CN111886206A

CN111886206A - Sludge discharge control device, water treatment system, and sludge discharge control method

Info

Publication number: CN111886206A
Application number: CN201880090310.3A
Authority: CN
Inventors: 明田川恭平; 平敷勇
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2018-04-03
Filing date: 2018-04-03
Publication date: 2020-11-03
Also published as: JP6430083B1; WO2019193646A1; JPWO2019193646A1

Abstract

The purpose is to obtain a sludge discharge control device, a water treatment system, and a sludge discharge control method, which can suppress the accumulation of inorganic substances in a biological treatment tank while suppressing the amount of excess sludge. A water treatment system (100) is provided with: a sludge-containing treated water returning pump (13) for returning treated water (5) containing sludge, which has been treated by ozone in the ozone reaction section (10), to the biological treatment tank (1), a solid-liquid separation tank (6) for separating the treated water (5) containing sludge into treated water (7) and concentrated sludge (8), a concentrated sludge returning pump (9) for returning a part of the concentrated sludge (8) to the biological treatment tank (1), a concentrated sludge discharge pump (15) for discharging excess concentrated sludge (8) as excess sludge to the outside of the system, and a sludge discharge control device (14) for controlling the discharge of excess sludge. A sludge discharge control device (14) is provided with: an ozone treatment start detecting part (141) for detecting the start of ozone treatment, and a sludge discharge instructing part (145) for causing the concentrated sludge discharge pump (15) to start discharge of excess sludge after the ozone treatment start detecting means (141) detects the start of ozone treatment.

Description

Sludge discharge control device, water treatment system, and sludge discharge control method

Technical Field

The present invention relates to a sludge discharge control device, a water treatment system, and a sludge discharge control method for controlling discharge of sludge generated in water treatment, and more particularly, to a sludge discharge control device, a water treatment system, and a sludge discharge control method for controlling discharge of sludge in a water treatment system in which the volume of generated sludge is reduced by ozone.

Background

As a method for treating water such as waste water containing organic substances, a treatment method such as a standard activated sludge method using microorganisms is known. In such a treatment method, wastewater is treated using sludge containing microorganisms, and if the wastewater is purified as the treatment progresses, the proliferation of the microorganisms also progresses. Microorganisms that grow as wastewater is treated are reused for wastewater treatment, but microorganisms may excessively grow. Sludge containing excessively produced microorganisms and other plankton and the like is referred to as excess sludge. Excess sludge is not required for water treatment and needs to be discharged outside the wastewater treatment system.

In a treatment method for performing treatment of wastewater using sludge containing microorganisms, treated water containing sludge is referred to as sludge-containing treated water. Since sludge and excess sludge necessary for wastewater purification are generated in a biological treatment tank for water purification using microorganisms and contained in the treated water, the treated water containing sludge is separated into concentrated sludge and treated water in a solid-liquid separation tank, and then the excess sludge is discharged out of the wastewater treatment system. The sludge required for purifying the wastewater is returned to the biological treatment tank, and the treated water is released to rivers or sea.

The discharged excess sludge is subjected to incineration, landfill treatment, or fermentation treatment under anaerobic conditions as industrial waste. For the implementation of such treatment, a large amount of energy, cost and new land are required, and therefore, reduction in the amount of excess sludge production is required.

Conventionally, as one of methods for reducing the amount of excess sludge generated, a sludge volume reduction treatment using high-concentration ozone is known. Specifically, sludge-containing treated water containing sludge is extracted from a biological treatment tank to the outside of the tank, and the extracted sludge-containing treated water is mixed with a high-concentration ozone gas to decompose organic substances forming sludge in the sludge-containing treated water (for example, patent document 1). Further, a return sludge path for returning sludge from the solid-liquid separation tank to the aeration tank is branched to the reforming layer, a part of the sludge separated in the solid-liquid separation tank is transferred to the reforming layer, and ozone is injected into the sludge transferred to the reforming layer (for example, patent document 2).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-226536

Patent document 2: japanese patent laid-open publication No. 2004-141746

Disclosure of Invention

Problems to be solved by the invention

Since water such as wastewater to be treated by microorganisms contains not only organic substances but also inorganic substances such as sand and metals, the sludge in the biological treatment tank is composed of "organic sludge in which microorganisms and organic substances are aggregated" (hereinafter referred to as "organic sludge") and "inorganic substances such as sand and metals" (hereinafter referred to as "inorganic substances"), and ozone decomposes the organic sludge in the sludge but does not decompose the inorganic substances. Therefore, in the conventional sludge volume reduction treatment in which ozone is injected into the treated water or sludge containing sludge, the amount of the organic sludge in the sludge is reduced to some extent, but the amount of the inorganic substances is not reduced. In order to reduce inorganic substances, the sludge separated in the solid-liquid separation tank may be discharged to the outside of the system, but when the sludge is discharged to the outside of the system, not only inorganic substances but also organic sludge are reduced. Therefore, the organic sludge in the sludge is reduced by both the ozone treatment and the discharge to the outside of the system, whereas the inorganic substances in the sludge are reduced only by the discharge to the outside of the system. On the other hand, if the amount of sludge discharged to the outside of the system is too large, the disposal cost of excess sludge increases as described above. In addition, the amount of sludge returned to the biological treatment tank becomes too small, and there is a possibility that the amount of microorganisms necessary for the treatment of wastewater cannot be maintained in the biological treatment tank. Therefore, if the treatment of the wastewater is performed while the amount of excess sludge discharged to the outside of the system is suppressed, the proportion of inorganic substances in the sludge gradually increases as the treatment proceeds, and the amount of inorganic substances returned to the biological treatment tank increases, so that there is a possibility that the inorganic substances are accumulated in the biological treatment tank.

If the concentration of inorganic substances in the biological treatment tank increases due to accumulation of inorganic substances, there is a possibility that the inorganic substances are not completely separated in the solid-liquid separation tank. In addition, the convection caused by aeration in the biological treatment tank is deteriorated, and the activity of microorganisms is lowered, so that the quality of the treated water may be deteriorated.

The present application discloses a technique for solving the above problem, and aims to: a sludge discharge control device, a water treatment system, and a sludge discharge control method are provided, which can suppress the amount of excess sludge discharged to the outside of the system and also suppress the accumulation of inorganic substances in the biological treatment tank.

Means for solving the problems

The sludge discharge control device disclosed in the present application is a sludge discharge control device that is provided in a water treatment system that controls discharge of excess sludge, the water treatment system including: the method for treating water by a biological treatment tank, wherein the water to be treated is biologically treated in the biological treatment tank, the treated water containing sludge produced by the biological treatment is returned to the biological treatment tank by ozone treatment, part of concentrated sludge separated from the treated water containing sludge by solid-liquid separation means is returned to the biological treatment tank by concentrated sludge returning means, and excess concentrated sludge not returned to the biological treatment tank is discharged outside the system as excess sludge by concentrated sludge discharging means, the method comprising: an ozone treatment start detection means for detecting the start of ozone treatment; and a sludge discharge instruction means for causing the concentrated sludge discharge means to start a concentrated sludge discharge process for discharging excess sludge after the start of ozone treatment is detected by the ozone treatment start detection means.

Further, the sludge discharge control method disclosed in the present application is a sludge discharge control method for controlling discharge of excess sludge in a water treatment system including: the method for treating water by a biological treatment tank, wherein the water to be treated is biologically treated in the biological treatment tank, wherein the treated water containing sludge produced by the biological treatment is returned to the biological treatment tank by ozone treatment, wherein a part of concentrated sludge separated from the treated water containing sludge by a solid-liquid separation means is returned to the biological treatment tank by a concentrated sludge returning means, and wherein the remaining concentrated sludge is discharged outside the system as excess sludge by a concentrated sludge discharging means, comprises: an ozone treatment start detection step of detecting the start of ozone treatment; and a sludge discharge step of discharging excess sludge outside the system after the ozone treatment start detection step.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the sludge discharge control apparatus and the sludge discharge control method disclosed in the present application, accumulation of inorganic substances in the biological treatment tank can be suppressed while suppressing the amount of excess sludge discharged to the outside of the system.

Drawings

Fig. 1 is a schematic diagram showing the configuration of a water treatment system according to embodiment 1.

Fig. 2 is a flowchart showing a sludge discharge control method according to embodiment 1.

Fig. 3 is a schematic diagram showing the configuration of a water treatment system according to embodiment 2.

Fig. 4 is a flowchart showing a sludge discharge control method according to embodiment 2.

Fig. 5 is a schematic diagram showing the configuration of a water treatment system according to embodiment 3.

Fig. 6 is a flowchart showing a sludge discharge control method according to embodiment 3.

Fig. 7 is a schematic diagram showing the configuration of a water treatment system according to embodiment 4.

Fig. 8 is a flowchart showing a sludge discharge control method according to embodiment 4.

Fig. 9 is a schematic diagram showing the configuration of a water treatment system according to embodiment 5.

Fig. 10 is a schematic diagram showing the configuration of a water treatment system according to embodiment 6.

Fig. 11 is a flowchart showing a sludge discharge control method according to embodiment 6.

Detailed Description

Embodiment 1.

Hereinafter, embodiment 1 will be described with reference to fig. 1 and 2. Fig. 1 is a schematic diagram showing the configuration of a water treatment system according to embodiment 1. The water treatment system 100 includes: a biological treatment tank 1 in which biological treatment of wastewater 4 is performed, an air diffuser 2 for feeding air into the biological treatment tank 1, a solid-liquid separation tank 6 for separating treated water 5 containing sludge generated in the biological treatment tank 1 into treated water 7 and concentrated sludge 8, an ozone reaction unit 10 for performing ozone treatment on the treated water 5 containing sludge, and a sludge discharge control device 14 for controlling discharge of the concentrated sludge 8. The wastewater 4 flowing into the biological treatment tank 1 contains organic matter. The wastewater 4 is an example of water to be treated in the water treatment system 100. The solid-liquid separation tank 6 is an example of a solid-liquid separation means. The ozone reaction part 10 is an example of an ozone treatment means.

