JP5990069B2 - Waste water treatment method and waste water treatment system - Google Patents

Description

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

  Wastewater discharged from food factories, hotels, restaurants, kitchens, etc. contains organic substances such as animal and vegetable oils and fats attached to kitchen equipment and tableware. It is difficult to satisfy the emission standards of the sewage law.

  Therefore, an oil separation tank called a grease trap is usually installed near each wastewater discharge source, and the oil is drained after removing the oil so as to satisfy the drainage standard value set before discharging into sewage.

  The grease trap is a facility that floats and separates the oil component due to the specific gravity difference between the oil component contained in the wastewater and the wastewater, and therefore does not have the ability to purify organic matter dissolved in the wastewater. Therefore, the grease trap alone may not satisfy the drainage standard, and in that case, the wastewater treated with the grease trap is often further microbially treated and then discharged into sewage or public water areas.

  Industrial wastewater treatment equipment that treats oil-bearing wastewater discharged from food factories, hotels, restaurants, kitchens, kitchens, etc., is equipped with a pressurized flotation separator or an oil adsorption mat, and discharges oil that has floated. Alternatively, oil is adsorbed on an oil adsorption mat and the mat is periodically replaced.

  In addition, the household wastewater treatment equipment includes an anaerobic filter bed tank and a contact aeration tank. The anaerobic filter bed tank decomposes organic matter in the wastewater with anaerobic bacteria generated on the filter medium surface, and then The wastewater is purified by oxidizing it with the biofilm in the contact aeration tank.

  However, when a pressurized flotation separator or an oil adsorption mat is used, the oil or mat must be collected in a bad odor environment generated from the separated oil or impurities. In addition, the oil and fat extracted by adsorbing to the mat cannot be discarded as it is, and must be incinerated or reprocessed.

  Furthermore, in food factories, hotels, restaurant kitchens, kitchens, etc., the flow rate of wastewater varies greatly depending on the time of day, so if there is wastewater that exceeds the capacity of the wastewater treatment device, oil-water separation cannot be performed sufficiently. In addition, when oils and fats flow into the biological treatment tank, decomposition by microorganisms becomes insufficient, and the quality of treated water and oil balls may be generated.

  In addition, in a household treatment apparatus, there is a problem that the degradation power of anaerobic bacteria is likely to vary due to fluctuations in the inflow of wastewater and changes in the treatment state, and the wastewater treatment apparatus does not function effectively. Furthermore, there is a problem that malodor is generated due to methane, hydrogen sulfide, mercaptan, etc. generated in the anaerobic filter bed tank.

  On the other hand, wastewater treatment that decomposes fats and oils by adding microorganisms with excellent oil decomposition characteristics to wastewater instead of pressurized flotation separators is also on the market, but it is difficult to manage microorganisms, and the added bacteria are not necessarily Since it does not always proliferate, the processing state tends to become unstable. Furthermore, the price of microorganisms with excellent oil decomposition characteristics is high and there is a need to add them continuously. In this way, due to technical problems and cost problems, the current situation is that they have not been fully spread.

  There is also a method of biological treatment after treating fat and oil in waste water with an oxidizing agent. (Patent Document 1)

  In the device described in Patent 1, purification of waste water is realized by oxidizing fats and oils with an oxidizing agent. However, in the apparatus described in Patent Document 1, since the oxidizing agent flows into the biological treatment unit, it is estimated that the oxidizing agent adversely affects the microorganisms and the processing performance deteriorates.

  In addition, there is a method of treating the oil-containing wastewater with ozone and then treating it with biological treatment. This method is a method of biologically treating oil after degrading the oil component with ozone to easily biodegrade.

JP 2004-351303 A JP 2009-90222 A JP-A-7-16589 Japanese Patent Laid-Open No. 9-248589 JP 2002-320990 A Japanese Patent Laid-Open No. 11-104614

  As described above, in the treatment of waste water, the activated sludge method is combined with techniques such as pressurized flotation separation of oil and low molecular weight of oil by ozone, and is used under various conditions. In the activated sludge method, microorganisms grow by using organic substances contained in wastewater as nutrients under the respective conditions, thereby forming a microflora suitable for treating the wastewater.

  However, in the case of schools, factories, etc., there are long holidays during the year-end and New Year holidays and summer, and the amount of wastewater decreases, so that microorganisms that use organic substances contained in the raw wastewater as nutrients cannot grow and microorganisms The flora changes. After a long vacation, the amount of drainage returns to its original state, but it takes time to return to the original microflora, so that there is a problem that appropriate microbial treatment cannot be performed during that time.

  In addition, it has also been proposed to make the treatment load equal to that in the normal state by putting digested sludge into the treatment tank during the holidays (Patent Document 3 and Patent Document 4). In this case, there is no problem as a nutrient source, but since the influent wastewater species changes, the microflora changes, and it takes time to return to the original state.

  Patent Document 5 proposes changing the amount of aeration between normal time and vacation time. Changing the amount of aeration according to the inflow load is generally performed, but in the case of a long vacation, the inflow load is very small, and dissolved oxygen may increase even if the aeration amount is reduced to the minimum. There is a limit to deal with changes in the amount of aeration. For example, if the amount of aeration is excessively reduced, sludge is precipitated, so that a minimum amount of aeration is required. Moreover, even if activated sludge can be maintained by changing the amount of aeration, the microflora will change as the inflow load decreases.

  Further, Patent Document 6 proposes that wastewater is stored in a large storage tank, drainage is supplied from the storage tank during a holiday, and a water amount equivalent to that in a normal time is input to the treatment tank. In order to realize the method of Patent Document 6, it is necessary to provide a large storage tank capable of storing the wastewater supplied at the time of vacation, and it is not realistic to apply it for a long vacation.

  Therefore, the present invention is a wastewater treatment technology that suppresses changes in the microflora at low load due to long-term suspension of the discharge source of organic wastewater, and can quickly return to the original treatment capacity when returning from low load. The purpose is to provide.

The present invention employs the following means in order to solve the above problems. That is, the wastewater treatment system according to the present invention is
A plurality of biological treatment tanks for storing organic wastewater to turbidize activated sludge and treating organic wastewater with microorganisms in the activated sludge;
A separation tank for separating the organic wastewater treated in the biological treatment tank into activated sludge and treated water;
A bypass passage for bypassing a part of the plurality of biological treatment tanks and allowing the organic wastewater to flow into the biological treatment tank or the separation tank;
A normal flow path for flowing the organic waste water into the separation tank through the plurality of biological treatment tanks;
Channel switching means for switching the channel of the organic waste water to the bypass channel or the normal channel;
A return path for sending the activated sludge separated in the separation tank to a biological treatment tank other than the bypassed biological treatment tank when the flow path of the organic wastewater is switched to the bypass path by the flow path switching means;
Equipped with.

