Method for treating phosphorous-containing water and apparatus for treating phosphorus-containing water

Abstract

To provide a treatment method for phosphorus-containing water that enables early recovery of phosphorus removal performance.SOLUTION: A method for treating phosphorus-containing water includes a continuous-flow biological treatment process in which the phosphorus-containing water is biologically treated with biological sludge while the phosphorus-containing water continuously flows into the continuous biological treatment tank 14, a granule sludge formation process in which granule sludge is formed in the semi-batch biological treatment tank 12, and a sludge supply process in which the granule sludge formed in the semi-batch biological treatment tank 12 is supplied to the continuous biological treatment tank 14 from the sludge supply pipe 40. In the sludge supply process, the granule sludge supply amount to be supplied to the continuous biological treatment tank 14 is controlled based on the phosphorus removal performance in the continuous biological treatment tank 14.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for treating phosphorus-containing water and a technique of a phosphorus-containing water treatment apparatus.

Background Art

[0002] Conventionally, in biological water treatment, the activated sludge method that utilizes aggregates of microorganisms called flocs (aerobic biological sludge) has been used. In the activated sludge method, it is possible to remove not only organic matter and nitrogen in water but also phosphorus.

[0003] For example, Patent Document 1 discloses a wastewater treatment apparatus including a membrane separation device and having a partition plate disposed above the membrane separation device. According to Patent Document 1, it is shown that nitrogen and phosphorus can be simultaneously removed from sewage.

[0004] Further, Patent Document 2 discloses a method in which influent sewage is subjected to solid-liquid separation into separated water and separated sludge, the separated water is introduced into a biological treatment tank for treatment, and the separated sludge is concentrated by a concentrator, and a concentrated separation liquid containing organic matter is transferred to a biological reaction tank.

[0005] Also, Patent Document 3 discloses a method for removing nitrogen and phosphorus in wastewater by performing intermittent aeration treatment using a first aeration tank and a second aeration tank connected in series.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] By the way, when biologically treating phosphorus-containing water, for example, when the phosphorus concentration in the phosphorus-containing water fluctuates due to rainfall or the like, the phosphorus removal performance may decrease. In this case, there is a problem that it takes a long time to recover the phosphorus removal performance.

[0008] Therefore, an object of the present disclosure is to provide a method for treating phosphorus-containing water and an apparatus for treating phosphorus-containing water that can quickly recover phosphorus removal performance.

Means for Solving the Problems

[0009] The method for treating phosphorus-containing water according to the present disclosure includes a continuous water flow type biological treatment step of biologically treating the phosphorus-containing water with biological sludge while continuously flowing the phosphorus-containing water into a continuous biological treatment tank, a granular sludge formation step of forming granular sludge, and a sludge supply step of supplying the granular sludge formed in the granular sludge formation step to the continuous biological treatment tank. In the sludge supply step, the supply amount of the granular sludge supplied to the continuous biological treatment tank is controlled based on the phosphorus removal performance in the continuous biological treatment tank.

[0010] Further, in the method for treating phosphorus-containing water, it is preferable to determine the daily supply amount of the granular sludge supplied to the continuous biological treatment tank based on the phosphorus removal performance in the continuous biological treatment tank within a past predetermined period and the daily supply amount of the granular sludge supplied to the continuous biological treatment tank within the past predetermined period.

[0011] Further, in the method for treating phosphorus-containing water, when the phosphorus removal performance in the continuous biological treatment tank deteriorates or is expected to deteriorate, it is preferable to increase the supply amount of the granular sludge supplied to the continuous biological treatment tank compared to when the phosphorus removal performance in the continuous biological treatment tank improves.

[0012] In the method for treating phosphorus-containing water, it is preferable to set the daily supply amount of the granular sludge supplied to the continuous biological treatment tank within the range of 0 to 20 times the daily supply amount of the granular sludge supplied to the continuous biological treatment tank on the previous day, based on the phosphorus removal performance in the continuous biological treatment tank.

[0013] The phosphorus-containing water treatment apparatus of the present disclosure includes a continuous biological treatment tank that continuously treats the phosphorus-containing water with biological sludge while continuously flowing in the phosphorus-containing water, a granular sludge forming means for forming granular sludge, a sludge supply means for supplying the granular sludge formed by the granular sludge forming means to the continuous biological treatment tank, and a control means for controlling the supply amount of the granular sludge supplied to the continuous biological treatment tank by the sludge supply means based on the phosphorus removal performance in the continuous biological treatment tank.

[0014] In the phosphorus-containing water treatment apparatus, it is preferable that the control means determines the daily supply amount of the granular sludge supplied to the continuous biological treatment tank based on the phosphorus removal performance in the continuous biological treatment tank within a past predetermined period and the daily supply amount of the granular sludge supplied to the continuous biological treatment tank within the past predetermined period.