The air diffuser 2 is connected to the air supply device 3, and supplies the air taken from the air supply device 3 into the biological treatment tank 1 to bring the interior of the biological treatment tank 1 into an aerobic condition. In the biological treatment tank 1, the wastewater 4 is treated under aerobic conditions with sludge that is an aggregate of microorganisms or the like, and sludge-containing treated water 5 containing sludge is produced. As the air supply device 3, a blower, a compressor, a pump, and the like can be used according to the necessary air supply amount. Since an environment having aerobic conditions may be present in a part of the biological treatment tank 1, an environment having anaerobic conditions in which air is not supplied or supplied only in a small amount may be present in a part of the biological treatment tank 1. The structure of the biological treatment tank 1 is not particularly limited, and a known technique such as A2O method including an anaerobic tank or an anoxic tank, OD (oxidation ditch method), or the like can be used.

The treated water 5 containing the sludge produced in the biological treatment tank 1 is sent to a solid-liquid separation tank 6 connected to the biological treatment tank 1. The solid-liquid separation tank 6 precipitates sludge in the sludge-containing treated water 5, and separates the sludge-containing treated water 5 into treated water 7 and concentrated sludge 8. The treated water 7 separated in the solid-liquid separation tank 6 flows out from the solid-liquid separation tank 6 only in the same amount as the amount of the treated water 5 containing sludge flowing into the solid-liquid separation tank 6 from the biological treatment tank 1. The method of discharging the treated water 7 is not particularly limited, and for example, an overflow system can be employed. In the case of the overflow system, the amount of the sludge-containing treated water 5 flowing into the solid-liquid separation tank 6 can be made equal to the amount of the treated water 7 flowing out from the solid-liquid separation tank 6 without using power of a pump or the like.

The concentrated sludge 8 separated in the solid-liquid separation tank 6 is sent to the outside of the solid-liquid separation tank 6 through a concentrated sludge pipe 101. The concentrated sludge pipe 101 has one end connected to the lower part or bottom part of the solid-liquid separation tank 6, and the other end branched and connected to the concentrated sludge return pipe 102 and the concentrated sludge discharge pipe 106. The condensed sludge returning pipe 102 is provided with a condensed sludge returning pump 9, and the condensed sludge discharge pipe 106 is provided with a condensed sludge discharge pump 15. Thus, a part of the concentrated sludge 8 sent to the concentrated sludge pipe 101 is returned to the biological treatment tank 1 through the concentrated sludge return pipe 102 by the suction of the concentrated sludge return pump 9, and the remaining concentrated sludge 8 is discharged out of the system of the water treatment system 100 through the suction of the concentrated sludge discharge pump 15 and the concentrated sludge discharge pipe 106. The concentrated sludge returning pump 9 is an example of a concentrated sludge returning means, and the concentrated sludge discharging pump 15 is an example of a concentrated sludge discharging means.

As the solid-liquid separation tank 6, a precipitation tank, a membrane separation tank, or the like is used. In the case of using a membrane separation tank, a membrane module used in a so-called membrane separation activated sludge process may be used.

The ozone reaction part 10 is connected to the biological treatment tank 1 via an extraction pipe 103, and the treated water 5 containing the sludge extracted from the biological treatment tank 1 is subjected to ozone treatment in the ozone reaction part 10. The extraction pipe 103 is provided with an extraction pump 11, and the treated water 5 containing the sludge in the biological treatment tank 1 can be continuously or intermittently fed to the ozone reaction section 10 by the suction of the extraction pump 11. The extraction pump 11 is an example of means for flowing the treated water 5 containing sludge into the ozone reaction part 10. In embodiment 1, the treated water 5 containing sludge in the biological treatment tank 1 is fed to the ozone reaction unit 10, but sludge in the treated water 5 containing sludge may be fed to the ozone reaction unit 10, and thus, for example, the concentrated sludge 8 separated in the solid-liquid separation tank 6 may be fed to the ozone reaction unit 10. In this case, the extraction pipe 103 has one end connected to the lower part or bottom part of the solid-liquid separation tank 6 and the other end connected to the ozone reaction section 10.

The ozone reaction portion 10 is connected to an ozone generator 12 via an ozone gas pipe 104. The ozone generator 12 generates ozone gas as gaseous ozone by, for example, a silent discharge method, and the gaseous ozone generated in the ozone generator 12 is supplied to the ozone reaction part 10 from the ozone gas pipe 104. The ozone supplied to the ozone reaction portion contacts and reacts with the organic sludge in the treated water 5 containing the sludge flowing from the biological treatment tank 1 into the ozone reaction portion 10, and decomposes the organic sludge. The sludge-containing treated water 5 obtained by decomposing the organic sludge with ozone is returned to the biological treatment tank 1 through the return pipe 105. The return pipe 105 is provided with a return pump 13, and the treated water 5 containing the sludge in the ozone reaction part 10 can be continuously or intermittently returned to the biological treatment tank 1 by the suction of the return pump 13. The ozone gas pipe 104 is provided with a gas flow meter 17, and the amount of ozone gas supplied from the ozone generator 12 to the ozone reaction part 10 is measured by the gas flow meter 17. The return pump 13 is an example of a means for returning the treated water containing sludge, and is not limited to the means for returning the treated water containing sludge. As a means for returning the treated water containing sludge, for example, when the ozone reaction part 10 is located at a higher position than the biological treatment tank 1, natural falling can be utilized. In embodiment 1, a control unit, not shown, is used to start and stop the extraction pump 11, the ozone generator 12, and the return pump 13.

The structure of the ozone reaction section 10 is not particularly limited, and any known technique capable of supplying ozone to the treated water 5 containing sludge can be used. For example, the ozone reaction section 10 is a tank in which the treated water 5 containing sludge can be stored and an ejector or the like as a gas diffusion pipe or a gas-liquid mixer is provided, and ozone can be supplied through the gas diffusion pipe or the ejector, and may be configured as follows: the ozone reaction section 10 is a gas-liquid mixer itself such as an eductor, and directly supplies ozone gas from an ozone gas pipe 104.

The ozone treatment in the ozone reaction section 10 may be performed by a known technique such as a batch method, a CSTR (continuous tank reactor) method, or a PFR (plug flow) method, and is not particularly limited. For example, the ozone reaction section 10 is a tank capable of storing the treated water 5 containing sludge, and the treated water 5 containing sludge is stored and held in the ozone reaction section 10 by the extraction pump 11, and the intermittent system is used when the treated water 5 containing sludge stored and held in the ozone reaction section 10 is supplied with ozone gas generated by the ozone generator 12 through a gas-liquid mixer such as a diffuser or an ejector, and then the treated water 5 containing sludge is returned to the biological treatment tank 1 by the return pump 13. For example, the CSTR system is a tank in which the treated water 5 containing sludge can be stored in the ozone reaction section 10, and is configured such that the treated water 5 containing sludge is fed into the ozone reaction section 10 by the extraction pump 11 and the treated water 5 containing sludge is returned to the biological treatment tank 1 by the return pump 13, and during this time, the ozone gas generated by the ozone generator 12 is supplied through a gas-liquid mixer such as an air diffuser or an ejector. Further, the case where the ozone reaction section 10 is a gas-liquid mixer itself such as an injector is a PFR system.

The ozone generator 12 generates ozone gas at a concentration and a flow rate necessary for the ozone treatment of the organic sludge contained in the sludge-containing treated water 5. The ozone generator 12 is connected to a raw material supply device (not shown) that supplies a raw material of the ozone gas to the ozone generator 12 and a cooling device (not shown) that cools the ozone generator 12.

The raw material of the ozone gas supplied to the ozone generator 12 is not particularly limited. For example, liquid oxygen or oxygen generated by psa (pressure Swing adsorption) or pvsa (pressure Vacuum Swing adsorption) can be used. An additive gas supply unit for adding nitrogen, air or carbon dioxide in an amount of 0.05 to 5% based on the flow rate of oxygen to be supplied can be provided as required.

The cooling device is provided with: a circulation pump for circulating a cooling medium for cooling the ozone generator 12, and a cooler for cooling the cooling medium whose temperature has risen by absorbing heat generated in the ozone generator 12. As the cooler, a heat exchange type cooler selected from a liquid-liquid type and a liquid-gas type, a liquid-freon refrigerant type cooler, or the like can be used. In addition, when cooling is performed at an extremely low temperature, a refrigerator may be used. As the cooling medium, for example, general tap water can be used. Further, water mixed with an antifreeze solution, a scale remover, or the like, ion-exchanged water, or pure water can be used. Further, ethylene glycol, ethanol, or the like can be used.

The concentration of the ozone gas generated by the ozone generator 12 is not particularly limited, but is preferably 100mg/L to 400mg/L, more preferably 250mg/L to 400mg/L, in consideration of the concentration of the ozone gas that can be generated only by the conventional ozone generator 12, while efficiently decomposing the organic sludge in the sludge-containing treatment water 5 to improve the biodegradability, promoting the reduction of the excess sludge in the biological treatment tank 1.

The ozone generator 12 includes a discharge start signal transmitting unit 121. The discharge start signal transmitter 121 transmits a discharge start signal if the ozone generator 12 is activated to start ozone treatment and discharge for ozone gas generation is started.

