JP6726954B2 - Sewage treatment control device - Google Patents

Description

The present invention relates to a sewage treatment control device that controls the quality of treated water in a sewage treatment plant.

Nowadays, it has become essential to deal with environmental problems and cost reductions, and even in sewage treatment plants, it is required to improve the quality of treated water discharged to public water bodies, further reduce energy consumption, and improve maintenance and management using ICT. ..

At a sewage treatment plant, organic matter, nitrogen, etc. in sewage are removed by a microbial suspension called activated sludge. A reaction tank in which air is blown into activated sludge by a blower is called an aerobic tank. In the aerobic tank, organic matter is ingested/consumed and removed by assimilation/catabolization reaction by microorganisms. Most of the nitrogen in the incoming sewage is contained in the form of ammoniacal nitrogen, which is oxidized to nitric nitrogen by nitrifying bacteria in the presence of oxygen. A part of this nitrate nitrogen remains in the returned sludge and is returned to the upstream side. At that time, a denitrification reaction of reducing to nitrogen gas occurs, and the nitrogen component is removed. On the other hand, if ammoniacal nitrogen remains in the effluent due to insufficient nitrification, there is concern about the impact on aquatic organisms in the effluent area and consumption of dissolved oxygen (DO). Management is required. For that purpose, it is necessary to properly control the air volume supply by the blower that consumes a lot of electric power. If the amount of air supply is not sufficient, it will cause an adverse effect on the environment due to insufficient nitrification. Alternatively, when the air flow rate is excessive, the air flow rate is wastefully supplied even after nitrification is completed, resulting in an increase in power consumption.

Control of sewage treatment includes DO control using DO of a DO meter installed at the downstream end of the aerobic tank as a control index. By controlling the blower air volume so as to keep the terminal DO on the downstream side of the aerobic tank constant, the activity of microorganisms is maintained, and the removal of organic substances and the nitrification reaction are controlled (for example, Non-Patent Document 1).

In recent years, the accuracy of the ammonia meter that measures the concentration of ammonia nitrogen in activated sludge has been improved, and the controllability of a small capacity blower suitable for individual biological reaction tanks has improved. A control method using an ammonia meter for control has been studied (Patent Document 1, Non-Patent Document 2).

Japanese Patent No. 4509579

"Sewerage Facility Planning/Design Guidelines and Commentary", 2009 Edition, Japan Sewer Association Kazuhiro Endo: Development of air flow control system using ammonia meter and DO meter, Proc. 47th Sewer Research Presentation, pp.918-920 (2010)

In the method of Non-Patent Document 1, DO is a parameter related to the reaction activity of microorganisms, but it is not the ammoniacal nitrogen itself that should be considered in the nitrification reaction. Therefore, due to fluctuations in the inflow flow rate and the inflow water quality, the treated water quality is likely to deteriorate due to insufficient air volume, or an excess air volume may result.

Next, the problems in the case of control using an ammonia meter will be described. In general, the ion electrode type ammonia meter is installed not in the last stage of the aerobic tank but in the middle stage on the upstream side, because the life of the electrode, which is a consumable item, shortens when the ammonia concentration decreases.

The methods of Patent Document 1 and Non-Patent Document 2 use an ammonia meter installed in the middle stage of the aerobic tank and a DO meter installed in the latter stage of the aerobic tank for control.

In the method of Patent Document 1, feedback (FB) control of the air volume by the ammonia meter is performed so that the measured ammonia concentration approaches the preset ammonia concentration, but at that time, the preset lower limit value of DO is set. When it falls below, it switches to FB control by DO. However, there were problems in the following cases. When the DO is larger than the lower limit value, if the FB control by the ammonia meter results in a rapid reduction of the air volume, the DO becomes smaller than expected and the water quality may deteriorate sharply. Alternatively, when DO is smaller than the lower limit value, the FB control is performed by the DO meter, but the DO concentration is directly reflected in spite of the rapid increase in the ammonia concentration and the increase in the air volume required for nitrification. As a result, there was a risk that the air volume would be too small and the water quality would deteriorate.

The method of Non-Patent Document 2 is a cascade-type feedback (FB) control that sets a target value of a DO value in the latter stage of the aerobic tank based on an ammonia meter installed in the middle stage of the aerobic tank. Since the control is based on the quality of the treated water during or after the treatment, if the influent water quality changes, the variation is not considered until the effect reaches the sensor position, and there is a problem that the treated water quality deteriorates due to insufficient air volume or becomes excessive air volume. there were. More specifically, for example, there is a large daily fluctuation, or a case where sewage in which ammonia is temporarily diluted flows in due to sudden rainfall. When the concentration measured by the ammonia meter in the middle is large, the total air volume increases. At that time, the diluted upstream side may be over-treated, and the target value of the treated water may be reached before reaching the downstream side. As a result, there is a possibility that after that, excessive treatment will be performed on the downstream side even under the minimum air flow rate, resulting in excessive aeration. Once it deviates largely from the target value at the position of the ammonia meter in the middle stage, the air volume will continue to oscillate and the processing may not be stable. Another issue is the issue of maintenance. It is necessary for the operator to adjust the relational expression between the ammonia concentration at the middle point used for control and the target value of DO by trial and error according to the treatment characteristics, and continuously according to the seasonal fluctuation of the activated sludge properties. However, maintenance is not always easy.