  The flow path switching means may switch the flow path according to a load caused by the organic waste water.

  The flow path switching means may switch the flow path to a bypass path when the load due to the organic waste water is low, or to a normal time path when the load is normal.

  The return path sends the activated sludge separated in the separation tank to a biological treatment tank other than the bypassed biological treatment tank when the load due to the organic wastewater is low, and in the normal state, The activated sludge separated in the separation tank may be sent to the most upstream biological treatment tank among the plurality of biological treatment tanks.

  In the wastewater treatment system, the organic wastewater may flow through the plurality of biological treatment tanks and the organic wastewater treated in the upstream biological treatment tank may be treated in the downstream biological treatment tank.

  The wastewater treatment system may further include an ozone supply device that supplies ozone-containing gas to the biological treatment tank in which the organic wastewater is stored.

  The wastewater treatment system may further include an ozone supply device that supplies ozone-containing gas to the most upstream biological treatment tank among the plurality of biological treatment tanks.

  In the wastewater treatment system, the volume of the biological treatment tank that supplies the ozone-containing gas may be 1/100 or more of the total volume of the plurality of biological treatment tanks.

  The wastewater treatment system includes a pretreatment unit that removes oil from the organic wastewater, and causes the organic wastewater having a normal hexane extractant concentration of 500 mg / L or less to flow into the biological treatment tank. May be.

In the wastewater treatment system, the ozone supply device supplies the ozone-containing gas to the biological treatment tank in a normal state, and supplies the ozone-containing gas to the biological treatment tank in a low load state as compared to a normal state. It may be stopped at least.
Moreover, the wastewater treatment method according to the present invention includes:
In a plurality of biological treatment tanks, a process of microbial treatment by storing organic wastewater and turbidizing activated sludge;
Separating the organic wastewater treated in the biological treatment tank into activated sludge and treated water;
Flowing the organic waste water into the biological treatment tank or the separation tank through a bypass path that bypasses a part of the plurality of biological treatment tanks;
A step of allowing the organic wastewater to flow into the separation tank through a normal flow path to the plurality of biological treatment tanks;
Switching the flow path of the organic wastewater to the bypass path or the normal time path;
Sending the activated sludge separated in the separation tank to a biological treatment tank other than the bypassed biological treatment tank when the flow path of the organic wastewater is switched to the bypass path;
I do.

  The means for solving the problems in the present invention can be combined as much as possible.

  According to the present invention, wastewater treatment technology that suppresses changes in the microflora at low load due to long-term suspension or the like of the discharge source of organic wastewater, and can quickly return to the original treatment capacity when returning from low load Can provide.

It is a figure which shows schematic structure of a waste water treatment system. It is a figure which shows the comparison result of the waste water treatment system which concerns on this invention, and the waste water treatment system which isolate | separates an oil component by the conventional pressurization floating separation system. It is a figure which shows the comparison result of the waste water treatment system which performs the pretreatment by the conventional ozone, and the waste water treatment system which concerns on this invention. It is a table | surface which shows the relationship between the ratio of an ozone addition tank, and the ratio of the activity of activated sludge. It is a figure which shows the example (Example 1) which the waste water treatment system implemented the normal process cycle. It is a table | surface which shows the water quality from before the process by a wastewater treatment system to after a process. It is a figure which shows the example (comparative example 1) which the waste water treatment system processed the oil-containing waste water, without adding ozone. It is a figure which shows the flow of a process when a wastewater treatment system implements the process cycle at the time of low load in the idle period of a discharge source. It is a figure which shows the example (Example 2) which implemented the processing cycle at the time of a low load of a waste water treatment system. It is a figure which shows the flow of a process when a wastewater treatment system implements a normal process cycle in the idle period of a discharge source. It is a figure which shows the example (comparative example 2) which the waste water treatment system implemented the normal treatment cycle in the idle period. It is a figure which shows the flow of a process when a wastewater treatment system implements the process cycle at the time of low load in the idle period of a discharge source. It is a figure which shows the example (Example 3) which implemented the processing cycle at the time of low load of a waste water treatment system. It is a figure which shows the example (comparative example 2) which processed by bypassing the pressurization floating separator in the conventional pressurization separation system. It is a figure which shows the control system of a waste water treatment system.

  Hereinafter, an embodiment of a waste water treatment apparatus according to the present invention will be described with reference to the drawings. Note that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention to those unless otherwise specified. is not.

  FIG. 1 is a diagram illustrating a schematic configuration of a wastewater treatment system according to the present embodiment. The wastewater treatment system 10 is a system that purifies organic wastewater containing organic substances such as factory wastewater, domestic wastewater, kitchen wastewater, and sewage by biological treatment with activated sludge. Activated sludge is generally a collection of various microorganisms for purifying organic wastewater such as bacteria, fungi, algae, protozoa, rotifers, nematodes and the like. As described later, when activated sludge is turbid, for example, aerated and mixed in waste water, in a good state, the microorganisms form a lint-like aggregate of several millimeters (hereinafter also referred to as floc). When pollutants contained in organic wastewater are physically taken into these flocs and come into contact with microorganisms (hereinafter this phenomenon is also referred to as “adsorption”), the pollutants become nutrient sources (food) for microorganisms, Some inorganic salts are used for the metabolism of microorganisms, and organic wastewater is purified by oxidative decomposition and absorption separation of the pollutants. The treatment for purifying organic wastewater by the action of activated sludge in this way is hereinafter referred to as microbial treatment.

  The waste water treatment system 10 mainly includes a grease trap 11, a plurality of biological treatment tanks 12, 13, a precipitation tank (separation tank) 14, an aeration device 15, an ozone supply device 16, and the like. Moreover, the waste water treatment system 10 may include a control device. FIG. 15 is a diagram showing a control system by the control device 17. In FIG. 15, the connection relationship between the control target element such as a valve and the control device 17 is indicated by a dotted line. In FIG. 15, some reference numerals are omitted mainly to show the control system.

  The grease trap 11 temporarily stores an organic wastewater before treatment introduced from an inflow pipe (not shown), floats the oil due to the specific gravity difference between the oil contained in the wastewater and the wastewater, and before roughing the floated oil It is a processing unit. In addition to this, the pretreatment unit may be one that removes impurities and adjusts the flow rate.

The biological treatment tanks 12 and 13 treat waste water using microorganisms, and can be used by combining one or more known aerobic treatments, anaerobic treatments or aerobic treatments and anaerobic treatments. The biological treatment tanks 12 and 13 are, for example, an aerobic tank (also referred to as an aeration tank, an activated sludge tank, a reaction tank), an anaerobic tank, an anaerobic filter bed tank, a contact aeration tank, a submerged membrane activated sludge tank (MBR), a carrier. A combination of one or more activated sludge tanks (fixed bed, carrier flow) and the like.

