JPH05240767A - Floc measuring/controlling device - Google Patents

Abstract

PURPOSE:To improve control accuracy when flocs are formed by controlling simultaneously both a coagulant injecting coefficient to a mixing pond being a factor to control floc formation and the number of revolutions of paddles in a flock forming pond. CONSTITUTION:A flock measuring/controlling device is provided with a mixing pond 2 wherein a coagulant is injected for mixing into treated water, a floc forming pond 3 to form flocs by agitating the treated water from this mixing pond 2 by means of paddles 11a, 11b and 11c, an underwater camera 8 arranged in the rear stage part of the floc forming pond, an image measuring device 15 to calculate various kinds of feature quantities relating to the flocs by discriminating the flocs according to image information obtained from this camera and a settling pond 4 to settle the flocs in the treated water from the floc forming pond, and is also provided with a control means to control simultaneously a coagulant injecting coefficient to the mixing pond 2 and the number of revolutions of respective paddles in the floc forming pond 3 while using the various kinds of feature quantities as a management index.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a floc measuring device for controlling operation of a coagulation-sedimentation process in a water purification plant,
In particular, the present invention relates to an apparatus for simultaneously controlling the coagulant injection rate for a mixing pond and the paddle rotation speed of a floc formation pond.

[0002]

2. Description of the Related Art Generally, in water purification plants, raw water taken from rivers and lakes is used in floc formation ponds, and flocculating agents (clay, algae, etc.) are flocculated by flocculants (polycalcium chloride, vantosulfate, etc.). Aggregated and removed in the next settling basin.

In the conventional floc formation control, in a new water treatment plant, floc formation is performed by a jar test (indoor experiment), and raw water turbidity and coagulant injection rate or ALT ratio (A
L ³⁺ / turbidity) and the control relational expression are obtained, and further, they are used on a real scale from parameters such as GCT value. In addition, in existing water treatment plants, floc formation control is performed using the accumulated data.

Since such flock formation control is a feed-forward control system, it cannot cope with a sudden change in the turbidity of raw water, and there is a possibility that the next-stage filter basin will be overloaded. Therefore, an aspect in which a feedback control system is incorporated has also been constructed.

Regarding the above, Japanese Patent Application No. 1-193629 previously proposed by the present applicant discloses an example of the flock measuring device shown in FIG. That is, raw water is taken into the landing well 1 and the coagulant is injected into the mixing pond 2. Then, the turbidity components in the raw water are aggregated into flocs in the bypass type floc formation pond 3. After that, flocs are settled in the settling tank 4, and the supernatant is discharged to a filter tank not shown. The landing well 1 is provided with a turbidity meter 5 for measuring raw water turbidity, and the settling tank 4 is provided with a turbidity meter 6 for measuring outflow turbidity. The values measured by the turbidimeters 5 and 6 are input to the coagulant injection controller 7.

At the last stage of the flock formation pond 3, an underwater camera 8 for photographing the treated water is provided.
Then, the image captured by the underwater camera 8 is processed by the floc measuring device 9 to identify the floc, statistical processing is performed to create various data regarding the floc, and this data is output to the coagulant injection controller 7.

The coagulant injection controller 7 calculates the coagulant injection amount based on the turbidity of the raw water and the outflow water measured by the turbidimeters 5 and 6 and the data obtained from the floc measuring device 9, Control the injection of coagulant into the mixing pond 2 (Coagulation Dispersion Analyzer "PHOTOMETRIC DISPERSION ANALYZER," PDA
An example of control using "abbreviated as method" is Japanese Patent Laid-Open No. 3-5144.
No. 3 gazette).

[0008]

The following three points are listed as optimum flock formation control conditions in a general flock measurement control device.

(1) Stable turbidity of effluent from the sedimentation basin is kept stable at a low value (2) Reduction of coagulant injection amount (3) Maintenance of maximum growth floc diameter Especially in the water treatment process The condition (1) is important. This is because if the outflow turbidity becomes high, the burden will increase in the filter tank at the next stage as described above. G and GT values, which are the factors that determine the maximum growth floc particle size of suspended solids, are usually used as operation management indexes for that purpose. The G value is the stirring strength of a paddle or the like during flock formation, the T value is the stirring duration, and the GT value is the degree of progress of flock formation. In addition to the above factors, the C value, which is the turbidity concentration of raw water, is involved in the formation of flock, and these factors are also design guidelines for the flock formation pond.

