Microbial reaction tanks and wastewater treatment processes.

Abstract

DC60 (05 / 09 / 57) What was revealed was a microbial reaction tank and the wastewater treatment process that uses that, which... Treatment with anaerobic / oxygen-requiring microorganisms can continue even if the tank capacity is exceeded. Although the reaction will be larger, it can also reduce construction costs by including an internal tank. The outer tank (2) and the inner cylindrical tank (3), which have upper and lower openings, are positioned inside the inner tank. In addition, there is a circulation control device (4) which controls the circulation rate within the tank of treated water. It is installed on top of the inner cylinder of this tank, along with cylinder control plate 5, which is installed. Place it around the outer top of the inner cylindrical tank to allow the sediment to settle. Water quality monitoring devices6, which are installed on the outside and inside of the cylindrical inner tank. And, there are 10 wastewater outlets installed in the recirculation path of the treated water that circulates in the tank. The outer and inner tanks, and the treated water discharge port 11, are installed on top of the outer tank.

Description

This invention relates to a microbial reactor and a wastewater treatment method. Wastewater containing high concentrations of pollutants such as nitrogen, phosphorus, and organic matter, which increase biochemical oxygen demand (BOD) and suspended solids (SS), is a cause of environmental pollution, including river contamination and red tide outbreaks. Conventionally, the so-called modified Barnard process, a type of aerobic-anaerobic circulation method, has been known as a method for treating wastewater containing such high concentrations of pollutants. In this method, in order to reuse the alkali released during the denitrification reaction in the nitrification reaction, the denitrification process in the activated sludge treatment process is divided into two stages: a first denitrification tank and a second denitrification tank located before and after the first nitrification tank, and a second nitrification tank is placed after the second denitrification tank, and the mixed liquid flowing out from the first and second nitrification tanks is circulated back to the first denitrification tank. However, this method of wastewater treatment has the following problems: (1) High concentrations of ammoniacal nitrogen have bactericidal properties themselves, and often inhibit the activity of activated sludge in the activated sludge treatment process. As a result, the activated sludge treatment becomes insufficient. (2) In so-called modified Barnard processes, the hydrogen ion concentration (hereinafter referred to as pH) decreases as the nitrification reaction progresses in the nitrification tank, but since the nitrification reaction depends on pH, the nitrification reaction slows down when the pH decreases. As a result, the activated sludge treatment becomes insufficient, and the removal of phosphorus, etc., also becomes insufficient. (3) If the activated sludge treatment is insufficient and the denitrification reaction slows down, the concentrations of residual ammonia, nitrate ions, nitrite ions, etc. increase, resulting in a high BOD that depends on these nitrogen compounds, and the wastewater treatment becomes insufficient. (4) In wastewater containing high concentrations of pollutants, high concentrations of activated sludge are required, and inevitably the concentration of activated sludge suspended solids (hereinafter referred to as MLSS) tends to be high. Therefore, oxygen supply becomes difficult, as does the stirring of activated sludge and solid-liquid separation in the sedimentation tank. (5) When denitrification and denitrification are performed by activated sludge treatment on wastewater that has a high nitrogen content despite a low concentration of organic pollutants, problems such as pH decrease and sludge floating due to denitrification occur. To address the above-mentioned methods, the present inventors have proposed a microbial reaction tank and a wastewater treatment method using the same that can efficiently treat activated sludge in wastewater containing high concentrations of nitrogen components, phosphorus components, organic substances, and other pollutants (Patent Document 1). This microbial reaction tank has an inner tank having a nitrification reaction section and a denitrification reaction section connected vertically by turbine blades. Japanese Patent Application Publication No. 11-128987 However, in the conventional microbial reaction vessel described above, the anaerobic tank where denitrification occurs, formed at the bottom of the inner tank, and the aerobic tank where nitrification occurs, formed at the top of the inner tank, were connected only by turbine blades. As the capacity of the reaction vessel increased, stirring in each tank became insufficient, resulting in problems such as inadequate progress of the anaerobic or aerobic reaction. In addition, there were problems such as high