JP2019171321A - Waste water treatment system and waste water treatment method - Google Patents

Abstract

To provide reduction of wastewater treatment load and improvement of wastewater treatment capacity.SOLUTION: A wastewater treatment system that separates the wastewater flowing into an activated sludge tank into treated water purified by biological treatment and activated sludge by biologically treating pollutants in the wastewater with the activated sludge, includes a sludge storage tank that stores the separated activated sludge in an aerated state, a sludge adsorption tank into which the activated sludge stored in the sludge storage tank and the wastewater before flowing into the activated sludge tank flow, and which adsorbs the pollutants in the wastewater onto the activated sludge flowed from the sludge adsorption tank, and discharge means that discharges the activated sludge having the pollutants in the wastewater adsorbed thereto.SELECTED DRAWING: Figure 1

Description

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

  As one of wastewater treatment methods, there is known an activated sludge method in which oxygen is given to activated sludge containing microorganisms by aeration, and pollutants in the wastewater are decomposed as feed. In an aeration tank (also called activated sludge tank) that treats pollutants (organic substances), if the amount of inflowing pollutants (hereinafter also referred to as pollution load) increases, until microorganisms decompose organic substances in the activated sludge tank The residence time becomes longer and the energy consumption due to aeration increases. Moreover, when the pollution load increases, excess sludge that becomes unnecessary due to the growth of microorganisms increases. On the other hand, a technique for reducing the volume of excess sludge has been proposed (see, for example, Patent Document 1).

JP 2005-28265 A

  Even if the volume of excess sludge is reduced, the wastewater treatment time is not shortened and the energy consumed by aeration is not suppressed unless the pollution load is reduced. Further, since the pollution load that can be treated in the wastewater treatment facility depends on the size of the activated sludge tank, it may be difficult to improve the wastewater treatment capacity in the existing wastewater treatment facility. Even in a new wastewater treatment facility, since an activated sludge tank having a size corresponding to the pollution load is installed, it may be difficult to reduce the size of the facility.

  Then, an object of this invention is to provide the technique which reduces the load of waste water treatment and improves waste water treatment capacity.

  In order to solve the above-mentioned problems, the present invention uses activated sludge that has been aerated to retain activated sludge used for biological treatment of wastewater in the activated sludge tank, before the biological treatment in the activated sludge tank. It was decided to remove some organic matter from the wastewater. The starvation state is a state in which the pollutant serving as food is consumed by aeration to such an extent that the activated sludge does not die.

  Specifically, the present invention is a wastewater treatment in which wastewater flowing into an activated sludge tank is biologically treated by decomposing pollutants in the wastewater with activated sludge and separated into treated water and activated sludge purified by biological treatment. The system consists of a sludge storage tank that stores the separated activated sludge in an aerated state, activated sludge stored in the sludge storage tank, and wastewater before flowing into the activated sludge tank. A sludge adsorption tank for adsorbing the activated sludge flowing in from the storage tank; and a discharge means for discharging the activated sludge adsorbing the pollutant in the waste water.

The above-described wastewater treatment system biologically treats pollutants in wastewater in an activated sludge tank, and stores activated sludge separated from the activated sludge tank in an aerated state in the sludge storage tank. The activated sludge separated from the activated sludge tank is starved by aeration in the sludge storage tank. The activated sludge that has become starved is sent to a sludge adsorption tank and used to adsorb pollutants in waste water. Prior to biological treatment in an activated sludge tank, the waste water treatment system adsorbs pollutants in the waste water to the activated sludge in a starved state in the sludge adsorption tank. The activated sludge that has adsorbed the pollutants in the sludge adsorption tank is discharged out of the system as surplus sludge and discarded without being returned to the biological treatment system of waste water. In the sludge adsorption tank, about 40% to 80% of the pollutants in the waste water are adsorbed and removed by the activated sludge in the starved state. For this reason, the quantity of the pollutant in the waste_water | drain flowing into an activated sludge tank is reduced. Therefore, the wastewater treatment system can increase the treatable load of pollutants in the wastewater and improve the quality of treated water. In addition, the load which can be processed is the quantity of the pollutant in the waste water which can be processed with activated sludge. The amount of the pollutant is also referred to as a BOD amount (Biochemical oxygen demand, biochemical oxygen demand).

