Phosphorus separation system

Abstract

To provide a phosphorus separation system capable of efficiently separating and recovering phosphorus in treated water.SOLUTION: A phosphorus separation system 100 includes an adding device 305 for adding a phosphorus separator to treated water in a water tank 300, an agitating device 306 for stirring treated water to which the phosphorus separator has been added, and a control device 310 for controlling the adding device 305 and agitating device 306. The control device 310 repeats the process of adding the phosphorus separator by the adding device 305, agitating the treated water to which the phosphorus separator has been added by the agitating device 306, and allowing the treated water to stand still after the agitating process is completed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a phosphorus separation system for separating and recovering phosphorus from treated water containing phosphorus.

Background Art

[0002] Conventionally, as a method for separating and recovering phosphorus from desorbed water generated from the sludge concentration step and dehydration step in a sewage treatment plant and returned to the previous step of sewage treatment, the HAP method using a calcium ion source is known.

[0003] The HAP method is a method that utilizes the crystallization phenomenon of hydroxyapatite generated by the reaction of PO4 3- , Ca 2+ and OH - . In this method, Ca 2+ and OH - are added to the treated water containing phosphorus and brought into contact with seed crystals in a supersaturated state (meta-stable region) to crystallize hydroxyapatite on the surface of the seed crystals, thereby separating and recovering phosphorus in the treated water. When the phosphorus concentration of the treated water is low, a competing reaction with calcium carbonate may occur, and thus a treatment such as decarbonation may be required. Substances such as phosphate ore, bone char, and calcium silicate hydrate are used as the seed crystals (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, as shown in the phosphorus removal device of Patent Document 1, in the method of simply mixing the treated water containing phosphorus and a phosphorus separation agent (phosphorus removal liquid) to crystallize calcium phosphate, there is a problem that a large amount of phosphorus separation agent is required to increase the phosphorus recovery efficiency.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a phosphorus separation system capable of efficiently separating and recovering phosphorus in water to be treated.

Means for Solving the Problems

[0007] To achieve the above object, the phosphorus separation system of the present invention includes an adding device, a stirring device, and a control device for controlling the adding device and the stirring device. The control device includes a step of adding a phosphorus separation agent to water to be treated containing phosphorus by the adding device, a step of stirring the water to be treated to which the phosphorus separation agent has been added by the stirring device, and a step of stopping the adding device and the stirring device and allowing the water to be treated after the stirring step to stand, and repeating these steps.

Effects of the Invention

[0008] According to the phosphorus separation system of the present invention, phosphorus in water to be treated can be efficiently separated and recovered.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0010] As a result of intensive research to achieve the above object, the inventors of the present invention devised a method of adding a phosphorus separation agent to the water to be treated containing phosphorus, performing stirring, and further allowing the water to be treated to stand for a predetermined time, and found that phosphorus can be efficiently separated and recovered, thus completing the present invention. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0011] [First Embodiment] FIG. 1 is a schematic diagram of a phosphorus separation system 100 according to the first embodiment of the present invention. Here, it is assumed that the water to be treated targeted by the present invention contains a phosphorus component.

[0012] The phosphorus separation system 100 is a system for recovering phosphorus contained in the water to be treated by treating the wastewater obtained from the final sedimentation tank 200 of a sewage treatment plant as the water to be treated. The water to be treated may be, for example, return water, industrial wastewater, garbage leachate, excrement, agricultural wastewater, livestock wastewater, aquaculture wastewater, etc., or treated wastewater such as raw water for water supply.

[0013] In the phosphorus separation system 100, the water to be treated is injected from the final sedimentation tank 200 into the water tank 300. Then, in the water tank 300, by adding a phosphorus separation agent, phosphorus in the water to be treated is separated and recovered, the reclaimed water (separated water) is taken out, and transferred to the phosphorus separation water tank 600. Hereinafter, each component provided in the water tank 300 will be described.

[0014] The water tank 300 is provided with a supply device 301 and a discharge device 302 for the water to be treated. The supply device 301 is a device for supplying the water to be treated from the final sedimentation tank 200 to the water tank 300. The supply device 301 has a valve 303 and is connected to the pipe 201 of the final sedimentation tank 200. Since the water level of the water tank 300 can be detected by a water level detection device 309 described later, the water to be treated is injected up to the water level during the phosphorus separation process.

