Method for renovating a sewage treatment system and sewage treatment system

Abstract

To provide a technology which deals with increase / decrease of a total amount of sewage water flowing into an influent water passage to recover a large amount of mud at high concentration efficiently in a sewage treatment system including primary sedimentation tanks.SOLUTION: Parts of multiple existing primary sedimentation tanks 10 are replaced with belt filters 20 which separate mud from sewage water flowing from an influent water passage 2 to an effluent water passage 4 by filtration, and parts of the multiple existing primary sedimentation tanks 10 are maintained as renovated primary sedimentation tanks 10. Sewage water flows from the influent water passage 2 into the renovated primary sedimentation tanks 10 and the belt filters 20 in a parallel state.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] In particular, the present invention relates to a sewage treatment system having a primary sedimentation tank for separating sludge by settling from sewage flowing from an inflow channel to an outflow channel. [Background technology]

[0002] A conventional sewage treatment system is known that includes multiple primary sedimentation tanks that separate sludge by settling from sewage flowing from an inflow channel to an outflow channel (see, for example, Patent Document 1). The primary sedimentation tanks provided in such sewage treatment systems are generally concrete structures, into which sewage continuously flows from a grit basin through an inflow channel, and solids in the sewage settle to the bottom by gravity. The supernatant liquid from which the solids have been removed passes over an overflow trough and is discharged through an outflow channel into a reaction tank for biological treatment. Meanwhile, the settled solids are collected in a sludge pit by a sludge collector and extracted as primary sedimentation sludge by a pump or the like. The extracted sludge (hereinafter sometimes referred to as "primary sedimentation sludge") is separated into solid and liquid by a thickener, dehydrator, or the like, and used for incineration or as a raw material for methane fermentation treatment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-34763 A Summary of the Invention [Problem to be solved by the invention]

[0004] Since the primary sedimentation tank separates solids by settling, it is necessary to ensure that the sewage detention time from the inflow channel to the outflow channel is at least a certain amount (for example, about 1 to 2 hours). Therefore, in order to ensure the sewage detention time, a relatively large site area is required for the sewage flow rate that can be treated. In addition, during times of flooding when the total amount of sewage inflow into the inflow channel increases due to rainfall, etc., the sewage detention time becomes shorter, which causes a problem of reduced efficiency in recovery of the primary sludge. Furthermore, the primary sludge withdrawn after settling in the primary sedimentation tank contains a lot of water and has a low concentration, so it is necessary to perform solid-liquid separation again using a thickener or dehydrator. In order to treat a sufficient amount of sewage even during such flooding, the sewage treatment system described in Patent Document 1 is configured to provide a high-speed filtration basin separately from the primary sedimentation basin, and treat the sewage with a sewage treatment flow that passes through the high-speed filtration basin separately from the sewage treatment flow that passes through the primary sedimentation basin, the biological reaction tank, and the final sedimentation basin. However, this high-speed filtration basin is not provided as a substitute for the primary sedimentation basin, but is used only to treat sewage with increased water content, so it does not contribute to improving the sludge recovery efficiency during normal times other than when the water level is high. In addition, the sludge recovered as backwash wastewater from the high-speed filtration basin contains a lot of water and has a low concentration, just like the sludge recovered from the primary sedimentation basin, so it is necessary to perform solid-liquid separation using a concentrator or dehydrator again. In view of this situation, the main object of the present invention is to provide a technology for efficiently recovering a large amount of sludge at a high concentration in a sewage treatment system equipped with a primary sedimentation tank in response to an increase or decrease in the total amount of sewage inflow into the inflow channel. [Means for solving the problem]

[0005] The first characteristic configuration of the present invention is a method for renovating a sewage treatment system equipped with a plurality of existing primary sedimentation tanks that separate sludge by settling from sewage flowing from an inflow water channel to an outflow water channel, A part of the plurality of existing primary sedimentation tanks is replaced with a belt filter that separates sludge from the sewage flowing from the inflow water channel to the outflow water channel by filtration, and a part of the plurality of existing primary sedimentation tanks is maintained as a renovated primary sedimentation tank; The sewage is introduced into the renovated primary sedimentation tank and the belt filter in parallel from the inflow water channel.