[0015] In the phosphorus-containing water treatment apparatus, when the phosphorus removal performance in the continuous biological treatment tank deteriorates or is expected to deteriorate, it is preferable that the control means increases the supply amount of the granular sludge supplied to the continuous biological treatment tank compared to when the phosphorus removal performance in the continuous biological treatment tank improves.

[0016] In the phosphorus-containing water treatment apparatus, it is preferable that the control means sets the daily supply amount of the granular sludge supplied to the continuous biological treatment tank within the range of 0 to 20 times the daily supply amount of the granular sludge supplied to the continuous biological treatment tank on the previous day, based on the phosphorus removal performance in the continuous biological treatment tank.

Advantages of the Invention

[0017] According to the present disclosure, it is possible to provide a method for treating phosphorus-containing water and a device for treating phosphorus-containing water that can quickly restore the phosphorus removal performance.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present disclosure will be described. Note that this embodiment is an example of implementing the present disclosure, and the present disclosure is not limited to this embodiment.

[0020] FIG. 1 is a schematic diagram showing an example of the configuration of a device for treating phosphorus-containing water according to the present embodiment. The device 1 for treating phosphorus-containing water shown in FIG. 1 includes a raw water tank 10, a semi-batch biological treatment tank 12, a continuous biological treatment tank 14, a sedimentation tank 16, and a control device 18. Here, the "continuous type" in this specification is a method as opposed to the batch type, and is distinguished from the semi-batch treatment in which the inflow of the water to be treated, biological treatment, sedimentation of sludge, and discharge of the treated water are performed in one tank, such as the semi-batch type. The continuous biological treatment tank 14 is continuously supplied with phosphorus-containing water, but this method is not limited to the method of continuously charging phosphorus-containing water into the tank for operation. It may also be a method of supplying phosphorus-containing water to the tank for operation by a pump using a principle such as a reciprocating motion of a diaphragm pump, etc., or controlling the operation - stop of the pump according to the water level of the raw water tank 10 installed in the previous stage of the tank (when the water level is high, the pump is operated, and when the water level is low, the pump is stopped) to supply phosphorus-containing water to the tank, such as a simulated continuous water flow method.

[0021] The phosphorus-containing water treatment apparatus 1 shown in Fig. 1 includes raw water pipes (20a, 20b), a first treated water pipe 22, a second treated water pipe 24, a third treated water pipe 26, sludge return pipes (28a, 28b, 28c), a sludge discharge pipe 30, a raw water pump 32, sludge return pumps (34a, 34b), electromagnetic valves (36a, 36b, 36c, 36d, 36e), a valve 38, a sludge supply pipe 40, and a sludge supply pump 42.

[0022] One end of the raw water pipe 20a is connected to the raw water tank 10, and the other end is connected to the semi-batch biological treatment tank 12 via the raw water pump 32 and the electromagnetic valve 36a. Also, one end of the raw water pipe 20b is connected to the raw water pipe 20a, and the other end is connected to the continuous biological treatment tank 14 via the electromagnetic valve 36b. One end of the first treated water pipe 22 is connected to the semi-batch biological treatment tank 12, and the other end is connected to the continuous biological treatment tank 14 via the electromagnetic valve 36e. One end of the second treated water pipe 24 is connected to the continuous biological treatment tank 14, and the other end is connected to the sedimentation tank 16. The third treated water pipe 26 is connected to the sedimentation tank 16. One end of the sludge return pipe 28a is connected to the continuous biological treatment tank 14, and the other end is connected to the semi-batch biological treatment tank 12 via the sludge return pump 34a. One end of the sludge discharge pipe 30 is connected to the sedimentation tank 16. One end of the sludge return pipe 28b is connected to the sludge discharge pipe 30, and the other end is connected to the continuous biological treatment tank 14 via the sludge return pump 34b and the electromagnetic valve 36c. One end of the sludge return pipe 28c is connected to the sludge return pipe 28b, and the other end is connected to the semi-batch biological treatment tank 12 via the electromagnetic valve 36d.

[0023] Also, one end of the sludge supply pipe 40 is connected to the semi-batch biological treatment tank 12, and the other end is connected to the continuous biological treatment tank 14 via the sludge supply pump 42.

[0024] In the phosphorus-containing water treatment apparatus 1 shown in Fig. 1, the semi-batch biological treatment tank 12 functions as a granule sludge forming means for forming granule sludge. In the semi-batch biological treatment tank 12, as will be described later, granule sludge is formed by carrying out an operation having an inflow step, a biological treatment step, a sedimentation step, and a discharge step. The granule sludge forming means in the present embodiment is not limited to the semi-batch biological treatment tank 12 in which an operation having an inflow step, a biological treatment step, a sedimentation step, and a discharge step is carried out, and a conventionally known apparatus capable of forming granule sludge may be used.