The sludge discharge control device 14 is connected to the ozone generator 12 via a signal line L1, and is connected to the concentrated sludge discharge pump 15 via a signal line L2. The sludge discharge control device 14 further includes: ozone treatment start detection means, which is an ozone treatment start detection unit 141 that detects the start of ozone treatment, and sludge discharge instruction means, which is a sludge discharge instruction unit 145 that instructs the start of concentrated sludge discharge. In the ozone treatment, the ozone gas generated by the ozone generator 12 is supplied to the ozone reaction section 10, and the ozone treatment of the treatment water 5 containing the sludge is performed in the ozone reaction section 10. The ozone treatment start detection unit 141 detects the start of ozone treatment by receiving a discharge start signal transmitted from the discharge start signal transmission unit 121 of the ozone generator 12 via the signal line L1. In embodiment 1, the following configuration is possible: the start of ozone treatment is detected by a discharge start signal from the discharge start signal transmitting unit 121, but the start of ozone treatment is detected by, for example, an inverter output signal from the ozone generator 12 or an analog signal from the gas flowmeter 17.

The reaction system of ozone and organic sludge in the ozone reaction section 10 is an intermittent system, and when the sludge-containing treated water 5 is stored and held in the ozone reaction section 10, ozone gas generated by the ozone generator 12 is supplied to the sludge-containing treated water 5 stored and held in the ozone reaction section 10, and then the sludge-containing treated water 5 is returned to the biological treatment tank 1 via the return pipe 105, the start of ozone treatment can be detected by a start signal of the return pump 13 provided in the return pipe 105, an analog signal of a sludge flow meter (not shown) provided in the return pipe 105, an on signal of an electric valve (not shown) provided in the return pipe 105, or the like.

The sludge discharge instructing unit 145, upon detection of the start of the ozone treatment by the ozone treatment start detecting unit 141, conveys the concentrated sludge 8 separated in the solid-liquid separation tank 6 to the concentrated sludge discharge pipe 106 and discharges the same to the outside of the system of the water treatment system 100. Specifically, the start signal is sent to the concentrated sludge discharge pump 15 via the signal line L2 to drive the concentrated sludge discharge pump 15. Thereby, the concentrated sludge 8 separated from the treated water 7 in the solid-liquid separation tank 6 is sucked to the concentrated sludge discharge pipe 106 side and discharged to the outside of the system of the water treatment system 100.

Since the concentrated sludge discharge treatment started in response to the instruction from the sludge discharge control device 14 is performed after the start of the ozone treatment, the concentrated sludge 8 discharged to the outside of the system is the concentrated sludge 8 separated from the treated water 5 containing the sludge treated by the ozone. In the ozone treatment, the organic sludge in the sludge of the treated water 5 containing sludge is decomposed by ozone and returned to the biological treatment tank 1, and therefore the sludge of the treated water 5 containing sludge returned from the ozone reaction part 10 to the biological treatment tank 1 in the ozone treatment step is in a state in which the ratio of inorganic substances to organic sludge (hereinafter referred to as "inorganic substance/organic sludge ratio") is high. Therefore, in the ozone treatment, the inorganic matter/organic sludge ratio in the biological treatment tank 1 is also increased, and the inorganic matter/organic sludge ratio of the treated water 5 containing sludge to be fed to the solid-liquid separation tank 6 and the concentrated sludge 8 separated from the treated water 5 containing sludge is also increased. Therefore, if the concentrated sludge discharge control device 14 starts the concentrated sludge discharge treatment after the start of the ozone treatment, the concentrated sludge 8 having a high inorganic/organic sludge ratio is discharged to the outside of the system, and even when the same amount of concentrated sludge 8 is discharged, the amount of inorganic substances that can be discharged becomes relatively large.

Next, the operation will be described. In the water treatment system 100, a biological treatment step of biologically treating the wastewater 4 in the biological treatment tank 1, a solid-liquid separation step of separating the treated water 5 containing the sludge generated in the biological treatment step into treated water 7 and concentrated sludge 8 in the solid-liquid separation tank 6, and a concentrated sludge returning step of returning a part of the concentrated sludge to the biological treatment tank 1 are performed.

First, in the biological treatment step, the wastewater 4 flows into the biological treatment tank 1, and the biological treatment of the wastewater 4 is performed in the biological treatment tank 1 to form sludge-containing treated water 5 containing sludge. Subsequently, the treated water 5 containing the sludge flows into the solid-liquid separation tank 6, and in the solid-liquid separation step, the treated water 5 containing the sludge is separated into treated water 7 and concentrated sludge 8. The concentrated sludge 8 to be separated is returned to the biological treatment tank 1 through the concentrated sludge return pipe 102 by the concentrated sludge return pump 9 in the concentrated sludge return step. This is an example of the concentrated sludge returning step.

The biological treatment step, the solid-liquid separation step and the concentrated sludge returning step may be performed in a predetermined order, or may be manually performed by a facility manager.

The sludge discharge control by the sludge discharge control device 14 is performed in parallel with the above-described biological treatment step and solid-liquid separation step. Fig. 2 is a flowchart showing a sludge discharge control method according to embodiment 1. The sludge discharge control method according to embodiment 1 includes a volume reduction process and a concentrated sludge discharge process. The volume reduction process comprises an ozone treatment step and a return step, and the concentrated sludge discharge process comprises an ozone treatment start detection step and a concentrated sludge discharge step.

First, the extraction pump 11 and the return pump 13 are started in response to a command from the control unit, and the treated water 5 containing sludge is circulated between the biological treatment tank 1 and the ozone reaction unit 10 (step ST 101). The treated water 5 containing sludge in the biological treatment tank 1 is extracted by suction by the extraction pump 11, and flows into the ozone reaction unit 10 through the extraction pipe 103. The treated water 5 containing the sludge in the ozone reaction part 10 is extracted by suction by the return pump 13 and returned to the biological treatment tank 1 through the return pipe 105.

Next, the ozone generator 12 is started to start generation of ozone gas by electric discharge. Upon the start of discharge, the discharge start signal transmitter 121 transmits a discharge start signal to the sludge discharge control device 14 (step ST 102). The ozone gas generated by the ozone generator 12 is supplied to the ozone reaction portion 10 through an ozone gas pipe 104. When ozone gas is supplied to the ozone reaction part 10, the sludge contained in the treated water 5 containing sludge in the ozone reaction part 10 is brought into contact with ozone and reacts with the ozone, and an ozone treatment is performed (step ST 103). The treated water 5 containing the sludge treated with ozone is returned to the biological treatment tank 1 through a return pipe 105. The ozone treatment performed in step ST103 is an example of the ozone treatment step, and the treatment of returning the treated water 5 containing the sludge treated with ozone to the biological treatment tank 1 via the return pipe 105 is an example of the return step.

On the other hand, the ozone treatment start detection unit 141 receives the discharge start signal transmitted from the discharge start signal transmission unit 121 of the ozone generator 12 in step ST102, and detects the start of the ozone treatment (step ST 111). Step ST111 is an example of the ozone treatment start detection process.

When the start of ozone treatment is detected by the ozone treatment start detector 141 in step ST111, the sludge discharge instructing unit 145 energizes the concentrated sludge discharge pump 15 to start the concentrated sludge discharge pump 15 (step ST 112). The concentrated sludge discharge pump 15 performs a concentrated sludge discharge process of sucking a part of the concentrated sludge 8 in the solid-liquid separation tank 6 and discharging the part to the outside of the system of the water treatment system 100 through the concentrated sludge discharge pipe 106 (step ST 113). The concentrated sludge discharge treatment performed in step ST113 is an example of the concentrated sludge discharge step. In this way, the sludge discharge instructing unit 145 causes the concentrated sludge discharge pump 15 to start the concentrated sludge discharge process after the start of the ozone process is detected by the ozone process start detecting unit 141.

The operating time of the ozone generator 12 can be appropriately set based on the ozone gas concentration and the gas flow rate of the ozone generator 12 so that the amount of ozone required for decomposing the organic sludge contained in the sludge-containing treated water 5 is supplied. The amount of the sludge-containing treated water 5 extracted by the extraction pump 11 to the ozone reaction section 10 can be appropriately set based on the amount of the organic sludge required for decomposition by ozone and the concentration of the organic sludge in the sludge-containing treated water 5.

After the operation time of the ozone generator 12 is finished, the ozone generator 12 is stopped (step ST104), and the extraction pump 11 and the return pump 13 are stopped (step ST 105).

The operation time of the concentrated sludge discharge pump 15 is not particularly limited, and is preferably set so that organic sludge that is not decomposed by ozone among organic sludge contained in excess sludge in the sludge-containing treated water 5 in the biological treatment tank 1 is discharged to the outside of the system of the water treatment system 100. That is, the concentrated sludge discharge pump 15 is operated so that a part of the organic sludge contained in the excess sludge in the sludge-containing treated water 5 is decomposed by ozone and the excess organic sludge that is not decomposed by ozone is discharged to the outside of the system of the water treatment system 100.

After the operation time of the concentrated sludge discharge pump 15 is finished, the sludge discharge instructing unit 145 stops the concentrated sludge discharge pump 15 and stops the discharge of the concentrated sludge 8 (step ST 114).

As described above, since the sludge discharge control device 14 starts the concentrated sludge discharge treatment after detecting the start of the ozone treatment, the concentrated sludge 8 in a state where the inorganic matter/organic sludge ratio is increased by the ozone treatment is discharged to the outside of the system of the water treatment system 100 in the concentrated sludge discharge process.

