JPH057879A - Treatment of waste water containing heavy metal - Google Patents

Abstract

PURPOSE:To obtain a sludge of high concn. and excellent dehydrating property and to obtain high quality processed water without complicating the process of treating waste water containing heavy metals by alkali sludge method. CONSTITUTION:An alkali sludge is added to raw water and neutralized, which is then sent to a thickener 6 for solid-liquid separation through a condensation tank 3. In this process, part of the raw water is poured to the condensation tank 3 through a tube 1B. Heavy metal ions in the branched raw water act as an inorg. flocculant and coarsen the fine particles in the condensation tank. Thereby, solid-liquid separation property can be improved and high quality processed water can be obtd. Since it is an alkali sludge method, the obtd. sludge has high concn. and excellent dehydrating property. This method is effective for the process of waste water containing phosphoric acid and iron (II) ion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating heavy metal-containing wastewater, and in particular, it efficiently removes heavy metals from heavy metal-containing wastewater to obtain treated water of excellent treated water quality and high dewaterability at high concentration. The present invention relates to a method for treating heavy metal-containing wastewater capable of obtaining improved sludge.

[0002]

2. Description of the Related Art In the treatment of wastewater containing heavy metals, there is an alkali sludge method as a method for obtaining heavy metal hydroxide sludge which is rich in concentration and dehydrated. This method is a method in which the alkaline agent is not directly added to the heavy metal-containing wastewater but is mixed with a part of the sludge discharged from the thickener in the subsequent step and added (Japanese Patent Publication No. 61-156).

The alkaline sludge method is specifically carried out by the method shown in FIG. In FIG. 2, reference numeral 21 is a raw water (heavy metal-containing wastewater) introduction pipe 22 and a neutralizing agent supply pipe 23.
Neutralization tank with 24, coagulation tank 24, thickener 2
Reference numeral 6 is a neutralizer reaction tank to which an alkaline agent supply pipe 27 and a sludge return pipe 28 are connected, 29 and 30 are treated water transfer pipes, and 31 is a treated water discharge pipe. in this way,
In the reaction tank 26, a neutralizing agent mixture prepared by mixing the returned sludge returned from the sludge return pipe 28 and the alkaline agent supplied from the supply pipe 27 (hereinafter referred to as “alkaline sludge”).
Called. ) Is supplied from the supply pipe 23 to the neutralization tank 21,
It is mixed with raw water from the introduction pipe 22 and neutralized. Next, this liquid is introduced into the aggregating tank 24 through a pipe 29 for aggregating treatment, and further introduced into a thickener 25 through a pipe 30 to be separated by sedimentation. The supernatant water of the thickener 25 is discharged from the pipe 31 as treated water. On the other hand, the settled sludge is returned to the reaction tank 26 through the pipe 28.

Such an alkaline sludge method has the advantages that the sludge concentration obtained is high and its dehydration property is also high.

That is, when the heavy metal-containing wastewater is treated by the usual alkali neutralization method, the concentration of thickener sludge is 200
The sludge produced by ordinary neutralization has a hydroxide gel as shown below, and since water is included in the hydroxide polymer gel, the sludge is concentrated, Difficult to dehydrate.

[0006]

[Chemical 1]

On the other hand, the sludge obtained by the alkaline sludge method is considered to be the dehydration condensation of hydroxide (for example, Fe (OH) ₃ → FeOOH, Cu (OH) ₂ → C.
uO, Zn (OH) ₂ → ZnO, etc.) and crystalline fine particles, so that they are excellent in concentration and dehydration.

[0008]

In the alkaline sludge method, the dehydrated condensate is deposited on the surface of the sludge, and therefore a maximum of 5
Although particles having a size of about μ can be obtained, on the other hand, fine particles having a size of 1 μ or less also exist. The fine particles have poor sedimentation and separability and are mixed in the treated water before being discharged. Therefore, the quality of the treated water is deteriorated.