  In the wastewater treatment system 10 of the present embodiment, ozone is added to at least one of a plurality of biological treatment tanks, and the biological treatment tank to which ozone is added is referred to as an ozone addition tank. In the example of FIG. 1, the wastewater treatment system 10 includes two ozone addition tanks 12 and biological treatment tanks 13. Not limited to this, the waste water treatment system 10 may include three or more biological treatment tanks. Further, in the example of FIG. 1, the ozone addition tank 12 is provided on the upstream side and the biological treatment tank 13 is provided on the downstream side of the ozone addition tank 12 in the direction in which the organic drainage is normally flowed. Although the example which connected in series was shown, it is good also as a structure which connected the several biological treatment tank in parallel, or the structure which connected the biological treatment tank connected in series in parallel.

  The organic waste water is supplied from the grease trap 11 to the ozone addition tank 12 through the pipe 23 by the pump 22. Activated sludge containing aerobic microorganisms that decompose organic wastewater supplied from the grease trap 11 is input to the ozone addition tank 12, and the organic wastewater that has flowed in is decomposed by microorganisms in the activated sludge. Is done.

  Organic wastewater treated in the ozone addition tank 12 is supplied to the biological treatment tank 13 through a pipe 25 by a pump 24. The biological treatment tank 13 is loaded with activated sludge containing aerobic microorganisms that mainly decompose organic wastewater supplied from the ozone addition tank 12, and the inflowed organic wastewater is microorganisms in the activated sludge. It is decomposed by.

  The ozone addition tank 12 and the biological treatment tank 13 are provided with an aeration device 15 for aeration mixing organic wastewater with activated sludge in order to maintain an aerobic environment. The aeration apparatus 15 includes an aeration blower 51, an aeration diffuser tube 52, and an aeration passage 53. The aeration diffuser pipe 52 is disposed at the bottom of the ozone addition tank 12 and the biological treatment tank 13 so as to be immersed in the organic waste water, and communicates with the aeration blower 51 via the aeration passage 53.

  In FIG. 1, one aeration diffuser pipe 52 is shown in the ozone addition tank 12 and two in the biological treatment tank 13 for convenience. However, the number is not limited to this, and the ozone addition tank 12 and the biological treatment tank 13 are not limited to this number. What is necessary is just to arrange | position a required number according to an area or a volume. The aeration passage 53 is branched from the middle into an aeration branch passage 53a corresponding to each aeration diffuser tube 52, and each aeration branch passage 53a is sent from the aeration blower 51 to the corresponding aeration diffuser tube 52. Supplying air (hereinafter referred to as “aeration air”).

  Of the aeration passage 53, a portion upstream of the branching portion to each aeration branch passage 53a is referred to as an “aeration main passage 53b”. A valve 54 is provided between the aeration branch passage 53 a connected to the aeration diffuser pipe 52 provided in the ozone addition tank 12 and the aeration main passage 53 b, and is supplied to the ozone addition tank 12 by opening and closing the valve 54. The amount of aeration air to be adjusted is adjusted. In addition, a valve 55 is provided between the aeration branch passage 53 a connected to the aeration diffuser pipe 52 provided in the biological treatment tank 13 and the main aeration passage 53 b, and the biological treatment tank 13 is opened and closed by opening and closing the valve 55. The amount of aeration air supplied is adjusted. In addition, in FIG. 1, although it was set as the structure which supplies the aeration air to the ozone addition tank 12 and the biological treatment tank 13 from one aeration blower 51, it is not restricted to this, for example, respectively to the ozone addition tank 12 and the biological treatment tank 13 An aeration apparatus is provided, and the amount of aeration air supplied to the ozone addition tank 12 and the biological treatment tank 13 can be controlled independently by controlling the amount of air supplied by the aeration blower in each aeration apparatus. May be. The valves 54 and 55 may be manual valves or electromagnetic valves. However, when the control device 17 automatically controls opening and closing, the electromagnetic valves may be used.

  The aeration diffuser tube 52 has a large number of small-diameter diffuser holes for aeration of the aeration air sent from the aeration blower 51 into the organic waste water. When aeration air (oxygen) is supplied into the ozone addition tank 12 or the biological treatment tank 13 from the aeration holes of the aeration pipe 52, microorganisms contained in the activated sludge explosively by the supply of oxygen (aeration). Breeding and breeding will promote biodegradation of pollutants contained in organic wastewater. In addition, the activated sludge floc that causes the organic wastewater to flow while the aeration air diffused at the bottom of the ozone addition tank 12 or the biological treatment tank 13 floats in the organic wastewater and entrains the activated sludge is organic. The microbial treatment such as decomposition of the pollutant is continued in a good state by turbidity in the effluent, that is, aeration and mixing.

  Further, in the wastewater treatment system 10, a small amount of ozone is added to the organic wastewater in the ozone addition tank 12 in order to reduce the oil content that could not be removed by the grease trap 11 and facilitate decomposition by biological treatment. It is supplied (added) by the supply device 16. Moreover, activation of activated sludge and suppression of filamentous fungal growth are achieved by the addition of ozone. The ozone supply device 16 includes a compressor 61, a dehumidifier 62, an ozone generator 63, an ozone diffuser pipe 64, an ozone system pipe 65 (ozone system passage) connecting these components, and the like.

The air compressed (pressurized) by the compressor 61 is introduced into the dehumidifier 62 through the ozone system pipe 65 to be dehumidified (dehumidified). Thus, the pressurized (compressed) and dehumidified (dehumidified) air is supplied to the ozone generator 63 as raw air (gas) for generating ozone. Moreover, the raw material air supplied to the ozone generator 63 is pressurized to, for example, about 0.4 to 0.8 Mpa, and dehumidified to a dew point temperature of about −40 ° C. to −70 ° C., for example. It may be. The above is an example in which an air source type ozone generator is used as the ozone generator 63, but an oxygen source type ozone generator may be used.

  In this way, when the raw material air that has been pressurized and dehumidified is introduced to the ozone generator 63 through the ozone system pipe 65, ozone is generated in the ozone generator 63. As the ozone generator 63, various known methods can be employed, and for example, a discharge method, an ultraviolet irradiation method, or the like can be suitably employed. The ozone generated in the ozone generator 63 is supplied with ozone-containing gas formed together with the remaining raw material air to the ozone diffuser pipe 64 through the ozone system pipe 65.

