JP6009362B2 - Wastewater treatment method - Google Patents

Description

  The present invention relates to a wastewater treatment method in which a substance to be treated in wastewater is biologically treated with microorganisms.

Conventionally, an activated sludge method using an aggregate of microorganisms called floc has been used for biological wastewater treatment. However, the activated sludge method may have a problem that when the floc is separated from the treated water in the sedimentation basin, the surface area of the sedimentation basin must be very large because the sedimentation speed of the floc is slow. The treatment rate of the activated sludge method depends on the sludge concentration in the tank, and the treatment rate can be increased by increasing the sludge concentration, but the sludge concentration will be increased to 3000 to 5000 mg / L or more. Then, solid-liquid separation troubles such as bulking may occur, and the processing may not be maintained. Therefore, the BOD processing speed of the conventional activated sludge method is about 0.5 to 0.8 kg / m ³ / day.

  In anaerobic biological treatment, it is common to use aggregates in which microorganisms called granules are gathered densely and become granular. Granules have a very fast sedimentation rate, and microorganisms gather densely, so that the sludge concentration in the treatment tank can be increased and high-speed wastewater treatment can be realized. However, the anaerobic biological treatment has problems such as the fact that the wastewater species to be treated is limited compared to the aerobic treatment (activated sludge method) and that the treated water temperature needs to be maintained at 30 to 35 ° C. May have. In addition, when the anaerobic biological treatment alone is poor in the quality of the treated water, it may be necessary to separately perform an aerobic treatment such as an activated sludge method when discharged into a river or the like.

  In recent years, it is clear that treatment can be performed even with aerobic activated sludge by performing treatment using a semi-batch treatment device that allows wastewater to flow into the reaction tank intermittently, and further reducing the sludge settling time. (For example, see Patent Documents 1 to 4). In the semi-batch treatment system, four steps are carried out in one reaction tank: (1) inflow of wastewater, (2) biological treatment of the material to be treated, (3) sedimentation of biological sludge, (4) discharge of treated water. The process is performed by going through.

By granulating as described above, high-speed treatment can be achieved. However, when a semi-batch type treatment device is used for a large-scale wastewater treatment facility, it may be necessary to install a huge wastewater storage tank. Therefore, a continuous processing device that continuously treats wastewater by flowing in and a semi-batch processing device that supplies aerobic granules are installed, and aerobic granules are supplied from the semi-batch processing device. Thus, a processing method for granulating the entire system has been proposed (for example, see Patent Document 5). By using this method, the sedimentation basin can be reduced in size, and the BOD treatment rate can be 1.5 to 3.0 kg / m ³ / day.

International Publication No. 2004/024638 JP 2008-212878 A JP 2009-18263 A JP 2009-18264 A JP 2007-136367 A

  An object of the present invention is to provide a wastewater treatment method capable of suppressing an increase in the SS concentration of treated water treated by continuous biological treatment in a system using both continuous biological treatment and semi-batch biological treatment. It is.

In the wastewater treatment method of the present invention, the treated water discharged from the continuous reaction tank is treated biologically with microbial sludge while the wastewater is continuously flowing into the continuous reaction tank. A continuous biological treatment process for separating microbial sludge from a solid-liquid separation tank, an inflow process for inflowing wastewater, a biological treatment process for biologically treating a target substance in the wastewater with microbial sludge, and the microbial sludge A semi-batch biological treatment process in which a sedimentation process for sedimentation and a discharge process for discharging treated water are repeated in a semi-batch reaction tank, and the microbial sludge in the settled semi-batch reaction tank in the continuous reaction tank. A sludge supply step to supply, and when the average SS concentration of the treated water discharged from the semi-batch reaction tank in the discharge step is 100 mg / L or less, the discharge destination of the treated water is the continuous reaction tank of When the average SS concentration of treated water discharged from the semi-batch reaction tank in the discharge step is more than 100 mg / L, the discharge destination of the treated water is the continuous type. At least one of the reaction tank system and the solid-liquid separation tank system.

