JP6829585B2 - Sewage treatment system and sewage treatment method - Google Patents

Description

The present invention relates to a sewage treatment system and a sewage treatment method.

Conventionally, as a method for treating sewage, for example, a standard activated sludge method has been known (see Patent Document 1). The standard activated sludge method was developed at the beginning of the 20th century and is a method of treating organic matter in sewage by maintaining a high concentration of microorganisms. The sewage is first sent to the sedimentation basin, where it separates into the supernatant sewage and sediment. The supernatant is sent to a reaction tank and mixed with activated sludge containing microorganisms. Air is sent to the reaction tank by a blower. As a result, organic matter in the sewage is decomposed. Subsequently, in the final settling basin, the activated sludge flocs and the supernatant are separated into solid and liquid. The supernatant of the final settling basin is discharged after disinfection. On the other hand, the excess activated sludge in the final settling basin is sent to the gravity concentration tank and then to the digestion tank together with the sludge settled in the settling basin first. The solid content remaining after passing through both tanks is used as a raw material (cement raw material) for building materials.

However, in the case of the above standard activated sludge method, a large space is required because it is necessary to provide a final settling basin, carryover occurs due to insufficient sludge sedimentation, and a large amount of sludge is generated. There is a problem such as what to do. In recent years, a membrane separation activated sludge method has been implemented as a sewage treatment method in order to eliminate such a defect (see Patent Documents 2 and 3). In a system using membrane separation activated sludge, the reaction tank is separated into an anaerobic tank, an oxygen-free tank, and an aerobic tank, and a membrane separation device is provided inside or outside the aerobic tank. The sewage is sent to the chlorine mixing pond via an anaerobic tank, an oxygen-free tank, an aerobic tank, and a membrane separation device (some of which is returned to the anaerobic tank). In some cases, the anaerobic tank is not provided. Such a membrane separation activated sludge system has the following advantages. First, it is excellent in area saving because it does not require a final sedimentation basin. Secondly, since the activated sludge and the treated water are separated by a separation membrane having a pore size of about 0.1 to 0.4 μm, the activated sludge is not contained in the treated water. Therefore, good treated water quality can be stably maintained. Third, in order to maintain a high concentration of activated sludge suspended matter (MLSS) of about 8000 to 12000 mg / L, the aerobic solids residence time (ASRT) becomes long, and the yield (weight gain / predatory bacteria amount) becomes long. ) Is relatively low, and micro-animals (protozoa, metazoans, etc.) can live in activated sludge. Therefore, the sludge generation rate is lower than that of the standard activated sludge method.

Japanese Unexamined Patent Publication No. 09-276884 Japanese Unexamined Patent Publication No. 2004-313923 Japanese Unexamined Patent Publication No. 2005-246310

However, the above-mentioned conventionally known membrane separation activated sludge method also has a problem to be solved. That is, the power cost required for cleaning the membrane surface is high in order to prevent the separation membrane from being blocked. Sewage treatment is generally a project that uses state subsidies and sewerage charges. For this reason, there is a strong demand for sound management of sewage treatment. There is also a request to effectively utilize the resources of sewage. Furthermore, there is also a demand to maintain stable sewage treatment even when rebuilding facilities due to aging.

The present invention has been made in view of the above problems, and an object of the present invention is to realize reduction of power consumption, utilization of resources of sewage treatment products, and space saving of sewage treatment system.

In order to achieve the above object, the present inventor has made extensive development, and as a result, based on the membrane separation activated sludge method without a final settling basin, in each facility of the sewage treatment system, in the reaction tank. Since the power consumption of the blower that blows air is the largest, it was considered to reduce the amount of air blown by the blower to effectively treat the sewage. Furthermore, the present inventor considers that the product of sewage treatment is not reduced but rather actively produced, the digested gas derived from the product is used for power generation, and the digested sludge is used as an organic fertilizer or sludge fuel after dehydration. We have developed a new sewage treatment method. The specific means are as follows.

The sludge treatment system according to one embodiment of the present invention has a product recovery space for aggregating and recovering agglomeration target substances from a mixture containing sewage and a coagulant for aggregating the agglomeration target substances in the sewage, and a product recovery space. An aerobic tank for decomposing organic substances in the sewage that has undergone recovery treatment using activated sludge in the presence of oxygen, and microorganisms in the activated sludge that can send air into the aerobic tank. A blower that blows air necessary for biological treatment, a membrane separation device that separates solids and liquids in an aerobic tank, and a reverse pump to collect excess sludge in the aerobic tank. It is equipped with a reverse pipe that returns to.

The sludge treatment system according to another embodiment further comprises a control device for controlling the reverse pump, the control device reverse so that the aerobic solids residence time is within the range of 0.5 to 3 days. The amount of excess sludge drawn out by the pump may be adjusted.

The sewage treatment system according to another embodiment further includes a control device for controlling the reverse pump, a first flow meter for measuring the flow rate of sewage flowing through the pipe on the upstream side of the product recovery space, and a reverse pipe. A second flow meter for measuring the flow rate of excess sludge flowing, and a third flow meter for measuring the flow rate of sludge flowing between the product recovery space and the concentration space for sending the collected sludge from the product recovery space. And the first ammonia nitrogen concentration meter for measuring the ammonia nitrogen concentration of the sewage flowing between the product recovery space and the aerobic tank, and the ammonia nitrogen concentration of the liquid downstream from the outlet of the membrane separation device. A second ammonia nitrogen concentration meter for measurement and an organic substance concentration meter for measuring the organic substance concentration of the liquid downstream from the outlet of the membrane separation device are provided, and the control device is a first flow meter and a second flow meter. Even if the amount of excess sludge drawn out by the reverse pump is adjusted based on the measured values from the flow meter, the third flow meter, the first ammonia nitrogen concentration meter, the second ammonia nitrogen concentration meter, and the organic matter concentration meter. good.

The sewage treatment system according to another embodiment may also have at least one of a chemical oxygen demand meter, a total organic carbon meter, and an ultraviolet absorbance meter as an organic substance concentration meter.

The sewage treatment system according to another embodiment may also have a product recovery space that recovers 70% by mass or more of the agglutinating target substance in the sewage flowing into the sewage treatment system.

The sewage treatment method according to one embodiment of the present invention is a sewage treatment method using the above-mentioned sewage treatment system, which includes a coagulant charging step of adding a coagulant to the sewage before putting the sewage into the product recovery space. In the product recovery space, a recovery step of recovering the agglomerated object from the mixture of the sewage and the coagulant, and an aerobic tank liquid feeding step of feeding the recovered sewage from the product recovery space to the aerobic tank. It includes at least an aeration step of blowing air into a mixture of sewage and activated sludge in an aerobic tank and a process of decomposing organic matter in the sewage sent into the aerobic tank using the activated sludge in the aerobic tank. A reverse pump removes excess sludge in the aerobic tank by a purification treatment step that performs purification treatment, a solid-liquid separation step that separates a mixture of solid and liquid in the aerobic tank into solid and liquid with a membrane separation device, and reverse piping. Includes excess sludge reverse step, which is returned to the product recovery space by.

In the sewage treatment method according to another embodiment, in the excess sludge reverse step, a control device for controlling the reverse pump is used so that the aerobic solid matter residence time is within the range of 0.5 to 3 days. It may include a step of adjusting the amount of excess sludge withdrawn by the reverse pump to adjust the amount of excess sludge withdrawn.

According to the present invention, it is possible to reduce power consumption, utilize resources of sewage treatment products, and save space in a sewage treatment system.

FIG. 1 shows a configuration diagram of an example of a sewage treatment system according to the first embodiment of the present invention. FIG. 2 shows a configuration diagram of an example of a sewage treatment system according to a second embodiment of the present invention. FIG. 3 shows a configuration diagram of a modified example of the sewage treatment system according to the second embodiment of the present invention. FIG. 4 shows the configuration of the control device shown in FIG. 2 or FIG. FIG. 5 shows a control flow of the second liquid feed pump based on information from various sensors in the sewage treatment method according to the second embodiment. FIG. 6 shows the relationship between ASRT (unit: day), membrane filtration water organic matter concentration (unit: mg / L), and nitrification concentration (unit: mg / L), and (6A) is at 15 ° C. (winter). , (6B) exemplify at 25 ° C. (summer), respectively. FIG. 7 shows a detailed flow of step S108 of FIG. FIG. 8 shows the features of each of the above embodiments of the present invention. FIG. 9 shows a comparison between each embodiment of the present invention and the conventional membrane separation activated sludge method.