  If it is said waste water treatment system, the load which can be processed per volume of an activated sludge tank or the day can be increased in the existing waste water treatment facility. In addition, even in a newly installed wastewater treatment facility, the volume of the activated sludge tank can be further reduced.

  The wastewater treatment system uses the initial adsorption of the activated sludge in a starved state to adsorb pollutants in the wastewater to the activated sludge and discharge it as excess sludge outside the system. The initial adsorption is a phenomenon in which activated sludge comes into contact with wastewater and adsorbs or supplements the pollutant, thereby removing the pollutant from the wastewater. In 20 to 30 minutes, 75% or more of the pollutant is reduced ( Reference: Japan Sewerage Corporation JS Technology Development Information Mail Sewerage Course No. 2 <Initial Adsorption> The activated sludge in the starved state has a higher initial adsorption capacity than the activated sludge not in the starved state, and adsorbs more pollutants. The wastewater treatment system discharges pollutants out of the system at the initial adsorption stage, thereby reducing the amount of aeration in the activated sludge tank and reducing energy consumption.

  Whether or not the activated sludge is starved can be determined from the respiration rate of the activated sludge. The respiration rate of activated sludge can be determined, for example, by aeration of sludge to increase the dissolved oxygen concentration, and then stop aeration and measure the rate of decrease in dissolved oxygen concentration. The faster the decrease in dissolved oxygen concentration, the faster the oxygen consumption rate (respiration rate) of the activated sludge, and it can be determined that the activated sludge is in a starved state. In the sludge storage tank of the above wastewater treatment system, activated sludge is starved and the concentration of organic matter in the sludge storage tank is low, so the decrease in dissolved oxygen concentration is delayed. That is, the respiration rate of activated sludge in the sludge storage tank is slow. On the other hand, in the activated sludge tank, the oxygen consumption rate of the activated sludge is high, and the organic substance concentration in the activated sludge tank is high, so that the decrease in the dissolved oxygen concentration is accelerated. That is, the activated sludge respiration rate in the activated sludge tank is increased.

  Further, the discharging means may include a sedimentation tank for precipitating activated sludge that has adsorbed the pollutant in the waste water. With such a discharge means, the waste water aerated in the sludge adsorption tank can be precipitated in the settling tank without stopping the aeration in the sludge adsorption tank. Therefore, the discharge means can efficiently discharge the sludge adsorbing the pollutant out of the system.

  Further, the sludge storage tank may store the separated activated sludge for a predetermined time until the separated activated sludge becomes starved. Such a wastewater treatment system can increase the amount of pollutant removed by initial adsorption in the sludge adsorption tank by starving the activated sludge sent to the sludge adsorption tank.

  Further, the sludge storage tank may be configured to be partitioned into a plurality of tanks so that the activated sludge can move between adjacent tanks, and the flow of the activated sludge between the plurality of tanks becomes a plug flow. . If it is such a sludge storage tank, activated sludge can be made into a starvation state in steps by a plug flow (extrusion flow) system. The sludge storage tank can send activated sludge in a more starved state to the sludge adsorption tank by gradually turning the activated sludge into a starved state.

The present invention can also be understood from the aspect of the method. For example, the present invention is a wastewater treatment method in which wastewater flowing into an activated sludge tank is biologically treated by decomposing pollutants in the wastewater with activated sludge and separated into treated water and activated sludge purified by biological treatment. In the sludge storage tank,
In the storage process of storing the separated activated sludge in an aerated state, the activated sludge stored in the sludge storage tank and the sludge adsorption tank into which the waste water before flowing into the activated sludge tank flows, the pollutants in the waste water are It may be a wastewater treatment method including an adsorption process for adsorbing activated sludge that has flowed in from a sludge storage tank and a discharge process for discharging activated sludge that adsorbs the pollutant in the wastewater.

  ADVANTAGE OF THE INVENTION According to this invention, the load of waste water treatment can be reduced and waste water treatment capacity can be improved.

FIG. 1 is a diagram illustrating a configuration of a wastewater treatment system according to an embodiment. FIG. 2 is a diagram illustrating a first modification of the wastewater treatment system. FIG. 3 is a diagram showing a second modification of the waste water treatment system. FIG. 4 is a view showing a first modification of the sludge storage tank. FIG. 5 is a view showing a second modification of the sludge storage tank. FIG. 6 is a diagram illustrating partitioning between a plurality of sludge storage tanks. FIG. 7 is a diagram illustrating a partition between a plurality of sludge storage tanks. FIG. 8 is a diagram illustrating the configuration of a wastewater treatment system according to a comparative example.

