JP2017100092A - Sewage treatment control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sewage treatment control device that improves maintenance and suppresses consumption energy while properly suppressing water quality of the sewage treatment.SOLUTION: A water quality value that is estimated by a water quality estimation part in an aerobic tank, which estimates a water quality value other than a dissolved oxygen concentration in the aerobic tank, which oxidizes water to be treated is a water quality value varying by blowing oxygen from a blower, a blower air volume calculation part for calculating an air volume of a blower outputs a larger blower air volume among a blower air volume calculated based on a target value of a dissolved oxygen concentration in the aerobic tank and an estimation value of the dissolved oxygen concentration by a dissolved oxygen concentration estimation part that estimates dissolved oxygen concentration in the aerobic tank, and a blower air volume calculated based on a target value of a water quality value other than the dissolved oxygen concentration in the aerobic tank and an estimation value of a water quality value in the aerobic tank by a water quality estimation part in the aerobic tank.SELECTED DRAWING: Figure 1

Description

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

  Now that environmental issues and cost reductions have become essential, sewage treatment plants are also required to improve the quality of treated water discharged into public water areas, further energy savings, and improvement in maintainability using ICT. .

  In the sewage treatment plant, organic matter, nitrogen, etc. in the 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 substances are ingested / consumed and removed by an assimilation / catabolic reaction by microorganisms. Most of the nitrogen in the influent sewage is contained in the form of ammoniacal nitrogen, which is oxidized to nitrate nitrogen by nitrifying bacteria in the presence of oxygen. Part of this nitrate nitrogen remains in the return sludge and is returned upstream. At that time, a denitrification reaction that reduces to nitrogen gas occurs, and the nitrogen component is removed. On the other hand, if ammonia nitrogen remains in the effluent due to insufficient nitrification, there are concerns about the impact on aquatic organisms in the effluent water area and consumption of dissolved oxygen (DO). Management is required. For this purpose, it is necessary to appropriately control the air volume supply by the blower that consumes a lot of electric power. If the air supply is not sufficient, it will cause adverse environmental effects due to insufficient nitrification. Alternatively, if the air volume supply amount is excessive, the air volume is supplied wastefully even after the completion of nitrification, resulting in an increase in power consumption.

The 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 organic matter removal and nitrification reaction are controlled (for example, Non-Patent Document 1).

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

Japanese Patent No. 4509579

“Sewerage Facility Planning and Design Guidelines and Explanations”, 2009 edition, Japan Sewerage Association Kazuhiro Endo: Development of air flow control system using ammonia meter and DO meter, pp.918-920 (2010)

  In the method of Non-Patent Document 1, DO is a parameter related to the reaction activity of microorganisms, but is not ammonia nitrogen itself to be considered in the nitrification reaction. For this reason, due to fluctuations in the inflow flow rate and inflow water quality, the quality of the treated water tends to deteriorate due to insufficient air volume or excessive air volume.

Next, problems in the case of control using an ammonia meter will be described. In general, an ion electrode type ammonia meter is installed not in the last stage of the aerobic tank but in the middle stage slightly upstream because the life of the consumable electrode is shortened when the ammonia concentration is lowered.

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

  In the method of Patent Document 1, air volume feedback (FB) control is performed by an ammonia meter so that the measured ammonia concentration approaches a preset ammonia concentration. At that time, a lower limit value of DO set in advance is set. If it falls below, it switches to FB control by DO. However, there were problems in the following cases. That is, when the DO is larger than the lower limit value, if the result of abruptly reducing the air volume by the FB control by the ammonia meter, the DO becomes smaller than expected, and the water quality may be rapidly deteriorated. Alternatively, when DO is lower than the lower limit, FB control is performed by the DO meter. However, although the ammonia concentration rapidly increases and the air volume necessary for nitrification increases, it is directly reflected in the DO concentration. As a result, there was a risk that the air volume would become too small and the water quality would deteriorate.