According to embodiment 1, accumulation of inorganic substances in the biological treatment tank can be suppressed while suppressing the amount of excess sludge discharged to the outside of the system. More specifically, the present invention provides: a sludge discharge control device for detecting the start of ozone treatment and starting the concentrated sludge discharge treatment after the detection of the start of ozone treatment. In the ozone treatment, since the inorganic matter/organic sludge ratio of the sludge contained in the treated water containing the sludge is increased and the inorganic matter/organic sludge ratio of the concentrated sludge separated from the treated water containing the sludge in the solid-liquid separation tank is also increased, the inorganic matter/organic sludge ratio of the concentrated sludge discharged from the solid-liquid separation tank to the outside of the system of the water treatment system becomes high in the concentrated sludge discharge treatment, and more inorganic matter can be discharged to the outside of the system without increasing the amount of excess sludge discharged to the outside of the system. Therefore, the ozone treatment can suppress the amount of excess sludge discharged to the outside of the system and the accumulation of inorganic substances in the biological treatment tank.

Further, since the inorganic matter/organic sludge ratio of the concentrated sludge discharged to the outside of the system is high, the amount of the organic sludge discharged to the outside of the system is suppressed by the concentrated sludge discharge treatment. Therefore, it is possible to prevent excessive discharge of microorganisms contained in the organic sludge to the outside of the system, and to maintain the amount of microorganisms necessary for wastewater treatment.

Embodiment 2.

Hereinafter, embodiment 2 will be described with reference to fig. 3 and 4. The basic configuration and operation of embodiment 2 are the same as those of embodiment 1, but are different from embodiment 1 in that a concentrated sludge return pump and a concentrated sludge discharge pump are omitted, a concentrated sludge pump is provided in a concentrated sludge pipe, and a concentrated sludge pipe, a concentrated sludge return pipe, and a concentrated sludge discharge pipe are connected via a switching valve. The same reference numerals are used for the same or corresponding portions as those in fig. 1 or 2, and the description thereof will be omitted unless otherwise particularly required.

Fig. 3 is a schematic diagram showing the configuration of a water treatment system according to embodiment 2. In the water treatment system 200, the sludge discharge control device 24 includes an ozone treatment start detection unit 241 and a sludge discharge instruction unit 245. The ozone treatment start detection unit 241 detects the start of ozone treatment by receiving a discharge start signal from the discharge start signal transmission unit 121 of the ozone generator 12, as in the ozone treatment start detection unit 141 of embodiment 1. Further, the sludge discharge instructing unit 245 starts the concentrated sludge discharge treatment after the start of the ozone treatment is detected by the ozone treatment start detecting unit 241, similarly to the sludge discharge instructing unit 145 according to embodiment 1.

The concentrated sludge pipe 201 is provided with a concentrated sludge pump 18, i.e., a concentrated sludge conveying means. The concentrated sludge pipe 201 has one end connected to the lower portion or bottom of the solid-liquid separation tank 6, and the other end connected to the concentrated sludge return pipe 102 and the concentrated sludge discharge pipe 106 via the switching valve 19. The switching valve 19 is connected to the sludge discharge control device 24 via a signal line L2, and switches the destination of the concentrated sludge 8 sent from the concentrated sludge pipe 201 in accordance with an instruction sent from the sludge discharge control device 24. Specifically, the return direction in which the concentrated sludge pipe 201 is connected to the concentrated sludge return pipe 102 and the discharge direction in which the concentrated sludge pipe 201 is connected to the concentrated sludge discharge pipe 106 are switched so that either the return direction or the discharge direction is opened. For example, the discharge direction is in the closed state when the return direction is in the open state, and the discharge direction is in the open state when the return direction is in the closed state. The concentrated sludge pump 18 sucks the concentrated sludge 8 separated from the sludge-containing treated water 5 in the solid-liquid separation tank 6 from the solid-liquid separation tank 6, and sends the sucked sludge to the switching valve 19 through the concentrated sludge pipe 201. When the return direction is opened at the switching valve 19, the concentrated sludge 8 from the concentrated sludge pipe 201 is returned to the biological treatment tank 1 via the concentrated sludge return pipe 102. When the discharge direction is in the open state at the switching valve 19, the concentrated sludge 8 from the concentrated sludge pipe 201 is discharged to the outside of the system of the water treatment system 200 through the concentrated sludge discharge pipe 106. As described above, the concentrated sludge pump 18 serves as a concentrated sludge returning means or a concentrated sludge discharging means depending on the state of the switching valve 19. The switching valve 19 is an example of a switching means.

The sludge discharge instructing unit 245 switches the switching valve 19 to the open state of the return direction before the start of the ozone treatment is detected by the ozone treatment start detecting unit 241, that is, before the ozone treatment start detecting unit 241 receives the discharge start signal transmitted from the discharge start signal transmitting unit 121 of the ozone generator 12, and sets the destination of the concentrated sludge 8 flowing out of the solid-liquid separation tank 6 to the concentrated sludge return pipe 102. Therefore, before the start of the ozone treatment is detected by the ozone treatment start detector 241, the concentrated sludge 8 separated by the solid-liquid separation tank 6 is returned to the biological treatment tank 1 by the concentrated sludge pump 18. When the start of ozone treatment is detected by the ozone treatment start detector 241, the sludge discharge instructing unit 245 switches the switching valve 19 to open the discharge direction, and causes the concentrated sludge 8 flowing out of the solid-liquid separation tank 6 to be delivered to the concentrated sludge discharge pipe 106 and to be discharged outside the system of the water treatment system 200. When the concentrated sludge pump 18 is stopped when the ozone treatment start detector 241 detects the start of the ozone treatment, the sludge discharge indicator 245 starts the concentrated sludge pump 18. When the discharge direction of switching valve 19 is opened, it is preferable to control concentrated sludge pump 18 not to stop.

The other parts are the same as those in embodiment 1, and therefore, the description thereof is omitted.

Next, the operation will be described. In the same manner as in embodiment 1, the water treatment system 200 performs a biological treatment step, a solid-liquid separation step, and a concentrated sludge returning step. In the concentrated sludge returning step, the switching valve 19 is switched so that the returning direction is opened.

The sludge discharge control by the sludge discharge control device 24 is performed in parallel with the above-described biological treatment step and solid-liquid separation step. Fig. 4 is a flowchart showing a sludge discharge control method according to embodiment 2. The sludge discharge control method in embodiment 2 includes a containing process and a concentrated sludge discharge process as in embodiment 1. The volume reduction process comprises an ozone treatment step and a return step, and the concentrated sludge discharge process comprises an ozone treatment start detection step and a concentrated sludge discharge step.

First, the volume reduction process is started in the same manner as in embodiment 1. That is, the extraction pump 11 and the return pump 13 are activated in response to a command from the control unit (step ST201), the ozone generator 12 is activated to start generation of ozone gas by electric discharge, and a discharge start signal is transmitted to the sludge discharge control device 24 (step ST 202). Ozone gas generated by the ozone generator 12 is supplied to the ozone reaction section 10, the treated water 5 containing sludge is subjected to ozone treatment in the ozone reaction section 10, and the treated water 5 containing sludge subjected to ozone treatment is returned to the biological treatment tank 1 (step ST 203).

On the other hand, the ozone treatment start detection unit 241 receives the discharge start signal transmitted from the discharge start signal transmission unit 121 of the ozone generator 12 in step ST202, and detects the start of the ozone treatment (step ST 211).

When the start of ozone treatment is detected by the ozone treatment start detector 241 in step ST211, the sludge discharge instructing unit 245 switches the switching valve 19 so that the discharge direction is opened and the return direction is closed (step ST 212). Next, the sludge discharge instruction unit 245 determines the start/stop state of the concentrated sludge pump 18 from the energization state of the concentrated sludge pump 18, and energizes the concentrated sludge pump 18 to start the concentrated sludge pump 18 when the concentrated sludge pump 18 is stopped without being energized (step ST 213). The concentrated sludge pump 18 started by the sludge discharge control device 24 performs a concentrated sludge discharge process of sucking a part of the concentrated sludge 8 in the solid-liquid separation tank 6 and discharging the part to the outside of the system of the water treatment system 200 through the switching valve 19 and the concentrated sludge discharge pipe 106 (step ST 214).

The operation time of the ozone generator 12 is the same as that in embodiment 1. After the operation time of the ozone generator 12 is completed, the ozone treatment is completed in the same manner as in embodiment 1. That is, the ozone generator 12 is stopped (step ST204), and the extraction pump 11 and the return pump 13 are stopped (step ST 205).

The operation time of the concentrated sludge pump 18 is the same as that of the concentrated sludge discharge pump 15 of embodiment 1. After the operation time of the concentrated sludge pump 18 is finished, the sludge discharge instructing unit 245 stops the concentrated sludge pump 18 and stops the discharge of the concentrated sludge 8, as in embodiment 1 (step ST 215). The sludge discharge instructing unit 245 switches the switching valve 19 so that the discharge direction is closed and the return direction is opened (step ST 216). Then, in the case of performing the concentrated sludge returning step or the like, the concentrated sludge pump 18 is started as necessary.

According to embodiment 2, the same effect as that of embodiment 1 can be obtained because the concentrated sludge discharge treatment is started after the start of the ozone treatment as in embodiment 1.

In addition, the accumulation of inorganic substances in the biological treatment tank can be further suppressed. More specifically, a switching valve is provided between the condensed sludge return pipe and the condensed sludge discharge pipe, and the condensed sludge pipe, one of which is opened and the other of which is closed. Therefore, in the concentrated sludge discharge process, when the discharge direction of the switching valve is switched to the open state, the return direction is set to the closed state, so that the concentrated sludge having a high inorganic/organic sludge ratio can be prevented from being returned from the solid-liquid separation tank to the biological treatment tank, and the accumulation of inorganic substances in the biological treatment tank can be further suppressed.