An embodiment of the present invention will be described with reference to the drawings. It should be noted that the embodiments described below do not limit the inventions claimed in the claims, and all of the elements and combinations thereof described in the embodiments are essential for the means for solving the invention. Is not always.

<First Embodiment>

1. 1. Sewage treatment system First, the sewage treatment system according to the first embodiment of the present invention will be described.

FIG. 1 shows a configuration diagram of an example of a sewage treatment system according to the first embodiment of the present invention.

The sewage treatment system 1 includes a pump well 10, a first liquid feed pump 11 that functions as a pump from the pump well 10, a first sedimentation space (also referred to as “first sedimentation”) 12 as an example of a product recovery space, and a fine grain 13. , The aerobic tank 14, the third liquid feed pump 15a functioning as a suction pump for membrane separation water, and the chlorine mixing pond 17 are connected in order in the direction of sewage flow. The membrane separation device 15 is arranged inside the aerobic tank 14. The chlorine mixing pond 17 is connected to the downstream side of the membrane separation device 15 via a pipe. The third liquid feed pump 15a is connected in series to the above-mentioned pipe connecting the membrane separation device 15 and the chlorine mixing pond 17. However, when the liquid is sent to the chlorine mixing pond 17 using a siphon, the third liquid feeding pump 15a is not always required. The aerobic tank 14 is connected to the blower 16. The air sent from the blower 16 is aerated in a mixture of sewage and activated sludge in the aerobic tank 14. The aerobic tank 14 is initially connected to the settling space 12 via the reverse pipe 19. The reverse pipe 19 includes a second liquid feeding pump 18 that functions as a surplus sludge transfer pump that draws excess sludge from the aerobic tank 14 in the path thereof. The initial settling space 12 is connected to the gravity concentrating tank 20 as an example of the concentrating space from the bottom or the vicinity of the bottom via a pipe. A fourth liquid feeding pump 19a, which functions as a sludge extraction pump for first extracting sludge from the sedimentation space 12, is connected to the path of the pipe. The gravity concentration tank 20 is connected to the digestion tank 21 from the bottom or the vicinity of the bottom via a pipe. A fifth liquid feeding pump 20a, which functions as a concentrated sludge extraction pump for extracting concentrated sludge from the gravity concentration tank 20, is connected to the path of the pipe. The digestion tank 21 is connected to the dehydrator 22 via a pipe. A sixth liquid feeding pump 21a, which functions as a digestive sludge extraction pump for extracting digestive sludge from the digestion tank 21, is connected to the path of the pipe.

(1) Pump well and first liquid feed pump The pump well 10 stores sewage (for example, water that requires purification such as sewage or factory wastewater), puts a coagulant into it, and feeds it first. This is an area for executing liquid feeding by the liquid pump 11. The coagulant is an inorganic material or an organic material that agglomerates an object to be aggregated (suspended solids, etc.) in sewage and coarsens it to a level at which it easily precipitates. Examples of the flocculant include inorganic flocculants such as aluminum sulfate, polyaluminum chloride, ferric polysulfate and ferric chloride, cationic, anionic, nonionic or amphoteric polymer flocculants, or the above-mentioned inorganic flocculants. A mixture with the above polymer flocculant can be preferably used. The flocculant may be charged between the first liquid feed pump 11 and the initial settling space 12. The first liquid feeding pump 11 is a pump capable of feeding sewage (whether or not it is a mixture containing a coagulant) from the pump well 10 to the first settling space 12.

(2) Initial settling space and fine grain The initial settling space 12 accepts a mixture of a flocculant and sewage (in many cases, suspended solids in the sewage are already in a floc state) to settle the agglomerated object. The place to do it. That is, the initial precipitation space 12 is a space for aggregating and precipitating the agglomeration target substance from a mixture containing sewage and a coagulant for aggregating the agglomeration target substance in the sewage. The initial settling space 12 is not particularly limited in its form, but is, for example, a tank-shaped form. Initially, in the sedimentation space 12, suspended solids in the sewage are precipitated by the flocculant. The amount of precipitation is preferably 70% by mass or more of the total suspended solids (100% by mass), and is practically in the range of 70 to 90% by mass. The initial settling space 12 is connected to the reverse pipe 19 and the gravity concentration tank 20, which will be described later, respectively. The fine mesh 13 is also referred to as a fine mesh screen, and is a member having a large number of slits or meshes, and is a member for removing fibers, hair, and the like to prevent them from being mixed into the aerobic tank 14.

(3) Aerobic tank The aerobic tank 14 is a tank for decomposing organic matter in the inflow sewage that has undergone the precipitation treatment in the first settling space 12 by using activated sludge in the presence of oxygen. In the aerobic tank 14, by shortening the ASRT, the growth of low-yield microorganisms is suppressed, and the autolysis of activated sludge (general term for bacterial killing, bacterial predation by low-yield microorganisms, etc.) is suppressed. I have to. When the ASRT is shortened, specifically, when it is set in the range of 0.5 to 3 days, the growth of nitrifying bacteria having a slower growth rate than that of organic oxidizing bacteria can be suppressed, and the amount of air blown from the blower 16 can be reduced. It can be carried out. ASRT can be determined by (aerobic tank capacity × MLSS concentration) / (excess sludge withdrawal amount × MLSS concentration), that is, aerobic tank capacity / excess sludge withdrawal amount. Here, "MLSS" means activated sludge suspended matter. Therefore, for example, when the operating condition of ASRT = 3 days is set, the excess sludge withdrawal amount (m ³ / day) = reaction tank capacity (m ³ ) / 3 days) is used as the excess sludge withdrawal amount (m ³ / day). How to move the second liquid feed pump 18) will be set. Since nitrate nitrogen is not generated in the aerobic tank 14, an oxygen-free tank and a nitrifying liquid circulation pump for denitrification become unnecessary. ASRT control is an operation method adopted from the viewpoint of the balance between the amount of growth of bacteria and microorganisms and the amount of removal by extracting excess sludge. For this reason, it is difficult to appropriately respond to changes in conditions in a period shorter than the microbial growth time. Therefore, in reality, there is a concern that the treated water quality may be worse than expected or may be too good due to fluctuations in the inflow water quality and water temperature. When such a concern is low, the excess sludge withdrawal amount of the second liquid feeding pump 18 can be set in advance as in this embodiment. On the other hand, when the above concern is high, it is preferable to maintain the operation under the optimum conditions while controlling the drive of the second liquid feed pump 18 by using various sensors as in the second embodiment. Such a control method will be described in detail in the second embodiment.

(4) Blower The blower 16 is one of the characteristic configurations in this embodiment. The blower 16 can supply air into the aerobic tank 14 and supply oxygen necessary for removing organic substances in the inflowing sewage. The amount of air blown is related to the amount of organic matter flowing into the aerobic tank 14. That is, the amount of air blown depends on the quality of the inflowing sewage and the removal rate of suspended matter (also referred to as "SS removal rate") by the initial sedimentation space 12. In addition, the amount of air blown is affected not only by the performance of the air diffuser, but also by the controlled value of the dissolved oxygen concentration (referred to as "DO concentration") in the aerobic tank 14. Therefore, the lower the DO concentration, the easier it is for oxygen to dissolve in the sewage in the aerobic tank 14, so that the amount of air blown can be reduced. Conventionally, in order to proceed with the nitrification reaction, the amount of air blown is controlled so that the DO concentration is about 1 to 2 mg / L. In this embodiment, in order to suppress the nitrification reaction, the DO concentration is preferably controlled to about 0.5 to 1 mg / L. From this point of view, from the blower 16, the blast magnification required for biological treatment by microorganisms in activated sludge (calculated by the amount of blast / treated water amount, also referred to as "necessary blast magnification for biological treatment") is 1 to 3 times. The amount of air blown is set so as to be (1 ≦ required air blowing ratio for biological treatment ≦ 3). Here, the required ventilation ratio for biological treatment is obtained from the capacity calculation on the assumption that the SS removal rate in the initial precipitation space 12 is 70 to 90% by mass. The required blast magnification for biological treatment in this embodiment corresponds to 1/5 to 3/5 as compared with the same magnification (about 5 times) of the sewage treatment system using the conventional membrane separation activation method.

