JP7595948B2 - Wastewater Treatment Plant - Google Patents

Description

The present invention relates to a wastewater treatment device that treats wastewater using only anaerobic treatment.

Conventionally, in wastewater treatment equipment, the front stage (upstream side) is generally filled with relatively large filters to carry out anaerobic treatment, while the rear stage (downstream side) is filled with small granular filter filters to carry out aerobic treatment with air supplied from an external fan.

Furthermore, in this type of wastewater treatment system, a backwash device is widely known that performs backflow cleaning (also called backwashing) in the aerobic treatment tank by instantly lowering the water level in the filter tank containing the filter carrier using air supplied from a blower (Patent Documents 1 to 4, etc.).

The backwashing device is equipped with an air supply pipe connected to a blower, an air chamber submerged in the treatment tank to store the air sent from the air supply pipe, and an exhaust pipe inserted into the air chamber to discharge the stored air out of the treatment tank when a predetermined amount of air has been stored in the air chamber. When the stored air in the air chamber is discharged from the exhaust pipe, the water in the treatment tank flows into the air chamber, instantly lowering the water level in the treatment tank and backwashing the filter carrier in the treatment tank.

Japanese Patent Application Publication No. 8-132082 JP 2010-184210 A JP 2010-207662 A JP 2021-10876 A

As of 2019, there are approximately 7.5 million wastewater treatment plants (septic tanks) installed and operational in Japan. Even if we assume that the fans attached to each septic tank operate 24 hours a day with an average power of 50W (0.05kW), this amounts to approximately 400,000kW of electricity, which is roughly the same amount of electricity consumed by one nuclear power plant just by the septic tanks.

Therefore, the main objective of the present invention is to provide a wastewater treatment device that does not require a blower and can perform backwashing without power.

In order to achieve the above object, a wastewater treatment device according to one embodiment of the present invention comprises an upstream anaerobic treatment tank, a downstream anaerobic treatment tank disposed downstream of the upstream anaerobic treatment tank, a gas collection unit disposed at a predetermined depth in the upstream anaerobic treatment tank for collecting organic gases generated in the wastewater by anaerobic microorganisms, and a backwash device for backwashing the anaerobic treatment carrier contained in the downstream anaerobic treatment tank. The backwash device comprises a gas supply pipe connected to the gas collection unit and a gas collection unit disposed at a submerged position in the downstream anaerobic treatment tank. The gas storage chamber is provided with a gas supply pipe that is inserted into the gas storage chamber to store the organic gas sent from the gas supply pipe, and a discharge pipe that is inserted into the gas storage chamber to discharge the stored organic gas to the upstream anaerobic treatment tank when a predetermined amount of organic gas is stored in the gas storage chamber. When the stored gas in the gas storage chamber is discharged from the discharge pipe, water outside the gas storage chamber flows into the gas storage chamber, instantly lowering the water level in the downstream anaerobic treatment tank and backwashing the anaerobic treatment carrier contained in the downstream anaerobic treatment tank.

In one embodiment, the exhaust pipe is substantially U-shaped with an opening in the upper space of the gas reservoir chamber.

The gas collection section has an inverted funnel-shaped section connected to the gas supply pipe, and the lower edge of the inverted funnel-shaped section can be disposed below the water surface and at a height of 50 cm or more above the bottom of the upstream anaerobic treatment tank.

The lower end of the internal flow passage of the exhaust pipe may be located at a water depth shallower than the water depth at the lower end of the gas collection section.

The gas collection section has an inverted funnel section connected to the gas supply pipe, and the upper part of the inverted funnel section can be positioned above the water surface.

According to the present invention, backwashing can be performed without power by operating the backwashing device using organic gases generated in the anaerobic treatment tank.

1 is a cross-sectional view showing a first embodiment of a wastewater treatment device according to the present invention. FIG. 2 is a partially enlarged view of FIG. FIG. 3 is a partial enlarged view showing the operation state of FIG. 2 . FIG. 4 is a partial enlarged view showing an operating state following FIG. 3 . FIG. 5 is a partial enlarged view showing an operating state following FIG. 4 . FIG. 4 is a cross-sectional view showing a second embodiment of a wastewater treatment device according to the present invention.

