JP3178908B2 - Return sludge control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a return sludge control device for a water treatment plant having an aeration tank and a final sedimentation basin, and more particularly to a return sludge control device capable of preventing sludge from flowing out of the final sedimentation basin.

[0002]

2. Description of the Related Art Conventionally, a water treatment plant having an aeration tank and a final sedimentation basin and treating water by an activated sludge method is known.

In the activated sludge method, purified microorganisms are continuously cultured in an aeration tank using organic substances contained in sewage as a culture medium in the presence of dissolved oxygen, and the microorganisms and the contaminating organic substances are mixed to oxidatively decompose the contaminating organic substances. -It is a method to remove by each action of aggregation, adsorption and precipitation. Activated sludge, which is microorganisms grown in the aeration tank, is separated into sludge and supernatant water in the final sedimentation basin. Part of the sludge settled in the final sedimentation basin is returned to the aeration tank as return sludge for seeding to promote the growth of microorganisms. The remaining sludge is used to extract excess microorganisms,
It is discharged outside the system as excess sludge.

When performing the activated sludge method, it is necessary to maintain an appropriate amount of microorganisms in an aeration tank in order to maintain the activity of microorganisms.
It is also necessary to prevent sludge from flowing out from the final sedimentation basin to the effluent.

Heretofore, in a water treatment plant using the activated sludge method, many control methods have been proposed as a return sludge control method for controlling the return sludge sent from the final settling basin to the aeration tank. For example, MLSS constant control to keep the amount of microorganisms in the aeration tank constant, F / M ratio constant control to keep the ratio of the inflow load into the aeration tank to the amount of microorganisms constant, and the operator sets the target return rate A return rate constant control has been proposed which obtains a return sludge target value by multiplying the input return rate and the raw water flow rate.

[0006]

The constant return rate control of the above-mentioned return sludge control method is to return the amount of returned sludge according to the inflow flow rate to the aeration tank, and to appropriately set the return rate. This prevents the accumulation of sludge in the final sedimentation basin and prevents the sludge from flowing into the effluent. However, it is difficult to return the product according to the amount of microorganisms, the concentration of inflowing organic matter, and the properties of sludge.

For this reason, constant MLSS control and constant F / M ratio control have been proposed. In any case, the operation of the amount of returned sludge is performed by circulating the sludge in the system. Since the MLSS concentration is governed by the operation of the amount of excess sludge, it is difficult to realize the MLSS constant control of circulating the sludge in the system and controlling the amount of returned sludge. In addition, in the F / M ratio constant control, the amount of inflowing organic matter must be continuously and automatically measured. However, compared to the SS and MLSS meters for measuring solid matter concentration, a water quality meter for measuring organic matter concentration has a structure. Vulnerable to dirt due to complexity. Therefore, it is actually difficult to perform the F / M ratio constant control for a long period of time.

On the other hand, when the return rate constant control is performed, there is a distance between the point where the inflow rate of the aeration tank is measured and the return sludge pump that returns the return sludge from the final sedimentation tank to the aeration tank. If the time during which the change in the flow rate is propagated from the aeration tank to the final sedimentation basin is not considered, there is a problem that the MLSS concentration decreases when the flow rate increases and increases when the flow rate decreases.

The present invention has been made in view of the above points, and it is possible to return the sludge to the effluent according to the amount of microorganisms and the properties of the sludge so as to prevent the sludge from flowing out into the effluent, and to control the long-term automatic control. It is an object of the present invention to provide a return sludge control device that enables operation.

[0010]

SUMMARY OF THE INVENTION The present invention provides an automatic measuring means for inputting a signal from a raw water flow meter and a signal from an MLSS meter installed in an aeration tank, and allows an operator to input various control parameters. Based on the MLSS concentration output from the automatic measurement means and the SVI value output from the input / output processing means, the sludge load flowing into the final sedimentation tank can be returned to the aeration tank as returned sludge. Return rate calculating means for obtaining a constant return rate by a predetermined theoretical formula for each constant control cycle, and a return sludge target value based on the return rate determined by the return rate calculation means and the raw water flow rate output from the automatic measuring means, A return sludge control device comprising: a return sludge operation unit that outputs the return sludge target value to the return sludge pump at a constant output cycle.

