JPH0256960B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a sewage treatment facility having a plurality of sewage treatment lines in which aeration tanks and sedimentation tanks are arranged in series. The present invention relates to an aeration tank flow rate distribution control method for controlling the distribution of treated water flowing into a sedimentation tank and sludge returned from a settling tank to an aeration tank.

(Prior art) Sewage treatment using the activated sludge method consists of activated sludge (hereinafter simply referred to as sludge), which is a collection of a wide variety of microorganisms mainly consisting of aerobic or facultative bacteria, and sewage (primary treated water). This is a type of biochemical sewage treatment method that removes sludge organic matter and other suspended substances from sewage by mixing and contacting sewage water (hereinafter referred to as treated water). Since this activated sludge method utilizes the living activities of living organisms, its treatment efficiency can be kept high and stable only if the sludge is maintained in a healthy state.

To maintain sludge in a healthy condition, BOD-SS
Load and BOD - volumetric load, etc. must be maintained appropriately.

In sewage treatment plants, the amount of returned sludge and surplus sludge is determined and the operation is controlled to prevent sludge failure, but sludge failure often occurs despite this. The reason for this is that even in sewage treatment plants that have multiple sewage treatment systems consisting of aeration tanks and settling tanks, the flow rate of sewage and return sludge is monitored all at once using a simulation model, for example. This is because the flow rate to each wastewater treatment train is not individually monitored.

In other words, the flow rate of sewage flowing into a sewage treatment plant varies greatly over time, and the flow rate of returned sludge must also change accordingly, but the distribution ratio to each sewage treatment line is determined by the total flow rate of sewage or sludge. There can be large variations in response to changes, which can result in longer or shorter sludge residence times in the aeration tank, resulting in sludge failure conditions.

As a method to eliminate this inconvenience, a sludge concentration meter is installed in the aeration tank of each sewage treatment line, and the flow rate adjustment valve provided at the inlet of each sewage treatment line is controlled so that the readings of these concentration meters are equal. That is what is being attempted.

(Problem to be solved by the invention) However, there are relatively large differences between these sludge concentration meters, and sludge does not adhere to the concentration meters equally, so the indicated value of each sludge concentration meter Even when the values were the same, there were considerable differences in the actual sludge concentrations.

On the other hand, for example, even if the sludge concentration in the aeration tank can be maintained constant, the distribution ratio of sewage and return sludge may deviate from the planned distribution ratio, and each sewage treatment There was a problem that the processing amount of the series varied greatly.

Furthermore, controlling individual flow rate adjustment valves in response to the detected value of the sludge concentration meter means that the flow rates of other sewage treatment systems will also change at the same time, and this mutual interference will result in loss of control. There were also problems.

This invention was made to solve the above problems, and even if a sludge concentration meter with machine differences and measurement errors is used, it is possible to target treated water and return sludge that flow into multiple sewage treatment lines. It is an object of the present invention to provide an aeration tank flow rate distribution control method that can distribute the sludge at a ratio (usually evenly) and keep the sludge in each aeration tank in a healthy state.

[Structure of the invention]

(Means for Solving the Problems) The present invention has an aeration tank and a settling tank arranged in series,
Each of these series is provided with a first flow rate control valve that adjusts the distribution amount of the water to be treated, and a second flow rate control valve that adjusts the distribution amount of the return sludge from the settling tank to the aeration tank, In the aeration tank flow rate distribution control method, the mixing state of the water to be treated and the sludge in the aeration tank is simulated, and the first and second flow rate control valves are controlled based on the result. The flow rate coefficient for each sewage treatment line with respect to the distribution ratio was set in the arithmetic processing device, and the total flow rate of the treated water flowing into the aeration tank, the total flow rate of the return sludge flowing into this aeration tank, and its concentration were measured. A signal and a signal obtained by sequentially sending a mixture of water to be treated and sludge in each of the aeration tanks to one concentration meter outside the aeration tank and measuring the sludge concentration for each aeration tank are taken into the arithmetic processing device. , the arithmetic processing device first stores these measurement data and simulates the mixing state of the water to be treated and sludge in the aeration tank for each of the sewage treatment lines based on the stored data,
The time series data of the sludge concentration corresponding to the actual measurement position of the sludge concentration in each aeration tank is calculated, and then this time series data and the actually measured sludge concentration data are compared for each of the sewage treatment series to determine the difference between both data. Find the flow rate coefficient of the treated water and return sludge flowing into the aeration tank of each sewage treatment system that has the smallest value, and then compare this flow rate coefficient with the flow rate coefficient based on the settings above to find the sewage water with the largest deviation. The method is characterized in that the first and second flow control valves of the processing series are adjusted.

