JP2861370B2 - Wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICATION The present invention relates to mine drainage and certain types of industrial wastewater,
Acidic wastewater containing dissolved metal components such as Fe (processed raw water)
Is a wastewater treatment method in which lime is neutralized with slaked lime, and metal components are precipitated and separated as hydroxide to treat the wastewater. In particular, to obtain a high-concentration sediment with good dehydration properties and to drain clear treated water About what you can do.

2. Description of the Related Art Conventionally, a so-called HDS method (abbreviation for High Density Sludge method, USPate) has been used to neutralize wastewater containing dissolved metal components such as Fe to obtain a suspension of a high-concentration sediment.
nt 3,738,942, June 12,1973).

In the HDS method, wastewater containing a dissolved metal component (processed raw water) is neutralized with slaked lime in a neutralization tank to precipitate the metal component as a hydroxide. Introduced into the sedimentation tank, sedimentation and concentration of the precipitate, a certain amount of high-concentration suspension containing the precipitate concentrated in the sedimentation tank,
The treated raw water is circulated and added to a condition tank in which slaked lime necessary for bringing the pH to a desired value is introduced, and the excess sediment is extracted from the sedimentation tank to be dehydrated and deposited (or landfilled). To discharge the overflow water.

In the HDS method, the concentration of the sediment settled and separated in the sedimentation tank is 15 to 50% (about 1 to 3% in a normal neutralization treatment).
(10 times or more). As a result, the volume of the precipitate to be treated is reduced, and there is an advantage that the dewatering property is improved.

However, in the HDS method, since the concentration of the sediment discharged from the neutralization tank is higher than that of the simple neutralized sediment formed by slaked lime in the ordinary wastewater treatment, the HDS method produces the sediment. There is a disadvantage that the sedimentation speed of the sediment is reduced, and the turbidity of the overflow water in the sedimentation tank, that is, the turbidity of the treated wastewater is increased. One example is a report by DJ, Bosman et al. (Journal of
the South African Institute of Mining and Metallu
rgy. Apr. 1974, 340-348.)
Even if it is as low as 0.57 m / h, the concentration of the suspension in the overflow water is 60 mg / h
It is said that was.

Suspended drainage standards based on the Water Pollution Control Act for suspended matter vary depending on the region, but in severe places, 10-50 mg /
, And the above HDS method is not always sufficient.

Therefore, it is conceivable to newly add a flocculant to the wastewater containing these low-concentration suspensions to cause coagulation and sedimentation. However, since the concentration of the suspension is low, the flocculation of suspended particles can be efficiently performed. The suspension cannot be settled or separated, probably because it is not performed well.

Further, in the HDS method, when the coagulant is added to the stage before the settling tank and the treatment is continued, the coagulant accumulates in the course of circulating the sediment, and the coagulability and dewatering property of the sediment are significantly deteriorated.

"Object of the Invention" The present invention has been made in view of the above circumstances,
A new efficient coagulation / precipitation step is added to obtain a high-concentration and dehydrated precipitate as in the HDS method,
It is an object of the present invention to provide a wastewater treatment method capable of draining clear treated water.

"Means for solving the problem" The wastewater treatment method according to claim 1 is characterized in that Fe2 ⁺ , Fe3 ⁺ , M
In a wastewater treatment method in which acidic treated raw water containing dissolved metal components such as n ²⁺ , Cu ²⁺ , Zn ²⁺ , Al ³⁺ is neutralized or alkaline with slaked lime, and precipitated and separated as hydroxide, The high-concentration suspension circulated in the fourth step is mixed with slaked lime necessary to bring the treated raw water to a desired pH in a condition tank.
The first step of stirring to form a mixed suspension, the treated raw water, and the mixed suspension generated in the first step are mixed and stirred in a first neutralization tank to neutralize the treated raw water. Or a second step of making alkaline and dissolving the dissolved metal component, and introducing a suspension containing the precipitate generated in the second step into a sedimentation tank to settle and concentrate the precipitate, and at the same time, removing the excess sediment from the sedimentation tank. A third step of discharging overflow water containing water, a fourth step of extracting a precipitate concentrated in the sedimentation tank as a high-concentration suspension, and circulating the suspension in the condition tank of the first step; A fifth step of mixing and stirring the overflow water discharged from the tank, treated raw water, and slaked lime necessary for neutralizing the treated raw water in the second neutralization tank to form a mixed suspension; The mixed suspension generated in the fifth step is led to a flocculation reaction tank, and a flocculant is added thereto. Sixth step in which the precipitate in the mixed suspension is aggregated, The mixed suspension in which the precipitate is aggregated in the sixth step is led to a sedimentation basin, and the precipitate is settled and separated, and the supernatant is clarified. A wastewater treatment method, comprising: a seventh step of discharging as water.

