U.S. patent application number 09/161188 was filed with the patent office on 2001-12-20 for method and apparatus for the removal of arsenic from water.
Invention is credited to FRIOT, PAUL H..
Application Number | 20010052495 09/161188 |
Document ID | / |
Family ID | 22580208 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010052495 |
Kind Code |
A1 |
FRIOT, PAUL H. |
December 20, 2001 |
METHOD AND APPARATUS FOR THE REMOVAL OF ARSENIC FROM WATER
Abstract
A method and apparatus for removing arsenic from water at point
of entry or point of use particularly for residential application.
The point of entry system comprises a first stage having a
manganese greensand oxidizer to convert arsenite (As+3) present in
the water to arsenate (As+5) and a second stage for passing the
water through an anion exchange resin. Each stage includes a
control head for automatic regeneration at a predetermined
frequency. The manganese greensand is regenerated with a solution
of potassium permanganate and the anion exchange resin is
regenerated with a salt solution. An alternate embodiment for point
of use application comprises a manganese greensand oxidizer
cartridge to convert arsenite (As+3) to arsenate (As+5) followed by
removal of the arsenate (As+5) with a reverse osmosis system.
Inventors: |
FRIOT, PAUL H.; (GROTON,
MA) |
Correspondence
Address: |
PEARSON & PEARSON
10 GEORGE STREET
LOWELL
MA
01852
|
Family ID: |
22580208 |
Appl. No.: |
09/161188 |
Filed: |
September 25, 1998 |
Current U.S.
Class: |
210/660 |
Current CPC
Class: |
C02F 1/441 20130101;
C02F 9/00 20130101; C02F 2101/203 20130101; C02F 1/722 20130101;
C02F 2001/422 20130101; C02F 1/72 20130101; C02F 2303/16 20130101;
B01J 41/04 20130101; C02F 2301/043 20130101; C02F 2209/44 20130101;
C02F 2101/206 20130101; C02F 1/64 20130101; C02F 1/42 20130101;
C02F 2101/103 20130101 |
Class at
Publication: |
210/660 |
International
Class: |
B01D 015/00 |
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A system for removing arsenic from water comprising: means
connected to said water for converting arsenite in said water to
arsenate; and means connected to said arsenite converting means for
removing arsenate in said water.
2. The system as recited in claim 1 wherein said arsenite
converting means comprises manganese greensand.
3. The system as recited in claim 2 wherein said system comprises a
solution of potassium permanganate for regenerating said manganese
greensand.
4. The system as recited in claim 3 wherein said arsenite
converting means comprises means for controlling the frequency of
regenerating said manganese greensand.
5. The system as recited in claim 1 wherein said means for removing
arsenate from said water comprises an anion exchange resin bed.
6. The system as recited in claim 5 wherein said system comprises a
salt solution for regenerating said anion exchange resin bed.
7. The system as recited in claim 6 wherein said arsenate removing
means comprises means for controlling the frequency of regenerating
said anion exchange resin bed.
8. The system as recited in claim 1 wherein said system comprises a
plurality of valve means for allowing said water to flow to a user
bypassing said arsenic removing system.
9. The system as recited in claim 1 wherein said means for removing
said arsenate comprises a reverse osmosis system.
10. A system for removing arsenic from water comprising: a first
control unit connected to said water; a container of manganese
greensand connected to said first control unit for converting
arsenite to arsenate as said water passes through said manganese
greensand; a container connected to said control unit for supplying
potassium permanganate to said manganese greensand for regenerating
said manganese greensand; a second control unit connected to said
first control unit for passing said water from said manganese
greensand container through an anion exchange resin bed for
removing arsenate from said water; and a salt tank connected to
said second control unit for regenerating said anion exchange resin
by passing a salt solution through said anion exchange resin.
11. The system as recited in claim 10 wherein each of said first
control unit and said second control unit determines the time of
regeneration of said manganese greensand and said anion exchange
resin respectively.
12. The system as recited in claim 10 wherein said system comprises
a plurality of valve means for allowing said water to flow to a
user bypassing said arsenic removing system.
13. A method of removing arsenic from water comprising the steps
of: providing means for converting arsenite in said water to
arsenate; and providing means connected to said arsenite converting
means for removing arsenate from said water.
14. The method as recited in claim 13 wherein said method comprises
the steps of providing first control means for regenerating said
arsenite converting means and second control means for regenerating
said arsenate removing means.