It is difficult to coarsen these fine particles only with the polymer coagulant. To remove them, the charge of the fine particles is neutralized with the inorganic coagulant, and then the polymer coagulant is added. It requires a complicated process of agglomeration treatment.

The present invention solves the above-mentioned conventional problems, and in a method for treating heavy metal-containing wastewater by an alkali sludge method, a sludge having a high concentration and excellent in dehydration property can be obtained without complicating the process. An object of the present invention is to provide a method for treating heavy metal-containing wastewater capable of obtaining treated water of water quality.

[0011]

A method for treating heavy metal-containing wastewater according to the present invention is a method of adding an alkali to heavy metal-containing wastewater to form an insoluble matter, and solid-liquid separating this into treated water and sludge. A method of reacting by adding alkali to the wastewater as a mixture obtained by mixing with a part of the separated sludge, part of the wastewater is separated, and the separated wastewater is mixed with the mixture. It is characterized in that it is added to and mixed with a reaction liquid with waste water.

The present invention will be described below in detail with reference to the drawings. FIG. 1 is a system diagram showing an example of implementation of the present invention. In FIG. 1, reference numeral 1 denotes an inlet pipe for raw water (heavy metal-containing wastewater), which is branched into a pipe 1A for introducing raw water into the neutralization tank 2 and a pipe 1B for introducing raw water into the coagulation tank 3. 2A
Is a pH meter provided in the neutralization tank 2. Reference numeral 4 is a pipe for feeding the liquid in the neutralization tank 2 to the flocculation tank 3, and 5 is a pipe for feeding the liquid in the flocculation tank 3 to the thickener 6. Reference numeral 7 is a treated water discharge pipe, 8 is a sludge discharge pipe separated by the thickener 6, and a discharge pipe 8A to the outside of the system and a return pipe 8 to the reaction tank 9
It branches to B. Reference numeral 10 is a pipe for supplying alkali to the reaction tank 9, and 11 is a pipe for supplying a polymer (polymer flocculant) to the coagulation tank 3. Reference numeral 12 is a pipe for feeding the alkaline sludge from the reaction tank 9 to the neutralization tank 2.

In this embodiment, part of the raw water from the introduction pipe 1 is supplied to the neutralization tank 2 through the pipe 1A, and the rest is supplied to the coagulation tank 3 through the pipe 1B. In the neutralization tank 2, the raw water is neutralized by the alkaline sludge supplied from the reaction tank 9 through the pipe 12, and the contained heavy metal ions are effectively insolubilized, and then fed to the coagulation tank 3 through the pipe 4. To be done. In the coagulation tank 3, raw water is further added to the neutralization reaction liquid of the raw water and the alkaline sludge through the pipe 1B (hereinafter,
Adding part of the raw water introduced into the system to this neutralization reaction solution is called "dispensing", and the amount of raw water dispensed with respect to the amount of raw water introduced is called "dispensing amount". ), A polymer is added from the pipe 11 and a coagulation treatment is performed.

That is, as described above, in the alkaline sludge method, coarse particles having good dewatering property and concentrating property as well as particle size of 1
Although fine particles having a poor sedimentation / separation property of about μ can be obtained, in the coagulation tank 3, the fine particles are neutralized by heavy metal ions contained in the raw water supplied from the pipe 1B, and further supplied from the pipe 11. The polymer is agglomerated and coarsened.

The liquid in which the particles have been sufficiently coarsened in the coagulation tank 3 is supplied to the thickener 6 through the pipe 5 and subjected to sedimentation separation treatment. Then, the obtained treated water is discharged from the pipe 7, sludge is extracted from the extraction pipe 8, a part of the sludge is returned to the reaction tank 9 from the pipe 8B as return sludge, and the rest is outside the system from the pipe 8A. Is discharged.

The sludge returned to the reaction tank 9 reacts with the alkali supplied from the pipe 10 to be reformed. That is, alkali is adsorbed on the sludge surface. This modified sludge is pipe 1
It is sent to the neutralization tank 2 from 2.

