JP3111508B2 - Treatment method for wastewater containing heavy metals - Google Patents

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 more particularly to a method for efficiently removing heavy metals from heavy metal-containing wastewater to obtain treated water having excellent treated water quality and having a high concentration and excellent dewaterability. The present invention relates to a method for treating heavy metal-containing wastewater capable of obtaining waste sludge.

[0002]

2. Description of the Related Art Recently, the following new techniques have been proposed as a method for treating heavy metal-containing wastewater, and some of them have been put to practical use. A method in which a magnesium compound is added to heavy metal-containing wastewater, the pH is adjusted to alkaline, and the resulting insolubilized product is subjected to membrane separation using a microfiltration membrane (MF membrane) (JP-A-2-157090). A method in which the alkali agent is not directly added to the heavy metal-containing wastewater but mixed with a part of the sludge of a thickener in a subsequent process and added (Japanese Patent Publication No. 61-156; hereinafter, referred to as "alkaline sludge method").

The above-mentioned method uses an MF membrane instead of a conventional thickener, thereby making it possible to reduce the installation area of the apparatus and improve the quality of treated water.

[0004] This method is specifically implemented by the method shown in FIG.

In FIG. 2, reference numeral 21 denotes a pH provided with an inlet pipe 22 for raw water (heavy metal-containing wastewater) and a supply pipe 23 for chemicals.
Adjustment tank, 24 is a circulation tank, 25 is MF provided with MF film 26
A membrane separation device, 27 is a backwash water tank, 28 is a pH meter, and 29 is a circulating pump, which are connected by pipes 30, 31, and 32. 33 is a discharge pipe of the treated water.

In this method, the introduction pipe 2 is connected to the pH adjusting tank 21.
Raw water (heavy metal-containing wastewater) is introduced from 2, and a magnesium compound (eg, Mg salt) and a pH adjuster are supplied from the supply pipe 23 to adjust the pH to alkaline, thereby coagulating the heavy metal-containing wastewater. . The coagulated water passes through the circulation tank 24 and is supplied to the pipe 30 through the MF by the power of the pump 29.
It is supplied to the membrane separation device 25. In the MF membrane separation device 25, the treated water that has passed through the MF membrane 26 is discharged out of the system through a pipe 32, a backwash water tank 27, and a discharge pipe 33. On the other hand, M
The concentrated liquid of the F membrane separation device 25 passes through the pipe 31 and is
Circulated to

On the other hand, the above-mentioned method is implemented by the method shown in FIG. In FIG. 3, reference numeral 41 denotes a raw water (heavy metal-containing wastewater) introduction pipe 42 and a neutralizing agent supply pipe 43.
, A coagulation tank, 45 a thickener, 4
Reference numeral 6 denotes a reaction tank for the neutralizing agent to which the alkali agent supply pipe 47 and the sludge return pipe 48 are connected, 49 and 50 are transfer pipes of the water to be treated, and 51 is a discharge pipe of the treated water. in this way,
In the reaction tank 46, a neutralizing agent mixture (hereinafter, referred to as “alkali sludge”) prepared by mixing return sludge returned from the sludge return pipe 48 and an alkali agent supplied from the supply pipe 47 is supplied to the supply pipe. The mixture is supplied from 43 to a neutralization tank 41, mixed with raw water from an introduction pipe 42, and neutralized. Next, this liquid is introduced into the coagulation tank 44 via a pipe 49 and subjected to coagulation treatment, and further introduced into a thickener 45 via a pipe 50 to be settled and separated. Thickener supernatant water is pipe 51
It is discharged as treated water. On the other hand, the settled sludge is returned to the reaction tank 46 from the pipe 48.

[0008] This alkali sludge method has a high sludge concentration,
It has the advantage that its dehydration is also high.

