JPS601073B2 - Method for removing heavy metals from wastewater - 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 waste has been disposed of by incineration, but with this method, heavy metals, hydrogen chloride, etc. present in the waste are discharged from chimneys, causing Z 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 the garbage is incinerated, the cinders are placed in an ash cooling water tank where they are cooled and washed, and this cooling washing water (usually called ash washing wastewater) usually contains cadmium, lead, zinc, etc., which does not contain mercury. Contains heavy metals,
It cannot be discharged into rivers, etc. as it is. The wastewater discharged from this pond garbage incinerator includes 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. Conventionally, wastewater discharged from municipal garbage incinerators has been treated by integrating all other wastewater such as the smoke washing wastewater mentioned above, ash washing wastewater, domestic wastewater, etc., into coagulation and sedimentation treatment - furnace overtreatment, 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 can be removed at 0.005p, which is the regulatory value.
It was extremely difficult to reduce the amount to below pm. For this reason,
The collectively integrated wastewater (hereinafter referred to as comprehensive wastewater) is subjected to repeated coagulation-sedimentation treatment, and during the treatment, sodium sulfide is added, followed by furnace filtration, neutralization, and adsorption treatment using a chelate resin for mercury adsorption. However, before and after the process, subzinc soda addition equipment, activated carbon adsorption equipment,
Various devices are required, such as an adsorption device using a general heavy metal chelate resin and the installation of a microfilter, resulting in extremely large equipment. However, the more equipment you have, the more problems you will encounter, especially microfilters, which quickly wear out and cannot be used continuously.

Furthermore, adding sodium sulfide during coagulation and precipitation treatment is extremely ineffective as a method for removing general heavy metals. 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 and be incompletely separated and removed in the thickener. Additionally, mercury sulfide may form fine colloidal particles, which can clog the furnace filtration tower, and furthermore, if it leaks from the furnace filtration*, 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 + S HgS Summer - Also, mercury sulfide is a very stable compound, and it is difficult to adsorb by chelate bonding with chelate resin. It is also difficult to remove by adsorption.

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 waste incinerators, and have developed the present invention. reached.

That is, the present invention separates wastewater discharged from a municipal waste incinerator into at least two streams, smoke washing wastewater and other wastewater, adjusting the pH of the smoke washing wastewater to a range of 2 to 10, and mixing it with a heavy metal scavenger. A method for removing heavy metals from municipal waste incinerator wastewater, which consists of mixing with other wastewater, performing coagulation sedimentation treatment, and furnace filtration treatment, and then adsorbing the furnace filtration mother liquor with a chelate resin for mercury adsorption. It is.

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 harm in treating each wastewater discharged from each drainage outlet. However, it is economically expensive, so it is more practical to separate the smoke washing wastewater, adjust the pH, mix it with a heavy metal scavenger, and then mix it with other wastewater for integrated treatment. It is.

The present invention will be explained in detail below.

The heavy metal scavenger to be mixed with smoke washing wastewater is not particularly limited, and examples include Sumifloc HM2000 and Sumifloc HM6.
000 (manufactured by Sumitomo Chemical Co., Ltd.), ALM-648 (manufactured by Nippon Soda Co., Ltd.), etc. are used.

The pH of the liquid to be treated is preferably in the range of 2 to 10, preferably in the range of 4 to 9.

This range is the optimum p for the heavy metal scavenger to capture mercury.
It's a different range. The smoke washing wastewater and the heavy metal scavenger may be mixed in a mixing tank or the like, or in a line in the middle of piping, but the mixing time must be at least 2 minutes to ensure sufficient mixing.

The smoke washing wastewater to which a heavy metal scavenger has been added and mixed is mixed with other wastewater at once, and then subjected to coagulation and sedimentation treatment, but a known method is applied to the coagulation and sedimentation treatment, and there are no restrictions on equipment or operating methods. The inorganic flocculants and polymer flocculants to be added are optional, and conventionally known ones are used.
There are no limitations at all, and it is also effective to use a heavy metal scavenger in combination at this time.

The pH of the liquid to be treated at this time is preferably in the range of 2 to 10, preferably 4 to 9 when a heavy metal scavenger is used in combination, and preferably in the range of 7 to 12 when not used in combination.
This is the p-law range that is commonly practiced and is called alkali precipitation.