In the present invention, if the amount of the raw water dispensed is too small, the effect of the present invention cannot be sufficiently obtained, but if it is too large, the above-mentioned hydroxide gel is produced in a large amount and the action and effect of the alkaline sludge method are obtained. Lost. Therefore, it is preferable that the dispensed amount is 20% or less of the raw water to be treated. In consideration of the aggregation effect of heavy metal ions in the raw water and the action effect of the alkaline sludge, the dispensed amount is particularly preferably 2 to 10%.

In the method of this embodiment, the amount of alkali added to the reaction tank 9 is such that the pH of the neutralization tank 2 is 8.0 to 1.
The amount is preferably about 1.0. The amount of sludge returned from the thickener 6 to the reaction tank 9 is preferably 0.5 to 3.0% with respect to the amount of raw water. Further, the pH of the flocculation tank 3 is preferably 7.0 to 9.0 by dispensing raw water, and the amount of polymer added is preferably 2 to 5 mg / l with respect to the amount of raw water.

In the present invention, the heavy metal-containing wastewater to be treated is a wastewater containing heavy metal ions, a heavy metal complex of a heavy metal and a chelating agent, and examples thereof include plating wastewater. Heavy metals include copper, zinc, nickel, cadmium, manganese, lead and iron. In general,
Most of the wastewater containing a heavy metal complex is acidic, but in the present invention, the pH of the wastewater to be treated is acidic wastewater of 4 or less, and the pH of wastewater having a high pH may be once adjusted to 2-3.

Examples of alkalis added to these wastewaters include alkali agents such as sodium hydroxide and slaked lime, and examples of polymers include polyacrylamide and partial hydrolysates thereof.

In the present invention, the solid-liquid separation means may be a membrane separation means other than a thickener.

[0022]

In the present invention, the heavy metal ions in the dispensed raw water act as an inorganic flocculant, and effectively act on the charge neutralization and coarsening of the fine particles produced by the reaction between the raw water and the alkaline sludge. .. That is, as the inorganic coagulant, an aluminum salt or an iron salt is generally used, but functionally, any heavy metal having a metal capable of forming a hydroxide gel as described above has a charge neutralizing action. Therefore, it can be used. Therefore, in the present invention, the raw water for dispensing acts as an inorganic coagulant to coarsen the fine particles without complicating the process.

In the present invention, since the fine particles are coarsened in this way, the separability in the thickener in the subsequent step is good and a treated water of high quality can be obtained.

By the way, when the wastewater containing phosphoric acid and ferrous ion is treated by the alkaline sludge method, the following problems occur. That is, in order to insolubilize the ferrous ions, the pH needs to be 9.5 or higher, but in this pH range, the treatment characteristics of phosphoric acid deteriorate. On the other hand, in order to remove phosphoric acid, the pH in the system should be 8 or less, preferably pH.
It is necessary to set the acidic range of 5 to 7, but in such an acidic range, elution of ferrous ions (ferrous hydroxide) once insolubilized occurs. Further, in the alkaline sludge method, since sludge is repeatedly returned, air oxidation occurs, ferrous hydroxide is oxidized to ferric hydroxide, ferrous phosphate is oxidized, and ferric hydroxide and phosphoric acid are oxidized. Since it becomes an ion, iron is insolubilized, but the deterioration of the treatment characteristics of phosphoric acid tends to be increased. Therefore, conventionally, it was very difficult to treat wastewater containing phosphoric acid and ferrous ions.

However, according to the method of the present invention, a portion of the raw water is dispensed, and the raw water is usually acidic. Therefore, the pH for removing phosphoric acid in the system, that is, pH 5 to 5 is obtained.
It can be lowered to 8, preferably 5.5 to 7, and phosphoric acid can be efficiently removed. Then, since ferrous ions and phosphate ions in the undiluted raw water react to produce insoluble ferrous phosphate, elution of iron ions does not occur even in this pH range, and good treatment is performed. It is possible to obtain water.