(Function) In this invention, the mixed liquid of treated water and sludge in each aeration tank is sequentially sent to one concentration meter outside the aeration tank, and the sludge concentration is measured for each aeration tank.
Moreover, it is possible to correct errors by simulating the mixing state, so even if a sludge concentration meter with machine differences and measurement errors is used, the target ratio of treated water and returned sludge flowing into multiple sewage treatment lines can be adjusted. can be distributed.

In addition, time series data of calculated sludge concentration,
The flow rate coefficient of the treated water and return sludge flowing into the aeration tank of each sewage treatment line is searched for by comparing the actually measured sludge concentration data and the difference between both data is the smallest, and then this flow rate coefficient and Since the flow rate coefficients according to the above settings are compared and the flow rate control valve of the sewage treatment line with the largest deviation is adjusted, the problem of loss of control, which was a problem with the conventional method, is also solved, and the sludge in each aeration tank is can be kept in a healthy state.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a flow rate distribution control device for implementing the aeration tank flow rate distribution control method according to the present invention, together with a sewage treatment system. Here, the sewage treatment system mixes the water to be treated and the returned sludge.
It consists of three aeration tanks 11, 12, and 13, and settling tanks 21, 22, and 23 that introduce the mixed liquid of these aeration tanks and sediment and separate the sludge. The aeration tank 12 and settling tank 22 form a second sewage treatment system, and the aeration tank 13 and settling tank 23 form a third sewage treatment system.

Further, flow rate control valves 41, 42, 43 are provided at the inlets of the aeration tanks 11, 12, 13, that is, the inlets of each sewage treatment system, for adjusting the distribution amount of the return sludge returned through the pipe 1. In addition,
A flow meter 3 is installed in the pipe line 1 to measure the total flow rate of the water to be treated.
However, the pipe line 2 is provided with a flow meter 4 for measuring the total flow rate of the returned sludge, and a sludge concentration meter 5 for measuring the concentration of the returned sludge.

In addition, in the aeration tanks 11, 12, and 13, there are
Pumps 51, 52, and 53 for pumping up the mixed liquid are provided, respectively. These pumps 51,5
2, 53 _are control signals Y a of the arithmetic processing unit 100,
It is sequentially driven by Y _b and Y _c and supplies the mixed liquid to one sludge concentration meter 6 installed outside the aeration tank.
Then, the sludge concentration signal X _a from the sludge concentration meter 6 is taken into the arithmetic processing device 100 .

Furthermore, the flow rate signals Q _S and Q _R measured by the flow meters 3 and 4 and the sludge concentration meter signal X _C measured by the sludge concentration meter 5 are also taken into the arithmetic processing device 100 .

On the other hand, the output signals P _S and P _R of the arithmetic processing unit 100
are added to the flow rate control valve control devices 110 and 120, of which the flow rate control valve control device 110 controls the opening degrees of the flow rate control valves 31, 32, and 33, and the flow rate control valve control device 120 controls the opening degrees of the flow rate control valves 41, 33, and 42,
The opening degree of 43 is controlled.

Here, the water to be treated sent through the pipe 1 is distributed to the aeration tanks 11, 12, 13 according to the opening degrees of the flow rate control valves 31, 32, 33, and at the same time is drawn out from the settling tanks 21, 22, 23. A part of the sludge returned through the pipe line 2 is distributed to the aeration tanks 11, 12, 13 according to the opening degree of the flow rate control valves 41, 42, 43, and both are mixed in the aeration tank. mixed. Next, this mixed liquid flows into the settling tanks 21, 22, and 23 of each sewage treatment system, and is separated into sludge and supernatant water.The sludge is pulled out from the lower part of the settling tank, and the supernatant water is discharged.

On the other hand, the arithmetic processing device 100 at least sends the water to be treated and the returned sludge to the aeration tanks 11, 12, 13.
A function to set a flow rate coefficient corresponding to the distribution ratio to be distributed to, a total flow rate signal Q _S of treated water, a total flow rate signal Q _R of returned sludge and its concentration signal X _C , and
The sludge concentration signal of the aeration tank is stored, and the mixed state of the water to be treated and the sludge in the aeration tank is simulated based on the stored data, and the pumps 51, 52,
The function calculates time series data of sludge concentration corresponding to the location where 53 is installed, and compares this time series data with the sludge concentration data actually measured by sludge concentration meter 6 to determine the aeration of each sewage treatment line. A function to search the distribution ratio of treated water flowing into the tank and return sludge, and a signal P _S , P _R that compares this distribution ratio and flow coefficient and controls the flow rate control valve of the sewage treatment line with the largest deviation. and a function to output.

