JP2002018485A - Method for treating metal-containing wastewater and method for recovery of valence metal from the metal- containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an amount of generated sludge by efficiently and safely treating metal-containing wastewater to recover a valuable metal from the metal-containing wastewater. SOLUTION: When metal-containing wastewater is treated, bivalent iron is oxidized to trivalent iron by using iron-oxidizing bacteria of common autotrophism at 1-3 pH. After decomposing by oxidizing organic matter in the wastewater, hydroxide of iron is generated at 3-5 pH, and the iron hydroxide is recovered. Thereafter, the pH is adjusted to 8-10 by an alkali agent, and hydroxides of other metals are generated to be recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently and stably treating metal-containing wastewater and reducing and generating sludge by recovering and reusing valuable metals contained in the metal-containing wastewater. It is about.

[0002]

2. Description of the Related Art Wastewater containing metals includes mine drainage, chemical factory drainage, sewage mill drainage, steel mill drainage, plating factory drainage, and waste incineration plant drainage. Among them, for example, plating factory wastewater has a low pH of 2-3, and although it depends on the type of plating, in addition to iron (divalent), nickel, zinc, tin, chromium,
It often contains metal ions such as copper. Since these metal ions are subject to wastewater regulations as harmful metals, it is necessary to remove them from wastewater to a regulated value. However, if it can be separated and recovered as metal, there is a possibility that its value as a resource will arise. Furthermore, plating plant wastewater may contain organic substances such as surfactants and plating bath additives, which are detected as COD (Chemical Oxygen Demand), which may require COD treatment. is there.

[0003] A conventional method for treating metal-containing wastewater will be described below.

A typical treatment method of metal-containing wastewater which has been widely used in the past is a neutralization coagulation sedimentation method. This method raises the pH of the wastewater with an alkaline agent such as calcium hydroxide, and converts metal ions in the wastewater into hydroxides.
The metal is removed from the water by sedimentation in a sedimentation basin or the like.

This method has the following problems.

[0006] 1) The flocs of metal hydroxide are fine, and sedimentation and separation in a sedimentation basin are not stable. In order to prevent this, it is necessary to add a polymer flocculant in addition to the alkali agent.

2) Since the slush generated is a mixture of various metals, it is difficult to reuse the slush, and most of the slush is disposed of by landfill.

[0008] 3) As a neutralizing agent for plating wastewater,
Slaked lime (Ca (OH) ₂ ) is used. this is,
Slaked lime is less expensive than sodium hydroxide, has relatively high solubility in water, and is highly reactive. However, the generated slush has a high water content of 99%, and is reduced to only 70 to 80% even after the dehydrator treatment. In addition, a large amount of undissolved calcium components is contained. For this reason, the volume of the sediment is large, and storage, transportation, and disposal costs increase.

[0009] 4) The effect of reducing organic matter in wastewater can hardly be expected by the neutralization coagulation sedimentation method alone. Because of this, CO
It may be necessary to remove organic matter measured as D.

[0010] In addition to the neutralization coagulation sedimentation method, sulfide precipitation method, ion exchange resin method, chelate resin method, membrane separation method (RO membrane), solvent extraction, etc. Method, bioconcentration method, activated carbon adsorption method and the like. The features are briefly described below.

1) Sulfide precipitation method: Sodium sulfide (N
a ₂ S) is injected to precipitate heavy metals as sulfides. Comparing the solubility products of hydroxide and sulfide,
Sulfides are much lower and lower concentrations of metals can be obtained. On the other hand, the sulfide precipitation method is difficult to separate the formed precipitate (it is easy to form colloid) and safety (sodium sulfide).
Da has not been used in practice because harmful hydrogen sulfide gas is easily generated by contact with acidic substances. In addition, the precipitate is a mixture of various metals, and must be disposed of in the same manner as in the neutralization coagulation sedimentation method.

2) Ion exchange resin method: The ion exchange resin method is widely used for producing pure water. When applied to wastewater treatment, metal ions are adsorbed on the cation exchange resin and / or the anion exchange resin. However, when the ion concentration in the wastewater is considerably high, as in wastewater treatment, adsorption and regeneration of the resin are not possible. There is a problem that gets complicated. Also, it is difficult in principle to selectively separate metal components other than cations and anions.