construction costs for the reaction vessel and high costs for fixing the inner tank within the outer tank. This invention was made to address these problems, and aims to provide a microbial reaction tank and a wastewater treatment method using the same that can efficiently treat activated sludge in wastewater containing high concentrations of pollutants, can continuously perform anaerobic and aerobic microbial treatment while maintaining a high internal circulation rate even when the reaction tank capacity is large, and can reduce construction costs. The microbial reaction tank of the present invention comprises an outer tank, a cylindrical inner tank disposed inside the outer tank and having openings at the top and bottom, a circulation rate control device provided at the top of the cylindrical inner tank for controlling the circulation rate of the treated water within the tank, a cylindrical control plate provided on the outer circumference of the top of the cylindrical inner tank for settling sludge, a treated water quality measuring device provided on the outside and inside of the cylindrical inner tank, and a raw water supply port provided in the circulation path of the treated water circulating within the outer tank and inner tank, and a treated water discharge port provided at the top of the outer tank. The cylindrical inner tank constituting the microbial reaction tank is divided into an upper cylindrical part and a lower cylindrical part by a partition wall having a communication hole in the center. The upper cylindrical part is an aerobic microbial treatment tank having a frustoconical shape with open top and bottom surfaces at its apex, and having a plurality of air inlets provided around the communication hole inside the upper cylindrical part and around the periphery of the partition wall. The lower cylindrical part is an anaerobic microbial treatment tank having an opening at its bottom, and is provided with a stirring device for stirring the inside of the aerobic microbial treatment tank and the inside of the anaerobic microbial treatment tank. The microbial reaction tank includes means for detecting at least one measurement value selected from the pH, oxidation-reduction potential (hereinafter referred to as ORP), and dissolved oxygen content (hereinafter referred to as DO) of the water to be treated, as measured by the water quality measuring device described above, and means for controlling the circulation rate of the water to be treated in the tank to 3 to 20 by controlling at least one amount selected from the opening and closing of a liquid level adjustment valve, the vertical movement of a liquid level adjustment control plate, and the amount of air blown in from the air inlet, provided in the circulation rate control device described above, according to the detected measurement value. Here, the circulation rate of the water to be treated in the reaction tank refers to the amount defined by the following formula. The treated water circulation rate = Amount of treated water discharged from the top of the inner tank (m³ / day) / Amount of raw water supplied (m³ / day) The microbial reaction tank is characterized in that anaerobic and aerobic microbial treatment is continuously performed by circulating the raw water supplied from the raw water supply port together with activated sludge through the inside of the cylindrical inner tank, the outer surface of the cylindrical inner tank, and the activated sludge settled at the bottom of the outer tank. In particular, the raw water supply port is characterized in that it is a plurality of discharge ports or slits provided in an annular raw water supply section located at the bottom of the opening of the anaerobic microbial treatment tank. Furthermore, the lower part of the cylinder is characterized in that it has a volume of 1 / 10 to 1 times that of the upper part of the cylinder. The wastewater treatment method of the present invention is a wastewater treatment method for treating raw water by a treatment process including an activated sludge treatment process. The activated sludge treatment process includes a sludge circulation process for forming a circulating flow of activated sludge and a raw water addition process for adding raw water into the circulating flow of the activated sludge. The circulating flow of the activated sludge circulates from an anaerobic microorganism treatment tank through an aerobic microorganism treatment tank disposed above the anaerobic microorganism treatment tank, and treated water is separated at a sludge precipitation portion formed on the outer peripheral surface of the aerobic microorganism treatment tank and sludge concentration is performed, and this concentrated sludge is sent to the anaerobic microorganism treatment tank. The activated sludge treatment process is characterized by being a sludge circulation process and a raw water addition process that are treated using the above-described microorganism reaction tank. Since the microorganism reaction tank of the present invention has a cylindrical inner tank disposed inside divided