JP4386054B2 - Intermittent biological treatment method - Google Patents

Description

  A treatment period in which the liquid to be treated is received into a biological treatment tank to continuously perform aerobic biological treatment, a part of the reaction liquid in the biological treatment tank is transferred to a solid-liquid separation tank, and solid-liquid separation is performed, and the treatment is suspended. The present invention relates to an intermittent biological treatment method that repeats a pause period.

  Accepts liquids such as sewage, human waste, and other organic wastewater into the biological treatment tank and continuously performs aerobic biological treatment. Transfers a part of the reaction liquid from the biological treatment tank to the solid-liquid separation tank and solidifies it. The aerobic biological treatment method for performing liquid separation is widely adopted as an activated sludge treatment method, a nitrification denitrification method, and the like. Since such a treatment method is a treatment that uses the activity of a living organism, or in the case of sewage or the like, a liquid to be treated is continuously generated. Therefore, the liquid to be treated is continuously received and continuously treated. Continuous processing is often used. However, continuous processing increases the running costs such as labor costs and power costs, so if the liquid to be processed is generated intermittently, the continuous processing is performed on weekdays and paused on weekends. This is advantageous in terms of running cost.

  In the case of human waste processing, the amount of human waste carried into the human waste treatment facility decreases due to the spread of sewage and septic tanks, or the proportion of septic tank sludge carried in increases, resulting in a lower load carrying capacity for facility treatment capacity. There is. Each facility and equipment in the human waste treatment facility is designed to process the planned load continuously, so there is room for each equipment and device due to a decrease in the load, thus reducing the running cost per treatment amount. For this purpose, intermittent processing that repeats the processing period and the pause period is advantageous.

  In general, the urine treatment facility is carried in from Monday to Friday or Saturday, pretreated and stored in a storage tank, and continuously processed for seven days a week. The reason for performing the continuous treatment is to perform the treatment with a constant load while suppressing the fluctuation of the load with respect to the biological treatment. If intermittent treatment is performed in such treatment, load fluctuations occur in biological treatment due to the suspension of operation of the facility, or sludge is maintained in an anaerobic state during the suspension, and pollutants are generated, and the quality of the treated water is adversely affected. .

  In Patent Document 1 (Japanese Patent Laid-Open No. 61-254296), as an intermittent operation method in the biochemical nitrification denitrification treatment of organic wastewater, the treatment is performed by shutting off the biological treatment apparatus and the precipitation tank with a valve. It is described that by stopping, inflow of liquid that has not been sufficiently nitrified and denitrified is prevented. In this method, it is shown that the biological activity is recovered in about 5 hours by resuming the treatment, but during that time, the untreated substance remaining in the aeration tank affects the quality of the treated water after the resumption and is suspended. There is no mention of sludge levitation and the like, resulting in water quality deterioration due to decomposition of the levitation sludge.

As a result of studying the intermittent operation of biological treatment, the inventors found the following. That is, when aerobic biological treatment in a biological treatment tank such as an aeration tank treating organic wastewater is stopped as it is, sludge in the aeration tank is decomposed and components such as BOD components and ammonia nitrogen are contained in the biological treatment tank. Therefore, a phenomenon occurs in which the quality of the treated water is deteriorated by shifting to a subsequent process when the operation is resumed. In addition, if the operation is stopped with sludge remaining in the solid-liquid separation tank such as a sedimentation tank, the sludge will rot during the outage, causing sludge spillage at the time of resumption of operation due to deterioration of the water quality or sludge rising. Gets worse. Conventionally, impurities have been removed by coagulation treatment of treated water as a countermeasure against such deterioration of water quality, but there has been a problem that the amount of coagulant used is increased.
JP-A 61-254296

  The problem of the present invention is that it is possible to pause while the sludge activity is maintained by minimizing the decay of sludge during suspension, and the quality of the treated water is deteriorated due to a decrease in treatment efficiency at the time of restarting operation, sludge outflow, etc. Can be started up and the treatment can be started, so that the continuous treatment and pause of the aerobic biological treatment can be repeated at a low cost and in a high treatment efficiency, and the intermittent organism can perform the low-cost treatment It is to propose a processing method.