3) Chelate resin method: The chelate resin method comprises:
Uses a resin that has particularly high selectivity for a specific metal (a resin in which a chelate-forming group that forms a complex with a metal ion is introduced into a polymer having a cross-linking structure). It can be removed up to the concentration. It is used to remove mercury from waste incineration plant effluent. After all, when the ion concentration in the wastewater is high, there is a problem that the adsorption and regeneration of the resin become complicated.

4) Membrane method: The membrane method is a reverse osmosis membrane (RO: Reve
Rse Osmosis) is widely used for desalination of seawater and reuse of industrial wastewater. Utilizing the osmotic pressure, only the solvent is moved through the membrane, and clear treated water can be obtained.
On the other hand, a liquid in which salts are concentrated is generated at the same time. In addition, complicated cleaning and pretreatment of the membrane and high pressure are required. It is difficult to selectively separate and concentrate metal ions.

5) Bioconcentration method: The bioconcentration method is a method in which a specific metal ion is ingested by a microorganism and a specific heavy metal is concentrated in the body of the microorganism.

6) As a method for recovering heavy metal ions from sludge containing heavy metals, a method of bacterial leaching and a method of solvent extraction have been proposed.

[0017]

The method for treating metal-containing wastewater which has been found to date has the following problems.

First, the neutralization coagulation sedimentation method and the sulfide sedimentation method. As described above, the generated sludge is a mixture of various metals contained in the wastewater. For this reason,
It is extremely difficult to reuse the generated slush. For this reason, most of the slashes that have occurred are currently landfilled. Further, since the generated slush contains undissolved slaked lime, there is a problem that the amount of solids increases. Further, since the generated slush has a very high water content of generally 70-80%, the volume thereof also increases. As a result, there is a problem that disposal costs increase due to an increase in the amount of slush generated.
In addition, there is almost no effect on the removal of organic substances measured as COD.

Next, problems of the ion exchange resin method will be described. Conventionally, ion exchange resins have been widely used for boiler water supply for thermal power generation, ultrapure water production for semiconductors, and the like. Raw water to be treated has an ion concentration of 1000 mg /
1 or less. It is difficult to apply to wastewater with high ion concentration. Further, since the regenerating solution of the ion exchange resin is a mixture of various heavy metal ions, it is difficult to reuse it. Furthermore, the operation is complicated (pretreatment, desorption), and the cost for wastewater treatment is high. Also, if you use it for a long time,
The ion exchange resin is contaminated with metal hydroxides, organic substances, bacteria and the like, and it is difficult to recover the resin by a normal resin regeneration operation. The chelate resin method also has the same problems as the ion exchange resin method, and it is considered difficult to apply the method to wastewater treatment aimed at recovering valuable metals.

Further, as a membrane method, a reverse osmosis membrane (RO)
Membrane: Reverse Osmosis) is widely used for raw water having a salt concentration of about 1,000 to 10,000 mg / l, such as desalination of seawater. In some cases, it has been applied to the reuse of plating wastewater. " (For example, reuse of plating effluent by reverse osmosis method, Yoroku Wada, PPM, 16-
27, 1986) When RO is used for wastewater treatment, not only heavy metals but also inorganic ions can be removed from raw water, so that there is an advantage that membrane permeated water can be reused as industrial water. However, a small amount of concentrated liquid is generated at the same time. Since this concentrated liquid contains not only heavy metal ions but also various inorganic ions, it is difficult to reuse the concentrated liquid. RO has a problem that the running diameter of wastewater treatment increases because the membrane diameter is extremely small and high pressure (1 to 6 MPa) is required. Regarding the plating wastewater treatment, UF membrane (UF: Ultra F)
illumination), MF film (MF: Micron)
Filtration) is rarely used alone. (For example, use of ultrafiltration membrane / microfiltration membrane in wastewater treatment Application example to wastewater treatment-plating wastewater,
Yoshimichi Mitsugami, Water Pollution Research, 10, 3, 153-154,
1987) For example, in the United States regarding plating wastewater treatment,
There is a study case combining a polymer flocculant and a UF membrane, but it has not been put to practical use. It is considered that the amount of permeated water of the UF membrane is small.

Finally, regarding the bioconcentration method, the uptake rate of heavy metals by living organisms is still small and unstable, and practical use is difficult at this stage. In addition, there seems to be a problem of separating and recovering heavy metals concentrated in living organisms.

