JPH0445237B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for treating wastewater from a waste incineration plant. Conventional techniques and their problems Conventionally, in garbage incineration plants, heavy metals such as mercury contained in the flue gas generated by incinerating garbage have been treated by the following methods. In other words, the heavy metals contained in flue gas are first captured in water by washing with water using a scrubber (the wastewater generated in this way is called "smoke washing wastewater"), and the purified flue gas is released into the atmosphere. Ru. on the other hand,
A liquid chelating agent (heavy metal scavenger) and iron chloride are added to the smoke washing wastewater containing heavy metals, which is neutralized to around 7 with caustic soda, and then a polymer condensing agent is added to undergo coagulation and sedimentation treatment. (Heavy metals other than mercury are below the emission standards.) Next, after sand filtering, the mercury that was not sufficiently coagulated and precipitated in the above coagulation-sedimentation treatment is removed by a chelate resin to a low concentration that meets the emission standards, and then becomes harmless. The converted wastewater has been discharged into sewers or public water bodies. JP-A No. 60-68094 discloses that a heavy metal fixing agent and an aluminum compound such as aluminum sulfate are added to wet gas cleaning wastewater from a municipal waste incinerator and mixed with stirring, and a pH adjuster is added to neutralize the pH. Adjust to near
A technique has been disclosed in which a polymeric auxiliary agent is then added, stirred and mixed, and then solid-liquid separation is performed to remove mercury and fluorine from the wastewater. According to this publication, it is possible to remove mercury to below the emission standard by the above method. However, when the inventor tried the method described in the above-mentioned publication, it was found that although there were cases where mercury could be removed to a level below the emission standard, there were more cases where mercury could not be removed to a level below the emission standard. In this case, as mentioned above, it is necessary to further remove the remaining mercury using a chelate resin to a low concentration that meets the emission standards, and it was therefore found that the method described in the above publication was not a practical technology at all (see comparison below). (see example). On the other hand, separate clean industrial water is used to cool the incinerated ash produced during garbage incineration (the wastewater generated in this way is called "ash sewage").
This ash wastewater is then mixed with equipment/floor cleaning wastewater, etc., and this mixed liquid (plant wastewater) is treated with coagulation and sedimentation in the same manner as above, rendered harmless, and currently discharged into sewers or public water bodies. be. However, in such conventional methods, the chelate resin used to remove mercury is expensive;
Moreover, the surface of this chelate resin is contaminated with suspended matter, colloidal substances, etc. that cause a decrease in mercury trapping performance, and microorganisms such as mold are likely to grow, making maintenance of the resin difficult. Furthermore, this method requires a large amount of industrial water for purposes such as cooling the incinerated ash. Therefore, there are demands for simplifying the treatment of wastewater from waste incineration plants, reducing treatment costs, and reducing industrial water costs, but no effective solution has yet been found. Means for Solving the Problems The present inventor has conducted extensive research in order to develop a wastewater treatment method for waste incineration plants that meets the above requirements. As a result, heavy metals such as mercury remaining in the supernatant liquid can be removed by mixing the supernatant liquid after coagulation-sedimentation treatment of smoke washing wastewater with ash wastewater and equipment/floor cleaning wastewater.
It is adsorbed by incinerated ash in ash wastewater and suspended particles in equipment/floor cleaning wastewater, and if this is coagulated and precipitated again using an inorganic flocculant, trace amounts of mercury remaining in the supernatant liquid can be removed. It has been found that a surprising effect that could not have been anticipated by those skilled in the art can be achieved, in that even the above-mentioned supernatant can be removed to a low concentration that satisfies the discharge standards. The present invention was completed based on this knowledge. That is, the present invention subjects wastewater from waste incineration plants to coagulation-sedimentation using a liquid chelating agent, an inorganic coagulant, and a polymeric coagulant, and then mixes ash wastewater and equipment/floor cleaning wastewater with this supernatant liquid, A method for treating waste incineration plant wastewater, characterized in that the mixture is coagulated and precipitated again using an inorganic coagulant and a polymer coagulant, and a method for cleaning waste incineration plants using a liquid chelating agent, an inorganic coagulant and a polymer coagulant. A waste incineration plant characterized in that after coagulating and precipitating wastewater, this supernatant liquid is used as cooling water for incinerated ash, and then this used liquid is subjected to coagulating and precipitating treatment again using an inorganic coagulant and a polymer coagulant. Concerning wastewater treatment methods. The method of the invention will be explained below with reference to FIG. FIG. 1 is a flowchart showing one embodiment of the method of the present invention. Smoke washing wastewater from a waste incineration plant, which is the object of treatment in the present invention, contains heavy metals. Examples of heavy metals include mercury, manganese, cadmium, chromium, lead, zinc, copper, nickel, and iron. First, the smoke washing wastewater is led to the first reaction tank through the first adjustment tank, where a liquid chelating agent, an inorganic flocculant, and a polymer flocculant are added, and then the wastewater is led to the first coagulation sedimentation tank. , where the first coagulation and precipitation treatment is performed. As the liquid chelating agent used, a wide variety of conventionally known ones can be used, such as Sumichelate.