[0015] The discharge device 302 is a device for discharging the water to be treated from the water tank 300 and transferring it to the phosphorus separation water tank 600. The discharge device 302 has a valve 304 and is connected to the pipe 601 of the phosphorus separation water tank 600. The opening and closing of the valves 303 and 304 are controlled by the control device 310. The control device 310 is composed of a CPU, RAM, ROM, etc., and has the function of a computer. Further, the water tank 300 is provided with a discharge port 311 for collecting the sediment (phosphorus-containing substance) deposited at the bottom thereof.

[0016] A phosphorus concentration detection device 202, which is a sensor for detecting the phosphorus concentration of the water to be treated, is provided in the pipe 201. Since the phosphorus concentration detection device 202 can detect the phosphorus concentration of the water to be treated supplied to the water tank 300, the total amount of the phosphorus separation agent to be added can be estimated according to the value of the phosphorus concentration.

[0017] Further, the water tank 300 is provided with an addition device 305 and a stirring device 306. The addition device 305 has a function of adding a predetermined amount of a phosphorus separation agent to the water tank 300 under the control of the control device 310. The stirring device 306 has a function of stirring the water to be treated in the water tank 300, and the start and stop of the stirring are controlled by the control device 310.

[0018] The phosphorus separation agent is a chemical for removing phosphorus contained in the water to be treated from the water to be treated. As the phosphorus separation agent, any known chemical can be arbitrarily used. For example, an alkaline chemical of sodium hydroxide type may be used. In this embodiment, a separation agent derived from concrete is used. The separation agent derived from concrete is mainly composed of concrete and processed into a form that can be added to the water to be treated. For example, concrete waste materials pulverized into powder, a liquid obtained by dissolving this in water, commercially available products (recycled products of concrete sludge), etc. may be mentioned. Concrete is a strong alkaline agent with a pH value of 12 or more and has a function of increasing the pH value itself. Further, since concrete is contained in lime-based waste materials, these waste materials can be reused, and the cost of the phosphorus separation agent can be suppressed.

[0019] The water tank 300 further includes a pH detection device 307, a phosphorus concentration detection device 308, and a water level detection device 309. The pH detection device 307 is a sensor for detecting the pH value of the water to be treated. When a phosphorus separation agent is added to the water to be treated, the pH value increases. In particular, since the separation of phosphorus is most promoted when the pH value of the water to be treated is 9 to 10, the first addition of the phosphorus separation agent is performed for the purpose of reaching the numerical value of the pH value.

[0020] The phosphorus concentration detection device 308 is a sensor for detecting the phosphorus concentration of the water to be treated. When a phosphorus separation agent is added and mixed with the water to be treated, the phosphorus component in the water to be treated precipitates, so the phosphorus concentration of the water to be treated decreases. When the phosphorus concentration in the water to be treated reaches a predetermined value, the control device 310 stops the repetition of each process. Note that the phosphorus concentration when stopping the repetition of each process can be set as appropriate, and for example, it is preferably in the range of 0.1 to 1.0 mg / L.

[0021] The water level detection device 309 is a sensor for detecting the water level of the water to be treated in the water tank 300. For example, when a part of the water to be treated or the separated water is discharged from the discharge device 302, the water level information is transmitted to the control device 310. When the control device 310 fills the water tank 300 with the water to be treated from the final sedimentation tank 200, it controls the valve 303 of the supply device 301.

[0022] Figure 2 is a schematic flow of the phosphorus separation process performed in the water tank 300. Note that the description will be supplemented with reference to FIGS. 3A and 3B as appropriate. In the phosphorus separation process of the present invention, the addition process, the stirring process, and the standing process are taken as one cycle, and this cycle is repeated a plurality of times. In this schematic flow, this cycle will be described as being performed twice each, but it may be performed three or more times.

