JP7488130B2 - Sewage treatment device and sewage treatment method - Google Patents

Description

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

Conventionally, a sewage treatment apparatus is known that includes a reaction tank for biologically treating sewage, a membrane separation device immersed in the reaction tank for removing solids from the biologically treated sewage, and an aeration pipe installed below the membrane separation device for supplying gas such as air to the membrane separation device. The biological treatment of sewage in the reaction tank is carried out based on the activated sludge method in which sewage is treated with organic sludge containing microorganisms, i.e., activated sludge. Specifically, in the activated sludge method, a nitrification reaction is carried out in the presence of oxygen (aerobic state) to convert ammonia to nitrite and nitrate, and a denitrification reaction is carried out in an anoxic state to convert nitrite and nitrate to nitrogen. The denitrification reaction may be carried out in a reaction tank different from the reaction tank in which the nitrification reaction is carried out, but in order to realize space saving in the sewage treatment apparatus, a sewage treatment apparatus in which the nitrification reaction and the denitrification reaction are carried out in a single reaction tank has been proposed (see, for example, Patent Documents 1 and 2).

Figure 3 is a schematic diagram of a conventional wastewater treatment device. The wastewater treatment device in Figure 3 includes a reaction tank 1 in which a nitrification reaction occurs under aerobic conditions and a denitrification reaction occurs under anaerobic conditions, and a raw water supply device 10 for supplying wastewater from a raw water tank 9 to the reaction tank 1. The reaction tank 1 has a partition plate 7 for dividing the reaction tank 1 into a plurality of compartments. Specifically, the reaction tank 1 is divided into a wastewater area A surrounded by the partition plate 7 and a wastewater area B surrounded by the partition plate 7 and the inner wall of the reaction tank 1, and the wastewater area A has a membrane separation device 2 and an aeration pipe 4. The reaction tank 1 has a minimum water level LWL (Low water level) and a maximum water level HWL (High water level), and the upper end of the partition plate 7 is located between the minimum water level LWL and the maximum water level HWL.

The wastewater treatment device in Figure 3 is configured so that the wastewater level in the reaction tank 1 changes by controlling the supply and stop of wastewater to the reaction tank 1. As a result, the wastewater level moves between a position higher than the upper end of the partition plate 7 (hereinafter referred to as the "sewage overflow position") and a position lower than the upper end of the partition plate 7 (hereinafter referred to as the "sewage non-overflow position").

Figure 4 is a schematic diagram showing the flow of wastewater when the water level in the reaction tank 1 in Figure 3 is at the wastewater overflow position.

When the wastewater level is at the wastewater overflow position, the air supplied from the air diffuser 4 to the membrane separation device 2 causes the wastewater to overflow the upper end of the partition plate 7, forming a circulating flow around the partition plate 7. This circulating flow causes nitric acid and other substances in the wastewater area A to move to the wastewater area B, and most of the air in the wastewater area A is released outside the reaction tank 1 without moving to the wastewater area B. In other words, when the circulating flow is formed, a nitrification reaction takes place in the wastewater area A in which ammonia is converted into nitrite and nitrate in the presence of oxygen, and a denitrification reaction takes place in the wastewater area B in which the nitrite and nitrate that have moved from the wastewater area A on the circulating flow are converted into nitrogen in an anoxic state.

On the other hand, when the wastewater level is at the wastewater non-overflow position, the flow of wastewater is interrupted between wastewater area A and wastewater area B, so even if the air diffuser 4 supplies air to the membrane separation device 2, no circulating flow is formed around the partition plate 7. That is, in wastewater area A, a nitrification reaction takes place in which ammonia is converted into nitrite and nitrate in the presence of oxygen, while in wastewater area B, a denitrification reaction takes place in which nitrite and nitrate that moved from wastewater area A before the flow of wastewater was interrupted are converted into nitrogen in anoxic conditions.

In this type of partition-insertion type wastewater treatment device, a method has been proposed for supplementing the electron donor required for the denitrification reaction that proceeds in an anaerobic state, in which when the wastewater level is at the non-overflow position, raw water is supplied to the area outside the partition (anaerobic area) in an amount that does not cause the water level in the reaction tank to exceed the upper end of the partition (see Patent Document 2).

JP 2004-261711 A JP 2018-103129 A

However, the amount of organic matter in the raw water supplied to the reaction tank of the sewage treatment device varies depending on the type of raw water. In addition, when sewage treatment is performed by combining the activated sludge process and membrane separation, as in the case of a partition-insertion type sewage treatment device, raw water in which the organic matter has been reduced in advance is often supplied to the reaction tank in order to reduce the load on the membrane separation. Therefore, even when raw water is supplied to an area where an anoxic state is maintained, it is not possible to supply a sufficient amount of electron donor required for the denitrification reaction, and there is a problem that sewage treatment with high nitrogen removal efficiency cannot be performed stably.

The present invention aims to provide a wastewater treatment device and a wastewater treatment method that can provide a sufficient supply of electron donors required for the denitrification reaction and can stably perform wastewater treatment with high nitrogen removal efficiency.

