The activated sludge process that minimizes excess sludge formation and methods for improving wastewater treatment equipment.

Abstract

DC60 (05 / 09 / 57) What was revealed was the activated sludge process that causes almost no excess sludge to be produced. The centers and methods for improving current wastewater treatment equipment using this treatment method include: Process 1, which serves to transfer sludge 2 from the sedimentation tank to the aeration tank of the wastewater, Activated sludge treatment with process 2, which adjusts the conditions of the wastewater containing this sludge. The mixture is aerated to bring the oxidation-reduction potential to the correct value before being sent to the tank. Flotation with dissolved air, process 3, which will produce sludge 1 from the treatment by the tank. Sludge is flotated with dissolved air to a microbial reaction tank in process 4, which then supplies treated wastewater. 1. The separable sludge from the flotation tank is transferred to the activated sludge aeration tank for light sludge production. The treatment is performed using process 5, which will dispense sludge 3 generated from microbial reaction tank treatment and... The wastewater is discharged to the activated sludge aeration tank, process 6, which then supplies treated wastewater 2. Which is separated from the activated sludge aeration tank and transferred to the sedimentation tank.

Description

[0001] The present invention relates to an activated sludge treatment method and a method for renovating an existing wastewater treatment facility using this activated sludge treatment method.

[0002] The activated sludge treatment method is an extremely effective wastewater treatment method and is therefore widely used in wastewater treatment, with various treatment methods being proposed depending on the type of raw water. Conventional activated sludge treatment methods utilize various microorganisms, ranging from soil bacteria to large protozoa, by leveraging the food chain. An example of an existing activated sludge treatment method is shown in Figure 4. The wastewater is introduced into a raw water adjustment tank, where it is pre-treated as needed, and then in a pressurized flotation tank, particles ranging from coarse to fine that were dispersed in the raw water are removed. In the case of wastewater with a high oil content, separation and coagulation using coagulants is performed as a primary treatment. For example, inorganic coagulants such as aluminum sulfate (called aluminum sulfate) or polyaluminum chloride (called PAC), or organic coagulants such as polyacrylamide polymers, are added to the wastewater to break down the emulsion state and separate the oil and water components. However, in this case, a large amount of this coagulant is generated as sludge. Also, during treatment in the pressurized flotation tank, pollutants contained in the raw water adhere to the inorganic coagulant and are removed, forming floating scum and generating sludge. This sludge is collected in a sludge storage tank. Soluble organic matter suitable for microbial treatment is sent to the aeration tank as raw water for treatment, and after aeration treatment with activated sludge, the raw water is separated from the activated sludge and discharged. The concentrated and separated activated sludge is collected in the sludge storage tank, and a portion of it is recycled back into the aeration tank as return sludge. The sludge collected in the sludge storage tank is sent to a dewatering device to become a dewatered cake, which is then disposed of in landfills, as microbial fertilizer, or by incineration.

[0003] Such activated sludge treatment methods have the following problems that need to be solved. (1) In the case of raw water containing many difficult-to-decompose substances such as proteins, denatured proteins, cellulose, starch, and oils and fats, a large amount of dewatered cake that produces a foul odor is generated as excess sludge. To reduce excess sludge, a method has been proposed to digest it by enlarging the aeration tank and aerating it for a long time (lagoon method / oxidation ditch). However, this method requires a huge aeration tank when the amount of wastewater is large or the load is high, which presents problems such as lack of land and enormous construction costs. Once bulking or a treatment abnormality occurs, it takes a great deal of time and money to recover, which is problematic for the stable operation of the plant. (2) When performing microbial treatment, it is necessary to neutralize the pH of the influent raw water. However, adding chemicals to neutralize the pH not only incurs chemical costs but also has the problem of accelerating equipment corrosion. Furthermore, adjusting the hydrogen ion concentration (hereinafter referred to as pH) of the influent raw water causes a significant change in the pH of the treated effluent. (3) In the activated sludge process, if harmful substances that sterilize the activated sludge are introduced, the activated sludge can be damaged, leading to a loss of raw water purification function or filamentous bacterial bulking. However, it is not possible to completely avoid releasing small amounts of disinfectants or substances that adversely affect the activated sludge into the wastewater, so the removal of these harmful substances is a problem. (4) Activated sludge treatment plants that process large amounts of organic pollutants face the following problems: The amount of influent decreases drastically at night and on holidays. Also, if there are many consecutive holidays, a certain amount of pollutants cannot be supplied, and the number of beneficial activated sludge bacteria decreases due to over-aeration. Furthermore, the sludge breaks down due to overload. As a result, stable proliferation of activated sludge bacteria cannot be ensured, and the activated sludge treatment capacity tends to decrease due to bulking and sludge flotation. In particular, bulking is more likely to occur when there are large fluctuations in the pollutant components of the influent raw water or when there is a sudden increase in load after consecutive holidays. To prevent this, large raw water adjustment tanks are built to store large amounts of raw water and homogenize the raw water, or the supply amount to the aeration tank is kept constant and continuous, but there are problems with site area constraints and construction costs. (5) The high-speed aeration activated sludge treatment method is a wastewater treatment method that requires a small installation area and has high efficiency. However, because it is a completely mixed type in which activated sludge and raw water are always present together, it has the problem of being prone to bulking by filamentous bacteria. In addition, it is generally classified as an intermediate treatment facility among sewage treatment facilities, and has disappeared in recent years as a facility that cannot provide sufficient treatment.