[0023] First, the water to be treated containing phosphorus is supplied from the final sedimentation tank 200 to the water tank 300 (step S01). As a result, a predetermined amount of the water to be treated is stored in the water tank 300. Then, the adding device 305 adds a phosphorus separation agent to the water tank 300 (step S02). Here, a part of the total amount of the phosphorus separation agent (that is, the total amount used in one phosphorus separation treatment) determined by the water quality of the water to be treated (phosphorus content rate, turbidity degree, etc.) is added. In other words, in the phosphorus separation treatment of the present invention, among a plurality of cycles, the phosphorus separation agent determined by the water quality of the water to be treated, etc. is added in a divided manner.

[0024] Thereafter, the stirring device 306 stirs the water to be treated (step S03), and further, the water to be treated is allowed to stand for a certain period of time (step S04). By this procedure (the first cycle), the separation of phosphorus is promoted. Then, the adding device 305 adds the remaining phosphorus separation agent of the total amount to the water tank 300 (step S05), and further, after the stirring device 306 stirs the water to be treated (step S06), standing is performed (step S07). By this procedure (the second cycle), the separation of phosphorus is completed.

[0025] FIG. 3A shows the change in the concentration of phosphorus (phosphate ion: PO4 3- ) when powder of PAdeCS (registered trademark, a recycled product of concrete sludge manufactured by Nippon Concrete Industry Co., Ltd.) having a weight ratio of 0.2% is divided and input in two portions at 0.1% by weight ratio as the phosphorus separation agent. Further, FIG. 3B shows the change in the phosphorus concentration when the powder of PAdeCS (registered trademark) having a weight ratio of 0.2% is input at once. That is, in FIGS. 3A and 3B, the addition amount (total amount) of the phosphorus separation agent is the same at 0.2% by weight ratio, but the number of addition times is different.

[0026] In (1) of FIG. 3A, powder of PAdeCS was added to the surplus sludge supernatant at 0.1% by weight ratio and stirred for 10 minutes. And after standing for 30 minutes, the supernatant was taken out. The concentration of phosphorus (PO4 3- ) at this time was 50 [mg / L].

[0027] In (2) of Fig. 3A, 0.1% by weight of PAdeCS powder was further added to the supernatant taken out in the above (1), and it was stirred for 30 minutes. Then, after standing for 30 minutes, the supernatant was taken out. As a result, the phosphorus concentration decreased to 20 [mg / L]. In (3) of Fig. 3A, the supernatant taken out in the above (2) was left standing overnight. As a result, the phosphorus concentration further decreased to 10 [mg / L].

[0028] On the other hand, Fig. 3B is a comparative example of the experiment (Fig. 3A) of the present invention and is a conventionally used method. In Fig. 3B, 0.2% by weight of PAdeCS powder was added to the excess sludge supernatant and stirred for 60 minutes. The PAdeCS added here corresponds to the total amount added in two times in the experiment of Fig. 3A. Then, after standing for 30 minutes, the supernatant was taken out. The phosphorus (PO4 3- ) concentration at this time was 50 [mg / L].

[0029] Although Fig. 3B does not have data on the phosphorus concentration corresponding to (3) in Fig. 3A (after standing overnight), comparing the results of Fig. 3A and Fig. 3B, it can be seen that the recovery efficiency of the phosphorus concentration is higher when the PAdeCS powder is added in small amounts in two divided portions. This is presumably because the PAdeCS added in the first time in Fig. 3A (strongly acidic with a pH value of 12) was mainly consumed for increasing the pH value of the water to be treated. Since the reaction efficiency of the water to be treated is the highest in the range of pH value 9 to 10, when the pH value reaches the above range by the first addition, the subsequent separation of phosphorus proceeds rapidly.

[0030] Returning to Fig. 2, in the second (second cycle) standing step (step S07), when the phosphorus concentration of the water to be treated reaches a predetermined value, the repetition of the addition step, stirring step, and standing step (one cycle) is terminated. Then, solid-liquid separation is performed (step S08). The liquid part (supernatant) of the water to be treated is taken out from the water tank 300 as "separated water" from which phosphorus has been separated and transferred to the phosphorus separation water tank 600. In addition, the precipitate deposited at the bottom of the water tank 300 is taken out as "phosphorus-containing matter" and recovered.

