JP7441078B2 - Sewage treatment system and method - Google Patents

Description

The present invention relates to a sewage treatment system and a sewage treatment method.

In recent years, sewage treatment plants have increased the concentration of nutrients (nitrogen and phosphorus) in sewage treatment water during the winter, taking into consideration the aquaculture and other activities that take place in the water areas where treated sewage water is discharged. Efforts are being made to actively manage water quality seasonally according to local needs, such as by supplying nitrogen and phosphorus to water bodies into which water is discharged (for example, see Non-Patent Document 1).

Active management of the water quality of effluent at a sewage treatment plant that performs seasonal operation management includes, for example, adjusting the biological treatment conditions in reaction tanks within the scope stipulated by laws and ordinances such as the Sewerage Act. (For example, see Patent Document 1).

JP 2019-141763 Publication

Ministry of Land, Infrastructure, Transport and Tourism, Water Management and Land Conservation Bureau, Sewage Department, “Procedures (Draft) for Operational Methods for Active Management of Nutrients Contained in Sewage Discharge Water,” September 2015.

However, with the above-mentioned conventional technology that actively manages the quality of effluent by adjusting the conditions of biological treatment, it is difficult to appropriately control the properties of the microorganisms used in biological treatment, and the quality of effluent cannot be controlled. There was room for improvement in that it was difficult to control to a desired level.

In addition, in recent years, sewage treatment plants are expected to function as energy supply bases that actively create energy, and sewage treatment plants that perform seasonal operation management can also perform the same energy supply function. It was desired to do so.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a sewage treatment system and a sewage treatment method that make it easy to actively manage the quality of effluent water and also make it possible to generate energy.

The purpose of the present invention is to advantageously solve the above problems, and the sewage treatment system of the present invention includes: a sewage treatment facility that processes sewage and discharges treated sewage water containing nutrients; A first discharge channel for discharging the treated sewage water flowing out from the treatment equipment to a destination, and a nutrient salt recovery facility for recovering nutrients in the treated sewage water using aquatic plants, a second discharge channel for discharging treated water obtained by recovering nutrients to the discharge destination; an amount of treated sewage water flowing from the sewage treatment equipment into the first discharge route; and a second discharge from the sewage treatment equipment. The system is characterized by comprising a flow rate adjustment mechanism that adjusts the amount of treated sewage water flowing into the road, and a power generation facility that collects the aquatic plants from the nutrient salt recovery facility and generates electricity using the collected aquatic plants as a raw material. do. In this way, by providing the first discharge channel, the second discharge channel having a nutrient recovery facility using aquatic plants, and the flow rate adjustment mechanism, active management of the water quality of the discharge water can be easily carried out. can. Furthermore, by installing a power generation facility that generates power using aquatic plants as raw materials, it is possible to actively manage nutrients in effluent water and generate energy.

Here, in the sewage treatment system of the present invention, the flow rate adjustment mechanism controls the amount of treated sewage water flowing into the first discharge channel and the amount of treated sewage water flowing into the second discharge channel according to the season. Preferably, a device is provided. If such a control device is provided, seasonal operation management can be appropriately performed.

Further, in the sewage treatment system of the present invention, the flow rate adjustment mechanism adjusts the amount of treated sewage water flowing into the first discharge channel and the amount of treated sewage water flowing into the second discharge channel as required at the discharge destination. It is preferable to include a control device that controls based on the amount of nutrient salts. If such a control device is provided, the quality of the discharged water can be appropriately managed actively according to the amount of nutrients required at the discharge destination.

In the sewage treatment system of the present invention, the control device controls the amount of treated sewage water flowing into the first discharge channel and the second It is preferable to control the amount of treated sewage water flowing into the outlet. If such a control device is provided, laws and ordinances such as the Sewerage Law can be properly complied with.

Further, in the sewage treatment system of the present invention, it is preferable that the nutrient salt recovery equipment includes a control device that adjusts the amount of the aquatic plants so that the amount of nutrient salts in the treated water approaches a target value. If such a control device is provided, it is possible to achieve a high level of both active management of the quality of discharged water and generation of energy using aquatic plants.

