JP7798458B2 - Wastewater treatment device and wastewater treatment method - Google Patents

Description

The present invention relates to a wastewater treatment device and a wastewater treatment method.

Traditionally, when treating wastewater such as sewage containing impurities, organic matter, and water, water treatment involves first removing bulky debris and large foreign matter from the wastewater using screening equipment, and then using activated sludge or other methods to decompose and remove the organic matter in the wastewater. While screening equipment can remove bulky debris and large foreign matter from the wastewater, the treated water still contains relatively large impurities such as hair and scum, as well as suspended organic matter. This places a heavy load on downstream water treatment equipment, causing problems such as scum accumulation within the water treatment equipment and clogging of measuring instruments.

Furthermore, in response to the recent aging society, it is expected that garbage disposals will become more widespread in the future. As garbage disposals become more widespread, food residues of sizes that cannot be removed using conventional screening equipment will increase in wastewater. Furthermore, it is expected that small-scale sewerage systems will be consolidated and abolished in the future due to the declining population, resulting in an increase in the amount of wastewater treatment. There are concerns that this increase in food residue in wastewater and the increase in the amount of water to be treated will further increase the load on water treatment equipment.

In response to this, filtration devices that use filter media such as porous materials to separate suspended organic matter from wastewater are known (see, for example, Patent Document 1). The filter device is filled with filter media, which form a filtration layer. When wastewater supplied to the filter device passes through the filtration layer, the water contained in the wastewater permeates the filter media, but the suspended organic matter is captured by the filter media because its pore size is larger than the filter media's pore size. This separates the suspended organic matter from the water in the wastewater.

Japanese Patent Application Laid-Open No. 2021-10888

However, in the case of filtration equipment that uses filter media to separate suspended organic matter from wastewater, continued filtration leads to the accumulation of suspended organic matter in the filter media, reducing filtration efficiency. This necessitates the need for complex processes such as chemical cleaning to remove the suspended organic matter that has accumulated in the filter layer. This poses the problem of being unable to efficiently remove and utilize the suspended organic matter separated by filtration.

The object of the present invention is to provide a wastewater treatment device and method that can efficiently remove and utilize suspended organic matter separated by filtration.

In order to achieve the above-mentioned object, the wastewater treatment device of the present invention is a wastewater treatment device that performs a filtration process in which wastewater containing suspended organic matter and water is filtered to separate the suspended organic matter from the water, and a decomposition process in which the suspended organic matter separated by the filtration process is anaerobically decomposed, and is characterized in that it has a filter medium that separates the suspended organic matter from the water, and a decomposition means that anaerobically decomposes the suspended organic matter separated by the filter medium , and the filter medium is a hollow cylindrical porous body with a specific gravity of 0.95 to 1.05, or a nonwoven fabric with a specific gravity of 0.95 to 1.05 .

In order to achieve the above-mentioned object, the wastewater treatment unit of the present invention is a wastewater treatment unit that performs a filtration process to filter wastewater containing suspended organic matter and moisture and separate the suspended organic matter from the moisture, and a decomposition process to anaerobically decompose the suspended organic matter separated by the filtration process, and is characterized by comprising a plurality of wastewater treatment devices each having a filter material that separates the suspended organic matter from the moisture and a decomposition means that anaerobically decomposes the suspended organic matter separated by the filter material , and a switching means for switching between the filtration process and the decomposition process performed in the plurality of wastewater treatment devices.

In order to achieve the above-mentioned object, the wastewater treatment method of the present invention is a wastewater treatment device that performs a filtration process to filter wastewater containing suspended organic matter and moisture and separate the suspended organic matter from the moisture, and a decomposition process to anaerobically decompose the suspended organic matter separated by the filtration process, and is characterized in that the wastewater treatment method using a wastewater treatment device has a filter material that separates the suspended organic matter from the moisture and a decomposition means that anaerobically decomposes the suspended organic matter separated by the filter material , and is characterized in that it has a filtration step that filters the wastewater and separates the suspended organic matter from the moisture, a decomposition step that anaerobically decomposes the separated suspended organic matter, and a switching step that switches between the filtration process and the decomposition process.

In order to achieve the above-mentioned object, the wastewater treatment method of the present invention is a wastewater treatment unit that performs a filtration process to filter wastewater containing suspended organic matter and water and separate the suspended organic matter from the water, and a decomposition process to anaerobically decompose the suspended organic matter separated by the filtration process, the wastewater treatment method using a wastewater treatment unit characterized by comprising: a plurality of wastewater treatment devices each having a filter material that separates the suspended organic matter from the water and a decomposition means that anaerobically decomposes the suspended organic matter separated by the filter material ; and a switching means that switches between the filtration process and the decomposition process to be performed in the plurality of wastewater treatment devices, the wastewater treatment method being characterized by comprising: a filtration and decomposition step in which the filtration process is performed in one of the plurality of wastewater treatment devices and the decomposition process is performed in another of the plurality of wastewater treatment devices; and a switching step in which the switching means switches the one device that performed the filtration process from the filtration process to the decomposition process, and switches the other device from the decomposition process to the filtration process.

According to the present invention, suspended organic matter separated by filtration can be efficiently removed and utilized.