[0025] In the phosphorus-containing water treatment apparatus 1 shown in Fig. 1, the sludge supply pipe 40 and the sludge supply pump 42 installed in the sludge supply pipe 40 function as sludge supply means for supplying the granule sludge formed in the semi-batch biological treatment tank 12 to the continuous biological treatment tank 14. An electromagnetic valve may be installed in the sludge supply pipe 40 as necessary.

[0026] The control device 18 is composed of, for example, a microcomputer and electronic circuits including a CPU that calculates a program, a ROM and a RAM that store the program and calculation results, reads out a predetermined program stored in the ROM or the like, and executes the program to control the operation of the water treatment apparatus 1. The control device 18 is electrically connected to each pump and each electromagnetic valve by, for example, wire or wirelessly, and is configured to control the operation of the pump and the opening and closing of the electromagnetic valve. Further, the control device 18 functions as control means for controlling the supply amount of the granule sludge supplied to the continuous biological treatment tank 14 based on the phosphorus removal performance in the continuous biological treatment tank 14.

[0027] An example of the operation of the phosphorus-containing water treatment apparatus 1 of the present embodiment will be described. The phosphorus-containing water to be treated may contain not only phosphorus but also organic substances and the like. Examples of the phosphorus-containing water include wastewater from food processing factories, chemical factories, semiconductor factories, machine factories, sewage, night soil, river water, and the like.

[0028] The control device 18 operates the treated water pump 32 and opens the electromagnetic valve 36b, so that the phosphorus-containing water in the raw water tank 10 is continuously supplied to the continuous biological treatment tank 14 through the treated water pipes 20a and 20b. In the continuous biological treatment tank 14, the phosphorus-containing water is biologically treated by the biological sludge in the tank (continuous water flow biological treatment process). In the continuous biological treatment tank 14, the phosphorus-containing water may be biologically treated under aerobic conditions or under anaerobic conditions. The continuous biological treatment tank 14 may be a biological treatment tank using the standard activated sludge method, but is not limited thereto. For example, in terms of efficiently performing biological phosphorus removal, a biological treatment system using the AO method, the A2O method, etc. (for example, a system composed of an anaerobic tank - an aerobic tank or an anaerobic tank - an anoxic tank - an aerobic tank) may also be used. In the case of the standard activated sludge method, in terms of biological phosphorus removal, it is preferable to adopt an operation method (pseudo-anaerobic aerobic method) in which the aeration amount in the upstream part of the continuous biological treatment tank 14 is restricted.

[0029] The treated water biologically treated in the continuous biological treatment tank 14 is supplied from the second treated water pipe 24 to the sedimentation tank 16, and biological sludge is separated from the treated water. The treated water from which the biological sludge has been separated is discharged out of the system from the third treated water pipe 26. The biological sludge deposited at the bottom of the sedimentation tank 16 is discharged out of the system from the sludge discharge pipe 30 when the valve 38 is opened, or the sludge return pump 34b is operated by the control device 18, and the electromagnetic valve 36c or 36d is opened, and it is returned to the continuous biological treatment tank 14 from the sludge return pipe 28b, or returned to the semi-batch biological treatment tank 12 from the sludge return pipe 28c. Also, for example, the sludge return pump 34a may be operated by the control device 18, and the biological sludge in the continuous biological treatment tank 14 may be returned to the semi-batch biological treatment tank 12 from the sludge return pipe 28a.

[0030] When operating the semi-batch biological treatment tank 12, the control device 18 opens the electromagnetic valve 36a, and a part of the phosphorus-containing water flows from the water pipe 20a to be treated into the semi-batch biological treatment tank 12 ((1) inflow step). After a predetermined amount of phosphorus-containing water has flowed into the semi-batch biological treatment tank 12, the electromagnetic valve 36a is closed and the inflow step is stopped. Then, in the semi-batch biological treatment tank 12, the water to be treated is biologically treated by biological sludge ((2) biological treatment step). For example, in the semi-batch biological treatment tank 12, under aerobic conditions, the organic matter in the phosphorus-containing water is oxidized and decomposed by aerobic biological sludge, the nitrogen compound is nitrified by biological sludge containing nitrifying bacteria, or under anaerobic conditions, the nitrogen compound is denitrified by biological sludge containing denitrifying bacteria. If the biological treatment by the continuous biological treatment tank 14 is aerobic treatment, it is preferable that the biological treatment by the semi-batch biological treatment tank 12 is also aerobic treatment. If the biological treatment by the continuous biological treatment tank 14 is anaerobic treatment, it is preferable that the biological treatment by the semi-batch biological treatment tank 12 is also anaerobic treatment.

[0031] After the above biological treatment process is carried out for a predetermined time, the inside of the tank is left in a static state, and the biological sludge in the semi-batch biological treatment tank 12 is allowed to settle for a predetermined time ((3) sedimentation step), and separated into biological sludge and treated water. Next, the control device 18 opens the electromagnetic valve 36e, and the supernatant water (treated water) in the semi-batch biological treatment tank 12 is discharged from the semi-batch biological treatment tank 12 ((4) discharge step) and supplied from the first treated water pipe 22 to the continuous biological treatment tank 14. By repeating the above steps (1) to (4), the biological sludge in the semi-batch biological treatment tank 12 is granulated, and granular sludge is formed (granular sludge formation step). However, the treatment by the semi-batch biological treatment tank 12 is not limited to the form in which the inflow step and the discharge step are performed separately as described above, and the discharge step may be performed while the inflow step is being performed. Taking the water treatment device 1 in FIG. 1 as an example, when the control device 18 opens the electromagnetic valve 36a and the electromagnetic valve 36e, a part of the phosphorus-containing water flows into the semi-batch biological treatment tank 12 from the water to be treated pipe 20a, and the treated water in the semi-batch biological treatment tank 12 is discharged to the first treated water pipe 22 ((1) inflow step / discharge step). After a predetermined time has elapsed, the electromagnetic valve 36a and the electromagnetic valve 36e are closed, and in the semi-batch biological treatment tank 12, the phosphorus-containing water is biologically treated by the biological sludge ((2) biological treatment step). After the biological treatment step, the inside of the tank is left in a static state, and the biological sludge in the semi-batch biological treatment tank 12 is allowed to settle for a predetermined time ((3) sedimentation step), and separated into biological sludge and treated water. By repeating the above steps (1) to (3), the biological sludge in the semi-batch biological treatment tank 12 is granulated, and granular sludge is formed (granular sludge formation step). The granular sludge formed in the semi-batch biological treatment tank 12 refers to sludge in which self-granulation has progressed. For example, it refers to biological sludge in which the average particle size of the sludge is 0.2 mm or more, and the proportion of sludge with a particle size of 0.2 mm or more is 40% or more. The particle size of the granular sludge can be measured by, for example, a laser diffraction particle size measuring device or a sieve.

[0032] In the water treatment apparatus 1 of FIG. 1, the treated water discharged from the semi-batch biological treatment tank 12 is supplied into the continuous biological treatment tank 14 from the first treated water pipe 22, but is not limited thereto. For example, it may be directly discharged out of the system without being supplied to the continuous biological treatment tank 14, or may be supplied to the sedimentation tank 16.

[0033] Also, in the water treatment apparatus 1 of FIG. 1, the control device 18 operates the sludge supply pump 42, and the granular sludge formed in the semi-batch biological treatment tank 12 is supplied from the sludge supply pipe 40 to the continuous biological treatment tank 14 (sludge supply step). In this sludge supply step, based on the phosphorus removal performance in the continuous biological treatment tank 14, the supply amount of the granular sludge supplied to the continuous biological treatment tank 14 is controlled. For example, when the phosphorus removal performance in the continuous biological treatment tank 14 deteriorates, the control device 18 controls the operation of the sludge supply pump 42 so that the supply amount of the granular sludge from the semi-batch biological treatment tank 12 to the continuous biological treatment tank 14 increases compared to when it was improving before the deterioration of the phosphorus removal performance. Further, after the phosphorus removal performance has recovered in the continuous biological treatment tank 14 (i.e., when the phosphorus removal performance improves), the control device 18 may control the operation of the sludge supply pump 42 so that the supply amount of the granular sludge decreases compared to when the phosphorus removal performance deteriorated. Regarding the supply amount of the granular sludge, it is desirable to increase or decrease the supply amount of the granular sludge per day, but it is not limited thereto.

[0034] Thus, by controlling the supply amount of the granular sludge from the semi-batch biological treatment tank 12 to the continuous biological treatment tank 14 based on the phosphorus removal performance in the continuous biological treatment tank 14, even when the phosphorus removal performance in the continuous biological treatment tank 14 deteriorates, the phosphorus removal performance in the continuous biological treatment tank 14 can be recovered early. The mechanism by which the above effect is achieved is not fully clear, but the following is speculated.

[0035] Phosphorus in phosphorus-containing water is treated by bacteria with a high phosphorus accumulation capacity contained in sludge (hereinafter referred to as phosphorus-accumulating bacteria). For example, phosphorus-accumulating bacteria take in organic matter under anaerobic conditions and discharge phosphorus, and phosphorus is removed from phosphorus-containing water by taking in more phosphorus than was discharged under aerobic conditions. Generally, a large number of phosphorus-accumulating bacteria are present in granular sludge. In particular, in the semi-batch biological treatment tank 12, since the conditions necessary for phosphorus-accumulating bacteria to discharge and take in phosphorus can be created in the biological treatment process, it is considered that more phosphorus-accumulating bacteria are present in the granular sludge formed in the semi-batch biological treatment tank 12. In particular, in the biological treatment process, by creating aerobic conditions by aeration, it becomes possible to have more phosphorus-accumulating bacteria in the granular sludge. Also, the average particle size of the granular sludge is large (for example, 0.2 mm or more), and the center of the granular sludge is in an anaerobic state. Therefore, the granular sludge is an environment in which phosphorus-accumulating bacteria can more easily release and take in phosphorus than ordinary activated sludge.

