JPH0415002B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a chemical injection control method in water purification treatment.

Conventional techniques and their problems As a conventional chemical injection control method in water purification treatment, an improved feedback control method, as shown by the solid line in Fig. 2, has been proposed (for example, in Japanese Patent Application Laid-Open No.
54-93848). This improved new chemical injection control method processes raw water taken from rivers, etc. into a settling basin 1 that removes sand, garbage, etc., a water intake flowmeter 2 that measures the amount of water intake, and a mixing tank that performs chemical injection and rapid stirring. Pond 3, floc formation pond 4 where flocs are formed and grown;
When purifying the sedimentation tank 5, which performs sedimentation and separation of the growing flocs, the water quality measurement position is changed from the outlet of the sedimentation tank 5, which is generally performed with conventional feedback control, to the inlet of the sedimentation tank 5 or the floc. We are moving to the final stage of Formation Pond 4. The measured value measured by the water quality measuring device 6 at this measurement point is fed back to the data processor 7 to determine the injection rate, and then the multiplier 8 calculates the above injection rate and the raw water flow rate from the water intake flow meter 2. The injection amount is determined by the multiplication, and the drug injection device 9 is controlled according to this injection amount, and a predetermined amount of the drug is injected into the mixing basin 3 through the device 9.

According to this improved new feedback control method, the time delay of feedback can be reduced to 1/5 of the 4 to 8 hours of the conventional old feedback control method.
Although it has the advantage of being able to shorten the time to about 1/3, it still has many problems as follows.

In other words, the new improved feedback control method is a method in which the water quality at the outlet of the sedimentation tank 5 is predicted and corrected based on the condition of the treated water at the inlet of the sedimentation tank 5 or at the final stage of the floc formation tank 4. In water purification equipment, the quality of floc formation may change during the rapid or slow agitation process in the mixing basin or flocculation basin, and the flow rate or flow velocity distribution in the settling basin may be uneven, or the sedimentation efficiency may be affected. The floc sedimentation area changes due to changes, and these changes affect the floc sedimentation in the sedimentation basin, so the correlation between water quality at the inlet and outlet of the sedimentation basin becomes quite unstable. There is a limit to the predictive correction of water quality based on such unstable correlations, which poses a problem in the accuracy of feedback control. Furthermore, the time delay for feedback has been reduced to 1/2 of the conventional 4 to 8 hours.
Although it can be shortened to about 5 to 1/3, it still causes a time delay of about 1 to 2 hours. According to the water supply facility design guidelines, the residence time in the water treatment facility is
~5 minutes, floc formation pond 20-40 minutes, sedimentation pond 3-5
This exceeds the retention time in the floc formation pond, so if the quality of the raw water changes, such as during rainfall, a considerable amount of turbid water that does not reach the target turbidity will flow out. Figure 3 is a graph showing the relationship between chemical injection rate and treated water turbidity.It is ideal and most economical to perform chemical injection at the lowest point _a1 of the injection rate. If there is such a time delay, for safety reasons, it is necessary to inject medicine at position _A2 , which has a higher injection rate than the lowest point _A1 , and
This increases consumption of expensive drugs and becomes uneconomical.

For such new feedback control, there is a known method in which the quality of the raw water is measured in advance with a water quality measuring device 10, and the injection rate is determined based on the reference injection rate formula based on the measured value, as shown by the broken line in FIG. There is also a proposal to combine so-called feed forward control, but this control method not only complicates the system, but also requires a large number of calculations for a wide range of water quality changes in order to create the standard injection rate formula required for forward control. It is necessary to collect actual measurement data, which requires a great deal of time and effort. Furthermore, even if these two control methods are combined, the problems of both control methods still remain and the problem cannot be solved.

The present invention has been made with the aim of eliminating such conventional problems.

Means for Solving the Problems The present invention provides a method for introducing chemicals into raw water from a floc formation pond to a sedimentation basin in an actual water purification facility, forming flocs, and then performing sedimentation separation of the flocs. At the stage before the pond, part of the above raw water is introduced into a continuous shear tester with the same chemical injection rate as in the actual water purification equipment, and the retention time is 20 to 20 minutes.
In the case of a floc formation pond in an actual facility that takes 40 minutes, purification is performed in a short time of about 5 to 15 minutes, and the water quality of the treated water is measured at the outlet of the tester, and based on this measurement value, the treatment in the actual facility is performed. The present invention relates to a chemical injection control method in water purification treatment, which is characterized by controlling chemical injection of raw water.

