Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1998-04-24
2001-12-11
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Ion exchange or selective sorption
74, C204S158200
Reexamination Certificate
active
06328896
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and process for removing strong oxidizing agents from liquids and, more particularly, to an apparatus and process for substantially reducing chlorine concentration in water.
2. Description of the Related Art
High purity water is required in many manufacturing and analytical applications in, for example, the chemical industry, the foodstuffs industry, the electronics industry, medical industry, and the pharmaceutical industry. These applications typically require treatment of a source water supply (such as a municipal drinking water supply) to reduce the levels of contaminants. Treatment processes and systems typically include combinations of: distillation, filtration, ion exchange (including electrodeionization), reverse osmosis (RO), photo oxidation, ozonation, and ultrafiltration.
In an effort to decrease biological contaminants in municipal water supplies, especially in warmer environments, the addition of chlorine has become commonplace. As used herein, the term “chlorine” can include various chlorine containing compounds, such as chloramines, chlorine dioxide, chlorite, chlorate, perchlorate, and the like. While effective as a biocide, chlorine becomes a contaminant itself in certain applications which are environmentally sensitive or require high purity water. Furthermore, it is widely known in the art that strong oxidizing agents, such as chlorine, have a deleterious effect on certain thin film membranes, such as those used in RO units, as well as on ion exchange resins. In this regard, municipal water supplies typically contain chlorine concentrations (e.g., approximately 1 ppm) that are unacceptable for these sensitive applications. Other strong oxidizing agents often found in municipal water supplies include percarbonate, perborate, peracetate, bromine, iodine, peroxide, and ozone. Any of these agents can be a contaminant in a given application.
In the medical industry, for example, purified water is used in various applications, such as for dialysis. Water for dialysis is typically produced by anion exchange using, for example, an electrodeionization unit to remove ionized contaminants from the water. As noted, strong oxidizing agents, such as chlorine, are known to have a deleterious effect on anion exchange resins. Chlorine, in particular, can react with anion exchange resins to form nitrosamines, a group of carcinogenic compounds which are known to cause cancer in a number of organs, including the liver and kidneys.
Nuclear and fossil-fuel power plants also have stringent water quality requirements to reduce corrosion and scaling and the associated expensive downtimes. In pressurized water reactor nuclear plants, for example, high-purity water is important in reducing corrosion in steam generators. In boiling water reactor nuclear plants, high-purity water is important in maintaining water quality in the nuclear reactor. Traditionally, makeup water treatment systems for power plants have relied almost exclusively on various combinations of filtration, ion-exchange, and reverse osmosis, with the latter two being especially sensitive to strong oxidizing agents.
Similarly, In the pharmaceutical industry, various degrees of purified water are used in drug manufacture, injection of drugs, irrigation, and inhalation. The United States Pharmacopoeia (USP) lists standards for the various types of water used in the pharmaceutical industry, including purified water, sterile purified water, water for injection, sterile water for injection, sterile bacteriostatic water for injection, sterile water for irrigation, and sterile water for inhalation. The prescribed source water for pharmaceutical grade waters is “drinking water” as defined by Environmental Protection Agency regulations.
Purified water can be used to process certain drugs, particularly as a cleaning agent for equipment and in the preparation of certain bulk pharmaceuticals. Purified water is produced from drinking water by pretreatment equipment followed by ion exchange, and/or RO, and/or distillation.
Sterile purified water is not used in any drug that will be introduced directly into the bloodstream. Purified water is made sterile by heating it to a minimum temperature of 121° C. for at least 15 minutes. Water for injection can be introduced directly into a patient's bloodstream and, therefore, must meet all purified water standards and endotoxin limits. In the processing of water for injection, a RO or distillation unit must be used.
Sterile water for injection can be used to dilute drugs which will be introduced into the bloodstream. Sterile water for injection is packaged in volumes not larger than 1 liter and is made sterile by the process noted above. Sterile bacteriostatic water for injection is similar to sterile water for injection including antimicrobial agents, and is packaged in volumes not larger than 30 milliliters. Sterile water for irrigation is used during surgical procedures to flush tissue within the body. Sterile water for inhalation is similar to sterile water for injection that is used in inhalers and in the preparation of inhalation solutions.
FIG. 1
illustrates a schematic process flow diagram of a typical prior art water treatment system
10
for producing purified water for various applications. As shown, feedwater, typically municipal drinking water, is fed through line
12
to a multimedia filter unit
14
to remove bulk particulate material. The water is then passed through a water softener
16
, most typically an ion exchange unit, to remove scale-forming cations such as calcium and magnesium. In addition, water softener
16
serves to remove divalent and trivalent cations and reduce the tendency for coagulation of colloids that could foul downstream RO membranes. The water is then passed through a heat exchanger
18
, which is typically used in system
10
if the source water is from a surface water source such as a lake or river.
The water is passed from heat exchanger
18
, if used, to a dechlorination unit
20
that can include an activated carbon bed to reduce the chlorine concentration, which, as noted above, is typically present in the municipal drinking water that serves as the source water for the system. After dechlorination, the water is passed to a cartridge filtration unit
22
, which provides a final filtration to protect the RO membranes from fouling or other damage caused by relatively large particles generated from upstream equipment. The water is then passed to an RO unit
24
, which removes nearly all of the particulate material from the feedwater. Typically, greater than 98 percent of dissolved substances are rejected by the RO membrane. Although not shown, a double-pass configuration of RO units can be used to achieve high quality purified water.
Optionally, the permeate from the RO unit(s) can be passed to a distillation unit
26
for the production of water for injection. A storage tank
28
may also be provided to store the distilled water prior to its use in production and/or packaging in unit
30
. In alternative applications, such as used in the power industry or the electronics industry for example, Other water treatment units may be substituted for distillation unit
26
. Suitable substitutions may include, for example, ion exchange units and the like.
As noted above, municipal drinking water is often chlorinated to control pathogenic microorganisms. Two treatment methods that are commonly used for chlorine removal are granulated activated carbon (GAC), and the direct injection of reducing agents such as sodium dioxide, sodium sulfite, sodium bisulfite, sodium metabisulfite, or other SO
2
− bearing chemicals. Other strong, scale-forming oxidizing agents can be removed by injection of various compounds. The type and concentration of the compounds necessarily depend on the type and concentration of oxidizing agent present and can include ascorbic acid, hydrazine, carbohydrazide, morpholine, and the like.
For RO pretreatment, dechlorination units
Atnoor Devendra
Ganzi Gary
Wood Jonathan
Zoccolante Gary
Fortuna Ana
United States Filter Corporation
Ward Richard W.
Wolf Greenfield & Sacks P.C.
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