On the other hand, as an operation control index for removing suspended matter components in raw water, the ALT ratio (A
A method using (L ³⁺ / turbidity) is known. AL above
The T ratio is the ratio of the amount of aluminum of the coagulant to the amount of suspended matter,
This ALT ratio is used as an index for determining the coagulant injection rate.

However, it is difficult to improve the control accuracy by using the G value, GT value, or ALT ratio as the operation management index in the water purification plant so that the turbidity of the sedimentation effluent is always below the control target value. is there. The reason is that the quantitativeness of G value and GT value is low, and further, the flock formation experiment in the jar test (indoor experiment) does not match the full scale flock formation control device. Therefore, in the existing water purification plants, the fact is that the floc formation control is performed using the accumulated data as described above, and in order to improve the efficiency, a correction term (such as raw water temperature or PH ) Is provided to control.

Particularly, the injection rate of the coagulant is controlled by feedforward control in which the relation between the ALT ratio and the raw water turbidity is made into a square root function formula or a power function formula. It is customary to set the injection rate to a high value and set it to a low value when the turbidity is high, and if flock formation is performed with the same water intake and the same agitation strength with such injection rate control, the ALT ratio will be high or low. It is known that the average particle size of the is changed. For example, Water Supply Society magazine, Vol. 60, No. 10
According to Tanbo's paper in No. 685, it is stated that the proportion of suspended solids and aluminum hydroxide (coagulant component) in floc volume is 55 times that of suspended solids. Judging from the above, at high turbidity, that is, low A
At the LT ratio, the floc capacity per unit volume (FV
Value) and the amount of floc sludge is expected to increase.

Further, according to the relationship graph between the turbidity of raw water and the floc formation time (FIG. 6 of Japanese Patent Application No. 1-193629), it is necessary to change the stirring time by the paddle as the turbidity of the raw water changes. Therefore, a stable treatment cannot be performed only by controlling the injection rate using the ALT ratio or turbidity as an index.

Further, the measurement control using the PDA method has various problems as described below. That is, as factors controlling floc formation, (1) concentration of suspended substance, (2)
There are four possible factors: coagulant injection rate, (3) stirring intensity and time of paddle, etc., and (4) fluctuation of water intake, and any one of these factors cannot be ignored. However, under the current circumstances, the above (2) coagulant injection rate and (3)
Only one of the stirring intensity and the stirring time of the paddle or the like is controlled independently. As a cause, there is a complicated interaction between the measured values of these two factors and the floc forming factor, so that a single measured signal value, for example, PD
It can be considered that it is difficult to estimate and quantify the relationship between the measured value and the floc formation factor from the light amount change (voltage value) by the A method.

In view of the above problems, in the present invention, in the flock formation control, the floc formation is controlled by controlling the coagulant injection rate into the mixing pond and the rotational speed of the paddles arranged in the flock formation pond at the same time. The purpose is to improve the control accuracy of time.

[0016]

In order to achieve the above object, the present invention provides a mixing pond for injecting a coagulant into treated water to mix the coagulant based on a set coagulant injection rate. The floc formation pond which stirs the treated water of the above with a paddle to form flocs, the treated water camera installed in the latter part of the floc formation pond, and the flocs are identified based on the image information from the treated water camera. The turbidity of the treated water flowing out from the settling basin is measured by an image measuring device that performs statistical processing to calculate various features of the floc and a settling basin that precipitates the flocs in the treated water from the flock formation basin. In controlling what is below the set turbidity, the coagulant injection rate to the mixing pond and the paddle of the floc formation pond are used as control indices for various characteristic amounts of flocs obtained from the image measurement device. It is the structure of floc measurement control unit provided with control means for controlling the number of rotation at the same time.

As various characteristic quantities of the above-mentioned flocs, the number of flocs per unit volume, the average particle diameter of the representative flocs after the flocculation pond, the floc capacity (FV value) per unit volume, the particle diameter per unit capacity of 0. It is characterized by using four items of fine floc capacity (MFV) of 5 mm or less. Further, a control means for simultaneously controlling the coagulant injection rate to the mixing pond and the paddle rotation speeds arranged in the middle and rear stages of the floc formation pond is provided with various characteristic amounts of the flocs as management indexes.

