Water softener abstract
Cation exchange water softeners may be regenerated and, then, the
regenerant wastes (brine) recovered, treated, and recycled. The
result is a closed system which is ecologically beneficial. The
regenerant brine is captured in as concentrated a form as possible
and then treated with a precipitant such as sodium or potassium
carbonate or mixtures of sodium or potassium carbonate with sodium
or potassium hydroxide. Calcium and magnesium compounds are precipitated
and the supernatant contains sodium or potassium chloride. These
are separated within the brine treatment tank, the precipitate being
disposed of as a sludge or sludge cake and the supernatant being
recycled to the water softener at the time of further regeneration.
Water softener claims
What is claimed is:
1. A closed-mode method for regenerating a water softener having
a cation exchange resin bed located therein and for recovering and
treating the regenerant brine from the water softener regeneration,
(a) backwashing said cation exchange resin bed,
(b) evacuating the liquid from said water softener,
(c) introducing a saturated brine of regenerating material selected
from the group consisting of potassium chloride and sodium chloride
into said water softener to a level of approximately 150% or greater
of said cation exchange resin bed depth to produce regenerant wastes
in the form of a calcium chloride and magnesium chloride containing
(d) evacuating said regenerant brine from said resin bed and recovering
a concentrated portion of said regenerant brine for further treatment,
(e) treating said regenerant brine with a treatment chemical selected
from the group consisting of sodium carbonate, potassium carbonate,
a mixture of potassium carbonate and potassium hydroxide, and a
mixture of sodium carbonate and sodium hydroxide to produce a calcium
and magnesium containing precipitate and a potassium chloride or
sodium chloride containing supernatant,
(f) separating said precipitate from said supernatant,
(g) resaturating said supernatant with additional potassium chloride
or sodium chloride regenerating material, and
(h) recycling said resaturated supernatant to said water softener
at the time of further regeneration, whereby a closed system for
water softening and water softener regenerating is achieved.
2. The method of claim 1 wherein said calcium and magnesium containing
precipitate is separated from said potassium chloride or sodium
chloride supernatant by decanting said supernatant from said precipitate
as it settles within a separation unit.
3. The method of claim 2 wherein filtration is used to further
dewater said precipitate.
4. The method of claim 1 wherein said regenerating material is
sodium chloride and said treatment chemical is sodium carbonate
which is added to said recovered regenerant brine, then, thoroughly
blended with said regenerant brine to rapidly and effectively produce
said calcium carbonate and magnesium carbonate precipitate.
Water softener description
BACKGROUND OF THE INVENTION
The present invention relates to a method for recovering and treating
the brine from water softener regeneration, and more particularly,
to a closed system for regenerating cation exchange water softeners
with potassium chloride or sodium chloride and, then, softening
the regenerant wastes (brine) produced during the regeneration.
Traditionally, cation exchange water softeners are regenerated
with a sodium chloride (NaCl) regenerating material. An excess of
NaCl is used. The sodium ions replace the magnesium and calcium
ions trapped on the ion exchange resin. Calcium chloride and magnesium
chloride are produced. Those chlorides, along with the excess NaCl,
are dumped into the sewers and eventually find their way into the
nation's rivers, streams and lakes.
This creates an ecologically undesirable result. Since all of these
materials in the regenerant wastes are soluble, their discharge
into a water course adds significantly to the total dissolved solids
which must be handled by a downstream user of the water course when
he attempts to treat the water to make it suitable for domestic
or industrial consumption. For this reason, pollution control laws
already enacted or about to be enacted may in the future prohibit
discharge of high concentration soluble inorganic salts into waters.
Accordingly, it becomes necessary to attempt to prevent such a discharge
or regenerant brine from cation exchange water softeners.
For this reason, Popper in U.S. Pat. No. 3528912 discloses a
process for treating regenerate brine with sodium carbonate to precipitate
calcium and magnesium carbonate. Regenerate liquor is flowed through
an ion-exchange column in an upflow mode, captured, and treated
with the sodium carbonate prior to being filtered. The filtrate
is replenished with sodium ions and recycled back to the ion-exchange
column to effect further regeneration. At Col. 3 lines 52-67 it
is explained that problems may occur with the precipitate if it
becomes gelatinous. Popper handles these problems by use of a special
Odland U.S. Pat. No. 3977968 however, indicates that a more
desirable solution is to dilute the regenerate brine so that the
alkaline earth metal content is less than 16000 ppm, calculated
as calcium carbonate. Odland states that only in this way it is
truly possible to avoid formation of a gelatinous precipitate and
make the process workable.
