JP2001347264A - Water treatment equipment and water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously treat a large amount of water at low cost without using a coagulant, and to simultaneously treat plural kinds of heavy metals. SOLUTION: Heavy metals are adsorbed on an adsorption medium by filtration without using coprecipitation by a coagulant, thereby purifying treated water. The pH value of the treated water is adjusted before the filtration to enhance the adsorption efficiency, which enables the continuous treatment of a large amount of water and the simultaneous treatment of plural kinds of the heavy metals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to water treatment, and more particularly to an apparatus and a method for removing and purifying heavy metals contained in water.

[0002]

2. Description of the Related Art In some cases, harmful heavy metals are contained in wastewater such as factory wastewater, run-off water flowing out from contaminated soil and the like, groundwater, hot springs and the like. Conventionally, as a method for removing heavy metals from water containing such heavy metals, a water purification operation by coagulation and sedimentation is known. In this coagulation precipitation, for example, Al (aluminum) or Fe
A coagulation operation is performed to neutralize the charge by adding a coagulant of a positively charged metal hydroxide such as (iron).
The floc is flocculated to a size that enables sedimentation by coagulation under gentle stirring, and physically separated by a filter. As a coagulant, a chelating agent which forms a chelate compound with a metal ion is known. Further, depth filtration is known as one method of filtering and separating fine particles that cannot be removed by sedimentation separation from insoluble suspended substances suspended in water. Depth filtration is a method in which a suspension is passed through a layer filled with a filter medium, such as a granular material, plastic, or fiber, to trap and clarify suspended substances in pores of the filter layer.

[0003]

The conventional treatment for removing heavy metals by using a chemical such as a chelating agent involves the problem of high cost due to the use of a chemical, and also involves a chemical injection operation and management of processing conditions. Since various processing operations are required, there is a problem that it is not suitable for continuous processing or mass processing. For example, heavy metals that have been agglomerated and precipitated by the flocculant clog the filter, and the filter must be replaced frequently to maintain the heavy metal removal efficiency, which is not suitable for continuous processing or mass processing. In addition, since the coagulant differs for each target metal, there is also a problem that it is difficult to treat a plurality of metals simultaneously.

There is also a problem that the treatment liquid itself may cause new contamination by the administered medicine itself.
The processing solution containing a heavy metal is generally in an acidic state to dissolve the metal element, though it depends on the individual use conditions. On the other hand, the conditions under which metals can be condensed are alkaline. Therefore, in order to condense and remove the metal dissolved in the acidic treatment liquid, a large amount of a pH adjuster such as caustic soda is added at the stage before adding the flocculant or at the stage of adding the flocculant. It is in a strongly alkaline state. In addition, since the treatment liquid after coagulation / precipitation becomes strongly alkaline, a neutralization treatment is required to discharge to the outside so as to meet the discharge standard. Therefore, the conventional water treatment has problems in terms of coagulant, continuous treatment and mass treatment, simultaneous treatment of plural types of heavy metals, and the like.

Accordingly, an object of the present invention is to solve the above-mentioned conventional problems and to provide a water treatment apparatus and a water treatment method capable of performing continuous treatment and mass treatment without using a flocculant. An object of the present invention is to provide a water treatment apparatus and a water treatment method capable of simultaneously treating a plurality of types of heavy metals without using a coagulant, and to provide a low-cost water treatment apparatus and a water treatment method. Aim.

[0006]

SUMMARY OF THE INVENTION The present invention expands the principle of deep-layer filtration, which has been conventionally used for filtering fine particles, to ions and molecules without using heavy metals for co-precipitation with a flocculant. It purifies treated water by adsorbing heavy metals to the adsorption medium.By adjusting the pH value of treated water in the pre-filtration stage to increase adsorption efficiency, continuous and large-scale treatment can be performed without using a flocculant. In addition, multiple types of heavy metals are simultaneously treated. Since addition of a flocculant and replacement of a filter are unnecessary, the cost can be reduced. The present invention has found for the first time that there is a dependency on the pH value in the adsorption efficiency of heavy metals adsorbed on the adsorption medium, utilizing the dependence of the adsorption efficiency on the pH value,
It is intended to efficiently separate heavy metals contained in the treated water without using a flocculant.

