JPS6211633B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing heavy metals from wastewater discharged from municipal waste incinerators. In recent years, much of municipal garbage has been disposed of by incineration, but with this method, heavy metals and hydrogen chloride present in the garbage are discharged from the chimney.
Causes air pollution. For this reason, a method of cleaning incineration smoke with an alkaline aqueous solution is generally adopted, but this cleaning wastewater (usually called smoke cleaning wastewater) contains heavy metals such as mercury, cadmium, lead, and zinc. Therefore, it is not possible to discharge the water into rivers, etc. as it is. On the other hand, after incinerating garbage, the cinders are put into an ash cooling water tank where they are cooled and washed, and this cooling washing water (usually called ash washing wastewater) usually does not contain mercury, but does contain cadmium, lead, and zinc. It contains heavy metals such as, and cannot be discharged into rivers as is. Other types of wastewater discharged from garbage incinerators include sewage that seeps from the dust layer deposited in the garbage moat, car wash wastewater from cleaning garbage transport vehicles, and domestic wastewater discharged from staff housing and factories. Traditionally, wastewater discharged from municipal garbage incinerators has been treated by integrating all of the above-mentioned smoke washing wastewater, ash washing wastewater, domestic wastewater, and other wastewater at once, using coagulation-sedimentation treatment, overtreatment, and chelate resin for mercury adsorption. The treatment was carried out by sequentially performing adsorption treatment. However, with such conventional methods, although general heavy metals can be removed, mercury does not meet the regulatory limits.
It was extremely difficult to reduce the content to 0.005 ppm or less. For this reason, coagulation and sedimentation treatment is repeated on the collectively integrated wastewater (hereinafter referred to as comprehensive wastewater), and sodium sulfide is added during the treatment.
Next, after filtration and neutralization, adsorption treatment using chelate resin for mercury adsorption is performed, but before and after this process, a sodium hypochlorite addition device, an activated carbon adsorption device, an adsorption device using chelate resin for general heavy metals,
This requires various devices such as the installation of a microfilter, resulting in extremely large equipment. However, the larger the equipment, the more problems will occur, especially the microfilter, which will quickly become clogged and cannot be used continuously. Also, adding sodium sulfide during coagulation and precipitation treatment is very effective as a method for removing general heavy metals, but is not very effective for mercury. In other words, mercury easily reacts with sodium sulfide to form mercury sulfide, which is precipitated to some extent by coprecipitation with iron hydroxide, but mercury sulfide is extremely hydrophobic, so some of the precipitate does not reach the surface of the treatment solution. It may float to the surface, resulting in incomplete separation and removal in the thickener. Additionally, mercury sulfide may form fine colloidal particles, which can clog the filter tower, and if it leaks from the filter tower, it can clog the chelate tower that follows it. Furthermore, if the amount of sodium sulfide added is excessive, there is a risk of giving odor to the treated water and causing secondary pollution, and mercury sulfide may be redissolved according to the following equation. HgS+SHgS ₂ ^--In addition, mercury sulfide is a very stable compound, and it is difficult to adsorb as it forms a chelate bond with a chelate resin, and it is difficult to adsorb and remove mercury sulfide with a chelate resin for mercury adsorption unless it can be passed through a series of steps. It is. For these reasons, the present inventors have conducted intensive studies on a method for economically and easily removing heavy metals, particularly mercury, from wastewater discharged from municipal garbage incinerators, and further, to a level below the regulation value. The present inventors have previously discovered the effectiveness of separating the wastewater into at least two streams, smoke washing wastewater and other wastewater, in the treatment of wastewater discharged from municipal waste incinerators (particularly Gansho 54-
No. 134776), we have discovered that even better results can be obtained by considering the pH and order of addition when carrying out coagulation-sedimentation treatment of smoke washing wastewater using a heavy metal scavenger, leading to the present invention. Ivy. That is, the present invention combines wastewater discharged from a municipal waste incinerator into at least two types of wastewater: smoke washing wastewater and other wastewater.
Separate into series, adjust the pH of the smoke washing wastewater to a range of 2 to 10, mix it with a heavy metal scavenger, and then add an inorganic flocculant,
Coagulation-sedimentation treatment is performed by sequentially mixing with a polymer flocculant, followed by overtreatment and adsorption treatment of the supernatant mother liquor using a chelate resin for mercury adsorption.For other wastewater, the pH is adjusted to a range of 7 to 12. This is a method for removing heavy metals from municipal waste incinerator wastewater, which involves performing coagulation-sedimentation treatment by sequentially mixing an inorganic flocculant and a polymer flocculant. The present invention separates municipal waste incinerator wastewater into at least two streams: smoke washing wastewater and other wastewater, but of course there is no problem in treating each wastewater discharged from each drainage outlet. No, but
Since it is economically expensive, it is more practical to treat only the smoke washing wastewater in a separate system and treat the other wastewater all at once. The present invention will be explained in detail below. In the coagulation and sedimentation treatment when treating smoke washing wastewater, the smoke washing wastewater is first treated with sulfuric acid, hydrochloric acid, caustic soda, etc.
After adjusting the pH to a range of 2 to 10 and mixing with a heavy metal scavenger, the mixture is sequentially mixed with an inorganic flocculant and a polymer flocculant, but the heavy metal scavenger used here is not particularly limited; for example, Sumifrock HM-
2000, Sumifloc HM-6000 (manufactured by Sumitomo Chemical Co., Ltd.), ALM648 (manufactured by Nippon Soda Co., Ltd.), etc. are used. The pH of the liquid to be treated is in the range of 2 to 10, preferably 4 to 10.