1 is a diagram schematically illustrating a wastewater treatment device according to an embodiment of the present invention. 2 is a flowchart showing a procedure of wastewater treatment performed by the wastewater treatment device of FIG. 1 . 2 is a diagram schematically illustrating a wastewater treatment unit including a plurality of wastewater treatment devices shown in FIG. 1. FIG. 4 is a flowchart showing the procedure of drainage treatment executed by the drainage treatment unit of FIG. 3 . FIG. 4 is a diagram showing a large-scale sewage treatment flow using the wastewater treatment unit of FIG. 3. FIG. 4 is a diagram showing a small-scale sewage treatment flow using the wastewater treatment unit of FIG. 3.

Embodiments of the present invention will be described in detail below with reference to the drawings.

Figure 1 is a schematic diagram showing a wastewater treatment device 10 according to an embodiment of the present invention.

(Wastewater treatment device 10)
The wastewater treatment device 10 in FIG. 1 includes a filtration and methane fermentation treatment tank 1 (hereinafter referred to as "treatment tank 1"), a gas holder 2, a heating device 3, a blower B, and a pump P. The treatment tank 1 is filled with a filter medium 11 (separation means) and has an aeration device 7 (agitation device). A wastewater storage tank (not shown) stores wastewater after treatment in a primary sedimentation tank or screen. The treatment tank 1 is connected to a wastewater inlet pipe 4, which has a pump P and valves V1, V2, and V3. The flow of wastewater from the wastewater storage tank (not shown) into the treatment tank 1 is controlled by opening and closing valves V1 and V3 while keeping valve V2 closed. The treatment tank 1 is also connected to a filtrate outlet pipe 5, which has a valve V5. The flow of filtered water out of the treatment tank 1 is controlled by opening and closing valve V5 of the filtrate outlet pipe 5.

Gas holder 2 stores digester gas, which is primarily composed of methane, and treatment tank 1 and gas holder 2 are connected via digester gas inlet pipe 6 and digester gas outlet pipe 8. Digestion gas inlet pipe 6 has blower B and valve V6, and the digester gas supplied from gas holder 2 to treatment tank 1 is controlled by opening and closing valve V6. The digester gas supplied to treatment tank 1 is diffused into the interior of treatment tank 1 by air diffuser 7 (agitation device). Digestion gas outlet pipe 8 has valve V8, and the digester gas flowing out of treatment tank 1 is controlled by opening and closing valve V8.

The treatment tank 1 and heating equipment 3 are connected via a steam inlet pipe 9, and digested sludge is supplied to the treatment tank 1 through a digested sludge supply pipe 12. Digested sludge is the sludge that remains after the organic matter in the sludge is broken down (hereinafter also referred to as digestion) by the action of methanogens, generating digester gas containing methane gas and carbon dioxide. The digested sludge contains methanogens that carry out methane fermentation.

(Treatment tank 1)
The treatment tank 1 is a rectangular, corrosion-resistant tank with external insulation, in which filtration and methane fermentation are carried out sequentially. The filter media 11 packed inside the treatment tank 1 also serves as a carrier for the microorganisms (decomposition means) used in the methane fermentation process, which will be described later. Two perforated plates (supports) made of punched metal or the like, with holes slightly smaller than the outer diameter of the filter media 11, are installed inside the treatment tank 1, and the filter media 11 is packed into the space between these two perforated plates to form a filtration layer.

The filter medium 11 is made of a porous material or nonwoven fabric. Examples of porous materials include a hollow cylindrical foam made of expanded polypropylene, with an uneven surface and numerous internal voids. The outer diameter and length of the hollow cylindrical foam are 5 mm to 20 mm, and the specific surface area is 500 to 1500 ^{m 2} /m ³ . Examples of nonwoven fabric include ball-shaped nonwoven fabric with numerous voids extending to the interior and a large amount of suspended solids (SS) retention. The outer diameter of the filter medium is typically 5 to 30 mm, preferably 10 to 20 mm, and the pore size of the foam filter medium and the gaps in the nonwoven fabric are typically 10 μm to 1 mm. Using such a filter medium increases the amount of SS retention and facilitates the retention of microorganisms. Furthermore, using a filter medium with a specific gravity of 0.95 to 1.05 allows for the achievement of appropriate shaking or moving mixing, as described below, without uneven distribution within the treatment tank 1. To enable rocking or moving mixing as described below, the filter media should be packed in the region between the two perforated plates so that there is a space above the filter media of 10 to 30% by volume. Note that a portion of the perforated plate installed above the filter media may be substituted with a water collection nozzle that is shaped to be less likely to clog.

Filtration is carried out by bringing wastewater containing suspended organic matter and moisture that has flowed into the treatment tank 1 into contact with the filter media 11. When the wastewater passes through the filtration layer, the moisture contained in the wastewater permeates the filter media 11, but the suspended organic matter is captured by the filter media 11, specifically on its surface and inside. Therefore, as the filtration process continues, suspended organic matter accumulates in the filter media 11.

Methane fermentation is a process in which microorganisms (anaerobic bacteria) decompose organic matter, producing digester gas and digestive fluids, primarily consisting of methane (hereinafter referred to as "digestion"). Specifically, the anaerobic bacteria first hydrolyze the organic matter, producing soluble amino acids, etc. The amino acids produced are then taken up into the cells of the anaerobic bacteria and metabolically broken down, producing acetic acid, hydrogen, carbon dioxide, etc. After that, methane is produced as biogas from the acetic acid, hydrogen, and carbon dioxide.

