JP5420467B2 - Flocculant injection amount determination device and flocculant injection amount control system - Google Patents

Description

  The present invention relates to the determination of flocculant injection in water treatment.

  In a water treatment facility such as a water purification plant, water is purified by, for example, a coagulation sedimentation treatment using a coagulant such as PAC (polyaluminum chloride) or a sand filtration treatment. Here, in this coagulation treatment, various control methods have been proposed in order to appropriately control the injection rate of the coagulant and perform sufficient treatment with a small amount of addition.

  Patent Documents 1 and 2 propose that a flow current value (SC value) corresponding to the zeta potential of micro floc in flocculant-mixed water is detected and the amount of flocculant injected is controlled based on the detection result. (See Patent Documents 1 and 2).

Japanese Patent No. 3522650 Japanese Patent No. 3485900

  Here, when the methods of Patent Documents 1 and 2 were further examined, it is necessary to conduct calibration curves for determining automatic conditions for automatic operation, and it is impossible to obtain them in an actual plant in operation. I understood that.

  The present invention relates to a pH measuring means for measuring the pH of raw water, a conductivity measuring means for measuring the conductivity of raw water, and a microscopic amount in the mixed water after mixing with the flocculant, which is determined based on the raw water having a specific pH and conductivity. A target flow current value calculating means for calculating a target flow current value by correcting an initial target flow current value, which is a target value of a flow current value indicating a flock charge state, based on the measured pH and conductivity; The mixing means for mixing the flocculant in the raw water with the residence time, the flowing current value detecting means for detecting the flowing current value of the mixed water after mixing the flocculant by the mixing means, and the detected flowing current value becomes a predetermined value An injection control means for determining a coagulant injection amount in the mixing means and controlling the coagulant injection amount in the mixing means, and determining the coagulant injection amount determined in the injection control means as a target coagulation amount. And outputs as the injection quantity.

In addition, the target flow current value I _sp is obtained by mixing the pH of the mixed water at the time of injecting the proper coagulant obtained from the result of the jar test on the raw water, the reference raw water conductivity, the measured raw water pH, and the measured raw water conductivity. It is preferable to calculate based on the rate.

In addition, the target flow current value I _sp was measured with the mixed water pH (pH ₀ ) at the time of injecting the proper coagulant obtained from the result of the jar test on the raw water, and the raw water conductivity (σ ₀ ) serving as a reference. Based on the raw water pH (pH), the measured raw water conductivity (σ), and the SC value conversion coefficient K (SC / pH), I _sp = I ₀ −I ₀ (1−σ / σ ₀ ) + K (pH− It is preferable to calculate by pH ₀ ). I ₀ is obtained by substituting pH _m = pH ₀ into SC calibration curve I = a * pH _m + b to obtain I ₀ and setting it as the set SC value of the micro floc. The SC calibration curve is obtained manually when the PAC injection rate is 4 to 5 points and the quality of the raw water is stable. The raw water conductivity at the time of measurement is the reference conductivity (σ ₀ ), and the SC value that is the reference when pH = pH ₀ obtained from the SC calibration curve is the set reference SC value I ₀ . Here, I = SC value, pH _m = mixed water pH, a and b are constants. The K value is obtained by either a trial and error method or an automatic measurement method.
Incidentally, when using acidic raw water, or equal to _{I sp = I 0 -I 0 (} 1-σ / σ 0) -K (pH-pH 0).

Further, it is preferable that K is obtained by K = K ₁ + K ₁ (1−σ / σ ₀ ) as a coefficient for converting K ₁ into a change amount of a flowing current value with respect to a change amount of pH.

  Further, the present invention is a flocculant injection amount control system of a water treatment facility having the above-described flocculant injection amount determination device, supplying inflow water as raw water to the flocculant injection amount determination device and supplying the raw water to the flocculant injection amount determination device. The flocculant treatment is performed by controlling the flocculant injection amount into the inflow water using the flocculant injection amount output from the flocculant injection amount determination device.

  Further, the present invention provides a flow current value indicating a charge state of the micro floc in the mixed water after mixing the flocculant determined based on the conductivity measuring means for measuring the conductivity of the raw water and the raw water having the reference conductivity. The initial target flowing current value, which is the target value, is corrected based on the conductivity measured by the conductivity measuring means, and the target flowing current value calculating means for calculating the target flowing current value and the raw water with a constant residence time. A mixing means for mixing the flocculant; a flowing current value detecting means for detecting the flowing current value of the mixed water after mixing the flocculant by the mixing means; and the mixing means so that the detected flowing current value becomes a predetermined value. An injection control means for determining a flocculant injection amount in the mixing means and controlling the flocculant injection amount in the blending means, and setting the flocculant injection amount determined in the injection control means as a target flocculant injection amount The And butterflies.

The target flow current value I _sp is determined based on the reference raw water conductivity (σ ₀ ), the measured raw water conductivity (σ), and the reference SC value (I ₀ ), I _sp = I it is preferable to calculate the _{0 -I 0 (1-σ /} σ 0). When the raw water pH is as low as 8.0 or less, for example, the above-described K = 0 can be obtained, and the term K (pH-pH ₀ ) can be omitted.

  Thus, according to the present invention, in the flocculant injection amount determination device, an appropriate flocculant injection rate can be determined in accordance with the water quality change of the raw water.