Further, the present invention aims to advantageously solve the above problems, and the sewage treatment method of the present invention includes a sewage treatment step of treating sewage to obtain treated sewage water containing nutrients; A discharge step in which the treated sewage water obtained in the sewage treatment step is discharged as it is and/or after recovering nutrients using aquatic plants to a destination; and a sewage treatment in which the treated sewage water is discharged as it is in the discharge step. The method includes a distribution step of determining the amount of water and the amount of treated sewage water to be discharged after collecting nutrients, and a power generation step of collecting the aquatic plants and generating power using the collected aquatic plants as a raw material. It is characterized by By performing the discharge process and the distribution process in this way, the quality of the discharged water can be easily managed actively. Furthermore, by implementing a power generation process that uses aquatic plants as raw materials to generate electricity, active management of nutrients in the effluent and generation of energy can be achieved.

Here, in the sewage treatment method of the present invention, in the distribution step, the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering nutrients may be determined depending on the season. preferable. If the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering nutrients are determined according to the season, seasonal operation management can be performed appropriately.

Further, in the sewage treatment method of the present invention, in the distribution step, the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering nutrients are adjusted to meet the requirements of the nutrient salts at the discharge destination. Preferably, the determination is based on the amount of In this way, the quality of the discharged water can be appropriately managed in accordance with the amount of nutrients required at the discharge destination.

Furthermore, in the sewage treatment method of the present invention, in the distribution step, the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering nutrients are determined based on the annual distribution of nutrients to the discharge destination. It is preferable to determine so that the discharge amount is equal to or less than a predetermined value. By keeping the annual amount of nutrient salts discharged to the destination below a predetermined value, laws and ordinances such as the Sewerage Act can be properly complied with.

In the sewage treatment method of the present invention, the discharge step is such that the amount of nutrients in the treated water obtained by recovering nutrients from the treated sewage water using the aquatic plants in the discharge step approaches a target value. Preferably, the method further includes a step of adjusting the amount of aquatic plants used in the method. By adjusting the amount of aquatic plants so that the amount of nutrients in the treated water approaches the target value, active management of nutrients in the effluent and generation of energy using aquatic plants can be achieved.

According to the sewage treatment system and sewage treatment method of the present invention, it is possible to easily actively manage nutrients in effluent water, and it is also possible to generate energy.

FIG. 1 is an explanatory diagram showing a schematic configuration of an example of a sewage treatment system.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.
Here, the sewage treatment system and sewage treatment method of the present invention are not particularly limited, and include, for example, seasonal operation management in which the quality of discharged water is actively managed seasonally according to local needs at a sewage treatment plant. It can be suitably used when carrying out.

(Sewage treatment system)
An example of the sewage treatment system of the present invention, as schematically shown in FIG. a bypass channel 23 that branches from the discharge channel 21 and joins the discharge channel 21 again on the downstream side (discharge destination side) of the branch position; It is equipped with salt recovery equipment 30. Moreover, the discharge path 21 and the bypass flow path 23 of the sewage treatment system 100 shown in FIG. A regulating valve 24 is provided. Furthermore, the sewage treatment system 100 includes an aquatic plant supply mechanism 31 that supplies aquatic plants used for recovering nutrients in the nutrient salt recovery facility 30 to the nutrient salt recovery facility 30, and an aquatic plant supply mechanism 31 that supplies aquatic plants used for recovering nutrients from the nutrient salt recovery facility 30. The control device 40 controls the operation of the first flow rate control valve 22, the second flow rate control valve 24, the aquatic plant supply mechanism 31, and the power generation facility 32.

The sewage treatment facility 10 processes inflowing sewage and discharges treated sewage water containing nutrients (nitrogen and/or phosphorus). Here, the sewage treatment equipment 10 is not particularly limited as long as it is capable of treating inflowing sewage, and any configuration of sewage treatment equipment can be used. Specifically, the sewage treatment equipment 10 is not particularly limited, and includes, for example, a primary sedimentation tank, a reaction tank provided downstream of the primary sedimentation tank for biologically treating inflow water, and a downstream stage of the reaction tank. A sewage treatment facility with a final settling tank provided therein, etc. can be used. In addition, from the viewpoint of reducing the energy consumption in the sewage treatment equipment 10 as much as possible, it is preferable that the sewage treatment equipment 10 treats inflowing sewage by nitrification suppression operation.

In addition, from the viewpoint of enabling active management of the water quality of effluent water, the sewage treatment facility 10 treats the sewage so that nutrients remain in the obtained sewage treatment water. In the treated sewage water 100, by intentionally leaving nutrients in the treated sewage water, the quality of the discharged water can be actively managed as described below.
Here, the nitrogen concentration in the sewage treatment water can be set to 30 mg-N/L or more and 40 mg-N/L or less, although it depends on the quality of the inflowing sewage water. When the nitrogen concentration is equal to or higher than the above lower limit, nutrient salts can be sufficiently supplied to the discharge destination by discharging treated sewage water as it is. Moreover, if the nitrogen concentration is set to be below the above upper limit value, when it is not necessary to supply nutrients to the discharge destination, the nutrients can be sufficiently recovered by the nutrients recovery equipment 30 before being discharged.