The following describes an embodiment of a wastewater treatment device according to the present invention with reference to Figures 1 to 6. Note that the same reference numerals are used to denote identical or similar components throughout all figures and all embodiments.

The wastewater treatment device 1 according to the first embodiment of the present invention comprises an upstream anaerobic treatment tank 2, a downstream anaerobic treatment tank 3 disposed downstream of the upstream anaerobic treatment tank 2, a gas collection unit 4 disposed at a predetermined depth in the upstream anaerobic treatment tank 2 for collecting organic gas G generated in the wastewater by anaerobic microorganisms, and a backwash device 5 for backwashing the anaerobic treatment carrier C1 contained in the downstream anaerobic treatment tank 3.

The backwash device 5 is equipped with a gas supply pipe 6 connected to the gas collection section 4, a gas storage chamber 7 disposed in a submerged position in the downstream anaerobic treatment tank 3 to store the organic gas sent from the gas supply pipe 6, and an exhaust pipe 8 inserted into the gas storage chamber 7 to discharge the stored organic gas G to the upstream anaerobic treatment tank 2 side when a predetermined amount of organic gas G is stored in the gas storage chamber 7. When the organic gas G stored in the gas storage chamber 7 is discharged from the exhaust pipe 8, water outside the gas storage chamber 7 flows into the gas storage chamber 7, instantly lowering the water level of the downstream anaerobic treatment tank 3 and backwashing the anaerobic treatment carrier C1 contained in the downstream anaerobic treatment tank 3.

In the illustrated example, the upstream anaerobic treatment tank 2 is divided into two chambers: the first chamber 2a on the upstream side and the second chamber on the downstream side separated by an overflow wall 9. The first chamber 2a is provided with a wastewater inlet 10. In the upstream anaerobic treatment tank 2, the first chamber 2a and the second chamber 2b are filled with anaerobic treatment carriers C2 and C3, respectively. Wastewater W is supplied to the first chamber 2a from the wastewater inlet 10, and the wastewater W supplied to the first chamber 2a passes through the anaerobic treatment carrier C2, then flows from the bottom of the first chamber 2a through the flow path 9b between the overflow wall 9 and the flow path wall 9a, over the overflow wall 9, and into the second chamber 2b. The anaerobic treatment carriers C2 and C3 filled in the first chamber 2a and the second chamber 2b are sandwiched from above and below by a net (not shown) or the like to keep them from falling apart.

Anaerobic treatment carriers C1 to C3 serve to increase and attach anaerobic microorganisms, and may be any conventionally known carrier, such as hollow cylindrical, granular, or small piece shaped carriers made of porous materials such as ceramics, polyethylene, or polyurethane. Anaerobic treatment carriers C2 and C3, located near the wastewater inlet, have a large outer diameter and large internal voids, making them less susceptible to clogging by sludge, whereas carrier C1, located near the outlet, is prone to clogging by sludge due to its large specific surface area and small granular shape, which is necessary to maintain high filtration performance, and requires cleaning by backwashing or other operations.

The downstream anaerobic treatment tank 3 is separated from the upstream anaerobic treatment tank 2 by an overflow wall 11. In the illustrated example, the overflow wall 11 is provided between the second chamber 2b of the upstream anaerobic treatment tank 2 and the downstream anaerobic treatment tank 3. Water that has passed through the anaerobic treatment carrier C3 in the second chamber 2b flows from the bottom of the second chamber 2b through the flow path 11b between the overflow wall 11 and the flow path wall 11a, over the overflow wall 11, and flows into the downstream anaerobic treatment tank 3. The downstream anaerobic treatment tank 3 can be formed with a partition wall 12 having a lower opening 12a, and the anaerobic treatment carrier C1 can be filled downstream of the partition wall 12. The water that has overflowed from the overflow wall 11 flows downward between the overflow wall 11 and the partition wall 12, passes through the lower opening 12a, and passes through the anaerobic treatment carrier C1. The anaerobic treatment carrier C1 packed in the downstream anaerobic treatment tank 3 is made of a finer mesh than the anaerobic treatment carriers C2 and C3 packed in the upstream anaerobic treatment tank 2. Water that has passed through the anaerobic treatment carrier C1 in the downstream anaerobic treatment tank 3 is discharged from the discharge port 13.