In the wastewater treatment method of the present invention, the treated water discharged from the continuous reaction tank is treated biologically with microbial sludge while the wastewater is continuously flowing into the continuous reaction tank. A continuous biological treatment process for separating microbial sludge from a solid-liquid separation tank, an inflow process for inflowing wastewater, a biological treatment process for biologically treating a target substance in the wastewater with microbial sludge, and the microbial sludge A semi-batch biological treatment process in which a sedimentation process for sedimentation and a discharge process for discharging treated water are repeated in a semi-batch reaction tank, and the microbial sludge in the settled semi-batch reaction tank in the continuous reaction tank. A sludge supply process to supply, wherein in the discharge process, the discharge process time is divided into the first and second periods, and the ratio of the second period is set to ½ or more of the total time. The destination In the system of the reaction tank and at least one of the system of the solid-liquid separation tank, during the latter period, the treated water discharge destination is outside the system of the continuous reaction tank and the solid-liquid separation tank. Out of the system.

In the wastewater treatment method of the present invention, the treated water discharged from the continuous reaction tank is treated biologically with microbial sludge while the wastewater is continuously flowing into the continuous reaction tank. A continuous biological treatment process for separating microbial sludge from a solid-liquid separation tank, an inflow process for inflowing wastewater, a biological treatment process for biologically treating a target substance in the wastewater with microbial sludge, and the microbial sludge A semi-batch biological treatment process in which a sedimentation process for sedimentation and a discharge process for discharging treated water are repeated in a semi-batch reaction tank, and the microbial sludge in the settled semi-batch reaction tank in the continuous reaction tank. A semi-batch biological treatment start-up period until the SVI5 (Sludge Volume Index 5) of the sludge in the semi-batch reaction tank reaches 50 to 80. Batch During the start-up period of the biological treatment, the treated water is discharged to at least one of the continuous reaction tank system and the solid-liquid separation tank system, and the semi-batch biological treatment is started. After the elapse of the raising period, the treated water is discharged outside the continuous reaction tank and the solid-liquid separation tank.

  According to the present invention, there is provided a wastewater treatment method capable of suppressing an increase in the SS concentration of treated water treated by continuous biological treatment in a system using both continuous biological treatment and semi-batch biological treatment. Can do.

It is a schematic diagram which shows an example of a structure of the waste water treatment system which concerns on this embodiment. It is a schematic diagram which shows another example of a structure of the waste water treatment system which concerns on this embodiment. It is a figure which shows the time-dependent change of the treated water SS density | concentration discharged | emitted from the sedimentation basin. It is a figure which shows the time-dependent change of the treated water SS density | concentration discharged | emitted from the semi-batch type tank.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  FIG. 1 is a schematic diagram illustrating an example of a configuration of a wastewater treatment system according to the present embodiment. The waste water treatment system 1 shown in FIG. 1 includes a waste water storage tank 10, waste water inflow lines 12, 28, semi-batch biological treatment reaction tank 14, treated water discharge line 16, sludge discharge line 18, treated water tank 20, continuous biological treatment. A reaction tank 24, a settling tank 26, a primary treated water discharge line 30, a treated water discharge line 32, and a sludge return line 34 are provided. In this specification, the “continuous type” is a method for the batch type, and like the semi-batch type, the inflow of wastewater, biological treatment, sedimentation of sludge, and discharge of treated water are performed in a single reaction tank. It is distinguished from formula processing. Further, in the present embodiment, the continuous type is not limited to a method in which drainage is continuously poured into the reaction tank and is operated, but the reaction is performed by a pump using a principle such as a reciprocating motion such as a diaphragm pump. The system may be operated by supplying wastewater to the tank, or a raw water tank is installed in front of the reaction tank, and the pump operation is controlled according to the water level of the raw water tank (when the water level is high). May be a simulated continuous water supply system that operates the pump and stops the pump when the water level is low) to supply waste water to the reaction tank.

  The semi-batch biological treatment reaction tank 14 is desirably provided with a stirrer (not shown) for stirring the waste water. The stirrer has a structure in which, for example, a shaft attached to the motor rotates by driving the motor, and a stirring blade attached to the tip of the shaft rotates with the rotation of the shaft. The stirrer is not limited to the above as long as the waste water in the semi-batch biological treatment reaction tank 14 can be stirred. For example, an aeration apparatus used when biological treatment is performed under aerobic conditions. But you can. By aeration of the aeration apparatus, it becomes possible to agitate the waste water in the tank.

