JPS5962393A - Sewage treating device - Google Patents

Abstract

PURPOSE:To stabilize SS amt. at all times by calculating the removal amt., removal start time and removal stop time of the excess sludge required for minimizing the calculated value for one day of deviation with respect to the target value of the SS concn. in the liquid mixture in an aeration tank and controlling a sludge return and removal mechanism in accordance with the results of the calculation. CONSTITUTION:An SS concn. detector 110 which detects the SS concn. of the liquid mixture in an aeration tank 10 and a pattern setting circuit 113 which stores the change chracteristic of the inflow rate in a day of the sewage flowed, into the tank up to the previous day and the change characteristic of the SS load and outputs the pattern signal thereof are provided. An arithmetic control circuit 116 which stores the rate of inflow sewage, the SS load of the outflow sewage, and the change characteristic of the SS concn. in the liquid mixture with respect to the amt. of return sludge, is inputted with the signals from the detetor 110 and the circuit 113, calculates the removal amt., removal start and stop time of the surplus sludge required for minimizing the integrated value for one day of deviation with respect to the target value of the SS concn. in the liquid mixture in accordance with said signals and controls the removal mechanism in accordance with the calculated results is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a sewage treatment apparatus that automates the extraction of excess sludge.

[Technical background of the invention and its problems]

A conventional sewage treatment apparatus using activated sludge will be explained with reference to FIG. 1 in the figure is an inflow sewage pipe, and through this inflow sewage pipe 1, solid suspended solids (hereinafter referred to as SS) are
Sewage containing dissolved organic matter to be treated flows into the aeration tank 2.

In this aeration tank 2, sewage and activated sludge are sufficiently mixed and aerated, organic matter in the sewage is absorbed into the activated sludge, and at the same time, the activated sludge is multiplied. This mixture of sewage and activated sludge is sent to the next settling tank 3, where the solid components and water are separated, and the separated supernatant water is discharged from the discharge pipe 4 to the outside of the system. Further, a part of the sludge including activated sludge settled in the settling tank 3 is drawn out of the system through the excess sludge drawing pipe 5 of the sludge return drawing mechanism, and most of the remaining activated sludge is drawn out by the front pump 6. Aeration tank 2 through return pipe 7
will be returned to.

By the way, in order to control the amount of sludge in the system that continues to increase due to this inflow SS and sludge multiplication, and to maintain an appropriate amount of suspended solids in the mixed liquid (hereinafter referred to as MLSS) in the first air tank 2 relative to the inflow organic matter. Conventionally, the daily surplus sludge removal time period is determined each time by the operator's judgment. For this reason, an operator must constantly monitor the plant, resulting in a problem that requires a lot of effort to operate, and it has been desired to automate this operation. A method of automating these tasks is to set a certain sludge order calculated based on the long-term operating status of the plant, and to extract excess sludge at the required flow rate at a set time, or to One possible method is to draw sludge at a constant flow rate for the required time from the drawing start time, or to measure ML and SS and give a set value for excess sludge drawing flow that corresponds to the deviation between this feedback value and the target value. It is being However, the method of controlling the sludge order by keeping it constant is MLSS in the short term.
Weird@-i! + cannot be suppressed, and the amount of sludge relative to the inflowing organic matter becomes inappropriate.In the case of control by feedback of the MLSS value, the deviation is Because the reaction is slow and the amount of operation is limited (-), it is impossible to perform better control than manual control by the operator.In other words, with MLSS control, if MLSS falls below its target value. stops drawing out excess sludge and returns to the aeration tank; it is necessary to increase the concentration and flow rate of the sludge.I
However, since the excess sludge extraction pipe at this time does not fall below zero, the MLSSO value that can be controlled is limited. It's ox, there is a lower limit to the amount of cultivation, so if you don't make the upper limit too small, it will be MLSS.
The average value will go down. Therefore, the control range of the MLSS solely by controlling the flow rate of excess sludge becomes small, and the MLSS in the aeration tank 2, which reacts slowly, cannot be sufficiently controlled.

OBJECT OF THE INVENTION The present invention has been made based on the above circumstances, and its purpose is to automatically control the extraction of excess sludge,
Moreover, it is an object of the present invention to provide a sewage treatment device that can stably control the MLSS of an aeration tank.