[0018]

According to the configuration of the flock measurement control device,
In the mixing pond, the flocculant injection rate controller injects the flocculant into the raw water, and then in the flock formation pond, the paddle rotation speed control device controls the paddle rotation speed to stir the mixture to remove the suspended matter in the raw water. Flocculates.
After that, the treated water has flocs settled in the settling tank, and the supernatant liquid is discharged to the filtration tank not shown.

Then, the flock image photographed by the underwater camera installed at the last stage of the flock formation pond is identified by the image measuring device, and various characteristic amounts of the flock are the number of flock per unit volume and a representative of the latter stage of the flock formation pond. The average particle size of flock, the flock capacity per unit volume, and the fine flock capacity with a particle size of 0.5 mm or less per unit capacity are continuously calculated and input to the control means. Then, the control signal is output to the flocculant injection rate control device and the paddle rotation speed control device using the flock feature amount as a management index, and the coagulant injection rate to the mixing pond and the paddle rotation speed of the floc formation pond are Controlled at the same time.

At the time of the above control, the floc characteristic amount significantly responds to the rotational speed of the paddle in the order of average particle size> number of floc> MFV value. And if the rotation speed of the paddle is lower than the rated rotation speed, the average particle size of the flocs becomes large,
On the contrary, when the rotational speed of the paddle is increased above the rated rotational speed, the average particle size of the flocs becomes smaller, and the rotational speed of the paddle is controlled.

The floc characteristic amount responds remarkably to the coagulant injection rate in the order of FV value> number of flocs> MFV value. By controlling the paddle rotation speed and the coagulant injection rate at the same time by the control means, the control accuracy during flock formation is improved.

Particularly, in controlling the paddle rotation speed, it is effective to control the rotation speeds of the middle stage paddle and the rear stage paddle according to the above-mentioned criteria.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the flock measurement control device according to the present invention will be described below in detail by assigning the same reference numerals to the same components as those of the conventional one. In the block diagram shown in FIG. 1, 1 is a landing well that takes in raw water, 2 is a rapid mixing basin that agitates coagulant in treated water and agitates, 3 is a floc formation basin that forms flocs, and 4 is flocculation It is a sedimentation pond. The landing well 1 is provided with a turbidimeter 5 for measuring raw water turbidity, and a turbidity signal measured by the turbidimeter 5 is input to a coagulant injection rate control device 13. The rapid mixing basin 2 is provided with a stirring mechanism 10 such as a stirring blade.

Further, the flock formation pond 3 is divided into a plurality of stages, and each stage has a paddle 11a, which constitutes a stirring mechanism.
11b and 11c are provided. This paddle 11a,
The rotation speeds of 11b and 11c are appropriately controlled based on the output signal of the paddle rotation speed control device 14.

At the final stage of the flock formation pond 3, an underwater camera 8 with a cleaning mechanism is installed as a treated water photographing device. In order to capture the flowing flocs as a completely still image, a fully interlaced camera in the electronic shutter mode is used as the underwater camera 8.

Reference numeral 15 is an image measuring device, and 16 is an operation / management computer as a control means. In addition to the data input from the image measurement device 15, the operation / management computer 16 has a pH value of the water to be treated. Water quality and operation information such as the amount of intake water and the amount of returned water are entered, and the coagulant injection rate control device 1 is operated from the operation / management computer 16.
3 and a control signal for the paddle rotation speed control device 14 are output.

The basic operation of this embodiment having such a configuration is as follows. First, the raw water is taken into the landing well 1,
After the turbidity meter 5 measures the turbidity of the raw water, the coagulant is injected from the coagulant injection rate control device 13 in the rapid mixing basin 2 in the next stage. At this stage, the turbidity components in the raw water have changed to microflocs. Next, in the flock formation pond 3, the paddle speed control device 14 controls the paddles 11a, 11a.
Stirring is performed while the rotation speeds of b and 11c are controlled, and the micro flocs are aggregated and produced in the flocs. After that, the treated water is transferred to the settling basin 4, the flocs generated are settled, and the supernatant liquid is discharged to a filter pod not shown.

Then, the flock generated by the underwater camera 8 installed at the last stage of the flock formation pond 3 is photographed, the obtained flock image is sent to the image measuring device 15, and the flock is identified by making full use of the image analysis technique. Then, statistical processing is performed to continuously calculate various feature amounts of flocs, and the flocc feature amounts are calculated by the operation / management computer 1.
6 is input. The operation / management computer 16 uses the above-mentioned floc characteristic amount as a management index, and p
A control signal is output to the coagulant injection rate control device 13 and the paddle rotation speed control device 14 in consideration of water quality and operation information such as H, water intake amount, and return water amount. The coagulant injection rate control device 13 calculates the coagulant injection rate based on the control signal and the turbidity signal of the raw water measured by the turbidity meter 5, and based on the calculated value the coagulant injection rate into the rapid mixing basin 2 is increased. Is injected.