The present invention is the following intermittent biological treatment method.
(1) Accepting the liquid to be treated into the biological treatment tank for aerobic biological treatment, transferring a part of the reaction liquid in the biological treatment tank to the solid-liquid separation tank, and suspending the treatment In the intermittent biological treatment method that repeats the rest period to
When shifting from the treatment period to the suspension period, the supply of the liquid to be treated is stopped,
Even after the supply of the liquid to be treated is stopped, aeration is stopped after the aeration is continued until the inside of the biological treatment tank becomes over-aerated.
And the process is stopped in the state which discharged | emitted the sludge in a solid-liquid separation tank, and lowered the liquid level of the solid-liquid separation tank, The intermittent biological treatment method characterized by the above-mentioned.
(2) The method according to (1) above, wherein the sludge discharged from the solid-liquid separation tank is returned to the biological treatment tank during aeration and / or after aeration is stopped.
(3) The method according to the above (1) or (2), wherein when discharging the sludge in the solid-liquid separation tank, the sludge is discharged until the interface becomes below a certain level using a sludge interface meter.
(4) Accepting the liquid to be treated into the biological treatment tank for aerobic biological treatment, transferring a part of the reaction liquid in the biological treatment tank to the solid-liquid separation tank and performing the solid-liquid separation, and pausing the treatment In the intermittent biological treatment method according to any one of (1) to (3) above, wherein the pause period is repeated,
When moving from the rest period to the treatment period, after aeration is continued until the inside of the biological treatment tank becomes over-aerated,
An intermittent biological treatment method characterized in that the treatment is started by starting the supply of the liquid to be treated.
(5) The method according to (4) above, wherein the aeration is started by returning the sludge in the solid-liquid separation tank to the biological treatment tank after the start of aeration and / or after the supply of the liquid to be treated.

  In the present invention, the biological treatment method that performs intermittent treatment accepts the liquid to be treated into the biological treatment tank, continuously performs the aerobic biological treatment, and transfers a part of the reaction liquid in the biological treatment tank to the solid-liquid separation tank. Thus, this is a processing method for performing solid-liquid separation. The aerobic biological treatment is a treatment method in which an aerobic biological treatment is performed by an aerobic treatment means such as aeration using an aerobic microorganism, and examples thereof include activated sludge treatment and biological nitrification. The biological treatment method only needs to include these aerobic biological treatment steps. In addition to the aerobic biological treatment step, anaerobic biological treatment steps such as anaerobic digestion and anaerobic denitrification, or aggregation, membrane treatment, etc. Other steps such as a physical treatment step may be included. Solid-liquid separation should just include the process process which isolate | separates the reaction liquid produced | generated by an aerobic biological process into a separated liquid and sludge by sedimentation separation, membrane separation, etc.

  As a simple example of the above biological treatment method, there is an activated sludge treatment method using activated sludge, which comprises an aerobic biological treatment step and a solid-liquid separation step, and is at least one of the separated sludges in the solid-liquid separation step. Part is returned to the aerobic biological treatment process. As another example, there is a combined treatment method of anaerobic treatment and aerobic treatment, which performs anaerobic treatment such as activated sludge treatment after anaerobic treatment such as anaerobic digestion and high-load anaerobic treatment. In this method, sludge is separated in the liquid separation process, and at least a part of the separated sludge is returned to the anaerobic treatment process or the aerobic biological treatment process. As another example, there is a nitrification denitrification treatment method comprising a combination of biological nitrification and anaerobic denitrification. In this method, after removing organic matter (BOD) from the liquid to be treated, ammonia nitrogen is nitrified to nitric acid or nitrite nitrogen, and the nitrification liquid is anaerobically treated for denitrification. An anaerobic denitrification step In the first stage, organic matter removal and denitrification are simultaneously performed, and then nitrification is performed to remove residual organic matter and nitrification at the same time. Further, in the solid-liquid separation process, sludge is separated, and at least the separated sludge is separated. In this method, a part is returned to the anaerobic treatment process or the aerobic biological treatment process.

  In these treatment methods, the liquid to be treated is usually introduced continuously to carry out the treatment continuously, whereby the load fluctuation can be suppressed and the treatment can be carried out stably. When intermittent treatment is performed in such treatment, the aerobic biological treatment step and the solid-liquid separation step are greatly affected. Even if an anaerobic treatment process is combined with these processes, the anaerobic treatment process is a process that does not inherently perform an aggressive treatment, so it is not seriously affected even when the operation is stopped, and is stirred when the operation is resumed. Restore to the original degree. In addition, the physical processing can be easily restored when the operation is resumed by taking thorough measures for the apparatus at rest.

  On the other hand, since the aerobic biological treatment process uses the activity of the aerobic organism, the activity of the aerobic organism is affected when the anaerobic state is brought about by the rest, and the organic matter present in the aerobic biological treatment is also present. Is decomposed due to anaerobic treatment, and when the operation is resumed, the process proceeds to a later process and the quality of the treated water deteriorates. Also, in the solid-liquid separation process, if the operation is stopped with sludge remaining in the solid-liquid separation tank, the sludge decays during the outage, causing sludge spillage at the time of resumption of operation due to deterioration of the water quality or sludge floating. Water quality deteriorates. For this reason, when performing an intermittent process in said process, it becomes possible to prevent the fall of process efficiency, the deterioration of a treated water quality, etc. by performing the process which does not produce such a problem.

