 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of water treatment, and more
particularly to the purification or sterilization of contaminated water
using halogens, e.g., iodine and bromine. More specifically, the invention
relates to methods and apparatus for the stepwise treatment of water for
human or animal consumption perferably using iodine and the removal of the
iodine to levels below that detectable by human taste or smell.
2. Description of the Prior Art
It has long been known that elemental iodine possesses bactericidal,
viricidal and cysticidal properties and that because of this biocidal
action, it is ideal for use as a water purifying agent. U.S. Pat. No.
3,408,295 discloses a method of purifying water for drinking purposes
utilizing elemental iodine. However it is also known that the use of
iodine in the purification of drinking water is not widely used because,
although sterile, the water has an objectionable odor, color and taste due
to the iodine present. As a practical matter, the use of iodine to provide
sterilized or purified drinking water is used only in emergency situations
or where there is no other alternative available. To meet the requirements
of potable water which also has acceptable taste, the iodine remaining
after the treatment must be removed.
U.S. Pat. No. 4,367,149 discloses a method of removing this elemental
iodine by the reaction of sodium or potassium thiosulfate. However,
although the iodine is removed, there is left in its place other inorganic
salts such as sodium iodide. Furthermore, unless the exact stoichiometric
amount of thiosulfate is used, either some iodine or the excess
thiosulfate will be present. Other chemical methods for removal of the
elemental iodine from the treated water have been proposed.
What is needed is a complexing agent, harmless to humans, which will act as
a scavenging agent removing all the iodine but leaving nothing in its
place. It is therefore an object of this invention to provide process and
apparatus using a complexing agent which will quickly and completely
remove all traces of iodine after its biocidal action has rendered the
water safe for human and animal consumption.
It is also an object of this invention to provide a simple and economical
method and apparatus for purifying and sterilizing water employing iodine
or bromine which results in potable water which contains none of the
characteristic taste or color of the elemental halogen employed as the
biocidal agent.
It is a further object of this invention to provide a method as described
above which can be practiced in either a batch or a continuous fashion.
It is another object of this invention to provide a method and apparatus in
which the material employed to remove the halogen biocidal agent can be
reactivated and reused repeatedly without loss in effectiveness.
SUMMARY OF THE INVENTION
It is disclosed in U.S. patent application Ser. No. 155,942 of Carl E.
Barnes, filed on Feb. 16, 1988, as well as in some foreign patents, e.g.
Canadian Patent No. 1,119,748, that polypyrrolidone also known as nylon 4,
very readily forms a complex with iodine. It has been found that this
tendency to form a complex with iodine is so strong that it acts
effectively as a scavenger for iodine. Even very small amounts of iodine
may be removed quickly and completely from an aqueous solution of iodine
by contact with nylon 4 whereby the nylon 4 forms a complex with the
iodine. The nylon 4 itself develops a pale yellow color while the solution
which contained the dissolved iodine is rendered completely colorless.
This result was surprising since it had previously been thought that an
excess of iodine in the solution was necessary in order to drive the
reaction toward the formation of the complex.
The nylon 4 is preferably in a form having a maximum surface area available
for complexing the iodine--e.g., tubing knit from a textured yarn is
preferable over that knit from flat yarn. It has been found that amorphous
or unoriented yarn is more effective than drawn yarn. Waste yarn formed
when "spinning on the floor" while waiting for conditions in an extruder
to stabilize is particularly useful. Nylon 4 "pulp" or fibrids are also
useful.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of one embodiment of the invention for the
apparatus for purification of water.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the purification of water to obtain potable drinking water, iodine is
introduced into the impure water by any method, e.g., the method disclosed
in U.S. Pat. No. 3,408,295 or in U.S. Pat. No. 4,367,149, or by contacting
the water with a nylon 4-iodine complex disclosed in Canadian Patent No.
1,119,748. Sufficient time is allowed for the iodine to destroy the
microbial organisms present and then, in order to make the water potable,
it is contacted with nylon 4 in a form which provides maximum surface
area. Within a short time the water becomes colorless, all the iodine
present having transferred to the nylon 4 where it is retained in the form
of a complex.
