JP2013103185A - Wastewater treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wastewater treatment apparatus capable of improving reaction speed in a ditch.SOLUTION: A wastewater treatment apparatus includes: a raw water inflow channel 18, a circulation liquid outlet channel 16, an endless water channel (ditch 11) which is provided with a circulation flow generation means 12 and an oxygen supply means (aeration device 13) and in which an aerobic region 14 and an anoxic region 15 are formed; and a solid-liquid separation means (final sedimentation tank 17) performing solid-liquid separation of circulation liquid flowing out from the circulation liquid outlet channel 15. A biological fixing carrier is put into the circulation liquid. The circulation flow generation means includes a rotary cylindrical body 12a having an axial line directed in the vertical direction and a protruding agitation blade 12b provided at an outer circumference of the rotary cylindrical body. The oxygen supply means includes a microbubble generator generating microbubbles having diameters equal to or less than 50 μm. The circulation liquid outlet channel includes a screen 16a preventing an outflow of the biological fixing carrier.

Description

  The present invention relates to a wastewater treatment apparatus, and more particularly to a wastewater treatment apparatus that performs purification treatment of wastewater including removal of nitrogen and phosphorus by a biological wastewater treatment method using an endless water channel.

  The oxidation ditch method is widely known as a biological wastewater treatment method. This oxidation ditch method forms an aerobic region and an anoxic region in the ditch by aerating part of the water in the endlessly formed ditch (endless water channel) while circulating it. In addition to decomposition, nitrogen is also removed by a nitrification reaction in an aerobic region and a denitrification reaction in an anoxic region. It is also possible to remove phosphorus by providing an anaerobic tank upstream of the ditch.

  The oxidation ditch method is suitable for small-scale treatment plants that have large daily fluctuations compared to large-scale treatment plants, but the load in the ditch varies greatly due to daily fluctuations. It is important to adjust the supply amount (aeration amount) and maintain a proper balance between the aerobic region and the anoxic region. For this reason, dissolved oxygen meters (DO meters) are installed at appropriate positions on the upstream side and downstream side of the aerobic region, respectively, and the flow rate of the circulating fluid and the oxygen concentration are measured based on the measured values (DO values) of each DO meter. By adjusting the supply amount, the balance between the aerobic region and the anaerobic region is appropriately maintained by so-called two-point DO control (see, for example, Patent Document 1).

JP 2005-52804 A

  By applying the treatment described in Patent Document 1, it is possible to always form a constant aerobic region and anoxic region even when there is a load fluctuation, and minimize ammonia concentration and nitrate nitrogen concentration in the treated water. It can be. However, in the case of a small scale and a low load, or when the flow path length is extremely short, the oxygen consumption rate is low, and it may be difficult to form a sufficient anoxic region. Also, when the raw water inflow is large, the load of the solid-liquid separation means provided in the subsequent stage of the ditch, for example, the sedimentation tank increases, so the capacity of the sedimentation tank is increased or the sedimentation tank is expanded. Need arises.

  On the other hand, it is possible to reduce the load on the sedimentation basin by increasing the reaction rate by increasing the amount of microorganisms in the ditch and reducing the amount of sludge flowing into the sedimentation basin by introducing the biofixation carrier into the ditch. is there. However, since the mechanical aeration device and stirring device provided in a general ditch stir the circulating fluid at high speed with the stirring blade, the biological fixed carrier is damaged by the large shearing force generated by the high-speed stirring of the stirring blade, Since microorganisms are peeled off from the biological immobilization carrier, the effect of introducing the biological immobilization carrier cannot be sufficiently improved and has not been put into practical use.

  Therefore, the present invention can form a sufficient anoxic region by improving the reaction rate using the biological immobilization carrier, and without increasing the load of the subsequent solid-liquid separation means, An object of the present invention is to provide a wastewater treatment apparatus capable of significantly improving treatment efficiency by suppressing damage and detachment of microorganisms.

  In order to achieve the above object, the wastewater treatment apparatus of the present invention comprises a raw water inflow portion and a circulating fluid outlet path, and also comprises a circulating flow generation means and an oxygen supply means, and an aerobic region downstream of the oxygen supply means, Drainage provided with an endless water channel that forms an oxygen-free region from the end of the aerobic region to the oxygen supply unit, and a solid-liquid separation unit that performs solid-liquid separation of the circulating fluid flowing out from the circulating fluid outlet channel In the treatment device, the biological immobilization carrier floating in the circulating fluid is introduced into the circulating fluid circulating in the endless water channel, and the circulating flow generating means includes a rotating cylindrical body whose axis is directed in the vertical direction, A plurality of stirring blades protruding from the outer periphery of the rotating cylindrical body, the oxygen supply means includes a fine bubble generator for generating fine bubbles having a diameter of 1 mm or less, and the circulating fluid outlet path The outflow of the biological immobilization carrier It is characterized in that it comprises a screen for stopping.

  Furthermore, the waste water treatment apparatus of the present invention is provided on the upstream side and the downstream side in the aerobic region, respectively, and an upstream dissolved oxygen meter and a downstream dissolved oxygen meter that measure the dissolved oxygen concentration in the circulating liquid, An oxygen supply amount control means for controlling an oxygen supply amount by the oxygen supply means based on an upstream dissolved oxygen concentration measured by an upstream dissolved oxygen meter and a preset upstream oxygen concentration target value; and the downstream side A flow rate control means for controlling the flow rate of the circulating fluid by the circulating flow generating means based on a downstream dissolved oxygen concentration measured by a dissolved oxygen meter and a preset downstream oxygen concentration target value; It is said.

  In addition, ammonia / nitric acid concentration measuring means for measuring the ammonia concentration and nitric acid concentration in the circulating fluid is provided, and at least one of the ammonia concentration and the nitric acid concentration measured by the ammonia / nitric acid concentration measuring means is provided. And a target value adjusting means for adjusting the upstream oxygen concentration target value and the downstream oxygen concentration target value based on the above, and in addition, anaerobic treatment of raw water is performed upstream of the raw water inflow portion. And an anaerobic tank for removing phosphorus, and a return sludge path for returning the sludge separated by the solid-liquid separation means to the anaerobic tank and mixing it with raw water.

  According to the waste water treatment apparatus of the present invention, by introducing the biological fixed carrier into the circulating liquid, the oxygen consumption rate in the aerobic region can be improved, and a sufficiently long anoxic region can be formed. In addition, by attaching microorganisms in the circulating fluid to the biological immobilization carrier, the concentration of microorganisms floating in the circulating fluid (floating microorganisms) can be reduced, and while maintaining the overall microorganism concentration, the floating microorganisms Therefore, the solid-liquid separation efficiency can be improved by reducing the load of the solid-liquid separation means in the subsequent stage while improving the biological reaction treatment efficiency in the circulating liquid. Furthermore, by using a circulating flow generating means having a plurality of stirring blades on the outer periphery of the cylindrical body with the axis line oriented in the vertical direction, damage to the biological immobilization carrier and detachment of microorganisms can be suppressed, and a fine bubble generator By using the oxygen supply means provided with the above, it is possible to prevent damage to the biological immobilization carrier and detachment of microorganisms due to intense collision between the biological immobilization carriers.

  In addition, the inflow load fluctuates by controlling the amount of oxygen supplied by the oxygen supplying means and the flow rate of the circulating fluid by the circulating flow generating means according to the dissolved oxygen concentration on the upstream side and downstream side in the aerobic region. In addition, a certain aerobic region and an oxygen-free region can be reliably formed in the endless water channel. Furthermore, phosphorus in raw water can be efficiently removed by providing an anaerobic tank upstream of the raw water inflow part provided in the upstream part of the oxygen-free region. In addition, by adjusting the upstream oxygen concentration target value and downstream oxygen concentration target value based on the ammonia concentration and nitric acid concentration in the circulating fluid, the concentration of ammonia nitrogen and nitrate nitrogen is adjusted to the appropriate concentration. The ratio between the aerobic region and the anaerobic region can be controlled to an optimal ratio according to the ammonia concentration and the nitric acid concentration, and the processing efficiency can be improved.