  One end of the drainage inflow line 12 is connected to the drainage storage tank 10, and the other end is connected to the semi-batch biological treatment reaction tank 14. One end of the treated water discharge line 16 is connected to the semi-batch biological treatment reaction tank 14, and the other end is connected to the treated water tank 20. One end of the drainage inflow line 28 is connected to the drainage storage tank 10, the other end is connected to the continuous biological treatment reaction tank 24, and one end of the primary treated water discharge line 30 is connected to the continuous biological treatment reaction tank 24, The other end is connected to the settling tank 26, one end of the treated water discharge line 32 is connected to the settling tank 26, the other end is connected to the treated water tank 20, and one end of the sludge return line 34 is connected to the settling tank 26. The other end is connected to the continuous biological treatment reaction tank 24. One end of the sludge discharge line 18 is connected to the semi-batch biological treatment reaction tank 14, and the other end is connected to the continuous biological treatment reaction tank 24. Hereinafter, the semi-batch biological treatment reaction tank 14 may be referred to as a semi-batch tank 14 and the continuous biological treatment reaction tank 24 may be referred to as a continuous tank 24. In addition, the connection point of the sludge discharge line 18 may be any place that is suitable for extracting the sludge from the semi-batch biological treatment reaction tank 14. In addition, it is desirable that each line is provided with a pump for feeding liquid such as drainage and sludge.

  Below, operation | movement of the waste water treatment system 1 shown in FIG. 1 is demonstrated.

  First, the waste water containing the treatment target substance is stored in the waste water storage tank 10 before being supplied to the semi-batch biological treatment reaction tank 14 or the continuous biological treatment reaction tank 24, and the water quality of the waste water is stabilized. preferable. At this time, when solid matter is contained in the waste water, it is desirable to remove the solid matter with a screen or the like. Moreover, in the waste water storage tank 10, in order to make the waste water uniform, it is desirable to install a stirring device (mechanical stirring, air stirring, etc.).

  Part of the wastewater in the drainage storage tank 10 intermittently flows into the semi-batch tank 14 from the drainage inflow line 12, and the rest continuously flows into the continuous tank 24 from the drainage inflow line 28. The semi-batch tank 14 is obtained by (1) inflow of wastewater, (2) biological treatment in which the target substance in the wastewater is biologically treated with microbial sludge, (3) sedimentation of sludge, and (4) biological treatment. The four steps of discharging the treated water are repeated. Specifically, the microbial sludge staying in the semi-batch biological treatment reaction tank 14 comes into contact with the treatment target substance in the wastewater flowing into the semi-batch biological treatment reaction tank 14, and the treatment target substance is decomposed. It is processed. After the biological treatment, the microbial sludge in the semi-batch biological treatment reaction tank 14 is allowed to settle. After sedimentation of microbial sludge (including granulated sludge; the same applies hereinafter), the microbial sludge is withdrawn from the semi-batch tank 14 and supplied to the continuous tank 24 from the sludge discharge line 18. The treated water (supernatant water) of the semi-batch tank 14 is supplied from the treated water discharge line 16 to the treated water tank 20. That is, in this embodiment, the discharge destination of the treated water discharged from the semi-batch tank 14 is outside the system of the continuous tank 24 and the system of the precipitation tank 26.

Microbial sludge (including granulated sludge) is supplied to the continuous tank 24 from the sludge discharge line 18 and the sludge return line 34, for example, under aerobic conditions (aeration treatment by an aeration apparatus or the like) and supply In the state where the microbial sludge (including granulated sludge) etc. coexisted, for example, the organic matter in the wastewater is oxidized to carbon dioxide. In the present embodiment, not only biological treatment by the standard activated sludge method as described above, but also a nutrient removal system (an oxygen-free treatment tank or the like) such as A ₂ O (Anaerobic-Anoxic Process) or AO (Anaerobic-Oxic Process). Biological treatment by systems such as an anaerobic treatment tank), oxidation ditch method, step-inflow type multi-stage activated sludge method, etc. is also possible.

  The primary treated water biologically treated in the continuous tank 24 passes through the primary treated water discharge line 30 together with microbial sludge (including granule sludge) and flows into the settling tank 26. In the sedimentation tank 26, microbial sludge (including granule sludge) is settled and separated from the primary treated water. The waste water from which microbial sludge (including granule sludge) is separated is discharged from the treated water discharge line 32 as treated water and supplied to the treated water tank 20. Microbial sludge (including granule sludge) is returned to the continuous tank 24 from the sludge return line 34.

