JP5947067B2 - Wastewater treatment system and method - Google Patents

Description

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

  The activated sludge process, which treats organic wastewater with activated sludge containing aerobic microorganisms, has advantages such as high purification capacity and relatively low processing costs, so various water treatment methods using the activated sludge method Has been proposed and widely used in sewage treatment and industrial wastewater treatment. In the activated sludge method, various organic wastewaters to be treated are guided to an aeration tank, and organic pollutant components in the wastewater are decomposed for purification treatment.

  In the activated sludge method, 50 to 70% of the decomposed organic matter is consumed as microbial maintenance energy, but the remaining 30 to 50% is used for the growth of bacterial cells, so the amount of activated sludge gradually increases. I will do it. For this reason, in general, the wastewater treated in the aeration tank is led to the sedimentation tank, and only the amount necessary for the purification treatment of organic wastewater from the precipitated activated sludge is returned to the aeration tank as return sludge. Since other activated sludge is processed as surplus sludge through processes such as concentration, digestion, dehydration, composting, and incineration, such treatment is costly and laborious.

  Therefore, as wastewater treatment technology that generates less sludge, a long-time aeration method that extends the sludge residence time in the aeration tank, a contact oxidation method that supports a large amount of sludge on the surface of the contact agent in the reaction tank, etc. have been proposed. It has been put into practical use.

  However, in these methods, it is necessary to prepare a large aeration tank in order to increase the sludge residence time. In the long-time aeration method, the activated sludge and the biofilm are deteriorated when the load is reduced, and the sludge is diffused, which impedes solid-liquid separation. Further, in the contact oxidation method, the generated sludge increases when the load increases, and clogging of the sludge may occur.

  Therefore, as a method for reducing the volume of generated sludge, after extracting the sludge from the aeration tank and performing ozone treatment, returning the sludge to the aeration tank and reducing the volume of the sludge (for example, see Patent Document 1-2), A sludge pretreatment method (for example, see Patent Document 3) in which sewage surplus sludge is oxidized and decomposed with ozone has been proposed. Further, a method has been proposed in which an ozone-containing gas is blown into and mixed with sludge mixed wastewater with an ejector disposed in an aerobic biological treatment tank (see, for example, Patent Document 4). Moreover, as a method for improving the biological treatment capacity while reducing the volume of generated sludge, a method of directly supplying ozone to the aeration tank has been proposed (see, for example, Patent Document 5).

  In the activated sludge method, the activated sludge discharged from the aeration tank is solid-liquid separated in a sedimentation tank, and the supernatant is drained. However, if the sedimentation property of activated sludge is poor, the sludge cannot be separated in the sedimentation tank, and the sludge is mixed with the supernatant water. Then, the method (Membrane separation activated sludge method: MBR) which filters with the film | membrane provided in the aeration tank is proposed. However, in the membrane separation activated sludge method, since clogging occurs, a large amount of aerated air is required for cleaning the membrane surface.

Therefore, in order to prevent clogging, a method has been proposed in which the reaction liquid is separated by a separation membrane while the activated sludge extracted from the activated sludge tank is subjected to ozone treatment and returned to the activated sludge tank again (for example, a patent). Reference 6). In addition, a method of directly supplying ozone to the immersion film has been proposed (see, for example, Patent Document 7). In addition, when using an immersion film, in order to prevent clogging, it is necessary to supply much air to an immersion film tank. Therefore, when ozone is directly supplied to the immersion film, the residence time of ozone in the liquid phase part of the immersion film tank is shortened, so a large amount of ozone that has not been dissolved is released into the gas phase part, and the utilization rate of ozone is reduced. .

Japanese Patent No. 2973761 JP 2003-126882 A JP-A-2-222798 JP 2001-259678 A JP 2006-314911 A JP-A-8-19789 JP 2001-62483 A

  In a situation where activated sludge is separated by membrane, clogging of the membrane can be prevented by adopting a method that separates the reaction liquid with membrane while applying ozone treatment to the activated sludge extracted from the activated sludge tank and returning it to the activated sludge tank again. Although it is possible, ozone is not directly supplied to the activated sludge, so the supplied ozone cannot contribute to improving the performance of the activated sludge. In addition, when adopting a method of directly supplying ozone to the immersion film, it is necessary to use a membrane or membrane module constituent member that is resistant to ozone, because ozone contacting the membrane deteriorates the membrane or membrane module constituent member. Sufficiently resistant membranes and membrane module components have not been put to practical use.

  The present invention has been made in view of such problems, and improves biological treatment capacity to improve wastewater treatment capacity, improve sludge settling by inhibiting the growth of filamentous fungi, prevent bulking damage, and increase the amount of sludge generated. It is an object of the present invention to provide a wastewater treatment system and method capable of achieving both ozone supply for volume reduction and prevention of sludge outflow by a membrane.

