Batch type organic wastewater treatment method and batch type organic wastewater treatment device

Abstract

To provide a batch type organic wastewater treatment method that can reduce unnecessary maintenance costs by accurately detecting nitrification states and controlling to proper aeration quantity.SOLUTION: In a batch type organic wastewater treatment method where nitrification processes by aeration and denitrification processes by non-aeration or weak-aeration are repeated in a biological treatment tank, pH of an active sludge retained in the biological treatment tank is measured; based on an aeration quantity or a time needed for switching pH change rates from a negative value to 0 or a positive value from the start of an aeration in the nitrification process, at least one of current aeration quantity in the nitrification process, an aeration quantity in the next time, aeration time, a supply amount of organic waste water in the next time in the denitrification process, a denitrification time, and an addition amount of a hydrogen donor is controlled.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a batch-type organic wastewater treatment method and a batch-type organic wastewater treatment device that repeat a nitrification step with aeration and a denitrification step without aeration in a biological treatment tank. [Background technology]

[0002] As disclosed in Patent Document 1, a batch organic wastewater treatment method has been conventionally adopted to purify organic wastewater such as human waste and septic tank sludge, in which a nitrification process using aeration and a denitrification process without aeration are repeated in a biological treatment tank.

[0003] In this organic wastewater treatment method, when nitrification and denitrification of organic wastewater is carried out using a complete mixing aeration tank, DO at the stage when nitrification is complete is detected, and the total volume of blown air required for the next nitrification and denitrification cycle is calculated from the relationship between the detected DO and the standard DO. The total volume of blown air is then distributed over two or more stages over time, with more air being supplied to the tank in the latter half.

[0004] Patent Document 2 proposes a method for treating wastewater in a single reaction tank by intermittently aerating wastewater while continuously stirring it, and alternately switching the state inside the tank between anaerobic and aerobic conditions, in which the anaerobic time period in the intermittent aeration cycle, in which no air is supplied, and the aerobic time period in which air is supplied, are set at a predetermined ratio, and during the aerobic time period, the amount of air supplied and / or the rotation speed of the agitator are increased during the period from the start of air supply until the DO inside the tank reaches a predetermined value.

[0005] Figure 5 shows an example of an organic wastewater treatment system that employs a batch-type organic wastewater treatment method using DO as an indicator. The system includes a single-tank batch-type nitrification / denitrification tank (a batch-type biological treatment tank), a secondary nitrification tank, a secondary denitrification tank, and a solid-liquid separation tank, in that order. Organic wastewater purified in the batch-type biological treatment tank is introduced into the secondary nitrification tank together with activated sludge, where residual ammonia undergoes secondary nitrification. The wastewater is then denitrified in the secondary denitrification tank, and solid-liquid separation is performed in a solid-liquid separation tank equipped with a settling tank. The separated liquid is disinfected as treated water and then discharged into a river. The separated solid, or sludge, is discarded as excess sludge, with a portion recycled and supplied to the batch-type biological treatment tank as return sludge.

[0006] As shown in Figures 6(a) and 6(b), in a batch biological treatment tank, for example, one cycle lasts for three hours, and one hour of biological treatment is repeated in each of parts 1 to 3. In part 1, organic wastewater such as human waste is supplied, and denitrification is carried out by gentle agitation using an agitator under anaerobic conditions with blower B stopped.

[0007] In the second part, blower B is operated to achieve a first aeration rate that is preset relative to the supply rate of organic wastewater, and nitrification treatment is carried out in an aerobic state with air supplied from an aeration device installed in the tank. Furthermore, in the third part, nitrification treatment is carried out at a predetermined aeration rate that is greater than the first aeration rate. The above-mentioned treatment times are examples and are not limited to these values.

[0008] The batch-type biological treatment tank is equipped with sensors that measure the oxidation-reduction potential (ORP) and dissolved oxygen concentration (DO), and the degree of nitrification treatment is determined using the sensor values ​​in Part 3 as an indicator, and the aeration volume is controlled based on those results. If the ORP or DO in Part 3 deviates above the preset appropriate range, the aeration volume is determined to be excessive, and the aeration volume in Part 3 of the current cycle is reduced, as well as the aeration volume in Part 2 of the next cycle. If the ORP or DO in Part 3 deviates below the preset appropriate range, the aeration volume in Part 2 of the next cycle is increased.