In order to achieve the above object, the sewage treatment device of the present invention is provided with a membrane separation device, an aeration pipe, and a partition plate that divides the inside of the reaction tank into a plurality of compartments inside the reaction tank for aerobic and anaerobic treatment of sewage, a means for supplying the sewage to be treated to the reaction tank, and a water level control means for switching the water level in the reaction tank between a state higher than the upper end of the partition plate and a state lower than the upper end of the partition plate, wherein at least one of the plurality of compartments is an aerobic compartment in which a membrane separation device and an aeration pipe are arranged, and anaerobic treatment is performed in the other compartments, and the sewage treatment device is characterized in that when the water level in the reaction tank is lower than the upper end of the partition plate, a means is provided for supplying an electron donor-containing liquid different from the sewage to be treated to the other compartments in the reaction tank , and the sewage to be treated is sewage that has been subjected to anaerobic treatment, and the electron donor-containing liquid is sewage that has not been subjected to anaerobic treatment .
In order to achieve the above-mentioned object, the sewage treatment device of the present invention is provided with a membrane separation device, an aeration pipe, and a partition plate that divides the inside of the reaction tank into a plurality of compartments inside the reaction tank for performing aerobic and anaerobic treatment of sewage, a means for supplying the sewage to be treated to the reaction tank, and a water level control means for switching the water level in the reaction tank between a state higher than the upper end of the partition plate and a state lower than the upper end of the partition plate, and is characterized in that at least one of the plurality of compartments is an aerobic compartment in which a membrane separation device and an aeration pipe are arranged, and anaerobic treatment is performed in the other compartments, and the sewage treatment device is provided with a means for supplying an electron donor-containing liquid different from the sewage to be treated to the other compartments in the reaction tank when the water level in the reaction tank is lower than the upper end of the partition plate, and the amount of the electron donor-containing liquid supplied is an amount that does not cause the water level in the reaction tank to exceed the upper end of the partition plate.

In order to achieve the above-mentioned object, the wastewater treatment method of the present invention is a method for performing aerobic and anaerobic treatment of wastewater in a reaction tank in which a membrane separation device and an aeration pipe are arranged, the periphery of the membrane separation device is partitioned with a partition plate, and aeration is performed with an aeration pipe from below the membrane separation device, while the water level in the reaction tank is adjusted to maintain an aerobic state in the compartment in which the membrane separation device and the aeration pipe are arranged while performing anaerobic treatment in the other compartments, characterized in that when the water level in the reaction tank is lower than the upper end of the partition plate, an electron donor-containing liquid different from the wastewater to be treated is supplied to the other compartments in the reaction tank , and the wastewater to be treated is wastewater that has been subjected to anaerobically treated wastewater, and the electron donor-containing liquid is wastewater that has not been subjected to anaerobically treated wastewater .
In addition, in order to achieve the above-mentioned object, the sewage treatment method of the present invention is a sewage treatment method for performing aerobic treatment and anaerobic treatment of sewage in a reaction tank in which a membrane separation device and an aeration pipe are arranged, the periphery of the membrane separation device is partitioned with a partition plate, aeration is performed with an aeration pipe from below the membrane separation device, and the water level in the reaction tank is adjusted to maintain an aerobic state in the compartment in which the membrane separation device and the aeration pipe are arranged while performing anaerobic treatment in the other compartments, characterized in that when the water level in the reaction tank is lower than the upper end of the partition plate, an electron donor-containing liquid different from the sewage to be treated is supplied to the other compartments in the reaction tank, and the amount of the electron donor-containing liquid supplied is an amount that does not cause the water level in the reaction tank to exceed the upper end of the partition plate .

According to the present invention, it is possible to supply a sufficient amount of electron donor required for the denitrification reaction, and it is possible to stably carry out wastewater treatment with high nitrogen removal efficiency.

1 is a diagram illustrating a schematic diagram of a wastewater treatment device according to a first embodiment of the present invention. FIG. 13 is a schematic diagram showing a wastewater treatment device according to a second embodiment of the present invention. FIG. 1 is a schematic diagram of a conventional wastewater treatment device. FIG. 4 is a side view showing a schematic diagram of the flow of wastewater in the reaction tank in FIG. 3 .

The following describes in detail the embodiments of the present invention with reference to the drawings.

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

The sewage treatment system in FIG. 1 comprises a raw water tank 9 for storing sewage, a single-tank reaction tank 1 for treating the sewage, an anaerobic treatment device 20 for anaerobically treating the sewage to be supplied to the reaction tank 1 in advance, and a bypass pipe 21 for supplying sewage that has not been anaerobically treated to the reaction tank 1.
In the present invention, the term "raw water" refers to water prior to wastewater treatment, including anaerobic treatment, and is typically wastewater such as sewage or human waste.

The reaction tank 1 has a membrane separation device 2 that separates pollutants contained in the wastewater, an aeration pipe 4 that supplies air bubbles to the membrane separation device 2, and a partition plate 7 that divides the inside of the reaction tank 1 into multiple areas. The bottom of the partition plate 7 is provided away from the bottom surface of the reaction tank 1. The partition plate 7 surrounds the entire lateral periphery of the membrane separation device 2 and divides the inside of the reaction tank 1 into an inner area 11 (aerobic section) where the membrane separation device 2 and the aeration pipe 4 are arranged, and an outer area 12 other than the inner area 11. The membrane separation device 2 is connected to a suction pump 3 outside the reaction tank 1. When the suction pump 3 is driven, the biologically treated wastewater is filtered by the membrane separation device 2, and the filtered water is taken out of the reaction tank 1.