  In order to solve the above-mentioned problems, the present invention passes from an activated sludge tank having activated sludge to which ozone is added, in the middle of a route for sending organic waste water to an immersed film tank in which the immersed film is disposed in the tank. It was decided to provide a retention means for retaining the organic waste water for a predetermined time or more.

  Specifically, it is a wastewater treatment system for treating organic wastewater, and has activated sludge, and an activated sludge tank that biologically treats the flowing organic wastewater, and ozone is applied to the activated sludge in the activated sludge tank. In the middle of the path leading from the activated sludge tank to the immersion membrane tank, the ozone supply device to be added, the organic waste water sent from the activated sludge tank, the immersion membrane tank to be purified by the immersion film disposed in the tank The organic wastewater that is provided and sent from the activated sludge tank to the immersion membrane tank is retained for a predetermined time or more so that the ozone concentration of the organic wastewater that passes through the immersion membrane is less than or equal to the allowable ozone concentration of the immersion membrane. A retention means.

  If it is the said waste water treatment system, while the sludge of an activated sludge tank will be activated by addition of ozone, the volume reduction of generated sludge will be implement | achieved. Moreover, the ozone in the organic wastewater added in the activated sludge tank is retained for a predetermined time by the retaining means and removed from the organic wastewater. Therefore, the immersion film of the immersion film tank into which the organic waste water sent from the retention means flows is not deteriorated by ozone.

Here, the predetermined time is the time required for the organic wastewater that has flowed into the retention means to flow out of the retention means. For example, the ozone concentration of the organic wastewater that passes through the immersion film is the allowable ozone of the immersion film. This is the time for ozone removal performed until the organic wastewater sent from the activated sludge tank is sent to the submerged membrane tank, which is required until the concentration becomes lower than the concentration. Moreover, the retention of the organic waste water by the retention means does not stop the movement of the organic waste water but means that the flow of the organic waste water flowing from the activated sludge tank to the submerged membrane tank is delayed.

  The waste water treatment system is a sludge return device for returning the activated sludge of the immersion membrane tank to the retention means or a path through which the organic waste water on the upstream side of the retention means passes. When it is detected that the ozone concentration or oxidation-reduction potential of the organic waste water passing through has increased, it may further include a sludge return device that increases the return amount of the activated sludge or starts returning the activated sludge. .

  Since activated sludge has the effect of lowering the ozone concentration of organic wastewater, when it is detected that the ozone concentration or oxidation-reduction potential of organic wastewater that passes through the immersion membrane has increased, the retention means or upstream of the retention means By increasing the return amount of sludge to be returned to the path through which the organic waste water passes, or by starting the return of activated sludge, the ozone concentration of the organic waste water passing through the immersion membrane can be quickly reduced to reduce the immersion membrane. Can be protected. Note that when the ozone concentration or oxidation-reduction potential of the organic waste water passing through the immersion membrane is detected, the measurement is performed by measuring the ozone concentration or oxidation-reduction potential of the organic waste water passing through the immersion membrane. It is not limited to the mode of directly detecting the increase in ozone concentration or redox potential of organic wastewater that passes through the membrane, but the ozone concentration or redox potential of organic wastewater flowing upstream of the submerged membrane tank. It is a concept including an aspect of indirectly detecting an increase in ozone concentration or oxidation-reduction potential of organic wastewater passing through the immersion membrane by measuring. If the ozone concentration is low, the ozone concentration meter may not be able to properly measure the ozone concentration, but if the redox potential is measured, the ozone concentration can be indirectly detected.

  Further, the retention means is a tank that retains the organic wastewater sent from the activated sludge tank to the immersion membrane tank for the predetermined time or more, or the organic wastewater that is sent from the activated sludge tank to the immersion membrane tank. It may be a pipe having a length for retaining the gas for a predetermined time or more.

  If the staying means is such a tank or pipe, the organic waste water from which ozone has been removed in the tank or the pipe is sent to the immersion film tank, so that deterioration of the immersion film can be prevented.

  Further, the retention means retains the organic wastewater sent from the activated sludge tank to the immersion membrane tank for the predetermined time or more and remains in the organic wastewater sent from the activated sludge tank. It is a tank for precipitating sludge, and the waste water treatment system may further comprise a sludge return device for returning the activated sludge that settles in the tank of the retention means to the activated sludge tank.

  With such a staying means, the suspended matter in the organic waste water flowing into the immersion film tank is removed by the staying means, so that the immersion film is not clogged.

  The waste water treatment system may further include air supply means for blowing air continuously or intermittently into the immersion membrane tank. If such an air supply means is provided, the surface of the immersion film disposed in the immersion film tank is cleaned with air, so that the immersion film can be prevented from being clogged.