  Hereinafter, embodiments of the present invention will be described. The embodiment described below exemplifies one aspect of the present invention, and does not limit the technical scope of the present invention to the following aspect.

  FIG. 1 is a diagram illustrating a configuration of a wastewater treatment system according to an embodiment. The wastewater treatment system 10 includes a sludge storage tank 1, a sludge adsorption tank 2, a precipitation tank A31, a precipitation tank B32, an activated sludge tank 4, and an excess sludge tank 5. Moreover, each tank with which the waste water treatment system 10 is provided is connected by the path | routes L1 to L7, and waste_water | drain or activated sludge can distribute | circulate between each tank with a pump etc.

  The sludge storage tank 1 stores activated sludge separated from wastewater purified by biological treatment with activated sludge. The sludge storage tank 1 includes an aeration device 11 and aerated activated sludge in the sludge storage tank 1. The aeration apparatus 11 should just aerate so that the activated sludge in the sludge storage tank 1 may not die. To the extent that the activated sludge does not die, it is sufficient that even a small amount of oxygen remains in the sludge storage tank 1, and the aerated oxygen remains without being consumed by microorganisms. Specifically, for example, the displayed value of the dissolved oxygen concentration meter measured in the water in the sludge storage tank 1 may be other than 0 mg / L. If even a small amount of oxygen remains in the sludge storage tank 1, the generation and growth of anaerobic bacteria are suppressed, and the action of aerobic bacteria is promoted.

  The pollutant remaining in the sludge storage tank 1 is further decomposed by being decomposed by the activated sludge. The activated sludge stays in the sludge storage tank 1 for several hours (for example, 4 hours) to several days, so that the activated sludge becomes starved due to a decrease in pollutant substances serving as food. The activated sludge in a starved state passes through the path L1 and is sent to the sludge adsorption tank 2 installed on the path where the wastewater flows into the activated sludge tank 4.

The residence time in the sludge storage tank 1 varies depending on the operation status of the wastewater treatment system 10. In the waste water treatment system 10, for example, when the BOD volume load is operated at 0.1 kg-BOD / m ³ · d, the pollutant in the waste water is almost consumed in about 2 to 3 hours and there is no food. The BOD volumetric load is one of the indexes indicating the pollutant load, and is the BOD amount that can be processed per unit volume of the activated sludge tank 4 per day. On the other hand, when the BOD volumetric load is operated at 1 kg-BOD / m ³ · d, the pollutant in the wastewater may take about 2 days to be consumed. The residence time in the sludge storage tank 1, that is, the time until the sludge becomes starved varies depending on the operation status of the wastewater treatment system 10 such as the BOD volume load.

  The volume of the sludge storage tank 1 is calculated based on the amount of wastewater flowing into the sludge adsorption tank 2 (the amount of pollutants in the wastewater) by obtaining the residence time until the activated sludge is starved after the pollutants in the wastewater are consumed. ) Can be set to stay for the time. Moreover, the waste water flowing into the sludge adsorption tank 2 is retained in a flow rate adjusting tank (not shown), and the amount of the waste water flowing into the sludge adsorption tank 2 can be adjusted to be substantially constant by a pump or the like.

  Although the sludge storage tank 1 is divided | segmented into 2 tanks in the example of FIG. 1, it is not restricted to 2 tanks. The sludge storage tank 1 may be one tank or may have a divided structure of three or more tanks. When the sludge storage tank 1 is divided into a plurality of tanks, the activated sludge flow in the sludge storage tank 1 is sent to the sludge adsorption tank 2 by plug flow (extrusion flow). May be. By making the flow of activated sludge between a plurality of tanks into a plug flow, it becomes possible to supply activated sludge in a more starved state to the sludge adsorption tank 2.

  Moreover, when the sludge storage tank 1 has a divided structure composed of a plurality of tanks, the sludge storage tank 1 may not be aerated to some tanks. Activated sludge does not die even if it is not aerated for several hours. For this reason, in the sludge storage tank 1, it is sufficient that aeration is performed to such an extent that the activated sludge is not killed. Of the divided tanks, aeration is performed in a tank having a residence time of several hours or more, thereby eliminating the sludge. It is possible to prevent. With such a sludge storage tank 1, since aeration to some tanks is not performed, energy consumption by aeration is reduced.

