Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1996-04-17
1997-03-11
Nessler, Cynthia L.
Liquid purification or separation
Processes
Ion exchange or selective sorption
210668, 210669, 210754, 210760, 210764, C02F 128, C02F 176, C02F 178
Patent
active
056097662
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for treating water using ozone.
If ozone is used during treatment of table water and mineral water, as well as drinking water, the problem arises that bromides contained in the water are partly oxidized by the ozone to bromate; bromates are regarded to be noxious. Though there are at present no limits for a content of bromate in water, it is known that bromates in a higher concentration may be carcinogenic.
The formation of bromate ions by ozonizing bromide-containing water is known. It is further known that the bromate formation under a constant concentration of ozone in water largely depends on the pH value of the water. See e.g., U. von Gunten and J. Hoigne, J. Water SRT-Aqua 41 (5): 299-304, 1992, Factors Controlling the Formation of Bromate Ion during Ozonation of Bromide-containing Waters. In this publication there is further on given the hint that ammonia may lead to formation of monobromamine which is subsequently further oxidized to nitrate and bromide ions. It is suggested to get rid of the bromate problem by adding ammonia. Addition of ammonia, however, influences the quality of the water and there are legal limits to be respected.
OBJECTIVES OF THE INVENTION
It is an object of the invention to modify the known process of water treatment with ozone in such a way and to further develop it that the formation of bromates is minimized, whereby the quality of the water is touched as little as possible.
This object is solved by a water treatment process using ozone whereby, to prevent bromate formation, a quantity of bromide-containing water to be treated is first set to a pH value of less than 6.5 by introducing CO.sub.2, unless the water already contains the requisite CO.sub.2, and ozone and CO.sub.2 are simultaneously introduced for a period of several minutes, whereby the amount of CO.sub.2 introduced is chosen in such a way that the pH value is maintained and sufficient ozone is introduced into the quantity of water to produce oxidation, sterilization and degermination.
It came out unexpectedly that by lowering the pH value to or below 6.5, it is possible to avoid the oxidation of bromide to bromate by ozone; in any case to at least minimize the formation of bromate. In experiments made according to the teaching of the invention, it was found that under the given conditions the content of bromide prior to and after the oxidation using ozone is almost identical. This proves that under the conditions of the invention there is practically no formation of bromates from bromides.
According to the invention, no additional chemicals, as for example ammonia, are added to the water to cover the bromate problem, but gaseous additions known per se are used--namely ozone and carbon dioxide--whereby the introduction of these additions and their influence on the water is well known and studied to a great extent. By a positive procedure-oriented handling, it is possible to minimize the bromate problem to a great extent. It is a special advantage that the pH values are not set by rather strong acids, e.g., hydrochloric acid or sulfuric acid, which principally may be added according to the regulations about drinking water, but only by introducing carbon dioxide.
The process according to the invention may be used for treating mineral and table waters, as well as drinking water. In spite of the modified pH value, an oxidation of iron and manganese is carried out successfully in mineral and table waters. By this, the known dimmings and opacities resulting from iron and manganese compounds, e.g., iron-(III)-oxide-hydrate-induced unclarities, no longer appear. The same problems are important in principal for drinking water, too. The cited compounds are not dangerous to health; iron compounds are essential for a large amount of organisms.
According to the invention, a water treatment--namely a water conditioning with ozone--is possible with all those steps and procedures and with the very result as previously known, but in addition the simultaneous intr
REFERENCES:
patent: 3805481 (1974-04-01), Armstrong
patent: 4136027 (1979-01-01), Sakamoto et al.
patent: 4453953 (1984-06-01), Tanaka et al.
patent: 4552659 (1985-11-01), Tabata et al.
patent: 5264136 (1993-11-01), Howarth et al.
Gerz Ralf
Schneider Wilhelm
Cornaby K. S.
Nessler Cynthia L.
Schmidding-Werke Wilhelm Schmidding GmbH & Co.
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