Further, the waste water treatment system is configured such that the exhaust from the activated sludge tank to which the ozone is added, the organic waste water retained in the retention means, and surplus sludge discharged from the waste water treatment system flows in. An air supply means for blowing into at least one of the sludge tanks may be further provided. If such an air supply means is provided, the ozone remaining in the exhaust gas of the activated sludge tank to which ozone is added is absorbed by the sludge of the retention means or the excess sludge tank, so that the ozone in the exhaust gas is purified. Ozone emission to the atmosphere can be prevented without using a dedicated purification device.

  The present invention can also be understood from the aspect of the method. For example, the present invention is a wastewater treatment method for treating organic wastewater, wherein the organic wastewater is biologically treated with an activated sludge tank having activated sludge to which ozone is added, and the organic wastewater is sent from the activated sludge tank. The organic wastewater to be purified by an immersion membrane tank in which an immersion membrane is disposed in the tank, and the organic wastewater sent from the activated sludge tank to the immersion membrane tank is passed through the immersion membrane. And a step of retaining for a predetermined time or more so that the ozone concentration of the effluent is equal to or less than the allowable ozone concentration of the immersion film.

  Improve biological treatment capacity to improve wastewater treatment capacity, improve sludge sedimentation and prevent bulking by controlling the growth of filamentous fungi, supply ozone for the purpose of reducing the volume of sludge generation, and prevent sludge from flowing out by membranes It is possible to achieve both. As a result, the wastewater can be filtered at a high treatment flow rate without deteriorating the membrane or the membrane module constituent member. In addition, it is possible to configure a system with a small site area, and to realize advanced wastewater treatment that does not leave solid matter in the discharged treated water.

It is a block diagram of the waste water treatment system which concerns on embodiment. It is the experimental data which showed the relationship between the residence time in a residence tank, and the dissolved ozone concentration of the organic waste water which flows out from a residence tank. It is a block diagram of the waste water treatment system which replaced the retention tank with the straight pipe which forms a water channel. It is the experimental data which showed the relationship between the ozone density | concentration of organic waste_water | drain, and MLSS when the residence time of a residence tank is 1 minute. It is an example of the experimental data which showed the relationship between the quantity of ozone added to organic waste water, and ORP. It is a block diagram of the waste water treatment system which provided the valve which opens and closes according to the measured value of a dissolved ozone concentration meter in the piping which supplies activated sludge to a retention tank. It is a block diagram of the waste water treatment system which concerns on a 1st modification. It is the figure which formed the anaerobic tank of the waste water treatment system which concerns on a 1st modification, and the activated sludge tank which is an aerobic tank in one tank. It is a block diagram of the waste water treatment system which concerns on a 2nd modification. It is a block diagram of the waste water treatment system which concerns on a 3rd modification. It is a block diagram of the waste water treatment system which concerns on a 4th modification.

  Hereinafter, embodiments of the present invention will be described. The embodiment described below exemplifies the embodiment of the present invention, and the technical scope of the present invention is not limited to the following embodiment.

  FIG. 1 shows a configuration of a wastewater treatment system according to an embodiment of the present invention. The wastewater treatment system 1 is a system for treating organic wastewater. The organic wastewater sent to the wastewater treatment system 1 flows in, the activated sludge tank 2 that functions as an aerobic tank, and the organic that has passed through the activated sludge tank 2. Retention tank 3 that retains the wastewater for a predetermined time, immersion membrane tank 4 into which the organic wastewater that has passed through the retention tank 3 flows, and sludge return device 5 that returns the activated sludge from the immersion membrane tank 4 to the activated sludge tank 2. With. The organic waste water is an aqueous medium containing organic matter that is purified by biological treatment with activated sludge. Examples of such organic wastewater include sewage, human waste, kitchen wastewater, food factory wastewater, and other industrial wastewater.

  The activated sludge tank 2 has activated sludge in the tank, and biologically processes the inflowing organic waste water. The activated sludge is activated sludge having an aerobic microorganism group used for biological treatment of organic wastewater, and an activated sludge composed of a normal aerobic microorganism group used for biological treatment of wastewater can be used. As the activated sludge tank 2, an aeration tank usually used in general wastewater treatment can be used. That is, the activated sludge tank 2 is provided with an air supply device 6A for supplying air for aeration of the organic waste water in the tank, and by sending air to the bottom of the activated sludge tank 2, Oxygen is supplied to activated sludge to activate aerobic microorganisms.

  Further, the activated sludge tank 2 is provided with an ozone supply device 7 for supplying ozone. By supplying ozone to the bottom of the activated sludge tank 2 with the ozone supply device 7, a small amount of ozone is added to the activated sludge. The activity of sludge is added to improve the treatment capacity and quality of the treated sludge tank 2. That is, a general aeration pipe is installed at the bottom of the activated sludge tank 2, and ozone is added to the activated sludge by aeration of ozone from the aeration pipe into the tank. The reason why sludge is activated when ozone is added is considered to be that when ozone is diffused in a small amount in the tank, microorganisms with low activity are sterilized and reduced by ozone, and microorganisms with high activity are oligopolized. In addition, when this inventor analyzed the DNA of the activated sludge which added ozone, it has confirmed that microflora changed by adding ozone.

