JPS5844003B2 - Sludge removal control device for sedimentation ponds at water treatment plants - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sludge removal control device for a sedimentation tank in a water purification plant.

A water treatment plant generally consists of a receiving well that takes in raw water from a river, etc.
It consists of an agitation tank for injecting and mixing a coagulant into raw water, a floc formation tank for forming flocs as a result, a settling tank for settling the formed flocs and turning it into sludge, and other parts such as a filtration tank and a water purification tank. , the raw water is purified by flowing through these masterpieces in sequence.

The present invention relates to a control device for a treatment operation (hereinafter sometimes referred to as sludge treatment) in which settled and accumulated sludge is removed from the sedimentation basin in a sedimentation basin of such a water purification plant.

Figure 1 is a top view showing an overview of the sedimentation basin.

Please refer to FIG. Raw water into which a flocculant has been injected and mixed flows into the floc formation pond 1, where flocs are formed.

The flocs then settle in the sedimentation tank 2 to become sludge.

The water treated in this way flows away through the outflow trough 2a to the waste pond.

Sedimentation tank 2 consists of the row closest to the entrance, and the following rows ■ and ■.
For example, row 0 is the closest to the outlet, and the degree of sludge deposition differs for each row.

Therefore, each row is equipped with a sludge scraper (C1 to C4), and this sludge scraper is driven by a motor (not shown) to scrape up the sludge. It is designed to be discharged to the outside of the sedimentation tank via V (in the diagram, two pieces are sent each month).

Although the operating speed of the sludge scraper itself can be changed, normally the operating speed is fixed at a constant speed, and sludge removal is controlled by changing the operating cycle.

Now, in the sludge removal process using the sludge scraper as described above, the conventional method is to give an operating command to the sludge scraper directly when the operator deems it necessary, and to set a timer to determine the sludge removal cycle. Generally, methods are used, such as adding up the operating time of the sedimentation tank and issuing a command to discharge sludge when the specified time has been reached. A method is also used in which a sludge interface meter is installed in the hopper to monitor the sludge level and issue a sludge removal command when the level reaches the upper limit.

However, the method of giving commands based on the operator's judgment is inefficient because it relies on the availability of information, and the method of using a timer or integrating operation time does not affect changes in the turbidity of raw water or the flocculant injection rate. If this occurs, it is not possible to automatically follow this change, and it is inconvenient that the setting must be changed manually.

In addition, the method using a sludge interface meter is not used much because the reliability of the interface meter is not sufficient for practical use.

The present invention has been made in view of the conventional technical background as described above, and therefore, an object of the present invention is to provide a system that can automatically follow changes in the water purification process and has sufficient reliability in practical use. Our goal is to provide mud control equipment.

(7) The main point of the invention is that in the water purification process,
The volume of sludge in the settling tank is calculated theoretically from the raw water turbidity, the turbidity of the treated water in the settling tank, the raw water flow rate, the type of flocculant and its injection rate, the sludge concentration in the settling tank, etc. It is used as a reference amount for sludge control.

Next, one embodiment of the present invention will be described in detail with reference to the drawings, but before that, the principle of the present invention will be explained in detail below.

Generally, the amount of settled solids Ds (1
77 days) is theoretically expressed as the sum of the amount of sludge d1 (177 days) based on turbidity removal in raw water and the amount of sludge d2 (177 days) based on the amount of undissolved water caused by the flocculant injected into the raw water. dl and d2 are expressed as in the following equation.

d1=QX(Tu-Tu')XIO' (177 days)
d2=QXPXa1×1O-6 (ton/mill) Ds-d1
+d2 (177 days) However, Q is raw water flow rate (m3/day), Tu is raw water turbidity (P
Pm), Tu' is the turbidity of the treated water in the sedimentation tank (PPm)
, P represents the flocculant injection rate (PPm), and al represents a constant determined depending on the type of flocculant.

Note that it is practical to calculate the amount of precipitated solids Ds by multiplying the sum of dl and d2 by a constant a2, which can also be called a safety factor, as shown in the following equation.

DS=(d,+d2)xa2 Using the amount of precipitated solids thus calculated as a parameter,
The principle of the present invention is to issue a sludge removal command when this value exceeds a specified value.

Figure 2 shows polyaluminum chloride (PAC) as a flocculant.
) is used to calculate the amount of settled solids Ds1 in the settling tank and the volume Dv of sludge in the settling tank.

In the flowchart, α represents the sludge concentration in the settling tank, and the volume of sludge should be calculated by dividing the amount of settled solids Ds by this α.

As for this sludge concentration, if the turbidity of the raw water is known, it is roughly determined what the sludge concentration will be when the raw water is treated in the settling tank.

That is, sludge concentration can be determined as a function of raw water turbidity.

The volume of sludge calculated in this way is used as a direct reference amount for sludge drainage control.

FIG. 3 is a schematic diagram showing an embodiment of the present invention.

See Figure 3. Raw water taken from rivers, etc., lands in the landing well 3, is distributed as appropriate, and reaches the stirring pond 4, where it is treated with polyaluminum chloride (PAC) as a flocculant, for example.
) is injected and mixed.

After that, as explained earlier with reference to Figure 1,
In the floc formation tank 1, colloidal particles coagulate with each other to form flocs, and in the subsequent settling tank 2, the flocs are removed by sedimentation, and then,
The treated water is filtered in a p filter pond 6 and then reaches a water purification pond 7.