In addition, the configuration can be made simpler. More specifically, a concentrated sludge pump is provided in the concentrated sludge pipe, and a concentrated sludge return pipe and a concentrated sludge discharge pipe are connected to the concentrated sludge pipe via a switching valve. The destination of excess sludge transported through the concentrated sludge piping is controlled by switching the selector valve, and the concentrated sludge can be returned and discharged only by pumping by the concentrated sludge pump. Therefore, the configuration is simplified by omitting the concentrated sludge returning pump and the concentrated sludge discharging pump.

Embodiment 3.

Hereinafter, embodiment 3 will be described with reference to fig. 6 based on fig. 5. The basic configuration and operation of embodiment 3 are the same as those of embodiment 2, but the sludge discharge control apparatus is different from embodiment 2 in that it includes an ozone treatment control unit that controls the start and stop of the extraction pump, the ozone generator, and the return pump. Note that the same reference numerals are used for the same or corresponding portions as those in fig. 3 and 4, and the description thereof will be omitted unless otherwise specified.

Fig. 5 is a schematic diagram showing the configuration of a water treatment system according to embodiment 3. In the water treatment system 300, the sludge discharge control device 34 includes: an ozone treatment start detector 341, a sludge discharge indicator 345, and an ozone treatment controller 342, that is, an ozone treatment control means. The ozone treatment start detection unit 341 detects the start of ozone treatment by receiving a discharge start signal from the discharge start signal transmission unit 121 of the ozone generator 12, as in the ozone treatment start detection unit 141 of embodiment 1. Further, the sludge discharge instructing unit 345 starts the concentrated sludge discharge treatment after the start of the ozone treatment is detected by the ozone treatment start detecting unit 341, similarly to the sludge discharge instructing unit 145 according to embodiment 1.

The ozone treatment control unit 342 is connected to the extraction pump 11, the ozone generator 12, and the return pump 13 via a signal line L1, transmits an ozone treatment start signal to the extraction pump 11, the ozone generator 12, and the return pump 13, and controls the start and stop of the ozone treatment by controlling the start of the extraction pump 11, the ozone generator 12, and the return pump 13. In addition, in the start and stop control of the ozone treatment, the ozone treatment control portion 342 controls so that the ozone treatment is intermittently performed. More specifically, the extraction pump 11 extracts the treated water 5 containing sludge from the ozone reaction part 10, the ozone gas generated by the ozone generator 12 is supplied to the treated water 5 containing sludge in the ozone reaction part 10, and the treated water 5 containing sludge is returned to the biological treatment tank 1 by the return pump 13, and the activation of the extraction pump 11, the ozone generator 12, and the return pump 13 is controlled so that the series of steps is intermittently performed at predetermined time intervals.

In the case of intermittently performing ozone treatment, the amount of organic sludge decomposed per 1 hour in ozone treatment and the inorganic matter/organic sludge ratio after ozone treatment are increased as compared with the case of continuously performing ozone treatment. The following description will be specifically made.

In the case of ozone treatment, since the treatment is performed in a manner to be kept constant in a case where the amount of organic sludge in the biological treatment tank 1 is observed for a long period of time, by intermittently performing ozone treatment in a short time, the amount of organic sludge decomposed per unit time in ozone treatment is increased as compared with the case where ozone treatment is continuously performed. For example, when the amount of organic sludge increased by 1 day is set to 48 (2 increases per 1 hour), about two thirds of the organic sludge decomposed by the ozone treatment is changed into organic sludge again, and therefore, in order to keep the amount of organic sludge constant, 144, which is 3 times the amount of organic sludge, is decomposed by the ozone treatment for 1 day. In the case where the ozone treatment was continued for 24 hours for 1 day, the amount of the organic sludge decomposed per 1 hour was 144/24-6. On the other hand, in the case of 1-time 1-hour ozone treatment performed 4 times in 1 day, the amount of decomposed organic sludge per 1 hour was 144/(1 × 4) ═ 36.

When the amount of sludge in the initial biological treatment tank 1 is 100, the amount of organic sludge therein is 72, and the amount of inorganic substances therein is 28 (the ratio of inorganic substances/organic sludge is 0.28),

when the ozone treatment is continuously performed, the inorganic matter/organic sludge ratio after 1 hour becomes 28/(72+2-6) ═ 0.41, and is kept constant.

When the ozone treatment is intermittently performed, the inorganic matter/organic sludge ratio after 1 hour is 28/(72+2-36) to 0.74, and the inorganic matter/organic sludge ratio is larger when the ozone treatment is performed than when the ozone treatment is continuously performed. Then, the inorganic matter/organic sludge ratio is decreased by the increase of the organic sludge, and immediately before the 2 nd ozone treatment, the same as the initial state is achieved, and in the 2 nd ozone treatment, the organic sludge is decomposed in the same manner as in the 1 st ozone treatment, so that the inorganic matter/organic sludge ratio in the ozone treatment is larger after the 2 nd ozone treatment than in the case of continuously performing the ozone treatment.

As described above, in the case where the ozone treatment is intermittently performed, the ratio of inorganic substances/organic sludge in the biological treatment tank 1 when the ozone treatment is performed becomes larger than that when the ozone treatment is continuously performed, and therefore the ratio of inorganic substances/organic sludge of the concentrated sludge 8 discharged as excess sludge from the solid-liquid separation tank 6 also becomes larger in the case where the ozone treatment is intermittently performed.

The time interval for the ozone treatment is not particularly limited, but is preferably 3 hours or more and 12 hours or less, and more preferably 4 hours or more and 6 hours or less. That is, the number of times (hours) of ozone treatment performed for 1 day is preferably 2 times (2 hours) or more and 8 times (8 hours) or less, and more preferably 4 times (4 hours) or more and 6 times (6 hours) or less. When the time interval between the ozone treatments is longer than 12 hours, that is, the number of times (hours) of the ozone treatments performed for 1 day is shorter than 2 times (2 hours), the amount of the organic sludge subjected to the ozone treatment per 1 time (1 hour) of the ozone treatment becomes excessively large, and the size and power of the extraction pump 11 and the return pump 13 become large, so that the initial cost and the running cost may increase. In addition, when the time interval between the ozone treatments is less than 3 hours, that is, the number of times (hours) of the ozone treatments performed for 1 day is greater than 8 times (8 hours), the amount of the organic sludge to be treated per 1 time (1 hour) of the ozone treatments is reduced, and the difference from the case where the ozone treatments are continuously performed is reduced, and there is a possibility that the effect of intermittently performing the ozone treatments is not obtained.

The other parts are the same as those in embodiment 2, and therefore, the description thereof is omitted.

Next, the operation will be described. In the same manner as in embodiment 2, the water treatment system 300 performs a biological treatment step, a solid-liquid separation step, and a concentrated sludge return step, and in the concentrated sludge return step, the switching valve 19 is switched so that the return direction is opened.

The sludge discharge control by the sludge discharge control device 34 is performed in parallel with the above-described biological treatment step and solid-liquid separation step. Fig. 6 is a flowchart showing a sludge discharge control method according to embodiment 3. The sludge discharge control method in embodiment 3 includes a volume reduction process and a concentrated sludge discharge process as in embodiment 2. The volume reduction process comprises an ozone treatment step and a return step, and the concentrated sludge discharge process comprises an ozone treatment start detection step and a concentrated sludge discharge step.

In the sludge discharge control method according to embodiment 3, since the ozone treatment is performed using a predetermined ozone treatment execution time (タイミング), the method first waits until a predetermined time interval elapses (step ST 301). When a predetermined time interval has elapsed, the ozone treatment control unit 342 transmits an ozone treatment start signal to the extraction pump 11, the ozone generator 12, and the return pump 13 (step ST 302). Thereby, the ozone treatment is started. After the transmission of the ozone treatment start signal, the ozone treatment control unit 342 stands by again until a predetermined time interval elapses.

The extraction pump 11 and the return pump 13 are started by receiving the ozone treatment start signal, and the treated water 5 containing the sludge is circulated between the biological treatment tank 1 and the ozone reaction unit 10 in the same manner as step ST101 of embodiment 1 (step ST 303).

Next, the ozone generator 12 is started to start generation of ozone gas by the electric discharge. Upon the start of discharge, the discharge start signal transmitter 121 transmits a discharge start signal to the sludge discharge control device 34 (step ST 304). The ozone gas generated by the ozone generator 12 is supplied to the ozone reaction section 10, the ozone treatment is performed on the treated water 5 containing the sludge in the ozone reaction section 10, and the treated water 5 containing the sludge after the ozone treatment is returned to the biological treatment tank 1 (step ST 305).

On the other hand, the ozone treatment start detection unit 341 receives the discharge start signal transmitted from the discharge start signal transmission unit 121 of the ozone generator 12 in step ST304, and detects the start of ozone treatment (step ST311), as in embodiment 2.

As in embodiment 2, if the ozone treatment start detector 341 detects the start of ozone treatment, the sludge discharge instructing unit 345 switches the switching valve 19 so that the discharge direction is opened and the return direction is closed (step ST 312). The sludge discharge instructing unit 345 determines the start/stop state of the concentrated sludge pump 18 from the energization state of the concentrated sludge pump 18, and energizes the concentrated sludge pump 18 to start the concentrated sludge pump 18 when the concentrated sludge pump 18 is stopped without being energized (step ST 313). The concentrated sludge pump 18 performs a concentrated sludge discharge process of sucking a part of the concentrated sludge 8 in the solid-liquid separation tank 6 and discharging the part to the outside of the system of the water treatment system 300 through the switching valve 19 and the concentrated sludge discharge pipe 106 (step ST 314).