The wastewater treatment method according to claim 2 is characterized in that Fe ²⁺ , Fe ³⁺ , Mn ²⁺ , C
In the wastewater treatment method in which acidic treated raw water containing dissolved metal components such as u ²⁺ , Zn ²⁺ , Al ³⁺ is neutralized or rendered alkaline with slaked lime, and precipitated and separated as hydroxide, The circulated high-concentration suspension and slaked lime required to bring the treated raw water to the desired pH are mixed and mixed in the condition tank.
The first step of stirring to form a mixed suspension, the treated raw water, and the mixed suspension generated in the first step are mixed and stirred in a first neutralization tank to neutralize the treated raw water. Or a second step of making alkaline and dissolving the dissolved metal component, and introducing a suspension containing the precipitate generated in the second step into a sedimentation tank to settle and concentrate the precipitate, and at the same time, removing the excess sediment from the sedimentation tank. A third step of discharging overflow water containing water, a fourth step of extracting a precipitate concentrated in the sedimentation tank as a high-concentration suspension, and circulating the suspension in the condition tank of the first step; A fifth step of filtering the overflow water discharged from the tank by a filtration tank to remove sediment, and a sixth step of washing the filtration tank used in the fifth step to obtain backwash water containing the precipitate Backwash water generated in the sixth step, treated raw water, and neutralizes the treated raw water. Mixing and stirring the slaked lime necessary for the second step in a second neutralization tank to form a mixed suspension; and guiding the mixed suspension generated in the seventh step to an agglutination reaction tank. Eighth step of adding a flocculant to agglomerate the precipitate in the mixed suspension, and introducing the mixed suspension in which the precipitate is agglomerated in the eighth step to a sedimentation tank to settle and separate the precipitate. And a ninth step of discharging the supernatant as clear treated water.

[Action] In the wastewater treatment method of the present invention, a high-concentration suspension containing concentrated sediment is withdrawn from the sedimentation tank, circulated through the condition tank, and mixed with slaked lime necessary for neutralizing the treated raw water. Stir. This is mixed and stirred with the raw water for treatment in the first neutralization tank to precipitate the dissolved metal component, and the suspension containing this precipitate is repeatedly settled and concentrated in the settling tank. By repeating this, as the concentrated sediment gradually accumulates in the sedimentation tank, overflow water in which the fine sediment is suspended is discharged from the sedimentation tank.

A certain amount of raw water and slaked lime necessary for neutralizing the raw water are continuously added to the overflow water discharged from the sedimentation tank or the backwash water obtained by filtering the overflow water. Mix and stir in neutralization tank. Further, the generated mixed suspension in the second neutralization tank is led to the coagulation reaction tank, and the sediment is efficiently coagulated by adding a coagulant to the mixed suspension.
Here, the fine sediment in the overflow water or backwash water discharged from the sedimentation tank contains the sediment generated when the treated raw water is neutralized, and is efficiently aggregated. The mixed suspension in the coagulation reaction tank is led to a sedimentation basin, and the sediment is settled and separated. Discharge as water. Thus, a precipitate having a high concentration and good dehydration properties is obtained, and clear treated water is discharged.

Example An example of the wastewater treatment method of the present invention will be described below with reference to the drawings.

<< First Embodiment >> FIG. 1 is a flow sheet diagram showing a wastewater treatment method according to a first embodiment of the present invention.

