JP3199897B2 - Coagulant injection control device for water purification plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulant injection control device, and more particularly to a coagulant injection control device suitable for a water purification plant.

[0002]

2. Description of the Related Art Raw water purification facilities for water supply at water purification plants are:
Generally, it was configured as shown in FIG. That is, the raw water and the flocculant injected from the flocculant injector 15 are rapidly mixed and contacted in the rapid mixing tank 14 to generate micro flocs incorporating impurities, and the micro flocs are formed into a plurality of stages of flocs. By gentle mixing in the pond 12, the particles collide with each other to form large flocs having high sedimentation, and the flocs thus formed settle in the sedimentation tank 13 to be separated from water. Also, treated water, which is supernatant water, is taken out of the sedimentation basin. At this time, a small amount of flocculated floc that has overflowed the carrier together with the treated water is removed by a rapid filtration pond (not shown) to become clear water.

[0003] The above-mentioned technology for removing impurities and the like is called a coagulation sedimentation method or a chemical precipitation method. As the coagulant, sodium sulfate as an aluminum salt and PAC (polyaluminum chloride) are used. Suspended substances and impurities contained therein were flocculated with aluminum hydroxide, which is hardly soluble in water, to settle, and raw tap water was treated.

The coagulant injection control and monitoring device measures the temperature, alkalinity, and turbidity of tap water raw water, and calculates the coagulant injection rate according to the following equations (1) and (2). Is calculated and displayed, and a device based on so-called feed-forward control is known.

Pac = {A · Turb ^N1 · AK ^N2 + B} Ft (1) Ft = F (Temp) (2) where Pac is the injection rate, Turb is the turbidity of the raw water, and A K
Is the alkalinity of the raw water, Temp is the temperature of the raw water, F is a function of the temperature, Ft is the temperature effect coefficient, and A, B, N1, and N2 are predetermined constants.

The above feedforward control is performed by:
This is because in a normal water purification plant, it takes about 2 to 4 hours from the injection of the flocculant to the extraction of filtered water for which the effect can be confirmed, so that feedback control cannot be substantially performed.

[0007] In the above-mentioned conventional water purification plant, when the fluctuation of the raw water turbidity is in a normal concentration range of 0 to 50 [mg / liter], even if the constant A and B are set to constant values, the operation is performed. Good results can be obtained. On the other hand, when the raw water turbidity increases significantly due to heavy rain, the above constants A,
In the calculation based on the value of B, a suitable injection rate cannot be obtained. The injection rate of the flocculant is calculated based on different values, for example, A 'and B', which are obtained in advance, and the flocculant is injected based on the calculated value. I was doing it.

In addition, the above-mentioned monitoring of the coagulant injection is performed by displaying time-series data of the raw water temperature, alkalinity, turbidity and coagulant injection status on a CRT or the like, and monitoring the water flowing out of the sedimentation basin. And time series data of the turbidity of the filtered water passing through the rapid filtration pond is displayed on the CRT or the like.

The turbidity of the filtered water is below the measurement limit when the coagulant is properly injected and the coagulation and sedimentation is good, but when the coagulant is insufficiently injected, the turbidity of the filtered water increases. However, there has been a problem that the water quality is unsafe.

In particular, when the coagulant is not properly injected as described above, there is no means for restoration, and the water that has failed to be treated must be discarded (discharged). There is.

According to the inventor's many years of experience, when the turbidity of the raw water is in the normal turbidity region, the injection of the coagulant does not fail due to the injection rate determined by the above-described equation (1) and equation (2). If the turbidity of the raw water or the components of the raw water changes drastically due to drought or drought, it is difficult to obtain an appropriate injection rate only by changing the constants A and B as described above, leading to insufficient injection of the flocculant. There was something.

Therefore, it has been considered that the state of floc formation due to the injection of the coagulant is captured, and the result is reflected in the control of the coagulant injector 15. For example, as shown in FIG. 3, the flocculated floc image detecting device 11 is provided at the exit point of the floc forming pond 12 or at the entrance portion of the sedimentation pond 13.
At this position, agglomerated flocs are sufficiently generated, so that an image of the agglomerated flocs is taken in, and image processing is performed by the control device 16 to monitor and monitor the particle size distribution and sedimentation velocity distribution of the flocs.