Still, by diluting the regenerate brine in this manner, difficulties
are encountered in producing a workable closed system. That is,
in a closed system, it is imparative from a processing and equipment
standpoint that the treatment chemicals be as concentrated as possible.
This means that the volume of sludge generated must be equal to
or greater than the displacement volume of the chemicals added for
brine treatment. Should the volume of the treatment chemicals be
greater than the volume lost from the sludge, cyclic operation will
give an even increasing dilution or volume of regenerate, which
ultimately causes failure of the system. In turn, dilution of the
regenerant brine merely aggrevates the problem.
Accordingly, the need exists for an effective and efficient means
for recovering and treating the brine from the regeneration cycle
of cation exchange water softeners. More importantly, a need exists
for a workable closed system for regenerating cation exchange water
softeners, and then, recovering and treating the brine in an ecologically
SUMMARY OF THE INVENTION
The present invention satisfies those needs by providing a method
for regenerating a cation exchange water softener followed by efficient
recovery and effective treatment of the brine from the water softener
regeneration as a closed system. The regenerating material used
is potassium chloride or sodium chloride. The brine produced during
the regeneration, therefore, will contain calcium chloride and magnesium
chloride as well as any unused potassium chloride or sodium chloride.
The major portion of the brine is recovered in as concentrated
a form as possible. This is done by draining the water softener
prior to regeneration and adding a finite volume of regenerating
material to the evacuated bed. The volume used should be sufficient
to reach a level of approximately 50% of bed depth over the resin.
The regenerant brine is then withdrawn from the water softener with
no additional dilution. This eliminates the need for water displacement
of the brine as is the typical practice when brine is forced from
the cation exchange column by flowing water therethrough. This brine
handling scheme is critical to the cyclic operation of the system
since any dilution with water requires additional and costly treatment
steps to keep the system operating in a closed mode.
In the subsequent treatment step, the brine is admixed in a brine
treatment tank with a precipitate in the form of sodium carbonate,
potassium carbonate, a mixture of potassium carbonate and potassium
hydroxide, or a mixture of sodium carbonate and sodium hydroxide.
Treatment of brine solutions with such chemicals or mixture of chemicals
is known. See, for example, U.S. Pat. Nos. 2628165; 3350294;
3528912; and 3977968. As disclosed in these patents, the possible
reactions involved are: ##EQU1## wherein M is either potassium (k)
or sodium (Na).
The precipitate is then separated from the supernatant. This may
simply be done by using a reaction chamber within the brine treatment
tank or a separate sludge storage tank, from which clean supernatant
is decanted after the precipitate has settled. The precipitate may
be disposed of as a sludge or sludge cake. As a modification, a
filter, such as a sand filter or a vacuum filter may be used. A
polyelectrolyte may be added prior to separation to aid in consolidation
of the precipitate.
The filtrate is supplemented with additional potassium chloride
or sodium chloride and recycled back into the cation exchange column
at the time of further regeneration. A bed of potassium chloride
or sodium chloride crystals may be used in the regenerating material
storage area (either within or without the brine treatment tank)
as a source of the additional regenerating material. The supernatant
is brought into contact with the resaturating chemical prior to
introduction into the cation exchange column during the next regeneration
In this manner, a closed system is provided which is ecologically
advantageous when compared to present day water softener regenerating
systems. As is apparent, by precipitating the magnesium and calcium
ions in the brine and reuse of the chloride ions in the form of
potassium or sodium chloride, there is eliminated substantial dumping
of chloride wastes into the sewers. The net discharge to the environment
is essentially nothing more than the salts that were originally
in the water prior to treatment. Likewise, the calcium carbonate
and magnesium carbonate or hydroxide containing sludge may be disposed
of in an ecological manner as a land-fillable substance or otherwise
as a soil conditioning agent.
Accordingly, it is an object of the present invention to provide
a method for regenerating cation exchange water softeners and treating
the brine recovered therefrom, all as an essentially closed system.
Other objects and advantages of the invention will be apparent
from the following description, the accompanying drawing and the
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a system for utilizing the method
of the present invention on a large scale.
FIG. 2 is a schematic diagram of the apparatus of a modified embodiment,
depicting the cation exchange column and the brine treatment tank
involved in a smaller scale system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 there is shown a schematic lay-out for an
industrial-scale or water treatment plant operation. In the one
shown, the treated waters are high in iron content and it is therefore
necessary in the closed system to provide for removal of the iron
in addition to the brine treatment of the present invention.