[0004] In order to solve the above problems, the applicant has developed a microbial reaction tank and a wastewater treatment method (Patent Document 1), and has achieved a track record in wastewater treatment in many fields. Furthermore, one method for reducing excess sludge is disclosed in which the excess sludge is treated with ozone before being returned to the aeration tank (Non-Patent Literature 1). Other known methods include treating the sludge with thermophilic bacteria, mechanically crushing it, or chemically treating it before returning it to the aeration tank. However, as wastewater treatment methods become more diverse and regulations on environmental impact become stricter, it may become difficult to reduce excess sludge even with the wastewater treatment methods described above. Furthermore, conventional wastewater treatment facilities have the problem of generating large amounts of excess sludge due to their large site area and insufficient activated sludge treatment.

[0005] Hidetoshi Yasui, Chemical Engineering, Vol. 66, No. 6, pp. 329-331, 2002.

[0006] Patent No. 4142138

[0007] The present invention has been made to address the above-mentioned problems, and aims to provide an activated sludge treatment method that uses an activated sludge treatment method to reduce the generation of excess sludge to almost zero, and a method for modifying existing wastewater treatment facilities using this activated sludge treatment method.

[0008] The activated sludge treatment method of the present invention is an activated sludge treatment method that treats wastewater by a circulation system in which sludge circulates between each tank, comprising a raw water aeration adjustment tank, a pressurized flotation concentration separation tank, a dilute activated sludge aeration tank, a microbial reaction tank, and a sedimentation tank, Step 1 involves supplying sludge 2 generated from the sedimentation tank to the raw water aeration adjustment tank to which raw water before treatment is supplied, Step 2 involves aerating the raw water mixed with the above-mentioned sludge 2 in the above-mentioned raw water aeration adjustment tank so that the oxidation-reduction potential (hereinafter referred to as ORP) becomes a positive value, and then supplying this adjusted raw water to the above-mentioned pressurized flotation concentration and separation tank. Step 3 involves supplying the sludge 1 generated by processing in the above-mentioned pressurized flotation concentration separation tank to the above-mentioned microbial reaction tank, Step 4 involves supplying the treated raw water 1 separated from the above-mentioned pressurized flotation concentration separation tank to the above-mentioned dilute activated sludge aeration tank, Step 5 involves supplying the sludge 3 and discharged water generated by processing in the above-mentioned microbial reaction tank to the above-mentioned dilute activated sludge aeration tank, The method is characterized by comprising a step 6 of supplying the treated raw water 2 separated from the above-mentioned dilute activated sludge aeration tank to the above-mentioned sedimentation tank.

[0009] The sludge 2 supplied to the raw water aeration adjustment tank is supplied in such a manner that the sludge concentration in the raw water aeration adjustment tank is in the range of 500 to 8000 mg / L as activated sludge suspended solids (hereinafter referred to as MLSS). Furthermore, the microbial reaction tank used in the activated sludge treatment method 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 water to be treated within the tank, a cylindrical control plate provided on the upper outer circumference of the cylindrical inner tank for settling sludge, a 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 water to be treated 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 vessel is divided into an upper and lower cylindrical section by a partition wall having a communication hole in the center. The upper cylindrical section is an aerobic microbial treatment tank with a frustoconical shape at its apex, with open top and bottom surfaces, and multiple air inlets provided around the communication hole and on the periphery of the partition wall within the upper cylindrical section. The lower cylindrical section is an anaerobic microbial treatment tank with an opening at its bottom, and stirring devices are provided to stir the contents of the aerobic and anaerobic microbial treatment tanks, respectively. 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. Water circulation rate = Amount of water to be treated discharged from the top of the inner tank (m³) 3 / day) / Raw water supply amount (m 3 / day) The microbial reaction tank is characterized in that raw water supplied from the raw water inlet circulates within the tank along 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, thereby enabling continuous anaerobic and aerobic microbial treatment. In particular, the raw water supply port is characterized by having multiple 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 by having a volume of 1 / 10 to 1 times that of the upper part of the cylinder.

[0010] The present invention relates to a method for renovating an existing wastewater treatment facility, which is a method for reducing the amount of sludge generated in the wastewater treatment facility compared to the amount of sludge generated in the existing wastewater treatment facility, The renovation method is characterized by comprising the steps of: installing the above-mentioned microbial reaction tank in an existing or renovated pressurized flotation concentration separation tank and a dilute activated sludge aeration tank; and circulating the sludge through the newly installed microbial reaction tank using the activated sludge treatment method of the present invention. ​​

[0011] The present invention provides an activated sludge treatment method that substantially does not discharge excess sludge by circulating the sludge generated in a pressurized flotation concentration and separation tank, an activated sludge aeration tank, and a microbial reaction tank, which are used as wastewater treatment facilities, among themselves using the method described in claim 1, and by supplying a portion of the sludge generated in the activated sludge aeration tank to the raw water aeration adjustment tank of the wastewater to be treated with activated sludge. Furthermore, by installing the microbial reaction tank described in claim 3, the existing wastewater treatment facility being remodeled will be able to perform wastewater treatment without substantially discharging excess sludge.