[0031] Next, with reference to FIG. 4, a timing chart regarding phosphorus separation of the water to be treated in the first embodiment will be described. Note that the timing of adding the phosphorus separation agent and stirring described below is merely an example.

[0032] First, by injecting the water to be treated into the water tank 300, the water level (liquid surface) gradually rises. The water level of the water tank 300 is detected by the water level detection device 309, and the water to be treated is injected until it reaches the water level during treatment. Also, in this embodiment, the first stirring step (''Stirring 1'' in the figure) by the stirring device 306 starts from the time T = t0 when the water is being injected.

[0033] When the water level of the water tank 300 reaches the predetermined water level during treatment, the adding step of the phosphorus separation agent by the adding device 305 starts. While continuing stirring, the phosphorus separation agent is added little by little, and the pH value of the water to be treated in the water tank 300 gradually rises. Thereafter, the pH value is detected by the pH detection device 307, and when the pH value reaches the preset value (time T = t2), the adding step of the phosphorus separation agent is terminated. Note that in this adding step, after estimating the total amount of the phosphorus separation agent required in advance, the phosphorus separation agent is added little by little, and the total amount of the phosphorus separation agent added during the period of time T = t1 to t2 is a part of the total amount of the phosphorus separation agent determined by the water quality of the water to be treated and the like.

[0034] In this timing chart, from when the water is being injected (time T = t0), the first cycle stirring step by the stirring device 306 is started, and when the water level reaches the predetermined level (time T = t1), the adding step is started. However, the start timing and end timing of the stirring step and the adding step are not limited to this. For example, the start timing of the stirring step may be at any point during the water injection, or when the predetermined water level is reached (that is, when the water injection is completed). Also, it may be before the start of the adding step of the phosphorus separation agent, or after the adding step (after the start or after the end). Also, it may be simultaneous with the start of the adding step of the phosphorus separation agent. That is, the phosphorus separation agent may be added while stirring, or stirring may be performed after the addition of the phosphorus separation agent.

[0035] In addition, in this timing chart, the stirring process ends in accordance with the timing of the end of the addition process of the phosphorus separating agent. However, after continuing the stirring for a while, it may shift to the standing process. By stopping the addition device 305 and the stirring device 306 with the control device 310, the first standing process ( "Standing 1" in the figure) of the water to be treated starts from time T = t2. Through the standing process, phosphorus is separated from the water to be treated to which the phosphorus separating agent has been added, and the phosphorus concentration of the water to be treated slightly decreases. Then, when a predetermined time has elapsed (time T = t4), the first standing process ends. Thereby, the first cycle (the first cycle) ends.

[0036] From time T = t4, the stirring process by the stirring device 306 ( "Stirring 2" in the figure) starts, and the second cycle (the second cycle) starts. Then, from time T = t5, the addition process of the phosphorus separating agent by the addition device 305 starts. This addition process is carried out during the period from time T = t5 to t6, and during that time, stirring continues. Then, the addition process of the phosphorus separating agent ends. Note that the addition process from time T = t5 to t6 is carried out in a shorter time than the first addition process. The addition amount of the phosphorus separating agent this time is the remaining amount obtained by subtracting the addition amount of the first time from the estimated total amount of the phosphorus separating agent.

[0037] Next, by stopping the addition device 305 and the stirring device 306 with the control device 310, the standing process of the water to be treated ( "Standing 2" in the figure) starts from time T = t6. In this standing process, since it starts from a state where the pH value is relatively high, the rate of decrease in the phosphorus concentration is fast. And when the phosphorus concentration reaches a predetermined value (time T = t7), the second standing process ends. Thereby, the second cycle (the second cycle) ends.

[0038] As described above, the control device 310 repeatedly performs a cycle consisting of an addition process, a stirring process, and a standing process. Thereby, the separated water of phosphorus can be extracted by automatic control, and phosphorus can be recovered. Note that after the end of the second cycle, one or more additional cycles (the third cycle) may be performed without discharging the water to be treated from the water tank 300.

