JP4309645B2 - Flocculant injection control method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flocculant injection control method and apparatus for injecting a flocculant after injecting the flocculant into water flowing into a filter basin after the precipitation treatment in a water purification plant.
[0002]
[Prior art]
In general, in a water purification plant, raw water is taken from a water source such as a river or a reservoir, and the raw water is processed by five unit processes of aggregation, flock formation, sedimentation, filtration and sterilization. As a result, suspended solids and colloids are removed from the water to be treated, and bacteria and the like are rendered harmless and supplied to consumers as clear tap water.
[0003]
In such a series of turbidity treatment by aggregation, floc formation, precipitation, and filtration, a method using a flocculant is common. As the flocculant, inorganic metal salts such as iron and aluminum are usually used. In addition, the flocculant is affected by various physical and biochemical effects, and the optimum flocculation condition is based on a complex equilibrium determined by many factors. Therefore, the injection amount of the flocculant is affected by factors such as the type and concentration of the flocculating component in the raw water, temperature, pH, coexisting components, and stirring conditions. Under the optimum conditions, flocculation and floc formation are performed smoothly, and the generated floc is precipitated and removed together with turbidity components in the raw water in the next precipitation process, and a small amount of remaining fine floc is completely removed in the next filtration process. Removed.
[0004]
By the way, according to the “Cryptosporidium Provisional Countermeasure Guidelines for Waterworks” notified by the Ministry of Health and Welfare (current Ministry of Health, Labor and Welfare) in October 1996, the turbidity at the outlet of the filtration basin is constantly grasped, and the turbidity at the outlet of the filtration basin is set to 0.1 It has been enacted to maintain the temperature below this level, and turbidity management at water treatment plants has become an important issue.
[0005]
However, if the coagulation conditions become severe due to the quality of raw water flowing into the water purification plant, floc formation may be insufficient. In this case, it has been reported that the removal efficiency of the next precipitation process and filtration process is lowered, and the turbidity at the outlet of the filtration basin becomes 0.1 degree or more.
[0006]
For example, as reported at the 52nd National Waterworks Research Conference (2001), in the case of the Murano Water Treatment Plant in Osaka, May (spring) and July to August (summer season) when pre-chlorination was completely stopped. ), An increase in turbidity at the outlet of the filter basin, estimated to be caused by picoplankton in the raw water, was observed. It has been reported that the turbidity of the filter basin periodically increases every day from the peak at night due to the amount of solar radiation and temperature, etc., and the optimum injection method is different from the normal flocculation treatment. .
[0007]
In such a case, it is considered effective to add a flocculant to the treated water at the outlet of the sedimentation basin, introduce it into the filtration process, and then perform flocculant treatment after laminating flocs on the surface of the filtration sand. Proposals have also been made (see, for example, Patent Document 1).
[0008]
[Patent Document 1]
JP-A-4-11905 gazette
[Problems to be solved by the invention]
However, in the conventional post-flocculating agent injection, the turbidity after coagulating sedimentation is detected and the injection rate of the flocculant is controlled, so there is little correlation with the turbidity at the outlet of the filtration pond, Unable to meet established turbidity standards.
[0010]
For this reason, manual injection is performed according to the judgment of the water quality engineer according to the appearance of the peak of the periodic turbidity increase described above, and there is a problem that it is difficult to optimize the injection rate while requiring labor for operation monitoring. It was.
[0011]
An object of the present invention is to provide a coagulant injection control method and apparatus capable of reducing the operation monitoring effort by automating the post-coagulant injection and optimizing the injection rate to satisfy strict turbidity standards. There is to do.
[0012]
[Means for Solving the Problems]
In the flocculant injection control method and apparatus according to the present invention, the turbidity of the water to be treated at the outlet of the filter basin of the water purification plant is detected, and the flocculant is injected into the inlet side of the filter basin according to the detected turbidity. When the turbidity increase rate is within the set range and the turbidity is equal to or greater than the outlet turbidity target value, the injection of the flocculant is started at a preset injection rate as a trigger, and the preset time After that, the injection is stopped .