HM6000 [manufactured by Sumitomo Chemical], Epofrock L-1,
Examples include L-2 and L-3 (both manufactured by Miyoshi Oil Co., Ltd.), Unitika UML5000 (manufactured by Unitika Co., Ltd.), and ALM-648 (manufactured by Nippon Soda Co., Ltd.). As the inorganic flocculant, a wide variety of conventionally known flocculants can be used, such as ferrous chloride, ferric chloride, ferric sulfate, polyaluminum chloride, aluminum sulfate, and the like. Furthermore, as a polymer flocculant, a wide range of conventionally known ones can be used, such as Konan Floc #2000 (manufactured by Konan Kagaku Kogyo Co., Ltd.), Himoroc L-
113 [manufactured by Kyowa Organic Co., Ltd.], Aron N-100 [manufactured by Toa Organic Gosei Co., Ltd.], and Kurita EDP Flock 101 [manufactured by Kurita Industries, Ltd.]. The amount of liquid chelating agent to be added to the smoke washing waste water is not particularly limited and can be appropriately selected from a wide range, but it is usually about 2 to 50 mg, preferably about 10 to 20 mg, per 1 part of the waste water. good. The amount of inorganic flocculant to be added to the smoke washing wastewater is not particularly limited and can be appropriately selected from a wide range, but it is usually about 50 to 2000 mg, preferably about 100 to 200 mg per 1 part of the waste water. good.
The amount of polymer flocculant to be added to the smoke washing waste water is not particularly limited and can be appropriately selected from a wide range, but it is usually about 1 to 10 mg, preferably about 2 to 4 mg, per 1 part of the waste water. It is better. If the amount of the liquid chelating agent, inorganic flocculant, or polymer flocculant added is less than the above range, there is a tendency that the desired heavy metal removal effect cannot be obtained. The effect of removing heavy metals in the process does not improve that much, and it is not economically desirable. The first coagulation and sedimentation treatment of the smoke washing wastewater can be carried out according to a conventional method, and by this coagulation and sedimentation treatment, it is separated into a supernatant liquid and sludge. The sludge separated here is sent to landfill together with the sludge obtained in the second coagulation and sedimentation treatment that will be performed later. Meanwhile, the supernatant liquid is sent to the plant wastewater storage tank. In addition, in the present invention, by the first coagulation sedimentation treatment,
Reduce the mercury content in the supernatant to a certain amount, e.g. 0.05
It is preferable to reduce the amount to less than mg/mg. If the amount of mercury contained in the supernatant liquid is too large, it tends to be difficult to reduce the mercury content to a level below the emission standard even with the secondary coagulation and precipitation treatment that is carried out later. Become. The supernatant liquid sent to the plant wastewater storage tank is here mixed with ash wastewater and/or equipment/floor washing wastewater. As ash wastewater and equipment/floor cleaning wastewater, conventionally known ones can be used as they are. The mixing ratio of supernatant liquid and ash wastewater and/or equipment/floor cleaning wastewater is not particularly limited, but the latter is usually about 0.5 to 4 times the former, preferably 1 to 2 times.