[0009] In the example of Figure 6(b), since the ORP in the third part of the Nth cycle is within the range between the upper and lower limits, the first aeration volume in the second part of the N+1th cycle is maintained (see the top row). When the ORP in the third part of the Nth cycle deviates upward from the upper limit, the aeration volume in the third part of the Nth cycle is decreased, and the first aeration volume in the second part of the N+1th cycle is decreased (see the middle row). When the ORP in the third part of the Nth cycle deviates downward from the lower limit, the first aeration volume in the second part of the N+1th cycle is increased (see the bottom row). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Special Publication No. 2-7720 [Patent Document 2] Japanese Patent Application Publication No. 5-237495 Summary of the Invention [Problem to be solved by the invention]

[0011] However, when the nitrification state is determined using ORP or DO as an indicator in a batch biological treatment tank, the optimal values ​​of ORP and DO fluctuate with the ammonia concentration, BOD, and SS contained in the organic wastewater, and the preset appropriate ranges of ORP and DO also fluctuate according to the optimal values. Therefore, if the appropriate ranges are fixed, it becomes difficult to adjust the first aeration volume supplied in the second part to the appropriate value.

[0012] It is also possible to use the value detected by an ammonia sensor as an indicator instead of ORP or DO to determine the nitrification state in the third part, but due to the characteristics of the ammonia sensor, the measurement accuracy decreases as the ammonia concentration decreases. As a result, in either case, the amount of aeration required to achieve sufficient nitrification and denitrification treatment becomes excessive, resulting in problems such as increased maintenance costs.

[0013] An object of the present invention is to provide a batch-type organic wastewater treatment method and a batch-type organic wastewater treatment device that can reduce unnecessary maintenance costs by properly detecting the nitrification state and controlling the aeration amount to an appropriate level. [Means for solving the problem]

[0014] In order to achieve the above-mentioned object, a first characteristic configuration of the batch organic wastewater treatment method according to the present invention is a batch organic wastewater treatment method that repeats a nitrification process using aeration and a denitrification process using no or weak aeration in a biological treatment tank, and that measures the pH of activated sludge stored in the biological treatment tank, and adjusts at least one of the current aeration amount, next aeration amount, aeration time in the nitrification process, the next organic wastewater supply amount in the denitrification process, the denitrification time, and the amount of hydrogen donor added, based on the aeration amount or time required from the start of aeration until the rate of pH change switches from a negative value to 0 or a positive value.

[0015] When the rate of change in pH from negative to zero or positive after the start of aeration in the nitrification process, it can be determined that almost all ammoniacal nitrogen has been oxidized and replaced with nitrate nitrogen. The level of organic wastewater load, i.e., the ammoniacal nitrogen content, can be estimated based on the aeration volume or time from the start of aeration until that point. Consequently, by adjusting at least one of the aeration volume and aeration time in the current or next nitrification process, the amount of organic wastewater supplied in the denitrification process, the denitrification time, and the amount of hydrogen donor added, it is possible to achieve an efficient and appropriate aeration volume for nitrification of ammoniacal nitrogen. For example, if the aeration volume is insufficient relative to the ammoniacal nitrogen content, the aeration volume can be increased, the aeration time can be extended, the amount of organic wastewater supplied in the denitrification process can be reduced, the denitrification time can be extended, the amount of hydrogen donor added can be increased, or any combination of these can be used to ensure sufficient nitrification in the next nitrification process.

[0016] The second characteristic configuration of the present invention is that, in addition to the first characteristic configuration described above, the treatment times of the nitrification step and the denitrification step are set constant, and a constant amount of organic wastewater to be treated is supplied to the denitrification step.

[0017] When it is necessary to maintain constant the treatment times of the nitrification step and the denitrification step and to maintain constant the supply amount of organic wastewater in the denitrification step, that is, to maintain constant the treatment time and the treatment amount of organic wastewater, it becomes possible to appropriately nitrify ammonia nitrogen with an appropriate aeration amount without waste by adjusting at least one of the aeration amount in the next nitrification step and the amount of hydrogen donor added in the next denitrification step.

[0018] The third characteristic configuration is that, in addition to the first characteristic configuration described above, the nitrification process is configured to perform either a first nitrification process with a variable aeration amount and a second nitrification process with a constant aeration amount, or a first nitrification process with a constant aeration amount and a second nitrification process with a variable aeration amount, in that order, and either the aeration amount of the first nitrification process or the aeration amount of the second nitrification process is adjusted based on the rate of change of pH in the second nitrification process.