In the methods of Non-Patent Document 1, Patent Document 1 and Non-Patent Document 2, parameters for control are manually given. Since the characteristics of activated sludge change with time, it is necessary to adjust the parameters by trial and error, and the labor for maintenance tends to increase.

Therefore, an object of the present invention is to provide a sewage treatment control device that improves maintenance and manages energy consumption while appropriately controlling the water quality of sewage treatment.

The sewage treatment control device of the present invention includes an aerobic tank for oxidizing treated water, a blower for sending air to the aerobic tank, and a dissolved oxygen concentration estimation unit for estimating a dissolved oxygen concentration in the aerobic tank. A dissolved oxygen concentration target setting unit that sets a target value of the dissolved oxygen concentration in the aerobic tank, and an aerobic tank water quality value estimation unit that estimates a water quality value other than the dissolved oxygen concentration in the aerobic tank, An aerobic tank water quality value target setting unit that sets a target value of a water quality value other than the dissolved oxygen concentration in the aerobic tank, a blower air flow rate estimation unit that estimates the air flow rate of the blower, and an air flow rate of the blower is calculated. In the sewage treatment control device including a blower air flow rate calculation unit, the water quality value estimated by the aerobic tank water quality value estimation unit is a water quality value that fluctuates by blowing oxygen from the blower, and the blower air flow rate calculation unit. Part, the blower air volume calculated based on the difference between the target value of the dissolved oxygen concentration in the aerobic tank and the estimated value of the dissolved oxygen concentration by the dissolved oxygen concentration estimation unit, and the dissolved oxygen concentration in the aerobic tank Of the blower air volume calculated based on the difference between the target value of the water quality value other than and the estimated value of the water quality value in the aerobic tank by the aerobic tank water quality value estimation unit, a large blower air volume is output. And

ADVANTAGE OF THE INVENTION According to this invention, maintainability can be improved and energy consumption can be suppressed, controlling the water quality of sewage treatment appropriately.

The block diagram of the sewage treatment control apparatus of Example 1. The block diagram of the sewage treatment control apparatus of Example 2. The figure which shows the upstream side air volume calculation by a virtual fluid mass. The figure which shows a processing characteristic function. The figure which shows the mode of update of a processing characteristic function. The figure which shows the time change of the extracted processing characteristic.

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

1 is a configuration diagram of a first embodiment of the present invention.

This embodiment is an example in which the sewage treatment control device 200 is applied to a sewage treatment plant of an anaerobic aerobic activated sludge method. From the upstream side, the first settling tank 1, the anaerobic tank 6, the aerobic tank 3, and the final settling tank 4 communicate with each other, and the aerobic tank 3 communicates with the blower 5. In the first settling basin 1, the inflowing sewage 100 is separated by gravity settling into a first settling overflow water 101 which is a supernatant and a first settling sludge which is a sediment. In the final settling tank 4, the inflowing activated sludge 102 is separated into treated water 103 which is a supernatant and return sludge 104 which is a sediment. The returned sludge 104 is mixed with the first settling water 101 and flows into the anaerobic tank 2 as activated sludge 102. Air 106 is sent from the blower 5 to the aerobic tank 3.

In the aerobic tank 3, a DO meter 16 which is a dissolved oxygen concentration estimation unit is installed. Further, an aerobic tank ammonia meter 12, which is a water quality value estimating unit in the aerobic tank, is installed to measure the concentration of ammonia nitrogen in the aerobic tank 3. The ammonia nitrogen concentration here is a water quality that changes by blowing oxygen from a blower like dissolved oxygen. An air flow meter 13, which is a blower air flow rate estimation unit, is installed in a pipe connecting the blower 5 and the aerobic tank 3 to measure the air flow rate of the air sent to the aerobic tank 3.

Measured values by the DO meter 16, the aerobic tank ammonia meter 12, and the airflow meter 13, the DO value set by the dissolved oxygen concentration target value setting unit 22, and the ammoniacal property set by the aerobic tank water quality target value setting unit 23 The nitrogen concentration value is transmitted to the blower air volume calculation unit 20. The calculation result of the blower air volume calculation unit 20 is transmitted to the blower air volume control unit 21, and the air volume of the blower 5 is controlled to the air volume calculated by the blower air volume calculation unit 20.