The operation time of the ozone generator 12 is the same as that in embodiment 1. After the operating time of the ozone generator 12 is finished, the ozone treatment is finished. That is, the ozone generator 12 is stopped (step ST306), and the extraction pump 11 and the return pump 13 are stopped (step ST 307).

The operation time of concentrated sludge pump 18 is the same as in embodiment 2. After the operation time of the concentrated sludge pump 18 is finished, the sludge discharge instructing unit 345 stops the concentrated sludge pump 18 and stops the discharge of the concentrated sludge 8, as in embodiment 2 (step ST 315). The sludge discharge instructing unit 345 switches the switching valve 19 so that the discharge direction is closed and the return direction is opened (step ST 316). Then, in the case of performing the concentrated sludge returning step or the like, the concentrated sludge pump 18 is started as necessary.

According to embodiment 3, the same effects as those of embodiment 2 can be obtained.

In addition, the accumulation of inorganic substances in the biological treatment tank can be more reliably suppressed. More specifically, the sludge discharge control device includes an ozone treatment control unit that controls the start of the extraction pump, the ozone generator, and the return pump so that the volume reduction process including the extraction of the treated water containing sludge and the ozone treatment is intermittently performed at predetermined time intervals. The ratio of inorganic matter/organic sludge when the ozone treatment is performed is larger when the ozone treatment is intermittently performed than when the ozone treatment is continuously performed. Therefore, in the concentrated sludge discharge treatment performed in response to the start of the ozone treatment, excess sludge having a higher inorganic matter/organic sludge ratio is discharged, and the accumulation of inorganic matter in the biological treatment tank is more reliably suppressed.

Embodiment 4.

Hereinafter, embodiment 4 will be described with reference to fig. 7 and 8. The basic configuration and operation of embodiment 4 are the same as those of embodiment 3, but are different from embodiment 3 in that the sludge discharge control device includes a timer. The same reference numerals are used for the same or corresponding portions as those in fig. 5 and 6, and the description thereof will be omitted unless otherwise specified.

Fig. 7 is a schematic diagram showing the configuration of a water treatment system according to embodiment 4. In the water treatment system 400, the sludge discharge control device 44 includes: ozone treatment start detector 441, sludge discharge indicator 445, ozone treatment controller 442, and timer 443. The timer 443 is an example of a standby time counting means. The ozone treatment start detector 441, the sludge discharge indicator 445, and the ozone treatment controller 442 are the same as the ozone treatment start detector 341, the sludge discharge indicator 345, and the ozone treatment controller 342 of embodiment 3.

The timer 443 counts the time until the concentrated sludge pump 18 starts discharging the concentrated sludge 8 after the start of the ozone treatment is detected by the ozone treatment start detector 441 as a standby time. The sludge discharge instructing unit 445 detects the start of counting when the timer 443 starts counting, and detects the end of counting when the timer 443 ends counting.

More specifically, when the start of ozone treatment is detected by the ozone treatment start detector 441 receiving a discharge start signal from the ozone generator 12, the timer 443 is operated to start counting, and the sludge discharge indicator 445 detects the start of counting. When concentrated sludge pump 18 is stopped, concentrated sludge pump 18 is energized and concentrated sludge pump 18 is started, sludge discharge instruction unit 445 that detects the start of counting. When the discharge direction of the switching valve 19 is in the open state, the switching is performed such that the return direction is in the open state. When the count of the standby time is completed, the timer 443 stops counting and resets the count. The sludge discharge instruction unit 445 detects the end of counting, switches the switching valve 19 to open the discharge direction, and discharges the concentrated sludge 8 separated in the solid-liquid separation tank 6 to the outside of the system of the water treatment system 400 by the concentrated sludge pump 18. During the standby time, that is, while the timer 443 counts, the concentrated sludge 8 separated in the solid-liquid separation tank 6 is returned to the biological treatment tank 1 by the concentrated sludge pump 18.

The standby time of the timer 443 is not particularly limited, and is preferably: the time required for returning the total amount of concentrated sludge 8 accumulated in solid-liquid separation tank 6 at the detection time of the start of the ozone treatment process by ozone treatment start detector 441 to biological treatment tank 1 by concentrated sludge pump 18.

Further, in the case where the ozone treatment is intermittently performed at predetermined time intervals by the ozone treatment control section 442, since the inorganic matter/organic sludge ratio of the concentrated sludge 8 in the solid-liquid separation tank 6 periodically increases and decreases throughout the day, the inorganic matter/organic sludge ratio of the concentrated sludge 8 may be measured in advance by an analysis such as a forced heat reduction test, and the waiting time may be set based on the period of fluctuation of the inorganic matter/organic sludge ratio of the concentrated sludge 8 in the solid-liquid separation tank 6.

The other parts are the same as those in embodiment 3, and therefore, the description thereof is omitted.

Next, the operation will be described. As in embodiment 1, the water treatment system 400 performs a biological treatment step, a solid-liquid separation step, and a concentrated sludge return step, and in the concentrated sludge return step, the switching valve 19 is switched so that the return direction is opened.

The sludge discharge control by the sludge discharge control device 44 is performed in parallel with the above-described biological treatment step and solid-liquid separation step. Fig. 8 is a flowchart showing a sludge discharge control method according to embodiment 4. The sludge discharge control method in embodiment 4 includes a volume reduction process and a concentrated sludge discharge process as in embodiment 1. The volume reduction process comprises an ozone treatment step and a return step, and the concentrated sludge discharge process comprises an ozone treatment start detection step and a concentrated sludge discharge step.

First, as in embodiment 3, the system waits until a predetermined time interval elapses (step ST 401). When a predetermined time has elapsed, the ozone treatment control unit 442 sends an ozone treatment start signal to the extraction pump 11, the ozone generator 12, and the return pump 13 (step ST402), and starts the ozone treatment. After the transmission of the ozone treatment start signal, the ozone treatment control section 442 stands by again until a predetermined time elapses.

The extraction pump 11 and the return pump 13 are started by receiving the ozone treatment start signal, and the treated water 5 containing the sludge is circulated between the biological treatment tank 1 and the ozone reaction unit 10 in the same manner as in step ST303 of embodiment 3 (step ST 403).

Next, the ozone generator 12 is started to start generation of ozone gas by electric discharge. Upon the start of discharge, the discharge start signal transmitter 121 transmits a discharge start signal to the sludge discharge control device 44 (step ST 404). The ozone gas generated by the ozone generator 12 is supplied to the ozone reaction part 10, the treated water 5 containing the sludge is subjected to ozone treatment in the ozone reaction part 10, and the treated water 5 containing the sludge subjected to ozone treatment is returned to the biological treatment tank 1 (step ST 405).

On the other hand, the ozone treatment start detection unit 441 receives the discharge start signal transmitted from the discharge start signal transmission unit 121 of the ozone generator 12 in step ST404 and detects the start of ozone treatment (step ST411) as in embodiment 1.

If the start of ozone treatment is detected by the ozone treatment start detecting portion 441 in step ST411, the timer 443 starts counting of a predetermined standby time (step ST412), and the sludge discharge instructing portion 445 detects the start of counting. The sludge discharge instruction unit 445 that detects the start of counting by the timer 443 determines the start/stop state of the concentrated sludge pump 18 from the state of energization of the concentrated sludge pump 18, and energizes the concentrated sludge pump 18 to start the concentrated sludge pump 18 when the concentrated sludge pump 18 is not energized and is stopped (step ST 413). Thus, when the concentrated sludge returning step has already started, the concentrated sludge returning step is performed next, and when the concentrated sludge returning step has not started, the concentrated sludge returning step is started.

If the count of the standby time is finished, the timer 443 is stopped and the count is reset. The sludge discharge instruction unit 445 detects the end of the count of the timer 443 (step ST 414).

The sludge discharge instruction unit 445, which detects the end of the count by the timer 443, switches the switching valve 19 so that the discharge direction is opened and the return direction is closed (step ST 415). The concentrated sludge pump 18 performs a concentrated sludge discharge process of sucking a part of the concentrated sludge 8 in the solid-liquid separation tank 6 and discharging the part to the outside of the system of the water treatment system 400 through the switching valve 19 and the concentrated sludge discharge pipe 106 (step ST 416).

The operation time of the ozone generator 12 is the same as that in embodiment 1. After the operating time of the ozone generator 12 is finished, the ozone treatment is finished. That is, the ozone generator 12 is stopped (step ST406), and the extraction pump 11 and the return pump 13 are stopped (step ST 407).

The operation time of concentrated sludge pump 18 is the same as in embodiment 2. After the operation time of concentrated sludge pump 18 is finished, sludge discharge instruction unit 445 stops concentrated sludge pump 18 and stops discharge of concentrated sludge 8, as in embodiment 2 (step ST 417). The sludge discharge instruction unit 445 switches the switching valve 19 so that the discharge direction is closed and the return direction is opened (step ST 418). Then, in the case of performing the concentrated sludge returning step or the like, the concentrated sludge pump 18 is started as necessary.

According to embodiment 4, the same effects as those of embodiment 3 can be obtained.

Further, only excess sludge having a high inorganic matter/organic sludge ratio can be discharged to the outside of the system, and shortage of organic sludge in the biological treatment tank can be prevented more reliably. More specifically, the sludge discharge control device includes a timer for counting a predetermined standby time, and controls the time from the start of the ozone treatment detected by the ozone treatment start detector to the start of the concentrated sludge discharge treatment by the standby time of the timer. Thus, the inorganic matter/organic sludge ratio does not rise immediately after the start of the ozone treatment, and excess sludge containing a large amount of organic sludge can be returned to the biological treatment tank without being discharged to the outside of the system. Therefore, only excess sludge having a high inorganic matter/organic sludge ratio can be discharged to the outside of the system, and shortage of organic sludge in the biological treatment tank can be prevented more reliably.