[0019] During the transition from the denitrification process to the nitrification process, denitrification and nitrification coexist. Therefore, the nitrification process is divided into a first nitrification process and a second nitrification process. The first nitrification process transitions from a state of coexistence with denitrification to nitrification. The aeration volume is variable to accommodate fluctuations in ammoniacal nitrogen content, while the second nitrification process, with a constant aeration volume, promotes stable nitrification. The level of organic wastewater load is estimated based on the aeration volume or time required for the pH change rate in the second nitrification process to switch from negative to zero or positive. Adjusting the aeration volume in the next first nitrification process allows for efficient and appropriate aeration volume for the nitrification of ammoniacal nitrogen.

[0020] Furthermore, by dividing the nitrification process into a first nitrification process and a second nitrification process, the first nitrification process transitions from a state where denitrification and denitrification coexist to nitrification, and by maintaining a constant aeration volume, nitrification can be promoted stably regardless of the ammoniacal nitrogen content, while the second nitrification process, with its variable aeration volume, can promote nitrification in response to fluctuations in the ammoniacal nitrogen content. Furthermore, by estimating the level of organic wastewater load based on the aeration volume or time required for the rate of pH change in the second nitrification process to switch from a negative value to zero or a positive value, and adjusting the aeration volume in the next second nitrification process, it becomes possible to appropriately nitrify ammoniacal nitrogen with an appropriate aeration volume without waste.

[0021] The fourth characteristic configuration of the present invention is that, in addition to the third characteristic configuration described above, the first nitrification step, the second nitrification step, and the denitrification step are each set to a constant treatment time, and a constant amount of organic wastewater to be treated is supplied to the denitrification step.

[0022] When it is necessary to maintain constant the treatment times of the first and second nitrification steps and the denitrification step, and to maintain constant the supply amount of organic wastewater in the denitrification step, that is, to maintain constant the treatment time and the amount of organic wastewater treated, the level of organic wastewater load can be estimated based on the aeration volume required for the rate of pH change in the second nitrification step to switch from a negative value to 0 or a positive value, and the aeration volume in the next first nitrification step can be adjusted, thereby enabling ammonia nitrogen to be appropriately nitrified with an appropriate aeration volume that is not wasteful.

[0023] The fifth characteristic configuration of the same system is that, in addition to any one of the first to fourth characteristic configurations described above, a secondary denitrification tank and a solid-liquid separation tank are provided in this order downstream of the biological treatment tank, and residual nitrate nitrogen is denitrified in the secondary denitrification tank, solid-liquid separation is performed in the solid-liquid separation tank, and the activated sludge in the solid-liquid separation tank is returned to the biological treatment tank.

[0024] By providing a secondary denitrification tank and a solid-liquid separation tank in this order downstream of the batch biological treatment tank, the remaining nitrate nitrogen can be denitrified in the secondary denitrification tank after the batch biological treatment, and a portion of the excess sludge separated into solid and liquid in the solid-liquid separation tank can be returned to the batch biological treatment tank, thereby achieving efficient biological treatment.

[0025] The sixth characteristic feature of the present invention is that, in addition to the fifth characteristic feature described above, the solid-liquid separation tank separates the activated sludge into treated water and concentrated activated sludge using a membrane separation device.

[0026] It is preferable to submerge a membrane separation device in a solid-liquid separation tank instead of a settling tank, since this allows the equipment to be made smaller.

[0027] A characteristic configuration of the batch-type organic wastewater treatment device according to the present invention is that it is a batch-type organic wastewater treatment device equipped with a biological treatment tank that repeatedly performs a nitrification process using aeration and a denitrification process using no or weak aeration, and is equipped with a control device that measures the pH of activated sludge stored in the biological treatment tank and adjusts at least one of the current aeration amount, next aeration amount, aeration time in the nitrification process, the next organic wastewater supply amount in the denitrification process, the denitrification time, and the amount of hydrogen donor added, based on the aeration amount or time required from the start of aeration in the nitrification process until the rate of pH change switches from a negative value to 0 or a positive value. [Effects of the Invention]