The air volume calculation method in the first embodiment will be described. If the DO value set by the dissolved oxygen concentration target value setting unit 22 is 1.0 mg/L and the ammonia nitrogen concentration value set by the aerobic tank water quality target value setting unit 23 is 3.5 mg-N/L, the blower In the air volume calculation unit 20, FB calculation by PI control (hereinafter, DO control) is carried out so that the DO meter becomes 1.0 mg/L, and a necessary air volume is obtained. In parallel, FB calculation by PID control (hereinafter, nitrification control) is performed so that the ammonia meter becomes 3.5 mg-N/L, and the required air volume is obtained. The blower air volume calculation unit 20 adopts the larger air volume out of the calculation results of the two air volumes and transmits it to the blower air volume control unit 21.

By selecting the result calculated in parallel instead of switching the control method, the quality of the treated water can be kept good. For example, if the DO value is larger than the DO value set by the dissolved oxygen concentration target value setting unit 22, the calculation result that targets the set DO value is adopted even for a sudden air volume reduction instruction by nitrification control, and the water quality is Can be maintained. Alternatively, even when the DO is smaller than the set DO value, it is possible to maintain the water quality by responding to the prompt air volume increase instruction by the nitrification control.

In this example, the anaerobic aerobic activated sludge method was taken up as an application example. Any method can be applied as long as it is a method for performing nitrification.

In the present embodiment, ammonia nitrogen was taken as an example of the water quality estimated by the inflow water quality, but the water quality estimated by the inflow water quality estimation unit is not limited to these, and oxidation by blowing oxygen from the blower, etc. The water quality may vary depending on. In this embodiment, the ammonia nitrogen was used as the water quality value fluctuating by blowing oxygen from the blower and the ammonia meter was used as its estimation means.However, the nitrate nitrogen concentration, the total nitrogen concentration, the phosphoric acid phosphorus concentration, the total phosphorus concentration and , BOD, COD _Mn , COD _Cr , TOC, etc. may be used.

In this embodiment, PI control is used as the calculation of the downstream air volume, but PID control or another feedback control method may be used.

Although the first settling tank 1 is installed in the present embodiment, the first settling tank 1 may be omitted. Further, as an alternative to the final settling tank 4, a membrane separation activated sludge method activated sludge method using a membrane for separating activated sludge and treated water may be used. In that case, for example, the membrane may be immersed in the aerobic tank 3.

FIG. 2 is a configuration diagram of the second embodiment of the present invention.

The present embodiment is an example in which the sewage treatment control device 200 is applied to a sewage treatment plant of a circulation type nitrification denitrification method. From the upstream side, the first settling tank 1, the anoxic tank 2, the aerobic tank 3, and the final settling tank 4 communicate with each other, and the aerobic tank 3 communicates with the blower 5. In the first settling basin 1, the inflowing sewage 100 is separated by gravity settling into a first settling overflow water 101 which is a supernatant and a first settling sludge which is a sediment. In the final settling tank 4, the inflowing activated sludge 102 is separated into treated water 103 which is a supernatant and return sludge 104 which is a sediment. The returned sludge 104 is mixed with the initial settling water 101 and flows into the anoxic tank 2 as activated sludge 102. From the end of the aerobic tank 3, a part of the activated sludge 102 circulates to the anoxic tank 2 as a circulating liquid 105. Air 106 is sent from the blower 5 to the aerobic tank 3.

In the configuration of the control system, in addition to the configuration of the first embodiment, the anoxic tank 3 is provided with a downflow meter 10 that is a downflow rate estimation section and an inflow ammonia meter 11 that is an upstream side water quality value estimation section. The flow rate of inflow water flowing into the tank 3 and the ammonia concentration are measured. The ammonia concentration here is a water quality that changes by blowing oxygen from the blower like dissolved oxygen.

In addition to the items of the first embodiment, the target value of the ammonia nitrogen concentration of the treated water set by the downstream side water quality value target setting unit 24 is transmitted to the blower air volume calculation unit 20. The calculation result of the blower air volume calculation unit 20 is transmitted to the blower air volume control unit 21, and the air volume of the blower 5 is controlled to the air volume calculated by the blower air volume calculation unit 20.

First, the features of the effects of the method of the second embodiment will be outlined.

In general DO control, the aerobic reaction is promoted by keeping the dissolved oxygen concentration in the aerobic tank constant. However, since DO is not a direct water quality that is the standard for discharge, it generally tends to maintain water quality on the over-treatment side, that is, excessive aeration and excessive power consumption. For example, when sewage temporarily diluted by sudden rainfall flows in, (1) constant DO operation at the end of the aerobic tank before dilution, (2) increase in total air volume due to increase in flow rate/retention time, (3) ) There is a possibility of excessive aeration due to excessive treatment on the diluted upstream side, and (4) excessive treatment on the downstream side after flowing down even under the minimum air volume. Even after that, the air volume may vibrate and the processing may not be stable. Furthermore, there is a problem regarding maintainability. It is necessary for the operator to adjust the set value of the relational expression of the target value of DO used for control by trial and error according to the treatment characteristics, and continuously according to the seasonal fluctuation of the activated sludge properties.

