JP5785816B2 - Water treatment process controller - Google Patents

Description

  The present invention relates to a water treatment process control device for controlling the quality of treated water and greenhouse gas emissions at a sewage treatment plant.

  In recent years when it has become necessary to deal with environmental problems, sewage treatment plants have been promoting efforts to reduce greenhouse gases in addition to improving the quality of treated water discharged into public water bodies.

Greenhouse gases emitted from sewage treatment plants include CO ₂ and dinitrogen monoxide (N ₂ O) derived from power consumption. N ₂ O released in the water treatment process accounts for about 9% of the greenhouse gas in the entire sewage treatment plant. Therefore, in the sewage treatment plant, in addition to improving the quality of treated water and reducing electric power, operation for reducing N ₂ O gas is required, and development of a control method that can be realized is desired.

  Various control indexes have been used for the purpose of realizing improved quality of treated water with low power. As a general control index, there are a dissolved oxygen concentration (DO) and an oxidation-reduction potential (ORP) that can be measured with an inexpensive measuring instrument. When using DO as a control index, for example, by maintaining DO at the end of the aerobic tank at a certain level or more, the activity of microorganisms is maintained, and organic matter / phosphorus removal and nitrification reaction are controlled. ORP is often used as a control index for maintaining an anaerobic state in order to manage phosphorus below a certain value and optimize phosphorus removal.

  In recent years, technological development to further control water quality has been advanced. For example, as described in [Non-Patent Document 1], a technique for controlling the ORP value of an anaerobic tank, an oxygen-free tank, and an aerobic tank to manage nitrogen / phosphorus removal, and [Non-Patent Document 2] As described above, a technique has been proposed in which nitrification is controlled with high accuracy using an ammonia meter in addition to a DO meter to reduce electric power.

N ₂ O released in the water treatment process is generated in both the nitrification reaction that proceeds under aerobic conditions and the denitrification reaction that proceeds under anoxic conditions in the biological reaction tank. Among them, in nitrification reaction oxidation reaction proceeding in the presence of oxygen, first ammonia nitrogen (hereinafter, NH ₄ ^- N) is mainly nitrite nitrogen by the action with ammonia-oxidizing bacteria (hereinafter, NO ₂ ^- N) to is oxidized further, nitrate nitrogen by the action of nitrous acid oxidation bacteria (hereinafter, NO ₃ ^- N) is oxidized to the.

In the reaction process, NO ₂ ^- mechanisms that part N ₂ O is produced as a by-product as it is reduced by the action of ammonia oxidation bacteria N is considered (see [Non-Patent Document 3]) .

This N ₂ O is generated in a dissolved state, but is released into the atmosphere by purging aerated bubbles in the aerobic tank. This mechanism, NO ₂ ^- N tends to increase the N ₂ O gas emissions easy storage, the treated water NO ₂ ^- N concentration correlation N ₂ O gas amount discharged from the treatment plant There is.

In the N ₂ O gas suppression control technology in the nitrification process, as described in [Patent Document 1], the concentration of N ₂ O gas generated from the biological reaction tank is directly measured to control the amount of oxygen supplied. There is a way. In this method, the progress of the nitrification reaction is suppressed by reducing the amount of oxygen to be supplied based on the increase in the N ₂ O gas concentration. As a result, the generation of dissolved N ₂ O and N ₂ O gas generated as a by-product of the nitrification reaction is suppressed.

Japanese Patent Application No. 2008-271664

Osamu Miki, Toshiro Kato, Naoya Takahashi, Takao Murakami: Development of efficient control method using ORP of advanced processing process, Journal of EICA, Vol.11, No.2-3, pp.37-40 (2006) ) Kazuhiro Endo: Development of air flow control system using ammonia meter and DO meter, 47th Sewerage Research Presentation, pp.918-920 (2010) Itokawa et al .: Generation and control of nitrous oxide from nitrification and denitrification processes in a human waste treatment facility with intermittent aeration, Environmental Engineering Research Papers, Vol. 32, pp. 311-319 (1995)

The methods of [Non-Patent Document 1] and [Non-Patent Document 2] control the quality of treated water, and there is a problem that the suppression of N ₂ O gas production is not considered. In the method of [Patent Document 1], the generation of N ₂ O gas is reduced by suppressing the nitrification reaction. That is, since the nitrification reaction is suppressed when the N ₂ O gas increases, there is a problem that the quality of the treated water may be deteriorated.