[0014]
Further, in coagulant injection system GoSo location according to the invention is provided in the filtration basin outlet water treatment plant, a turbidity meter for detecting turbidity of treatment water flowing out from the filtration basin, to the inlet side of the filtration basin The flocculant injection device for injecting the flocculant into the water to be treated flowing into the filtration pond and the detected value of the turbidimeter are input, and the rate of increase is within a preset setting range, and the detected turbidity The first output unit on the condition that the degree is equal to or higher than the preset outlet turbidity target value, or the state of the detected turbidity of the turbidimeter is higher than the preset outlet turbidity target value, Output from the second output unit on condition that the preset time range has been continued, and the output from any one of the first output unit and the second output unit as an injection start command to the coagulant injection device and an arithmetic unit and a condition means that the coagulant injection device, before If you enter the injection start command, an aggregating agent, it may be injected preset time at a preset injection rate.
[0015]
In the flocculant injection control device of the present invention, the setting range of the turbidity increase rate preset in the calculation unit is 2.0 × 10 ^{−5 to} 15.0 × 10 ⁻⁵ per unit time. The preset outlet turbidity target value is 0.02 degree or higher, and the value higher than the outlet turbidity target value preset in the calculation unit is 0.04 degree and preset in the calculation unit. What is set so that the time range is 60 to 120 minutes may be used.
[0017]
Further, in the flocculant injection control device of the present invention, the calculation unit changes the injection rate of the flocculant injected by the flocculant injection device in response to the change in turbidity detected by the turbidimeter. Good.
[0018]
Further, in the flocculant injection control device of the present invention, a convex approximate curve is set in the calculation unit after approximating a change in turbidity, and the flocculant injection rate is calculated by this approximate curve. Good.
[0019]
In this case, a trigonometric function curve or a quadratic function curve may be used as the approximate curve.
[0020]
In these inventions, the turbidity of the water to be treated at the filter pond outlet of the water purification plant is monitored, the increase rate of the detected turbidity is within the set range, and the turbidity is equal to or greater than the target turbidity at the outlet. Or when the state of turbidity higher than the target turbidity value continues for a set time range, the injection of flocculant on the inlet side of the filter basin is started as a trigger. The turbidity of can be controlled to a value satisfying strict turbidity standards.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a flocculant injection control method and apparatus according to the present invention will be described with reference to the drawings.
[0022]
FIG. 1 shows a flocculant injection control device in a raw water treatment process in a general water treatment plant. FIG. 2 is a flowchart for explaining the flocculant injection control method in this embodiment.
[0023]
As shown in FIG. 1, raw water to be treated is taken into a water intake well 12 from a water source 11 such as a river or a water reservoir, and is introduced from the water intake well 12 through a water conduit A into a landing well 13. In the landing well 13, pH is adjusted as one of the coagulation conditions, and then introduced into a rapid agitation pond (hereinafter abbreviated as “rapid agitation basin”) 14 through the conduit B. Although not shown, the rapid agitation pond 14 is provided with a flocculant addition device, and a predetermined amount of the flocculant corresponding to the raw water treatment amount is added. Aggregation reaction and floc formation reaction occur due to the stirring action.
[0024]
A sedimentation basin 15 is adjacent to the rapid stirring basin 14, and flocs that grow large and have good sedimentation properties are settled and removed. Fine flocs that have not been removed in the sedimentation basin 15 are led out to the water conduit C together with the water to be treated. The water conduit C is connected to the inlet side of the subsequent filtration basin 16, and the flocculant is injected again into the water to be treated flowing into the filtration basin 16.
[0025]
That is, a flocculant injection device 17 is connected to the water conduit C, and a predetermined amount of the flocculant is injected into the water to be treated in the water conduit C via the flow meter 18. For this reason, a minute floc is formed in the water conduit C, and this minute floc further flows into the filtration basin 16 and is captured by the filtered sand. As a result, clear filtered water flows out from the outlet of the filtration basin 16 and is stored in the clean water basin 19 through the water conduit D.
