JP2002045869A - Waste water treating method and device for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treating method which is little in the amount of the sludge containing dioxins to be generated and facilitates the treatment of the sludge, and a device for the same. SOLUTION: The treating method for the waste water containing the dioxins has a process step of accepting the waste water containing the dioxins, subjecting the waste water to a first step of pH regulation for regulating the pH to a range below 6 and separating the solid content contained in the water subjected to the pH regulation, and a process step for subjecting the pH of the water separated of the solid content to a second step of the pH regulation for regulating the pH of the water separated of the solid content in this process step to a range of alkalinity, then separating the solid content included in the water subjected to the pH regulation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a wastewater such as a wastewater generated when an incineration exhaust gas discharged from a waste incinerator is subjected to wet smoke treatment, a leachate at a final waste disposal site, and an industrial wastewater. The present invention relates to a method and an apparatus for treating wastewater containing dioxins.

[0002]

2. Description of the Related Art Dioxins are contained in wastewater generated when wet incineration exhaust gas discharged from a waste incinerator is subjected to wet smoke treatment and leachate generated at a final waste disposal site. Some wastewaters also contain dioxins.

[0003] In the treatment of these wastewaters, for example, wastewater generated when wet incineration exhaust gas is subjected to wet smoke treatment, and leachate such as leachate from a landfill for final disposal of general waste and industrial waste are treated. In this case, the processing is performed according to the processing flow shown in FIG.

In this treatment method, wastewater received in a wastewater tank 60 is introduced into a regulating tank 61, and a treatment is performed to add an alkali to precipitate heavy metals. The water discharged from the adjusting tank 61 is introduced into the sedimentation tank 62, and a coagulant is added to cause coagulation and sedimentation to separate sludge. In the case of containing organic pollutants such as leachate, the water from which the sludge has been separated is sent to the biological treatment tank 63 for biological treatment to decompose organic matter. Then, the biologically treated water is sent to the sedimentation tank 64, where necessary, a coagulant is added to cause coagulation and sedimentation, and the sludge is separated.

[0005] Next, in both cases where the biological treatment was not performed and where the biological treatment was performed, the water from which the sludge was separated was sent to the sand filtration tower 65 to remove the remaining SS, and then subjected to the ozone / ultraviolet treatment. The dioxin is introduced into a dioxin decomposer 66 by an accelerated oxidation method to decompose dioxins, and, if necessary, an activated carbon treatment is carried out to discharge as treated water. In the dioxin decomposer 66, a process for reducing the dioxin content to a level of 1 pg / l or less is performed.

[0006]

However, since dioxins have a very low solubility in water, most of the dioxins contained in the wastewater are discharged from the settling tank 62 in the prior art. Mixed into
Before reaching the dioxin decomposer 66, it is discharged out of the system. Therefore, when treating wastewater in which a large amount of sludge is generated, a large amount of sludge containing dioxins must be treated. In particular, when treating wastewater containing heavy metals, sludge containing a large amount of dioxins and heavy metals is generated. For the same sludge, there are two types of treatments, a treatment for decomposing dioxins and a treatment for stabilizing heavy metals. Must be done. For this reason,
Sludge treatment becomes very complicated.

[0007] It is an object of the present invention to provide a wastewater treatment method and a wastewater treatment method that generate a small amount of sludge containing dioxins and that can easily treat sludge.

[0008]

The above object is achieved by the following invention.

According to the first aspect of the present invention, there is provided a method for treating wastewater containing dioxins, wherein a first stage of pH adjustment for receiving wastewater containing dioxins and adjusting the pH to a range of 6 or less is performed. After the step of separating the solid content contained in the obtained water and the second stage of pH adjustment for adjusting the pH of the water from which the solid content was separated in this step to an alkaline range, the pH was adjusted. Separating a solid content contained in water.

According to a second aspect of the present invention, there is provided the wastewater treatment method according to the first aspect of the present invention, wherein a substance containing a component that does not dissolve in acidic water is added during the first-stage pH adjustment. It is.

According to a third aspect of the present invention, in the first or second aspect of the invention, after performing the first-stage pH adjustment, a part of the sludge discharged when the solid content is separated is replaced with a solid content. A wastewater treatment method characterized by returning to the stage before separation of the wastewater and circulating a part of the sludge.

According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, after performing the pH adjustment in the first stage, the sludge discharged when the solid content is separated is directly or as-is. A wastewater treatment method characterized by performing a treatment of decomposing dioxins in sludge by heating to a high temperature after dehydration treatment.