The discharge path 21 having the first flow rate control valve 22 directly connects the sewage treatment equipment 10 and the discharge destination. That is, in the illustrated example, by opening the first flow rate control valve 22 provided downstream of the branching position of the bypass channel 23, the discharge channel 21 directs the treated sewage water flowing out from the sewage treatment equipment 10 to the discharge destination. It can be made to function as a first discharge path for discharging water to.

In the bypass channel 23 having the second flow rate control valve 24 and the nutrient recovery equipment 30, the second flow rate control valve 24 is opened and the treated sewage water is allowed to flow into the nutrient recovery equipment 30. Treated water can be obtained by recovering salts. That is, in the illustrated example, by opening the second flow rate control valve 24, the upstream side of the position where the bypass flow path 23 branches out of the discharge path 21 and the downstream side of the position where the bypass flow path 23 joins, The bypass channel 23 can be made to function as a second discharge channel for discharging treated water obtained by recovering nutrients from treated sewage water to a destination.

In the sewage treatment system 100, the first flow rate control valve 22 and the second flow rate control valve 24 control the amount of treated sewage water that is discharged as it is to the discharge destination (i.e., the amount of treated sewage water that flows through the discharge channel 21 as the first discharge channel). The amount of treated sewage water that is discharged to the discharge destination after recovering nutrients (i.e., the amount of treated sewage water that flows through the second discharge channel consisting of a part of the discharge channel 21 and the bypass channel 23) It functions as a flow rate adjustment mechanism to adjust the flow rate. Therefore, in the sewage treatment system 100, by adjusting the opening degrees of the first flow rate control valve 22 and the second flow rate control valve 24 and changing the ratio of treated sewage water that is discharged after recovering nutrients, The amount of nutrients contained in water can be actively controlled.

In the example shown in Figure 1, there is a first discharge channel in which treated sewage water is directly discharged to the discharge destination, and a first discharge channel in which the nutrient salts are recovered from the treated sewage water in the nutrient recovery equipment and the treated water is discharged to the discharge destination. Although the case where a part is common with the second discharge channel has been shown, in the sewage treatment system of the present invention, the first discharge channel and the second discharge channel may be provided separately.

The nutrient salt recovery equipment 30 recovers nutrient salts from treated sewage water using aquatic plants, and discharges the treated water from which the nutrient salts have been recovered. Here, the aquatic plants are not particularly limited as long as they can recover nutrients from treated sewage water, and for example, duckweed, microalgae, etc. that can take in and immobilize nutrients can be used. Further, the nutrient salt recovery equipment 30 is not particularly limited, and an aquarium or the like in which aquatic plants such as duckweed and microalgae can be cultured can be used.

Note that the nitrogen concentration in the treated water obtained by recovering nutrients in the nutrient salt recovery equipment 30 should be 5 mg-N/L or more and 15 mg-N/L or less, although it depends on the quality of the inflowing sewage treated water. I can do it. If the nitrogen concentration is within the above range, by appropriately operating and managing the nutrient salt recovery equipment 30, the annual discharge amount of nutrient salts to the discharge destination can be easily adjusted to a predetermined value or less.

The aquatic plant supply mechanism 31 is not particularly limited, and includes, for example, a storage for storing aquatic plants and a transport device for transporting the aquatic plants from the storage to the nutrient salt recovery facility. The aquatic plant supply mechanism 31 supplies aquatic plants to the nutrient salt recovery equipment 30, for example, when the amount of aquatic plants used when treating sewage water in the nutrient salt recovery equipment 30 is insufficient.

The power generation equipment 32 is not particularly limited as long as it is possible to generate electricity using the aquatic plants collected from the nutrient salt recovery equipment 30 as raw materials, and for example, the power generation equipment 32 may be used to collect surplus aquatic plants from the nutrient salt recovery equipment 30. A power generation facility can be used that includes a collection mechanism for collection, a digestion tank for obtaining digested gas by anaerobically digesting the collected aquatic plants, and a generator for generating power using the digested gas. By using surplus aquatic plants as a raw material to generate electricity, electrical energy can be created while actively managing the amount of nutrients contained in the effluent.
In addition, in addition to aquatic plants, the power generation equipment 32 may use initial settling sludge discharged from the sewage treatment equipment 10 as a raw material to generate power.