[0012] This is a block diagram of an activated sludge treatment method. This is a cross-sectional view of a microbial reaction tank. This is a diagram showing the circulation pathway of the water to be treated and activated sludge in the microbial reaction tank. This is a block diagram of an existing activated sludge treatment method.

[0013] A block diagram of the activated sludge treatment method of the present invention is shown in Figure 1. Sludge 1, sludge 2, and sludge 3, generated in the pressurized flotation concentration and separation tank, the dilute activated sludge aeration tank, the microbial reaction tank, and the sedimentation tank, respectively, are circulated through the routes shown in steps 1 to 5. During the circulation process, the sludge is digested, and virtually no excess sludge is discharged. Each step is described below in order.

[0014] Process 1: Step 1 is the process of supplying sludge 2 generated by the sedimentation tank to the raw water aeration adjustment tank of the wastewater to be treated with activated sludge. A raw water aeration adjustment tank can be obtained by adding an air injection system to an existing raw water tank when modifying an existing wastewater treatment facility. Large solid particles in the wastewater to be treated are removed by screens, etc., and stored in a raw water aeration adjustment tank as raw water to be treated. Sludge 2 generated in the sedimentation tank is supplied to this raw water aeration adjustment tank and mixed with the raw water, so that pollutants that are difficult to decompose and harmful substances that destroy activated sludge, etc., which tend to cause abnormalities in the activated sludge treatment, come into contact with and adsorb onto the sludge 2. Since this sludge 2 has been treated in a dilute activated sludge aeration tank and passed through a sedimentation tank, it has activated sludge bacteria suitable for the wastewater to be treated. Therefore, by supplying sludge 2 to the raw water, damage to the activated sludge in the dilute activated sludge aeration tank is prevented and the activity of the activated sludge is kept at a high level, so the occurrence of abnormal phenomena such as swelling of the dilute activated sludge and foaming scum of the dilute activated sludge is reduced and the treatment can be stabilized.

[0015] The sludge 2 supplied to the raw water aeration adjustment tank is supplied in a range where the sludge concentration in the raw water aeration adjustment tank is 500 to 8000 mg / L as MLSS. Preferably, it is supplied in a range where it is 1000 to 5000 mg / L. If the MLSS is less than 500 mg / L, the sludge 2 cannot adsorb pollutants that adversely affect the activated sludge, making the activated sludge treatment unstable. Also, if the MLSS exceeds 8000 mg / L, the sludge 2 adsorbs almost all of the pollutants, and the biochemical oxygen demand (hereinafter referred to as BOD) contained in the treated raw water decreases.

[0016] Process 2: Step 2 involves aerating the raw water mixed with sludge 2 in a raw water aeration adjustment tank so that the ORP of the raw water becomes a positive value, and then supplying the raw water to a pressurized flotation concentration and separation tank. By aerating the water to a positive value, hydrogen sulfide, ammonia, mercaptans, and other substances that cause malodors are oxidized, enabling activated sludge treatment with almost no odor. Aeration treatment in the raw water aeration adjustment tank is carried out by aeration treatment with a residence time of 3 hours or more, preferably 5 hours or more, of the raw water. After aeration treatment in the presence of sludge 2, the raw water containing sludge is supplied to the pressurized flotation concentration and separation tank.

[0017] Process 3: Step 3 is the process of supplying the sludge 1 generated by processing in the pressurized flotation concentration separation tank to the microbial reaction tank. Here, the sludge 1 is not dry sludge, but sludge water containing water. The raw water supplied to the pressurized flotation concentration and separation tank undergoes aeration treatment in the raw water aeration adjustment tank. Through this treatment, the pH is naturally adjusted by the pH buffering action of microorganisms, eliminating the need for chemicals or equipment to neutralize acids and alkalis. As a result, not only is the site used more efficiently, but chemical costs are also saved because the treatment is performed without the use of chemicals. Furthermore, even if there are harmful substances such as disinfectants in the raw water that adsorb to the activated sludge and destroy it, sludge 2 adsorbs these substances in advance and is removed from the system as sludge 1 by pressurized flotation. Therefore, the activated sludge in the dilute activated sludge aeration tank is not adversely affected, and stable activated sludge treatment can be performed even where disinfectants are mixed into the wastewater.

[0018] Process 4: Step 4 is a process in which the treated raw water 1 separated from the pressurized flotation concentration separation tank is supplied to a dilute activated sludge aeration tank for treatment. The dilute activated sludge aeration tank can utilize the existing aerobic activated sludge treatment tank used in the existing activated sludge treatment method. The dilute activated sludge aeration tank is supplied with raw water 1 for treatment, as well as sludge 3 generated in the microbial reaction tank shown in step 5. This sludge 3 is aerated with oxygen-containing gas in the dilute activated sludge aeration tank for 1 to 7 days to digest and become digested sludge.

