JP2001300575A - Sludge outflow preventive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent the outflow of sludge from a settling tank with a small amount of a settling agent to be added by exactly controlling a chemical feed in accordance with the result of detection of the sludge boundary height in the settling tank. SOLUTION: This sludge outflow preventive device consists of a chemical storage tank 4 which stores the settling accelerator for sludge, a chemical-feed pump P1 which is connected to the chemical storage tank 4 and supplies the chemicals in the tank to a chemical adding place, a boundary detecting means 3 which detects the sludge boundary height in the settling tank 2 and a control means 5 controls the operation of the chemical-feed pump P1 by judging the operating time of the chemical-feed pump P1 in accordance with the result of the detection and the amount of the settling accelerator to be added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the outflow (carryover) of sludge from a sludge settling tank for the purpose of solid-liquid separation.
In particular, based on the detection result of the interface detecting means for detecting the height of the sludge interface, by appropriately controlling the amount, time and time of addition of the sedimentation accelerator for sludge, The present invention relates to a sludge outflow prevention device that performs stable and efficient treatment with an added amount of a chemical to reliably prevent sludge from flowing out and to always obtain clear treated water.

[0002]

2. Description of the Related Art In a sludge settling tank for solid-liquid separation,
In order to prevent the outflow of sludge, addition of a sedimentation promoting agent for sludge (hereinafter sometimes referred to as “sedimentation agent”) is performed. Conventionally, as a method of adding the settling agent, a constant amount is always added. An exclusive manager always sets the SV (Sludge V)
olume: Volume ratio of settled sludge when allowed to stand for a predetermined time)
The injection time and the time are determined as necessary, and the injection pump is manually controlled to add. The water quality (BOD, SS concentration, turbidity, etc.) and water volume of the raw water and treated water are measured, and based on the results, the amount and timing of chemical injection are controlled and added. Although such a method has been adopted, the method cannot cope with fluctuations in the quality of the raw water or the amount of water, and the outflow of sludge cannot be reliably prevented.
In addition, in the method (1), it is necessary for the administrator to constantly monitor sludge properties and the like, which requires a great deal of labor and time. Also,
It is very difficult to determine the appropriate amount of injection and the timing of injection from the quality of raw water and treated water by the method described above, and the time of injection is delayed due to time delay due to feedback control from the measurement results. There is also.

[0003] Therefore, in any of the above methods (1) to (4), an excessive amount of the settling agent is set in order to prevent the sludge from flowing out. It was a fact that sludge spill accidents occurred even if they did.

On the other hand, JP-A-3-56105 discloses that
A method is described in which the height of the sludge interface in the settling tank is detected, and the amount of the settling agent added is controlled based on the result. According to this method, the addition amount of the sedimentation agent can be controlled according to the sedimentation state of the sludge in the sedimentation tank, so that more accurate chemical injection control can be performed as compared with the above methods (1) to (4).

[0005]

However, since the sludge interface in the sedimentation tank undulates (hunts) due to the inflow of raw water or the extraction of sludge, it is difficult to use a simple method as described in JP-A-3-56105. In the method of controlling the chemical injection based on the detection information of the sludge interface height, there is a disadvantage that the amount of chemical injection is excessive or insufficient, and the outflow of the sludge cannot be reliably prevented.

The present invention solves the above-mentioned conventional problems, and performs accurate chemical injection control based on the detection result of the sludge interface height in the sedimentation tank to reduce the amount of sludge from the sedimentation tank with a small amount of sedimentation agent added. An object of the present invention is to provide a sludge outflow prevention device that reliably prevents outflow.

[0007]

SUMMARY OF THE INVENTION A sludge outflow prevention device according to the present invention is a device for preventing the outflow of sludge from a sedimentation tank by adding a chemical. A chemical injection pump connected to the storage tank, for supplying a chemical solution in the tank to the chemical addition location, an interface detecting means for detecting the sludge interface height in the sedimentation tank, and a detection result detected by the interface detecting means. And control means for controlling the operation of the chemical injection pump by judging the operation time of the chemical injection pump and the amount of the sedimentation promoter to be added.

In the present invention, based on the detection result of the sludge interface height in the sedimentation tank, not only the amount of the settling agent added but also the operation time of the chemical injection pump is controlled, so that accurate chemical injection control can be performed.