into a cylindrical upper part and a cylindrical lower part by a partition wall having a communication hole at the center, anaerobic and aerobic microorganism treatment of raw water containing a high concentration of pollutants can be continuously performed while maintaining a high tank internal circulation rate. In addition, since the cylindrical inner tank can have a simple shape, installation of the microorganism reaction tank becomes easy even if the capacity of the reaction tank increases. The wastewater treatment method of the present invention has the following superior features compared to conventional wastewater treatment methods. Conventional wastewater treatment methods involve mixing raw water and return sludge in a fixed ratio and flowing into an aeration tank. The raw water is pushed out and flows through a process in which the same activated sludge bacteria come into contact with the return sludge that came into contact with the raw water until the sludge and the water to be treated are separated in the next step, a sedimentation tank, and the activated sludge and raw water that were initially mixed come into contact with the raw water until the water is discharged. The wastewater treatment method of the present invention involves forming a circulating flow of activated sludge that circulates vertically and adding raw water to this circulating flow. This method is energy-saving because it does not use a circulation pump to create the circulating flow of activated sludge, but instead utilizes the upward flow of aerated air used for microbial treatment to form the sludge circulating flow. Furthermore, it is a treatment method that allows for efficient aeration of the aerobic microbial treatment tank. The raw water can be added anywhere within the path of the circulating flow, but preferably in the aerobic microbial treatment tank. More preferably, an anaerobic microbial treatment tank is suitable. In the wastewater treatment method of the present invention, when treatment is performed using a circulating flow, even if the raw water has a BOD of at least 800 mg / L and a total nitrogen content (hereinafter referred to as T-N) of 40 mg / L or more, the BOD of the treated water is usually extremely low, at 20 mg / L or less, and generally, operation is possible with a BOD of 10 mg / L or less for the effluent water quality. However, if raw water is added to the sludge sedimentation section in the circulating flow path formed on the outer surface of the cylindrical inner tank, which is an aerobic microbial treatment tank, contact between the sludge and the raw water may become insufficient, resulting in insufficient adsorption of pollutants. In that case, some untreated pollutants from the raw water may be mixed into the treated water, leading to deterioration of the treated water. However, in cases where water quality regulations are lax, for example, in primary treatment facilities such as those for sewage discharge where the BOD is 300 mg / L or less or 600 mg / L or less, raw water may be added to the sludge sedimentation section in the circulating flow path. This is a cross-sectional view of a microbial reaction tank. This diagram shows the circulation pathway of the treated water and activated sludge in the microbial reaction tank. The microbial reaction tank of the present invention will be explained with reference to Figure 1. Figure 1 is a cross-sectional view of the microbial reaction tank. The microbial reaction tank 1 consists of an outer tank 2, a cylindrical inner tank 3 located inside the outer tank 2, a circulation rate control device 4 provided at the top of the cylindrical inner tank 3, a cylindrical control plate 5 provided on the outer circumference of the cylindrical inner tank 3, a water quality measuring device 6, a raw water supply port 10 provided in the circulation path of the water to be treated circulating within the outer tank 2 and inner tank 3, and a treated water discharge port 11 provided at the top of the outer tank 2. A sludge extraction port 13 can also be provided. The present invention does not limit the volume of the water tank of the microbial treatment equipment and can be applied to small-scale to large-scale systems, but its effects are most significantly demonstrated when the microbial reaction tank 1 has an internal volume of 20 m3 or more, preferably 30 to 6000 m3. When the volume of the treatment tank exceeds 6000 m3, it becomes difficult to create a circulating flow. Furthermore, in the case of small-scale systems with volumes less than 20 m³, the advantages of circulating the sludge vertically within the microbial reaction tank 1 become less significant. The outer tank 2 has a cylindrical appearance consisting of a base 2a that forms the bottom, cylindrical sides 2b, and a top surface 2c. A rotating shaft 7 for attaching agitators and the like is provided at the center of the cylinder. This rotating shaft 7 is rotatably fixed by a frame 2d provided at the center of the base 2a and a bearing 2e provided at the center of the top surface 2c. The rotating shaft 7 is also rotated by a