[0028] As described above, according to the present invention, it is possible to provide a batch-type organic wastewater treatment method and a batch-type organic wastewater treatment device that can reduce unnecessary maintenance costs by properly detecting the nitrification state and controlling the aeration amount to an appropriate level. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1(a) is an explanatory diagram of a batch-type organic wastewater treatment method according to the present invention, and FIG. 1(b) is an explanatory diagram showing the transition state of pH. [Figure 2]FIG. 1 is a flow chart showing the procedure of a first embodiment of a batch-type organic wastewater treatment method according to the present invention. [Figure 3] FIG. 2 is a flow chart showing the procedure of a second embodiment of the batch-type organic wastewater treatment method according to the present invention. [Figure 4] 1(a) to 1(d) are explanatory diagrams of an embodiment of a batch-type organic wastewater treatment apparatus according to the present invention. [Figure 5] FIG. 1 is an explanatory diagram of a conventional batch-type organic wastewater treatment device. [Figure 6] FIG. 1(a) is an explanatory diagram of a conventional batch-type organic wastewater treatment method, and FIG. 1(b) is an explanatory diagram showing the transition state of ORP, which is used as an indicator of the progress of nitrification treatment, in the conventional batch-type organic wastewater treatment method. DETAILED DESCRIPTION OF THE INVENTION

[0030] BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a batch-type organic wastewater treatment method and a batch-type organic wastewater treatment apparatus according to the present invention will be described with reference to the drawings.

[0031] Figure 1(a) shows the flow of biological treatment in a single-tank batch-type nitrification / denitrification tank, which is a batch-type biological treatment tank. In a batch-type biological treatment tank, the denitrification process, the first nitrification process, and the second nitrification process are repeated in this order.

[0032] First, organic wastewater, such as sewage or septic tank sludge, is introduced into a biological treatment tank already filled with activated sludge. A denitrification process, in which nitrate nitrogen is reduced to nitrogen under anaerobic conditions, is carried out for a predetermined period of time. Next, aeration is supplied from Blower B to the aeration device at a first aeration rate, and a first nitrification process, in which ammonia nitrogen contained in the organic wastewater is oxidized to nitrite and nitrate, is carried out for a predetermined period of time. Furthermore, a second aeration rate, which may be different from or equal to the first aeration rate, is supplied from Blower B to the aeration device. A second nitrification process, in which almost all of the ammonia nitrogen contained in the organic wastewater is oxidized to nitrite and nitrate, is carried out for a predetermined period of time. After that, the system returns to the denitrification process, and new organic wastewater is introduced. At least during the denitrification process, the activated sludge in the biological treatment tank is circulated and agitated between the upper and lower layers via an external pump and circulation path, or by weak or intermittent weak aeration using an internal agitator or Blower B, maintaining anaerobic conditions.

[0033] Each process takes one hour, and the denitrification process, first nitrification process, and second nitrification process are repeated in this order, with one cycle taking three hours. Note that the time required for each process and the time required for one cycle can be set appropriately based on factors such as the capacity of the biological treatment tank, and are not fixed values. In the denitrification process, anaerobic microorganisms reduce nitrite and nitrate to nitrogen as shown in the following formula: 2NO2 - + 3H2 → N2+ 2OH - + 2H2O 2NO3 - + 5H2 → N2+ 2OH - + 4H2O In the second nitrification step, ammonia is oxidized to nitrite and nitrate by aerobic microorganisms. 2NH4 + + 3O2 → 2NO2 - + 2H2O + 4H + 2NO2 - + O2 → 2NO3 - The first nitrification step is a step in which the denitrification step described above is transitioned to the nitrification step, and both the denitrification step and the nitrification step proceed, with the nitrification step becoming predominant over time.

[0034] Figure 1(b) shows the behavior of the pH of activated sludge (shown by black circles in the figure) and the rate of change of pH (shown by open diamonds in the figure) detected by a pH sensor immersed in the biological treatment tank.

[0035] When moving from the second nitrification process to the denitrification process, the process becomes anaerobic and the reduction process to nitrogen progresses, causing the pH to gradually rise. When moving from the denitrification process to the first nitrification process, the process becomes aerobic and the denitrification reaction gradually slows down, and as shown in the above formula, the nitrification reaction progresses, in which the ammonia nitrogen contained in the wastewater is oxidized to nitrite and nitrate, causing the pH to gradually drop. When moving from the first nitrification process to the second nitrification process, the nitrification reaction progresses further, causing the pH to drop further, and eventually the pH to rise. In other words, the nitrification process of ammonia nitrogen can be determined to be almost complete when the rate of change of pH switches from a negative value to 0 or a positive value.