  The objective of this invention is providing the water treatment process control apparatus which can implement the control which makes compatible maintenance of the quality of treated water in a water treatment process, and greenhouse gas reduction.

In order to achieve the above object, the water treatment process control device of the present invention comprises:
An estimation unit that estimates the nitrification degree of water to be treated in a water treatment process, a target value setting unit that sets a target value of the nitrification degree, a blower that sends air into an aerobic tank of the water treatment process, and the nitrification degree A control unit for controlling the air volume of the blower so that the estimated value becomes the target value, and includes an oxidation-reduction potentiometer as means for estimating the nitrification degree, and an estimation unit As input information, at least a redox potential is used.

  Alternatively, the target value is at least two of a first target value and a second target value larger than the first target value, and the first target value or the second target value is set according to a control mode to be selected. And a target value setting unit for setting the target value of the degree of nitrification.

  Alternatively, when the inflow load to the water treatment process estimated by the inflow load estimation unit is larger than the threshold value, the target value is set as the first target value, and when the inflow load is less than the threshold value, the target value is set. Is the second target value.

  Alternatively, when the nitrification degree of the treated water is larger than the target value, the air volume of the blower is controlled so that the nitrification degree approaches the target value, and the nitrification degree of the treated water is equal to or less than the target value. In this case, the air volume of the blower is controlled based on a preset control rule.

  Alternatively, when the nitrification degree of the treated water is smaller than the target value, the air volume of the blower is controlled so that the nitrification degree becomes the target value, and the nitrification degree of the treated water is equal to or higher than the target value. In this case, the air volume of the blower is controlled based on a preset control rule.

  Alternatively, an estimation unit that estimates a nitrification degree of water to be treated in a water treatment process, a target value setting unit that sets a target value of the nitrification degree, a blower that sends air into an aerobic tank of the water treatment process, A control unit that controls the air volume of the blower so that the estimated value of the nitrification level becomes the target value, and when the nitrification level of the water to be treated is larger than the target value, The blower air volume is controlled so that the nitrification degree becomes a target value. When the nitrification degree of the treated water is equal to or less than the target value, the blower air volume is controlled based on a preset control rule. And a control unit.

  Alternatively, an estimation unit that estimates a nitrification degree of water to be treated in a water treatment process, a target value setting unit that sets a target value of the nitrification degree, a blower that sends air into an aerobic tank of the water treatment process, A control unit that controls the air volume of the blower so that the estimated value of the nitrification level becomes the target value, and when the nitrification level of the water to be treated is smaller than the target value, The blower air volume is controlled so that the nitrification degree becomes a target value. When the nitrification degree of the treated water is equal to or higher than the target value, the blower air volume is controlled based on a preset control rule. And a control unit.

  Or the input to the estimation part which estimates the nitrification degree of the to-be-processed water of the said water treatment process is an ammonia meter, It is characterized by the above-mentioned.

  Or the input to the estimation part which estimates the nitrification degree of the to-be-processed water of the said water treatment process is a nitric acid meter, It is characterized by the above-mentioned.

  Alternatively, a display unit that displays the amount of dinitrogen monoxide estimated from the nitrification degree and the power consumption of the blower is provided.

  Alternatively, a nitrous oxide amount acquisition unit that acquires the amount of nitrous oxide in water to be treated in the water treatment process, and a nitric oxide amount estimation unit that estimates the amount of nitric oxide from the nitrous oxide concentration. It is characterized by that.

  ADVANTAGE OF THE INVENTION According to this invention, the control which makes compatible the maintenance of the quality of treated water in a water treatment process, and greenhouse gas reduction can be implemented.