The aeration pipe 4 is installed at the bottom of the membrane separation device 2 and is connected to a blower 5 outside the reaction tank 1, and the blower 5 supplies air to the aeration pipe 4. Since the membrane separation device 2 filters wastewater, sludge substances in the wastewater adhere to the membrane surface of the membrane separation device 2. If the sludge substances in the wastewater adhering to the membrane surface of the membrane separation device 2 are left as they are, the membrane separation device 2 will become clogged and will no longer be able to properly filter the wastewater. Therefore, the aeration pipe 4 supplies air to the membrane surface of the membrane separation device 2, preventing sludge substances from adhering to the membrane surface of the membrane separation device 2.

The reaction tank 1 contains organic sludge containing microorganisms, i.e., activated sludge, which decomposes organic matter and performs biological treatment. The microorganisms include nitrifying bacteria for carrying out a nitrification reaction in the inner region 11 and denitrifying bacteria for carrying out a denitrification reaction in the outer region 12 in order to treat the wastewater. The sludge itself containing these microorganisms is well known in this field.

For the membrane separation device 2, a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, etc. can be used, and the shape of the membrane can be a flat membrane, a hollow fiber membrane, etc. The membrane separation device used in the present invention is itself well known in this field.

The anaerobic treatment device 20 performs anaerobic treatment of wastewater supplied from the raw water tank 9 in order to reduce the load on the membrane separation device 2 in the reaction tank 1. Anaerobic treatment is a process in which polymeric organic matter in wastewater is converted into ammonia, methane gas, carbon dioxide, etc. by anaerobic microorganisms under anoxic conditions. Specifically, polymeric organic matter in wastewater is hydrolyzed by anaerobic microorganisms to become soluble amino acids, sugars, and higher fatty acids. Next, the amino acids, sugars, and higher fatty acids taken into the cells of the microorganisms are metabolically decomposed and converted into acetic acid, hydrogen, carbon dioxide, ammonia, and hydrogen sulfide. The acetic acid, hydrogen, and carbon dioxide are finally converted into methane gas that can be used as bioenergy. The wastewater containing ammonia produced in this anaerobic treatment is supplied to the reaction tank 1 and subjected to aerobic treatment (nitrification reaction) and anaerobic treatment (denitrification reaction).

In this embodiment, various treatment methods can be applied to the anaerobic treatment depending on the properties of the wastewater. For high-concentration wastewater containing a large amount of solids, a complete mixing type methane fermentation tank equipped with a mechanical stirring device or a gas stirring device is generally applied. For relatively low-concentration wastewater containing few solids, an anaerobic filter bed method filled with filter media, an anaerobic fluidized bed method filled with carriers, an upflow anaerobic sludge blanket method (hereinafter referred to as the UASB method), an anaerobic membrane bioreactor method (hereinafter referred to as the AnMBR method), etc. can be used. The UASB method is an anaerobic treatment method that retains a high concentration of microorganisms in a reaction tank and enables high-speed treatment by forming granular sludge with excellent settling properties by utilizing the coagulation and agglomeration functions of anaerobic microbial groups. The reactor of the UASB system is composed of a raw water inlet at the bottom, a reaction section (sludge bed and sludge blanket section), and a gas-liquid-solid separation section at the top. Specifically, wastewater flows in uniformly from the raw water inlet at the bottom of the reactor, passes through the reaction section as an upward flow, and is anaerobically treated in contact with granular sludge, and the three phases of gas, sludge, and liquid are separated in the gas-liquid-solid separation section at the top of the reactor. The UASB method has the advantage of being more economical than other anaerobic treatment technologies, as construction and maintenance costs are low due to its simple configuration, and high-speed treatment allows the fermentation tank to be made compact.

The AnMBR method combines anaerobic treatment with membrane separation technology (hereinafter referred to as MBR technology). MBR technology uses a separation membrane such as a microfiltration membrane with pores smaller than the microorganisms, which can prevent the outflow of microorganisms outside the reaction tank. In other words, the AnMBR method installs a membrane separation device in the reaction tank where anaerobic treatment is performed, and can separate pollutants in the wastewater using the filtration membrane and decompose organic matter using anaerobic microorganisms held in the reaction tank. With this configuration, the AnMBR method has the advantage of being able to hold a high concentration of anaerobic microorganisms in the reaction tank and obtain purified treated water through membrane separation.

The wastewater anaerobically treated in the anaerobic treatment device 20 has, for example, a BOD (biochemical oxygen demand) of 200 to 3000 mg/L, preferably 100 to 1000 mg/L, and a T-N (total nitrogen concentration) of 100 to 2000 mg/L. Therefore, the BOD/T-N ratio is often 1 or less. For this reason, when only anaerobically treated wastewater is supplied to the reaction tank 1, there is often a shortage of electron donors required for denitrification in the reaction tank 1. The BOD is measured in accordance with the method described in the Sewerage Testing Method.

The wastewater anaerobically treated in the anaerobic treatment device 20 is supplied to the reaction tank 1 via the pump 15. In FIG. 1, the anaerobically treated wastewater is supplied to the outer region 12 of the partition plate 7, but it may also be supplied to the inner region 11.

In this embodiment, a water level control means (not shown) is provided for adjusting the water level in the reaction tank 1 and switching the water level in the reaction tank between a state higher than the upper end of the partition plate and a state lower than the upper end of the partition plate. An example of the water level control means is a liquid level sensor that detects the water level in the reaction tank 1, i.e., the position of the liquid surface. The liquid level sensor detects the wastewater level, and the pump 15 controls the supply and stop of the wastewater to the reaction tank 1 based on the detected water level, so that the wastewater level can be switched between a wastewater overflow position and a wastewater non-overflow position.