  By adding ozone, the treatment capacity and quality of the activated sludge tank 2 can be improved, and the propagation of filamentous fungi can be suppressed to improve sludge sedimentation and prevent bulking damage. Reduction in sludge generation is achieved by increasing the amount of self-digestion due to improved activity and lysing some of the growing bacteria. That is, by adding ozone to the activated sludge tank 2, the activated sludge tank 2 is reduced in size, improved in adaptability to load fluctuations such as the quality and amount of waste water, and the volume of generated sludge is reduced. The amount of ozone added to the activated sludge is such that the effect of improving the treatment capacity and treated water quality of the activated sludge tank 2, the effect of preventing bulking failure, the effect of reducing sludge generation, etc. It is determined appropriately. In addition, when adding ozone, by adding a ultrasonic wave, adding a micro bubble, adding with stirring, adding using an ejector, etc., ozone is made into activated sludge by using a known ozone dissolution promotion method. Furthermore, it can also be added efficiently.

  The staying tank 3 is an organic wastewater sent from the activated sludge tank 2 to the submerged membrane tank 4, and the ozone concentration of the organic wastewater passing through the submerged film 4A provided in the submerged membrane tank 4 is an allowable ozone of the submerged film 4A. It is allowed to stay for a predetermined time or less that is below the concentration. The organic wastewater sent from the activated sludge tank 2 and flowing into the staying tank 3 is in a state where many microorganisms of activated sludge are mixed.

  FIG. 2 is experimental data showing the relationship between the residence time in the residence tank 3 and the dissolved ozone concentration of the organic waste water flowing out from the residence tank 3 in the wastewater treatment system 1 according to the present embodiment. The dissolved ozone concentration was measured using ELP-200 (diaphragm polarographic dissolved ozone monitor) manufactured by Sugawara Jitsugyo Co., Ltd. As is apparent from the graph of FIG. 2, it can be seen that when the residence time is 30 seconds or more, the dissolved ozone concentration is less than or equal to the measurement lower limit value. From this, it is preferable that the retention tank 3 is capable of retaining at least organic wastewater for 30 seconds or more.

  The residence time of the organic waste water in the residence tank 3 may be any time as long as it is at least the predetermined time or more. However, as the residence time becomes longer, the capacity of the residence tank 3 increases. It is preferable to determine the residence time in the residence tank 3 so that 3 falls within an appropriate size range. If the residence time is set to about 1 minute, for example, the dissolved ozone concentration is made sufficiently low and the residence tank 3 does not become unnecessarily large.

In order for the organic waste water to stay in this way for a predetermined time or longer, the staying tank 3 is provided with an air supply device 6B for supplying air for aeration of the organic waste water in the tank. The organic waste water in the tank is agitated by sending air to the bottom of the inside. By stirring the organic waste water in the tank of the retention tank 3, the occurrence of a short-circuit flow is prevented, and the organic waste water is prevented from flowing out within a predetermined time after flowing into the tank. Moreover, the ozone concentration is rapidly lowered by driving out ozone in the organic wastewater with aerated air.

  If the air supply device 6B is provided in the staying tank 3, the staying tank 3 can be reduced in size, but the air supply device 6B is not necessarily provided, and the organic waste water flowing into the tank is retained for a predetermined time or more. The air supply device 6B may be omitted as long as it is possible to flow out. For example, by providing a baffle plate in the tank of the retention tank 3 or by providing a stirring device using a screw, the occurrence of a short-circuit flow is prevented, and the organic wastewater flows into the tank in less than a predetermined time. It may be prevented from leaking.

  Moreover, the means for retaining the organic waste water sent from the activated sludge tank 2 to the submerged membrane tank 4 for a predetermined time or more is not limited to the water tank. For example, the staying tank 3 may be replaced with a straight pipe 9 that forms a water channel as shown in FIG. 3, or may be replaced with a meandering pipe for the purpose of securing a staying time, or temporarily in a tank or the like. It is also possible to adopt a configuration in which it is stored in the tank and sent to the immersion film tank 4 by a batch method.

  The immersion membrane tank 4 purifies the organic wastewater sent from the activated sludge tank 2 via the retention tank 3 by the immersion membrane 4A disposed in the tank, and is a device downstream of the immersion membrane tank 4 or a wastewater treatment system. 1 out of the system. Since the organic wastewater flowing into the immersion membrane tank 4 is discharged through the immersion membrane 4A, the activated sludge floating in the organic wastewater even if the flow rate of the organic wastewater flowing into the immersion membrane tank 4 fluctuates. Etc. will not flow out of the system.