In this embodiment, microorganisms (decomposition means) are supported on the filter medium 11 (separation means), and suspended organic matter captured on the filter medium 11 during filtration is brought into contact with the microorganisms on the filter medium, thereby enabling efficient methane fermentation. The microorganisms are anaerobic bacteria, primarily methane bacteria, and are contained in the digested sludge supplied to the treatment tank 1 from the digested sludge supply pipe 12. To support the microorganisms on the filter medium, the digested sludge supplied to the treatment tank 1 is simply mixed with the filter medium 11. Mixing the digested sludge and the filter medium 11 allows the microorganisms to quickly penetrate into the filter medium 11 and become supported on the filter medium 11. The microorganisms supported on the filter medium 11 are not destroyed by the typical agitation performed inside the treatment tank 1, and remain supported on the filter medium 11.

The aeration device 7 (agitation device) diffuses the digester gas supplied from the gas holder 2 into the treatment tank 1 as coarse bubbles. The coarse bubbles diffused by the aeration device 7 rise throughout the entire interior of the treatment tank 1, agitating the interior of the treatment tank 1 and shaking or moving and mixing the filter media 11. This agitation by the digester gas promotes contact between the suspended organic matter captured by the filter media 11 and microorganisms during methane fermentation, thereby accelerating methane fermentation. Uniform agitation within the treatment tank 1 also prevents the formation of scum and separation into a sludge layer and a liquid layer. Furthermore, it accelerates the heat transfer of the wastewater within the treatment tank 1 during methane fermentation, thereby enabling uniform temperature control within the treatment tank 1. Agitation can be performed continuously or intermittently, for example, once every 1 to 3 hours for 10 to 30 minutes. Methods of agitation inside the treatment tank 1 include gas agitation by diffusing digester gas from the aeration device 7, mechanical agitation using paddles, and agitation by controlling the amount of steam injected.

FIG. 2 is a flowchart showing the procedure of wastewater treatment carried out by the wastewater treatment device of FIG.
Hereinafter, the wastewater treatment method performed by the wastewater treatment apparatus of FIG. 1, that is, the filtration treatment, the switching from the filtration treatment to the methane fermentation treatment, and the methane fermentation treatment, will be described with reference to FIGS. 1 and 2.

(Filtration process)
In the wastewater treatment device 10, first, valve V2 is closed to block the outflow of wastewater to the methane fermentation facility, and V6 and V8 are closed to block the circulation of digester gas between the treatment tank 1 and the gas holder 2. Next, valves V1, V3, and V5 are opened and pump P is driven, so that wastewater is supplied from a wastewater storage tank (not shown) through wastewater inlet pipe 4 to the treatment tank 1 (S201).

Wastewater flowing into treatment tank 1 rises within the tank as an upward flow, passing through the filtration layer and coming into contact with filter media 11. At this time, the water contained in the wastewater permeates filter media 11, but because the outer diameter of the suspended organic matter is larger than the pore size of filter media 11, the suspended organic matter is captured by filter media 11 and remains (S202: filtration step). Consequently, as the filtration process continues, suspended organic matter accumulates in filter media 11, reducing filtration efficiency. Generally, in filtration devices filled with filter media, the filter media is periodically cleaned to remove the captured matter. However, in this embodiment, the suspended organic matter captured by filter media 11 is decomposed by methane fermentation, as described below, so filter media cleaning is not necessary. The filtered water that permeates filter media 11 is transported via filtrate outlet pipe 5 to the next water treatment facility.

(Switching from filtration to methane fermentation)
Next, in order to remove suspended organic matter accumulated in the filter medium 11 by filtration through methane fermentation, which anaerobic decomposition, the inside of the treatment tank 1 is switched to an environment in which methane fermentation (decomposition) can be performed. When the filtration efficiency of the filtration process decreases, the operation of the pump P of the wastewater treatment device 10 is stopped and the valves V1, V3, and V5 are closed, thereby stopping the inflow of wastewater into the treatment tank 1 and the outflow of filtered water from the treatment tank 1, and terminating the filtration process (S203).

Next, while valve V8 of digester gas outlet pipe 8 is closed, valve V6 of digester gas inlet pipe 6 is opened and blower B is driven to supply digester gas from gas holder 2 into treatment tank 1 (S204). The digester gas supplied into treatment tank 1 is diffused into treatment tank 1 by aeration device 7 (agitation device) installed below the filter media filling area. At this time, coarse bubbles of digester gas rise from the aeration device 7 and agitate the entire interior of treatment tank 1, causing the filter media 11 to oscillate or move and mix. This causes the wastewater present around the filter media 11 to leave the filter media 11 and move to the bottom of treatment tank 1. Because treatment tank 1 is sealed except for the point connected to digester gas inlet pipe 6, the pressure of the digester gas causes the wastewater present at the bottom of treatment tank 1 to flow into wastewater inlet pipe 4. Valves V2 and V3 are then opened, and the wastewater is transferred to a methane fermentation tank for primary sludge and screen residue (S204: switching step). After the wastewater has been discharged, valve V3 is closed to stop the flow of wastewater through treatment tank 1.