The above-mentioned problem is solved by the method of the second embodiment by (1) upstream/downstream side individual air volume calculation, (2) visualization of processing characteristics, and (3) automatic update of control model (control parameter).

(1) In the upstream/downstream individual air volume calculation, the nitrification operation control that takes into consideration the intermediate point ammonia concentration in addition to the treated water ammonia concentration target value stabilizes the treatment and suppresses excessive aeration and insufficient aeration. The upstream air volume is calculated from the upstream ammonia concentration measurement value and the intermediate point ammonia concentration calculation value. For downstream air volume, PI control is performed based on the ammonia concentration at the midpoint. The upstream air volume here is based on the feed forward (FF) calculation, and the downstream air volume is based on the feedback (FB) operation. The air flow rate by nitrification control is weighted to balance FF-like elements and FB-like elements. The final air volume in the nitrification operation control is selected by paralleling the air volume in the nitrification control with the operation in the DO control conventionally used. This is to realize stable control by incorporating empirical factors and stable control results in maintenance and management so far.

(2) In the visualization of processing characteristics, a function that can be visualized as a model representing processing characteristics is used. Furthermore, by plotting the actual measurement points based on the processing results, the current processing status that is important for maintenance is visualized. The function of the visualized processing characteristic model is used for aeration air volume calculation. FIG. 3 shows a method of calculating the feedforward air volume on the upstream side. The upstream side is from the aerobic tank inlet to the aerobic tank where the midpoint ammonia meter is installed. The treatment characteristic graph is expressed as a function of the treatment ammonia concentration and the required cumulative air volume, which are the differences between the inflow and intermediate point ammonia concentrations. The required cumulative air volume [m ³ ] corresponds to the integral of the air volume [m ³ /h]. A Lagrangian method of tracking a virtual fluid mass was used to calculate the required cumulative air volume and the upstream air volume Q _Bup . Considering the virtual fluid mass flowing in at every constant control cycle, the virtual fluid mass flowing in at t = t ₀ (gray part) reaches the rear end of the aerobic tank where the midpoint ammonia meter is installed at t = t _N. To do. The cumulative air volume is the addition of the air volume blown into the virtual fluid mass at each time. Each virtual fluid mass has the cumulative air volume accumulated up to that point and the required cumulative air volume calculated from the processing characteristic graph and the inflow/target ammonia concentration. From this difference and the remaining residence time (predicted value), an appropriate air volume for each fluid mass is calculated, and the upstream air volume Q _Bup (t _N ) at time t _N can be derived from this average value.

(3) The automatic updating of the control model (control parameter) can be realized by using the concept of the virtual fluid mass. At t = t _N , the virtual fluid mass that reaches the aerobic tank where the midpoint ammonia meter is installed has information on the inflow ammonia concentration, midpoint ammonia concentration, and cumulative air volume. From this, the relationship between the treated ammonia concentration and the cumulative air flow can be extracted for each control cycle, and the current point can be plotted on the treatment characteristic graph. Although the properties of activated sludge gradually change over the whole year, the innovative technology can automatically update the treatment characteristic graph from each sensor information. Furthermore, the change with time accelerates the awareness of the abnormality. Automatically updating the control parameters based on the actual value ensures control accuracy and at the same time improves maintainability.

The air volume calculation method in the second embodiment will be described below as the details of the calculation method. In the second embodiment, of the aerobic tank 3, the aerobic tank upstream of the aerobic tank ammonia meter 12 is the upstream aerobic tank, and the downstream aerobic tank is the downstream aerobic tank.

In the second embodiment, the upstream air flow rate is calculated by the feed forward (FF) operation, the downstream air flow rate is calculated by the feedback (FB) operation, the DO control operation is further performed, and these are combined to calculate the overall air flow rate. In the FB calculation, a time-dependent water quality calculation value calculated from the past ammonia nitrogen concentration by the inflow ammonia meter 11 and the ammonia nitrogen concentration of the treated water set by the downstream water quality value target setting unit 24 The target value of the nitrogen concentration is set as a target value, and PI control for comparing with the current ammonia nitrogen concentration of the aerobic tank ammonia meter 12 is executed. The control is possible only by the FB control, but the calculation mechanism using the past value is the same as that of the FF control described below. Therefore, the FF operation will be described first below.

Hereinafter, the term ammonia nitrogen concentration is referred to as NH4. FB ratio FB _rt [-], upstream side treatment rate UP _rt [-], treated water NH4 target value NH4 _{out_tgt} [mg-N/L]. The upstream side here refers to the aerobic tank up to the intermediate point ammonia meter. The measured values at time t are inflow NH4 measured value NH4 _in (t) [mg-N/L], intermediate NH4 measured value NH4 _md (t) [mg-N/L], and flow down the aerobic tank (circulation method. In the case of, total of sewage flow rate, return flow rate, circulation flow rate) Downflow rate Q _in (t) [m ³ /h], measured air flow rate Q _B (t) [m ³ /h], DO at aerobic tank end The measured value is DO(t) [mg/L]. Variables are shown here in italics.