That is, in the treatment of heavy metal-containing wastewater, the concentration of the thickener sludge when the thickener is used as a sludge separating means for the heavy metal hydroxide after neutralization is usually 20,000.
The sludge generated by ordinary neutralization is, for example, the following hydroxide gel in the case of iron ions, and the water content is contained in the hydroxide polymer gel. Therefore, concentration is difficult.

[0010]

Embedded image

On the other hand, since the neutralization reaction in the alkali sludge method is a neutralization reaction between the alkali adsorbed on the sludge surface and the metal ions, Fe (OH) ₃ , Fe (O
Since monomolecular hydroxides such as H) ₂ , Cu (OH) ₂ and Zn (OH) ₂ precipitate on the sludge surface, they do not form a hydroxide gel, but have a high concentration of 30 to 40% by weight and a dehydrating property. You get good thickener sludge.

[0012]

SUMMARY OF THE INVENTION Among the above conventional methods, M
The method using the F membrane has a drawback that a large number of MF membranes are required due to a low membrane permeation (filtration) rate, and equipment costs are increased. Further, when the concentration of the sludge in the circulating concentrated water is high, the permeation rate is extremely reduced, so that there is a disadvantage that high-concentration sludge cannot be obtained. By the way,
The flux (permeation) with respect to the concentration of sludge (ferric hydroxide sludge) when treated with an MF membrane (tubular) having a pore diameter of 0.2 μm at a membrane inlet pressure of 2 kg / cm ² and a circulating water volume of 8.5 l / min. The change over time of the flux is as shown in FIG. From FIG. 4, it is clear that the permeation rate decreases with the increase in the sludge concentration, and the decrease is particularly remarkable when SS = 50,000 mg / l or more.

On the other hand, in the alkaline sludge method, sludge having a high concentration and good dehydration properties can be obtained, but a thickener is required, and the installation area of the apparatus cannot be reduced, which is industrially disadvantageous.

The present invention solves the above-mentioned problems of the conventional method. In the treatment of heavy metal-containing wastewater, the MF membrane is treated at a high membrane permeation rate without using a thickener, thereby providing a high-density and high-density dewatering property. An object of the present invention is to provide a method for treating heavy metal-containing wastewater, which makes it possible to obtain sludge.

[0015]

DISCLOSURE OF THE INVENTION The heavy metal-containing wastewater of the present invention
Is to add an alkali to the heavy metal-containing wastewater to generate insolubles, and then supply the wastewater to an MF membrane separation apparatus,
In the method for treating heavy metal-containing wastewater in which the treated water and the concentrated liquid are separated by membrane separation in a separation device , the insolubles are generated.
The liquid is supplied to the membrane separation device through the circulation tank, and the separated
The reduced solution was supplied to the circulation tank, a portion of the liquid of the circulating tank is mixed with the <br/> alkali, resulting alkaline mixture (alkaline
(Sludge) is added to the heavy metal-containing water.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a system diagram showing an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a pipe for introducing raw water (water containing heavy metals), and a pipe 1 for introducing raw water to the neutralization layer 2.
A and a pipe 1B for introducing raw water into the circulation tank 3. Reference numeral 4 denotes a pipe for supplying the liquid in the neutralization tank 2 to the circulation tank, and reference numeral 5 denotes a pipe for supplying the liquid in the circulation tank 3 to the MF membrane separation device 6 having the MF membrane 6A. 7 is a treated water discharge pipe,
Reference numeral 8 denotes a discharge pipe for the concentrate, and reference numeral 9 denotes a pipe for feeding the concentrate to the circulation tank 3. 10 is a pipe for supplying the liquid in the circulation tank 3 to the reaction tank 11, and 12 is a pipe for supplying alkali to the reaction tank 11. Reference numeral 13 denotes a pipe for feeding alkali sludge mixed with alkali from the reaction tank 11 to the neutralization tank 2.