In the present invention, the control means of the chemical pump comprises a start delay timer for setting a time from when the interface height detected by the interface detecting means reaches the chemical addition level to when chemical injection is started, It is preferable to provide a stop delay timer for setting a time from when the height becomes equal to or lower than the chemical addition level to when the chemical injection is stopped. By delaying the start and stop of the chemical injection in this way, the sludge interface Deficiency of the chemical injection caused by the detection error due to the hunting can be solved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a sludge outflow prevention device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a sludge outflow prevention device according to the present invention.

In this embodiment, a sludge outflow prevention device of the present invention is applied to a water treatment device using activated sludge. In this water treatment device, raw water is introduced into an activated sludge tank 1 and aerated. Thereby, the organic matter in the raw water is decomposed by the activated sludge, and the activated sludge treated water is sent to the settling tank 2. Separating the sludge settling tank 2 is periodically withdrawn by the sludge pump P _2, part of which is returned to the activated sludge tank 1 as return sludge, and the remainder is discharged from the system as excess sludge is dewatered.

In this water treatment apparatus, a chemical injection pump P ₁ for adding a settling agent to an inflow pipe from the activated sludge tank 1 to the settling tank 2.
And a chemical storage tank 4 are provided. On the other hand, the sedimentation tank 2 is provided with an interface meter 3 for detecting the height of the sludge interface in the tank, and the detected value of the interface meter 3 is input to the control device 5,
Operation of the result in the basis with chemical feed pump P ₁ in the control unit 5 is controlled.

[0014] operation control of the chemical feed pump P ₁ is specifically preferably carried out in the following manner.

First, the sludge interface height at which chemical injection is to be started is set. At this time, the sludge interface height and the chemical injection amount corresponding to the sludge interface height are provided at two or more points. The sludge interface height at which this chemical injection should be started depends on the height of the sedimentation tank,
Generally, it is preferable to set the range from 0 to 3 m below the water surface. For example, when the first sludge interface height L ₁ m below the water surface is detected, the chemical injection amount is set to R ₁ mg / L.
When the second sludge interface height L ₂ m below the water surface is detected, the chemical injection amount is set to R ₂ mg / L.
Set multiple doses. However, L ₁ > L ₂ , R ₁ <
Is R _2, chemical feeding, chemical dosing amount corresponding to the detected value of each of the sludge interface height may be set to predetermined through desk experiment.
The injection amount may be set to three or more stages, and as the number of stages is increased, the accuracy of the injection control is improved.

The control of the chemical injection amount may be such that the discharge amount of the pump is changed by frequency control by the chemical injection inverter. A plurality of pumps are provided, and the number of pumps to be operated according to the chemical injection amount is provided. May be changed.

The detected value of the interface meter is a moving average of 100 times or more in the past, preferably 50 to 300 times, for example, 200 times (measurement frequency is once per second). This is preferable in that good control can be performed by preventing a detection error.

When the moving average is taken in this way, the detected value of the interface meter may be output lower than the actual sludge interface height, so that the sludge interface height at which chemical injection should be started is higher than the target value. It is also preferable to set a lower value.

Further, in the present invention, the minimum operation time of the pump corresponding to each sludge interface height is provided by using the setting of the sludge interface height. For example, the operation time of the pump is set in multiple stages so that the minimum operation time when the first sludge interface height is detected is T1 minutes and the minimum operation time when the second sludge interface height is detected is T2 minutes. I do. The control device controls the pump so that the operation time of the pump becomes (X + T1) when the detected time of the sludge interface height continuously detects the first sludge interface height is X minutes.

With this pump control, even if the sludge interface height detection result temporarily drops below the actual sludge interface height due to waving, the shortage of chemical injection can be resolved.

In the present invention, as a means for controlling the operation time of the pump, a chemical injection start delay timer and a chemical injection stop delay timer are provided, and the sludge interface height at which chemical injection is to be started is detected. The time until the start of the injection at the injection amount corresponding to the sludge interface height and the time until the injection is stopped when the sludge interface height decreases and the injection becomes unnecessary are now delayed. It is preferable to reduce the effect of hunting on the sludge interface height.

With this configuration, in addition to the above-mentioned effects, even if the sludge interface height detection result temporarily rises above the actual interface due to waving, chemical injection excessive injection can be eliminated.

That is, for example, when the first sludge interface L ₁ m below the water surface of the settling tank is detected (hereinafter, referred to as “first detection signal”), the chemical injection is performed at the chemical injection amount R ₁ mg / L. Start,
When the second sludge interface L ₁ m below the surface of the settling tank is detected (hereinafter referred to as “second detection signal”), the chemical injection amount R ₂
In the case of starting drug injection at mg / L, a delay time is provided as follows.