[0036] By the way, the deterioration of phosphorus removal performance generally becomes prominent when the phosphorus concentration of phosphorus-containing water decreases due to rainfall or the like. This is due to the decrease in the amount of phosphorus discharged by phosphorus-accumulating bacteria in the tank and the decrease in the phosphorus removal activity of phosphorus-accumulating bacteria. Therefore, when the phosphorus concentration of phosphorus-containing water decreases, the phosphorus removal performance in the continuous biological treatment tank 14 may deteriorate. On the other hand, in the semi-batch biological treatment tank 12, as described above, since it is an environment where phosphorus-accumulating bacteria are likely to exist, even when the phosphorus concentration of phosphorus-containing water decreases, the impact on phosphorus removal performance is minor, and it is possible to form granular sludge with high phosphorus removal activity. Therefore, when the phosphorus removal performance in the continuous biological treatment tank 14 deteriorates due to fluctuations in the phosphorus concentration in phosphorus-containing water, by increasing the supply amount of granular sludge from the semi-batch biological treatment tank 12 to the continuous biological treatment tank 14 compared to when it was improved before the deterioration of the phosphorus removal performance, the phosphorus removal performance in the continuous biological treatment tank 14 can be restored early. After the phosphorus removal performance in the continuous biological treatment tank 14 has recovered, it is desirable to reduce the supply amount of granular sludge compared to when the phosphorus removal performance deteriorated.

[0037] The determination of the phosphorus removal performance in the continuous biological treatment tank 14 may be made, for example, based on the phosphorus concentration in the treated water. In the phosphorus-containing water treatment apparatus 1 of FIG. 1, for example, a phosphorus concentration sensor is installed in the second treated water pipe 24, and the phosphorus concentration in the treated water passing through the second treated water pipe 24 is measured by the phosphorus concentration sensor. Then, when the phosphorus concentration measured by the phosphorus concentration sensor is equal to or lower than a predetermined reference value, for example, the control device 18 determines that it is the time of improvement of the phosphorus removal performance, and when the phosphorus concentration measured by the phosphorus concentration sensor exceeds the predetermined reference value, it determines that it is the time of deterioration of the phosphorus removal performance, and performs the control of the granule sludge supply amount described above.

[0038] In addition, the determination of the phosphorus removal performance in the continuous biological treatment tank 14 is preferably based on, for example, the oxidation-reduction potential (hereinafter referred to as ORP) at a predetermined position in the continuous biological treatment tank 14 or the anaerobic discharge concentration of phosphorus, in terms of being able to quickly grasp the phosphorus removal performance in the continuous biological treatment tank 14. The measurement point of the ORP is preferably set at the location where the ORP decreases the most after previously grasping the ORP profile in the continuous biological treatment tank 14 in a state where phosphorus removal is performed well (for example, the concentration of phosphate phosphorus in the treated water is 1 mgP / L or less, or the removal rate of total phosphorus is 90% or more). Then, for example, when the ORP measured at the above location is equal to or lower than a predetermined reference value, the control device 18 determines that it is a time when the phosphorus removal performance is improving, and when the ORP measured at the above location exceeds the predetermined reference value, the control device 18 determines that it is a time when the phosphorus removal performance is deteriorating, and performs the control of the granule sludge supply amount described above. When the continuous biological treatment tank 14 is equipped with an anaerobic tank, the ORP in the anaerobic tank may be measured. Regarding the measurement point of the anaerobic discharge concentration of phosphorus, the profile of the phosphate phosphorus concentration in the continuous biological treatment tank 14 in a state where phosphorus removal is performed well is previously grasped, and it is preferably set at the location where the phosphate phosphorus concentration increases the most (that is, the location where the increase in the phosphorus concentration due to the discharge of phosphorus is the highest). Then, for example, when the phosphate phosphorus concentration measured at the above location exceeds a predetermined reference value, the control device 18 determines that it is a time when the phosphorus removal performance is improving, and when the phosphate phosphorus concentration measured at the above location is equal to or lower than the predetermined reference value, the control device 18 determines that it is a time when the phosphorus removal performance is deteriorating, and performs the control of the supply amount of the granules described above. When the continuous biological treatment tank 14 is equipped with an anaerobic tank, the phosphate phosphorus concentration in the anaerobic tank may be measured.