drive device 2f. The top surface 2c rotatably fixes the rotating shaft 7 and also holds the cylindrical inner tank 3 with a support or the like. A raw water supply port 10 is provided at the bottom of the outer tank 2. The raw water supply port 10 consists of multiple discharge ports 10b or slits provided in an annular raw water supply section 10a located below the lower opening 3f of the cylindrical inner tank 3. By arranging the raw water supply port 10 in this way, the anaerobic sludge is sufficiently stirred. Note that this raw water supply port 10 can be provided anywhere other than the bottom of the cylindrical inner tank 3, as long as it is part of the circulation path of the water to be treated. Furthermore, a treated water outlet 11 is provided at the top of the outer tank 2, and a sedimentation and solidification prevention device 12 is provided on the inner surface of the outer tank to prevent the settled sludge from settling and becoming fixed. The cylindrical inner tank 3, which has a nearly circular cross-section, is divided into an upper cylindrical section 3c and a lower cylindrical section 3d by a partition wall 3a. A communication hole 3b is provided in the center of the partition wall 3a, connecting the upper cylindrical section 3c and the lower cylindrical section 3d. Due to the presence of this partition wall 3a, even when the volume of the microbial reaction tank increases, the upper cylindrical section 3c and the lower cylindrical section 3d are sufficiently separated, and activated sludge treatment can be carried out in each tank. Aerobic microbial treatment reactions can be carried out sufficiently in the upper cylindrical section 3c, and anaerobic microbial treatment reactions can be carried out sufficiently in the lower cylindrical section 3d. If the area of ​​the partition wall 3a increases, it is reinforced with a support member 3g or the like. The communication hole 3b has a diameter large enough for the anaerobic microbially treated activated sludge to move from the lower cylindrical section 3d to the upper cylindrical section 3c, which is the aerobic microbial treatment tank. The diameter of this communication hole 3b is adjusted according to the volume of the microbial reaction tank, the properties and amount of raw water to be treated, etc. The upper cylindrical part 3c has a frustoconical apex with open top and bottom surfaces. That is, the tip of the cylindrical part is shaped to narrow in diameter at a predetermined angle in the height direction. The inclination angle of the cross-section in the height direction passing through the center of the frustoconical shape is 40 to 60 degrees, preferably 45 degrees. By setting the inclination angle within this range, the sludge contained in the water to be treated discharged from the upper part of the aerobic tank flows down the outer surface of the frustoconical shape, making it easier for the sludge to coagulate and enabling rapid forced sedimentation of the sludge. Furthermore, the coagulation of the sludge makes it easier to separate the sludge from the purified treated water. The upper cylindrical part 3c is an aerobic microbial treatment tank with air inlets 8 and 8a provided inside. The air inlets 8 are located around the central axis 7 and around the communication hole 3b, and can be fixed on the partition wall 3a by support columns or the like (not shown). It is preferable that the air outlet of the air inlets 8 is positioned downwards, as this contributes to the stirring of the water to be treated and the sludge in the aerobic tank. The air inlet 8a can be an air inlet 8b arranged in a circular pattern in plan view on the surface or above the partition wall at the periphery of the partition wall inside the upper part 3c of the cylinder, with multiple air holes 8c provided in the air inlet 8b, or a slit formed on the surface of the air inlet 8b, preferably on the lower surface. The amount of air blown in from the air inlets 8 and 8a and the control amount of the circulation rate control device described later can be varied within the range of 3 to 20 without using a circulation pump. This makes it easy to set appropriate nitrification conditions for aerobic microbial treatment and appropriate denitrification conditions for anaerobic microbial treatment. Furthermore, since the solid-liquid separation of sludge is performed very efficiently by the forced sedimentation principle on the outer surface of the aerobic microbial treatment tank having the above-mentioned inclination angle, the aerobic and anaerobic microbial treatment reactions can be efficiently carried out in the same vertical tank. Note that an alkali supply port or an acid supply port, not shown in the figure, can be provided in the aerobic tank. The lower cylindrical section 3d is an anaerobic microbial treatment tank having a volume of 1 / 10 to 1 times that of the upper cylindrical section. Within this volume range, for example, aerobic and anaerobic microbial treatment reactions can be efficiently carried out on raw water containing high concentrations of nitrogen-containing pollutants. A