FIG. 1 (b) schematically shows the dependence of the adsorption efficiency of heavy metals on the pH value, and the selective adsorption of heavy metals using the dependence. Regarding the adsorption efficiency of a certain heavy metal, for example, the adsorption efficiency at a pH value a is 20%, while the adsorption efficiency at a pH value b is almost 100%.
Accordingly, the pH value of the treated water is set to a pH value b at which the adsorption efficiency of the heavy metal becomes almost 100%, and by filtering in this state, the heavy metal in the treated water can be efficiently adsorbed to the filter medium and separated. Therefore, according to the present invention, a coagulant or a filter is unnecessary, and purification is performed by adsorption. Therefore, continuous processing and large-scale processing can be performed without clogging of the filter due to aggregation or sedimentation. In addition, as an application example of the present invention, utilizing the fact that the dependence of the adsorption efficiency on the pH value differs for each heavy metal, a plurality of types of heavy metals are separated,
They can be processed simultaneously.

Therefore, the water treatment apparatus of the present invention (FIG. 1A)
Is a pH for adjusting the pH value of the treated water.
It has a configuration including an adjusting means (indicated by reference numeral 2 in FIG. 1 (a)) and a filtration means (indicated by reference numeral 3 in FIG. 1 (a)) for deeply filtering the treated water after pH adjustment. The adjusting means adjusts the adsorption efficiency of heavy metals contained in the treated water before filtration, and forms selectivity for adsorption and separation of heavy metals by the filtering means. Further, the water treatment method of the present invention, a step of adjusting the pH of the treated water to adjust the adsorption efficiency of heavy metals contained in the treated water,
This is a treatment method including a step of deep-filtration of treated water after pH adjustment to adsorb and separate heavy metals, in which heavy metals contained in treated water are separated to purify the water. FIG. 1 is a schematic diagram for explaining a water treatment apparatus and a water treatment method of the present invention.

Here, the treated water is water to be treated containing heavy metals, and is, for example, industrial wastewater. The treated water containing the heavy metal is often strongly acidic because it is treated in a state where the heavy metal is dissolved in the water. The pH adjusting means is a means for adjusting the pH value of the treated water to a predetermined pH value by adding an alkali or an acid to the treated water, and an introducing means for introducing a pH adjuster into the treated water, and measuring the pH value. By providing a measuring means for controlling the pH adjusting agent based on the measured pH value, the treated water can be automatically adjusted to a predetermined pH value.

[0010] The pH setting conditions in the pH adjustment include not only a pH value exhibiting high adsorption efficiency for heavy metals, but also a pH value which does not destroy the adsorption medium (filter medium).
In some cases, precipitation does not occur due to alkalinity of wastewater. The filtration means of the present invention is for performing deep-layer filtration, in which treated water is passed through a layer filled with a filter medium such as a granular material, plastic, or fiber, and heavy metals are captured in the filter layer gap. Sand filtration using sand as a filter medium can be used.

The heavy metals to be separated according to the present invention include, for example, Cd, Pb, As, Cr, Cu, and Hg, and the treated water may contain one or more of these heavy metals. The dependence of the adsorption efficiency of heavy metals on the pH value differs for each heavy metal, and the pH value to be adjusted can form the selectivity of adsorption and separation of heavy metals. Cd, P
Among b, As, Cr, Cu, and Hg, Cd shows the strongest dependence of the adsorption efficiency on the pH value, and Pb and Cr have little dependence. This dependence shows that the adsorption efficiency tends to increase from acidic to alkaline, and Cd, Pb,
For heavy metals such as As, Cr, Cu and Hg, the pH value is almost 4
7 shows an adsorption efficiency close to 100%.