Time t _{1 -ON} from start of output of first detection signal
After _R 1 mg / L in dosing started first detection signal output time from the stop _{t 1-off R} 2 mg from chemical feeding, chemical dosing stop the second detection signal output start after a time _{t 2-ON} after
/ L Stops the injection after a time t2 _-off from the stop of the output of the second detection signal. When the second detection signal is output during the output of the first detection signal, the time t starts after the output of the second detection signal. _2- Change the injection amount from R ₁ mg / L to R ₂ mg / L after _ON . If the first detection signal is output after the second detection signal is stopped, stop the output of the second detection signal. Time t
_{After 2-off} , the injection amount is changed from R ₂ mg / L to R ₁ mg / L.
The delay time can be appropriately set according to the sludge properties of the water treatment system and other operating conditions. For example, the start delay times t _1-ON and t _2-ON are 3 to 3
After the detection signal is continuously output for about 0 seconds, that is, for 3 to 30 seconds, it is preferable to start the injection or change the injection amount. Further, the stop delay time t _{1 -off} , t
_2-off is about 1 to 10 minutes, that is, it is preferable to stop the injection or change the injection amount after the injection is continued for 1 to 10 minutes after the detection signal is stopped.

In the present invention, the sedimentation agent added to prevent the sludge from flowing out includes sulfuric acid bands (aluminum sulfate), PAC (polyaluminum chloride), aluminum oxide, iron chloride, iron sulfate, polyiron, slaked lime and the like. An inorganic coagulant or an organic polymer coagulant such as polyacrylamide, a partial hydrolyzate thereof, and polyacrylic partial cationization can be used. Among them, cationic dimethylaminoester acrylic acid-based and dimethylaminoester methacrylic acid-based polymer flocculants are most suitable because they have an immediate effect on accelerating the settling of sludge.

There is no particular limitation on the place where the sedimentation agent is added. As shown in FIG. 1, the sedimentation agent may be directly added to the sedimentation tank in addition to the addition of the sedimentation agent to the inflow pipe to the sedimentation tank.
Further, a mixing tank for the sedimentation agent may be provided before the sedimentation agent, and the sedimentation agent may be added to the mixing tank.

The measuring method of the interface meter for detecting the height of the sludge interface in the sedimentation tank is not limited, but the optical type and the ultrasonic type have good sensitivity to activated sludge, and are excellent in performance and cost.

Such a sludge outflow prevention device of the present invention has the following features.
As long as the treatment system adopts measures to prevent sludge from flowing out by adding a sedimentation agent, the treatment system is not limited to the activated sludge water treatment apparatus shown in FIG. 1 and can be employed in various treatment systems.

[0029]

The present invention will be described more specifically below with reference to examples and comparative examples.

In the following examples and comparative examples, the system to which the chemical dispensing control of the sedimentation agent is applied is used as the sedimentation agent in the water treatment apparatus shown in FIG. 1 as a cationic dimethylaminoester acrylic acid-based sedimentation agent. Is a system that performs treatment under the following conditions.In this system, in the chemical injection control of the sedimentation agent by the monitoring of the site manager,
The monthly chemical consumption was 2,000 kg (average over the past three years), and even when such a large amount of sedimentation agent was added, sludge runoff occurred occasionally at night. [Treatment conditions] Drainage load (MLSS): 5000 mg / L Influent water amount: 50 m ³ / hour (1200 m ³ / day) BOD load of activated sludge tank: 125 kg / hour (3 t / day) Sludge amount drawn from sedimentation tank: 12 m ³ × 12 hours In addition, the activated sludge treated water SV30 of this treatment system
(Volume ratio of settled sludge after standing for 30 minutes) is 99%
The amount of the sedimentation agent required to bring the SV30 to 60% is 70 mg / L, and the amount of the sedimentation agent required to bring the SV30 to 70% is 50 mg / L.
The required injection amount of the above settling agent for making 0 0 80% is 3
It was 5 mg / L.

In each of the following Examples and Comparative Examples, a control experiment was performed for one month in each case, and during this period, the amount of settling agent used, the presence or absence of outflow of sludge, and the appearance of sludge interface height were observed.

Example 1 The level of chemical addition at the sludge interface height was set at two points, and when the sludge interface height reached 1.0 m below the water surface of the settling tank,
The first upper limit alarm is output, and when the sludge interface height reaches 0.5 m below the water surface, the second upper limit alarm is output, and the discharge amount of the chemical injection pump is set at the time of the first upper limit alarm. Quantity is 3
Inverter control was performed so that 5 mg / L (ON-1) and the set medicine injection amount at the time of outputting the second upper limit alarm were 70 mg / L (ON-2).