denitrifying microbial nutrient supply port (not shown in the figure) can be provided in the anaerobic microbial treatment tank. Furthermore, when there are few hydrogen donors in the raw water and denitrification is performed by supplying hydrogen donors such as methanol or acetic acid to remove nitrogen from nitrates, it is preferable to make the volume of the anaerobic microbial treatment tank larger than that of the aerobic microbial treatment tank. The shape of the lower cylindrical section 3d is an inverted truncated cone shape with an opening 3f at the bottom of the cylinder that has a larger area than the opening 3e of the upper cylindrical section 3c. That is, the tip of the cylindrical section narrows in diameter at a predetermined angle downwards. By increasing the area of ​​the opening 3f, the stirring of sludge in the anaerobic microbial treatment tank can be facilitated. When the shape of the lower part 3d of the cylinder is the inverted truncated cone shape described above, it is preferable that the lower inner surface 2g of the outer tank 2 be at the same angle as the predetermined angle described above, in order to prevent the sludge from settling and becoming fixed. The cylindrical inner tank 3 is equipped with a stirring device to ensure sufficient treatment reaction between the water to be treated and the activated sludge in the aerobic microbial treatment tank (upper cylindrical part 3c) and the anaerobic microbial treatment tank (lower cylindrical part 3d). The stirring device is preferably a stirring blade 7a or 7b fixed to a rotating shaft 7 attached to the center of the cylindrical inner tank 3. The stirring blade 7a is provided in the upper cylindrical part 3c and is preferably a turbine blade capable of ensuring sufficient aerobic microbial treatment reaction. In addition to a turbine blade, any blade that can mix air and water with a relatively low rotational speed and does not significantly reduce aeration performance depending on the amount of air blown in can be used. The stirring blade 7b is provided in the lower cylindrical part 3d and can be any stirring blade capable of ensuring sufficient anaerobic microbial treatment reaction, but a turbine blade or propeller blade is preferred. The partition wall 3a located inside the cylindrical inner tank 3 is supported by support columns 9 that are fixed to and erected on the base 2a which forms the bottom surface of the outer tank 2. The cylindrical inner tank 3 is held inside the outer tank by the support of these support columns 9 and by a support device that bridges across the upper part of the outer tank 2. A circulation rate control device 4 is provided at the top of the cylindrical inner tank 3 to control the circulation rate of the treated water within the reaction tank. Specifically, the circulation rate of the treated water within the reaction tank is controlled by the circulation rate control device 4 by opening and closing a liquid level adjustment valve or by moving a liquid level adjustment plate up and down. The water level of the treated water is lowest when the liquid level adjustment valve is fully open or when the liquid level adjustment plate is at its lowest position. The water level is indicated by A. The circulation rate within the reaction tank can also be controlled by the amount of air blown in from the air inlet 8 and / or 8a. Increasing the amount of air blown in increases the circulation rate. It is also possible to combine opening and closing the liquid level adjustment valve and adjusting the amount of air. As anaerobic and aerobic microbial treatment tanks become larger, aeration air alone may not be sufficient to maintain the sludge circulation flow rate, or problems may occur due to excessive air blowing. To prepare for such cases, the air inlet shown in 8a of Figure 1 is necessary. This air inlet 8a, which has poor aeration efficiency, has the advantage of making it much easier to adjust the air injection volume and ORP. For example, the air inlet 8a is located on the aerobic portion of the upper surface of the partition wall 3a, with the stirring blade 7a at its center, and an annular air injection section 8b in plan view that communicates with an external blower or the like, and holes or slits are provided in this air injection section 8b. This not only simply increases the amount of air, but also exerts the baffling effect of the stirring blade 7a, resulting in a synergistic effect that enables efficient stirring. The circulation rate of the treated water can be varied without using a pump by opening and closing the liquid level adjustment valve and / or adjusting the amount of air injected. As described later, the treated water is circulated from the aerobic microbial treatment tank 3c through the cylindrical control plate 5 located outside this tank to the anaerobic microbial treatment tank 3d, and then from the anaerobic microbial treatment tank 3d back to the aerobic microbial treatment tank 3c, thereby performing denitrification, dephosphorization, etc. Therefore, by controlling the circulation rate of the treated