As described above, the currently known method is constructed from the viewpoint of removing metal from water containing metal to a regulated value or less from the water or effectively using treated water. There is a lack of viewpoints to reduce generated slush by recovering and reusing valuable metal resources from wastewater. At the end of the day, neutralization coagulation and sedimentation is the most widely used metal-containing wastewater treatment, and the generated sludge is disposed of in landfills regardless of whether it contains valuable metals.

[0023]

SUMMARY OF THE INVENTION The gist of the present invention is to develop a process for purifying water and treating valuable metals at the same time when treating metal-containing wastewater, thereby significantly reducing the amount of slush. And the following (1) to (11) as described in the claims. (1) When treating metal-containing wastewater, oxidize ferrous iron to trivalent iron and oxidatively decompose organic matter in the wastewater using a facultative autotrophic iron-oxidizing bacterium under conditions of pH 1 to 3. A method for treating metal-containing wastewater, comprising: (2) When treating metal-containing wastewater, use the method described in (1) above.
After oxidizing ferrous iron to ferric iron, the pH is adjusted to 3 with an alkaline agent.
A method for recovering valuable metals from metal-containing wastewater, wherein the method comprises forming iron hydroxide and recovering the iron hydroxide. (3) In treating the metal-containing wastewater, the pH is 3 to 4 to oxidize ferrous iron to ferric iron using a fermentative autotrophic iron-oxidizing bacterium and oxidatively decompose organic substances in the wastewater, A method for recovering valuable metals from metal-containing wastewater, comprising forming an iron hydroxide and recovering the iron hydroxide. (4) After treating the metal-containing wastewater by the method of (2) or (3), the pH is adjusted to 8 to 10 with an alkali agent to form and collect the metal hydroxide. A method for recovering valuable metals from metal-containing wastewater. (5) The method for recovering valuable metals from metal-containing wastewater according to any of (1) to (4), wherein a facultative autotrophic iron-oxidizing bacterium acclimated from activated sludge is used. (6) Any one of the above (1) to (5), characterized in that a chemical oxidizing agent and / or an apparatus for oxidizing organic substances in wastewater by using ultraviolet light and / or a photocatalyst is used at the latter stage of the reaction tank for iron oxidizing bacteria. 3. The method for recovering valuable metals from metal-containing wastewater according to 1. (7) The amount of air blown into the reaction tank of facultative autotrophic iron-oxidizing bacteria is determined by measuring the oxidation-reduction potential (based on silver and silver chloride) at +550 mV (silver /
The method for recovering valuable metals from metal-containing wastewater according to any one of the above (1) to (6), wherein the value is adjusted so as to be not less than silver chloride. (8) The method for recovering valuable metals from metal-containing wastewater according to any of (2) to (7) above, wherein a membrane separation device is used as a method for recovering the metal hydroxide. (9) The method for recovering valuable metals from metal-containing wastewater according to any of (2) to (8) above, wherein a membrane made of ceramics is used as the membrane separation device. (10) The method for recovering valuable metals from metal-containing wastewater according to any one of the above (2) to (9), wherein a membrane separation device having a pore diameter of 0.1 μm or more is used. (11) When adjusting the pH with an alkaline agent, the (1) ~ characterized in that a polymer coagulant or a liquid chelating agent is introduced
The method for recovering valuable metals from metal-containing wastewater according to any of (10).

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the present invention will be described below in detail.

[0025] The present inventors first use a facultative autotrophic iron-oxidizing bacterium to biologically oxidize ferrous iron into trivalent iron in advance and recover it, and oxidize and remove organic substances serving as COD components. For example, the inventors proposed that recovery of valuable metals in wastewater becomes easier, and applied a membrane separation method as a method of recovering valuable metals, thereby successfully separating and recovering each valuable metal type. According to this method, the quality of the treated water can be made equal to or lower than the wastewater regulation value, and valuable metals can be separated, collected and reused from the metal-containing wastewater. Hereinafter, a description will be given of a plating factory wastewater containing iron, nickel, and zinc as an example of the metal-containing wastewater.