[0036] The level of organic wastewater load, i.e., the ammoniacal nitrogen content, can be estimated based on the aeration volume or time from the start of aeration in the first nitrification process to the point at which the rate of pH change switches from a negative value to 0 or a positive value in the second nitrification process, and the reaction equation described above.

[0037] The probability that the properties of the organic wastewater supplied to the denitrification process will change suddenly is low, and if the amount of organic wastewater supplied to the next denitrification process remains constant, the amount of aeration required to nitrify the ammonia nitrogen contained in the organic wastewater can be determined.

[0038] [First embodiment of batch-type organic wastewater treatment method] A first embodiment of the batch-type organic wastewater treatment method will be described below. When the time required for each process and the time required for one cycle are fixed, and the amount of organic wastewater supplied to the denitrification process is fixed, by fixing the amount of aeration in the second nitrification process to a sufficient amount among the aeration amounts required for one cycle and variably setting the amount of aeration in the first nitrification process, it becomes possible to avoid unnecessary aeration and properly purify the organic wastewater with an appropriate amount of aeration.

[0039] In other words, in the first aspect, the nitrification process is configured to carry out a first nitrification process with a variable aeration rate and a second nitrification process with a constant aeration rate in that order, and the aeration rate of the first nitrification process is adjusted based on the rate of change of pH in the second nitrification process.

[0040] In order to realize such a batch-type organic wastewater treatment method, the batch-type organic wastewater treatment device is provided with a control device that controls the inflow rate of organic wastewater and the aeration rate by blower B, as well as controls the time and cycle time of each of the denitrification step, first nitrification step, and second nitrification step to be constant, and detects the point in time when the rate of change of pH in the second nitrification step switches from a negative value to 0 or a positive value, thereby variably controlling the aeration rate in the first nitrification step.

[0041] A specific example of a batch organic wastewater treatment method executed by a control device is shown in Figure 2. The control device can be configured with a general-purpose computer equipped with a CPU board, memory board, and input / output board, and the following processes are executed based on a control program installed on the memory board.

[0042] At the beginning of each cycle, blower B is stopped, the denitrification process is carried out, and a predetermined amount of organic wastewater is fed into the biological treatment tank (SA1). The denitrification process is maintained until one hour has elapsed from the start of the denitrification process (SA2, N), and once one hour has elapsed (SA2, Y), the process moves to the first nitrification process, and the valve opening of blower B or the air supply pipe from blower B is adjusted so that the first aeration volume calculated by calculation is supplied during the first nitrification process (SA3).

[0043] After another hour has passed (SA4, Y), the process moves to the second nitrification step, and the valve opening of blower B or the air supply pipe from blower B is adjusted so that a preset second aeration volume is supplied during the second nitrification step (SA5). In step S5, the values ​​of the pH sensor are read at a predetermined sampling timing and stored in memory, and a calculation process is performed to calculate the rate of change of pH (SA6).

[0044] In step SA6, the average pH value for a specified time in the most recent past is updated at specified update intervals, and when the difference between the updated values ​​becomes 0 or positive a specified number of times in succession, the amount of aeration supplied up to that point is calculated, and the amount of ammonia nitrogen corresponding to that aeration amount is estimated to be the amount of ammonia nitrogen contained in the organic wastewater supplied in the denitrification process.

[0045] In this embodiment, pH is sampled at 1-second intervals, and the average of the most recent 60 (1-minute) sampled values ​​is calculated at 5-second intervals. To eliminate the influence of noise, the difference between the average calculated at 5-second intervals and the previous average is calculated, and if the difference is 0 or positive for five consecutive samples, it is determined that the nitrification process has ended (SA7). Note that the pH sampling period and the end determination algorithm are not limited to this example.

[0046] When the control device determines in step SA7 that the nitrification process has ended, it reduces the amount of air supply by 50% or stops it until a predetermined time has elapsed in the second nitrification process (SA8), and sets the aeration amount for the next first nitrification process (SA9). The degree of reduction is not particularly limited.