The method of Non-Patent Document 2 is cascade-type feedback (FB) control that sets a target value of the DO value at the rear stage of the aerobic tank based on an ammonia meter installed at the middle stage of the aerobic tank. Because of the control based on the quality of the treated or treated water, if the influent water quality fluctuates, the fluctuation is not taken into account until the effect reaches the sensor position. there were. More specifically, for example, when the daily fluctuation is large or when sewage in which ammonia is temporarily diluted flows due to sudden rain. If the concentration measured with the middle ammonia meter is large, the total air volume will increase. At this time, the diluted upstream side is excessively 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 the downstream side that has flowed down will be excessively processed even under the minimum air volume, resulting in excessive aeration. Once it deviates significantly from the target value at the middle ammonia meter position, the air volume may vibrate thereafter and the processing may not be stable. Another issue is related to maintenance. The relational expression between the ammonia concentration at the middle stage used for control and the target value of DO must be adjusted by the operator on a trial and error basis according to the treatment characteristics and continuously according to the seasonal variation of the activated sludge properties. 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, the parameters need to be adjusted on a trial and error basis, and the maintenance effort tends to increase.

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

  The sewage treatment control device of the present invention includes an aerobic tank for oxidizing the water to be treated, a blower for sending air to the aerobic tank, a dissolved oxygen concentration estimating unit for estimating a 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; a water quality value estimating unit in the aerobic tank for estimating 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 volume estimation unit that estimates the air volume of the blower, and calculates the air volume of the blower In the sewage treatment control device comprising a blower air volume calculation unit, the water quality value estimated by the aerobic tank water quality value estimation unit is a water quality value that varies when oxygen is blown from the blower, and the blower air volume calculation The target value of the dissolved oxygen concentration in the aerobic tank and the The blower air volume calculated based on the estimated value of the dissolved oxygen concentration by the existing oxygen concentration estimation unit, the target value of the water quality value other than the dissolved oxygen concentration in the aerobic tank, and the aerobic performance of the water value estimation unit in the aerobic tank Of the blower air volumes calculated based on the estimated value of the water quality value in the tank, a larger blower air volume is output.

  According to the present invention, it is possible to improve maintenance and manageability and suppress energy consumption while appropriately controlling the quality of sewage treatment.

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

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

  FIG. 1 is a configuration diagram of Embodiment 1 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 with an anaerobic aerobic activated sludge method. From the upstream side, the first sedimentation tank 1, the anaerobic tank 6, the aerobic tank 3, and the final sedimentation tank 4 communicate with each other, and the aerobic tank 3 communicates with the blower 5. In the first sedimentation basin 1, the inflowing sewage 100 is separated by gravity sedimentation into first sedimentation water 101 as a supernatant and primary sedimentation sludge as a sediment. In the final sedimentation basin 4, the activated sludge 102 that flows in is separated into treated water 103 that is a supernatant and return sludge 104 that is a sediment. The returned sludge 104 is mixed with the first subsidence flowing water 101 and flows into the anaerobic tank 2 as the activated sludge 102. Air 106 is sent from the blower 5 to the aerobic tank 3.

  The aerobic tank 3 is provided with a DO meter 16 which is a dissolved oxygen concentration estimation unit. Also, an aerobic tank ammonia meter 12 which is an aerobic tank water quality value estimation unit is installed to measure the ammoniacal nitrogen concentration in the aerobic tank 3. Here, the ammoniacal nitrogen concentration is a water quality that fluctuates by blowing oxygen from a blower in the same manner as dissolved oxygen. An air flow meter 13 that is a blower air volume estimating unit is installed in a pipe communicating the blower 5 and the aerobic tank 3 to measure the air volume of air sent to the aerobic tank 3.