However, even with the above-described configuration, it takes about 30 to 40 minutes from the injection point a of the flocculant to the raw water to the exit point b of the floc formation pond 12 in the flow of the treated water in the ordinary water purification plant. . This is the time required for floc formation and cannot be reduced. For this reason, it takes about 30 to 40 minutes to obtain the result of the suitability of the coagulant injection based on the detection data from the image detection device 11,
According to this result, even if the coagulant injector 15 is controlled,
The control is performed based on the result of minutes to 40 minutes before. As described above, since the raw water turbidity changes suddenly due to heavy rain, drought, etc. due to a large time delay, injection of the coagulant is delayed, that is, insufficient or excessive injection occurs. In order to prevent such a situation, the operator must constantly monitor the raw water turbidity while referring to the weather, etc., and in some cases, the operation of the device is complicated and requires skill, such as manual control. did.

[0014]

As described above, in the prior art, it takes a long time from the injection of the flocculant to the confirmation of the suitability of the injection. However, appropriate control could not be performed when the situation suddenly changed.

An object of the present invention is to detect the excess or deficiency of coagulant injection from the state of coagulant floc within 5 to 10 minutes after injection of coagulant, and to inject proper coagulant in a short time. It is an object of the present invention to provide a coagulant injection control device for a water purification plant that controls so as to carry out the above.

[0016]

A coagulant injection control device for a water purification plant according to the present invention includes a rapid mixing tank, a floc formation pond, and a sedimentation tank, and the coagulant is rapidly mixed by a coagulant injection machine. In a water purification plant for purifying raw tap water by injecting it into a tank, a floc image detecting device is provided near the entrance of the floc forming pond or between the rapid mixing tank and the floc forming pond to capture an image of flocculated floc. A control device is provided which grasps the characteristics of the floc formation state from the detection data of the device and controls the flocculant injector based on the characteristics.

The control device performs image processing on an image captured by the floc image detecting device, and measures the particle size distribution of the flocculated flocs based on the processing data of the image processing device. A calculating means for calculating a median value and a skewness of the particle size distribution based on the distribution, and calculating an injection amount of the flocculant based on the median value and the skewness.

[0018]

[Action] The raw water flowing into the rapid relaxation tank is rapidly mixed with the coagulant, and then flows out to the floc formation pond. In the floc formation pond, the raw water and the flocculant are mixed slowly, and the flocculant reaction proceeds as it flows down the first floc formation pond, the second floc formation pond, and the third floc formation pond, and the flocculent floc becomes larger and more sedimentable. It grows up to.

The generated floc is settled and separated in the sedimentation basin, and the supernatant water flows down to the rapid filtration basin. A floc image detection device that captures an image of the flocculation floc being generated is provided near the entrance of the floc formation pond or at the outlet of the rapid mixing tank, and based on the captured image data, the injection of the flocculant is performed. Control.

Since the floc image detecting device is provided near the entrance of the floc forming pond or between the rapid mixing tank and the floc forming pond as described above, the flocculant is detected within 5 to 10 minutes after injection of the flocculant. Since excess or deficiency of the injection can be detected, appropriate injection of the coagulant can be performed in a short time.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a coagulant injection control device for a water purification plant according to the present invention will be described with reference to FIGS. In the figure, reference numeral 1 denotes a pipeline for introducing raw tap water (hereinafter referred to as raw water) into the system, and guides the raw water to the rapid mixing tank 2. Rapid mixing tank 2
Causes the raw water introduced through the pipe 1 to rapidly mix and contact with the flocculant to generate microfloc surrounding the impurities. Reference numeral 3 denotes a floc formation pond, which is an outflow culvert from the rapid mixing tank 2.
Flocculated by gentle flocculation of the microfloc of water flowing down through the
To be generated. The floc formation pond 3 is composed of a first floc formation pond 3a and a second floc formation pond 3
Flock forming pond 3b and third floc forming pond 3 in the next process
c.

Reference numeral 5 denotes a sedimentation basin;
a is provided as the next step, and these floc forming ponds 3
The flocculated floc F generated in the above is settled and separated from water. The flocculated floc F that has partially flowed out together with the treated water from the sedimentation basin 5 is obtained as water that cannot be completely removed by a rapid filtration pond (not shown).

Reference numeral 7 denotes a coagulant injection machine for injecting the coagulant into the rapid mixing tank 2 through a chemical injection tube 7a. Reference numeral 8 denotes a floc image detection device, which has a microscope-like optical system that captures and enlarges the water to be treated including the flocculated floc F in the outflow culvert 4, captures an enlarged image of the optical system with a television camera, and generates an image signal. Output as A control device 9 controls the coagulant injector 7 based on an image signal detected by the floc image detection device 8. The control device 9 performs image processing means 9a for performing predetermined image processing on the flock image signal detected by the flock image detection device 8, and performs necessary calculations based on image data output from the image processing means 9a. Calculating means 9b for calculating the coagulant injection rate, and an injection controller 9c for controlling the coagulant injecting machine 7 based on the calculation result (injection rate) of the arithmetic means 9b.
And a display device 9d for displaying data necessary for driving.