[0026]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1 According to the method of the present invention shown in FIG. 1, pH 2, Cu ²⁺ 5
Treatment of sulfuric acid acid wastewater of 00 mg / l was carried out. The device specifications and operating conditions are as follows.

Reaction tank capacity: 200 ml Neutralization tank capacity: 500 ml Coagulation tank capacity: 500 ml Thickener capacity: 3 l Treated raw water amount: 3 l / hr Raw water injection amount: 100 ml / hr Sludge return amount: 50 ml / Hr Neutralization tank pH: 9.0 Polymer injection amount: 3 mg / l In addition, 100 g / l NaOH aqueous solution was used as an alkali, and it injected in conjunction with the pH meter installed in the neutralization tank.
Table 1 shows the changes over time in the water quality of the treated water.

Comparative Example 1 The procedure of Example 1 was repeated, except that the pH of the neutralization tank was set to 8 and the raw water was not dispensed. Table 1 shows the changes over time in the water quality of the obtained treated water.

[0030]

[Table 1]

Example 2 Sulfuric acid acidic wastewater having a pH of 1.6 and Fe ^{2+ of} 500 mg / l,
The water quality of the treated water obtained by treating in the same manner as in Example 1 is shown in Table 2.

Comparative Example 2 Sulfuric acid acidic wastewater having a pH of 1.6 and Fe ^{2+ of} 500 mg / l,
Table 2 shows the changes over time in the water quality of the treated water obtained by treating in the same manner as in Comparative Example 1.

[0033]

[Table 2]

Example 3 pH 2.0, Fe ²⁺ 500 mg / l, PO ₄ -P100
The mg / l acidic wastewater was treated as in Example 1.
The neutralization tank had a pH of 10, and the raw water injection into the coagulation tank was 150 ml / hr so that the treated water had a pH of 7. As the water quality of the treated water, the water quality of the filtrate filtered with filter paper No. 5A was examined. Table 3 shows changes in water quality over time.

Comparative Example 3 The same procedure as in Example 3 was carried out except that the raw water was not dispensed.
It was shown to.

[0036]

[Table 3]

From Tables 1 to 3, it is clear that according to the present invention, treated water of extremely high quality can be obtained. In particular,
From Table 3, it is clear that the method of the present invention can also favorably treat wastewater containing phosphoric acid and ferrous ions. That is, in general, the elution of ferrous ions starts at pH 9 or lower, so the Fe concentration in the treated water increases, but when the raw water is dispensed according to the present invention,
There is almost no elution of iron, and both iron and phosphoric acid can be highly treated.

On the other hand, in Comparative Example 3, the pH is high and the removal of phosphoric acid is insufficient.

[0039]

As described in detail above, according to the method for treating heavy metal-containing wastewater of the present invention, the sludge is easily and efficiently treated by the alkali sludge method to obtain sludge having a high concentration and excellent dewaterability. At the same time, it is possible to obtain treated water of high quality. In particular, according to the method of the present invention, wastewater containing phosphoric acid and ferrous ions, which has hitherto been difficult to treat, can be favorably treated, and its industrial utility is extremely large.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the method for treating heavy metal-containing wastewater according to the present invention.

FIG. 2 is a system diagram showing a conventional example.

[Explanation of symbols]

 2 Neutralization tank 3 Coagulation tank 6 Thickener 9 Reaction tank

Claims (1)

Claim: What is claimed is: 1. A method of adding an alkali to wastewater containing heavy metals to form an insoluble matter, and solid-liquid separating the insoluble matter into treated water and sludge. A method of reacting by adding to the wastewater as a mixture obtained by mixing with a part thereof, wherein a part of the wastewater is fractionated, and the fractionated wastewater is added and mixed to a reaction liquid of the mixture and the wastewater. A method for treating heavy metal-containing wastewater, comprising: