JP2022048901A - Nitrification denitrification device - Google Patents

Abstract

To provide a nitrification denitrification device that can efficiently treat sewage.SOLUTION: A nitrification denitrification device 1 includes: a nitrification denitrification tank 2,; a sewage supply line 31 that supplies sewage to the nitrification denitrification tank 2; a circulation pump 42 that draws out an internal liquid of the nitrification denitrification tank 2 from the nitrification denitrification tank 2 and sends it out; an overflow shaft 43 that mixes a circulating fluid drawn from the nitrification denitrification tank 2 with air and injects it into the nitrification denitrification tank 2; a circulation line 41 that circulates the circulating fluid to the nitrification denitrification tank 2 through the overflow shaft 43; an ammonia sensor 7 that measures an ammonia concentration in the internal liquid; and a control unit 6 that can change an output value of a first output and/or an output value of a second output of the circulation pump 42 based on a measurement result of the ammonia sensor 7.SELECTED DRAWING: Figure 1

Description

The present invention relates to a nitrification denitrification apparatus.

It is known to treat sewage such as human waste by the biological nitrification denitrification method. Such a biological nitrification denitrification method includes a nitrification step and a denitrification step. In the nitrification step, activated sludge (microorganisms) oxidizes ammoniacal nitrogen in the sewage to nitrite or nitrate nitrogen. In the denitrification step, activated sludge reduces nitrite or nitrate nitrogen to nitrogen.

A nitrification denitrification device capable of simultaneously performing such a nitrification step and a denitrification step in a single tank has been put into practical use.

For example, a nitrification denitrification apparatus including a nitrification denitrification tank, a circulation line, an ejector, and a redox potential (ORP) meter has been proposed (see, for example, Patent Document 1). The circulation line draws the internal liquid of the nitrification denitrification tank from the nitrification denitrification tank as a circulation liquid and returns it to the nitrification denitrification tank. As a result, the internal liquid of the nitrification denitrification tank is circulated through the circulation line. The ejector is provided on the circulation line and mixes the circulating liquid passing through the circulation line with air. The ORP meter measures the ORP of the internal liquid in the nitrification denitrification tank.

In such a nitrification denitrification device, the amount of air mixed with the circulation liquid in the ejector is adjusted by adjusting the flow rate of the circulation liquid passing through the circulation line, and the oxygen supply amount to the nitrification denitrification tank is adjusted. do.

When the flow rate of the circulating fluid passing through the circulation line becomes small, the amount of oxygen supplied to the nitrification denitrification tank decreases. As a result, in the inner liquid of the nitrification denitrification tank, the anaerobic region where the dissolved oxygen concentration is relatively low expands, and the denitrification step becomes dominant.

On the other hand, when the flow rate of the circulating liquid passing through the circulation line increases, the amount of oxygen supplied to the nitrification denitrification tank increases. As a result, in the inner liquid of the nitrification denitrification tank, an aerobic region having a relatively high dissolved oxygen concentration expands, and the nitrification step becomes dominant.

Then, in the nitrification denitrification apparatus described in Patent Document 1, the amount of oxygen supplied to the nitrification denitrification tank is increased or decreased based on the measurement result of the ORP meter, and the first treatment in which the denitrification step is superior and the nitrification step are performed. The superior second treatment is carried out alternately.

Japanese Unexamined Patent Publication No. 2001-17992

However, the ORP is affected by the properties of the internal liquid in the nitrification denitrification tank. Examples of the properties of the internal liquid include ammonia concentration, organic matter amount, dissolved oxygen amount, liquid temperature and pH. Also, the waveform of the ORP is not uniform and unstable.

Therefore, even if the ORP is measured, it is difficult to accurately determine the degree of progress of the nitrification step and / or the denitrification step. As a result, even if the first treatment and the second treatment are switched based on the measurement result of the ORP meter as in the nitrification denitrification device described in Patent Document 1, there is a limit to improving the treatment efficiency of sewage. be.

The present invention provides a nitrification denitrification apparatus capable of efficiently treating sewage.

The present invention [1] comprises a nitrification denitrification tank, a sewage supply line for supplying sewage to the vitrification denitrification tank, and an internal liquid in which the sewage is treated with active sludge in the vitrification denitrification tank. A circulation pump that is drawn out from the vitrification denitrification tank and sent out, an injection unit that mixes the internal liquid and air and injects into the vitrification denitrification tank, and the internal liquid drawn from the vitrification denitrification tank. A circulation line that circulates to the vitrification denitrification tank via the injection unit, an ammonia sensor that measures the ammonia concentration in the internal liquid, and a control unit that can control the circulation pump. The control unit includes a control unit capable of alternately executing a first control driven by one output and a second control driving the circulation pump with a second output larger than the first output. It includes a vitrification denitrification device capable of changing the output value of the first output and / or the output value of the second output of the circulation pump based on the measurement result of the ammonia sensor.

According to such a configuration, in the first control, the circulation pump is driven by a relatively small first output. Therefore, the amount of oxygen supplied to the nitrification denitrification tank via the injection unit is relatively small. As a result, in the first control, the denitrification step becomes dominant in the internal liquid of the nitrification denitrification tank, and nitrite or nitrate nitrogen is reduced to nitrogen.

Further, in the second control, the circulation pump is driven by a relatively large second output. Therefore, the amount of oxygen supplied to the nitrification denitrification tank via the injection unit is relatively large. As a result, in the second control, the nitrification step becomes dominant in the inner liquid of the nitrification denitrification tank, and ammoniacal nitrogen is oxidized to nitrite or nitrate nitrogen.

The ammonia sensor measures the concentration of ammonia in the internal liquid. Since ammoniacal nitrogen is consumed in the nitrification process, the degree of progress of the nitrification process can be directly confirmed by measuring the ammonia concentration.

Then, the control unit changes the output value of the first output and / or the output value of the second output of the circulation pump based on the measurement result of the ammonia sensor. That is, the control unit can adjust the output value of the first output and / or the output value of the second output of the circulation pump based on the degree of progress of the nitrification process.

Therefore, in the first control and the second control, the amount of oxygen supplied to the nitrification denitrification tank can be adjusted accurately, and the nitrification step and the denitrification step can be carried out in a well-balanced and efficient manner. As a result, sewage can be treated efficiently.

In the present invention [2], the control unit calculates the rate of decrease in the ammonia concentration from the start of the second control to the lapse of a predetermined time from the measurement result of the ammonia sensor, and from the rate of decrease in the ammonia concentration, the first. 2 The predicted value of the ammonia concentration of the internal liquid at the end of control is calculated, and when the predicted value is within the predetermined range, the output value of the second output of the circulation pump is maintained, and the predicted value is within the predetermined range. If it is less than, the output value of the second output of the circulation pump is decreased, and if the predicted value exceeds a predetermined range, the output value of the second output of the circulation pump is increased. The vitrification denitrification device described in 1.

According to such a configuration, the control unit calculates the predicted value of the ammonia concentration of the internal liquid at the end of the second control, and based on the predicted value of the ammonia concentration, the output value of the second output of the circulation pump is calculated. adjust.

When the predicted value of the ammonia concentration at the end of the second control is within a predetermined range, the nitrification step is appropriately progressing in the second control, and the ammoniacal nitrogen is appropriately consumed. Therefore, the control unit maintains the output value of the second output of the circulation pump.

Further, when the predicted value of the ammonia concentration at the end of the second control is less than the predetermined range, the ammoniacal nitrogen is excessively consumed in the second control, and the oxygen supply amount to the nitrification denitrification tank is excessive. In this case, the denitrification step may be insufficient. Therefore, the control unit reduces the output value of the second output of the circulation pump to reduce the oxygen supply amount to the nitrification denitrification tank.