In this system where the nylon 4 is in considerable excess and the iodine
concentration is very low, the equilibrium is virtually 100% in the form
of the complex. If, on the other hand, a more heavily "loaded" nylon
4-iodine complex (say 5% iodine) is added to water, some of the iodine
will leave the complex establishing an equilibrium where some of the
iodine is in the water. This provides a means of introducing controlled
amounts of iodine into the water.
This purification system may be used to make small portions of potable
drinking water in the field or adapted to a larger scale continuous
purification process. In the case of larger scale purification systems it
may be desirable to rejuvenate the nylon 4 sequestering agent. This is
conveniently accomplished by contacting the nylon 4 containing complexed
iodine with a solution of sodium bisulfite or sodium thiosulfate. The
iodine will be completely removed leaving white nylon 4. The nylon 4 is
then rinsed with water to remove the sodium bisulfite or sodium
thiosulfate reaction products. The nylon 4 is then ready for reuse.
Alternatively, the nylon 4 sequestering agent may be immersed in boiling
water for a few minutes after which all the iodine will have been removed
and the nylon 4 is ready for reuse.
As mentioned above it is desirable to use a form of nylon 4 which provides
maximum surface area. For this reason nylon 4 in staple form is better
than, for example, untexturized knit tubing. The staple also packs well in
a column.
The ideal nylon 4 material is either a mat or staple form made from
textured undrawn yarn. The unoriented fiber absorbs iodine more rapidly
and the texturizing provides more surface area. This material also packs
better in the column.
It may be advantageous to wash the nylon 4 in whatever form it is used in
hot water containing a detergent followed by rinsing to remove any finish
or low molecular weight material which may be present.
Where a complex of nylon 4 and iodine is employed to introduce iodine into
the water to be purified, the complexed material should be washed before
being contacted with the water in order to remove any excess iodine.
The temperature of the water to be treated is not critical, but the
temperature is desirably in the range from 0.degree. to 40.degree. C., and
preferably in the range of 10.degree. to 25.degree. C.
DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic representation of one embodiment of an apparatus for
use in the practice of the process of this invention. Treatment chamber 10
is adapted to maintain complexed material 17 in a first treatment zone or
compartment and untreated nylon 4 material 15 in a second treatment zone,
and both in position within the flow path of the liquid to be treated.
Chamber 10 may be a section of pipe fabricated from metal, opaque or
transparent plastic, or from glass, which is provided with inlet 12 and
outlet 14 to permit passage of the liquid. In order to facilitate
installation of the complexed material, chamber 10 can be provided with a
removable fluid-tight cap 16 at its upstream end and coupling which 20
permits separation of the chamber into two parts above the region in which
the nylon 4 is retained. Perforated retainers 18 and 22 are securely fit
within the interior of chamber 10 and are adapted to maintain the
complexed material and nylon 4, respectively, in position and to permit
free flow of the liquid through the chamber. Liquid inlet conduit 24 and
outlet conduit 26 are adapted to mate in a fluid-tight seal with chamber
inlet 12 and outlet 14, respectively. In the embodiment of FIG. 1, pump 28
is adapted to mate with outlet conduit 26 to facilitate and control the
rate of flow of the liquid through the treatment chamber 10, and thereby
control the contact time of the liquid with the complexed material 17, and
the untreated nylon 4 material 15. As will be apparent to one familiar
with the art, pump 28 can be positioned upstream of chamber 10 on conduit
24, or the entire system can be gravity fed, with a valve or other
restriction means replacing pump 28 to control the rate of flow of liquid
through the chamber.
In the operation of the apparatus illustrated in the embodiment of FIG. 1,
the water or other liquid to be treated enters chamber 10 through inlet
conduit 24 and contacts a mass of complexed material 17. In a preferred
embodiment the complexed material is in the form of yarn or fibers which
comprise a non-woven structure through which the liquid will uniformly
pass without channelling. During the liquid's contact with the complex of
iodine and nylon 4, a predetermined amount of iodine passes into the
liquid and functions as a biocide to eliminate bacteria contamination or
other organisms which are present. The iodine-containing liquid then
passes through a similar mass of yarn or non-woven fiber of nylon 4,
during which contact, the free iodine complexes with the nylon 4 and is
removed from the liquid.