The gas collection unit 4 is disposed above the anaerobic treatment carriers C2 and C3 and has an inverted funnel-shaped portion 4a connected to a gas supply pipe 6. Due to the metabolic action of anaerobic microorganisms in the anaerobic treatment carriers C2 and C3, organic matter contained in the wastewater (organic wastewater, waste, etc.) is decomposed into organic gases (methane gas, ammonia gas, hydrogen sulfide, etc.), which are generated in the wastewater W. The organic gas G generated in the wastewater W is collected by the inverted funnel-shaped portion 4a of the gas collection unit 4. The gas collection unit 4 can be preferably disposed so that the lower edge of the inverted funnel-shaped portion 4a is submerged at a height position from a distance of 50 cm or more from the bottom of the upstream anaerobic treatment tank ² to the water surface. For example, the organic gas G collected by the gas collection unit 4 at a water depth of 30 cm is transferred to the gas reservoir chamber 7 through the gas supply pipe 6 while maintaining a maximum gauge pressure of 0.03 kgf/cm2, and is forced into the gas reservoir chamber 7. The gas collection section 4 is preferably positioned so that the upper part of the inverted funnel-shaped section 4a is above the water surface, thereby preventing sludge in the tank from being captured along with the organic gas G captured by the inverted funnel-shaped section 4a, thereby preventing the gas supply pipe 6 from becoming clogged with sludge.

The gas reservoir chamber 7 is formed in a box shape with an open bottom 7a, and the gas supply pipe 6 is connected in communication with its top plate 7b. The gas reservoir chamber 7 can be disposed between the overflow wall 11 and the partition wall 12. One end of the exhaust pipe 8 is roughly U-shaped, and has an opening 8a in the upper space of the gas reservoir chamber 7. The other end 8b of the exhaust pipe 8 is disposed above the upstream anaerobic treatment tank 2, in the illustrated example, above the first chamber 2a. The lower end of the exhaust pipe 8 is disposed at a position higher than the lower end of the gas reservoir chamber 7.

When the organic gas G captured in the gas collection unit 4 is forced into the gas chamber 7 through the gas supply pipe 6, the water level L1 in the gas chamber 7 drops (Figure 3). At this time, the water in the exhaust pipe 8 is also pushed by the organic gas G at the liquid level on the side of the exhaust pipe 8 that contacts the gas chamber 7, and moves inside the exhaust pipe 8, while the liquid level L2 on the side not in contact with the gas chamber 7 rises. The amount of water equivalent to the water pushed out of the gas chamber 7 from inside the gas chamber 7 is discharged from the discharge port 13.

As shown in FIG. 4, the moment the water level L1 in the gas storage chamber 7 drops and reaches the bottom end of the exhaust pipe 8, the organic gas G in the gas storage chamber 7 is able to rise through the water column W2 in the exhaust pipe 8 through the bottom part of the approximately U-shaped part of the exhaust pipe 8, and the organic gas G enters the water column W2 in the exhaust pipe 8 all at once. As a result, the specific gravity of the water column W2 in the exhaust pipe 8 decreases, and the pressurized organic gas G in the gas storage chamber 7 undergoes a so-called breakdown, pushing out the water column W2 in the exhaust pipe 8 all at once and being discharged into the upstream anaerobic treatment tank 2. At the same time, water flows into the gas storage chamber 7 from the open bottom 7a of the gas storage chamber 7, and the water level in the gas storage chamber 7 rises again.

The break point BP at which the discharge pipe 8 causes a breakdown is at a water depth D2 shallower than the water depth D1 at the lower end position 4L of the gas collection section 4, i.e., at a vertically upper position. Therefore, the lower end position of the internal flow path of the discharge pipe 8 (corresponding to BP) is located at a water depth D2 shallower than the water depth D1 at the lower end position 4L of the gas collection section 4. If the lower end position of the internal flow path of the discharge pipe 8 (corresponding to BP) is located at a position deeper than the water depth D1 at the lower end position 4L of the gas collection section 4, the gas pressure of the organic gas G will be lower than the water depth pressure of the water in the gas storage chamber 7 at the break point, and the water level L1 in the gas storage chamber 7 cannot be lowered to the break point, and the organic gas G captured by the gas collection section 4 will overflow and leak out from the lower opening of the inverted funnel-shaped section 4a of the gas collection section 4.