[0006] According to this configuration, some of the existing primary sedimentation tanks before renovation are replaced with belt filters that can separate sludge from sewage and recover high-concentration sludge with low moisture content, so that in the renovated sewage treatment system, a large amount of sludge can be recovered efficiently and at a high concentration. Furthermore, by maintaining and continuously using the primary sedimentation tanks that were not replaced with belt filters after renovation, it is possible to prevent deterioration of the equipment installed in the primary sedimentation tank, such as the sludge scraper, while stably demonstrating the treatment capacity that can handle even during times of flooding. By using such a renovated primary sedimentation tank in combination with a belt filter, the retention time of the sewage from the inflow water channel to the outflow water channel in the primary sedimentation tank becomes relatively long, and the sludge recovery efficiency in the primary sedimentation tank can be improved. Therefore, the present invention provides a technology for rationally constructing a sewage treatment system that can efficiently recover a large amount of sludge at a high concentration in response to increases or decreases in the total amount of sewage inflow into the inflow channel, in a method for renovating a sewage treatment system equipped with multiple existing primary sedimentation tanks.

[0007] The second characteristic configuration of the present invention is to use some of the existing primary sedimentation tanks as reserve tanks capable of storing sewage, A reserve pond inlet / outlet means capable of switching between a reserve pond inlet state in which sewage from the primary side of the belt filter is supplied to the reserve pond and a reserve pond outlet state in which sewage from the reserve pond is supplied to the primary side of the belt filter; A sewage inflow state detection means for detecting a sewage inflow state into the belt filter; and a control means for executing reserve pond sewage inflow / outflow control for controlling the reserve pond inflow / outflow means based on the detection result of the sewage inflow state detection means.

[0008] According to this configuration, when the belt filter is installed, a reserve pond is provided, and reserve pond sewage inflow / outflow control is performed by controlling the reserve pond inflow / outflow means by the control means. As a result, even if the total amount of sewage inflow into the inflow channel fluctuates or the amount of sewage inflow into the belt filter increases or decreases due to fluctuations in the clogging state of the belt filter, the sewage inflow state into the belt filter can always be kept in an appropriate state by appropriately switching between a reserve pond inflow state in which the sewage on the primary side of the belt filter is supplied to the reserve pond and temporarily stored therein, and a reserve pond outflow state in which the sewage on the primary side of the belt filter is supplied to the reserve pond and returned to the primary side of the belt filter. That is, when the total amount of sewage inflow into the inflow channel increases, the sewage on the primary side of the belt filter can be switched to a reserve pond inflow state and supplied to the reserve pond and temporarily stored therein, rather than being discharged to the outflow channel. Then, high concentration sludge can be collected from sewage limited to an appropriate amount while suppressing an excessive increase in the amount of sewage inflow into the belt filter. On the other hand, when the total amount of sewage flowing into the inflow channel is decreasing, the sewage stored in the reserve pond can be switched to the reserve pond outflow state and returned to the primary side of the belt filter. This allows a large amount of sludge to be collected from a large amount of sewage while maintaining an appropriate amount of sewage flowing into the belt filter and adding the amount returned from the reserve pond.

[0009] The third characteristic configuration of the present invention is that the reserve pond inlet / outlet means is configured to include a reserve pond inlet conduit gate capable of adjusting the water flow rate of the reserve pond inlet conduit that guides the sewage from the inflow conduit to the reserve pond, and a return pump capable of sending the sewage from the reserve pond to the primary side of the belt filter.

[0010] According to this configuration, in the reserve pond inlet / outlet means, the reserve pond inlet state can be achieved by opening the reserve pond inlet gate while stopping the return pump, and the reserve pond outlet state can be achieved by operating the return pump while closing the reserve pond inlet gate.

