JP4811899B2 - Method for determining required addition amount of chelating heavy metal treating agent and method for controlling chemical injection - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention adds a chelate heavy metal treating agent to a heavy metal-containing wastewater and removes heavy metal components in the wastewater, and a method for easily and accurately determining the required addition amount of the chelate heavy metal treating agent, The present invention relates to a method for performing effective chemical injection control based on the obtained required addition amount.
[0002]
[Prior art]
Heavy metal-containing wastewater such as plating wastewater and paint wastewater contains heavy metals such as copper, chromium, zinc, lead, manganese, iron, nickel, and cadmium. These heavy metal-containing wastewater is appropriate according to the Water Pollution Control Law, etc. Is obliged to carry out appropriate processing.
[0003]
Conventionally, there are the following methods for treating heavy metal-containing wastewater.
(1) A method in which an alkali agent such as caustic soda and slaked lime is added to perform a coagulation precipitation treatment at a pH at which the heavy metal hydroxide (insolubilization) is formed. Method of adding and precipitating and precipitating (3) Method of adding precipitating and precipitating and coagulating and precipitating Of these, the method using alkali agent (1) has an insufficient heavy metal removal rate; Since it is treated with a neutralization treatment at the time of discharge, the construction of the treatment equipment becomes complicated; when organic acid or the like is contained in the wastewater, it becomes difficult to remove it by forming a complex compound with heavy metals; sludge There is a problem that the amount of generation is large.
[0004]
Further, the method (3) using sulfides has a drawback that although a relatively high heavy metal removal rate can be obtained at a low cost, odor (hydrogen sulfide odor) is generated and the working environment is poor.
[0005]
In contrast, the method (2) using the chelate heavy metal treating agent has no odor problem, has a high removal rate of heavy metals, and can be treated in a neutral pH range, so there is no need for neutralization. Even when an organic acid or the like is contained in the wastewater to form a complex compound with heavy metal, it can be said that it is the most excellent method because the heavy metal removal rate is relatively high.
[0006]
[Problems to be solved by the invention]
However, in the method using a chelate heavy metal treatment agent, the chelate heavy metal treatment agent is generally expensive, so the treatment cost is increased, and the chelate heavy metal treatment agent is excessively added to the heavy metal concentration in the waste water. In such a case, there is a drawback that the processing effect is deteriorated. For this reason, regardless of the daily water quality fluctuation of heavy metal-containing wastewater, if the chelating heavy metal treatment agent is treated with quantitative addition, the heavy metal component will be sufficient in both cases where the amount of chelating heavy metal treatment agent is insufficient or excessive. It cannot be removed, the quality of treated water is lowered, and in the case of excessive addition, the economic efficiency is remarkably impaired.
[0007]
The present invention solves the above-mentioned conventional problems, and when adding a chelate heavy metal treatment agent to heavy metal-containing wastewater to remove heavy metal components in the wastewater, the required amount of chelate heavy metal treatment agent can be simply and accurately determined. It is an object of the present invention to provide a method for performing effective drug injection control based on a determination method and a necessary addition amount obtained by this method.
[0008]
[Means for Solving the Problems]
The method for determining the required addition amount of the chelate heavy metal treatment agent of the present invention is the required addition amount of the chelate heavy metal treatment agent for adding the chelate heavy metal treatment agent to the heavy metal-containing wastewater and removing the heavy metal component in the wastewater. The chelate heavy metal treating agent is added to the wastewater while the pH of the heavy metal-containing wastewater is kept within the range of ± 0.5 in the vicinity of neutral pH 6-8, It is a method of measuring the amount of addition of a heavy metal treatment agent and the amount of change in oxidation-reduction potential of the waste water before and after the addition of the chelate heavy metal treatment agent, and determining the necessary addition amount based on the measurement result, The addition amount of the chelate heavy metal treatment agent when the amount of change in the oxidation-reduction potential becomes the maximum with respect to the addition amount of the chelate heavy metal treatment agent is a required addition amount. In the present invention, the amount of change in oxidation-reduction potential refers to the absolute value of the potential difference between the potential measurement point and the previous measurement point, and the slope of the oxidation-reduction potential described later refers to the amount added between these two measurement points. This is the rate of increase in potential. The measurement interval is preferably set so that the addition amount is constant.
[0010]
The chelate heavy metal treating agent has a chelate-forming group (dithiocarbamic acid group), and this group reacts with heavy metal ions in the wastewater to form an insolubilized product and generate a precipitate. When the heavy metal ions that react in this way disappear and the concentration of the free chelating heavy metal treating agent increases, the redox potential (ORP) decreases. The method of claim 1 utilizes this change in ORP.
[0011]
The method of claim 1 is that the amount of change in ORP with respect to the amount of chelating heavy metal treating agent added is not constant, but suddenly changes, and the point of this sudden change is the optimum amount of chelating heavy metal treating agent added. For example, as shown in FIG. 3, in the graph in which ORP and its inclination are the vertical axis and the chemical injection amount is the horizontal axis, the inclination gradually decreases as the chemical injection amount increases, and after taking the minimum value of the inclination, the inclination is again The point at which the ORP value changes rapidly with respect to the amount of chelating heavy metal treatment agent added can be obtained as the maximum value of the amount of change, and the heavy metal ions and chelates in the wastewater to be treated are around this maximum value. It is estimated that there is an end point of reaction with the system heavy metal treating agent.
[0012]
In this ORP measurement, it is extremely important to keep the pH of the heavy metal-containing wastewater in the test water constant. Since this pH is kept constant, the measurement accuracy of the ORP is increased for the following reasons, thereby changing the ORP. The amount can be accurately determined, and accurate drug injection can be performed based on this result. That is, the present invention utilizes the fact that the value of ORP depends on the concentration of the residual chelate heavy metal treating agent in water, but ORP varies with changes in pH. In the present invention, the ORP can be accurately measured by keeping the pH of the test water constant and eliminating the fluctuation of the ORP due to the change in pH.
[0013]
In the present invention, keeping the pH of the heavy metal-containing wastewater that is the test water constant means that the fluctuation range of the pH of the heavy metal-containing wastewater during the ORP measurement is kept within approximately ± 0.5.
[0014]
The chelating heavy metal treating agent chemical injection control method of the present invention controls the amount of chelating heavy metal treating agent used when adding a chelating heavy metal treating agent to a heavy metal-containing wastewater to remove heavy metal components in the wastewater. In the method, the chemical injection control of the chelate heavy metal treating agent is performed according to the required addition amount obtained according to the method for determining the required addition amount of the chelate heavy metal treating agent of the present invention.
[0015]
In this method, the calculated value of the required addition amount may be displayed at the site, and the administrator may manually change the discharge volume setting of the chemical injection pump based on the value, but the required addition amount that has been determined From the viewpoint of labor saving, it is preferable that the setting of the discharge amount of the medicinal pump is automatically changed based on the amount value. Further, the processing accuracy can be further improved by providing a function of detecting a change in the amount of heavy metal-containing wastewater and changing the amount of the chelating heavy metal treatment agent added so as to correspond to it.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is a system diagram showing an embodiment of a wastewater treatment system for treating heavy metal-containing wastewater by the chemical injection control method of the chelate heavy metal treatment agent of the present invention, and FIG. 2 is a system diagram showing the configuration of an ORP automatic measuring instrument. It is.
[0018]
In this wastewater treatment system, an acid (HCl, etc.) or alkali (NaOH, etc.) pH adjuster is added to the heavy metal containing wastewater in the neutralization tank 1 to adjust the pH, and then introduced into the reaction tank 2, from the chemical storage tank 3. The chelating heavy metal treatment agent is added and reacted with the chemical injection pump P ₁ , the inorganic flocculant is added to the reaction liquid, the flocculant is treated in the first flocculant tank 4, and then the polymer flocculant is added to the second flocculant. Agglomeration treatment is performed in the tank 5, the aggregation treatment liquid is solid-liquid separated in the sedimentation basin 6, and the obtained supernatant water is discharged as treated water. The separated sludge is dehydrated by the dehydrator 7.
[0019]
A sampling line 8 is connected to a pipe that feeds the neutralization treatment liquid of heavy metal-containing wastewater from the neutralization tank 1 to the reaction tank 2, and the ORP of the sampled sample liquid (sampling water) is ORP automatic measuring instrument 9. It is configured to measure with. This ORP measurement value is input to the control arithmetic unit 10, and the required addition amount of the chelate heavy metal treating agent is calculated based on the ORP measurement value. The calculation result is outputted to the pump controller 11 of the inverter such as a control signal for chemical feed pump P _1, chemical feed pump P ₁ by the pump controller 11 is controlled, proper chemical feeding, chemical dosing rows of chelate heavy metals treatment agent Is called.
[0020]
In this way, by measuring the ORP of the heavy metal-containing wastewater (neutralization treatment liquid) and calculating the appropriate chemical injection amount (necessary addition amount of the chelate heavy metal treatment agent) based on this measurement value, at regular intervals, Efficient processing can be performed by performing stable chemical injection control.