When the wastewater level is at the wastewater overflow position, the air supplied from the air diffuser 4 to the membrane separation device 2 causes the wastewater to overflow the upper end of the partition plate 7, forming a circulation flow that circulates around the partition plate 7. This circulation flow causes nitric acid and the like in the internal region 11 to migrate to the external region 12, and most of the air in the internal region 11 is released to the outside of the reaction tank 1 without migrating to the external region 12. In other words, when the circulation flow is formed, a nitrification reaction proceeds in the internal region 11, in which nitrifying bacteria convert ammonia to nitrite and nitrate in the presence of oxygen, and a denitrification reaction proceeds in the external region 12, in which denitrifying bacteria convert the nitrite and nitrate that have migrated from the wastewater region on the circulation flow into nitrogen in anoxic conditions.

On the other hand, when the wastewater level is at the wastewater non-overflow position, the flow of wastewater is interrupted between the inner region 11 and the outer region 12, so even if the air diffuser 4 supplies air to the membrane separation device 2, no circulation flow is formed around the partition plate 7. That is, in the inner region 11, a nitrification reaction takes place in which ammonia is converted into nitrite and nitrate in the presence of oxygen, while in the outer region 12, a denitrification reaction takes place in which nitrite and nitrate that moved from the inner region 11 before the flow of wastewater was interrupted are converted into nitrogen in anoxic conditions.

The denitrification reaction that takes place in the external region 12 is a reaction in which nitrite and nitrate are reduced to nitrogen under anoxic conditions, and requires a sufficient amount of electron donor to reduce the electron acceptors, nitrite and nitrate. However, as described above, the concentration of electron donors in wastewater that has been anaerobically treated is low, and there are cases in which the electron donors required for the denitrification reaction are insufficient.

In this embodiment, to compensate for this lack of electron donors, a portion of the wastewater supplied from the raw water tank 9 is supplied to the external region 12 of the reaction tank 1 via a bypass pipe 21 that bypasses the anaerobic treatment device 20. The wastewater supplied to the reaction tank 1 via the bypass pipe 21 has not been subjected to anaerobic treatment, and is therefore the same wastewater that was contained in the raw water tank 9, and contains a higher concentration of electron donors than the wastewater supplied via the anaerobic treatment device 20. In other words, by supplying the wastewater from the raw water tank 9 to the reaction tank 1 via the bypass pipe 21, wastewater containing a higher concentration of electron donors can be supplied to the external region 12 where the denitrification reaction proceeds.

When wastewater is supplied to the external area 12 through the bypass pipe 21 while the wastewater level is at the wastewater overflow position, the electron donors contained in the wastewater migrate through the lower part of the partition plate 7 to the wastewater area 11, which is an aerobic compartment, due to the circulation flow circulating around the partition plate 7. As a result, the electron donors cannot be efficiently used for the denitrification reaction in the external area 12. In addition, in the internal area 11, the electron donors migrated from the external area 12 consume oxygen, so the amount of aeration from the air diffuser 4 increases to compensate for the oxygen supply, and as a result, the amount of power consumed for aeration increases.

Therefore, the supply of wastewater through the bypass pipe 21 must be performed when the wastewater level is in the wastewater non-overflow position, i.e., when the water level in the reaction tank 1 is lower than the upper end of the partition plate 7. When the wastewater level is in the wastewater non-overflow position, no circulating flow is formed around the partition plate 7. Therefore, the electron donor contained in the wastewater supplied to the outer region 12 is used for the denitrification reaction without almost migrating to the inner region 11. In addition, the increase in the aeration amount in the inner region 11 can be suppressed, and the increase in the power consumption required for aeration can be suppressed. Therefore, the amount of wastewater supplied through the bypass pipe 21 is preferably an amount that allows the water level in the reaction tank 1 to maintain a divided state without exceeding the upper end of the partition plate.

The wastewater supplied to the reaction tank 1 through the bypass pipe 21 is the same wastewater contained in the raw water tank 9 as it has not been subjected to anaerobic treatment, and has, for example, a BOD of 500 to 15,000 mg/L, preferably 500 to 5,000 mg/L, a T-N (total nitrogen concentration) of 100 to 2,000, preferably 100 to 500, and a BOD/T-N of 1 to 50, preferably 5 to 50.

The anaerobically treated wastewater is supplied to the reaction tank 1 for the purpose of aerobically and anaerobicly treating the wastewater and for the purpose of controlling the water level in the reaction tank 1 to switch between a state higher than the upper end of the partition plate and a state lower than the upper end of the partition plate. The wastewater that passes through the bypass pipe 21 is supplied to the reaction tank 1 for the purpose of supplying sufficient electron donors required for the denitrification reaction to the wastewater area 12.

In this embodiment, the flow rate of wastewater (anaerobically treated wastewater) passing through the anaerobic treatment device 20 and the flow rate of wastewater (not anaerobically treated wastewater) passing through the bypass pipe 21 can be controlled by adjusting the flow rate of the bypass pump and the opening of the valve installed in the bypass line. In addition, the flow rate of wastewater that is anaerobically treated and supplied to the reaction tank 1 and the flow rate of wastewater that is not anaerobically treated and supplied to the reaction tank 1 through the bypass pipe 21 can be supplied by setting the bypass flow rate so that the BOD/T-N of the mixed liquid supplied to the reaction tank 1 is 2 to 5, preferably 3.