It is explanatory drawing which shows one example of the waste water treatment apparatus of this invention.

  The wastewater treatment apparatus shown in the present embodiment includes a pair of circulation flow generation means 12 and oxygen supply means, which are circulation flow generation means, in a ditch 11 that performs purification treatment of wastewater including nitrogen removal by a biological wastewater treatment method. By providing a diffuser 13 and forming a circulating flow in the direction indicated by the arrow F in the ditch 11, an aerobic region 14 is formed between the diffuser 13 and a predetermined distance. The oxygen-free region 15 is formed in a predetermined balance between the end of the gas and the diffuser 13 and floats in the circulating fluid circulating in the aerobic region 14 and the oxygen-free region 15. A biological immobilization carrier is used.

  A final sedimentation basin 17 is provided downstream of the aerobic zone 14 via a circulating fluid outlet route 16 that is a circulating fluid outlet route, and a raw water inlet route that is a raw water inlet portion is provided upstream of the anoxic zone 15. 18 is provided, and an anaerobic tank 19 is provided in the middle of the raw water inflow path 18. Further, in the final sedimentation basin 17, a treated water outflow path 20 through which the separated supernatant water flows out, a return sludge path 21 through which the settled and separated sludge is returned to the anaerobic tank 19, and sludge that extracts a part of the sludge as excess sludge. An extraction path 22 is provided, and the anaerobic tank 19 mixes the raw water flowing into the anaerobic tank 19 and the sludge returned from the return sludge path 21 and keeps them in an anaerobic state for a predetermined time. Process. Further, a screen 16 a for preventing the biological immobilization carrier from flowing out of the ditch 11 into the circulating fluid outlet passage 16 is provided at the inflow portion to the circulating fluid outlet passage 16.

  The pair of circulating flow generating means 12 are respectively arranged at both ends of the partition wall 11a partitioning the inside of the ditch 11, and projecting to the outer periphery of the rotating cylinder 12a with the axis line oriented in the vertical direction. It is a vertical axis type water flow generator provided with a plurality of stirring blades 12b provided, and the plurality of stirring blades 12b are moved into the ditch 11 by rotating the rotating cylindrical body 12a with a motor at a predetermined rotational speed around the axis. To form the circulating flow. Such a vertical flow circulation means 12 can generate water flow (circulation flow) by extruding water, that is, circulation liquid, downstream of the plurality of stirring blades 12b as a whole. By rotating 12a at a low speed of about 10 to 20 revolutions per minute, a circulating flow with an appropriate flow rate can be formed in the ditch 11, and the rotational speed is slow and the shearing force by the stirring blade 12b is small. It can suppress that a fixed support | carrier is damaged or that microorganisms peel from a biological fixed support | carrier.

  The air diffuser 13 includes a fine bubble generator that generates fine bubbles having a diameter of 1 mm or less. Fine bubbles with a diameter of about 1 mm have a sufficiently low ascending rate in water, so that the oxygen dissolution efficiency is high, and sufficient oxygen can be supplied with a small amount of air diffused. Since a swirl flow is not generated, the biological immobilization carriers do not collide violently and are not damaged, and microorganisms are not separated.

  The biological immobilization carrier introduced into the circulating fluid does not settle in the ditch 11 and does not float completely, but is dispersed in the whole circulating fluid and floats in a state where microorganisms are appropriately attached. A specific gravity of around 1 is selected. In particular, in the circulating fluid circulating in the ditch 11, a plurality of biological reactions such as oxidation of organic substances, nitrification of ammonia nitrogen, and denitrification of nitrate nitrogen proceed at the same time, so that microorganisms contributing to these reactions are combined. As the biological immobilization carrier, an object of an appropriate size made of a material that easily adheres to microorganisms is used, and various microorganisms existing in the system adhere to the carrier and proliferate. It is preferable to use a binding type microorganism holding carrier. Furthermore, in the case of a conjugated microorganism-supporting carrier, since a gradient occurs in the dissolved oxygen concentration on the surface and inside of the carrier, mainly aerobic bacteria, for example, nitrifying bacteria are given priority on the surface of the carrier, For example, denitrifying bacteria are prioritized.