[0026]
Further, a flow meter 21 is disposed in the water conduit C, and the flow rate of the water to be treated flowing into the filtration basin 16 is measured. Further, a turbidity meter 22 is disposed in the water conduit D and measures the turbidity of the water to be treated at the outlet of the filtration basin 16. Since this turbidimeter 22 is monitored so that the outlet turbidity of the filtration basin 16 is maintained at 0.1 degrees or less, a highly sensitive turbidimeter is used.
[0027]
The calculation unit 23 inputs the measurement values of the flow meters 18 and 21 and the turbidity meter 22, controls the flocculant injection device 17 based on the conditions described later, and treats the treated water flowing into the filter basin 16. A predetermined amount of flocculant is injected.
[0028]
In the above-described configuration, the flocculant is injected by monitoring the turbidity of the water to be treated flowing out from the outlet of the filter basin 16 using the measured value of the turbidimeter 22. If the raw water contains a large amount of components such as picoplankton, it is assumed that the outlet turbidity of the filter basin 16 periodically increases every day with a certain time zone (nighttime) as a peak.
[0029]
Therefore, by using the rate of increase in turbidity and the absolute value as an injection trigger, injection of the flocculant is started at a preset injection rate. That is, the calculating part 23 inputs the measured value of the turbidimeter 22, and calculates | requires the increase rate of turbidity from the value. The rate of increase in turbidity is calculated from the turbidity increased at a certain time interval, and the time interval can be arbitrarily set. According to the study by the present inventors, the interval is preferably about 10 minutes.
[0030]
The turbidity increase rate may be obtained from the turbidity slope at the future time based on the turbidity at the current time, or may be obtained from the turbidity slope going back to the past time.
[0031]
The injection of the flocculant is started when the increase rate thus obtained is within a preset range and the turbidity is equal to or greater than the outlet turbidity target value. In other words, the turbidity increase rate and absolute value are constantly monitored against the turbidity at the filter basin outlet of the water purification plant that periodically rises in units of one day at the peak of a certain time zone due to the amount of solar radiation and temperature changes. By doing so, optimal flocculant injection can be performed.
[0032]
Specifically, as shown in FIG. 2, an increase rate range (mesh portion) 231 that is a flocculant injection start condition is set in advance in the calculation unit 23. In addition to the turbidity increase rate, an absolute value of turbidity (which is also an outlet turbidity target value) 232 is set as a flocculant injection start condition. As described above, the turbidity increase rate (slope) based on the measured value is within the preset range 231, and the absolute value of the measured turbidity is the preset outlet turbidity target value 232. In addition, if it is determined that these are not instantaneous and have continued for a certain time by a time circuit (not shown), the condition means 233 and 234 detect that these conditions are satisfied. Then, when this condition is met as a trigger, a coagulant injection start command 235 is output to the coagulant injection device 17 to start injection of the coagulant into the water to be treated flowing into the filtration basin 16.
[0033]
Here, the range 231 of the turbidity increase rate per unit time of the filtration pond outlet turbidity which is a start condition for the flocculant injection is, for example, a lower limit of 2.0 × 10 ⁻⁵ and an upper limit of 15.0 × 10 ^−5. It is preferable that By setting the range in this way, it is possible to prevent the flocculant injection when the turbidity at the outlet of the filtration basin suddenly increases due to external factors such as washing of the basin. This value can be arbitrarily set according to the operation management policy of the water purification plant.
[0034]
The above figures are based on experimental values. That is, the outlet turbidity of the filter basin 16 is measured to control the flocculant injection rate at the inlet of the filter basin 16, and it is desirable to determine the rate of increase in turbidity in a shorter time. Even if the rate of increase is judged in a too long time, the water will flow so much by the time the injection is started, so there is no point in injecting much. Therefore, it was determined that the time was desirably 10 minutes and at most 50 minutes. On the other hand, since the minimum unit of the turbidimeter is 0.001 degree, the minimum value can be obtained from the following equation.
[0035]
0.001 / 50 = 2.0 × 10 ⁻⁵
Further, the maximum value is obtained by shortening the time. For example, when the 1 minute, 0.001 / 1 = 1.0 becomes a × ^{10 -3,} since the actual 1-2 minutes some characteristics on the variation of the saddle Medical instrument, it is determined from the data 7 It was a little weaker. As a result, the maximum value is obtained as in the following equation.