In the wastewater treatment method of this embodiment, first, in a condition tank 1, an amount of slaked lime milk supplied by a slaked lime feeder 2 and required for neutralizing treated raw water is circulated from a settling tank 3 by a sludge pump. And a high-concentration suspension. (First Step) Next, in the first neutralization tank 4, the treated raw water and the mixed suspension containing slaked lime coming from the condition tank 1 are mixed and stirred to neutralize. (Second Step) Next, the mixed suspension after neutralization is introduced from a cylindrical feed well provided in the settling tank 3 to concentrate the precipitate, and overflow overflow water containing fine precipitate. Let it. (Third Step) Further, a high-concentration suspension of the sediment concentrated in the sedimentation tank 3 is withdrawn from the bottom of the sedimentation tank 3 and sent to the condition tank 1 by a sludge pump to be circulated. The high-concentration suspension has a concentration of 15 to 50% at the stage when the processing step is in a steady state, but can be easily flowed by a usual slurry pump. (Fourth Step) Next, overflow water discharged from the settling tank 3 is introduced into the second neutralization tank 5 by a pump. The second neutralization tank 5
In the second neutralization tank 5, treated raw water and slaked lime necessary for neutralizing the treated raw water are introduced, and the overflow water, treated raw water and slaked lime are mixed and stirred in the second neutralization tank 5. It becomes a liquid.
This stirring causes a neutralization reaction to generate a precipitate. (Fifth Step) Further, the mixed suspension containing the precipitate generated in the fifth step is led to the flocculation reaction tank 6 and flocculates the flocculant liquid supplied from the flocculant dissolution tank by the flocculant addition pump. The precipitate is aggregated by adding and stirring in the reaction tank 6.
(Sixth Step) Next, the suspension after the agglutination reaction is introduced into the sedimentation basin 7, the sediment is settled and separated, and the supernatant water is discharged. The sediment sedimented and separated is withdrawn from the bottom of the sedimentation basin 7,
The concentrated sediment precipitated in the settling tank 3 is extracted from the bottom of the settling tank 3. Then, these precipitates are removed from the dehydrator 8.
After dehydration, dispose of it by methods such as deposition and landfill. (Seventh Step) However, according to the above-mentioned wastewater treatment method, overflow water with excess sediment discharged from the sedimentation tank 3 overflows. Is mixed and agitated with slaked lime necessary for neutralizing the precipitate to form a precipitate. Thereafter, the precipitate is efficiently flocculated by adding a flocculant, and the precipitate is collected in the sedimentation basin 7. The sedimentation / sedimentation is performed, and this sediment is extracted from the sedimentation basin, dehydrated, deposited (or reclaimed), and the clear, clear supernatant water is discharged. At the same time, clear treated water can be drained.

Further, the above-mentioned wastewater treatment method can be easily carried out simply by adding a second neutralization tank 5, a coagulation reaction tank 6 and a sedimentation tank 7 to an apparatus for performing the conventional HDS method.

<< Second Embodiment >> FIG. 2 is a flow sheet diagram showing a wastewater treatment method according to a second embodiment of the present invention.

