JPH02218408A - Method for regulating injection rate of flocculant by means of floc measuring device - Google Patents

Abstract

PURPOSE:To reduce delay time in regulating injection rate of flocculant by correcting feedback correction term at specified intervals based on the difference between predicted mean particle diameter determined from raw water and injection rate of flocculant and actually measured mean particle diameter of floc. CONSTITUTION:By detecting turbidity of raw water and turbidity at the outlet of a settling pond 4, flocculant injection rate is controlled using flocculant injection equation: D=A.TB<n>+B (D: flocculant injection rate, TB: turbidity of raw water, A, n: coefficient, B: feedback correction term). ALT ratio (quantity of Al ion relative to turbidity of raw water) is determined from raw water and flocculant injection rate, whereby predicted mean particle diameter of floc is determined from ALT ratio thus obtained and equation relating to mean particle diameter of floc. Further, actually measured value of geometrical mean particle diameter of floc is obtained by image processing of floc measuring device 10 provided in a floc formation pond 3. By feeding back the difference between the predicted and measured mean particle diameter of floc at specified intervals, correction term B is corrected and injection rate of flocculant is regulated.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for controlling a flocculant injection rate using a flocculant measuring device for water treatment by injecting a flocculant.

B5 Summary of the Invention The flocculant injection rate control method using the flocculant injection device of the present invention is for controlling the flocculant injection rate using the flocculant injection formula D=A-TB″×B, in which the raw water and the flocculant injection rate are In addition to calculating the predicted average particle size of the flocs from This shortens the time and improves control accuracy.

C0 Conventional technology In water purification plants, raw water taken from rivers, lakes and marshes is treated with a flocculant (polycalcium chloride (PAC)) in a floc formation pond.
), sulfuric acid bands, etc.) to aggregate suspended components (clay, class III, etc.) and remove them in a settling tank.

However, changes in the water quality (water temperature) of the raw water used for flocculation treatment.

Seasonal fluctuations in pH, inorganic/organic ratio of turbidity components, etc. are becoming more pronounced. The causes include pollution of rivers, lakes and marshes, and changes in rainfall. Therefore, based on the above factors, injection control is performed by automatically changing the flocculant injection rate.

To determine the flocculant injection rate, the injection formula % (1) is generally used as a function of turbidity, which is the main factor (see curve 1 in Figure 10).

A feature of this equation is that data analysis is easy to determine the coefficients a and b.

However, since the only coefficient that can be changed to fine-tune this injection formula (1) is b, feedforward control is possible. for,
Since it is determined by the coefficients a and b, it is impossible to correct the injection formula just by using the coefficients. That is, to determine the coefficients a and b,
Low, medium.

A considerable amount of aggregation data is required for high turbidity, and if the amount of data is small, the accuracy of the injection method may decrease.

Therefore, in order to apply feedback control,
To further improve accuracy, from the relationship between the ALT ratio (AAl ion amount (1”) to raw water turbidity) and raw water turbidity, D=A・TBn+B ・・・・・・・・・(2)
The formula (D: flocculant injection rate, TB: raw water turbidity) is used (see curve ■ in Figure 1).

In other words, the characteristics of injection type (2) are that, compared to injection type (1), low, medium, and high turbidity can be approximated with one injection type, and the coefficients A,
Regardless of the water treatment plant, n is within a certain range (A”-85, n4
0.25).

Therefore, by employing the initial value coefficients A and n even in a new business or a water purification plant where the aggregation data is insufficiently prepared, an injection method with higher accuracy than the injection method (1) can be realized. That is, A-TBrl is a feedforward control term, and B is a feedback correction term, and when B=0, there is no injection rate correction, and a correction term is actually required.