  Moreover, when the sludge storage tank 1 has a divided structure including a plurality of tanks, some tanks may have stirring means. If it is such a sludge storage tank 1, sedimentation of activated sludge can be prevented and decay and death can be suppressed.

  The sludge adsorption tank 2 retains the waste water to be treated which flows in and the starved activated sludge sent out from the sludge storage tank 1. The wastewater flowing into the sludge adsorption tank 2 once stays in a flow rate adjusting tank (not shown) and can be made to flow into the sludge adsorption tank 2 at a substantially constant flow rate by a pump or the like. The sludge adsorption tank 2 includes an aeration device 21 and aerates the waste water and activated sludge staying in the tank. The activated sludge stays in the sludge adsorption tank 2 in an aerated state for a predetermined time, thereby adsorbing the pollutant in the waste water. The predetermined time may be any time as long as the activated sludge can adsorb the pollutant and discharge it out of the system, and is preferably shorter than the time during which the activated sludge decomposes the pollutant by biological treatment. The predetermined time is, for example, 20 minutes to 60 minutes. Since it is not necessary to allow time for the activated sludge to decompose the pollutant by biological treatment, the sludge adsorption tank 2 can be reduced. The activated sludge is assumed to adsorb 40% to 80% of the pollutant in the wastewater in the sludge adsorption tank 2. The waste water and activated sludge that stayed in the sludge adsorption tank 2 for a predetermined time pass through the path L2 and are sent to the sedimentation tank A31.

  The sedimentation tank A31 settles and separates the activated sludge adsorbing the pollutant from the wastewater mixed with the activated sludge adsorbing the pollutant flowing in from the sludge adsorption tank 2. The activated sludge that has adsorbed the pollutants settles in the sedimentation tank A31, and is sent to the surplus sludge tank 5 through the path L3. In addition, the wastewater separated from the activated sludge and from which part of the pollutant material has been removed passes through the path L4 and is sent to the activated sludge tank 4.

  The activated sludge tank 4 retains the waste water flowing from the settling tank A31. The activated sludge tank 4 includes an aeration device 41 and aerates the waste water and activated sludge staying in the tank. Activated sludge decomposes pollutants in wastewater by biological treatment. In the sludge adsorption tank 2, the pollutant in the waste water has already been removed by about 40% to 80%. Therefore, the activated sludge tank 4 can be reduced in volume and the amount of aeration can be reduced. The biologically treated waste water and activated sludge are sent to the sedimentation tank B32 through the path L5.

  The sedimentation tank B32 separates and separates the waste water flowing from the activated sludge tank 4 and the activated sludge. Part of the activated sludge that has settled in the sedimentation tank B32 passes through the path L6 and is returned to the activated sludge tank 4. The activated sludge returned to the activated sludge tank 4 decomposes the pollutant in the activated sludge tank 4 by biological treatment. The activated sludge that is not returned to the activated sludge tank 4 passes through the path L7 and is sent to the sludge storage tank 1. The supernatant sedimented and separated from the activated sludge in the sedimentation tank B32 is obtained as treated water by the wastewater treatment system 10.

  The surplus sludge tank 5 stores activated sludge that has adsorbed the pollutants flowing from the settling tank A31. The activated sludge that flows into the surplus sludge tank 5 is surplus sludge to be discarded, and may be aerated to the extent of avoiding corruption.

  FIG. 2 is a diagram illustrating a first modification of the wastewater treatment system. The wastewater treatment system 10A includes a submerged membrane activated sludge tank 4A instead of the settling tank B32 and the activated sludge tank 4 shown in FIG. The components common to the wastewater treatment system 10 of FIG.

  The submerged membrane activated sludge tank 4A separates treated water and activated sludge using a membrane such as a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) unlike the sedimentation separation in the sedimentation tank B32. . The submerged membrane activated sludge tank 4 </ b> A includes a separation membrane 42 in the tank and is aerated by an aeration apparatus 41. The treated water filtered by the separation membrane 42 can be obtained by suction. A part of the activated sludge that has settled passes through the path L7 and is sent to the sludge storage tank 1.