  DO meter 16, aerobic tank ammonia meter 12, air flow meter 13 measured value, dissolved oxygen concentration target value setting unit 22 set DO value, aerobic tank water quality target value setting unit 23 ammoniacal The nitrogen concentration value is transmitted to the blower air volume calculator 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 Example 1 is demonstrated. When the DO value set in the dissolved oxygen concentration target value setting unit 22 is 1.0 mg / L and the ammonia nitrogen concentration value set in the aerobic tank water quality target value setting unit 23 is 3.5 mg-N / L, The air volume calculation unit 20 performs FB calculation (hereinafter referred to as DO control) by PI control so that the DO meter becomes 1.0 mg / L, and obtains a necessary air volume. In parallel, the FB calculation by PID control (hereinafter, nitrification control) is performed so that the ammonia meter becomes 3.5 mg-N / L, and the necessary air volume is obtained. The blower air volume calculation unit 20 adopts a large air volume among 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 rather than switching the control method, the quality of treated water can be kept good. For example, when the DO value is larger than the DO value set by the dissolved oxygen concentration target value setting unit 22, the calculation result targeting the DO value set for a sudden air volume reduction instruction by nitrification control is adopted. 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 an immediate air volume increase instruction by nitrification control.

  In this example, the anaerobic aerobic activated sludge method was taken up as an application example. Any system that performs nitrification can be applied.

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

In this embodiment, PI control is used as the calculation of the downstream air volume, but PID control and other feedback control methods may be used.

In this embodiment, the first settling basin 1 is installed, but a configuration excluding the first settling basin 1 may be used. As an alternative to the final sedimentation basin 4, a membrane separation activated sludge method activated sludge method using a membrane for separation of 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 Embodiment 2 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 sedimentation tank 1, the anoxic tank 2, the aerobic tank 3, and the final sedimentation tank 4 communicate with each other, and the aerobic tank 3 communicates with the blower 5. In the first sedimentation basin 1, the inflowing sewage 100 is separated by gravity sedimentation into first sedimentation water 101 as a supernatant and primary sedimentation sludge as a sediment. In the final sedimentation basin 4, the activated sludge 102 that flows in is separated into treated water 103 that is a supernatant and return sludge 104 that is a sediment. The return sludge 104 is mixed with the first subsidence flowing water 101 and flows into the anoxic tank 2 as the activated sludge 102. From the end of the aerobic tank 3, a part of the activated sludge 102 circulates as a circulating liquid 105 to the anoxic tank 2. 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 anaerobic tank 3 is provided with a downstream flow meter 10 that is a downstream flow rate estimation unit and an inflow ammonia meter 11 that is an upstream water quality estimation unit. The flow rate of the inflow water flowing into the tank 3 and the ammonia concentration are measured. The ammonia concentration here is a water quality that varies as oxygen is blown from a blower in the same manner as 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 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 characteristics of the effects in the method of Example 2 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 serves as a discharge standard, it generally tends to maintain water quality on the overtreatment side, that is, over-aeration and over-power consumption. For example, when sewage temporarily diluted due to sudden rain flows, (1) DO constant operation at the end of the aerobic tank before dilution, (2) Increase in overall air volume due to increase in flow rate and decrease in residence time, (3 There is a possibility of over-aeration on the upstream side that is diluted), and (4) over-treatment even on the downstream side that has flowed down, even under the minimum airflow. After that, the air volume may vibrate and the process may not be stable. In addition, there are issues regarding maintenance. The set value of the relational expression of the target value of DO used for the control needs to be adjusted by the operator on a trial and error basis according to the processing characteristics and continuously according to the seasonal variation of the activated sludge properties.

  In the method of the second embodiment, the above-described problems are solved by (1) upstream / downstream individual air volume calculation, (2) visualization of processing characteristics, and (3) automatic update of the control model (control parameter).

  (1) In the upstream / downstream individual air volume calculation, nitrification operation control that takes into account the intermediate ammonia concentration in addition to the target ammonia concentration in the treated water stabilizes the treatment and suppresses excessive aeration and shortage of aeration. The upstream air volume is calculated from the upstream ammonia concentration measurement value and the midpoint ammonia concentration calculation value. The downstream air volume will be PI controlled by 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) calculation. The air volume by nitrification control is weighted to balance the FF and FB elements. The air volume in the final nitrification operation control is selected by paralleling the calculation based on the DO control that has been conventionally used to the air volume in the nitrification control. This is to incorporate empirical elements and stable control results so far in order to realize stable control.