  Like the aeration diffuser 52, the ozone diffuser 64 is arranged at the bottom of the ozone addition tank 12 so as to be immersed in organic waste water. In the illustrated example, only one ozone diffusion pipe 64 is shown in the ozone addition tank 12 for convenience, but a plurality of ozone diffusion pipes 64 may be arranged according to the size and volume of the ozone addition tank 12. When a plurality of ozone diffuser pipes 64 are arranged, that is, the ozone system pipe 65 is branched from the middle to the ozone system branch pipes 65a corresponding to the ozone diffuser pipes 64, and the respective ozone system branch pipes. The ozone-containing gas is supplied to the ozone diffuser 64 corresponding to 65a. In addition, in the ozone system pipe 65, a portion upstream of a branching portion to each ozone system branch pipe 65a is referred to as an “ozone system main pipe 65b”. The ozone diffusing tube 64 may be installed at a depth at which ozone is sufficiently dissolved until it floats on the nest surface, and is not necessarily installed at the bottom of the ozone addition tank 12.

  Further, the ozone air diffuser 64 has a large number of fine air diffuser holes that are finer than the air diffuser holes of the aeration air diffuser 52. As a material of the ozone diffusing tube 64, for example, ceramics having excellent ozone resistance and a fine porous structure can be suitably used.

  In the ozone diffuser 64 configured in this way, ozone-containing gas (ozone-containing air) containing ozone sent from the ozone generator 63 is diffused as ultrafine bubbles into the organic waste water through the air holes. The

  The ozone supply device 16 further includes a control unit 66 that is a control unit for controlling the ozone generator 63. The control unit 66 is connected to the ozone generator 63 via electric wiring, and controls the ozone generator 63 according to the quality of the organic waste water and the amount of water in the ozone addition tank 12. And the control part 66 may stop the operation | movement of the ozone generator 63 temporarily, for example, when the organic waste water which should be processed is no longer supplied to the ozone addition tank 12, or decreases. The control content of the ozone generator 63 by the controller 66 includes the ozone generation amount (output) according to the processing load in addition to the intermittent control (ON-OFF control) of the ozone generator 63 as described above. Variable capacity control can also be included.

  The organic waste water biologically treated in the biological treatment tank 13 is taken in by the pump 31 and transferred to the sedimentation tank 14 by the transfer pipe 32.

The sedimentation tank 14 retains the organic wastewater treated in the biological treatment tanks 12 and 13 for a predetermined time, and separates it into natural sludge activated sludge and supernatant treated water. The separation of activated sludge and treated water is not limited to natural precipitation, and other methods such as precipitation of activated sludge using a flocculant or solid-liquid separation using an immersion membrane may be used.

The separated treated water is drained out of the system from the water distribution pipe 42. On the other hand, the activated sludge precipitated in the settling tank 14 is returned to the ozone addition tank 12 by the pump 44 through the return pipe 43. The surplus activated sludge can be discharged out of the system as drawn sludge by opening the valve 46 of the branch pipe 45.

  As described above, the wastewater treatment system 10 of the present embodiment performs treatment by circulating organic wastewater in the order of the grease trap 11 → the ozone addition tank 12 → the biological treatment tank 13 → the precipitation tank 14 in a normal treatment cycle. .

However, if the source of organic wastewater is a factory, school, etc. and is a facility that is suspended for a long period of time during the year-end and New Year holidays, summer, etc., the amount of organic wastewater discharged will be drastically reduced, that is, low load When the wastewater treatment system 10 performs a normal treatment cycle in this low load state, the contaminants that the microorganisms in the activated sludge feed becomes insufficient, and the activity of the microorganisms in the biological treatment tank decreases. The state of activated sludge flocs deteriorates. In addition, the microflora changes. For this reason, after the rest period is over, the microflora returns to its original state, and it takes a long time to return to the original processing capacity. For example, it takes about twice as long as SRT (Sludge retention time) to return to the original microflora. In order to avoid a decrease in sludge activity during long-term suspension, inexpensive nutrients such as molasses may be added, but if nutrients with components different from actual wastewater are added, the proportion of microorganisms that prefer the nutrients will be normal More than the proportion of microorganisms suitable for the quality of wastewater, the microflora changes. Therefore, the period until the original microbiota is restored after the long vacation is over is shorter than the case where no nutrient is added, but it may take a long time. In addition, adding nutrients only for the growth of microorganisms is wasteful in cost, and adding too much will degrade the quality of the treated water, so it will be kept to the minimum necessary and the effect of shortening the recovery period will be limited. It is.

  Therefore, the wastewater treatment system 10 of the present embodiment employs a treatment cycle in which a part of the treatment tanks is bypassed and the microorganism treatment is performed as a treatment cycle at a low load. For example, the wastewater treatment system 10 performs the treatment by circulating the organic wastewater in the order of the grease trap 11 → the ozone addition tank 12 → the precipitation tank 14 in the treatment cycle at a low load. In order to bypass the biological treatment tank 13 in this way, the wastewater treatment system 10 branches the pipe 25 for discharging the organic wastewater treated in the ozone addition tank 12, and the organic wastewater is separated from the ozone addition tank 12 at a normal time. A normal branch pipe 25a that discharges to the biological treatment tank 13 and a bypass branch pipe (bypass path) 25b that bypasses the biological treatment tank 13 and discharges organic wastewater from the ozone addition tank 12 to the precipitation tank 14 when the load is low. Prepare.

  The normal branch pipe 25a is provided with an automatic valve V3 such as an electromagnetic valve, the bypass branch pipe 25b is provided with an automatic valve V4, and the controller 17 controls the opening and closing of the automatic valves V3 and V4. Change the destination of the organic wastewater treated in step 1. In the present embodiment, the automatic valve is not limited to a solenoid valve, and any automatic valve may be used as long as it can automatically switch the water in the flow path to a flow state or a stop state by control. May be.

  The control device 17 is an information processing device (computer) including a CPU, a memory, an input / output unit, and the like. The control device 17 detects the flow rate and BOD value of the organic wastewater flowing into the wastewater treatment system 10 by a sensor (not shown), inputs the suspension period (schedule) of the discharge source of the organic wastewater in advance, Based on the comparison or the input of an operation instruction by the operator, it is determined whether the state is a normal state or a low load state.

  When the normal state is determined, the control device 17 opens the automatic valve V3 and closes the automatic valve V4, and the normal flow path, in this embodiment, the grease trap 11 → the ozone addition tank 12 → the normal branch pipe 25a as described above. → Organic wastewater is circulated through the biological treatment tank 13 → transfer pipe 32 → precipitation tank 14 and a normal treatment cycle is performed.

