Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2001-02-23
2002-07-23
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S616000, C210S623000, C210S631000, C210S705000, C210S193000, C210S196000, C210S199000, C210S220000
Reexamination Certificate
active
06423228
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a waste water treatment method capable of treating fluorine waste water containing organic matter (in particular, surface active agent having low biodegradability), phosphor and hydrogen peroxide discharged from a semiconductor plant, a liquid crystal plant or the like while producing a small amount of waste as sludge, saving energy and reusing chemicals, and the invention also relates to waste water treatment equipment implementing this waste water treatment method.
In a semiconductor plant, a liquid crystal plant or the like, a surface active agent is used while being mixed in a variety of chemicals used by the manufacturing apparatus. In the manufacturing apparatus of the semiconductor plant or the like, it is a general practice to use phosphoric acid, hydrogen peroxide and hydrofluoric acid, and among others, there is a tendency that a large amount of hydrofluoric acid is used. For the above reasons, fluorine waste water containing a surface active agent, phosphor and hydrogen peroxide is discharged from the semiconductor plant, the liquid crystal plant or the like.
In this case, the aforementioned “fluorine waste water containing a surface active agent, phosphor and hydrogen peroxide” means an “acid waste water that mainly includes fluorine and contains a small amount of surface active agent, phosphor and hydrogen peroxide” and further means a “hydrofluoric acid waste water that mainly includes fluorine and contains a small amount of surface active agent, phosphor and hydrogen peroxide”.
The mixture of the surface active agent in the various chemicals in the semiconductor plant, the liquid crystal plant or the like is for the reasons as follows. That is, under the circumstances of the rapid microstructural progress of semiconductor devices, elaborate portions cannot be sufficiently cleaned by only the aqueous cleaning with ultrapure water due to the surface tension of the water. Therefore, a method for cleaning the elaborate portions by reducing the surface tension with the mixture of a surface active agent in the ultrapure water and a method for executing the cleaning by reducing the surface tension with the mixture of a surface active agent (for example, a chemical such as buffered hydrofluoric acid containing a surface active agent) in a variety of cleaning chemicals are gaining popularity. In such a case, the types of the various surface active agents to be mixed in the chemicals are the important know-how of the chemical manufacturers, and newly developed surface active agents are consistently mixed.
Among the newly developed surface active agents, there are ones that have low biodegradability from the viewpoint of molecular formula, structural formula, effervescence, sterilizing performance and so on. This means that the conventional activated sludge method, catalytic oxidation method or the like as a representative of the biotic treatment, the methods become incapable of coping with the surface active agents since the methods have a microorganic concentration of about 2000 ppm to 5000 ppm.
According to a recent report, there is the indication that some surface active agents become hormone disrupters, and some countermeasures are required to be taken. On the other hand, from the viewpoint of the destruction of the environment, it is an important urgent problem that the enterprises should tackle to reuse the used chemicals, reduce waste generated from the plants and conserve energy of a variety of equipment for the achievement of cost reduction.
Conventionally, as a waste water treatment method for reusing the sludge including unreacted chemicals, there are the methods disclosed in the prior art references of Japanese Patent Laid-Open Publication Nos. HEI 5-39830, HEI 8-197070 and HEI 10-5769. Each of these three waste water treatment methods sends the sludge precipitated in the sedimentation tank back to the reaction tank or the coagulation tank where a stirrer is installed. It is to be noted that the prior art reference of Japanese Patent Laid-Open Publication No. HEI 5-39830 discloses pneumatic stirring in addition to the stirring by means of the stirrer.
The fluorine waste water is basically treated by forming a slightly-soluble calcium fluoride. In this case, for the purpose of reducing the sludge as a water generated from the waste water treatment equipment, there is adopted a method for using calcium carbonate mineral instead of the conventional slaked lime method for using slaked lime. As described above, the slightly-soluble calcium fluoride is formed through the fluorine waste water treatment. The calcium fluoride is not dissolved under the condition of either acid or alkali. Therefore, the calcium agent of slaked lime or calcium carbonate mineral can be reused again and again through circulation or another method to enable the formation of calcium fluoride that acts as the core of floc, so that the reduction of waste and the reduction in amount of use of chemicals are achieved to allow efficient waste water treatment to be achieved.
The above matter will be simply described. First of all, in a first step, the calcium agent of slaked lime or calcium carbonate mineral is added to form slightly-soluble calcium fluoride, by which the fluorine in the waste water is treated to a concentration of about 20 ppm to 40 ppm. Next, in a second step, an inorganic coagulant of polychlorinated aluminum or the like is added to the waste water obtained through the first step, and then a macromolecular coagulant is added to reduce the concentration to the intended concentration. In the above second step, the fluorine concentration cannot be reduced to the intended concentration unless a large amount of inorganic coagulant such as the polychlorinated aluminum or the macromolecular coagulant with respect to the amount of fluorine in the waste water is added. As a result, the unreacted aluminum, macromolecular coagulant and so on precipitate together with the slightly-soluble calcium fluoride to be consequently included in the sludge. Therefore, by sending the sludge including the unreacted aluminum, macromolecular coagulant and so on back to the reaction tank or the coagulation tank, the unreacted aluminum and the unreacted macromolecular coagulant are reused.
As a method for treating the water containing fluorine by means of calcium carbonate, there is the prior art reference of Japanese Patent Laid-Open Publication No. HEI 7-136667. According to this treatment method, the water containing fluorine is made to flow through a plurality of towers containing calcium carbonate, and after the outflow water that has flowed through each tower containing calcium carbonate is aerated, part of the water is made to flow through the immediately preceding tower containing calcium carbonate. By thus aerating the outflow water of each tower containing calcium carbonate, H
2
CO
3
in the outflow water is discharged as a CO
2
gas. By subsequently making the water flow through the same tower containing calcium carbonate, the amount of H
2
CO
3
to flow into the tower containing calcium carbonate can be reduced as far as possible. Consequently, the amount of addition of the alkali agent of ammonia, ammonium fluoride or the like for the prevention of the collapse of the calcium carbonate filler material due to H
2
CO
3
can be reduced.
A method for treating an organic waste water containing fluorine is disclosed in the prior art reference of Japanese Patent Laid-Open Publication No. HEI 5-4090. According to this treatment method, the water-soluble calcium compound of slaked lime, calcium chloride or the like is added to the organic waste water containing fluorine so as to coagulate and precipitate the calcium fluoride. After adjusting pH of the supernatant liquid to 6.5 to 7.0, the water is brought in contact with fixed microorganic pellets to undergo an aeration treatment for the removal of BOD (Biological Oxygen Demand) components. Subsequently, a coagulant is added to precipitate together the microorganisms leaked from the fixed mi
Sakata Kazuyuki
Tanaka Noriyuki
Yamasaki Kazuyuki
Barry Chester T.
Sharp Kabushiki Kaisha
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