[0021]
In the wastewater treatment system of FIG. 1, the measurement result of the ORP automatic measuring instrument 9 and the calculation result of the control arithmetic unit 10 at the site where the heavy metal containing wastewater is treated are sent to the remote center via the communication terminal 12 via a telephone line. Control change through the communication terminal 12 via the communication line 12 over the telephone line (for example, setting change of measurement interval, change of control setting value such as correction coefficient, etc.) from the central monitoring device 13 It can be transmitted to the device 10, and is configured to be able to grasp, monitor and remotely control the processing status in a remote place through data communication between the local / center.
[0022]
Next, in the present invention, the configuration of the ORP automatic measuring instrument 9 for calculating the necessary addition amount of the chelate heavy metal treating agent will be described with reference to FIG.
[0023]
This ORP automatic measuring instrument is usually provided in a sampling line 8 for taking out heavy metal-containing wastewater neutralized in the neutralization tank 1 as shown in FIG.
[0024]
The calculation procedure in the ORP automatic measuring instrument of FIG. 2 is as follows.
[0025]
( ₁ ) When the ORP measurement operation is started, the electromagnetic valve V ₁ on the raw water side (sampling line) and the electromagnetic valve V ₂ for inflow / outflow at the bottom of the measuring tank 21 are opened, and the sampling water to be measured enters the measuring tank 21. Inflow. These solenoid valves V ₁ and V ₂ are closed at a predetermined value of the level switch 22 in the measuring tank 21 and the inflow of the sampling water is stopped.
[0026]
(2) A predetermined amount (a constant amount) of the chelate heavy metal treating agent in the chemical solution tank 24 is pumped while the sampling water is stirred by the motor agitator 23 in the measurement tank 21 and the pH of the sampling water is kept constant. It added at regular intervals by P _2. This addition may be continuous or intermittent, but in order to stably measure the ORP measurement value after addition, set the dispensing pump discharge amount so that the required amount can be added in a short time, and add It is desirable to mix thoroughly by post-stirring and perform ORP measurement after a certain period of time.
[0027]
In the present invention, when measuring the ORP, the pH of the sampling water in the measuring tank 21 is kept constant in order to eliminate the fluctuation of the ORP value due to the change in pH and increase the measurement accuracy. For this reason, the measuring tank 21 is provided with a pH meter 30, and based on this result, an acid or alkali pH adjuster is added as required by a pH adjuster adding means (not shown), thereby sampling during ORP measurement. Keep the pH change of water within ± 0.5.
[0028]
That is, this sampling water is a heavy metal-containing wastewater to which a pH adjusting agent is added in the neutralization tank 1, and the pH is within a predetermined range, but fluctuates due to factors such as addition of a chelating agent during ORP measurement, The fluctuation range is usually ± 2.0 and cannot be said to be constant. Therefore, in the present invention, the pH during the ORP measurement of such sampling water is measured, and if necessary, a pH adjuster is added to adjust the pH. Keep constant.
[0029]
Note that the pH of the sampling water during this ORP measurement is preferably kept constant within the range of the treatment conditions of the heavy metal-containing wastewater (that is, for example, the pH of the reaction tank 2 to which the chelate heavy metal treating agent is added), type of heavy metal-containing wastewater and chelate heavy metals treatment agent varies depending on the specifications of the processing equipment, usually shall be the pH constant at around neutral pH 6-8.
[0030]
(3) The operation (2) is repeated to convert the ORP calculated value signal by the A / D converter 28 and input to the control arithmetic unit 10. The control arithmetic unit 10 obtains the relationship between the chelate heavy metal treatment agent addition amount and the ORP measurement value as shown in FIG. 3 (hereinafter, the relation line between the chelate heavy metal treatment agent addition amount and the ORP measurement value is “titration”. The amount of change in ORP with respect to the addition amount of the chelating heavy metal treating agent, that is, the slope of the titration curve at each chelating heavy metal treatment agent addition amount is obtained. The ORP change amount may be the change amount of the ORP measurement value in the addition amount of the chelate heavy metal treating agent at two adjacent points in the titration curve. Then, the amount of change is averaged several times, and the relationship between the addition amount of the chelate heavy metal treatment agent and the ORP change amount is obtained (hereinafter, the relationship line between the addition amount of the chelate heavy metal treatment agent and the ORP change amount is expressed as “ In some cases, it is referred to as an “inclination curve.”) The addition amount of the chelating heavy metal treating agent at which the inclination curve takes the minimum value is defined as the necessary addition amount of the chelating heavy metal treating agent.
[0031]
Then, stop the motor agitation in the measurement tank 21, and the solenoid valve V ₃ drainage outlet side electromagnetic valve V ₂ of the outflow necessity of measuring tank 21 to the open discharging sampling water.
[0032]
▲ 4 ▼ after discharge, in order to maintain the ORP electrode 26 of the ORP meter 25 is cleaned, washed by ejecting solenoid valve V ₄ Shimizu such as tap water from the cleaning nozzle 27 is opened.
[0033]
(5) Thereafter, the above operation is repeated when measuring the ORP.
[0034]
In the present invention, in particular, sampling water is collected at regular time intervals, for example, 0.5 to 2 hour intervals, more specifically, every hour, and the ORP automatic measuring instrument as shown in FIG. For example, 10 to 120 seconds, specifically, a chelate heavy metal treating agent is added in a certain amount at intervals of 30 seconds, the ORP is measured by stirring, and the minimum value of the slope is determined from the titration curve and the slope curve as shown in FIG. The amount of the chelating heavy metal treating agent that is obtained and takes this minimum value is taken as the required amount.
[0035]
When performing chemical injection control according to the present invention based on the required addition amount thus obtained, in the titration curve, several additions before and after the addition amount of the chelating heavy metal treating agent determined as the required addition amount By setting the chemical injection control means to control the chemical injection amount of the chelate heavy metal treatment agent based on the achievement status of the target heavy metal concentration in the treated water within the amount range, finer chemical injection amount Adjustments can be made.
[0036]
The chelate heavy metal treating agent used in the present invention includes complex-forming functional groups such as dialkyldithiocarbamate, piperazine bisdithiocarbamate, cycloalkyldithiocarbamate, dithiocarbamate, and pyrrolidinedithiocarbamate. Examples of such compounds include, but are not limited to.
[0037]
The method of the present invention is preferably applied particularly to heavy metal-containing wastewater containing heavy metal ions such as Zn, Ni, Cu, and Pb at a concentration of about 1 to 50 mg / L. Depending on the type of heavy metal ion, it can be applied at a concentration higher or lower than this range.
[0038]
Such a method of the present invention can be applied to heavy metal-containing wastewater containing heavy metal ions capable of reacting with a chelate heavy metal treatment agent, but is not limited to heavy metal ions, and reacts with a chelate heavy metal treatment agent. The present invention can be effectively applied to any wastewater containing a substance that forms an insoluble salt.
[0039]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0040]
Example 1
In the wastewater treatment system shown in FIG. 1, heavy metal-containing wastewater (Ni-containing wastewater) of an automobile factory having the following properties is used as raw water, adjusted to pH 7.5 with NaOH, and then a chelate heavy metal treatment agent (Kurita Industry Co., Ltd.) ) "Wellclin K800" manufactured by 1% by weight aqueous solution), and then added with an inorganic flocculant (polyferric sulfate) and an anionic polymer flocculant (polyacrylamide). The drug injection control was performed.
[Ni-containing drainage properties]
pH: 7.3
SS: 150 mg / L
Ni: 5.0 mg / L
[0041]
The required addition amount of the chelate heavy metal treating agent was determined by the following ORP test.
<ORP test>
1 L of the raw water pH adjustment treatment solution (pH 7.5) was sampled, and a chelate heavy metal treatment agent was additionally added by 10 mg / L every 30 seconds, and ORP was continuously measured. At this time, the pH of the sampling water was measured, and NaOH or HCl was added as necessary so that the pH was constant at 7.5.
[0042]
With respect to the ORP measurement value for each addition amount of the chelate heavy metal treatment agent, the change amount of the ORP is obtained from the addition amount of the chelate heavy metal treatment agent at the previous point as follows, and before and after the addition amount of the chelate heavy metal treatment agent Average the amount of change in ORP at 2 points, a total of 3 points, and from the relationship between this average change amount and the addition amount of the chelate heavy metal treatment agent, the point with the largest average change amount is the required addition amount of the chelate heavy metal treatment agent did. In order to specify the point with the largest average change amount, it is easy to specify the change rate, that is, the slope of the graph in relation to the addition amount of the heavy metal treating agent.
[0043]
That is, in the relationship (titration curve) between the addition amount of the chelating heavy metal treating agent and the ORP measurement value shown in FIG. 3, for example, the ORP value (ORP ₅₀ ) when 50 mg / L of the chelating heavy metal treating agent is added. From the ORP value (ORP ₄₀ ) when the chelating heavy metal treating agent is added at 40 mg / L, the slope of the titration curve is obtained and this is the slope of the ORP when the chelating heavy metal treating agent is added at 50 mg / L (ΔORP ₅₀ ). It was. The ORP slope (ΔORP ₄₀ ) when the chelate heavy metal treatment agent addition amount is 40 mg / L, the ORP slope (ΔORP ₅₀ ) when the chelate heavy metal treatment agent is 50 mg / L, and the chelate heavy metal treatment. The ORP slope (ΔORP ₆₀ ) when the agent was 60 mg / L was averaged to obtain the ORP slope when the chelate heavy metal treating agent was 50 mg / L.