15. The method as recited in claim 12 wherein said step of
providing first control means and second control means comprises
the step of providing timer means in each of said first control
means and said second control means for determining when
regeneration occurs.
16. The method as recited in claim 14 wherein said step of
providing means for converting arsenite to arsenate comprises the
step of flowing said water through manganese greensand.
17. The method as recited in claim 14 wherein said step of removing
arsenate comprises the step of providing an anion exchange resin
bed for said water from said arsenite converting means to flow
through.
18. The method as recited in claim 16 wherein said step of
regenerating said arsenite converting means comprises the step of
passing potassium permanganate through said manganese
greensand.
19. The method as recited in claim 17 wherein said step of
regenerating said arsenate removing means comprises the step of
passing a salt solution through said anion exchange resin bed.
20. The method as recited in claim 13 wherein said step of removing
arsenate comprises the step of providing a reverse osmosis means
for removing arsenate from said water from said arsenite converting
means.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a method and apparatus for
removing arsenic from drinking water and in particular to removing
arsenite (As+3) and arsenate (As+5) from a water system at a point
of entry or point of use by first converting arsenite (As+3) to
arsenate (As+5) and then removing the arsenate.
[0003] 2. Description of Related Art
[0004] Arsenic is a naturally occurring substance found in a
variety of combined forms in the earth. Arsenic is a Group 5A
nonmetal with the more common valences of -3, 0, +3 and +5.
Arsenite (As+3) and arsenate (As+5) are the most common forms found
in drinking water and waste water streams. The United States
Environmental Protection Agency maximum contaminant level (MCL) for
arsenic is 50 parts per billion (ppb). The World Health
Organization's (WHO) standard MCL for arsenic is 10 ppb.
[0005] The United States Environmental Protection Agency (EPA) has
stated that arsenic in drinking water causes cancer in humans and
that the amount of arsenic in water at the current allowed
concentration may equal that caused by smoking cigarettes. There
are negotiations to reduce the current maximum concentration limit
of 50 ppb to as low as 10 ppb. Therefore, water providers have a
need for an economical safe method to remove arsenic from drinking
water. Further, residential homes obtaining water from wells have a
need for a low cost, safe, and efficient point of entry or point of
use arsenic removal system.
[0006] Technologies which have been used for removal of arsenic
include the following: (1) adsorption onto activated alumina within
a fixed bed contactor; (2) complexing arsenic with hydrous metallic
floc, previously aluminum and iron hydroxides or oxyhydroxides, in
conventional water treatment plants; (3) sieving the metal from
water by membrane technologies such as reverse osmosis; and (4)
electro-dynamic processes such as electrodialysis.
[0007] However, most technologies for arsenic removal are plagued
by the basic difficulty of removing arsenite (As+3). The more
successful techniques are ones that have been used on large
municipal supplies, but they are not practical for residential
application because of space requirements, the use of dangerous
chemicals, frequent monitoring and expense. The two most common
techniques for residential water correction have been reverse
osmosis (RO) and activated alumina. Activated alumina requires the
use of caustic chemicals and a very large volume for the high flow
rates available with this invention. RO is no longer certified as
an arsenic removal technique because of its inability to reduce
arsenite (As+3) significantly.
[0008] U.S. Pat. No. 5,368,703 issued Nov. 29, 1994 to Michael D.
Brewster describes a process and apparatus for removing arsenic
from wastewater. The process comprises the steps of providing a
bipolar electrochemical cell 10 comprising a pair of outer
electrode elements, passing the wastewater through the cell 10
while applying an electric potential across the electrodes so that
the anode and cathode are oppositely charged, positive and
negative, producing anodically ferrous ion in the form of an
insoluble iron compound, specie, or complex in the ionizing media,
and subjecting the media containing the iron compound specie or
complex to a mild oxidation sufficient to convert the ferrous ion
present therein to ferric ion and to oxidize the arsenic therein to
+5 valence specie to form ferric arsenate and an hydroxy ferric
oxide-arsenate complex which are insoluble and removable from the
media in a clarifier. However, this method is incumbered by the
need for an electrochemical cell, multiple chemical feed pumps, the
addition of chemicals requiring precision monitoring and
necessitating storage and repressurization of the water.
[0009] U.S. Pat. No. 5,575,919 issued Nov. 19, 1996 to Peter F.