[0039] Basically, in one phosphorus separation process, the water volume (water level) in the water tank 300 is constant (i.e., the water volume in the water tank 300 is the same in the first cycle and the second cycle), and when one process is completed, all the water to be treated is discharged. Also, when starting the next phosphorus separation process (the first cycle in the second treatment), new water to be treated is supplied to the water tank 300. If the water to be treated decreases and the water level drops during one cycle, it is also possible to replenish the reduced amount of water to be treated when starting the next cycle (for example, the stirring process or the adding process). Note that instead of discharging all the water to be treated, a part of the water to be treated may be left in the water tank 300 and the water to be treated may be added. In this case, since a part of the water to be treated in the first treatment is used in the water to be treated used in the second treatment, the pH value of the water to be treated can be increased, and phosphorus in the water to be treated can be separated and recovered more efficiently in the second treatment.

[0040] In this way, in the treatment by the phosphorus separation system 100, by dividing and charging the phosphorus separation agent little by little and repeating stirring and standing, phosphorus in the water to be treated can be efficiently separated and recovered. When dividing and adding the necessary total amount determined by the water quality of the water to be treated etc. as in this embodiment (i.e., when using the same amount of phosphorus separation agent as in the prior art), the target value of the phosphorus concentration can be set lower than in the prior art, and the recovery amount of phosphorus can be improved. On the other hand, from the viewpoint of recovering a certain amount of phosphorus, the total amount of the phosphorus separation agent used can be suppressed compared to the prior art.

[0041] Also, in this timing chart, although it has been described that the phosphorus separation agent is added according to the change in the pH value over a predetermined time (the period of time T = t1 to t2, the period of time T = t5 to t6), the adding method (the adding amount and the adding time) is not limited to this. Regarding the adding amount, after estimating in advance the total amount of the phosphorus separation agent required according to the water quality of the water to be treated etc., the adding amount in each cycle may be determined according to the number of adding times (the number of cycles). When the adding amount in each cycle is predetermined, it may be added over a predetermined time or added at once.

[0042] In addition, the addition amount in each cycle may evenly divide the total amount of the phosphorus separation agent determined by the quality of the water to be treated or the like among each cycle, or may increase or decrease within the cycle. For example, for the purpose of initially raising the pH value, the addition amount in the first cycle may be increased. In this case, the amounts for the second and subsequent cycles may be made equal, or the addition amount may be decreased with each additional cycle. Alternatively, for the purpose of improving the phosphorus separation efficiency, the addition amount in the last cycle may be increased. For example, the addition amount may be increased with each additional cycle, or may be increased every certain number of cycles. Further, these may be combined such that the addition amounts at the beginning and end are increased and the addition amount in the middle is decreased.

[0043] In addition, in the standing step in each cycle, the target value of the phosphorus concentration in the step may be determined according to the number of repetitions. When the phosphorus concentration of the water to be treated reaches a predetermined value, the standing step is terminated. If a predetermined number of cycles have been performed, the repetition is terminated and the process proceeds to the solid-liquid separation step. If a predetermined number of cycles have not been performed, the next cycle is started.

[0044] Note that in this embodiment, the cycle has been described as being repeated twice, but the number of repetitions may be three or more. The number of repetitions can be appropriately set based on, for example, the quality of the water to be treated, the target phosphorus concentration (phosphorus recovery amount) of the water to be treated, and the like.

[0045] [Second Embodiment] Next, with reference to FIGS. 5 and 6, a second embodiment of the phosphorus separation system of the present invention will be described. In the phosphorus separation system 150 of the second embodiment, the water tank is separated into a stirring water tank that adds a phosphorus separation agent and stirs the water to be treated, and a standing water tank that stands the water to be treated.

[0046] FIG. 5 is a schematic diagram of a phosphorus separation system 150 according to the second embodiment of the present invention. The phosphorus separation system 150 is composed of two stirring water tanks 400 and 450 and two standing water tanks 500 and 550. In this embodiment, one unit is composed of one stirring water tank and one standing water tank, and two units are composed.