  FIG. 3 is a diagram showing a second modification of the waste water treatment system. The waste water treatment system 10B includes an anaerobic-anoxic-aerobic tank 4B instead of the activated sludge tank 4 shown in FIG. The components common to the wastewater treatment system 10 of FIG.

  The anaerobic-anoxic-aerobic tank 4B includes an anaerobic tank 4B1 that suppresses the growth of filamentous bacteria and removes phosphorus, an anaerobic tank 4B2 that removes nitrogen, and an aerobic tank 4B3 that performs aeration treatment with the aeration apparatus 41. . The activated sludge returned from the settling tank B32 to the anaerobic-anoxic-aerobic tank 4B through the path L6 flows into the anaerobic tank 4B1 to remove phosphorus. The activated sludge that has moved to the anaerobic tank 4B2 uses the nitric acid generated in the aerobic tank 4B3 to remove nitrogen. In the aerobic tank 4B3, the activated sludge decomposes the pollutant (biological treatment) by aeration by the aeration apparatus 41. In the aerobic tank 4B3, nitric acid is generated by nitrification of ammonia in the waste water. The mixed liquid of activated sludge containing nitric acid passes through the path L8 and is sent to the oxygen-free tank 4B2. Nitric acid in the mixed solution is used to remove nitrogen in the oxygen-free tank 4B2. The wastewater and activated sludge that have been biologically treated in the aerobic tank 4B3 are sent to the sedimentation tank B32 through the path L5.

  The biological treatment of wastewater with activated sludge is not limited to the system using the activated sludge tank 4 in FIG. 1, the submerged membrane activated sludge tank 4A in FIG. 2, and the anaerobic-anoxic-aerobic tank 4B shown in FIG. Any method may be used as long as activated sludge is generated by the decomposition of the pollutant at 4 or the like. The biological treatment system using activated sludge is, for example, a long time aeration method, oxidation ditch method (oxidation ditch method), anaerobic aerobic method (AO method), circulating anaerobic aerobic method (A2O method), membrane separation activated sludge. And various biological treatment methods such as contact aeration method.

(Sludge storage tank)
FIG. 4 is a view showing a first modification of the sludge storage tank. The sludge storage tank 1A illustrated in FIG. 4 is divided into three division tanks 1A1, a division tank 1A2, and a division tank 1A3. The activated sludge sent out from the sedimentation tank B32 flows into the dividing tank 1A1, moves in the order of the dividing tank 1A2 and the dividing tank 1A3, and is sent out to the sludge adsorption tank 2. Since activated sludge does not die even if it is not aerated for several hours, it is not necessary to aerate in the dividing tank 1A1 and the dividing tank 1A2. When the residence time is several hours or longer, the activated sludge can be prevented from being killed by aeration with the aeration apparatus 11 in the dividing tank 1A3 on the side of sending the activated sludge to the sludge adsorption tank 2. By not performing aeration in some divided tanks, energy consumption for aeration is reduced.

  FIG. 5 is a view showing a second modification of the sludge storage tank. The sludge storage tank 1B illustrated in FIG. 5 is divided into two division tanks 1B1 and a division tank 1B2. The activated sludge sent out from the sedimentation tank B32 flows into the dividing tank 1B1, moves to the dividing tank 1B2, and is sent out to the sludge adsorption tank 2. Since activated sludge does not die even if it is not aerated for several hours, it does not need to be aerated in the division tank 1B1 as in the case of the sludge storage tank 1A of FIG. In the example of FIG. 5, the stirring device 12 installed in the division tank 1 </ b> B <b> 1 stirs the activated sludge to prevent sedimentation of the activated sludge and suppress the decay or death of the activated sludge. The activated sludge can be prevented from being killed by aeration by the aeration apparatus 11 in the dividing tank 1B2 on the side of sending the activated sludge to the sludge adsorption tank 2.

  FIG. 6 is a diagram illustrating partitioning between a plurality of sludge storage tanks. The sludge storage tank 1C illustrated in FIG. 6 is divided into two division tanks 1C1 and a division tank 1C2 by a partition S1. The partition S1 has a flow hole S1a and a flow hole S1b through which activated sludge can flow. In the example of FIG. 6, the flow hole S1a is provided in the upper front part of the partition S1, and the flow hole S1b is provided in the lower rear part of the partition S1, but the position of the flow hole is not limited to this. The number and position of the circulation holes may be any number and position where activated sludge can flow into the dividing tank 1C2 from the dividing tank 1C1. The activated sludge sent out from the sedimentation tank B32 flows into the division tank 1C1 and moves to the division tank 1C2 through the circulation hole S1a and the circulation hole S1b. The activated sludge moved to the division tank 1C2 is sent to the sludge adsorption tank 2.