Further, when the predicted value of the ammonia concentration at the end of the second control exceeds a predetermined range, the consumption of ammoniacal nitrogen is insufficient in the second control, and the oxygen supply amount to the nitrification denitrification tank is insufficient. Therefore, the control unit increases the output value of the second output of the circulation pump to increase the oxygen supply amount to the nitrification denitrification tank.

As a result, the control unit can appropriately adjust the oxygen supply amount to the nitrification denitrification tank based on the measurement result of the ammonia sensor. As a result, the nitrification denitrification device can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently.

The present invention [3] further includes a supply pump provided in the sewage supply line, the control unit can control the supply pump, and the ammonia concentration of the internal liquid at the start of the second control is a set value. In the following case, in the next first control, when the supply pump is driven by the third output and the ammonia concentration of the internal liquid at the start of the second control exceeds the set value, the next first control is performed. The control includes the vitrification denitrification apparatus according to the above [2], which drives the supply pump with a fourth output smaller than the third output.

According to such a configuration, when the ammonia concentration of the internal liquid at the start of the second control is equal to or less than the set value, the control unit drives the supply pump with the third output in the next first control. Therefore, the sewage is supplied to the nitrification denitrification tank during the first control in which the denitrification step is dominant. As a result, the organic matter contained in the sewage can be effectively used in the denitrification step.

Further, if the ammonia concentration of the sewage supplied to the nitrification denitrification tank in the first control is relatively high, the ammonia concentration of the internal liquid at the start of the second control may exceed the set value. In this case, the control unit drives the supply pump with a fourth output smaller than the third output in the next first control. As a result, the amount of sewage supplied to the nitrification denitrification tank in the next first control is reduced. As a result, it is possible to suppress an excessive increase in the ammonia concentration in the inner liquid of the nitrification denitrification tank, and the nitrification step can be stably advanced.

In the present invention [4], when the moving average of the measurement result of the ammonia sensor rises beyond a predetermined range, the output value of the second output of the circulation pump is increased, and the measurement result of the ammonia sensor is increased. The vitrification denitrification device according to the above [1], which reduces the output value of the second output of the circulation pump when the moving average falls beyond a predetermined range.

According to such a configuration, the control unit adjusts the output value of the second output of the circulation pump based on the moving average of the measurement result of the ammonia sensor.

When the moving average of the measurement result of the ammonia sensor rises beyond a predetermined range, the consumption of ammoniacal nitrogen in the second control is insufficient, and the amount of oxygen supplied to the vitrifying denitrification tank is insufficient. Therefore, the control unit increases the output value of the second output of the circulation pump to increase the oxygen supply amount to the nitrification denitrification tank in the second control.

Further, when the moving average of the measurement result of the ammonia sensor falls beyond a predetermined range, the amount of oxygen supplied to the nitrification denitrification tank in the second control is excessive. Therefore, the control unit lowers the output value of the second output of the circulation pump, and lowers the oxygen supply amount to the nitrification denitrification tank in the second control.

As a result, the nitrification denitrification device can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently.

In the present invention [5], when the ammonia concentration of the internal liquid at the start of the second control is less than a predetermined range, the control unit receives the first output of the circulation pump in the next first control. When the output value is lowered and the ammonia concentration of the internal liquid at the start of the second control exceeds a predetermined range, the output value of the first output of the circulation pump is increased in the next first control. The nitrification denitrification apparatus according to any one of the above [1] to [4] is included.

According to such a configuration, the control unit adjusts the output value of the first output of the circulation pump based on the ammonia concentration of the internal liquid at the start of the second control.

When the ammonia concentration of the internal liquid at the start of the second control is less than the predetermined range, the amount of oxygen supplied to the nitrification denitrification tank is excessive. Therefore, in the next first control, the control unit lowers the output value of the first output of the circulation pump, and lowers the oxygen supply amount to the nitrification denitrification tank in the first control.

Further, when the ammonia concentration of the internal liquid at the start of the second control exceeds a predetermined range, the oxygen supply amount to the nitrification denitrification tank is insufficient. Therefore, in the next first control, the control unit increases the output value of the first output of the circulation pump to increase the oxygen supply amount to the nitrification denitrification tank in the first control.

As a result, the nitrification denitrification device can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently.

In the present invention [6], when the ammonia concentration of the internal liquid at the start of the second control is less than a predetermined range, the control unit receives the second output of the circulation pump in the next second control. When the output value is lowered and the ammonia concentration of the internal liquid at the start of the second control exceeds a predetermined range, the output value of the second output of the circulation pump is increased in the next second control. The nitrification denitrification apparatus according to the above [1] is included.

According to such a configuration, the control unit adjusts the output value of the second output of the circulation pump based on the ammonia concentration of the internal liquid at the start of the second control.

When the ammonia concentration of the internal liquid at the start of the second control is less than the predetermined range, the amount of oxygen supplied to the nitrification denitrification tank is excessive. Therefore, in the next second control, the control unit lowers the output value of the second output of the circulation pump, and lowers the oxygen supply amount to the nitrification denitrification tank in the second control.

Further, when the ammonia concentration of the internal liquid at the start of the second control exceeds a predetermined range, the oxygen supply amount to the nitrification denitrification tank is insufficient. Therefore, in the next second control, the control unit increases the output value of the second output of the circulation pump to increase the oxygen supply amount to the nitrification denitrification tank in the second control.

As a result, the nitrification denitrification device can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently.

In the present invention [7], when the minimum value per unit time of the ammonia concentration of the internal liquid is less than a predetermined range, the control unit controls the second output of the circulation pump in the next second control. When the output value is lowered and the minimum value of the ammonia concentration of the internal liquid exceeds a predetermined range, the output value of the second output of the circulation pump is increased in the next second control. When the maximum value of the ammonia concentration of the internal liquid per unit time is less than a predetermined range, the output value of the first output of the circulation pump is lowered in the next first control, and the ammonia concentration of the internal liquid is reduced. The vitrification denitrification device according to the above [1], which increases the output value of the first output of the circulation pump in the next first control when the maximum value per unit time of the above exceeds a predetermined range. include.

According to such a configuration, the control unit adjusts the output values of the first output and the second output of the circulation pump based on the minimum and maximum values of the ammonia concentration of the internal liquid per unit time.

When the minimum value of the ammonia concentration of the internal liquid per unit time is less than the predetermined range, the amount of oxygen supplied to the nitrification denitrification tank is excessive. Therefore, in the next second control, the control unit lowers the output value of the second output of the circulation pump, and lowers the oxygen supply amount to the nitrification denitrification tank in the second control.

Further, when the minimum value of the ammonia concentration of the internal liquid per unit time exceeds a predetermined range, the oxygen supply amount to the nitrification denitrification tank is insufficient. Therefore, in the next second control, the control unit increases the output value of the second output of the circulation pump to increase the oxygen supply amount to the nitrification denitrification tank in the second control.

Further, when the maximum value of the ammonia concentration of the internal liquid per unit time is less than a predetermined range, the amount of oxygen supplied to the nitrification denitrification tank is excessive. Therefore, in the next first control, the control unit lowers the output value of the first output of the circulation pump, and lowers the oxygen supply amount to the nitrification denitrification tank in the first control.

Further, when the maximum value of the ammonia concentration of the internal liquid per unit time exceeds a predetermined range, the oxygen supply amount to the nitrification denitrification tank is insufficient. Therefore, in the next first control, the control unit increases the output value of the first output of the circulation pump to increase the oxygen supply amount to the nitrification denitrification tank in the first control.

As a result, the nitrification denitrification device can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently.