[0011]

The MLSS concentration and the SV are calculated by the return rate calculating means.
Based on the I value, a return rate at which the entire sludge load flowing into the final sedimentation basin can be returned to the aeration tank as return sludge is determined for each predetermined control cycle by a predetermined theoretical formula, and based on the return rate and the raw water flow rate. Then, a return sludge target value is obtained by the return sludge calculating means, and is output to the return sludge pump at a constant output cycle.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 to FIG. 4 are views showing an embodiment of a return sludge control device according to the present invention.

FIG. 1 shows a water treatment plant for performing treatment by the activated sludge method. This water treatment plant has an aeration tank 1 and a final sedimentation basin 2 arranged in series. Further, a raw water flow meter 4 is arranged in the raw water inflow path 3 to the aeration tank 1, and an MLSS concentration meter 5 is arranged at the outlet of the aeration tank 1. A return sludge line 6 for returning the settled sludge to the aeration tank 1 is connected to the bottom of the final settling tank 2,
The return sludge line 6 is provided with a return sludge pump 7 for returning the sludge and a return sludge amount meter 8 for measuring the amount of the return sludge. An excess sludge pipe 9 for discharging sludge to the outside of the system is connected to the final sedimentation basin 2, and an excess sludge pump 10 is disposed in the excess sludge pipe 9.

As shown in FIG. 1, the water treatment plant is provided with a return sludge control device 11 according to the present invention.

As shown in FIG. 1, the return sludge control device 11 controls the signal from the raw water flow meter 4 and the M installed in the aeration tank 1.
Automatic measuring means 12 to which the signal from the LSS meter is input
And a return rate based on signals from the input / output processing means 13 to which various control parameters can be input by an operator, the automatic measuring means 12 and the input / output processing means 13, and the return rate is determined based on the raw water flow rate. And an arithmetic processing unit 14 for obtaining a return sludge target value and outputting the target value to the return sludge pump 7.

Here, the input / output processing means 1 is operated by the operator.
An example of the control parameters input to No. 3 is shown in the table below.

Table Returned sludge amount control parameters No. Symbol Name Set value Unit 1 T Output cycle 60 min 2 N Control cycle 5 min 3 SVI Manual input SVI 804 Rsafe Safety factor 10% 5 D Return rate change range 5% 6 TR Return rate transition time 20 min 7 QSD Raw water flow rate fluctuation 5 m3 / min 8 TQ Return quantity transition time 15 min 9 MLSS meter is being checked 0 10 Maximum return sludge quantity 25 m3 / min 11 Minimum return sludge quantity 5 m3 / min 12 Statistical totaling period 10 min Further, as shown in FIG. 2, the arithmetic processing means 14 includes a return rate calculating means (first calculating means) 15 for obtaining a return rate by a predetermined theoretical formula at every constant control cycle, and Return sludge calculating means (second calculating means) 16 for obtaining a return sludge target value based on the return rate and raw water flow rate obtained by the rate calculating means 15, and round-up calculation for rounding up the return rate obtained by the return rate calculating means 15. Means (No. 3 calculation means) 17, return rate correction means (fourth calculation means) 18 for correcting the return rate obtained by the return rate calculation means 15 to gradually change, and return sludge target value obtained by the return sludge calculation means 16. And return sludge correcting means (fifth calculating means) 19 for correcting so that the temperature changes gradually.

Although not shown, treated water is regularly collected by an operator near the outlet of the aeration tank 1. Then, the MLSS concentration and SV30 are measured by the operator's hand, and SVI is obtained.

Next, the operation of the present embodiment having such a configuration will be described.

First, raw water sent from a first settling tank (not shown) flows into the aeration tank 1 and is treated in the aeration tank 1 by the activated sludge method. Thereafter, the treated water in the aeration tank 1 is sent to the final sedimentation basin 2, where it is separated into a supernatant and a settled sludge.

Of these, the supernatant liquid is discharged as discharge water. Part of the settled sludge is returned to the aeration tank 1 by the return sludge pump 7, and the rest is
Is discharged out of the system.

During this time, the returned sludge control device 11 performs the following arithmetic processing to control the returned sludge pump 7.