The treated liquid discharged from conduit 26 is free of bacterial
contamination and contains no iodine which is detectable by taste or odor.
PREPARATION OF NYLON 4 COMPLEXED WITH IODINE FOR EXAMPLES
For convenience, the complex of nylon 4 and iodine is referred to in these
examples as "complexed material." A complex of iodine with nylon 4 knit
tubing was prepared as follows. Nylon 4 tubing, 68 grams, was soaked in
several liters of water containing a few drops of liquid detergent for 2-3
minutes. Excess detergent solution was squeezed out of the tubing. An
iodine solution was prepared by dissolving 56 grams of potassium iodide in
approximately 100 ml. tap water followed by the addition of 28 grams of
iodine crystals. When all of the iodine had dissolved the solution was
diluted to 1400 ml. The wetted undrawn yarn was immersed in the iodine
solution, with stirring, for approximately 5 minutes and then removed from
the iodine solution, immersed in cold tap water, and rinsed twenty times
to remove excess iodine. The treated yarn was hung to dry overnight.
The dry complexed material was brown in color and contained approximately
10% iodine.
The amount of iodine complexed with the nylon 4 material can be varied by
adjusting the concentration of the iodine solution and the time during
which the nylon 4 is in contact with the solution. Complexed material
containing from 1% to 20% of iodine based on the weight of the nylon 4
material can be prepared for use in the invention, and complexed material
containing from 5% to 15% of iodine are particulary suitable.
METHOD OF STERILIZATION OF APPARATUS AND ASSAY FOR BACTERIA FOR EXAMPLES
In several of the examples which followed a glass column fitted with a
filter at its base was employed. The glass filter has a sufficient pore
size so that water flow through the apparatus is not unduly restricted.
The filter column used in the examples was sterilized by exposure to
ethanol overnight and between repacking of the column. Tubing used for
sample collection was also sterilized with ethanol. The column and tubing
were rinsed three times with 15 sterile water prior to packing the column
with the complexed material.
The waste water sample was collected from a municipal sewage treatment
facility located at Bethlehem, Pennsylvania and stored at 4.degree. C.
prior to use. The waste water sample consisted of treated, clarified,
unchlorinated municipal waste water, with a pH of 5-6.
Ten milliliter samples for coliform bacterial analysis were collected in
duplicate. Samples were stored at 4.degree. C. and were analyzed and
showed the presence of Gram negative lactose-fermenting bacilli (coliform)
and Gram positive staphylococci, streptococci and enterococci by
enumeration of colony forming units/ml on MacConkey agar and Columbia
Colinstin Naladixic Acid agar, respectively.
Colorimetric assays for iodine in aqueous solutions were employed having a
lower level of detection of 2 micrograms per milliliter ("2.mu.g/ml.")
EXAMPLE 1
A saturated solution of elemental iodine was prepared by adding a
sufficient quantity of elemental iodine crystals to one liter of water at
room temperature so that undissolved crystals remained after allowing the
mixture to stand for a few hours. The liquid was then decanted from the
crystals.
50 grams of suitably washed knit tubing made of 100% drawn nylon 4 yarn was
immersed in the saturated aqueous iodine solution and within 5 minutes the
water was colorless, all the iodine having complexed with the nylon 4. No
trace of the characteristic odor or taste of iodine remained in the
treated water, and there were no pathogens present.
EXAMPLE 2
A saturated solution of iodine in water was prepared as described in
Example 1 and the solution decanted from the crystals. The solution was
divided into 2 parts of 500 ml each. To one part was added 5 grams of knit
tubing made from drawn yarn and to the other part was added 5 grams of a
bundle of undrawn yarn.
The iodine was removed from solution more rapidly (150 seconds) when the
undrawn yarn was used. The drawn yarn in the form of knit tubing required
twice as long (300 seconds) to remove the iodine.
EXAMPLE 3
The procedure of Example 1 was followed, except that bromine water was
substituted for the aqueous iodine solution. The nylon 4 tubing completely
decolorized the bromine water within 5 minutes.
EXAMPLE 4
This example demonstrates the release of iodine from complexed material.