Santina describes a method and system for removing toxic substances
from drinking water such as arsenic by the use of finely divided
metallic iron in the presence of powdered elemental sulfur or other
sulfur components such as manganese sulfide followed by an
oxidation step to effect arsenic recovery as a precipitate which is
separated from the water. However, this method requires a mixing
vessel, the creation and use of sulfur modified iron, and the
addition of acid as well as other chemicals requiring precision
monitoring.
[0010] U.S. Pat. No. 5,591,346 issued Jan. 7, 1997 describes a
water or wastewater purification process for reducing selenium and
arsenic concentrations in contaminated water by the use of a cation
exchange resin. Contacting the contaminated water stream with an
iron (III)--complexed cation exchange resin in an ion exchange
column forms an acid exchangeable iron III arsenate complex
immobilized on the cation exchange resin and in effluent stream
having reduce arsenic concentration. However, this method is
incumbered by the need for a chemical feed pump to inject an
oxidizing agent, the addition of an acid to regenerate the resin
and the addition of deionized water for rinsing of the resin.
[0011] In the above three patents each system requires highly
skilled personnel for operation and maintenance on an ongoing
basis. Therefore they are not suitable for residential use at point
of entry.
SUMMARY OF THE INVENTION
[0012] Accordingly it is therefore an object of this invention to
provide a method and apparatus for removing arsenic from water
including arsenite (As+3) and arsenate (As+5).
[0013] It is another object of the invention to remove arsenic from
water by pre-oxidizing the arsenic to convert arsenite (As+2) to
arsenate (As+5).
[0014] It is a further object of this invention to provide an
arsenic removal system that is suitable in cost, space required,
and efficiency for residential environment or commercial
application.
[0015] It is yet another object of this invention to reduce the
concentration of arsenic in drinking water to below 10 ppb and in
some applications to a nondetectable level.
[0016] These and other objects are further accomplished by a system
for removing arsenic from water comprising means connected to the
water for converting arsenite in the water to arsenate, and means
connected to the arsenite converting means for removing arsenate in
the water. The arsenite converting means comprises manganese
greensand. The system comprises a solution of potassium
permanganate for regenerating the manganese greensand. The arsenite
converting means comprises means for controlling the frequency of
regenerating the manganese greensand. The means for removing
arsenate from the water comprises an anion exchange resin bed. The
system comprises a salt solution for regenerating the anion
exchange resin bed. The arsenate removing means comprises means for
controlling the frequency of regenerating the anion exchange resin
bed. The system comprises a plurality of valve means for allowing
the water to flow to a user bypassing the arsenic removing system.
In an alternate embodiment the means for removing the arsenate
comprises a reverse osmosis system.
[0017] The objects are further accomplished by a system for
removing arsenic from water comprising a first control unit
connected to the water, a container of manganese greensand
connected to the first control unit for converting arsenite to
arsenate as the water passes through the manganese greensand, a
container connected to the control unit for supplying potassium
permanganate to the manganese greensand for regenerating the
manganese greensand, a second control unit connected to the first
control unit for passing the water from the manganese greensand
container through an anion exchange resin bed for removing arsenate
from the water, and a salt tank connected to the second control
unit for regenerating the anion exchange resin by passing a salt
solution through the anion exchange resin. Each of the first
control unit and the second control unit determines the time of
regeneration of the manganese greensand and the anion exchange
resin respectively. The system comprises a plurality of valve means
for allowing the water to flow to a user bypassing the arsenic
removing system.
[0018] The objects are further accomplished by a method of removing
arsenic from water comprising the steps of providing means for
converting arsenite in the water to arsenate, and providing means
connected to the arsenite converting means for removing arsenate
from the water. The method comprises the steps of providing first
control means for regenerating the arsenite converting means and
second control means for regenerating the arsenate removing means.
The step of providing first control means and second control means
comprises the step of providing timer means in each of the first
control means and the second control means for determining when
regeneration occurs. The step of providing means for converting
arsenite to arsenate comprises the step of flowing the water
through manganese greensand. The step of removing arsenate
comprises the step of providing an anion exchange resin bed for the
water from said arsenite converting means to flow through. The step
of regenerating the arsenite converting means comprises the step of
passing potassium permanganate through the manganese greensand. The
step of regenerating the arsenate removing means comprises the step
of passing a salt solution through the anion exchange resin bed. In
an alternate embodiment, the step of removing arsenate comprises
the step of providing a reverse osmosis means for removing arsenate
from the water from said arsenite converting means.