The water purification process is as described above, and in such a water purification plant, a turbidity meter 8 is installed to measure the turbidity of raw water flowing into the receiving well 3.
A flow meter 9 for measuring the flow rate of raw water flowing into the stirring tank 4 is installed in the pipe, and a turbidity meter 10 is installed for measuring the turbidity of the treated water in the settling tank 2. The calculated value is input to the arithmetic unit 11 as data.

On the other hand, the injection rate of the flocculant PAC injected into the stirring pond 4 is calculated, and the data of this injection rate, the constant 31 determined by the type of flocculant, and the raw water flow rate Q measured by the flow meter 9 are used. It is input to the computing unit 13.

In addition, constant a1 is expressed as follows when the flocculant is PAC.

al-γ1 °r2°γ3 However, γ1: Specific gravity of PAC γ2: Content rate of (A1203) in PAC γ3: PAC
Among the (A1203) components inside, when injected into raw water, each calculation output of the weight ratio calculators 11 and 13 of the amount converted to water-insoluble 2Al(OH3) and the sludge concentration α in the sedimentation tank 2 are calculated. The data is input to the computing unit 12.

Now, the present invention is a sludge drainage control device comprising the above-mentioned configuration, and its operation will be explained next.

As has already been made clear in the detailed description of the present invention, the computing unit 11 calculates the raw water turbidity Tu measured by the turbidity meter 8 and the turbidity of the treated water in the sedimentation tank 2 similarly measured by the turbidity meter 10. A calculation is performed in which the difference from the degree Tu' is multiplied by the raw water flow rate Q measured by the flow meter 9, and the sludge amount d1 accompanying turbidity removal in the raw water is output as the calculation result.

In addition, the calculator 13 calculates the product of the raw water flow rate Q, the flocculant injection rate P, and a constant a1 determined by the type of flocculant.
The amount of sludge d2 is calculated based on the amount of flocculant that is not dissolved in the raw water.

The calculator 12 performs a calculation to divide the sum of the first sludge amount d1 and the second sludge amount d2 calculated as described above by the sludge concentration α, thereby increasing the volume Dv of the accumulated sludge in the settling tank 2. Calculate.

This volume 1)v is used as the reference amount for sludge drainage control in the settling tank 2.

As shown in detail in Figure @1, the sedimentation basin 2 is divided into, for example, four rows, and sludge removal control is performed for each row.

However, the sludge deposition ratio for each row in the settling tank is
' is known to be constant.

In other words, the sludge deposition ratio is high from near the entrance to the middle of the settling tank, and low near the exit.

For example, ■Column: ■Column: ■Column: ■Column -30:42:23:
The ratio is often something like 5.

Therefore, once the total amount Dv of deposited sludge is calculated, the amount of sludge for each row can be determined by dividing it by the above ratio, so that sludge drainage control can be performed for each row.

In practice, sludge drainage control is based on the relationship between the capacity of the sludge hopper that collects sludge and the amount of sludge deposited, which determines the number of times sludge is emptied in a certain period (therefore, the sludge interval), and this also determines the operating speed of the sludge scraper. be able to.

However, rather than controlling the operating speed, a method of keeping the operating speed constant and controlling the operating cycle is often adopted depending on facility conditions and other constraints.

As explained above, this invention can be said to be equivalent to a feedforward method, whereas the conventional timer method and sludge interface meter method are feedback methods, and it can be said to be equivalent to a feedforward method, and has the following effects. You can expect it.

(b) In the case of the conventional sludge drainage interval setting method using a timer, the operator had to change the timer settings if the turbidity of the raw water or the coagulant injection rate changed. However, in the present invention, this is not necessary, and sludge removal control can be performed automatically to follow changes in the process.

(O) Particularly when a computer system for process control is adopted for control, the calculations of calculation units 11 to 13 can be performed by a computer, and complete automation of sludge drainage control can be achieved in parallel with flocculant injection control. Therefore, high efficiency of water purification process operation can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a top view showing an overview of the sedimentation tank, Fig. 2 is a flowchart of the calculation process performed in this invention, and Fig. 3 is a top view showing an overview of the sedimentation tank.
The figure is a schematic diagram showing an embodiment of the present invention. In the figure, 1 is a floc formation pond, 2 is a settling basin, 2a is an outflow trough, 3 is a landing well, 4 is an agitation wave, and 5 is a sludge basin)6
1 is a water purification pond, 8 is a raw water turbidity meter, 9 is a raw water flowmeter, 10 is a treated water turbidity meter, and 11 to 13 are computing units, respectively.

Claims (1)

[Claims] 1 A sedimentation tank drainage control device in a water treatment plant, which includes a turbidity measuring device and a flow rate measuring device for raw water to be purified, a turbidity measuring device for treated water in the sedimentation tank, and raw water turbidity and treated water. a first calculating means for calculating a first sludge amount by multiplying the difference in turbidity by the raw water flow rate; and externally given data on an injection rate of a flocculant to be injected into the raw water and data on a constant determined by the flocculant; The first sludge amount and the second sludge amount are calculated by a second calculating means for calculating the second sludge amount expressed as the product of the data and the raw water flow rate, and the settling tank sludge concentration that is inevitably determined from the raw water turbidity. and third calculation means for calculating the volume of sludge in the sedimentation tank by dividing the sum of the sludge amounts, and using the volume of sludge calculated by the third calculation means as a reference amount for control. A sludge control device featuring: