Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2002-03-05
2003-10-28
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S630000, C210S616000
Reexamination Certificate
active
06638427
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a waste water treatment method and waste water treatment equipment capable of treating the organic matter discharged from a semiconductor plant, a liquid crystal plant or the like, and in particular, fluorine waste water containing a surface active agent, nitrogen, phosphor and hydrogen peroxide of poor biodegradability. The present invention relates, in particular, to a waste water treatment method and waste water treatment equipment that generates little sludge (waste) and is able to treat the waste water by reusing chemicals.
In a semiconductor plant, liquid crystal plant or the like, surface active agents are mixed in various chemicals for use in the production apparatuses in line with the rapid progress in microstructure. It is general to use nitric acid, ammonia water, phosphoric acid, hydrogen peroxide and hydrofluoric acid in the manufacturing equipment of the semiconductor plant or the like. Among others, the amount of use of hydrofluoric acid tends to be generally great as compared with the other chemicals. For the above reasons, the fluorine waste water containing a surface active agent, nitrogen, phosphor, hydrogen peroxide and so on is discharged from the production rooms of the plant. It is to be noted that the fluorine waste water is an acid waste water that has fluorine as a main ingredient and contains a small amount of surface active agent, nitrogen, phosphor and hydrogen peroxide.
As described above, under the conditions of the rapid progress in microstructure of semiconductor devices, a surface active agent is used since aqueous cleaning by means of ultrapure water cannot sufficiently clean the minute portions due to the surface tension of water. For this reason, the surface active agent is mixed in the waste water.
As described above, in the semiconductor plant or the like, a method for cleaning the minute portions through the reduction of the surface tension by mixing a surface active agent into ultrapure water and a method for executing cleaning through the reduction of the surface tension by mixing a surface active agent into a variety of chemicals for cleaning use are gaining popularity. For example, a chemical such as buffered hydrofluoric acid containing a surface active agent is used. A variety of surface active agents to be mixed in the chemical are the important know-how of each chemical manufacturer, and newly-developed surface active agents are opportunely used. The newly-developed surface active agents include those of poor biodegradability in terms of the molecular formula, structural formula, effervescence, sterilizing performance and so on of the substance. Therefore, the conventional activated sludge method, catalytic oxidation method or the like as a representative of the biotic treatment become unable to cope with the decomposition treatment since the methods have a low microorganic concentration of about 2000 ppm to 5000 ppm.
Then, the latest report says that some surface active agents might become hormone disrupters, and prompt countermeasures are required.
The waste water also contains nitrogen and phosphor attributed to nitric acid, ammonia water and phosphoric acid, and it is required to treat the nitrogen and phosphor from the point of view of eutrophication and red tide. However, the general denitrification equipment and dephosphorization equipment disadvantageously require high initial cost and running cost.
The waste water also contains hydrogen peroxide, and in order to treat the hydrogen peroxide that serves as an oxidizing agent in the waste water, a treatment method using sodium bisulfite added as a reductant and a treatment method using activated carbon as a catalyst. However, those methods also require high initial cost and running cost.
In this age where environmental conservation is regarded as important, it is an important urgent problem that the enterprises should tackle to reuse the used chemicals and reduce waste generated from the plants for the achievement of cost reduction.
Conventionally, as a waste water treatment method for reusing the sludge including unreacted chemicals, there have been proposed the following methods (1), (2) and (3).
(1) First prior art: Japanese Patent Laid-Open Publication No. HEI 6-343974.
(2) Second prior art: Japanese Patent Laid-Open Publication No. HEI 8-197070.
(3) Third prior art: Japanese Patent Laid-Open Publication No. HEI 10-5769.
Each of the above three waste water treatment methods sends the sludge precipitated in the sedimentation tank back to the reaction tank or the coagulation tank, in which a stirrer is placed.
According to the first prior art, stirring is executed by stirring use air concurrently with stirring by the stirrer, however, the retention time is short. By comparing the stirring that continues for a short retention time (20 minutes, for example) by a stirrer to the stirring with a long reaction time (2 hours, for example) by air, it was discovered that the latter was more efficient in releasing calcium ions and aluminum ions from the hydroxide in the sludge particularly when utilizing again the sludge by sending back.
The fundament of the treatment of fluorine waste water is to form slightly-soluble calcium fluoride for the treatment. For the purpose of reducing the sludge that is the waste generated from the waste water treatment equipment, a method for using calcium carbonate mineral is adopted instead of the conventional slaked lime method for using slaked lime.
What is important in this case is that the fundament of the treatment of fluorine is to form slightly-soluble calcium fluoride and remove the same. If the slightly-soluble calcium fluoride is formed, then the calcium fluoride is not redissolved under either acid condition or alkali condition. That is, if the calcium fluoride that becomes the cores of flocs by reusing again and again the calcium agent (slaked lime or calcium carbonate mineral), then the waste generated from the waste water treatment equipment can be reduced. Furthermore, the chemicals can be reused to allow the waste water treatment to be efficiently achieved.
The sludge as the conventional waste also includes the aforementioned calcium fluoride, however, a large amount of unreacted slaked lime and unreacted coagulant has existed.
As a prior art that uses calcium carbonate, there is a fourth prior art reference (Japanese Patent Laid-Open Publication No. HEI 7-136667). According to this method, fluorine-containing water is made to serially flow through a plurality of towers filled with calcium carbonate, and after the outflow water of each tower filled with calcium carbonate is aerated, part of the water is made to flow again through the same tower filled with calcium carbonate. According to this fourth prior art example, by aerating the outflow water of each tower filled with calcium carbonate, C
0
2
gas from CaCO
3
contained in this outflow water is discharged. By subsequently making the water flow again through the same tower filled with calcium carbonate, the amount of CaCO
3
that flows into the tower filled with calcium carbonate is reduced as far as possible. Through the above treatment, 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 CaCO
3
can be reduced.
As a fifth prior art example, there is a “method for treating fluorine-containing organic waste water” disclosed in the prior art reference of Japanese Patent Laid-Open Publication No. HEI 5-4090. According to this treatment method, although the calcium carbonate mineral is not used, the water-soluble calcium compound of slaked lime, calcium chloride or the like is added to the fluorine-containing organic waste water 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 components. Subsequently, a coagulant is added
Matsumoto Shigeki
Tanaka Noriyuki
Yamasaki Kazuyuki
Barry Chester T.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
LandOfFree
Waste water treatment method being able to treat surface... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Waste water treatment method being able to treat surface..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Waste water treatment method being able to treat surface... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3125978