(5) Membrane Separation Device The membrane separation device 15 is a device for solid-liquid separation of a liquid in an aerobic tank 14 using a fine mesh (pore diameter: about 0.1 to 0.4 μm). Since the pore size is smaller than that of bacteria, bacteria cannot pass through the membrane separation device 15. As the membrane to be used, a flat membrane or a hollow fiber membrane can be preferably exemplified. By using the membrane separation device 15, suspended solids, solids in activated sludge, etc. initially carried from the precipitation space 12 can be separated from the liquid component. By continuing such solid-liquid separation for a long period of time, the mesh in the membrane separation device 15 may be clogged. In order to prevent the clogging and realize normal solid-liquid separation, it is preferable to send a part of the air from the blower 16 to the mesh to clean the mesh. In this embodiment, a part of the air from the blower 16 is used for aeration (also referred to as "auxiliary air diffuser") in the aerobic tank 14, and a part is used for cleaning the mesh. Although the membrane separation device 15 is installed inside the aerobic tank 14 in this embodiment, it may be installed outside the aerobic tank 14 as shown in the embodiment described later.

(6) Chlorine mixing pond The chlorine mixing pond 17 is a space for disinfecting a liquid (mainly water) that has passed through the membrane separation device 15, and is connected to the membrane separation device 15 without passing through a further precipitation space. Corresponds to a disinfection tank. As described above, since the pore size of the membrane of the membrane separation device 15 does not allow bacteria to pass through, it is usually not necessary to put a disinfectant in the chlorine mixing pond 17. However, as a countermeasure when the membrane separation device 15 does not operate normally due to damage to the membrane or the like, a disinfectant (for example, sodium hypochlorite) can be added as needed. The water that has passed through the chlorine mixing pond 17 is then discharged.

(7) Reverse piping The reverse piping 19 is one of the characteristic configurations in this embodiment. The reverse pipe 19 is a pipe that returns excess sludge (a part of activated sludge and also water) existing in the aerobic tank 14 to the first settling space 12 by the second liquid feeding pump 18. Although the amount of suspended solids in the sewage initially sent from the settling space 12 to the aerobic tank 14 is very small, this embodiment is a system for actively increasing sludge. Therefore, the amount of excess sludge drawn from the reverse pipe 19 is relatively large. However, the concentration of the excess sludge is the same as the concentration of activated sludge (750 to 4000 mg / L) in the aerobic tank 14, which is lower than the concentration of activated sludge in the conventional reaction tank. Even if such a liquid having a low concentration of excess sludge is connected to the gravity concentration tank 20, the efficiency of gravity concentration becomes extremely low. For this reason, preferably, the reverse pipe 19 is first sent to the settling space 12 instead of the gravity concentrating tank 20 to be adsorbed by a relatively large floc and settled.

(8) Second Liquid Feed Pump The second liquid feed pump 18 is one of the characteristic configurations in this embodiment. The second liquid feed pump 18 is a reverse pump for returning excess sludge in the aerobic tank 14 to the first settling space 12. In this embodiment, preferably, the liquid feed amount of the second liquid feed pump 18 is adjusted to keep the MLSS concentration in the aerobic tank 14 low and increase the sludge generation amount. The second liquid feed pump 18 in this embodiment is more preferably operated so as to make the ASRT shorter than before. Specifically, the second liquid feed pump 18 draws out excess sludge so that the ASRT is within the range of 0.5 to 3 days.

(9) Gravity Concentration Tank, Digestion Tank and Dehydrator The gravity concentration tank 20 collects aggregates of aggregated objects settled from a mixture of excess sludge returned by the reverse pipe 19 and sewage that first flows into the settling space 12. It is a tank for feeding, and is a tank that concentrates agglomerates by a natural sedimentation method using gravity. In addition, instead of the gravity concentrating tank 20, a mechanical concentrator as another example of the concentrating space may be used. When the gravity concentrator 20 is used, the running cost can be reduced as compared with the case where the mechanical concentrator is used. On the other hand, when the mechanical concentrator is used, the concentration of the concentrated sludge can be increased as compared with the case where the gravity concentrating tank 20 is used, so that the digestion tank 21 in the subsequent stage can be made smaller. The digestion tank 21 is a tank for decomposing the organic matter in the sludge sent from the gravity concentration tank 20 and positively generating digestion gas (including methane gas, carbon dioxide gas, etc.). Digestion gas can be used for digestion gas power generation and the like. However, the digestion gas may be used for other purposes. The liquid / solid mixture in the digestion tank 21 is dehydrated by the dehydrator 22 to become a cake-like semi-solid. The semi-solid material can then be reused for organic fertilizers, sludge fuels, building materials and the like. The digestion tank 21 is not an essential configuration. It is also possible to use the whole amount as sludge fuel without digesting the recovered product without providing the digestion tank 21.

2. 2. Sewage treatment method Next, a sewage treatment method using the sewage treatment system 1 will be described.

The sewage treatment method according to this embodiment is
A coagulant charging step of adding a coagulant to the sewage before first filling the settling space 12 with sewage.
First, in the precipitation space 12, a precipitation step of precipitating the object to be aggregated from the mixture of sewage and the coagulant,
An aerobic tank liquid feeding step of first feeding the sewage after the sedimentation treatment from the settling space 12 to the aerobic tank 14.
An aeration step of blowing a gas containing at least oxygen (for example, air) into a mixture of sewage and activated sludge in the aerobic tank 14.
A purification treatment step of performing a purification treatment including at least a treatment of decomposing organic matter in a mixture of sewage and activated sludge sent into the aerobic tank 14 using the activated sludge in the aerobic tank 14.
A solid-liquid separation step of solid-liquid separating a mixture of a solid and a liquid in the aerobic tank 14 by the membrane separation device 15.
The excess sludge reverse step in which the excess sludge in the aerobic tank 14 is returned to the first settling space 12 by the second liquid feed pump 18 by the reverse pipe 19 and
including.

The sewage treatment method may further include a gravity concentration tank liquid feeding step in which excess sludge from the reverse pipe 19 is returned to the first settling space 12 and the sediment settled in the first settling space 12 is sent to the gravity concentration tank 20. ..

Each of the above steps is not necessarily performed in the order of coagulant charging step, settling step, aerobic tank liquid feeding step, aeration step, purification treatment step, solid-liquid separation step, excess sludge reverse step, and gravity concentration tank liquid feeding step. Absent. During the implementation of the sewage treatment method, a plurality of these steps are usually performed in parallel. Hereinafter, the aeration step, the purification treatment step, and the excess sludge reverse step will be described.

(1) Aeration step and purification treatment step The aeration step is a step of aerating an oxygen-containing gas typified by air in a mixture of sewage and activated sludge in an aerobic tank 14. The purification treatment step is a step of decomposing organic matter in the inflowing sewage using activated sludge in the presence of oxygen.

(2) Excess sludge reverse step The excess sludge reverse step is a step of returning the excess sludge in the aerobic tank 14 to the first settling space 12 by the second liquid feeding pump 18. The surplus sludge is a part of the activated sludge in the aerobic tank 14. In the excess sludge reverse step, preferably, the ASRT is made shorter than before to operate the second liquid feed pump 18. Specifically, the second liquid feed pump 18 draws out excess sludge so that the ASRT is within the range of 0.5 to 3 days. The second liquid feed pump 18 may be operated intermittently or continuously.

<Second Embodiment>

1. 1. Sewage treatment system First, the sewage treatment system according to the second embodiment of the present invention will be described.

