Water treatment system and process

Details Water treatment system and process Water treatment system and process

1998-03-31

2002-06-04

Fortuna, Ana (Department: 1723)

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

C210S900000, C210S639000, C210S257200, C210S663000

Reexamination Certificate

active

06398965

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water treatment system and process and, more particularly, to a water treatment system and process for producing purified water for high purity applications.
2. Description of the Related Art
High purity water is required in many industries such as the chemical industry, the foodstuffs industry, the electronics industry, the power industry, and the pharmaceutical industry. Typically these applications require treatment of a source water supply (such as from a municipal water supply) to reduce the level of contaminants. These treatment techniques can include distillation, filtration, ion exchange, reverse osmosis, photooxidation, ozonation, and combinations thereof.
In an effort to decrease biological contaminants in municipal water supplies, especially in warmer environments, the addition of chloramine to municipal water supplies has become commonplace. While effective as a biocidal agent, chloramine becomes a contaminant itself in certain industrial applications requiring high purity water. Furthermore, chloramine is difficult to remove from water without producing other unwanted contaminants such as ammonia. Municipal water supplies can also contain unacceptable levels of dissolved carbon dioxide, boric acid, silicic acid (hydrated silica) and/or organic materials. These weakly ionized and organic materials are also difficult to remove from water.
Nuclear and fossil-fuel power plants, in particular, 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.
Similarly, the pharmaceutical industry requires various degrees of purified water for use 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.
While drinking water is not covered by the USP, water that complies with the U.S. Environmental Protection Agency (EPA) drinking water regulations is the prescribed source water for the production of pharmaceutical grade waters. 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, according to the USP, must meet almost all of the same purity requirements as water for injection with the exception of bacteria and pyrogen levels. As noted, purified water is produced using drinking water as the source water, which is purified using pretreatment equipment followed by at least one of ion exchange, reverse osmosis, and 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, according to the USP, may be used in the production of certain drugs, also as a rinsing agent for certain equipment and the preparation of certain bulk pharmaceuticals. Water for injection can be introduced directly into a patient's bloodstream and, therefore, must meet all purified water standards and additionally meet endotoxin limits. In the processing of water for injection, a reverse osmosis or distillation unit must be used. Relatedly, sterile water for injection is packaged in volumes not larger than 1 liter and is made sterile as noted above.
Typically, sterile water for injection is used to dilute drugs which will be introduced into the bloodstream. Sterile bacteriostatic water for injection is similar to sterile water for injection that is packaged in volumes not larger than 30 milliliters and to which is added antimicrobial agents. Sterile water for irrigation is used during surgical procedures to flush tissue within the body. Lastly, 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 prior art water treatment system
10
for producing purified water and/or water for injection for use in pharmaceutical applications. As shown, feedwater, typically municipal drinking water, is fed through line
12
to a media filter unit
14
to remove bulk particulate material. The water is then passed through a water softener
16
, most typically an ion exchange unit. The ion exchange unit is typically a sodium-cycle cation exchange unit that is used to remove scale-forming cations such as calcium and magnesium. In addition, water softener
16
serves to remove double and triple charged cations and reduce the tendency for coagulation of colloids that could foul downstream reverse osmosis 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 includes an activated carbon bed to remove chlorine, which is typically present in the municipal drinking water that serves as the source water for the system. A dechlorination unit is necessary because the most commonly used reverse osmosis membranes, thin film composite polyamide membranes, typically have low tolerance to oxidizing agents such as chlorine. The water is then passed to a cartridge filtration unit
22
, which provides a final filtration to protect the reverse osmosis membranes from fouling or other damage caused by relatively large particles generated from upstream equipment. The water is then passed to a reverse osmosis unit
24
, which typically removes greater than 98 percent of dissolved substances from the feedwater. Although not shown, a double-pass configuration of reverse osmosis units can be used to achieve high quality purified water. The permeate from the reverse osmosis unit(s) is then 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
.
As noted above, municipal drinking water is either chlorinated or chloraminated to control pathogenic microorganisms. In recent years many municipalities have changed methods of water supply disinfection from chlorine to chloramines to reduce the formation of trihalomethanes (THM's), which the EPA currently limits to 100 parts per billion in potable water. THM's are formed by the reaction of chlorine with organic substances. Chloramines are formed by the addition of chlorine, which forms hypochlorous acid, and ammonia to the water. Chloramine form (mono, di, tri) is a function of pH and the chlorine/ammonia ratio, with monochloramine predominating at pH 7 or higher; dichloramine predominating at pH 4 to 5.5; and trichloramine predominating at pH 3 to 4.5 by the following reactions:
Cl
2
+H
2
O→HCl+HOCl (hypochorous acid)
NH
3
+HOCl⇄H
2
O+NH
2
Cl (monochloramine)
NH
2
Cl+HOCl⇄H
2
O+NHCl
2
(dichloramine)
NH
2
Cl+HOCl⇄H
2
O+NCl
3
(trichloramine)
A dechlorination unit, including an activated carbon bed, is effective for the reduction of free aqueous chlorine by the following reactions:
C+HOCl→CO+H
+
+Cl
−
and
C+OCl
−
→CO+Cl
−
and has also been used to remove chloramines, with consid

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