[Summary of the invention]

The present invention provides an aeration tank that mixes and aerates inflowing sewage and activated sludge, sucks organics contained in the sewage into the activated sludge, and multiplies this activated sludge, and an aeration tank that mixes and aerates inflowing sewage and activated sludge. A settling tank separates the activated sludge mixture into solid components and water, and the sludge containing the activated sludge precipitated in this settling tank is returned to the aeration tank, and a portion of this sludge is removed from the system as surplus sludge. A device equipped with a sludge return and extraction mechanism that can be pulled out, and a suspended solids concentration detector that detects the suspended solids concentration in the mixed liquid in the aeration tank, and a daily flow rate of sewage that has flowed in until the previous day. A pattern setting circuit that stores the change characteristics and daily change characteristics of the inflow sewage suspended solids load in a pattern and outputs this 9-tap signal, and the amount of inflow sewage in the aeration tank and the floating solids load of the inflow sewage. The change characteristics of the suspended solids concentration in the mixed liquid with respect to the sludge load and the amount of returned sludge are stored in advance, and signals from the suspended solids concentration detector and pattern setting circuit are input, and the system is configured based on these signals. Then, calculate the amount of excess sludge to be drawn, the time to start drawing, and the time to stop drawing necessary to minimize the daily cumulative value of the deviation from the target value of the suspended solids concentration in the mixed liquid in the aeration tank. The apparatus is equipped with an arithmetic control circuit that controls the sludge return and extraction mechanism based on the results. Therefore, the amount of inflow sewage in the trench and the SS in the sewage are
Since it is controlled according to the load fluctuation pattern, the MLSS concentration in the aeration tank can be stabilized and controlled automatically! This can be controlled using ffIJ.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to Figures 2 to 4 of the lower box. In the figure, 101 is an aeration tank, and the aeration tank 101 is configured so that sewage flows into it from an inflow sewage pipe 102. The sewage is thoroughly mixed with activated sludge in this aeration tank 101, stirred, and aerated.
The organic matter in the sewage is absorbed into the activated sludge, and at the same time the activated sludge is grown, the aeration tank 1
The mixed liquid of sewage and sludge in 01 is sent to settling tank 103,
The solid components are precipitated and the separated supernatant water is discharged into the discharge pipe 104.
is discharged to the outside. In addition, the sludge containing the activated sludge settled in the sedimentation tank 103 is returned to the aeration tank 101 by the sludge return/extraction mechanism 105, or a portion is drawn out of the system as surplus sludge. In other words, 106 is a sludge feed pump, which sucks the sludge settled in the sedimentation tank 103 and pumps it. And this sludge sending l? The sludge pumped by the pump 106 is sent to the aeration tank 101 via the return pipe 1θ7.
will be returned to. Further, an excess sludge drawing pipe 108 is branched and connected to the discharge side of this sludge feed pump 106, and a flow rate regulating valve 109 is provided in the middle of this excess sludge drawing pipe 1θ8. 109 and is drawn out of the system as surplus sludge. Such sewage treatment equipment is equipped with a mechanism for automatically controlling the sludge extracted. 110 is its suspended solids concentration detector (hereinafter M
ML in the aeration tank 101
It is configured to detect ss. And this ML
The signal from the SS detector 110 is configured to be sent to a short-term MLSS target value calculation circuit 111. This short-term MLSS target value calculation circuit 111 calculates the long-term MLSS that is sent from the long-term MLSS target value setting circuit 112.
It is generally configured to calculate a short-term MLSS target value based on the deviation between the JJ degree target value and the signal sent from the MLSS detector 110 and output it. Also, 1
13 is a pattern setting circuit. This i? The turn setting circuit 113 is input with the amount of inflowing sewage at the previous day's turn and the fluctuation data of 5Sil in this inflowing sewage, that is, the inflowing SS load, and these data are converted into 9 turns as shown in Figs. 3 and 4. The nose turn signal is configured to output a nose turn signal. Reference numeral 114 is a standard surplus sludge withdrawal time zone setting circuit, which stores a standard surplus sludge withdrawal time zone 115 corresponding to the amount of inflowing sewage in one day as shown in FIG. Standard surplus sludge removal time zone 115...
It is configured to output a signal. These standard surplus sludge extraction time periods 115... are set so that the stop time coincides with the time when the amount of inflowing sewage and the inflowing SS load are the minimum1, and these short-term ML
SS target value performance 9 circuits 11 no, no! Turn setting circuit 113
The signal from the standard excess sludge removal time zone setting circuit 114 is configured to be sent to the arithmetic control circuit 116. Based on these signals, the arithmetic control circuit 116 determines the amount of excess sludge to be extracted and the time period for the extraction.
The timer 117 further sends a signal to the drawn sludge flow rate controller 118, which in turn sends a command signal to the scene adjustment valve 109, and the command signal is sent to the timer 117. It is constructed so that the sludge is pulled out of the system as surplus sludge.