  In the present embodiment, the waste water treatment is performed in this way. Usually, in the treatment water discharge step in the semi-batch tank 14, a large amount of the treatment water is discharged in a short time of about 15 minutes. When the water discharge destination is the continuous tank 24 or the precipitation tank 26, the surface area load of the precipitation tank 26 temporarily increases, SS flows out into the treated water discharged from the precipitation tank 26, and the SS concentration in the treated water There is a risk of rising. Therefore, in this embodiment, as described above, the microbial sludge of the semi-batch tank 14 is supplied to the continuous tank 24, but the destination of the treated water discharged from the semi-batch tank 14 is the continuous tank. 24 out of the system and out of the settling tank 26. Thereby, since the temporary rise of the surface area load of the sedimentation tank 26 can be suppressed, SS flows out into the treated water discharged from the sedimentation tank 26, thereby suppressing an increase in the SS concentration in the treated water. it can. Here, the out-of-system tank 24 and the out-of-settling tank 26 point to a location where treated water is not supplied to the continuous-type tank 24 and the settling tank 26. In this embodiment, for example, , Treated water tank 20 and the like.

  FIG. 2 is a schematic diagram illustrating another example of the configuration of the wastewater treatment system according to the present embodiment. In the waste water treatment system 2 shown in FIG. 2, the same reference numerals are given to the same components as those in the waste water treatment system 1 shown in FIG. 1, and the description thereof is omitted. The waste water treatment system 2 shown in FIG. 2 includes a treated water supply line 36, a solenoid valve 38, and an SS densitometer 40. One end of the treated water supply line 36 is connected to the treated water discharge line 16, and the other end is connected to the continuous tank 24. The other end of the treated water supply line 36 may be connected to at least one of the system of the continuous tank 24 and the system of the settling tank 26. For example, the drainage inflow line 28, the primary treated water discharge You may connect to the line 30 or the sedimentation tank 26 grade | etc.,. That is, the inside of the continuous tank 24 and the inside of the settling tank 26 refer to a place where treated water is supplied to the continuous tank 24 and the settling tank 26. Further, a tank such as a temporary storage tank or a pH adjustment tank is provided at the other end of the treated water supply line 36 to temporarily store the treated water in the semi-batch tank 14, and then the continuous tank 24 and the sedimentation tank 26. You may supply.

  A solenoid valve 38 is installed at the connection point between the treated water discharge line 16 and the treated water supply line 36, and an SS concentration meter 40 is installed in the treated water discharge line 16 upstream of the solenoid valve 38. The solenoid valve 38 and the SS densitometer 40 are electrically connected. The electromagnetic valve 38 switches the path through which the treated water flows to the treated water discharge line 16 side or the treated water supply line 36 side based on the measurement value of the SS densitometer 40. The SS densitometer 40 is not particularly limited as long as it can measure the SS concentration in the treated water, and examples thereof include an MLSS meter and a turbidimeter.

  Below, operation | movement of the waste water treatment system 2 shown in FIG. 2 is demonstrated.

  Part of the wastewater in the drainage storage tank 10 intermittently flows into the semi-batch tank 14 from the drainage inflow line 12, and the rest continuously flows into the continuous tank 24 from the drainage inflow line 28. In the semi-batch tank 14, as described above, after the target substance in the wastewater is decomposed, microbial sludge (including granulated sludge; the same applies hereinafter) is allowed to settle. The microbial sludge is extracted from the semi-batch tank 14 and supplied to the continuous tank 24 from the sludge discharge line 18, and the treated water (supernatant water) of the semi-batch tank 14 is discharged from the treated water discharge line 16.

  Here, since the sludge in the tank is not sufficiently granulated at the start of biological treatment in the semi-batch tank 14, the discharge process is started before all of the sludge has settled in the sedimentation process. Sludge (SS) may flow out to the treated water side, and the treated water SS concentration may be 100 to 4000 mg / L. Therefore, the discharge destination of the SS concentration high treatment water (SS concentration 100 to 4000 mg / L) in the first half of the discharge process in the semi-batch tank 14 is at least one of the continuous tank 24 and the precipitation tank 26 in the system, It is effective to set the discharge destination of the treated water having a low SS concentration (SS concentration of 100 mg / L or less) in the latter stage of the discharge process outside the continuous tank 24 and the precipitation tank 26.

  In the present embodiment, the SS concentration of the treated water passing through the treated water discharge line 16 is measured by the SS densitometer 40 and the measurement data is transmitted to the electromagnetic valve 38. And when the measurement data by SS densitometer 40 exceeds 100 mg / L, the path | route by the side of the treated water discharge line 16 is closed by the solenoid valve 38, the path | route by the side of the treated water supply line 36 is opened, and it is a semi-batch type. Treated water having a high SS concentration discharged from the tank 14 is supplied to the continuous tank 24. When the measurement data by the SS densitometer 40 is 100 mg / L or less, the route on the treated water supply line 36 side is closed by the electromagnetic valve 38 and the route on the treated water discharge line 16 side is opened, so that the semi-batch method is used. The treated water having a low SS concentration discharged from the tank 14 is supplied to the treated water tank 20.

  Moreover, it is also preferable to divide the path of the treated water as described above by the time of the discharge process. This is because treated water with a high SS concentration may be discharged from the semi-batch tank 14 in the first half of the discharging step. Therefore, the entire time of the discharge process is divided into the first half and the second half, and during the first half, the discharge destination of the treated water discharged from the semi-batch tank 14 is set in the continuous tank 24 system and the precipitation tank 26 system. At least one of them, and during the latter period, the discharge destination of the treated water discharged from the semi-batch tank 14 is outside the system of the continuous tank 24 and the system of the precipitation tank 26. Here, the latter period of the discharge process time is preferably set to 1/2 or more of the total time of the discharge process, and is set to 1/2 or more and 2/3 or less (at least 1/3 of the total time of the discharge process is set) It is more preferable to use the time of the previous period. In order to switch the route of treated water during the time of such a discharge process, a timer may be installed in the solenoid valve 38 or the like, and the route of treated water may be switched based on the time set by the timer.

In addition, it is preferable that the switching of the treatment water path as described above is performed before or after the start-up period of the semi-batch biological treatment. That is, in the start-up period of the semi-batch biological treatment, the discharge destination of the treated water discharged from the semi-batch tank 14 is at least one of the continuous tank 24 system and the precipitation tank 26 system, After the start-up period of the semi-batch biological treatment, the destination of the treated water discharged from the semi-batch tank 14 is set outside the continuous tank 24 and the precipitation tank 26. Here, the start-up period of the semi-batch biological treatment is prescribed by the SVI5 (Sludge Volume Index 5) of the sludge in the semi-batch tank 14 in addition to the SS concentration of the treated water as described above. For example, the period until the SVI5 of the sludge in the semi-batch tank 14 reaches the range of 50 to 80 may be set as the start-up period of the biological treatment. The SVI5 of the sludge in the semi-batch tank 14 is measured as follows. First, 1 L of sludge is put into a 1 L graduated cylinder, stirred, and then the sludge interface when allowed to stand for 5 minutes is measured. Then, the volume ratio (%) of sludge in the measuring cylinder is calculated. Next, MLSS (mg / L) of sludge is measured. By applying these to the following equation, SVI5 is calculated.
SVI5 = volume ratio occupied by sludge × 10,000 / MLSS

  Below, each tank which comprises the waste water treatment systems 1 and 2 of this embodiment is explained in full detail.

  The biological treatment reaction in the semi-batch tank 14 may be performed only under anaerobic (anoxic) conditions, only aerobic conditions, or anaerobic (anoxic) -aerobic alternating operation. However, conditions including aerobic conditions are preferable from the point of increasing sludge growth rate and granule formation rate, and conditions including anaerobic (anoxic) conditions from the viewpoint of stable formation of granules. Therefore, it is desirable to set conditions including anaerobic (anoxic) -aerobic conditions. Substances to be treated are, for example, organic substances, nitrogen-containing substances such as ammonia nitrogen, nitrate nitrogen, etc., and organic substances are decomposed to carbon dioxide by contact with microorganisms, and nitrogen-containing substances etc. are in contact with microorganisms. Is decomposed into nitrogen gas.

In the semi-batch tank 14, for example, when the wastewater BOD concentration is 200 to 1000 mg / L and the BOD load is 1.5 to 3.0 kg / m ³ / day, the wastewater inflow time is 15 minutes, and the oxygen-free reaction time is 30. Minute, aerobic reaction time 60-400 minutes, sludge settling time 15 minutes, treated water discharge time 15 minutes, it is desirable to set the total time of one cycle to 2.3-8.0 hours.

