of phosphorus-accumulating bacteria that have accumulated a high concentration of organic matter in the organic wastewater, and is therefore a highly concentrated organic sludge (concentrated organic sludge).

[0037] The obtained surplus sludge is transferred to the sludge treatment device 5, where it is subjected to drying, dewatering, carbonization, or fermentation treatment as needed, and can be made available for use as fertilizer, fuel, fuel raw material, or raw material for methane fermentation.

[0038] (Method for producing concentrated organic sludge) The method for producing organic concentrated sludge in this embodiment includes the following steps (1) to (3), but step (1) may be performed as needed. (1) A process to remove impurities such as solid matter and soil contained in organic wastewater. (2) A step of performing organic wastewater treatment by passing organic wastewater through an anaerobic tank and an aerobic tank in sequence to produce concentrated organic sludge, wherein the hydraulic residence time (HRT) in the anaerobic tank is 1 hour or more and less than 2 hours. (3) A process for settling and separating organic matter concentrated sludge.

[0039] The inventors focused on the correlation between the amount of phosphorus released by phosphorus-accumulating bacteria and the amount of organic matter taken up, and investigated the optimal hydrological residence time (HRT) for phosphorus-accumulating bacteria to more efficiently take up organic matter in an anaerobic tank. As a result, they found that by setting the hydrological residence time (HRT) in the anaerobic tank to 1 hour or more and less than 2 hours, organic matter contained in organic wastewater can be efficiently recovered via phosphorus-accumulating bacteria, leading to the completion of the present invention. Here, hydrological residence time (HRT) refers to the time that organic wastewater remains in the treatment tank, and is expressed by the following relational equation (Equation 1) based on the amount of organic wastewater flowing into the treatment tank and the tank volume (effective capacity). Hydraulic residence time (HRT) = Tank volume / Inflow rate per unit time ... (Equation 1)

[0040] In step (2) above, the hydrological residence time (HRT) in the anaerobic tank is preferably 1.1 hours or more and 1.95 hours or less, more preferably 1.2 hours or more and 1.95 hours or less, and even more preferably 1.2 hours or more and 1.5 hours or less.

[0041] Furthermore, in step (2) above, the total hydrological residence time (HRT) in the anaerobic tank and the aerobic tank may be set to 2.0 hours or more and 5.0 hours or less, preferably 2.4 hours or more and 4.5 hours or less, and more preferably 2.4 hours or more and 4 hours or less.

[0042] By setting the total hydrological residence time (HRT) in the anaerobic and aerobic tanks to between 2.0 hours and 5.0 hours, it is possible to more reliably incorporate a larger amount of organic matter into the phosphorus-accumulating bacteria.

[0043] Furthermore, in step (2) above, the total sludge retention time (SRT) in the anaerobic tank and the aerobic tank may be set to 1.5 days or more and 4 days or less, preferably 1.5 days or more and 2 days or less. Here, sludge retention time (SRT) refers to the time required for the sludge in the treatment tank to be completely replaced by newly generated sludge, and is expressed by the following relational equation (Equation 2) based on the amount of sludge withdrawn and the tank volume (effective capacity). Sludge retention time (SRT) = (tank volume × MLSS concentration) / amount of sludge extracted per day ... (Equation 2) Here, MLSS (Mixed Liquor Suspended Solids) refers to the concentration of organic matter and other substances in the mixed liquid within the reaction vessel, and is also used as an indicator of microbial concentration.

[0044] By setting the total sludge retention time (SRT) in the anaerobic and aerobic tanks to between 0.5 and 4 days, solid-liquid separation can be performed before excessive decomposition of organic matter by phosphorus-accumulating bacteria and BOD-degrading bacteria occurs, thereby improving the recovery rate of organic matter. Furthermore, it is possible to decompose some of the organic matter within the bacterial cells and use the energy obtained in the process to promote the uptake of dissolved phosphorus into the bacterial cells. In other words, it becomes possible to efficiently recover organic matter and remove phosphorus from wastewater.