  In the present invention, a liquid to be treated is received in a biological treatment tank to perform aerobic biological treatment, a part of the reaction liquid in the biological treatment tank is transferred to a solid-liquid separation tank, and a solid-liquid separation is performed. In order to adopt the intermittent biological treatment method that repeats the pause period, the aeration is performed until the inside of the biological treatment tank becomes over-aerated after the supply of the liquid to be treated is stopped when shifting from the treatment period to the pause period. Aerobic biological treatment process and solid-liquid separation process by stopping aeration after stopping aeration after continuing and discharging sludge in the solid-liquid separation tank and lowering the liquid level of the solid-liquid separation tank The above-mentioned problems can be solved, and the reduction of the treatment efficiency and the deterioration of the treated water can be prevented.

  The liquid to be treated to be received into the biological treatment tank is a liquid to be treated for aerobic biological treatment. In the activated sludge treatment method, the liquid to be treated such as organic waste water to be accepted into the aerobic biological treatment process for the activated sludge treatment. However, in the case of the combined treatment method of anaerobic treatment and aerobic treatment, this is the anaerobic treatment liquid, and in the nitrification denitrification treatment method, the liquid to be treated which is accepted into the nitrification process after removal of organic substances or after denitrification Is this.

  In the aerobic biological treatment, these treatment liquids are received in the biological treatment tank and mixed with the returned sludge, or the organic substances in the treatment liquid are decomposed by aerobic treatment means such as aeration without mixing, or nitrification, etc. This is a step of oxidizing. In solid-liquid separation, part of the reaction liquid in the biological treatment tank is transferred to the solid-liquid separation tank, solid-liquid separation such as sedimentation and membrane separation is performed, the separated liquid is discharged as the treatment liquid, and the separated sludge is returned. It is the process of returning to aerobic biological treatment etc. as sludge, or discharging to a sludge treatment system as surplus sludge. The treatment period in the intermittent biological treatment is a period in which the liquid to be treated is continuously received and the aerobic biological treatment and the solid-liquid separation are continuously performed, and is usually 4 to 7 days. The rest period is a period in which aerobic processing means such as supply of the liquid to be treated and aeration are stopped to stop these processes, and is usually 2-3 days.

  When shifting from the treatment period to the suspension period, after the supply of the liquid to be treated is stopped, by continuing aeration until the inside of the biological treatment tank is in an over-aerated state, untreated organic substances existing in the aerobic biological treatment system And aerobic organisms are starved to maintain aerobic biological activity and prevent organic matter from undergoing anaerobic treatment during the rest period to produce pollutants. The microorganisms used in the aerobic biological treatment system are mainly facultative anaerobic bacteria and grow using oxygen in the aerobic state, but when there is no substrate (BOD component), it moves to endogenous respiration and oxygen Since it is no longer used, the dissolved oxygen tends to rise, resulting in an over-aerated state. Even if aeration is stopped in this state, there is no unprocessed organic matter, so no spoilage occurs, the aerobic organism is kept in the state of endogenous breathing, and processing is resumed as soon as aeration is resumed. The state can be maintained.

  In such an over-aerated state, the amount of dissolved oxygen in the biological treatment tank tends to increase, so the aeration may be stopped by detecting the time when the amount of dissolved oxygen increases, and the amount of dissolved oxygen is a constant value. At the point of time, aeration can be stopped and a suspension period can be entered. The value of the dissolved oxygen amount at which aeration is stopped is a value that serves as an index when the dissolved oxygen amount tends to increase. Generally, the upper limit value of the fluctuation value of the dissolved oxygen amount during the treatment period, for example, 3 to 8 mg. / L, preferably 4-7 mg / L. In addition, since the over-aerated state occurs when there is no untreated organic matter in the biological treatment tank, it is possible to experimentally confirm in advance the time when the untreated organic matter does not exist and continue the aeration for that time. Since the time during which the untreated organic matter does not exist usually corresponds to the residence time of the biological treatment tank, aeration may be continued for the time corresponding to the residence time of the biological treatment tank. The degree of this air aeration is not limited, but it may be the same as the aeration in the processing step.

  When shifting from the treatment period to the suspension period, the sludge in the solid-liquid separation tank is discharged and the treatment is stopped in a state where the liquid level of the solid-liquid separation tank is lowered, thereby reducing the amount of sludge retained during the suspension period. In addition to reducing water quality deterioration and sludge floating due to sludge decay, it is possible to prevent outflow from the solid-liquid separation tank even if sludge decays during suspension and water quality deteriorates and sludge rises. . In addition, when the operation is restarted with the liquid level of the solid-liquid separation tank lowered, the reaction liquid transferred from the biological treatment tank is stored for a while until the liquid level rises, and the sludge that stays in the meantime is removed. It can be returned to the biological treatment tank and aerated to prevent deterioration of the treated water quality. The liquid level to be lowered when moving to the rest period is below the liquid level necessary to prevent the floating sludge and separated liquid from flowing out during the rest and to store the reaction liquid transferred from the biological treatment tank for a while when the operation is resumed. In general, it can be 50 to 150 mm, preferably 60 to 110 mm from the overflow liquid surface.

