Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 -
T~IHALOMETHANE PRECURSOR REMOVAL
NS
Back~round of the Inventi n
The ubiquitous use of chlorine as a disinfectant in
public water supplies has introduced a subtle health
hazard of its own. Chlorine has been shown to react
with humic substances present in such waters to produce
trihalomethanes (THM) such as chloroform. The
Environmental Protection Agency has identified
trihalomethanes as carcinogens in animals, and has
published a maximum contaminant level of 0.10 mg/liter
(lOO ppb) for total THM in communit~ water s~stems
(National Interim Primary Drinking Water Regulations;
Control of Trihalomethanes in Drinking Water; Final
Rules. U.S. Environmental Protection Agency, Federel
Register, Vol. 44, No. 231, November 29, 1979)o
Attempts at removing trihalomethanes from
chlorinated drinking water have met with but limited
success. If THM i5 removad, ~ut residual chlorine and
humic substances remain, the THM will re-form. If the
active chlorine is removed, as with granular
~'.
6~7
activated charcoal, the water must be re-chlorinated to
meet standards, and THM again may re form.
An alternative approach is to remove the humic
substances that are THM precursors. These substances
are found in many natural waters, are probably leached
from organic materials found in soil, and are usually
found at high concentrations in surface waters, and at
lower concentrations in most ground waters. Materials
that previously have been used for removing them from
water include adsorbents such as granular activated
carbon, coagulants such as alum and ferric sulfate, and
conventional ion exchange resins, especially weakly
basic anion exchanga resins. Each o~ these processes
shares the problem that relatively large amounts of
lS treating agents must be added to the drinking water to
effectively reduce the THM precursor levels to below
permissible limits. In addition, each possesses
additional problems o~ its own, some of which are
described above.
Accordingly, an object o~ the present invention i9
to minimize the amount of treating agent that must be
added to water to signi~icantly reduce its T~IM
precursor content. Another obJect is to remove THM
precursors in a way that does not interfere with
conventional drinking water disinfectant processes.
Additional objects will beoome apparent upon
consideration of the follol~ing disclosure.
The Invention
.
~e have diqcovered a process for removing the
precursors of trihalomethane ~rom water, and especially
from drinking water containing such trihalomethane
precursors, which comprises treating the water with
submicroscopic ion exchange resin particles having a
diameter smaller than about 1.5,~ m. The
submicroscopic ion exchange particles may be anion
exchange particles alone, or ani~n exchange particles
combined with cation exchange particles in the ~orm of
a ~loc. These submicroscopic ion exchange particles
are surprisingly e~fective in removing THM precursors,
and are effective at surprisingly low concentrations.
The preferred treatment levels for removal of THM from
drinking water are ~rom about 1 to about 50 milligrams
per liter of water (mg/l), and more preferably about 10
mg/l or lessO
A convenient process by which water such as
drinking water may be treated according to the process
oP the present invention is to introduce the
sub~icroscopic anion exchange resin in the ~orm of an
lS emulsion, or to introduce a water~suspended floc of the
anion and cation exchange resins, into the water prior
to the settling and filtration treatment normally given
to waters during pu-ification for drinking purposes.
It i9 beneficial to combine coagulant treatment and
treatment with the submicroscopic anion exchange
resin. Coagulant treatment is a well-known water
treatment process; the coasulants used are similarly
well known and include soluble polyelectrolytes, which
may be cationic, anionic or nonionic polyelectrolytes,
including polyacrylic acid and soluble, polymeric
quaternary amines. The coagulants may also be metal
salts, including the sulfates and chlorides of
aluminum, ferrous and ferric ircn, magnesium carbonate
and aluminum silicates including clays. Other
coagulants will be aPParent to those skillea in the
art. The coagulant treatment may occur prior to,
simultaneous with, or subsequent to treatment with the
submicroscopic anion exchange resin; it should
preferably occur prior to any filtration step.
In the absence of a coagulant cr L locculant that
;~ ~
~ ~`
will flocculate any excess submicroscopic cation
exchange resin, either present in the water prior to
treatment or introduced as described above, the resin
may pa~s through ~ubsequent filters and produce
turbidity. Treatment with a soluble cationic
flocculant or submicroscopic cation exchange resin may
be necessary to prevent this turbidity. The
conventional settling and filtration step removes the
flocculated resin, and with it the THM precursors, ~rom
the water. Chlorination or other disinfectant
processes may be applied at any point during the water
treatment, but desirably the disinfectant should be
introduced subse~uent to treatment with, and more
desirably subsequent to removal o~, the submicroscoDic
ion exchange resins. Chlorination prior to treatment
with the submicroscopic ion exchange resin allows the
THM precursors to react with the chlorine prior to
their removal, thus defeating the purpose of the
present process, and chlorination prior to removal of
the submicroscopic ion exc~ange resin allows the resin
itself to react with the chlorine. The consequence of
the latter reaction is unknown, but inasmuch as it
introduces chlorinated organic materials tu the
drinking water, it is considered undesirable.
