Water treatment process

Details Water treatment process Water treatment process

2000-03-07

2001-10-02

Cintins, Ivars (Department: 1724)

Liquid purification or separation

Plural chambers with movement of granules therebetween

C210S269000, C210S284000

Reexamination Certificate

active

06296761

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to water treatment and more particularly to an improved process for softening water while reducing anion content.
DESCRIPTION OF RELATED ART
Hardness in water is a common problem. Hardness in water is due primarily to the presence of Ca
2+
and Mg
2+
, and also to the presence of Ba
2+
and Sr
2+
, all of these being hardness ions. Water is said to be “softened” when these cations are removed, such as by water softening equipment. For large-scale or large volume water softening, the traditional process is called cold lime or cold lime-soda softening. In this process the lime can be either hydrated lime (Ca(OH)
2
) or quicklime (CaO). In large systems the lime source is stored in a storage vessel. If quicklime is used, it must first be converted to hydrated lime (Ca(OH)
2
) by being slaked, that is, combined with water. In any event, Ca(OH)
2
is provided and is diluted in a lime slurry, where the Ca(OH)
2
dissociates into Ca
2+
and
2
OH
−
. This lime slurry is then fed to the reaction section of the lime softening equipment, where the OH− combines with Mg
2+
to form Mg(OH)
2
, which precipitates out. The original Ca
2+
hardness in the water, and the Ca
2+
introduced via dissolved lime, are removed by a different reaction. If there is sufficient natural bicarbonate (HCO
3
−
) in the water, some of the OH
−
will react therewith to yield carbonate (Co
3
2−
), which will combine with the Ca
2+
to form CaCO
3
, which precipitates out. If there is insufficient natural bicarbonate, soda ash (Na
2
CO
3
) is added (which converts to
2
Na
+
and CO
3
2−
) and again the CaCO
3
forms and precipitates out. (Soda ash usage unfortunately adds substantial Na
+
to the finished water). As an alternative to using Ca(OH)
2
as the source of OH
−
, sodium hydroxide (caustic soda) (NaOH) has been and is used. Sodium hydroxide also adds significant quantities of sodium ion to the final water and removes essentially no anions other than bicarbonate.
The traditional lime process generates considerable sludge, being CaCO
3
and Mg(OH)
2
, and does little if anything to reduce chloride content and has limited capability to reduce any of the other anion content (sulfate, phosphate, nitrate) of the initial water. When it is necessary to use soda ash (due to low influent bicarbonate content), the traditional process increases the sodium content of the final effluent.
As can be seen, the key to removing hardness is the introduction of OH
−
. The OH
−
converts Mg
2+
to Mg(OH)
2
, and converts HCO
3
−
to CO
3
2−
, which then reacts with Ca
2+
to form CaCO
3
. (If there is insufficient natural HCO
3
−
, Na
2
CO
3
is added). In the traditional hydrated lime treatment process, the OH
−
is supplied via Ca(OH)
2
.It is also traditional to use NaOH as the OH
−
source with the lime treatment equipment.
There is a need for an improved water softening process which eliminates or reduces the drawbacks of the traditional lime softening process.
SUMMARY OF THE INVENTION
A process for softening water comprising the steps of
(a) passing a first stream of water through an anion-exchange unit to raise the pH of said first stream and provide a second stream of water having a pH of at least 9.5;
(b) providing said second stream of water to water softening equipment comprising reactor and clarifier sections, said second stream of water being used as a source of hydroxyl ions in said water softening equipment;
(c) processing a fourth stream of water through said water softening equipment, said fourth stream comprising said second stream; and
(d) operating said water softening equipment on said fourth stream of water to remove via precipitation reactions hardness ions from said fourth stream and to provide thereby a fifth stream of water.
An anion-exchange system comprising a counter-current continuous resin regeneration unit is also provided.


REFERENCES:
patent: 2697724 (1954-12-01), Collier
patent: 2702275 (1955-02-01), Bauman
patent: 2754261 (1956-07-01), Akeroyd
patent: 3445382 (1969-05-01), Wace
patent: 3607739 (1971-09-01), Thorborg
patent: 3658699 (1972-04-01), Ryan et al.
patent: 3691109 (1972-09-01), Larsen
patent: 3985648 (1976-10-01), Casolo
patent: 4299922 (1981-11-01), Holl et al.
patent: 4894168 (1990-01-01), Holl et al.
patent: 5292439 (1994-03-01), Morita et al.
patent: 5306399 (1994-04-01), Bradbury et al.
patent: 5378366 (1995-01-01), Yen
patent: 5468395 (1995-11-01), Caroon et al.
patent: 5500127 (1996-03-01), Carey et al.
patent: 5569380 (1996-10-01), Sullivan
patent: 5571419 (1996-11-01), Obata et al.
Kirk-Othmer Concise Encyclopedia of Chemical Technology, John Wiley & Sons, Inc. (1985) pp. 665-666.

Affiliated with

Also associated with

Rating

Water treatment process does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Water treatment process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Water treatment process will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2550553