[0047] Similar to the phosphorus separation system 100 of the first embodiment, one cycle consists of an addition step, a stirring step, and a standing step, and the standing step is the last of one cycle. In this embodiment, one cycle is performed by one unit, and the next cycle is performed by a different unit. Therefore, the water to be treated is transferred in the order of the stirring tank 400, the standing tank 500, the stirring tank 450, and the standing tank 550. The first cycle is performed in the first unit consisting of the stirring tank 400 and the standing tank 500, and the second cycle is performed in the second unit consisting of the stirring tank 450 and the standing tank 550.

[0048] The stirring tank 400 (corresponding to the "first tank" of the present invention) is provided with a supply device 401 (valve 403), a transfer device 402 (valve 404), an addition device 405, a stirring device 406, a pH detection device 407, and a water level detection device 409. The stirring tank 400, the standing tank 500, the stirring tank 450, and the standing tank 550 perform interlocking processes and are controlled by the control device 700. It should be noted that a control device may be provided in each water tank, and each control device may be comprehensively controlled by an overall control device.

[0049] The supply device 401 is connected to the pipe 201 of the final sedimentation tank 200 and supplies the water to be treated to the stirring tank 400. Since the water level of the stirring tank 400 can be detected by the water level detection device 409, the water to be treated is filled up to the water level during the phosphorus separation process. The addition device 405 has a function of adding a predetermined amount of phosphorus separation agent to the stirring tank 400 under the control of the control device 410. The stirring device 406 has a function of stirring the water to be treated in the stirring tank 400 under the control of the control device 410.

[0050] The transfer device 402 is a device for transferring the water to be treated from the stirring water tank 400 to the settling water tank 500. The transfer device 402 has a function of transferring the water to be treated when the addition of the required amount of phosphorus separation agent is completed and the pH value of the water to be treated detected by the pH detection device 407 reaches a predetermined set value. Note that since the water to be treated transferred from the stirring water tank 400 to the settling water tank 500 is a part of the water to be treated at the start of the treatment, the water to be treated left in the stirring water tank 400 will have each process performed again thereafter.

[0051] The settling water tank 500 (corresponding to the "second water tank" of the present invention) is provided with a supply device 501 (valve 503), a discharge device 502 (valve 504), a phosphorus concentration detection device 508, a water level detection device 509, and a discharge port 510.

[0052] The supply device 501 is connected to the pipe 411 of the stirring water tank 400 and supplies the water to be treated to the settling water tank 500. Since the water level of the settling water tank 500 can be detected by the water level detection device 509, the water to be treated is filled to a predetermined water level. Thereafter, in the settling water tank 500, the water to be treated is allowed to settle for a predetermined time. That is, each process of the first cycle in the first embodiment is performed by the stirring water tank 400 and the settling water tank 500 that constitute the first unit.

[0053] The water to be treated in the settling water tank 500 is a liquid in which phosphorus separation has progressed to a certain extent, but the phosphorus concentration further decreases after the settling process. The discharge device 502 has a function of discharging the water to be treated from the settling water tank 500 when the phosphorus concentration of the water to be treated reaches a predetermined first predetermined value α1. The water to be treated discharged from the settling water tank 500 is transferred to the stirring water tank 450 via the pipe 511. Also, at the timing of the transfer, the phosphorus-containing precipitate is taken out and recovered from the discharge port 510.

[0054] The stirring water tank 450 (corresponding to the "first water tank" of the present invention) is equipped with a supply device 451 (valve 453), a transfer device 452 (valve 454), an addition device 455, a stirring device 456, a pH detection device 457, and a water level detection device 459. In the stirring water tank 450, a phosphorus separation agent is added to and the water to be treated (supernatant) transferred from the stationary water tank 500 is stirred.

[0055] The transfer device 452 is a device for transferring the water to be treated from the stirring water tank 450 to the stationary water tank 550. The transfer device 452 has a function of transferring the water to be treated in which phosphorus separation has progressed when the addition of the required amount of phosphorus separation agent (remaining amount) is completed. The water to be treated discharged from the stirring water tank 450 is transferred to the stationary water tank 550 via the pipe 461.

