JPS6226806B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a settling tank sludge extraction control device for a water purification plant, and in particular, to perform sludge recycling for the purpose of improving the chemical injection effect and reducing the amount of flocculant used.
The present invention relates to a sedimentation tank sludge extraction control device that allows a predetermined amount of sludge to stay in a settling tank at all times, and also reduces the amount of accumulated sludge as much as possible in order to keep solid matter settling efficiency higher.

As is well known in water treatment plants,
Raw water is purified through the following three steps:

(1) Raw water taken from the river and stored in the landing well is led to a mixing pond and a flocculant is injected.

(2) The raw water injected with the flocculant is introduced into the stirring pond, and the two are sufficiently stirred to react and grow flocs.

(3) The mixed water is led to a sedimentation tank, where the flocs (solid matter) are precipitated into sludge, and the treated water is led to a sedimentation tank. Sedimented sludge will be appropriately pulled out and disposed of.

In the above-mentioned process, when the turbidity of the raw water introduced into the mixing pond is low, the effect of the coagulant is small, resulting in a disadvantage that the burden on the mixing pond becomes large. As a countermeasure to this problem, a method conventionally used in some cases is to mix an appropriate amount of mud into the raw water when the turbidity of the raw water is low. However, we cannot expect much effect from this.

To solve this problem, the applicant has previously proposed a floc (sludge) recycling method. According to this float recycling method, even when the raw water turbidity was low, the turbidity of the inflow water to the pond could be kept at a constant low value. It was also effective against wide-ranging changes in raw water turbidity, making it possible to reduce the amount of flocculant used.

On the other hand, conventionally, all the sludge has been extracted from the settling tank, but in order to reliably recycle the sludge, it is necessary to keep a certain amount or more of sludge in the settling tank at all times. On the other hand, in order to maintain the sedimentation efficiency in the sedimentation tank at a predetermined value or higher, it is necessary to suppress the amount of sludge deposited in the sedimentation tank below the predetermined amount.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to ensure sludge recycling and to prevent accumulated sludge from exceeding preset upper and lower limit accumulation amounts. Therefore, it is an object of the present invention to provide a settling tank sludge extraction control device for a water purification plant for improving the water purification effect by efficiently pulling out accumulated sludge.

Therefore, the feature of the present invention is that the amount of generated sludge is calculated from the turbidity changes of raw water and sediment water and the chemical injection rate, and the value obtained by subtracting the amount of returned sludge from this calculation is made such that the value remains within the specified value. Its purpose is to control the opening of the sludge valve.

The present invention will be explained in detail below with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention.

In the figure, 1 is a chemical mixing pond, 2 is a stirring pond, and 3 is a chemical mixing pond.
is a sedimentation pond. Reference numerals 11 and 12 indicate a raw water turbidity meter and a raw water flow meter that measure the turbidity and flow rate of raw water introduced from a landing well (not shown), and 13 and 14 return the raw water from the sedimentation tank 3 to the chemical mixing tank 1. These are a return sludge flow meter and a return sludge turbidity meter that measure the flow rate and concentration of sludge.

15 and 16 are a drawn sludge flowmeter and a drawn sludge turbidity meter for measuring the flow rate and concentration of drawn sludge drawn out and discharged from the settling tank 3; 17 is the settling tank 3;
This is a turbidity meter for water sent from the water to the pond (not shown).

21 is a sludge return pump, 22 is a sludge valve, 23 is a sludge valve drive motor, 31 is a flocculant injector, 32 is a chemical injection rate calculator, 33 and 35 are generated solid matter (flocculate) amount calculators, 34 3 is a return sludge amount calculator, 36 is a settling tank deposited sludge amount calculator, and 37 is a drawn sludge amount calculator.

Further, 38 and 39 are totalizers, and 40 is an opening request calculator that calculates the deviation of the amount of accumulated sludge in the sedimentation tank from the reference value (upper and lower limit values) and outputs an opening request command based on this. 41 is a reference value setting device, 42 is an opening measuring device for the sludge valve 22, and 43 is a device that calculates the deviation of the opening of the sludge valve 22 from the required opening value, and outputs a valve control amount based on this. It is a control amount calculator.

Raw water is supplied to chemical mixing pond 1 from the receiving well (not shown).
After being appropriately injected there, it flows into the stirring pond 2. The flocs (solid matter) grown here are sent together with water to the sedimentation tank 3, where they settle and become sludge. The precipitated water obtained by such treatment flows out of the settling basin and flows into a filter basin (not shown).

The sludge return pump 21 is for returning an appropriate amount of sludge deposited in the settling tank 3 to the mixing tank 1 in order to effectively and economically chemically treat raw water.

The sludge extraction control in water treatment plants as described above is
The process is roughly as follows.

First, the chemical dosing rate calculator 32 calculates the turbidity of the raw water.
A flocculant injection rate C proportional to Tu ₁ and flow rate Q ₁ is determined and given to the flocculant injector 31 as its command. Based on the flocculant injection rate C and raw water flow rate Q ₁ from the calculator 32, the calculator 33 calculates the amount of solid matter S ₂ generated by the chemical injection according to equation (1).

S ₂ = K ₂ CQ ₁ ......( ₁ ) However, K ₂ is _the precipitated solids conversion _coefficient . The amount of generated solids S ₁ depending on the temperature is calculated according to equation (2).

S ₁ = K ₁ Q ₁ (Tu ₁ − Tu ₄ ) ......(2) However, K ₁ is SS - turbidity conversion coefficient Flow rate Q ₂ and concentration of returned sludge from flow meter 13 and turbidity meter 14 D ₁ is supplied to the calculator 34, and the returned sludge amount S ₃ is calculated as a value proportional to the product of both.

