JPH01176493A - Treatment of waste water from incineration plant - Google Patents

Abstract

PURPOSE:To enable simple reduction of the content of residual harmful heavy metals such as mercury in a supernatant liquid to a level below a standard discharge value without use of chelate resin by mixing a supernatant liquid obtained after flocculation and settlement of waste water produced after washing a flue with ash-contaminated water or waste water used for washing a device and a floor. CONSTITUTION:Waste water produced by washing of a flue at an incineration plant is conducted to the first reaction tank via a first adjustment tank, and liquid chelate, inorganic flocculant and polymer flocculant are added to the waste water in a first reaction tank. The waste water is guided to a first flocculation/settlement tank, where primary flocculation/ settlement treatment takes place. Then a supernatant liquid is supplied to a plant waste water storage tank, where the supernatant liquid is mixed with ash-contaminated water and/or waste water produced by washing of a device and a floor. After this, heavy metals such as mercury remaining in the supernatant liquid are allowed to be adsorbed into incineration ash in the ash-contaminated water or suspended particles in the waste water produced after washing a device and a floor. Then this mixture liquid is conducted to the second flocculation/settlement tank through the second adjustment tank and the second reaction tank for additional flocculation/settlement treatment. Consequently, a trace of mercury remaining in the supernatant liquid is removed from the supernatant liquid to such an extent that low density meeting a discharge standard is obtained.

Description

[Detailed description of the invention] Industrial applications 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 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 exhaust gas is released into the atmosphere.

On the other hand, liquid chelate (heavy metal scavenger) and iron chloride are added to smoke washing wastewater containing heavy metals, and pH is adjusted with caustic soda.
After being neutralized to around 7, a polymer flocculant is further added to perform a coagulation-sedimentation treatment (heavy metals other than mercury are below the emission standards), and then after sand filtration, the above-mentioned coagulation-sedimentation treatment is sufficient to flocculate. The unprecipitated mercury is removed using chelating resins to a low concentration that meets emission standards, and the detoxified wastewater is then discharged into sewers or public waters. On the other hand, separate clean industrial water is used to cool the incinerated ash generated from garbage incineration (the wastewater generated in this way is called ``ash wastewater''), and this ash wastewater is then used as wastewater from the equipment φ floor cleaning drain. etc., and this mixed liquid (plant wastewater) is subjected to coagulation and sedimentation treatment in the same manner as above, and rendered harmless.
Currently, it is discharged into sewers or public water bodies.

However, in such conventional methods, the chelate resin used to remove mercury is expensive, and the surface of this chelate resin is often contaminated with suspended matter, colloidal substances, etc. that reduce mercury capture performance, and mold, etc. The drawback is that microorganisms tend to propagate, making it difficult to maintain and manage the resin. 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. the result,
If the supernatant liquid after coagulating and settling the smoke washing wastewater is mixed with ash wastewater and equipment/floor washing wastewater, heavy metals such as mercury remaining in the supernatant liquid can be removed from the incinerated ash and equipment in the ash wastewater.・If the suspended particles in the floor cleaning wastewater are adsorbed, and if this is coagulated and precipitated again using an inorganic flocculant, the trace amount of mercury remaining in the supernatant can be removed from the supernatant. 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 it can be removed to a low concentration that meets the standards. The present invention was completed based on this knowledge.

That is, the present invention coagulates and settles smoke washing wastewater from a waste incineration plant using a liquid chelate, an inorganic flocculant, and a polymer flocculant, and then mixes ash wastewater and equipment/floor cleaning wastewater with this supernatant liquid. A method for treating waste incineration factory wastewater, which is characterized by subjecting the mixture to coagulation and sedimentation treatment again using an inorganic flocculant and a polymer flocculant, and a waste incineration factory wastewater treatment method using a liquid chelate, an inorganic flocculant, and a polymer flocculant. After coagulation and sedimentation treatment, this supernatant liquid is used as cooling water for incinerated ash, and then this used liquid is subjected to coagulation and sedimentation treatment again using an inorganic flocculant and a polymer flocculant. It concerns the processing method.

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 a first reaction tank through a first adjustment tank, where a liquid chelate, an inorganic flocculant, and a polymer flocculant are added, and then the wastewater is led to a first coagulation sedimentation tank, Here, the first coagulation and precipitation treatment is performed.