[0036]
0.001 / 7≈15 × 10 ⁻⁵
Here, the upper limit is set for the rate of increase in turbidity, as described above, in order to prevent the flocculant injection from being started due to a rapid increase in turbidity due to backwashing of the filter basin 16 or the like. That is, during the backwashing, the washing water is caused to flow through the filter basin 16 in a manner opposite to the normal flow, so that the sand rolls up. For this reason, filtration stops and the washed water is discharged to another system. The operation is resumed after the sand has sufficiently rolled up, but due to some operational malfunction, a sudden increase in turbidity is detected when part of the sand flows out to the treated water side when the operation is resumed. The The flocculant is injected before sand filtration, and for such a sudden increase in turbidity at the filter basin outlet side, there is no point in injecting the flocculant at the filter basin entrance. Because.
[0037]
Moreover, it is preferable that the absolute value 232 of the turbidity which a trigger works is 0.02 degree | times or more. This value is also the target turbidity at the outlet of the filtration basin 16, and can be arbitrarily set according to the operation management policy of the water purification plant.
[0038]
Next, another condition for starting the injection of the flocculant will be described. For example, the outlet turbidity of the filter basin 16 is 2. When it rises gently at an increase rate of 0 × 10 ⁻⁵ or less, or when it rises rapidly at an increase rate of 15 × 10 ⁻⁵ or more, the flocculant injection is not performed under the above-described conditions. Therefore, the flocculant is injected even when the absolute value of turbidity above a certain level continues for a certain period of time.
[0039]
In other words, the set value 236 of the turbidity absolute value and its duration 237 are set in advance in the calculation unit 23 as shown in FIG. The absolute value of the outlet turbidity measured by the turbidity meter 22 exceeds the set value 2 3 6, and outputs an injection start command 235 via the condition unit 234 on condition that continued its state set time 237 or more .
[0040]
In this case, the set value 236 of the turbidity absolute value is preferably larger than the exit target value 232, for example, 0.04 degree. This value can be set arbitrarily according to the operation management policy of the water treatment plant. The time for which the absolute value of turbidity continues is preferably about 70 minutes, and there is no problem as long as it is within the range of 60 to 120 minutes. This value can also be set arbitrarily according to the operation management policy of the water treatment plant.
[0041]
In this way, the turbidity at the outlet of the filtration basin 16 is agglomerated as a trigger when a state of a value (for example, 0.04) higher than the outlet turbidity target value (for example, 0.02) continues for a set time range. Agent infusion can begin.
[0042]
Here, since the condition means 234 is an OR condition, the condition is established according to the setting conditions 231 and 232, that is, when the turbidity increases and the turbidity increase rate (slope) falls within the setting range, and the setting condition When the conditions of 236 and 237 are satisfied, that is, when turbidity of a certain level or more continues for a set time or longer, injection of the flocculant can be started.
[0043]
The injection rate of the flocculant to be injected is set to a predetermined constant value, and this is injected for a preset time. The actual amount of flocculant injected is calculated from the inflow amount of the water to be treated into the filtration basin 16 measured by the flow meter 21. The method for stopping the injection of the flocculant is performed by setting a timer or time. That is, it is performed by starting a timer from the start of injection or by setting a certain time on the next day. The lower limit value of turbidity is preferably set according to this timer interval or stop set time.
[0044]
Although the injection rate of the flocculant is a constant value, the injection rate of the flocculant injected by the flocculant injection device 17 may be changed corresponding to the change in turbidity detected by the turbidimeter 22. Good.
[0045]
In this case, the turbidity at the outlet of the filter basin usually increases periodically with a peak at a certain time of day (usually midnight) as described above. In this case, the turbidity change is a convex curve, For example, it can be approximated by a trigonometric function curve or a quadratic function curve. Therefore, calculation is facilitated by obtaining and changing the injection rate of the flocculant according to the approximate curve.