[0019] Process 5: Step 5 is the process of supplying the sludge 3 generated by processing in the microbial reaction tank to the dilute activated sludge aeration tank. In the present invention, anaerobic treatment refers to treatment in a state where DO is less than 0.05 mg / L, and aerobic treatment refers to treatment in a state where DO is 0.05 mg / L or more, preferably 0.1 mg / L or more, more preferably 0.2 mg / L or more. Furthermore, anaerobic treatment refers to an operation in which ORP is less than -80 mV, and aerobic treatment refers to an operation in which ORP is -80 mV or more, preferably positive. The microbial reaction tank digests sludge 1 anaerobically and aerobically, decomposing most of the pollutants adsorbed by sludge 1 into gases such as carbon dioxide, water, nitrogen gas, and methane gas. Furthermore, sludge 1 is used for the proliferation of microorganisms, and since it mostly becomes digested sludge transformed into microbial cells, the amount of sludge is significantly reduced. Even if a very small amount of sludge is generated, it will have good coagulation and dewatering properties, and the amount of dewatered cake generated will be significantly reduced due to the decrease in the water content of the dewatered cake. Since the resulting dewatered cake is obtained from sludge 3 in a fully matured bacterial state, it has a low moisture content, suppresses the generation of foul odors, and is a dewatered cake that can be disposed of in landfill at a low cost.

[0020] The microbial reaction tank can be composed of two tanks: an anaerobic microbial reaction tank for concentrated sludge and, for example, an aerobic microbial reaction tank with a larger internal volume than the anaerobic microbial reaction tank. Here, the anaerobic microbial reaction tank can be any tank capable of treating activated sludge under anaerobic conditions. The aerobic microbial reaction tank is substantially the same as the activated sludge aeration tank described above. Oxygen-containing gas may be supplied as needed. The amount of sludge 3 generated in the aerobic microbial reaction tank supplied to the dilute activated sludge aeration tank is determined by adjusting the concentration so that the amount of dry sludge solids contained in sludge 3 is approximately the same as the amount of dry sludge solids contained in the reaction sludge in the dilute activated sludge aeration tank, thereby maintaining a constant amount of sludge in the dilute activated sludge aeration tank. For example, 1 m³ of reaction sludge with a concentration of 6000 mg / L contained in the dilute activated sludge aeration tank is supplied. 3 If supplied at a rate of / hour, sludge 3 with a concentration of 22,000 mg / L will be supplied in a quantity of 0.27 m³. 3 It should be supplied at a rate of / hours. However, if the amount of water entering the dilute activated sludge aeration tank decreases, the supply rate of sludge 3 should be increased to 20-200% of the normal rate.

[0021] A microbial reaction tank is shown in Figure 2. Figure 2 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 on the upper part of the cylindrical inner tank 3, a cylindrical control plate 5 provided on the outer circumference of the cylindrical inner tank 3, a water treatment quality measuring device 6, and a sludge outlet 13.

[0022] The outer tank 2 has a true cylindrical appearance consisting of a cylindrical side surface 2b and an upper surface portion 2c on a base 2a that serves as the bottom surface. A rotating shaft 7 for attaching a stirring blade or the like is provided at the center of the cylinder. This rotating shaft 7 is rotatably fixed by a pedestal 2d provided at the center of the circle of the base 2a and a bearing 2e provided at the center of the circle of the upper surface portion 2c. Also, the rotating shaft 7 is rotated by a driving device 2f. The upper surface portion 2c rotatably fixes the rotating shaft 7 and holds the cylindrical inner tank 3 with a support or the like. Further, a raw water supply port 10 is provided at the bottom of the outer tank 2. The raw water supply port 10 is composed of a plurality of discharge ports 10b or slits provided in an annular raw water supply portion 10a disposed below the lower opening 3f of the cylindrical inner tank 3. By arranging the raw water supply port 10 in this manner, the stirring of the anaerobic sludge is sufficiently performed. Incidentally, if this raw water supply port 10 is a circulation path of the treated water, it can also be provided outside the lower part of the cylindrical inner tank 3. Further, a purified treated water discharge port 11 is provided at the upper part of the outer tank 2, and a sedimentation fixation prevention device 12 for preventing the sedimentation and fixation of the sedimented sludge is provided on the inner surface of the outer tank.