It is a block diagram which shows the whole structure of a water treatment system. It is a vector diagram explaining the content of control. It is a figure which shows SC calibration curve. It is a figure (trend graph) which shows a time-dependent change of various data. It is a trend graph of processing. It is a trend graph of processing. It is a figure which shows the relationship between SC value and mixing water pH (it calculates | requires pH-SC conversion coefficient).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Drawing 1 is a figure showing the schematic structure of the water treatment facility provided with the flocculant injection amount determination device concerning an embodiment. This water treatment system includes a water treatment system 100 that performs normal water treatment, and a flocculant injection amount determination device 200 for determining a flocculant injection rate in the water treatment facility.

"Composition of water treatment facility"
Raw water that is an object to be purified, such as river water, flows into the landing well 10 of the water treatment system 100. The raw water in the landing well 10 is supplied to the rapid stirring pond 12 where it is mixed with the flocculant. Here, the flocculant is stored in the medicine tank 14 and mixed with the raw water by the medicine pump 16. Although the flocculant is illustrated as being injected in the flow path leading to the rapid stirring value, it may be supplied directly to the rapid stirring pond 12.

  Further, the amount of raw water supplied from the landing well 10 to the rapid stirring pond 12 is measured by the flow meter 18, and the measured flow rate is supplied to the control device 20. In the control device 20, the injection amount of the flocculant is determined according to the instruction about the flocculant injection rate supplied from the flocculant injection amount determination device 200 and the flow rate from the flow meter 18, and the liquid feed amount of the drug pump 16 is determined. To control the injection rate of the flocculant with respect to the raw water. As the flocculant, PAC (polyaluminum chloride) is usually used, but other flocculants such as aluminum sulfate and ferric chloride may be used.

  In the rapid stirring pond 12, the flocculant and the raw water are rapidly stirred and mixed by the stirrer, and the colloid and the flocculant contained in the raw water react to form particles. Here, the reaction of the flocculant and the colloid is referred to as particles, and the particles that have passed a certain reaction time are referred to as micro flocs. However, if the amount of water is constant, the reaction time of the rapid stirring pond 12 is constant. The particles in the mixed water flowing out from here are called micro flocs. The admixed water containing micro flocs is supplied to the floc formation pond 22 where it is gently stirred to increase the floc particle size.

  The floc-containing water whose flocs are coarsened by the floc-forming pond 22 is introduced into the coagulation sedimentation basin 24, where the floc is precipitated and separated, and coagulation-precipitation treated water is obtained in the supernatant. The sediment sludge generated in the coagulation sedimentation basin 24 is disposed of separately.

  The coagulated sediment treated water is supplied to the rapid filtration pond 26, where it is rapidly filtered and the filtered treated water is introduced into the disinfection / distribution reservoir 28. The rapid filtration basin 26 is usually sand filtration. The treated water in the sterilization / distribution reservoir 28 is distributed as tap water after being sterilized by chlorine injection or the like.

“Configuration of the flocculant injection amount determination device”
In the present embodiment, the water treatment system has a flocculant injection amount determination device 200. The flocculant injection amount determination apparatus 200 samples a part of raw water, performs a flocculation process on the sample, and determines the flocculant injection amount. The flocculant injection amount determination apparatus 200 only needs to be able to determine the injection amount of the flocculant, and the amount of treated water is preferably as small as possible (about several tens of liters / minute) within a range in which the pump and the like can be accurately controlled. Hereinafter, the flocculant injection amount determination device 200 will be described.

  The raw water in the landing well 10 is introduced into the raw water tank 42 by a certain amount. In the example shown in the drawing, the sampling pump 40 discharges a predetermined amount, so that a constant amount of raw water is introduced into the raw water tank 42. In this case, it is preferable to measure the amount of water with a flow meter or the like and perform feedback control. Further, the raw water may be introduced into the raw water tank 42 by natural flow instead of the sampling pump 40. In this case, the amount of raw water to be introduced is made constant by the water sampling valve of the raw water conduit.

  The raw water tank 42 is provided with a conductivity meter 44 and a pH meter 46, and the conductivity σ and pH of the raw water in the raw water tank 42 are measured. If the conductivity and pH of the raw water can be measured, the raw water in the landing well 10 may be measured. However, the coagulant injection amount determination device 200 is a compact device, and it is better to place the measuring instrument nearby. The raw water tank 42 is preferably provided with a conductivity meter 44 and a pH meter 46. Further, when the raw water pH is low, or when the raw water pH is lowered by using carbon dioxide or the like, the raw water pH meter can be omitted.

  The raw water in the raw water tank 42 is supplied to the rapid stirring tank 50 by natural flow. Further, the flocculant from the drug tank 52 is injected into the raw water supplied to the rapid stirring tank 50 by the drug pump 54. The flocculant injection rate at this time is determined by the controller 56. The amount of water flowing into the rapid stirring tank 50 is a constant amount as described above, and a flocculant obtained by multiplying this constant amount by the flocculant injection rate is supplied to the rapid stirring tank 50. In order to control the discharge amount of the drug pump 54, the discharge amount of the sampling pump 40 needs to be grasped by the control device 56.

  The rapid stirring tank 50 is provided with a stirrer, and the raw water into which the flocculant is injected is rapidly stirred to form colloids and flocculant particles in the raw water. The flocculant may be directly injected into the rapid stirring tank 50. Further, the coagulant stored in the drug tank 52 is the same as the drug tank 14 and is preferably a PAC of the same manufacturer.

  In the rapid stirring tank 50, the flocculant admixed water in which micro flocs are formed is supplied to the SC meter 58, where the flowing current value (SC value) is measured. This SC meter 58 outputs the flowing current corresponding to the flowing potential according to the movement of the charged particles by moving the mixed water as the SC value, and the SC value corresponds to the charged state of the micro floc in the mixed water. Corresponding to the zeta potential of micro flocs. Here, the scale of the SC meter 58 can be selected from two types of 0 to 500 units and ± 250 units. In this apparatus, the latter is used, and the flow potential of the micro floc is normally a negative value. The SC meter 58 is a conventionally known instrument, and detailed description thereof is omitted. The SC value measured by the SC meter 58 is supplied to the control device 56. The mixed water after detection of the SC value is discharged through the drainage tank 60. The drainage tank 60 is provided with a pH meter 62, whereby the pH of the mixed water is measured, and the mixed water is measured. Although pH is not used for control, it is necessary when measuring an SC calibration curve, and is usually used as a monitor for the pH of the mixed water and supplied to the controller 56. If you can measure at the same time as the SC value, do not stick to the drain tank. Here, the mixed water supplied to the SC meter 58 may be only a part of the mixed water flowing out of the rapid stirring tank 50 that is necessary for measurement. Further, the drainage water from the drainage tank 60 may be supplied to the wastewater treatment facility, but may be introduced into the landing well 10 or the rapid stirring pond 12. Moreover, you may membrane-filter and use it as drinking water.

  The control device 56 controls the amount of coagulant injected by the drug pump 54 so that the SC value measured by the SC meter 58 becomes a predetermined value. This will be described below.

  First, a batch jar test has been conventionally used to determine the injection amount of the flocculant, and this is also used in this embodiment.

  In this batch jar test, after rapid stirring with a magnetic stirrer, the rough flocs are coarsened by slow stirring with an experimental electric stirring blade, and an appropriate amount of flocculant added is selected from the target turbidity of the supernatant water. . Such a batch jar test corresponds to the determination of the amount of flocculant added when the surface charge of the micro floc formed by the reaction of the colloid and the flocculant in tap water (raw water) is neutralized. Yes. That is, the surface charge is neutralized, the flocs are coarsened, and by confirming that the supernatant water turbidity has reached the target value, the flocculant injection rate can be optimized, The agent injection rate can be determined.

  In this manner, the appropriate flocculating agent injection rate is determined for the raw water at that time by the batch jar test, and the appropriate flocculating agent injection amount is determined by multiplying this by the treated water amount. However, the quality and quantity of raw water flowing into actual water treatment facilities will change. In addition, since the flocculant injection rate determined by the batch jar test cannot be measured continuously, there is a drawback that it cannot follow a rapid change in water quality.

  The batch jar test as described above should be measured over time or whenever the quality and quantity of raw water changes. However, most water treatment plants are laborious and economical. For this reason, the injection of the flocculant is determined by a test once a day. For safety reasons, excessive injection of the flocculant was effective nationwide as a countermeasure against Cryptosporidium, so it was performed nationwide. However, there is a problem of aluminum elution into tap water, and it is desirable to reduce the injection rate. ing. The reduction rate of the flocculant at the water purification plant that takes measures against excessive injection is reported to be about 30%, and appropriate injection of the flocculant is desired. The reduction rate confirmed by this apparatus can be reduced to 10 mg / L or less by using raw water having an average PAC injection rate of 30 mg / L together with carbon dioxide as a pH neutralizer.

  In particular, the appropriate flocculant injection rate varies depending on the colloid concentration in the raw water, pH, conductivity, and the like. According to the SC meter 58 in the coagulant injection amount determining apparatus 200 of the present embodiment, the SC value corresponding to the micro floc charge of the coagulant admixture water can be detected continuously. Therefore, by controlling the injection amount of the flocculant using this SC value, more accurate control of the flocculant injection amount can be performed.

  Although it has been stated that the SC value changes depending on the raw water pH, conductivity, etc., the flow potential of the micro floc also changes depending on the residence time (reaction time) of the rapid stirring tank. Therefore, even if the SC value of coagulant admixed water is measured in a water treatment facility where the amount of treated water fluctuates, accurate flocculant injection amount control cannot be performed unless a means for correcting flow rate fluctuations is developed.

In the present embodiment, the sampling pump 40 is used to control the reaction time of the flocculant and raw water to be constant. Further, the raw water pH and the raw water conductivity σ are measured, and a target flowing current value (target SC value = I _sp ) is determined according to these measured values. This target SC value is an appropriate SC value in a state in which the raw water pH and conductivity are taken into consideration and the reaction time is kept constant. In addition, since the target SC value also affects the change in the mixed water pH due to the change in the raw water pH, in this embodiment, the reference SC value (I ₀ ) corresponding to the target value pH ₀ of the mixed water pH is determined. . The set SC value I ₀ is obtained from the SC calibration curve, but is close to the microflock surface charge at an appropriate PAC injection rate unless there is a fundamental change (for example, insufficient alkalinity) of the flocculant or raw water. .