The process employed the steps of the filtration of sterile water through
the complexed material, supported by the glass column described above,
followed by quantitative analysis of iodine in the liquid effluent from
the column. A pump was connected to the column in order to draw the water
through it and vary the flow rate through the complexed material and nylon
4.
Iodine was readily released from the complexed material upon the addition
of water at room temperature. At a flow rate of 450 ml/min a concentration
of iodine of 260 .mu.g/ml was found to be present.
COMPARATIVE EXAMPLE 5
Sterile water and then waste water were filtered through untreated nylon 4
packed in the glass column described above followed by quantitative
analysis for viable bacteria in the filtered water.
Analysis of waste water samples collected at flow rates of 120 ml/min and
500 ml/min all showed Gram negative bacteria in a concentration of about 2
or 3.times.10.sup.3 CFU/ml, and Gram negative bacteria in a concentration
of about 1.times.10.sup.2 CFU/ml. No bacteria were found in the sterile
water samples.
EXAMPLE 6
Waste water was sequentially filtered through complexed material and nylon
4 packed in the glass column described above, followed by quantitative
analysis for viable bacteria and iodine in the liquid effluent from the
column.
A total of 16 liters of waste water was collected and analyzed. As the
waste water passed through the column it was observed that iodine rapidly
moved down the nylon 4 sample in the column. After 16 liters passed
through the column, the iodine colored the top portion of the nylon 4
sample brown while the bottom portion was only a faint yellow. Samples
were collected after 1 liter, 4 liters, 6 liters, 8 liters, and 16 liters.
Nylon 4 and the complexed material were used in a ratio 2:1, specifically
100 gm:50 gm. This ratio can be adjusted to prevent the excess leaching of
iodine from the complexed material into the treated water and its passage
through the nylon 4.
Iodine was effectively removed by nylon 4 from the effluent which had first
passed through the complexed material as shown by the presence of only 2
.mu.g/ml of iodine in the effluent in all samples. In addition, all
samples showed the complete absence of the gram positive and gram negative
bacteria tested for.
EXAMPLE 7
A sample of unoriented nylon 4 yarn having a high surface area especially
adapted for removing traces of iodine from water was made as follows:
Filaments of nylon 4 were taken as they emerged from an extruder and
collected on a tube in a take-up machine without the application of any
finish, or alternatively, simply with the application of water. This
undrawn yarn was then texturized, or crimped, and cut into short lengths
to form a staple material which, unlike conventional staple, was
unoriented. This material packs well in a glass column or filter cartridge
with a minimum of voids. Being amorphous it complexes with iodine more
rapidly and completely than other forms of fibers.
EXAMPLE 8
With reference to FIG. 1, a treatment chamber 10 is fabricated from two
sections of threaded steel pipe three inches in diameter which are joined
by threaded coupling 20. Perforated retainers 18 and 22 are fabricated
from steel screening having a mesh opening of one-eighth inch and securely
fitted within the sections of the chambers, as illustrated. Approximately
50 grams each of complexed material 17 and untreated nylon 4 material 15
in the form of undrawn yarn prepared in accordance with Example 7 are
compressed lightly to form pads which are placed on the upstream sides of
the retainers 18 and 22, respectively. The sections are joined by coupling
20, and threaded closures 16 having central apertures are placed on the
inlet and outlet ends of chamber 10. Inlet conduit 24 and outlet conduit
26 are secured to the closure at either end of the chamber.
A source of waste water from a municipal sewage treatment plant is tested
for the presence of bacterial contamination and found to contain coliform,
staphlococci, streptococci and enterococci bacterial contamination. Waste
water to be treated is admitted from a source, (not shown), into the
chamber via inlet conduit 24, and pump 28 is activated; the flow rate is
adjusted until a steady flow rate is observed. The treated effluent from
outlet conduit is sampled and tested for the presence of bacterial
contamination and iodine. Plate assays performed as described above are
negative, indicating the absence of bacterial contamination of the types
originally determined to be present in the liquid stream before treatment.
Tests for free iodine are also negative indicating that no iodine was
present at the sensitivity levels of the test, e.g., less than 2 .mu.g/ml.
* * * * *
|
|
 |
|
 |
Description |
|