The block diagram of the water treatment process control apparatus of Example 1. FIG. The graph showing the relationship between oxidation-reduction potential (ORP) and nitrification rate. Graph showing the average N ₂ O gas release rate relationship between nitrification rate. 4 is a display screen example of the first embodiment. 3 is a graph showing a time history of oxidation-reduction potentials under the control of Example 1. FIG. The block diagram of the water treatment process control apparatus of Example 2. FIG. 7 is a control flowchart according to the second embodiment. 6 is a graph showing a time history of an oxidation-reduction potential under the control of Example 2. The block diagram of the water treatment process control apparatus of Example 3. FIG. 10 is a control flowchart of Embodiment 3. 10 is a display screen example of the third embodiment. 10 is a graph showing a time history of the oxidation-reduction potential under the control of Example 3. The graph showing the time history of the oxidation-reduction potential at the time of combining DO control and ORP control at the time of nitrification promotion mode.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram of a water treatment process control apparatus that is Embodiment 1 of the present invention. This embodiment is an example in which a water treatment process control device is applied to a standard activated sludge method, and controls the treatment of the aerobic tank 1 for treating sewage with activated sludge.

  The aerobic tank 1 includes a blower 2 for supplying air, an air diffuser 3 installed at the bottom of the aerobic tank 1 to diffuse air supplied from the blower 2, and water to be treated in the aerobic tank 1. An oxidation-reduction potentiometer 4 for measuring the oxidation-reduction potential is installed. Sewage 100 flows into the aerobic tank 1 and is separated into solid and liquid in the sedimentation basin 5, and the supernatant liquid flows out as treated water 101.

  The estimation unit 10 connected to the oxidation-reduction potentiometer 4 acquires the measurement value in the oxidation-reduction potentiometer 4 and calculates the nitrification degree. The control unit 11 controls the blower 2 so that the nitrification degree estimated by the estimation unit 10 becomes the target nitrification degree set by the target value setting unit 12. The display unit 13 displays the measurement value of the oxidation-reduction potentiometer 4 and the corresponding nitrification degree, the target nitrification degree set by the target value setting unit 12 and the corresponding oxidation-reduction potential value.

In this example, the nitrification rate was used as an index representing the progress of nitrification. The nitrification rate is generally defined as the ratio of the nitrate nitrogen of the treated water and the nitrogen removed by denitrification to the total nitrogen concentration of the influent water, but in this example, in each aerobic tank to assess the progress of the nitrification, NO ₃ aerobic tank ^- N concentration [mgN / L] and NH ₄ ^- occupying the sum of the N concentration _{[mgN / L], NO 3} - N nitrification ratio of concentration The rate was defined as [%]. The definition formula is shown in Equation 1.

  Other nitrogen components include organic nitrogen and nitrite nitrogen, but here, from a practical point of view, only the main components ammonia nitrogen and nitrate nitrogen were considered.

  The inventor found the relationship between the nitrification rate and the ORP through experiments. The results are shown in FIG. The results shown in FIG. 2 are measured values at the end of the aerobic tank. As can be seen from FIG. 2, although there is an error, it can be considered that the nitrification rate is uniquely determined for the ORP, and the nitrification rate can be estimated by the ORP.

  The ORP is defined by the Nernst equation and can be calculated by the concentration of the oxidant and the reductant. The calculation formula is shown in Formula 2.

Here, Ox is an oxidant substance, Red is a reductant substance, and m and n are coefficients in an equilibrium equation. E _h [V]: Electrode potential, E ₀ [V]: Standard electrode potential, R [J / (K · mol)]: Gas constant, T [K]: Absolute temperature, n [mol]: Redox Number of electrons exchanged in the reaction, F [C / mol]: Faraday constant. Of the oxidation-reduction substances contained in the activated sludge mixture, in the nitrification reaction, the reaction in which NO ₃ —N is oxidized to NH ₄ —N is the main reaction, and assuming that the concentration of other substances is constant, the ORP value is , Log ([NO ₃ —N] / [NH ₄ —N]). Accordingly, the nitrification rate [%] of Equation 1 is expressed by Equation 3.

  Here, A and B are coefficients used for estimating the nitrification rate, and ORP [mV] is an actual measurement value. In this experimental result, A = −0.013 and B = 0.94, which is a good approximation with a correlation coefficient of 0.95. In other experiments, the coefficient values were different, but the correlation coefficients were similar. It is considered that the difference in the count value is influenced by the activated sludge flora, the water temperature, the difference in the activity of the activated sludge due to the influence of the water temperature and the like. The creation of an estimation formula that takes these effects into consideration is an issue for the future, but in practice, a count value is obtained for each target sewage treatment plant, and calibration is performed when the treatment status changes greatly due to the influence of water temperature, etc. It can respond by doing.