The intermediate NH4 calculated value NH4 _{md_FFtgt} (t) [mg-N/L] in the feedforward calculation is the position of the passing point for the inflow NH4 measured value NH4 _in (t) to become the treated water NH4 target value NH4 _{out_tgt} , The larger the NH4 _in (t), the larger. NH4 _{md_FFtgt} (t) is calculated by the equation (1) using the upstream processing rate UP _rt .

In the feed-forward calculation, the feed-forward calculation air volume _{QB_FF} (t+Δt) at which this NH4 _{md_tgt} (t) becomes a passing point is obtained.

First, consider a virtual fluid mass that one-dimensionally flows into the calculation system (here, the biological reaction tank from the ammonia meter on the upstream side to the ammonia meter at the intermediate point) at a constant control cycle Δt, and trace this in a Lagrangian manner. (Fig. 1-2). The virtual fluid mass shown in gray flows into the calculation system at time t ₀ and reaches the rear end of the calculation system at time t _N. The size of the virtual fluid mass depends on the flow rate Q _in (t). If the position of the i-th virtual fluid mass i from the upstream side at time t is X _{vc, i} (t) [m], then X _{vc, 1} (t) and X _{vc, i} (t+Δt) are 2) It is represented by (3).

Here, S [m ² ] is the cross-sectional area in the downward direction of the biological reaction tank. Each virtual fluid mass flows down while holding the unique value measured and calculated at the time of inflow. The inflowing ammonia concentration NH4 _{in, i} (t) [mg-N/L] corresponding to the virtual fluid mass i is represented by the equation (4).

The required cumulative air volume V _{B_tgt, i} [m ³ ] required to control the virtual fluid mass i to the calculated water quality is represented by the function on the left side of equation (5), which is the processing characteristic model.

Here, a and b are coefficients, and ΔNH4 _tgt (t) [mg-N/L] is the treated ammonia concentration target value, which is given by equation (6).

The time at which the virtual fluid mass i flows into the calculation system is t _{0, i} , and the aeration air volume to the upstream aerobic tank (aerobic tank up to the intermediate ammonia meter) is Q _Bup (t) [m ³ /h] , And the airflow distribution density at the position X _i (t) is D(X _i (t)) [-], the cumulative airflow V _{B, i} (t) [m ³ ] to the virtual fluid mass i at time t is It is expressed by equation (7).

Here, the air volume distribution density D(X _i (t)) is a function that represents the distribution rate of the aeration air volume to each upstream aerobic tank, and the average of the distribution ratios in the entire upstream aerobic tank is 1. V _{rt, i} (t) [-] is the volume ratio of the virtual fluid mass i to the total volume V _all [m ³ ] of the upstream aerobic tank, and is represented by the equation (8).

Since the virtual fluid mass i has the required cumulative air volume V _{B_tgt,i} shown in equation (5), the value obtained by dividing the difference with the cumulative air volume V _B,i (t) by the remaining residence time is required for the fluid mass i. It will be a large air volume. Therefore, _assuming that the calculation system is filled with N virtual fluid masses, the calculated value Q _Bup (t+Δt) [m ³ /h] of the upstream air volume at time t+Δt is expressed by equation (9). To be done.

L _all [m] is the total length of the upstream aerobic tank. The amount of aeration air required for the fluid mass i is shown in the curly braces, but by setting the upper limit value and the lower limit value according to the operation of the implementation, it is possible to avoid an excessive value or a negative value due to a small denominator.

For the evaluation of the calculated air flow rate, the feed-forward calculated air flow rate Q _{B_FF} (t+Δt) is calculated as From the air volume distribution ratio D _up [-] and the downstream air volume distribution ratio D _down [-], the equation (10) is obtained. The airflow distribution density D(X _i (t)) described above is a form in which the airflow distribution ratio here is generalized as a function.

The treatment characteristic model of equation (5) is a visualization of the treatment capacity of the target sewage treatment plant by the ammonia concentration that can be treated with respect to the input air volume. The function representing the model is one of the control parameters, and the information (measured value) of the virtual fluid mass reaching the end of the upstream aerobic tank is used for its construction. Assuming that the number of virtual fluid masses at time t is N(t) [pieces], the virtual fluid mass N(t) at the end of the aerobic tank where the midpoint ammonia meter is installed is the inflowing ammonia concentration NH4 _in at inflow _{, It has information on N(t)} (t), midpoint ammonia concentration NH4 _md (t), cumulative air volume V _{B, and N(t)} (t). The treated ammonia concentration ΔNH4(t) [mg-N/L], which is the concentration of ammonia treated while flowing down, is represented by the equation (11).