Thus, iron filters 12(a)-(f) are shown for that purpose. The treated
water exiting from iron filters 12(a)-(f) is directed, then, to
the ion exchange columns which are central to the system of the
instant invention. As shown, reclaimed water from iron filter backwash
settling tank 14 may also be directed to the ion exchange columns.
Ion exchange columns 16(a)-(d) are shown, although obviously fewer
or more could be used depending on the size of the installation
needed to soften the amount of water to be treated. Each may be
any of the numerous cation exchange units available for water softening.
A typical one will contain a bed of ion exchange resin positioned
within a cylindrical column. An inlet hard water line is provided,
as is an outlet soft water line.
As is customary, after a given amount of water has been softened,
the resin bed must be regenerated. Sodium chloride (salt) is the
usual regenerating material and is preferred here. But, of course,
potassium chloride may be also used in the alternative. Ion exchange
columns 16(a)-(d) are first backwashed with the wastewater going
to iron filter backwash settling tank 14. The ion exchange column
is then evacuated of any remaining liquid. Regenerating material
is drawn from salt storage tank 18. The regenerant amount utilized
is sufficient to fill the cation exchange column to a level so that
it covers the resin bed completely and rises approximately an additional
50% of the resin bed depth over the resin, i.e., the regenerant
is introduced to a level of approximately 150% or greater of the
bed depth. It may be introduced into the ion-exchange column either
by up flow or down flow.
The amount of regenerating material used is an important aspect
of the present invention since it is an object of this invention
to keep the brine to be treated in a concentrated form. It has been
discovered that by using a volume of regenerating material which
is sufficient only to cover the resin bed by an additional 50% an
acceptable capacity for water treatment is achieved and yet the
volume of brine to be later treated is a manageable amount.
Following regeneration, the brine is evacuated from the ion exchange
column without significant dilution. This may be done by pumping
the concentrated brine directly into brine treatment tanks 20(a)
and 20(b). After a preset amount of concentrated brine is collected
in a brine treatment tank, an appropriate amount of chemical precipitant
is added from chemical feed 22. When the sodium form of regenerant
is used, the preferred precipitant is sodium carbonate. It may also
be a mixture of sodium carbonate and sodium hydroxide, if desired.
When the potassium form is used, it may be potassium carbonate or
a mixture of potassium carbonate and potassium hydroxide.
Since the brine to be treated contains calcium chloride and magnesium
chloride, upon addition of sodium carbonate as a precipitant, calcium
carbonate and magnesium carbonate precipitates begin to form. A
stirrer may be used in brine treatment tanks 20(a) and (b) to give
uniform mixing and promote precipitate formation. After a certain
period of mixing, the stirrer is stopped and the tank contents allowed
The supernatant which forms may be decanted and returned to salt
storage tank 18. It will contain dissolved sodium chloride because
of the reaction mechanism set forth previously. It is then used
as a supply of regenerant material for future regenerations.
The partially settled remainder of the treated brine is then conveyed
to sludge storage tank 24. This may be done by using the low solids
content iron sludge from iron filter backwash settling tank 14 as
a wash and transfer water to convey the brine softening sludge to
sludge storage tank 24. Of course, other means may be used to do
so, and it is simply convenient to use the iron sludge for that
purpose in the system layed out in FIG. 1.
In sludge storage tank 24 additional settling takes place. A polyelectrolyte
may be added at appropriate times to aid in that settling and form
a more compact sludge cake. Likewise, filtration may be used to
dewater the sludge. Contrary to the experience of Popper in U.S.
Pat. No. 3528912 and Odland in U.S. Pat. No. 3977968 problems
have not been encountered with the sludge being too gelatinous to
handle in this manner. Rather, settling and decanting alone have
for the most part been sufficient to permit adequate separation.
Again, the supernatant is conveyed to salt storage tank 18 for
reuse as a regenerating material. The sludge is, then, disposed
of in an ecologically sound manner. Because the contents of the
sludge are generally not detrimental to the environment, the sludge
cake may be used as a land fill or as a soil conditioner.
In this way, an essentially closed system is provided for softening
water and regenerating the ion exchange columns without the discharge
of harmful pollutants into the nation's streams and waterways. This
is particularly important for large scale water softening operations
such as industrial or municipal treatment facilities. Of course,
the process and apparatus of the present invention can also be used
on a home or industrial scale water softening unit as well.