The nitrification denitrification device of the present invention can efficiently treat sewage.

FIG. 1 is a schematic configuration diagram of an embodiment of the nitrification denitrification apparatus of the present invention. FIG. 2 is a timing diagram for explaining a first embodiment of a method for nitrifying and denitrifying sewage by the nitrification denitrification apparatus shown in FIG. FIG. 3 is a flow chart for explaining the nitrification denitrification method shown in FIG. FIG. 4 is a flow chart for explaining the first control shown in FIG. FIG. 5 is a flow chart for explaining the second control shown in FIG. FIG. 6 is a timing diagram for explaining a second embodiment of the nitrification and denitrification method of sewage, and shows a state in which the moving average (dashed line) of the ammonia concentration rises beyond a predetermined range. FIG. 7 is a timing diagram for explaining the second embodiment of the nitrification and denitrification method of sewage, and shows a state in which the moving average (dashed line) of the ammonia concentration falls beyond a predetermined range. FIG. 8 is a timing diagram for explaining the second embodiment of the nitrification and denitrification method of sewage, and shows a state in which the moving average (dashed line) of the ammonia concentration is within a predetermined range. FIG. 9 is a timing diagram for explaining a third embodiment of the method for nitrifying and denitrifying sewage.

1. 1. Nitrification denitrification device The nitrification denitrification device 1 as an embodiment of the nitrification denitrification device of the present invention will be described with reference to FIG.

The nitrification denitrification device 1 biologically nitrifies and denitrifies the supplied sewage with activated sludge, and discharges the treated water. Sewage and activated sludge will be described later.

The nitrification denitrification device 1 includes a nitrification denitrification tank 2, a sewage supply unit 3, a circulation unit 4, an ammonia sensor 7, a treatment liquid discharge unit 5, and a control unit 6.

The nitrification denitrification tank 2 contains activated sludge. Activated sludge contains at least nitrifying bacteria and denitrifying bacteria. Activated sludge preferably further comprises heterotrophic bacteria.

Nitrifying bacteria oxidize ammoniacal nitrogen to nitrite or nitrate nitrogen under aerobic conditions. Denitrifying bacteria reduce nitrite or nitrate nitrogen to nitrogen under anaerobic conditions. Heterotrophic bacteria decompose organic matter in sewage under aerobic and / or anaerobic conditions.

The nitrification denitrification tank 2 has a hollow shape that is sealed. The nitrification denitrification tank 2 includes a side wall 21, an upper wall 22, and a bottom wall 23.

The side wall 21 has a square tube shape or a cylindrical shape. The side wall 21 extends in the vertical direction. The upper wall 22 closes the upper end of the side wall 21. The bottom wall 23 closes the lower end of the side wall 21. The inner surface of the bottom wall 23 faces the upper wall 22 in the vertical direction. The inner surface of the bottom wall 23 is recessed in a pyramidal or conical shape.

The sewage supply unit 3 supplies sewage to the nitrification denitrification tank 2. The sewage supply unit 3 includes a sewage supply line 31 and a supply pump 32.

The sewage supply line 31 is a pipe for supplying sewage to the nitrification denitrification tank 2. The upstream end of the sewage supply line 31 in the supply direction is connected to a sewage storage tank (not shown). The downstream end of the sewage supply line 31 in the supply direction is connected to the lower end of the side wall 21. The internal space at the downstream end of the sewage supply line 31 in the supply direction communicates with the lower portion of the internal space of the nitrification denitrification tank 2.

When the supply pump 32 is driven, the supply pump 32 supplies the sewage in the sewage storage tank (not shown) to the nitrification denitrification tank 2 through the sewage supply line 31. The supply pump 32 is provided in the sewage supply line 31. The supply pump 32 is, for example, a known liquid feeding pump.

The circulation unit 4 draws a part of the internal liquid of the nitrification denitrification tank 2 from the nitrification denitrification tank 2 and circulates it. The internal liquid of the nitrification denitrification tank 2 is sewage treated with activated sludge in the nitrification denitrification tank 2. The circulation unit 4 includes a circulation line 41, a circulation pump 42, and an overflow shaft 43 as an example of an injection unit.

The circulation line 41 is a pipe for drawing out a part of the internal liquid of the nitrification denitrification tank 2 from the nitrification denitrification tank 2 and supplying it to the overflow shaft 43. The circulation line 41 circulates the internal liquid drawn from the nitrification denitrification tank 2 to the nitrification denitrification tank 2 via the overflow shaft 43. In the following, the internal liquid passing through the circulation line 41 is referred to as a circulating liquid to distinguish it from the internal liquid contained in the nitrification denitrification tank 2. The circulation line 41 has an intermediate portion 411, an upstream portion 412, and a downstream portion 413.

The intermediate portion 411 extends in the vertical direction. The upstream portion 412 is continuous with the lower end of the intermediate portion 411. The upstream portion 412 extends horizontally from the lower end of the intermediate portion 411 and then bends downward. The horizontally extending portion of the upstream portion 412 penetrates the side wall 21. The upstream portion 412 has an upstream end 41A. The upstream end 41A is an upstream end of the circulation line 41 in the circulation direction and is open. The upstream end 41A is located on the opposite side of the continuous portion between the intermediate portion 411 and the upstream portion 412 with respect to the side wall 21. The upstream end 41A is located in the lower portion of the internal space of the nitrification denitrification tank 2. The upstream end 41A faces the inner surface of the bottom wall 23.

The downstream portion 413 is continuous with the upper end of the intermediate portion 411. The downstream portion 413 extends horizontally from the upper end of the intermediate portion 411. The downstream portion 413 has a downstream end 41B. The downstream end 41B is the downstream end of the circulation line 41 in the circulation direction. The downstream end 41B is connected to the overflow shaft 43.

When the circulation pump 42 is driven, the circulation pump 42 draws the internal liquid of the nitrification denitrification tank 2 from the nitrification denitrification tank 2 and sends it to the overflow shaft 43 via the circulation line 41. The circulation pump 42 is provided in the circulation line 41. Specifically, the circulation pump 42 is located outside the nitrification denitrification tank 2 and is provided in a continuous portion between the intermediate portion 411 and the upstream portion 412. The circulation pump 42 is, for example, a known liquid feeding pump.

The overflow shaft 43 mixes the circulating liquid and air and injects them into the nitrification denitrification tank 2. The overflow shaft 43 is supported by the upper wall 22. The overflow shaft 43 has, for example, an ejector structure. The overflow shaft 43 has a body 431 and a diffuser 432.

The body 431 is located on the opposite side of the bottom wall 23 with respect to the upper wall 22. The body 431 has a cylindrical shape. The body 431 extends in the vertical direction. The downstream end 41B of the circulation line 41 is connected to the side wall of the body 431. The internal space of the body 431 communicates with the internal space at the downstream end 41B of the circulation line 41.

The diffuser 432 has a cylindrical shape. The inner diameter of the diffuser 432 is smaller than the inner diameter of the body 431. The diffuser 432 extends in the vertical direction. The diffuser 432 penetrates the upper wall 22. The upper end 432A of the diffuser 432 is connected to the lower end of the body 431. The internal space of the diffuser 432 communicates with the internal space of the body 431. The lower end 432B of the diffuser 432 is located in the upper part in the internal space of the nitrification denitrification tank 2. The lower end 432B of the diffuser 432 is located on the opposite side of the bottom wall 23 with respect to the upstream end 41A of the circulation line 41. The lower end 432B of the diffuser 432 is located upwardly away from the upstream end 41A. The lower end 432B of the diffuser 432 is located between the upper wall 22 of the nitrification denitrification tank 2 and the upstream end 41A in the vertical direction.