(Methane fermentation treatment)
Next, steam is supplied from the heating equipment 3 to the inside of the treatment tank 1 via the steam inlet pipe 9, and the inside of the treatment tank 1 is controlled to be maintained at a predetermined temperature at which methane fermentation progresses (S205). In the case of mesophilic methane fermentation, the temperature is maintained at 35 to 38°C, and in the case of thermophilic methane fermentation, the temperature is controlled to be maintained at 53 to 57°C. The temperature inside the treatment tank 1 may be controlled by installing a hot water pipe. Next, digested sludge is supplied into the treatment tank 1 through the digested sludge supply pipe 12 (S205). The digested sludge supplied to the treatment tank 1 comes into contact with and mixes with the filter medium 11, causing the methane bacteria in the digested sludge to penetrate into the filter medium 11 and be supported on the filter medium.

Then, valve V8 of the digester gas outlet pipe 8 is opened, creating a circulating flow of digester gas between the treatment tank 1 and the gas holder 2. The digester gas supplied from the gas holder 2 to the treatment tank 1 is diffused into the treatment tank 1 as coarse bubbles by the aeration device 7 (agitation device). The coarse bubbles of the diffused digester gas rise throughout the entire interior of the treatment tank 1, agitating the interior of the treatment tank 1 (S205). This causes the filter media 11 carrying methane bacteria to oscillate or move and mix. This gas agitation promotes contact between the suspended organic matter remaining on the filter media 11 and the methane bacteria, thereby carrying out methane fermentation (S206: decomposition step). In this embodiment, the suspended organic matter and the methane bacteria are fixed in close proximity to each other on the filter media 11. Therefore, methane fermentation proceeds more efficiently than in conventional methane fermentation processes in which wastewater containing suspended organic matter is supplied to a reaction tank containing methane bacteria and the two are brought into contact. Furthermore, gas agitation by the bubbles uniformly controls the temperature and conditions inside the treatment tank 1, preventing the formation of scum and the separation of the sludge and liquid layers. By using filter media 11 with a specific gravity of 0.95 to 1.05, when digester gas is diffused from the air diffuser 7, the filter media 11 can be appropriately shaken or moved and mixed without uneven distribution inside the treatment tank 1.

When methane fermentation is carried out, organic matter is decomposed, producing digester gas and digester liquid. The produced digester gas, along with the digester gas supplied from gas holder 2 to treatment tank 1, is circulated and stored in gas holder 2 via digester gas outlet pipe 8. Some of the digester gas stored in gas holder 2 is recovered as energy, and some is supplied again to treatment tank 1 by blower B.

Then, when the suspended organic matter is decomposed and digester gas production by methane fermentation ceases, the methane fermentation process is terminated (S207). The methane fermentation process can be terminated by stopping the steam supply from the heating equipment 3 and closing valve V8 on the digester gas outlet pipe 8 to stop the outflow of digester gas from the treatment tank 1. Digestion gas is supplied to the treatment tank 1 from the gas holder 2 by blower B. Therefore, by opening valves V3 and V2 on the wastewater inlet pipe 4, the blower pressure causes the digester fluid inside the treatment tank 1 to flow out of the system of the wastewater treatment device 10 from the bottom of the treatment tank 1. The outflowing digester fluid can be effectively used as fertilizer, for example, or discharged after further water treatment. The process then terminates.

As described above, by performing filtration, switching from filtration to methane fermentation, and then performing methane fermentation, suspended organic matter accumulated in the filter media 11 during filtration can be efficiently removed by methane fermentation without the need for a separate, complicated cleaning process, thereby reducing the load on the water treatment system in the next step. Furthermore, because suspended organic matter can be converted into digester gas through methane fermentation, energy can be recovered, achieving energy savings.

By sequentially repeating the above filtration process, switching from filtration process to methane fermentation process, and methane fermentation process, filtration process and methane fermentation process can be carried out continuously within the treatment tank 1.

Figure 3 is a schematic diagram of a wastewater treatment unit 30 equipped with multiple wastewater treatment devices as shown in Figure 1.

The wastewater treatment unit 30 in Figure 3 comprises five filtration and methane fermentation treatment tanks 1a-1e (hereinafter referred to as "treatment tanks 1a-1e"), a gas holder 2, a heating system 3, a blower B, and a pump P. Treatment tanks 1a-1e are filled with filter media 11a-11e (separation means), respectively, and have air diffusers 7a-7e (agitation devices). A wastewater storage tank (not shown) stores wastewater after it has been treated in a primary sedimentation tank and screen. Treatment tanks 1a-1e have the same configuration and function as treatment tank 1 described above.

Each of the five treatment tanks 1a-1e is connected to a wastewater inlet pipe 4 and a filtered water outlet pipe 5. The wastewater inlet pipes 4 connected to the treatment tanks 1a-1e are interconnected and include a pump P and valves V1, V2, and V3a-V3e. Wastewater flowing into the treatment tanks 1a-1e from the wastewater storage tank (not shown) is controlled by opening and closing valves V1, V2, and V3a-V3e. The filtered water outlet pipes 5 connected to the treatment tanks 1a-1e are interconnected and include valves V5a-V5e. The filtered water flowing out of the treatment tanks 1a-1e is controlled by opening and closing valves V5a-V5e. The treatment tanks 1a-1e are connected to the gas holder 2 via a digester gas inlet pipe 6 and a digester gas outlet pipe 8. The digester gas inlet pipe 6 includes a blower B and valves V6a-V6e, and the digester gas outlet pipe 8 includes valves V8a-V8e. Treatment tanks 1a-1e are connected to heating equipment 3 via steam inlet pipe 9. Similar to treatment tank 1 described above, treatment tanks 1a-1e each sequentially perform filtration and methane fermentation, and the filtration and decomposition processes performed can be switched by opening and closing the above-mentioned valves V1, V2, V3a-V3e, V4a-V4e, V5a-V5e, and V6a-V6e (switching means).