  The ozone added to the activated sludge is removed from the organic waste water in the process of passing through the retention tank 3. Therefore, any known film can be applied to the immersion film 4A regardless of the ozone resistance. Examples of applicable membrane shapes include known membranes such as flat membrane types, hollow fiber membrane types, spiral types, tube types, and monolith types. Applicable membrane materials include, for example, PSF (polysulfone), PE (polyethylene), CA (cellulose acetate), PAN (polyacrylonitrile), PP (polypropylene), PVDF (polyvinylidene fluoride), PTFE (polyethylene). Examples thereof include organic films such as tetrafluoroethylene), ceramics such as aluminum oxide, titanium oxide, and zirconium oxide, and inorganic films such as metals.

  In the immersion film 4A, the surface of the immersion film 4A is washed with air by an air supply device 6C that continuously or intermittently blows air into the lower part of the immersion film 4A in the immersion film tank 4 to prevent clogging. For example, the residence tank 3 is configured to function as a sedimentation tank so that suspended matter in the organic waste water flowing into the immersion membrane tank 4 is removed in advance, and the supernatant and microorganisms of the residence tank 3 are diluted. If the wastewater treatment system 1 is configured so that the wastewater flows into the immersion film tank 4, the immersion film 4A is less likely to be clogged, so that the air blown into the immersion film tank 4 can be intermittent. If the air blown into the immersion film tank 4A can be intermittent, it is possible to reduce the energy consumption of the power required for blowing the air.

  In addition, activated sludge adhering to the membrane surface that causes clogging of the immersed membrane 4A due to the property change of the activated sludge such as improvement of the microbial phase composition of activated sludge by ozone addition and improvement of performance and improvement of sludge sedimentation The amount is reduced. As a result, the performance of the immersion film 4A can be maintained for a long time.

The sludge return device 5 is a device usually used for biological treatment of organic wastewater by activated sludge. For example, the activated sludge in the submerged membrane tank 4 is removed from the activated sludge tank 2, the retention tank 3, or the wastewater treatment system 1. Provide piping and pumps to transport to

The wastewater treatment system 1 according to the present embodiment returns the activated sludge returned from the submerged membrane tank 4 to the activated sludge tank 2 so that MLSS (Mixed Liquor Suspended Solids) of the activated sludge tank 2 is maintained at a predetermined concentration. The amount is determined by feedback control or the like. Then, the sludge return device 5 returns a part or all of the activated sludge in the submerged membrane tank 4 to the activated sludge tank 2 in accordance with the determined return amount, and discharges the unnecessary activated sludge to the outside of the waste water treatment system 1. Mud. The predetermined concentration here is the concentration of MLSS in the activated sludge tank 2 that allows the quality of the treated water treated in the activated sludge tank 2 to be equal to or lower than the predetermined upper limit of pollution, It is a value determined appropriately according to the quality of water to be used. This value can be determined from, for example, the relationship between the water quality obtained by experimenting with various MLSS concentrations and the MLSS concentration.

  By the way, when the inventors of the present invention diligently researched, it was found that the ozone concentration of the organic waste water depends on MLSS. FIG. 4 shows experimental data showing the relationship between the ozone concentration of organic waste water and MLSS when the residence time of the residence tank 3 is 1 minute. From the experimental data shown in FIG. 4, it can be seen that, for example, when the MLSS is increased, the ozone concentration of the organic waste water decreases. In particular, when MLSS is set to a certain value or more, it can be seen that the dissolved ozone concentration is equal to or lower than the measurement lower limit value. This is considered because activated sludge consumes ozone when MLSS is increased.

  Therefore, in the wastewater treatment system 1 according to the present embodiment, the amount of activated sludge returned from the immersion membrane tank 4 is controlled so that the ozone concentration of the organic wastewater flowing into the immersion membrane tank 4 is equal to or lower than the measurement lower limit value. That is, in the wastewater treatment system 1 according to the present embodiment, the ozone concentration of the organic wastewater flowing into the immersion membrane tank 4 is temporarily increased, and ozone is detected in the organic wastewater flowing into the immersion membrane tank 4. In a case, MLSS in the organic waste water sent to the immersion membrane tank 4 is increased. The ozone concentration of the organic waste water flowing into the immersion membrane tank 4 can be measured, for example, by installing a known dissolved ozone concentration measuring device in the pipe on the outlet side of the staying tank 3 or in the staying tank 3. it can.

The amount of ozone added to organic wastewater and ORP (Oxidation-Reduction Potential:
It has been experimentally confirmed that there is a positive correlation with the oxidation-reduction potential. FIG. 5 is an example of experimental data showing the relationship between the amount of ozone added to the organic waste water and the ORP. The “amount of ozone” shown in FIG. 5 indicates the amount of ozone per liter of waste water. In addition, “X” shown in FIG. 5 means the organic inflow load concentration in the influent wastewater, and BOD (Biochemical Oxygen Demand) and organic SS (Suspended) not included in BOD.
Solid: suspended solids). Moreover, ORP is shown in the ratio which set the value when ozone is not added to 1.