D2 Problem to be solved by the invention This correction term is influenced by the amount of change in water quality, but when PAC is used as a flocculant, the optimal flocculation range is wide, so water temperature and pH do not matter much. Rather, there are large fluctuations in influencing factors such as the turbidity at the outlet of the settling tank and the raw water turbidity components (clay, sand chromaticity, ratio of raw water turbidity to raw water suspension amount (SS amount)). The turbidity at the outlet of the sedimentation tank can be corrected by setting standard values for each water treatment plant and comparing them, but there are few indicators that can be feedback-controlled for raw water turbidity components, and chromaticity is a possible indicator. However, it is removed to some extent in the floc formation tank, and by performing intermediate chlorination treatment (chlorine injection before and after the settling tank), it does not appear in the turbidity at the exit of the settling tank and is removed during the process. I can't control it. Furthermore, regarding the ratio of raw water turbidity to raw water SS amount, it is currently not possible to continuously measure it, and even if it is introduced from a correlation formula, there is a wide range of variation and high accuracy cannot be achieved. That is,
The current injection rate control method calculated from the raw water turbidity and the turbidity at the outlet of the sedimentation tank cannot further improve accuracy, and the turbidity information at the outlet of the sedimentation tank does not allow for rapid fluctuations in raw water turbidity. However, due to the residence time, real-time control is difficult.

The present invention has been made in view of the above-mentioned problems of the conventional technology, and its purpose is to improve the injection type D=A-TB'+B which is capable of feedback control.
An object of the present invention is to provide a flocculant injection rate control method using a flocculant injection rate applying image measurement that can improve the precision of a bypass type floc formation pond, which is one method of floc formation.

E9 Means for Solving Problems In order to achieve the above object, the flocculant injection rate control method using the floc measuring device of the present invention detects raw water turbidity and sedimentation tank outlet turbidity, and uses the flocculant injection method D= A-TB”+B
(D is flocculant injection rate, TB is raw water turbidity, A, n are coefficients,
B is a feedback correction term) in which the flocculant injection rate is controlled, the ALT ratio (AQ ion amount to raw water turbidity) is calculated from the flocculant injection rate of the raw water, and this ALT
In addition to calculating the predicted average particle size of the flocs from the equation between the ratio and average particle size of the flocs, the actual measured value of the geometric average particle size of the flocs was obtained from image processing of the floc measurement device installed in the floc formation pond, and this prediction and actual measurement were performed. correcting the correction term B by feeding back the difference in average particle diameter of the flocs at predetermined time intervals;
This controls the flocculant injection rate.

The F3 action flocculant injection rate has a relationship with the raw water turbidity TB and D = A-TB'10B, where the A-TB' term is controlled as a feedford control term by the raw water turbidity, and B is controlled as a feedback control term. .

Calculate the ALT ratio for turbidity from raw water and flocculant injection rate,
The predicted average particle size can be predicted from the relational expression between the ALT ratio and the average particle size.

The geometric mean particle size of the flocs can be determined by installing a floc measuring device in the floc forming pond and processing the image.

The measured average particle diameter of this floc is the factor SS amount/
Since the value includes the factor of TB, the flocculant injection rate can be corrected by controlling the feedback control term B based on the difference between the predicted average particle diameter and this measured value.

Since the actual measurement of the average floc particle size is performed in the floc formation pond, the residence time of the flocs to the actual measurement point of the floc average particle size is 30 to 60 minutes, and the residence time of the flocs to the turbidity detection point at the exit of the sedimentation tank is 2 hours or more. Compared to the above, the time is significantly shortened, and feedback sampling control can be performed every 30 to 60 minutes, improving control accuracy.

G. Example As an index for controlling the injection rate of the flocculant, the turbidity components suspended in the raw water can be measured using a turbidity meter. However, turbidity is a macroscopic indication value, and the turbidity component includes a mixture of inorganic viscosity, sand, etc., and organic algae, etc., so even in actual floc format, the ratio of inorganic to organic matter varies. If different, the state of floc formation will also change. In other words, compared to inorganic clay, the density of organic algae is quite close to the density of water, and if there is a large amount of organic algae at the same turbidity indicator value, floc flocculation becomes poor; There is a risk that the effective density of the flocs will decrease and the flocs in a coagulated state will dissociate. As a result of applying this concept to an actual floc-forming pond and analyzing images using an underwater camera, we discovered the phenomena shown in Figures 2 to 5.