[0044]
From the average slope thus determined, a slope curve as shown in FIG. 3 was obtained, and it was determined that the addition amount of the chelate heavy metal treating agent showing the minimum value was 80 mg / L.
[0045]
When chemical injection control was performed with this chelate heavy metal treatment agent addition amount of 80 mg / L, it was possible to prevent excessive addition of chelate heavy metal treatment agent and stably obtain high water treated water of Ni 0.1 mg / L or less. did it.
[0046]
Comparative Example 1
In Example 1, a titration curve was obtained in the same manner except that the pH control was not performed during the ORP test. As shown in FIG. 4, unlike the titration curve obtained in Example 1, it was gentle. Even if the average change amount is obtained from this titration curve, a clear maximum value of the ORP change amount cannot be obtained as in Example 1, and the optimum addition amount of the chelating heavy metal treating agent is not obtained. I couldn't ask for it.
[0047]
In addition, since pH control was not performed during the ORP test, the pH of the sampling water varied in the range of 7.3 to 8.5 by the addition of the chelating agent.
[0048]
【The invention's effect】
As described above in detail, according to the present invention, when adding a chelate heavy metal treating agent to heavy metal-containing wastewater to remove heavy metal components in the wastewater, the required addition amount of the chelate heavy metal treating agent can be easily and accurately determined. Can be determined, and based on this value, effective dosing control can be performed,
{Circle around (1)} Excessive addition of chelate heavy metal treating agents can be prevented, and drug costs and treatment costs can be reduced.
(2) The quality of treated water is stable and always below the target standard value because the chelating heavy metal treatment agent can be poured in an appropriate amount without excess or deficiency in response to fluctuations in water quality of daily heavy metal-containing wastewater. Can be obtained stably and reliably.
Such excellent effects can be obtained.
[0049]
In particular, according to the chemical injection control according to the present invention, the chemical injection amount corresponding to the water quality fluctuation of the heavy metal-containing wastewater can be changed by automatic control, and the operation management work can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of a wastewater treatment system for treating heavy metal-containing wastewater by a chemical injection control method of a chelate heavy metal treatment agent of the present invention.
FIG. 2 is a system diagram showing a configuration of an ORP automatic measuring instrument.
3 is a graph showing a titration curve and an inclination curve in Example 1. FIG.
4 is a graph showing a titration curve in Example 1 and a titration curve in Comparative Example 1. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Neutralization tank 2 Reaction tank 3 Chemical storage tank 4 1st flocculation tank 5 2nd flocculation tank 6 Sedimentation basin 7 Dehydrator 8 Sampling line 9 ORP automatic measuring instrument 10 Control calculator 11 Pump controller 12 Communication terminal 13 Central monitoring apparatus 21 Measurement tank 24 Chemical solution tank 25 ORP meter 26 ORP meter electrode 27 Cleaning nozzle 28 A / D converter 30 pH meter

Claims (2)

In a method of determining a necessary addition amount of the chelate heavy metal treating agent for removing a heavy metal component in the waste water by adding a chelate heavy metal treating agent to the heavy metal-containing waste water,
The chelate heavy metal treating agent is added to the wastewater containing the heavy metal containing wastewater while the pH fluctuation range is kept within ± 0.5 in the vicinity of neutral pH 6-8, and the amount of the chelate heavy metal treating agent added. And measuring the amount of change in oxidation-reduction potential of the wastewater before and after the addition of the chelate heavy metal treating agent, and determining the necessary addition amount based on the measurement result,
A chelating heavy metal treatment agent characterized in that the addition amount of a chelating heavy metal treatment agent when the amount of change in the oxidation-reduction potential becomes maximum is a necessary addition amount with respect to the addition amount of the chelating heavy metal treatment agent. Of determining the required amount of addition. In the method of controlling the chemical injection amount of the chelate heavy metal treatment agent when removing the heavy metal component in the waste water by adding the chelate heavy metal treatment agent to the heavy metal containing waste water,
3. Chemical injection control of a chelate heavy metal treatment agent, characterized in that the chemical injection control of the chelate heavy metal treatment agent is performed according to the required addition amount determined according to the method for determining the required addition amount of the chelate heavy metal treatment agent according to claim 1. Method.

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