  Therefore, in the wastewater treatment system 1 according to the present embodiment, the amount of activated sludge returned from the immersion membrane tank 4 is controlled based on the instruction value of the ORP meter that measures the ORP of the organic wastewater flowing into the immersion membrane tank 4. By doing so, you may make it the ozone concentration of the organic waste water which flows into the immersion film tank 4 become low.

  In order to increase the MLSS in the organic waste water sent to the submerged membrane tank 4, for example, the sludge return device so that a part of the activated sludge returned from the submerged membrane tank 4 to the activated sludge tank 2 is sent to the staying tank 3. 5 is controlled. When MLSS of the retention tank 3 increases, the ozone concentration of the organic waste water flowing into the immersion film tank 4 decreases. In this case, the amount of activated sludge sent to the retention tank 3 may be adjusted manually by the operator. For example, as shown in FIG. 6, a dissolved ozone concentration meter installed on the outlet side of the immersion membrane tank 4 A valve 5B that opens and closes according to the measurement value of 5A may be provided in a pipe that supplies activated sludge to the staying tank 3, and the amount of activated sludge sent to the staying tank 3 may be automatically adjusted.

  But the waste water treatment system 1 which concerns on this embodiment does not necessarily need to send the activated sludge of the immersion membrane tank 4 to the retention tank 3, when the ozone concentration of the organic waste water which flows into the immersion membrane tank 4 becomes high. . For example, the piping for sending activated sludge to the retention tank 3 is omitted, and the amount of activated sludge to be returned to the activated sludge tank 2 is increased when the ozone concentration of the organic waste water flowing into the submerged membrane tank 4 becomes high. It may be.

  When the organic wastewater is supplied to the wastewater treatment system 1 configured as described above, the organic wastewater is purified by biological treatment using activated sludge in the activated sludge tank 2 and discharged from the activated sludge tank 2 as treated water. . The treated water discharged from the activated sludge tank 2 is returned or discharged from the bottom of the submerged membrane tank 4 by the sludge return device 5. Further, the treated water that has passed through the immersion film 4 </ b> A installed in the immersion film tank 4 is discharged from the immersion film tank 4.

  With the wastewater treatment system 1 configured as described above, it is possible to achieve both the supply of ozone for the purpose of improving the biological treatment capacity and reducing the amount of sludge generated, and the prevention of sludge outflow by the membrane. . That is, since ozone added to the activated sludge does not reach the immersion film 4A, it is possible to use a film that is not resistant to ozone. Therefore, it is possible to prevent the outflow of sludge by the membrane while improving the performance of activated sludge with ozone to reduce the amount of sludge generated.

  In addition, the waste water treatment system 1 which concerns on this embodiment may be provided with the equipment which performs processes other than the process which each equipment mentioned above in the range with which the effect of this invention is acquired. Examples of such treatment include removal of suspended matter in organic wastewater supplied to the activated sludge tank, and physical properties such as temperature and pH of organic wastewater or treated water supplied to the activated sludge tank. The process etc. which adjust and make it the conditions suitable for the biological treatment by activated sludge are mentioned. These treatments can be performed using known techniques in biological treatment of organic wastewater with activated sludge.

  Moreover, the waste water treatment system 1 which concerns on this embodiment is not limited to the structure provided with each one installation mentioned above, The specific equipment or all the equipment may be equipped with two or more. For example, if a plurality of activated sludge tanks 2 are provided in parallel, it is possible to continue the wastewater treatment without stopping the wastewater treatment system 1 even if any one of the activated sludge tanks 2 breaks down. .

  Moreover, although the waste water treatment system 1 which concerns on this embodiment has determined the residence time of the residence tank 3 so that the ozone concentration of the organic waste water which passes the immersion membrane 4A may become below a measurement lower limit, it is immersion membrane 4A. The ozone concentration of the organic waste water that passes through the water does not necessarily need to be lower than the lower limit of measurement, and may be, for example, lower than the ozone concentration that the immersion film 4A can accept. Since the ozone concentration allowable in the immersion film 4A differs depending on the material constituting the immersion film 4A, the residence time of the residence tank 3 is appropriately determined according to the material constituting the immersion film 4A.

<First modification>
In addition, you may deform | transform the waste water treatment system 1 which concerns on the said embodiment as follows, for example. A wastewater treatment system according to the first modification is shown in FIG. In the wastewater treatment system 1 according to the embodiment, all three tanks are aerobic tanks, but as shown in FIG. 7, the wastewater treatment system 11 according to this modification is a wastewater treatment according to the embodiment. The system configuration is such that an anaerobic tank 8 is further provided on the upstream side of the system 1. Since the activated sludge tank 2, the staying tank 3 and the submerged membrane tank 4 are the same as the waste water treatment system 1 described above, the same reference numerals are given and the description thereof is omitted. The anaerobic tank 8 is provided with a stirrer 8A so that the concentration of activated sludge is uniform.