In the coagulant injection control device configured as described above, the raw water flowing into the rapid relaxation tank 2 via the pipe line 1 is rapidly mixed with the coagulant injected through the chemical injection pipe 7a, and then the floc It flows into formation pond 3.

In the floc formation pond 3, the raw water is slowly mixed with the flocculant, and the floc coagulation reaction proceeds as it flows down the first floc formation pond 3a, the second floc formation pond 3b, and the third floc formation pond 3c. Bigger and more
It grows into flocculated floc with high sedimentation.

Then, the formed flocculated floc is settled and separated in the sedimentation basin 5, and the supernatant water flows down to the rapid filtration basin.
The outflow culvert 4 which is the outlet of the rapid mixing tank 2 is provided with the floc image detecting device 8 for photographing the image of the flocculent floc F being generated as described above. The image data is sent to the means 9a, where necessary image processing such as shading processing such as contrast enhancement, binarization processing, binary processing, particle classification, particle size measurement, and particle size distribution diagram (histogram) creation are performed. . The created particle size distribution map is output to the calculating means 9b, and the median value and skewness of the particle size distribution map are calculated. Based on the obtained skewness, the correction amount of the coagulant injection is calculated by a predetermined calculation formula. Is done.

Here, in the outflow culvert 4, the flocculated floc F imaged by the image detecting device 8 is within 5 to 10 minutes after the flocculant is injected, and may not be sufficiently generated. Absent. For this reason, it is difficult to judge the suitability of the coagulant injection from the shape of the floc generated sufficiently and the sedimentation speed as in the conventional case. However, even if it is within 5 to 10 minutes after the coagulant injection, if the injection amount is appropriate or inappropriate, characteristics such as distortion occur in the floc formation state (particle size distribution state). I found that.
Therefore, by grasping this feature, it was decided whether or not the coagulant was properly injected.

Hereinafter, this method will be described. After smoothing the particle size distribution of the flocs obtained from the image signal, the calculating means 9b calculates the median M and the skewness W with respect to the normal distribution.

Next, based on the obtained median value M and skewness W, the correction amount ΔS of the injection rate of the flocculant is calculated by the following equation (3).
Is calculated. ΔS = K _W (W−W _N ) −K _m (M−M _N ) (3) where W _N is a target value of skewness, M _N is a target value of a median value,
K _W and K _m are coefficients (constants) obtained by experiments.

The median value M, the skewness W, and the injection correction amount ΔS of the coagulant are displayed on the display device 9d and used for monitoring the operation state. The correction amount ΔS is output to the coagulant injection controller 9c, and the coagulant injection machine 7 supplies the required amount of the coagulant to the rapid mixing tank 2 based on the output of the injection controller 9c taking into account the correction amount ΔS. inject.

Next, the present invention will be described in more detail with reference to FIG. The particle size distribution chart of the aggregated flocs in FIG. 2 is obtained by the control device 9. In the figure, the horizontal axis represents the particle size m (mm) of the aggregated floc F, and the vertical axis represents the frequency (histogram) f.

The curve A in FIG. 2A shows that when the quality of the raw water changes abruptly and the coagulant is insufficiently injected and the coagulation ability is low,
Curve C is a graph showing the particle size distribution of floc showing an intermediate state between Curve A and Curve C, when the coagulant injection is optimal and the coagulation ability is high.

In the case of the curve A having a low aggregation ability, the left side (low particle size side) and the right side (high particle size side) of the central value m ₁ of the distribution are:
The shape of the curve is not symmetric and is distorted compared to the shape of a so-called normal distribution function.

When the injection rate of the coagulant is the optimum curve C, the change is gentle on the left side (lower particle size side) of the central value M ₃ (m ₁ << m ₃ ) of the distribution, but on the right side (lower side). On the high particle size side), the frequency f sharply decreases, and the center value m ₃ is on the high particle size side compared to the curve A. The center value m ₂ of the distribution of the curve B is an intermediate value of m ₁ and m _3.

FIG. 2 (b) shows the change in the particle size distribution when the coagulant is optimally injected and the coagulation ability is high. This shows a situation where the particle size distribution changes.

A curve D1 in FIG. 2B shows a state of the flocculated floc near the entrance of the first floc forming pond 3a.
2 indicates the state of the flocculated floc near the center of the second floc forming pond 3b, and curve 3D indicates the particle size distribution of the flocculated floc near the outlet of the third floc forming pond 3c. Of course,
The relationship among the center values d ₁ , d ₂ , and d ₃ of the particle size is d ₁ <d ₂ <d ₃ .

In either case, the flocculation ability is high, so that the floc on the right side of the high particle size is smoothly generated by the mixing energy, and the frequency of destruction is low, so that the distribution curve shows a sharp drop on the high particle size side. Is distorted.

Curves E1, E2 and E3 in FIG. 2 (c) show the particle size distribution of the aggregated flocs collected at the same points as the curves D1, D2 and D3.
Indicates the case where the injection rate of the coagulant is not appropriate or the water quality of the raw water changes and the coagulation ability is low.

Therefore, the central value e ₁ of the particle size at each measurement point,
The magnitude relation between e ₂ , e ₃ and the above-mentioned median values d ₁ , d ₂ , d _{3 of} the particle size is as follows: e ₁ <d ₁ , e ₂ <d ₂ , e ₃ <d ₃ . . In the curves E1, E2, and E3, the low particle size side slightly to the left of the central value is distorted in such a manner as to drop sharply. In this case, the central value does not become too large even when flowing down the floc formation pond 3. Accordingly, no large flocculated floc is formed, and the flocculated floc in this state is a floc having a low sedimentation speed and hardly settled and separated in the sedimentation basin 5.

As apparent from these characteristics, FIG. 2 shows that the injection of the coagulant is optimal and the injection of the coagulant is not.
As shown in (a), there is a characteristic in the particle size distribution of the floc. That is, there is a difference between the distortion with respect to the normal distribution and the median of the distribution. And these values are shown in FIG.
As shown in (b) and (c), it appears early after the coagulant injection, such as near the entrance of the first floc forming pond 3a.

Therefore, by analyzing the particle size distribution of these flocs and grasping the above characteristics, the injection control of the flocculant can be properly performed. In the present invention, an image of the flocculated floc is worked in the initial stage of flocculated floc 5 to 10 minutes after the injection of the flocculant. Can be calculated as a moment (moment), and the excess or deficiency in coagulant injection can be corrected and optimized in a short time using the correction amount ΔS obtained by the above equation (3).

In this embodiment, the floc image detecting device 8 is provided in the outflow culvert 4. However, the flocculant is injected into the inlet of the floc forming pond 3, for example, near the inlet of the first floc forming pond 3a. Any point within 5 to 10 minutes from the river is acceptable.

[0043]

According to the flocculant injection control apparatus for a water purification plant according to the present invention, as described above, the floc growth process is determined by analyzing the particle size distribution of the floc image in the initial state of flocculation. Therefore, the flocculation ability of the floc, which has been reduced due to the sudden change of the raw water, can be recovered at an early stage, and flocculated flocs with good sedimentation properties can be generated.

Further, since the flocculation state of flocs can be grasped at an early stage, a water purification plant that takes water from a river in Japan, whose rainfall effect affects the raw water in a short time,
Particularly preferred.

Further, since the injection of the flocculant can be properly corrected in a short time, there is no failure of the water purification treatment that significantly delays the injection of the flocculant, and there is a risk of sending dangerous water. Is completely gone. There are also excellent effects such as easy operation of the system.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a coagulant injection control device of a water purification plant according to the present invention.

FIG. 2 is a view showing a particle size distribution of flocculated flocs in a floc forming pond in FIG. 1;

FIG. 3 is a diagram showing a conventional technique.

[Explanation of symbols]

2 rapid mixing tank 3 floc forming pond 4 outflow culvert 5 sedimentation basin 7 flocculant injection machine 8 floc image detection device 9
……Control device

Continuation of the front page (56) References JP-A-63-252512 (JP, A) JP-A-1-168308 (JP, A) JP-A-63-278508 (JP, A) JP-A-63-252511 (JP, A) JP-A-62-266107 (JP, A) JP-A-62-250919 (JP, A) JP-A-65-278509 (JP, A) JP-A-63-256108 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 21/30-21/32 C02F 1/52-1/56 G01N 15/02

Claims (2)

(57) [Claims] 1. A coagulant injection control device for a water purification plant, comprising a rapid mixing tank, a floc forming pond, and a sedimentation tank, wherein a coagulant is injected into the rapid mixing tank by a coagulant injector to purify raw water. Providing a floc image detecting device that captures an image of flocculated floc near the entrance of the floc forming pond or between the rapid mixing tank and the floc forming pond, grasping the characteristics of the floc forming state from the detection data of the floc image detecting device, A coagulant injection control device for a water purification plant, wherein a control device is provided to control the coagulant injection machine based on this feature. 2. A control device, comprising: an image processing means for performing image processing on an image taken by a floc image detecting device; a particle size distribution of aggregated flocs based on processing data of the image processing means; The arithmetic means for calculating a median value and a skewness of the particle size distribution based on the size distribution, and calculating an injection amount of the flocculant based on the median value and the skewness. Coagulant injection control device for water purification plant.