As a result of the breakdown, as shown in FIG. 5, water flows into the gas storage chamber 7 all at once, causing the water level L1 in the gas storage chamber 7 to rise all at once, while the water level L4 in the downstream anaerobic treatment tank 3 drops sharply, causing a downward flow in the anaerobic treatment carrier C1, and backwashing the anaerobic treatment carrier C1. This operation can be estimated to capture approximately 100 liters of organic gas in a septic tank (sewage treatment device) for a typical five-person household, so if the capacity of the gas storage chamber 7 is 50 liters, backwashing can be performed twice a day, making it possible to continuously maintain treatment performance.

As described above, the wastewater treatment device of the present invention uses the organic gas generated by anaerobic treatment as the driving source for the backwash device, so no blower is required and it can operate without power.

Figure 6 shows a wastewater treatment device according to a second embodiment of the present invention. The wastewater treatment device 1 of the second embodiment differs from the first embodiment in that a partition wall 14 having a lower flow passage 14a is formed instead of the overflow wall 11 of the first embodiment, but the other configurations are the same as those of the first embodiment. In the second embodiment, the water level of the second chamber 2b and the water level of the downstream anaerobic treatment tank 3 drop simultaneously during backwashing.

The present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention. For example, in the above first embodiment, the upstream anaerobic treatment tank is divided into a first chamber and a second chamber, but it may be a single chamber or three or more chambers. In addition, the backwash device is not limited to the above embodiment, and may be any backwash device that stores gas in a gas reservoir chamber and replaces the gas in the gas reservoir chamber with surrounding water by breakdown. Backwash devices disclosed in the above prior art documents, backwash devices equipped with a gas-operated volumetric pump, and other known backwash devices may be used.

Reference Signs List 1 Sewage treatment device 2 Upstream anaerobic treatment tank 3 Downstream anaerobic treatment tank 4 Gas collection section 4a Reverse funnel section 5 Backwash device 6 Gas supply pipe 7 Gas storage chamber 8 Discharge pipe

Claims (3)

an upstream anaerobic treatment tank;
a downstream anaerobic treatment tank disposed downstream of the upstream anaerobic treatment tank via an overflow wall ;
a gas collector disposed at a predetermined depth in the upstream anaerobic treatment tank for collecting organic gases generated in the wastewater by anaerobic microorganisms;
a backwash device comprising a gas supply pipe connected to the gas collection unit, a gas storage chamber disposed in a submerged position in the downstream anaerobic treatment tank for storing organic gas sent from the gas supply pipe, and a discharge pipe inserted into the gas storage chamber for discharging the stored organic gas to the upstream anaerobic treatment tank when a predetermined amount of organic gas has been stored in the gas storage chamber, wherein when the organic gas stored in the gas storage chamber is discharged from the discharge pipe, water outside the gas storage chamber flows into the gas storage chamber, instantaneously lowering the water level in the downstream anaerobic treatment tank and backwashing the anaerobic treatment carrier contained in the downstream anaerobic treatment tank;
Equipped with
the exhaust pipe is substantially U-shaped and has an opening in an upper space of the gas reservoir chamber,
The lower end position of the internal flow path of the discharge pipe is disposed at a water depth shallower than the water depth at the lower end position of the gas collection unit.
Sewage treatment plant. The wastewater treatment device according to claim 1, wherein the gas collection section has an inverted funnel-shaped section connected to the gas supply pipe, and the lower edge of the inverted funnel-shaped section is disposed so as to be submerged below the water level and at a height of 50 cm or more above the bottom of the upstream anaerobic treatment tank. The wastewater treatment device according to claim 1, wherein the gas collection section has an inverted funnel-shaped section connected to the gas supply pipe, and the upper part of the inverted funnel-shaped section is positioned above the water surface.

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