The control device 40 controls the operations of the first flow rate control valve 22, the second flow rate control valve 24, the aquatic plant supply mechanism 31, and the power generation equipment 32. Specifically, the control device 40 controls the opening degree of the first flow rate control valve 22 and the second flow rate control valve 24 as a flow rate control mechanism, and controls the amount of nutrient salts and treated sewage water that is directly discharged to the discharge destination. The amount of nutrients contained in the effluent can be actively controlled by changing the ratio of recovered sewage water to the treated sewage water that is discharged. The control device 40 also controls the amount of aquatic plants supplied from the aquatic plant supply mechanism 31 and the amount of aquatic plants collected by the power generation equipment 32 (in particular, the collection mechanism of the power generation equipment 32), and The amount of nutrient salts in the treated water is appropriately managed by adjusting the amount of aquatic plants used for recovering nutrient salts in step 30.

Here, the control device 40 may determine the ratio of treated sewage water that is discharged as is and treated sewage water that is discharged after recovering nutrients, depending on the season, or may be determined at the discharge destination. This may be done based on the amount of nutrient salts used.

Specifically, for example, the control device 40 increases the amount of treated sewage water that is directly discharged during the winter (January to March) when nutrients tend to be insufficient at the discharge destination, and increases the amount of treated sewage water that is discharged as is during the summer (July to September). Control may be performed to increase the amount of treated sewage water that is discharged after nutrient salts have been recovered. In this way, seasonal operation management can be appropriately performed.

In addition, the control device 40 increases the amount of treated sewage water that is directly discharged when the amount of nutrients required at the discharge destination is large, and increases the amount of sewage treated water that is discharged as is when the amount of nutrients required at the discharge destination is small. Control may be performed to increase the amount of treated sewage water that is discharged after salts have been recovered. In this way, the amount of nutrients supplied can be appropriately managed in accordance with the quality of the water at the destination.
The amount of nutrients required at the destination is determined by, for example, measuring the concentration of nutrients in the destination water area and calculating the difference between the target value and the measured value of the nutrient concentration in the destination area. It can be determined by

Furthermore, for example, if the total amount of nutrient salts that can be discharged into the water area of the discharge destination is specified by laws and ordinances such as the Sewerage Act, the control device 40 can control the annual amount of nutrient salts that can be discharged to the discharge destination from a predetermined amount. The ratio between the amount of treated sewage water that is discharged as is and the amount of treated sewage water that is discharged after nutrient salts have been recovered may be controlled so as to be equal to or less than this value. Specifically, the control device 40, for example, creates an annual operation plan, measures the concentration of nutrients in the effluent and the flow rate of the effluent, and calculates the integrated value of the amount of nutrient salts supplied to the destination. Then, in order to ensure a sufficient supply amount in the winter, the supply amount can be suppressed in advance in the summer so that the integrated value does not exceed the regulated value of laws and ordinances.

Further, the amount of aquatic plants can be adjusted using the control device 40, for example, so that the amount of nutrients in the treated water flowing out from the nutrient recovery equipment 30 approaches a target value. Specifically, when the amount of sewage treatment water flowing into the nutrient salt recovery equipment 30 and/or the concentration of nutrient salts in the sewage treatment water increases, the aquatic plant supply mechanism 31 supplies aquatic plants to the nutrient salt recovery equipment 30. By supplying plants, the amount of nutrient salts that can be recovered by the nutrient salt recovery equipment 30 can be increased. Additionally, when the amount of sewage treated water flowing into the nutrient salt recovery equipment 30 and/or the concentration of nutrient salts in the sewage treatment water decreases, the nutrient salts are recovered by the power generation equipment 32 (in particular, the recovery mechanism of the power generation equipment 32). By increasing the amount of aquatic plants, the amount of power generated in the power generation facility 32 can be increased while maintaining the quality of the treated water.
The target value for the amount of nutrient salts in treated water is not particularly limited, and may be set as appropriate based on the amount of nutrient salts required in the water area to which it is discharged, and the regulatory values stipulated in laws and ordinances. Can be set to .