First, return rate calculating means (first calculating means)
At 15, the MLSS concentration is input from the automatic measuring means 12,
At the same time, the SVI value is input from the input / output processing means 13, and the return rate calculation means 15 calculates the return rate based on the MLSS concentration and the SVI value.

The principle for appropriately obtaining the return rate by the return rate calculating means 15 will be described with reference to equations (1) to (7).

The material balance of the sludge in the final sedimentation basin is shown by equation (1). (Qat + Qrs) × MLSS = Qat × SSef + (Qrs + Qws) × Crs (1) In equation (1), Qat: Raw water flow rate [m ³ / day] Qrs: Returned sludge amount [m ³ / day] Qws: Excess sludge amount [m ³ / day] MLSS ... MLSS concentration [mg / L] SSef ... Discharged water SS concentration [mg / L] Crs ... Returned sludge concentration [mg / L].

Here, since Qrs >> Qws, (1)
Equation (2) is obtained from the equation. (Qat + Qrs) × MLSS = Qat × SSef + Qrs × Crs (2) Load (product of microbial mass and flow rate) flowing into the final sedimentation basin
Can be prevented from flowing out from the final sedimentation basin if all of them can be returned to the aeration tank as return sludge except for the SS contained in the discharge water in a small amount. The return rate R at which such return is possible is obtained by equation (3) using equation (2).

[0027] In the equation (3), R is a return rate [%].

Also, since MLSS >> SSef,
Equation (4) is obtained from equation (3).

[0029] The treated water that has flowed into the final sedimentation basin is settled as sludge at the bottom over several tens of minutes, and the precipitated sludge is pulled out of the final sedimentation basin by the return sludge pump and sent to the aeration tank. Therefore, it is necessary to consider the time delay required for the precipitation between the MLSS concentration and the returned sludge concentration in the equation (4). The time required for precipitation depends on the properties of the sludge at that time. Therefore, it is necessary to incorporate an index indicating the property of the sludge into the equation (4). There is an SVI defined by the equation (5) as an index indicating the sludge property, and the SVI and the returned sludge concentration are related by the equation (6).

[0030] In the formula (5), SVI is a sludge capacity index [mL / g] SV30 is a sludge settling rate [%] Crsmax is a maximum returned sludge concentration [mg / L].

The formula (6) is substituted into the formula (4), and a return rate at which the load flowing into the final sedimentation tank can be completely returned to the aeration tank as returned sludge is obtained by a predetermined theoretical formula (7). .

[0032] Regarding the method of measuring the MLSS concentration and the SVI value in the expression (7), there are two methods, a method by automatic measurement and a method of inputting an operator's manual analysis value. Regarding the MLSS concentration, it is considered that the automatic measuring instrument has a relatively simple structure and is resistant to dirt. For this reason, the method of automatic measurement of the MLSS concentration is preferable. On the other hand, the SVI value is obtained from the SV30 value and the MLSS concentration as shown in (5). Automatic measurement of SV30 value makes it difficult to detect the sludge interface,
Further, the SVI value does not change in a short period of time, and is often in a certain range for 20 days or more. Therefore, as the SVI value, an operator's hand analysis value is input.

On the basis of the above principle, the return rate calculating means 15 uses the aeration tank MLSS concentration MLSSpv inputted from the automatic measuring means 12 at every constant control period N as described above.
And the SVI value SVI input from the input / output processing means 13
mv and a safety rate Rsafe for setting a return rate higher than the return rate theoretically obtained by the equation (7) in order to measure the safe operation of the plant, using the return rate R according to the equation (8).
Find 1

As the MLSS concentration automatic measurement value, a value obtained by averaging the values of the statistical aggregation period input to the input / output processing means 13 as a control parameter is used. If the MLSS densitometer indicates that the inspection is being performed, processing is performed using the value of the MLSS concentration before the inspection.

[0035] In the formula (8), R1: Return rate [%] SVImv: Manually input SVI (parameter) [mL / g] MLSSpv: MLSS concentration automatic measurement value [mg / L] (Average value during the statistics collection period, MLSS meter During inspection, the previous value is held.) Rsafe: Safety factor [%]. The control parameters such as the control cycle N, the proposed rate Rsafe, the statistics collection period, and the MLSS meter inspection are as shown in the above-mentioned table, and are input in advance in the input / output processing means 13, and thereafter, the return rate calculation means 15 is input.