  It is preferable that the amount of sludge discharged from the solid-liquid separation tank when shifting to the suspension period is discharged as much as possible to shift to the suspension period. In other words, the solid-liquid separation tank is anaerobic during the outage period, so the sludge in the solid-liquid separation tank decays, causing sludge spillage when the operation resumes due to water quality deterioration or sludge floating. These sludges can be prevented by discharging as much as possible. The amount of sludge discharged at this time can be 30 to 100% by volume, preferably 50 to 100% by volume, of the sludge layer below the separation interface of the solid-liquid separation tank. In order to obtain such a sludge discharge amount, a sludge interface meter that detects the sludge interface in the solid-liquid separation tank can be used, and the sludge can be discharged until the sludge interface in the solid-liquid separation tank becomes below a certain level. . The target sludge interface at this time is generally 200 to 400 mm lower than the steady interface.

  Sludge discharged from the solid-liquid separation tank can be returned into the biological treatment tank as much as possible, but sludge that cannot be returned into the biological treatment tank can be discharged as excess sludge. The return sludge and the excess sludge used in the normal treatment process may be divided and returned and discharged. The sludge to be returned to the biological treatment tank during aeration is retained in the biological treatment tank in a state activated by aeration. When the biological treatment system includes an anaerobic tank in addition to the aeration tank, it can be returned to the anaerobic tank, but is activated by aeration when transferred from the anaerobic tank to the aeration tank. The sludge may be returned after the aeration is completed, and the sludge returned from the solid-liquid separation tank is in an endogenous breathing state, and thus is retained in the biological treatment tank as it is. At this time, since aeration is stopped in the biological treatment tank, the returned sludge is accumulated and concentrated as it is, and the separated liquid is circulated to the solid-liquid separation tank. Thereby, a large amount of sludge is held in the biological treatment tank in a concentrated state and an activated state.

  After shifting to the rest period as described above, when advancing the operation and shifting to the treatment period, the air aeration was continued without supplying the liquid to be treated until the inside of the biological treatment tank was over-aerated. Thereafter, the supply of the liquid to be processed is started to start the processing, and the processing period is started. By continuing the aeration, it is possible to oxidize the anaerobic degradation products of the organic matter generated in the aerobic biological treatment system during the rest period and to activate the aerobic organisms so that they can be continuously treated. When anaerobic decomposition products are oxidized and the aerobic organism is activated, it becomes over-aerated, so when the dissolved oxygen amount tends to increase or when the dissolved oxygen amount exceeds a certain value, The supply of the treatment liquid is started and the processing period starts. The value of the dissolved oxygen amount serving as an index for starting the supply of the liquid to be treated is a value that serves as an index when the dissolved oxygen amount tends to increase. The upper limit value can be set to, for example, 3 to 8 mg / L, preferably 4 to 7 mg / L. Further, the time point when the over-aeration state is reached may be determined by the aeration time in the same manner as described above. The aeration conditions may be the same as the aeration conditions when shifting from the treatment process to the rest period.

  When shifting from the rest period to the treatment period, it is preferable to perform aeration by returning the sludge in the solid-liquid separation tank to the biological treatment tank after the start of aeration and / or after the supply of the liquid to be treated. When the aeration is stopped from the processing period and the suspension period is shifted to the suspension period, it is preferable to discharge the sludge in the solid-liquid separation tank as much as possible and shift to the suspension period. However, it is difficult to discharge completely, and some remains. In this way, the sludge remaining in the solid-liquid separation tank decays, the activity decreases, and the water quality deteriorates.By returning the sludge containing the deteriorated water to the biological treatment tank and performing aeration, The sludge can be activated and the anaerobic decomposition product contained in the deteriorated water can be oxidatively decomposed.

  When sludge is returned to the aerated biological treatment tank, the liquid level in the biological treatment tank rises and the liquid in the biological treatment tank flows out into the solid-liquid separation tank, but the liquid level in the solid-liquid separation tank is lowered. Therefore, the separation liquid is not discharged from the solid-liquid separation tank, the residual sludge in the solid-liquid separation tank is returned to the biological treatment tank and aerated, and the sludge of the entire treatment system is activated. When supply of the liquid to be treated is started in such a state, the liquid in the biological treatment tank flows out to the solid-liquid separation tank, and the liquid level of the solid-liquid separation tank rises. Is discharged as a processing solution. After starting the supply of the liquid to be treated, even if the liquid level in the solid-liquid separation tank is below the overflow liquid level, the sludge is returned to continuously activate the sludge and oxidatively decompose the anaerobic decomposition products. Therefore, the sludge of the whole processing system is activated, and the return to the continuous processable state becomes faster. After exceeding the overflow liquid level, the sludge is returned to the normal state and the transition to the treatment period is completed.