(Sewage treatment method)
The sewage treatment method of the present invention is not particularly limited, and can be suitably used when treating sewage in the sewage treatment system of the present invention. The sewage treatment method of the present invention includes a sewage treatment process in which sewage is treated to obtain sewage treated water containing nutrients, and the sewage treated water obtained in the sewage treatment process is treated as it is and/or is treated with aquatic plants. A discharge process in which the nutrients are collected using a water bottle and then discharged to a destination, and a distribution process in which the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering the nutrients are determined in the discharge process. and a power generation step of collecting aquatic plants and generating electricity using the collected aquatic plants as raw materials. By performing the discharge process and the distribution process in this way, the quality of the discharged water can be easily managed actively. Also, by implementing the power generation process, active management of the quality of the effluent and energy generation can be achieved.

Here, in the sewage treatment step, sewage is treated using, for example, the above-mentioned sewage treatment equipment to obtain treated sewage water containing nutrients (nitrogen and/or phosphorus). Note that the nitrogen concentration in the sewage treatment water can be the same as described above regarding the sewage treatment system.

In addition, in the discharge step, the treated sewage water is discharged as it is, or after recovering nutrients, such that the amount ratio determined in the distribution step is achieved. Here, in the sewage treatment method of the present invention, the amount of nutrient salts contained in the effluent is actively controlled by changing the ratio of sewage treated water that is discharged after nutrient salts have been recovered. I can do it.
Note that the nitrogen concentration in treated water obtained by recovering nutrients from treated sewage water can be the same as that described above regarding the sewage treatment system.

In the distribution process, the ratio of treated sewage water that is discharged as is and treated sewage water that is discharged after recovering nutrients may be determined depending on the season, or may be determined based on the nutrient salts required at the destination. It may also be done based on the amount of

Specifically, for example, in the distribution process, the amount of treated sewage water that is directly discharged is increased during the winter (January to March), when nutrients tend to be insufficient at the discharge destination, and during the summer (July to September), the amount of treated sewage water is increased. The above ratio may be determined so as to increase the amount of treated sewage water that is discharged after nutrient salts have been recovered. In this way, seasonal operation management can be appropriately performed.

In addition, in the distribution process, if the amount of nutrient salts required at the destination is large, the amount of treated sewage water is increased, and if the amount of nutrient salts required at the destination is small, the amount of nutrient salts is increased. The above ratio may be determined so as to increase the amount of treated sewage water that is collected and then discharged. In this way, the quality of the discharged water can be appropriately managed in accordance with the amount of nutrients required at the discharge destination.
The amount of nutrients required at the destination is determined by, for example, measuring the concentration of nutrients in the destination water area and calculating the difference between the target value and the measured value of the nutrient concentration in the destination area. It can be determined by

Furthermore, in cases where the total amount of nutrient salts that can be released into the water area at the destination is stipulated by laws and ordinances such as the Sewerage Act, in the distribution process, the annual amount of nutrient salts discharged to the destination should be set at a predetermined value. The above ratio may be determined to be as follows. Specifically, in the distribution process, for example, an annual operation plan is drawn up in advance, and the concentration of nutrients in the effluent and the flow rate of the effluent are measured to calculate the cumulative amount of nutrient salts supplied to the destination. By calculating the amount, it is possible to suppress the supply amount in advance in the summer so that the integrated value does not exceed the regulated value of laws and ordinances in order to ensure a sufficient supply amount in the winter.

In addition to the steps described above, the sewage treatment method of the present invention may further include an aquatic plant amount adjustment step of adjusting the amount of aquatic plants used in the discharge step.
Here, adjustment of the amount of aquatic plants in the aquatic plant amount adjustment step is performed by, for example, recovering nutrients from treated sewage water using aquatic plants in the discharge step so that the amount of nutrient salts in the treated water reaches a target value. It can be done to get closer. Specifically, if the amount of treated sewage water from which nutrient salts are recovered using aquatic plants and/or the concentration of nutrient salts in the treated sewage water increases, the amount of aquatic plants used in the discharge process is increased. be able to. In addition, if the amount of sewage treated water from which nutrient salts are recovered using aquatic plants and/or the concentration of nutrient salts in sewage treated water decreases, increasing the amount of aquatic plants recovered in the power generation process , it is possible to increase the amount of power generated in the power generation process while maintaining the quality of treated water.
The target value for the amount of nutrient salts in the treated water is not particularly limited, and may be determined as appropriate based on the amount of nutrient salts required in the water area to which it is discharged, and the regulatory values stipulated in laws and ordinances. Can be set to .