[0011] A fourth characteristic configuration of the present invention is a belt filter that separates sludge from sewage flowing from an inflow water channel to an outflow water channel by filtration; A primary sedimentation tank for separating sludge by settling from the sewage flowing from the inflow water channel to the outflow water channel, The sewage is introduced into the primary sedimentation tank and the belt filter in parallel from the inflow water channel.

[0012] According to this configuration, it is possible to provide a renovated sewage treatment system constructed by the method for renovating a sewage treatment system according to the present invention having the above first to third characteristic configurations. This configuration exerts the same effects as those described above, and makes it possible to efficiently recover high-concentration sludge while stably exerting a treatment capacity that can cope with even when the total amount of sewage inflow into the inlet channel increases. [Brief description of the drawings]

[0013] [Figure 1] Schematic diagram of the existing sewage treatment system [Diagram 2] Schematic diagram of the renovated sewage treatment system [Diagram 3] Cross-sectional view of the belt filter portion of the sewage treatment system shown in Figure 2. [Figure 4] Cross-section of the reserve pond in the sewage treatment system shown in Figure 2 [Diagram 5] Cross-section of the primary sedimentation tank after renovation in the sewage treatment system shown in Figure 2 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. A sewage treatment system 101 according to the first embodiment shown in FIG. 2 is constructed by repairing the existing sewage treatment system 100 shown in FIG.

[0015] An existing sewage treatment system 100 shown in FIG. 1 is configured to include a plurality of existing primary sedimentation tanks 10 that separate sludge by settling from sewage flowing from an inflow water channel 2 to an outflow water channel 4. In such an existing sewage treatment system 100, sewage continuously flows from the grit basin 1 through the inflow water channel 2 into each existing primary sedimentation basin 10. In the existing primary sedimentation basin 10, as shown in Fig. 5, solids (sludge) in the sewage that flows in from the inflow water channel 2 through the primary sedimentation basin inlet water channel 10i settle to the bottom 10d by gravity, and the supernatant liquid from which the solids have been removed flows over the overflow trough 17 and is discharged into the outflow water channel 4 through the primary sedimentation basin outlet water channel 10o. As shown in FIG. 1, the supernatant liquid from the existing primary sedimentation tank 10 discharged into the outflow channel 4 is biologically treated in the biological reactor 5, and then discharged into a river or the like via the final sedimentation tank 6 and the disinfection / discharge section 7. Meanwhile, the solid matter (sludge) that has settled to the bottom 10d is collected by a collector (not shown) etc. Since the collected sludge contains a relatively large amount of water, it is again subjected to solid-liquid separation using a thickener or a dehydrator, and then is suitably used as a raw material for methane fermentation treatment etc.

[0016] In the sewage treatment system 101 (see Figure 2) of this embodiment, when renovating an existing sewage treatment system 100 (see Figure 1), some of the existing primary sedimentation tanks 10 are replaced with belt filters 20 that separate sludge by filtration from the sewage flowing from the inflow water channel 2 to the outflow water channel 4.

[0017] As shown in FIG. 3, this belt filter 20 has an endless filtration belt 21 supported by a plurality of rollers 26 interposed at the boundary between a primary storage section 22 and a secondary storage section 23, and the rollers 26 are driven to rotate by a control device 50 to move the filtration belt 21 in such a manner that the portion of the filtration belt 21 facing the primary storage section 22 is sent toward the sludge discharge section 27. The primary-side storage section 22 is connected to the inflow water channel 2 via a belt filter inlet water channel 20i, while the secondary-side storage section 23 is connected to the outflow water channel 4 via a belt filter outlet water channel 20o. The primary sedimentation tank inlet water channel 10i that already exists in the existing primary sedimentation tank 10 is utilized as the belt filter inlet water channel 20i, and the primary sedimentation tank outlet water channel 10o that already exists in the existing primary sedimentation tank 10 is utilized as the belt filter outlet water channel 20o.