The ammonia sensor 7 can measure the ammonia concentration in the internal liquid of the nitrification denitrification tank 2. In the present embodiment, the ammonia sensor 7 measures the ammonia concentration in the circulating fluid passing through the circulation line 41. The ammonia sensor 7 is connected to the downstream portion 413 of the circulation line 41. Examples of the ammonia sensor 7 include a known ammonia detector. The ammonia sensor 7 is electrically connected to the control unit 6. The ammonia sensor 7 can output the measurement result to the control unit 6.

Further, the ammonia sensor 7 may measure the ammonia concentration of the internal liquid obtained by extracting the internal liquid of the nitrification denitrification tank 2 with a sampling pump. In this case, the internal liquid of the nitrification denitrification tank 2 is drawn from the nitrification denitrification tank 2 separately from the circulation line 41 and sent to the sampling tank, and the ammonia sensor 7 is sent to the sampling tank or the nitrification denitrification tank 2. Install on the sampling line that returns the internal liquid.

The treatment liquid discharge unit 5 discharges the treatment liquid from the nitrification denitrification tank 2. The treatment liquid is an internal liquid discharged from the nitrification denitrification tank 2 after the biological nitrification denitrification treatment is carried out in the nitrification denitrification tank 2. The treatment liquid discharge unit 5 has a discharge line 51.

The discharge line 51 is a pipe for discharging the treatment liquid from the nitrification denitrification tank 2. The upstream end of the discharge line 51 in the discharge direction is connected to the side wall 21. The internal space at the upstream end of the discharge line 51 in the discharge direction communicates with the internal space of the nitrification denitrification tank 2. The downstream end of the discharge line 51 in the discharge direction is connected to a water tank (not shown). In a water tank (not shown), activated sludge contained in the treatment liquid is separated into solid and liquid by precipitation, membrane separation, mechanical separation, or the like.

The control unit 6 includes a central processing unit (CPU), a ROM, a RAM, and the like. The control unit 6 can control the circulation pump 42, the supply pump 32, and the ammonia sensor 7. The control unit 6 is electrically connected to the circulation pump 42, the supply pump 32, and the ammonia sensor 7.

Specifically, the control unit 6 can adjust the dissolved oxygen concentration of the internal liquid of the nitrification denitrification tank 2 by controlling the circulation pump 42. In particular, preferably, the control unit 6 controls the circulation pump 42 to adjust the dissolved oxygen concentration of the internal liquid of the vitrification denitrification tank 2 to a relatively low anaerobic state, and the vitrification denitrification tank 2. It is possible to alternately carry out the second control for adjusting the dissolved oxygen concentration of the internal liquid to a relatively high aerobic state.

When the control unit 6 executes the first control for adjusting the dissolved oxygen concentration of the internal liquid of the nitrification denitrification tank 2 to a relatively low anaerobic state, the control unit 6 drives the circulation pump 42 at the first output. In the first control, the circulating fluid drawn from the nitrification denitrification tank 2 is guided to the overflow shaft 43 at a relatively small flow rate. By adjusting to an anaerobic state, denitrifying bacteria reduce nitrite or nitrate nitrogen contained in the internal solution of the nitrification denitrification tank 2 to nitrogen (denitrification step).

Further, when the control unit 6 executes the second control for adjusting the dissolved oxygen concentration of the internal liquid of the nitrification denitrification tank 2 to a relatively high aerobic state, the control unit 6 outputs the circulation pump 42 at the second output. Drive. The second output of the circulation pump 42 is larger than the first output of the circulation pump 42. In the second control, the circulating fluid drawn from the nitrification denitrification tank 2 is guided to the overflow shaft 43 at a relatively large flow rate. By adjusting to an aerobic state, the nitrifying bacteria consume oxygen and oxidize the ammoniacal nitrogen contained in the internal solution of the nitrifying denitrification tank 2 to nitrite or nitrate nitrogen (nitrification step).

As will be described in detail later, the control unit 6 can change the output values of the first output and the second output of the circulation pump 42 based on the measurement result of the ammonia sensor 7. The control unit 6 stores in advance a predetermined range of the ammonia concentration, which is a reference for changing the output value of the second output of the circulation pump 42 (see FIG. 2). The predetermined range of the ammonia concentration stored in the control unit 6 is the allowable range of the ammonia concentration of the internal solution of the nitrification denitrification tank 2 at the end of the second control, and the ammonia concentration of the internal solution of the nitrification denitrification tank 2. It has an upper limit value X of the above and a lower limit value Y of the ammonia concentration of the internal solution of the nitrification denitrification tank 2. The predetermined range of ammonia concentration is appropriately changed according to the properties of sewage.

Further, the control unit 6 can switch between the drive state and the drive stop state of the supply pump 32. As will be described in detail later, the control unit 6 can change the output value of the output of the supply pump 32. The control unit 6 stores in advance the set value Z of the ammonia concentration, which is a reference for changing the output value of the output of the supply pump 32 (see FIG. 2). The set value Z of the ammonia concentration is an upper limit value of the ammonia concentration at the start of the second control, and is appropriately changed according to the properties of the sewage.

2. 2. Sewage treatment method Next, a sewage treatment method using the nitrification denitrification device 1 will be described.

As shown in FIG. 1, in the sewage treatment method, a predetermined amount of sewage is supplied to and contained in the nitrification denitrification tank 2 in advance.

Examples of sewage include sewage sludge and human waste sewage.

The sewage sludge is sludge produced when the sewage collected by the sewage is treated, and includes human wastewater from a flush toilet, domestic wastewater generated in daily life, rainwater, and the like. The human waste system sewage is sewage collected separately from the sewage, and includes human waste stored in the toilet jar of a pumping toilet and septic tank sludge generated in a septic tank for treating human waste and domestic wastewater.

The sewage may consist of one type or a mixture of two or more types. The sewage preferably contains human waste sewage.

The total nitrogen content (TN) of the sewage is, for example, 92 mg / L or more and 5000 mg / L or less. TN can be measured, for example, by pretreating sewage by the Kjeldahl method and measuring it by the neutralization titration method or the summation method.

The ammoniacal nitrogen concentration of the sewage is, for example, 20 mg / L or more and 3000 mg / L or less. The ammoniacal nitrogen concentration can be measured by, for example, a neutralization titration method or an ionic electrode method.

The nitrate nitrogen concentration of the sewage is, for example, 0.0 mg / L or more and 1.0 mg / L or less. The nitrate nitrogen concentration can be measured by, for example, a colorimetric method or an ion chromatograph method.

The biochemical oxygen demand (BOD) of sewage is, for example, 200 mg / L or more and 21000 mg / L or less. The BOD can be measured by, for example, an iodine titration method or a diaphragm electrode method.

The SS concentration of sewage is, for example, 640 mg / L or more and 35,000 mg / L or less. The SS concentration can be measured by, for example, a glass fiber filter paper method or a centrifugation method.

Next, as shown in FIGS. 2 and 3, the control unit 6 controls a first control (S1) for adjusting the internal liquid to an anaerobic state and a second control (S2) for adjusting the internal liquid to an aerobic state. , Alternate until a stop signal is received. In the present embodiment, the control unit 6 maintains the first control for the first set time, then switches to the second control and maintains the second set time. The control unit 6 stores the first set time and the second set time in advance. The first set time and the second set time are appropriately changed according to the properties of the sewage. In the present embodiment, the second control for adjusting the internal liquid to the aerobic state is carried out after the first control for adjusting the internal liquid to the anaerobic state, but the order of the first control and the second control is particularly limited. Not done. The control unit 6 may perform the first control after the second control.

