JPH04267994A - Treatment method for metal-containing wastewater - Google Patents

Abstract

PURPOSE:To heighten the precipitation speed of produced sludge in a method wherein metal hydroxides are produced by adding alkali to metal-containing waste-water and treated water and sludge are separated by solid-liquid separa tion. CONSTITUTION:A part of sludge separated by solid-liquid separation and alkali with a polymer flocculant are mixed together and the obtained mixture is added to metal-containing waste-water. The precipitation speed of the produced sludge is increased. For this, it can be possible to make a thickener compact.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for treating metal-containing wastewater, and in particular to a method of adding alkali to metal-containing wastewater to generate metal hydroxides and separating the solid-liquid into treated water and sludge. , relates to a method for treating metal-containing wastewater that reduces the size of the device by increasing the sedimentation rate of generated sludge.

0002

[Prior Art] Conventionally, as a technique for improving the treatment method of metal-containing wastewater, Japanese Patent Publication No. 156/1983 proposed a technique in which thickener waste sludge was mixed with an alkaline agent such as sodium hydroxide or slaked lime for hydration of wastewater, and mixed sludge was produced. A method has been proposed in which sludge with a high solids concentration is obtained by neutralizing wastewater and the volume of the produced sludge is reduced. The mechanism of action of the method of Japanese Patent Publication No. 61-156 is based on the statement in the publication, namely, ``The present invention adsorbs the neutralizing agent on the surface of the carrier...'' and ``Most, but not all, of the neutralizing agent...'' is almost immediately adsorbed on the surface of carrier particles...'', it is inferred that sludge with a high solids concentration is obtained by precipitating heavy metals on the surface of the carrier.

[0003] In addition, Japanese Patent Publications Nos. 49-36879 and 51-37278, which target aluminum, are methods for treating metal-containing wastewater by mixing alkali with returned sludge.
No. 51-48386, Special Publication No. 55-1 for iron
No. 9643, Special Publication No. 50-23397 for zinc
No. 51-10200 and Japanese Patent Publication No. 51-20823 targeting cadmium have been proposed.

0004

[Problems to be Solved by the Invention] Obtaining sludge with a high concentration of solids is effective in reducing the amount of sludge produced, thereby making it possible to downsize dewatering equipment. On the other hand, in actual treatment equipment, generating sludge with a high sedimentation rate is also an important factor, and if the sludge has a high sedimentation rate, the thickener can be designed smaller, significantly reducing the equipment installation area. can do. However, in the past, no mention has been made of the sedimentation properties of sludge, and at present no studies have been conducted on techniques for producing sludge with a high sedimentation rate.

The present invention has been made in view of the above-mentioned conventional situation, and includes a method for adding an alkali to metal-containing wastewater to generate metal hydroxides and separating the solid-liquid into treated water and sludge. The object of the present invention is to provide a method for treating metal-containing wastewater that increases the sedimentation rate of generated sludge.

[0006]

[Means for Solving the Problems] The method for treating metal-containing wastewater of the present invention includes adding an alkali to metal-containing wastewater to generate metal hydroxide, and performing solid-liquid separation into treated water and sludge. It is characterized by mixing a portion of solid-liquid separated sludge with an alkali and a polymer flocculant, and adding the resulting mixture to metal-containing wastewater.

The present invention will be explained in detail below with reference to the drawings. FIG. 1 is a system diagram showing one implementation method of the metal-containing wastewater treatment method of the present invention.

In the illustrated method, metal-containing wastewater, which is raw water, is first fed to a coagulation tank 1 via a pipe 11, and inside the coagulation tank 1, it is supplied from a sludge mixing tank 2, which will be described later, via a pipe 12. Sludge, alkali and polymer flocculant (hereinafter referred to as “polymer”)
It is called. ) (hereinafter referred to as "sludge mixture")
and mix thoroughly using stirrer 1A. This generates metal hydroxide, so the coagulated water is transferred to the pipe 13.
The liquid is then fed to a thickener (sedimentation tank) 3 for solid-liquid separation treatment. The liquid obtained by solid-liquid separation is taken out of the system as treated water through piping 14. On the other hand, the solid content (sludge) is in pipe 1
5, a portion is sent to the sludge mixing tank 2 as return sludge through piping 16, and the remaining portion is sent to a dehydrator or the like through piping 17 for dehydration treatment. In the sludge mixing tank 2, alkali and polymer are added to the returned sludge through pipes 18 and 19, respectively, and mixed by the stirrer 2A, and the resulting sludge mixture is fed to the flocculation tank 1 through the pipe 12.

[0009] In the present invention, preferably, by adding the polymer also to the coagulation tank 1 (piping 20),
Even better processing results can be obtained.

Examples of the polymer used in the present invention include polyacrylamide, polymethacrylamide or a partial hydrolyzate thereof, a copolymer of acrylamide or methacrylamide and acrylic acid or methacrylic acid, and acrylamide or methacrylamide. Examples include polyamide polymers such as copolymers with 2-acrylamide-2-methylpropanesulfonate.

[0011] As the alkali, conventionally used sodium hydroxide, potassium hydroxide, calcium carbonate, limestone, calcium oxide, etc. can be used.