[0045] This invention makes it possible to recover dissolved organic matter and colloidal organic matter that were previously unrecoverable and decomposed by bacteria. For example, when methane fermentation is performed in the sludge treatment device 5, this contributes to an increase in methane production. Since dissolved organic matter and colloidal organic matter are easily assimilated by methanogenic bacteria, the recovery effect is very large. [Examples]

[0046] (Phosphorus release test) In the organic sludge production facility of the above-described embodiment, sewage from a sewage treatment plant (the COD value of the sewage inflow can generally vary in the range of 200 to 500 mg / L) was used as the organic wastewater, and the hydrological residence time (HRT) and sludge residence time (SRT) were set to different times. Sewage flowing from the grit chamber to the reaction tank was sampled appropriately at various points in the reaction tank, and the phosphate concentration in the wastewater at the reaction tank inlet and the phosphate concentration in the wastewater at the aerobic tank outlet were measured using a known phosphate concentration measurement method. For Examples 1 to 8, the organic sludge production facility according to Figure 1 was used, and for Examples 9 to 17, the organic sludge production facility according to Figure 2 was used. In the organic sludge production facility according to Figure 1, the effective capacity of the anaerobic tank was 6.5 L, the effective capacity of the aerobic tank was 13 L, and the volume ratio was anaerobic tank:aerobic tank = 1:2. Furthermore, in the organic matter concentrated sludge production facility shown in Figure 2, the effective capacity of the anaerobic tank was set to 13 L and the effective capacity of the aerobic tank to 17 L, with a volume ratio of anaerobic tank:aerobic tank = 1.3:1.7. In the anaerobic tank, phosphorus was released while stirring was performed with a stirrer, and in the aerobic tank, phosphorus was taken up by aeration. The wastewater that passed through the aerobic tank was subjected to solid-liquid separation using a solid-liquid separator.

[0047] The results are shown in Tables 1 and 2 below. The criteria for determining the "high" or "low" level of phosphate release were as follows: "High" was defined as a greater phosphorus uptake in the aerobic tank than phosphorus release in the anaerobic tank, and "Low" was defined as a less phosphorus uptake in the aerobic tank than phosphorus release in the anaerobic tank. The organic matter recovery rate (%) was calculated by measuring the concentrations of phosphorus in the influent and effluent water daily, determining the average values ​​A and B for the target period, and then formulating the average phosphorus removal rate (%) as (AB) ÷ B × 100. Furthermore, for the organic matter recovery rate (%), if the influent water volume is C [L / day] and the COD concentration in the influent water is D [mg / L], the total COD influent into the test equipment during the test period is Σ(C × D) [mg]. Also, if the amount of recovered excess sludge is E [L / day] and the COD concentration in the excess sludge is F [mg / L], the total COD transferred to the excess sludge during the test period is Σ(E × F) [mg] (i.e., the total recovered COD). Therefore, the organic matter recovery rate (%) was calculated as follows: Σ(E×F)÷Σ(C×D)×100. [Table 1] [Table 2]

[0048] Although the present invention has been described above with reference to the drawings, the present invention is not limited to the configuration shown in the drawings, and can be implemented in various forms without departing from the spirit of the invention. [Industrial applicability]

[0049] The method for producing concentrated organic sludge according to the present invention can be suitably used, for example, in sewage treatment facilities. [Explanation of symbols]

[0050] 1: Organic matter concentrated sludge production facility 2: Sedimentation basin 3: Reaction vessel 30: Anaerobic tank 31:Aerobic tank 4: Solid-liquid separator 5: Sludge treatment equipment 6. Return method

Claims

1. A method for producing concentrated organic sludge from organic wastewater using at least a reaction tank and a solid-liquid separator, The reaction tank comprises an anaerobic tank and an aerobic tank. Phosphate-accumulating bacteria are present inside the anaerobic tank. The organic wastewater is passed through the anaerobic tank, the aerobic tank, and the solid-liquid separator in that order. A method for producing organic matter-concentrated sludge, wherein the hydraulic residence time in the anaerobic tank is 1 hour or more and less than 2 hours.

2. A method for producing organic matter concentrated sludge according to claim 1, wherein the total hydraulic residence time in the anaerobic tank and the aerobic tank is 2 hours or more and 5 hours or less.

3. A method for producing organic matter-concentrated sludge according to claim 1, wherein the total sludge retention time in the anaerobic tank and the aerobic tank is 1.5 days or more and 4 days or less.

4. The method for producing concentrated organic sludge according to claim 1, wherein the organic wastewater is sewage, and the organic wastewater is passed through the reaction tank and the solid-liquid separator in that order, without passing through the sedimentation tank before the anaerobic tank.

5. Organic concentrated sludge produced using the method for producing organic concentrated sludge described in any one of claims 1 to 4.

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