(2) In the process characteristic visualization, a function that can be visualized as a model representing the process characteristic is used. Furthermore, by plotting the actual measurement points based on the processing results, it is possible to visualize the processing status important for maintenance. This visualized function of the processing characteristic model is used for aeration air volume calculation. FIG. 3 shows a method of calculating the upstream feedforward air volume. 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 accumulated air volume as the difference between the ammonia concentration at the inflow and the intermediate point. The required accumulated air volume [m ³ ] corresponds to the integration 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 upstream air volume Q _Bup . Considering a virtual fluid mass that flows in every fixed control cycle, the virtual fluid mass (gray part) that flows in at t = t ₀ 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 an addition of the air volume blown into the virtual fluid mass at each time. Each virtual fluid mass has a cumulative air volume accumulated so far and a 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) Automatic update of the control model (control parameter) can be realized by using the concept of the virtual fluid mass. t = t _N virtual fluid mass midpoint ammonia meter reaches the aerobic tank installed in has inlet ammonia concentration, midpoint ammonia concentration, the information of the cumulative airflow. As a result, the relationship between the treatment ammonia concentration and the cumulative air volume can be extracted for each control period, and the current point can be plotted on the treatment characteristic graph. Although the properties of activated sludge change gradually throughout the year, the innovative technology can automatically update the processing characteristic graph from each sensor information. Furthermore, the change in time accelerates the awareness of the abnormality. Maintenance accuracy is improved at the same time as ensuring control accuracy by automatically updating control parameters based on actual values.

  Below, the air volume calculation method in Example 2 is demonstrated as the detail of the calculation method. In Example 2, an aerobic tank upstream of the aerobic tank ammonia meter 12 in the aerobic tank 3 is an upstream aerobic tank, and a downstream aerobic tank is a downstream aerobic tank.

  In the second embodiment, the upstream air volume is derived by feed forward (FF) calculation, the downstream air volume is derived by feedback (FB) calculation, calculation by DO control is also performed, and these are combined to calculate the total air volume. In the FB calculation, a water quality calculation value that varies with time, 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, PI control or the like is performed as a target value for the nitrogen concentration and compared with the current ammonia nitrogen concentration of the aerobic tank ammonia meter 12. Although the control is possible only by the FB control, the calculation mechanism using the past value is the same as that of the FF control described below. Therefore, first, the FF calculation will be described below.

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

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

In the feed-forward calculation, a feed-forward calculation air volume Q _{B_FF} (t + Δt) where NH4 _{md_tgt} (t) is a passing point is obtained.

First, consider a virtual fluid mass that flows one-dimensionally into the calculation system (in this case, the biological reaction tank from the upstream ammonia meter to the intermediate ammonia meter) at a constant control period Δt, and track 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 varies depending on the flow rate Q _in (t). _{Assuming that} the position of the i-th virtual fluid mass i from the upstream side at time t is X _{vc, i} (t) [m], X _{vc, 1} (t) and X _{vc, i} (t + Δt) 2) It is expressed by (3).

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

The necessary 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 of Expression (5), which is a processing characteristic model.

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

The time when virtual fluid mass i flows into the calculation system is t _{0, i} , and the amount of aeration air to the upstream aerobic tank (aerobic tank up to the middle point ammonia meter) is Q _Bup (t) [m ³ / h] When the air volume distribution density at position X _i (t) is D (X _i (t)) [-], the cumulative air volume 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 representing the distribution ratio of the aeration air volume to each upstream aerobic tank, and the average of the distribution ratio in the entire upstream aerobic tank is 1. V _{rt, i} (t) [−] is a volume ratio of the virtual fluid mass i to the total volume V _all [m ³ ] of the upstream aerobic tank, and is expressed 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 from the accumulated air volume V _{B, i} (t) by the remaining residence time is required for the fluid mass i The air volume is large. 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). Is done.