  The wastewater inflow rate of the semi-batch tank 14 is 20% to 80%, preferably 40% to 60%. As sludge repeatedly experiences a state in which the concentration of organic matter, which is the treatment target substance, is very high (immediately after the inflow process, a satiety state) and a state in which the organic matter concentration is very low (the end of the biological treatment process, starvation state), Granulation is thought to progress. Therefore, it is better to take the drainage inflow rate as high as possible from the viewpoint of forming granules, but on the other hand, the higher the drainage inflow rate, the larger the capacity of the inflow pump and the higher the cost. The drainage inflow rate is preferably 40% or more and 60% or less.

  The pH in the semi-batch tank 14 is preferably 6 to 9, particularly 6.5 to 7.5, which is suitable for general microorganisms. When the pH value is out of the above range, it is preferable to carry out pH control by adding acid and alkali. The dissolved oxygen (DO) in the semi-batch biological treatment reaction tank 14 is preferably 0.5 mg / L or more, particularly 1 mg / L or more under aerobic conditions.

  The semi-batch tank 14 is generally operated at a sludge concentration of about 3000 to 30000 mg / L. In order to maintain the soundness (sedimentation, activity, etc.) of the sludge, the sludge load is set to 0.05 to 0.00. It is preferable to keep at 60 kg / MLSS / day, more preferably from 0.1 to 0.5 kg / MLSS / day, so if the sludge concentration increases above the predetermined concentration, it is necessary to pull it out from the reaction tank. It becomes.

  The continuous tank 24 may be one tank, may be a multistage treatment of two or more tanks, or may be a combined tank combining an aerobic tank, an anaerobic tank, and an oxygen-free tank. Alternatively, biological treatment may be performed by filling the continuous tank 24 with a carrier such as polyurethane, plastic, or resin.

  The pH in the continuous tank 24 is preferably 6 to 9, which is suitable for general microorganisms, and more preferably 6.5 to 7.5. Further, it is desirable that the dissolved oxygen (DO) be 0.5 mg / L or more, particularly 1 mg / L or more under aerobic conditions. Although the residence time of the continuous tank 24 is not particularly limited, it is usually preferably set between 4 hours and 24 hours.

  In the present embodiment, the solid-liquid separation device that separates the microbial sludge from the treated water is not limited to the sedimentation tank 26, and may be a membrane separation device such as MBR, a hydrocyclone, GSS, or the like.

  The microbial sludge extracted from the semi-batch tank 14 is easily obtained as granulated sludge. And in the waste water treatment system which put the granular sludge, it becomes possible to improve the sedimentation property of sludge remarkably. When the solid-liquid separator that separates sludge from the treated water is the sedimentation tank 26, the linear flow rate of the sedimentation tank 26 is set to around 0.6 m / hr. However, when granule is charged, the linear flow rate is 1 It can be set to ˜5 m / hr.

  However, when the solid-liquid separation of the wastewater treatment system 2 is gravity sedimentation as in the sedimentation tank 26, rapid sludge input from the semi-batch biological treatment reaction tank 14 temporarily increases the linear flow velocity in the sedimentation tank 26. And sludge may flow out of the sedimentation tank 26. Usually, since the sludge interface of the sedimentation tank 26 is ½ or less of the water depth, the sludge supply amount per time is preferably ½ or less of the volume of the sedimentation tank 26 in order to prevent the sludge from flowing out. . In addition, even when solid-liquid separation such as membrane separation is employed, sudden sludge charging causes a rise in the water level and may cause sludge outflow from the upper part of the continuous tank 24. It is preferable to be in the range. Regardless of the solid-liquid separation method, the sludge supply rate from the semi-batch tank 14 to the continuous tank 24 is changed to the continuous tank 24 in order to prevent a rapid increase in the amount of treated water in the continuous tank 24. It is preferable to set it to 1/20 or less and 1/2 or less of the inflow rate of raw water. Moreover, while supplying the sludge from the semi-batch tank 14, the drainage inflow rate to the continuous tank 24 is reduced by a predetermined amount or the inflow of drainage in order to prevent a rapid increase in the amount of treated water in the continuous tank 24. It is also preferable to stop the operation. The predetermined amount is appropriately set within a range that prevents a rapid increase in the amount of treated water in the continuous tank 24.