Metal-containing wastewater such as plating factory wastewater usually has a low pH of 2 to 3, and iron contained therein is ferrous iron.
Divalent iron has high solubility at low pH. For this reason, in order to separate and recover only iron in advance, first, in a low pH region, 2
It is necessary to oxidize ferrous iron to trivalent iron. As a method of oxidizing ferrous iron contained in metal-containing wastewater to ferric iron,
Although a method of oxidizing using a chemical oxidizing agent such as ozone, chlorine, potassium permanganate, and hydrogen peroxide is conceivable, the present inventors set the pH to 1 with an alkali agent and an acid when treating metal-containing wastewater. It has been found that by using a facultative autotrophic iron-oxidizing bacterium while maintaining at ~ 3, ferrous iron can be oxidized to trivalent iron and the organic matter in wastewater can be easily reduced.

The inventive process consists of the following three stages. 1) Oxidation of ferrous iron and oxidative degradation of organic matter by facultative autotrophic iron-oxidizing bacteria (optimal pH: 1 to 3) 2) Aggregation and precipitation of ferric iron and soluble organic matter (optimal pH: 3) 5) 3) Aggregation / precipitation removal process of metal ions other than iron (optimum p
H: 8 to 10) First, the process of oxidizing ferrous iron and oxidative decomposition of organic matter by the facultative autotrophic iron-oxidizing bacteria will be described.

The iron oxidizing bacteria widely known so far include neutral and active heterotrophic filamentous bacteria and Thiobachillus ferrooxida which is a chemoautotrophic bacterium active in the acidic region.
ns). Biological methods for oxidizing ferrous iron in wastewater to trivalent iron using Thiobachillus ferrooxidans are described in JP-B-47-38981, JP-B-55-18559, JP-B-55-22345, and JP-B-57-44393. Although known in the gazettes and the like, all of these methods use Thiobachillus ferrooxidans, which is an absolute autotrophic bacterium. When treating wastewater containing ferrous iron with Thiobachillus ferrooxidans, there is an advantage that ferrous iron can be rapidly oxidized to ferrous iron at a low pH stage.

However, it is an iron-oxidizing bacterium of absolute autotroph.
Since Thiobachillus ferrooxidans cannot decompose and assimilate organic matter, if organic matter is present in the wastewater, it is susceptible to this inhibition and the oxidation rate of ferrous iron tends to decrease. Thus, the present inventors have developed a neutral (pH: 6 to 8) active sludge that decomposes organic substances in sewage from a facultative autotrophic iron-oxidizing bacterium that is active in an acidic region to a low-pH metal. It has been found that it can be easily acclimated using the contained wastewater.
Such a facultative autotrophic iron-oxidizing bacterium can decompose and assimilate organic substances such as surfactants that inhibit the absolute autotrophic bacterium Thiobachillus ferrooxidans, so that it can be easily applied to plating wastewater treatment. There is.

Furthermore, it was found that the facultative autotrophic iron-oxidizing bacteria had the highest oxidation rates of ferrous iron and organic substances in the pH range of 1 to 3. Therefore, it is desirable to maintain the pH of the biological reaction tank at 1 to 3 from the viewpoint of oxidation of ferrous iron and oxidative decomposition of organic substances.

However, when the pH is less than 3, trivalent iron generated as a result of the oxidation reaction is likely to be present in a dissolved state. For this reason, it is necessary to separately provide an iron recovery tank for recovering the hydroxide of trivalent iron. In order to recover the hydroxide of trivalent iron, a tank may be provided at the latter stage of the reaction tank for the iron-oxidizing bacteria, and the pH of the tank may be maintained at 3 to 5 with an alkaline agent. If the pH exceeds 5, metal ions other than iron tend to be formed as hydroxides. Further, when the pH is less than 3, the trivalent iron generated as a result of the oxidation reaction is likely to be present in a dissolved state.

In order to oxidize ferrous iron in one tank and collect the hydroxide of ferrous iron, it is possible to set the pH control range to 3-4. The oxidation rate of ferrous iron is slightly smaller than the maximum rate, but there is an advantage that the reaction tank and the iron recovery tank can be integrated into one. These methods may be selected from the viewpoint of economy.

After removing iron and organic substances by such a method, when the pH is adjusted to 8 to 10 with an alkaline agent, precipitation of hydroxides of valuable metals such as zinc and nickel occurs, which may be collected. The control pH may be determined by using a metal solubility curve based on cost, required treatment water quality, and the like. In the case of an amphoteric metal, if the pH exceeds 10, generally, re-dissolution may occur. If the pH is less than 8, the solubility is generally high. For this reason, the pH is desirably about 8 to 10. However, when it is desired to completely remove the amphoteric metal, for example, zinc or lead, the pH may be adjusted to 12 or more and the amphoteric metal may be removed from the collected material.