In the present embodiment, the following four items are adopted as the characteristic amount of the flocs calculated by the image measuring device 15 during the above operation.

(1) Number of flocs per unit volume (2) Average particle size of representative flocs in the latter stage of flocculation pond (3) Flock capacity per unit volume (hereinafter abbreviated as FV value) (4) Per unit capacity Fine floc volume of 0.5 mm or less (hereinafter abbreviated as MFV) This control device uses the floc characteristic amounts of the above four items as basic indexes, and further, the pH of treated water, water intake, return water, etc. A feature is that the control of the injection rate of the coagulant into the rapid mixing tank and the control of the rotational speed of the paddles 11a, 11b, 11c are performed at the same time by taking into consideration the operation information.

The time series change and process data when the floc measuring device according to the present embodiment is actually installed in a water purification plant and the flock characteristic amount is continuously measured by the image measuring device 15 will be illustrated below.

(A) Influence of the number of rotations of the paddle It was found that the four items of the floc characteristic amount responded remarkably in the order of average particle size> number of flocs> MFV value, and FV value was difficult to respond. It was also found that the amount of process changes such as turbidity and amount of returned water responded to the residence time due to changes in the amount of water.

(B) Effect of coagulant injection rate It was found that the floc characteristic amount responds remarkably in the order of FV value> number of flocs> MFV value, and the average particle size is difficult to respond. It was also found that the amount of process change responded to the ALT ratio.

As described above, it was confirmed that the four floc feature quantities calculated by the image measuring device 15 have an operation factor for the control target of the paddle rotation speed for floc formation and the coagulant injection rate. Was done.

Explaining in more detail with respect to the above, the average particle size in the latter stage of the floc formation pond changes greatly depending on the rotation speed of the paddle. That is, if the rotation speed of the paddle is lower than the rated rotation speed, the average particle diameter of the flocs becomes large, and conversely, if the rotation speed of the paddle is made higher than the rated rotation speed, the average particle diameter of the flock becomes smaller.

The relationship between the number of rotations of the paddle and the particle size of flocs is described in, for example, Journal of Water Supply Society, No. 441, June 1972.
According to the monthly issue, it is shown that the maximum flock particle size is inversely proportional to the rotational speed of the paddle, as shown in equation (1).

[0037]

[Equation 1]

Here, dmax is the maximum growth floc grain size, Nr
Is the rotation speed of the paddle, and kρ is a coefficient. In general, kρ
= 1.2-1.5 is used.

However, if the number of rotations of the paddle is extremely reduced, flocs may settle in the flocs forming pond. Particularly, the flock feature amount in which this change appears is a fine floc volume of 0.5 mm in particle diameter. It is the MFV value. In the steady state, the MFV value is stable against changes in the average particle size. That is, individual fine flocs collide with each other due to the stirring stress of the paddle and grow, but on the other hand, the grown flocs are also destroyed by the stress of the paddle, and the floc particle diameters are distributed as shown in FIG. 2 due to their mutual balance. .. Therefore, it is considered that the state in which the average particle size X becomes large and the amount of fine flocs decreases decreases the stirring efficiency by the paddle.

Further, as shown in FIG. 3, when the balance of the floc particle size is lost and especially the MFV value is suddenly decreased, it is considered that the flocs have settled in the floc formation pond 3. You can judge. Therefore, it is necessary to set the minimum number of rotations of the paddle and to make the time series change of the MFV value a judgment item.

According to the control according to this embodiment, the floc concentration as a function of the suspended matter concentration and the amount of the flocculant at a given time must be constant in the floc formation pond system. FIGS. 4A and 4B show a state in which floc sedimentation occurs. When the paddle rotation speed is low, the average particle size becomes constant over time, while the MFV value rapidly decreases. There is. On the other hand, FIGS. 5 (A) and 5 (B) show a state in which flocs are stably formed, and the MFV value is in a state of flattening with respect to changes in the average particle size over time, which is extremely high. Not getting smaller.