[0039] Also, in the phosphorus-containing water treatment apparatus 1 shown in FIG. 1, when the control device 18 assumes deterioration of the phosphorus removal performance in the continuous biological treatment tank 14, the amount of granular sludge supplied from the semi-batch biological treatment tank 12 to the continuous biological treatment tank 14 may be increased compared to (more than when it improves) before the assumption of deterioration of the phosphorus removal performance. The assumption of deterioration of the phosphorus removal performance may be made, for example, based on a precipitation forecast in a weather forecast. For example, the control device 18 communicates with a weather information server installed in an organization that handles weather information such as the Japan Meteorological Agency via a wired or wireless communication network to obtain a future precipitation forecast in the area where the phosphorus-containing water to be treated is discharged. Then, when the rainfall amount after a predetermined time (for example, 1 hour) from the original time exceeds a preset reference value among the obtained precipitation forecasts, the control device 18 increases the amount of granular sludge supplied assuming that the deterioration of the phosphorus removal performance is expected. By such control, deterioration of the phosphorus removal performance of the continuous biological treatment tank 14 can be prevented in advance, and stable phosphorus treatment becomes possible.

[0040] When the phosphorus removal performance of the continuous biological treatment tank 14 deteriorates or is assumed to deteriorate, it is preferable to increase the amount of granular sludge supplied to the continuous biological treatment tank 14 to 2 times or more the amount of granular sludge supplied during improvement, or to increase it so as to increase by 4% or more with respect to the proportion of granular sludge in the continuous biological treatment tank 14 during improvement.

[0041] The daily supply amount of granular sludge to the continuous biological treatment tank 14 is preferably determined based on the phosphorus removal performance in the continuous biological treatment tank 14 within a predetermined past period (the predetermined past period is, for example, a past period (e.g., one week) from the present), and the daily supply amount of granular sludge supplied to the continuous biological treatment tank 14 within the predetermined past period. For example, during the past week, if the phosphorus removal performance is good and there is no variation in the daily supply amount of granular sludge, it may not be necessary to supply granular sludge to the continuous biological treatment tank. The daily supply amount of granular sludge is preferably 0.2% or more based on the sludge amount in the continuous biological treatment tank 14, and more preferably, the supply is made so that the occupancy rate of granular sludge in the sludge in the continuous biological treatment tank 14 is 2% or more in order to further stabilize the phosphorus removal performance.

[0042] The daily supply amount of granular sludge to be supplied to the continuous biological treatment tank 14 is preferably set within the range of 0 to 20 times the daily supply amount of granular sludge supplied to the continuous biological treatment tank 14 the previous day based on the phosphorus removal performance in the continuous biological treatment tank 14, for example, in terms of suppressing the deterioration of the sludge properties in the continuous biological treatment tank 14. For example, when the phosphorus removal performance of the continuous biological treatment tank 14 deteriorates or is expected to deteriorate, the daily supply amount of granular sludge to be supplied to the continuous biological treatment tank 14 is preferably set within the range of more than 1 time and 20 times or less the daily supply amount of granular sludge supplied to the continuous biological treatment tank the previous day, and more preferably within the range of 2 times or more and 20 times or less. Also, for example, when the phosphorus removal performance of the continuous biological treatment tank 14 improves, the daily supply amount of granular sludge to be supplied to the continuous biological treatment tank 14 is preferably set within the range of 0 times or more and 1 time or less the daily supply amount of granular sludge supplied to the continuous biological treatment tank 14 the previous day. Such setting is performed, for example, by the control device 18.

[0043] After increasing the supply amount of granular sludge to the continuous biological treatment tank 14, when a recovery trend is observed in the phosphorus removal performance in the continuous biological treatment tank 14, the supply amount of the granular sludge may be restored. For example, the supply of the increased granular sludge is continued until an increase in the phosphate phosphorus concentration measured at the above-described measurement points in the continuous biological treatment tank 14 is confirmed. Then, when an increase in the phosphate phosphorus concentration is confirmed, it is assumed that the phosphorus removal performance is trending towards recovery, and the supply amount of the granular sludge is restored. The determination of the recovery trend of the phosphorus removal performance is not limited to the phosphate phosphorus concentration. For example, the aforementioned ORP or the phosphorus concentration in the treated water may also be used.

[0044] The MLSS concentration in the semi-batch biological treatment tank 12 is preferably operated in the range of 2000 to 20000 mg / L. In addition, in order to maintain the soundness (sedimentation property, activity, etc.) of the biological sludge, it is desirable to maintain an appropriate sludge load, preferably in the range of 0.05 to 0.60 kg BOD / MLSS / day, more preferably in the range of 0.1 to 0.5 kg BOD / MLSS / day. Therefore, it is desirable to withdraw the granular sludge from the tank.