FIG. 2 is illustrative of a modified form of the system which is
applicable to home use.
In this embodiment, the means for subsequent treatment of the regenerant
wastes is principally brine treatment tank 26 connected to water
softener 30 having a hard water inlet 45 and soft water outlet 47.
Either of inlets/outlets 28 or 29 from water softener 30 are used
to withdraw the brine for transfer to brine treatment tank 26. The
brine withdrawn is that formed during a regenerating cycle.
Again, the procedure for recovering the regenerant waste is important
since the volume of the recovered brine should be kept as nearly
constant as possible in order to efficiently operate on a continuous
cycle basis. The recovered brine should also be as concentrated
as possible so that the major portion of the brine from the regenerating
cycle is recovered in the desired volume to be treated.
For this reason, the regenerating material used is as mentioned
sufficient to cover approximately 150% or greater of the bed depth.
After water softener 30 is evacuated, the regenerating material
is introduced using pump 33 either by upflow through inlet/outlet
29 or downwardly through inlet/outlet 28. Valves 41 and 43 are used
to control this. The column is then completely evacuated through
either of inlet/outlets 28 or 29 into brine treatment tank 26 again
using pump 33 (or gravity) and valves 41 and 43.
A source of regenerating material is the bed of sodium or potassium
chloride crystals 32 located in the bottom of brine treatment tank
26. Line 35 is connected to brine treatment tank 26 for transferring
an appropriately controlled (controls not shown) amount of regenerating
material in solution form from brine treatment tank 26. Once the
closed system of the present invention has been initiated, regenerating
material is for the most part produced by the brine treatment process
Upon recovery of the brine and transfer to the brine treatment
tank 26 the brine is introduced into a separation unit 34. The
separation unit shown is essentially a reaction chamber having an
approximately five-gallon capacity. Through inlet 36 the precipitant
is introduced. The treating chemicals are mixed thoroughly with
the brine by the turbulence caused on introduction of the reactants
or by use of a spiral raceway or other means of creating turbulence
for mixing (not shown).
Since an objective is to be able to treat as large a portion of
the regenerant wastes (brine) as possible, the treatment chemicals
should also be as concentrated as possible. Desirably, the volume
of sludge removed is greater than or equal to the volume of treatment
chemical added. A more dilute treatment chemical would not allow
this condition and would thus decrease the volume of the regenerant
wastes which may be recovered. The amounts of treatment chemicals
needed vary depending on the amount of magnesium chloride and calcium
chloride in the brine. This in turn depends on the initial hardness
of the water softened. However, once determined for a particular
water hardness, a fixed, predetermined amount of treatment chemicals
may be used for each brine softening cycle.
As shown in FIG. 2 and as distinct from the system of FIG. 1
the reaction chamber may itself serve as the separation unit 34.
Thus, in its simplest form, the separation unit 34 may comprise
a reaction chamber in which the precipitate is allowed to settle
after reaction. The clear supernatant formed is decanted from separation
unit 34 via line 38. In another modified embodiment, the reaction
chamber may be the upper portion of the unit and the bottom of the
unit may be a filter. It may comprise a sand filter with a sand
bed, gravel base, glass wool retainer, and gauze overlay. The sand
bed may be pea gravel. Of course, other filter arrangements may
also be used.
The filter would be used to separate the supernatant from the precipitate.
Since the precipitates form and settle rapidly, often times a clear
supernatant is formed which need not be passed through the sand
filter but may simply be decanted off.
As mentioned, the supernatant (supernatant-filtrate), which already
contains sodium chloride (in the preferred embodiment) as a result
of the brine treatment, is further supplemented by means of the
bed of sodium chloride crystals 32 to form a regenerating solution
which is used for further regeneration of the water softener 30.
Of course, when potassium chloride is used as the regenerating material,
potassium chloride crystals will be used rather than sodium chloride
In this manner, a totally closed-regenerating-brine softening system
is provided. The sodium chloride of the supernatant from the separation
unit 34 is reused. The magnesium and calcium ions in the brine from
the cation exchange unit are precipitated in the same reaction.
The precipitate collected may conveniently be disposed of as a sludge
or filter cake.
While the method and apparatus of the present invention constitutes
a preferred embodiment of the invention, it is to be understood
that the invention is not limited to this precise method and apparatus,
and that changes may be made therein without departing from the
scope of the invention which is defined in the appended claims.