Method of drinking water disinfection

Liquid purification or separation – Processes – Ion exchange or selective sorption

Reexamination Certificate

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C210S764000, C210S501000, C210S502100, C210S505000

Reexamination Certificate

active

06514413

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a water disinfection method wherein composite bactericidal adsorption materials are used for the treatment of drinking water from the tap and other fresh water sources.
BACKGROUND OF THE INVENTION
During the last two decades, various adsorbents have been used to disinfect water. The most common of them are activated carbon materials and ion exchange resins with bactericidal compounds, such as iodine, bromine and silver. The strong bactericidal properties of iodine and silver make them ideal disinfectants for small scale water supply systems.
It is known in the prior art of drinking water disinfection to use powdered activated carbon with particle sizes from 0.1 to 2000 &mgr;m, as a carrier for silver in metallic form or as a nitrate salt (West German Patent Application No. 3229340, published 1984, B01I20/20), or to use activated carbon impregnated with silver salt (USSR Patent No. 971 464, published 1982, B01I20/20).
For the simultaneous disinfecting and purification of drinking water it is known to use a composition of coarse and fine carbon fibers, including carbon fibers activated with metal salts; for instance, silver in an amount of 0.01 to 8% deposited thereon as a bactericidal additive (Switzerland, Patent No. 556,680, published 1974, B01D39/00).
The disinfection of drinking water by passing it through the above described activated materials which were treated with silver salts was not sufficiently efficient due to the fact that the improvement in the bactericidal properties was effected by silver ions released into water in the course of the treatment. To ensure longevity of the bactericidal properties, it is necessary to treat said materials with concentrated silver salt solutions, which may adversely affect human health if imbibed.
U.S. Pat. No. 4,555,347 teaches the use of filtration material in the form of activated carbon and iodine crystals for water disinfection. However, the method, which is based on releasing iodine into water, can not be used for continuous consumption.
In order to eliminate bacteria in drinking water, it is known to use anion-exchange resin treated with silver nitrate solution (U.S. Pat. No. 2,434,190), and to use a cation exchange resin treated with a silver salt solution (U.S. Pat. No. 2,692,855).
In the case of long term use of bactericide containing ion-exchange resins, water also accumulates large amounts of silver ions. It happens in the same manner as with activated materials. In addition, in the course of disinfection, the resin becomes contaminated and loses its ion-exchange properties.
U.S. Pat. No. 3,817,860 discloses a water disinfection method where water is brought into contact with layers of an iodine containing resin and treatment by silver salts. U.S. Pat. No. 5,366,636 and the Journal of Water Chemistry and Technology, USSR, 1989, vol. 11, No. 2 disclose methods wherein the water passes through layers of iodine and silver containing ion-exchange resins. In the abovementioned cases, iodine is released into the water in the course of the drinking water disinfection, and then iodine is removed due to binding into the insoluble AgI compound.
According to the U.S. Pat. No. 5,366,636, water was passed through a porous, granular, iodine containing anion-exchange resin. As water actively contacted the resin, the iodine was released into the water. Then the treated water was passed through the porous granules of a chelating Ag-Chelex resin, which contains iminodiacetate groups and bound silver ions. The silver ions react with the iodide ions forming insoluble silver iodide. This method has a disadvantage, because to be effective large amounts of iodine must be released into the water from the anion-exchange resin. Then it is necessary to trap this iodine in the subsequent layers of adsorbents. In the likely event that there are channeling effects in the subsequent layers of adsorbents, or, if the adsorbent becomes saturated by other contaminants, iodine will leak into the purified water.
The process of water disinfection by passing it successively through layers of iodine containing anion exchange resin, synthetic activated carbon and macroporous strong acid cation exchange resin treated with silver nitrate solution allows to efficiently disinfect water of microorganisms (
E. Coli
). However, it implies the use of high concentrations of bactericidal components. As a result, molecular I
2
and Ag+ ions remain in the water and have to be purged out in the course of subsequent treatment (Journal of Water Chemistry and Technology, USSR, 1989, vol. 11, No. 2).
There is also known in the prior art a method of water disinfection using filtering material composed of an ion-exchange resin mixture. The essence of the method is in passing water through the mixture of ion-exchange resins (99%) and bacteriostatic resin (1%). The bacteriostatic properties of the resin are related to the metallic silver grains present on the surface and inside the granules of the resin. The mixture of resins prevents biomass development in the ion-exchange filter and the infiltration of bacteria into the water (“Eau et Ind.”, 1981, No. 58, 88 -90). However, despite the mentioned merits of the method, the silver ions are still washed out of resin in the course of time, getting into the water and, being accumulated in it, adversely affect human health.
Although much attention has been given to the issues of drinking water disinfection, and while iodine and silver have been used in the prior art, it was not known how to avoid, with the course of time, leakage of the iodine and/or the silver into the filtered water. For instance, if water contains an increased concentration of dissolved salts (high hardness), silver is quickly washed out due to the ion exchange mechanism. Problems arise during disinfection of drinking water with iodine, because it is necessary to enrich the water with a large quantity of iodine (at least 1 mg/l). The iodine has to remain in contact with the water for a long time, followed by the subsequent removal of iodine from the outflowing water. At iodine concentrations in water exceeding 4 mg/l, water acquires a distinct iodine odor. Long term consumption of iodinated water affects the thyroid gland. Secondly, when water passes through bactericide layers of resins, with time there is an accumulation of bacteria and biomass in the layer that does not contain bactericides, and bacteria subsequently infects the drinking water.
SUMMARY OF THE INVENTION
An object of this invention is the development of a new drinking water disinfection method which ensures disinfection reliability and efficiency with the preservation over time of the degree of water purification in removing heavy metal ions, organic matter and the improvement of taste and odor.
The present invention solves the problems of the prior art, and comprises filtration of drinking water through a composite material containing uniformly distributed granules of iodine containing anion exchange resin, granulated activated carbon, amphoteric fibers, and silver containing adsorbent; which will generally be a granular cation exchange resin such as C249 from Sybron, USA with Ag
+
ions thereon. Silver containing adsorbent in granular form is preferred over the fibrous form, because it has been found that granules release silver more easily by ion-exchange mechanism.
An important aspect of our invention is to maintain the exterior surface area of the iodine containing anion-exchange resin granules at not more than 1% of the exterior surface area of the amphoteric fibers, and is preferably kept at less than 0.2% of the exterior surface thereof. In addition, in accordance with this invention, the total equivalent content of silver in the said composite material must exceed the equivalent content of iodine therein. While almost any excess of silver over iodine can be used (e.g., as little as 0.1%), desirably the excess equivalent content of silver will be more than about 10 percent. Preferably, the excess equivalent content of silver will be f

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