Therefore, for example, by adjusting the pH value to 4, the heavy metals of the treated water can be separated by adsorption. Further, as an application example of the application of the present invention, heavy metals contained in the treated water can be selectively separated by filtering while adjusting the pH value to alkaline in order from acidic. Further, according to the present invention, in addition to removing heavy metals from the treated water to purify the water, the heavy metals can be extracted by adsorbing the heavy metals to the filter medium.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a diagram for explaining a configuration example of the water treatment apparatus of the present invention. In FIG. 2, the water treatment apparatus 1 includes a pH adjusting means 2 and a filtering means 3, removes heavy metals contained in the introduced treated water, and discharges water free of heavy metals. The pH adjusting means 2 includes a pH adjusting tank 20 for introducing treated water through an introduction pipe 27, an acid storage tank 24 for storing an acidic pH adjuster, and an alkaline storage tank 25 for storing an alkaline pH adjuster. .
The treated water introduced into the pH adjusting tank 20 is fed from the acid storage tank 24 or the alkaline storage tank 25 to the introduction pipes 28 and 2.
Acidic pH adjuster or alkaline pH through 9
A regulator is introduced, and the pH value of the treated water is adjusted by stirring with a stirrer 22.

The filtration means 3 includes a filtration reactor 31 containing a filter medium 32 therein, and introduces treated water whose pH has been adjusted from the pH adjustment tank 20 and discharges water from which heavy metals have been removed. As the filter medium, besides sand, granular materials, plastics, fibers and the like can be used. In addition, the pH adjusting means 2 has a pH
A sensor 21 and a pH meter 23 for measuring the pH value of the treated water in the adjustment tank 20, and an acid storage tank 24 according to the measured pH value.
Alternatively, a control device 26 for selecting the alkaline storage tank 25 and controlling the amount of the acidic pH adjuster or the alkaline pH adjuster to be introduced can be provided. Control device 26
Is the acidic pH introduced to reach a preset pH value.
The amount of the H adjuster or the alkaline pH adjuster is controlled. By setting the pH value in accordance with the heavy metal adsorption efficiency, the target heavy metal can be selectively and automatically removed.

Next, the procedure for removing heavy metals from treated water according to the present invention will be described with reference to the flowchart of FIG. Treated water containing heavy metals such as industrial wastewater is introduced into the pH adjusting tank 20 (step S1), and the pH value of the introduced treated water is adjusted (step S2). The pH adjustment can be performed according to the following steps (Steps S21 to S25).
First, in step S21, a pH value corresponding to the heavy metal to be removed is set in advance. The pH setting conditions in the pH adjustment are a pH value that does not destroy the adsorption medium (filter medium) (setting condition 1), and a pH value that prevents generation of a precipitate due to alkalinization of wastewater (setting condition 2). PH value indicating high adsorption efficiency for heavy metals (setting condition 3).

FIG. 4 is a diagram for explaining the conditions for setting the pH, and shows the relationship between the pH value and the adsorption efficiency. The setting condition 1 is a condition for preventing the adsorption medium (filter medium) from being destroyed by strong acidity. Usually, industrial wastewater has a strongly acidic pH value because heavy metals are dissolved in a solution. The strong acid destroys the adsorption medium (filter medium) such as sand installed in the filtration device. Therefore, in order to pass the treated water through the filtration device, the pH value of the treated water is such that the adsorption medium (filter material) is not destroyed. Need to adjust to the value. Does not destroy the adsorption medium (filter medium)
Assuming that the maximum value of the H value is set, the setting condition 1 is to satisfy a pH value larger than the value. The setting condition 2 is a condition for preventing the wastewater from being precipitated by becoming alkaline. Generally, alkalinity is one condition under which metals can condense. Therefore, in the method of condensing and removing heavy metals dissolved in the treatment liquid using a coagulant, a heavy alkali is added by adding a large amount of a pH adjuster such as caustic soda to coagulate and precipitate heavy metals. ing.