[0018] In the belt filter 20 configured as described above, solids (sludge) in the sewage that flows from the inflow water channel 2 through the belt filter inlet water channel 20i into the primary side storage section 22 are removed by the filter belt 21, and the filtrate that passes through the filter belt 21 and is supplied to the secondary side storage section 23 is discharged into the outlet water channel 4 through the belt filter outlet water channel 20o. On the other hand, the solid matter (sludge) removed by the filter belt 21 falls into the sludge discharge section 27 as the filter belt 21 moves and is collected by a screw conveyor or the like. The sludge collected in this manner has a low moisture content and a high concentration compared to the sludge collected in the existing primary sedimentation tank 10 (see FIG. 5), and can be suitably used as a raw material for methane fermentation treatment or the like. In addition, in the belt filter 20, the filter belt 21 from which the solid matter has been removed is sequentially moved to the boundary between the primary side storage section 22 and the secondary side storage section 23, thereby suppressing clogging of the filtration surface, and since the solid matter can be removed from the sewage without waiting for sedimentation as in the primary sedimentation tank 10 (see FIG. 5), the belt filter 20 has a processing capacity for separating sludge from more sewage (for example, twice as much) than the primary sedimentation tank 10.

[0019] The primary storage section 22 of the belt filter 20 is provided with a belt filter primary water level sensor 28 (one example of a belt filter primary water level detection means) that detects the water level in the primary storage section 22, and the detection result of this belt filter primary water level sensor 28 is input to the control device 50. Since this belt filter primary water level sensor 28 detects the water level in the primary storage section 22, it can be said to be a sewage inflow state detection means B that detects the sewage inflow state into the belt filter 20. Furthermore, an overflow section 25 is provided which, when the water level in the primary storage section 22 exceeds the upper limit, discharges the stored sewage above the upper limit through an overflow discharge path 33 into a reserve pond 30 described later.

[0020] In the belt filter 20 thus configured, it is desirable to appropriately set the operating conditions such as the speed and inclination angle of the filtration belt 21 according to the moisture content of the collected solids (sludge) and the treatment capacity of the sewage. For example, when the speed of the filtration belt 21 is increased or the inclination angle of the filtration belt 21 is decreased, the sewage is filtered through a wide filtering surface with as little clogging as possible, and therefore an operating mode prioritizing the amount of processing can be set so that a large amount of sewage can be treated. On the other hand, when the speed of the filtration belt 21 is decreased or the inclination angle of the filtration belt 21 is increased, the sewage is filtered through a narrow surface with as much sludge piled up as possible, and therefore an operating mode prioritizing the sludge concentration can be set so that a high concentration of sludge can be collected. In the sewage treatment system 101 of this embodiment, a plurality of belt filters 20 are provided, and sewage flows into these plurality of belt filters 20 in parallel from the inflow water channel 2. When treating sewage with a plurality of belt filters 20 in this manner, the operation modes of the respective belt filters 20 can be appropriately set to be the same, to be different individually, or to be switched sequentially, depending on the total amount of inflow sewage and other conditions. In this embodiment, a plurality of belt filters 20 are provided, but the number of belt filters 20 installed can be appropriately changed, and may be a single belt filter.

[0021] In the sewage treatment system 101 (see Figure 2) of this embodiment, when renovating an existing sewage treatment system 100 (see Figure 1), some of the existing primary sedimentation tanks 10 that are not replaced with the above-mentioned belt filters 20 are used as reserve tanks 30 capable of storing sewage.

[0022] As shown in Fig. 4, the reserve pond 30 utilizes the existing primary sedimentation pond 10 almost as it is. That is, the primary sedimentation pond inlet channel 10i is used as the reserve pond inlet channel 30i almost as it is, and the overflow trough 17 and the primary sedimentation pond outlet channel 10o are used as the overflow trough 37 and the reserve pond outlet channel 30o almost as it is. That is, in the reserve pond 30, the stored sewage above the discharge water level defined by the overflow trough 37 overflows the overflow trough 37, overflows into the reserve pond outflow channel 30o, and is discharged into the outflow channel 4. A sludge collector (not shown) is installed in the existing primary sedimentation pond 10, but when using it as the reserve pond 30, the sludge collector may or may not be removed.