Embodiment An embodiment of the present invention will be described below based on the accompanying drawings.

An embodiment of the chemical injection control method according to the present invention is shown in FIG. A portion of the raw water is taken, and the taken raw water is led to a continuous jar tester 11, and is continuously tested for a short time, for example, with a residence time of 5 to 15 minutes in the case of the floc formation pond 4, where the residence time is 20 to 40 minutes. is purified.

The continuous jar tester 11 is a scaled-down version of the actual water purification equipment, and is composed of a floc formation basin section 11a and a sedimentation basin section 11b, both of which are scaled-down versions of the actual water purification facility.

The scale of the tester 11 is 1/500 to 1/100,000, preferably 1/3,000 to 1/100,000 of one pond of the actual equipment in terms of capacity.
It is about 1/30,000, more preferably about 1/10,000.
If the length, width, and depth of the tester 11 are equally reduced in proportion to the capacity ratio, the depth will become too small and there is a risk of problems in terms of purification performance, so the depth has nothing to do with the capacity proportion. First, the width and length are determined to be within a range that does not interfere with the purification process, for example, 20 to 50 cm, and the width and length are preferably reduced by the same ratio so that the capacity ratio can be obtained.

A stirring blade 11a ₁ is provided in the floc formation pond portion 11a of the tester 11 as in the actual equipment, and the area, number and rotation speed of the stirring blade 11a ₁ are as follows.
It is determined as appropriate so that stirring power comparable to that of the actual equipment can be obtained. The stirring means may be either a water flow type or a mechanical type.

Preferably, the sedimentation basin section 11b of the tester 11 has a sedimentation efficiency comparable to that of the actual equipment. Appropriate measures may be taken.

By arranging the floc formation basin section 11a and the settling basin section 11b in series, a continuous jar tester 11 having reduced functions of the actual equipment can be obtained. It should be noted that the capacity of the tester 11 should be larger from a performance standpoint, but this would result in high equipment costs, including securing land, so as long as there is no problem in terms of performance,
It is better to have as small a capacity as possible, and based on this, the scale of capacity is 1/10 of the capacity of the actual equipment.
Around 000 is appropriate.

The flow rate of raw water guided to the continuous jar tester 11 is determined by the degree of reduction in capacity, and in principle may be made proportional to the degree of reduction in capacity, but is not necessarily limited to this, and may be proportional to the capacity of the tester 11. Any amount is sufficient. In addition, it is desirable to adjust the above flow rate according to changes in water intake flow rate.
It is not necessarily limited to this.

The raw water introduced into the continuous jar tester 11 is purified for a short time, for example, in the case of the floc formation pond 4, which has a residence time of 20 to 40 minutes, the residence time is about 5 to 15 minutes. Since the above-mentioned jar tester 11 has a reduced function of the actual equipment, and the processing flow rate is also reduced by the reduced capacity, purification can be performed in a short time of 5 to 15 minutes to a degree of purification close to that of the actual equipment.

The quality of the treated water from the continuous jar tester 11 is measured by a water quality meter 12, and the measured value is fed back to the data processor 7 for determining the injection rate, similar to the feedback control described above.

Since the function of the continuous jar tester 11 is reduced, raw water is purified using the same coagulation and sedimentation mechanism as in the actual equipment, and the quality of the treated water obtained from the tester 11 is the same as that of the actual equipment. This directly reflects the quality of water treated at the facility. Based on the quality of the treated water from the tester 11, the quality of the treated water in the actual facility can be accurately and reliably predicted and corrected.

It is most desirable that the continuous jar tester 11 has the same purification performance as the actual equipment, but in reality, there is a difference in water quality between it and the actual equipment due to the reduction in capacity and processing time. Since the coagulation and sedimentation mechanism of Tester 11 and the actual equipment are the same,
By understanding this correlation in advance, it is possible to accurately predict and correct the water quality in the actual facility based on the water quality in the tester 11. For example, if the turbidity of the water treated with the jar tester 11 is T ₁ , α ₁ T ₀
It can be converted to +α ₂ (T ₁ −T ₀ ) ^x . However, T ₀ : Target turbidity of actual equipment α ₁ : Coefficient at low turbidity due to the degree of reduction of tester 11 α ₂ : Coefficient at high turbidity due to degree of reduction of tester 11 x:z Measurement from water quality measuring device 12 Coefficient for converting value into injection amount The above calculation formula is calculated in the data processor 7 to determine the appropriate injection rate.