In the present invention, since the heavy metal is removed by adsorption instead of removal of the heavy metal by coagulation / precipitation, the treated water does not need to be alkaline to coagulate / precipitate the heavy metal. It may cause clogging. Therefore, it is necessary that the metal is not alkaline so as to aggregate and precipitate. Assuming that the minimum value of the pH value at which the metal aggregates and precipitates is set, the setting condition 2 is to satisfy a pH value smaller than the value. Setting condition 3
Is a condition for efficiently adsorbing heavy metals dissolved in the treated water. The present invention has found that the adsorption efficiency of heavy metals adsorbed on an adsorption medium depends on the pH value, as described in the explanation using the above item 1 (b). The pH value is set so as to efficiently separate heavy metals contained in the treated water without using a coagulant, and to increase the adsorption efficiency of heavy metals.

In FIG. 4, the bold line is a characteristic curve showing the relationship between the pH value and the adsorption efficiency. In this characteristic curve, when the minimum pH value at which the adsorption efficiency becomes almost 100% is taken, the pH value is larger than the value. Satisfy the value is the setting condition 3
Becomes PH that satisfies the above set conditions 1 to 3
The value becomes the set pH value to be obtained. Setting conditions 1 to 3
The pH value that satisfies is a pH value between the pH value and the pH value in FIG. 4, but since the treated water in which the heavy metal is dissolved is generally acidic, it is possible to adjust the pH from the acidic to the alkaline direction. Since the amount is large and the amount of the pH adjuster introduced is required to be small due to demands such as cost and environmental considerations, the pH value shown here is the optimum value as the set pH value.

Next, the pH value of the treated water is measured by the sensor 21 and the pH meter 23 (step S22). The control device 26 compares the set pH value with the measured pH value, and selects a pH adjuster to be introduced into the treated water. If the measured pH value is more acidic than the set pH value, an alkaline pH adjuster is selected from the alkaline storage tank 25, and conversely, the measured pH value is more alkaline than the set pH value. In some cases, acidic p
The H adjuster is selected (Step S23). Further, the control device 26 compares the set pH value with the measured pH value, and calculates the amount of the pH adjuster to be introduced into the treated water, using the difference between the pH values, the concentration of each pH adjuster, and the like. (Step S
24).

The controller 26 commands the amount of the pH adjuster to be introduced into the acid storage tank 24 or the alkali storage tank 25, and introduces the pH adjuster into the treated water (step S25). The treated water, the adsorption efficiency of which has been increased by the pH adjustment step of Step S2, is introduced into the filtration reactor 31 to perform deep-layer filtration, and the heavy metal is adsorbed on the adsorption medium (filter medium) (Step S3).

The treated water after filtration is discharged outside from the filtration reactor 31. The discharge water has a discharge standard for the pH value separately from the discharge standard for the heavy metals, and is required to be equal to or lower than a predetermined pH value. Then, when the pH value of the treated water after filtration does not satisfy the discharge standard (Step S4), after performing the neutralization treatment so that the pH value of the discharged water is within the discharge standard (Step S5), It is discharged (step S6). Further, in the present invention, when plural kinds of heavy metals are contained in the treated water, each heavy metal can be selectively adsorbed and removed by using a different pH value-adsorption efficiency characteristic for each heavy metal. FIG. 5 is a diagram for explaining selective adsorption of a plurality of types of heavy metals according to the present invention. In FIG. 5, α, β, and γ indicate heavy metals.

The dependence of the adsorption efficiency of each heavy metal on the pH value is such that, when α is the smallest and γ is the largest, each heavy metal is selectively adsorbed by setting the pH value to a pH value corresponding to each heavy metal. Can be removed. For example, by setting the pH value to pHa and setting the adsorption efficiency of heavy metal α to 100%, heavy metal α is selectively adsorbed from heavy metals α, β, and γ, and then the pH value is set to pHb to adsorb heavy metal β. Heavy metal β, with efficiency as 100%
The heavy metal β is selectively adsorbed from γ, and finally, the pH value is set to pHc, so that the adsorption efficiency of heavy metal γ is 100
% To adsorb heavy metal β.