[0023] The reserve pond inlet conduit 30i is provided with a reserve pond inlet conduit gate 32 that can adjust the water flow rate of the reserve pond inlet conduit 30i, which guides sewage from the inflow conduit 2 into the reserve pond 30, and the control device 50 is configured to be able to control the opening and closing operation of the reserve pond inlet conduit gate 32. Furthermore, the reserve pond 30 is provided with a return pump 35 for returning the stored sewage in the reserve pond 30 through a return path 34 to the inflow water channel 2, which is the primary side (upstream side) of the belt filter 20 described above.

[0024] The reserve pond inlet conduit gate 32 and the return pump 35 function as a reserve pond inlet / outlet means A that can switch between a reserve pond inlet state in which sewage from the inflow conduit 2, which is the primary side (upstream side) of the belt filter 20, is supplied to the reserve pond 30, and a reserve pond outflow state in which sewage from the reserve pond 30 is supplied to the inflow conduit 2, which is the primary side of the belt filter 20. That is, the control device 50 can set the reserve pond inlet state by opening the reserve pond inlet conduit gate 32 while stopping the return pump 35, and can set the reserve pond outflow state by operating the return pump 35 while closing the reserve pond inlet conduit gate 32. In the above embodiment, the inflow waterway 2 is the source of sewage flow into the reserve pond 30 when the reserve pond is filled with water, and the destination of sewage return from the reserve pond 30 by the return pump 35. However, the source of sewage flow and the destination of sewage return in the reserve pond 30 may be the primary side (upstream side) of the belt filter 20, and may be, for example, the primary side storage section 22 of the belt filter 20 or the grit tank 1. The reserve pond 30 is provided with a reserve pond water level sensor 38 (an example of a reserve pond water level detection means) that detects the water level of the reserve pond 30, and the detection result of this reserve pond water level sensor 38 is input to the control device 50.

[0025] In addition, the reserve pond inlet state and the reserve pond inlet state are switched by alternatively opening the reserve pond inlet gate 32 and operating the return pump 35. However, the reserve pond inlet state and the reserve pond inlet state may be switched by adjusting the opening of the reserve pond inlet gate 32 and the water supply rate of the return pump 35 to balance the amount of supply while simultaneously supplying sewage from the inflow waterway 2 to the reserve pond 30 and from the reserve pond 30 to the inflow waterway 2.

[0026] In the sewage treatment system 101 (see Figure 2) of this embodiment, when renovating an existing sewage treatment system 100 (see Figure 1), at least some of the multiple existing primary sedimentation tanks 10 that have not been replaced with the above-mentioned belt filters 20 or used as the above-mentioned reserve tanks 30 are maintained as primary sedimentation tanks 10 in approximately their original form even after the renovation. The renovated primary sedimentation tank 10 is provided with a primary sedimentation tank inlet conduit gate 12 that can adjust the water flow rate of the primary sedimentation tank inlet conduit 10i, which guides sewage from the inflow conduit 2 into the primary sedimentation tank 10, and the control device 50 is configured to be able to control the opening and closing operation of the primary sedimentation tank inlet conduit gate 12.

[0027] In the sewage treatment system 101, when the primary sedimentation tank inlet waterway gate 12 is open, sewage is introduced from the inflow waterway 2 into the primary sedimentation tank 10 and the belt filter 20 in parallel. This allows the primary sedimentation tank 10 that is not replaced by the belt filter 20 and is not used as the reserve tank 30 to be utilized even after the renovation.