[0023] As the sedimentation fixation prevention device, (1) a vibration device provided on the inner wall or outer wall of the lower part of the outer tank where the sludge settles, (2) a vibration plate provided near the inner wall and a vibration generator provided at the upper part of the outer tank for transmitting vibration to the vibration plate, (3) a scraper provided on the inner wall of the lower part of the outer tank where the sludge settles, (4) a stirring flow generation device for generating a stirring flow of the sludge along the inner wall of the lower part of the outer tank, particularly a mobile fluid spraying nozzle that sprays the fluid while moving on the inclined surface of the inner wall, or a fluid spraying nozzle fixed at a predetermined interval on the inclined surface of the inner wall, (5) a pump in which the stirring flow generation device moves on the inclined surface or the lower surface of the inner wall to suck the sludge settled in the lower part of the outer tank and discharge it into the anaerobic microorganism treatment tank, or a pump fixed at a predetermined interval on the inclined surface or the lower surface of the inner wall to suck the sludge settled in the lower part of the outer tank and discharge it into the anaerobic microorganism treatment tank, etc. can be mentioned.

[0024] The cylindrical inner tank 3 is arranged in the outer tank provided with the sedimentation fixation prevention device 12. The cylindrical inner tank 3 with a substantially circular cross-section is divided by a partition wall 3a into an upper cylindrical part 3c and a lower cylindrical part 3d. A communication hole 3b for connecting the upper cylindrical part 3c and the lower cylindrical part 3d is provided at the center of the partition wall 3a. Due to the presence of this partition wall 3a, even when the volume of the microbial reaction tank increases, the upper cylindrical part 3c and the lower cylindrical part 3d are sufficiently separated, and activated sludge treatment can be performed in each tank. An aerobic microbial treatment reaction can be sufficiently carried out in the upper cylindrical part 3c, and an anaerobic microbial treatment reaction can be sufficiently carried out in the lower cylindrical part 3d. When the area of the partition wall 3a becomes large, it is reinforced with a support member 3g or the like. The communication hole 3b has a diameter large enough for the activated sludge treated anaerobically to move from the lower cylindrical part 3d to the upper cylindrical part 3c, which is an aerobic microbial treatment tank. The diameter of this communication hole 3b is adjusted according to the volume of the microbial reaction tank, the nature and quantity of the raw water to be treated, etc.

[0025] The upper cylindrical part 3c has a frustum-shaped top with an open top and bottom. That is, the tip of the cylindrical part has a shape in which the diameter is reduced 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 frustum is 40 degrees to 60 degrees, preferably 45 degrees. By setting the inclination angle within this range, the sludge contained in the treated water discharged from the upper part of the aerobic tank flows down along the outer surface of the frustum, making it easier to aggregate and enabling rapid forced sedimentation of the sludge. Also, the aggregation of the sludge facilitates the separation of the sludge and the purified treated water. The upper cylindrical part 3c is an aerobic microbial treatment tank provided with air inlets 8 and 8a inside. The air inlet 8 is provided around the central axis 7 and around the communication hole 3b, and can be fixed to the partition wall 3a by support columns or the like (not shown in the figure). It is preferable that the air ejection openings of this air inlet 8 are preferably arranged downward because it can contribute to the agitation of the treated water and sludge in the aerobic tank. The air inlet 8a can be a plurality of air holes 8c provided in an annular air blowing part 8b arranged in an annular shape in plan view at the peripheral edge of the partition wall inside the upper cylindrical part 3c, or a slit formed on the upper surface or side surface of the air blowing part 8b. By adjusting the amount of air blown in from air inlets 8 and 8a and the control amount of the circulation rate control device described later, the circulation rate of the water to be treated 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 forced sedimentation principle on the outer surface of the aerobic microbial treatment tank with the above-mentioned inclination angle allows for extremely efficient solid-liquid separation of sludge, aerobic and anaerobic microbial treatment reactions can be efficiently carried out in the same vertical tank. Furthermore, an alkali supply port or an acid supply port, not shown in the diagram, may be provided inside the aerobic tank.

[0026] The lower cylindrical part 3d is an anaerobic microbial treatment tank having a volume of 1 / 10 to 1 times that of the upper cylindrical part. Within this volume range, for example, aerobic microbial treatment reactions and anaerobic microbial treatment reactions can be efficiently carried out on raw water containing high-concentration nitrogen-containing pollutants. A denitrifying bacteria nutrient supply port, not shown in the figure, can be provided inside 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 part 3d of the cylinder is an inverted frustoconical shape with an opening 3f that is larger in area than the opening 3e of the upper part 3c of the cylinder. In other words, the tip of the cylindrical part is shaped to narrow in diameter at a predetermined angle downwards. By increasing the area of ​​the opening 3f, the agitation 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.

[0027] The cylindrical inner tank 3 is equipped with a stirring device to ensure that the treatment reaction between the water to be treated and the activated sludge is carried out sufficiently in the aerobic microbial treatment tank which is the upper part of the cylinder 3c and the anaerobic microbial treatment tank which is the lower part of the cylinder 3d. The stirring device is preferably a stirring blade 7a, 7b fixed to a rotating shaft 7 attached to the center of the cylindrical inner tank 3. The stirring blade 7a is preferably a turbine blade provided in the upper part 3c of the cylinder that can sufficiently carry out the aerobic microbial treatment reaction. In addition to turbine blades, any shape that can mix air and water and has a relatively low rotational speed without significantly reducing aeration performance depending on the amount of air blown in can be used. The stirring blade 7b is located inside the lower part 3d of the cylinder and is a propeller blade that allows the anaerobic microbial treatment reaction to proceed sufficiently.

