JP4985088B2 - Chemical injection control method - Google Patents

Description

  The present invention relates to a chemical injection control method for controlling the amount of chemical to be treated (chemical injection amount), and more particularly to a chemical injection control method suitable for controlling the chemical injection amount of a flocculant.

  When the flocculant is added to the water to be treated, it is preferable to add the flocculant so that the quality of the treated water is good. For that purpose, the water quality of the flocculated water is measured, and this measurement result is used. It is widely practiced to control the amount of medicine injected (for example, Patent Documents 1 to 4 below).

In addition, it is also desirable to prevent the amount of flocculant from being excessively injected, and in Patent Document 1 below, excessive addition is detected based on the deterioration of the turbidity of flock accompanying water, and the amount of flocculant added is reduced. It is described.
JP-A-9-19606 JP 2002-320975 A JP-A-2005-7338 JP 2006-55804 A

  In the above prior art, when the quality of the treated water is good, the dosage of the flocculant is not changed, and when the quality of the treated water is deteriorated, the dosage is changed.

  For example, in Patent Document 1, when the turbidity of the treated water is less than 30 mg / L, the amount of chemical injection at that time is maintained (FIG. 4 of the same publication).

  In Patent Document 3, when the floc in the coagulated liquid has a size within the reference range, the amount of the drug injected at that time is maintained (paragraph 0028 of the same publication).

  In such a control system, when the current treated water quality is good, the chemical injection amount is maintained, so that the chemical cost cannot be reduced.

  An object of the present invention is to provide a chemical injection control method in which it is attempted to reduce the chemical injection amount even when the current treated water quality is good, and thereby the chemical cost can be reduced. To do.

The chemical injection control method according to claim 1 is a setting in which a chemical is added to water to be treated, a water quality index value of the water after the addition is measured, and a chemical injection amount and / or chemical injection amount is controlled based on the measurement result. In the chemical injection control method for controlling the value, after determining that the water quality index value is within the preset reference range for a predetermined time or longer , the chemical injection amount and / or the setting value for controlling the chemical injection amount is set. The method includes a step of reducing a predetermined amount.

  According to a second aspect of the present invention, there is provided a chemical injection control method according to the first aspect, wherein a minimum setting value for controlling a minimum chemical injection amount and / or a chemical injection amount is set, and the chemical injection amount and / or the set value is set. Control is performed in a range not less than the minimum dose and / or not less than the minimum set value.

The chemical injection control method according to claim 3 determines that the water quality index value deviates from the reference range after reducing the chemical injection amount and / or the set value for controlling the chemical injection amount in claim 1 or 2 . Thereafter, the method includes a step of increasing the dose and / or a set value for controlling the dose.

  According to a fourth aspect of the present invention, there is provided a chemical injection control method according to the third aspect, wherein a maximum setting value for controlling a maximum chemical injection amount and / or a chemical injection amount is set, and the chemical injection amount and / or the set value is set. Control is performed within a range below the maximum dose and / or below the maximum set value.

  The chemical injection control method of claim 5 is characterized in that, in any one of claims 1 to 4, the chemical is a flocculant, and the chemical injection amount is a chemical injection amount of the flocculant. is there.

  The chemical injection control method of claim 6 is the chemical injection control method according to any one of claims 1 to 4, wherein the chemical is a flocculant and a pH adjuster, and the chemical injection amount of the flocculant and the addition amount of the pH adjuster are controlled. The pH set value is controlled.

  The chemical injection control method of claim 7 is characterized in that, in claim 5 or 6, the flocculant is an inorganic flocculant.

  An eighth aspect of the chemical injection control method according to the fifth or sixth aspect is characterized in that the flocculant is an inorganic flocculant and an organic flocculant.

  According to the chemical injection control method of the present invention, even when the water quality after chemical addition is within the reference range and is good, if this good state continues for a specified time or more, the chemical injection amount and / or chemical Decrease the set value for controlling the injection amount by a predetermined amount. If the water quality is still in the good range over the specified time even if the setting value for controlling the dosage and / or dosage is decreased, the dosage and / or dosage is further controlled. Try decreasing the value.

  In this way, even if the current water quality index value is within the reference range (good range), by trying to reduce the dosage and / or the set value that controls the dosage, a smaller dosage Thus, it is possible to obtain treated water with good water quality, and it is possible to achieve a reduction in chemical costs.

