Liquid purification or separation – With gas-liquid surface contact means – With separator
Reexamination Certificate
2000-01-28
2002-07-02
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
With gas-liquid surface contact means
With separator
C210S195200, C210S195300, C210S199000, C210S202000, C210S205000, C210S206000, C210S223000, C210S908000, C210S915000, C210S919000
Reexamination Certificate
active
06413417
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a waste water treatment method and apparatus which utilizes silicon sludge obtained from silicon waster water, discharged from for example a semiconductor factory, for treating fluorine waster water in a separate waster water treatment system.
2. Description of the Related Art
In a semiconductor factory, after a silicon wafer is polished, it is cleaned with water. Thus, the factory has silicon waste water containing silicon particles.
Treated water derived from the silicon waste water, from which the silicon particles have been separated, has a high quality. Therefore, the treated water is discharged from the factory without being subjected to a further treatment or recycled as the raw water to be treated in an ultrapure water system.
On the other hand, the separated silicon particles exist in an aggregated form of sludge. The silicon sludge is dehydrated by a dehydrator and then disposed of, for example, as landfill, outside the semiconductor factory.
Japanese Patent Publication No. 2720830 discloses that silicon particles are recovered from a suspension which is a silicon particle-suspended calcium hydroxide solution, and that the recovered silicon particles are mixed with activated sludge to increase the settling performance of the activated sludge.
On the other hand, to treat fluorine waste water, hitherto, a calcium agent such as calcium hydroxide or calcium carbonate mineral is added or loaded to the waste water to chemically react fluorine contained in the waste water with calcium of the calcium agent, using a stirring means such as a stirrer or pneumatic stirring.
Conventionally, such stirring means has been infallibly used to cause a neutralization reaction of waste water and a chemical reaction of fluorine in the waste water. In those days not requiring complete implementation of energy-saving measures, however, the cost for electricity consumed by the stirring means was not regarded as important.
A conventional waste water treatment method is shown in FIG.
1
B. In the conventional method, acid waste water is introduced into a neutralization tank
46
from an introduction tank
1
by a pump
2
and an alkali agent such as caustic soda is added to the waste water there. Then, the acid waste water loaded with the alkali agent is stirred by a rapid stirrer
18
to get neutralized.
FIG. 1C
shows another conventional waste water treatment method. In
FIG. 1C
, parts similar to the parts shown in
FIG. 1B
are denoted by the same reference numerals. In the conventional method shown in
FIG. 1C
, acid waste water is pumped into a neutralization tank
46
from an introduction tank
1
by a pump
2
. An alkali agent such as caustic soda is added to the acid waste water, and air generated by a blower
14
is discharged from an air-diffusing pipe
22
to neutralize the acid waste water by pneumatic stirring.
Returning to the treatment of fluorine waste water, fluorine waste water discharged from the semiconductor factory contains not only hydrofluoric acid which is a main component of the fluorine waste water but also nitric acid, ammonia water, phosphoric acid, hydrogen peroxide, and organic matters including a surfactant. Thus, it is necessary to also treat the latter components.
It is reported that a part of the surfactant may become an environmental hormone. Thus, reliable treatment is demanded.
Nitrogen and phosphorous resulting from the nitric acid, the ammonia water, and the phosphoric acid are considered to be substances causing eutrophication. Thus, it is necessary to treat nitrogen and phosphorus from the viewpoint of preventing red tide that is generated on the sea. In ordinary denitrifying equipment and phosphorus-removing equipment, however, the initial cost and the running cost are high.
In recent years, the pollution of ground water caused by an organic chlorine compound, or organic chloride, discharged from existing factories has been taken up as a serious problem. According to an ordinary method, the ground water containing the organic chloride is drawn up and aerated so that the vaporized organic chloride is adsorbed to activated charcoal. There is known another method in which the organic chloride is decomposed by being irradiated with ultraviolet light. According to another known method, the organic chloride is dechlorinated by its contact with a metal surface. According to still another known method, it is treated by microorganisms (bio-remediation).
Still another conventional method of treating the organic chloride is disclosed in Japanese Patent Application Laid-Open No. 10-113679. In the conventional method, silicon is added to a polluted environment to accelerate dechlorination reaction of the organic chlorides (contaminant), such as carbon tetrachloride, tetrachloroethylene, and the like, to thereby decompose it.
Examples of the conventional waste water treatment methods will be described below in more detail with reference to
FIGS. 19 and 20
in which parts similar to the parts shown in
FIGS. 1B and 1C
are denoted by the same reference numerals.
In a first example of treating silicon waste water shown in
FIG. 19
, silicon and treated water are separated from each other by a coagulation and settlement method, and the treated water is utilized as raw water in an ultrapure water system.
In the method of treating silicon waste water shown in
FIG. 19
, silicon waste water is introduced into a storage tank
30
and stored therein and then fed to a reaction tank
32
by a storage tank pump
31
. Polychlorinated aluminum (not shown) serving as a flocculating agent and caustic soda (not shown) serving as a neutralization agent are loaded into the reaction tank
32
to form flocs containing silicon
42
. The silicon flocs are introduced into a settling tank
33
in which the flocs are separated into silicon as a solid matter and treated water as a supernatant liquid.
The treated water, supernatant, is introduced into a storage tank
37
. Then, by a high-pressure pump
38
, the treated water is fed to a prefilter
39
, then to a reverse osmosis membrane device
40
, and finally to a ultrapure water system
41
in which the water is utilized as raw water. On the other hand, the silicon floc that has precipitated in the settling tank
33
becomes silicon sludge. Then, a concentration
44
concentrates the silicon sludge. A filter press pump
45
feeds the concentrated silicon sludge to a filter press
46
for dehydration. After the silicon is dehydrated, it is disposed of as landfill, without being recycled, as described above. The disposal by landfill has been a typical method.
Fluorine waste water is treated by a different waste water treatment system. Fluorine waste water is introduced into an introduction tank
1
and then fed to a calcium hydroxide tank
17
by an introduction tank pump
2
. Calcium hydroxide is added to the fluorine waste water contained in the calcium hydroxide tank
17
in which a rapid stirrer
18
stirs the fluorine waste water and the calcium hydroxide to mix and react them with each other. That is, calcium ions of the calcium hydroxide and fluorine contained in the fluorine waste water react with each other to form fine and refractory particles of calcium fluoride. The fine particles of calcium fluoride formed in the calcium hydroxide tank
17
are introduced into a polychlorinated aluminum tank
19
in which polychlorinated aluminum serving as a flocculating agent is added to the calcium fluoride to form flocs. Then, the flocs are introduced into a macromolecular flocculant tank
21
in which a macromolecular flocculant is added to the flocs to form larger stable flocs. Those flocs are introduced into a settling tank
23
in which the flocs are separated into a supernatant liquid and a precipitated matter, or sludge. The treated water, or the supernatant liquid, is discharged outside. The calcium fluoride sludge obtained as the precipitated matter is introduced into a concentration tank
26
and concentrated. Finally, the concentrated calciu
Chujo Kazumi
Okamoto Seiji
Tao Yukihiro
Yamasaki Kazuyuki
Hruskoci Peter A.
Nixon & Vanderhye PC
Sharp Kabushiki Kaisha
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