In the present embodiment, part of the raw water from the introduction pipe 1 is supplied to the neutralization tank 2 from the pipe 1A, and the remainder is supplied to the circulation tank 3 from the pipe 1B. In the neutralization tank 2, the raw water is supplied to the reaction tank 11
After being neutralized by alkaline sludge supplied through a pipe 13 from the MF membrane separator 6 through a pipe 4, a circulation tank 3, and a pipe 5, and subjected to a membrane separation treatment. Thus, the permeated water of the membrane separation treatment is discharged from the pipe 7 as treated water.
On the other hand, part of the concentrated liquid is discharged from the pipe 8, and the remaining part is circulated to the circulation tank 3. The liquid in the circulation tank 3 is returned to the reaction tank 11 via the pipe 10, and the contained sludge is mixed with the alkali supplied from the pipe 12. This alkaline sludge is fed from the pipe 13 to the neutralization tank 2.

In the neutralization tank 2, the heavy metal ions in the raw water are effectively insolubilized by the alkali sludge, and a modified sludge having excellent dehydration properties is produced.

By the way, the reformed sludge which has been sufficiently reformed becomes particles having a maximum diameter of about 5 μm. This one is
It is presumed that the particles are crushed by a circulation pump (not shown) for feeding the liquid to the MF membrane separation device to become fine particles having a particle size of 1 μm or less. It is considered that some of these fine particles close the pores of the MF membrane and reduce the membrane permeation rate. However, if an inorganic coagulant is applied to these fine particles to make them coarse, A decrease in speed can be prevented.
Therefore, in this embodiment, instead of adding an inorganic coagulant such as an iron chloride or a sulfuric acid band, a circulating tank 3 in which a concentrated solution is circulated is used.
Then, a part of raw water is injected (hereinafter, this may be referred to as “dispensing”), and heavy metal ions contained in the raw water act as an inorganic coagulant. By dispensing raw water in this manner, the permeation rate of the membrane can be further improved by 20 to 50%.

If the amount of the raw water is too small, the above effect cannot be obtained. Conversely, if the amount is too large, the amount of hydroxide gel having poor filterability increases, and the pH of the circulating water becomes low. The amount is preferably 2 to 20%, particularly 5 to 10%, based on the amount of the introduced raw water.

In such a method, the amount of alkali to be added to the reaction tank 11 is adjusted such that the pH of the neutralization tank 2 is 8.0 to 11.1.
The amount is preferably about 0. Further, the circulating amount of the concentrated liquid from the MF membrane separation device 6 to the circulation tank 3 and the liquid return amount from the circulation tank 3 to the reaction tank 11 are preferably set to the following ratios. Concentrated liquid circulation amount: 20 to 60 times the raw water amount Liquid return amount: 0.5 to 3.0% based on the raw water amount In the present invention, heavy metal-containing wastewater to be treated includes heavy metal ions and And wastewater containing a heavy metal complex of a heavy metal and a chelating agent, such as plating wastewater and pickling wastewater of a steel sheet. Heavy metals include copper, zinc, nickel, cadmium, manganese, lead, iron and the like. Generally, wastewater containing heavy metal complexes is often acidic, but in the present invention, the pH of wastewater to be treated is an acidic wastewater of 4 or less, and the pH of wastewater having a high pH is once reduced to 2 pH.
It may be adjusted to ~ 3.

As the alkali to be added to these wastewaters, there may be mentioned alkali agents such as sodium hydroxide and slaked lime.

In the present invention, the material of the MF membrane is not particularly limited, and the operating conditions are not particularly limited. MF
The pore size of the membrane is 0.1 to 0.1 from the viewpoint of improving treatment efficiency and treatment water quality.
The thickness is preferably about 1 μm. Also, there is no particular limitation on the membrane separation method using the MF membrane.
Any type of flow type may be used, but when the turbid concentration of the inflow water into the membrane separation device is high, it is preferable to use a cross flow type in which raw water flows in parallel to the membrane surface. According to the cross flow method, clogging of the membrane can be reduced even in raw water having a high turbid concentration.