  When the transition to the treatment period is completed, it enters a continuous treatment state and treatment is performed under normal treatment conditions.In this case, since aeration is performed before and after the suspension period, untreated organic matter or anaerobic degradation products are decomposed. Thus, the aerobic organism is maintained in an activated state, thereby quickly returning to a continuously processable state, and normal processing in the continuous process state is performed. The activity of sludge in the aerobic biological treatment system after the transition to the treatment period is substantially completely restored. Since the sludge in the solid-liquid separation tank is discharged as much as possible, the amount of returned sludge is small immediately after the transition to the treatment period, but sufficient MLSS can be obtained by returning and holding a large amount of sludge before suspension. Can be secured. Even when the amount of sludge retained is small, the sludge rapidly grows by the start of supply of the liquid to be treated and recovers sufficient MLSS.

  The sludge remaining in the solid-liquid separation tank generates anaerobic decomposition products during the suspension period and part of the sludge floats, but part of the anaerobic decomposition products is returned together with the sludge. The remaining decomposed products and floating sludge flow into the treated water after the transition to the treatment period, but are easily removed in a subsequent treatment step such as a subsequent coagulation step. By discharging the sludge in the solid-liquid separation tank as much as possible, the remaining sludge becomes a small amount, and the anaerobic decomposition product and the floating sludge that flow out also become a small amount, so that the treatment cost in the post-treatment process is lowered.

  According to the present invention, when shifting to the suspension period, the supply of the liquid to be processed is stopped, and after the supply of the liquid to be processed is stopped, the aeration is continued until the inside of the biological treatment tank becomes over-aerated, and then the aeration is stopped. In addition, when the treatment is stopped in a state where the sludge in the solid-liquid separation tank is discharged and the liquid level of the solid-liquid separation tank is lowered, and the transition to the treatment period, the biological treatment tank is in an over-aerated state. After aeration is continued until starting, supply of the liquid to be treated is started and the treatment is started, so that it is possible to pause while maintaining sludge activity while minimizing rot during the pause It is possible to start up treatment by preventing deterioration of treatment water quality due to reduction in treatment efficiency at restart, sludge outflow, etc., thereby repeating continuous treatment and pause of aerobic biological treatment at low cost and high treatment efficiency Can do low cost processing Intermittent biological treatment method can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart of the intermittent biological treatment method of the embodiment, and shows an example applied to the biological treatment method of human waste by nitrification denitrification. In FIG. 1, 1 is a denitrification tank, 2 is a nitrification tank, 3 is a second denitrification tank, 4 is a re-aeration tank, and 5 is a solid-liquid separation tank. The denitrification tank 1 is configured to perform denitrification by stirring with a stirrer 6 in an anaerobic state. The nitrification tank 2 is configured to be aerobically oxidized and nitrified by aeration with an air diffuser 7. The second denitrification tank 3 is configured to perform second denitrification by stirring with a stirrer 8 in an anaerobic state. The re-aeration tank 4 is configured to be aerobically oxidized by aeration with an air diffuser 9. The solid-liquid separation tank 5 is configured to separate the separation liquid and sludge by sedimentation separation.

  In the treatment method of FIG. 1, the liquid to be treated (human waste) is introduced into the denitrification tank 1 from the liquid passage 11, diluted with a diluting liquid such as miscellaneous wastewater from the dilution liquid passage 12, and diluted from the return sludge passage 13 The return sludge is introduced, the nitrification liquid is introduced from the nitrification liquid passage 14, stirred and mixed by the stirrer 6 in an anaerobic state, and denitrifying bacteria are used as a carbon source, thereby using the organic matter in the liquid to be treated as a carbon source. Denitrify nitric acid or nitrite nitrogen. A part of the reaction solution in the denitrification tank 1 is taken out from the line 15 to the nitrification tank 2 and aerated by the air diffuser 7 to aerobically oxidize the remaining organic matter and to convert the remaining ammonia nitrogen to the action of nitrifying bacteria. Nitrates to nitrite or nitrite nitrogen.

  A part of the reaction liquid in the nitrification tank 2 is taken out from the line 16, and a part is introduced into the denitrification tank 1 from the nitrification liquid passage 14 as a nitrification liquid. The remaining portion is introduced into the second denitrification tank 3, a nutrient source such as methanol is supplied from the line 17, and the second denitrification is performed by stirring with the stirrer 8 in an anaerobic state. A part of the reaction solution in the second denitrification tank 3 is taken out from the line 18 to the re-aeration tank 4 and aerated by the air diffuser 9 to aerobically oxidize the remaining organic matter. A part of the reaction solution in the re-aeration tank 4 is taken out from the line 19 to the solid-liquid separation tank 5 and separated into solid and liquid by sedimentation separation, and the separated liquid is discharged from the line 21 as a processing liquid. The separated sludge is taken out from the line 22, a part is returned from the return sludge passage 13 as return sludge to the denitrification tank 1, and the remaining part is discharged from the line 23 as excess sludge.