FIG. 2 shows the output of the circulation pump 42, the output of the supply pump 32, and the ammonia concentration in the first cycle to the fifth cycle, with the period from the start of the first control to the end of the second control as one cycle for convenience.

As shown in FIG. 4, in the first control for adjusting the internal liquid to an anaerobic state, the control unit 6 first reads out the output value of the first output of the circulation pump 42 stored in advance, and causes the circulation pump 42. It is driven by the first output (S1-1). As a result, as shown in FIG. 1, the internal liquid of the nitrifying denitrification tank 2 is sucked into the upstream end 41A of the circulation line 41 as a circulating liquid. Then, the circulating liquid passes through the circulation line 41 and flows into the overflow shaft 43.

Then, when the circulating liquid passes through the body 431 from the circulation line 41 toward the diffuser 432, a negative pressure is generated inside the body 431. As a result, the air near the upper end of the body 431 is sucked into the inside of the body 431. Then, the circulating liquid and air are mixed in the overflow shaft 43, and the circulating liquid and air are injected from the lower end 432B of the diffuser 432.

In the first control for adjusting the internal liquid to an anaerobic state, the output of the circulation pump 42 is smaller than that in the second control for adjusting the internal liquid to an aerobic state. Therefore, in the first control, the circulation speed of the circulating fluid is smaller than that in the second control. The circulation speed of the circulating liquid in the first control is, for example, 33 m ³ / h or more and 3000 m ³ / h or less.

When the circulation speed of the circulating liquid in the first control is equal to or higher than the above lower limit, the internal liquid contained in the nitrification denitrification tank 2 can be stably agitated. When the circulation speed of the circulating liquid in the first control is not more than the above upper limit, the amount of oxygen supplied to the nitrification denitrification tank 2 can be reduced.

As a result, in the first control for adjusting the internal liquid to an anaerobic state, in the internal liquid of the nitrification denitrification tank 2, the region near the lower end 432B of the diffuser 432 becomes an aerobic state, while most of the rest is anaerobic. It becomes a state. In the first control, the dissolved oxygen concentration in the internal liquid of the nitrification denitrification tank 2 is maintained, for example, less than 0.5 mg / L.

In the aerobic region, nitrifying bacteria consume oxygen to oxidize ammoniacal nitrogen to nitrite or nitrate nitrogen (nitrification step).

Also, in the anaerobic region, denitrifying bacteria reduce nitrite or nitrate nitrogen to nitrogen (denitrification step). The generated nitrogen is discharged from the nitrification denitrification tank 2 via an exhaust pipe (not shown).

Then, the anaerobic internal liquid is sucked into the upstream end 41A of the circulation line 41, passes through the circulation line 41 as the circulation liquid, and flows into the overflow shaft 43. After that, the overflow shaft 43 injects the circulating liquid together with air into the nitrification denitrification tank 2. Such circulation of the circulating fluid is continued until the driving of the circulation pump 42 is stopped.

Further, the sewage treated as described above is discharged as treated water from the nitrification denitrification tank 2 via the discharge line 51 by an overflow between the first control and the second control.

The total soluble nitrogen content (STN) of the treatment solution is, for example, 1 mg / L or more and 20 mg / L or less. The ammoniacal nitrogen concentration of the treatment liquid is, for example, 0.1 mg / L or more and 20 mg / L or less. The nitrate nitrogen concentration of the treatment liquid is, for example, 0.1 mg / L or more and 20 mg / L or less.

Next, as shown in FIGS. 2 and 4, the control unit 6 supplies sewage to the nitrification denitrification tank 2 during the period of the first control. Specifically, after a predetermined time has elapsed from the start of driving of the circulation pump 42 at the first output, the control unit 6 reads out the output value of the supply pump 32 stored in advance and makes the supply pump 32 the third output or the fourth output. It is driven by the output (S1-2). The third output and the fourth output of the supply pump 32 will be described in detail later.

After that, the control unit 6 drives the supply pump 32 for a predetermined time, and then stops driving the supply pump 32 before the first control is completed (S1-3). The amount of sewage supplied during the period of the first control is appropriately changed according to the properties of the sewage, but is, for example, 1/100 or more and 1/500 or less with respect to the volume of the nitrification denitrification tank 2.

Then, the control unit 6 continues to drive the circulation pump 42 at the first output until the drive time at the first output of the circulation pump 42 elapses, and then performs the first control. Switch to control (see Figure 3).

As shown in FIGS. 2 and 5, in the second control, the control unit 6 reads out the output value of the second output of the circulation pump 42 stored in advance and drives the circulation pump 42 with the second output ( S2-1).

The second output is larger than the first output. Therefore, in the second control, the circulation speed of the circulating fluid is higher than that in the first control. The circulation speed of the circulating liquid in the second control is, for example, 100 m ³ / h or more and 3000 m ³ / h or less.

When the circulation speed of the circulating liquid in the second control is equal to or higher than the above lower limit, sufficient oxygen can be supplied to the nitrification denitrification tank 2.

As a result, in the second control, most of the internal solution of the nitrification denitrification tank 2 is in an aerobic state, while the other part (lower part) is in an anaerobic state. In the second control, the dissolved oxygen concentration in the internal liquid of the nitrification denitrification tank 2 is maintained at, for example, 0.5 mg / L or more. As a result, in the second control, the nitrification step proceeds predominantly as compared with the first control.

In the second control, the pH and temperature suitable for the growing environment are maintained. The pH of the internal solution of the nitrification denitrification tank 2 in the second control is, for example, 5.0 or more, preferably 6.0 or more, and for example, 9.0 or less, preferably 8.0 or less. The temperature of the internal liquid of the nitrification denitrification tank 2 in the second control is, for example, 15 ° C. or higher and 38 ° C. or lower.

Further, the control unit 6 starts driving the circulation pump 42 at the second output, and causes the ammonia sensor 7 to measure the ammonia concentration of the circulation liquid. As a result, the control unit ₆ acquires the ammonia concentration C1 of the circulating fluid at the start of the second control. Then, the control unit 6 determines whether or not the ammonia concentration C ₁ of the circulating fluid at the start of the second control is equal to or less than the set value Z of the ammonia concentration at the start of the second control (S2-2).

When the ammonia concentration C ₁ of the circulating fluid at the start of the second control is equal to or less than the set value Z (Yes in S2-2), the control unit 6 reads out the output value corresponding to the third output stored in advance (Yes). S2-3). Then, the control unit 6 drives the supply pump 32 with the third output in the next first control (see the first cycle to the third cycle in FIG. 2). In other words, when the ammonia concentration C ₁ of the circulating fluid at the start of the second control is equal to or less than the set value Z, the control unit 6 drives the supply pump 32 with the third output in the next first control.

When the ammonia concentration C ₁ of the circulating fluid at the start of the second control exceeds the set value Z (No in S2-2), the control unit 6 reads out the output value corresponding to the fourth output stored in advance (No). S2-4). Then, the control unit 6 drives the supply pump 32 at the fourth output in the next first control (see the fourth cycle and the fifth cycle in FIG. 2). In other words, when the ammonia concentration C ₁ of the circulating fluid at the start of the second control exceeds the set value Z, the control unit 6 drives the supply pump 32 with the fourth output in the next first control. The fourth output is smaller than the third output. The output value of the fourth output is, for example, 70% or more and 90% or less with respect to the output value of the third output.

Next, the control unit 6 causes the ammonia sensor 7 to measure the ammonia concentration of the circulating fluid after a predetermined time has elapsed from the start of driving the circulation pump 42 at the second output (S2-5). As a result, the control unit 6 acquires the ammonia concentration C ₂ of the circulating fluid when a predetermined time has elapsed from the start of the second control. Then, the control unit 6 calculates the rate of decrease in the ammonia concentration from the start of the second control to the elapse of the predetermined time based on the ammonia concentration C ₁ at the start of the second control and the ammonia concentration C ₂ at the elapse of the predetermined time. (S2-6).