[0056] The stationary water tank 550 (corresponding to the "second water tank" of the present invention) is equipped with a supply device 551 (valve 553), a discharge device 552 (valve 554), a phosphorus concentration detection device 558, a water level detection device 559, and a discharge port 560. In the stationary water tank 550, the water to be treated is allowed to stand for a predetermined time. That is, each step of the second cycle in the first embodiment is performed by the stirring water tank 450 and the stationary water tank 550 that constitute the second unit.

[0057] The water to be treated in the stationary water tank 550 is a liquid in which phosphorus separation has progressed considerably, but through the standing process, the phosphorus concentration further decreases. The discharge device 552 has a function of discharging the water to be treated from the stationary water tank 550 when the phosphorus concentration of the water to be treated reaches a predetermined second value α2 (<α1). The supernatant (separated water) extracted from the stationary water tank 550 is transferred to the phosphorus separation water tank 600 via the pipe 601. Also, at the timing of the transfer, the phosphorus-containing matter precipitated from the discharge port 560 is taken out and recovered.

[0058] Figure 6 is a schematic flow of the phosphorus separation process performed in the stirring water tanks 400 and 450 and the stationary water tanks 500 and 550.

[0059] First, treated water containing phosphorus is supplied from the final sedimentation tank 200 to the stirring water tank 400 (step S11). As a result, a predetermined amount of treated water is stored in the stirring water tank 400.

[0060] Thereafter, the adding device 405 adds a phosphorus separating agent to the stirring water tank 400 (step S12). Here, a part of the total amount of the phosphorus separating agent is added. Thereafter, the stirring device 406 stirs the treated water (step S13), and the transfer device 402 transfers the treated water to the standing water tank 500. Next, in the standing water tank 500, the treated water is left standing for a certain period of time (step S14), so that the separation of phosphorus is promoted. Further, after the standing process, the precipitate that has settled to the bottom of the standing water tank 500 is taken out from the discharge port 510 as a "phosphorus-containing substance" and recovered.

[0061] Furthermore, after the discharging device 502 transfers the treated water to the stirring water tank 450, the adding device 455 adds the remaining phosphorus separating agent (step S15). Thereafter, the stirring device 456 stirs the treated water (step S16), and the transfer device 452 transfers the treated water to the standing water tank 550. Further, in the standing water tank 550, the treated water is left standing for a certain period of time (step S17). And when the phosphorus concentration of the treated water reaches a predetermined value, the standing is terminated.

[0062] Thereafter, solid-liquid separation is performed (step S18). Here, the supernatant is taken out from the standing water tank 550 as "separated water" from which phosphorus has been separated. Also, "phosphorus-containing substances" are taken out from the discharge port 560 of the standing water tank 550 and recovered. Thus, the extraction process of the first "separated water" is completed.

[0063] In the first treatment, after the treated water in the stirring water tank 400 is transferred to the standing water tank 500, the treated water used for the second treatment is supplied to the stirring water tank 400 (step S19). Note that, similar to the first embodiment, not all of the treated water needs to be transferred to the standing water tank 500, and a part of the treated water may be left in the stirring water tank 400 and additional treated water may be added.

[0064] Thereafter, the adding device 405 adds a phosphorus separating agent to the water to be treated in the stirring water tank 400 (step S20), and the stirring device 406 stirs the water to be treated (step S21). The processes after step S21 are the same as those of the first extraction process. The second extraction process proceeds with a time difference so as to follow the first extraction process. For example, the standing process (step 14) in the standing water tank 500 and the second stirring process (step 21) in the stirring water tank 400 may be executed simultaneously.

[0065] In this way, the phosphorus separation system 150 starts the extraction processes after the second time with a time difference. Since the processes in the stirring water tanks 400 and 450 and the processes in the standing water tanks 500 and 550 are performed in parallel, the phosphorus separation process can be performed rapidly. A system provided with units after the third unit may be used from the viewpoint of efficiently separating and recovering phosphorus.

[0066] When the timings of the processes in the stirring water tank and the standing water tank do not match, a plurality of stirring water tanks and standing water tanks may be provided and switched so as to correspond to their respective processing times. For example, when the processing time of the standing process is shorter than that of the stirring process, a unit having a plurality of standing water tanks corresponding to one stirring water tank may be provided, and the water to be treated after the first stirring process in the unit may be supplied to the first standing water tank, and the water to be treated after the second stirring process may be supplied to the second standing water tank. Alternatively, it is also possible to make the stirring water tank wait until the standing process is completed (a part of the standing time occurs in the stirring water tank).

