JP2833466B2 - Treatment method for metal-containing wastewater - 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 metal-containing wastewater, and more particularly, to a method for adding an alkali to wastewater containing metal ions to generate insolubilized substances and separating the insolubles from the treated water as sludge. In addition, the present invention relates to a method for treating alkali water mixed with a part of the separated sludge and adding it to wastewater, in which the quality of treated water at the start of operation is prevented from deteriorating, and a method for stably obtaining high-quality treated water.

[0002]

2. Description of the Related Art In the treatment of metal-containing wastewater, the HDS method (High Density Sodium) is used as a method for obtaining high-concentration metal hydroxide sludge rich in concentration and excellent in dehydration.
lid method: U.S. Pat. No. 3,738,932;
No. 1-156). This method is a method in which an alkali agent is not added directly to a metal-containing wastewater, but is added by mixing with a part of sludge separated in the treatment of wastewater, and is also called an alkali sludge method.

[0003]

The HDS method uses Fe ²⁺ , F
It has been applied to the treatment of wastewater containing dissolved metal components such as e ³⁺ , Cu ²⁺ , Al ³⁺ , Cu ²⁺ , Zn ^2+, etc. Since the SS in the treated water obtained is large, there are problems such as poor transparency of the treated water and strong coloring. In particular, the phenomenon of the deterioration of the treated water quality tends to appear remarkably during the start-up operation of the apparatus at the start of the treatment. For example, the chromaticity of the treated water is 20 to 30 degrees during the steady operation after the start-up. In the treatment of wastewater, the chromaticity may be 200 to 400 degrees at startup.

As a method for improving the chromaticity of the treated water,
There is also a method of mixing the treated water with the sedimentation-concentrated sludge for further coagulation and sedimentation treatment. However, this method is not industrially advantageous because the treatment flow is complicated and the amount of liquid distribution is difficult to control. .

[0005] The present invention solves the above-mentioned conventional problems and provides an HD
It is an object of the present invention to provide a method for treating metal-containing wastewater in a method for treating metal-containing wastewater by the S method, in which the quality of treated water during a start-up operation is prevented from deteriorating and stable high-quality treated water is obtained.

[0006]

According to the method for treating metal-containing wastewater of the present invention, an alkali is added to a metal-containing wastewater to form an insolubilized product, which is separated as sludge from treated water, and the alkali is separated. In the method of adding to the wastewater as a mixture obtained by mixing with a part of the sludge, after the start of treatment,
The amount of the separated sludge mixed with the alkali is controlled so that R does not exceed 8 for 1 to 3 days after the value of the return ratio R obtained by the following formula reaches 8, and then R = 12
It is characterized in that the processing is performed at 20.

[0007]

(Equation 2)

[0008]

[Action] In the treatment of metal-containing wastewater by the HDS method,
The return sludge concentration during the start-up operation of the treatment apparatus gradually increases from several g / l with the elapse of the operation, and finally reaches several hundred g / l (normally about 100 to 300 g / l). .

In the HDS method, the amount of SS (kg / hr) generated by neutralizing raw water is represented by the following equation (1), while the amount of returned sludge is represented by the following equation (2).

[0010]

(Equation 3)

Therefore, the return ratio R is represented by the following equation (3).

[0012]

(Equation 4)

In the present invention, at the time of start-up of operation start,
When the return ratio R is from R = 1 to 2 to R = 8, the operation is made to depend on the concentration of returned sludge over time. That is, the flow rate of the returned sludge is set to a predetermined (constant) value without any particular control. As a result, R increases in association with the increase in the sludge concentration.

After the start of the treatment, the return ratio R increases and the discharge amount of the return sludge pump is controlled so that R does not exceed 8 for at least one day, preferably 3 days, from the time when the value of R reaches 8. The amount of separated sludge mixed with the alkali is controlled by controlling the amount of sludge.

Thereafter, the discharge amount of the return sludge pump is increased, and the operation is continued at R = 12 to 20.

In the above equation (3), the flow rate Q of the raw water and the flow rate q of the returned sludge are set by the discharge rates of the raw water pump and the returned sludge pump, respectively. Further, the SS concentration a generated by the neutralization of the raw water is obtained from the quality of the raw water. Therefore, the concentration b of the returned sludge may be detected, and the return amount q of the returned sludge may be adjusted so that the return ratio R calculated from the detected value is within the above range.

As described above, by performing the control based on the return ratio R, it is possible to minimize the deterioration of the treated water quality during the start-up operation.

Incidentally, after controlling so that R does not exceed 8, immediately after the operation is started at R = 12 to 20, the treated water may be slightly deteriorated. It is possible to respond sufficiently by increasing the number of times.

[0019]

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

FIG. 1 is a system diagram showing one embodiment of the method for treating metal-containing wastewater of the present invention. In FIG. 1, 1 is a raw water tank, 2 is a pre-neutralization tank, 3 is a neutralization tank, 4 is a coagulation tank, 5 is a sedimentation tank, 6 is a reaction tank, 7 is an alkaline storage tank, and 8 is a polymer tank. In addition, 2A, 3A, 4A and 6A are stirrers,
B and 3B are pH meters, P ₁ , P ₂ , P ₃ and P ₄ are pumps,
V is a valve, 10 is an air supply pipe, and 11 to 22 are pipes.

In the method of this embodiment, the metal-containing wastewater as raw water is introduced into the pre-neutralization tank 2 via the pipe 11, the raw water tank 1 and the pipe 12. In this preliminary neutralization tank 2,
The raw water is preferably returned to pH by the returned sludge from the pipe 18.
Adjusted to 4-5. The effluent from the pre-neutralization tank 2 is
3 and is introduced into the neutralization tank 3. The neutralization tank 3 has a reaction tank 6
A mixture (hereinafter referred to as “HDS sludge”) prepared by mixing the returned sludge from the pipe 19 with the alkali fed from the alkali storage tank 7 via the pipe 21 is supplied to the pipe 22.
Supplied by PH meter 3B of the neutralization tank 3, in conjunction with the alkali supply pump P _3, intracisternal solution preferably by the addition of HDS sludge so that pH 7-9, are controlled.

The effluent from the neutralization tank 3 is introduced into the coagulation tank 4 from the pipe 14, and is subjected to coagulation by the polymer injected from the polymer tank 8 through the pipe 20. This polymer injection amount is usually about 1 to 5 ppm.

The coagulation solution is then supplied from the pipe 15 to the settling tank 5.
And separated into solid and liquid. Separated water is discharged out of the system through a pipe 16 as treated water, and settled sludge is extracted through a pipe 17, a part of which is returned to a pre-neutralization tank 2 through a pipe 18, and the rest is returned to a reaction tank 6 through a pipe 19. Is done.

In the present invention, during the start-up operation period at the start of operation of the apparatus, the returned sludge concentration is measured continuously or intermittently, and the flow rate Q of raw water and the SS concentration generated by neutralization of raw water are measured. from the a and return sludge concentration b, return ratio R is calculated so that the following ranges I to III, to control the feed volume q of return sludge (discharge amount of the pump P ₂₎ by the equation (3) .

I Period from the start of operation until the return ratio R reaches 8: The amount of the returned sludge is not particularly controlled, and is set to a predetermined amount.

II From the point in time when the return ratio R reaches 8, and for the next 1 to 3 days:
Controls the amount of returned sludge.

III After the above-mentioned II: the return amount of the returned sludge is returned to a predetermined value without being controlled.

By performing such control, the quality of the treated water during the start-up operation can be made good and a stable treatment can be performed.

At the time of the transition from II to III, the quality of the treated water temporarily deteriorates, but this deterioration must be effectively prevented by increasing the polymer injection amount at this transition. Can be. In this case, the amount of the injected polymer at the time of this transition is about 1.5 to 2 times that of the steady state.

In the present invention, the metal-containing wastewater to be treated is a wastewater containing a heavy metal ion or a heavy metal complex of a heavy metal and a chelating agent, such as plating wastewater. Heavy metals include copper, zinc, nickel, cadmium, manganese, lead, iron and the like. Generally, wastewater containing a heavy metal complex is often acidic, but in the present invention, the pH of the wastewater to be treated is an acidic wastewater of 4 or less. Need to be ionized.

The alkali added to these wastewaters includes alkali agents such as sodium hydroxide and slaked lime, and the polymer includes polyacrylamide and partially hydrolyzed products thereof.

Hereinafter, the present invention will be described in more detail with reference to specific examples and comparative examples.

Example 1 According to the method of the present invention shown in FIG.
g and 25 ml of sulfuric acid (98% concentration) dissolved in 200 liters of tap water were treated as raw water. The SS concentration a generated by the neutralization of the raw water is 2520 mg / l.
It is. The device specifications and operating conditions were as follows. Slaked lime was used as the alkali, and polyacrylamide partially hydrolyzed product was used as the polymer.

Reaction tank capacity: 500 ml Pre-neutralization tank capacity: 500 ml Neutralization tank capacity: 1000 ml Precipitation tank capacity: about 3000 ml (diameter 150 mm) Pre-neutralization tank pH: 4.5 Neutralization tank pH: 8.5 Polymer injection Amount: 1 ppm Raw water flow rate Q = 2000 ml / hr and returned sludge quantity q =
Water was continuously passed at 800 ml / hr, during which time the sludge concentration (returned sludge concentration b) was appropriately detected, the return ratio R was calculated, the chromaticity of the treated water was measured, and the relationship with the return ratio R was examined. .

As a result, after the processing started, the chromaticity of the treated water was 30 degrees at the return ratio R = 3, but the chromaticity of the treated water was deteriorated to 50 degrees at the return ratio R = 6. At = 8, the chromaticity of the treated water further deteriorated to 80 degrees.