  As a result, a large amount of microorganisms adhering to the biological immobilization carrier and the circulating fluid are efficiently and effectively brought into contact with each other in the aerobic region 14 and the anoxic region 15, thereby improving the processing efficiency. Further, by selecting a biological immobilization carrier having a diameter of about several millimeters, a relatively coarse screen can be used as the screen 16a, and the surface of the screen 16a on the Ditch 11 side is always filled with circulating fluid. Since it flows at a predetermined flow rate, clogging hardly occurs. In particular, clogging can be prevented more reliably by forming the screen 16a with a slit in a direction parallel to the circulating fluid flow direction. it can.

  Thus, the treatment efficiency can be significantly improved by introducing the biological immobilization carrier into the circulating fluid circulating in the ditch 11. Further, by forming a circulating flow by the circulating flow generating means 12 provided with a plurality of stirring blades 12b on the outer periphery of the cylindrical body 12a, damage to the biological immobilization carrier and detachment of microorganisms can be suppressed. By using oxygen supply means equipped with a vessel, the oxygen dissolution efficiency can be improved and the biofixation carriers will not collide violently, preventing damage to the biofixation carriers and detachment of microorganisms from the biofixation carriers. can do.

  Further, in the wastewater treatment apparatus shown in the present embodiment, an upstream dissolved oxygen meter that measures the dissolved oxygen concentration in the circulating liquid is provided upstream and downstream in the circulating fluid flow direction in the aerobic region 14 in the ditch 11. 23 and a downstream dissolved oxygen meter 24 are provided, and ammonia (ammonia nitrogen) and nitric acid (nitric acid) and nitric acid (circulating fluid) in the circulating fluid are disposed at an appropriate position in the ditch 11, preferably in the vicinity of the circulating fluid outlet passage 16. An ammonia / nitric acid concentration measuring means 25 for measuring the concentration of (nitric nitrogen) is provided.

  Furthermore, the oxygen supply amount control means 26 for controlling the oxygen supply amount by the air diffuser 13 based on the upstream dissolved oxygen concentration measured by the upstream dissolved oxygen meter 23 and the downstream dissolved oxygen meter 24 On the basis of the ammonia concentration and nitric acid concentration measured by the flow rate control means 27 for controlling the flow rate of the circulating fluid by the set of circulating flow generation means 12 and the ammonia / nitric acid concentration measurement means 25 based on the downstream dissolved oxygen concentration. A target value control means 28 for adjusting the upstream oxygen concentration target value of the oxygen supply amount control means 26 and the downstream oxygen concentration target value of the flow rate control means 27 is provided.

  The raw water flowing into the anaerobic tank 19 from the raw water inflow path 18 becomes a mixed liquid mixed with the sludge returned from the final sedimentation basin 17 through the return sludge path 21, and after being held in an anaerobic state in the anaerobic tank 19, 11 flows into the oxygen-free region 15 and joins with the circulating liquid, and is maintained in an oxygen-free state in the oxygen-free region 15, so that nitrate nitrogen is denitrified and nitrogen is removed from the circulating liquid.

  When the circulating liquid passes through the air diffuser 13, it comes into contact with fine bubbles made of air that is pumped from the blower B and supplied from the fine bubble generator into the circulating liquid, and takes oxygen into the liquid and is aerobic. The organic matter is decomposed and ammonia nitrogen is nitrified while flowing through the aerobic region 14, and the organic matter and ammonia nitrogen are removed from the circulating fluid.

  A part of the circulating fluid flowing through the end portion of the aerobic region 14 is extracted to the final sedimentation basin 17 through the circulating fluid outlet path 16, and the circulating fluid is subjected to solid-liquid separation in the final sedimentation basin 17. The supernatant liquid separated in the final sedimentation basin 17 is discharged from the treated water outflow path 20, a part of the precipitated sludge is extracted as excess sludge from the sludge extraction path 22, and the remaining sludge passes through the return sludge path 21. It passes through and returns to the anaerobic tank 19. In addition, the circulating fluid that has not been withdrawn into the final sedimentation basin 17 becomes oxygen-free due to a decrease in dissolved oxygen, and merges with the mixed solution from the anaerobic tank 19 in the upstream portion of the oxygen-free zone 15 to enter the interior of the ditch 11. Circulate.