water according to the detected value based on a predetermined control program, optimal denitrification, dephosphorization, etc., can be performed. A cylindrical control plate 5 is positioned on the upper outer circumference of the cylindrical inner tank 3. The cylindrical control plate 5 is a cylinder with openings on its top and bottom surfaces, and the bottom surface 5a of the cylindrical control plate 5 is positioned close to the inclined surface of the cylindrical inner tank 3. A sludge sedimentation section is formed in this close-proximity portion of the inclined surface, where sludge concentration occurs and treated water is separated. Furthermore, by positioning the bottom surface 5a close, rapid forced sedimentation of the sludge becomes possible. It is preferable that the distance of the bottom surface 5a from the inclined surface of the cylindrical inner tank 3 can be adjusted. The shape of the cylindrical control plate 5 can be a straight cylinder with the same area of ​​openings on the top and bottom surfaces, or an inverted truncated cone shape where the opening area of ​​the top surface is larger than the opening area of ​​the bottom surface. Inside the microbial reaction tank, a water treatment quality measuring device 6 is provided both inside and outside the cylindrical inner tank 2. This water treatment quality measuring device 6 is a device that measures the pH, ORP, and DO of the water to be treated. The water circulation rate in the microbial reaction tank of the present invention is 3 to 20, preferably 5 to 20. If the water circulation rate is less than 3, the aerobic microbial treatment reaction will occur more easily, and if it exceeds 20, the balance between the aerobic and anaerobic microbial treatment reactions will be disrupted, making it impossible to denitrify and dephosphorize the raw water. In other words, by setting the water circulation rate within this range, the ORP of the water to be treated, as measured by the water quality measuring device, can be maintained at -10 mV or less, preferably -50 mV or less, in the anaerobic microbial treatment reaction tank, and at +10 mV or more, preferably +100 mV or more, in the aerobic microbial treatment reaction tank. As a result, the aerobic and anaerobic microbial treatment reactions are carried out sufficiently, and denitrification and dephosphorization are performed continuously. Under these conditions, the pH in the aerobic microbial treatment reaction tank is in the range of 4.5 to 8.5, preferably 5.5 to 7.5. The wastewater treatment method using the microbial reaction tank 1 will be described below with reference to Figure 2. Figure 2 is a diagram showing the circulation pathway of the water to be treated and activated sludge in the microbial reaction tank 1. In Figure 2, the shaded area represents a region with a high concentration of activated sludge, and the arrows indicate the circulation direction of the water to be treated and activated sludge. The raw water to be treated, which contains pollutants from which solid components have been separated by a wedge wire screen or the like, is continuously supplied from the raw water supply port 10 located at the bottom of the microbial reaction tank 1. It is preferable to measure the BOD and SS of the supplied raw water in advance. The wastewater treatment method using the microbial reaction tank 1 of the present invention is suitable for treating wastewater discharged from food factories, and suitable raw water for this purpose is, for example, raw water containing a BOD of 800 mg / L or more, a chemical oxygen demand (hereinafter referred to as COD) of 300 mg / L or more, and T-N of 40 mg / L or more. It is also suitable for treating raw water containing a n-hexane extractable oil concentration (hereinafter referred to as n-Hex) in the range of 50 mg / L or more. The microbial reaction tank 1 contains activated sludge at a concentration of 5,000 to 12,000 mg / L in terms of solid content. Raw water first comes into contact with the activated sludge in an anaerobic state within the lower part of the cylinder 3d, where a denitrification reaction takes place. The raw water to be treated, supplied from the raw water supply port 10, and the circulating activated sludge are circulated within the lower part of the cylinder 3d by the rotation of the stirring blades or the ejection of air from the diffuser pipes, where an anaerobic microbial treatment reaction takes place. Next, the raw water and activated sludge move through the communication holes 3b to the upper part of the cylinder 3c, where air is blown in. In an aerobic state, they come into contact with the activated sludge in the upper part of the cylinder 3c, and circulate within the upper part of the cylinder 3c by the rotation of the stirring blades or the ejection of air from the air inlet, where an aerobic microbial treatment reaction, the nitrification reaction, proceeds. As the nitrification reaction progresses, the pH of the treated water decreases. The pH, ORP, and DO of the treated liquid are measured by the treated water quality measuring