Next, returned sludge calculating means (second calculating means) 1
In step 6, the return sludge target value Q is calculated in accordance with equation (9) using the return rate R1 obtained by the return operation means 15 and the raw water flow rate Qatpv input from the automatic measurement means 12 at every constant output period T.
Find rs2.

Qrs2 = R1 × Qatpv (9) In the equation (9), Qrs2 is a return sludge target value [m ³ / min] R1 is a return rate [%] Qatpv is a raw water flow rate automatic measurement value [m ³ / min]. is there.

The constant output period T is a control parameter determined by the performance of the return sludge pump 7 as shown in the above table.

Next, round-up operation means (third operation means) 1
In step 7, the return rate R1 obtained by the return rate calculating means 15 at every constant control cycle N is rounded up based on a predetermined return rate change width D, and the return rate R3 is newly obtained. R1 and R
When the value of 3 is different, using the returned sludge calculating means 16,
The return sludge target value Qrs2 is calculated again. In this case (9)
In the formula, substitute R3 instead of R1.

The change rate of the return rate D is a control parameter as shown in the above-mentioned table, and the return rate R3 is set to, for example, 25%, 30%, or 35% in order to facilitate later calculation processing.
Is a value that is well separated.

Next, return rate correcting means (fourth calculating means) 18
Then, the return rate calculating means 15 or the round-up calculating means 17
When the return rate R3 obtained in the step f1 changes from the previous value to the current value during the control cycle N, the previous value R3 (n
-1) so that it gradually changes from the current value R3 (n) to R3 (n).
Is corrected according to equation (10). In this case, the corrected return rate is R4.

[0042] In equation (10), R4 (t): Return rate after correction R3 (n-1): Previous value of return rate R3 (n): Current value of return rate TR: Return rate transition period t: Return rate transition period Medium output period TR... Return period transition period [min] FIG. 3 shows how the return ratio R4 corrected by the return ratio correction means 18 gradually changes.

In FIG. 3, (a) shows the return rate R before correction.
3 and (b) show the corrected return rate R4. During the return rate transition period TR, the return sludge calculating means 16 substitutes R4 instead of R1 into the equation (9), and recalculates the return sludge amount target value Qrs2.

Next, return sludge correction means (fifth calculation means) 1
9, the average value of the raw water flow rate during the statistical tabulation period is observed for each output cycle T described above, and when the average value of the raw water flow rate fluctuates by the predetermined raw water flow rate variation QSD or more, during the return quantity transition period TQ The return sludge target value Qrs2 obtained by the return sludge calculation means 16 is the value Qrs2 (PQ) before the fluctuation of the raw water flow rate.
The return sludge target value Qrs2 is corrected according to the equation (11) so as to gradually change from −1) to the value Qrs2 (PQ) after the change. Then, the corrected return sludge target value is set to Qrs5.

[0045] In the formula (11), Qrs5 (t): Return sludge target value after correction Qrs2 (PQ-1): Value before return sludge target value before raw water flow rate fluctuation Qrs2 (PQ): After return sludge target value raw water flow rate change TQ: Return amount transition period t: Output cycle during return amount transition period In equation (11), both the raw water flow rate fluctuation amount QSD and the return amount transition period TQ are input to the input / output processing means 13 by the operator. Control parameters to be performed.

Next, when the return rate R3 is constant and the raw water flow rate automatic measurement value Qatpv suddenly changes during PQ, the return sludge target value Qrs5 is changed to the return amount transition period TQ.
4 (a) and 4 (b) show a state of gradually changing during the period.

In FIG. 4, (a) shows the return rate R3,
(B) shows the raw water flow rate Qatpv, (c) shows the return sludge target value Qrs2 before correction, (d) shows the return sludge target value Qrs5 after correction, and (e) shows the return rate actual value.

As shown in FIG. 4E, the actual return rate Qat5 / Qatpv during the return amount transition period TQ is
This is different from the return rate R3 shown in FIG. Compensating for the delay in the change in flow rate can return the sludge amount commensurate with the load flowing into the final sedimentation tank as return sludge, rather than keeping the return rate constant, so the return sludge target value itself is gradually increased in this way. The change was prioritized over the fixed return rate.