  On the other hand, when it determines with a low load state, the control apparatus 17 opens the automatic valve V4, closes the automatic valve V3, supplies the organic waste water processed with the ozone addition tank 12 to the precipitation tank 14, The separated treated water is discharged from the water distribution pipe 42. That is, the wastewater treatment system 10 is configured to circulate the organic wastewater in the order of the grease trap 11 → the ozone addition tank 12 → the bypass branch pipe (bypass path) 25 b → the sedimentation tank 14 during the suspension period of the organic wastewater discharge source. Perform the processing cycle under load. At this time, the control device 17 may control the aeration device 15 and the ozone supply device 16 based on the load due to the organic waste water, and may control the amount of ozone supplied to the ozone addition tank 12 and the amount of aeration air.

  When the discharge source pause period ends and the load due to organic drainage returns, the control device 17 opens the automatic valve V3 and closes the automatic valve V4, and the wastewater treatment system 10 returns to the normal treatment cycle. In the above example, the control device 17 controls the automatic valves V3 and V4 to switch the organic drainage channel between the normal channel and the bypass channel. That is, in the above example, the control device 17 and the automatic valves V3 and V4 function as switching means. The switching means is not limited to the one that automatically switches the flow path by the control device 17, but includes a manual valve instead of the automatic valves V3 and V4, and the operator manually opens and closes the flow path. A configuration for switching may be used.

  As described above, the wastewater treatment system 10 of the present embodiment is a treatment tank that bypasses some of the treatment tanks (biological treatment tanks 13) out of the plurality of treatment tanks (12, 13) and performs microbial treatment when the load is low. By performing an operation (hereinafter referred to as a degenerate operation) with a reduced number of (ozone addition tanks 12), the activity of the microflora can be maintained even in a low load state where there are few nutrient sources for microorganisms. When the load due to the organic wastewater is restored and the wastewater treatment system 10 returns to the normal treatment cycle, the activated sludge in which the original microbial flora is maintained from the ozone addition tank 12 together with the organic wastewater to the biological treatment tank. 13, the original microflora is quickly formed from the activated sludge, and can quickly return to the original processing capacity. That is, when a normal treatment cycle is performed at a low load and the microbial flora of all activated sludge changes, it takes time to return to the original microbial flora, whereas the wastewater treatment system 10 of the present embodiment. Can maintain the original microbial flora even with a small amount of activated sludge, and when returning to the normal state, microorganisms grow using the activated sludge as a so-called inoculum so that the original microbial flora can be formed quickly.

  Moreover, the waste water treatment system 10 of this embodiment is not restricted to bypassing the biological treatment tank 13 at the time of low load, but can also bypass the ozone addition tank 12. For this reason, the waste water treatment system 10 branches a pipe 23 for supplying organic waste water from the grease trap 11, and a normal branch pipe 23 a for discharging the organic waste water from the grease trap 11 to the ozone addition tank 12 at normal times, and a low load. A bypass branch pipe (bypass path) 23b that sometimes bypasses the ozone addition tank 12 and supplies the biological treatment tank 13 is provided.

  The normal branch pipe 23 a is provided with an automatic valve V 1 such as an electromagnetic valve, the bypass branch pipe 23 b is provided with an automatic valve V 2, and the controller 17 controls the opening and closing of the automatic valves V 1 and V 2. The treatment tank (ozone addition tank 12 or biological treatment tank 13) for supplying waste water is switched.

  Furthermore, the wastewater treatment system 10 of the present embodiment branches a return pipe 43 that returns activated sludge precipitated in the settling tank 14, a return branch pipe 43 a that returns the returned sludge to the ozone addition tank 12, and return sludge. Is provided to the biological treatment tank 13. The return branch pipe 43a is provided with an automatic valve V5 such as an electromagnetic valve, the return branch pipe 43b is provided with an automatic valve V6, and the control device 17 controls the opening and closing of the automatic valves V3 and V4 to return the return sludge. Switch.

The control device 17 determines whether it is in a normal state or a low load state, and when it is determined as a normal state, the automatic valves V1 and V3 are opened and the automatic valves V2 and V4 are closed. As described above, the organic waste water is circulated through the grease trap 11 → normal branch pipe 23a → ozone addition tank 12 → normal branch pipe 25a → biological treatment tank 13 → transfer pipe 32 → precipitation tank 14 to perform a normal treatment cycle.

  On the other hand, if it is determined that the load is low, the control device 17 opens the automatic valve V2, closes the automatic valve V1, bypasses the ozone addition tank 12, and passes the organic waste water from the grease trap 11 to the biological treatment tank 13. The organic waste water supplied and treated in the biological treatment tank 13 is supplied to the settling tank 14, and the treated water separated in the settling tank 14 is discharged from the water distribution pipe 42. That is, the wastewater treatment system 10 is configured to discharge the organic wastewater in the order of the grease trap 11 → bypass branch pipe (bypass path) 23 b → the biological treatment tank 13 → the transfer pipe 32 → the sedimentation tank 14 during the suspension period of the organic wastewater discharge source. Distribute and perform processing cycle at low load. At this time, the control device 17 may control the aeration device 15 based on the load due to the organic waste water, and may control the amount of aeration air supplied to the biological treatment tank 13. The control device 17 opens the automatic valve V6, closes the automatic valve V5, and returns the return sludge separated in the sedimentation tank 14 to the biological treatment tank 13 via the return branch pipe 43b by the pump 44.

  When the discharge source pause period is over and the load due to organic wastewater is restored, the control device 17 opens the automatic valves V1 and V5 and closes the automatic valves V2 and V6. Return to the cycle. In the above example, the control device 17 controls the automatic valves V1 and V2 to switch the organic drainage channel between the normal channel and the bypass channel. That is, in the above example, the control device 17 and the automatic valves V1 and V2 function as switching means.

  In this case as well, the wastewater treatment system 10 can maintain the activity of the microflora in the biological treatment tank 13 by reducing the number of treatment tanks that perform microbial treatment at a low load. When returning, since the microorganisms grow based on the maintained microflora, it is possible to quickly return to the original processing capacity.

  The wastewater treatment system 10 of this embodiment is configured to have two bypass passages, a bypass branch pipe 25b and a bypass branch pipe 23b, to bypass the ozone addition tank 12 or the biological treatment tank 13, but the bypass path is one. One of the ozone addition tank 12 and the biological treatment tank 13 may be bypassed. For example, the bypass path is only the bypass branch pipe 25b and the biological treatment tank 13 is bypassed.

  The characteristics of the wastewater treatment system 10 according to the first embodiment described above (hereinafter also referred to as the present system 10) will be described below in comparison with a conventional system.

  FIG. 2 shows a comparison result between the present system 10 and a wastewater treatment system (hereinafter also referred to as a conventional pressure separation system) that separates oil components by a conventional pressurized flotation separation method.

  As shown in FIG. 2, in the oil content processing method, the present system 10 readily biodegrades the oil content turbid in the wastewater after being treated with the grease trap 11, whereas the conventional pressure separation system is the floating separation. Remove with.

  In addition, with regard to the amount of sludge generated, in the present system 10, about half of the inflow oil becomes sludge, that is, the amount of self-oxidation due to biological treatment is reduced. A large amount of sludge is generated. Regarding the odor, the present system 10 has a weak to medium microbial odor, whereas the conventional pressure separation system has a strong odor when removing oil.

  Regarding the influence on biological treatment, the present system 10 biologically treats readily biodegradable oil, so that the load in biological treatment is large and the volume of the biological treatment tank needs to be increased. Then, since the oil is removed, the load on the biological treatment tank is reduced.

  That is, the present system 10 has the merit that the amount of sludge generation and odor is less than the conventional system that separates the oil component under pressure, and has the demerit that the volume of the biological treatment tank needs to be increased. If the volume of the biological treatment tank is increased, the adverse effects on the microflora at low loads will increase, and the period (return period) from when the load returns to the normal state until it returns to the original processing capacity may be longer. Since the waste water treatment system 10 of this embodiment performs degeneracy operation at the time of low load, even if the volume of a biological treatment tank is enlarged, a return period does not become long. On the other hand, in the conventional pressure separation system, a flocculant is added to remove the oil, so that a large amount of sludge is generated. In addition, since the kitchen wastewater contains a surfactant that hinders the effect of the flocculant, it is necessary to add a large amount of flocculant, leading to an increase in cost.

  FIG. 3 shows a comparison result between the present system 10 and a wastewater treatment system that performs pretreatment with conventional ozone (hereinafter also referred to as a conventional ozone treatment system).

  Conventionally, as a method for treating organic wastewater containing oil discharged from kitchens or the like (also referred to as oil-containing wastewater), a conventional ozone treatment system in which oil-containing wastewater is pretreated with ozone and then treated with biological treatment is known. ing. This conventional ozone treatment system performs biological treatment after degrading an oil component with ozone to easily biodegrade it.

  As shown in FIG. 3, the system 10 is a biological treatment tank (ozone addition tank 12) that performs microbial treatment on the place where ozone is added, whereas the conventional ozone treatment system does not perform treatment with microorganisms. This tank is dedicated to ozone addition.

Regarding the amount of ozone, this system 10 adds a small amount of ozone within the range where the activity of microorganisms in the biological treatment tank is improved, while the conventional ozone addition dedicated tank 12 is added to the ozone addition dedicated tank, so the influence on microorganisms is considered. A relatively large amount of ozone is added as necessary to solubilize the oil. According to Japanese Patent Laid-Open No. 2006-314911, the range in which the activity of microorganisms is improved is 0.0005X to 0.15X [g] (X: organic inflow load concentration (BOD [g] / L] + organic SS [g / L]).

  Regarding the influence on microorganisms, the present system 10 improves the activity of microorganisms, whereas the conventional ozone treatment system has no change in microorganisms.

  Regarding the volume of the water tank, the present system 10 adds ozone to the biological treatment tank, so that a separate ozone addition tank is unnecessary and the microbial activity is improved. A dedicated water tank is required separately from the biological treatment tank, and since the microbial activity does not change, a biological treatment tank of a normal size is necessary.

  That is, the present system 10 needs to consider the influence on microorganisms when adding ozone as compared with the conventional ozone treatment system, but it is not necessary to prepare a dedicated tank for adding ozone separately, and the biological treatment tank is also small. There is a merit that you can.

  It is desirable to add ozone to the most upstream biological treatment tank among the plurality of biological treatment tanks. The upstream side is rich in contaminants that serve as nutrients for the microorganisms, so that the microorganisms are proliferated and activated. Adding ozone to the proliferated and activated microorganisms provides a higher activation effect. In the case of treating oil-containing wastewater, since the oil component is readily biodegraded on the most upstream side and flows to the downstream tank, the upstream biological treatment tank (the ozone addition tank 12 of the present embodiment), Any of the downstream biological treatment tanks (the biological treatment tank 13 of the present embodiment) can be efficiently decomposed by microorganisms.

  In addition, the system 10 requires an extra volume of the biological treatment tank because the load on the biological treatment is increased by the amount of oil that has been readily biodegraded as compared with the conventional pressure separation system. However, the wastewater treatment capacity of the microorganism treatment unit is improved by 20 to 30% due to the addition of ozone as compared with the activated sludge not added with ozone. Therefore, the required water tank volume is obtained by calculating the volume that increases due to the BOD amount increased by the readily biodegradable oil and the volume that can be decreased by adding ozone.

  The volume of the ozone addition tank 12 is 1/100 (1%) or more of the total biological treatment tank volume. This is because the effect of improving microbial performance cannot be obtained unless the volume of the ozone addition tank 12 is 1/100 or more of the total biological treatment tank 12, 13 volume. If the volume of the ozone addition tank 12 is smaller than this lower limit value, only some of the microorganisms come into contact with ozone, and the microorganisms are inactivated.

  FIG. 4 is a table showing the relationship between the volume ratio of the ozone addition tank and the activity ratio of the activated sludge. Here, the activity of activated sludge is indicated by the oxygen consumption rate (mg / l · h), and the rate of activity means that the oxygen consumption rate of activated sludge in a biological treatment tank not added with ozone is 100%, and the ozone addition tank for this. Is the rate of oxygen consumption rate of activated sludge in The oxygen consumption rate is indicated by the amount of oxygen consumed by a unit volume of the activated sludge mixed solution within a unit time, and can be measured by a known oxygen consumption rate measuring device. As shown in FIG. 4, when the ratio of the volume of the ozone addition tank to the whole biological treatment tank was 100%, the ratio of the activated sludge activity in the ozone addition tank was 135%. When the ratio of the volume of the ozone addition tank to the whole biological treatment tank decreases, the ratio of the activated sludge activity decreases, and when the ratio of the volume of the ozone addition tank to the whole biological treatment tank is 1%, the activated sludge of the ozone addition tank The percentage of activity was 102%. And when the ratio of the volume of the ozone addition tank with respect to all the biological treatment tanks was 0.5%, the ratio of the activity of the activated sludge of an ozone addition tank was 85%. For this reason, the lower limit of the volume of the ozone addition tank 12 is 1/100 (1%) of the total biological treatment tank volume as described above. If it is more than this lower limit, the volume of the ozone addition tank 12 may be a volume corresponding to the amount of drainage during the rest period.