The apparatus in FIG. 1 further includes a nitrate nitrogen concentration meter 17 that measures the nitrate nitrogen concentration in the filtered water obtained after membrane separation by the membrane separation device 2. A target value for the nitrate nitrogen concentration in the filtered water is set in advance to optimize the nitrogen removal efficiency and energy efficiency. The amount of wastewater supplied from the bypass pipe 21 to the reaction tank 1 is controlled so that the nitrate nitrogen concentration measured by the nitrate nitrogen concentration meter 17 reaches the preset target value.

Specifically, when the nitrate nitrogen concentration in the filtered water after membrane separation is higher than a preset target value, the denitrification reaction proceeding in the outer region 12 is insufficient, so the amount of wastewater supplied through the bypass pipe 21 can be increased to increase the amount of electron donor required for the denitrification reaction. Also, when the nitrate nitrogen concentration in the filtered water is lower than a preset target value, the denitrification reaction proceeds sufficiently, but an excessive amount of electron donor is supplied. When an excessive amount of electron donor is supplied, the electron donor migrates from the outer region 12 to the inner region 11 even when the wastewater level is at the non-overflow position. The electron donor that migrates to the inner region 11 consumes oxygen, so the amount of aeration from the aeration pipe 4 is increased to compensate for the oxygen supply, and as a result, the amount of power consumed for aeration increases. Therefore, when the nitrate nitrogen concentration in the filtered water is lower than a preset target value, the amount of wastewater supplied through the bypass pipe 21 can be controlled to be reduced.

In addition, instead of the nitrate nitrogen concentration meter 17 that measures the nitrate nitrogen concentration in the filtered water after membrane separation, a pH sensor that can evaluate the amount of nitrate nitrogen remaining in the filtered water may be used. In this case, the amount of wastewater supplied from the bypass pipe 21 to the wastewater area 12 is controlled so that the target value of the pH of the filtered water measured by the pH sensor is in the optimal range.

Specifically, when the pH of the filtered water is lower than a preset target value, the denitrification reaction proceeding in the external region 12 is insufficient, so the amount of wastewater supplied through the bypass pipe 21 can be increased to increase the amount of electron donor required for the denitrification reaction. Also, when the pH of the filtered water is higher than a preset target value, the amount of wastewater supplied through the bypass pipe 21 can be reduced to prevent an excessive amount of electron donor from being supplied in order to suppress an increase in the amount of aeration from the aeration pipe 4.

As described above, the wastewater treatment device according to the first embodiment of the present invention (FIG. 1) includes both a means for supplying wastewater to be treated aerobically and anaerobically from the anaerobic treatment device 20 to the reaction tank 1, and a means for supplying wastewater containing a higher concentration of electron donor and different from the wastewater to be treated aerobically and anaerobically via the bypass pipe 21. With this configuration, even if the amount of organic matter varies depending on the type of wastewater, the optimal amount of electron donor-containing liquid required for the denitrification reaction can be supplied to the external region 12.

In addition, in this embodiment, the partition plate 7 surrounds the entire periphery of the membrane separation device 2, but it is sufficient that it substantially surrounds the periphery of the membrane separation device 2, and the membrane separation device 2 may be surrounded by the partition plate 7 and the tank wall of the reaction tank 1. Specifically, the membrane separation device 2 may be surrounded by two opposing tank walls of the reaction tank 1 and two rectangular partition plates 7, or the membrane separation device 2 may be surrounded by three tank walls of the reaction tank 1 and one rectangular partition plate 7. In addition, when the reaction tank 1 is large, multiple internal areas 11 in which the aeration pipes 4 are arranged may be provided in order to increase the processing volume per unit time.

Next, we will explain the wastewater treatment method performed by the wastewater treatment device (Figure 1) according to the first embodiment.

As described above, the wastewater treatment device of this embodiment (FIG. 1) includes a raw water tank 9, a reaction tank 1, an anaerobic treatment device 20, and a bypass pipe 21. The reaction tank 1 also includes a membrane separation device 2, an aeration pipe 4, and a partition plate 7, and contains wastewater to be aerobically and anaerobicly treated, and organic sludge containing microorganisms. The interior of the reaction tank 1 is divided into multiple compartments by the partition plate 7. The aeration pipe 4 aerates from below the membrane separation device 2, and the compartment in which the membrane separation device 2 and the aeration pipe 4 are located is maintained in an aerobic state.

The wastewater contained in the raw water tank 9 is supplied to the anaerobic treatment device 20 and subjected to anaerobic treatment to reduce the load on the membrane separation device 2 in the reaction tank 1. This anaerobic treatment converts some of the polymeric organic matter in the wastewater into ammonia, methane gas, carbon dioxide, etc. The anaerobically treated wastewater with a reduced organic matter content is supplied to the reaction tank 1 via the pump 15, where it is subjected to aerobic treatment and anaerobic treatment. In addition, the water level in the reaction tank can be adjusted by controlling the supply and stop of the anaerobically treated wastewater to the reaction tank 1 using a water level control means (not shown) and the pump 15, and the water level in the reaction tank 1 can be switched between a wastewater overflow position and a wastewater non-overflow position.

When the wastewater level is in the wastewater overflow position or in the wastewater non-overflow position, the nitrification reaction (aerobic treatment) that converts ammonia to nitrite and nitrate in the presence of oxygen proceeds in the inner area 11, while the denitrification reaction (anaerobic treatment) that converts nitrite and nitrate to nitrogen in the absence of oxygen proceeds in the outer area 12.

The denitrification reaction that takes place in the wastewater area 12 requires sufficient electron donors to reduce nitrite and nitrate. However, as described above, wastewater that has been anaerobically treated has a low concentration of electron donors, and so there may be a shortage of electron donors required for the denitrification reaction.

To make up for this shortage of electron donors, a portion of the wastewater contained in the raw water tank 9 is supplied to the external region 12 of the reaction tank 1 via the bypass pipe 21. The wastewater supplied via the bypass pipe 21 has not been anaerobically treated and contains a higher concentration of electron donors. Therefore, by supplying wastewater via the bypass pipe 21, the amount of electron donor required for the denitrification reaction can be supplied to the external region 12 of the reaction tank 1. This allows for stable wastewater treatment with high nitrogen removal efficiency.

When the suction pump 3 is driven, the biologically treated wastewater is filtered by the membrane separation device 2, and the filtered water is sucked up by the suction pump 3 and removed from the reaction tank 1.

The nitrate nitrogen concentration of the filtered water obtained after membrane separation by the membrane separation device 2 is measured by the nitrate nitrogen concentration meter 17. A target value for the nitrate nitrogen concentration in the filtered water is set in advance.
When the nitrate nitrogen concentration in the filtrate after membrane separation is higher than a preset target value, the denitrification reaction proceeding in the external region 12 is insufficient, so that the supply amount of wastewater supplied through the bypass pipe 21 can be increased to increase the supply amount of the electron donor required for the denitrification reaction. When the nitrate nitrogen concentration in the filtrate is lower than a preset target value, the supply amount of wastewater supplied through the bypass pipe 21 can be controlled to be reduced in order to suppress an increase in the aeration amount from the aeration pipe 4.

In this way, by controlling the amount of wastewater supplied to the external area 12 via the bypass pipe 21 so that the nitrate nitrogen concentration in the filtered water after membrane separation is in the optimal range, it is possible to supply the electron donor necessary for the denitrification reaction to improve the nitrogen removal efficiency, while suppressing an increase in the amount of aeration from the aeration pipe 4 and preventing an increase in the amount of power consumed for aeration.

Figure 2 is a schematic diagram of a wastewater treatment device according to a second embodiment of the present invention.

The reaction tank 1, membrane separation device 2, aeration pipe 4, and raw water tank 9 in FIG. 2 are basically the same in configuration and function as the reaction tank 1, membrane separation device 2, aeration pipe 4, and raw water tank 9 in FIG. 1. The wastewater treatment device in FIG. 2 differs from the wastewater treatment device in FIG. 1 in that wastewater contained in the raw water tank 9 is directly supplied to the reaction tank 1, and electron donor-containing liquid is supplied from the electron donor-containing liquid tank 22 to the wastewater area 12 of the reaction tank 1 without using the anaerobic treatment device 20 and bypass pipe 21. Below, explanations of the overlapping configurations and functions will be omitted, and different configurations and functions will be explained.

The reaction tank 1 is connected to the raw water tank 9 via the raw water pump 8, and when the raw water pump 8 is driven, wastewater is supplied from the raw water tank 9 to the reaction tank 1. In the reaction tank 1, the wastewater is treated aerobicly and anoxically. The reaction tank 1 is also connected to the electron donor-containing liquid tank 22, which contains the electron donor-containing liquid, via the pump 16, and when the pump 16 is driven, the electron donor-containing liquid is supplied from the electron donor-containing liquid tank 22 to the external region 12 of the reaction tank 1.

In FIG. 2, the wastewater contained in the raw water tank 9 is supplied directly to the reaction tank 1, but the amount of organic matter contained varies depending on the type of wastewater. As a result, there may be a shortage of electron donors required for the denitrification reaction in the external region 12, making it impossible to carry out a stable denitrification reaction. To compensate for this shortage of electron donors, an electron donor-containing liquid is supplied from the electron donor-containing liquid tank 22 to the external region 12 of the reaction tank 1.

The electron donor contained in the electron donor-containing liquid is not particularly limited as long as it is an organic or inorganic substance that can be used as an electron donor. Specific examples of electron donors include at least one selected from the group consisting of alcohols such as methanol and ethanol, organic acids such as acetic acid, sulfur, and hydrogen. The electron donor-containing liquid is prepared by dissolving the electron donor in a solvent such as water, or by adding a solid in the form of a powder slurry, or by sparging with a gas. Since the electron donor is contained in the electron donor-containing liquid at a high concentration, the electron donor can be efficiently replenished by supplying the electron donor-containing liquid. The concentration of the electron donor in the electron donor-containing liquid can be determined taking safety and economical efficiency into consideration. Usually, a concentration as high as possible is advantageous, and it is preferable to use the original liquid as it is.

When treating wastewater from food factories and the like that contains sewage or organic solids, the wastewater introduced into the raw water tank 9 can be pretreated in advance using a screen or a sedimentation tank. Solid organic matter such as screen residue and sedimented sludge removed from the wastewater by such pretreatment contains a high concentration of organic matter, so energy can be recovered by performing anaerobic treatment (methane fermentation). At this time, excess sludge (activated sludge that has grown in the reaction tank 1 and become excess) can also be subjected to anaerobic treatment. In such anaerobic treatment of solid organic matter, the solid organic matter is finally converted into methane gas through the hydrolysis process (solubilization process), acid fermentation process, and methane fermentation process in sequence. Since the effluent obtained from the hydrolysis process and acid fermentation process contains a large amount of electron donors that are useful for denitrification, this effluent can be introduced into the electron donor-containing liquid tank 22 for use.

In other words, in the apparatus of FIG. 2, an electron donor-containing liquid different from the wastewater to be aerobically and anaerobicly treated is supplied from the electron donor-containing liquid tank 22 to the wastewater region 12 of the reaction tank 1. Therefore, even if the electron donor required for the denitrification reaction is insufficient due to the type of wastewater, the missing electron donor can be efficiently supplied to the external region 12. Therefore, a stable denitrification reaction can be carried out in the external region 12 of the reaction tank 1.

The apparatus in FIG. 2 also includes a nitrate nitrogen concentration meter 17 that measures the nitrate nitrogen concentration in the filtered water obtained after membrane separation by the membrane separation device 2. A target value for the nitrate nitrogen concentration in the filtered water is set in advance to optimize the nitrogen removal efficiency and energy efficiency. The amount of electron donor-containing liquid supplied from the electron donor-containing liquid tank 22 to the reaction tank 1 is controlled so that the nitrate nitrogen concentration measured by the nitrate nitrogen concentration meter 17 becomes the preset target value.

Specifically, when the nitrate nitrogen concentration in the filtered water after membrane separation is higher than a preset target value, the denitrification reaction proceeding in the external region 12 is insufficient, so the supply amount of electron donor-containing liquid supplied from the electron donor-containing liquid tank 22 to the reaction tank 1 can be increased to increase the supply amount of electron donor required for the denitrification reaction. Also, when the nitrate nitrogen concentration in the filtered water is lower than a preset target value, the supply amount of electron donor-containing liquid supplied from the electron donor-containing liquid tank 22 to the reaction tank 1 can be controlled to be reduced in order to suppress an increase in the aeration amount from the aeration tube 4.

As in the first embodiment, instead of the nitrate nitrogen concentration meter 17 that measures the nitrate nitrogen concentration in the filtered water after membrane separation, a pH sensor that can evaluate the amount of nitrate nitrogen remaining in the filtered water may be used.

As described above, the wastewater treatment device according to the second embodiment of the present invention (Figure 2) includes both a means for supplying wastewater to be aerobically and anaerobically treated from the raw water tank 9 to the reaction tank 1, and a means for supplying an electron donor-containing liquid that contains a higher concentration of electron donor and is different from the wastewater to be aerobically and anaerobically treated. With this configuration, even if the amount of organic matter varies depending on the type of wastewater, the optimal amount of electron donor-containing liquid required for the denitrification reaction can be supplied to the external region 12.

Next, we will explain the wastewater treatment method performed by the wastewater treatment device (Figure 2) according to the second embodiment.

The wastewater contained in the raw water tank 9 is supplied to the reaction tank 1 via the raw water pump 8, where it is subjected to aerobic and anaerobic treatment. In addition, by controlling the supply and stop of wastewater to the reaction tank 1 using the raw water pump 8, the water level in the reaction tank can be adjusted, and the water level in the reaction tank 1 can be switched between a wastewater overflow position and a wastewater non-overflow position.

When the wastewater level is in the wastewater overflow position or in the wastewater non-overflow position, the nitrification reaction (aerobic treatment) that converts ammonia to nitrite and nitrate in the presence of oxygen proceeds in the wastewater area 11, while the denitrification reaction (anaerobic treatment) that converts nitrite and nitrate to nitrogen in the absence of oxygen proceeds in the wastewater area 12.

The denitrification reaction that takes place in the wastewater area 12 requires sufficient electron donors to reduce nitrite and nitrate. However, the amount of organic matter contained in the wastewater supplied from the raw water tank 9 via the raw water pump 8 varies depending on the type of wastewater, and there may be a shortage of electron donors required for the denitrification reaction.

In this embodiment, the electron donor-containing liquid is supplied from the electron donor-containing liquid tank 22 to the outer region 12 of the reaction tank 1. The electron donor-containing liquid supplied from the electron donor-containing liquid tank 22 contains a high concentration of electron donor. Therefore, by supplying the electron donor-containing liquid to the reaction tank 1, the amount of electron donor required for the denitrification reaction can be efficiently supplied to the outer region 12 of the reaction tank 1. This allows for stable wastewater treatment with high nitrogen removal efficiency.

When the suction pump 3 is driven, the biologically treated wastewater is filtered by the membrane separation device 2, and the filtered water is sucked up by the suction pump 3 and removed from the reaction tank 1.

The nitrate nitrogen concentration of the filtered water obtained after membrane separation by the membrane separation device 2 is measured by the nitrate nitrogen concentration meter 17. If the nitrate nitrogen concentration in the filtered water after membrane separation is higher than a preset target value, the denitrification reaction proceeding in the external region 12 is insufficient, so the supply amount of the electron donor-containing liquid can be controlled to be increased. Also, if the nitrate nitrogen concentration in the filtered water is lower than a preset target value, the supply amount of the electron donor-containing liquid can be controlled to be reduced in order to suppress an increase in the aeration amount from the aeration tube 4.

In this way, by controlling the supply amount of the electron donor-containing liquid so that the nitrate nitrogen concentration in the filtered water after membrane separation is in the optimal range, it is possible to supply the electron donor necessary for the denitrification reaction and improve the nitrogen removal efficiency, while suppressing an increase in the aeration volume from the aeration tube 4 and preventing an increase in the amount of power required for aeration.

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

The present invention provides a wastewater treatment device and method that can stably perform wastewater treatment.

REFERENCE SIGNS LIST 1 Reaction tank 2 Membrane separation device 4 Aeration pipe 7 Partition plate 9 Raw water tank 10 Raw water supply device 11 Outer area of partition plate 12 Inner area of partition plate 17 Nitrate nitrogen concentration meter 20 Anaerobic treatment device 21 Bypass pipe 22 Electron donor-containing liquid tank

Claims (12)

A wastewater treatment device is provided with a membrane separation device, an aeration pipe, and a partition plate that divides the inside of the reaction tank into a plurality of compartments, inside the reaction tank for performing aerobic and anaerobic treatment of wastewater, a means for supplying the wastewater to be treated to the reaction tank, and a water level control means for switching the water level in the reaction tank between a state higher than the upper end of the partition plate and a state lower than the upper end of the partition plate, wherein at least one of the plurality of compartments is an aerobic compartment in which the membrane separation device and the aeration pipe are disposed, and anaerobic treatment is performed in the remaining compartments,
providing a means for supplying an electron donor-containing liquid different from the wastewater to be treated to the other compartment in the reaction tank when the water level in the reaction tank is lower than the upper end of the partition plate ;
1. A wastewater treatment apparatus comprising : said wastewater to be treated is wastewater that has been subjected to anaerobically treated water; and said electron donor-containing liquid is wastewater that has not been subjected to anaerobically treated water . The wastewater treatment device according to claim 1 , wherein the BOD of the wastewater not subjected to anaerobic treatment is 500 to 15,000 mg/L. The wastewater treatment device according to claim 1, wherein the electron donor contained in the electron donor-containing liquid is at least one selected from the group consisting of alcohols, organic acids, sulfur, and hydrogen. The wastewater treatment device according to claim 1, wherein the electron donor-containing liquid is a wastewater obtained by anaerobic treatment of screen residue and/or precipitated sludge that has been previously removed from the wastewater. The wastewater treatment device according to any one of claims 1 to 4, further comprising a nitrate nitrogen concentration meter for measuring the nitrate nitrogen concentration in the filtrate obtained after the membrane separation by the membrane separation device, and a means for controlling the supply amount of the electron donor-containing liquid so that the nitrate nitrogen concentration measured by the concentration meter becomes a preset target value. A wastewater treatment device is provided with a membrane separation device, an aeration pipe, and a partition plate that divides the inside of the reaction tank into a plurality of compartments, inside the reaction tank for performing aerobic and anaerobic treatment of wastewater, a means for supplying the wastewater to be treated to the reaction tank, and a water level control means for switching the water level in the reaction tank between a state higher than the upper end of the partition plate and a state lower than the upper end of the partition plate, wherein at least one of the plurality of compartments is an aerobic compartment in which the membrane separation device and the aeration pipe are disposed, and anaerobic treatment is performed in the remaining compartments,
providing a means for supplying an electron donor-containing liquid different from the wastewater to be treated to the other compartment in the reaction tank when the water level in the reaction tank is lower than the upper end of the partition plate;
1. A wastewater treatment device comprising: a reactor for treating wastewater containing a liquid; and a separator for separating the liquid from the reactor; A wastewater treatment method for performing aerobic and anaerobic treatment of wastewater in a reaction tank in which a membrane separation device and an aeration pipe are disposed, the membrane separation device is partitioned off from the periphery thereof with a partition plate, and aeration is performed from below the membrane separation device with an aeration pipe, and the water level in the reaction tank is adjusted to maintain an aerobic state in the compartment in which the membrane separation device and the aeration pipe are disposed while performing anaerobic treatment in the other compartments.
When the water level in the reaction tank is lower than the upper end of the partition plate, an electron donor-containing liquid different from the wastewater to be treated is supplied to the other compartment in the reaction tank ;
A wastewater treatment method, characterized in that the wastewater to be treated is wastewater that has been subjected to anaerobically treated water, and the electron donor-containing liquid is wastewater that has not been subjected to anaerobically treated water . The wastewater treatment method according to claim 7 , wherein the BOD of the wastewater not subjected to anaerobic treatment is 500 to 15,000 mg/L. The wastewater treatment method according to claim 7 , wherein the electron donor contained in the electron donor-containing liquid is at least one selected from the group consisting of alcohols, organic acids, sulfur, and hydrogen. 8. The wastewater treatment method according to claim 7 , wherein the electron donor-containing liquid is an effluent obtained by anaerobic treatment of screen residue and/or precipitated sludge previously removed from the wastewater. The wastewater treatment method according to any one of claims 7 to 10, wherein the nitrate nitrogen concentration in the filtrate obtained after the membrane separation by the membrane separation device is measured, and the supply amount of the electron donor - containing liquid is controlled so that the measured nitrate nitrogen concentration becomes a preset target value. A wastewater treatment method for performing aerobic and anaerobic treatment of wastewater in a reaction tank in which a membrane separation device and an aeration pipe are disposed, the membrane separation device is partitioned off from the periphery thereof with a partition plate, and aeration is performed from below the membrane separation device with an aeration pipe, and the water level in the reaction tank is adjusted to maintain an aerobic state in the compartment in which the membrane separation device and the aeration pipe are disposed while performing anaerobic treatment in the other compartments.
When the water level in the reaction tank is lower than the upper end of the partition plate, an electron donor-containing liquid different from the wastewater to be treated is supplied to the other compartment in the reaction tank;
A wastewater treatment method, characterized in that the amount of the electron donor-containing liquid supplied is an amount such that the water level in the reaction tank does not exceed the upper end of the partition plate.

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