A fifth aspect of the present invention is the wastewater treatment method according to the fourth aspect of the present invention, wherein the sludge is put into a waste incinerator and heated to a high temperature.

According to a sixth aspect of the present invention, there is provided an apparatus for treating wastewater containing dioxins, comprising: a first pH adjusting tank for receiving at least wastewater containing dioxins and performing a first-stage pH adjustment; A first solid content separation device for separating solid content contained in water discharged from the adjustment tank, and a second stage pH adjustment of water separated and discharged by the first solid content separation device. A wastewater treatment apparatus comprising: a second pH adjustment tank; and a second solid content separation device that separates solid content contained in water discharged from the second pH adjustment tank. .

As described above, in the present invention, the pH of the received wastewater is adjusted to an acidic range and then to an alkaline range in two steps. In the first step, the pH is adjusted to 6 or less. Adjust to a range. Then, for the water whose pH has been adjusted in the first and second stages, a process of separating solids such as precipitated products is performed in each of the pH adjustment stages. At this time, most of the dioxins contained in the received wastewater are separated together with the solid content during the first solid content separation treatment performed after the first-stage pH adjustment,
It is taken out of the system.

In the wastewater, zinc (Z
n ²⁺ ), lead (Pb ²⁺ ), cadmium (Cd ²⁺ ), iron (F
e ²⁺ ) has a pH lower than around pH 6.
In a region, particularly in a pH region lower than around pH 4, a considerable amount thereof exists in a dissolved state. For this reason, p in the first stage of adjusting the wastewater to pH 6 or less
At the time of H adjustment, most of the metal is dissolved in the wastewater. Most of the dissolved metals precipitate during the second stage of pH adjustment, which is adjusted to an alkaline range.
For this reason, the discharge amount of the sludge at the time of the first-stage pH adjustment in which most of the dioxins in the wastewater is collected is very small, and the sludge treatment amount for decomposing the dioxins is small. .

When trivalent iron (Fe ³⁺ ) is dissolved in wastewater in a larger amount than other metal components, the pH adjustment in the first stage is adjusted to a region lower than around pH 3. Is good. Specifically, the pH is preferably adjusted to a range of about pH 3 to pH 1.5. This is because trivalent iron has a considerable amount as hydroxide in the region where the pH exceeds 3, and the hydroxide adsorbs other heavy metals. Is to increase.

Table 1 shows the smoke washing wastewater of the refuse incinerator.
It is an experimental result which performed pH adjustment and solid content separation processing of the first stage. This experimental result was obtained as follows. The pH-adjusted supernatant water was adjusted to pH 2 by adding hydrochloric acid to 10 liters of the smoke washing wastewater from a garbage incinerator, mixed by stirring for 10 minutes, and then allowed to stand for 3 hours. It was obtained by measuring the concentrations of dioxins and heavy metals in the supernatant water.
The result of the pH-adjusted supernatant water is 10
After stirring and mixing the liter for 10 minutes, the mixture was allowed to stand for 3 hours, and the supernatant water was collected to obtain the concentration of dioxins and heavy metals in the supernatant water.

[0019]

[Table 1]

According to Table 1, even when the solid content is simply separated by standing and sedimentation is separated, or when the solid content is separated after adjusting the pH, the solid content is not changed after the separation treatment. About 98% or more of the dioxins contained in the wastewater before the separation treatment are removed. However, for heavy metals, a very large difference was observed with and without pH adjustment.If the pH was adjusted appropriately, most of the heavy metals remained in the supernatant, and separation and recovery of dioxins and heavy metals were achieved. Is done.

As described above, in the solid content separation treatment performed after the pH adjustment in the first step, most of the dioxins contained in the wastewater are separated together with the solid content,
Removed from wastewater. As described above, even when sedimentation and separation are performed, most of dioxins are separated into sludge only when solids (SS) in wastewater adhere or adsorb dioxins. It is considered to be separated and to serve as an aid in separating dioxins.

For this reason, a substance containing a component that does not dissolve in acidic water and has a function of promoting adsorption to dioxins is added to the wastewater before the first-stage solid content separation treatment, and the solid content is reduced. If the number of dioxins is increased, the separation rate (removal rate) of dioxins can be increased. The amount of solids added to the wastewater depends on the content of dioxins, but the effect is usually obtained with a small amount of about 100 mg / l or less.

The additive substance may be any substance containing a component that does not dissolve in acidic water, and is not particularly limited.
For example, powders such as fly ash and incinerated ash generated during incineration of municipal solid waste, paper, soil such as Kanto loam and shirasu, and activated carbon, activated clay and inorganic adsorbent such as zeolite can be used.

The additive substance may be an organic substance, and a solid organic powder or a gel organic substance can be used. In the case of organic substances, the affinity with dioxins, such as styrene-divinylbenzene copolymers and synthetic rubbers, which are used as substrates for general-purpose plastics, celluloses, ion-exchange resins, etc., having a higher specific gravity than liquids, is generally high. It is expensive and may be effective even when a small amount of organic solvent is mixed.

From the results shown in Table 1, the sludge discharged when the solid content was separated after the first-stage pH adjustment was confirmed to have an adsorption effect. If the sludge is returned to the stage before the solid content separation treatment and recycled, the adsorption of dioxins can be promoted without adding new solid content or by adding only a small amount of solid content. .

After the first stage of pH adjustment, if the sludge discharged when the solid content is separated is heated to a high temperature, for example, by throwing it into a waste incinerator, dioxins can be reduced. Can be broken down. Therefore, if such a heat treatment is performed, a treatment for decomposing dioxins in sludge can be performed without providing a special dioxin decomposer.

Further, by applying the present invention, it is possible to reduce the amount of sludge containing dioxins. However, in particular, when heat treatment or incineration treatment is performed, heavy metal The major problems of volatilization and circulating concentration to render it impossible to process and equipment trouble caused by the volatilized heavy metal adhering to the vessel wall are greatly reduced.

[0028]

FIG. 1 is a diagram showing an example of an embodiment of the configuration of a wastewater treatment apparatus according to the present invention. In FIG. 1, reference numeral 10 denotes a wastewater tank for receiving wastewater containing dioxins, reference numeral 20 denotes a first pH adjustment tank for performing a first-stage pH adjustment, and reference numeral 21 denotes water contained in the water discharged from the first pH adjustment tank 20. Is a solid content separation device that separates the solid content
Settling tank, 30 is the second pH for performing the second stage pH adjustment
The adjustment tank 31 is a second solid content separation device that separates solid content contained in water discharged from the second pH adjustment tank.
, 40 is a sand filtration tower.

In FIG. 1, a sedimentation tank is provided as a solid content separation device for separating the solid content contained in the water discharged from the first pH adjustment tank 20. Is not limited to a sedimentation tank, and may be a filtration device such as a sand filtration tower or a membrane filtration device.

The wastewater treatment by the above-structured apparatus is performed as follows. The wastewater containing dioxins received in the wastewater tank 10 is introduced into the first pH adjustment tank 20, and an acid such as hydrochloric acid or sulfuric acid is added to adjust the pH in the first step. The pH adjustment value at this time is appropriately determined depending on the type and amount of metals contained in the wastewater, but is usually set to a range of pH 6 or lower, preferably pH 4 or lower. or,
When treating wastewater containing a large amount of trivalent iron, pH 3
The pH is set in the range of 1.5.

When the first-stage pH adjustment is performed as described above, a solid which acts as an auxiliary agent for promoting the adsorption of dioxins is added, if necessary. Additives include fly ash, incinerated ash, paper,
It is selected from Kanto loam soil, Shirasu soil, activated carbon, activated clay, zeolite and the like.

The amount of the solid to be added is determined by the amount of the solid contained in the wastewater and its properties. If a large amount of solids is contained in the wastewater, the solid is not added. The addition of these solids increases the amount of sludge discharged in the subsequent solid content separation treatment, but the amount of sludge is only slightly increased since the amount of addition may be about 100 mg / l or less.

When the above solid is added, it may be added to the first pH adjusting tank 20 or may be added to wastewater before being introduced into the first pH adjusting tank 20. As an addition method, water may be added to the above-mentioned solid to form a slurry and then added.

The water discharged from the first pH adjusting tank 20 is introduced into the first sedimentation tank 21, and a coagulant is added as necessary to settle solids and separate sludge. At this time, a part of the separated sludge may be returned to the first pH adjustment tank 20 or a place before the first pH adjustment tank 20, and may be recycled. In this case, the quantitative constraint is reduced.