  In order to efficiently use the sludge from the semi-batch tank 14 in the continuous tank 24, the volume of the semi-batch tank 14 is in the range of 1/100 to 1/3 with respect to the volume of the continuous tank 24. Preferably, the size is in the range of 1/20 to 1/5. Moreover, when discharging the treated water of the semi-batch tank 14 into the system of the continuous tank 24, depending on the volume ratio of the semi-batch tank 14 to the volume of the continuous tank 24 and the drainage inflow rate of the semi-batch tank 14, Since the degree of influence on the increase in the SS concentration of treated water in the settling tank 26 is different, it is necessary to set the linear flow rate of the settling tank 26 in consideration of the volume ratio and the drainage inflow rate. For example, when the volume ratio is 1/5 and the drainage ratio is 60%, the degree of influence on the sedimentation tank 26 is considered to be relatively large. Therefore, the linear flow velocity of the sedimentation tank 26 is set to about 1 to 2 m / hr. preferable.

  The wastewater applied to the treatment of the present embodiment contains biodegradable substances (organic matter) such as food processing factory wastewater, chemical factory wastewater, semiconductor factory wastewater, machine factory wastewater, sewage, human waste, river water, and the like. It is drainage. Moreover, when processing the wastewater which shows a biodegradability, it becomes possible by performing a physicochemical process beforehand and converting into the biodegradable substance. For oils and fats that are often contained in food processing factory effluent, etc., there is a high possibility that they will adhere to the sludge containing granules and have an adverse effect. It is desirable to remove fats and oils to a normal hexane extraction concentration of about 150 mg / L or less by existing methods such as flotation separation, coagulation pressure flotation device, adsorption device and the like.

Nucleus is considered necessary for granulating microbial sludge. Since normal effluent contains such fine particles as nuclei, it is not particularly necessary to add them, but in terms of promoting nucleation, water such as Fe ²⁺ , Fe ³⁺ , Ca ²⁺ , Mg ^2+, etc. It is desirable to add to the waste water ions that form oxides.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail more concretely, this invention is not limited to a following example.

Example 1
Waste water treatment was carried out using a continuous tank with a volume of 72.5 L, a sedimentation tank with a surface area of 86.5 cm ² and a semi-batch tank with a volume of 7.25 L. One end of the treated water discharge line was connected to the semi-batch tank, and the other end was connected to the continuous tank. The drainage flow rate of the continuous tank was 145 L / day, the drainage inflow rate of the semi-batch tank was 50%, and the discharge process time was 15 minutes. The treated water discharged from the sedimentation basin was sampled every 5 minutes from 5 minutes before the start of the discharge process in the semi-batch tank, and the SS concentration was measured.

  FIG. 3 is a diagram showing the change with time of the concentration of the treated water SS discharged from the sedimentation basin. As can be seen from FIG. 3, the SS concentration of the treated water discharged from the sedimentation basin was about 50-60 mg / L until the treated water flowed from the semi-batch tank to the continuous tank, but the semi-batch type When the treated water began to flow from the tank into the continuous tank, the SS concentration of the treated water increased to 500-4500 mg / L. Thereafter, when the inflow of the treated water from the semi-batch tank to the continuous tank was completed, the SS concentration of the treated water immediately discharged from the sedimentation basin decreased to 10 mg / L or less. From the above, it can be said that it is effective that the treated water discharged from the semi-batch tank is outside the continuous tank and the settling tank.

(Example 2)
Waste water treatment was carried out using a semi-batch tank with an effective volume of 3.5 L. Simulated drainage mainly composed of skipjack extract and peptone was used as drainage, and the BOD concentration was adjusted to about 1000 mg / L. The water temperature was adjusted to 20 ° C., and the pH of the simulated waste water was adjusted to 7.2 using hydrochloric acid and sodium hydroxide. The cycle time of the semi-batch treatment was 10 minutes for the inflow, 30 minutes for the anaerobic reaction, 670 minutes for the aerobic reaction, 1 minute for the sludge settling time, and 10 minutes for the treated water discharge time. In order to grasp the change with time of the SS concentration of the treated water discharged from the semi-batch tank, the treated water was sampled every minute from the start of the discharging process, and the SS concentration was measured.