[0012] The amount of returned sludge, the pH in the coagulation tank 1, and the amount of polymer added that are suitable for the present invention are appropriately determined depending on the quality of raw water and other treatment conditions, but in normal cases, the amount of returned sludge: 10-100% pH of coagulation tank based on raw water amount: 7
~11 Amount of polymer added: 2 to 1 for the amount of SS generated from raw water
Preferably, it is 0% by weight. Moreover, when adding a polymer to a flocculation tank, it is preferable that the addition amount shall be 1-3 mg/l with respect to raw water.

Although there is no particular restriction on the metals contained in the metal-containing wastewater to be treated by the method of the present invention, the present invention particularly applies to iron, zinc, cadmium, nickel, tin,
Effective for wastewater containing lead, copper, aluminum, etc.

[0014]

[Function] It is quite conceivable to use polymers to improve the sedimentation of solids or the clarity of liquid during solid-liquid separation, but it is possible to use polymers to improve the settling of solids or the clarity of liquids. In order to achieve this purpose in a method of generating hydroxide and separating it into solid and liquid into treated water and sludge,
It is generally added to the flocculation tank 1.

[0015] By the way, as mentioned above, the special public
In the method No. 6, the main mechanism of action is to precipitate heavy metals on the carrier surface. Therefore, it is presumed that if the specific gravity of this carrier is increased, its sedimentation properties will be improved.

Therefore, in the present invention, in order to increase the specific gravity of the carrier, a polymer is added to the mixing system of return sludge and alkali, that is, the sludge mixing tank 2, and the sludge is pulverized by the return pump during return from the thickener. The sludge particles are sufficiently coagulated and coarsened. As a result, the sludge mixing tank 2 has p
Despite being under highly alkaline conditions of H12 to H14 or higher, the returned sludge aggregates and becomes coarse, and the sludge settling rate is significantly increased compared to the case where polymer is added to the aggregation tank 1.

[0017]

[Examples] The present invention will be explained in more detail with reference to Examples and Comparative Examples below. Example 1 Artificial wastewater having the following water quality was treated with the apparatus shown in FIG. Artificial wastewater quality pH = 1.2 Fe2+ = 500ppm Zn2+ = 100ppm Mn2+ = 50ppm Free sulfuric acid = 600ppm The capacity of coagulation tank 1 is 500 ml, and the capacity of sludge mixing tank 2
The capacity of Thickener 3 is 150 ml, and the capacity of Thickener 3 is 4
The alkali used for neutralization was sodium hydroxide at 50 g/l. Sodium hydroxide is in flocculation tank 1
When the pH of the sludge becomes 10 or less, it is poured into the sludge mixing tank 2. Raw water flow rate is 3.2 l/hr, sludge return amount is 0.8
l/hr, return sludge concentration is 80 g-drySS
/l-sludge. As a polymer, "Cliffrock PA-331" (manufactured by Kurita Water Industries, Ltd.) was used in the sludge mixing tank.
mg/l or 6 mg/l was added. The sludge settling curve at this time is shown in Figure 2. Further, Table 1 shows the measurement results of the sedimentation rate and supernatant SS.

Comparative Example 1 The treatment was carried out in the same manner as in Example 1 except that the polymer was injected into the coagulation tank, and the sludge settling curve, settling rate, and supernatant liquid S
The measurement results for S are shown in FIG. 2 and Table 1.

Example 2 The treatment was carried out in the same manner as in Example 1 except that 1 ppm of the polymer "Cliffrock PA-331" was added to the coagulation tank 1, and the sludge settling rate and supernatant liquid SS were measured. The results are shown in Table 1.

[0020]

[Table 1]

From Table 1, the following is clear. In other words, by adding polymer to the sludge mixing tank (Example 1), compared to adding the polymer to the coagulation tank (Comparative Example 1), the settling rate of sludge increased by about twice or more, and the settling property was significantly improved. will be improved. By the way, adding a polymer to the sludge mixing tank improves the settling properties of sludge, but the supernatant liquid SS
decreases slightly. On the other hand, by adding a polymer to the coagulation tank (Example 2), it is possible to improve both the supernatant clarity and the sludge settling properties.

[0022]

[Effects of the Invention] As detailed above, according to the method for treating metal-containing wastewater of the present invention, the sedimentation rate of the produced sludge can be significantly increased. Therefore, it is possible to significantly reduce the thickener volume and installation area, which is extremely effective for downsizing and space saving of the device.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing one implementation method of the metal-containing wastewater treatment method of the present invention.

FIG. 2 is a graph showing sludge settling curves of Example 1 and Comparative Example 1.

[Explanation of symbols]

1 Coagulation tank 2 Sludge mixing tank 3 Thickener

Claims (1)

[Claims] Claim 1: In a method of adding an alkali to metal-containing wastewater to generate metal hydroxides and separating the solid-liquid into treated water and sludge, a part of the solid-liquid separated sludge, the alkali and the polymer A method for treating metal-containing wastewater, which comprises mixing a coagulant with a flocculant and adding the resulting mixture to the metal-containing wastewater.