[0028] The partition wall 3a provided 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 the support column 9 and by a support device that bridges across the upper part of the outer tank 2.

[0029] A circulation rate control device 4 for controlling the circulation rate of the water to be treated within the reaction tank is provided at the top of the cylindrical inner tank 3. Specifically, the circulation rate of the water to be treated 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 water to be treated 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 vessel can also be controlled by the amount of air injected from the air inlets 8 and / or 8a. Increasing the amount of air injected increases the circulation rate. This can also be done in combination with opening and closing the liquid level control valve and adjusting the amount of air. As anaerobic and aerobic microbial treatment tanks become larger, maintaining the sludge circulation flow rate may become impossible with aeration air alone, or problems may arise due to excessive air injection. To address such situations, the air inlet shown in Figure 2, 8a, is necessary. This air inlet 8a, which has poor aeration efficiency, has the advantage of making it significantly easier to adjust the air injection volume and ORP. For example, the air inlet 8a is installed in 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, etc., and this air injection section 8b is provided with holes or slits. 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.

[0030] By opening and closing the liquid level adjustment valve and / or adjusting the amount of air injected, the circulation rate of the water to be treated can be varied without using a pump. As will be described later, the water to be treated 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 water to be treated according to the detected value based on a predetermined control program, optimal denitrification, dephosphorization, etc. can be performed.

[0031] 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 an open top and bottom, 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 settling section is formed in this close-proximity inclined surface portion, where sludge is concentrated and treated water is separated. Furthermore, by positioning the bottom surface 5a close, rapid forced settling 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. Within the microbial reaction tank, water treatment quality measuring devices 6 are installed both inside and outside the cylindrical inner tank 2. These water treatment quality measuring devices 6 are devices that measure the pH, ORP, and DO of the water being treated.

[0032] The water circulation rate in the microbial reaction tank 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 microbial treatment reaction and the anaerobic microbial treatment reaction 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 microbial treatment reaction and the anaerobic microbial treatment reaction 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.

[0033] The wastewater treatment method using the microbial reaction tank 1 has the following advantages compared to conventional wastewater treatment methods. Conventional wastewater treatment methods involve mixing raw water and return sludge in a certain ratio and flowing into an aeration tank. The raw water is then pushed out and flows until the sludge and the water to be treated are separated in the next step, a sedimentation tank, from the return sludge that came into contact with the raw water. The wastewater treatment method using the microbial reaction tank 1 involves creating a circulating flow of activated sludge that moves up and down, and then adding raw water to this circulating flow. Since the circulating flow of activated sludge is created using the upward flow of aerated air used in microbial treatment, without the need for a circulation pump, this is an energy-saving wastewater treatment method. 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 circulation flow path, but preferably in an aerobic microbial treatment tank. More preferably, an anaerobic microbial treatment tank is suitable. In the wastewater treatment method of the present invention, 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, the effluent can be operated with a BOD of 10 mg / L or less. Furthermore, 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 such cases, 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 for sewage discharge where the BOD is 300 mg / L or less or 600 mg / L or less, it may be possible to add raw water to the sludge sedimentation section in the circulating flow path.

[0034] The circulation of the treated water and activated sludge in the microbial reaction tank 1 will be explained below with reference to Figure 3. Figure 3 is a diagram showing the circulation pathway of the treated water and activated sludge in the microbial reaction tank 1. In Figure 3, the shaded areas are areas with high activated sludge concentration, and the arrows indicate the circulation direction of the treated water and activated sludge.

[0035] The microbial reaction tank 1 contains activated sludge at a concentration of 5,000 to 12,000 mg / L in terms of solid content. The raw water to be treated 1 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 1 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, raw water and activated sludge move through the communication holes 3b into the upper cylindrical part 3c into which air is blown. In an aerobic state, the nitrification reaction, an aerobic microbial treatment reaction, proceeds as the nitrification reaction circulates within the upper cylindrical part 3c while in contact with the activated sludge inside the upper cylindrical part 3c, due to the rotation of the stirring blades or the ejection of air from the air inlet. As the nitrification reaction progresses, the pH of the treated water decreases. The pH value, ORP, and DO of the treated liquid are measured by the treated water quality measuring device 6, and the circulation amount of raw water or treated water is determined based on these values. Specifically, the amount of air blown in is adjusted to circulate the treated water so that the ORP is maintained at +10 mV or higher in the aerobic reaction treatment tank where the nitrification reaction takes place, and at -10 mV or lower in the anaerobic reaction treatment tank where the denitrification reaction takes place. The circulation amount 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, the equipment including the microbial reaction tank of the present invention allows for the individual adjustment of each unit of the microbial reaction, making it easy to pre-program these controls and operate them automatically without human intervention, thus possessing the characteristics of a labor-saving plant.