A range of 9 is good. This range is the optimum pH range for heavy metal scavengers to capture mercury. The smoke washing wastewater and the heavy metal scavenger may be mixed in a mixing tank equipped with an agitator or in a line in the middle of the piping, but in order to mix thoroughly, the mixing time must be at least It takes more than 2 minutes. The inorganic flocculant to be mixed next is, for example, polyaluminum chloride, aluminum sulfate, iron chloride, etc., and the polymer flocculant is, for example, Sumifloc FA.
-50, Sumifrock FA-40, Sumifrock FA-
30〓 (products of Sumitomo Chemical Co., Ltd.), Sunpoly (products of Sankyo Kasei Co., Ltd.), Sunfloc (products of Sanyo Chemical Co., Ltd.), Hiset (products of Daiichi Kogyo Seiyaku Co., Ltd.), etc. are used. This coagulation-sedimentation treatment method is a method known per se, and is not limited in any way to the apparatus and operating method. The purpose of using a heavy metal scavenger in the present invention is not only to more reliably remove general heavy metals by coagulation and precipitate, but also to coagulate and precipitate them in a more stable form. In other words, general heavy metals can be precipitated and removed by simple alkali coagulation and precipitation treatment, and the separated sludge is often disposed of in landfills, but not only general heavy metals but also some mercury are mixed in the sludge. If these heavy metals are disposed of directly in a landfill, there is a risk that these heavy metals will leach out and cause secondary pollution, but if a heavy metal scavenger is used in conjunction with coagulation and sedimentation treatment, heavy metals can be kept in a stable form in the sludge. Since heavy metals are present in the sludge, they will not be leached even if the sludge is disposed of in a landfill, making it extremely effective not only for the removal of heavy metals from wastewater but also for the comprehensive treatment of wastewater. There are two methods of overtreatment in the overtreatment process: gravity overtreatment and rapid overtreatment, and the present invention can use either method. Further, materials include sand, anthracite, etc., and in the method of the present invention, either material can be used, and multilayer filtration using a combination of both materials can also be used. The mother liquor filtered here is sent to the next adsorption treatment step. The mercury-adsorbing chelate resin used in the adsorption treatment step with mercury-wearing chelate resin is not particularly limited, and examples include Sumikylate Q-10R (Sumitomo Chemical Co., Ltd.), ALM125 (Nippon Soda Co., Ltd.), and Eporus Z-7 (Miyoshi Yushi Co., Ltd.). UR-120H (Unitika product), Chelate MA (Hokuetsu Tanso product), etc. are used. In addition, the adsorption treatment itself can be applied using conventionally known methods and is not particularly limited, but the PH of the wastewater subjected to the adsorption treatment is
8 or less, preferably in the range of PH2 to 7. General heavy metals and mercury in the sequentially treated smoke washing wastewater are completely removed to levels below regulation values, and after pH adjustment, it can be discharged directly into rivers, etc., or it can be recycled within the factory. However, it can also be used, for example, as cooling water for washing rice husks from incinerated garbage. In addition, since the smoke washing wastewater treatment water contains a large amount of salt, it is possible to recover the salt by concentrating it, or to produce a sodium hypochlorite aqueous solution by electrolysis. It is also possible. Next, the other wastewater referred to in the present invention is subjected to coagulation and sedimentation treatment, and the coagulation and sedimentation treatment method may be a completely general alkali coagulation and sedimentation method. i.e. PH
is adjusted to a range of 7 to 12 and sequentially mixed with an inorganic flocculant and a polymer flocculant. General heavy metals in treated water that has been subjected to alkali coagulation and precipitation treatment are completely removed to levels below regulatory limits, and the water can be discharged into rivers, etc., as is after adjusting the pH. When discharging directly into rivers or sea areas, if COD and BOD still remain, biological treatment equipment will be installed after this to remove COD and BOD.
It goes without saying that other factors must be kept below regulation values. As described above, the method of the present invention uses at least two types of wastewater discharged from a municipal garbage incinerator: smoke washing wastewater and other wastewater.
Separated into series, the smoke washing wastewater is sequentially subjected to a first step in which a heavy metal scavenger is added and subjected to coagulation and sedimentation treatment, a second step in which overtreatment is performed, and a third step in which adsorption treatment is performed using a chelate resin for mercury adsorption. It is characterized in that only coagulation and sedimentation treatment is performed on other wastewater, but it is also possible to incorporate various treatments as necessary.In this way, heavy metals in wastewater from municipal waste incinerators can be removed very economically. And it can be completely removed to below the regulation value. The method of the present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 The pH of the smoke washing wastewater from factories A, B, C, and D, which are municipal waste incineration plants, was adjusted to 7 using sulfuric acid or caustic soda, and Sumifloc HM6000 was
After adding 10 ppm and stirring for 10 minutes, add 200 ppm of ferric chloride, stir rapidly for 5 minutes, add caustic soda again to adjust the pH to 7, add 1 ppm of Sumifloc FA50, and stir for 5 minutes. Slow stirring was performed for a minute. Next, the treated liquid was passed through a sand-anthracite multilayer filter to separate sludge, and sulfuric acid was added to the mother liquor to adjust the pH to 4, which was used as raw water. Analysis of general heavy metals in this raw water revealed that A.
The wastewater from factories B, C, and D all had concentrations below the regulation value, but only mercury did not fall below the regulation value, and the concentration was as shown in Table 1. This raw water was filled with Sumikylate Q-10R 500ml.Inner diameter 28mm, height 1500
Two mm PVC columns were arranged in series and liquid was passed through them at SV=5. As shown in Table 1, mercury was completely removed.

[Table] Example 2 The pH of smoke washing wastewater from Factory A, which is a municipal waste incinerator, was adjusted to 7 by adding sulfuric acid, and Sumifloc was
After adding 20 ppm of HA6000 and stirring for 10 minutes, 200 ppm of ferric chloride was added, rapid stirring was performed for 5 minutes, and caustic soda was added again to bring the pH to 7.
Sumifloc FA-50 was added to 2 ppm and stirred slowly for 5 minutes. Next, the sludge was separated through a sand-anthracite multi-layer filtration machine, and the pH was adjusted to make the liquid pH 4, which was used as raw water. When the general heavy metals in this raw water were analyzed, they were found to be below the regulation value and there were no problems, but the mercury was not below the regulation value and was 0.0112ppm. This raw water is treated with various commercially available chelate resins for adsorbing mercury.
Two PVC columns packed with 500 ml and having an inner diameter of 28 mm and a height of 1500 mm were lined up and the liquid was passed in series at SV=5.
As shown in Table 2, mercury was completely removed no matter what chelate resin for adsorbing mercury was used.

[Table] Example 3 Using caustic soda, the pH of other wastewater other than smoke washing wastewater (ash washing wastewater, dust leaching wastewater, car washing wastewater, domestic wastewater, etc.) at Factory A, which is a municipal garbage incinerator, was determined. Adjust to 11 and add ferric chloride to 200ppm.
Add and stir rapidly for 5 minutes, then add caustic soda again to adjust the pH to 11, and add Sumifloc.
FA50 was added at 2 ppm and stirred slowly for 5 minutes. The supernatant liquid was analyzed for common heavy metals. The results are shown in Table 3, and it was found that general heavy metals were completely removed to below the regulatory values.