[0028] In the sewage treatment system 101 of this embodiment, during a steady state in which the total amount of sewage inflowing into the inflow channel 2 is not increasing, the primary sedimentation tank inlet channel gate 12 is opened, and sewage flows from the inflow channel 2 into the primary sedimentation tank 10 and the belt filter 20 in parallel, and sludge separation processing is performed in both the primary sedimentation tank 10 and the belt filter 20. This allows a stable processing capacity to be achieved even during times of flooding, and the equipment such as a sludge collector provided in the primary sedimentation tank 10 is continuously operated, preventing the deterioration of the equipment. Then, since the primary sedimentation tank 10 after such repair is used in combination with the belt filter 20, the retention time of sewage from the inflow channel 2 to the outflow channel 4 in the primary sedimentation tank 10 becomes relatively long, and the sludge recovery efficiency in the primary sedimentation tank 10 is improved. The hydraulic retention time (hereinafter referred to as HRT) in the primary sedimentation tank 10 is not particularly limited as long as the sludge settles, but is preferably longer than 1 to 2 hours, which is common in existing systems, more preferably 2 to 5 hours, and even more preferably 4 to 5 hours. Furthermore, although not limited, the retention time of sewage in the primary sedimentation tank 10 after renovation is preferably 1.5 times or more, more preferably 2 times or more, and even more preferably 2.5 times or more, and preferably 5 times or less, compared to the retention time before renovation. By lengthening the retention time of sewage in the primary sedimentation tank 10, the amount of sludge recovered in the primary sedimentation tank 10 can be increased. On the other hand, even if the retention time of sewage in the primary sedimentation tank 10 is maintained for a predetermined time or more, the amount of sludge recovered does not change significantly. Furthermore, when the total amount of sewage flowing into the inflow channel 2 is decreasing during low water levels, the primary sedimentation tank inlet channel gate 12 can be closed by automatic control using the control device 50. For example, when the water level of the reserve pond 30 detected by the reserve pond water level sensor 38 falls below a predetermined set water level, the primary sedimentation tank inlet channel gate 12 is closed, so that all the sewage can be treated by the belt filter 20 and high-concentration sludge can be efficiently collected.

[0029] Furthermore, a total sewage flow rate meter 9a is provided as total sewage inflow rate detection means 9 for detecting the total sewage inflow rate supplied to the inflow channel 2, which measures the sewage flow rate flowing from a pumping station (not shown) into the grit chamber 1 as the total sewage inflow rate. Since the total sewage inflow rate detection means 9 detects the total sewage inflow rate into the inflow channel 2 leading to the belt filter 20, it can be said to be sewage inflow state detection means B for detecting the sewage inflow state into the belt filter 20. The location of the total sewage flow rate measuring device 9a can be changed as appropriate, and can be provided, for example, in the inflow water channel 2 on the sewage outflow side of the grit basin 1. Also, instead of the total sewage flow rate measuring device 9a, a means for calculating the total sewage flow rate based on the water level of a water tank in a pumping station located upstream of the grit basin 1, or a means for predicting the total sewage flow rate based on the amount of precipitation predicted in a weather forecast, or the like, can be provided as the total sewage inflow rate detecting means 9.

[0030] In the sewage treatment system 101 (see FIG. 2) of this embodiment, when the existing sewage treatment system 100 (see FIG. 1) is renovated, a control device 50 (one example of a control means) that controls the sewage inflow and outflow to the reserve pond, which will be described later, is provided. Details of these controls will be described below.

[0031] (Reserve pond sewage inflow and outflow control) In the reserve pond sewage inflow and outflow control, the reserve pond inflow and outflow means A (reserve pond inlet waterway gate 32, return pump 35) is controlled based on the detection results of the sewage inflow condition detection means B (belt filter primary side water level sensor 28, total sewage inflow volume detection means 9), and the sewage inflow condition into the belt filter 20 is always kept appropriate.