[0019] Additional objects, features and advantages of the invention
will become apparent to those skilled in the art upon consideration
of the following detailed description of the preferred embodiment
exemplifying the best mode of carrying out the invention as
presently perceived.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The appended claims particularly point out and distinctly
claim the subject matter of this invention. The various objects,
advantages and novel features of this invention will be more fully
apparent from a reading of the following detailed description in
conjunction with the accompanying drawings in which like reference
numerals refer to like parts, and in which:
[0021] FIG. 1 is a block diagram of the preferred embodiment of the
present invention for reducing the concentration of arsenic in
water at a point of entry;
[0022] FIG. 2 is a flow chart of the method of removing arsenic
from water; and
[0023] FIG. 3 is a block diagram of an alternate embodiment of the
present invention for reducing the concentration of arsenic in
water at a point of use.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0024] Referring to FIG. 1. a block diagram of the invention is
shown for removing arsenic (As) from water. This invention is
particularly optimized for residential application, but is equally
applicable for commercial use. FIG. 1 shows a system 10 for
removing arsenic from a well water source or from a public water
supply where the user flow rates are typically 5-10 GPM through the
system 10. Where the source of water is from a well, a pressure
tank 12 is required. No pressure tank is generally required when
the water is from a public water system.
[0025] The most common forms of arsenic found in drinking water or
waste water streams are arsenite (As+3) and arsenate (As+5). The
important feature of this system is that arsenite (As+3) is first
converted to arsenate (As+5) and then the arsenate (As+5) is
removed from the water. This method is very efficient, cost
effective and safe for residential application. In particular,
there are no chemicals requiring precision monitoring, and the
chemicals used are commonly used in residential equipment.
[0026] Still referring to FIG. 1, the conversion of arsenite (As+3)
to arsenate (As+5) and removal from the water is accomplished in
two stages. In the first stage water with the arsenic passes
through a tank 19 comprising manganese greensand 18. A timer and
control unit 16 is attached to the top of the tank 19 comprising
the manganese greensand 18 to control flows during the conversion
process and also during a process of regeneration of the manganese
greensand 18 using potassium permanganate 20. A tank 21 comprising
the Potassium Permanganate is coupled to the timer and control 16
allowing flow in either direction.
[0027] The timer and control unit 16 controls four steps in the
regeneration process for the manganese greensand 18. First, the
timer and control 16 initiates a backwash causing water to flow
into the bottom of the tank 19 comprising manganese greensand 18
and up through the manganese greensand 18 and out drain 17; second,
the timer and control 16 sucks the potassium permanganate 20 out of
its tank 21, flushes it through the manganese greensand 18, and
then a slow rinse is performed; third, a fast rinse of the
manganese greensand 18 occurs to purge it of the potassium
permanganate 20; and fourth, the timer and control 16 causes fresh
water to be put back into the potassium permanganate 20 container
or tank 21. During regeneration there is a no raw water bypass
which precludes the untreated raw water (with arsenic) from being
drawn by a user. This regeneration process occurs typically on a
weekly basis.
[0028] Still referring to FIG. 1 the second stage performs the
removal of arsenate (As+5) from the water. The water flows through
an anion exchange resin 30 in a tank 31 via a timer and control
unit 28 which controls flow during arsenate (As+5) removal from the
water and controls regeneration of the anion exchange resin 30.
After the water passes through the anion exchange resin 30 for the
arsenate (As+5) removal, it is directed by the timer and control
unit 28 out of the system 10 for general use.
[0029] The regeneration of the anion exchange resin 30 is
determined by the timer and control unit 28 which controls four
steps. First the timer and control 28 initiates a backwash causing
water to flow into the bottom of the anion exchange resin 30 and up
through the resin 30 and out drain 29; second, the timer and
control 28 sucks a salt solution out of its container or tank 33,
flushes it through the ion exchange resin 30, and then a slow rinse
is performed; third, a fast rinse of the resin 30 occurs to purge
it of the salt 32; and fourth, the timer and control 28 causes
fresh water to be put back into the salt tank 33. During
regeneration there is a no raw water bypass which precludes the
untreated raw water (with arsenic) from being drawn by a user. The
salt may be sodium chloride or other suitable salt product.
Regeneration typically occurs on a weekly basis.
[0030] The point of entry, arsenic removal system 10 can be
bypassed so that the user can always draw water. Closing In Valve
22, Out Valve 24, In Valve 34 and Out Valve 36 and opening Bypass
Valve 26 and Bypass Valve 28 accomplishes the removal of system 10.