[0067] Conversely, when the processing time of the standing process is longer than that of the stirring process, a unit having a plurality of stirring water tanks corresponding to one standing water tank may be provided, and the water to be treated after the stirring processes performed in parallel in the plurality of stirring water tanks in the unit may be supplied to one standing water tank to perform the standing process. When this system is composed of a plurality of units, the stirring water tanks and the standing water tanks constituting each unit are not distinguished. For example, one or a plurality of the other water tanks may be made to correspond to one or a plurality of one of the water tanks, and the empty water tanks may be used sequentially.

[0068] As described above, the present invention is not limited to the above-described embodiments and modified forms, and can be implemented in various forms without departing from the gist thereof. In each of the above embodiments, the timing of injecting the water to be treated, stirring, and adding the phosphorus separation agent is arbitrary, and these processes may be executed in that order, or some of them may be executed in parallel. Further, the method of adding the phosphorus separation agent (for example, the addition amount, addition time, number of additions, etc.) and the number of cycles, etc. can be appropriately set from the viewpoints of the water quality of the water to be treated or the phosphorus recovery amount, etc., as described in the first embodiment.

Explanation of Reference Numerals

[0069] 100, 150... Phosphorus separation system, 200... Final sedimentation tank, 300... Water tank, 301, 401, 451, 501, 551... Supply device, 302, 502, 552... Discharge device, 305, 405, 455... Addition device, 306, 406, 456... Stirring device, 307, 407, 457... pH detection device, 308, 508, 558... Phosphorus concentration detection device, 309, 409, 459, 509, 559... Water level detection device, 311, 510, 560... Drain port, 400, 450... Stirring water tank, 402, 452... Transfer device, 500, 550... Standing water tank, 600... Phosphorus separation water tank, 700... Control device.

Claims

1. An addition device, a stirring device, and a control device for controlling the addition device and the stirring device, wherein: The control device: An addition step of adding a phosphorus separation agent to the water to be treated containing phosphorus by the addition device; A stirring step of stirring the water to be treated to which the phosphorus separation agent has been added by the stirring device; A standing step of stopping the addition device and the stirring device and allowing the water to be treated after the stirring step to stand; Is repeatedly performed, At least the standing step is performed in a state where the water to be pre-treated has a pH value in the range of 9 to 10, a phosphorus separation system.

2. The total amount of the phosphorus addition separation agent added in the repeated addition step is an addition amount determined by the quality of the water to be treated, the phosphorus separation system according to claim 1.

3. Further comprising a pH detection device for detecting the pH value of the water to be treated, In the addition step, the phosphorus separation agent is added to the water to be treated until the pH value detected by the pH detection device reaches a predetermined value, and when the pH value reaches the predetermined value, the addition of the phosphorus separation agent is terminated and the process proceeds to the stirring step or the standing step, the phosphorus separation system according to claim 1.

4. Further comprising a phosphorus concentration measuring device for detecting the phosphorus concentration of the water to be treated, In the standing step, the water is allowed to stand until the phosphorus concentration detected by the phosphorus concentration measuring device reaches a predetermined value, and when the phosphorus concentration reaches the predetermined value, the standing is terminated and the process proceeds to the addition step or the repetition is terminated, the phosphorus separation system according to any one of claims 1 to 3.

5. A unit comprising a first water tank for performing the addition step and the stirring step and a second water tank for performing the standing step, The water to be treated that has undergone the standing step in the second water tank is supplied to the first water tank of another unit, and the addition step and the stirring step are performed in the first water tank, the phosphorus separation system according to any one of claims 1 to 4.

6. At least one of the units is composed of a plurality of the second water tanks corresponding to one or more of the first water tanks, or is composed of a plurality of the first water tanks corresponding to one or more of the second water tanks, the phosphorus separation system according to claim 5.

7. Using a separation agent derived from concrete as the phosphorus separation agent, the phosphorus separation system according to any one of claims 1 to 6.

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