It is best to mix at twice the ratio. The mixed liquid in the plant wastewater storage tank is then sent to the second reaction tank via the second adjustment tank, where an inorganic flocculant and a polymer flocculant are added, and then led to the second coagulation and sedimentation tank. Secondary flocculation and precipitation treatment is performed. As the inorganic flocculant and the polymer flocculant, any of the inorganic flocculants and polymer flocculants used in the above-mentioned first coagulation and precipitation treatment can be used. The amount of the inorganic flocculant to be used is not particularly limited and can be appropriately selected within a wide range, but it is usually about 100 to 4000 mg, preferably about 100 to 300 mg, per 1 of the mixed liquid to be treated. The amount of polymer flocculant to be used is not particularly limited and can be appropriately selected from a wide range, but usually 1 to 10
The amount is preferably about 2 to 4 mg. If the amount of the inorganic flocculant and polymer flocculant added is less than the above range, there is a tendency that the mercury removal effect cannot be obtained. The removal effect is not improved that much and it is economically unfavorable. Such secondary flocculation and sedimentation treatment can also be carried out according to a conventional method, and by this coagulation and sedimentation treatment, supernatant water and sludge are separated. The sludge separated here is sent to landfill as described above, while the supernatant water is neutralized in a neutralization tank, rendered harmless, and discharged into the sewer. Neutralization of the supernatant water can also be carried out according to conventionally known methods. According to another preferred embodiment of the present invention, after the supernatant liquid obtained in the first coagulation-sedimentation treatment described above is used as cooling water for incinerated ash, it is sent to a plant wastewater storage tank, and then further to a second adjustment tank. Here, the second flocculation and sedimentation treatment is carried out in the same manner as above (see Figure 2). According to this embodiment, the heavy metals contained in the smoke washing wastewater can be reduced to a level below the emission standard, and the amount of industrial water used for cooling the incineration ash can be greatly reduced. The cost required for this can be further reduced. Effects of the Invention According to the method of the present invention, harmful heavy metals such as mercury can be reduced to a level below the emission standard value without using an expensive chelate resin as in the conventional method. Furthermore, in the method of the present invention, the supernatant liquid obtained in the first coagulation-sedimentation treatment can be used as water for cooling the incinerated ash, so that industrial water costs can be reduced. Therefore, the method of the present invention makes it possible to simplify wastewater treatment, reduce treatment costs, reduce industrial water costs, etc., and allows waste incineration plant wastewater to be treated on an industrial scale. Examples The present invention will be further clarified with reference to Examples below. Example 1 Smoke washing wastewater from a garbage incineration plant 1 (containing 3.4 mg of mercury/
(contained at a concentration of
After adding 10 mg of ferric chloride and 300 mg of ferric chloride and neutralizing it to pH 7 with a 20% caustic soda solution, 2 mg of polymer flocculant (Konan Floc #2000) was added.
After 5 minutes of rapid stirring and 10 minutes of slow stirring, the mixture was left to settle and separated into precipitated sludge and supernatant liquid. The concentrations and removal rates of various heavy metals in this supernatant are as follows.

[Table] Among these various heavy metals, the concentration of mercury is higher than the wastewater standard, so 500ml of plant wastewater collected from an incineration plant was added to 500ml of the above supernatant liquid, and ferric chloride was added.
300mg/, add 2mg/polymer flocculant (Konan Floc #2000), and mix with 10% caustic soda solution.
After neutralization to pH 7, rapid stirring for 5 minutes and slow stirring for 10 minutes, the mixture was allowed to settle. As a result, the mercury concentration in the supernatant water was 0.0005 mg/lower than the discharge standard of 0.005 mg/
It became. Example 2 An incineration factory that incinerates 550 tons of general waste per day discharges 145 ^m3 of smoke washing wastewater per day, and the heavy metal concentration is 3.0 to 3.4 mg/day for mercury and 0.03 mg/day for lead.
~0.41mg/, cadmium 0.005~0.02mg/,
Zinc 0.01~3.0mg/, chromium 0.05~0.82mg/
It is. This smoke washing wastewater is led to the first reaction tank via the first adjustment tank, where 10mg/of Sumikylate 6000H and 300mg/of ferric chloride are added, and the pH is brought to 7 with caustic soda solution.
After neutralization, 2 mg of polymer flocculant (Konan Floc #2000) was added, and after rapid stirring for 10 minutes and slow stirring for 25 minutes, the supernatant was transferred to the primary coagulation and sedimentation treatment tank. and sludge were precipitated and separated. Through this coagulation and precipitation treatment, lead is less than 0.02 to 0.07mg/, cadmium is less than 0.002 to 0.02mg/, and zinc is 0.001 to 0.02mg/.