[0047] The aeration volumes in the first and second nitrification steps are initially set based on the supply volume of organic wastewater (ammoniacal nitrogen content). For example, the first nitrification step, which is the transition period from the denitrification step to the nitrification step, can be initially set to supply approximately 30% of the required aeration volume, and the remaining approximately 70% can be initially set to supply the second nitrification step. The aeration volume to be supplied in the first nitrification step can be calculated by subtracting the initially set aeration volume to be supplied in the second nitrification step from the required aeration volume calculated in step SA6.

[0048] If a predetermined time has elapsed (SA10, Y) and it is not possible to determine the completion of the nitrification treatment in the second nitrification step at this point (SA11, N), it is determined that the aeration amount is insufficient, and the aeration amount in the next first nitrification step is either uniformly increased to a preset value, or the degree of insufficiency of the aeration amount is determined based on the rate of change of pH and the degree of increase is adjusted (SA12).If it is determined in step SA11 that the completion of the nitrification treatment has been determined, the process returns to step SA1 and proceeds to the next cycle (SA11, Y).

[0049] [Second embodiment of batch-type organic wastewater treatment method] A second embodiment of the batch-type organic wastewater treatment method will be described below. When the time required for each process and the time required for one cycle are fixed, and the amount of organic wastewater supplied to the denitrification process is fixed, among the aeration amounts required for one cycle, the aeration amount in the first nitrification process can be fixed and the aeration amount in the second nitrification process can be variably set, thereby avoiding unnecessary aeration and enabling the organic wastewater to be properly purified with an appropriate aeration amount.

[0050] In other words, in the second aspect, the nitrification process is configured to perform a first nitrification process with a constant aeration volume and a second nitrification process with a variable aeration volume in that order, and the aeration volume of the second nitrification process is adjusted based on the rate of change of pH in the second nitrification process.

[0051] In order to realize such a batch-type organic wastewater treatment method, the batch-type organic wastewater treatment device is provided with a control device that controls the inflow rate of organic wastewater and the aeration rate by blower B, as well as controls the time and cycle time of each of the denitrification step, first nitrification step, and second nitrification step to be constant, and detects the point in time when the rate of change of pH in the second nitrification step switches from a negative value to 0 or a positive value, thereby variably controlling the aeration rate in the second nitrification step.

[0052] A specific example of a batch organic wastewater treatment method executed by a control device is shown in Figure 3. The control device can be configured with a general-purpose computer equipped with a CPU board, memory board, and input / output board, and the following processes are executed based on a control program installed on the memory board.

[0053] At the beginning of each cycle, blower B is stopped, the denitrification process is carried out, and a predetermined amount of organic wastewater is fed into the biological treatment tank (SB1). The denitrification process is maintained until one hour has passed from the start of the denitrification process (SB2, N), and once one hour has passed (SB2, Y), the process moves to the first nitrification process, and the valve opening of blower B or the air supply pipe from blower B is adjusted so that a predetermined first aeration volume is supplied during the first nitrification process (SB3).

[0054] After another hour has passed (SB4, Y), the process moves to the second nitrification step, and the valve opening of blower B or the air supply pipe from blower B is adjusted so that the second aeration volume calculated by the calculation process executed in the previous cycle is supplied during the second nitrification step (SB5). In step SB5, the value of the pH sensor is read at a predetermined sampling timing and stored in memory, and calculation process is executed to calculate the rate of change of pH (SB6).

[0055] In step SB6, the average pH value for a predetermined time in the most recent past is updated at predetermined update intervals. When the difference between the updated values ​​becomes zero or positive a predetermined number of times in succession (SB7), the amount of aeration supplied up to that point is calculated, and the amount of ammonia nitrogen corresponding to that aeration amount is estimated to be the amount of ammonia nitrogen contained in the organic wastewater supplied in the denitrification process.

[0056] A determination is made as to whether that time falls within a specific time period from a predetermined time prior to the end of the second nitrification step to the end of the step (SB8), and if it falls within the specific time period (SB8, Y), the amount of air supply is reduced by 50% or stopped until the predetermined time has elapsed in the second nitrification step, and the aeration volume for the next first nitrification step is maintained at the current value (SB9), and if it falls before the specific time period (SB8, N), the amount of air supply is reduced by 50% or stopped until the predetermined time has elapsed in the second nitrification step, and the aeration volume for the next first nitrification step is reduced by a predetermined amount (SB10). The degree of reduction is not particularly limited.