There are two methods of furnace overtreatment in the furnace overtreatment process: gravity furnace overtreatment and rapid furnace overtreatment, and the present invention can use either method. Furnace materials include sand, anthracite, etc., and in the method of the present invention, any furnace material may be used, and a multi-layer filtration combining the two may 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 process with mercury-wearing chelate resin is not particularly limited, and examples thereof include Sumikylate Q-10R (Sumitomo Chemical Co., Ltd.), ALM125 (Nippon Soda Co., Ltd.), Eporus Z-
7 (product of Miyoshi Oil Co., Ltd.), UR-120 day (product of Unitika Co., Ltd.), and Chelate MA (product of Hokuetsu Tansen Co., Ltd.) are used.

Furthermore, the adsorption treatment itself can be carried out using conventionally known methods and is not particularly limited, but the pH of the wastewater to be subjected to the adsorption treatment is preferably 8 or less, preferably in the range of 2 to 7, in view of the ability to remove mercury.

As described above, the method of the present invention separates wastewater discharged from municipal garbage incinerators into at least two streams, smoke washing wastewater and other wastewater, and adjusts the pH of the smoke washing wastewater to a range of 2 to 10 to supplement heavy metals. After mixing with a collection agent, mixing with other wastewater, performing coagulation-sedimentation treatment, and furnace filtration treatment, the furnace filtration mother liquor is adsorbed using a chelate resin for mercury adsorption. In this way, all heavy metals in municipal waste incinerator wastewater can be removed very economically and completely below regulatory values, although it is also possible to incorporate various treatments. The method of the present invention will be explained in more detail below with reference to Examples.

Example 1 Sulfuric acid was added to the smoke washing wastewater of the A municipal garbage incinerator to adjust the ZpH to 7, loppm of Sumifloc HM6000 was added, and after 1 minute of drying, other wastewater (ash washing wastewater, Mixed wastewater (mixed wastewater such as dust leached sewage, car wash wastewater, domestic wastewater, etc.) was mixed at a volume ratio of 1:1 and poured for 2 hours.

*Add caustic soda to adjust the pH to 11, then add 200 ppm of ferric chloride, perform rapid hydration for 5 minutes, add caustic soda again to adjust the pH to 11, and add Sumifloc FA- 50(
Polymer flocculant (manufactured by Sumitomo Chemical Co., Ltd.) lppm was added, and slow hawking was performed for 5 minutes. Next, this was passed through a sand-anthracite multi-layer furnace filter to separate the sludge, and sulfuric acid was added to the mother liquor to adjust the pH to 7.

This solution was passed in series at SV=5 between two glass columns filled with Sumikylate Q-10R200 and having an inner diameter of 25 mm and a height of 1,000 mm. As shown in Table 1, all heavy metals were below regulatory limits.

Table 1 Example 2 The operation was exactly the same as in Example 1 except that smoke washing wastewater from B municipal waste incinerator and other wastewater were used.・※Natsuta.

As shown in Table 2, all heavy metals were below regulatory limits.

Table 2 Comparative Example 1 Volume ratio of smoke washing wastewater and other wastewater from A municipal garbage incinerator to 1
: 1 and stirred for 2 hours.

The pH of this solution was adjusted to pH 7 by adding sulfuric acid, 20 ppm of Sumifloc HM6000 was added, and the mixture was stirred for 1 minute. Then, 200 ppm of ferric chloride was added, and the mixture was rapidly stirred for 5 minutes. pH by adding caustic soda
was adjusted to 7, 501 ppm of Sumifloc FA was added, and the mixture was stirred slowly for 5 minutes. The subsequent furnace filtration step and adsorption step were performed in exactly the same manner as in Example 1.

As shown in Table 3, general heavy metals were below the regulatory values, but mercury was above the regulatory values**.

Table 3 Comparative Example 2 The operation was exactly the same as in Comparative Example 1 except that smoke washing wastewater from B municipal waste incinerator and other wastewater were used.

As shown in Table 4, general heavy metals were below the regulated values, but mercury was above the regulated values.

Table 4 Comparative Example 3 Smoke washing wastewater from A municipal waste incinerator and other wastewater were used, and ALM-125 Eporus Z- was used in place of the heavy metal scavenger.
7. UR-120 Days, exactly the same operation as in Comparative Example 1 was performed except that chelate MA was used.

As a result, general heavy metals were below the regulation value, but mercury was over the regulation value as shown in Table 5. table
5 House 9 Mercury concentration unit: ppm

Claims (1)

[Claims] 1. Separate wastewater discharged from municipal garbage incinerators into at least two lines, smoke washing waste water and other waste water, and
After adjusting the H2 to H10 range and mixing with a heavy metal scavenger, mixing with other wastewater, performing coagulation sedimentation treatment, and filtration treatment, the filtration mother liquor is adsorbed using a chelate resin for mercury adsorption. A method for removing heavy metals from wastewater from municipal waste incinerators.