Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-05-04
2002-02-05
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S626000, C210S709000, C210S713000, C210S724000, C210S195200, C210S195300, C210S257200, C210S202000, C210S915000, C210S603000
Reexamination Certificate
active
06344142
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a waste water treatment method and apparatus for minimizing the amount of sludge generated in a waste water treatment apparatus for treating fluorine-containing waste water discharged from a semiconductor factory.
With reference to
FIG. 19
, a first prior art is described below. In the first prior art, fluorine-containing waste water is introduced into a raw water tank
101
. The fluorine-containing waste water in the raw water tank
101
is transferred, with its quality and amount being adjusted to a slaked lime reaction tank
114
by a first pump
102
. In the slaked lime reaction tank
114
, fluorine in the waste water reacts with calcium from slaked lime, resulting in calcium fluoride
130
.
A quick stirrer
115
serving as a reaction-accelerating stirring means is installed in the slaked lime reaction tank
114
and stirs the waste water. However, the retention time of the waste water in the slaked lime reaction tank
114
is set to less than one hour. Thus, unreacted slaked lime flows out from the slaked lime reaction tank
114
and flows into a poly aluminum chloride coagulating tank
116
. A quick stirrer
115
is also installed in the poly aluminum chloride coagulating tank
116
. The fine calcium fluoride
130
as a reaction product in the slaked lime reaction tank
114
is coagulated with poly aluminum chloride serving as an inorganic coagulant to form flocs. The unreacted slaked lime is also coagulated with the poly aluminum chloride to form flocs. Because the coagulated floc of slaked lime does not contain calcium ions, the coagulated floc is not effective for treating fluorine. This means nothing else but waste of chemicals and the coagulated floc constitutes the unreacted chemicals
129
. The calcium fluoride
130
in floc form becomes a more stable and larger floc in a high molecular coagulating tank
117
to which a high-molecular coagulant is added.
On the other hand, although the unreacted floc
129
of slaked lime is not effective for treating the fluorine, the unreacted floc
129
becomes a more stable and larger floc in the high molecular coagulating tank
117
by addition of the high-molecular coagulant.
The more stable and larger floc of the calcium fluoride
130
and the more stable and larger floc of the slaked lime flow into a settling tank
119
and settle therein. A scraper
120
scrapes the settled flocs to the center of the bottom of the settling tank
119
. The flocs become sludge.
That is, the amount of the sludge is the sum of the sludge arising from the calcium fluoride
130
and the unreacted slaked lime as well as the sludge arising from the unreacted coagulant. The sludge scraped to the center of the bottom of the settling tank
119
flows into a thickening tank
122
having a scraper
123
and is thickened therein. Then the sludge is transferred to a filter press
125
by a filter press pump
124
and dehydrated. Because the amount of the sludge generated in the waste water treatment apparatus is large, there are installed two presses
125
.
A supernatant liquid of the thickening tank
122
is introduced into the raw water tank
101
through an overflow pipe (not shown).
Meanwhile, a waste water treatment equipment that generates a small amount of dehydrated cake, namely, a small amount sludge is recently required. However, the sludge generated in the waste water treatment equipment of the first prior art contains the sludge of the calcium fluoride and the floc of the unreacted slaked lime. Therefore, a large amount of sludge is generated in the waste water treatment equipment of the first prior art. Varying in accordance with conditions of waste water discharged from factories, the amount of the sludge of the unreacted slaked lime is generally more than twice as large as that of the sludge of the calcium fluoride.
(Second Prior Art)
The second prior art is shown in FIG.
20
. The second prior art differs from the first prior art in that a part of the sludge discharged from the settling tank
119
of the first prior art is returned to the raw water tank
101
by a sludge return pump
121
.
Because in the second prior art, a part of the sludge discharged from the settling tank
119
is returned to the raw water tank
101
, sludge containing the unreacted chemicals is consumed by the fluorine-containing waste water. Therefore, the amount of the sludge generated in the waste water treatment apparatus of the second prior art is smaller than that generated in the waste water treatment apparatus of the first prior art shown in FIG.
19
.
(Third Prior Art)
FIG. 21
shows the third prior art. The third prior art differs from the first prior art in that a part of the sludge discharged from the settling tank
119
is returned to the slaked lime reaction tank
114
by the sludge return pump
121
. Because in the third prior art, a part of the sludge discharged from the settling tank
119
is returned to the slaked lime reaction tank
114
, the sludge containing the unreacted chemicals is consumed by the fluorine-containing waste water. Therefore, the amount of the sludge generated in the waste water treatment apparatus of the third prior art is smaller than that generated in the waste water treatment apparatus of the first prior art.
(Reference Example)
FIG. 22
shows a reference example. In the reference example, the fluorine-containing waste water is introduced into the raw water tank
101
. The first pump
102
transfers the fluorine-containing waste water in the raw water tank
101
, with quality and amount of the water being adjusted, to a reaction tank
126
.
The fluorine-containing waste water is introduced into the reaction tank
126
at the lower portion of an anaerobic sludge zone
109
through a lower inflow pipe
104
.
Both the fluorine-containing waste water and the sludge containing the unreacted chemicals (sum of unreacted slaked lime and unreacted coagulant)
129
returned by the pump
121
from the settling tank
119
are introduced into the reaction tank
126
. Therefore, in the reaction tank
126
, the anaerobic sludge zone
109
is always formed.
In the reaction tank
126
, fluorine contained in the fluorine-containing waste water and calcium contained in the unreacted chemicals
129
react with each other to form calcium fluoride
130
. That is, the calcium is recycled, which contributes to reduction of the amount of generated sludge.
Thus, the amount of the sludge generated in the waste water treatment apparatus of the reference example is smaller than that generated in the waste water treatment apparatus of the first prior art, but is not sufficient.
The amount of sludge generated in the waste water treatment apparatus of the reference example is smaller than that of sludge generated by the waste water treatment apparatus of the first prior art. Because in the reference example, the fluorine-containing waste water in the reaction tank
126
is not aerated, the calcium fluoride
130
settles. In the reaction tank
126
, the amount of the settled calcium fluoride
130
increases with the elapse of time. Thus the height of the anaerobic sludge zone
109
increases. As a result, the calcium fluoride
130
and the treatment water (waste water) flow into the slaked lime reaction tank
114
.
In the slaked lime reaction tank
114
, unreacted fluorine in the waste water reacts with calcium arising from added slaked lime to form calcium fluoride
130
. However, all calcium does not form the calcium fluoride
130
but unreacted calcium, namely, unreacted slaked lime is also present.
A phenomenon to which attention should be paid occurs in the slaked lime reaction tank
114
. That is, when a large amount of the calcium fluoride
130
discharged from the reaction tank
126
flows into the slaked lime reaction tank
114
and thus the concentration of the sludge rises, the neutralizing action of the alkaline slaked lime becomes weak. Therefore, there occurs a phenomenon that a large amount of the slaked lime is added to the slaked lime reaction tank
114
.
The quick stirrer
115
Chujo Kazumi
Sawai Norio
Yamasaki Kazuyuki
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Upton Christopher
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