Table 1 below shows an example of an operating cycle for wastewater treatment using the wastewater treatment unit shown in Figure 3.

In the operating cycle shown in Table 1, the filtration process lasts for two days, and the process switches from filtration to methane fermentation (digestion) once every two days in a merry-go-round fashion, starting with treatment tank 1a and ending with treatment tank 1e, with filtration performed in all treatment tanks over a 10-day period. Furthermore, when filtration is performed in one of treatment tanks 1a-1e, methane fermentation (digestion) is performed in the other treatment tanks.

(Performance of filtration and methane fermentation)
The following describes a method in which the treatment tank 1a performs filtration treatment and the other treatment tanks 1b to 1e perform methane fermentation treatment on the first and second days in Table 1.
When performing the first day of treatment using the wastewater treatment unit 30, it is assumed that filtration has already been performed in the treatment tanks 1b to 1e, since the methane fermentation treatment is a process for decomposing suspended organic matter that has accumulated in the filter media due to the filtration process.

First, in the wastewater treatment unit 30 shown in Figure 3, valve V2 is closed to block the outflow of wastewater to the methane fermentation equipment. Next, valves V1, V3a, and V4a are opened to allow the inflow and outflow of wastewater into treatment tank 1a, and valves V3b-V3e and V4a-V4e are closed to block the inflow and outflow of wastewater into treatment tanks 1b-1e. Steam is supplied to treatment tanks 1b-1e from heating equipment 3 to control the temperature suitable for methane fermentation, and digested sludge is supplied to support the methane bacteria in the digested sludge on filter media 11b-11e. Valves V6a and V8a are then closed to block the circulation of digester gas between treatment tank 1a and gas holder 2, and valves V6b-6e and V8b-8e are opened to circulate digester gas between treatment tanks 1b-1e and gas holder 2. By setting each valve (switching means) as described above, the inflowing wastewater comes into contact with the filter media 11a in treatment tank 1a, causing filtered water to flow out, while in treatment tanks 1b-1e, a methane fermentation process is carried out to decompose the suspended organic matter accumulated in the filter media 11b-11e. Furthermore, even if filtration is carried out in one treatment tank other than treatment tank 1a and methane fermentation is carried out in the other treatment tanks on days 3-10, this can be done by opening and closing each valve as appropriate according to the above valve settings.

(Switching between filtration and methane fermentation)
Next, a method for switching the treatment tank 1a from filtration to methane fermentation treatment and the treatment tank 1b from methane fermentation to filtration and then to decomposition treatment will be described below.
(1) First, the filtration process in the treatment tank 1a is stopped by closing the valves V1 and V5a (completion of the filtration process in the treatment tank 1a).
(2) Next, valve V2 is opened to allow the wastewater to flow into the methane fermentation facility.

(3) Next, valve V6a is opened to transfer the digester gas from the gas holder 2 to the aeration device 7 of the treatment tank 1a, and the digester gas is diffused from the aeration device 7 to agitate the inside of the treatment tank 1a. This causes the filter material 11a to oscillate or move and mix, and the sludge present around the filter material 11a moves downward, so that air pressure based on the digester gas causes wastewater with a high sludge concentration, for example, wastewater with an SS (suspended solids) concentration of approximately 5% by weight, to flow out from the bottom of the treatment tank 1a. The wastewater flowing out from the bottom of the treatment tank 1a is transferred to a methane fermentation facility (not shown) for treating sludge from a primary sedimentation tank, etc. (wastewater outflow due to aeration from the device 1a). If sludge is to remain in the treatment tank 1a, digester gas can be introduced through a digester gas inlet pipe (not shown) installed at the top of the treatment tank 1a rather than through the aeration device 7, making it possible to discharge wastewater with a low sludge concentration, for example, wastewater with a suspended solids (SS) concentration of approximately 1% by weight, without stirring the filter media 11a (wastewater outflow from the treatment tank 1a).

(4) Then, the supply of steam from the heating equipment 3 to the treatment tank 1b is stopped, and valve V8b of the digester gas outlet pipe 8 is closed to stop the outflow of digester gas from the treatment tank 1b, thereby ending the methane fermentation process in the treatment tank 1b (end of methane fermentation process in the treatment tank 1b).

(5) Furthermore, by increasing the amount of digestion gas supplied from the gas holder 2 to the aeration device 7 in the treatment tank 1b and diffused from the aeration device 7, the inside of the treatment tank 1b is agitated more strongly than during methane fermentation treatment, thereby separating the digested sludge adhering to the filter 11b from the filter material (sludge separation by aeration in device 1b). The agitation time using the digestion gas is 10 to 30 minutes. By using a filter material 11b with a specific gravity of 0.95 to 1.05, the filter material 11b is properly shaken or moved and mixed without being unevenly distributed inside the treatment tank 1b, separating the digested sludge from the filter material.