FIG. 6 and Table 1 are diagrams and tables showing one application example according to the present invention. In this example, A is used as the heavy metal.
The case of s, Cd, Pb, and Cr is shown. The concentration of each heavy metal was 2.11 mg / l, 2.15 mg / l,
5.14 mg / l and 5.12 mg / l, and sand is used as an adsorption medium.

[0024]

Table 1 As (2.11 mg / l) Cd (2.15 mg / l) Cr (5.14 mg / l) Pb (5.12 mg / l)

According to the above application example, As and Cd have a high dependence of the adsorption efficiency on the pH value, and As has a pH value in the range of 2.5 to 7, and Cd has a pH value in the range of 4 to 9 in Cd. It shows high adsorption efficiency. In addition, Cr and Pb have low dependence of the adsorption efficiency on the pH value, and exhibit high adsorption efficiency in a wide pH value range. Therefore, when the above setting conditions are applied to the above application example, the pH values satisfying the setting conditions 1 to 3 are in the range of 4 to 7. further,
In this pH value range, it is desirable to set the pH value to 4 in order to obtain the same adsorption efficiency with the introduction of a small pH adjusting agent.

Although not shown in the above application example, C
The heavy metals u and Hg also show a low dependence on the pH value of the adsorption efficiency and can be applied to the water treatment of the present invention. Therefore, even when Cu and Hg are included in the above application example, heavy metals can be adsorbed with high adsorption efficiency by setting the pH value in the range of 4 to 7.

[0027]

As described above, continuous processing and mass processing can be performed without using a flocculant. Multiple types of heavy metals can be simultaneously treated without using a coagulant. Further, water treatment can be performed at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a water treatment apparatus and a water treatment method of the present invention.

FIG. 2 is a diagram for explaining a configuration example of a water treatment device of the present invention.

FIG. 3 is a flowchart illustrating a procedure for removing heavy metals from treated water according to the present invention.

FIG. 4 is a flowchart for explaining a setting condition of pH.

FIG. 5 is a diagram for illustrating selective adsorption of a plurality of types of heavy metals according to the present invention.

FIG. 6 is a diagram showing an application example according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Water treatment apparatus, 2 ... pH adjustment means, 3 ... Filtration means, 2
0: pH adjustment tank, 21: Sensor, 22: Stirrer, 23:
pH meter, 24 acid storage tank, 25 alkaline storage tank, 26
... Control device, 27, 28, 29 ... Introductory tube, 31 ... Filtration reactor, 32 ... Adsorption medium (filter medium).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/62 C02F 1/62 EZ 1/66 510 1/66 510K 530 530Q 540 540A 540Z F term (reference 4D024 AA04 AB16 BA17 BB01 BB02 BB05 DA03 DB03 DB20 4D038 AA08 AB65 AB68 AB70 AB71 AB73 AB74 BB06 BB13 BB17

Claims (5)

[Claims] 1. A method comprising: a pH adjusting means for adjusting a pH value of treated water; and a filtering means for deep-filtrating the treated water after the pH adjustment, wherein the pH adjusting means reduces the adsorption efficiency of heavy metals contained in the treated water. A water treatment apparatus, wherein the water treatment apparatus adjusts and forms selectivity of adsorption and separation of heavy metals by a filtration means. 2. The pH adjusting means includes an introducing means for introducing a pH adjusting agent into treated water, a measuring means for measuring a pH value, and a control means for controlling the pH adjusting agent based on the measured pH value. The water treatment apparatus according to claim 1, wherein the treated water is automatically adjusted to a predetermined pH value. 3. The heavy metal is Cd, Pb, As, Cr,
It contains at least one of Cu and Hg, and the pH value is 4 to
The water treatment apparatus according to claim 1 or 2, wherein 4. A process for adjusting the pH of treated water to adjust the adsorption efficiency of heavy metals contained in the treated water, and the process of deeply filtering the treated water after the pH adjustment to adsorb and separate heavy metals. Water treatment method. 5. The heavy metal is Cd, Pb, As, Cr,
It contains at least one of Cu and Hg, and the pH value is 4 to
The water treatment method according to claim 4, wherein