Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1999-03-08
2001-03-27
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S726000, C210S752000
Reexamination Certificate
active
06207062
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the treatment of aqueous effluents. The invention relates more specifically to an improvement to processes, according to the prior art, for treating such aqueous effluents. The said improvement facilitates the removal of materials in suspension and/or colloidal materials present in the treated effluents. These effluents, which are more or less concentrated suspensions, can consist in particular of processing waters, for example from the paper industry, industrial or urban waste waters, or even river waters or alternatively sludges, derived in particular from such waste waters.
2. Description of the Related Art
Processes for treating such effluents are directed towards producing, depending on the context, more concentrated effluents, liquid sludges or thickened sludges. They can also be directed towards depositing charges on a substrate; more generally, towards ridding the industrial effluents concerned of at least some of their charges. The said processes generally comprise several steps and involve large amounts of treatment reagents: chemical conditioning reagents and antifoaming agents, if necessary. These chemical conditioning reagents of the inorganic salt or synthetic organic polymer type, which are known to those skilled in the art, are used as coagulant and/or flocculant. They facilitate the aggregation of the solid particles in suspension—small-sized particles, colloidal particles—and, consequently, the subsequent separation of the solid and liquid phases by treatments which exert essentially physical actions (decantation, centrifugation, filtration, etc.). In paper manufacture, in the processing waters, they improve the aggregation and binding of the charges (such as talc, kaolin, etc.) or of the pigments (organic or inorganic) to the cellulosic substrate.
The costs of chemical reagents of this type can represent more than 50% of the running expenses of an aqueous effluent treatment plant, such as an urban waste water purification plant.
The improvement, proposed according to the present invention, developed earlier in the present text, is advantageous in particular in that its use allows a substantial reduction in the amounts of treating reagents required and thus a saving of the same magnitude in the running expenses of the process.
Processes for treating aqueous effluents in which an inorganic acid is added to the said effluents in order to generate carbon dioxide therein have been described in patent applications Ser. Nos. JP-A-51,124,042 and JP-A-59,010,388. The said inorganic acid consumes, by chemical reaction, carbonates present in the effluent or added thereto, so as to generate the said carbon dioxide in situ. Document JP-A-59,010,388 describes the treatment of very basic effluents. In these effluents, the acid is added in an amount such that their pH is brought to a value of between 4 and 5.
The carbon dioxide, thus generated in situ by the action of a strong acid on an alkaline material, exerts, with reference to the physical phenomenon of flotation, a purely mechanical, beneficial action. This beneficial action is based on the action of the gas bubbles which rise to the surface: this is referred to as a flotation action. It cannot be based on an actual chemical action of the said gas, which, under the conditions specified, can only dissolve in the effluent in very small amounts.
It is moreover imagined that the beneficial action of the said gas is countered by the drawbacks present, on the one hand, in using a strong acid in the process, and, on the other hand, in introducing anions such as sulphate or chloride into the treated effluent, via the addition of the said acid.
SUMMARY OF THE INVENTION
The improvement according to the invention is not based on the action, in the treated effluents, of an inorganic acid, or on the mechanical action of a gas. It is based on the chemical action of carbon dioxide, in other words on a doping of the treated effluent with bicarbonates and carbonates. A person skilled in the art will readily understand this on reading the text herein below.
The Applicant thus proposes a novel process for treating more or less concentrated aqueous effluents, such as processing waters, industrial or urban waste waters, and sludges, in particular sludges derived from these waste waters. Conventionally, the said process comprises at least one step of physical separation of a liquid phase and of a solid phase dispersed in the said liquid phase (by processes such as decantation, flotation, filtration, etc.) (a step of this type is carried out on the effluent to be treated which contains such a solid phase dispersed in a liquid phase and in the situation in which the process includes several steps of this type, the said steps of this type, which are different from the first step, are carried out on some of the effluent which has undergone the previous steps) and, in order to optimize the implementation and the yield for this separation step, the addition (at least one addition) to the treated effluents of chemical conditioning reagents and optionally, if necessary, antifoaming agents. Characteristically, the said process also comprises the injection of carbon dioxide (CO
2
) into the treated effluents, in an amount which is sufficient to give them a pH of less than 7.8.
This injection of carbon dioxide constitutes the improvement within the meaning of the invention, since the Applicant has shown its beneficial effect on removing materials in suspension and/or colloidal materials present in the treated effluent, and, more generally, on the separation of liquid and solid phases of the said effluent.
REFERENCES:
patent: 3833463 (1974-09-01), Croom
patent: 4137158 (1979-01-01), Ishida et al.
patent: 4188291 (1980-02-01), Anderson
patent: 4350597 (1982-09-01), Selm et al.
patent: 41 36 616 A1 (1993-05-01), None
patent: 0 451 434 A1 (1991-10-01), None
Patent Abstract of Japanese JP 59 199097 A.
Patent Abstract of Japanese JP 58 098185.
Database WPI, Section Ch, Week 8329, XP002084318 “Treating acid waste water from incinerator waste gas processing . . . ”.
Database WPI, Section Ch, Week 8451, XP002084317, “Treating chromium-and calcium-containing dioxide and ferrous salt and opt. coagulant”.
Database WPI, Section Ch, Week 7850, XP002084319, “Increasing dehydrability of sludge sediment from effluent treatment . . . ”.
Burns Doane Swecker & Mathis L.L.P.
Hoey Betsey Morrison
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Simmons David A.
LandOfFree
Treatment of aqueous effluents by injection of carbon dioxide does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Treatment of aqueous effluents by injection of carbon dioxide, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Treatment of aqueous effluents by injection of carbon dioxide will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2474764