  In addition, if the chemical injection amount and / or the set value that controls the chemical injection amount are reduced too much, if the water quality index value deteriorates due to sudden fluctuations in the raw water quality, it immediately recovers to a value that satisfies the water quality index value. Therefore, set the minimum dose and / or the minimum set value for the above set value, and set the minimum dose and dose that do not fall below the minimum set value. It is preferable to perform control so that the set value is controlled.

  When the amount of chemical injection and / or the setting value for controlling the amount of chemical injection is decreased, if the water quality index value deviates from the reference range, the amount of chemical injection should be increased (for example, restored). preferable.

  In this case, if the water quality index value does not improve even if the set amount for controlling the dose and / or the dose is increased, the set value for controlling the dose and / or the dose is further increased. However, since the water quality index value may be deteriorated due to factors other than the chemical injection amount and the control value for controlling the chemical injection amount, the chemical injection amount and / or the control value for controlling the chemical injection amount should be set in advance. It is preferable to control so as not to exceed the set maximum dose and maximum set value.

  In the present invention, examples of the setting value for controlling the chemical injection amount include a pH setting value for controlling the chemical injection amount of the pH adjusting agent, and a redox potential setting value for controlling the chemical injection amount of the oxidizing agent and the reducing agent. However, there is no limitation as long as it is a set value that affects the dose. Any method may be used as a method for controlling the amount of medicine to be carried out according to the set value controlled according to the present invention. For example, the drug injection is performed so that the pH set value is controlled by the control method according to the present invention. The dosage of the pH adjusting agent to be applied is preferably PID control, PI control or P control, but is not limited thereto.

  The present invention is suitable for application to the dosage control of a flocculant, and it becomes possible to obtain agglomerated water having good water quality at a low chemical cost.

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

  FIG. 1 is a system diagram of an aggregating treatment apparatus to which a chemical injection control method according to an embodiment is applied, and FIG. 2 is a flowchart showing the chemical injection control method according to the embodiment.

  In FIG. 1, raw water (treated water) is introduced into a first reaction tank 1, and an alkaline aqueous solution and an inorganic flocculant are added from an alkali addition device and an inorganic flocculant addition device 3, respectively. Abbreviated).

As this alkali, NaOH, Ca (OH) ₂ , Na ₂ CO ₃ , NaHCO _{3 and the} like are suitable.

  Examples of the inorganic flocculant include PAC (polyaluminum chloride), sulfuric acid band, ferric chloride, and polyiron sulfate.

  The first reaction tank is provided with a pH meter 4, and the amount of alkali added from the alkali addition device 2 is a chemical injection controller (not shown) so as to be a pH set value by the control of FIG. 2 described later. Controlled by. In addition, although control of this alkali chemical injection amount is suitable for PID control, PI control, or P control, it is not limited to this. In the 1st reaction tank 1, a floc produces | generates from an inorganic flocculant and the suspended solid in raw | natural water aggregates.

  In addition, what is necessary is just to add an acid from the addition apparatus 2 when raw | natural water is alkaline. Moreover, you may make it add an acid and an alkali according to the property of raw | natural water.

  This agglomeration reaction liquid is introduced from the first reaction tank 1 to the second reaction tank 5, and the polymer flocculant is added by the adding device 6 and gently stirred by the stirrer (not shown). By adding this polymer flocculant, flocs grow and the agglutination reaction further proceeds. This aggregation state is detected by the aggregation state detection sensor 10. The detection signal of the aggregation state detection sensor 10 is input to a chemical injection controller (not shown), and the addition amount of the inorganic flocculant, the pH set value, and the polymer flocculant is controlled by the control signal from the chemical injection controller. Is done.

  The agglomerated reaction solution in the second reaction tank 5 flows around the lower part of the vertical partition wall 8 and flows into the ascending flow path 9, and the treated water not containing floc flows out from the upper part of the ascending flow path 9 as treated water. Sludge made of settled floc is taken out from the lower part of the second reaction tank 5.

  In addition, you may introduce | transduce the aggregation reaction liquid in the 2nd reaction tank 5 into a solid-liquid separator, and may perform a solid-liquid separation process.

  The agglomeration state detection sensor 6 may be of various types such as a turbidimeter, a viscometer, a thermal conductivity meter, a conductivity meter, a colorimeter (colorimeter), and a fluorometer. An aggregation monitoring device described in JP-A No. 2002-195947 is suitable. This agglomeration monitoring device is an improvement of the light scattering method in which a fluid is irradiated with laser light and the scattered light is received.

  Next, an example of a method for controlling the amount of medicine injected from each of the addition devices 2, 3, and 6 in this coagulation treatment device will be described.

