JPS6068094A - Treatment of waste water from wet gas washing apparatus - Google Patents

Abstract

PURPOSE:To remove mercury simultaneously with fluorine with a single solid and liquid separation by adding a heavy metal fixing agent to waste water from a wet gas washing apparatus of a city garbage incinerator, regulating the pH almost to neutrality, and adding a high molecular assistant. CONSTITUTION:The waste water from a wet gas washing apparatus is introduced into a high-speed agitating and flocculating tank 7 wherein sodium hydroxide, a heavy metal fixing agent, and an aluminum compd. are added, agitated, and mixed. The pH is regulated to 6-8, preferably to 6.5-7.5. A liquid chelating resin having a sulfur-contg. chelating group is used as the heavy metal fixing agent. Then the waste water is charged into a low-speed agitating and flocculating tank 8, added with a high molecular assistant, and slowly agitated. The waste water is then sent to a settling tank 9 wherein sludge and the treated water are separated. By said method, the effluent standard of 0.005mg/l Hg and 15mg/l fluorine can be satisfied with a single solid and liquid separation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing mercury and fluorine from wet gas cleaning wastewater discharged when exhaust gas from a municipal waste incinerator is wet cleaned.

Conventionally, as a method for removing mercury from wet gas cleaning wastewater, a coagulation-precipitation method in which sodium sulfide and ferric chloride are added has been used. That is, as shown in FIG. 1, raw water (wastewater) is introduced into the first rapid stirring coagulation tank 1, and is rapidly stirred while adding sodium sulfide and ferric chloride and adjusting the pH with a pH adjuster. The mixture was then introduced into the first slow stirring aggregation step (2), a polymer auxiliary agent was added thereto, the mixture was slowly stirred, and then sent to the first settling tank 6 for solid-liquid separation to remove mercury. In order to remove fluorine, the supernatant is further introduced into a second rapid stirring flocculation tank 4,
After adding Al salt or Ca salt and stirring rapidly while adjusting the pH with a pH adjuster, the mixture was then introduced into the second slow stirring aggregation tank 5, and after adding a polymer auxiliary agent and stirring slowly, The sludge was sent to the second settling tank 6 and separated into sludge and treated water. In order to remove mercury and fluorine in this way, solid-liquid separation is required twice, and there are also the following problems regarding the mercury removal performance.

(1) Mercury that reacts with sodium sulfide becomes mercury sulfide and is separated into solid-liquid, but mercury sulfide is so fine that solid-liquid separation is difficult, and mercury leaks to the subsequent stage, resulting in unstable performance.

(2) There is a risk of hydrogen sulfide generation, and ventilation equipment needs to be strengthened.

(3) The removed mercury is carried out as sludge, and mercury is eluted from this sludge.

(4) It was difficult to achieve the mercury emission regulation value of 0.005fnV'β, and processing equipment such as activated carbon, ion exchange resin, and chelate resin was required at the subsequent stage.

As described above, multiple solid-liquid separation operations are required, operation management is difficult, and equipment costs and installation area are large, resulting in high costs.

The present invention was made in view of the above points, and includes adding a heavy metal fixative and an aluminum compound such as sulfuric acid to wet gas cleaning wastewater from a municipal waste incinerator, stirring and mixing the same, and adding a pH adjuster to adjust the pH. By adjusting the liquid to around neutrality, then adding a polymeric auxiliary agent, stirring and mixing, and then performing solid-liquid separation, mercury and fluorine can be removed at the same time with one solid-liquid separation, and it is easy to operate. The present invention aims to provide an economical method for treating wet gas cleaning wastewater with small equipment costs and small installation area.

Hereinafter, the configuration of the present invention will be explained based on the drawings.

FIG. 2 shows an example of an apparatus for carrying out the method of the invention. Wet gas cleaning wastewater (raw water) is introduced into a rapid stirring coagulation tank 7, and caustic soda, a heavy metal fixative, and an aluminum compound are added and mixed with stirring. pH is 6-8, preferably 6.5
Adjust so that it becomes ~7.5. As the heavy metal fixing agent, a liquid chelate resin having a chelate group containing sulfur is used.

Next, this wastewater flows into a slow agitation flocculating tank 8, where a polymeric auxiliary agent is added and slowly stirred, and then sent to a settling tank 9 where it is separated into sludge and treated water.

According to the method of the present invention, the discharge regulation value of mercury and fluorine is 0.005 mf/I in one solid-liquid separation! ,,15'q/j
2 (-) It is possible to satisfy each of these requirements, and it is safe with no risk of hydrogen sulfide generation, and has the effect that mercury does not elute from the sludge.

Next, embodiments of the present invention will be described.

EXAMPLE An experiment was conducted according to the flow shown in FIG. 2 using wet gas cleaning wastewater from a municipal waste incinerator having the following water quality.

Fluorine 20-507nf/Il - average 26.5fn9
/ft Mercury 1-2Vβ Average 1.4 q/2 Dissolved salt 22% Iron 2.8-130 fng/fi Average 46.8q/4
2 Lead 0.01-0.46 Ml/It average 0.2
3q/n This wastewater is treated with a heavy metal fixative (
A liquid chelating agent) and sulfuric acid were added, and at the same time the pH was adjusted to 7 with caustic soda. The addition rate of heavy metal fixative is 10 ppm, the addition rate of sulfuric acid band is 500 pl)m,
There were three types: 1000 ppm and 2000 ppm. The rapid stirring time is approximately 10 minutes, and the rotation speed of the stirrer is 35.
It was 0 rpm. Further, 3 ppm of a 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. Solid-liquid separation was then performed in a settling tank, and the quality of the supernatant water was analyzed. The results were as shown in the table below.

(Left below) Breaking G・- From the table, it can be seen that according to the method of the present invention, only a single solid-liquid separation is required.
It can be seen that it is possible to remove fluorine and mercury to levels below the emission standards. It is also possible to remove heavy metals such as iron and lead.

[Brief explanation of drawings]

FIG. 1 is a 70-sheet of a conventional wet gas cleaning wastewater treatment apparatus, and FIG. 2 is a flow sheet showing an example of a wet gas cleaning wastewater treatment apparatus implementing the method of the present invention.

Claims (1)

[Claims] 1 Add heavy metal fixatives and aluminum compounds such as sulfuric acid to wet gas cleaning wastewater from municipal waste incinerators, stir and mix, add a pH adjuster to adjust the pH to around neutrality, and then add polymer additives. A method for treating wet gas cleaning wastewater, which is characterized by adding a chemical agent and stirring and mixing, and then performing solid-liquid separation to remove mercury and fluorine from the wastewater.