  Then, the controller 56 of the coagulant injection amount determination device 200 controls the driving of the drug pump 54 so that the SC value of the coagulant admixture water matches the target SC value. Therefore, the control device 56 always injects the coagulant of the appropriate coagulant injection amount, and the coagulant injection amount at that time can be determined.

Here, calculation of the target SC value will be described. As described above, at the start time, the appropriate flocculant injection rate is determined by a batch jar test, and the pH ₀ value at that time is detected.

  For the alkaline raw water, the target SC value is determined by the coagulant injection amount determination device 200, and this target SC value is determined as follows.

I _sp = I ₀ −I ₀ (1−σ / σ ₀ ) + K (pH−pH ₀ ) (1)
K = K ₁ + K ₁ (1-σ / σ ₀ ) (2)
I = apH _m + b (3)

Here, I _sp is the target SC value (units), I ₀ which is the set SC value is the SC value when pH _m = pH ₀ from Equation (3) of the SC calibration curve, and σ ₀ is when the SC calibration curve is created The raw water conductivity, pH ₀ is the mixed water pH obtained in the batch test, σ is the current raw water conductivity, and pH is the current raw water pH. K ₁ is a pH-SC conversion coefficient (= ΔSC / ΔpH) which is obtained from a trial and error method and shows an SC value which changes per unit pH, and K is a pH-SC conversion coefficient taking into account the change in conductivity in K _1. It is. Note that K ≧ 0, K ₁ ≧ 0, and I ₀ <0. In the case of alkaline raw water, the raw water pH is larger than pH _0, which is one of the mixed water pH _m after the addition of PAC, and pH> pH ₀ . The K value can also be obtained from an automatic measurement method. A set SC value I ₀ which is an SC value when pH _m = pH ₀ is obtained from Equation (3), I ₀ is substituted into Equation (1), and automatic operation is performed with K = 0, whereby the K value is obtained. Formula (2) will be described later.

Equation (1) is obtained when σ = σ ₀ .
I _sp = I ₀ + K ₁ (pH−pH ₀ ).
When σ <σ ₀ , the river water is diluted with rain, and the electrical resistance of the water increases. For this purpose, the target SC value is increased, and the coagulant injection rate is increased even at the same colloid concentration.
I _sp = I ₀ −I ₀ (1−σ / σ ₀ ) + {K ₁ + K ₁ (1−σ / σ ₀ )} (pH−pH ₀ )
Here, the SC value is the amount of current, and from the Ohm's law, the SC value decreases as the conductivity increases, and the SC value increases as the conductivity decreases. As the agglutination proceeds, the flow potential (= I ₀ / σ ₀ : dimension mV) becomes constant, so that using I ₀ / σ ₀ = I / σ = constant makes it possible to correctly cope with changes in conductivity. It became.

Since the scale of the SC meter is amplification gain (gain) X1 and a scale of ± 250 is used, I ₀ is negative, meaning that I ₀ becomes larger is closer to +250, and I ₀ becomes smaller. It means approaching 250.

In the case of σ> σ ₀ , it occurs when the river water becomes drought, but the electric resistance value becomes small, and conversely the target value is made small.
I _sp = I ₀ −I ₀ (1−σ / σ ₀ ) + {K ₁ + K ₁ (1−σ / σ ₀ )} (pH−pH ₀ )
I _sp moves to the −250 side, and K <K ₁ .

This device is intended for control of water sources where σ <σ ₀ during rain and σ> σ ₀ during drought, and flocculant control becomes difficult when there are multiple water sources and the water intake location is a confluence. There are many.

As shown in FIG. 2, according to this embodiment, the target SC value I _sp is corrected in consideration of the raw water conductivity σ and the raw water pH. The pH of the water mixture is basically neutralized to the target pH of pH ₀ (in this case, by PAC). Therefore, (pH-pH ₀ ) is the flocculant (PAC) injection rate. I _sp is obtained by adding Ix, which is a vector and multiplied by the pH-SC conversion coefficient K, to the conductivity term.

  Thus, an appropriate target SC value can be determined even when the raw water conductivity and pH change.

"How to find an SC calibration curve"
The basic formula (3) is called an SC calibration curve. In I = a · pH _m + b which is the basic formula (3), a is the pH-SC gradient (different from the K value) of the basic formula (3) obtained from the negative regression equation of the pH of the mixed water and the SC value. Yes, b represents the y-intercept constant (SC: units) of the basic formula (3) obtained from the negative regression equation of the pH of the mixed water and the SC value, and is the minimum SC value when the injection rate of the flocculant is zero.

Further, I = a · pH _m + b which is the basic formula (3) represents the correlation between the pH of the mixed water and the SC value, and the correlation coefficient in the basic formula (3) as the SC calibration curve is R ² = 0.95. The above is desirable.

  In order to obtain this SC calibration curve, when the raw water pH and the raw water conductivity σ (μS / cm) are stable, the PAC injection rate is changed by 4 to 5 points and obtained from the regression equation.