  The above is continuous processing in the processing period, for example, it is performed on a weekday of one week, and the above-mentioned continuous processing is stopped and shifted to a rest period on the weekend. When shifting from the treatment period to the suspension period, the supply of the liquid to be treated from the liquid path 11 to be treated and the dilution liquid from the dilution liquid path 12 to the denitrification tank 1 is stopped, and then inside the nitrification tank 2 as a biological treatment tank Aeration by the air diffusing device 7 is continued until is in an over-aerated state. At this time, returning the return sludge from the return sludge passage 13, introducing the nitrification solution from the nitrification passage 14, supplying the nutrient source from the line 17, aeration by the air diffuser 9, stirring by the stirrers 6 and 8, from the line 23 The discharge of excess sludge will continue. As a result, even after the supply of the liquid to be processed is stopped, the organic matter and ammonia nitrogen in the liquid to be processed already processed are processed and the return sludge is activated. The liquid level drops.

  In the over-aeration state in the nitrification tank 2, when the DO meter 24 installed in the nitrification tank 2 detects that the DO value exceeds a predetermined value, the blower 25 of the air diffuser 7 is stopped and aeration is stopped. However, it may be stopped by elapse of a preset time. At the same time, the introduction of the nitrification liquid from the nitrification liquid passage 14, the supply of the nutrient source from the line 17, aeration by the aeration device 9, agitation by the agitators 6 and 8 are also stopped. As a result, the process itself is suspended, but by returning the returned sludge from the return sludge passage 13 and discharging the excess sludge from the line 23, a part of the sludge in the solid-liquid separation tank 5 is denitrified. 1. The liquid level of the solid-liquid separation tank 5 is lowered by holding it in the nitrification tank 2 and discharging the remainder. The sludge in the solid-liquid separation tank 5 is taken out by detecting the interface with the interface meter 26 provided in the solid-liquid separation tank 5 to detect the time when the sludge layer 27 in the solid-liquid separation tank 5 is discharged, and removing the sludge. Although the pump 28 can be stopped, the pump 28 may be stopped by visual inspection or the elapse of a set time.

  In this way, the processing period shifts to the suspension period. At this time, after the supply of the liquid to be processed is stopped, the aeration is continued until the inside of the nitrification tank 2 and the re-aeration tank 4 is over-aerated. Decompose untreated organic matter present in the aerobic biological treatment system, maintain the aerobic biological activity of the retained sludge, and prevent the organic matter from undergoing anaerobic treatment during the downtime to produce pollutants Can do. Further, when shifting from the treatment period to the suspension period, the sludge staying during the suspension period is stopped by discharging the sludge in the solid-liquid separation tank 5 and lowering the liquid level of the solid-liquid separation tank 5. Decrease the volume to reduce water quality deterioration and sludge floating due to sludge decay, and prevent outflow from the solid-liquid separation tank even if sludge decays during suspension and water quality deteriorates and sludge rises. be able to.

  When the operation is resumed after the transition to the pause period as described above and the transition to the treatment period is performed, the liquid to be treated from the liquid path 11 to be treated and the dilution liquid from the dilution liquid path 12 to the denitrification tank 1 are transferred. In a state where supply is stopped, aeration by the aeration device 7 is started until the inside of the nitrification tank 2 as a biological treatment tank is in an over-aerated state. At this time, returning of the return sludge from the return sludge passage 13, introduction of the nitrification liquid from the nitrification passage 14, aeration by the air diffuser 9, stirring by the stirrers 6 and 8 are also started. As a result, the anaerobic decomposition product of the organic matter generated in the aerobic biological treatment system during the rest period can be oxidized, and the aerobic organism can be activated to be in a continuously processable state. During this time, the return sludge from the return sludge passage 13 and the introduction of the nitrification liquid from the nitrification passage 14 cause the reaction liquid in the denitrification tank 1 to flow through each tank sequentially to reach the solid-liquid separation tank 5. Since the liquid level of the solid-liquid separation tank 5 is in a lowered state, excess sludge is not discharged from the line 23, but the sludge returned from the return sludge passage 13 is recycled from the denitrification tank 1 to the nitrification tank 2. The anaerobic decomposition product of the organic matter that enters the aeration tank 4 and is aerated and generated during the rest period is oxidized.

  After aeration is continued until the inside of the nitrification tank 2 and the re-aeration tank 4 as biological treatment tanks are in an over-aerated state, the liquid to be treated from the liquid treatment path 11 to the denitrification tank 1 and the dilution liquid path 12 The supply of the diluent is started, the process is started, and the process proceeds to the process period. Continuation of air aeration oxidizes the anaerobic degradation products of organic matter generated in the aerobic biological treatment system during the suspension period and activates the aerobic organisms, allowing continuous treatment as soon as the liquid to be treated is supplied It is. The sludge can be returned from the solid-liquid separation tank 5 even after the start of the supply of the liquid to be treated, and the returned sludge enters the nitrification tank 2 from the denitrification tank 1 and is generated during the pause period. The anaerobic decomposition product of the organic matter is oxidized, the sludge and liquid in the solid-liquid separation tank 5 are replaced, and the pollutant is reduced.