  The oxygen supply amount control means 26 controls the supply amount of oxygen (air) by the diffuser 13 so that the measured upstream dissolved oxygen concentration becomes a preset upstream oxygen concentration target value. For example, if the upstream dissolved oxygen concentration falls below the appropriate range set as the upstream oxygen concentration target value due to fluctuations in the load of the inflow raw water, the amount of air diffused by the air diffuser 13 is reduced because the oxygen is insufficient. The upstream dissolved oxygen concentration is controlled so as to be within the proper range, and when it exceeds the proper range, it is an oxygen excess state. Therefore, the amount of air diffused by the air diffuser 13 is reduced and the upstream dissolved oxygen concentration is reduced. Is controlled to be within the proper range.

  The flow rate control means 27 controls the rotational speed of the circulating flow generating means 12 so that the measured downstream dissolved oxygen concentration becomes a preset downstream oxygen concentration target value. For example, when the downstream dissolved oxygen concentration measured by the downstream dissolved oxygen meter 24 exceeds the appropriate range set as the downstream oxygen concentration target value due to fluctuations in the load of the inflow raw water, the circulation flow When the generation means 12 is decelerated and the flow rate of the circulating fluid is decreased, the downstream dissolved oxygen concentration is controlled to fall within the proper range, and the downstream dissolved oxygen concentration falls below the proper range and becomes low. Then, the circulating flow generating means 12 is accelerated to increase the flow rate of the circulating fluid, thereby controlling the downstream dissolved oxygen concentration to fall within an appropriate range.

  Then, when the ammonia concentration measured by the ammonia / nitric acid concentration measuring means 25 falls below a preset ammonia concentration lower limit value, the target value control means 28 sets the upstream oxygen concentration target value and the downstream oxygen concentration target value. At least one of them, preferably both are adjusted to a low value, and when the measured ammonia concentration exceeds the ammonia concentration upper limit value, at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value, Preferably both are adjusted to a high value.

  That is, the target value control means 28 determines the upstream oxygen concentration target value of the oxygen supply amount control means 26 when the ammonia concentration of the circulating fluid in the ditch 11 measured by the ammonia / nitric acid concentration measurement means 25 is lower than the ammonia concentration lower limit value. Is reduced to an upstream low oxygen concentration target value that is lower than the upstream oxygen concentration target value, or the downstream oxygen concentration target value of the flow rate control means 27 is set lower than the downstream oxygen concentration target value. Also lower the lower oxygen concentration target value on the downstream side to a lower dissolved oxygen concentration.

  Thus, when the oxygen supply amount control means 26 determines that the upstream dissolved oxygen concentration measured by the upstream dissolved oxygen meter 23 exceeds the appropriate range set as the upstream low oxygen concentration target value, The amount of air diffused by the air diffuser 13 is reduced so that the upstream dissolved oxygen concentration falls within the appropriate range of the upstream low oxygen concentration target value.

  Similarly, when the flow rate control means 27 determines that the downstream dissolved oxygen concentration measured by the downstream dissolved oxygen meter 24 exceeds the appropriate range set as the downstream low oxygen concentration target value, the circulation flow is generated. By decelerating the means 12 and decreasing the flow rate of the circulating fluid, the downstream dissolved oxygen concentration is controlled to fall within the appropriate range of the downstream low oxygen concentration target value.

  In this way, by controlling at least one of the upstream oxygen concentration target value of the oxygen supply amount control means 26 and the downstream oxygen concentration target value of the flow rate control means 27 to the low oxygen target value, Thus, the dissolved oxygen concentration in the circulating fluid is controlled to be low as a whole, and the region of the aerobic region 14 decreases and the region of the anoxic region 15 increases. Thereby, the oxidizing action of ammonia by nitrifying bacteria is suppressed, and the ammonia concentration in the circulating fluid gradually increases. In addition, it is possible to prevent the nitrifying bacteria from undergoing auto-oxidative decomposition due to excessive dissolved oxygen, and it is possible to reduce the power consumed by the air diffuser 13 and the circulating flow generating means 12.

  Conversely, when the ammonia concentration of the circulating fluid in the ditch 11 measured by the ammonia / nitric acid concentration measuring means 25 exceeds the ammonia concentration upper limit value, the upstream oxygen concentration target value of the oxygen supply amount control means 26 is set to the upstream oxygen concentration. The upstream oxygen concentration target value is set to an upstream high oxygen concentration target value that is higher than the concentration target value, or the downstream oxygen concentration target value of the flow rate control means 27 is set to a dissolved oxygen concentration that is higher than the downstream oxygen concentration target value. Or increase the target value to the downstream high oxygen concentration target value.

  Thus, when the oxygen supply amount control means 26 determines that the measured upstream dissolved oxygen concentration falls below the appropriate range set as the upstream oxygen concentration target value, the oxygen supply amount control means 26 increases the amount of air diffused by the air diffuser 13. Control is performed so that the upstream dissolved oxygen concentration falls within an appropriate range of the upstream high oxygen concentration target value. Similarly, in the flow rate control means 27, when it is determined that the measured downstream dissolved oxygen concentration falls below the appropriate range set as the downstream high oxygen concentration target value, the circulating flow generating means 12 is accelerated to increase the circulating fluid. Is controlled so that the downstream dissolved oxygen concentration falls within an appropriate range of the downstream high oxygen concentration target value.

  In this way, by controlling at least one of the upstream oxygen concentration target value of the oxygen supply amount control means 26 and the downstream oxygen concentration target value of the flow velocity control means 27 to the high oxygen concentration target value, control is performed. The dissolved oxygen concentration in the circulating fluid is controlled to be high overall, so that the region of the aerobic region 14 increases and the region of the anoxic region 15 decreases. As a result, the oxidizing action of ammonia by nitrifying bacteria is promoted, and the ammonia concentration in the circulating fluid is gradually lowered by changing the ammonia to nitrous acid or nitric acid.

  In any control, when the ammonia concentration measured by the ammonia / nitric acid concentration measuring means 25 becomes equal to or higher than the ammonia concentration lower limit value or lower than the ammonia concentration upper limit value, the upstream oxygen concentration target value and By returning the downstream oxygen concentration target value to the original target value set in advance, normal control set in advance can be performed, and wastewater treatment can be performed efficiently.

  Furthermore, even if the ammonia concentration measured by the ammonia / nitric acid concentration measuring means 25 is not less than the ammonia concentration lower limit value and not more than the ammonia concentration upper limit value, and the ammonia concentration is within an appropriate range, the ammonia / nitric acid concentration measuring means. When the nitric acid concentration measured in 25 exceeds the preset nitric acid concentration upper limit value, at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value is adjusted to the low oxygen concentration target value. As a result, as described above, the amount of diffused air by the diffuser 13 is reduced or the circulating flow generating means 12 is decelerated, so that the region of the anoxic region 15 is increased, and the denitrification reaction in the anoxic region 15 is performed. Is promoted, and the nitric acid concentration gradually decreases. Also in this case, when the nitric acid concentration falls below the upper limit of nitric acid concentration, the upstream high oxygen concentration target value and the downstream high oxygen concentration target value are returned to the original target values.

  Thus, in order to control the ammonia concentration in the circulating fluid to a certain concentration range between the ammonia concentration lower limit value and the ammonia concentration upper limit value, and to control the nitric acid concentration in the circulating fluid below the nitric acid concentration upper limit value, Since the upstream oxygen concentration target value of the oxygen supply amount control means 26 and the downstream oxygen concentration target value of the flow rate control means 27 are adjusted based on the ammonia concentration and the nitric acid concentration, respectively, the oxygen supply amount control means 26 and The dissolved oxygen concentration in the ditch 11 can be reliably controlled by the flow rate control means 27, and the ratio of the aerobic region 14 and the anoxic region 15 is controlled to an optimum ratio according to the ammonia concentration and the nitric acid concentration. Can do.