  As described above, it was found that the nitrification rate of the aerobic tank can be calculated with an ORP meter installed in the aerobic tank. Here, the nitrification rate is a value at the end of the aerobic tank, but since nitrification does not proceed in the sedimentation basin, it can be regarded as the nitrification rate of treated water. In addition, the nitrification rate of the treated water can be similarly estimated on the upstream side of the aerobic tank using a function that considers nitrification after the measurement point. Examples of the function considering nitrification after the measurement point include treated water nitrification rate = C × measured nitrification rate + D.

The inventor found through experiments the relationship between this nitrification rate and the amount of N ₂ O gas released from the aerobic tank into the atmosphere. The results are shown in FIG. Here, the average N ₂ O gas release rate [mgN / (m ³ · h)] is the N ₂ O gas release rate released from the unit activated sludge suspension volume, and N ₂ contained in the collected gas. O gas concentration was calculated from ^{[mgN / m 3 (gas)} ] and feed amount ^{[m 3 (gas) / h} ] and aerobic tank volume [m ^3]. Thus, the average N ₂ O gas release rate tended to have a maximum value with respect to the nitrification rate.

When nitrification was promoted to some extent, the average N ₂ O gas release rate decreased, but DO increased. Increase in DO is, NH ₄ consumes oxygen ^- N and organic matter is considered to be due to decreased with the progress of the biological reaction. Generation of N ₂ O has been to be suppressed at a high DO, which NO ₃ ^- N, NO ₂ ^- with respect to the reduction reaction to N ₂ O is produced lower the DO locally from N Since the oxidation reaction proceeds rapidly at high DO, there is a possibility that dissolved N ₂ O will not accumulate.

As described above, in activated sludge treatment, it has become clear that the amount of N ₂ O gas released has a maximum value with respect to the nitrification rate, and that the nitrification rate can be estimated with an ORP meter in the aerobic tank. It was found that greenhouse gas can be reduced by controlling.

In the operation of a sewage treatment plant, the required water quality differs depending on the situation, and there are cases where a nitrification suppression operation is performed or a nitrification promotion operation is performed. In order to achieve both water quality maintenance and N ₂ O gas reduction, as can be seen from the results in FIG. 3, nitrification is promoted by targeting a nitrification rate smaller than the nitrification rate in the region where the amount of N ₂ O emission is large when suppressing nitrification. In some cases, a nitrification rate larger than the nitrification rate in a region where the amount of N ₂ O released becomes large may be targeted.

  An example of a screen displayed on the display unit 13 is shown in FIG. In this example, the measured oxidation-reduction potential value and the corresponding nitrification rate are displayed at the top of the screen. In this example, the target value setting unit 12 is displayed in the middle of the screen, and the nitrification suppression mode and the nitrification promotion mode can be selected as the control mode. Further, a target oxidation-reduction potential can be input, and a target nitrification rate corresponding to the target nitrification degree value is displayed. Alternatively, by inputting the target nitrification rate, the corresponding target oxidation-reduction potential is displayed.

In this way, by displaying the target value of the nitrification rate that is the processing target and the target value of the oxidation-reduction potential that is the measured value side by side, the processing target and the control target can be easily grasped, and an appropriate operation method is derived. It becomes support information in the above. Greenhouse gases showed CO ₂ emissions in terms of CO ₂ emissions and N ₂ O gas from the power of the blower. The CO ₂ emission amount derived from the power of the blower can be calculated by multiplying the power consumption of the blower by the basic unit of the CO ₂ emission amount with respect to the power consumption.
The N ₂ O gas emission can be estimated by applying the estimated nitrification rate to the relationship shown in FIG. 3, and the CO ₂ emission can be calculated by multiplying the N ₂ O greenhouse effect coefficient.

The relationship shown in FIG. 3, that is, the average N ₂ O gas release rate, has a qualitative tendency to have a maximum value with respect to the nitrification rate, but varies quantitatively. Emissions of N ₂ O gas, since it is correlated with the NO ₂ concentration in the treated water, by measuring the NO ₂ concentration in the treated water, from the measured value, for example determined proportionality constant or function type, N ₂ The amount of O gas discharged can be estimated. Since the NO ₂ concentration of the treated water does not change greatly on a daily basis, a value measured periodically may be used. As described above, the display of the nitrification rate of treated water and the amount of greenhouse gas emissions in a trade-off relationship is support information for deriving an optimum operation method.