Therefore, as a criterion for determining the paddle rotation speed, when the paddle rotation speed is not the minimum rotation speed, if the MFV value becomes small when the paddle rotation speed is lowered from the rotation speed before the variable speed, the rotation of the paddle rotation speed. It is necessary to increase the number and control the rotation speed to decrease when the MFV value becomes stable.

When carrying out the above control, it is particularly effective to control the rotational speeds of the middle paddle 11b and the rear paddle 11c of FIG. That is, the first stage paddle 11a
Keeps the rotation speed at a constant high speed in order to efficiently form the flocs, and controls the rotation speeds of the middle-stage paddle 11b and the rear-stage paddle 11c according to the above-mentioned criteria.

An actual example of control of the paddle rotation speed and the coagulant injection rate in this embodiment will be described below.

First, regarding the relationship between the paddle rotation speed and the maximum flock growth, in the case of a paddle type flock formation pond,
By controlling the rotation speed of the paddle, it is possible to control the stirring strength, which is a growth factor of flocs. As can be seen from the above formula (1), the maximum growth floc grain size dma
x is inversely proportional to the rotational speed N _r of the paddle. Therefore, in order to maintain stable growth of flocs, the rotation speed may be adjusted appropriately.

In the above equation (1), n = 1.349, which is the slope of the floc density function obtained from the geometric mean grain size of floc.
Substituting 8 gives equation (2).

Dmax ∝ Nr ^{−1 · 0345} ··· (2) As described above, for the growth of the flocs, the stirring strength (G value) of the paddle, In addition to the stirring duration (T value), the turbidity concentration (C value) of the raw water is related. FIG. 6 shows the effect of the GCT value on the growth of flocs. In the figure, the horizontal axis represents the raw water turbidity, and the vertical axis represents the time required for floc formation. The GCT is constant (about 1,000,000). For example, when the stirring strength G = 20 and the raw water turbidity C = 10, the time T = 5000 (seconds) required for the formation of flocs. Of these GCT values, only the stirring strength (G value) of the paddle is suitable for control.

The paddle rotation speed control by image measurement is basically performed by sampling control (at intervals of 30 to 60 minutes). The image measurement device 15 performs image measurement at the sampling time intervals. That is, an image is taken in from the underwater camera 8, binarization processing is performed, and then the image is inverted,
A process such as volume conversion is performed to extract the characteristic amount such as the particle size and number of flocs.

The maximum amount of flock particle diameter dmax obtained from the number of revolutions of the paddle by performing statistical processing by repeating the extraction of the characteristic quantity a predetermined number of times and the floc geometric mean particle diameter H obtained by the statistical processing.
Compare with D _AVE . Furthermore, the predicted outflow turbidity T _TB obtained from the floc particle size distribution is compared with a preset outflow turbidity set value (threshold value), and the rotation speed of the paddle is controlled based on the comparison result. ..

Table 1 shows the judgment conditions and control conditions for controlling the rotational speed of the paddle.

[0051]

[Table 1]

When the conditions in the table are satisfied, the predicted flocculation turbidity is predicted even though the floc geometric mean particle diameter obtained by image measurement is larger than the maximum floc diameter d _max obtained from the current rotational speed. High runoff turbidity. This phenomenon is not practical in view of the particle size distribution of flocs. It is considered that the cause of this phenomenon is that a large amount of flock exists in the visual field range in image measurement and the flock overlaps with each other, resulting in an apparently large flock particle size. Therefore, it is necessary to lower the stirring strength (paddle rotation speed).

When the conditions are satisfied, the maximum flock diameter dmax is small and the predicted outflow turbidity is high. That is, it is considered that flocs have not grown because the current stirring strength is high. Therefore, the paddle rotation speed is reduced.

Further, if the conditions are met, the predicted outflow turbidity is low, so there is basically no problem, but if the stirring strength is too low, flocs may settle in the flocculation pond. Therefore, the rotation speed of the paddle is increased to prevent the flocs from settling.

When the conditions are satisfied, the particle size of flocs is small, but the outflow turbidity satisfies the conditions. Therefore, in order to give priority to runoff turbidity, the number of rotations of the paddle will be maintained.

In the cases of conditions (1) to (4), the conditions are further classified according to the difference between the threshold value and the control factor.
It is also possible to adopt a mode in which the amount of change in the paddle rotation speed is determined stepwise according to the difference between the two.

