JP4632372B2 - Treatment method of waste water from hot-dip galvanized steel sheet manufacturing equipment - Google Patents

Description

  The present invention relates to a method for treating concentrated acidic wastewater, diluted acidic wastewater and diluted alkaline wastewater discharged from hot-dip galvanized steel sheet manufacturing equipment.

  Concentrated acidic wastewater, dilute acidic wastewater and dilute alkaline wastewater are discharged from the hot dip galvanized steel sheet manufacturing facility. Here, examples of concentrated acidic wastewater include pickle (pickling wastewater) dump solution, nickel (Ni) dump solution, Co (cobalt) dump solution, and pure acid acidic wastewater includes pickle rinse, Ni rinse, and Co. Rinsing etc. are mentioned, and examples of the diluted alkaline drainage include washing water after degreasing and dumping solution of an aqueous caustic soda solution used for degreasing.

Thus, as a method for treating the concentrated acidic wastewater, the diluted acidic wastewater and the diluted alkaline wastewater discharged from the hot dip galvanized steel sheet manufacturing facility, a method of separately treating the diluted alkaline wastewater separately from the acidic wastewater, There is known a method (see Patent Document 1) in which wastewater is separated into lean wastewater and rich wastewater, and the diluted alkaline wastewater is treated together with the lean acidic wastewater as the lean wastewater by the alkali neutralization method.
JP-A-5-337474

  However, both of the above two methods have a problem in terms of cost and space because a large amount of acid such as sulfuric acid is necessary for neutralization of alkaline waste water and a large number of treatment facilities are required.

  The present invention has been made in view of the above problems, and the purpose of the treatment is to reduce the amount of acid necessary for neutralization of alkaline wastewater and to reduce the cost of the processing equipment and to save space. The object is to provide a method for treating galvanized steel sheet production facility waste water.

In order to achieve the above object, the present invention is a method for treating concentrated acidic wastewater, diluted acidic wastewater and diluted alkaline wastewater discharged from hot-dip galvanized steel sheet manufacturing equipment.
A process of introducing concentrated acidic wastewater, diluted acidic wastewater and diluted alkaline wastewater into the raw water tank;
A first neutralization step of adjusting the waste water from the raw water tank to pH 2.5-3 acidic water;
A second neutralization step of adjusting the acidic water from the first neutralization step to pH 6-11 to produce an insolubilized product;
An aggregating step for aggregating the insolubilized product produced in the second neutralization step;
A solid-liquid separation step of separating the agglomerates from the treated water as sludge in the aggregation step;
An alkali sludge return step of adding alkali to a part of the sludge separated in the solid-liquid separation step and returning it to the second neutralization step;
It is characterized by treating concentrated acidic wastewater, diluted acidic wastewater and diluted alkaline wastewater.

  According to the present invention, since acidic wastewater and alkaline wastewater are introduced into the raw water tank and mixed with each other, the pH of the mixed wastewater (raw water) is lowered by the acidic wastewater, and the sulfuric acid necessary for the first neutralization step is correspondingly reduced. The amount of the acid such as suffices is small and economical. Further, since the processing facilities are integrated into one system, the structure of the processing facilities can be simplified and miniaturized, and the cost of the processing facilities can be reduced and the space can be saved.

  And, in order to adjust the wastewater to pH 2.5-3 acidic water in the first neutralization step in the first stage, fully dissolve heavy metals etc. contained in the wastewater in the neutralization step. The heavy sludge is deposited around the sludge added in the second neutralization step as a core, and a dense and large insolubilized product can be obtained. When such a large insolubilized material is obtained, solid-liquid separation in the subsequent solid-liquid separation step is easily performed, and the quality of treated water is improved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a system diagram showing a basic configuration of a processing apparatus for carrying out the method of the present invention, in which 1 is a raw water tank, 2 is a first neutralization tank, 3 is a second neutralization tank, and 4 is A coagulation tank, 5 is a precipitation tank, and 6 is a reaction tank. 2A, 3A, 4A, 5A, and 6A are agitators, P1 and P2 are pumps, and 7 to 19 are pipes.

  Thus, the method of treating the galvanized steel sheet manufacturing facility wastewater according to the present invention includes a wastewater introduction step of introducing concentrated acidic wastewater, diluted acidic wastewater, and diluted alkaline wastewater into the raw water tank 1, and the raw water tank 1 First neutralization step of adjusting the waste water from the pH to acidic water of pH 2.5 to 3, and second neutralization step of adjusting the acidic water from the first neutralization step to pH 6 to 11 to produce an insolubilized product A coagulation step for aggregating the insolubilized product generated in the second neutralization step, a solid-liquid separation step for separating the aggregate from the treated water as sludge in the coagulation step, and a sludge separated in the solid-liquid separation step It is a method of treating concentrated acidic wastewater, dilute acidic wastewater and dilute alkaline wastewater through an alkali sludge returning step in which alkali is partially added and returned to the second neutralization step, and each step is described below. To do.