[0032] Specifically, in the reserve pond sewage inflow / outflow control, when the water level of the primary side storage section 22 of the belt filter 20 detected by the belt filter primary side water level sensor 28 is above a preset water level, the reserve pond inflow state is switched to by opening the reserve pond inlet gate 32 while stopping the return pump 35. Then, the sewage of the inflow water channel 2, which is the primary side of the belt filter 20, is not discharged to the outflow water channel 4 side, but is supplied to the reserve pond 30 through the reserve pond inlet gate 32 and temporarily stored therein. This suppresses an excessive increase in the amount of sewage inflow to the belt filter 20, suppresses an excessive rise in the water level of the primary side storage section 22 of the belt filter 20, and recovers high-concentration sludge from the sewage limited to an appropriate amount. Later, when the water level of the primary side storage section 22 of the belt filter 20 falls below the above-mentioned set water level, the reserve pond inflow state is terminated by executing the reserve pond sewage inflow / outflow control. This prevents the water level in the primary reservoir 22 of the belt filter 20 from dropping unnecessarily due to the reserve pond being filled with water, and allows the belt filter 20 to efficiently collect sludge. The set water level of the primary storage section 22 of the belt filter 20, which is an index for determining whether or not to switch to the reserve pond water inflow state, can be appropriately set within a range below the water level of the overflow section 25 of the primary storage section 22 as an upper limit water level at which the belt filter 20 can operate efficiently. The set water level set for the water level of the primary storage section 22 of the belt filter 20 as an index for determining whether or not to switch to the reserve pond water inflow state may be controlled by providing a first set water level at which the reserve pond water inflow state is switched to and a second set water level, which is a water level lower than the first set water level and at which the reserve pond water inflow state is terminated.

[0033] During flooding, when the total amount of sewage inflowing into the inflow channel 2 increases, the reserve pond 30 may be switched to the reserve pond inflow state by executing the reserve pond sewage inflow / outflow control as described above, and the sewage from the inflow channel 2 is supplied to the reserve pond 30, so that the water level of the reserve pond 30 may exceed the discharge water level close to the upper limit. Even in such a case, the stored sewage exceeding the discharge water level will be discharged through the overflow trough 37 to the outflow channel 4 through the primary sedimentation pond outflow channel 10o, so leakage from the reserve pond 30 to surrounding facilities is avoided. If there are multiple primary sedimentation ponds 10, the stored sewage exceeding the discharge water level may be discharged to another primary sedimentation pond 10 that is not operated in conjunction with the belt filter 20.

[0034] On the other hand, in the reserve pond sewage inflow / outflow control, when the total sewage inflow amount into the inflow channel 2 detected by the total sewage inflow amount detection means 9 is equal to or less than the set total sewage inflow amount, the reserve pond inflow state is switched to by operating the return pump 35 while closing the reserve pond inflow channel gate 32. Then, the sewage in the reserve pond 30 is supplied to the inflow channel 2, which is the primary side of the belt filter 20, through the return pump 35 and returned. This maintains the sewage inflow amount into the belt filter 20 at an appropriate amount, suppresses an excessive drop in the water level of the primary side storage section 22 of the belt filter 20, and recovers a lot of sludge from a lot of sewage, including the amount returned from the reserve pond 30. Later, when the total sewage inflow amount into the inflow channel 2 increases to exceed the set total sewage inflow amount, the reserve pond sewage inflow / outflow control is executed to end the reserve pond outflow state. This prevents the water level in the primary reservoir 22 of the belt filter 20 from rising unnecessarily due to the reserve pond being kept in a flooded state, and allows the belt filter to efficiently collect sludge. The set total sewage inflow rate of the total sewage inflow rate into the inflow channel 2, which is an index for determining whether or not to switch to the reserve pond outflow state, can be appropriately set as a lower limit water level at which the belt filter 20 can operate efficiently. The set total sewage inflow rate set for the total sewage inflow rate into the inflow channel 2 as an index for determining whether or not to switch to the reserve pond outflow state, may be controlled by providing a first set total sewage inflow rate at which the reserve pond outflow state is switched to and a second set total sewage inflow rate that is a water volume higher than the first set total sewage inflow rate at which the reserve pond outflow state is terminated.

[0035] [Another embodiment] Other embodiments of the present invention will be described below. Note that the configurations of the embodiments described below are not limited to being applied alone, but may also be applied in combination with the configurations of other embodiments.

[0036] (1) In the above embodiment, when renovating the existing sewage treatment system 100, some of the existing primary sedimentation tanks 10 that were not replaced with belt filters 20 were used as reserve tanks 30 capable of storing sewage. However, the renovated sewage treatment system 101 may be configured so as not to have reserve tanks 30.