“Set SC value I ₀ to pH correction”
Here, a vector amount Ix necessary for control represented by ΔpH = (pH−pH _m ) is shown in FIG. FIG. 2 is a control principle diagram when pH _m = pH ₀ . Thus, the pH is on the x-axis and the SC value is on the y-axis. In this case, ΔpH = 0 depending on whether the raw water pH is lowered or the raw water pH is decreased by PAC.

The pH ₀ means the set water pH of the mixed water, which is the mixed water pH at the PAC injection rate (PAC ₀ ) obtained by the batch jar test (satisfying the supernatant turbidity target value). Substituting pH ₀ into equation (3) to obtain I ₀ . If I ₀ is obtained, point B in FIG. 2 is automatically selected. FIG. 2 is an assumption diagram when pH ₀ = 7.3.

On the other hand, in the SC meter, the SC meter ± scales are arranged so that all the SC calibration curves pass through the singular point A (pH 7.0, 0). At point A (pH 7.0, ₀ ), point B ((7.3, I ₀ ), and point C (7.3, ₀ ), it becomes stationary and becomes an eigenvalue, which is the SC dose used. Since Eq. (3) passes through AB, the SC calibration curve is inserted into the control if point I ₀ is determined, and point B moves up and down the y-axis with the raw water conductivity.

  On the other hand, as the raw water pH increases or decreases, the point D also moves horizontally on the x axis. Since the point A is fixed and the points B and D move up and down and left and right, the basic formula (3) exists infinitely. Actually, when the basic formula (3) is obtained every day, a different formula is obtained each time. Since the SC value is a relative value, the PAC injection rate has the same result because it moves relatively the same regardless of which formula is used. There is no need to change every day.

If the point C is determined, the point A & C does not move. Therefore, the ΔABC and ΔBCD triangles can be calculated by holding the appropriate I _sp by the vector indicating the size. ΔABC indicates conductivity control, and ΔBCD indicates pH control. The vector BC shows the effect of conductivity, whereas that of pH is the vector DE. This is shown in equation (4).

I _sp = vector BC + vector DE = basic formula (1) (4)

  It was confirmed that the value of point A basically converges to point A (pH 7.0, 0) although it differs depending on the SC calibration curve. Although it differs depending on the operation, it basically converges to point A (pH 7.0, 0).

Although point B may be on the + side, at this time, when vector BC <vector DE, I _sp ≧ 0 holds.

PAC ₀ , pH ₀ , I ₀ , and σ ₀ selected at start-up to use the target SC value are called set points (set values), but the target SC value I _sp is an appropriate PAC injection rate based on these. Keeps moving.

The pH-SC proportionality constant K ₁ related to pH is positive, unlike the gradient a of the SC calibration curve of the formula (3). Regardless of where the point D is, the control is used so as to converge to the point C. The method for obtaining the K value has been described above.

A vector CD shown in FIG. 2 (= raw water pH−7.3) forms a vector DE and has an SC value of I _x . The above description is omitted, and K (pH−pH ₀ ) in the basic formula (1).

"Find K value"
The pH-SC coefficient K (SCunits / pH) can be determined by a trial and error method or an automatic measurement method that satisfies PAC ₀ at the start.

  Furthermore, in this embodiment, the flocculant injection amount determination device performs continuous processing and continuous measurement on a certain amount of raw water by means of the sampling pump 40 (the flow rate may be confirmed even under natural flow). Since the reaction time can be made constant while compensating for the shortcomings of the batch jar test, the precise flocculant injection rate can be determined by controlling the flocculant injection amount based on the target SC value.

In FIG. 2, I _x increases as the pH is greater than pH ₀ , as indicated by the straight line indicated by + K ₁ . On the other hand, if the pH is pH ₀ smaller than, I _x increases as the pH as a straight line represented by -K ₁ is small.

"Determination of K1 (1)"
FIG. 3 shows the experimental results of the SC calibration curve showing the relationship between the pH of the mixed water and the SC value when the automatic operation of the apparatus 200 is stopped, the operation is switched to the manual operation, and the addition amount of PAC is changed. Thus, it was found that the raw water at this time had a relationship of I = −108.8 pH _m +756.8. The correlation coefficient R ² at this time was 0.9857. The target value of the mixed water pH _m is obtained by a jar test. When pH _m = pH ₀ = 7.3, I ₀ is obtained by substituting it into this correlation equation. Since I _sp is determined from the equation (1), K is increased or decreased so as to be PAC ₀ by trial and error, and K is obtained. When the target pH _m = pH ₀ is not reached by operating the equation (1), the K value is obtained by back calculation.

The PAC injection rate obtained from the jar test results varies depending on the measurement, but pH ₀ is almost the same. Therefore, pH ₀ is substituted into the basic equation (1) to obtain I ₀ . The K value is obtained by a thought-and-error method. With reference to PAC ₀ , K = 40, 30, 25, 20, and 10 are changed to obtain the optimum value.

As the operating conditions of this automatic jar test apparatus, pH ₀ = 7.3, I ₀ = −67, σ ₀ = 150 μS / cm, and automatic operation was performed with K ₁ = 25 from the trial and error method. The results are shown in Table 1.

Since it corresponds to the time of drought, use the average value in Table 1, and from the basic formula (2),
K = 25 + 25 * (1-1169.1 / 150) = 25 + 25 * (− 0.1273) = 21.8 (units)
I _sp = −67 − (− 67) * (1-1169.1 / 150) + 21.8 * (8.0−7.3)
= −67 − (− 67) * (− 0.1273) + 21.8 * (0.7) = − 67−8.5 + 15.26 = −60.24 (units). The indicated target SC value and the actually measured SC value were substantially the same value. It was estimated that K = 20 (ΔSC / ΔpH). Moreover, although it was a little high at pH _m = 7.4, PAC was also a reasonable value with an average of 30.6 mg / L.

"Determination of K value (2)"
As described above, the K value can be obtained by a trial and error method. However, the K value can also be obtained from automatic operation with K = 0.

(Basic formula)
The basic formula has been described above, but is shown below again. The experiment is performed with K = 0 in the equations (1) and (2), and the characteristic of the K value is obtained from the result analysis.
I _sp = {I ₀ −I ₀ (1−σ / σ ₀ )} + K (pH−pH ₀ ) (1)
K = K ₁ + K ₁ (1−σ / σ ₀ ) (2)
I = a * pH _m + b (3)

(Procedure for obtaining K value)
Next, a procedure for obtaining the K value will be described.

1) to determine the start I ₀ is required SC calibration curve. Formula (3) is calculated | required by manual operation of an automatic jar test apparatus. When the PAC injection rate is increased with dose1, dose2, dose3, dose4, dose5, dose6, etc., the mixed water pH _m decreases and the SC value moves to the +250 side. When the correlation equation between the pH _m and the SC value at this time is obtained, Equation (3) is obtained. Equation (4) was obtained from this experiment. At this time, σ ₀ = 150 μS / cm.
I = −213.06 pH _m +1488.7 (4)

2) Substituting pH ₀ = 7.3 into equation (4) gives I ₀ = −67, but switches to automatic operation at K = 0.

3) In this automatic operation, the trend graph of FIG. 5 was obtained as data for two days. The operating conditions at this time are K = 0, I ₀ = −67, pH ₀ = 7.3, and σ ₀ = 150 μS / cm. The operation results are shown in Table 2. In this table, the raw water conductivity EC1, pH 1 raw water pH, are mixed water pH the (pH _m) described as pH 2.

4) The maximum pH _m , average pH _m , and minimum pH _m at this time were 7.8, 7.6, and 7.4, respectively. The corresponding SC values were -71.2, -74.3, and -77.7.

5) From the above results, the correlation equation between pH _m and SC value was obtained as Equation (5).
I = 16.25 pH _m -197.9 (5)

6) Although it was estimated that K ₁ = 20 in the trial and error method, K = 16.25 was obtained from the equation (5). Substituting it into equation (3), we obtain K ₁ = 18.3.

(Operation result of K = 18.3)
The trend graph of FIG. 6 is operated at K = 18.3. Further, I ₀ = −67, pH ₀ = 7.3, and σ ₀ = 150 μS / cm. Although the control was good, the average pH _m = 7.35 (minimum value 7.2 to maximum value 7.54) was slightly larger than the design value. The operation results are shown in Table 3. In this table, the raw water conductivity EC1, pH 1 raw water pH, are mixed water pH the (pH _m) described as pH 2.

(Automatic measurement of K value)
In the trend graph of FIG. 5, what happens when K = 0 is not necessarily known from the beginning. Considering the definition of the K value anew from the principle diagram, if pH ₀ = 7.3, I ₀ = −67 is determined from equation (3). It was discovered that the pH-SC value conversion coefficient (K value) when this is automatically controlled and maintained at pH _m = pH ₀ = 7.3 can be obtained from the SC gradient of FIG. 7 or formula (5). FIG. 7 is a plot of the relationship between the mixed water pH _m and the SC value, and showed an SC gradient = 16.25. This is clearly different from the SC slope in equation (4). The K value was initially thought to have a negative slope, but was wrongly positive.

  Color colloids that could not be detected by the turbidimeter flowed in. At this time, the PAC injection rate increased by 10 mg / L or more than usual, and the pH of the mixed water decreased to 7.0 to 7.3.

(Application of K = 0 to alkaline raw water)
Equation (5) shows that when the raw water colloid concentration is low (turbidity of 5 degrees or less), the K value is proportional to the mixed water pH (or raw water pH) and I ₀ increases. In order to reduce PAC, the raw water pH may be lowered. For this purpose, a method in which CO ₂ or the like is mixed with raw water when the pH of the raw water is high and the peak is cut is already employed. In the basic formula of the automatic jar test apparatus at this time, it is preferable to perform automatic operation with K = 0.

"Summary of flocculant injection control by SC value"
The flowing current (SC value = streaming current: units) is a micro-floc surface charge converted to a current value, although it is a relative value (SC value varies depending on the display range of the amplification factor and measurement value: dimension mA). Follow the law. In this embodiment, the electrical resistance of water is obtained from the conductivity of water, and a calibration curve is obtained from the relationship between the pH of the admixed water and the SC value. The target SC value I _SP (units) is calculated using the appropriate flocculant injection rate PAC ₀ and the appropriate pH ₀ determined in the jar test, and the flocculant is injected so as to match the current SC value. In a normal case, if the mixed water pH maintains the initial set value pH ₀ , the correct control is performed. Although it may be less than that, the appropriate injection rate can be calculated. The amount of water was kept constant so that a calibration curve experiment could be performed at any time, and it was cut off from the water purification plant facility to create a compact continuous flocculant injection rate control device. Since the SC meter reacts only with the colloid, measurement of raw water turbidity etc. is unnecessary, and the turbidimeter is excluded from the control. Further, the slow stirring is omitted because it is not necessary to confirm with the flocculant injection rate determining device if the set pH ₀ of the PAC ₀ injection rate is appropriate.