【table】

[Table] Comparative Example 1 The PH of the smoke washing wastewater from factories A, B, C, and D, which are municipal waste incinerators, was adjusted to 10 using sulfuric acid or caustic soda, and 10 ppm of sodium sulfide was added to it for 10 minutes. After stirring, add 200ppm of ferric chloride.
After stirring rapidly for 5 minutes, add caustic soda again to adjust the pH to 10, and add Sumifloc FA.
-50 was added at 1 ppm and slowly stirred for 5 minutes. Next, the sludge was separated through a sand-anthracite multi-layer filtration machine, and the pH was adjusted to make the liquid pH 4, which was used as raw water. When general heavy metals in this raw water were analyzed, the wastewater from factories A, B, C, and D were all below the regulatory value, but only mercury did not fall below the regulatory value, and the concentration was as shown in Table 4. It was hot.
This raw water was passed in series at SV=5 through two PVC columns with an inner diameter of 28 mm and a height of 1500 mm filled with 500 ml of Sumikylate Q-10R. As shown in Table 4, the mercury was not completely below the regulatory value.

[Table] Comparative Example 2 The pH of the comprehensive wastewater from each of the municipal waste incineration plants A, B, C, and D was adjusted to 11 using caustic soda, 200 ppm of ferric chloride was added, and the mixture was heated for 5 minutes. Stir rapidly and add caustic soda again to adjust the pH.
Adjust to 11, add Sumifloc FA50 2ppm,
Slow stirring was performed for 5 minutes. Thereafter, overtreatment and Sumichylate Q-10R treatment were carried out in exactly the same manner as in Comparative Example 1. The results are shown in Table 5, and the mercury did not fall below the regulatory value.

[Table] Comparative Example 3 The same operation as in Comparative Example 2 was carried out on general wastewater from Factory A, which is a municipal waste incinerator, and the mercury concentration in the raw water was measured and found to be 0.0131 ppm.
This raw water was filled with 500 ml of commercially available chelate resin for mercury adsorption as shown in Table 6, with an inner diameter of 28 mm and a height of
Two 1500mm PVC columns are connected in series with SV=
The liquid was passed through the tube at step 5. As shown in Table 6, mercury did not fall below the regulatory value in any of the resins.

【table】

Claims (1)

[Claims] 1. Separate wastewater discharged from municipal garbage incinerators into at least two streams: smoke washing wastewater and other wastewater,
After adjusting the pH of the smoke washing wastewater to a range of 2 to 10 and mixing it with a heavy metal scavenger, a coagulation-sedimentation treatment is performed by sequentially mixing it with an inorganic flocculant and a polymer flocculant, followed by overtreatment and filtration. The mother liquor is sequentially adsorbed using a chelate resin for mercury adsorption, and other wastewater is
A method for removing heavy metals from municipal waste incinerator wastewater, which comprises adjusting the pH to a range of 7 to 12 and performing a coagulation-sedimentation treatment by sequentially mixing an inorganic flocculant and a polymer flocculant.