In the calculator 36, the amount of generated solids S ₁ , S ₂ and the amount of returned sludge S ₈ calculated as described above are input, so that the amount S of sludge deposited in the settling tank 3 is calculated as follows.
Calculated according to equation (3).

S=S ₁ +S ₂ −S ₃ (3) The calculator 37 calculates the amount of drawn sludge based on the flow rate Q ₃ of the drawn sludge and its concentration D ₂ .

Numerals 38 and 39 are totalizers that respectively total the amount S of sludge deposited and the amount pulled out in the sedimentation tank 3. The difference value SC obtained by subtracting SB from the integrated value SA is
As is clear, this represents the amount of sludge currently deposited in settling tank 3.

As mentioned earlier, in order to ensure the settling efficiency in settling tank 3 at the planned value and also to ensure sludge recycling to mixing tank 1, it is necessary to
The amount of sludge deposited in the sludge must be maintained within the lower limit as planned.

The reference value setter 41 is for setting the above-mentioned upper and lower limit values and supplying them to the arithmetic unit 40. The calculator 40 compares the current sludge accumulation amount SC in the sedimentation tank 3 with the upper and lower limit values, and outputs an opening request command for the sludge valve 22 based on the deviation.

Such functions, for example, increase the amount of sludge deposited,
The relationship between the deviation from the lower limit value and the opening request command is
This can be easily realized by storing it in advance.

The control amount calculator 43 calculates the deviation of the opening measurement value obtained from the opening measurement device 42 from the opening request command, and based on this deviation, adjusts the control amount of the sludge valve 22 by an appropriate method. Calculate and output. Based on the output, the sludge valve drive motor 23 is controlled,
The opening degree of the mud removal valve 22 is made to match the opening degree request command.

FIG. 2 is a block diagram of main parts of a second embodiment of the present invention, which replaces the computing units 40 and 43 and the sludge valve drive motor 23 in FIG. 1.

40A determines whether or not the accumulated sludge amount SC in the sedimentation tank 3 is between the upper limit value and the lower limit value set by the setting device 41, and when the accumulated sludge amount SC exceeds the upper limit value. is the opening signal of the mud removal valve 22,
Further, when the lower limit is exceeded, the valve opening/closing signal output device outputs a closing signal for the valve 22 to the sludge valve drive motor 23, respectively.

FIG. 3 is a diagram showing one aspect of controlling the amount of sludge deposited according to the second embodiment described above, in which the horizontal axis is time;
The vertical axis represents the amount SC of sludge deposited in the sedimentation tank 3. Further, (22) shows the open and closed states of the mud draining valve 22.

As is clear from this figure, when the sludge accumulation amount SC in the settling tank 3 exceeds its upper limit set value Lu, the sludge discharge valve 22 is opened, and on the contrary, the sludge accumulation amount SC exceeds its lower limit set value Ld. Closed when closed.

In this case, in order to prevent hunting in opening and closing the valve and smoothing the control, it is desirable to provide hysteresis characteristics to the opening and closing control of the mud removal valve.

In addition, in calculating the amount of generated solids by the calculator 35 explained above, from the mixing tank 1 to the settling tank 3,
Of course, it is desirable to take into account the residence time.

As is clear from the above description, according to the present invention, the amount of sludge deposited in the settling tank can be constantly monitored and controlled to an optimal value or an optimal range. Through this, (1) securing the minimum amount of sludge necessary for sludge recycling;
and (2) to maintain sedimentation efficiency in the sedimentation basin.
It simultaneously satisfies the two requirements of suppressing the amount of accumulated sludge and provides excellent water purification effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a block diagram of essential parts of a second embodiment of the present invention, and FIG. 3 is a waveform diagram for explaining the operation of the present invention. 1...Mixing basin, 2...Agitation basin, 3...Sedimentation basin, 21...
Sludge return pump, 22... Sludge valve, 23... Sludge valve drive motor, 31... Coagulant injector, 32... Chemical injection rate calculator, 33, 35... Generated solids (floe) amount calculator, 34... Return Sludge amount calculator, 36... Sedimentation tank deposited sludge amount calculator, 37... Pulled sludge amount calculator, 3
8, 39... Totalizer, 40... Opening request calculator, 41
...Reference value setter, 42...Opening degree measuring device, 43...Controlled amount calculator.

Claims (1)

[Scope of Claims] 1. Injecting a flocculant into raw water in a mixing basin, forming flocs in a stirring basin, settling turbidity as sludge in a settling basin, and removing a part of the sludge through a sludge valve. At the same time, the sedimentation tank sludge extraction control device at the water treatment plant, which returns a portion of the sludge to the raw water, calculates the amount of solid matter generated in the sedimentation tank from the turbidity and flow rate of the raw water, the sedimentation water turbidity, and the flocculant injection rate. A generated solids amount calculation means, a returned sludge amount calculation means for calculating the amount of returned sludge from the flow rate and concentration of the returned sludge, and a sludge accumulation amount calculation means for calculating the difference between the outputs of the generated solids amount calculation means and the returned sludge amount calculation means. , a drawn sludge amount calculating means for calculating the drawn sludge amount from the flow rate and concentration of the drawn sludge, and a first sludge accumulation amount calculating means for integrating the accumulated amount which is the output of the sludge accumulation amount calculating means.
an integrating means, a second integrating means for integrating the amount of drawn sludge that is the output of the drawn sludge amount calculation means, and a means for determining the difference between the output of the first integrating means and the output of the second integrating means as the currently accumulated sludge amount. and a means for comparing the currently accumulated sludge amount with a set value, and when the currently accumulated sludge amount is larger than the set value, the opening degree of the sludge valve is increased; 1. A settling tank sludge extraction control device for a water purification plant, comprising means for controlling the opening of the sludge valve to be small when the sludge valve is small.