device 6, and the circulation rate of the raw water or treated water is determined based on these values. Specifically, the treated water is circulated by adjusting the amount of air injected, etc., so that the ORP is maintained at +10 mV or higher in the aerobic reaction tank where nitrification occurs, and at -10 mV or lower in the anaerobic reaction tank where denitrification occurs. The circulation rate can be easily controlled by controlling the air volume and / or circulation rate control device without using a circulation pump or the like. For this reason, the wastewater treatment method of the present invention is an energy-saving wastewater treatment method. Furthermore, since each unit of the microbial reaction in the equipment including the microbial reaction tank of the present invention can be adjusted individually, it is easy to pre-program these controls and operate them automatically without human intervention, thus possessing the characteristics of a labor-saving plant. The circulation rate is controlled by the circulation rate control device 4, and a portion of the treated water and activated sludge discharged from the top of the cylindrical upper part 3c flows down the frustoconical outer surface which has a 45-degree inclination angle. This discharged treated water and activated sludge passes through the cylindrical control plate 5, which is positioned close to the inclined surface of the frustoconical outer surface, and the sludge concentration section 5b formed by the inclined surface, enabling rapid forced settling of the activated sludge. This also facilitates the separation of the purified treated water and activated sludge, and the separated treated water is discharged from the treated water outlet 11. The rapidly forced-settling activated sludge concentrates and accumulates between the inner surface of the outer tank and the outer surface of the inner tank. This accumulated activated sludge moves to the anaerobic microbial treatment reaction section while mixing with the treated water and circulates within the microbial reaction tank. The wastewater treatment method of the present invention can easily absorb fluctuations in the load of raw water by circulating the activated sludge within the anaerobic / aerobic tank at a circulation rate of 3 to 20 while it is concentrated. Furthermore, by maintaining the circulation rate within this range, the activated sludge is acclimated and becomes optimal for wastewater treatment. In a microbial reaction tank, if the nitrogen concentration is high despite a low BOD load of the raw water, it is preferable to add denitrifying microbial nutrients, such as methanol, which consists of organic substances like proton donors, to the anaerobic reaction tank for treatment. In this case, since the pH of the treated water tends to rise, it is preferable to add a mineral acid such as hydrochloric acid. The wastewater treatment method of the present invention may use one microbial reaction tank, or it may use multiple tanks. In this case, the effluent from the first tank is introduced into the raw water supply port of the second tank. Furthermore, for example, when two microbial reaction tanks are connected in series, wastewater treatment can be performed more effectively by changing the ratio of the volume of the nitrification reaction section to the volume of the denitrification reaction section in the second tank from the ratio in the first tank. Specifically, denitrification and dephosphorization can be performed by making the volume ratio smaller than that of the first tank. Furthermore, the wastewater treatment method of the present invention can be carried out in combination with conventional wastewater treatment methods. For example, in a wastewater treatment facility consisting of an existing aerobic nitrification tank and an anaerobic denitrification tank connected together, the effluent from each tank can be supplied to the microbial reaction tank of the present invention to more effectively digest the sludge load and perform denitrification and phosphorus removal. Example: Wastewater discharged from a food manufacturing plant was treated using the microbial reaction tank shown in Figure 1. Before treatment, the wastewater had a BOD of 1200 mg / L, a chemical oxygen demand (hereinafter referred to as COD) of 750 mg / L, T-N of 130 mg / L, n-Hex of 250 mg / L, and SS of 200 mg / L, with a treatment volume of 1500 m3 / day. The microbial reaction tank consists of an anaerobic microbial treatment tank with a volume of 250 m³ and an aerobic microbial treatment tank with a volume of 650 m³. The treatment raw water circulation rate in the microbial reaction tank was circulated within the range of 3 to 6. As a pretreatment, the treatment raw water, which had been aerated and adjusted in a raw water aeration adjustment tank so that the ORP was a positive value, was sent to the microbial reaction tank for treatment. In the microbial reaction tank, the pH in the anaerobic microbial treatment tank was 6.9, the ORP was -350 mV, and the DO was 0, while the pH in the aerobic microbial