Ammonia treated with the cumulative air volume V _B,N(t) (t) is the treated ammonia concentration ΔNH4(t), and these represent the treatment characteristics themselves. The least squares method was applied to these measured data to derive the processing characteristic model. As the function form, any function form (FIG. 4) such as a linear function, a quadratic function, and a logarithmic function can be selected, but in the formula (5) of the second embodiment, a linear function is used, and the slope a and the intercept b are used. On the processing characteristic graph, the actual measured values are plotted at the same time as the processing characteristic function. This makes it possible to visualize changes in processing characteristics.

In the present embodiment, the treatment characteristics visualized as a treatment characteristic function fluctuate according to the seasonal variation of the activated sludge property, but this method of updating the treatment characteristic function is important for improving the maintainability. By the actual operation of the present embodiment, the inflow ammonia concentration, the aerobic tank ammonia concentration, and the cumulative air volume based on the measured values are accumulated in the virtual fluid mass that has reached the end of the upstream aerobic tank. The current value of the processing characteristic function can be statistically updated based on this information. Further, the change with time accelerates the awareness of abnormal times. In the development control, it is possible to ensure control accuracy and improve maintainability by automatically updating the control parameters based on the actual values.

FIG. 5 shows the state of updating. Every time the control is executed using the function before the update, the actual value information is accumulated from the inflow ammonia concentration, the aerobic tank ammonia concentration, and the cumulative air volume. It is possible to update the processing characteristic function based on the actual value by drawing an approximate curve by regression analysis for the actual value group at an arbitrary timing (at a constant interval or at the operator's discretion). The approximate curve here is y=ax +b or y=ax ^-1 +b if it is a curve that accurately approximates the measured value.
It may be a monomial expression represented by the positive or negative power of x, or a polynomial combining them. Further, it may be combined with a mathematical function such as exponential, logarithmic or trigonometric function. Further, it is not necessarily a function, and a discontinuous and stepwise correspondence table may be used. In that case, the processing characteristic function may be updated in a correspondence relation based on a database prepared in advance or the operator's judgment.

Regarding the temporal change of the processing characteristic, for example, the temporal change of the index obtained from the processing characteristic function of FIG. 6 may be displayed on the operation screen. In FIG. 6, as an index, the amount of air required for treating 25 kg of ammonia nitrogen was selected and the time change was plotted. Generally, the nitrification reaction rate decreases in the low temperature period, but the effect of temperature is removed here. From this, it is estimated that there was something unusual such as a decrease in the amount of nitrifying bacteria at the A treatment plant because the air volume increased rapidly in October. By visualizing the treatment characteristics and continuously monitoring it, this anomaly can be immediately detected, and as shown in FIG. 5, it can be seen as an increase in a short period of time. Also, B treatment plant requires larger air volume than A treatment plant throughout the year. This indicates that the A treatment plant is operating more efficiently than the B treatment plant, suggesting that operational improvement should be considered with reference to the operation of the A treatment plant.

In the feedback calculation, the feedback calculation based on the PID control is performed on the calculated value NH4 _{md_FBtgt} (t) of the intermediate point ammonia concentration in the feedback control shown in Expression (12).

NH4 _{in, N(t)} (t) is the measured value of the ammonia concentration at the time of inflow of the water to be treated that has reached from the upstream side to the downstream side, and the time delay of the concentration fluctuation due to the concept of virtual fluid mass is Is being considered. From the equation (12), the calculated value NH4 _{md_FBtgt} (t) of the midpoint ammonia concentration is calculated as a value having a fluctuation range as the midpoint between the varying influent side ammonia concentration and the fixed treated water ammonia concentration. Equation (13) shows the feedback calculation air volume Q _{B_FB} (t+Δt) [m ³ /h] at time t+Δt calculated based on this.

Conceptually, it is the air volume for appropriately controlling the aerobic tank on the downstream side, but the evaluation of the calculated air volume is the same as that on the upstream side. Since it becomes easier, it was calculated based on the air volume Q _B (t) [m ³ /h] at time t. C _par (Z) is the transfer function of the discrete-time parallel PI controller, and the parameter of the proportional term is P, the parameter of the integral term is I, and the sampling time is T _s [min](=60Δt). ..

From the above, the nitrification control air volume Q _{B_NF} (t+Δt) [m ³ /h] uses the feedforward calculated air volume Q _{B_FF} (t+Δt), the feedback calculated air volume Q _{B_FB} (t+Δt), and the FB ratio FB _rt . Is expressed by equation (15).

As described above, the final air volume by the nitrification operation control is selected by paralleling the air volume by the nitrification control combining the FF control and the FB control with the calculation by the DO control conventionally used. DO control is the PI control of equation (14), and DO (lower side) [mg/L] and DO (upper side) [mg/L] are set as target values. Further, the upper limit value of the air flow rate, the lower limit value of the air flow rate, and the upper and lower limit values of the increase in the air flow rate per unit time, that is, the upper limit value of the air flow rate and the lower limit value of the air flow rate are set. This is to realize stable control by incorporating empirical factors and stable control results in maintenance and management so far.