The calculation control circuit 116 is configured to perform the following calculations. That is, in such a sewage treatment system, there is a characteristic that the integral of the excess sludge flow area is related to the response of the MLSS value, and if the flow rate is kept constant, the MLSS value can be controlled by the drawing time. In order to optimally set the time period for this withdrawal throughout the day, a mathematical model simulation is used to calculate the sludge concentration at the outlet of the aeration tank and settling tank.For the aeration tank 101, f1? Using the IS higher-order delay model, and settling pond 1
For 03, a first-order lag model is used. -1 Then, in order to avoid a large number of searches for extraction time periods performed by the simulator, the search will be performed only within the vicinity of a certain reference time. First, a method for setting the reference time will be given, and the search will be performed as follows: Daily "' of aeration tank MLSS
This is done by using the sum of squared deviations for one day between the "short-term target value" and the total X value of the simulation as an index, and selecting the minimum case.This "short-term target value"
The deviation between the average calculated value and the long-term target value, which is fixed for one month or more, is calculated as the previous day's short-term target value.
It is obtained by making corrections each time in addition to . The above mathematical model is shown in equations (1) to (5).

In other words, for the aeration tank model sea millage, hole = (Ql・Xl-1-QR-XR)/(Ql-I-Q
R) ・・・・・・・・・(1), 1 sedimentation pond model simulation is X5-(Q1+QR)
・XN/(QR-+-QW) ・・・・・・
......(4).

Here, the hole is the aeration inlet MLSS concentration CmVL]
X1 is the ss concentration in influent sewage Cwt)XR is the return sludge concentration C7n9/l]Xn(
n = 1.2.3...N) is the n-stage combination of the aeration tank with a first delay (if the aeration tank is set as a higher order delay, Mu of the high mouth of each stage is 889 degrees Cmy/1]X8 is 2. Final Virtual concentration of precipitated light inflow sludge at the start of descent
Cmf/l〕Q1 is the inflow sewage flow rate
b'/h] QR is the return sludge flow rate
Qw is the excess sludge flow rate [
m/h] TA, time delay constant of aeration tank [h
]T8 is the time constant of the final settling tank [hla,
l) is a constant.

On the other hand, the reference time for searching for the optimum extraction time slot is given as follows. In other words, now from the processing system data,
The flow rate of inflowing sewage under normal sunny weather changes in the pattern shown in Figure 3, and the time when the flow rate takes the lowest minimum value of the day as shown in OB in Figure 3 is determined during the drawing time once a day. The reference time is set so that it almost coincides with the stop time, and the time when the flow rate becomes saddle-shaped as shown at A in FIG. 3 almost coincides with the time when drawing starts. The reason why the extraction stop time is made to correspond to the minimum point of the inflowing sewage flow rate is because at this time the MLSS dilution effect becomes the smallest and the MLSS value reaches its maximum, so sludge extraction is already started before that time, and the sludge is removed at the maximum time. This is to maximize the integrated effect of , that is, to minimize the MLSS peak. In other words, the relationship between the extraction start and stop times and the flow and human sewage flow knowledge is based on the pattern of the inflow sewage flow rate, which has already been determined based on past results, and the times A and B in Figure 3 are used as the reference extraction start times, respectively. , as the reference withdrawal stop time, shift the start and stop times in 1-hour increments within a range of 1 to 4 hours before and after this, calculate the MLS S at each time of the day using the mathematical model, and find the optimal start and stop time. Select the time. This allows a more appropriate drawing time period than the standard drawing time period from start to stop. This reduces the number of cases compared to searching for all possible combinations of extraction start and stop times for 24 hours a day, making calculations easier. Then, in consideration of the negative impact that errors between the mathematical model and the actual predictions have on the control effect, feedback elements are incorporated to determine the true target value of the MLSS, the ``long-term target value,'' and the results obtained from the previous day's operation. The deviation of the MLS S average price is added to the previous day's short-term target value for use in calculations, plus the current day's short-term target value, and the day's withdrawal time is calculated based on this. Then output MLS like this.
Control the S average value so that it does not deviate from the long-term target value.