[0036] 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 upper cylindrical 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 thickening section 5b formed by the inclined surface, thereby 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 and forcibly settled 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, mixing with the water to be treated, and circulates within the microbial reaction tank. The wastewater treatment method of the present invention allows for easy absorption of raw water load fluctuations by circulating activated sludge through anaerobic and aerobic tanks at a circulation rate of 3 to 20 while the activated sludge is concentrated. Furthermore, by maintaining the circulation rate within this range, the activated sludge is acclimated and becomes optimal for wastewater treatment. Under these conditions, the pH in the aerobic treatment tank is in the range of 4.5 to 8.5, preferably 5.5 to 7.5.

[0037] 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 consisting of organic substances such as proton donors, such as methanol, to the anaerobic reaction section for treatment. In this case, the pH of the treated water tends to rise, so it is preferable to add a mineral acid such as hydrochloric acid.

[0038] 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.

[0039] By placing the microbial reaction tank in the wastewater treatment process, (1) the generation of harmful gases can be suppressed and anaerobic aerobic operation can be performed, thereby improving the self-digestion capacity of activated sludge bacteria, and (2) as a selective culture tank, bacteria that can selectively decompose pollutants in the raw water are cultivated, making it possible to easily treat difficult-to-decompose substances.

[0040] Process 6: Step 6 is the process of supplying the treated raw water 2, separated from the dilute activated sludge aeration tank, to the sedimentation tank. The sludge contained in the treated raw water 2 settles in the sedimentation tank, and the supernatant liquid is discharged as effluent.

[0041] The method for renovating an existing wastewater treatment facility of the present invention is a method of newly adding the above microbial reaction tank to an existing wastewater treatment facility. By newly adding a microbial reaction tank and circulating sludge through this microbial reaction tank, the amount of sludge generated in an existing wastewater treatment facility installed particularly in a food manufacturing factory can be made almost zero. Therefore, the sludge storage tank and the dehydration device, which occupied important parts in the existing wastewater treatment facility, become unnecessary, and the installation area of the wastewater treatment facility can be reduced.

[0042] Example 1 The wastewater discharged from the food manufacturing factory was treated by the method shown in FIG. 1. Before treatment, the wastewater had a BOD of 800 mg / L, a chemical oxygen demand (hereinafter referred to as COD) of 300 mg / L, a T-N of 50 mg / L, a normal hexane extract oil concentration (hereinafter referred to as n-Hex) of 50 mg / L, and a suspended solid concentration (hereinafter referred to as SS) of 200 mg / L, and the treated water volume was 1500 m 3 / day. Incidentally, this wastewater has conventionally been treated by the method shown in FIG. 4, and 150 tons / month of dehydrated cake has been generated. The volume of the raw water aeration adjustment tank is 1500 m 3 The volume of the pressurized flotation concentration separation tank is 250 m 3 The volume of the diluted activated sludge aeration tank is 1500 m 3 The volume of the sedimentation tank is 800 m 3 is. The microbial reaction tank has an anaerobic treatment tank with a volume of 80 m 3 and an aerobic treatment tank with a volume of 250 m 3 The treatment raw water circulation rate in the microbial reaction tank was circulated in the range of 3 to 6.

[0043] The sludge generated in the sedimentation tank was continuously added to the raw water aeration adjustment tank with a metering pump. The addition amount was supplied in the range where the sludge concentration in the raw water aeration adjustment tank was 1500 to 2000 mg / L as MLSS. Also, the aeration amount was adjusted until the ORP became +50 mV. The treated raw water whose aeration was adjusted so that the ORP became a positive value in the raw water aeration adjustment tank was supplied to a non-chemical injection type pressurized flotation concentration separation tank KF800 (manufactured by Nippon Alcy Co., Ltd.). This pressurized flotation concentration separation tank is 5 Kg / cm without chemical injection for 100 parts by weight of the treated raw water2 Pressurized water is mixed and circulated at a rate of 100 parts by weight.

[0044] The sludge separated in the pressurized flotation concentration separation tank was sent to a microbial reaction tank for treatment. In the microbial reaction tank, the pH in the anaerobic treatment tank was 7.1, the ORP was -350 mV, and the DO was 0, while the pH in the aerobic treatment tank was 6.1, the ORP was +210 mV, and the DO was 0.8 mg / L. The excess sludge generated in the microbial reaction tank was supplied to the dilute activated sludge aeration tank. In addition, all of the wastewater discharged from the microbial reaction tank was supplied to the dilute activated sludge aeration tank.

[0045] The raw water to be treated obtained in the pressurized flotation concentration separation tank was sent to the dilute activated sludge aeration tank for treatment. Excess sludge generated in the microbial reaction tank was supplied to the dilute activated sludge aeration tank. In the dilute activated sludge aeration tank, the excess sludge was acclimated to activated sludge suitable for the raw water to be treated.

[0046] The treated raw water, which had been treated in the dilute activated sludge aeration tank, was discharged after passing through the sedimentation tank. The sludge that settled in the sedimentation tank was then recirculated back to the raw water aeration adjustment tank. This sludge circulation process reduces the amount of sludge. The water quality of the discharged water was as follows: BOD 8 mg / L, COD 10 mg / L, T-N 0 mg / L, n-Hex 0 mg / L, and SS 1 mg / L. Furthermore, the amount of dehydrated cake generated ranged from 0 to 20 tons per month.