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

For the evaluation of the calculated air volume, the air volume required upstream is set as the air volume of the entire aerobic tank, so that it becomes easier to understand sensuously, so the feedforward calculated air volume Q _{B_FF} (t + Δt) is From the air volume distribution ratio D _up [-] and the downstream air volume distribution ratio D _down [-], Equation (10) is obtained. The air volume distribution density D (X _i (t)) described above is a generalized form using the air volume distribution ratio here as a function.

The treatment characteristic model of Equation (5) visualizes the treatment capacity of the target sewage treatment plant with 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 information (actual measurement value) of the virtual fluid mass reaching the upstream aerobic tank end is used for the construction. If 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 inflow ammonia concentration NH4 _in at the time of inflow _{, It has information on N (t)} (t), intermediate point 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 ammonia concentration treated during the flow down, is expressed by 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 square method was applied to these measured data to derive the processing characteristic model. As the function form, an arbitrary function form (FIG. 4) such as a linear function, a quadratic function, a logarithmic function or the like can be selected. However, in the expression (5) of Example 2, the linear function is assumed to have a slope a and an intercept b. In the processing characteristic graph, the measured values are plotted at the same time as the processing characteristic function. Thereby, a change in processing characteristics can be visualized.

In the present embodiment, the processing characteristics visualized as the processing characteristics function vary with the seasonal variation of the activated sludge properties. However, the updating method of the processing characteristics function is important for improving the maintainability. By actual operation of the present embodiment, the inflow ammonia concentration, the aerobic tank ammonia concentration, and the accumulated air volume based on the actually measured values are accumulated in the virtual fluid mass that has reached the end of the upstream aerobic tank. Based on this information, the current value of the processing characteristic function can be updated statistically. In addition, the change in time accelerates the awareness of abnormal times. In development control, control accuracy is ensured by automatically updating control parameters based on actual values, and at the same time, maintenance can be improved.

FIG. 5 shows the update. Each time control is performed using the function before the update, information on the actual value is accumulated from the inflow ammonia concentration, the aerobic tank ammonia concentration, and the cumulative air volume. The processing characteristic function based on the actual value can be updated by drawing an approximate curve by, for example, regression analysis from the actual value group at an arbitrary timing (may be a fixed interval or an operator's judgment). 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 represented by a positive or negative power of x, or a polynomial combining these. Also, combinations with mathematical functions such as exponents, logarithms, and trigonometric functions may be used. Moreover, 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 with a correspondence prepared based on a database prepared in advance or the operator's judgment.

For example, the time change of the index obtained from the process characteristic function of FIG. 6 may be displayed on the operation screen. In FIG. 6, the air volume required for treating 25 kg of ammoniacal nitrogen was selected as an index, and the change with time was plotted. In general, the nitrification reaction rate decreases in the low temperature period, but the influence of temperature is removed here. From this, it is presumed that there was some change such as a decrease in the amount of nitrifying bacteria because the air volume suddenly increased in October at the A treatment plant. By visualizing the processing characteristics and monitoring them continuously, this anomaly can be immediately detected, and as shown in FIG. In addition, the B treatment plant requires a larger air volume than the 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 improvements should be considered with reference to the operation of the A treatment plant.

In the feedback calculation, feedback calculation based on 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 a measured value of the ammonia concentration at the inflow of water to be treated that has reached the downstream side from the upstream side. Has been taken into account. From equation (12), the calculated value NH4 _{md_FBtgt} (t) of the intermediate point ammonia concentration is calculated as a value having a fluctuation range as an intermediate point between the varying inflow side ammonia concentration and the fixed treated water ammonia concentration. The feedback calculation air volume Q _{B — FB} (t + Δt) [m ³ / h] at time t + Δt calculated based on this is shown in equation (13).

Conceptually, it is the air volume for properly controlling the downstream aerobic tank, but the evaluation of the calculated air volume is sensuously understood by using the air volume of the entire aerobic tank as with the upstream side. In order to facilitate, it was determined based on the air volume Q _B (t) [m ³ / h] at time t. C _par (Z) is a transfer function of a discrete-time parallel PI controller. The proportional term parameter is P, the integral term parameter 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 This is expressed by equation (15).