Next, valve V2 is closed and valves V3b and V8a are opened. The air pressure generated by the digester gas diffused from the aeration device 7b causes the exfoliated digested sludge to flow out from the bottom of treatment tank 1b and be transferred to treatment tank 1a as seed sludge for the methane fermentation process. By transferring the digested sludge from treatment tank 1b, for which methane fermentation has been completed, to treatment tank 1a in this way, the methane fermentation process in treatment tank 1a can be rapidly advanced (transfer of digested sludge from treatment tank 1b to treatment tank 1a).

(6) Thereafter, valve V3a is closed, and steam is supplied from heating equipment 3 to treatment tank 1a to control the temperature, while a circulating flow of digester gas is formed between treatment tank 1a and gas holder 2. As a result, on the third and fourth days, treatment tank 1a performs methane fermentation treatment, while treatment tanks 1c to 1e continue methane fermentation treatment. Also, valve V6b of digester gas inlet pipe 6 is closed to block the inflow of digester gas from gas holder 2 to treatment tank 1b, and valves V1 and V5b are opened to allow the inflow and outflow of wastewater to treatment tank 1b, thereby causing treatment tank 1b to perform filtration treatment on the third and fourth days.
The above switching operation can be performed in 15 minutes to 1 hour.

Methanogens are microorganisms that are extremely sensitive to temperature changes and oxygen. However, by performing the above switching operation, the activity of the methanogens in the digested sludge can be maintained while the digested sludge used in the methane fermentation process can be transferred to a treatment tank where filtration has been completed as seed sludge for the next methane fermentation process, thereby shortening the processing time for the methane fermentation process itself.

Fig. 4 is a flowchart showing the procedure for wastewater treatment performed by the wastewater treatment unit of Fig. 3 in the operation cycle of Table 1. In the wastewater treatment of Fig. 4, a CPU (control means) of an information processing device (not shown) alternates between the filtration treatment and the decomposition treatment in each of the treatment tanks 1a to 1e.
The wastewater treatment procedure according to the operation cycle of Table 1 will be explained below with reference to FIGS.

First, on the first and second days, the treatment tank 1a performs a filtration process, and the other treatment tanks 1b to 1e perform a methane fermentation process (S401). Next, the switching means switches the treatment tank 1a from a filtration process to a decomposition process, and the treatment tank 1b from a decomposition process to a filtration process (S402).
Subsequently, on the third and fourth days, the treatment tank 1b performs the filtration process, and the other treatment tanks 1a, 1c to 1e perform the decomposition process (S403). Next, the switching means switches the treatment tank 1b from the filtration process to the decomposition process, and the treatment tank 1c from the decomposition process to the filtration process (S404).
Then, on the fifth and sixth days, the treatment tank 1c performs the filtration process, and the other treatment tanks 1a, 1b, 1d, and 1e perform the decomposition process (S405). Next, the switching means switches the treatment tank 1c from the filtration process to the decomposition process, and the treatment tank 1d from the decomposition process to the filtration process (S404).
Furthermore, on the 7th and 8th days, the treatment tank 1d performs the filtration process, and the other treatment tanks 1a to 1c and 1e perform the decomposition process (S405). Next, the switching means switches the treatment tank 1d from the filtration process to the decomposition process, and the treatment tank 1e from the decomposition process to the filtration process (S404).
Subsequently, on the ninth and tenth days, the treatment tank 1e performs a filtration process, and the other treatment tanks 1a to 1d perform a decomposition process (S405). Through the above operation, filtration processes are performed in all treatment tanks over a period of 10 days (S406). Thereafter, this process ends.

After performing the filtration process in all treatment tanks over a 10-day period using the above operation, treatment tank 1e is switched from filtration to decomposition, and treatment tank 1a is switched from decomposition to filtration. By repeating the above processes and switches, wastewater treatment can be carried out continuously using the wastewater treatment unit 30. This allows the suspended organic matter separated by filtration to be efficiently removed and recovered as digester gas, reducing the load on the water treatment device and enabling energy-saving wastewater treatment.

Figure 5 shows the flow of large-scale sewage treatment using the wastewater treatment unit shown in Figure 3.

In Figure 5, sewage discharged from homes, factories, etc. is transported to equipment 51, which consists of a grit basin and a primary sedimentation basin, or a grit basin and a screening facility, where coarse solids in the sewage are removed. The sediment, screen residue, and primary sludge removed in equipment 51 are disposed of or effectively utilized, or crushed in a crusher and then transported to a conventional methane fermentation facility 52 for methane fermentation treatment. The treated water from equipment 51 is added with a flocculant and then transported to the wastewater treatment unit (filtration and methane fermentation treatment unit) 30 (Figure 3) in this embodiment. Various types of flocculants can be used, but iron-based compounds and organic polymers can be used to reduce digestion inhibition. Adding such flocculants to the treated water from equipment 51 can improve the removal rate of the filtration process in the wastewater treatment unit 30. The wastewater treatment unit 30 is equipped with five treatment tanks 1a-1e (Figures 1 and 3), each of which performs filtration and methane fermentation, with switching between filtration and methane fermentation in a merry-go-round fashion.