As the liquid chelate used, conventionally known ones can be used (for example, Sumikire) HM6000 [manufactured by Sumire Kagaku Co., Ltd.], Epofloc-1°L-2, L-3 (both manufactured by Miyoshi Yushi Co., Ltd.), Unitika UML5000 (
Unitika Co., Ltd.], ALM-648 (Nippon Soda Co., Ltd.), etc. As the inorganic flocculant, a wide variety of conventionally known coagulants can be used, such as ferrous chloride, ferric chloride,
Examples include ferric sulfate, polyaluminum chloride, aluminum sulfate, and the like. Also, as a polymer flocculant,
A wide variety of conventionally known products can be used, such as Konan Flock #2000 C (manufactured by Konan Kagaku Kogyo Co., Ltd.), Himorok L
-113 [manufactured by Kyowa Organic Co., Ltd.], Aron N-100 (manufactured by Toa Organic Gosei Co., Ltd.), Kurita EDP Flock 101 [manufactured by Kurita Water Industries, Ltd.], etc.The amount of liquid chelate to be added to the smoke washing wastewater is as follows: There is no particular restriction and the amount can be appropriately selected within a wide range, but it is usually about 2 to 50 mg, preferably about 10 to 20 mg, based on the wastewater IQ.

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;
About 50 to 2000 mg, preferably 100 mg to Q
The amount is preferably about 200 mg.

In addition, the amount of polymer flocculant that should be added to smoke washing wastewater is as follows:
There is no particular limit and it can be selected appropriately from a wide range, but it is usually about 1 to 10 mg, preferably 2 to 4 mg, based on the drainage IQ.
It is preferable to use about mg. If the amount of liquid chelate, inorganic flocculant, and polymer flocculant added is less than the above range, there will be a tendency that the desired heavy metal removal effect cannot be obtained; The removal effect of heavy metals is not significantly improved, and it is economically unfavorable.

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 supernatant liquid and sludge. The sludge separated here is sent to landfill together with the sludge obtained in the secondary coagulation and sedimentation treatment that will be performed later. Meanwhile, the supernatant liquid is sent to the plant wastewater storage tank.

In the present invention, it is preferable to reduce the mercury content in the supernatant liquid to a certain amount or less, for example, 0.05 mg/Q or less, by the first coagulation and precipitation treatment.

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 in the subsequent secondary coagulation and precipitation treatment.

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. Supernatant liquid and ash wastewater and/or equipment/
The mixing ratio with the floor washing waste water is not particularly limited, but it is usually good to mix the latter at a ratio of about 0.5 to 4 times, preferably about 1 to 2 times, to the former.

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 coagulation and sedimentation 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 from a wide range, but it is usually 1
00~4000mg, preferably 100~300m
The amount of polymer flocculant used should be approximately
There is no particular restriction and the amount can be appropriately selected within a wide range, but it is usually about 1 to 10 mg, preferably about 2 to 4 mg, for the mixed liquid IQ to be treated. If the amount of the inorganic flocculant and polymer flocculant added is less than the above range, there will be a tendency that the mercury removal effect will not be obtained.
On the other hand, if the amount exceeds the above range, the effect of removing mercury from the mixed liquid will not improve much, and this is not economically preferable.

Such secondary flocculation and sedimentation treatment can also be carried out according to a conventional method, and by this flocculation 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.
It is rendered harmless and discharged into the sewer system. Neutralization of the supernatant water can also be carried out according to conventionally known methods.

According to another preferred embodiment of the present invention, the first
After using the supernatant liquid obtained in the secondary coagulation-sedimentation treatment as cooling water for the incinerated ash, it is sent to the plant wastewater storage tank, and further sent to the second adjustment tank, where it is subjected to the second coagulation-sedimentation treatment in the same manner as above. (See Figure 2). According to this embodiment, it is possible to reduce the heavy metals contained in the smoke washing wastewater to a level below the emission standard, and it is also possible to greatly reduce the amount of industrial water used for cooling the incineration ash, thereby reducing waste incineration. The required costs 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.
The amount of industrial water can be reduced. Therefore, with the method of the present invention, it is possible to simplify wastewater treatment, reduce treatment costs, reduce the amount of industrial water, etc., and it is possible to treat wastewater from waste incineration plants on an industrial scale.

Example Examples are given below to further clarify the present invention.

Example 1 Take 1 g of smoke washing wastewater from a garbage incineration factory (containing mercury at a concentration of 3.4 mg/Q) in a beaker, and add Sumikylate 6 to it.
After adding 10 mg of 000H (liquid chelate, manufactured by Sumima Kagaku Co., Ltd.) and 300 mg of ferric chloride and neutralizing it to pH 7 with a 20% caustic soda solution, 2 mg/Q of a polymer flocculant (Konan Floc #2000) was added. Rapid stirring 5 minutes,
After 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.