  In addition, according to the present embodiment, it is possible to accurately define the set points (plurality) at the start point at which the control is started, match the dimensions of the basic formula, and cope with when the set value increases or decreases.

"Control when pH is low with alkaline raw water"
Here, when the raw water pH is high, the term of K (pH−pH ₀ ) in the above formula (1) is important. On the other hand, when the raw water pH is relatively low, the importance of this K (pH-pH ₀ ) term is low. For example, if pH = pH ₀ , this term is not necessary. Even when the raw water pH is high, the pH can be lowered by injection of carbon dioxide gas or the like. Therefore, when the raw water pH is 8 or less, it is preferable to operate with K = 0.

That is, the set SC value I ₀ is obtained by substituting pH ₀ into the equation (3) of the SC value calibration curve. I _sp = I ₀ −I ₀ (1−σ / σ ₀ ) (6)
, The target SC value (flow current value) is determined and the flocculant injection amount determination device is operated to determine the injection rate of the flocculant (PAC). At this time, the pH meter of the raw water tank becomes unnecessary for control.

"Example of automatic operation"
The raw water was supplied to the raw water tank 42 under the natural flow from the water sampling valve of the A water purification plant conduit, and was fixed to the drain tank from here with the water quantity Q = 26.4L / min and two inflow control valves. The flow rate was measured in the raw water tank.

  A commercially available PAC packaged in a 20 L bag was placed in a 20 L drug tank 52 and injected into the raw water by a drug pump 54 which is a submerged pump of the type in which the suction port is immersed in the liquid. The performance of this pump was able to accurately discharge the minimum PAC injection rate of this device, which was confirmed as a good correlation coefficient. The drainage from the drainage tank 60 was returned to the landing well 10 of the A water purification plant by a line pump.

  The flocculant (PAC) was provided with a back pressure valve and was dropped from the top of the inlet pipe 40φ from the raw water tank 42 to the rapid stirring tank. The inflow pipe is discharged at the lower part of the rapid stirring tank 50, stirred and mixed by the upward flow, over the overflow weir, and flows down to the drainage tank 60 via the SC meter 58 provided downstream thereof.

The controller 56 has a PID proportional controller and continues and holds the flocculant injection so that the SC value sent from the SC meter 58 matches the target SC value I _sp calculated from the mixed water pH and the raw water conductivity σ. By doing so, proper injection that is proportional to the colloid concentration and consumed for pH neutralization is performed.

Here, the microflock surface charge of the mixed water can be set by (pH ₀ , I ₀ ) and can be made constant by adjusting the PAC injection rate. The discharge amount of the PAC pump is controlled so that the target SC value and the mixed water SC value coincide. The maximum infusion rate of the drug pump 54 with respect to the treatment amount Q (= 26.4 L / min) is 180 mg / L. The rotation speed is calculated from the ratio and the PAC is automatically controlled.

  The water quality, SC value, target SC value, etc. are collected in a data logger and displayed and recorded on a PC. The capacities of the raw water tank, the rapid stirring tank and the drainage tank are 30, 150 and 30 L, respectively, the residence time is about 8 minutes, and the residence time of the rapid stirring tank 50 is 5.7 minutes. The stirrer is 60W, the drainage pump is 200V x 250W, and the entire facility has an AC 200V and a maximum electric capacity of 8.64A. The entire device was placed in a prefab with a width of 1.8m, a length of 3.6m, and a height of 2.4m, and the room temperature exceeded 40 degrees in the summer with a ventilation fan and electric fan. I endured it.

FIG. 4 shows a trend graph of experimental results in which the mixed water pH reached the target average of 7.3. This figure shows changes over time of raw water pH, raw water conductivity, mixed water pH (pH _m ), target SC value (I _sp ), measured SC value (I), and PAC addition amount (PAC). This data is shown in Table 4.

Thus, the state where the target SC value is corrected and the addition amount of the flocculant is updated with changes in the raw water pH is shown. By such control, the micro floc state could be set to a desired appropriate one. In this way, the PAC injection rate and the mixed water pH similar to the jar test can be maintained with the determined flocculant injection rate, and effective coagulation treatment can be continued.

"SC calibration curve of automatic jar tester for acid raw water"
FIG. 3 shows an example of the experimental results of the SC calibration curve of the alkaline raw water. The SC calibration curve of the acidic raw water is prepared by injecting a certain amount of NaOH or the like into the raw water and adjusting the pH, for example, by adjusting the acidic raw water pH to 7.75 (or alkalinity 25 mg). / L) to obtain an SC calibration curve. Obtain pH ₀ by a manual jar test, obtain I ₀ from the SC calibration curve, and perform automatic injection of PAC so that the SC value of mixed water and I ₀ coincide.