In the wastewater treatment method of this embodiment, first, in a condition tank 1, an amount of slaked lime milk supplied by a slaked lime feeder 2 and required for neutralizing treated raw water is circulated from a settling tank 3 by a sludge pump. And a high-concentration suspension. (First Step) Next, in the first neutralization tank 4, the treated raw water and the mixed suspension containing slaked lime coming from the condition tank 1 are mixed and stirred to neutralize. (Second Step) Next, the mixed suspension after neutralization is introduced from a cylindrical feed well provided in the settling tank 3 to concentrate the precipitate, and overflow overflow water containing fine precipitate. Let it. (Third Step) Further, a high-concentration suspension of the sediment concentrated in the sedimentation tank 3 is withdrawn from the bottom of the sedimentation tank 3 and sent to the condition tank 1 by a sludge pump to be circulated. The high-concentration suspension has a concentration of 15 to 50% at the stage when the processing step is in a steady state, but can be easily flowed by a usual slurry pump. (Fourth Step) Next, the overflow water containing fine sediment is sent to the filtration tank 9, and the fine sediment contained in the overflow water is removed, and clear filtered water is obtained. (Fifth Step) Next, the filtration tank 9 used in the fifth step is washed with water, the fine precipitate removed by the filtration tank 9 is washed away, and the so-called reverse containing the fine precipitate is removed. Wash water is generated. (Sixth Step) The backwash water generated in the sixth step is introduced into the second neutralization tank 5 by a pump. In the second neutralization tank 5, treated raw water and slaked lime necessary for neutralizing the treated raw water are introduced, and in the second neutralization tank 5, backwash water, treated raw water and slaked lime are introduced. Are mixed and stirred to form a mixed suspension. This stirring causes a neutralization reaction to generate a precipitate. (7th
Step) Further, the mixed suspension containing the precipitate generated in the seventh step is guided to the coagulation reaction tank 6 and the coagulant liquid supplied from the coagulant dissolution tank by the coagulant addition pump is mixed with the coagulation reaction tank 6. And agitate to precipitate the precipitate.
(Eighth Step) Next, the suspension after the agglutination reaction is introduced into the sedimentation basin 7 to precipitate and separate the precipitate, and the supernatant water is discharged. The sediment settled and separated is discharged from the bottom of the sedimentation basin 7,
The concentrated sediment precipitated in the settling tank 3 is extracted from the bottom of the settling tank 3. Then, these precipitates are removed from the dehydrator 8.
After dehydration, dispose of it by methods such as deposition and landfill. (Ninth Step) However, according to the above wastewater treatment method, overflow water with excess sediment discharged from the sedimentation tank 3 overflows, and the overflowed overflow water is filtered by the filtration tank 9. And
By mixing and stirring the treated raw water and slaked lime necessary for neutralizing the treated raw water with the backwash water generated when the filtration tank 9 is washed, a precipitate is formed, and thereafter, a flocculant is added. The sediment is efficiently aggregated, the sediment is settled and separated in the sedimentation basin 7, the sediment is extracted from the sedimentation basin 7, dehydrated, deposited (or reclaimed), and the supernatant is treated with clear treated water. Is discharged, so that a precipitate having a high concentration and good dehydration properties can be obtained, and clear treated water can be drained.

Further, the above-mentioned wastewater treatment method can be easily carried out simply by adding a second neutralization tank 5, a coagulation reaction tank 6, a sedimentation tank 7, and a filtration tank 9 to a device for performing the conventional HDS method.

"Experimental Examples" Next, the effects of the wastewater treatment method of the present invention will be clarified by giving experimental examples.

The experiment was performed by the following two methods under the condition that the processing of the HDS method was constantly maintained.

(A) Conventional HDS method A certain amount of the suspension of the precipitate concentrated in the sedimentation tank 3 (1/4 to 1/5 of the amount of raw water to be treated) is circulated to the condition tank 1 and at the same time, a part of the concentration is The sediment is periodically extracted and dehydrated, and settling tank 3
The treatment was continued while keeping the interface of the precipitate inside as constant as possible.

Further, after a flocculant is added to the overflow water in the sedimentation tank 3 to cause a flocculation reaction, sedimentation and sedimentation of sediment are performed in the sedimentation basin. However, with this conventional method, effective coagulation is difficult, and sedimentation / separation of suspended particles is not observed in the sedimentation basin.
The quality of the overflow water could not be improved.

(B) About the method of the present invention A certain amount of the suspension of the concentrated precipitate in the settling tank 3 is similarly circulated to the condition tank 1. In addition, a certain amount of the treated raw water (1/4 to 1/5 of the total raw water amount) and the neutralized water are added to overflow water containing fine sediment in the settling tank 3 or backwash water from the filtration tank 9. Slaked lime necessary for the mixing is continuously added to the second neutralization tank 5 and mixed.
Stirred. Further, the mixed suspension in the second neutralization tank 5 is guided to an agglutination reaction tank 6, and a coagulant is added to the agglutination reaction tank 6 to cause an agglutination reaction. Try to separate.

For these two methods, the concentration of sediment in the overflow water of the settling tank 3 and the settling basin was measured periodically during the experiment.

Table 1 shows the average water quality of the treated raw water (mine drainage) used in the experiment.

The results of the experiment and measurement are shown in Tables 2 and 3.

From the results of the above experiments and measurements, the concentration of the sediment in the treated wastewater overflowing from the sedimentation basin 7 is reduced to 1/4 to 1/5 by the method of the present invention as compared with the conventional HDS treated wastewater. I have. Further, it can be seen that, at the same time as obtaining a sediment having a high concentration equivalent to that of the HDS method and having good dehydration properties, the concentration of the sediment in the post-treatment wastewater overflowing from the sedimentation basin 7 can be sufficiently reduced.