  That is, the balance between the aerobic region 14 and the anaerobic region 15 is larger than in the conventional case where these concentrations are directly controlled based on the measured nitrate nitrogen concentration and ammonia nitrogen concentration. Since it does not collapse, the state of the circulating fluid extracted from the ditch 11 to the final sedimentation basin 17 is stable, the concentration of nitrogen contained in the circulating fluid is also stable, and wastewater treatment efficiency can be improved. It is also possible to reduce power consumption.

  Furthermore, when it is necessary to keep the ammonia concentration in the effluent water as low as possible, it is possible to perform reliable control only by reducing the upper limit value of the ammonia concentration. Similarly, the nitric acid concentration in the effluent water is as low as possible. When it is necessary to suppress this, it is possible to perform reliable control only by reducing the upper limit value of the nitric acid concentration. In addition, when it is necessary to keep the nitrogen content in the effluent water as low as possible, the sum of ammonia concentration and nitric acid concentration is calculated as the total nitrogen concentration, and the upstream side is calculated based on the ratio of ammonia concentration and nitric acid concentration set in advance. It is possible to control the total nitrogen concentration to be the minimum by adjusting the oxygen concentration target value and the downstream oxygen concentration target value, respectively. By reducing the area, it is possible to reduce the power consumption of the blower B of the air diffuser 13 that is the oxygen supply means and the motor that is the drive source of the circulation flow generation means 12 that is the circulation flow generation means.

  Therefore, even in a small-scale ditch 11 having a very short circumference and difficult to balance the aerobic region 14 and the anaerobic region 15, an aerobic region can be obtained with an appropriate balance by introducing a biological fixing carrier into the circulating fluid. 14 and the oxygen-free region 15 can be formed. In addition, when processing at low water temperature in cold regions, the growth rate of nitrifying bacteria is drastically reduced compared to other bacteria, so biological nitrogen removal, especially nitrification reaction, is difficult to proceed. By doing so, the nitrifying bacteria can be reliably attached to the surface of the carrier and kept semi-permanently regardless of the operating conditions such as sludge concentration and residence time, so the solids residence time (SRT) of the nitrifying bacteria Can be taken longer. In addition, under low water temperature, the activity of microorganisms in general decreases and the oxygen consumption rate decreases, but the amount of microorganisms can be increased by the introduction of a biofixation carrier, so the oxygen consumption rate can be kept high, The anoxic region 15 can be reliably formed.

  Further, by providing an anaerobic tank 19 that mixes return sludge and raw water in the raw water inflow path 18 and keeps them in an anaerobic state for a predetermined time, intake of organic substances and release of phosphorus by microorganisms are performed. By excessive intake of microorganisms by the aerobic treatment in the aerobic region 14, the microorganisms can biologically remove phosphorus from the water. At this time, in the biological phosphorus removal process, it is necessary to extract the biologically concentrated phosphorus in the sludge in the form of excess sludge. If the amount of sludge extraction is simply increased, the solids retention time (SRT) will be shortened. As described above, a large amount of nitrifying bacteria can be retained on the biological immobilization carrier, so biological nitrogen removal must be ensured even if the amount of sludge withdrawn is increased. The amount of sludge withdrawn can be increased, and phosphorus can be removed reliably.

  In addition, by holding most of the microorganisms in the circulating fluid on the biological immobilization carrier, the concentration of suspended microorganisms floating in the fluid in the system can be lowered, while maintaining or increasing the amount of microorganisms in the entire system, The solid-liquid separation efficiency in the final sedimentation basin 17 can be improved by lowering the floating microorganism concentration. Thereby, the improvement of the biological reaction processing efficiency in the ditch 11 and the improvement of the solid-liquid separation efficiency in the final sedimentation basin 17 can be achieved at the same time. Can be achieved.

  Further, by controlling the circulating flow generating means 12 and the air diffuser 13 according to the oxygen concentration upstream and downstream of the aerobic region 14, even if the load fluctuates greatly, the aerobic region 14 and the anaerobic region 15 can be optimized, and nitric acid, which is an inhibitory factor for biological phosphorus removal, can be removed to near zero in the ditch 11, so that the processing efficiency in the anaerobic tank 19 can be further improved. Further, the nitrogen removal efficiency can be improved by adjusting the oxygen concentration according to the ammonia / nitric acid concentration.