At this time, it can be handled as K = 0. Only the conductivity is controlled.
I _sp = {I ₀ −I ₀ (1−σ / σ ₀ )} ± K (pH−pH ₀ ) (1)
K = K ₁ + K ₁ (1−σ / σ ₀ ) (2)
I = a × pH _m + b (3)
In the basic formula, the second term on the right side of formula (1) and formula (2) are not required, and the pH-adjusted raw water is controlled only by formula (4) and formula (3).
I _sp = I ₀ −I ₀ (1−σ / σ ₀ ) (4)
I = a × pH _m + b (3)

"Flow for acidic raw water"
The flow of the automatic raw tester device for acidic raw water is the same as that in the case of alkaline raw water described above, but in order to make the concentration of alkaline agent such as NaOH uniform in acidic raw water, a stirrer similar to a rapid stirring tank is used. Required for tanks. If the pH-adjusted raw water can be obtained from the actual plant (water purification facility), a stirrer is not required in the raw water tank. Needless to say, the pH must be made uniform when CO ₂ for adjusting the pH of the alkaline raw water is injected.

  The pH-adjusted raw water refers to raw water that is completely mixed by injecting NaOH or the like into the raw water for lack of alkalinity or pH adjustment.

  10 landing wells, 12 rapid agitation ponds, 14 drug tanks, 16 drug pumps, 18 flow meters, 20 control devices, 22 floc formation ponds, 24 coagulation sedimentation ponds, 26 rapid filtration ponds, 28 disinfection / distribution ponds, 40 sampling pumps, 42 raw water tank, 44 conductivity meter, 46 pH meter, 50 rapid stirring tank, 52 chemical tank, 54 chemical pump, 56 control device, 58 SC meter, 60 drainage tank, 62 pH meter, 100 water treatment system, 200 flocculant Injection volume determination device.

Claims (7)

PH measuring means for measuring the pH of raw water;
A conductivity measuring means for measuring the conductivity of the raw water;
The initial target flow current value, which is the target value of the flow current value indicating the charge state of the micro floc in the mixed water after mixing with the flocculant, determined based on the raw water having a specific pH and conductivity, A target flowing current value calculating means for calculating a target flowing current value by correcting based on the pH and conductivity measured by the rate measuring means;
A mixing means for mixing the flocculant in the raw water with a certain residence time;
A flow current value detection means for detecting the flow current value of the mixed water after mixing the flocculant by the mixing means;
An injection control means for determining a flocculant injection amount in the mixing means so that the detected flow current value becomes a predetermined value, and controlling the flocculant injection amount in the mixing means;
Have
A flocculant injection amount determining apparatus that determines the flocculant injection amount determined by the injection control means as a target flocculant injection amount. The flocculant injection amount determination device according to claim 1,
The target flow current value I _sp is determined based on the mixed water pH at the time of injecting the proper coagulant selected from the result of the jar test on the raw water, the reference raw water conductivity, the measured raw water pH, and the measured raw water conductivity. , A flocculant injection amount determination device for calculating based on The flocculant injection amount determination device according to claim 1,
The target flowing current value I _sp is determined by mixing the pH of the proper flocculant injected from the result of the jar test on the raw water (pH ₀ ), the reference raw water conductivity (σ ₀ ), and the measured raw water pH. (PH), measured raw water conductivity (σ), and coefficient K,
I _sp = I ₀ −I ₀ (1−σ / σ ₀ ) + K (pH−pH ₀ )
The flocculant injection amount determination device calculated by A flocculant injection amount determination device according to claim 3,
The above K is a coefficient for converting K ₁ into the amount of change in flowing current value with respect to the amount of change in pH.
K = K ₁ + K ₁ (1−σ / σ ₀ )
The flocculant injection amount determination device determined by A flocculant injection amount control system for a water treatment facility having the flocculant injection amount determination device according to any one of claims 1 to 4,
Inflow water is supplied to the flocculant injection amount determination device as raw water, and the flocculant injection amount output from the flocculant injection amount determination device using the raw water is used to inject the flocculant into the inflow water. Coagulant injection amount control system for water treatment facilities that control the amount and perform flocculation treatment. A conductivity measuring means for measuring the conductivity of the raw water;
Conductivity obtained by measuring the initial target flowing current value, which is a target value of the flowing current value indicating the charged state of the micro floc in the mixed water after mixing with the flocculant, determined based on the raw water having a specific conductivity measured by the conductivity measuring means. A target flowing current value calculating means for correcting the ratio based on the rate and calculating a target flowing current value;
A mixing means for mixing the flocculant in the raw water with a certain residence time;
A flow current value detection means for detecting the flow current value of the mixed water after mixing the flocculant by the mixing means;
An injection control means for determining a flocculant injection amount in the mixing means so that the detected flow current value becomes a predetermined value, and controlling the flocculant injection amount in the mixing means;
Have
A flocculant injection amount determination apparatus that uses the flocculant injection amount determined by the injection control means as a target flocculant injection amount. The flocculant injection amount determination device according to claim 6,
The target flowing current value I _sp is based on the reference raw water conductivity (σ ₀ ), the measured raw water conductivity (σ), and the reference SC value (I ₀ ).
I _sp = I ₀ −I ₀ (1−σ / σ ₀ )
The flocculant injection amount determination device calculated by