[0045] In the formation of granular sludge by the semi-batch biological treatment tank 12, it is desirable to appropriately control the sedimentation time and the drainage inflow rate per batch. The sedimentation time of the biological sludge is calculated from the distance from the water surface to the target sludge interface position and the sedimentation rate of the biological sludge. For example, it is preferably set between 4 minutes / m and 15 minutes / m, and more preferably set between 5 minutes / m and 10 minutes / m. In addition, the drainage inflow rate (the ratio of the influent water to the effective volume during the reaction) is preferably in the range of 20% or more and 120% or less, and more preferably in the range of 40% or more and 120% or less.

[0046] The pH in the semi-batch biological treatment tank 12 is preferably adjusted to the range of 6 to 9 suitable for general biological treatment, and more preferably to the range of 6.5 to 7.5. When the pH value is outside the above range, it is preferable to adjust the pH using an acid or an alkali. The dissolved oxygen (DO) in the semi-batch biological treatment tank 12 is preferably 0.5 mg / L or more, and more preferably 1 mg / L or more, which is suitable for general biological treatment.

[0047] In the continuous biological treatment tank 14, for example, the biological treatment may be performed in a form by the standard activated sludge method, or may be a system such as the A2O method (Anaerobic - Anoxic - Oxic Process) or the AO method (Anaerobic - Oxic Process) (a system equipped with an anoxic treatment tank or an anaerobic treatment tank), or may be a device for performing biological treatment by a system such as the oxidation ditch method or the step - inflow type multi - stage activated sludge method. Also, it may be a device for performing biological treatment in the presence of a carrier such as polyurethane, plastic, or resin.

[0048] The continuous biological treatment tank 14 is preferably operated, for example, with the sludge concentration in the tank in the range of 2000 to 20000 mg / L. Also, in order to maintain the soundness (sedimentation property, activity, etc.) of the biological sludge, the sludge load is preferably in the range of 0.05 to 0.6 kgBOD / MLSS / day, and more preferably in the range of 0.1 to 0.5 kgBOD / MLSS / day.

[0049] In this embodiment, a sedimentation tank 16 is used as the solid - liquid separation device for separating biological sludge from the treated water, but it is not limited thereto. For example, a pressurized flotation device, a filtration device, a membrane separation device, etc. may also be used.

Examples

[0050] Hereinafter, examples will be given to explain the present disclosure more specifically in detail, but the present disclosure is not limited to the following examples.

[0051] Using the apparatus shown in Fig. 1, simulated wastewater treatment was carried out. As the simulated wastewater, simulated sewage mainly composed of skipjack extract and peptone (organic matter concentration: 100 - 150 mg / L, total phosphorus concentration: 4 - 6 mg / L) was used. For the continuous biological treatment tank, a system of the AO method consisting of an anaerobic tank and an aerobic tank was used.

[0052] The volume loading of the continuous biological treatment tank was set to 0.4 - 0.7 kg / (m 3 ·d), and the SRT of the continuous biological treatment tank was set to 20 days. The above simulated wastewater was continuously fed into the continuous biological treatment tank. The return sludge from the sedimentation tank to the continuous biological treatment tank was set to a flow rate of 30% of the flow rate of the simulated wastewater. Also, as the initial input sludge of the continuous biological treatment tank, floating activated sludge was used. Further, the granular sludge formed by the semi-batch biological treatment tank was supplied to the continuous biological treatment tank at a rate of 0.24 g per day, and the presence rate of the granules in the sludge in the continuous biological treatment tank was set to 2.3%.

[0053] Fig. 2 is a graph showing the changes in the phosphorus concentration of the simulated wastewater, the phosphorus concentration of the treated water discharged from the continuous biological treatment tank, and the phosphate phosphorus concentration in the anaerobic tank during the test period of the example. However, Fig. 2 shows the concentration changes after the 644th day from the start of water flow. From the 644th day to the 653rd day after the start of continuous water flow of the simulated wastewater, the phosphate phosphorus concentration in the anaerobic tank changed at a value nearly twice that of the phosphorus concentration in the simulated wastewater, and the phosphorus concentration in the treated water changed at a low concentration. Although not shown in the figure, during the same period, the ORP in the anaerobic tank changed in the range of -150 mV to -200 mV. From the 654th day after the start of continuous water flow of the simulated wastewater for 2 days, the supply of the simulated wastewater was stopped, and instead, well water (organic matter concentration: 0 mg / L, total phosphorus concentration: 0 mg / L) was continuously fed. When the continuous water flow of well water to the continuous biological treatment tank was started, the phosphate phosphorus concentration in the anaerobic tank decreased rapidly and reached 0 mg / L on the 2nd day after the start of well water flow. Although not shown in the figure, during the same period, the ORP in the anaerobic tank increased from 0 mV to 90 mV.