Further, when many organic substances which are difficult to decompose even when using facultative autotrophic iron-oxidizing bacteria are contained and it is highly necessary to promote the removal of the organic substances, if the iron-oxidizing bacteria need to be promoted, an oxidation tank using iron-oxidizing bacteria may be further provided. It is desirable to provide one or more oxidation tanks selected from an oxidation tank using a chemical oxidant, an oxidation tank using ultraviolet light, and an oxidation tank using a photocatalyst. This method can promote the oxidative decomposition of organic substances that are hardly decomposed.

Further, if ferrous iron or hydrogen peroxide remains in the treated water, it is measured as COD, so that the oxidation-reduction potential (OR
P) can be maintained at + 550mV (silver / silver chloride standard) or higher.
The number of blowers and the number of rotations may be controlled by the amount of air blown into the reaction tank for iron oxidizing bacteria. The amount of the chemical oxidizing agent to be added may be controlled so that the oxidation-reduction potential (ORP) of the chemical oxidizing tank subsequent to the iron oxidizing bacteria oxidizing tank can be maintained at +550 mV or more (based on silver / silver chloride). Redox potential is +550 mV (silver /
If it is equal to or greater than silver chloride, ferrous iron has been oxidized to 99% or more up to trivalent iron.

Next, a method for recovering metal hydroxide using a membrane will be described. The inventors measured the size of the flocs of metal hydroxides of iron, nickel, and zinc, and found that
m to about 50 μm. It is difficult to remove this hydroxide by sedimentation and separation using a sedimentation basin or the like as it is, and it is conceivable to remove the hydroxide by membrane separation. However, when applying the membrane separation process, the following points are important. 1) The membrane continuously obtains a predetermined separation performance with respect to metal hydroxide. 2) The permeated water volume of the membrane is large and the aging is small. 3) The operating pressure of the membrane is small and the aging is small. 4) The membrane is not easily clogged and the regeneration is easy. 5) The operating pH range of the membrane is wide and the high water temperature can be used. It can be seen that it is necessary to use a membrane having a large pore diameter as much as possible in order to secure the drainage amount. However, RO membranes and UF membranes which have been studied conventionally have extremely small amounts of permeated water, and are difficult to apply to wastewater treatment.

However, from the size of the metal hydroxide after the pH adjustment, it was found that 99 to 100% of the metal hydroxide could be separated if the membrane had a diameter of 0.1 μm or more and 1 μm or less. . Also, even if the diameter is up to 10 μm, 90-100%
Can be separated. By permeating the pH-adjusted metal-containing wastewater through a membrane, a membrane-permeated liquid and a concentrated solution of a metal hydroxide can be obtained. For example, in the case of plating wastewater mainly composed of nickel and zinc, the concentrated solution is concentrated at a high concentration with hydroxides of nickel and zinc. On the other hand, since the membrane permeated liquid hardly contains nickel ions and zinc ions, it can be discharged as it is.

Next, the promotion of floc formation by the polymer flocculant will be described. The polymer flocculant desirably reacts selectively with metal ions in water to form a water-insoluble metal floc. Examples of the polymer flocculant for selective collection of heavy metals include polyacrylic acid, polyvinyl alcohol, and polyethylenemine. The size of the floc is 50 μm or more. As a result, it is sufficient that the membrane used has a pore size of 50 μm. Instead of the polymer flocculant, a liquid chelating agent having a certain ability to selectively remove heavy metals may be used. When it is difficult to selectively adsorb and aggregate metals even when a liquid chelating agent is used, selective recovery of metal ions may be possible by changing the pH at the time of metal desorption from the liquid chelating agent.