FIG. 2 shows a configuration diagram of an example of a sewage treatment system according to a second embodiment of the present invention.

Unlike the sewage treatment system 1 according to the first embodiment, the sewage treatment system 1a according to the second embodiment can finely control the operation of the second liquid feed pump 18 based on various sensors and data from those sensors. It is equipped with a control device. Other than the above differences in the sewage treatment system 1a, it is common to the sewage treatment system 1. Hereinafter, only the differences will be described.

Various suitable sensors provided in the sewage treatment system 1a include a flow meter A30a as a first flow meter, a flow meter B30b as a second flow meter, a flow meter C30c as a third flow meter, and a first ammonia nitrogen concentration meter. The NH _4- N meter A32, the NH _4- N meter B33 as the second ammonia nitrogen concentration meter, and the organic substance concentration meter 34.

The sewage treatment system 1a first includes a flow meter A30a for measuring the flow rate of sewage flowing through the pipe on the upstream side of the sedimentation space 12, and a flow meter B30b for measuring the flow rate of excess sludge flowing through the reverse pipe 19. A flow meter C30c for measuring the flow rate of sludge flowing between the settling space 12 and the gravity concentration tank 20 for sending the settled sludge from the first settling space 12, and flowing between the first settling space 12 and the aerobic tank 14. Membrane separation with NH _4- N meter A32 for measuring the ammonia nitrogen concentration of sewage and NH _4- N meter B33 for measuring the ammonia nitrogen concentration of the liquid downstream from the outlet of the membrane separation device 15. It includes an organic substance concentration meter 34 for measuring the organic substance concentration of the liquid downstream from the outlet of the device 15, and a control device 35 capable of adjusting the amount of excess sludge drawn out by the second liquid feeding pump 18. The control device 35 is the second pump based on each data (each measured value) from the flow meter A30a, the flow meter B30b, the flow meter C30c, the NH _4- N meter A32, the NH _4- N meter B33, and the organic matter concentration meter 34. The amount of excess sludge drawn out by the liquid pump 18 is adjusted. The organic matter concentration meter 34 is preferably at least one of a chemical oxygen demand measuring meter (COD meter), a total organic carbon amount measuring meter (TOC meter), and an ultraviolet absorbance meter (UV meter).

FIG. 3 shows a configuration diagram of a modified example of the sewage treatment system according to the second embodiment of the present invention.

In the sewage treatment system 1b according to this modification, unlike the sewage treatment system 1a according to the second embodiment, the membrane separation device 15 is arranged outside the aerobic tank 14 and on the downstream side thereof. A pump 36 is preferably arranged in the pipe connecting the aerobic tank 14 and the membrane separation device 15. Further, since the membrane separation device 15 is arranged outside the aerobic tank 14, the air supplied from the blower 16 to the aerobic tank 14 is aerated into the mixture of the sewage and the activated sludge in the aerobic tank 14. The purpose is (also called aeration). However, although not shown in FIG. 3, the mesh in the membrane separation device 15 can be washed by the water supply from the pump through the air supply from the blower 16 to the pump. Other than the above differences in the sewage treatment system 1b, it is common to the sewage treatment system 1a.

FIG. 4 shows the configuration of the control device shown in FIG. 2 or FIG.

The control device 35 preferably includes a flow meter measurement value reception unit 40, an NH _4- N meter measurement value reception unit 41, an organic substance concentration meter measurement value reception unit 42, a tank inflow time calculation unit 43, and a nitrification concentration calculation unit 44. Estimated BOD calculation unit 45, measurement value / calculation value reception unit 46, NH _4- N total measurement value discrimination unit 47, first estimated BOD calculation value discrimination unit 48, second estimated BOD calculation value discrimination unit 49, first nitrification concentration It includes a calculated value determination unit 50, a second nitrification concentration calculated value determination unit 51, an excess sludge withdrawal amount determination unit 52, a pump drainage amount determination unit 53, various information storage units 54, and an information recording medium insertion unit 55.

The above-mentioned flow meter measurement value reception unit 40, NH _4- N meter measurement value reception unit 41, organic substance concentration meter measurement value reception unit 42, tank inflow time calculation unit 43, vitrification concentration calculation unit 44, estimation BOD calculation unit 45, Measured value / calculated value receiving unit 46, NH _4- N total measured value discriminating unit 47, first estimated BOD calculated value discriminating unit 48, second estimated BOD calculated value discriminating unit 49, first vitrification concentration calculated value discriminating unit 50, The second vitrification concentration calculation value determination unit 51, the excess sludge extraction amount determination unit 52, and the pump drainage amount determination unit 53 are stored in a central processing device (CPU) and various information storage units 54 (software). It is a part that performs various processes in collaboration with (also called). The various information storage units 54 include a read-only memory (ROM) and a readable / writable memory (RAM). The various information storage units 54 may be provided with other storage devices such as EEPROM and a hard disk (HD). In this embodiment, the information recording medium insertion unit 55 is a tray on which a CD-R can be loaded, in order to explain an example in which the CD-R is used as the information recording medium. However, the information recording medium insertion unit 55 can be changed to various forms depending on the form of the information recording medium inserted or connected to the control device 35.

Next, various components in the control device 35 will be described. The flow meter measurement value receiving unit 40 is a component unit that receives each data from the flow meter A30a, the flow meter B30b, and the flow meter C30c. The NH _4- N total measurement value receiving unit 41 is a component unit that receives both data from the NH _4- N total A32 and the NH _4- N total B33. The organic substance concentration meter measurement value receiving unit 42 is a component unit that receives data from the organic substance concentration meter 34. The tank inflow time calculation unit 43 measured the capacity of the aerobic tank 14 with the flow meter C30c from the sum of the flow rate per unit time measured by the flow meter A30a and the flow rate per unit time measured by the flow meter B30b. It is a component that performs the calculation of dividing by the value obtained by subtracting the flow rate per unit time. The vitrification concentration calculation unit 44 is a component that calculates the NH _4- N concentration difference in consideration of the tank inflow time obtained by the tank inflow time calculation unit 43. Specifically, it is before the tank inflow time. performs operation of subtracting the _NH 4 -N concentration of a predetermined time from the _NH 4 -N concentration. The estimated BOD calculation unit 45 is a component unit that calculates the estimated BOD by substituting the measured value (x) from the organic matter concentration meter 34 into the function f (x) for the estimated BOD calculation. Here, "BOD" means a biochemical oxygen demand (Biochemical Oxygen Demand). The function f (x) is stored in various information storage units 54. The estimation BOD calculation unit 45 reads out the function f (x) from the various information storage units 54, substitutes the measurement value (x) received by the organic matter concentration meter measurement value reception unit 42, and executes the calculation. The function f (x) can be appropriately input by the user and may not be fixed. As the function f (x), A * exp (B * x) can be preferably exemplified. A and B mean coefficients, respectively, and for example, A = 0.1212 and B = 0.3539.

The measured value / calculated value receiving unit 46 is a component unit that receives data necessary for determining the amount of excess sludge withdrawn. In this embodiment, the measured value / calculated value receiving unit 46 is, for example, each measured value from the flow meter A30a, the flow meter B30b and the flow meter C30c, and each from the NH _4- N meter A32 and the NH _4- N meter B33. Accepts measured values, nitrification concentration and estimated BOD. However, the measured value / calculated value receiving unit 46 can accept not only the above-exemplified data but also data necessary for determining the amount of excess sludge withdrawn. The NH _4- N meter measurement value determination unit 47 determines whether or not the value measured by the NH _4- N meter A32 is equal to or less than the lower limit of the ammonium nitrogen concentration (L _NH4-N ) of the inflow water (sewage). It is a component that determines. L _NH4-N is stored in various information storage units 54. L _NH4-N can be stored in various information storage units 54, for example, through input by a user, download from an external database, calculation by various components in the control device 35, and the like.