  As described above, the liquid level of the solid-liquid separation tank 5 is lowered at the stage of shifting to the pause period, but the solid-liquid separation tank 4 is re-exposed from the re-aeration tank 4 by starting the supply of the liquid to be processed by shifting to the processing period. The amount of the reaction liquid transferred to 5 increases, the liquid level of the solid-liquid separation tank 5 rises, and the processing liquid eventually overflows. At the same time, the sludge interface also rises due to the growth of the organisms, so that the discharge of excess sludge from the line 23 is started when the sludge interface exceeds the set interface. As a result, the processing is completely started, and normal continuous processing is performed.

  The sludge that remains in the solid-liquid separation tank 5 after the transition to the suspension period generates anaerobic decomposition products during the suspension period and part of the sludge floats up, but part of the anaerobic decomposition products is returned together with the sludge, The remaining decomposed products and floating sludge flow into the treated water after the transition to the treatment period, but are easily removed in a subsequent treatment step such as a subsequent coagulation step. By discharging the sludge in the solid-liquid separation tank 5 as much as possible, the remaining sludge becomes a small amount, and the anaerobic decomposition product and the floating sludge that flow out also become a small amount, so that the processing cost in the post-treatment process becomes low.

  In the above-mentioned treatment, it is possible to pause while maintaining the sludge activity while minimizing the rot during the suspension, and to prevent deterioration of the treated water quality due to reduction in treatment efficiency at the time of restarting operation and sludge outflow. The treatment can be started up, and the continuous treatment and the pause of the aerobic biological treatment can be repeated at a low cost and in a high treatment efficiency, thereby performing the intermittent biological treatment capable of performing the low-cost treatment. be able to.

[Example 1]:
In the facility for processing liquid treatment capacity of 30 kL / day shown in FIG. 1, the facility was operated during the daytime on Friday and stopped during the daytime on Friday. Within one week, actual operation was performed for 4 days, and the facility was shut down for 3 days. The weekly carry-in amount is 124 kL and the daily average is 17.8 kL / day, but the amount of liquid to be treated per operation day is about 31 kL / day, the MLSS in the nitrification tank 2 is 6200 mg / L, and sludge The continuous treatment was carried out at a withdrawal amount of 248 kg · ds / day. Supply amount of liquid to be treated to denitrification tank 1 3.5 m ³ / h, supply amount of diluting liquid such as miscellaneous wastewater 19.0 m ³ / h, return amount of sludge 18.3 m ³ / h, nitrile solution circulation rate 166.0 m ³ / H, the amount of surplus sludge discharged from the solid-liquid separation tank 5 is 2.1 m ³ / h, the residence time is 2.6 hr for the denitrification tank 1 and the nitrification tank 2, and 6.2 hr for the second denitrification tank 3. The tank 4 is 2.1 hr and the solid-liquid separation tank 5 is 6.0 hr.

  The supply of the liquid to be treated and the diluent was stopped on Friday afternoon, and the aeration of the nitrification tank 2 and the re-aeration tank 4 was performed for 2.9 hours in a state where the nitrification liquid circulation, the return sludge was returned, and the excess sludge was discharged. Aeration was stopped when the DO value increased by about 4 mg / L. Returning the returned sludge from the solid-liquid separation tank 5 and discharging the excess sludge were continued for 1.6 hours even after the aeration was stopped, and most of the sludge at the bottom of the solid-liquid separation tank 5 was discharged. Thereby, the liquid level of the solid-liquid separation tank 5 was lowered by 100 mm, and the sludge interface was lowered by about 400 mm. In this state, the transition to the suspension period is completed.

  While the supply of the liquid to be treated and the dilution liquid was stopped on Monday morning, the aeration of the nitrification tank 2 and the re-aeration tank 4 was performed while returning the sludge and liquid remaining from the solid-liquid separation tank 5 to the denitrification tank 1. After a minute, the DO value increased to about 3 mg / L, and supply of the liquid to be treated and the diluent was started. The liquid level of the solid-liquid separation tank 5 rose and the treated water overflowed in 1.5 hours after the supply of the liquid to be treated and the diluent was started. When the sludge interface of the solid-liquid separation tank 5 returned to a predetermined level, extraction of excess sludge was started and the process was returned to continuous processing.