[Effects of the Invention] As described above, according to the wastewater treatment method of the present invention,
Raw water and slaked lime necessary for neutralizing the raw water are added to the overflow water overflowing from the sedimentation tank or the backwash water from the filtration tank, and mixed and stirred in the second neutralization tank. The liquid is introduced into the coagulation reaction tank, and the coagulant is added to coagulate the sediment. The sediment is settled and separated in the sedimentation basin. At the same time, clear treated water can be drained.

[Brief description of the drawings]

FIG. 1 is a flow sheet diagram showing a first embodiment of the waste water treatment method of the present invention, and FIG. 2 is a flow sheet diagram showing a second embodiment of the waste water treatment method of the present invention. DESCRIPTION OF SYMBOLS 1 ... Condition tank, 2 ... Slaked lime feeder, 3 ... Sedimentation tank, 4 ... 1st neutralization tank, 5 ... 2nd neutralization tank, 6 ... Agglomeration reaction tank, 7 ... Settling tank, 9 …… Filter tank.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C02F 1/58-1/64

Claims (2)

(57) [Claims] Claims: 1. An acidic treated raw water containing dissolved metal components such as Fe ²⁺ , Fe ³⁺ , Mn ²⁺ , Cu ²⁺ , Zn ²⁺ , and Al ³⁺ is neutralized or slaked with slaked lime, In a wastewater treatment method that precipitates and separates as hydroxide, a high-concentration suspension circulated in the fourth step and slaked lime required to bring the treated raw water to a desired pH are mixed and stirred in a condition tank. A first step of forming a mixed suspension, the raw water for treatment, and the mixed suspension produced in the first step are mixed and stirred in a first neutralization tank to neutralize the raw water for treatment. A second step of precipitating the dissolved metal component, and introducing a suspension containing the precipitate generated in the second step into a settling tank to settle and concentrate the precipitate, and at the same time, including a surplus sediment from the settling tank. A third step of discharging the overflow water overflowing, and extracting the sediment concentrated in the settling tank as a high-concentration suspension. And circulating it to the condition tank of the first step.
Process, overflow water discharged from the sedimentation tank, treated raw water, and slaked lime necessary for neutralizing the treated raw water are mixed and stirred in the second neutralization tank to form a mixed suspension. Fifth step, guiding the mixed suspension generated in the fifth step to the flocculation reaction tank,
A sixth step of adding a flocculant thereto to aggregate the precipitate in the mixed suspension, and introducing the mixed suspension in which the precipitate is aggregated in the sixth step to a sedimentation basin to settle the precipitate. A wastewater treatment method, comprising: a seventh step of separating and discharging a supernatant liquid as clear treated water. 2. An acidic treated raw water containing dissolved metal components such as Fe ²⁺ , Fe ³⁺ , Mn ²⁺ , Cu ²⁺ , Zn ²⁺ , and Al ³⁺ is neutralized or slaked with slaked lime, In a wastewater treatment method that precipitates and separates as hydroxide, a high-concentration suspension circulated in the fourth step and slaked lime required to bring the treated raw water to a desired pH are mixed and stirred in a condition tank. A first step of forming a mixed suspension, the raw water for treatment, and the mixed suspension produced in the first step are mixed and stirred in a first neutralization tank to neutralize the raw water for treatment. A second step of precipitating the dissolved metal component, and introducing a suspension containing the precipitate generated in the second step into a settling tank to settle and concentrate the precipitate, and at the same time, including a surplus sediment from the settling tank. A third step of discharging the overflow water overflowing, and extracting the sediment concentrated in the settling tank as a high-concentration suspension. And circulating it to the condition tank of the first step.
A step of filtering the overflow water discharged from the sedimentation tank with a filtration tank to remove sediment; and washing the filtration tank used in the fifth step and backwashing water containing sediment. And the backwash water generated in the sixth step, the treated raw water, and the slaked lime required to neutralize the treated raw water are mixed and stirred in the second neutralization tank, and mixed. A seventh step of forming a suspension, and introducing the mixed suspension generated in the seventh step to an agglutination reaction tank,
Eighth step of adding a flocculant to this to agglomerate the sediment in the mixed suspension. The mixed suspension in which the sediment is aggregated in the eighth step is led to a sedimentation basin to settle the sediment. A ninth step of separating and discharging the supernatant as clear treated water.