[0057] If the difference in the average pH values ​​becomes 0 or positive by the time the predetermined time has elapsed until the end of the second nitrification step, and it is determined that the nitrification process has been completed, the process returns to step SB1 and proceeds to the next cycle (SB11, Y, SB12, Y).If the difference in the average pH values ​​does not become 0 or positive by the time the predetermined time has elapsed until the end of the second nitrification step, and it is determined that the nitrification process has not been completed (SB11, Y, SB12, N), the aeration volume for the next first nitrification step is increased by a predetermined amount (SB13).

[0058] In this embodiment, the specific time period is set to 10 minutes from the time 10 minutes before the end of the second nitrification step, which is 1 hour, to the end of the second nitrification step. The specific time period is not particularly limited, but may be set in the latter half of the time required for the second nitrification step.

[0059] As in the first embodiment described above, in the second embodiment, pH is sampled at 1-second intervals, and the average of the most recent 60 (1-minute) sampled values ​​is calculated at 5-second intervals. To eliminate the effects of noise, the difference between the average calculated at 5-second intervals and the previous average is calculated, and if the difference is zero or positive for five consecutive samples, it is determined that the nitrification process has ended (SB7). Note that the pH sampling period and end-of-treatment determination algorithm are not limited to this example.

[0060] The aeration volumes in the first and second nitrification steps are initially set based on the supply volume of organic wastewater (ammoniacal nitrogen content). For example, the first nitrification step, which is the transition period from the denitrification step to the nitrification step, can be initially set to supply approximately 30% of the required aeration volume, and the remaining approximately 70% can be initially set to supply the second nitrification step. The aeration volume to be supplied in the second nitrification step can be calculated by subtracting the initially set aeration volume to be supplied in the first nitrification step from the required aeration volume calculated in step SB6.

[0061] The organic wastewater treatment apparatus equipped with the batch-type biological treatment tank described in the first and second embodiments is realized in the manner shown in FIGS. 4(a) to 4(d). In Figure 4(a), a secondary nitrification tank, a secondary denitrification tank, and a solid-liquid separation tank are provided in this order downstream of a batch-type biological treatment tank, and the system is configured so that remaining ammonia nitrogen is nitrified in the secondary nitrification tank, remaining nitrate nitrogen is denitrified in the secondary denitrification tank, and solid-liquid separation is performed in the solid-liquid separation tank. A sludge return line is provided so that a portion of the activated sludge separated from the solid-liquid separation tank is continuously returned to the biological treatment tank as returned sludge.

[0062] In Figure 4(b), a secondary denitrification tank and a solid-liquid separation tank are provided in this order downstream of the batch biological treatment tank, and the remaining nitrate nitrogen is denitrified in the secondary denitrification tank, followed by solid-liquid separation in the solid-liquid separation tank. A sludge return line is provided so that a portion of the activated sludge separated from the solid-liquid separation tank is returned to the biological treatment tank as returned sludge.

[0063] In Figure 4(c), a secondary denitrification tank, a reaeration tank, and a solid-liquid separation tank are provided in this order downstream of the batch biological treatment tank, and the system is configured so that remaining nitrate nitrogen is denitrified in the secondary denitrification tank, reaeration is performed in the reaeration tank, and solid-liquid separation is performed in the solid-liquid separation tank. A sludge return line is provided so that a portion of the activated sludge separated from the solid-liquid separation tank is returned to the biological treatment tank as returned sludge.

[0064] In Figure 4(d), a secondary nitrification tank, a secondary denitrification tank, and a solid-liquid separation tank are provided in this order downstream of a batch-type biological treatment tank, and the remaining ammonia nitrogen is nitrified in the secondary nitrification tank, the remaining nitrate nitrogen is denitrified in the secondary denitrification tank, and the activated sludge is separated into treated water and concentrated activated sludge by a membrane separation device immersed in the solid-liquid separation tank. A sludge return line is provided so that a portion of the activated sludge separated from the solid-liquid separation tank is returned to the biological treatment tank as returned sludge.

[0065] In the above-described embodiment, the treatment times of the first and second nitrification steps and the denitrification step are maintained constant, and the supply amount of organic wastewater in the denitrification step is maintained constant; that is, the treatment time and treatment amount of organic wastewater are maintained constant. However, if fluctuations in the treatment time of each step and the supply amount of organic wastewater in the denitrification step are acceptable, it is possible to appropriately nitrify ammonia nitrogen with an appropriate aeration amount without waste by adjusting at least one of the aeration amount and aeration time in the next nitrification step, and / or the supply amount of next organic wastewater in the denitrification step, the denitrification time, and the amount of hydrogen donor added, or by adjusting any combination thereof.