1) Wastewater introduction process:
In the wastewater introduction process, concentrated acidic wastewater, diluted acidic wastewater and diluted alkaline wastewater discharged from the hot dip galvanized steel sheet manufacturing facility are introduced into the raw water tank 1 through the pipes 7, 8, and 9 and mixed. The In addition, although the mixed waste water (raw water) in the raw water tank 1 shows alkalinity, the pH is finely adjusted by the sulfuric acid supplied into the raw water tank 1 from the piping 10 as needed.

2) First neutralization step:
The mixed waste water (raw water) in the raw water tank 1 is pumped through the pipe 11 by the pump P 1 and introduced into the first neutralization tank 2. In the first neutralization tank 2, the waste water (raw water) is adjusted to pH 2.5 to 3 with an acid such as sulfuric acid supplied from the pipe 12 to the first neutralization tank 2. In addition, when the pH of the raw water (acidic water) is as low as less than 2.5, for example, alkali such as slaked lime supplied to the second neutralization tank 2 through the pipe 13 is added to the raw water (acidic water), The pH of the raw water is adjusted to 2.5-3.

3) Second neutralization step:
The raw water (acidic water) whose pH is adjusted to 2.5 to 3 in the first neutralization step in the previous stage is introduced into the second neutralization tank 3. In the second neutralization tank 3, a mixture (hereinafter referred to as “alkaline”) prepared by mixing return sludge from the pipe 15 and slaked lime (alkali) supplied through the pipes 13 and 14 in the reaction tank 6. Sludge) is supplied from the pipe 16 to the raw water (acidic water), and the raw water (acidic water) is adjusted to pH 6-11 to produce insolubilized material.

  In addition, pH suitable for raw | natural water (acidic water) producing | generating an insolubilized material is 6-11, and pH of raw | natural water is adjusted to the range of 6-11 by addition of alkali sludge.

4) Aggregation step:
In the coagulation step, a coagulant such as a polymer coagulant is supplied from the pipe 17 to the coagulation tank 4 and the insolubilized product generated in the second neutralization step is coagulated by the coagulant.

5) Solid-liquid separation process & alkaline sludge return process:
The treatment liquid subjected to the aggregation treatment in the aggregation process is introduced into the precipitation tank 5 in the solid-liquid separation process, and is solid-liquid separated in the precipitation tank 5. The separated water is discharged as treated water from the pipe 18 to the outside of the system, and a part of the settled sludge (separated sludge) is pumped out of the pipes 15 and 19 by the pump P2, and the rest is returned sludge. And returned to the reaction tank 6 through the pipe 15 in the alkaline sludge returning step.

  As described above, slaked lime is mixed with the returned sludge returned to the reaction tank 6 to adjust the alkaline sludge, and this alkaline sludge is used for pH adjustment of the raw water in the second neutralization tank 3.

  The separated water discharged from the pipe 18 is treated with a high-speed filter, an activated carbon tower, or the like, then neutralized with sulfuric acid, and discharged as treated water to the outside of the system.

  As described above, according to the treatment method of the present invention, concentrated acidic wastewater (rich acidic wastewater and diluted acidic wastewater) and alkaline wastewater (dilute alkaline wastewater) are introduced into the raw water tank 1 and mixed. Therefore, the pH of the mixed waste water (raw water) is lowered by the acidic waste water, and the amount of acid such as sulfuric acid necessary for the first neutralization step can be reduced by that amount, which is economical. Further, since the processing facilities are integrated into one system, the structure of the processing facilities can be simplified and miniaturized, and the cost of the processing facilities can be reduced and the space can be saved.

  And, in order to adjust the wastewater to pH 2.5-3 acidic water in the first neutralization step in the first stage, fully dissolve heavy metals etc. contained in the wastewater in the neutralization step. The heavy sludge is deposited around the sludge added in the second neutralization step as a core, and a dense and large insolubilized product can be obtained. When such a large insolubilized material is obtained, solid-liquid separation in the subsequent solid-liquid separation step is easily performed, and the quality of treated water is improved.

It is a systematic diagram which shows the basic composition of the processing apparatus for implementing this invention method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 1st neutralization tank 3 2nd neutralization tank 4 Coagulation tank 5 Precipitation tank 6 Reaction tank 2A-6A Agitator P1, P2 Pump 7-19 Piping

Claims (1)

A method for treating concentrated acidic wastewater, dilute acidic wastewater and dilute alkaline wastewater discharged from hot-dip galvanized steel sheet manufacturing equipment,
A wastewater introduction process for introducing concentrated acidic wastewater, diluted acidic wastewater and diluted alkaline wastewater into the raw water tank;
A first neutralization step of adjusting the waste water from the raw water tank to pH 2.5-3 acidic water;
A second neutralization step of adjusting the acidic water from the first neutralization step to pH 6-11 to produce an insolubilized product;
An aggregating step for aggregating the insolubilized product produced in the second neutralization step;
A solid-liquid separation step of separating the agglomerates from the treated water as sludge in the aggregation step;
An alkali sludge return step of adding alkali to a part of the sludge separated in the solid-liquid separation step and returning it to the second neutralization step;
A method for treating hot dip galvanized steel sheet manufacturing facility wastewater, characterized by treating concentrated acidic wastewater, diluted acidic wastewater and diluted alkaline wastewater.

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