0.09mg/, chromium is reduced to 0.01~0.07mg/, to the extent that it meets the emission standards. Mercury is 0.0041~
Although it decreased to about 0.047mg/, it still did not reach the emission standard. On the other hand, incineration ash cooling wastewater (ash wastewater) has a pH of 7.85~
11.69, mercury 0.0015-0.0049mg/, lead
12.2-40.9mg/, cadmium 0.05-0.20mg/
, zinc 1.5-20mg/, chromium 0.04-0.56
mg/, and suspended solids are contained at a ratio of 84 to 335 mg/. The plant wastewater (278 m ³ /day), which is a combination of this ash wastewater and the equipment/floor washing wastewater, and the supernatant liquid obtained above are sent to the second adjustment tank, and then ferric chloride is added to the second reaction tank. After adding 300mg/ and neutralizing it to pH 10 with caustic soda solution, 2mg/ of polymer flocculant (Konan Floc #2000) was added.
After 10 minutes of rapid stirring and 20 minutes of slow stirring, the mixture was led to a second coagulation and sedimentation treatment tank, where it was separated into supernatant water and sludge, and neutralized to pH 6.5 to 7.5 in a final neutralization tank. Through this treatment, mercury is less than 0.0005 to 0.0029mg/(average value 0.0011mg/), lead is 0.05 to 0.14mg/, cadmium is less than 0.002mg/, and zinc is less than 0.001mg/.
The amount of chromium was reduced to less than 0.01 to 0.04 mg/, sufficiently meeting the emission standards. Furthermore, the emission standards are 0.005mg/for mercury, 1mg/for lead, 0.1mg/for cadmium, and 5mg/for zinc.
mg/, and chromium is 2 mg/. Example 3 An incineration factory that incinerates 540 tons of general waste per day discharges 151 ^m3 of smoke washing wastewater per day, and the heavy metal concentration is 2.8 to 5.2 mg/day for mercury and 0.25 mg/day for lead.
~0.53mg/, cadmium 0.008~0.025mg/,
Zinc 0.020-3.5mg/, chromium 0.20-0.83
mg/. This smoke washing wastewater is led to the first reaction tank through the first adjustment tank, and 10mg/Epofloc L-2 [liquid chelating agent, manufactured by Miyoshi Oil Co., Ltd.] and 300mg/300ml of ferric chloride are added.
mg/added, and after neutralizing to pH7 with caustic soda solution, polymer flocculant (Konan Flock #2000)
After 5 minutes of rapid stirring and 10 minutes of slow stirring, the mixture was introduced into the first coagulation and sedimentation treatment tank, where it was separated into supernatant liquid and sludge. After the supernatant liquid obtained above is used to cool the incinerated ash, it is sent to the second adjustment tank, and in the second reaction tank, 300 mg of ferric chloride is added, and the pH is neutralized to 10 with caustic soda solution. After that, add 2 mg of polymer flocculant (Konan Flock #2000) and stir rapidly.
After 10 minutes of slow stirring and 20 minutes of slow stirring, the mixture was led to a second coagulation and sedimentation treatment tank, where it was separated into supernatant water and sludge, and neutralized to pH 6.5 to 7.5 in a final neutralization tank. Through this treatment, mercury is less than 0.0005 to 0.0018mg/, lead is 0.02mg/
Less than 0.13 mg/, cadmium less than 0.002, zinc less than 0.001 mg/0.05 mg/, chromium 0.01
mg/ to less than 0.04 mg/, which was sufficient to meet the emission standards. Example 4 A certain incineration factory incinerates 570 tons of general waste per day and uses 584 m ³ of industrial water. 168 per day
In the smoke washing wastewater generated ^m3 , mercury is 0.11 to 6.1
mg/, lead 0.09 to 1.49 mg/, cadmium
0.046 to 0.13 mg/, zinc 0.36 to 3.9 mg/, and chromium 0.12 to 4.63 mg/. This smoke washing wastewater is led to the first reaction tank through the first adjustment tank, and 10mg/of ALM-648 and ferric chloride are added.