Figure 2 shows the relationship between the ALT ratio and the geometric mean particle size, which introduces the injection rate formula (2), where the * mark is when there is almost no organic matter, and the x mark is when there is a lot of organic matter mixed in. G mark and X
An approximate formula can be established using the mark as the variation width. However, in reality, differences occur at the same turbidity. As a result of investigating this tendency by image analysis and manual analysis, we obtained the image analysis results shown in Figure 3. FIG. 3(a) shows the floc luminance when the turbidity is rich in inorganic matter, and FIG. 3(b) is the floc luminance when the turbidity is rich in organic matter.

Comparing the two, flocs with a lot of inorganic matter showed a high brightness value (on the contrary, flocs with a lot of organic matter showed a lower brightness value than inorganic matter. Based on this result, the second result was compared with manual analysis.
The x mark in the figure is SS amount/TB#0゜78, the O mark is SS amount/T
The relationship was B-1.0. Generally, the relationship between turbidity and SS amount is as follows: SS amount (my/Q) = A (T B Cm /
Q)+M), and the correction term M is given by the chromaticity f, etc.

Therefore, if a near-infrared turbidity meter that is hardly affected by the chromaticity f is used, the correction term M can be ignored.

Therefore, the SS amount (x9/I2) = A - TB, and the coefficient A can be expressed as 5Sli/TB. This coefficient A must be O<At≦1. However, even when this condition is met, there may be deviations from the trend. Figure 5 shows the agitation intensity (G
This shows the change in floc formation due to the difference in T value).In the case of a bypass type, when designing a formation pond, the target water volume to be treated and the agitation intensity are set. Generally, in the bypass type, the flow path is fixed, so changing the water amount will also change the stirring intensity, so the general condition is not to allow the water amount to fluctuate.

Figure 5 shows the GT value when the water volume is changed in a floc formation pond with a set GT value of 200.000. A high GTI value means a low water volume, and conversely a low GT value means a low water volume. This is when there is a lot of water. That is, the floc average particle size will vary depending on the stirring intensity even at the same -ALT value. The curve ■ in Figure 5 is the design value of G for the formation pond.
The relational expression between the ALT ratio and the average particle size at the T value, the curve ■ shows the relationship between the ALT ratio and the average particle size when the GT value is 220,000 and the water amount is less than the design value, and the curve ■ shows the relationship between the ALT ratio and the average particle size when the GT value is 220,000 and the water amount is less than the designed value.
The relational expression when the water amount is larger than the design value at 2O3000 is shown. From this relational expression, it can be seen that the diameter of the flocs changes depending on the agitation intensity that occurs when the water intake amount is changed.

The calculation method for this stirring intensity G is as follows: G=J e/a = J rhrg-/μT, where ε
: Total energy consumption rate (erg/cm3・5ec) μ:
Water viscosity (gs/sea-am) gc: Newton's conversion factor 980 (gpengcm/gw・5ec) T: Residence time in flocculation pond (sec) ht: Total length of bypass type flocculation pond Head loss (C■) r: Unit volume weight of water l (g w/cm') (Note)
Generally, the total energy consumption rate ε is the energy consumption rate ε effective for floc formation. It can be considered to be - orders of magnitude larger than . Therefore, ε. = 0.18.

In the case of a bypass-type floc formation pond, the G value is obtained from a calculation formula, and the value obtained by multiplying this G value by the residence time T of the floc formation pond becomes the GT value (dimensionless number).

That is, the GT value is determined by whether flocs grow or not depending on the length of residence time in a bypass type floc formation pond, and floc dissociation also occurs. Also, from Figure 5, the same -
Image analysis using information from an underwater camera revealed that the average particle size changes due to the difference in stirring intensity depending on the ALT ratio.
By determining the average particle size, control that corresponds to changes in water amount becomes possible.

<Injection type B correction of D=A-TB"+H> Average particle size prediction (1) Calculated from the number of flocs (4000 or more flocs) that satisfies statistical conditions by image analysis using information from an underwater camera. The design value has a relationship between the geometric mean particle size (conditions for obtaining a normal distribution when the particle size value is logarithmically converted) obtained from the histogram of volume and average particle size shown in Figure 4 and the above SS/TB~10. (GT value 200.000) The average particle size (H
Find D).

HD=a eALT-” (H: predicted average particle diameter, a, -n coefficient) (2) When the predicted average particle diameter is plotted over time, the seventh
It will look like the broken line ■ in the figure. Furthermore, the average particle diameter of the actually measured flocs after the delay time (residence time) from the injection of the flocculant to the flocculation pond where the underwater camera is installed is as shown by the broken line ■. The injection amount is corrected based on the difference between the predicted average particle size and the measured average particle size.

D=A-TBn±(Predicted HD-Actual HD) If the difference between predicted HD and actual measured HD is expressed as B+=HDe, when HDe<0, it becomes -B, (reduce the injection amount), and when HDe≧0 Sometimes Bt=±0.

The reason for this is: (1) From the relationship of SS amount/TB, coefficient 1 is 0≦a≦
Must be 1.

(2) When the intake amount shown by the curve ■ in Figure 5 increases and the GT value decreases, the floc growth time is determined from the relationship between the time required for floc formation and turbidity as shown in Figure 6. However, when the turbidity concentration is high, that is, when the ALT ratio shown in Fig. 5 is a low value (after 0,1 moe), there is almost no effect; , around 3).

For example, when the turbidity concentration is low at 10 degrees as shown in Figure 6,
The time required for floc growth is 5,000 seconds, and at a turbidity concentration of 20 degrees, it only takes about 3,000 seconds.

Therefore, when the GT value is higher than the design value (the residence time becomes longer), the injection amount is reduced and the effect of the longer residence time is used to grow the flocs.

Conversely, when the GT value is lower than the design value (residence time becomes shorter), there is no correction factor, so the injection amount is not increased, and the change in the turbidity meter at the downstream sedimentation tank outlet, i.e. , the difference between the set turbidity and the measured turbidity is corrected by the correction term Bt = "set -r
Assign as .

D=A-TB”±HDe±(rset-r)rgeL:
Sedimentation basin effluent turbidity set value r: The difference between the effluent turbidity set value and the actual measurement value is expressed as B*=re.When re≧0, B=±O (does not change the injection rate), and ``eku0 However, since setting the outflow turbidity to a low value will lead to an increase in the amount of injection, it is necessary to replace the turbidity with a level of 1 ppm.

The above is the feedback control in flocculant injection control.

Next, this control method will be explained with reference to the control system shown in FIG.

Raw water from rivers, lakes, etc. enters the receiving well 1, and the turbidity of the raw water in the receiving well 1 is detected by a turbidity meter 6. This turbidity signal is input to the control unit 13, and the flocculant controlled by the flocculant injection method of the control unit 13 is injected into the mixing pond 2 from the pipe 4.
The mixed liquid mixed by the stirrer 15 flows into the floc formation pond 3. During this time, the control unit 13 calculates the ALT ratio from the raw water turbidity and the flocculant injection rate, and from the ALT ratio, the relational expression between the ALT ratio and the average particle size at the design value shown in FIG.
The predicted average particle diameter at the installation point of the floc measuring device 10 is predicted.

The mixed liquid that entered the floc formation pond 3 has a convection effect (stirring)
Alternatively, the floc diameter gradually grows depending on the residence time (30 to 60 minutes). This growing floc is recognized by the underwater camera 9, and the geometric mean diameter of the floc is determined by image processing by the floc measurement device IO.

The actual measured average diameter at this time includes the factor of water volume fluctuation and SS volume/T.
This value includes the factor of B. The control unit 13 controls the amount of coagulant injection by substituting the difference between the predicted value and the measured value into the feedback control term B.

The water that has passed through the floc formation pond enters the settling basin, where flocs and the like are precipitated. A turbidity meter 8 is installed at the exit of the sedimentation tank to detect the turbidity at the exit of the sedimentation tank, and calculate the effect of the increase in water intake (reduction in GT value), which is not a factor in control parameter B1, between the set value of the turbidity meter and the actual measured value. Substitute the difference between them into the correction term B. However, the control of B1 is sampling control and correction is applied every 30 to 60 minutes.

The correction width shall be within ±5 ppm.

From the above configuration, changes in turbidity components (SS amount/TB).

A control system that can respond to fluctuations in water intake,
It is particularly effective when the amount of water intake is reduced and 5SIi/TB>1, and the injection amount can be reduced, making it possible to create a more accurate control system.