As described above, the flock formation pond 3 is provided with a plurality of paddles 11a, 11b, 11c, and the stirring system is a control system for keeping all the paddle rotation speeds constant, and a rear stage. A tapered flocculation control method that lowers the number of rotations is considered. The latter method maintains a high collision probability due to strong stirring force in the first stage,
In the latter stage, the stirring force is weakened to avoid re-dissociation and destruction of flocs.

FIG. 7 shows the control range of the paddle rotation speed in the former control method, and FIGS. 8A, 8B, and 8C show the control range of the paddle rotation speed in the latter control method. In the figure, R _O is a steady speed, Rmin is a minimum speed, Rma
x is the maximum speed. In the latter control method, for example, the ratio of R _O is first stage: middle stage: second stage = 5: 3: 1.

Therefore, in this embodiment, based on the latter method, various characteristic amounts of flocs are used as management indexes.
Paddles 1 arranged in the middle and rear stages of the flock formation pond 3
One of the features is to control the rotation speed of 1b and 11c.

Next, a practical example of controlling the coagulant injection rate will be described. In general, the formula (3) is given as a coagulant injection rate formula that allows feedback control.

D = A · TB ⁿ + B ········· (3) where D is coagulant injection Rate, TB is raw water turbidity, B is a correction term, and A and n are coefficients.

First, similarly to the above, the image measuring device 15 measures an image at a predetermined sampling time interval. That is, an image is taken in from the underwater camera 8, binarization processing is performed, then the image is inverted, and processing such as area / volume conversion is performed to extract the characteristic quantities such as the particle size and number of flocs. This feature amount extraction is repeated a predetermined number of times for statistical processing.

The relationship between the average particle size of flocs and the number of flocs / screen with respect to the turbidity of outflow will be described. FIG. 9 shows the relationship between the geometric mean particle size of flocs and the turbidity of sedimentation basins. The sediment effluent turbidity treated here is that after 6 hours from photography. As can be seen from this figure, the outflow turbidity increases as the floc geometric mean particle size decreases, and the outflow turbidity decreases as the floc geometric mean particle size increases.

FIG. 10 shows the relationship between the number of flocs / screen and the turbidity of sedimentation basin. As can be seen from this figure, when the number of flocks / screen increases, the turbidity of outflow increases, while when the number of flocks / screen decreases, the turbidity of outflow decreases. It does not change.

Thus, there is a strong alternating relationship between the average particle size of flock and the number of flock particles / screen, and when the average particle size of flock is large and the number of flock particles / screen is small, the outflow turbidity is low. I understand. The turbid water phenomenon handled here is different from the white turbidity phenomenon of aluminum that occurs due to excessive injection of the coagulant.

Since the relationship between the geometric mean particle size of flocs and the sedimentation basin was clarified in this way, the influence of fine floc particles on the turbidity of sedimentation sediment was evaluated based on this. In this evaluation, a commonly used surface area load factor will be used. The surface area load factor is an index for evaluating how much floc particles are removed when a certain size of floc particles are allowed to flow into a sedimentation tank under a certain condition.

In the equation (4), the surface area load factor W ₀ (cm / se
c) is shown.

W ₀ = Q / A ... (4) where Q is the flow rate in the sedimentation basin (Cm ³ / sec), A is the surface area (cm ² ) of the sedimentation basin.

The surface area load factor W ₀ has the same dimension as the floc sedimentation velocity. That is, it is a basic numerical value that gives a removal rate of floc particles having a floc sedimentation velocity W smaller than the surface area load factor W ₀ . The criteria for this judgment are as follows.

When W <W ₀ ... Removal rate W / W _{0 When} W ≧ W ₀ ... Removal rate 100% Based on this determination, the results of obtaining the removal rate of fine floc particles are shown in Table 2. In Table 2, the surface area load factor W ₀ =
It is set to 0.05 (cm / sec).

[0071]

[Table 2]

In Table 2, when the removal rate is less than 100%, that is, when fine flock particles may flow out, they are underlined and emphasized.

Generally, the flow velocity of the chemical sedimentation tank is 0.66c.
m / sec or less, flow velocity in inclined plate sedimentation basin is 1.0 cm / se
It is less than or equal to c. In Table 2, the flow velocity is 0.05 cm / se
c, which is 1/10 to 1/20 of the actual flow velocity.
Despite the degree, fine floc particles of about 150 μm may flow out.

Next, the fine flock capacity per unit capacity in image measurement will be described. In the image measurement, the fine floc amount Mg (g / l) per unit capacity is (5)
It can be obtained by a formula.

[0075]

[Equation 5]

Here, X _n is the diameter n (50 to 300 μm)
Volume of flock by series (cm ³ ), Gc is the number of image measurements,
Gs is the capacity (1) in the screen visual field range, and ρ _E2 is the average fine floc density (density of 150 μm = 0.074 g / cm ³ ).

Next, the predicted outflow turbidity of the sedimentation pond obtained from the screen measurement is obtained. That is, based on the surface area load factor W ₀ and the floc sedimentation velocity W, the predicted outflow turbidity T _TB (m
When calculating g / l, equation (6) is used.

T _TB = Mg {1- (WG _AVE / W ₀ )} × 1000 (6) Here, WG _AVE is the sedimentation of the average fine flock diameter. Speed (150
μm sedimentation velocity = 0.04 cm / sec), and W ₀ is a surface load factor (cm / sec) at the time of image measurement. In the actual image measurement, the geometric mean particle size was 1.095 mm and Mg = 0.
If 00457, WG _AVE = 0.04, W ₀ = 0.05,
The predicted outflow turbidity T _TB is 0.914 mg / l from the equation (6).

Similarly, with a geometric mean particle size of 1.795 mm
When Mg = 0.0004, WG _AVE = 0.04, W ₀ = 0.05, the predicted outflow turbidity T _TB is 0.1 mg / l.

As can be seen from these results, there is a relationship between the average particle size and the fine floc capacity. That is, there is dispersion in the floc particle size distribution, and if the floc average particle size becomes large, the proportion of fine flocs inevitably decreases and the outflow turbidity also decreases.

Next, the intake amount Q of raw water and the rated water amount Q _SET are compared. The amount Q of intake water fluctuates due to the return of backwash water from the filter basin, etc., and the fluctuation of the amount Q of water intake is the main cause of the fluctuation of the stirring strength G in the floc formation pond. Further, the predicted outflow turbidity T _TB obtained from the floc particle size distribution is compared with a preset set outflow turbidity (threshold) TB _SET, and based on the comparison result, the coagulant injection rate formula is corrected. Increase or decrease term B.

Therefore, the coagulant injection rate formula in this embodiment is expressed by the following formula (7).

D = A · TB ⁿ ± B (Q _DIFF and TB _DIFF ) ... (7) where D is the coagulant injection rate (mg / l or g / m ³ ), T
B is the raw water turbidity, Q _DIFF is the difference between the rated water quantity Q _SET and the intake quantity Q, TB _DIFF is the difference between the set runoff turbidity TB _SET and the predicted runoff turbidity T _TB , and A and n are coefficients.

As a result of the above comparison, when the water amount difference Q _DIFF is 10% or less of the rated water amount Q _SET , the correction term B is corrected according to the turbidity difference T _DIFF . That is, when the predicted outflow turbidity T _TB is larger than the set outflow turbidity TB _{SET, the} correction term B is decreased, and when the predicted outflow turbidity T _TB is smaller than the set outflow turbidity TB _{SET, the} correction term B is increased.

Further, the water quantity difference Q _DIFF is 10 of the rated water quantity Q _SET .
If it is more than%, the correction term B is determined according to the criteria shown in Table 3.
Is corrected.

[0086]

[Table 3]

When the conditions in Table 3 are met, the water intake Q
It is considered that due to the increase in the stirring force, the stirring strength was high and the residence time was short, so that the flocs were destroyed, and as a result, the predicted outflow turbidity T _TB was increased. In this case, the correction term B is reduced to increase the floc density,
It is possible to reduce the runoff turbidity of the sedimentation pond.

When the condition is satisfied, the water intake Q is decreased, the stirring strength is low and the residence time is long, but the predicted outflow turbidity T _TB is high because the flocs are not grown. Conceivable. In this case, by increasing the correction term B, the ALT ratio is also increased and the floc density is slightly reduced, but the average particle size of the flocs can be increased and the outflow turbidity of the sedimentation pond can be reduced.

When the condition is satisfied, for example, as a result of controlling under the condition, it is determined that stable floc formation is performed, and the current state is maintained.

When the condition is further satisfied, for example, as a result of controlling under the condition, it is determined that stable floc formation is performed, and the current state is maintained.