The chemical pump operates when both the first and second upper limit alarms are output for 20 seconds.
N) Then, the output of the upper limit alarm was set to operate for 10 minutes after the stop and then stopped, that is, the start delay timer was set to 20 seconds and the stop delay timer was set to 10 minutes.

Therefore, the ON / OFF control of the pump in response to the first and second upper limit alarms is as shown in FIG.
When the upper limit alarm is output for 20 seconds, the drug injection pump is operated to start the drug injection at a dose of 35 mg / L.
After the upper limit alarm is stopped, the pump is stopped by continuing the injection for another 10 minutes.

The same applies to the second upper limit alarm, except that 10 minutes after the output of the second upper limit alarm is stopped,
If the first upper limit alarm has been output, the pump continues to operate at the drug injection amount of 35 mg / L, and after the first upper limit alarm has stopped, the pump continues to be injected for another 10 minutes to stop the pump.

Table 1 shows the amount of used chemicals, the height of sludge interface, and the presence or absence of sludge outflow when such chemical injection control was performed for one month.

Comparative Example 1 In Example 1, only one chemical addition level for the sludge interface height was set, and an upper limit alarm was output only when the sludge interface height reached 1.0 m below the water surface of the settling tank. Along with
At this time, the set dosing amount is set to 70 mg / L, and as shown in FIG. 3, when the upper limit alarm is output for 20 seconds, the pump is operated to perform the dosing at the dosing amount of 70 mg / L. Is stopped for another 10 minutes after the stoppage, and the drug injection control is performed in the same manner except that the pump is stopped so that the pump is stopped. Table 1 shows the amount used, the height of the sludge interface, and the presence or absence of sludge outflow.

Comparative Example 2 In Example 1, when the sludge interface height reached 1.0 m below the water surface of the settling tank, an upper limit alarm was output, and the sludge interface height reached 1.5 m below the water surface. When the lower limit alarm is output, the set medicine injection amount at the time of the upper limit alarm output is 70 mg /
As shown in FIG. 4, when the upper limit alarm is output for 20 seconds, the pump is operated to perform the injection at a dose of 70 mg / L, and then when the lower limit alarm is output for 20 seconds, the pump is operated. The chemical injection control was performed in the same manner except that the chemical injection was stopped. Table 1 shows the amount of chemicals used, the sludge interface height, and the presence or absence of sludge run-out when the chemical injection control was performed for one month.

For comparison, Table 1 also shows the current state of drug injection control by the site manager.

[0040]

[Table 1]

Table 1 shows that the present invention can reliably prevent sludge from flowing out with a small amount of chemicals used.

[0042]

As described in detail above, according to the sludge outflow prevention device of the present invention, accurate chemical injection control is performed based on the detection result of the sludge interface height in the sedimentation tank, and a small amount of sedimentation agent is added. Can reliably prevent sludge from flowing out of the sedimentation tank,
Along with reducing the chemical cost, stable and efficient treatment can be performed in the sedimentation tank to obtain clear treated water.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a sludge outflow prevention device of the present invention.

FIG. 2 is a time chart showing a method of controlling the operation of the chemical injection pump in the first embodiment.

FIG. 3 is a time chart showing an operation control method of a chemical injection pump in Comparative Example 1.

FIG. 4 is a time chart showing an operation control method of a chemical injection pump in Comparative Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Activated sludge tank 2 Sedimentation tank 3 Interface meter 4 Chemical storage tank 5 Control device

Claims (2)

[Claims] An apparatus for preventing sludge from flowing out of a sedimentation tank by adding a chemical, comprising: a chemical storage tank for storing a sludge settling accelerator; a chemical storage tank connected to the chemical storage tank; A pump for supplying the liquid, an interface detecting means for detecting the height of the sludge interface in the sedimentation tank, and an operation time of the chemical pump and the promotion of the sedimentation based on the detection result detected by the interface detecting means. A sludge outflow prevention device comprising: control means for judging an amount of an agent to control the operation of the chemical injection pump. 2. The start delay timer according to claim 1, wherein the control means sets a time from when the interface height detected by the interface detection means reaches a chemical addition level to when chemical injection is started, A sludge outflow prevention device comprising a stop delay timer for setting a time from when the interface height becomes equal to or lower than the chemical addition level to when chemical injection is stopped.