  Moreover, it is better to provide the ozone addition tank separately from the biological treatment tank not containing ozone. This is because the ozone addition tank is preferably made of an ozone-resistant material, and it is preferable to provide additional equipment such as a lid, an exhaust facility, and a waste ozone treatment facility in consideration of ozone leakage. Therefore, the smaller the ozone addition tank, the smaller the additional equipment and the lower the cost. However, 1/100 of the total biological treatment tank volume is the lower limit.

  Moreover, this system can be applied to an existing wastewater treatment system without modifying the existing biological treatment tank by providing the ozone addition tank separately from the biological treatment tank not containing ozone.

  For example, an existing conventional pressure separation system can be modified to provide the wastewater treatment system 10 of the present embodiment. When the conventional pressure separation system is changed to the present system 10, the pressure floating separation device of the conventional pressure separation system is removed, and instead, the ozone addition tank 12, the ozone supply device 16, the bypass passages 23b and 25b, Attached equipment such as valves inside

  As described above, the conventional pressure separation system has a large amount of sludge generation and has problems such as bad odor. However, by changing to the present system 10, it is possible to reduce bad odor and reduce sludge generation amount.

<Example 1>
FIG. 5 is a diagram illustrating an example (Example 1) in which the wastewater treatment system 10 performs a normal treatment cycle. In FIG. 5, the waste water treatment system 10 is schematically shown, and the flow of organic waste water or the like is indicated by arrows.

In Example 1, valves V1, V3 and V5 were opened, valves V2, V4 and V6 were closed, and 10 m ³ of organic waste water (oil-containing waste water) per day was operated for 1 month in a normal treatment cycle. That is, after the oil-containing wastewater is treated with the grease trap 11, ozone is added in the ozone addition tank 12 for biological treatment, further biological treatment is performed in the biological treatment tank 13, and the treated water flows into the sedimentation tank 14 to make sludge. And the treated water were separated, the treated water was discharged, and the sludge was returned to the ozone addition tank 12. As a result, the water quality shown in FIG. 6 was obtained.

That is, according to the wastewater treatment system 10 of Example 1, the oil-containing wastewater having a BOD of 1000 [mg / L] and an n-HEX extract material of 800 [mg / L] at the grease trap 11 inlet, The treated water discharged from the sedimentation tank 14 has a BOD of 12 [mg / L] and an n-HEX extract of 5 [mg / L], which is appropriate so that it meets the discharge standards of the Water Pollution Control Law and the Sewerage Law. You can see that it is being processed.
<Comparative example 1>
FIG. 7 is a diagram showing an example (Comparative Example 1) in which the wastewater treatment system 10 treats oil-containing wastewater without adding ozone.

In Comparative Example 1, as in FIG. 5, the valves V1, V3, V5 were opened, the valves V2, V4, V6 were closed, and 10 m ³ of oil-containing wastewater per day was operated for one month with ozone stopped.
The water quality at the inlet of the grease trap 11 is the same as in the first embodiment. As a result, the sludge state of the biological treatment tanks 12 and 13 deteriorated, causing bulking, and the treatment became impossible.

This is because, in the biological treatment tanks 12 and 13 to which ozone is not added, the oil content becomes excessive, and for example, when the n-HEX extract is 100 [mg / L] or more, the treatment becomes difficult. In this comparative example 1, the n-HEX extract was 300 [mg / L] at the inlet of the ozone addition tank 12 as shown in FIG. 6, and the treatment was difficult when ozone was stopped.

  Thus, it can be seen from the comparison between Example 1 and Comparative Example 1 that the processing capacity of the oil-containing wastewater is improved in the present system 10 due to the addition of ozone. In this system, if the n-HEX extract is 500 [mg / L] or less at the inlet of the ozone addition tank 12, it can be processed.

<Example 2>
FIG. 8 is a diagram showing a flow of processing when the wastewater treatment system 10 performs a low load treatment cycle during a discharge source suspension period, and FIG. 9 shows an example in which the wastewater treatment system 10 performs a low load treatment cycle. (Example 2) It is a figure which shows.

In the second embodiment, the wastewater treatment system 10 first opens the valves V1, V3, V5 and closes the valves V2, V4, V6 as shown in FIGS. 8 and 9A, and 10 m ³ per day.
Organic wastewater (oil-containing wastewater) was operated for 1 month in a normal treatment cycle.

Then, assuming the time of ejection original resting, as shown in FIG. 8 and FIG. 9 (B), the the valve V1, V3, V4, V5 closed, and the valves V2, V6 open, daily 1 m ³ Organic The wastewater (oil-containing wastewater) was operated for 1 week in the treatment cycle at low load. During this time, the addition of ozone was stopped due to the low load of organic waste water.

  That is, after the oil-containing wastewater is treated with the grease trap 11, the ozone addition tank 12 is bypassed, the organic wastewater treated with the grease trap 11 is supplied to the biological treatment tank 13 and biologically treated, and the treated water is precipitated. The sludge and treated water were separated by flowing into the tank 14, the treated water was discharged, and the sludge was returned to the biological treatment tank 13.

And after a rest period, as shown in FIG.8 and FIG.9 (C), valve | bulb V1, V3, V5 is opened,
Valves V2, V4, and V6 were closed and returned to the normal treatment cycle, and 10 m ³ of organic wastewater (oil-containing wastewater) was treated per day. As a result, the processing capacity of the system 10 returned to its original state, and it took 3 days to obtain the water quality equivalent to that shown in FIG.

<Comparative example 2>
FIG. 10 is a diagram showing a flow of processing when the wastewater treatment system 10 performs a normal treatment cycle during the suspension period of the discharge source, and FIG. 11 is an example in which the wastewater treatment system 10 performs a regular treatment cycle during the suspension period ( It is a figure which shows the comparative example 2).

In the second comparative example, the wastewater treatment system 10 first opens the valves V1, V3, V5 and closes the valves V2, V4, V6 as shown in FIGS. 10 and 11A, and 10 m ³ per day. Organic wastewater (oil-containing wastewater) was operated for 1 month in a normal treatment cycle.

Next, assuming that the discharge source is at rest, as shown in FIG. 10 and FIG. 11 (B), 1 m ³ of organic waste water (oil-containing waste water) per day was operated for 1 week with a normal treatment cycle. During this time, the addition of ozone was stopped due to the low load of organic waste water.

Then, after the rest period, as shown in FIGS. 10 and 11C, 10 m ³ of organic wastewater (oil-containing wastewater) was treated per day in a normal treatment cycle. As a result, this system 1
The processing capacity of 0 returned to its original state, and it took 7 days to achieve the same water quality as in FIG.

  Thus, by comparing Example 2 and Comparative Example 2, the present system 10 maintains the microflora by bypassing the ozone addition tank 12 during the discharge source pause period and performing a low load treatment cycle. It can be seen that the recovery time can be shortened.

<Example 3>
FIG. 12 is a diagram showing a flow of processing when the wastewater treatment system 10 performs a low load processing cycle during a discharge source suspension period, and FIG. 13 shows an example in which the wastewater treatment system 10 performs a low load processing cycle. (Example 3) It is a figure which shows.

In the second embodiment, the wastewater treatment system 10 first opens the valves V1, V3, V5 and closes the valves V2, V4, V6 as shown in FIGS. 12 and 13A, and 10 m ³ per day. Organic wastewater (oil-containing wastewater) was operated for 1 month in a normal treatment cycle.

Then, assuming the time of ejection original resting, as shown in FIG. 12 and FIG. 13 (B), the valve V1, V4, V5 open, the valve V2, V3, V6 closed, per day 1 m ³ Organic The wastewater (oil-containing wastewater) was operated for 1 week in the treatment cycle at low load. During this time, the addition of ozone was stopped due to the low load of organic waste water.

  That is, after the oil-containing wastewater is treated with the grease trap 11, it is biologically treated with the ozone addition tank 12, and the organic wastewater treated with the ozone addition tank 12 bypassing the biological treatment tank 13 is caused to flow into the sedimentation tank 14, and sludge And the treated water were separated, the treated water was discharged, and the sludge was returned to the ozone addition tank 12.

Then, after the rest period, as shown in FIG. 12 and FIG. 13C, the valves V1, V3, V5 are opened, the valves V2, V4, V6 are closed, and the normal processing cycle is returned to 10 m ³ per day. Organic wastewater (oil-containing wastewater) was treated. As a result, the processing capacity of the system 10 returned to its original state, and it took 3 days to obtain the water quality equivalent to that shown in FIG.

Thus, by comparing Example 3 with Comparative Example 2, the present system 10 maintains the microflora by bypassing the biological treatment tank 13 during the suspension period of the discharge source and performing a treatment cycle at low load. It can be seen that the recovery time can be shortened.

<Comparative Example 3>
FIG. 14 is a view showing an example (Comparative Example 3) in which processing is performed by bypassing the pressurized floating separator in the conventional pressurized separation system.

In Comparative Example 3, 10 m ³ of organic wastewater (oil-containing wastewater) was allowed to flow into a conventional pressure separation system per day. Then, when the pressurized flotation separation device 120 is bypassed and directly flowed into the biological treatment tank 130, the quality of the treated water deteriorates and an oil ball is formed in the biological treatment tank 130, and then sludge is bulked. It can no longer be processed.

  After that, when the ozone addition tank 12 was provided in place of the pressurized flotation separation device 120 to form a system as shown in FIG. 9B, normal processing could be performed.

  The embodiment described above is an example for explaining the present invention, and various modifications can be made without departing from the spirit of the present invention. For example, in the present embodiment, the treatment of oil-containing wastewater has been mainly described, but the present invention can also be applied to the treatment of organic wastewater that does not contain oil. In addition, when processing the organic waste water which does not contain an oil component, the waste water treatment system 10 may abbreviate | omit the ozone supply apparatus 16 and the grease trap 11. FIG. Moreover, the ozone supply apparatus applied to the waste water treatment system according to the present invention is not limited to the embodiments and the embodiments, and can include combinations thereof as much as possible.

10 Wastewater treatment system 11 Grease trap 12 Ozone addition tank 13 Biological treatment tank 14 Precipitation tank (separation tank)
15 Aeration device 16 Ozone supply device 17 Control device

Claims (8)

A plurality of biological treatment tanks for storing organic wastewater to turbidize activated sludge and treating organic wastewater with microorganisms in the activated sludge;
A separation tank for separating the organic wastewater treated in the biological treatment tank into activated sludge and treated water;
A bypass passage for bypassing a part of the plurality of biological treatment tanks and allowing the organic wastewater to flow into the biological treatment tank or the separation tank;
A normal flow path for flowing the organic waste water into the separation tank through the plurality of biological treatment tanks;
Channel switching means for switching the channel of the organic waste water to the bypass channel or the normal channel;
A return path for sending the activated sludge separated in the separation tank to a biological treatment tank other than the bypassed biological treatment tank when the flow path of the organic wastewater is switched to the bypass path by the flow path switching means;
Among the plurality of biological treatment tanks, an ozone supply device that supplies an ozone-containing gas to the most upstream biological treatment tank;
Wastewater treatment system equipped with.   The waste water treatment system according to claim 1, wherein the flow path switching means switches the flow path to a bypass path when the load due to the organic waste water is low, and to a normal time path when the load is normal.   The return path sends the activated sludge separated in the separation tank to a biological treatment tank other than the bypassed biological treatment tank when the load due to the organic wastewater is low, and in the normal state, The wastewater treatment system according to claim 1 or 2, wherein the activated sludge separated in the separation tank is sent to the biological treatment tank on the most upstream side of the plurality of biological treatment tanks.   4. The organic wastewater treated in the upstream biological treatment tank is treated in the biological treatment tank in the downstream side by causing the plurality of biological treatment tanks to communicate and flowing the organic wastewater. 5. The described wastewater treatment system. The wastewater treatment system according to any one of claims 1 to 4, wherein a volume of the biological treatment tank for supplying the ozone-containing gas is set to 1/100 or more of a total volume of the plurality of biological treatment tanks. Includes a preprocessing section for removing oil from the organic wastewater, the pre-processing unit with n-hexane extracts the organic waste water was below 500 mg / L of substance concentration of claims 1 to flow into the biological treatment tank 5 The wastewater treatment system according to any one of the above. The ozone supply device supplies the ozone-containing gas to the biological treatment tank in a normal state, and reduces or stops the supply of the ozone-containing gas to the biological treatment tank in a low load state compared to a normal state. Item 6. The waste water treatment system according to any one of Items 1 to 5 . In a plurality of biological treatment tanks, a process of microbial treatment by storing organic wastewater and turbidizing activated sludge;
Separating the organic wastewater treated in the biological treatment tank into activated sludge and treated water;
Flowing the organic waste water into the biological treatment tank or the separation tank through a bypass path that bypasses a part of the plurality of biological treatment tanks;
A step of allowing the organic wastewater to flow into the separation tank through a normal flow path to the plurality of biological treatment tanks;
Switching the flow path of the organic wastewater to the bypass path or the normal time path;
Sending the activated sludge separated in the separation tank to a biological treatment tank other than the bypassed biological treatment tank when the flow path of the organic wastewater is switched to the bypass path;
Of the plurality of biological treatment tanks, supplying ozone-containing gas to the most upstream biological treatment tank;
Wastewater treatment method.

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