  As described above, the final air volume by the nitrification operation control is selected by paralleling the calculation by the DO control that has been conventionally used to the air volume by nitrification control that combines FF control and FB control. DO control is PI control of equation (14), and sets DO (lower side) [mg / L] and DO (upper side) [mg / L] as target values. Also, an air volume upper limit value, an air volume lower limit value, and an air volume gradient upper limit value and an air volume gradient lower limit value, which are upper and lower limit values of the air volume increase per unit time, are set. This is to incorporate empirical elements and stable control results so far in order to realize stable control.

  First, the nitrification control air volume obtained by equation (15) is compared with the air volume calculated by 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 instead of switching the control method, the quality of the treated water can be kept good. For example, when DO is larger than DO (lower side), it is possible to maintain the water quality by adopting a calculation result targeting DO (lower side) even for a sudden air volume reduction instruction by nitrification control. Alternatively, even when DO is smaller than DO (lower side), it is possible to maintain the water quality by responding to an prompt air volume increase instruction by nitrification control. The minimum air volume is guaranteed or over-aeration is suppressed by correcting the air volume to be within the range of the upper and lower limits of the aeration air volume and the slope of the variation of the aeration air volume with respect to the last selected air volume. In addition, damage to the blower equipment due to sudden changes in airflow can be prevented.

By using the total air volume Q _B (t + Δt) obtained by adding the upstream air volume and downstream air volume at time t + Δt obtained by calculation, the air volume that can achieve energy conservation with stable tracking of the water quality target value Can be requested. In the present embodiment, the upstream air volume and the downstream air volume are added together, but the weight may be changed as required, for example, by placing importance on the downstream feedback element. Also,
The amount of air sent individually to the upstream / downstream aerobic tank may be controlled by controlling a plurality of blowers and valves communicating with the upstream / downstream aerobic tank. In this case, it is not necessary to distribute the total air volume according to the equation (1) to the upstream / downstream air volume, and the upstream air volume and the downstream air volume may be calculated by the method of this embodiment.

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

In this embodiment, the flow-down flow meter 10 installed in the aerobic tank is used. However, since it is sufficient to know the flow velocity flowing down the biological reaction tank in the region to be controlled, as an alternative to the flow-down flow meter, for example, inflow sewage It is good also as a total value of the flow rate measured with the flowmeter, the return sludge flowmeter, and the circulation flowmeter.

In this example, the circulation nitrification denitrification method was taken up as an application example, but the standard method, AO method, A2
The present invention can be applied to all methods as long as nitrification is performed in an aerobic tank, such as the O method, the semi-advanced processing method, and a method in which step feed is applied thereto. In that case, for example, in the standard method or the AO method, the flow rate is the sum of the inflow sewage flow rate and the return sludge flow rate.
The total value of the inflow sewage flow meter and the return sludge flow meter may be used.

In this embodiment, an inflow ammonia meter 1 is used for feedforward control in the upstream aerobic tank.
1 is used, but other alternative means for estimating the ammonia concentration from the correlation such as an ammonia meter or UV meter installed in the sewage 100 or the first subsidence water 101 portion may be used. Alternatively, an estimated value of ammonia concentration from flow rate fluctuation, daily fluctuation, and seasonal fluctuation may be used. In these cases, when obtaining the ammonia concentration flowing into the aerobic tank, the sewage flow rate, the return sludge flow rate, the circulation flow rate, and the ammonia by the aerobic tank ammonia meter 12 with respect to the ammonia concentration of the sewage 100 and the first overflow water 101. The inflow ammonia concentration may be estimated using the return 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 and other feedback control methods may be used.

In this example, feedback control was performed using an aerobic tank ammonia meter, but in actual operation, a lower limit value was set for DO on the downstream side of the aerobic tank based on the empirical operating policy of the facility, and downstream of the aerobic tank. When the DO value by the installed DO meter is below the lower limit value, DO control with the lower limit value as the target may be used.