  FIG. 7 is a diagram illustrating a partition between a plurality of sludge storage tanks. The sludge storage tank 1D illustrated in FIG. 7 is divided into three divided tanks 1D1, 1D2, and 1D3 by a partition S2 and a partition S3. The partition S2 is disposed with a flow path of activated sludge in a slit shape between the front wall surface of the sludge storage tank 1D. The partition S3 is provided with a flow path of activated sludge in a slit shape between the partition wall S3 and the wall surface behind the sludge storage tank 1D. The flow path of the activated sludge is not limited to the case where it is provided in front of or behind the sludge storage tank 1D by a plurality of partitions. The flow path of activated sludge should just be provided so that activated sludge may move in order of division tank 1D2, division tank 1D2, and division tank 1D3. The activated sludge sent out from the sedimentation tank B32 flows into the division tank 1D1, and moves to the division tank 1D2 through a gap provided on the front side of the partition S2. The activated sludge that has moved to the dividing tank 1D2 moves to the dividing tank 1D3 through a gap provided on the rear side of the partition S3. The activated sludge moved to the division tank 1D3 is sent to the sludge adsorption tank 2.

(Volume reduction effect of wastewater treatment system)
It is assumed that the wastewater treatment system 10 according to the present embodiment removes about 40% to 80% of pollutants in the wastewater in the sludge adsorption tank 2. For this reason, the magnitude | size of the activated sludge tank 4 can be made small compared with the system which does not provide the sludge adsorption tank 2. FIG. Moreover, the sludge adsorption tank 2 of this embodiment should just be smaller than the case where activated sludge can adsorb | suck a pollutant, and can discharge | emit it outside a system, and activated sludge decomposes | disassembles a pollutant. That is, the wastewater treatment system 10 according to the present embodiment can reduce the size of the activated sludge tank 4 and the sludge adsorption tank 2. Therefore, the volume reduction effect of the wastewater treatment system 10 according to the present embodiment will be described by comparison with the wastewater treatment system according to the comparative example shown in FIG.

  FIG. 8 is a diagram illustrating the configuration of a wastewater treatment system according to a comparative example. The wastewater treatment system 100 according to the comparative example includes an activated sludge tank 40, a sedimentation tank 320, and an excess sludge tank 60. Moreover, each tank with which the waste water treatment system 100 is provided is connected by the path | route L10, the path | route L20, and the path | route L30.

  When the wastewater to be treated flows into the activated sludge tank 40, it is aerated by the aeration device 410, and the pollutant in the wastewater is decomposed by biological treatment. The wastewater and activated sludge that have been biologically treated in the activated sludge tank 40 are sent to the sedimentation tank 320 through the path L10. The sedimentation tank 320 settles and separates the activated sludge from the wastewater flowing from the activated sludge tank 40. Part of the activated sludge settled in the settling tank 320 is returned to the activated sludge tank 40 through the path L20. Excess activated sludge that is not returned to the activated sludge tank 40 is sent to the excess sludge tank 60 through the path L30. The supernatant sedimented and separated from the activated sludge in the sedimentation tank 320 is obtained as treated water by the wastewater treatment system 100. The surplus sludge tank 60 stores the activated sludge that is unnecessary in the activated sludge tank 40 and is discharged outside the system.

  In order to compare the volume of each tank provided in the wastewater treatment system 10 according to the present embodiment and the wastewater treatment system 100 according to the comparative example shown in FIG. 8, the total volume of each tank in each system is estimated. Table 1 shows the conditions for the trial calculation.