Table 1 shows the water quality immediately after the suspension of the nitrification tank 2 reaction liquid and the solid-liquid separation tank 5 separation liquid (immediately after stopping aeration for the suspension) and immediately after restarting (immediately after charging at the time of restarting). In Table 1, the BOD value of the nitrification tank 2 reaction liquid indicates that BOD is treated by air aeration. The COD value of the nitrification tank 2 reaction liquid increases immediately after restarting, but can be removed by a subsequent aggregation process. The NO ₂ —N value of the reaction solution in the nitrification tank 2 indicates that the nitrogen eluted by the air aeration can be processed. The MLSS value of the nitrification tank 2 reaction solution indicates that MLSS has decreased due to sludge dismantling. The BOD and COD values of the separated liquid-liquid separation tank 5 indicate that SS-related BOD and COD have decreased due to the decrease in SS, respectively. The SS value of the solid-liquid separation tank 5 separation liquid shows that SS decreased due to a long residence time. The TN value of the separation liquid in the solid-liquid separation tank 5 indicates that SS TN has decreased due to the decrease in SS. The NO ₂ -N value of the solid-liquid separation tank 5 separation liquid indicates that there is no elution of nitrogen because sludge is excluded.

[Comparative Example 1]
After the operation as in Example 1 was continued for 2 months, the operation in Comparative Example 1 was started. First, the operation was continued from Monday to Friday in the same manner as in Example 1, and the supply of the liquid to be treated and the dilution liquid, the aeration of the nitrification tank and the re-aeration tank, and the extraction of the sludge from the settling tank were all stopped on Friday afternoon. . At this time, the on-off valve provided between the re-aeration tank and the precipitation tank was closed. This was maintained until Monday morning. When the liquid level of the precipitation tank was visually observed on Monday morning, the presence of scum covering about 30% of the liquid level was recognized. Next, each on-off valve was opened to shift to a normal operation state at once. Table 2 shows the water quality immediately after the transition.

Comparing Table 2 and Table 1, it can be seen that in Table 2, sludge decays during suspension and BOD, TN, NH ₄ -N, etc. are greatly increased. On the other hand, it becomes anaerobic atmosphere because it does not over-aeration, it is found that the NO 2 _-N and NO 3 _-N is reduced. It is considered that a rise time of about 5 hours is required to return from such deterioration of water quality to the water quality at the time of steady operation as in Example 1, and the operation efficiency is reduced during that time.

[Example 2, Comparative Example 2]:
When normal operation and operation of Comparative Example 1 were performed, ferric chloride was added as a flocculant to the precipitation treated water to obtain agglomerated treated water. The results shown in Table 3 were obtained. From this, when a predetermined amount of ferric chloride was added to the final treated water during normal operation, treated water with a predetermined water quality was obtained, whereas during the operation of Comparative Example 1, twice the amount of ferric chloride as compared to normal operation was obtained. Even when iron was added, the water quality of the coagulated treated water did not reach the water quality during normal operation. However, even the water quality of Comparative Example 2 is treated by post-treatment, so there is no problem.

  A treatment period in which the liquid to be treated is received into a biological treatment tank to continuously perform aerobic biological treatment, a part of the reaction liquid in the biological treatment tank is transferred to a solid-liquid separation tank, and solid-liquid separation is performed, and the treatment is suspended. It can be used for an intermittent biological treatment method that repeats a pause period.

It is a flowchart of the intermittent biological treatment method of an embodiment.

Explanation of symbols

1 Denitrification tank 2 Nitrification tank 3 Second denitrification tank 4 Re-aeration tank 5 Solid-liquid separation tank

Claims (5)

A treatment period in which a liquid to be treated is received in a biological treatment tank to perform aerobic biological treatment, a part of the reaction liquid in the biological treatment tank is transferred to a solid-liquid separation tank, and a solid-liquid separation is performed, and a pause period in which the process is suspended In the intermittent biological treatment method,
When shifting from the treatment period to the suspension period, the supply of the liquid to be treated is stopped,
Even after the supply of the liquid to be treated is stopped, aeration is stopped after the aeration is continued until the inside of the biological treatment tank becomes over-aerated.
And the process is stopped in the state which discharged | emitted the sludge in a solid-liquid separation tank, and lowered the liquid level of the solid-liquid separation tank, The intermittent biological treatment method characterized by the above-mentioned.   The method according to claim 1, wherein the sludge discharged from the solid-liquid separation tank is returned to the biological treatment tank during aeration and / or after aeration is stopped.   The method according to claim 1 or 2, wherein when the sludge in the solid-liquid separation tank is discharged, the sludge is discharged until the interface becomes a certain level or less using a sludge interface meter. A treatment period in which a liquid to be treated is received in a biological treatment tank to perform aerobic biological treatment, a part of the reaction liquid in the biological treatment tank is transferred to a solid-liquid separation tank, and a solid-liquid separation is performed, and a pause period in which the process is suspended In the intermittent biological treatment method according to any one of claims 1 to 3 ,
When moving from the rest period to the treatment period, after aeration is continued until the inside of the biological treatment tank becomes over-aerated,
An intermittent biological treatment method characterized in that the treatment is started by starting the supply of the liquid to be treated.   The method according to claim 4, wherein the aeration is performed by returning the sludge in the solid-liquid separation tank to the biological treatment tank after the start of aeration and / or after the supply of the liquid to be treated.

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