The reason why the pumps 51, 52, and 53 are installed at approximately 1/3 of the length of the aeration tank when viewed from the downstream direction of the water to be treated is that if they are located near the inlet of the water to be treated, the mixing state will be unstable. This means measuring a sufficient sludge concentration of the mixed liquid; on the other hand, if it is brought further back than this, the response will be delayed.

Hereinafter, the operation of the arithmetic processing device 100 will be explained in more detail.

First, the processing unit 100 receives the flow rate signal Q _S of the flow meter 3 , the flow rate signal Q _R of the flow meter 4 , the sludge concentration X _C of the sludge concentration meter 5 , and the sludge concentration signal of the sludge concentration meter 6 .
Read X _a at regular time intervals and store the data for one control cycle as time series data.

Next, the aeration tank simulator uses this time series data as input and combines it with a flow coefficient search program, for example, to find the flow coefficients of the treated water flowing into each aeration tank and the returned sludge.

The flow coefficient referred to here is the ratio of the total flow rate of treated water Q _S to the flow rate of treated water flowing into each aeration tank, and the total flow rate of returned sludge Q _R as shown in Figure 2. and the return sludge flow rate flowing into each aeration tank.The flow coefficients of the water to be treated flowing into the aeration tanks 11, 12, and 13 are A _S1 , A _S2 , A _S3 , and the flow coefficient of return sludge is A When _R1 , A _R2 , and A _R3 , the following relationship holds true.

A _S1 +A _S2 +A _S3 =1...(1) A _R1 +A _R2 +A _R3 =1...(2) Therefore, the flow rate of the treated water flowing into the aeration tanks 11, 12, and 13, respectively, is A _S1・Q _S , A _S2・Q _S ,
A _S3・Q _S , and the flow rate of the returned sludge is A _R1・Q _R ,
A _R2・Q _R and A _R3・Q _R.

Here, the arithmetic processing unit 100 calculates the flow coefficient A _S1 ,
The procedure for finding A _S2 , A _S3 , A _R1 , A _R2 , and A _R3 is as follows: First, assuming that these flow coefficients are all equal, use time series data in the arithmetic processing unit.
A simulation is performed for each sewage treatment series, and the difference between the sludge concentration at the position corresponding to the actual measurement point calculated by the simulator and the time series data of the actually measured sludge concentration is calculated. Next, the step size of the flow coefficient is set to 1/10, and a maximum gradient hill climbing search method is used to find the flow coefficient that minimizes the difference between the simulation value and the actual measurement value.
Furthermore, the same search is repeated with the step width set to 1/10 until the required number of digits is obtained.

The processing unit 100 calculates the flow rate coefficients of the water to be treated and the returned sludge in this manner, but the processing unit 100 also determines the ratio at which the water to be treated and the returned sludge are to be distributed to each sewage treatment line. A flow rate coefficient is set, and then this processing unit 100 calculates the flow rate coefficient obtained by calculation and the set flow rate coefficient for each of the water to be treated and the returned sludge for each sewage treatment line. The comparison is made, the sewage treatment system with the largest deviation is selected, and a signal P _S , which controls the flow rate control valve of this sewage treatment system is selected.
P _R is applied to flow control valve controllers 110 and 120, respectively.

As a result, only the flow rate control valve of the sewage treatment system with the largest deviation from the set value is controlled and its flow rate changes, and the flow rates of the other sewage treatment systems also change accordingly. Such operations are repeated every control cycle.

In this case, since the arithmetic processing unit 100 performs simulation using time-series data to search for the flow rate coefficient, the control period needs to be longer than the time required to collect enough time-series data to perform the simulation. In this embodiment, the original purpose can be fully achieved by setting the data sampling period to 10 minutes and the control period to several hours.

On the other hand, as mentioned above, sludge concentration meters have low reliability due to machine differences and measurement errors. Conventionally, flow control valves were controlled so that the indicated values of sludge concentration meters were equal, so machine differences and measurement errors had a direct effect. However, in this embodiment, the mixed liquid is switched and fed to one sludge concentration meter to measure the sludge concentration in the aeration tank of each sewage treatment system, so the adverse effects due to differences in machines can be eliminated. Furthermore, in this embodiment, since the mixing state is simulated by the arithmetic processing unit, measurement errors of the sludge concentration meter can be easily corrected. The specific method will be briefly explained below.