Note that the present invention is not limited to the above embodiment, and for example, instead of using the sum of squares of the target value deviation of MLSS for one day as the optimization index value, the sum of absolute deviation values may be used. Furthermore, in the simulation model, the aeration tank is assumed to have a high-order lag, and this time lag constant is fixed, but this constant may be set as the quotient of the aeration tank volume and the flow rate of inflowing sewage and returned sludge. In that case, it becomes a multi-stage complete mixture model. Further, in this embodiment, a common pump is used for both the return and surplus sludge, but it can also be applied to a case where separate pumps 7'' are used to keep the flow rate of the return sludge pump constant and controlled by the surplus sludge pump.

〔Effect of the invention〕

As described above, the present invention includes an aeration tank that mixes and aerates inflowing sewage and activated sludge, sucks organics contained in the sewage into the activated sludge, and multiplies this activated sludge, and an aeration tank that mixes and aerates incoming sewage and activated sludge. A settling tank separates the mixed liquid of sewage and activated sludge into solid components and water by precipitation, and the sludge containing the activated sludge precipitated in this settling tank is returned to the aeration tank, and a portion of this sludge is removed from the system as surplus sludge. A device equipped with a sludge return and extraction mechanism that can scrape the sludge, and a suspended solids concentration detector that detects the suspended solids concentration in the mixed liquid in the aeration tank, and a suspended solids concentration detector that detects the suspended solids concentration in the mixed liquid in the aeration tank, and a suspended solids concentration detector that detects the suspended solids concentration in the mixed liquid in the aeration tank, A setting circuit that stores a pattern of flow rate change characteristics and daily change characteristics of the inflow sewage suspended solids load and outputs this pattern signal, and the inflow sewage amount of the aeration tank and the inflow sewage suspended solids load. The characteristics of changes in the concentration of suspended solids in the mixed liquid with respect to the amount of returned sludge are stored in advance, and signals from the suspended solids concentration detector and the i, 4-tap setting circuit are input, and based on these signals, In order to minimize the daily cumulative value of the deviation from the target value of the suspended solids concentration in the mixed liquid in the aeration tank, the amount of excess sludge to be extracted, the extraction start time, and the extraction stop time are calculated, and the calculation results are calculated. The apparatus is equipped with an arithmetic control circuit for controlling the sludge return/extraction mechanism based on the above.

Therefore, the amount of inflow sewage until the day before the extraction of excess sludge is
The MLSS concentration in the aeration tank can be stably and automatically controlled because it is controlled in accordance with the fluctuating pattern of the SS load in the sewage, and its effects are outstanding.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional sewage treatment device. Second
The figure is a schematic configuration diagram of an embodiment of the present invention. Amada Figure 3 is a line diagram showing the daily changes in the amount of inflow sewage, and Figure 4 is a line diagram showing the daily changes and set turns in the inflow SS square load. 10... Aeration tank, 103... Sedimentation tank, 106...
・Bonfu 0, lθ7...Return pipe, 108...Dropout pipe, 110...M'LSS detector, 113...ie
Turn setting circuit, 116... Arithmetic control circuit. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] an aeration tank that mixes and aerates inflowing sewage and activated sludge; a settling tank that separates the mixed liquid of sewage and activated sludge sent from the aeration tank into solid components and water; Detecting the concentration of suspended solids in the mixed liquid in the aeration tank, in a device equipped with a sludge return/extraction mechanism that returns sludge to the aeration tank and pulls a portion of this sludge out of the system as surplus sludge. Suspended solids concentration detector and the previous day 1
The daily flow rate change characteristics of the inflowing sewage and the daily change characteristics of the inflowing sewage suspended solids load. This pattern signal is output as a pattern signal.
The change characteristics of the suspended solids concentration in the mixed liquid with respect to the setting circuit, the amount of sewage flowing into the aeration tank, the suspended solids load of the inflowing sewage, and the amount of returned sludge are recorded in advance, and the above suspended solids are Signals from the solid matter temperature detector and flat turn setting circuit are input, and based on these signals, the daily integrated value of the deviation from the target value of the suspended solids concentration in the mixed liquid in the aeration tank is minimized. A sewage treatment device comprising: an arithmetic control circuit that calculates the amount of excess sludge to be drawn, a drawing start time, and a drawing stop time, and controls the sludge return and drawing mechanism based on the calculation results. .