The first estimated BOD calculated value discriminating unit 48 is a component unit that determines whether or not the estimated BOD received by the measured value / calculated value receiving unit 46 is equal to or higher than the upper limit value (H _BOD ) of the estimated BOD. is there. The H _BOD can be stored in the various information storage units 54, for example, through input by the user, download from an external database, calculation by various components in the control device 35, and the like. The second estimated BOD calculated value discriminating unit 49 is a component unit that determines whether or not the estimated BOD received by the measured value / calculated value receiving unit 46 is equal to or less than the lower limit value (referred to as L _BOD ) of the estimated BOD. is there. The _LBOD can be stored in various information storage units 54 through, for example, input by a user, download from an external database, calculation by various components in the control device 35, and the like.

In the first nitrification concentration calculation value determination unit 50, when the estimated BOD is _LBOD or less, the nitrification concentration received by the measurement value / calculation value reception unit 46 is equal to or higher than the upper limit value of the nitrification concentration (referred to as H _{nitrification} ). It is a component that determines whether or not it is. Second nitrification density calculation value determination unit 51, when the estimated BOD is greater than L _BOD, nitrification concentration accepted by measurement and calculation value receiving section 46 determines whether the H or higher _{nitrification} structure It is a department. The H _{nitrification} can be stored in various information storage units 54, for example, through input by a user, download from an external database, calculation by various components in the control device 35, and the like.

The excess sludge extraction amount determination unit 52 includes an NH _4- N meter measurement value determination unit 47, a first estimated BOD calculation value determination unit 48, a second estimated BOD calculation value determination unit 49, a first nitrification concentration calculation value determination unit 50, and This is a component that determines the amount of excess sludge extracted from the aerobic tank 14 based on various discrimination results of the second nitrification concentration calculation value discriminating unit 51. The surplus sludge extraction amount determination unit 52 selects (1) from a plurality of extraction amounts stored in advance in various information storage units 54, and (2) selects a coefficient stored in advance in various information storage units 54. It is also possible to calculate the withdrawal amount, or (3) calculate the withdrawal amount without making any selection from the various information storage units 54. For example, a time zone in which the amount of inflow water is large in a day may be set in advance, and the amount of excess sludge drawn out may be controlled by a value obtained from various sensors 32 or the like in that time zone. In that case, it is preferable to multiply the withdrawal amount in the previous control (previous day) by various coefficients determined today to set the excess sludge withdrawal amount for today. The excess sludge is preferably extracted every hour, but the amount of the excess sludge extracted every hour may be the same amount or may be changed according to the fluctuation pattern of the inflowing sewage.

An exemplary determination process by the excess sludge extraction amount determination unit 52 is as follows. Excess sludge withdrawal amount determination unit 52, when the measured value by _NH 4 -N meter A32 is equal to or less than _{L NH4-N,} the (n + 1) withdrawal of excess sludge at _{(Q es,} and _{n + 1),} the It shall be the same as the amount of excess sludge extracted (referred to as _{Qes, n} ) at the previous time (n o'clock). Furthermore, excess sludge withdrawal amount determining section 52, when the measured value by _NH 4 -N meter A32 is greater than _{L NH4-N,} when the estimated BOD is not less than _{H BOD, Q es,} a _{n + 1, Q es , N} * a (a is a numerical value in the range of 0 or more and less than 1). Further, the excess sludge extraction amount determination unit 52 determines that the estimated BOD is less than H _BOD , the estimated BOD is less than L _BOD , and the nitrification concentration is higher than the L _NH4-N measured value by the NH _4- N meter A32. When H _{nitrification} or higher, Q _{es, n + 1} is set to Q _{es, n} * b (b is a value significantly exceeding 1).

On the other hand, the excess sludge extraction amount determination unit 52 determines that the estimated BOD is less than H _BOD , the estimated BOD exceeds L _BOD , and the nitrification concentration is obtained when the value measured by the NH _4- N total A32 exceeds L _NH4-N. When is H _{nitrification} or higher, Q _{es, n + 1} is set to Q _{es, n} * c (c is a value larger than 1 and smaller than b). The excess sludge extraction amount determination unit 52 determines that the estimated BOD is less than H _BOD , the estimated BOD is less than L _BOD , and the nitrification concentration is H when the value measured by the NH _4- N meter A32 exceeds L _NH4-N. Even when it is less than _{nitrification} , Q _{es, n + 1} is set to Q _{es, n} * c (c is a value larger than 1 and smaller than b). Further, the excess sludge extraction amount determination unit 52 determines that the estimated BOD is less than H _BOD , the estimated BOD exceeds L _BOD , and the nitrification concentration is obtained when the value measured by the NH _4- N meter A32 exceeds L _NH4-N. When is less than H _{nitrification} , Q _{es, n + 1} is made the same as Q _{es, n} . The above a, b, and c are set values relating to the amount of excess sludge drawn out, and are preferably stored in advance in various information storage units 54. Further, the initial setting value (default setting value) stored in the various information storage units 54 can be changed by the user. Further, the user may input at least one of a, b, and c at the time of calculation.

The pump drainage amount determination unit 53 is a component that determines the operating conditions (drainage amount, etc.) of the second liquid feed pump 18 based on the determination of the excess sludge withdrawal amount determination unit 52. The pump drainage amount determination unit 53 sends a control signal to the second liquid feed pump 18 based on the determination of the excess sludge extraction amount determination unit 52.

2. 2. Sewage treatment method Next, a sewage treatment method using the sewage treatment systems 1a and 1b will be described.

The sewage treatment method according to the second embodiment is generally the same as the sewage treatment method according to the first embodiment described above, but the second liquid feed pump 18 is finely controlled based on information from various sensors. different. Therefore, the processing flow of the precision control portion of the second liquid feed pump 18 will be described below, and the description of the portion common to the first embodiment will be omitted by substituting the description of the first embodiment. To do. In the sewage treatment method in this embodiment, in the excess sludge reverse step in the first embodiment, the ASRT is within the range of 0.5 to 3 days by using the control device 35 that controls the second liquid feed pump 18. The excess sludge withdrawal amount adjusting step for adjusting the withdrawal amount of the excess sludge by the second liquid feeding pump 18 is included. The specific flow of adjustment will be described below.

FIG. 5 shows a control flow of the second liquid feed pump based on information from various sensors in the sewage treatment method according to the second embodiment.

First, the flow meter measurement value receiving unit 40 receives each data from the flow meter A30a, the flow meter B30b, and the flow meter C30c (step S101). Subsequently, the tank inflow time calculation unit 43 measures the capacity of the aerobic tank 14 from the sum of the flow rate per unit time measured by the flow meter A30a and the flow rate per unit time measured by the flow meter B30b. The calculation is performed by dividing by the value obtained by subtracting the flow rate per unit time measured in (step S102). Next, the NH _4- N total measurement value receiving unit 41 receives both data from the NH _4- N total A32 and the NH _4- N total B33 (step S103). Next, the nitrification concentration calculation unit 44 calculates the NH _4- N concentration difference in consideration of the tank inflow time calculated by the tank inflow time calculation unit 43 (step S104). Further, the organic matter densitometer measurement value receiving unit 42 receives the data from the organic matter densitometer 34 (step S105). Next, the estimated BOD calculation unit 45 is a component unit that calculates the estimated BOD by substituting the measured value (x) from the organic matter concentration meter 34 into the function f (x) for the estimated BOD calculation (step S106). ). Next, the measured value / calculated value receiving unit 46 receives the data necessary for determining the amount of excess sludge withdrawn (step S107). Next, the NH _4- N total measurement value determination unit 47, the first estimated BOD calculation value determination unit 48, the second estimated BOD calculation value determination unit 49, the first vitrification concentration calculation value determination unit 50, and the second vitrification concentration calculation value. The determination unit 51 and the excess sludge withdrawal amount determination unit 52 cooperate with each other to calculate the excess sludge withdrawal amount (step S108). Next, the pump drainage amount determination unit 53 determines the drainage amount of the second liquid feed pump 18 based on the determination of the excess sludge withdrawal amount determination unit 52 (step S109).

FIG. 6 shows the relationship between ASRT (unit: day), membrane filtration water organic matter concentration (unit: mg / L), and nitrification concentration (unit: mg / L), and (6A) is at 15 ° C. (winter). , (6B) exemplify at 25 ° C. (summer), respectively.