The amount of inflow water is the amount of wastewater that flows in each day in each wastewater treatment system, and is assumed to be 100 m ³ / d. Inflow BOD is the amount of pollutant contained in 1 L of waste water, and is assumed to be 1000 mg / L. BOD volumetric load is the amount of pollutant that can be treated per unit volume per unit volume of the biological treatment tank (activated sludge tank 4 or activated sludge tank 40). 0.5 kg-BOD / (m ³ · d ). The organic matter removal rate of the sludge adsorption tank is a rate at which activated sludge removes organic substances (sludge substances) by adsorption in the sludge adsorption tank 2 according to this embodiment, and is assumed to be 60%. The residence time of the sludge adsorption tank is the residence time of waste water and activated sludge in the sludge adsorption tank 2 according to this embodiment, and is assumed to be 40 minutes. The residence time of the sludge storage tank is the residence time in the sludge storage tank 1 according to the present embodiment, and is assumed to be 1 day. The sludge conversion rate is the ratio of the amount of excess sludge generated to the amount of polluted substances removed, and is assumed to be 0.3. Sludge moisture content is 99%. The residence time of the excess sludge tank is the residence time of the excess sludge discharged outside the system in the excess sludge tank (the excess sludge tank 5 or the excess sludge tank 60), and is assumed to be 2 days.

Table 2 shows the volume of each tank provided in the wastewater treatment system 10 according to the present embodiment and the wastewater treatment system 100 according to the comparative example shown in FIG.

In the wastewater treatment system 10 according to the present embodiment, the volumes of the sludge adsorption tank 2, the sedimentation tank A31, the activated sludge tank 4, the sedimentation tank B32, the sludge storage tank 1, and the surplus sludge tank 5 are 2.7 m ³ and 16. It is estimated to be 7m ³ , 80m ³ , 16.7m ³ , 3m ³ , 6m ³ . In this case, the total volume of each tank provided in the wastewater treatment system 10 according to the present embodiment is 125.1 m ³ .

Here, the detail of the trial calculation of each tank with which the waste water treatment system 10 is provided is demonstrated. The volume of the conventional activated sludge tank is assumed to be 200 m ³ . In addition, the amount of wastewater that flows into the wastewater treatment system 10 in one day (the amount of wastewater to be treated) is 100 m ³ .

In the wastewater treatment system 10 according to the present embodiment, 60% of organic substances (contaminating substances) are removed in the sludge adsorption tank 2. For this reason, in order to remove the remaining organic matter, it is estimated that the size of the activated sludge tank 4 may be 80 m ³ which is 60% smaller than the conventional 200 m ³ .

Next, the residence time of the waste water in the sludge adsorption tank 2 is assumed to be 20 minutes to 60 minutes. Taking the average value, the residence time in the sludge adsorption tank 2 is 40 minutes. In this case, the size of the sludge suction tank 2, in terms of amount of waste water to process the wastewater 100 m ³ / d flowing a day 40 minutes, 100m ³ / d ÷ 24 hours ÷ 60 minutes × 40 min = 2. It is estimated to be 7m ^3.

Moreover, the volume of the sedimentation tank A31 and the sedimentation tank B32 can be set so that it may be substantially proportional to the amount of drainage 100m < ³ > / d which flows in a day. Here, assuming that the residence time is 4 hours, the volume of the precipitation tank A31 and the precipitation tank B32 is calculated as 100 m ³ / d ÷ 24 hours ÷ × 4 hours = 16.7 m ³ .

Moreover, in order to estimate the volume of the sludge storage tank 1, first, the sludge generation amount is obtained. 100m ³ / d of inflow water per day, BOD at the inlet (amount of pollutants in the inflow waste water) 1000mg-BOD / L, BOD at the outlet (amount of pollutants in the treated water) 20mg- Assume BOD / L. In this case, the removal amount of BOD is (1000-20) [mg / L] / 1000 [unit conversion] × 100 [m ³ / d] = 98 kg-BOD / d. Assuming that the sludge conversion rate is 0.3, the amount of generated excess sludge is 98 kg−BOD / d × 0.3 = 29.4 kg−
It is calculated as drySS / d. Assuming that the sludge moisture content of the generated excess sludge is 99%, the sludge generation amount is calculated as 29.4 kg−drySS / d × 100 ÷ (100−99) = 2,940 kg−wetSS / d. The residence time of the wastewater in the sludge storage tank 1 is assumed to be 2 hours to 2 days, but here it is assumed to be 1 day. In this case, the volume of the sludge storage tank 1 is estimated to be 2,940 kg-wetSS / d × 1d≈3 m ³ .

The residence time of the excess sludge tank 5 is assumed to be 2 days. The volume of the excess sludge tank 5 is estimated the amount of sludge and 6 m ³ When ^3m 3 / d.