  The control unit 11 controls the blower 2 according to the target value of the selected mode. FIG. 4 shows an example in which the nitrification suppression mode is selected, and FIG. 5 shows the control status in the nitrification suppression mode.

The first target redox potential that is the first target value is the target value in the nitrification suppression mode, and the second target redox potential that is the second target value is the target value in the nitrification promotion mode, and the second target value in the nitrification promotion mode. The target redox potential is larger than the first target redox potential in the nitrification suppression mode. These target values are desirably set avoiding the region where the amount of N ₂ O gas released becomes large as shown in FIG. 3 from the viewpoint of N ₂ O gas suppression.

In this embodiment, the nitrification suppression mode is selected, and the measured value of the oxidation-reduction potential indicated by the solid line is controlled to be in the vicinity of the first target oxidation-reduction potential 110 mV. That is, as shown in FIG. 4, the nitrification rate is controlled to be around 70%. By this control, it is possible to avoid deterioration of water quality due to insufficient blower air volume, and to suppress an increase in N ₂ O gas and CO ₂ derived from power consumption due to excessive blower air volume.

When the nitrification promotion mode is selected, by controlling to be close to the second target redox potential, it is possible to avoid water quality deterioration and N ₂ O increase due to insufficient blower air volume, and CO 2 derived from electric power due to excessive blower air volume. ₂ increase can be suppressed.

In this embodiment, the oxidation-reduction potentiometer 4 is used for estimating the nitrification rate, but an ammonia meter that measures the ammonium ion concentration may be used. In this case, the water quality before treatment is required for the calculation of the nitrification rate. For this, a measured value of the quality of the influent water or an estimated value from an existing value may be used. Further, the ammonium ion concentration may be directly used as an index representing the nitrification degree. The ammonium ion concentration has a negative correlation with the nitrification rate. Therefore, as in FIG. 3, there is a region where the N ₂ O gas becomes large. Therefore, by using two target values, it is possible to reduce the N ₂ O gas while obtaining a desired water quality.

In this embodiment, the oxidation-reduction potentiometer 4 is used for estimating the nitrification rate, but a nitric acid meter that measures the nitrate ion concentration may be used. In this case, the water quality before treatment is required for the calculation of the nitrification rate, but a measured value of the influent water quality or an estimated value from an existing value may be used. Further, the nitrate ion concentration may be directly used as an index representing the nitrification degree. The nitrate ion concentration has a positive correlation with the nitrification rate. Therefore, as in FIG. 3, there is a region where the N ₂ O gas becomes large. Therefore, by using two target values, it is possible to reduce the N ₂ O gas while obtaining a desired water quality.

  In this embodiment, the control modes are two, namely, nitrification promotion and nitrification suppression, and control target values corresponding to the control modes are shown, but these may be three or more.

  FIG. 6 is a configuration diagram of a water treatment process control apparatus that is Embodiment 2 of the present invention. In the present embodiment, a flow meter is installed as the inflow load estimation unit 6 for estimating the inflow load to the water treatment process in the configuration diagram of the water treatment process control apparatus of the first embodiment.

As in the first embodiment, there are two control modes, the nitrification suppression mode and the nitrification promotion mode, and the values of the first target oxidation-reduction potential and the second target oxidation-reduction potential are assigned to each. To reduce the N ₂ O gas, it is desired to avoid these N ₂ O regions gas amount becomes maximum between the target value. However, since the blower air volume has an upper limit value and a lower limit value and the inflow load is small, the nitrification rate, that is, the redox potential may not be lowered to the first target redox potential.
Further, since the inflow load is large, the redox potential may not be raised to the second target redox potential.

  Therefore, in this embodiment, a threshold is provided for the inflow load, and the control mode is switched according to the inflow load. FIG. 7 shows the control flow, and FIG. 8 shows the time variation of the oxidation-reduction potential during control.

In step (S1), in addition to the first target oxidation-reduction potential and the second target oxidation-reduction potential, an inflow load threshold value is input. In step (S2), the ORP value of the aerobic tank is measured, and step (S3). Then measure the inflow load. In step (S4), when the inflow load is compared with its threshold value and this inflow load is larger than the threshold value, in step (S5-1), the control mode is set with the first oxidation-reduction potential as the target value. Is a control mode in which the second redox potential is set as a target value in step (S5-2). In step (S6), ORP control is performed with the obtained target value, and in step (S7), the blower air volume is output. The above is performed in one control cycle, and the ORP value is measured again in step (S2). Thus, while obtaining a certain level or more of the treated water quality can be avoided an increase in the N ₂ O gas.

In this embodiment, the oxidation-reduction potentiometer 4 is used for estimating the nitrification rate, but an ammonia meter that measures the ammonium ion concentration may be used. In this case, the water quality before treatment is required for the calculation of the nitrification rate. For this, a measured value of the quality of the influent water or an estimated value from an existing value may be used. Further, the ammonium ion concentration may be directly used as an index representing the nitrification degree. The ammonium ion concentration has a negative correlation with the nitrification rate. Therefore, as in FIG. 3, there is a region where the N ₂ O gas becomes large. Therefore, by using two target values, it is possible to reduce the N ₂ O gas while obtaining a desired water quality.

In this embodiment, the oxidation-reduction potentiometer 4 is used for estimating the nitrification rate, but a nitric acid meter that measures the nitrate ion concentration may be used. In this case, the water quality before treatment is required for the calculation of the nitrification rate. For this purpose, a measured value of the influent water quality or an estimated value from the existing value may be used. Further, the nitrate ion concentration may be directly used as an index representing the nitrification degree. The nitrate ion concentration has a positive correlation with the nitrification rate. Therefore, since the region where the N ₂ O gas increases is present as in FIG. 3, the N ₂ O gas can be reduced while obtaining desired water quality by using two target values.

  In this embodiment, the control modes are two, namely, nitrification promotion and nitrification suppression, and control target values corresponding to the control modes are shown, but these may be three or more.

  Since the water quality to be treated is not limited to the amount of nitrification, in the operation of the water treatment process, using DO control, flow proportional control, inflow load control, and combinations of these, using control methods according to the past operation results Driving is being carried out. In this embodiment, a case where these driving methods are combined will be described. As an example, a control method in which a preset control rule is DO control and this is combined with a nitrification control method will be described.

  FIG. 9 is a configuration diagram of a water treatment process control apparatus that is Embodiment 3 of the present invention. In this embodiment, the DO meter 7 for measuring the dissolved oxygen concentration in the aerobic tank is installed in the configuration diagram of the water treatment process control apparatus of the first embodiment.

  FIG. 10 is a display screen of the display unit 13. In this embodiment, DO control + nitrification control is performed in the nitrification suppression mode, and nitrification control is performed in the nitrification promotion mode. In the DO control, a target DO value and a DO lower limit value can be set.

  FIG. 11 shows a control flow. In step (S1), in addition to the first target value and the second target value, the target DO value in the nitrification suppression mode and the DO lower limit value in the overall control are input. In step (S2), the ORP value of the aerobic tank In step (S3), the DO value is measured. In step (S4), the measured DO value is compared with the set DO lower limit value. If the measured value is large, the operation mode is confirmed in step (S5).

If it is the nitrification promotion mode, the second target value is set as the redox potential target value in step (S7-1). If the operation mode is the nitrification suppression mode, the ORP measurement value is compared with the first target value in step (S6), and if the first target value is large, the first target value is set as the redox potential target value.
Otherwise, in step (S8-2), the set target DO value is set as the DO target value, the DO control is performed in step (S9-1), and the blower air volume is output in step (S10). If the DO value is equal to or less than the DO lower limit value, the DO lower limit value is set as the DO target value in step (S8-1), and the DO control is performed in step (S9-1). When the redox potential target value is set in steps (S7-1) and (S7-2), ORP control is performed in step (S9-2), and the blower air volume is output in step (S10). To do. The above is performed in one control cycle, and the ORP value is measured again in step (S2). Thus, while using the air volume control method having a proven so far, can suppress the formation of N ₂ O gas.

FIG. 12 is a diagram showing a time history of combined control of DO control and nitrification (ORP) control in the nitrification suppression mode. When the oxidation-reduction potential exceeds the first target value, ORP control is performed, and when it is below, DO control is performed. FIG. 13 is an example of a time history when the DO control and the nitrification (ORP) control are combined in the nitrification promotion mode. When the redox potential is lower than the second target value, the ORP control is performed, and the redox potential is the second target. When it exceeds the value, it is DO control. In either case, the conventional control method may increase the amount of N ₂ O generated, but N ₂ O generation can be suppressed by switching to ORP control in the vicinity of this region.

  In the present embodiment, the method of controlling the blower air volume with the DO value is shown as a preset control rule, but the blower air volume constant control and the inflow flow rate proportional control may be used. Moreover, the control method which measures inflow load and uses this as a function may be used. Moreover, the combination of the control method demonstrated above may be sufficient. Further, the increase / decrease value of the blower air volume may be obtained from the difference between the target value of the oxidation-reduction potential and the ORP measurement value, and the blower air volume value calculated by a preset control rule may be increased or decreased.

In this embodiment, the oxidation-reduction potentiometer 4 is used for estimating the nitrification rate, but an ammonia meter that measures the ammonium ion concentration may be used. In this case, the water quality before treatment is required for the calculation of the nitrification rate. For this, a measured value of the quality of the influent water or an estimated value from the existing value may be used. Further, the ammonium ion concentration may be directly used as an index representing the nitrification degree. The ammonium ion concentration has a negative correlation with the nitrification rate. Therefore, as in FIG. 3, there is a region where the N ₂ O gas increases, and therefore, switching to the ORP control in the vicinity of this region can reduce the N ₂ O gas.

In this embodiment, the oxidation-reduction potentiometer 4 is used for estimating the nitrification rate, but a nitric acid meter that measures the nitrate ion concentration may be used. In this case, the water quality before treatment is required for the calculation of the nitrification rate. For this purpose, a measured value of the influent water quality or an estimated value from the existing value may be used. Further, the nitrate ion concentration may be directly used as an index representing the nitrification degree. The nitrate ion concentration has a positive correlation with the nitrification rate. Therefore, as in FIG. 3, there is a region where the N ₂ O gas increases, and therefore, by using two target values, it is possible to reduce the N ₂ O gas while obtaining a desired water quality.

  In this embodiment, the control modes are two, namely, nitrification promotion and nitrification suppression, and control target values corresponding to the control modes are shown, but these may be three or more.

DESCRIPTION OF SYMBOLS 1 Aerobic tank 2 Blower 3 Aeration pipe 4 Oxidation reduction potential meter 5 Sedimentation basin 6 Inflow load estimation part 7 DO meter 10 Estimation part 11 Control part 12 Target value setting part 13 Display part

Claims (3)

An estimation unit for estimating the nitrification rate of the water to be treated in the aerobic tank from the measurement value of the oxidation-reduction potentiometer provided in the aerobic tank of the water treatment process;
A target value setting unit for setting a target value of the nitrification rate of the water to be treated in the aerobic tank;
A blower for sending air to the aerobic tank;
A control unit that controls the air volume of the blower within a range between an upper limit value and a lower limit value so that the estimated value of the nitrification rate estimated by the estimation unit becomes a target value of the nitrification rate of the water to be treated in the aerobic tank; With
The target value of the nitrification rate of the water to be treated in the aerobic tank is the maximum value of the average N2O gas release rate relative to the nitrification rate in relation to the nitrification rate and the amount of N2O gas released from the aerobic tank to the atmosphere. At least two of a first target value set avoiding the region and a second target value greater than the first target value,
The target value setting unit sets a threshold value of the inflow load corresponding to an upper limit value and a lower limit value of the wind power of the blower, and when the inflow load is larger than the threshold value, the first target value is aerobic. A target value for the nitrification rate of the water to be treated in the tank, and when the inflow load is equal to or less than the threshold, the second target value is a target value for the nitrification rate of the water to be treated in the aerobic tank. Water treatment process control device. The water treatment process control device according to claim 1,
A nitric acid meter is provided instead of the oxidation-reduction potentiometer provided in the aerobic tank of the water treatment process, and the estimation unit estimates a nitrification rate of water to be treated in the aerobic tank by the nitric acid meter. Water treatment process control device. In the water treatment process control device according to claim 1 or 2,
A water treatment process control device comprising: a display unit that displays a dinitrogen monoxide amount estimated from the nitrification rate and a power consumption amount of the blower.