Under the condition that the nitrification reaction proceeds, the ASRT becomes relatively long, and the autolysis of the activated sludge easily proceeds. For this reason, the ammonia nitrogen concentration (NH _4- N) in the inflow water into the aerobic tank 14 and the membrane filtration water is continuously monitored, and the difference (nitrification concentration) is calculated. In addition, using the monitoring results of the organic matter concentration and the ammonia nitrogen concentration, the stage where the organic matter concentration in the membrane filtered water is lower than the predetermined range and the nitrification concentration is higher than the predetermined range (step (1)), the organic matter concentration in the membrane filtered water and Depending on each stage of the stage where both the nitrification concentration is within the predetermined range (step (2)) and the stage where the organic matter concentration in the membrane filtration water is higher than the predetermined range and the nitrification concentration is within the predetermined range (step (3)). , The rotation speed and / or operating time of the second liquid feeding pump 18 is controlled to adjust the amount of excess sludge drawn out. Specifically, in the step (1), the withdrawal amount is increased. In step (2), the withdrawal amount is maintained. In step (3), the withdrawal amount is reduced. It is preferable that the amount of excess sludge drawn out is adjusted during the time period when the inflow load of sewage is the largest in the day. This is because it is necessary to prevent the concentration of the activated sludge suspended matter (MLSS) from becoming too low and the organic matter concentration of the membrane filtration water not exceeding the permissible limit value.

For example, in the case where the water temperature shown in (6A) is low, when the ASRT is shorter than one day (step (3)), the organic matter concentration becomes too high. If the ASRT is longer than 3 days (step (1)), the nitrification concentration becomes too high. Therefore, the second liquid feed pump 18 is controlled so that the ASRT is in the range of 1 to 3 days to keep the step (2). Further, for example, when the water temperature shown in (6B) is high, when the ASRT is shorter than 0.5 days (step (3)), the organic matter concentration may become too high. Moreover, when ASRT is longer than one day (step (1)), the nitrification concentration becomes too high. Therefore, the second liquid feed pump 18 is controlled so that the ASRT is in the range of 0.5 to 1 day to keep the step (2). Here, to give an example, the upper limit of the organic matter concentration is preferably an arbitrary value within the range of 1 to 3 mg / L (here, the maximum value does not exceed 3 mg / L). The upper limit of the nitrification concentration is preferably 3 mg / L. Therefore, it can be said that the ASRT control is a control in which the organic matter concentration does not exceed 3 mg / L and the nitrification concentration does not exceed 3 mg / L. Therefore, the control device 35 adjusts the amount of excess sludge drawn out by the second liquid feed pump 18 so that the organic matter concentration does not exceed 3 mg / L and the nitrification concentration does not exceed 3 mg / L. However, the range of organic matter concentration can be changed by the user, for example, to 2 to 5 mg / L. Similarly, the range of nitrification concentration can be changed by the user. It is also a preferable category to set both the upper limit of the organic matter concentration and the upper limit of the nitrification concentration to 5 mg / L. In this case, the control device 35 adjusts the amount of excess sludge drawn out by the second liquid feed pump 18 so that the organic matter concentration does not exceed 5 mg / L and the nitrification concentration does not exceed 5 mg / L.

Next, a method of calculating the amount of excess sludge withdrawn based on the above control concept will be described.

FIG. 7 shows a detailed flow of step S108 of FIG.

First, the excess sludge withdrawal amount determination unit 52 determines whether or not the value measured by the NH _4- N meter A32 is L _NH4-N or less (step S1081). As a result of the determination in step S1081, when the measured value ≤ L _NH4-N (discrimination result: Yes), the excess sludge extraction amount determination unit 52 sets _{Qes, n + 1} = _{Qes, n} and changes the extraction amount. Maintain without (step S1082). On the other hand, when the measurement value> L _NH4-N (discrimination result: No) as a result of the determination in step S1081, the first estimated BOD calculation value determination unit 48 determines whether or not the estimated BOD is H _BOD or more. Discrimination (step S1083). As a result of the determination in step S1083, when the estimated BOD ≥ H _BOD (discrimination result: Yes), the excess sludge extraction amount determination unit 52 sets Qes _{, n + 1} = _{Qes, n} * a (0≤a <1). ), The amount of withdrawal is reduced (step S1084). On the other hand, when the estimation BOD <H _BOD (discrimination result: No) as a result of the determination in step S1083, the second estimated BOD calculation value determination unit 49 determines whether or not the estimated BOD is _LBOD or less. (Step S1085). As a result of the determination in step S1085, when the estimated BOD is _LBOD or less (discrimination result: Yes), the first nitrification concentration calculation value determination unit 50 determines whether or not the nitrification concentration is H _{nitrification} or more (step S1086). ). As a result of the determination in step S1086, when the nitrification concentration ≥ H _{nitrification} (discrimination result: Yes), the excess sludge extraction amount determination unit 52 sets Qes _{, n + 1} = _{Qes, n} * b (1 << b). , The pull-out amount is increased (step S1087).

As a result of the determination in step S1085, when the estimated BOD> _LBOD (discrimination result: No), the second nitrification concentration calculation value determination unit 51 determines whether or not the nitrification concentration is H _{nitrification} or higher (step S1088). .. As a result of the determination in step S1088, when the nitrification concentration ≥ H _{nitrification} (discrimination result: Yes), the excess sludge extraction amount determination unit 52 sets Qes _{, n + 1} = _{Qes, n} * c (1 <c). The withdrawal amount is increased (step S1089). This amount of increase is smaller than in step S1087. Further, as a result of the determination in step S1086, even when the nitrification concentration <H _{nitrification} (discrimination result: No), the excess sludge extraction amount determination unit 52 sets Qes _{, n + 1} = _{Qes, n} * c (1 <c). ), Step S1089 is executed. On the other hand, as a result of the determination in step S1088, when the nitrification concentration <H _{nitrification} (discrimination result: No), the excess sludge extraction amount determination unit 52 sets Qes _{, n + 1} = _{Qes, n} and changes the extraction amount. Maintain without (step S1090). Following steps S1082, S1084, S1087, S1089 or S1090, the process proceeds to step S109 of FIG.

Next, the above flow will be described more specifically by exemplifying using numerical values.

For example, the capacity of the aerobic tank 14: 2500 m ³ , the residence time in the aerobic tank 14: 2 hr, the measured value of the flow meter A30a: 1250 m ³ / hr, the measured value of the flow meter B30b: 83 m ³ / hr, the flow meter C30c. Measured value: Set to 15 m ³ / hr. The flowmeter measurement value receiving unit 40 receives the measurement values (1250 m ³ / hr and 83 m ³ / hr and 15 m ³ / hr) from the flow meter A30a, the flow meter B30b, and the flow meter C30c (step S101). Subsequently, the tank inflow time calculation unit 43 measures the capacity (2500 m ³ ) of the aerobic tank 14 by adding the flow rate per unit time measured by the flow meter A30a and the flow rate per unit time measured by the flow meter B30b. The operation is performed by dividing by the value obtained by subtracting the flow rate per unit time measured by the flow meter C30c (1250 m ³ / hr + 83 m ³ / hr-15m ³ / hr = 1318m ³ / hr) (step S102). As a result, the inflow time in the tank can be calculated as 1.9 hr.

Next, the NH _4- N total measurement value reception unit 41 receives the measurement value of the NH _4- N total A32 before 1.9 hr and the measurement value of the NH _4- N total B33 at the current time (step S103). As a result, the measured value of the NH _4- N total A32 was 30 mg / L, and the measured value of the NH _4- N total B33 was 29.2 mg / L. Next, the nitrification concentration calculation unit 44 calculates the NH _4- N concentration difference in consideration of the tank inflow time (1.9 hr) (step S104). As a result of this calculation, the nitrification concentration is 0.8 mg / L (calculated as 30 mg / L-29.2 mg / L). The organic substance concentration meter measurement value receiving unit 42 receives the measured value (COD = 5 mg / L) from the organic substance concentration meter 34 (step S105). Next, the estimation BOD calculation unit 45 substitutes COD = 5 mg / L into the function f (x) = 0.1212 * exp (0.3539 * COD) for estimation BOD calculation, and sets the estimated BOD to 0. It is determined to be 7 mg / L (step S106). Next, the measured value / calculated value receiving unit 46 receives data necessary for determining the amount of excess sludge withdrawn including one or two or more of the measured value and the calculated value (step S107).