The sludge return device 15 of the wastewater treatment system 11 according to this modification returns the activated sludge in the submerged membrane tank 4 not only to the activated sludge tank 2 but also to the anaerobic tank 8. The sludge return device 15 is a device that is normally used for biological treatment of organic wastewater with activated sludge, similar to the sludge return device 5 described above. , A dwell tank 3 or a pipe or pump for transferring the waste water treatment system 11 out of the system.

  The wastewater treatment system 11 according to this modification is an activated sludge that is returned from the immersion membrane tank 4 to the activated sludge tank 2 or the anaerobic tank 8 so that the MLSS of the anaerobic tank 8 and the activated sludge tank 2 is maintained at a predetermined concentration. Is returned by feedback control or the like. Then, the sludge return device 15 returns the activated sludge from the submerged membrane tank 4 to the anaerobic tank 8 and the activated sludge tank 2 in accordance with the determined return amount, and discharges unnecessary activated sludge out of the waste water treatment system 11. To do.

  When the organic waste water is supplied to the waste water treatment system 11 configured as described above, the organic waste water is subjected to removal of nitrogen by nitrifying bacteria and denitrifying bacteria in the activated sludge in the anaerobic tank 8 as treated water. It is discharged from the anaerobic tank 8. The treated water discharged from the anaerobic tank 8 is sent to the activated sludge tank 2, where organic substances are removed by biological treatment with the activated sludge, and discharged from the activated sludge tank 2 as treated water. The treated water discharged from the activated sludge tank 2 passes through the immersion film 4 </ b> A installed in the immersion film tank 4 and is discharged from the immersion film tank 4.

  Even in the wastewater treatment system 11 configured as described above, as with the above-described wastewater treatment system 1, the activated sludge performance is improved with ozone to reduce the amount of sludge generation, and the sludge outflow by the membrane is prevented can do. A small amount of ozone added to the activated sludge tank 2 is also consumed in the retention tank 3, and the dissolved ozone concentration in the submerged membrane tank 4 is sufficiently low, so that ozone is contained in the sludge returned to the anaerobic tank 8. It is not included, and ozone does not affect nitrifying bacteria and denitrifying bacteria in the anaerobic tank 8.

  In the waste water treatment system 11 according to this modification, the anaerobic tank 8 is separated from the activated sludge tank 2, but for example, as shown in FIG. 8, the activated sludge tank that is an anaerobic tank 8 and an aerobic tank. 2 may be formed in one tank, and the tank may be divided into an anaerobic tank region and an aerobic tank region.

<Second modification>
Moreover, you may deform | transform the waste water treatment system 1 which concerns on the said embodiment as follows, for example. A wastewater treatment system according to the second modification is shown in FIG. In the wastewater treatment system 1 according to the above embodiment, when air is diffused into the immersion membrane tank 4 for the purpose of preventing clogging of the immersion membrane 4A, the concentration of sludge returned by the sludge return device 5 inevitably decreases. To do.

  Therefore, the wastewater treatment system 21 according to the present modification further includes a sedimentation tank 5C that concentrates the activated sludge discharged from the submerged membrane tank 4 in the wastewater treatment system 1 described above. If such a sedimentation tank 5C is provided, the activated sludge discharged from the immersion film tank 4 is concentrated even if air is diffused into the immersion film tank 4 for the purpose of preventing clogging of the immersion film 4A. As a result, the concentration of sludge discharged outside the system increases. As a result, the volume of excess sludge to be discharged can be reduced.

<Third modification>
Moreover, you may deform | transform the waste water treatment system 1 which concerns on the said embodiment as follows, for example. A wastewater treatment system according to the third modification is shown in FIG. The wastewater treatment system 1 according to the above-described embodiment is used only for the purpose of retaining organic wastewater for a predetermined time to remove ozone. On the other hand, the retention tank 33 of the wastewater treatment system 31 according to the present modification includes an organic wastewater flowing from the activated sludge tank 2 to the submerged membrane tank 4 in addition to the purpose of retaining the organic wastewater for a predetermined time to remove ozone. It is also used for the purpose of removing the suspended matter, and is a settling tank-like residence tank 33 for precipitating the suspended matter. For this reason, a pipe for discharging activated sludge precipitated in the tank of the staying tank 33 is connected to the bottom of the staying tank 33, and the activated sludge discharged from the staying tank 33 is returned to the sludge return device 3.
5 is returned to the activated sludge tank 2 or drained out of the system.

  Even in the wastewater treatment system 31 configured as described above, ozone in the organic wastewater can be sufficiently removed in the retention tank 33 to prevent the immersion film 4A from deteriorating due to ozone, and also flows into the immersion film tank 4. Since the suspended matter in the organic waste water to be reduced is reduced by the retention tank 33, the clogging of the immersion film 4A can be prevented.