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

In this embodiment, an ammonia meter is used as the aerobic tank water quality estimation unit, but a DO meter may be installed as a second aerobic tank water quality measurement unit on the downstream side thereof. In that case, equation (2) may be feedback control such as PI control based on the target DO value. The target DO value here may be 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 difference to the target value NH4 _{out_tgt} of the treated water ammonia concentration is large, so the DO setting value is increased and the measured value of the aerobic tank ammonia concentration When NH4 _md (t) is small, it is conceivable to decrease the DO set value.

In this embodiment, the first settling basin 1 is installed, but a configuration excluding the first settling basin 1 may be used. As an alternative to the final sedimentation basin 4, a membrane separation activated sludge method activated sludge method using a membrane for separation of activated sludge and treated water may be used. In that case, for example, the membrane may be immersed in the aerobic tank 3.

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

1. First sedimentation basin 2. 2. Anoxic tank Aerobic tank 4. 4. Final sedimentation basin Blower 6. Anaerobic tank 100. Sewage 101. First subsidence water 102. Activated sludge 103. Treated water 104. Return sludge Circulating fluid 106. Air 10. 10. Inflow flow meter Inflow ammonia meter 12. Aerobic tank ammonia meter13. Air flow meter16. DO total 20. Blower air volume calculation unit 21. Blower air volume control unit 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 controller

Claims (7)

An aerobic tank for oxidizing the water to be treated;
A blower for sending air to the aerobic tank;
A dissolved oxygen concentration estimating unit for estimating a 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 estimation unit for estimating a water quality value other than the dissolved oxygen concentration in the aerobic tank;
An aerobic tank water quality 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 estimating unit for estimating the air volume of the blower;
A blower air volume calculator for calculating the air volume of the blower;
In the sewage treatment control device comprising
The water quality value estimated by the aerobic tank water quality value estimation unit is a water quality value that varies by blowing oxygen from the blower,
The blower air volume calculation unit calculates the blower air volume calculated based on 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 in the aerobic tank Of the blower air volume calculated based on the target value of the water quality value other than the 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. Sewage treatment control device. 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 ammoniacal nitrogen concentration. In claim 1 or 2,
A flow rate estimator for estimating a flow velocity in the aerobic tank;
An upstream water quality estimation unit that estimates a water quality value upstream from a water quality value other than the dissolved oxygen concentration in the aerobic tank;
A downstream water quality value target setting unit for setting a target value of a downstream water quality value from a water quality value other than the dissolved oxygen concentration in the aerobic tank;
With
The water quality value estimated by the upstream water quality value estimation unit and the water quality value set by the downstream water quality value target setting unit are water quality values that vary by blowing oxygen from the blower,
The aerobic tank water quality value target setting unit includes a current water quality value estimated by the aerobic tank water quality value estimation unit, a past water quality value estimated by the upstream water quality value estimation unit, and the downstream A sewage treatment characterized by setting a calculated water quality value that varies depending on a time calculated from a water quality value set by a side water quality value target setting unit as a target value for a water quality value other than the dissolved oxygen concentration in the aerobic tank. Control device. In claim 3,
The sewage treatment control apparatus, wherein the water quality value estimated by the upstream water quality value estimation unit and the water quality value set by the downstream water quality value target setting unit are ammonia nitrogen concentrations. In claim 3 or 4,
The blower air volume calculation unit has a necessary air volume calculation function that describes a relationship between at least the water quality value estimated by the upstream water quality value estimation unit and the required air volume,
A sewage treatment control apparatus that calculates a blower air volume using a required air volume calculated based on a current time value of a water quality value estimated by the upstream water quality value estimating unit and a required air volume calculated based on a past value. . In claim 5,
Based on the required air volume calculated by the upstream air quality value estimating unit, the aerobic tank water quality value estimating unit, and the required air volume calculating function, the blower air volume calculating unit calculates the water quality value and the required air volume in the required air volume calculating function. The sewage treatment control device characterized by updating the relationship with 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 volume in time series.

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