On the other hand, the wastewater treatment system 100 according to the comparative example does not have a tank corresponding to the sludge adsorption tank 2, the sedimentation tank A31, and the sludge storage tank 1. The wastewater treatment system 100 according to the comparative example, the volume of the activated sludge tank 40, settling tank 320 (corresponding to sedimentation tank B32), and excess sludge tank 60 is estimated to respectively 200m ^3, 16.7m ^3, 6m ³ . The wastewater treatment system 100 according to the comparative example does not include the sludge adsorption tank 2, and the pollutant in the inflowing wastewater is biologically treated in the activated sludge tank 40. For this reason, the size of the activated sludge tank 40 is estimated to be 200 m ³ . The total volume of each tank provided in the wastewater treatment system 100 according to the comparative example is 222.7 m ³ .

  The wastewater treatment system 10 according to the present embodiment is capable of removing approximately 40% to 80% of pollutants in the wastewater by the sludge adsorption tank 2 having a smaller capacity than the sedimentation tank A31 and the activated sludge tank 4. For this reason, it becomes possible to reduce the pollutant load flowing into the activated sludge tank 4, and the volume of the activated sludge tank 4 is reduced by about 60% compared to the waste water treatment system 100 according to the comparative example. The wastewater treatment system 10 according to the present embodiment includes the sludge adsorption tank 2, the sedimentation tank A31, and the sludge storage tank 1 that are not used in the comparative example, but the entire system is also compared with the wastewater treatment system 100 according to the comparative example. A volume of 40% or more can be reduced.

<Effect>
The wastewater treatment system 10 according to the present embodiment can remove about 40% to 80% of the pollutants in the wastewater by the activated sludge in the sludge adsorption tank 2 that is returned from the sludge storage tank 1. Therefore, the pollution load in the activated sludge tank 4 can be reduced. Therefore, the wastewater treatment system 10 can increase the amount of wastewater treated or reduce the volume of the activated sludge tank 4. Moreover, since the pollution load in the activated sludge tank 4 is reduced, the energy consumption by aeration is also reduced.

10, 10A, 10B ... Wastewater treatment system: 1, 1A, 1B, 1C, 1D Sludge storage tank: 2, Sludge adsorption tank: 31, 32 Precipitation tank: 4, Activated sludge tank: 4A・ Immersion membrane activated sludge tank: 4B ・ ・ Anaerobic-anoxic-aerobic tank: 5 ・ ・ Excess sludge tank: 11,21,41 ・ ・ Aeration device, 12 ・ ・ Agitator

Claims (5)

A wastewater treatment system for separating wastewater flowing into an activated sludge tank into biological treatment by decomposing the pollutants in the wastewater with activated sludge and separating the treated water and activated sludge purified by the biological treatment,
A sludge storage tank for storing the separated activated sludge in an aerated state;
The activated sludge stored in the sludge storage tank and the waste water before flowing into the activated sludge tank, and the sludge adsorption tank for adsorbing the pollutants in the waste water to the activated sludge flowing in from the sludge storage tank; ,
A discharge means for discharging activated sludge adsorbing the pollutants in the waste water,
Wastewater treatment system. The discharge means includes a settling tank for precipitating activated sludge adsorbing the pollutant in the waste water,
The wastewater treatment system according to claim 1. The sludge storage tank stores the separated activated sludge for a predetermined time until the separated activated sludge is starved.
The wastewater treatment system according to claim 1 or 2. The sludge storage tank is divided into a plurality of tanks so that the activated sludge can move between adjacent tanks, and the flow of the activated sludge between the plurality of tanks is configured as a plug flow.
The waste water treatment system according to any one of claims 1 to 3. A wastewater treatment method in which wastewater flowing into an activated sludge tank is biologically treated by decomposing pollutants in the wastewater with activated sludge, and separated into treated water and activated sludge purified by the biological treatment,
A storage step of storing the separated activated sludge in an aerated state in a sludge storage tank;
In the sludge adsorption tank into which the activated sludge stored in the sludge storage tank and the waste water before flowing into the activated sludge tank flow, the pollutants in the waste water are adsorbed to the activated sludge flowing in from the sludge storage tank. An adsorption process,
A discharge step of discharging activated sludge adsorbing the pollutant in the waste water,
Wastewater treatment method.

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