When the method of the present invention is carried out, a cake layer of an insolubilized substance is formed on the surface of the MF membrane due to the passage of water through the MF membrane separation apparatus, and the filtration rate decreases with time. For this reason, it is preferable to perform the backwashing by returning the treated water from the backwash water tank (not shown) from the permeation side of the membrane to the MF membrane separation device at regular intervals.

[0026]

[Function] The concentrated water separated by the MF membrane is supplied to the circulation tank,
By mixing the liquid in the circulating tank with the alkali, the alkali is adsorbed on the sludge surface in the concentrated circulating water, as in the case of the alkali sludge method described above. When the alkali adsorbed on the sludge surface is added to the heavy metal-containing wastewater, metal ions in the wastewater react with the alkali on the sludge surface and precipitate on the sludge surface as monomolecular hydroxides. This one is
It has excellent filterability and can maintain a high permeation rate without lowering the membrane permeation flux.

[0027]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 to 3 In accordance with the method of the present invention shown in FIG. 1, wastewater containing heavy metals having the following water quality was treated. Raw water quality pH = 1.7 Fe ³⁺ = 500 mg / l Cr ³⁺ = 100 g / l Ni = 20 g / l The capacity of the neutralization tank is 10 liters, the capacity of the circulation tank is 40 liters, and the MF membrane (tubular) The pipe diameter is 5.5mm,
The pore size was 0.2 μm, and the membrane was operated at an inlet pressure of 2 kg / cm ² . The alkali in the alkali sludge reaction tank (1 liter capacity) was injected in conjunction with a pH meter installed in the neutralization tank. The operating conditions are as shown in Table 1. In Example 1, the raw water was not dispensed into the circulation tank.
In No. 3, dispensing was performed at a rate of 2 liter / hr.

Table 1 shows the change over time in the transmission speed of the MF membrane separation device.

Comparative Examples 1 and 2 Raw water having the same water quality as that of Example 1 was treated under the operating conditions shown in Table 1 by the method shown in FIG. The changes are shown in Table 1.

[0031]

[Table 1]

As is apparent from Table 1, according to the method of the present invention, the permeation speed of the membrane separation device is about twice or more of the conventional one,
The efficiency is greatly improved, and the treatment can be performed efficiently even at a high sludge concentration.

[0033]

As described in detail above, according to the method for treating heavy metal-containing wastewater of the present invention, the permeation speed can be reduced by using a MF membrane separation apparatus without using a thickener having a large installation area. Can be kept high. For this reason, it is possible to reduce the number of membranes to be installed and to reduce the equipment cost. In addition, it is possible to increase the sludge concentration, and it is possible to obtain sludge with good dewatering properties, so that the load on the sludge dewatering machine in the subsequent process is reduced, processing costs are reduced, and processing efficiency is improved. Can be achieved. For this reason, according to the present invention, heavy metal-containing wastewater can be efficiently treated with a simple operation, and highly treated water with extremely high water quality can be recovered in a large amount and quickly.

[Brief description of the drawings]

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

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

FIG. 3 is a system diagram showing a conventional example.

FIG. 4 is a graph showing the change over time of the flux of the MF film with respect to the SS concentration.

[Explanation of symbols]

 2 Neutralization tank 3 Circulation tank 6 MF membrane separation device 11 Reaction tank

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ identification symbol FI C02F 9/00 504 C02F 9/00 504B (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1 / 62,1 / 44,9 / 02 B01D 61/14

Claims (1)

(57) [Claims] An alkali is added to a heavy metal-containing wastewater to
After generating the solution, a microfiltration membraneTo the separation device,
Membrane separation deviceSeparation into treated water and concentrated liquid by membrane separation
In the method for treating heavy metal-containing wastewater,The liquid in which the insolubles are generated is passed through a circulation tank to a membrane separation device.
Supply, Supplying the separated concentrate to the circulation tank, In the circulation tank Part of the liquidSaidMixed with alkali and obtained
WasalkaliCharacterized by adding the mixture to heavy metal-containing water
Heavy metal-containing wastewater treatment method.