Most of the dioxins contained in the received wastewater are trapped in the sludge separated in the sedimentation tank 21, and the sludge is dewatered as it is or in a sludge dewatering machine 50. After that, it is put into the incinerator 51 of the waste incineration equipment, and the dioxins are thermally decomposed. At this time, the incineration residue of the sludge is mixed with the incineration residue of the waste. Disposed in the same manner as waste incineration residues.

The water from which the sludge has been separated in the sedimentation tank 21 is introduced into the second pH adjustment tank 30, and an alkali such as sodium hydroxide, sodium carbonate, calcium hydroxide or the like is added to precipitate heavy metals. The pH at this time is adjusted to an alkaline range of about 8 to 10.

The water discharged from the second pH-adjusting tank 30 is introduced into the second sedimentation tank 31, and solids such as heavy metal precipitates generated in the second pH-adjusting tank 30 are settled to remove sludge. To separate. At this time, a flocculant such as a polymer flocculant is added.

Then, the water discharged as a result of the two-stage pH adjustment and solid content separation treatment as described above is passed through the sand filtration tower 40.
After removal of the SS content by introducing into the apparatus, a treatment for reducing the concentration of dioxins to a regulated value or less by an ozone / ultraviolet treatment or the like is performed.

When the wastewater containing dioxins is treated as described above, most of the dioxins are removed by the solid content separation performed after the pH adjustment in the first stage where the pH is adjusted to an acidic range. The amount of sludge that needs to be decomposed is greatly reduced. In addition, since sludge containing dioxins and sludge containing heavy metals are separately discharged, dioxin treatment or heavy metal treatment may be performed independently when disposing of these sludges, which facilitates disposal of sludge. become.

[0040]

The present invention includes a two-step treatment in which the pH of wastewater containing dioxins is adjusted in two stages, the first stage is adjusted to an acidic range, and the second stage is adjusted to an alkaline range. Wastewater treatment technology. For this reason, the amount of sludge in the pH adjustment in the first stage in which sludge containing dioxins is generated is small, and the load required for the decomposition treatment of dioxins is reduced. Further, since sludge containing dioxins and sludge containing heavy metals are separately discharged, the treatment of those sludges is performed independently for each treatment purpose. For this reason,
The processing when disposing of sludge is facilitated.

Further, according to the present invention, if the sludge discharged at the time of solid content separation after the pH adjustment in the first step is heated to a high temperature, for example, by throwing it into a waste incinerator, dioxins can be decomposed. And there is no need to provide a special dioxin decomposition device.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment according to a configuration of a wastewater treatment device of the present invention.

FIG. 2 is a diagram showing an example of a conventional wastewater treatment flow.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Wastewater tank 20 1st pH adjustment tank 21 1st sedimentation tank 30 2nd pH adjustment tank 31 2nd sedimentation tank 40 Sand filtration tower 50 Sludge dewatering machine 51 Incinerator of waste incineration equipment

Claims (6)

[Claims] In the method for treating wastewater containing dioxins, a first stage of pH adjustment is performed in which wastewater containing dioxins is received and the pH is adjusted to a range of 6 or less. After performing the step of separating the solid content and the second stage of pH adjustment to adjust the pH of the water from which the solid content has been separated in this step to an alkaline range,
separating the solid content contained in the pH-adjusted water. 2. The wastewater treatment method according to claim 1, wherein a substance containing a component that does not dissolve in acidic water is added during the first-stage pH adjustment. 3. After the pH adjustment in the first step, a part of the sludge discharged when the solid content is separated is returned to a stage before the solid content is separated, and a part of the sludge is circulated. The wastewater treatment method according to claim 1, wherein the method is characterized in that: 4. After the pH adjustment in the first step, the sludge discharged when the solids are separated is subjected to a treatment for decomposing dioxins in the sludge by heating it to a high temperature as it is or after dehydrating the sludge. The wastewater treatment method according to any one of claims 1 to 3, wherein: 5. The wastewater treatment method according to claim 4, wherein the sludge is charged into a waste incinerator and heated to a high temperature. 6. A treatment apparatus for wastewater containing dioxins, wherein the wastewater containing at least dioxins is received and subjected to a first-stage pH adjustment, and discharged from the first pH adjustment tank. A first solid content separation device for separating solid content contained in water, and a second pH adjustment tank for performing a second-stage pH adjustment of water separated and discharged by the first solid content separation device. And a second solid content separation device for separating solid content contained in water discharged from the second pH adjustment tank.