Heavy metals Smoke washing wastewater Supernatant liquid Removal rate (mg #!
) (mg#!) (%) Mercury 3.4 0
．． 042 99 Zinc 11.7 0.4 97 Lead 5.2 0.01 10
0 Cadmium 0.2 0.01 95 Among these various heavy metals, the concentration of mercury is higher than the emission standard, so
500 mQ of plant wastewater collected from the incineration plant was added to the above supernatant liquid 500n+Q, and 300 mg of ferric chloride/
Q, polymer flocculant (Konan Floc #2000) 2
mg/Q was added, neutralized to pH 7 with 10% caustic soda solution, stirred rapidly for 5 minutes and slowly for 10 minutes, and then allowed to settle. As a result, the mercury concentration in the supernatant water was 0.0, which was the emission standard.
0.05mg/2 or less. 0005mg/Q.

Example 2 An incineration factory that incinerates 550 tons of general waste per day discharges 14'5 m3 of smoke washing wastewater per day, and the heavy metal concentration is 3.0 to 3.4 mg/Q of mercury.

, Lead 0.03~0.41mg/&, Cadmium 0.005~0.02mg/R1 Zinc 0.01
~3.0mg/Q, chromium 0.05~0.82mg/
It is Q.

This smoke washing waste water is led to the first reaction tank via the first adjustment tank, 10 mg/2 of Sumikylate 6000H and 300 mg/Q of ferric chloride are added, and after neutralized to pH 7 with a caustic soda solution, a polymer flocculant is added. (Konan Flock #2000
) was added at 2 mg/Q, followed by rapid stirring for 10 minutes and slow stirring for 25 minutes.
After a few minutes, the mixture was introduced into a primary coagulation and sedimentation treatment tank, where it was separated into a supernatant liquid and sludge. Through this coagulation and sedimentation treatment, lead is reduced to 0.
．． Less than 0'2 ~ 0. 07mg/Q, cadmium less than 0.002~0.02mg/Q, zinc 0.001
~0.09n+g/Q, chromium is 0. 01~0. 0
The amount decreases to 7mg/Q, which meets the emission standards. Mercury is 0.0041-0.047mg/! However, it still does not meet the emission standards.

On the other hand, incineration ash cooling wastewater (ash sewage) is 11yH7,85
~11.69, mercury is 0, OO15~O,'0049mg/Q, lead is 12.2~40.9mg/Q, cadmium is 0,05
~0.20mg/Q, zinc 1.5~20mg/
Qs chromium is 0. 04-0. 56mg/L7. Suspended solids are contained at a rate of 84 to 33'5 mg/Q. The plant wastewater (278 m3/day), which is a combination of this ash wastewater and the equipment/floor cleaning wastewater, and the supernatant liquid obtained above are sent to the second adjustment tank, and further in the second reaction tank.
After adding 00mg/Q and neutralizing to pH 10 with caustic soda solution, polymer flocculant (Konan Floc #200
0) was added at 2 mg/R, followed by rapid stirring for 10 minutes and slow stirring for 2 minutes.
After 0 minutes, it is led to the second coagulation and sedimentation treatment tank, where it is separated into supernatant water and sludge, and the final neutralization tank has a pH of 6.5 to 7.5.
was neutralized. Through this treatment, mercury is less than 0.0005 to 0.0029 mg/2 (average value 0.0011 mg/2).
Q), lead is 0.05 to 0.14 mg/Q, cadmium is less than 0.002 mg/Q, zinc is less than 0.001 to 0
．． 09mg/Q, chromium less than 0.01~0.04mg
/Q, and the amount was reduced to a level that satisfies the emission standards. In addition, the emission standards are 0.005mg/Q of mercury,
Lead is 1 mg/Q.

Cadmium is O, 1 mg/Q, zinc is 5 mg/(2, and chromium is 2 mg/(2).

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/Q of mercury.

Lead is 0.25~O,! 53D/f2. Cadmium is 0.
008-0.025mg/12. Zinc is 0.020-3
．． 5 mg/Q, and chromium is 0.20 to 0.83 mg/Q.

This smoke washing waste water was led to the first reaction tank through the first adjustment tank, and Epofloc L-2 [liquid chelate, manufactured by Miyoshi Oil Co., Ltd.] was added at 1'Omg/Q and ferric chloride was added at 300mg/Ω.
After adding and neutralizing to pH 7 with caustic soda solution, add 2 mg/Q of polymer flocculant (Konan Floc #2000).
After 5 minutes of rapid stirring and 10 minutes of slow stirring,
Next, it was led to a coagulation sedimentation treatment tank, where it was separated into supernatant liquid and sludge by sedimentation.