<Fourth modification>
Moreover, you may deform | transform the waste water treatment system 1 which concerns on the said embodiment as follows, for example. FIG. 11 shows a wastewater treatment system according to the fourth modification. The wastewater treatment system 41 according to this modification is configured so that exhaust from the activated sludge tank 2 to which ozone is added is sucked by a fan (which is an example of an air supply means in the present application) 43, and sludge that the sludge return device 5 discharges is sludge. It blows into the surplus sludge tank 42 which flows in, and the stay tank 3.

  In the case of the wastewater treatment system 41 configured as described above, the ozone remaining in the exhaust gas of the activated sludge tank 2 to which ozone is added is absorbed by the sludge in the retention tank 3 and the excess sludge tank 42. Ozone emission to the atmosphere can be prevented without using a dedicated purification device for purifying ozone. The exhaust from the activated sludge tank 2 may be blown into either one of the surplus sludge tank 42 and the staying tank 3 instead of both.

1,11,21,31,41 ... Wastewater treatment system: 2 .... Activated sludge tank: 3, 33 ... Residence tank: 4 .... Immersion membrane tank: 4A ... Immersion membrane: 5, 15, 35 ... Sludge return device: 6A, 6B, 6C ・ ・ Air supply device: 7 ・ ・ Ozone supply device: 8 ・ Anaerobic tank: 8A ・ ・ Agitator: 9 ・ ・ Straight pipe: 5A ・ ・ Dissolved ozone concentration meter: 5B ・ ・Valve: 5C ・ ・ Settling tank: 42 ・ ・ Surplus sludge tank: 43 ・ ・ Fan

Claims (9)

A wastewater treatment system for treating organic wastewater,
An activated sludge tank having activated sludge and biologically treating the inflowing organic wastewater;
An ozone supply device for adding ozone to the activated sludge in the activated sludge tank;
An immersion membrane tank for purifying the organic wastewater sent from the activated sludge tank with an immersion membrane disposed in the tank;
The ozone concentration of the organic wastewater that passes through the immersion membrane is the organic wastewater that is provided in the middle of the path leading from the activated sludge tank to the immersion membrane tank, and is sent from the activated sludge tank to the immersion membrane tank. A retention means for retaining the immersion membrane for a predetermined time or less that is equal to or lower than an allowable ozone concentration of the immersion film,
Wastewater treatment system. The sludge returning device for returning the activated sludge of the immersion membrane tank to the retention means or a path through which the organic waste water on the upstream side of the retention means passes, wherein ozone of the organic waste water that passes through the immersion membrane When detecting that the concentration or oxidation-reduction potential has increased, the apparatus further comprises a sludge return device that increases the return amount of the activated sludge or starts returning the activated sludge.
The wastewater treatment system according to claim 1.   An anaerobic tank is further provided upstream of the activated sludge tank,
  The sludge return device returns the activated sludge of the immersion membrane tank to the anaerobic tank,
  The wastewater treatment system according to claim 2. The retention means is a tank that retains the organic wastewater sent from the activated sludge tank to the immersion membrane tank for the predetermined time or more, or the organic wastewater that is sent from the activated sludge tank to the immersion membrane tank. A pipe having a length of staying for a predetermined time or more.
The wastewater treatment system according to any one of claims 1 to 3 . The retention means retains the organic wastewater sent from the activated sludge tank to the submerged membrane tank for the predetermined time or longer, and the activated sludge remaining in the organic wastewater sent from the activated sludge tank. A tank for precipitation,
The wastewater treatment system further comprises a sludge return device that returns the activated sludge that settles in the tank of the staying means to the activated sludge tank.
The wastewater treatment system according to claim 1. Air supply means for continuously or intermittently blowing air into the immersion film tank;
The waste water treatment system according to any one of claims 1 to 5 . The activated sludge tank to which ozone is added is at least one of the organic waste water retained in the retention means and the excess sludge tank into which excess sludge discharged from the waste water treatment system flows. Further comprising air supply means for blowing into
The waste water treatment system according to any one of claims 1 to 6 . A wastewater treatment method for treating organic wastewater,
A step of biologically treating the organic wastewater by an activated sludge tank having activated sludge to which ozone is added;
Purifying the organic wastewater sent from the activated sludge tank by an immersion film tank in which an immersion film is disposed in the tank;
A step of retaining the organic wastewater sent from the activated sludge tank to the immersion membrane tank for a predetermined time or more in which the ozone concentration of the organic wastewater passing through the immersion membrane is equal to or lower than an allowable ozone concentration of the immersion membrane; Having
Wastewater treatment method.   A sludge return step for returning the activated sludge in the submerged membrane tank to a retention means used in the step of retaining or a path through which the organic drainage upstream of the retention means passes, and passes through the submerged membrane. When it detects that the ozone concentration or oxidation-reduction potential of the organic waste water has increased, it further includes a sludge return step for increasing the return amount of the activated sludge or starting the return of the activated sludge.
  The wastewater treatment method according to claim 8.

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