Embodiment 5.

Hereinafter, embodiment 5 will be described with reference to fig. 9. The basic configuration and operation of embodiment 5 are the same as those of embodiment 4, but are different from embodiment 4 in that the piping connecting the biological treatment tank and the solid-liquid separation tank is made as coagulation piping and a coagulant addition device for adding an additive to the coagulation piping is provided. The same reference numerals are used for the same or corresponding portions as those in fig. 7, and the description thereof will be omitted unless otherwise specified.

Fig. 9 is a schematic diagram showing the configuration of a water treatment system according to embodiment 5. The water treatment system 500 includes: and a flocculant adding device (22) for adding a flocculant for insolubilizing soluble phosphorus to the treated water (5) containing sludge. The flocculant adding device 22 is connected to a flocculant pipe 107 as a pipe connecting the biological treatment tank 1 and the solid-liquid separation tank 6, and adds a flocculant to the treated water 5 containing sludge flowing from the biological treatment tank 1 into the solid-liquid separation tank 6. The additive to be added by the flocculant adding device 22 insolubilizes soluble phosphorus in the treated water 5 containing sludge. The treated water 5 containing sludge and containing additives in the coagulation piping 107 is insolubilized with soluble phosphorus in the solid-liquid separation tank 6. Thus, phosphorus is separated from the sludge-containing treated water 5 in the solid-liquid separation tank 6, and treated water 7 from which phosphorus is removed is produced. Since phosphorus separated in the solid-liquid separation tank 6 is an inorganic substance, the phosphorus is discharged to the outside of the system together with excess sludge by the concentrated sludge discharge treatment, similarly to other inorganic substances. The coagulant adding device 22 is an example of coagulant adding means.

The soluble phosphorus in the treated water 5 containing the sludge is mainly eluted from the microorganisms decomposed by the ozone treatment. Therefore, since there is a possibility that the concentration of soluble phosphorus increases during the ozone treatment step, the sludge discharge control device 44 can be provided with the following control functions: after the start of the ozone treatment is detected by the ozone treatment start detector 441, the amount of the coagulant to be added by the coagulant adding device 22 is increased only for a certain time.

The amount of addition and the time period for increasing the amount of the flocculant to be added by the flocculant adding device 22 are not particularly limited as long as the soluble phosphorus in the sludge-containing treated water 5 can be insolubilized, and the time period for increasing the amount of addition is preferably set to coincide with the start-up time of the ozone generator 12. This can increase the amount of aggregation while the organic sludge is decomposed in the ozone reaction section 10, phosphorus is eluted into the treated water 5 containing sludge, and the concentration of soluble phosphorus is increased. Further, a phosphorus concentration measuring device for measuring the soluble phosphorus concentration of the treated water 5 containing sludge is provided in the flocculation pipe 107, and the amount of addition is increased in a time zone where the value measured by the phosphorus concentration measuring device is high.

The flocculant to be added by the flocculant adding device 22 is not particularly limited as long as it can insolubilize soluble phosphorus in the treated water 5 containing sludge. For example, inorganic flocculants such as polyaluminum chloride, aluminum sulfate, ferric chloride, and ferric polysulfate, organic flocculants, and the like can be used.

According to embodiment 5, the same effects as those of embodiment 4 can be obtained.

In addition, the outflow of phosphorus into the treated water can be prevented. More specifically, the system is provided with a flocculant adding device for adding a flocculant to the sludge-containing treated water flowing from the biological treatment tank into the solid-liquid separation tank. Thus, in the sludge-containing treated water to which the flocculant has been added, soluble phosphorus is insolubilized in the solid-liquid separation tank, and phosphorus is separated from the sludge-containing treated water. Therefore, phosphorus is removed from the treated water flowing out of the solid-liquid separation tank, and outflow of phosphorus can be prevented.

Further, by temporarily increasing the amount of the coagulant added in accordance with the execution of the ozone treatment, the insolubilization of the soluble phosphorus can be more reliably performed.

Embodiment 6.

Embodiment 6 will be described below with reference to fig. 10 and 11. The basic configuration and operation of embodiment 6 are the same as those of embodiment 5, but are different from embodiment 5 in that an ozone gas pipe is provided with an ozone concentrator, and the ozone generator and the ozone concentrator are connected via an oxygen return pipe. The same reference numerals are used for the same or corresponding portions as those in fig. 8 or 9, and the description thereof will be omitted unless otherwise specified.

Fig. 10 is a schematic diagram showing the configuration of a water treatment system according to embodiment 6. In the water treatment system 600, the sludge discharge control device 64 includes: an ozone treatment start detection unit 641, a sludge discharge instruction unit 645, an ozone treatment control unit 642, and a timer 643. The sludge discharge instruction unit 645, the ozone treatment control unit 642, and the timer 643 are the same as the sludge discharge instruction unit 445, the ozone treatment control unit 442, and the timer 443 of embodiment 4. The ozone treatment start detection unit 641 detects the start of ozone treatment by receiving a supply start signal from the ozone concentrator 23 described later.

The water treatment system 600 includes an ozone concentrator 23 downstream of the ozone generator 12. The ozone gas generated by the ozone generator 12 is concentrated by the ozone concentrator 23. The concentrated ozone gas, i.e., the concentrated ozone gas, is supplied to the ozone reaction part 10 through the ozone gas pipe 104 and the gas flow meter 17, and contacts and reacts with the organic sludge in the treated water 5 containing the sludge flowing from the biological treatment tank 1 into the ozone reaction part 10, thereby decomposing the organic sludge. The ozone concentrator 23 includes an adsorption tower (not shown) that contains an adsorbent and generates ozone gas at a desired concentration. In the case of the adsorption column, conditions most suitable for adsorption and desorption of ozone are formed by controlling the temperature and pressure inside. When the ozone concentrator 23 is used, the concentrated ozone gas having a concentration of 400mg/L or more can be relatively easily supplied to the treated water 5 containing sludge. Specifically, the concentrated ozone gas can be supplied to the treated water 5 containing the sludge at a concentration of up to 2000 mg/L. The adsorbent for adsorbing and concentrating the ozone gas in the ozone concentrator 23 is not particularly limited, and for example, silica gel can be used. The ozone concentrator 23 is an example of an ozone concentrating means.

The ozone concentrator 23 is also connected to the ozone generator 12 via an oxygen return pipe 108. Therefore, when the ozone gas generated by the ozone generator 12 is generated as a by-product of oxygen that is not adsorbed in the step of adsorbing and concentrating by the ozone concentrator 23, the oxygen gas that is not adsorbed is returned to the ozone generator 12 through the oxygen return pipe 108, and is reused as a raw material gas of ozone in the ozone generator 12.

The concentration of the concentrated ozone gas supplied from the ozone concentrator 23 to the treated water 5 containing sludge is not particularly limited, but is preferably 600mg/L to 1000 mg/L. When the concentration of the concentrated ozone gas is less than the above range, the initial cost is increased by providing the ozone concentrator 23, and the life cycle cost of the entire system is increased, compared to the reduction in the running cost due to the reduction in the amount of ozone used resulting from the improvement in the reactivity with the organic sludge and the contact efficiency. On the other hand, when the concentration of the concentrated ozone gas is larger than the above range, since the self-decomposition of ozone molecules is promoted, most of the ozone in the concentrated ozone gas generated in the ozone concentrator 23 may be returned to the oxygen gas in the ozone gas pipe 104. The concentration of the ozone gas fed from the ozone generator 12 to the ozone concentrator 23 is preferably 150mg/L to 310mg/L, and more preferably 190mg/L to 290mg/L, from the viewpoint of running cost.

The ozone concentrator 23 sends a supply start signal to the ozone treatment start detector 641 when starting supply of the concentrated ozone gas to the ozone reaction part 10. The start of ozone treatment is detected by the ozone treatment start detection portion 641 which receives the supply start signal. The start of the supply of the concentrated ozone gas by the ozone treatment start detector 641 can be realized by, for example, an analog signal of a thermometer, a manometer, or the like provided in the ozone concentrator 23, an analog signal of the gas flowmeter 17 provided in the ozone gas pipe 104, or the like.

The rest is the same as embodiment 5, and therefore, the description thereof is omitted.

Next, the operation will be described. As in embodiment 1, the water treatment system 600 performs a biological treatment step, a solid-liquid separation step, and a concentrated sludge return step, and in the concentrated sludge return step, the switching valve 19 is switched so that the return direction is opened.

The sludge discharge control by the sludge discharge control device 64 is performed in parallel with the above-described biological treatment step and solid-liquid separation step. Fig. 11 is a flowchart showing a sludge discharge control method according to embodiment 6. The sludge discharge control method in embodiment 6 includes a volume reduction process and a concentrated sludge discharge process as in embodiment 1. The volume reduction process comprises an ozone treatment step and a return step, and the concentrated sludge discharge process comprises an ozone treatment start detection step and a concentrated sludge discharge step.

First, as in embodiment 3, the system waits until a predetermined time interval elapses (step ST 601). When a predetermined time has elapsed, the ozone treatment control unit 642 transmits an ozone treatment start signal to the extraction pump 11, the ozone generator 12, and the return pump 13 (step ST602), and starts the ozone treatment. After the ozone treatment start signal is sent, the ozone treatment control unit 642 stands by again until a predetermined time interval elapses.

The ozone generator 12 is activated upon receiving an ozone treatment start signal, starts generation of ozone gas by electric discharge, and supplies the ozone gas to the ozone concentrator 23. The ozone is concentrated by adsorption in the ozone concentrator 23 (step ST 603).