Wastewater discharged from the wastewater treatment unit 30 when switching between filtration and methane fermentation is transported to the methane fermentation facility 52 for methane fermentation. The digester gas discharged from the wastewater treatment unit 30 is transported to the energy recovery facility 53 for effective utilization, along with the digester gas discharged from the methane fermentation facility 52. The treated filtered water from the wastewater treatment unit 30 is transported to the water treatment facility 54 along with the digested sludge discharged from the methane fermentation facility 52. In large-scale sewage treatment, the water treatment facility 54 may employ a standard activated sludge process or a membrane separation activated sludge process, and soluble organic matter in the wastewater is oxidized and decomposed by the activated sludge. A portion of the activated sludge used for wastewater treatment in the water treatment facility 54 is subjected to conditioning treatment, and then transported as excess sludge to the dehydration facility 55 for dehydration. The dehydrated filtrate discharged from the dehydration facility 55 is transported to the grit chamber facility 51, and the dehydrated cake is then disposed of or utilized. Furthermore, the treated water from the water treatment facility 54 is either discharged or put to effective use.

As described above, in large-scale sewage treatment, by using the wastewater treatment unit 30 of this embodiment as a pre-processing step for the water treatment facility 54, suspended organic matter and other substances in the wastewater can be efficiently removed without the need for complicated cleaning processes, while the digester gas can be effectively utilized. This significantly reduces the load on the water treatment facility 54 and increases the amount of energy recovered, enabling energy-saving wastewater treatment.

Figure 6 shows the flow of small-scale sewage treatment using the wastewater treatment unit of Figure 3.

In Figure 6, sewage discharged from homes, factories, etc. is transported to equipment 61, which is composed of a grit chamber and a fine mesh screen, where coarse solids are removed. The fine mesh screen equipment has a screen with a mesh size of 0.5 to 10 mm, preferably 1 to 5 mm. For example, a drum-type separator/dehydrator (such as the new Mae Sepa Press manufactured by Maezawa Industries, Inc.) capable of separating and dehydrating impurities or a screen with rotating perforated panels (such as the MMS (Multi-Mesh Screen) manufactured by Maezawa Industries, Inc.) are effective. The treated water from equipment 61 is added with a coagulant similar to that used in the large-scale sewage treatment flow shown in Figure 5, and then transported to the wastewater treatment unit (filtration and methane fermentation treatment unit) 30 of this embodiment. Adding such a coagulant to the treated water from equipment 61 improves the removal rate of the filtration process in the wastewater treatment unit 30.

Since the fine screen equipment can reliably remove relatively large impurities such as hair and scum, installing it as a pre-processing step before the wastewater treatment unit 30 can prevent problems such as the formation of scum and clogging of measuring equipment in the treatment tank of the wastewater treatment unit 30. Furthermore, by reliably removing relatively large impurities using the fine screen equipment, it is possible to select a filter material effective for methane fermentation treatment as the filter material to be filled into the treatment tank of the wastewater treatment unit 30. The sediment, screen residue, and primary sludge removed by equipment 61 can be disposed of or effectively utilized, or crushed in a crusher and then transferred to the wastewater treatment unit (filtration and methane fermentation treatment unit) 30 along with the treated water from equipment 61. The screen residue removed by the fine screen equipment can be dehydrated and disposed of, or it can also be crushed in a crusher and then subjected to methane fermentation treatment.

The wastewater treatment unit 30 is equipped with five treatment tanks 1a-1e (Figures 1 and 3), each of which performs filtration and methane fermentation, with switching between filtration and methane fermentation in a merry-go-round fashion.

The digester gas flowing out of the wastewater treatment unit 30 is transported to an energy recovery facility 53 for effective utilization. Furthermore, filtered water, which is treated water from the wastewater treatment unit 30, is transported to a water treatment facility 54. For small-scale sewage treatment with a maximum wastewater volume of 5,000 ^m3 /day or less, an oxidation ditch (OD) system is used as the water treatment facility 54. In an OD system, an endless channel is used as a ditch (reaction tank) to perform activated sludge treatment of soluble organic matter. A portion of the activated sludge used for wastewater treatment in the water treatment facility 54 is subjected to conditioning treatment and then transported as excess sludge to a dehydration facility 55 for dehydration. The dehydrated filtrate discharged from the dehydration facility 55 is transported to a facility 61 equipped with a fine screen, and the dehydrated cake is then disposed of or effectively utilized as garden soil, cement raw material, etc. to reduce environmental impact. Furthermore, the treated water from the water treatment facility 54 is either discharged or effectively utilized.

As described above, in small-scale sewage treatment, by using the wastewater treatment unit 30 of this embodiment as a pre-processing step for the water treatment facility 54, suspended organic matter and other substances in the wastewater can be efficiently removed without the need for complicated cleaning processes, while the digester gas can be effectively utilized. This significantly reduces the load on the water treatment facility 54 and increases the amount of energy recovered, enabling energy-saving wastewater treatment. As a result, it is possible to provide a wastewater treatment system that can adequately handle the expected increases in food residue in wastewater and increases in the amount of treated water in the future.