In the power generation process, there is no particular limitation as long as it is possible to generate electricity using the collected aquatic plants as raw materials. Electric power can be generated by performing a digestion step to obtain digestive gas by performing natural digestion and a power generation step to generate power using the digestive gas. By using surplus aquatic plants as raw materials to generate electricity, it is possible to generate electrical energy while actively managing the amount of nutrients contained in the effluent.
In addition, in the power generation process, in addition to aquatic plants, surplus sludge generated in the sewage treatment process may also be used as a raw material to generate power.

Although the sewage treatment system and sewage treatment method of the present invention have been described above using one example, the sewage treatment system and sewage treatment method of the present invention are not limited to the above-mentioned example. Specifically, in the sewage treatment system and sewage treatment method of the present invention, it may be possible to predict the amount of power generated when power is generated using aquatic plants as raw materials. More specifically, for example, the amount of nutrients to be recovered from treated sewage water is determined based on the amount of nutrients required by the water area to which it is discharged, and the amount of aquatic plant growth is calculated from the amount of recovered nutrients. However, the amount of power that can be generated may be predicted by calculating the amount of digestion gas generated and the amount of power generated when using the digestion gas from the amount of proliferation. If it is possible to predict the amount of power generated, it will be possible to supply energy more efficiently as an energy supply base.

According to the sewage treatment system and sewage treatment method of the present invention, it is possible to easily actively manage the quality of effluent water, and it is also possible to generate energy.

10 Sewage treatment equipment 21 Discharge channel 22 First flow rate control valve 23 Bypass channel 24 Second flow rate control valve 30 Nutrient recovery facility 31 Aquatic plant supply mechanism 32 Power generation facility 40 Control device

Claims (8)

A sewage treatment facility that processes sewage and discharges treated sewage water containing nutrients;
a first discharge path for discharging the treated sewage water flowing out from the sewage treatment facility to a destination;
a second discharge channel comprising a nutrient salt recovery facility for recovering nutrients in the treated sewage water using aquatic plants, and discharging the treated water obtained by recovering the nutrients from the treated sewage water to the discharge destination; ,
a flow rate adjustment mechanism that adjusts the amount of treated sewage water flowing from the sewage treatment equipment into the first discharge channel and the amount of treated sewage water flowing from the sewage treatment facility into the second discharge channel;
a power generation facility that collects the aquatic plants from the nutrient salt recovery facility and generates power using the collected aquatic plants as raw materials;
Equipped with
A sewage treatment system , wherein the nutrient salt recovery equipment includes a control device that adjusts the amount of the aquatic plants so that the amount of nutrient salts in the treated water approaches a target value . The sewage system according to claim 1, wherein the flow rate adjustment mechanism includes a control device that controls the amount of treated sewage water flowing into the first discharge channel and the amount of treated sewage water flowing into the second discharge channel according to the season. processing system. The flow rate adjustment mechanism controls the amount of treated sewage water flowing into the first discharge channel and the amount of treated sewage water flowing into the second discharge channel based on the amount of nutrients required at the discharge destination. A sewage treatment system according to claim 1, comprising an apparatus. The flow rate adjustment mechanism controls the amount of treated sewage water flowing into the first discharge channel and the amount of treated sewage water flowing into the second discharge channel so that the annual discharge amount of nutrients to the discharge destination is equal to or less than a predetermined value. The sewage treatment system according to any one of claims 1 to 3, comprising a control device for controlling the sewage treatment system. a sewage treatment process for treating sewage to obtain treated sewage water containing nutrients;
A discharge step of discharging the treated sewage water obtained in the sewage treatment step to a destination as it is and/or after recovering nutrients using aquatic plants;
In the discharge step, a distribution step of determining the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering nutrients;
a power generation step of collecting the aquatic plants and generating electricity using the collected aquatic plants as raw materials;
including;
In the discharge step, the amount of the aquatic plants used in the discharge step is adjusted so that the amount of nutrients in the treated water obtained by recovering nutrients from the treated sewage water using the aquatic plants approaches a target value. A sewage treatment method further comprising a step of adjusting the amount of aquatic plants . The sewage treatment method according to claim 5 , wherein in the distribution step, the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering nutrients are determined depending on the season. In the distribution step, the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering the nutrient salts are determined based on the amount of nutrient salts required at the discharge destination. The sewage treatment method described in 5 . In the distribution step, the amount of treated sewage water to be discharged as is and the amount of treated sewage water to be discharged after recovering nutrients are adjusted such that the annual amount of nutrients discharged to the discharge destination is below a predetermined value. The sewage treatment method according to any one of claims 5 to 7 , wherein the sewage treatment method is determined.

Images