[0054] When the concentration of phosphorus in phosphorus in the anaerobic tank decreased to 0 mg / L, the supply of well water was stopped, the continuous water flow to the simulated wastewater was resumed, and the daily supply amount of granular sludge to the continuous biological treatment tank was increased to twice the original amount (0.48 g). By resuming the continuous water flow of the simulated wastewater, the phosphorus concentration in the treated water temporarily increased to 5.8 mg / L, and the phosphorus removal performance of the continuous biological treatment tank deteriorated. However, by continuing to supply the increased amount of granular sludge, the phosphorus concentration in the treated water rapidly decreased to 1 mg / L or less thereafter. After the phosphorus concentration in the treated water decreased to 1 mg / L or less, the daily supply amount of granular sludge to the continuous biological treatment tank was returned to 0.24 g, but the phosphorus concentration in the treated water remained at 1 mg / L or less thereafter.

[0055] The rapid recovery of the phosphorus removal performance shown in the examples is a result that cannot be obtained when the supply is continued at the normal amount without increasing the supply amount of granular sludge.

Explanation of Signs

[0056] 1 Treatment apparatus for phosphorus-containing water, 10 Raw water tank, 12 Semi-batch biological treatment tank, 14 Continuous biological treatment tank, 16 Settling tank, 18 Control device, 20a, 20b Treated water pipe, 22 First treated water pipe, 24 Second treated water pipe, 26 Third treated water pipe, 28a~28c Sludge return pipe, 30 Sludge discharge pipe, 32 Treated water pump, 34a, 34b Sludge return pump, 36a~36e Electromagnetic valve, 38 Valve, 40 Sludge supply pipe, 42 Sludge supply pump.

Claims

1. A continuous water flow type biological treatment step of biologically treating the phosphorus-containing water with biological sludge while continuously flowing the phosphorus-containing water into a continuous type biological treatment tank; A granular sludge forming step of forming granular sludge; A sludge supply step of supplying the granular sludge formed in the granular sludge forming step to the continuous type biological treatment tank, comprising: In the sludge supply step, a method for treating phosphorus-containing water, characterized in that the supply amount of the granular sludge supplied to the continuous type biological treatment tank is controlled based on the phosphorus removal performance in the continuous type biological treatment tank.

2. The method for treating phosphorus-containing water according to claim 1, characterized in that the daily supply amount of the granular sludge supplied to the continuous type biological treatment tank is determined based on the phosphorus removal performance in the continuous type biological treatment tank within a past predetermined period and the daily supply amount of the granular sludge supplied to the continuous type biological treatment tank within the past predetermined period.

3. The method for treating phosphorus-containing water according to claim 1, characterized in that when the phosphorus removal performance in the continuous type biological treatment tank deteriorates or is assumed to deteriorate, the supply amount of the granular sludge supplied to the continuous type biological treatment tank is increased compared to when the phosphorus removal performance in the continuous type biological treatment tank improves.

4. The method for treating phosphorus-containing water according to claim 1, characterized in that the daily supply amount of the granular sludge supplied to the continuous type biological treatment tank is set within a range of 0 to 20 times the daily supply amount of the granular sludge supplied to the continuous type biological treatment tank on the previous day based on the phosphorus removal performance in the continuous type biological treatment tank.

5. A continuous type biological treatment tank for biologically treating the phosphorus-containing water with biological sludge while continuously flowing the phosphorus-containing water; Granular sludge forming means for forming granular sludge; Sludge supply means for supplying the granular sludge formed by the granular sludge forming means to the continuous type biological treatment tank; A treatment apparatus for phosphorus-containing water, comprising control means for controlling the supply amount of the granular sludge supplied to the continuous type biological treatment tank by the sludge supply means based on the phosphorus removal performance in the continuous type biological treatment tank.

6. The control means determines the daily supply amount of the granular sludge supplied to the continuous biological treatment tank based on the phosphorus removal performance in the continuous biological treatment tank within a past predetermined period and the daily supply amount of the granular sludge supplied to the continuous biological treatment tank within the past predetermined period. The treatment apparatus for phosphorus-containing water according to claim 5, characterized in that.

7. When the phosphorus removal performance in the continuous biological treatment tank deteriorates or is assumed to deteriorate, the control means increases the supply amount of the granular sludge supplied to the continuous biological treatment tank compared to when the phosphorus removal performance in the continuous biological treatment tank improves. The treatment apparatus for phosphorus-containing water according to claim 5, characterized in that.

8. The control means sets the daily supply amount of the granular sludge supplied to the continuous biological treatment tank within a range of 0 to 20 times the daily supply amount of the granular sludge supplied to the continuous biological treatment tank on the previous day based on the phosphorus removal performance in the continuous biological treatment tank. The treatment apparatus for phosphorus-containing water according to claim 5, characterized in that.

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