After the adsorption of the ozone gas to the ozone concentrator 23 is completed in step ST603, the extraction pump 11 and the return pump 13 are started, and the treated water 5 containing the sludge is circulated between the biological treatment tank 1 and the ozone reaction unit 10 in the same manner as in step ST303 of embodiment 3 (step ST 604).

Next, the concentrated ozone gas is supplied from the ozone concentrator 23 to the ozone reaction portion 10 through the ozone gas pipe 104. If the supply of the concentrated ozone gas is started, the ozone concentrator 23 sends a supply start signal to the ozone treatment start detection part 641 (step ST 605). When the concentrated ozone gas is supplied from the ozone concentrator 23 to the ozone reaction part 10, the sludge contained in the treated water 5 containing the sludge in the ozone reaction part 10 is brought into contact with the ozone of the concentrated ozone gas and reacts with the ozone, and the ozone treatment is performed (step ST 606). The treated water 5 containing the sludge treated with ozone is returned to the biological treatment tank 1 through a return pipe 105.

On the other hand, the ozone treatment start detection unit 641 receives the supply start signal transmitted from the ozone concentrator 23 in step ST604, and detects the start of the ozone treatment (step ST 611).

If the start of ozone treatment is detected by ozone treatment start detector 641 in step ST611, timer 643 starts counting a predetermined standby time (step ST612) and sludge discharge indicator 645 detects the start of counting, as in embodiment 4. The sludge discharge instruction unit 645, which detects the start of counting by the timer 643, activates the concentrated sludge pump 18 when the concentrated sludge pump 18 is stopped (step ST 613).

If the count of the standby time is finished, the timer 643 is stopped and the count is reset. The sludge discharge instructing unit 645 detects the end of the count of the timer 643 (step ST 614).

The sludge discharge control device 64 that has detected the end of the count of the timer 643 switches the switching valve 19 so that the discharge direction is opened and the return direction is closed (step ST 615). The concentrated sludge pump 18 performs a concentrated sludge discharge process of sucking a part of the concentrated sludge 8 in the solid-liquid separation tank 6 and discharging the part to the outside of the system of the water treatment system 600 through the switching valve 19 and the concentrated sludge discharge pipe 106 (step ST 616).

The operation time of the ozone generator 12 is the same as that in embodiment 1. After the operating time of the ozone generator 12 is finished, the ozone treatment is finished. That is, the supply of the concentrated ozone gas is stopped, the ozone generator 12 is stopped (step ST607), and the extraction pump 11 and the return pump 13 are stopped (step ST 608).

The operation time of concentrated sludge pump 18 is the same as in embodiment 2. After the operation time of concentrated sludge pump 18 is completed, sludge discharge instructing unit 645 stops concentrated sludge pump 18 and stops discharge of concentrated sludge 8, in the same manner as in embodiment 2 (step ST 617). The sludge discharge instructing unit 645 switches the switching valve 19 so that the discharge direction is closed and the return direction is opened (step ST 618). Then, in the case of performing the concentrated sludge returning step or the like, the concentrated sludge pump 18 is started as necessary.

According to embodiment 6, the same effects as those of embodiment 5 can be obtained.

In addition, the organic sludge in the sludge-containing treated water can be efficiently decomposed, the inorganic matter/organic sludge ratio of the sludge-containing treated water in the biological treatment tank can be increased, and the inorganic matter can be more efficiently discharged to the outside of the system. More specifically, since the ozone concentrator is provided downstream of the ozone gas generator, it is possible to supply the concentrated ozone gas having a concentration of 400mg/L or more to the treated water containing the sludge. Since the concentrated ozone gas has high reactivity with the organic sludge and high contact efficiency, the organic sludge in the treated water containing the sludge can be efficiently decomposed. This promotes the improvement of the biodegradability of the organic sludge in the treated water containing sludge, increases the amount of the organic sludge to be reduced in the biological treatment tank, and further increases the inorganic matter/organic sludge ratio in the biological treatment tank. As a result, the inorganic matter/organic sludge ratio of the concentrated sludge discharged as excess sludge from the solid-liquid separation tank is also increased, and the inorganic matter can be more efficiently discharged to the outside of the system.

Further, the oxygen gas that is not adsorbed in the ozone concentrator can be returned to the ozone generator through the oxygen gas return pipe and reused as a raw material of ozone, and therefore, ozone can be generated more efficiently.

While various exemplary embodiments and examples have been described in the present application, the various features, aspects, and functions described in 1 or more embodiments are not limited to the application to the specific embodiments, and may be applied to the embodiments individually or in various combinations.

Therefore, a myriad of modifications not illustrated can be conceived within the technical scope disclosed in the present application. For example, the case where at least 1 component is modified, added, or omitted, and the case where at least 1 component is extracted and combined with the components of the other embodiments are included.

Description of reference numerals

1 biological treatment tank, 4 wastewater, 5 sludge-containing treated water, 6 solid-liquid separation tank, 7 treated water, 8 concentrated sludge, 9 concentrated sludge return pump, 10 ozone reaction unit, 11 extraction pump, 12 ozone generator, 121 discharge start signal transmission unit, 13 return pump, 14, 24, 34, 44, 64 sludge discharge control unit, 141, 241, 341, 441, 641 ozone treatment start detection unit, 145, 245, 345, 445, 645 sludge discharge instruction unit, 15 concentrated sludge discharge pump, 18 concentrated sludge pump, 19 switching valve, 22 flocculant addition unit, 23 ozone concentrator, 100, 200, 300, 400, 500, 600 water treatment system, 101, 201 concentrated sludge piping, 102 concentrated sludge return piping, 103 extraction piping, 105 return piping, 106 concentrated sludge discharge piping, 107 concentrated sludge piping, 108 oxygen return piping, 342, 442, 642 ozone treatment control unit, 342, 201 ozone treatment system control unit, and oxygen return piping, 443. 643 timer

Claims

1. A sludge discharge control device provided in a water treatment system for controlling discharge of excess sludge, the water treatment system comprising: a method for treating water to be treated biologically in a biological treatment tank, wherein the treated water containing sludge produced in the biological treatment is returned to the biological treatment tank by ozone treatment, wherein a part of concentrated sludge separated from the treated water containing sludge by a solid-liquid separation means is returned to the biological treatment tank by a concentrated sludge returning means, and wherein the excess concentrated sludge is discharged outside the system as excess sludge by a concentrated sludge discharging means, the method comprising:

ozone treatment start detection means for detecting the start of the ozone treatment; and

and a sludge discharge instructing means for causing the concentrated sludge discharging means to start a concentrated sludge discharge process of discharging the excess sludge after the start of the ozone treatment is detected by the ozone treatment start detecting means.

2. The sludge discharge control device according to claim 1, further comprising: and an ozone treatment control means for controlling the start and stop of the ozone treatment.

3. The sludge discharge control apparatus according to claim 2, wherein the ozone treatment control means intermittently performs the ozone treatment at predetermined time intervals.

4. The sludge discharge control device according to any one of claims 1 to 3, further comprising: and a standby time counting means for counting a predetermined standby time from the start of the ozone treatment, wherein the sludge discharge instructing means causes the concentrated sludge discharging means to start the concentrated sludge discharge treatment after the count of the standby time is completed.

5. A water treatment system, comprising:

a biological treatment tank for performing biological treatment on water to be treated;

an ozone treatment means for subjecting the treated water containing sludge produced by the biological treatment to ozone treatment;

a sludge-containing treated water returning means for returning the treated water containing sludge treated by the ozone treatment to the biological treatment tank;

a solid-liquid separation means for separating the treated water containing the sludge into treated water and concentrated sludge;

a concentrated sludge returning means for returning a part of the concentrated sludge separated from the sludge-containing treated water to the biological treatment tank;

a concentrated sludge discharge means for discharging the excess concentrated sludge as excess sludge to the outside of the system; and

the sludge discharge control apparatus described in any one of claims 1 to 4 that controls discharge of the excess sludge.

6. The water treatment system according to claim 5, wherein the concentrated sludge returning means and the concentrated sludge discharging means are: and a concentrated sludge transport means for transporting the concentrated sludge flowing out from the solid-liquid separation means and switching a transport destination of the concentrated sludge by switching means for switching a return direction and a discharge direction, wherein the sludge discharge control device switches the switching means to the discharge direction after detecting the start of the ozone treatment and discharges the concentrated sludge to the outside of the system.

7. The water treatment system according to claim 5 or 6, further comprising: flocculant adding means provided between the biological treatment tank and the solid-liquid separation means for adding a flocculant for insolubilizing soluble phosphorus to the sludge-containing treatment water.

8. The water treatment system according to claim 7, wherein the flocculant addition means increases the amount of flocculant added to the treated water containing sludge during a predetermined time period from the start of the ozone treatment.

9. The water treatment system according to any one of claims 5 to 8, further comprising: ozone concentration means for concentrating the ozone supplied to the ozone treatment means.

10. A sludge discharge control method for controlling discharge of excess sludge in a water treatment system comprising: a method for treating water to be treated biologically in a biological treatment tank, wherein treated water containing sludge produced by the biological treatment is returned to the biological treatment tank by ozone treatment, a part of concentrated sludge separated from the treated water containing sludge by a solid-liquid separation means is returned to the biological treatment tank by a concentrated sludge returning means, and the remaining concentrated sludge is discharged as excess sludge to the outside of the system by a concentrated sludge discharging means, the method comprising:

an ozone treatment start detection step of detecting the start of the ozone treatment; and

and a sludge discharge step of discharging the excess sludge outside the system after the ozone treatment start detection step.