Therefore, the return ratio R does not exceed 8.
As a result of controlling the amount of returned sludge, the chromaticity of the treated water, which was 80 degrees immediately after reaching the return ratio of 8, changed to 60 degrees after 12 hours,
The temperature gradually decreased to 50 degrees after 4 hours, 40 degrees after 48 hours, and 35 degrees after 72 hours.

Then, after 72 hours (3 days), when the chromaticity of the treated water decreased to 35 degrees, the amount of returned sludge was changed so that the return ratio R = 12. 3
Degraded from 5 degrees to 90 degrees. However, at this time, it was confirmed that the chromaticity of the treated water could be set to 40 degrees by setting the amount of the injected polymer to 2 ppm from the result of the same experiment separately performed at the amount of the injected polymer of 2 ppm. The increase in chromaticity when this return ratio is changed from R <8 to R = 12 is a temporary phenomenon. Thereafter, at R = 12, the chromaticity of the treated water becomes 35 at a polymer injection amount of 1 ppm.
About 40 degrees could be maintained.

The return ratio, the chromaticity of the treated water (value obtained after standing for 3 minutes in the jar test) and the sludge concentration over time in this embodiment are as shown in FIGS. 2, 3 and 4, respectively. Was.

COMPARATIVE EXAMPLE 1 Returned sludge amount was fixed at q = 800 ml / hr, returned sludge amount was not controlled, and after the start of water supply, the returned sludge was allowed to increase in concentration over time until a return ratio R = 15. Processing was performed in the same manner as in Example 1 except that the ratio was increased.

As a result, the treated water quality was relatively good and the chromaticity was not more than 50 degrees up to the return ratio R = 8.
= 24, the chromaticity of the treated water rapidly deteriorates to 300 to 400 degrees, and this chromaticity deterioration can only be improved to around 120 degrees even if the polymer injection amount is 2 ppm. It was confirmed from the results of the same operation performed separately at a polymer injection amount of 2 ppm.

After the elapse of 12 hours, 24 hours, 48 hours, and 60 hours, the treated water was subjected to coagulation sedimentation treatment by a jar test. For example, the chromaticity of the treated water after 60 hours was as follows: 80% even if 3 ppm of polymer is added.
It was confirmed that the quality of the treated water deteriorated, which could not be dealt with by simply increasing the amount of injected polymer.

Thereafter, from around 72 hours after the start of the treatment, the quality of the treated water was recovered, and a water quality with a chromaticity of about 50 degrees was obtained. This is presumed to be due to the aging of HDS sludge.

The time-dependent changes in the return ratio, the chromaticity of the treated water (value obtained after standing for 3 minutes in the jar test) and the sludge concentration in this comparative example were as shown in FIGS. 5, 6 and 7, respectively.

In this comparative example, the quality of the treated water deteriorates during the start-up operation of the apparatus for about 1 to 2 days.
After that, a certain degree of recovery is seen, but even if the chromaticity exceeds 100 continuously for 1 to 2 days, the treated water can be discharged even only during the start-up operation of the apparatus. Therefore, it is extremely important to improve the quality of the treated water during the start-up operation because it requires separate treatment.

[0045]

As described above in detail, according to the method for treating metal-containing wastewater of the present invention, an alkali is added to wastewater containing metal ions to generate insolubilized substances, which are separated as sludge from treated water. A method in which an alkali is mixed with a part of the separated sludge and added to wastewater. In the treatment method, it is possible to prevent deterioration of treated water quality at the start of operation and to obtain high-quality treated water stably. It is possible.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a change over time in a return ratio in Example 1.

FIG. 3 is a graph showing the change over time in the chromaticity of treated water in Example 1.

FIG. 4 is a graph showing the change over time in the sludge concentration in Example 1.

FIG. 5 is a graph showing a change over time in a return ratio in Comparative Example 1.

FIG. 6 is a graph showing the change over time in the chromaticity of treated water in Comparative Example 1.

FIG. 7 is a graph showing the change over time in the sludge concentration in Comparative Example 1.

[Explanation of symbols]

 1 Raw water tank 2 Pre-neutralization tank 3 Neutralization tank 4 Coagulation tank 5 Sedimentation tank 6 Reaction tank 7 Alkaline storage tank 8 Polymer tank

Claims (1)

(57) [Claims] 1. An alkali is added to a metal-containing wastewater to produce an insolubilized product, which is separated as sludge from treated water, and the alkali is mixed with a part of the separated sludge to form a mixture obtained in the wastewater. In the method of adding, after the start of the treatment, from the time when the value of the return ratio R calculated by the following formula reaches 8, so that R does not exceed 8 for 1 to 3 days,
A method for treating metal-containing wastewater, comprising controlling the amount of the separated sludge to be mixed with an alkali, and then treating the sludge at R = 12 to 20. (Equation 1)