  The alkali chemical injection amount may be controlled so that the detected pH of the pH meter 4 is in a neutral range, for example, 6.5 to 7.5, or may be controlled according to the method of FIG.

  The dosage of the inorganic flocculant is controlled according to the flow of FIG. 2 described below.

  The dose of the polymer flocculant is controlled in proportion to the dose of the inorganic flocculant or is controlled according to the flow of FIG.

  With reference to FIG. 2, the chemical injection control method of the inorganic flocculant will be described.

  The definitions of symbols in the following description are as follows.

A: Drug dosage
A _min : Minimum dosage
A _max : The most frequent dose
a: Change in drug injection
G: Water quality index value (detection value of aggregation state detection sensor 10)
G _max : upper limit of reference range of water quality index value

In FIG. 2, the water quality index value G, which is the current aggregation state detected by the aggregation state detection sensor 10 in step 11, falls within a range (reference range) smaller than a preset reference range upper limit value _Gmax. Judgment is made. When it is in this range (that is, when the aggregation state is good), the process proceeds to step 12 and waits until a specified time (for example, 0.1 to 60 minutes) elapses. While the predetermined time has elapsed, if the water quality index value G continuously is in the range smaller than G _max, the process proceeds to step 13, chemical feeding, chemical dosing amount that is less dosing amount by a predetermined amount (A-a) It calculates a determines whether the a-a does not fall below a minimum chemical feed amount a _min. If A-a is equal to or greater than A _min , the process proceeds to step 14 where A-a is set to a new dosage A, and the dosage is reduced by a less than the previous dosage for a predetermined time. After waiting (for example, 1 to 60 minutes), the process returns to step 11. In step 13, when the A-a is below the minimum chemical feed amount _{A min} is Kusurichuryou returns to step 11 without changing.

In step 11, if the current G value deviates from the above-mentioned reference range, the process proceeds to step 15 where a chemical injection amount (A + a) obtained by increasing the chemical injection amount by a predetermined amount is calculated, and this A + a is the upper limit drug. It is determined whether the dosage A _max is exceeded. If A + a is equal to or less than _Amax , the process proceeds to step 16 where A + a is set to a new dosage A, and the dosage is increased by a as much as a from the previous time, and a predetermined time (for example, 0. 0) is set. After waiting for 1 to 60 minutes, return to Step 11. In step 15, when A + a exceeds the upper limit medicine injection amount _Amax , the medicine injection amount is not changed and the process returns to step 11.

  According to steps 11 to 14, even when the aggregation state is good, the drug injection amount is sequentially decreased by a, so that the drug injection amount is reduced within the range in which the good aggregation state can be maintained. The amount can be reduced to a small amount, the chemical cost can be reduced, and the amount of generated sludge can be reduced.

  In this embodiment, the inorganic flocculant is controlled by the control method of FIG. 2, but it is preferable to control the pH set value and the amount of the polymer flocculant to be controlled by the control method of FIG. .

  In the embodiment of controlling the pH set value by the control method of FIG. 2, the definition of the symbol is read as follows, and the pH set value is controlled in the same manner as the inorganic flocculant.

A: pH set value
A _min : Minimum pH setting value
A _max : Maximum pH setting value
a: pH set value change
G: Water quality index value (detection value of aggregation state detection sensor 10)
G _max : upper limit of reference range of water quality index value

When controlling both the inorganic flocculant and the pH set value, control the dosage of inorganic flocculant and control the pH set value in advance by setting the time for each control. It is preferable that the control is performed alternately. Further, instead of setting the time for each control, it is also possible to preset the number of repetitions of each control program, for example, the number of times calculated in step 11, and move to another control when the set number is reached. . In this embodiment, since the cost of reducing the sludge amount is higher when the amount of the inorganic flocculant is reduced than when the pH adjuster is reduced, the control time or control of the amount of the inorganic flocculant is reduced. It is preferable to set the number of repetitions of the program to be larger than the control time of the pH set value or the number of repetitions of the control program. Further, when the dosage of the inorganic flocculant or the pH set value exceeds the preset upper limit value A _max or falls below the lower limit value A _min , the control is performed alternately so as to shift to another control. You can also.

In the above embodiment, since the value obtained by the aggregation state detection sensor indicating that the aggregation state is better as the value is smaller as the water quality index value, the reference range of the water quality index value is set as G ≦ G _max However, when using a water quality index value indicating that the larger the value is, the better the condition is, the reference range of the water quality index value is G ≧ G _min (G _min : lower limit of the reference range of the water quality index value). In the case where a water quality index value having an upper limit value and a lower limit value in a good state is used, the reference range of the water quality index value can be set to G _min ≦ G ≦ G _max .