First, the nitrification control air volume obtained by the equation (15) is compared with the air volume calculated by the DO (lower) control, and a large air volume is selected. Next, the selected air volume is compared with the air volume calculated by DO (upper) control, and a smaller air volume is selected. By selecting the control method instead of switching it, the quality of the treated water can be kept good. For example, when the DO is larger than the DO (lower side), it is possible to maintain the water quality by adopting the calculation result of targeting the DO (lower side) even for a sudden air volume reduction instruction by nitrification control. Alternatively, even when the DO is smaller than the DO (lower side), it is possible to maintain the water quality by responding to the prompt air volume increase instruction by the nitrification control. By correcting the last selected air volume so that it falls within the upper and lower limits of the aeration air volume and the upper and lower limits of the slope of the variation of the aeration air volume, the minimum air volume is guaranteed or excessive aeration is suppressed. Moreover, it is possible to prevent damage to the blower device due to a sudden change in the air volume.

By using by summing the upstream airflow and the downstream side air volume at time t + Delta] t obtained by the calculation obtained Zenkazeryou Q _B (t + Δt), air volume attained energy savings in a stable follow to the target value of the water Can be asked. In the present embodiment, the upstream air volume and the downstream air volume are summed up as they are, but the weighting may be changed according to the request, for example, by emphasizing the feedback element on the downstream side. Also,
By controlling a plurality of blowers and a valve that communicates with the upstream/downstream aerobic tank, the amount of air sent to the upstream/downstream aerobic tank may be controlled individually. In that case, it is not necessary to distribute the total air volume according to the equation (1) to the upstream/downstream air volumes, and the upstream air volume and the downstream air volume may be calculated by the method of this embodiment.

As described above, by applying the sewage treatment control device of the present embodiment, it is possible to stabilize the treated water quality, save energy, and improve the maintainability.

In the present embodiment, the downflow meter 10 installed in the aerobic tank was used, but since it is only necessary to know the flow velocity flowing down the biological reaction tank in the region to be controlled, as an alternative to the downflow meter, for example, inflow sewage is used. It may be the total value of the flow rates measured by the flow meter, the returned sludge flow meter, and the circulation flow meter.

In this example, the circulation type nitrification denitrification method was taken up as an application example, but the standard method, the AO method, the A2 method
It can be applied to all methods such as the O method, the semi-advanced processing method, and the method in which step feed is applied to these methods, as long as the method performs nitrification in an aerobic tank. In that case, for example, in the standard method and the AO method, the downflow rate is the sum of the inflow sewage flow rate and the return sludge flow rate.
It may be the total value of the inflow sewage flowmeter and the returned sludge flowmeter.

In this embodiment, inflow ammonia meter 1 is used for feedforward control in the upstream aerobic tank.
Although the ammonia concentration according to No. 1 is used, other alternative means for estimating the ammonia concentration from correlation such as an ammonia meter installed in the sewage 100 or the first settling running water 101 portion or a UV meter may be used. Alternatively, the estimated value of the ammonia concentration based on the flow rate fluctuation, the daily fluctuation, and the seasonal fluctuation may be used. In these cases, when the concentration of ammonia flowing into the aerobic tank is obtained, the sewage flow rate, the return sludge flow rate, the circulation flow rate, and the ammonia by the aerobic tank ammonia meter 12 are compared with the ammonia concentrations of the sewage 100 and the first settling runoff water 101. The inflow ammonia concentration may be estimated by using the returned sludge estimated from the concentration and the ammonia concentration contained in the circulating fluid.

In this embodiment, PI control is used as the calculation of the downstream air volume, but PID control or another feedback control method may be used.

In this example, feedback control was performed by the aerobic tank ammonia meter. When the DO value by the installed DO meter is lower than the lower limit value, the DO control targeting the lower limit value may be performed.

In this embodiment, the ammonia meter is used as the aerobic tank water quality estimation unit, but a DO meter may be used. In that case, the equation (2) may be feedback control such as PI control based on the target DO value. The target DO value here may be a fixed set value, or may be changed according to time, season, flow rate, or the like. In the case of time, it is conceivable to increase the DO setting value during the daytime when the load is heavy and decrease the DO setting value during the nighttime when the load is small. In the case of seasons, it is possible to increase the DO set value in winter when the water temperature is low and the reaction rate is small, and decrease the DO set value in large summer. In the case of flow rate, it is conceivable to increase the DO set value during the period when the flow rate is large and the residence time is short, and decrease the DO set value during the period where the residence time is long.

In the present embodiment, the ammonia meter is used as the aerobic tank water quality estimating section, but a DO meter may be installed as a second aerobic tank water quality measuring section on the downstream side thereof. In that case, the equation (2) may be feedback control such as PI control based on the target DO value. The target DO value here may be a cascade control corresponding to the measured value NH4 _md (t) of the aerobic tank ammonia concentration. For example, if the measured value NH4 _md (t) of the aerobic tank ammonia concentration is large, the DO set value is large and the measured value of the aerobic tank ammonia concentration is large because the difference between the treated water ammonia concentration and the target value NH4 _{out_tgt} is large. If NH4 _md (t) is small, it is possible to reduce the DO setting value.