[0047] 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, (1) the amount of dewatered cake discharged can be significantly reduced, and (2) malodorous odors near the pressurized flotation concentration separation tank can be eliminated.

[0048] Example 2 We treated the wastewater discharged from a Western-style confectionery factory. The wastewater before treatment had the following concentrations: BOD 6000 mg / L, COD 3500 mg / L, T-N 120 mg / L, n-Hex 3000 mg / L, and ss 3500 mg / L. The treated water volume was 120 m³. 3This was the amount per day. At this factory, inorganic flocculants such as polyaluminum chloride were added to a pressurized flotation tank to cause flocculation and sedimentation, and then wastewater was conventionally treated using the method shown in Figure 4. As a result, 150 tons of dewatered cake (water content 85% by weight) were generated per month. The sludge storage tank and dewatering equipment shown in Figure 4 will be removed, and a portion of the site where they were removed will be used to construct the sludge storage tank and dewatering equipment shown in Figure 2, with a volume of 100 m³. 3 An anaerobic treatment tank and a volume of 250 m³ 3 A microbial reaction tank equipped with an aerobic treatment tank was constructed. The raw water treatment circulation rate within the microbial reaction tank was maintained in the range of 5 to 8. Furthermore, an aeration device was installed in the conventional raw water adjustment tank shown in Figure 4, and it was converted into a raw water aeration adjustment tank. The conventional aeration tank was reused as a dilute activated sludge aeration tank, and the sedimentation tank was reused as a sedimentation tank, and the sludge circulation path shown in Figure 1 was installed in each. The volume of the raw water aeration adjustment tank at this plant is 100 m³. 3 The volume of the pressurized flotation concentration and separation tank is 10 m³. 3 The volume of the dilute activated sludge aeration tank is 120 m³. 3 The volume of the sedimentation tank is 30 m³. 3 That is the case.

[0049] Sludge generated in the sedimentation tank was continuously added to the raw water aeration adjustment tank using a metering pump. The amount added was supplied in a range where the sludge concentration in the raw water aeration adjustment tank was 3500 to 5000 mg / L as MLSS. In addition, the aeration rate was adjusted until the ORP was +100 mV. In the raw water aeration adjustment tank, the treated raw water, whose ORP has been adjusted to a positive value, is supplied to the KF800 pressurized flotation concentration and separation tank (manufactured by Nippon Alcy Co., Ltd.) without chemical injection. This pressurized flotation concentration and separation tank has a chemical-free concentration of 4.5 kg / cm³ per 100 parts by weight of treated raw water. 2 220 parts by weight of pressurized water is mixed and circulated.

[0050] The sludge separated in the pressurized flotation concentration separation tank was sent to a microbial reaction tank for treatment. In the microbial reaction tank, the pH in the anaerobic treatment tank was 7.4, the ORP was -400 mV, and the DO was 0, while the pH in the aerobic treatment tank was 7.8, the ORP was +210 mV, and the DO was 1.8 mg / L. The excess sludge and wastewater generated in the microbial reaction tank were supplied to the dilute activated sludge aeration tank.

[0051] The treated raw water obtained in the pressurized flotation concentration separation tank was sent to the dilute activated sludge aeration tank for treatment, as in Example 1, and the treated water was discharged after passing through the sedimentation tank. The sludge that settled in the sedimentation tank was then recycled back to the raw water aeration adjustment tank. The water quality of the discharged water was as follows: BOD 18 mg / L, COD 30 mg / L, T-N 1 mg / L, n-Hex 1 mg / L, and SS 30 mg / L. Furthermore, the amount of dehydrated cake generated was 0 tons per month. In wastewater treatment at a Western-style confectionery factory, the following effects were observed: (1) a significant reduction in the amount of dewatered cake discharged, and (2) the elimination of malodorous odors near the pressurized flotation concentration separation tank.

[0052] The present invention's method does not discharge any excess sludge, making it an environmentally friendly wastewater treatment method that causes less damage to the environment. Furthermore, it does not require equipment for dewatering cake treatment, so it can be used as a method for modifying many existing wastewater treatment facilities in the future. In particular, factories in urban areas usually require deodorizing equipment because a large amount of malodorous odor is generated from the raw water adjustment tank, pretreatment equipment, and dewatering treatment equipment. However, when this treatment method is introduced, no malodorous odor is generated from the raw water adjustment tank to the final treatment process of wastewater treatment. For this reason, this treatment method is suitable for odor control as it suppresses the generation of malodorous odors associated with treatment, and may even eliminate the need for deodorizing equipment.

[0053] 1 Microbial reaction tank 2 Outer tank 3. Cylindrical inner tank 4. Circulation Rate Control Device 5. Cylindrical control plate 6. Water treatment quality measurement device 7. Rotation axis 8. Air intake 9 Support pillar 10. Raw water supply port 11 Treated water outlet 12. Device to prevent sedimentation and immobilization 13. Sludge outlet