The material of the film used in this process is p
Since H is maintained at about 3 to 10, acid resistance and alkali resistance are indispensable conditions. Further, since the water temperature of the waste water is 20 ° C to 40 ° C, it is required that the wastewater has heat resistance and further that it has abrasion resistance. Examples of the material of the film include stainless steel fiber as a metal material, ceramics and glass fiber as an inorganic material, and polysulfone, polyolefin, polypropylene, polyvinyl alcohol, and polyacrylonitrile as an organic polymer material. Among them, ceramics are excellent in acid resistance, abrasion resistance, and heat resistance, and are most suitable as a material of a film used for plating drainage and the like. As a ceramic material, it is desirable that silica-alumina-based clay is mainly used.Fresh ash which is a by-product of a power plant and blast furnace slag and a converter slag which are a by-product of a steel plant are mixed with this. I don't care. Next, examples of the present invention will be described.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the method of the present invention is applied to the treatment of plating wastewater generated from an ironworks will be described. FIG. 1 shows the process flow.

The process comprises a prior iron oxidation tank (2) using facultative autotrophic iron-oxidizing bacteria, a membrane separation tank A (3), and a membrane separation tank B (4). The membrane separation tank A (3) and the membrane separation tank B (4) are controlled by a pH meter (7). Ceramic film (5) by the floor (8) supplied to the air diffuser
Is constantly cleaned from the outside.

Table 1 summarizes the tank functions.

[0043]

[Table 1]

First, facultative autotrophic iron-oxidizing bacteria were selectively grown. Iron-oxidizing bacteria (Thioba)
chillus ferrooxidans) is low p with almost no organic matter
H inhabits mine drainage and acid drainage pits in rivers and steelworks, but it is difficult to obtain due to the special environment. The inventors have found that activated oxidized bacteria of facultative autotroph inhabit in activated sludge used for organic wastewater such as municipal sewage and food industry wastewater, and propagated it in a short period of time.
The present invention is applied to a method for treating metal-containing wastewater and recovery of valuable metals from metal-containing wastewater. Hereinafter, a method for growing facultative autotrophic iron-oxidizing bacteria will be described.

The activated sludge collected from the sewage treatment plant is put into the iron oxidation tank (2) in advance, and the pH is adjusted to pH = NaOH.
Adjusted to 2.5. Thereafter, the mixture was allowed to stand for 2 hours, and the supernatant was discarded. Then, plating wastewater containing an organic substance was poured in until the tank (2) in advance was filled with ferric acid. Further, air was supplied by a blower so that the dissolved oxygen in the pre-ferric acid lower tank (2) became 2 mg / l or more. Thereafter, the oxidation-reduction potential (ORP) of the ferric acid lower tank (2) was monitored in advance, and when the ORP reached +550 mV, the supply of air was stopped and the mixture was allowed to stand for 2 hours, and the supernatant was discarded. Sludge of facultative autotrophic iron-oxidizing bacteria was deposited on the bottom. Thereafter, the plating wastewater is again charged until the preliminary iron oxidation tank (2) is full, and the same operation is repeated.
Faculty autotrophic iron-oxidizing bacteria were grown.

When the weight concentration of facultative autotrophic iron-oxidizing bacteria is 20
When the water content reaches 00 mg / l, the pH of the iron oxidation tank (2) is adjusted to N
While maintaining the pH at 2 to 2.5 with aOH and sulfuric acid, the plating wastewater is pre-residence time (HR) in the iron oxidation tank (2).
T) was continuously supplied so as to be 60 minutes. In continuous treatment, the oxidation-reduction potential (ORP) of the iron oxidation tank (2) is +
The rotation speed of the blower was controlled and aerated so as to be maintained at 550 mV.

Further, in the membrane separation tank A (3), the pH was adjusted to 4 with a 1 mol / l NaOH solution, and an iron hydroxide was formed with stirring. The membrane has a pore size of 1
A μm silica-alumina ceramic film (5) was used. The amount of permeated water was operated at 20 m / day. Part of the concentrated iron sludge (9) is returned to the pre-oxidation tank (2).

Subsequently, in the membrane separation tank B (4), the pH was adjusted to 10 with a 1 mol / l NaOH solution, and nickel and zinc hydroxides were formed with stirring. As the film, a silica-alumina-based ceramic film (5) having a pore diameter of 1 μm was used. The amount of permeated water was operated at 20 m / day.

Table 2 shows the average water quality of drainage and permeated water.

The wastewater is mainly composed of iron (average 150 mg / l), zinc (average 90 mg / l) and nickel (average 51 mg / l). Iron in the wastewater is on average 99% by the membrane separation tank A (3).
% Removed. Zinc and nickel were almost completely removed by the membrane separation tank B (4). Organic substances represented by TOC (total carbon concentration) could be removed by 95% or more.