Although the first settling tank 1 is installed in the present embodiment, the first settling tank 1 may be omitted. Further, as an alternative to the final settling tank 4, a membrane separation activated sludge method activated sludge method using a membrane for separating activated sludge and treated water may be used. In that case, for example, the membrane may be immersed in the aerobic tank 3.

In the present embodiment, ammonia nitrogen was taken as an example of the water quality estimated by the inflow water quality, but the water quality estimated by the inflow water quality estimation unit is not limited to these, and oxidation by blowing oxygen from the blower, etc. The water quality may vary depending on.

1. First settling tank 2. Anoxic tank 3. Aerobic tank 4. Final settling tank 5. Blower 6. Anaerobic tank 100. Sewage 101. First sinking water 102. Activated sludge 103. Treated water 104. Return sludge 105. Circulating fluid 106. Air 10. Inflow meter 11. Inflow ammonia meter 12. Aerobic tank ammonia meter 13. Air flow meter 16. DO total 20. Blower air flow calculation unit 21. Blower air flow controller 22. Dissolved oxygen concentration target value setting unit 23. Aerobic tank water quality target value setting unit 24. Downstream water quality target setting unit 200. Sewage treatment control device

Claims (7)

An aerobic tank that oxidizes the water to be treated,
A blower that sends air to the aerobic tank,
A dissolved oxygen concentration estimating unit for estimating the dissolved oxygen concentration in the aerobic tank,
A dissolved oxygen concentration target setting unit for setting a target value of the dissolved oxygen concentration in the aerobic tank,
An aerobic tank water quality value estimation unit that estimates a water quality value other than the dissolved oxygen concentration in the aerobic tank,
An aerobic tank water quality value target setting unit for setting a target value of a water quality value other than the dissolved oxygen concentration in the aerobic tank,
A blower air volume estimation unit that estimates the air volume of the blower,
A blower air volume calculation unit for calculating the air volume of the blower,
In a sewage treatment control device equipped with
The water quality value estimated by the aerobic tank water quality value estimation unit is a water quality value that fluctuates by blowing oxygen from the blower,
The blower air volume calculation unit, the blower air volume calculated based on the difference between the target value of the dissolved oxygen concentration in the aerobic tank and the estimated value of the dissolved oxygen concentration by the dissolved oxygen concentration estimation unit, and in the aerobic tank Of the blower air volume calculated based on the difference between the target value of the water quality value other than the dissolved oxygen concentration and the estimated value of the water quality value in the aerobic tank by the aerobic tank water quality value estimation unit, a large blower air volume is output. A sewage treatment control device characterized by: In claim 1,
The sewage treatment control apparatus, wherein the water quality value estimated by the aerobic tank water quality value estimation unit is an ammonia nitrogen concentration. In claim 1 or 2,
A downflow rate estimating unit for estimating downflow velocity in the aerobic tank,
An upstream water quality value estimation unit that estimates the upstream water quality value from a water quality value other than the dissolved oxygen concentration of the water to be treated that flows into the aerobic tank,
A downstream side water quality value target setting unit for setting a target value of the water quality value on the downstream side of the water quality value other than the dissolved oxygen concentration of the treated water flowing out from the aerobic tank,
Equipped with
And water quality value estimated by the upstream quality value estimator, the water quality value to be set in the downstream quality value target setting unit, write the water to be treated blown oxygen from the blower flows into the aerobic tank or Is the value of the water quality that fluctuates when
The aerobic tank water quality value target setting unit, the current water quality value estimated by the aerobic tank water quality value estimation unit, the past water quality value estimated by the upstream side water quality value estimation unit, and the downstream It is characterized in that a water quality value that varies with time calculated from a difference from the water quality value set in the side water quality value target setting unit is set as a target value of the water quality value other than the dissolved oxygen concentration in the aerobic tank. Sewage treatment control device. In claim 3,
The sewage treatment control device, wherein the water quality value estimated by the upstream side water quality value estimation unit and the water quality value set by the downstream side water quality value target setting unit are ammonia nitrogen concentrations. In Claim 3 or 4,
The blower air volume calculation unit has at least a necessary air volume calculation function that describes the relationship between the water quality value estimated by the upstream water quality value estimation unit and the required air volume,
The sewage characterized by calculating the blower air volume using the required air volume calculated by feedforward calculation based on the current time value of the water quality value estimated by the upstream side water quality value estimation section and the necessary air volume calculated by feedback calculation based on the past value Processing controller. In claim 5,
The sewage treatment control device, wherein the blower air volume calculation unit updates the relationship between the water quality value and the required air volume in the required air volume calculation function based on the calculated required air volume. In claim 6,
A sewage treatment control apparatus comprising: a treatment characteristic display unit that displays treatment characteristic information extracted from the relationship between the water quality value and the required air flow in time series.

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