The return sludge target value Qrs2 obtained in this manner or the return sludge target value Qrs5 during the return amount transition period TQ is output to the return sludge pump 7 to control the return sludge amount.

As described above, according to the present embodiment, it is possible to control the return sludge according to the amount of microorganisms and the properties of sludge by using the automatically measured value of the MLSS concentration and the manually analyzed value of the SVI. The outflow of sludge into water can be reliably prevented. In addition, only the MLSS concentration meter that has been used in many treatment plants and has a proven track record is used as the water quality automatic measurement instrument, and the SVI that does not change much over several days uses the hand-analyzed value, thereby deteriorating the performance of the water quality automatic measurement instrument. , It is possible to suppress a decrease in the accuracy of the automatic control due to this. In addition, the return rate can be set to a numerical value with a good separation so that the operator can easily manage the return rate. Furthermore, it is possible to prevent sudden fluctuations in the plant due to rapid fluctuations in the return rate, and to gradually adjust the return rate and the return sludge target value, taking into account the time required for the fluctuations in the raw water flow rate to propagate from the aeration tank to the final sedimentation basin. The sludge can be prevented from being pulled too early or left too early. In addition, such a returned sludge control device enables an automatic control operation of returned sludge for a long period of time.

[0051]

As described above, according to the present invention, M
By using the LSS concentration and the SVI value, return sludge control can be performed according to the amount of microorganisms in the aeration tank and the properties of sludge, and the outflow of sludge into the discharge water can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a water treatment plant provided with a return sludge control device according to the present invention.

FIG. 2 is a detailed view of a main part of the return sludge control device shown in FIG.

FIG. 3 is a diagram showing a state in which a return rate is gradually changed using a return rate correction unit.

FIG. 4 is a diagram showing a state in which a return sludge target value is gradually changed using return sludge correction means.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Aeration tank 2 Final sedimentation basin 4 Raw water flow meter 5 MLSS meter 7 Return sludge pump 11 Return sludge control device 12 Automatic measuring means 13 Input / output processing means 14 Calculation processing means 15 Return rate calculation means 16 Return sludge calculation means 17 Rounding calculation means 18 Return rate correction means 19 Return sludge correction means

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mayumi Kurata 1 Toshiba-cho, Fuchu-shi, Tokyo Toshiba Corporation Fuchu Plant (72) Inventor Ryosuke Miura 1 Toshiba-cho, Fuchu-shi Tokyo Prefecture Toshiba Fuchu Plant (72) Inventor Mitsuo Oku 1-1-1, Shibaura, Minato-ku, Tokyo Inside the head office of Toshiba Corporation (72) Inventor Hidekazu Takashima 4-29 Honcho, Higashi-ku, Osaka-shi, Osaka Toshiba Kansai branch office (56) References JP-A-60-75395 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 3/12 C02F 3/00

Claims (3)

(57) [Claims] An automatic measuring means for receiving a signal from a raw water flow meter and a signal from an MLSS meter installed in an aeration tank; an input / output processing means for allowing an operator to input various control parameters; Based on the MLSS concentration output from the measuring means and the SVI value output from the input / output processing means, a predetermined theoretical formula is used to determine a return rate at which all sludge load flowing into the final settling tank can be returned to the aeration tank as return sludge. The return sludge calculation means obtained at every constant control cycle, and the return sludge target value is obtained based on the return rate obtained by the return rate calculation means and the raw water flow rate output from the automatic measurement means, and the return sludge target value is fixed. A return sludge control device, comprising: return sludge operation means for outputting to the return sludge pump every output cycle. 2. The method according to claim 1, wherein the return rate calculated by a predetermined theoretical formula by the return rate calculation means varies from a previous value to a current value during a control cycle. 2. The returned sludge control device according to claim 1, further comprising a return rate correcting means for correcting the return rate so that the return rate gradually changes from the previous value to the current value during the transition period. 3. The return processing output from the input / output processing means when the raw water flow rate input to the automatic measurement means fluctuates by more than a predetermined fluctuation amount output from the input / output processing means during the output cycle. Further includes return sludge correction means for correcting the return sludge target value such that the return sludge target value obtained by the return sludge calculation means gradually changes from the value before the change in the raw water flow rate to the value after the change during the transition period. 2. The method according to claim 1, wherein
Return sludge control device as described.