The coefficient in the above calculation formula is a fixed value determined by the degree of reduction of the tester 11, and once determined, it can follow minute changes in the quality of raw water.

The treatment time of raw water in the continuous jar tester 11 should be as short as possible in order to shorten the time delay of feedback, but if it is too short, the prescribed coagulation and sedimentation treatment cannot be performed. Depending on the degree of reduction, 5 to 15
About a minute is appropriate.

The present inventors conducted research into which stage of the flocculation mechanism a time delay in drug injection is permissible in a flocculation pond with a residence time of 20 to 40 minutes, for example, during the early stages of flocculation. 5~
It was found that a time delay of about 15 minutes had virtually no negative effect on the aggregation mechanism.

Therefore, when raw water is treated in the continuous jar tester 11 for a short period of time, for example, in the case of the floc formation pond 4 with a residence time of 20 to 40 minutes, for 5 to 15 minutes, there is a time delay of 5 to 15 minutes in the feedback. Regardless of the occurrence of such occurrences, there is virtually no adverse effect on actual water purification equipment, and it is possible to sufficiently cope with sudden changes in the quality of raw water such as during rainfall.

In the present invention, as shown by the dashed line in Fig. 1, a part of the raw water is taken out from the part near the inlet of the settling basin 1, and this is used in an actual facility for chemical injection and rapid stirring. If it is introduced to the tester 11 via the mixer 13 whose function is reduced, the residence time in the settling tank 1 (for example, 10 to 20 minutes) and the mixing tank 3
The purification process in the tester 11 can be completed using the residence time (for example, 1 to 5 minutes) in the tester 11. Therefore, if this is done, the installation of the conduit and the mixing basin 13 will cause a slight increase in equipment costs, but since there will be no time delay in optimally injecting the chemicals, it will be possible to achieve even higher accuracy. Chemical injection control becomes possible.

Effects According to the drug injection control method of the present invention, the following effects can be obtained.

B. In the continuous jar tester, raw water is purified using the same coagulation-sedimentation mechanism and the same chemical injection rate as in the actual equipment, so the water quality from this tester can accurately measure the water quality in the actual equipment. In addition, the processing time with the above tester is short, and the initial stage of floc formation in the actual floc formation pond, for example, the residence time of 20~
In the case of a 40-minute floc formation pond, the time does not exceed 5 to 15 minutes, so there is virtually no time delay in chemical injection control, and highly accurate chemical injection control can be achieved. In addition, since only one system of the tester is required, the tester is compact and the equipment cost is low.

(b) Since drug injection control can be performed with high precision, drug injection can be performed at the minimum injection rate, that is, the lowest point _a1 shown in Figure 3, and the drug consumption can be greatly reduced, for example at the second
It can save 30 to 40% compared to the conventional method shown in the figure.

C. It does not require the creation of a "standard injection rate formula," which requires a great deal of time and effort, as seen in conventional control methods, so it can be applied immediately to newly constructed water treatment plants.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a conventional example, and FIG. 3 is a graph showing the relationship between turbidity and injection rate. In the figure, 1 is a settling basin, 2 is an intake flowmeter, 3 is a mixing basin, 4 is a floc formation basin, 5 is a settling basin,
6, 10, and 12 are water quality measuring instruments, 7 is a data processor, 8 is a multiplier, 9 is a chemical injection device, and 11 is a continuous jar tester.

Claims (1)

[Claims] 1. While injecting chemicals into the raw water, the raw water is guided from the floc formation pond to the settling basin in the actual water purification equipment, and when forming flocs and then sedimentation and separation of the formed flocs, the raw water is In the case of a floc formation pond of an actual facility, a part of the water was introduced into a continuous shear tester with a reduced function of the actual water purification facility under the same chemical injection rate as the actual water purification facility, and the residence time was 20 to 40 minutes. In addition to purifying the water in a short time of about 5 to 15 minutes, the water quality of the treated water is measured at the outlet of the tester, and chemical dosing of the raw water in the actual equipment is controlled based on this measured value. Chemical injection control method in water purification treatment.