treatment tank was 7.1, the ORP was +210 mV, and the DO was 1.1 mg / L. The microbial concentration in both the aerobic and anaerobic microbial treatment tanks was 6400 mg / L. Two 25 kW blowers were used at this time; one was connected to the piping of air inlet 8a in commercial operation, and the other was connected to air inlet 8, which is a diffuser, and operated while adjusting the air volume with an inverter. The normal air injection rate for the two units was 18 m³ / min. The water quality of the effluent discharged from the microbial reaction tank was as follows: BOD 8 mg / L, COD 11 mg / L, n-Hex 0.8 mg / L, T-N 2 mg / L, and SS 8 mg / L. Furthermore, virtually no dewatered cake formation was observed. The wastewater treatment method described above allows for anaerobic-aerobic operation in the microbial reaction tank while suppressing the generation of harmful gases, thereby improving the self-digestion efficiency of the microbial cells. Furthermore, through the circulation of sludge, microbial cells capable of selectively decomposing sludge substances in the raw water are cultivated, making it possible to easily treat difficult-to-decompose pollutants. As a result, the amount of dewatered cake discharged was reduced to almost zero. In addition, compared to the conventional push-flow treatment method shown in the comparative example below, this wastewater treatment method allows for a reduced aeration airflow, enabling the treatment of the same amount with at least half the electricity cost, thus significantly contributing to energy conservation. Comparative Example The treatment situation before introducing the microbial reaction tank of the present invention at the same factory as the example is shown as a comparative example of the present invention. The water quality of the raw wastewater before treatment is the same as in the example, with BOD of 1200 mg / L, COD of 750 mg / L, T-N of 130 mg / L, n-Hex of 250 mg / L, and SS of 200 mg / L, and the amount of water to be treated is 1500 m3 / day. Wastewater discharged from a food manufacturing plant was first treated in a 500 m³ raw water adjustment tank to adjust the raw water flow rate. Then, in a coagulation reaction tank, 850 mg / L of polyaluminum chloride (PAC), 380 mg / L of 25% by weight caustic soda, and 1.5 mg / L of anionic polymer flocculant were added to create coagulated flocs. These flocs were then separated by flotation in a 120 m³ pressurized flotation tank to remove oil and suspended solids. After that, the wastewater was treated in a 1400 m³ push-flow type aerobic activated sludge treatment tank, and finally separated into sludge and treated water in a 350 m³ sedimentation tank before being discharged. Four 25 kW aeration blowers were used to maintain a dissolved oxygen concentration of 1.5 mg / L or higher near the outlet of the aeration tank. The treated water quality after pressurized flotation treatment showed BOD of 900 mg / L, COD of 550 mg / L, T-N of 130 mg / L, n-Hex of 10 mg / L, and SS of 20 mg / L. Furthermore, the flotation scum separated by pressurized flotation produced 22.8 tons of sludge with a water content of 96% by weight per day. Using cationic and anionic polymer flocculants, 6 tons of dewatered cake with a water content of 85% by weight were generated daily. Therefore, sludge disposal was required daily, and outsourced disposal of more than 150 tons of dewatered cake was required every month. The effluent separated in the sedimentation tank had the following water quality: BOD 18 mg / L, COD 25 mg / L, n-Hex 1 mg / L, T-N 25 mg / L, and SS 5 mg / L. Maintaining a pH of 6 or higher was often difficult in order to reduce the effluent's BOD to below 20 mg / L, due to aeration conditions and fluctuations in the raw water. The microbial reaction tank of the present invention can continuously treat raw water with anaerobic and aerobic microorganisms in a simple form, even when the reaction tank capacity is large, without substantially discharging excess sludge. Therefore, it can be used as a wastewater treatment facility for wastewater containing high concentrations of pollutants. Furthermore, since the wastewater treatment method of the present invention uses the above-mentioned microbial reaction tank, it can be used as an environmentally friendly wastewater treatment method that causes less damage to the environment. Compared to conventional push-flow activated sludge treatment methods, it requires less aeration airflow, produces better treated water quality, generates almost no excess sludge, and consumes less electricity. Therefore, it can be used as a particularly preferable wastewater treatment facility in factories that manufacture international products aiming for a clean factory. 1. Microbial reaction tank 2. Outer tank 3. Cylindrical inner tank 4. Circulation rate control device 5. Cylindrical control plate 6. Treated water quality measuring device 7. Rotating shaft 8. Air inlet 9. Support column 10. Raw water supply port 11. Treated water discharge port 12. Settlement and solidification prevention device 13. Sludge extraction port