After the supernatant liquid obtained above is used to cool the incinerated ash, it is sent to the second adjustment tank, and further in the second reaction tank, ferric chloride 3
After adding 00mg/Q and neutralizing the solution to pH 10 with a caustic saw, a polymer flocculant (Konan Floc #200
0) was added at 2 mg/Q, followed by rapid stirring for 10 minutes and slow stirring for 2 minutes.
After 0 minutes, it is led to the second coagulation and sedimentation treatment tank, where it is separated into supernatant water and sludge, and the final neutralization tank has a pH of 6.5 to 7.5.
was neutralized. Through this treatment, mercury is less than 0.0005 to 0.0018 mg/Q, and lead is less than 0.02 to 0.13.
mg/Q, cadmium less than 0.002, zinc 0.0
Less than 01 to 0.05mg/Q, chromium 0.01mg/
It was less than Q to 0.04 mg/12, which was sufficient to meet the emission standards.

Example 4 A certain incineration factory incinerated 570 tons of general waste per day.
584m3 of industrial water is used.

Mercury is 0.1 in the smoke washing wastewater generated in 168 m3 per day.
1~6.1111g/2, lead 0.09~1.49B/2
Q. Cadmium is 0.046~0, 13mg/Q
, zinc 0.36-3.9mg/R, chromium 0.12
~4.63 mg/Q.

This smoke washing waste water is led to the first reaction tank via the first adjustment tank,
LM-648 10mg/Q and ferric chloride 300m
After adding gIQ and neutralizing to pH 7 with caustic soda solution, 2 mL of polymer flocculant (Konan Floc #2000) was added.
mg/Q was added, and after rapid stirring for 5 minutes and slow stirring for 10 minutes, the mixture was introduced into a first coagulation and sedimentation treatment tank, and separated into supernatant liquid and sludge by sedimentation. Through this coagulation and sedimentation treatment, lead was reduced to 0.02 m
less than g/2, cadmium 0.002-0.057 mg
/R, zinc 0.18-2.54mg/Q, chromium 0
．． 15 to 3.86 mg/(2), which is reduced to the extent that it meets the emission standards.Mercury is 0.0048 to 0.053 mg/Q
However, 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 to 11.75.
mercury is 0.0050 to 0.064 mg/Q, and lead is 15.5 to 22. OB/f2. Cadmium is 0.08
6-0.41mg/Q, zinc 8.68-17.6mg
/Q, chromium is contained at a ratio of 0.43 to 1.21 mg/Ω, and suspended solids are contained at a ratio of 116 to 282 mg/Q. Plant wastewater (340m3/day), which is a combination of this ash wastewater and equipment/floor cleaning wastewater, is sent to the second adjustment tank, where 300mg/Q of ferric chloride is added in the second reaction tank, and the pH is brought to 10 with caustic soda solution. After neutralization, 2 mg/Q of polymer flocculant (Konan Floc #2000) was added, and after rapid stirring for 10 minutes and ultra-fast stirring for 20 minutes, it was led to the second coagulation and sedimentation treatment tank, where supernatant water and sludge were mixed. Separated by precipitation,
It was neutralized to pH 6.5 to 7.5 in the final neutralization tank. Through this treatment, mercury is less than 0.0005 to 0.0034mg/
Q. Lead is 0. 03~0. 18mg/Q, cadmium less than 0.002~0.02801g/Q, zinc 0.024~0.134D/Q.

Chromium was reduced to 0.06 to 0.40 mg/Q, which was sufficient to meet the emission standards. This treated water could then be discharged into the sewer system.

In this way, the smoke washing wastewater is treated economically without using chelate resin, and the supernatant liquid obtained by coagulation and sedimentation of 168 m3 of smoke washing wastewater per day is reused as water for cooling the incinerated ash. Chelate resin cost 4 million yen per year,
We were able to significantly reduce water costs by 4 million yen, and also avoided the difficulty of maintaining and managing the chelate resin tower.

[Brief explanation of the drawing]

1 and 2 are flowchart diagrams illustrating a preferred embodiment of the method of the present invention. (that's all)

Claims (2)

[Claims] (1) After coagulating and settling the smoke washing wastewater from a waste incineration plant using a liquid chelate, an inorganic coagulant, and a polymer coagulant, this supernatant liquid is mixed with ash wastewater and equipment/floor cleaning wastewater, and the mixture is inorganic. A method for treating wastewater from a waste incineration plant, characterized by subjecting it to coagulation and sedimentation treatment again using a flocculant and a polymer flocculant. (2) After coagulating and settling wastewater from a waste incineration plant using a liquid chelate, an inorganic flocculant, and a polymer flocculant, this supernatant liquid is used as cooling water for the incinerated ash, and then this used liquid is inorganic. A method for treating wastewater from a waste incineration plant, characterized by subjecting it to coagulation and sedimentation treatment again using a flocculant and a polymer flocculant.