[0066] For example, when it is necessary to increase the aeration volume, the aeration volume can be maintained or the degree of increase in the aeration volume can be suppressed by reducing the supply amount of organic wastewater. Furthermore, it is possible to substantially increase the aeration volume by extending the treatment time of the first and / or second nitrification steps. Furthermore, when it is necessary to increase the aeration volume, the ammonia nitrogen concentration in the organic wastewater is high, so increasing the amount of hydrogen donor added in the denitrification step can promote the denitrification process.

[0067] In the above-described embodiment, an example was described in which the nitrification process consists of two steps, the first and second nitrification steps, and the time when the rate of change of pH switches from a negative value to 0 or a positive value is detected in the second nitrification step. However, if the nitrification process consists of a single step, it is sufficient to detect the time when the rate of change of pH switches from a negative value to 0 or a positive value in that nitrification step.

[0068] In the above-described embodiment, only pH is used as an indicator for controlling the aeration amount, but other indicators such as dissolved oxygen concentration (DO) and oxidation-reduction potential (ORP) may also be added in addition to pH, and the completion time of the nitrification treatment may be determined using all or any two or more of these indicators.

[0069] The above-described embodiments are merely examples of the present invention, and the present invention is not limited by the description. It goes without saying that the specific conditions and numerical values ​​of each process can be appropriately changed and designed within the scope of the effects of the present invention. Furthermore, any one or more of the above-described embodiments may be appropriately combined.

Claims

1. A batch-type organic wastewater treatment method in which a nitrification process by aeration and a denitrification process by non-aeration or weak aeration are repeated in a biological treatment tank, The method for batchwise organic wastewater treatment includes measuring the pH of activated sludge stored in the biological treatment tank, and adjusting at least one of the current aeration amount, the next aeration amount, and the aeration time in the nitrification step, the next supply amount of organic wastewater in the denitrification step, the denitrification time, and the amount of hydrogen donor to be added, based on the aeration amount or the time required from the start of aeration in the nitrification step until the rate of change of pH switches from a negative value to 0 or a positive value.

2. 2. A batch-type organic wastewater treatment method according to claim 1, wherein the treatment times of said nitrification step and said denitrification step are set constant, and a constant amount of organic wastewater to be treated is supplied to said denitrification step.

3. The nitrification step is configured to carry out either a first nitrification step with a variable aeration amount and a second nitrification step with a constant aeration amount, or a first nitrification step with a constant aeration amount and a second nitrification step with a variable aeration amount, in this order; 2. The batch organic wastewater treatment method according to claim 1, wherein the aeration amount in either the first nitrification step or the second nitrification step is adjusted based on the rate of change of pH in the second nitrification step.

4. 4. A batch-type organic wastewater treatment method according to claim 3, wherein the first nitrification step, the second nitrification step and the denitrification step are each set to a constant treatment time, and a constant amount of organic wastewater to be treated is supplied to the denitrification step.

5. 5. The batch organic wastewater treatment method according to claim 1, further comprising a secondary denitrification tank and a solid-liquid separation tank, in this order, downstream of the biological treatment tank, wherein residual nitrate nitrogen is denitrified in the secondary denitrification tank, solid-liquid separation is performed in the solid-liquid separation tank, and the activated sludge in the solid-liquid separation tank is returned to the biological treatment tank.

6. 6. A batch-type organic wastewater treatment method according to claim 5, wherein the solid-liquid separation tank separates the activated sludge into treated water and concentrated activated sludge by a membrane separator.

7. A batch-type organic wastewater treatment device equipped with a biological treatment tank that repeats a nitrification process by aeration and a denitrification process by no aeration or weak aeration, A batch-type organic wastewater treatment device equipped with a control device that measures the pH of activated sludge stored in the biological treatment tank, and adjusts at least one of the current aeration amount, the next aeration amount, and the aeration time in the nitrification step, the next organic wastewater supply amount, the denitrification time, and the amount of hydrogen donor added in the denitrification step, based on the aeration amount or the time required from the start of aeration in the nitrification step until the rate of change of pH switches from a negative value to 0 or a positive value.

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