Creation of the standard formula for the ALT ratio and average particle size in Figure 5> Obtain the geometric mean diameter by image processing of the floc measurement device IO during a period when the occurrence of organic matter such as algae is relatively low, and create a relational formula with the ALT ratio. .

Conditions: ■Design water intake amount (GT value).

■SS amount/TB#1.0 ■Where to install the underwater camera.

■Uses a near-infrared turbidity meter (eliminates the influence of chromaticity).

In water treatment plants where the impact of (2) is relatively small, it is possible to remove it from the conditions. ■ and ■ require certain conditions. Regarding ■, it is related to the effect of ■, so if another turbidity meter is used, the item ■ must also be deleted.

H1 Effects of the Invention Since the present invention is configured as described above, it produces the following effects.

(2) The predicted average particle size is derived from the relational expression of the ALT ratio and the average particle size, and the injection amount of the flocculant can be controlled from the value compared with the actual measured value of the floc average particle size.

■In the conventional injection control of the bypass type floc formation pond, control was performed between the inflow locality of the nursing well and the turbidity of the outflow from the settling tank, but there was a delay in control because the residence time was over 2 hours. An underwater camera is installed in the floc formation pond, and information on the floc formation status is also used, so the delay time is 30 to 60 minutes.
The control accuracy can be significantly improved.

■From the relationship between the average floc particle size and the ALT ratio, the fluctuation factor of the average floc particle size is the water intake fluctuation (stirring intensity index GT value)
It became clear that this was the SS amount/TB ratio.

■It is now possible to automatically correct changes in turbidity components due to seasonal changes.

■Since the amount of coagulant to be injected can be set to an appropriate amount, the amount of coagulant tends to be saved.

■Injection rate correction, which is a drawback of conventional feedforward control, can be automated.

(2) By further adding factors such as alkalinity, pH, and water temperature to the correction term B, it becomes possible to control the amount of coagulant injected to a high degree.

[Brief explanation of the drawing]

Figure 1 is a graph of raw water turbidity and flocculant injection rate curve, Figure 2 is AL
Diagram showing the relationship between T ratio and geometric mean particle size of flocs, 3rd
The figure is a distribution diagram of the floc volume and average particle size obtained from image analysis, Figure 4 is a diagram showing the relationship between the horizontal scanning line direction of the underwater camera screen and the luminance of flocs, and Figure 5 (a), ( b)
are diagrams showing the relationship between floc average particle size and ALT ratio, respectively;
Figure 6 is a curve diagram showing the relationship between raw water turbidity and the time required for floc formation, Figure 7 is a line diagram showing changes in the predicted average floc diameter and measured average floc diameter over time, and Figure 8 is a flocculant FIG. 1 is a schematic configuration diagram showing an example of an injection control system. ! ...Water landing well, 2...Mixing pond, 3...Detour type floc formation pond, 4...Sedimentation basin, 6, 8...Turbidity meter, 9
...Underwater camera, lO...floc measuring device, 13
. . . Control unit, 14 . . . Coagulant injection pipe. Figure 2 Figure Raw water turbidity TB (m9/1) Figure 3 Figure 2 Geometric mean particle diameter (mm) 09 Figure 4 Volume histogram ALT ratio (Al'7Ts> Figure 6 Raw water turbidity (degrees) ) og ALT ratio (At”/TB) Procedural amendment (. 1. Indication of the incident Heisei Patent Application No. 4141 No. 1 2゜ Title of invention Coagulant injection rate control method using a floc measuring device 3゜ Correction Relationship with the incident

Claims (1)

[Claims] (1) Detect the raw water turbidity and settling tank outlet turbidity, and use the flocculant injection formula D=A・TB^n+B (D is the flocculant injection rate, TB is the raw water turbidity, A, n are coefficients, and B is feedback correction term)
In systems that control the flocculant injection rate by
The predicted average particle size of the flocs is determined from this ALT ratio and the floc average particle size relational expression, and the geometric average particle size of the flocs is actually measured from the image processing of the floc measurement device installed in the floc formation pond. A flocculant injection using a flocculant measuring device, characterized in that the flocculant injection rate is controlled by calculating the value and feeding back the difference between the predicted and actually measured floc average particle diameter at predetermined time intervals to correct the correction term B. Rate control method.