  Such a control method is suitable for application to the flocculation treatment of waste water, but can also be applied to other water flocculation treatments. Further, the present invention can be applied to the control of set values for controlling the amount of chemical injection and the amount of chemical injection, such as floating processing other than the aggregation processing, biological phosphorus removal processing, chromaticity removal processing, and deodorization processing.

Example 1
In the coagulation treatment apparatus shown in FIG. 1, biological treatment wastewater was treated under the following conditions. In this case, a chemical feeding, chemical dosing amount _{A PAC} of inorganic coagulant and a pH set value _{A pH} was controlled according to the flow of FIG. 2.

First reaction tank volume: 1 m ³
Second reaction tank volume: 1 m ³
Aggregation state detection sensor: described in JP-A No. 2002-195947
Aggregation monitoring device
Raw water flow rate: 333L / min
Flocculant: PAC 10 wt% aqueous solution (asAl ₂ O ₃ )
Alkali: NaOH 25 wt% aqueous solution
Specified time for step 12: 30 seconds
Predetermined time of steps 14 and 16: 25 seconds
Water quality index value upper limit G _max : 10
Reference range of water quality index value G: G ≦ 10
PAC maximum dose A _max : 120 mL / min
PAC minimum dosage _Amin : 5 mL / min
PAC dose change a _PAC :
a _PAC = (G _max /2-G)×0.5/100×A _PAC
However, A _PAC is the current dose of PAC.

Maximum pH set value A _max : 7 (−)
Minimum pH setting value _Amin : 6 (-)
Change in pH set value a _pH :
a _pH = (G _max /2-G)×0.1/100×A _pH
However, A _pH is the current pH setting value.

The control time of the _PAC injection amount A _PAC and the pH set value A _pH was set to 10 minutes and 5 minutes, respectively, and when the control time passed, the control was performed alternately so as to shift to the other control. .

  FIG. 3 shows the changes over time of the flocculant drug dosage, pH set value, and aggregation state index value G when operated for 110 minutes under these conditions.

  As shown in FIG. 3, according to this example, while maintaining a good aggregation state, the PAC injection amount was reduced by about 20%, and the alkaline injection amount was reduced by about 5%.

It is a systematic diagram of an aggregating apparatus. It is a flowchart which shows a chemical injection control method. It is a graph which shows the result of an Example.

Explanation of symbols

1 1st reaction tank 2 2nd reaction tank 9 Ascending flow path

Claims (8)

In the chemical injection control method of adding a chemical to the water to be treated, measuring the water quality index value of the water after the addition, and controlling the setting value for controlling the chemical injection amount and / or the chemical injection amount based on the measurement result,
After determining that the water quality index value is within a preset reference range continuously for a specified time or longer , the method includes a step of decreasing a chemical injection amount and / or a setting value for controlling the chemical injection amount by a predetermined amount. A chemical injection control method.   In Claim 1, the minimum setting value which controls the minimum dosage amount and / or the dosage amount is set, and the dosage amount and / or the set value is equal to or more than the minimum dosage amount and / or A chemical injection control method, wherein control is performed in a range equal to or greater than the minimum set value. According to claim 1 or 2, after the water quality index value is determined to be outside the above reference range after reducing the set value for controlling the chemical feeding, chemical dosing amount and / or dosing quantity, chemical feeding, chemical dosing amount and / or chemical feeding, chemical dosing A drug injection control method comprising a step of increasing a set value for controlling the amount.   In Claim 3, the maximum setting value of the setting value for controlling the most frequently injected dose and / or the injected dose is set, and the lesser dose and / or the set value is less than the most injected dose and / or the A chemical injection control method, wherein control is performed within a range not exceeding the maximum set value.   5. The chemical injection control method according to claim 1, wherein the chemical is a flocculant, and the chemical injection amount is a chemical injection amount of the flocculant.   5. The method according to claim 1, wherein the chemical is a flocculant and a pH adjuster, and controls a chemical injection amount of the flocculant and a pH set value for controlling an addition amount of the pH adjuster. A chemical injection control method.   7. The chemical injection control method according to claim 5, wherein the flocculant is an inorganic flocculant.   7. The chemical injection control method according to claim 5, wherein the flocculant is an inorganic flocculant and an organic flocculant.

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