[0037] (2) In the above embodiment, the reserve pond inlet / outlet means A is opened to supply sewage from the inlet conduit 2, which is the primary side of the belt filter 20, to the reserve pond 30, thereby creating a reserve pond inlet state. However, even if the reserve pond inlet conduit gate 32 is constantly closed, the reserve pond inlet state may be created by supplying stored sewage above the upper limit of the primary side storage section 22, which is the primary side of the belt filter 20, to the reserve pond 30 through the overflow section 25 and the overflow discharge conduit 33.

[0038] (3) In the above embodiment, the belt filter primary side water level sensor 28 is installed to detect the water level in the primary side storage section 22 of the belt filter 20, but this belt filter primary side water level sensor 28 may be installed to detect the water level on the primary side of the belt filter 20, for example, to detect the water level in the inflow water channel 2. [Explanation of symbols]

[0039] 2 Inflow channel 4 Outflow channel 9. Means for detecting total sewage inflow 9a Total sewage flow rate meter (total sewage inflow detection means) 10 Primary Sedimentation Tank 10i Primary Sedimentation Tank Inlet Channel 12 Primary Sedimentation Pond Inlet Gate 20 Belt Filter 22 Primary storage section 25 Overflow section (means for water inflow and outflow from reserve pond) 28 Belt filter primary side water level sensor (belt filter primary side water level detection means) 30 Reserve Pond 30i Reserve Pond Inlet Channel 30o Reserve Pond Outlet Channel 32 Reserve Pond Inlet Gate 35 Return pump 38 Reserve pond water level sensor (reserve pond water level detection means) 50 Control device (control means) 100 Sewage Treatment System 101 Sewage Treatment System A. Means of inflow and outflow of water from reserve pond B. Sewage inflow condition detection means

Claims

1. A method for renovating a sewage treatment system having a plurality of existing primary sedimentation tanks that separate sludge by settling from sewage flowing from an inflow channel to an outflow channel, comprising the steps of: A part of the plurality of existing primary sedimentation tanks is replaced with a belt filter that separates sludge from the sewage flowing from the inflow water channel to the outflow water channel by filtration, and a part of the plurality of existing primary sedimentation tanks is maintained as a renovated primary sedimentation tank; Sewage is introduced from the inflow waterway in parallel into the renovated primary sedimentation tank and the belt filter, A part of the plurality of existing primary sedimentation tanks is used as a reserve tank capable of storing sewage, A reserve pond inlet / outlet means capable of switching between a reserve pond inlet state in which sewage from the primary side of the belt filter is supplied to the reserve pond and a reserve pond outlet state in which sewage from the reserve pond is supplied to the primary side of the belt filter; A sewage inflow state detection means for detecting a sewage inflow state into the belt filter; A control means for executing reserve pond sewage inflow / outflow control for controlling the reserve pond inflow / outflow means based on the detection result of the sewage inflow state detection means.

2. The method for renovating a sewage treatment system as described in claim 1, wherein the reserve pond inlet / outlet means is configured to include a reserve pond inlet conduit gate capable of adjusting the water flow rate of the reserve pond inlet conduit that guides the sewage from the inflow conduit to the reserve pond, and a return pump capable of sending the sewage from the reserve pond to the primary side of the belt filter.

3. A belt filter that separates sludge from sewage flowing from an inflow water channel to an outflow water channel by filtration; A primary sedimentation tank for separating sludge by settling from the sewage flowing from the inflow water channel to the outflow water channel, Sewage is introduced into the primary sedimentation tank and the belt filter in parallel from the inflow waterway, A reserve pond capable of storing sewage; A reserve pond inlet / outlet means capable of switching between a reserve pond inlet state in which sewage from the primary side of the belt filter is supplied to the reserve pond and a reserve pond outlet state in which sewage from the reserve pond is supplied to the primary side of the belt filter; A sewage inflow state detection means for detecting a sewage inflow state into the belt filter; and a control means for executing reserve pond sewage inflow / outflow control for controlling the reserve pond inflow / outflow means based on a detection result of the sewage inflow state detection means.

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