  The upper limit value, lower limit value, and target value for control in the oxygen supply amount control means and target value control means can be set in multiple stages, and the target value can be increased or decreased in two or more stages. The width of the appropriate range for the value can be arbitrarily set, and the upstream oxygen concentration target value and the downstream oxygen concentration target value can be continuously changed with respect to the measured value of the ammonia concentration. The ammonia / nitric acid concentration measuring means is preferably one that can simultaneously measure ammonia ions and nitrate ions with a single sensor, but it can also be used for ammonia and nitric acid, respectively. Furthermore, depending on the state of the raw water and the configuration of the ditch, the target value control according to the ammonia / nitric acid concentration can be omitted, and the oxygen supply amount control according to the oxygen concentration in the aerobic region can be omitted. The anaerobic tank can be omitted. The form of the solid-liquid separation means is also arbitrary.

  DESCRIPTION OF SYMBOLS 11 ... Ditch, 11a ... Partition, 12 ... Circulating flow generation means, 12a ... Rotating cylindrical body, 12b ... Stirrer blade, 13 ... Air diffuser, 14 ... Aerobic region, 15 ... Anoxic region, 16 ... Circulating fluid outlet path 16a ... Screen, 17 ... Final sedimentation basin, 18 ... Raw water inflow route, 19 ... Anaerobic tank, 20 ... Treated water outflow route, 21 ... Return sludge route, 22 ... Sludge extraction route, 23 ... Upstream dissolved oxygen meter, 24 ... downstream dissolved oxygen meter, 25 ... ammonia / nitric acid concentration measuring means, 26 ... oxygen supply amount control means, 27 ... flow rate control means, 28 ... target value control means

Claims (4)

  A raw water inflow section and a circulating fluid outlet path are provided, a circulation flow generating means and an oxygen supply means are provided, an aerobic region is provided downstream of the oxygen supply unit, and an oxygen-free region extending from the end of the aerobic region to the oxygen supply unit In a wastewater treatment apparatus comprising endless water channels each having a zone and solid-liquid separation means for performing solid-liquid separation of the circulating liquid flowing out from the circulating fluid outlet path, the circulating liquid circulating in the endless water channel In addition, the biological immobilization carrier floating in the circulating liquid is introduced, and the circulating flow generating means includes a rotating cylindrical body whose axis is directed in the vertical direction, and a plurality of stirring blades protruding from the outer periphery of the rotating cylindrical body The oxygen supply means includes a microbubble generator that generates microbubbles having a diameter of mm or less, and the circulating fluid outlet path includes a screen that prevents the biological immobilization carrier from flowing out. Characterized drainage Management apparatus.   An upstream dissolved oxygen meter and a downstream dissolved oxygen meter that are provided on the upstream side and the downstream side, respectively, in the aerobic region and measure the dissolved oxygen concentration in the circulating fluid, and the upstream side measured by the upstream dissolved oxygen meter An oxygen supply amount control means for controlling the oxygen supply amount by the oxygen supply means based on a dissolved oxygen concentration and a preset upstream oxygen concentration target value, and downstream dissolved oxygen measured by the downstream dissolved oxygen meter The waste water treatment apparatus according to claim 1, further comprising a flow rate control means for controlling a flow rate of the circulating fluid by the circulating flow generation means based on a concentration and a preset downstream oxygen concentration target value. .   An ammonia / nitric acid concentration measuring means for measuring the ammonia concentration and the nitric acid concentration in the circulating fluid is provided, and based on at least one of the ammonia concentration and the nitric acid concentration measured by the ammonia / nitric acid concentration measuring means. The waste water treatment apparatus according to claim 2, further comprising target value adjusting means for adjusting the upstream oxygen concentration target value and the downstream oxygen concentration target value.   An anaerobic tank for anaerobic treatment of raw water is provided upstream of the raw water inflow section, and a return sludge path is provided for returning the sludge separated by the solid-liquid separation means to the anaerobic tank and mixing it with the raw water. The wastewater treatment apparatus according to any one of claims 1 to 3.

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