Further, it is possible to adopt a mode in which the value of the correction term B is determined stepwise according to the magnitude of the water amount difference Q _DIFF and the turbidity difference TB _{DIFF under} the condition or.

In this example, the water intake Q and the predicted outflow turbidity T
_{Although TB} is used as a control factor, it is also possible to adopt a mode in which the correction term B is controlled using water temperature or the like as a control factor.

[0093]

As described above, in the flock measurement control device according to the present invention, the flock image photographed by the treated water photographing device installed at the rear stage of the flock formation pond is identified by the image measuring device, and the image measurement is performed. The number of flocs per unit volume of flocs obtained from the device, the average particle size of the flocs, the floc volume per unit volume and the fine floc volume, which are four feature values, are continuously calculated and input to the control means. The control signal is output to the flocculant injection rate control device and the paddle rotation speed control device using the floc feature amount of the control index as a management index, and the coagulant injection rate to the mixing pond and the paddle rotation speed of the floc formation pond are simultaneously controlled. can do.

Therefore, it becomes possible to estimate and quantify the relationship between the measured value and the floc forming factor with respect to the coagulant injection rate, the paddle stirring strength and the stirring time, which are particularly important as factors controlling the floc formation. By simultaneously controlling the above, there is an effect that the control accuracy at the time of flock formation can be increased and a finer control can be realized.

Particularly, in controlling the paddle rotation speed, it is effective to control the rotation speeds of the middle paddle and the rear paddle of the flock formation pond according to the above-mentioned criteria.

[Brief description of drawings]

FIG. 1 is a block diagram showing a flock measurement control device according to an embodiment of the present invention.

FIG. 2 is a distribution chart showing the particle size of flock in a floc formation pond.

FIG. 3 is a distribution chart in the case where the floc particle size is out of balance in a floc formation pond.

FIGS. 4A and 4B are graphs showing a state in which flocs settle.

5 (A) and 5 (B) are graphs showing a state in which flocs are stably formed.

FIG. 6 is a graph showing an example of the relationship between raw water turbidity and floc formation time.

FIG. 7 is a graph showing a control range of the paddle rotation speed in a system in which all the paddle rotation speeds are kept constant.

FIGS. 8A, 8B, and 8C are graphs showing the control range of the paddle rotation speed in the system in which the paddle rotation speed on the rear side is reduced.

FIG. 9 is a graph showing the relationship between the geometric mean particle size of flocs and the turbidity of sedimentation basins.

FIG. 10 is a graph showing the relationship between the number of flocs / screen and the turbidity of sedimentation basin.

FIG. 11 is a block diagram showing an example of a conventional bypass type floc measurement control device.

[Explanation of symbols]

1 ... Landing well, 2 ... Rapid mixing pond, 3 ... Flock formation pond, 3
... sedimentation tank, 5 ... turbidity meter, 8 ... underwater camera (processed water camera), 10 ... stirring mechanism, 11a, 11b, 11c ... paddle, 13 ... flocculant injection rate control device, 14 ... paddle rotation speed control device , 15 ... Image measuring device, 16 ... Computer for operation / management (control means).

Claims (3)

[Claims] 1. A mixing pond for injecting and mixing a coagulant into treated water based on a set coagulant injection rate, and a floc formation pond for agitating the treated water from this admixture with a paddle to form flocs. And a treated water camera installed in the latter part of the flock formation pond, and identifying the floc based on image information from the treated water camera, and performing statistical processing to calculate various characteristic amounts of the floc. An image measuring device and a settling basin for settling the flocs in the treated water from the floc forming pond, and controlling the turbidity of the treated water flowing out of the settling effluent to below the set turbidity A control means for simultaneously controlling the coagulant injection rate to the mixing pond and the paddle rotation speed of the floc formation pond is provided with various characteristic amounts of the obtained flocs as a management index. That flock measurement and control equipment. 2. The various characteristic quantities of the flocs, the number of flocs per unit volume, the average particle diameter of the representative flocs in the latter stage of the flocculation pond, the flock capacity (FV value) per unit volume, and the particle diameter per unit capacity. The flock measurement control device according to claim 1, wherein four items of a fine flock capacity (MFV) of 0.5 mm or less are used. 3. The coagulant injection rate into the mixing pond and the paddle rotation speeds arranged in the middle and rear stages of the floc formation pond are simultaneously controlled using various characteristic amounts of flocs obtained from the image measuring device as management indices. A flock measurement control device, characterized in that it is provided with control means for controlling.