Next, the control unit 6 calculates the predicted value _Cp of the ammonia concentration of the sewage at the end of the second control from the rate of decrease in the ammonia concentration and the second set time (S2-7).

Next, the control unit 6 determines whether or not the predicted value C _p of the ammonia concentration is less than the lower limit value Y of the ammonia concentration at the end of the second control (S2-8).

When the predicted value C _p of the ammonia concentration is less than the lower limit value Y of the ammonia concentration at the end of the second control (Yes in S2-8), the control unit 6 lowers the output value of the second output of the circulation pump 42. (See S2-9, the second cycle of FIG. 2). In other words, when the predicted value C _p of the ammonia concentration is less than the predetermined range, the control unit 6 lowers the output value of the second output of the circulation pump 42. The rate of decrease in the output value of the second output is, for example, 70% or more and 90% or less with respect to the output value of 100% of the second output of the current circulation pump 42. Then, the control unit 6 updates the output value of the stored second output.

When the predicted value C _p of the ammonia concentration is equal to or higher than the lower limit value Y of the ammonia concentration at the end of the second control (No in S2-8), the control unit 6 controls the predicted value C _p of the ammonia concentration by the second control. It is determined whether or not the upper limit value X of the ammonia concentration at the end is exceeded (S2-10).

When the predicted value C _p of the ammonia concentration exceeds the upper limit value X of the ammonia concentration at the end of the second control (Yes in S2-10), the control unit 6 increases the output value of the second output of the circulation pump 42. (See S2-11, the third cycle and the fourth cycle in FIG. 2). In other words, when the predicted value C _p of the ammonia concentration exceeds a predetermined range, the control unit 6 raises the output value of the second output of the circulation pump 42. The rate of increase in the output value of the second output is, for example, 110% or more and 130% or less with respect to the output value of 100% of the second output of the current circulation pump 42. Then, the control unit 6 updates the output value of the stored second output.

When the predicted value C _p of the ammonia concentration is equal to or less than the upper limit value X of the ammonia concentration at the end of the second control (No in S2-10), the control unit 6 maintains the output value of the second output of the circulation pump 42. (See the 5th cycle in FIG. 2). In other words, when the predicted value _Cp of the ammonia concentration is equal to or more than the lower limit value Y of the ammonia concentration at the end of the second control and is equal to or less than the upper limit value X, that is, the control unit 6 has the circulation pump 42. 2 Maintain the output value of the output.

Then, the control unit 6 continues to drive the circulation pump 42 at the second output until the drive time at the second output of the circulation pump 42 elapses, and then, as shown in FIG. , It is determined whether or not the stop signal is received (S-3). When the control unit 6 receives the stop signal (Yes in S-3), the nitrification denitrification device 1 ends the sewage treatment operation. On the other hand, when the control unit 6 has not received the stop signal (No of S-3), the control unit 6 repeats the first control and the second control again.

3. 3. Action effect In the nitrification denitrification device 1, the circulation pump 42 is driven by a relatively small first output in the first control. Therefore, the amount of oxygen supplied to the nitrification denitrification tank 2 via the overflow shaft 43 is relatively small. As a result, in the first control, the denitrification step becomes dominant in the internal liquid of the nitrification denitrification tank 2, and nitrite or nitrate nitrogen is reduced to nitrogen.

Further, in the second control, the circulation pump 42 is driven by a relatively large second output. Therefore, the amount of oxygen supplied to the nitrification denitrification tank 2 via the overflow shaft 43 is relatively large. As a result, in the second control, the nitrification step becomes dominant in the internal liquid of the nitrification denitrification tank 2, and the ammoniacal nitrogen is oxidized to nitrite or nitrate nitrogen.

The ammonia sensor 7 measures the ammonia concentration in the internal liquid of the nitrification denitrification tank 2. Since ammoniacal nitrogen is consumed in the nitrification process, the degree of progress of the nitrification process can be directly confirmed by measuring the ammonia concentration.

Then, the control unit 6 changes the output value of the second output of the circulation pump 42 based on the measurement result of the ammonia sensor 7. That is, the control unit 6 can adjust the output value of the second output of the circulation pump 42 based on the degree of progress of the nitrification step, and can adjust the oxygen supply amount to the nitrification denitrification tank 2 in the second control.

Therefore, in the first control and the second control, the amount of oxygen supplied to the nitrification denitrification tank 2 can be adjusted accurately, and the nitrification step and the denitrification step can be carried out in a well-balanced and efficient manner. As a result, sewage can be treated efficiently.

Further, the absolute value of the ammonia concentration can be directly compared between a plurality of nitrification denitrification devices 1 which are different from each other. Therefore, it is possible to adopt the same reference value of ammonia concentration in the plurality of nitrification denitrification devices 1, and it is easy to control the nitrification denitrification device 1. Further, the measurement result of the ammonia sensor 7 can be used for the water quality evaluation of the treated water.

Further, the control unit 6 calculates the rate of decrease in the ammonia concentration from the start of the second control to the elapse of a predetermined time, and calculates the predicted value _Cp of the ammonia concentration of the sewage at the end of the second control from the rate of decrease in the ammonia concentration. do.

When the predicted value _Cp of the ammonia concentration at the end of the second control is within a predetermined range, the nitrification step is appropriately progressing in the second control, and the ammoniacal nitrogen is efficiently oxidized. Therefore, the control unit 6 maintains the output value of the second output of the circulation pump 42.

Further, when the predicted value _Cp of the ammonia concentration at the end of the second control is less than the predetermined range, the ammoniacal nitrogen is excessively consumed in the second control, and the oxygen supply amount to the nitrification denitrification tank 2 is excessive. be. In this case, the denitrification step may be insufficient. Therefore, the control unit 6 lowers the output value of the second output of the circulation pump 42, and lowers the oxygen supply amount to the nitrification denitrification tank 2.

Further, when the predicted value _Cp of the ammonia concentration at the end of the second control exceeds a predetermined range, the consumption of ammoniacal nitrogen is insufficient in the second control, and the oxygen supply amount to the nitrification denitrification tank 2 is insufficient. ing. Therefore, the control unit 6 increases the output value of the second output of the circulation pump 42 to increase the oxygen supply amount to the nitrification denitrification tank 2.

As a result, the control unit 6 can appropriately adjust the oxygen supply amount to the nitrification denitrification tank 2 based on the measurement result of the ammonia sensor 7. As a result, the nitrification denitrification apparatus 1 can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently.

Further, when the ammonia concentration C ₁ of the internal liquid of the nitrification denitrification tank 2 at the start of the second control is equal to or less than the set value Z, the control unit 6 drives the supply pump at the third output in the next first control. Let me. Therefore, sewage containing organic matter is supplied to the nitrification denitrification tank 2 during the first control in which the denitrification step is dominant. As a result, organic matter in sewage can be effectively used in the denitrification step.

Further, when the ammonia concentration of the sewage supplied to the nitrification denitrification tank 2 in the first control is relatively high, the ammonia concentration C1 of the internal solution of the nitrification denitrification tank 2 at the start of the _second control exceeds the set value Z. May be done. In this case, the control unit 6 drives the supply pump with a fourth output smaller than the third output in the next first control. As a result, the amount of sewage supplied to the nitrification denitrification tank 2 in the next first control is reduced. As a result, it is possible to suppress an excessive increase in the ammonia concentration in the internal liquid of the nitrification denitrification tank 2, and the nitrification step can be stably advanced.