Now, _let L _NH4-N = 20 mg / L, H _BOD = 3 mg / L, L _BOD = 1 mg / L, and H _{nitrification} = 3 mg / L. The excess sludge withdrawal amount determination unit 52 determines whether or not the value (30 mg / L) measured by the NH _4- N meter A32 is L _NH4-N (20 mg / L) or less (step S1081). As a result, since the measured value by the NH _4- N total A32> L _NH4-N , the discrimination result becomes No, and the process proceeds to step S1083. Next, the first estimated BOD calculation value determination unit 48 determines whether or not the estimated BOD (0.7 mg / L) is H _BOD (3 mg / L) or more (step S1083). As a result, since the estimated BOD <H _BOD , the discrimination result becomes No, and the process proceeds to step S1085. Next, the second estimated BOD calculation value determination unit 49 determines whether or not the estimated BOD (0.7 mg / L) is _LBOD (1 mg / L) or less (step S1085). As a result, it is estimated BOD _{<L BOD,} the determination result is Yes, the process proceeds to step S1086. Next, the first nitrification concentration calculation value determination unit 50 determines whether or not the nitrification concentration (0.8 mg / L) is H _{nitrification} (3 mg / L) or more (step S1086). As a result, since the nitrification concentration <H _{nitrification} , the discrimination result becomes No, and the process proceeds to step S1089.

Now, let c = 1.05. The surplus sludge extraction amount determination unit 52 calculates Q _{es, n + 1} = Q _{es, n} * 1.05. Q _{es, n} is because it is _{^{83m 3 / hr, Q es,}} n + 1 becomes ^{83m 3 /hr*1.05=87m} 3 / hr. That is, excess sludge withdrawal amount determination unit 52 determines the amount of pull out the ^4m 3 / hr by more ^87m 3 / hr than ^83m 3 / hr (step S1089).

<Various features of each embodiment of the present invention>
FIG. 8 shows the features of each of the above embodiments of the present invention.

In the present embodiment, since the precipitation treatment using the coagulant is performed in the first precipitation space 12, more inflow water fouling substances and organic substances can be removed. As a result, clogging in the membrane separation device 15 can be reduced, so that the energy blown from the blower 16 for cleaning the membrane can be reduced. In addition, the frequency of cleaning the membrane with chemicals is reduced. Further, the amount of air exposed to the aerobic tank 14 (auxiliary aeration amount) can be reduced. These contribute to energy saving of the sewage treatment systems 1, 1a and 1b ((1) and (5) in FIG. 8). Further, since sludge is actively generated in the first settling space 12 and sludge from the aerobic tank 14 is also added by using the reverse pipe 19, resources used for digestion gas, organic fertilizer, etc. increase. ((7) in FIG. 8). Further, in the present embodiment, since the low MLSS operation is performed, fouling by microorganisms can be suppressed in the membrane separation device 15 ((2) in FIG. 8). In the present embodiment, since the short HRT operation (about 2 hours) is performed, the capacity of the aerobic tank 14 can be made smaller than before. Here, "HRT" means a hydraulic residence time. This contributes to saving the pace of the sewage treatment systems 1, 1a and 1b ((9) in FIG. 8).

The low MLSS operation and the low HRT operation result in a short ASRT operation, and as a result, the occurrence of autolysis fouling is suppressed and the nitrification reaction is suppressed. This contributes to energy saving of the blower 16 that sends air to the membrane separation device 15 and the aerobic tank 14 ((3) and (4) in FIGS. 8). In addition, the short ASRT operation leads to an increase in the amount of surplus sludge, so that the resources used for digestion gas, organic fertilizer, etc. increase ((8) in FIG. 8). Further, since the operation with a low dissolved oxygen concentration (DO) (low DO operation) can be realized, the oxygen dissolution rate can be improved, which contributes to the reduction of the amount of auxiliary air diffused ((6) in FIG. 8).

FIG. 9 shows a comparison between each embodiment of the present invention and the conventional membrane separation activated sludge method.

As shown in the two tables shown in each of the two stages of FIG. 9, each embodiment of the present invention has many features as compared with the conventional membrane separation activated sludge method. In the conventional membrane separation activated sludge method, no flocculant was used, and the initial deposition SS removal rate remained at 40 to 60%. In addition, the excess sludge generation rate is as low as 0.6 to 0.8 times, and an operation method that does not generate excess sludge as much as possible has been carried out. The conventional HRT was as long as about 6 hr, and the MLSS concentration was as high as 8000 to 12000 mg / L. Furthermore, the DO concentration was relatively high at 1 to 2 mg / L, and the required ventilation ratio for biological treatment was as high as about 5 times. The blast magnification is a required blast magnification when the oxygen dissolved by the membrane cleaning air is not taken into consideration. In addition, since the nitrification reaction was actively carried out and denitrification was performed using an oxygen-free tank, the entire reaction tank was large. In addition, a nitrifying liquid circulation pump was needed to send nitrate ions from the aerobic tank to the anoxic tank.

On the other hand, in the present embodiment, a flocculant is used to increase the initial deposition SS removal rate to 70% by mass or more, and more realistically to the range of 70 to 90% by mass. The surplus sludge generation rate is not reduced but rather increased (2 to 4 times compared to the conventional 0.6 to 0.8 times). A major feature is that the HRT is as short as 1 to 2 hours and the MLSS concentration is as low as 750 to 4000 mg / L. The DO concentration is 0.5 to 1 mg / L, which is lower than the conventional value (1 to 2 mg / L). The required ventilation ratio for biological treatment is much lower than before, and is 1 to 3 times. As a result, the energy required for the blower 16 can be reduced, and the sludge treatment systems 1, 1a and 1b can be operated at an extremely low cost. Moreover, since the nitrification reaction is suppressed, the oxygen-free tank and the nitrification liquid circulation pump become unnecessary.

<Other Embodiments>
Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-described embodiments and can be applied to various other aspects.

Instead of the air blown from the blower 16 into the aerobic tank 14, a gas containing oxygen at a higher concentration or a lower concentration than the air may be used. That is, the gas blown from the blower 16 into the aerobic tank 14 is not limited to air as long as it is a gas containing oxygen. The air volume of the blower 16 is preferably in the range of 1 to 3 times, but is preferably close to 1 time, in the required air blowing ratio (air blowing amount / treated water amount) for biological treatment. The chlorine mixing pond 17 as a disinfection tank may be in the form of a tank as well as a civil engineering skeleton. Further, in each of the above embodiments, the first precipitation space 12 is used as an example of the product recovery space, but as a product recovery method other than precipitation, for example, the filtration space that employs filtration is replaced with the first precipitation space 12. You may be prepared.

The second liquid feed pump 18 may be operated so as to continuously send excess sludge from the aerobic tank 14 to the first settling space 12, or the second liquid feed pump 18 may be operated intermittently (every hour, 1). . May be every 5 hours or every 2 hours). It is preferable that the operation of the second liquid feed pump 18 is precisely controlled by using various sensors 30a to 34 as described in the second embodiment, but the operating conditions can be known in advance depending on the conditions such as the season or the weather. In this case, the second liquid feeding pump 18 may be operated with a fixed liquid feeding amount without using the various sensors 30a to 34. Even in that case, the liquid feed amount of the second liquid feed pump 18 is preferably set so that both the organic substance concentration and the nitrification concentration are within a predetermined allowable range.