300 mg/added, neutralized to pH 7 with caustic soda solution, 2 mg/polymer flocculant (Konan Floc #2000) added, and after rapid stirring for 5 minutes and slow stirring for 10 minutes, primary flocculation It was led to a sedimentation treatment tank and separated into supernatant liquid and sludge. Through this coagulation and precipitation treatment, lead is less than 0.02mg/, cadmium is 0.002~0.057mg/, zinc is 0.18~2.54mg/,
Chromium content is reduced to 0.15 to 3.86mg/, an amount that meets the emission standards. Although mercury has been reduced to about 0.0048-0.053mg/, it still does not meet the emission standards. As a result of using this supernatant liquid as water for cooling incinerated ash, the incinerated ash cooling wastewater (ash wastewater) has a pH of 10.75~
11.75, mercury 0.0050-0.064mg/, lead
15.5-22.0mg/, cadmium 0.086-0.41mg/
, zinc 8.68~17.6mg/, chromium 0.43~
1.21mg/, and suspended solids were contained at a rate of 116-282mg/. Plant wastewater (340
m ³ /day) is sent to the second adjustment tank, and in the second reaction tank, 300 mg of ferric chloride is added and neutralized to pH 10 with a caustic soda solution. Add 2mg/of and stir rapidly for 10 minutes.
After 20 minutes of slow stirring, the mixture was introduced into a second coagulation-sedimentation treatment tank, where it was separated into supernatant water and sludge, and neutralized to a pH of 6.5 to 7.5 in a final neutralization tank. With this process,
Mercury less than 0.0005~0.0034mg/, lead 0.03~
0.18mg/, cadmium less than 0.002~0.028mg/
, zinc 0.024~0.134mg/, chromium 0.06~
The amount was reduced to 0.40mg/, sufficiently meeting the emission standards. This treated water could then be discharged into the sewer system. In this way, smoke washing wastewater can be treated economically without using chelate resin, and 168 m ³ per day can be treated.
By reusing the coagulated and precipitated supernatant liquid of smoke washing wastewater as water for cooling incinerated ash, it is possible to significantly reduce chelate resin costs by 4 million yen and water costs by 4 million yen per year. Moreover, it was possible to avoid the difficulty of maintaining and managing the chelate resin tower. Comparative example Smoke washing wastewater from garbage incineration plants A to E shown in Table 1 below (Mercury concentration in each wastewater is as shown in Table 1)
was treated by the method shown in the Examples of JP-A No. 60-68094. That is, a sulfuric acid band and a heavy metal fixative were added to each smoke washing wastewater at a rate of 1000 mg/10 mg/10 mg/each in a rapid agitation coagulation tank, and at the same time the pH was adjusted to 7 with caustic soda. The rapid stirring time was about 10 minutes, and the rotation speed of the stirrer was 350 rpm.
Furthermore, 3 g/polymer auxiliary agent was added in a slow stirring coagulation tank, and stirring was performed for 10 minutes at a stirrer rotation speed of 36 rpm. Next, solid-liquid separation was performed in a settling tank, and the water quality of the supernatant was separated. The mercury concentration in the liquid is as shown in Table 1, and there was one case in which the mercury concentration was lowered to a level below the emission standard, but in the remaining four cases, the mercury concentration was lowered to a level below the emission standard. I couldn't bring it down to that level. Next, when such a supernatant liquid was further treated with a chelate resin, as shown in Table 1, the mercury concentrations of the smoke washing wastewater A to E were all able to be lowered to a level below the emission standard.

【table】 [Brief explanation of drawings]

1 and 2 are flowcharts showing a preferred embodiment of the method of the present invention.

Claims (1)

[Scope of Claims] 1. After coagulating and precipitating wastewater from a waste incineration plant using a liquid chelating agent, an inorganic flocculant, and a polymer flocculant, the supernatant liquid is mixed with ash wastewater and equipment/floor cleaning wastewater. . A method for treating wastewater from a waste incineration plant, which comprises subjecting the mixture to coagulation and sedimentation treatment again using an inorganic flocculant and a polymer flocculant. 2. After coagulating and precipitating wastewater from a waste incineration plant using a liquid chelating agent, an inorganic coagulant, and a polymer coagulant, this supernatant liquid is used as water for cooling the incinerated ash, and then this used liquid is subjected to inorganic coagulation. A method for treating wastewater from a waste incineration plant, characterized by subjecting it to coagulation and sedimentation treatment again using an agent and a polymer flocculant.