The actual measured value of sludge concentration in the three aeration tanks is x ₁
(t), X ₂ (t), X ₃ (t), and the simulated values are Y ₁ (t), Y ₂ (t), Y ₃ (t). The average value of the measured values and the average value of the calculated values of sludge concentration for all series are:
It should be constant whether the distribution of each series is constant or not.

If and are equal here, then
This means that there is an error in the sludge concentration meter. For example, if the slope of a correction curve that correlates multiple pieces of data is A and the intercept is B, then this error is =
It can be corrected as A/+B.
With this, even if there is an error in the sludge concentration meter, it can be corrected.

Furthermore, conventionally, the flow distribution to each sewage treatment line has mostly been done by adjusting the opening degree of the gate. In this case, even if the gate opening degree is the same, it is structurally unavoidable that the amount of inflow into the aeration tank at the end will increase.
Naturally, in lines where a large amount of sewage flows into the system, the time that the sewage remains in the aeration tank becomes shorter and the quality of the treated water deteriorates. In this example, the flow rate is controlled based on the flow rate coefficient of each sewage treatment line, so except for special cases where the flow rate of a certain sewage treatment line is intentionally increased to find out the limits of treatment, general This makes it easier to equalize the flow rates required.

In addition, in the above embodiment, a sludge concentration meter is used to detect the concentration of sludge, but it is also possible to use an electrical conductivity meter instead.

In addition, in the above embodiment, the pump was installed at a position approximately 1/3 of the length of the aeration tank when viewed from the downstream direction of the water to be treated.
As long as it is an area where the water to be treated and sludge are sufficiently mixed, it may be placed before or after this, and if it is moved to the rear, the response will be delayed, but it is not limited to this position.

Furthermore, although the above embodiment shows an example in which treated water and sludge are distributed equally to each sewage treatment line, it goes without saying that the present invention can also be applied to cases where the water and sludge are distributed at different ratios.

〔Effect of the invention〕

As is clear from the above explanation, according to the aeration tank flow rate control method of the present invention, even if a sludge concentration meter with machine differences and measurement errors is used, the amount of water to be treated flowing into multiple sewage treatment lines and The return sludge can be distributed in a targeted ratio, and the sludge in each aeration tank can be kept in a healthy condition, which has the excellent effect of providing good treated water in each sewage treatment line. be.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of an apparatus for implementing the aeration tank flow rate distribution control method of the present invention, together with a sewage treatment system, and Fig. 2 is a block diagram showing an example of an apparatus for implementing the aeration tank flow rate distribution control method of the present invention, together with a sewage treatment system. It is an explanatory diagram showing the relationship between flow coefficients of treated water and returned sludge. 1, 2... Pipe line, 3, 4... Flow meter, 5, 6... Sludge concentration meter, 11, 12, 13... Aeration tank, 21, 2
2, 23... Sedimentation basin, 31, 32, 33, 41, 4
2, 43...Flow rate control valve, 51,52,53...Pump, 100...Arithmetic processing unit, 110,120...Flow rate control valve control device.

Claims (1)

[Claims] 1. The aeration tank and the settling tank are arranged in series, and the first one adjusts the amount of water to be treated to be distributed to each of these series.
and a second flow rate regulating valve for regulating the distribution amount of return sludge from the settling tank to the aeration tank, and simulating the mixing state of the water to be treated and the sludge in the aeration tank. , in the aeration tank flow rate distribution control method of controlling the first and second flow rate control valves based on the results, the flow rate coefficient for each sewage treatment line with respect to the distribution ratio of the water to be treated and the return sludge is determined by an arithmetic processing device. The total flow rate of the water to be treated flowing into the aeration tank, the total flow rate and concentration of return sludge flowing into the aeration tank, and the signal obtained by measuring the concentration of the water to be treated and the sludge in each of the aeration tanks. A signal obtained by sequentially sending the mixed liquid to one concentration meter outside the aeration tank and measuring the sludge concentration for each aeration tank is taken into the arithmetic processing unit, and the arithmetic processing unit first stores these measurement data and , by simulating the mixing state of the water to be treated and sludge in the aeration tank for each of the sewage treatment lines based on the stored data,
The time series data of the sludge concentration corresponding to the actual measurement position of the sludge concentration in each aeration tank is calculated, and then this time series data and the actually measured sludge concentration data are compared for each of the sewage treatment series to determine the difference between both data. Find the flow rate coefficient of the treated water and return sludge flowing into the aeration tank of each sewage treatment system that has the smallest value, and then compare this flow rate coefficient with the flow rate coefficient based on the settings above to find the sewage water with the largest deviation. An aeration tank flow rate distribution control method, comprising adjusting the first and second flow rate control valves of a treatment series.