When the second liquid feed pump 18 is precisely controlled by using various sensors 30a to 34, the liquid feed amount per unit time (unit is, for example, m ³ / hr) by the second liquid feed pump 18 is membrane separation. The concentration of organic matter in the liquid passing downstream through the device 15 is controlled so as not to be too high and not too low, and the nitrification concentration in the aerobic tank 14 is not too high. The absolute value of the liquid feed amount of the second liquid feed pump 18 does not have a great meaning. This is because the liquid feed amount varies depending on various conditions such as the capacity of the aerobic tank 14 and the inflow amount of sewage per unit time. The liquid feed amount of the second liquid feed pump 18 is controlled so that both the organic substance concentration and the nitrification concentration are within an allowable range. The permissible range of the organic substance concentration is preferably 1 to 3 mg / L or 2 to 5 mg / L, and any other value within the range of 0 to 1 mg / L, 0 to 2 mg / L, and 1 to 2 mg / L can be used. You may set it. The allowable range of nitrification concentration is preferably 0 to 5 mg / L, more preferably 1 to 3 mg / L, 0 to 1 mg / L, 0 to 2 mg / L, and 1 to 2 mg / L. Is.

The organic substance concentration meter 34 is preferably a chemical oxygen demand measuring meter (COD meter), but may be a total organic carbon amount measuring meter (TOC meter) or an ultraviolet absorbance meter (UV meter). Instead of the gravity concentrating tank 20, a mechanical concentrator as described above may be adopted. The initial precipitation space 12 is preferably a place where 70% by mass or more of the substance to be aggregated in the sewage flowing into the precipitation space 12 is precipitated, but it may be 70 to 90% by mass or 80 to 90% by mass.

The present invention can be used for wastewater treatment.

1,1a, 1b Sewage treatment system 12 First settling space (example of product recovery space)
14 Aerobic tank 15 Membrane separation device 16 Blower 17 Chlorine mixing pond (an example of disinfection tank)
18 Second liquid feed pump (reverse pump)
19 Reverse piping 20 Gravity concentration tank (an example of concentration space)
30a Flowmeter A (1st flowmeter)
30b Flowmeter B (second flowmeter)
30c flow meter C (third flow meter)
32 NH _4- N meter A (1st ammonia nitrogen concentration meter)
33 NH _4- N meter B (second ammonia nitrogen concentration meter)
34 Organic matter densitometer (chemical oxygen demand meter, total organic carbon meter, ultraviolet absorbance meter, etc.)
35 Control device

Claims (5)

A product recovery space for recovering the substance to be aggregated as a product from a mixture containing sewage and a coagulant for aggregating the substance to be aggregated in the sewage, and an organic substance in the sewage that has undergone recovery treatment in the product recovery space. An aerobic tank for decomposing using activated sludge in the presence of oxygen,
A blower that can blow air into the aerobic tank and blows air necessary for biological treatment by microorganisms in the activated sludge.
A membrane separation device for solid-liquid separation of solids and liquids in the aerobic tank,
A reverse pipe that returns excess sludge existing in the aerobic tank to the product recovery space with a reverse pump, and
A control device that controls the reverse pump and
With
The control device reverses the aerobic solids so that the residence time is within the range of 0.5 to 1 day under the condition of water temperature of 25 ° C. and within the range of 1 to 3 days under the condition of water temperature of 15 ° C. Septic systems that adjust the pulling amount of the excess sludge by the pump. A first flow meter for measuring the flow rate of sewage flowing through the upstream side of the pipe before the SL product recovery space,
A second flow meter for measuring the flow rate of the excess sludge flowing through the reverse pipe, and
A third flow meter for measuring the flow rate of sludge flowing between the product recovery space and the concentration space for sending sludge collected from the product recovery space, and
A first ammonia nitrogen concentration meter for measuring the ammonia nitrogen concentration of the sewage flowing between the product recovery space and the aerobic tank, and
A second ammonia nitrogen concentration meter for measuring the ammonia nitrogen concentration of the liquid downstream from the outlet of the membrane separation device, and
An organic substance concentration meter for measuring the organic substance concentration of the liquid downstream from the outlet of the membrane separation device, and
With
The control device is
The NH _4- N meter measurement value determination unit for determining whether or not the value measured by the first ammonia nitrogen concentration meter is equal to or less than the lower limit of the ammonia nitrogen concentration in sewage .
A first estimated BOD calculation value determination unit for determining whether or not the estimated BOD calculated from the measured value from the organic matter densitometer is equal to or higher than the upper limit value of the estimated BOD.
A second estimated BOD calculation value determining unit for determining whether or not the estimated BOD is equal to or less than the lower limit of the estimated BOD,
When the estimated BOD is equal to or less than the lower limit of the estimated BOD, the nitrification concentration calculated by subtracting the NH _4- N concentration at a predetermined time from the NH _4- N concentration before the inflow time into the tank is the nitrification concentration. The first nitrification concentration calculation value determination unit that determines whether or not it is equal to or higher than the upper limit value,
When the estimated BOD exceeds the lower limit of the estimated BOD, the second nitrification concentration calculation value determination unit for determining whether or not the nitrification concentration is equal to or higher than the upper limit of the nitrification concentration,
The NH _4- N meter measurement value discrimination unit, the first estimated BOD calculation value discrimination unit, the second estimated BOD calculation value discrimination unit, the first nitrification concentration calculation value discrimination unit, and the second nitrification concentration calculation value discrimination unit. Excess sludge extraction amount determination unit that determines the amount of excess sludge extracted from the aerobic tank based on the various discrimination results of
Including
The excess sludge withdrawal amount determination unit
When the value measured by the first ammonia nitrogen concentration meter is equal to or less than the lower limit of the ammonia nitrogen concentration, or
The value measured by the first ammonia nitrogen concentration meter exceeds the lower limit of the ammonia nitrogen concentration, the estimated BOD is less than the upper limit of the estimated BOD and exceeds the lower limit, and the nitrification concentration is the upper limit of the nitrification concentration. If it is less than the value, maintain the withdrawal amount and
When the value measured by the first ammonia nitrogen concentration meter exceeds the lower limit of the ammonia nitrogen concentration and the estimated BOD is equal to or more than the upper limit of the estimated BOD, the extraction amount is reduced.
When the value measured by the first ammonia nitrogen concentration meter exceeds the lower limit of the ammonia nitrogen concentration, the estimated BOD is less than the upper limit of the estimated BOD and less than or equal to the lower limit, or the estimated BOD. The first aspect of claim 1, wherein the drawing amount is determined to be increased when the amount is less than the upper limit of the estimated BOD and exceeds the lower limit and the nitrification concentration is equal to or higher than the upper limit of the nitrification concentration. Sewage treatment system. The sewage treatment system according to claim 2 , wherein the organic matter concentration meter is at least one of a chemical oxygen demand meter, a total organic carbon meter, and an ultraviolet absorbance meter. The sewage treatment according to any one of claims 1 to 3 , wherein the product recovery space recovers 70% by mass or more of the substance to be aggregated in the sewage flowing into the space. system. A sewage treatment method using the sewage treatment system according to claim 1.
Before filling the product recovery space with sewage, a coagulant charging step of adding a coagulant to the sewage and
In the product recovery space, a recovery step of recovering an object to be aggregated from a mixture of sewage and a coagulant, and a recovery step.
An aerobic tank liquid feeding step of feeding the recovered sewage from the product recovery space to the aerobic tank,
An aeration step of blowing air into a mixture of the sewage and activated sludge in the aerobic tank,
A purification treatment step of performing a purification treatment including at least a treatment of decomposing organic matter in the sewage sent into the aerobic tank using the activated sludge in the aerobic tank.
A solid-liquid separation step of solid-liquid separating a mixture of a solid and a liquid in the aerobic tank with the membrane separation device.
The excess sludge reverse step of returning the excess sludge in the aerobic tank to the product recovery space by the reverse pump by the reverse piping, and
Only including,
In the excess sludge reverse step, using the control device that controls the reverse pump, the aerobic solid matter residence time is in the range of 0.5 to 1 day under the condition of water temperature 25 ° C., and 1 under the condition of water temperature 15 ° C. A sewage treatment method for adjusting the amount of excess sludge drawn out by the reverse pump so as to be within the range of ~ 3 days .

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