4. Second Embodiment Next, a second embodiment of the present invention will be described.

In the first embodiment, the control unit 6 changes the output value of the second output of the circulation pump 42 based on the predicted value _Cp of the ammonia concentration in the second control, but the present invention is not limited to this.

As shown in FIGS. 6 and 7, in the second embodiment, in the second control, the control unit 6 determines the output value of the second output of the circulation pump 42 based on the moving average of the measurement results of the ammonia sensor 7. change.

In the second embodiment, the control unit 6 calculates the moving average of the measurement results of the ammonia sensor 7. In the first control and the second control, the control unit 6 causes the ammonia sensor 7 to measure the ammonia concentration of the circulating fluid every unit time (for example, every second). Then, the control unit 6 calculates the average value of the ammonia concentration in one cycle, with the period from the start of the first control to the end of the second control as one cycle. Next, the control unit 6 calculates a moving average of the ammonia concentration from the average value of the ammonia concentration in at least two cycles. Then, the control unit 6 calculates the fluctuation amount of the moving average of the ammonia concentration from the moving average of the ammonia concentration calculated this time and the moving average of the ammonia concentration calculated last time.

As shown in FIG. 6, when the fluctuation amount of the moving average of the measurement result of the ammonia sensor 7 rises beyond a predetermined range, the consumption of ammoniacal nitrogen in the second control is insufficient, and the nitrification denitrification tank 2 is used. Insufficient oxygen supply. Therefore, the control unit 6 increases the output value of the second output of the circulation pump 42 to increase the oxygen supply amount to the nitrification denitrification tank 2 in the second control. In other words, when the moving average of the measurement result of the ammonia sensor 7 rises beyond a predetermined range, the control unit 6 raises the output value of the second output of the circulation pump 42.

Further, as shown in FIG. 7, when the fluctuation amount of the moving average of the measurement result of the ammonia sensor 7 falls beyond a predetermined range, the oxygen supply amount to the nitrification denitrification tank 2 in the second control is excessive. In this case, the control unit 6 lowers the output value of the second output of the circulation pump 42, and lowers the oxygen supply amount to the nitrification denitrification tank 2 in the second control. In other words, the control unit 6 lowers the output value of the second output of the circulation pump 42 when the moving average of the measurement result of the ammonia sensor 7 drops beyond a predetermined range.

Further, as shown in FIG. 8, when the fluctuation amount of the moving average of the measurement result of the ammonia sensor 7 is within a predetermined range, the vitrification step is appropriately advanced in the second control, and the ammoniacal nitrogen is efficiently oxidized. Will be done. Therefore, the control unit 6 maintains the output value of the second output of the circulation pump 42. In other words, the control unit 6 maintains the output value of the second output of the circulation pump 42 when the fluctuation amount of the moving average of the measurement result of the ammonia sensor 7 is within a predetermined range.

As a result, the nitrification denitrification apparatus 1 can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently. Even in such a second embodiment, the same effect as that of the first embodiment can be obtained.

5. Third Embodiment Next, a third embodiment of the present invention will be described.

In the first embodiment, the control unit 6 changes the output value of the second output of the circulation pump 42 in the second control based on the measurement result of the ammonia sensor 7, but the present invention is not limited to this.

In the third embodiment, the control unit 6 changes the output value of the first output of the circulation pump 42 in the first control based on the measurement result of the ammonia sensor 7. Further, the control unit 6 may change the output value of the second output of the circulation pump 42 in the second control based on the ammonia concentration of the internal liquid of the nitrification denitrification tank 2 at the start of the second control.

As shown in FIG. 9, when the ammonia concentration C1 of the internal solution of the nitrification denitrification tank ₂ at the start of the second control is less than the allowable lower limit value Z1 (less than a predetermined range) of the ammonia concentration at the start of the second control. , The amount of oxygen supplied to the nitrification denitrification tank 2 is excessive (see the second cycle and the third cycle of FIG. 9). Therefore, in the next first control, the control unit 6 lowers the output value of the first output of the circulation pump 42, and lowers the oxygen supply amount to the nitrification denitrification tank 2 in the first control. Further, in the next second control, the control unit 6 lowers the output value of the second output of the circulation pump 42, and lowers the oxygen supply amount to the nitrification denitrification tank 2 in the second control.

In other words, when the ammonia concentration C ₁ of the internal liquid of the nitrification denitrification tank 2 at the start of the second control is less than a predetermined range, the control unit 6 outputs the first output of the circulation pump 42 in the next first control. The value is lowered, and the output value of the second output of the circulation pump 42 is lowered in the next second control.

When the ammonia concentration C1 in the internal solution of the nitrification denitrification tank ₂ at the start of the second control exceeds the allowable upper limit value Z2 of the ammonia concentration at the start of the second control (exceeds a predetermined range), the nitrification denitrification is performed. The amount of oxygen supplied to the tank 2 is insufficient (see the 4th cycle and the 5th cycle of FIG. 9). Therefore, in the next first control, the control unit 6 increases the output value of the first output of the circulation pump 42 to increase the oxygen supply amount to the nitrification denitrification tank 2 in the first control. Further, in the next second control, the control unit 6 increases the output value of the second output of the circulation pump 42 to increase the oxygen supply amount to the nitrification denitrification tank 2 in the second control.

In other words, when the ammonia concentration C ₁ of the internal liquid of the nitrification denitrification tank 2 at the start of the second control exceeds a predetermined range, the control unit 6 outputs the first output of the circulation pump 42 in the next first control. The value is increased, and the output value of the second output of the circulation pump 42 is increased in the next second control.

Further, when the ammonia concentration C1 of the internal solution of the nitrification denitrification tank ₂ at the start of the second control is equal to or more than the allowable lower limit value Z1 of the ammonia concentration at the start of the second control and is equal to or less than the allowable upper limit value Z2 (within a predetermined range). In the next first control, the control unit 6 maintains the output value of the first output of the circulation pump 42 to be the same as the previous first control (see the first cycle and the second cycle of FIG. 9). In this case, the control unit 6 maintains the output value of the second output of the circulation pump 42 at the same level as the previous second control in the next second control.

In other words, when the ammonia concentration C ₁ of the internal liquid of the nitrification denitrification tank 2 at the start of the second control is within a predetermined range, the control unit 6 outputs the first output of the circulation pump 42 in the next first control. The value is maintained the same as the previous first control, and the output value of the second output of the circulation pump 42 is maintained the same as the previous second control in the next second control.

As a result, the nitrification denitrification apparatus 1 can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently. Even in such a third embodiment, the same effect as that of the first embodiment can be obtained.

Further, in order to suppress excessive fluctuation of the output value of the circulation pump 42, the average value of the ammonia concentration C1 at the start of the second control for a plurality of cycles is calculated, and the _first of the circulation pump 42 is based on the average value. The output values of the 1st output and / or the 2nd output may be changed.

6. Fourth Embodiment Next, a fourth embodiment of the present invention will be described.

In the fourth embodiment, the control unit 6 uses the minimum and maximum values of the ammonia concentration of the internal liquid of the nitrification denitrification tank 2 in one cycle as a reference as a reference, and the first of the circulation pump 42 in the next cycle. Change the output values of the output and the second output.

When the minimum value of the ammonia concentration of the internal solution of the nitrification denitrification tank 2 in one cycle is less than the allowable lower limit range (less than a predetermined range) of the ammonia concentration in the cycle, oxygen is supplied to the nitrification denitrification tank 2. The amount is excessive. Therefore, in the next second control, the control unit 6 lowers the output value of the second output of the circulation pump 42, and lowers the oxygen supply amount to the nitrification denitrification tank 2 in the second control. In other words, the control unit 6 lowers the output value of the second output of the circulation pump 42 when the minimum value per unit time of the ammonia concentration of the internal liquid of the nitrifying denitrification tank 2 in one cycle is less than a predetermined range. Let me.

Further, when the minimum value per unit time of the ammonia concentration of the internal liquid of the nitrification denitrification tank 2 in one cycle exceeds the allowable lower limit range of the ammonia concentration in the cycle (exceeds a predetermined range), the nitrification denitrification tank 2 Insufficient oxygen supply to. Therefore, in the next second control, the control unit 6 increases the output value of the second output of the circulation pump 42 to increase the oxygen supply amount to the nitrification denitrification tank 2 in the second control. In other words, the control unit 6 increases the output value of the second output of the circulation pump 42 when the minimum value per unit time of the ammonia concentration of the internal liquid of the nitrifying denitrification tank 2 in one cycle exceeds a predetermined range. Let me.

Further, when the minimum value per unit time of the ammonia concentration of the internal liquid of the nitrifying denitrification tank 2 in one cycle is within the allowable lower limit range (within a predetermined range) of the ammonia concentration in the cycle, the control unit 6 sets the following. In the second control of the above, the output value of the second output of the circulation pump 42 is maintained the same as the previous second control. In other words, when the minimum value per unit time of the ammonia concentration of the internal liquid of the nitrifying denitrification tank 2 in one cycle is within a predetermined range, the control unit 6 sets the output value of the second output of the circulation pump 42. Maintain the same as the previous second control.

Further, when the maximum value per unit time of the ammonia concentration of the internal solution of the nitrification denitrification tank 2 in one cycle is less than the allowable upper limit range (less than a predetermined range) of the ammonia concentration in the cycle, the nitrification denitrification tank 2 is used. The oxygen supply is excessive. Therefore, in the next first control, the control unit 6 lowers the output value of the first output of the circulation pump 42, and lowers the oxygen supply amount to the nitrification denitrification tank 2 in the first control. In other words, the control unit 6 lowers the output value of the first output of the circulation pump 42 when the maximum value per unit time of the ammonia concentration of the internal liquid of the nitrifying denitrification tank 2 in one cycle is less than a predetermined range. Let me.

When the maximum value of the ammonia concentration in the internal solution of the nitrification denitrification tank 2 in one cycle exceeds the allowable upper limit range of the ammonia concentration in the cycle (exceeds a predetermined range), the nitrification denitrification tank 2 Insufficient oxygen supply to. Therefore, in the next first control, the control unit 6 increases the output value of the first output of the circulation pump 42 to increase the oxygen supply amount to the nitrification denitrification tank 2 in the first control. In other words, the control unit 6 increases the output value of the first output of the circulation pump 42 when the maximum value per unit time of the ammonia concentration of the internal liquid of the nitrifying denitrification tank 2 in one cycle exceeds a predetermined range. Let me.

Further, when the maximum value per unit time of the ammonia concentration of the internal liquid of the nitrification denitrification tank 2 in the cycle is within the allowable upper limit range (within a predetermined range) of the ammonia concentration in the cycle, the control unit 6 is in the next second order. In one control, the output value of the first output of the circulation pump 42 is maintained the same as the previous first control. In other words, when the maximum value per unit time of the ammonia concentration of the internal liquid of the nitrifying denitrification tank 2 in one cycle is within a predetermined range, the control unit 6 sets the output value of the first output of the circulation pump 42. Maintain the same as the previous first control.

As a result, the nitrification denitrification apparatus 1 can carry out the nitrification step and the denitrification step in a well-balanced and stable manner, and can treat the sewage more efficiently. Even in such a fourth embodiment, the same effect as that of the first embodiment can be obtained.

The above-mentioned first to fourth embodiments and modifications can be combined as appropriate.

1 Nitrification denitrification device 2 Nitrification denitrification tank 31 Sewage supply line 41 Circulation line 42 Circulation pump 43 Overflow shaft 6 Control unit 7 Ammonia sensor

Claims (7)

Nitrification denitrification tank and
A sewage supply line that supplies sewage to the nitrification denitrification tank,
A circulation pump that draws out the internal liquid in which the sewage is treated with activated sludge in the nitrification denitrification tank and sends it out from the nitrification denitrification tank.
An injection unit that mixes the internal liquid and air and injects it into the nitrification denitrification tank.
A circulation line that circulates the internal liquid drawn from the nitrification denitrification tank to the nitrification denitrification tank via the injection portion.
An ammonia sensor that measures the ammonia concentration in the internal liquid and
A control unit capable of controlling the circulation pump, the first control for driving the circulation pump at the first output, and the second control for driving the circulation pump with a second output larger than the first output. With a control unit that can be executed alternately,
The control unit can change the output value of the first output and / or the output value of the second output of the circulation pump based on the measurement result of the ammonia sensor. Device. The control unit
From the measurement result of the ammonia sensor, the rate of decrease in the ammonia concentration from the start of the second control to the lapse of a predetermined time is calculated.
From the rate of decrease in the ammonia concentration, the predicted value of the ammonia concentration in the internal liquid at the end of the second control was calculated.
When the predicted value is within a predetermined range, the output value of the second output of the circulation pump is maintained.
When the predicted value is less than a predetermined range, the output value of the second output of the circulation pump is lowered.
The nitrification denitrification apparatus according to claim 1, wherein when the predicted value exceeds a predetermined range, the output value of the second output of the circulation pump is increased. Further equipped with a supply pump provided in the sewage supply line,
The control unit
The supply pump can be controlled and
When the ammonia concentration of the internal liquid at the start of the second control is equal to or less than the set value, in the next first control, the supply pump is driven by the third output.
When the ammonia concentration of the internal liquid exceeds the set value at the start of the second control, the supply pump is driven by a fourth output smaller than the third output in the next first control. The nitrification denitrification apparatus according to claim 2. The control unit
When the moving average of the measurement result of the ammonia sensor rises beyond a predetermined range, the output value of the second output of the circulation pump is raised.
The nitrification denitrification apparatus according to claim 1, wherein when the moving average of the measurement result of the ammonia sensor drops beyond a predetermined range, the output value of the second output of the circulation pump is lowered. The control unit
When the ammonia concentration of the internal liquid at the start of the second control is less than a predetermined range, the output value of the first output of the circulation pump is lowered in the next first control.
When the ammonia concentration of the internal liquid exceeds a predetermined range at the start of the second control, the first control is to increase the output value of the first output of the circulation pump. The nitrification denitrification apparatus according to any one of claims 1 to 4. The control unit
When the ammonia concentration of the internal liquid at the start of the second control is less than a predetermined range, the output value of the second output of the circulation pump is lowered in the next second control.
When the ammonia concentration of the internal liquid exceeds a predetermined range at the start of the second control, the second control is characterized in that the output value of the second output of the circulation pump is increased. The nitrification denitrification apparatus according to any one of claims 1 to 5. The control unit
When the minimum value of the ammonia concentration of the internal liquid per unit time is less than a predetermined range, the output value of the second output of the circulation pump is lowered in the next second control.
When the minimum value of the ammonia concentration of the internal liquid per unit time exceeds a predetermined range, the output value of the second output of the circulation pump is increased in the next second control.
When the maximum value of the ammonia concentration of the internal liquid per unit time is less than a predetermined range, the output value of the first output of the circulation pump is lowered in the next first control.
A claim characterized by increasing the output value of the first output of the circulation pump in the next first control when the maximum value of the ammonia concentration of the internal liquid per unit time exceeds a predetermined range. Item 1. The nitrification denitrification apparatus according to Item 1.

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