In this embodiment, the wastewater treatment unit 30 (Figure 3) has been described as having five treatment tanks 1a to 1e, but the effects of the present invention can also be achieved when using, for example, 2 to 20 treatment tanks, and preferably 3 to 15 treatment tanks.

In this embodiment, if the treatment tanks 1a to 1e have a filtration area of approximately 4 ^m2 , they can be manufactured in a factory and transported in an assembled state. If the filtration rate is set to 200 m/day, a single treatment tank with a filtration area of 4 ^m2 can filter 800 ^m3 /day of wastewater. By configuring one unit with five treatment tanks as shown in FIG. 3 to perform filtration, one unit can treat 800 ^m3 /day, and 6 to 7 units can be used to perform filtration of a treated water volume of 5,000 ^m3 /day. As described above, according to this embodiment, the size of each treatment tank can be reduced and small treatment tanks can be manufactured in-house at a wastewater treatment plant. This allows high-performance treatment tanks to be manufactured at low cost and with a short delivery time and used for wastewater treatment.

The present invention has been described above using the above-mentioned embodiment, but the present invention is not limited to the above-mentioned embodiment.

1 Filtration and methane fermentation treatment tank 2 Gas holder 3 Heating equipment 7 Aeration device 10 Wastewater treatment device 11 Filter material (microbial carrier)
30 Wastewater treatment unit V1, V2, V3, V4, V5, V6 valves

Claims (12)

A wastewater treatment device that performs a filtration process in which wastewater containing suspended organic matter and moisture is filtered to separate the suspended organic matter from the moisture, and a decomposition process in which the suspended organic matter separated by the filtration process is anaerobically decomposed,
The apparatus comprises a filter medium for separating the suspended organic matter from the water, and a decomposition means for anaerobically decomposing the suspended organic matter separated by the filter medium ,
The wastewater treatment device is characterized in that the filter material is a hollow cylindrical porous body having a specific gravity of 0.95 to 1.05, or a nonwoven fabric having a specific gravity of 0.95 to 1.05 . 2. The wastewater treatment device according to claim 1, wherein the decomposition means is a microorganism, and the microorganism is supported on the filter medium . 3. The wastewater treatment device according to claim 1 , further comprising an agitator. 4. The wastewater treatment device according to claim 1 , further comprising a wastewater inlet pipe, a filtered water outlet pipe, a digester gas outlet pipe, and a heating device. A wastewater treatment unit that performs a filtration process of filtering wastewater containing suspended organic matter and water to separate the suspended organic matter from the water, and a decomposition process of anaerobically decomposing the suspended organic matter separated by the filtration process,
a plurality of wastewater treatment devices each having a filter medium for separating the suspended organic matter from water and a decomposition means for anaerobically decomposing the suspended organic matter separated by the filter medium ;
a switching means for switching between the filtration treatment and the decomposition treatment to be performed in the plurality of wastewater treatment devices. The wastewater treatment unit according to claim 5, characterized in that it has a control means for controlling the other wastewater treatment devices to perform decomposition treatment when filtration treatment is performed in one of the plurality of wastewater treatment devices, and the one device performing filtration treatment is sequentially changed by the switching means. 7. The wastewater treatment unit according to claim 5 , wherein the switching means includes means for transferring digested sludge from a wastewater treatment device after completion of decomposition treatment to another wastewater treatment device after completion of filtration treatment. A wastewater treatment method using a wastewater treatment device that performs a filtration process in which wastewater containing suspended organic matter and water is filtered to separate the suspended organic matter from the water, and a decomposition process in which the suspended organic matter separated by the filtration process is anaerobically decomposed, the method comprising: a filter medium that separates the suspended organic matter from the water; and a decomposition means that anaerobically decomposes the suspended organic matter separated by the filter medium ,
a filtration step of filtering the wastewater to separate suspended organic matter and water;
a decomposition step of anaerobic decomposition of the separated suspended organic matter;
and a switching step of switching between the filtration treatment and the decomposition treatment. 9. The wastewater treatment method according to claim 8 , wherein the filtering step, the switching step, and the decomposition step are repeatedly performed in this order. A wastewater treatment method using a wastewater treatment unit that performs a filtration process of filtering wastewater containing suspended organic matter and water to separate the suspended organic matter from the water, and a decomposition process of anaerobically decomposing the suspended organic matter separated by the filtration process, the wastewater treatment unit comprising a plurality of wastewater treatment devices each having a filter medium that separates the suspended organic matter from the water and a decomposition means that anaerobically decomposes the suspended organic matter separated by the filter medium , and a switching means that switches between the filtration process and the decomposition process that are performed in the plurality of wastewater treatment devices,
a filtration and decomposition step of performing a filtration treatment in one of the plurality of wastewater treatment devices and performing a decomposition treatment in another of the plurality of wastewater treatment devices;
a switching step in which the switching means switches one device that has been performing the filtration treatment from filtration treatment to decomposition treatment, and switches another device from decomposition treatment to filtration treatment. The wastewater treatment method according to claim 10 , wherein the filtering and decomposition step and the switching step are repeatedly performed, so that the plurality of wastewater treatment devices sequentially perform the filtering treatment. 12. The wastewater treatment method according to claim 10 , wherein the switching step includes a step of transferring digested sludge from the wastewater treatment device after completion of decomposition treatment to another wastewater treatment device after completion of filtration treatment.