Therefore, maintenance activities or a problem with the system 10
do not prevent a user from drawing untreated water.
[0031] Referring now to FIG. 2 a flow chart is shown of the two
stage method of removing arsenic from water using system 10. The
method comprises the step 52 of passing the water through a timer
and control unit 16, and step 54 provides for oxidizing the water
with manganese greensand 18 for converting the arsenite (As+3) to
arsenate (As+5). In the next step 58 water passes through another
timer and control unit 28, and in step 60 the water passes through
the anion exchange resin 30 where arsenate (As+5) is removed
resulting in water having an arsenic concentration below 10 ppb and
in some cases nondetectable. Step 56 provides for the regeneration
of the manganese greensand 18 with potassium permanganate 20 which
is controlled by the timer and control unit of step 52. Step 62
provides for the regeneration of the anion exchange resin 30 with a
salt solution which is controlled by timer and control 58.
[0032] Referring again to FIG. 1, the manganese greensand 18 may be
embodied by Model 1054 greensand medium (1.5 cubic feet) sold by
Inversand Company of Clayton, N.J. The timer and control 16 may be
embodied by a Model 2500 manufactured by Fleck Controls, Inc. of
Brookfield, Wis. with the following characteristic: (1) backwash
rate of 7 GPM, (2) Brine refill rate of 0.5 GPM and (3) a no raw
water bypass piston. The potassium permanganate may be embodied by
a 10".times.16" permanganate tank 21 with a grid and a float safety
manufactured by Clack Corporation of Windsor, Wis.
[0033] Further, the anion exchange resin 30 may be embodied by a
Model 1054 anion resin system manufactured by Sybron Chemicals,
Inc. of Birmingham, N.J. including 1.5 cu.ft. of anion resin Model
A-554. The timer and control unit 28 may be embodied by a Model
2500 control head manufactured by Fleck Controls, Inc. of
Brookfield, Wis. having the following features: (1) backwash rate
of 1.2 GPM; (2) brine refill rate of 0.5 GPM; (3) brine draw rate
of 0.26 GPM; and (4) a no raw water bypass piston. The salt tank 33
is 18".times.33" with a grid and a float safety.
[0034] Experimental test results in a residential environment from
the point of entry system 10 have indicated that with the arsenic
level in the raw water at 211 ppb, the arsenic level in the
intermediate water at the output of the first stage (between the
manganese greensand 18 and the anion exchange resin 30) is measured
at 204 ppb, and the arsenic level in the treated water at the
output of system 10 is measured to be less than 6 ppb (which is the
testing laboratory detection limit).
[0035] Referring now to FIG. 3. an alternate embodiment is shown of
a point of use system 70 for removing arsenic from water. This
embodiment is useful for point of use application having low flow
rates by a user such as 14-20 gallons per day. As stated previously
a pressure tank 72 is generally only required when the water source
is from a well.
[0036] In this process water passes through a manganese greensand
oxidizer 78 which converts arsenite (As+3) to arsenate (As+5). The
water then passes into a reverse osmosis (RO) system 80 which
removes the arsenate (As+5). The reverse osmosis system 80 may be
embodied by Model N4000 TFCM S0 manufactured by CUNO/Water Factory
System of Meriden, Conn. The Model N4000 comprises a space for a
prefilter so the manganese greensand oxidizer 78 may be inserted
within the Model N4000 RO package. RO systems have been known to
reduce arsenate (As+5) by 90% but typically arsenite (As+3) is
reduced by only 50 to 60% In system 70, the total arsenic is
reduced to below 10 ppb and in some cases the arsenic
nondetectable.
[0037] Experimental test results in a residential environment for
the point of use system 70 have indicated that with the arsenic
level in the raw water at 70 ppb, the arsenic level in the treated
water at the output of system 70 is less than 5 ppb (which is the
detection limit of an alternate testing laboratory). Without the
manganese greensand oxidizer 78 connected in the system 70, thereby
feeding the raw water with 70 ppb of arsenic directly into the
reverse osmosis system 80, the treated water output arsenic level
is measured at 40 ppb.
[0038] This invention has been disclosed in terms of certain
embodiments. It will be apparent that many modifications can be
made to the disclosed apparatus without departing from the
invention. Therefore, it is the intent of the appended claims to
cover all such variations and modifications as come within the true
spirit and scope of this invention.
* * * * *