  FIG. 4 is a diagram showing the change with time of the concentration of the treated water SS discharged from the semi-batch tank. As can be seen from FIG. 4, a high concentration of SS of about 4000 mg / L was discharged immediately after the start of the treatment water discharge, but after 1 minute, it was greatly reduced to about 140 mg / L. And 3 minutes after the start of discharge of the treated water, the SS concentration became 100 mg / L or less which is a level at which discharge is possible. From this result, when the discharge destination of the treated water discharged from the semi-batch tank is divided by time, at least one third (3 minutes) of the total time (10 minutes) of the discharge process is set as the previous period. It is preferable to supply the treated water to a continuous tank or a precipitation tank. That is, it is preferable that 2/3 of the total time of the discharge process, which is the remaining time, be the latter period, and the treated water be discharged out of the continuous tank system and out of the precipitation tank system.

  1, 2 Wastewater treatment system, 10 Wastewater storage tank, 12,28 Wastewater inflow line, 14 Semi-batch biological treatment reaction tank (semi-batch tank), 16 Treated water discharge line, 18 Sludge discharge line, 20 Treated water tank, 24 Continuous biological treatment reaction tank (continuous tank), 26 sedimentation tank, 30 primary treated water discharge line, 32 treated water discharge line, 34 sludge return line, 36 treated water supply line, 38 solenoid valve, 40 SS concentration meter.

Claims (3)

While the wastewater is continuously flowed into the continuous reaction tank, the target substance in the wastewater is biologically treated with microbial sludge, and the microbial sludge is separated from the treated water discharged from the continuous reaction tank. A continuous biological treatment process separated by
The semi-batch reaction tank includes an inflow process for inflowing wastewater, a biological treatment process for biologically treating the target substance in the wastewater with microbial sludge, a settling process for settling the microbial sludge, and a discharge process for discharging treated water. A semi-batch biological treatment process that is repeatedly performed,
A sludge supply step of supplying the microbial sludge in the semi-batch reaction tank that has settled to the continuous reaction tank, and
When the average SS concentration of the treated water discharged from the semi-batch reaction tank in the discharge step is 100 mg / L or less, the discharge destination of the treated water is set outside the continuous reaction tank and the solid-liquid separation tank. When the average SS concentration of treated water discharged from the semi-batch reaction tank in the discharge step is more than 100 mg / L, the discharge destination of the treated water is set in the continuous reaction tank system and the solid reaction tank. A wastewater treatment method characterized by comprising at least one of the liquid separation tanks . While the wastewater is continuously flowed into the continuous reaction tank, the target substance in the wastewater is biologically treated with microbial sludge, and the microbial sludge is separated from the treated water discharged from the continuous reaction tank. A continuous biological treatment process separated by
The semi-batch reaction tank includes an inflow process for inflowing wastewater, a biological treatment process for biologically treating the target substance in the wastewater with microbial sludge, a settling process for settling the microbial sludge, and a discharge process for discharging treated water. A semi-batch biological treatment process that is repeatedly performed,
A sludge supply step of supplying the microbial sludge in the semi-batch reaction tank that has settled to the continuous reaction tank, and
In the discharge process, the discharge process time is divided into the first and second periods, the ratio of the second period is set to 1/2 or more of the total time, and during the first period, the treated water is discharged to the continuous reaction tank. At least one of the inside of the system and the system of the solid-liquid separation tank, and during the latter period, the discharge destination of the treated water is outside the system of the continuous reaction tank and the system of the solid-liquid separation tank A wastewater treatment method characterized by that. While the wastewater is continuously flowed into the continuous reaction tank, the target substance in the wastewater is biologically treated with microbial sludge, and the microbial sludge is separated from the treated water discharged from the continuous reaction tank. A continuous biological treatment process separated by
The semi-batch reaction tank includes an inflow process for inflowing wastewater, a biological treatment process for biologically treating the target substance in the wastewater with microbial sludge, a settling process for settling the microbial sludge, and a discharge process for discharging treated water. A semi-batch biological treatment process that is repeatedly performed,
A sludge supply step of supplying the microbial sludge in the semi-batch reaction tank that has settled to the continuous reaction tank, and
The semi-batch biological treatment is started up until the SVI5 (Sludge Volume Index 5) of the sludge in the semi-batch type reactor reaches 50 or more and 80 or less. The discharge destination of the treated water is at least one of the continuous reaction tank system and the solid-liquid separation tank system, and after the start-up period of the semi-batch biological treatment, A wastewater treatment method characterized in that water is discharged outside the continuous reaction tank and outside the solid-liquid separation tank .

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