[0046]
In this way, the turbidity of the water to be treated at the outlet portion of the filtration pond 16 is directly detected, and the rate of increase in the outlet turbidity has risen within the set range, or the turbidity of a certain level or more is longer than the set time. Since the flocculant is injected on the inlet side of the filter basin 16 on the condition that it has passed, the criteria described in the “Provisional Guidelines for Cryptosporidium Temporary Measures in Waterworks” that strictly set the outlet turbidity of the filter basin 16 are ensured. Can be cleared.
[0047]
Needless to say, the same effect can be obtained when a particle size analysis system or a particle counter is installed on the outlet side of the filtration basin 16.
[0048]
【The invention's effect】
According to the present invention, the post-flocculating agent injection can be automated to reduce the operation monitoring effort, optimize the injection rate, and clear strict turbidity standards.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a flocculant injection control device according to the present invention.
FIG. 2 is a flowchart for explaining the operation in the embodiment.
[Explanation of symbols]
16 Filtration pond 17 Flocculant injection device 22 Turbidimeter 23 Calculation unit 231 Preset turbidity increase rate range 232 Preset outlet target turbidity 236 Predetermined outlet target turbidity or higher turbidity setting Value 237 Turbidity duration

Claims (11)

It is a flocculant injection control method for detecting the turbidity of water to be treated at the filter pond outlet of the water purification plant, and injecting the flocculant into the inlet side of the filter basin according to the detected turbidity,
The turbidity increase rate is within the set range, and when the turbidity is equal to or greater than the outlet turbidity target value, the injection of the flocculant is started at a preset injection rate, and the injection is performed after a preset time. A control method for injecting the flocculant. A turbidimeter that is installed at the outlet of the filtration pond of the water treatment plant and detects the turbidity of the water to be treated flowing out of the filtration pond,
A flocculant injection device that is provided on the inlet side of the filtration basin and injects the flocculant into the water to be treated flowing into the filtration basin;
The detection value of the turbidimeter is input, the rate of increase is within a preset setting range, and the flocculant injection device is provided on the condition that the detected turbidity is equal to or greater than a preset outlet turbidity target value. A calculation unit that outputs an injection start command ,
The flocculant injection control device, when the injection start command is input, injects the flocculant at a preset injection rate for a preset time . A turbidimeter that is installed at the outlet of the filtration pond of the water treatment plant and detects the turbidity of the water to be treated flowing out of the filtration pond,
A flocculant injection device that is provided on the inlet side of the filtration basin and injects the flocculant into the water to be treated flowing into the filtration basin;
A first output unit that inputs the detected value of the turbidimeter, the rate of increase is within a preset setting range, and the detected turbidity is equal to or greater than a preset outlet turbidity target value ; Or a second output unit on condition that a state in which the detected turbidity of the turbidimeter is higher than a preset outlet turbidity target value continues for a preset time range, and the first output unit and An operation unit having a condition means for outputting an output from any one of the second output units to the flocculant injection device as an injection start command ;
When the flocculant injection device inputs the injection start command, the flocculant is injected at a preset injection rate for a preset time.
Coagulant injection control apparatus characterized by. Setting range of a preset turbidity increase rate calculation portion, claim 2 or claim 3, characterized in that it is 2.0 × ^{10 -5} ~15.0 × ¹⁰ -5 per unit time Flocculant injection control device. The flocculant injection control device according to claim 2 or 3, wherein an outlet turbidity target value preset in the calculation unit is 0.02 degrees or more. The flocculant injection control device according to claim 3 , wherein a value higher than the outlet turbidity target value preset in the calculation unit is 0.04 degrees. The flocculant injection control device according to claim 3, wherein a time range preset in the calculation unit is 60 to 120 minutes. Calculation unit, in response to changes in the detected turbidity turbidimeter any of claims 2 to 7, characterized in that changing the injection rate of the coagulant to be injected by the coagulant injection device coagulant injection control apparatus crab according. The calculation section trendline projections are set on approximating the change in turbidity, to any of the claims 2 to 7, characterized in that computing the injection rate of flocculant by the approximate curve The flocculant injection control device described. 10. The flocculant injection control device according to claim 9 , wherein the approximate curve is a trigonometric function curve. The flocculant injection control device according to claim 9 , wherein the approximate curve is a quadratic function curve.

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