[0051]

[Table 2]

Further, the membrane separation tank A (3) and the membrane separation tank B
Table 3 shows the average value of the component analysis after drying the concentrated slush in (4).

In the membrane separation tank A (3), iron (average 40)
%) As a main component. Almost no zinc or nickel. In the membrane separation tank B (4), a slush II (10) mainly composed of zinc (average 41%) and nickel (average 15%) was obtained. Contains almost no iron.

[0054]

[Table 3]

From these results, it is considered that iron and nickel / zinc can be almost completely separated by pre-oxidation using a facultative autotrophic iron-oxidizing bacterium and ceramic membrane separation with a particle diameter of 1 micron. In addition, organic substances serving as a COD source can also be removed by facultative autotrophic iron-oxidizing bacteria.

According to the present method, the metal component in the plating wastewater is
Separation and recovery made it possible to reuse, and as a result, almost no amount was disposed of as sludge. In addition, 80-90% of organic matter as COD source in plating waste water is removed by the facultative autotrophic iron oxidizing bacteria.
There were no water quality problems.

[0057]

According to the present invention, wastewater containing metals can be treated efficiently and stably, valuable metals can be separated and recovered from wastewater containing metals, and the amount of sludge generated can be reduced. .

[Brief description of the drawings]

FIG. 1 is a processing flow of the present invention.

[Explanation of symbols]

 (1) Drainage tank (2) Pre-iron oxidation tank using facultative autotrophic iron-oxidizing bacteria (3) Membrane separation tank A (4) Membrane separation tank B (5) Ceramic membrane (6) ORP meter (7) pH meter (8) Blower (9) Iron-based sludge (10) Nickel / zinc-based sludge (11) Treated water tank (12) Alkaline agent (NaOH) (13) Acid (sulfuric acid)

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Claims (11)

[Claims] In treating metal-containing wastewater, ferrous iron is oxidized to trivalent iron using a facultative autotrophic iron-oxidizing bacterium at a pH of 1 to 3, and organic substances in the wastewater are oxidatively decomposed. A method for treating metal-containing wastewater. 2. When treating metal-containing wastewater, ferrous iron is oxidized to ferric iron by the method of claim 1, and then the pH is adjusted to 3 to 5 with an alkali agent to form iron hydroxide to form iron hydroxide. A method for recovering valuable metals from metal-containing wastewater, comprising recovering a hydroxide. 3. When treating metal-containing wastewater, ferrous iron is oxidized to trivalent iron using a facultative autotrophic iron-oxidizing bacterium at a pH of 3 to 4 and organic matter in the wastewater is oxidatively decomposed. And a method of recovering valuable metals from metal-containing wastewater, wherein at the same time, an iron hydroxide is formed to recover the iron hydroxide. 4. The metal-containing waste water according to claim 2 or 3.
A method of recovering valuable metals from metal-containing wastewater, wherein the pH is adjusted to 8 to 10 with an alkali agent to form and recover metal hydroxides. 5. The method for recovering valuable metals from metal-containing wastewater according to claim 1, wherein a facultative autotrophic iron-oxidizing bacterium acclimated from activated sludge is used. 6. An apparatus for oxidizing organic substances in wastewater using a chemical oxidizing agent and / or ultraviolet light and / or a photocatalyst in a stage subsequent to a reaction tank for iron oxidizing bacteria.
5. The method for recovering valuable metals from wastewater containing metals according to any one of 5. 7. The redox potential (based on silver / silver chloride) of the sub-air volume blown into the reaction tank of facultative autotrophic iron-oxidizing bacteria is +
The method for recovering valuable metals from metal-containing wastewater according to any one of claims 1 to 6, wherein the value is adjusted to be 550 mV (based on silver / silver chloride). 8. A method for recovering a metal hydroxide,
The method for recovering valuable metals from metal-containing wastewater according to any one of claims 2 to 7, wherein a membrane separation device is used. 9. The method for recovering valuable metals from metal-containing wastewater according to claim 2, wherein a membrane made of ceramics is used as the membrane separation device. 10. The method for recovering valuable metals from metal-containing wastewater according to claim 2, wherein a membrane separation device having a pore size of 0.1 μm or more is used. 11. The method according to claim 1, wherein a polymer coagulant or a liquid chelating agent is added when adjusting the pH with an alkali agent. Collection method.