The submicroscopic ion exchange particles ussd in
the process of the present invention are those resins
having a diameter of 1.5,ti m or smaller, and bearing
from about 0.7 to about 1.5 ion exchange functional
groups ~er monomer unit. Such submicroscopic ion
exchange resins may be prepared as taught in U.S. Patent No.
4,200,695, of B.P. Chong et al, issued ~pril 29, 1980, said patent
being assigned to Rchm and Haas Company.
The follow~ng examples are intended to illustrate
the present invention, but not to limit it except as it
is limited in the claims. All reagents used are of
good commercial quality, and all percentages and other
proportions are by weight, unless otherwise indicated.
In the following examples, samples of raw water
were treated according to the process of the present
invention, and for comparative purposes, according to
conventional processes. Raw water was collected from
the Delaware River at Philadelphia, Pennsylvania,
filtared through a coarse screen, and sub~equently
filtered through glass wool prior to testing. Raw
water was sampled by the U.S. Environmental Protection
Agency from the Ohio River at Cinoinnati, Ohio, and
from the Preston Water Treatment Plant at Hialeah,
Florida; these samples were tested as supplied.
The experimental procedure used was similar for
each of the following examples. For the small-scale
examples the material to be tested was added to 800 ml
of the specified test water in a 1000-ml beaker. The
submicroscopic ion exchange resins were added as
aqueous suspensions containing 6.25% solids, and the
other THM-precursor removers were added as dry
solids. The water oontaining the THM-precursor
removers to be tested was stirred for 5 minutes at 100
rpm using a Phipps and Bird jar test appanatus, and for
an additional 20 minutes at 30 rpm, after which the
water was allowed to stand undisturbed while the solidæ
settled. At 30 and 60 minut0s during the settling
; period the turbidity of the water was determined using
a Hellige Turbidimeter and APHA Method No. 163b (APHA
Standard Methods, 13th edition, 1971~; if a sample
containing the submicroscopic anion exchange resin
still showed turbidity after 60 minutes of settling, a
small amount of submicroscopic cation exchangs resin
was added to flocculate the excsss anion exchange
6~
rssin. Subsaquent to the settlin~ period the water
samples were filtered using"Whatman'i~1 filter paper.
Several 50-ml samples of the treated, filtered
water were chlorinated to different levels of chlorine,
using an approximately 4000-6000 ppm stock solution of
chlorine gas dissolved in water; these chlorinated
samples were allowed to stand in the dark ~or 24 hours,
after which they were analyzed for chlorine
spectrophotometrically using APHA Method No. 114g (APHA
Standard Methods, 13th edition, 1971~, to determine the
sample containing a residual chlorine content of
1.0-1.5 ppm chlorine after 24 hours. The sample
containing this specified amount of chlorine after 24
hours was treated with 0.25 ml of O.lN sodium
thiosulfate to reduce the free chlorine and prevent
further chlorination during analysis. The THM formed
during the 24-hour period was determined using a
gas-liquid chromatograph with electron-capture
detector, direct injection of the aqueous sample, and
similar injection of aqueous chloroform standards.
Examples 1-29, the results of which are given in
Table 1, illustrate the removal of THM precursors, as
evidenced by the reduction in THM following overnight
chlorination, by a strongly ba ic, submicroscopic anion
exchange resin of the present invention, in the
hydroxyl form. In Examples 1~10 and 23 29 the tested
waters were samples of Delaware River water, in
Examples 11-16 they were settled Ohio River water, and
in Examples 17-22 they were raw waters from the Preston
Water Treatment Plant in Hialeah, Florida.
* Trad~k
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TA3EE 1
Treatment THM Gontent
Level ~ g~ THM
Example (m~ Treated Control Reduction
1 1 66 100 34.0
2 3 - 54 100 46.0
3 5 44 100 56.0
4 7 32 100 68.0
9 25 100 25O0
6 1 124 138 10.1
7 3 70.6 138 50.7
8 5 36.1 138 73.8
9 7 34.9 138 74.7
9 30.2 138 78.1
11 2 120 148 18.9
~ 12 5 84 148 43.2
;~ 13 10 87 148 41.2
~` 14 15 67 148 54.7
148 62.8
16 25 56 148 62.1
17 2 340 600 43.3
18 5 360 600 40.0
19 10 319 600 46.8
242 600 59.7
21 20 232 600 61.3
22 25 176 600 70.7
23 7.8 35 148 76.2
24 15.7 25 148 82.8
23.5 29 148 80.4
26 31.3 37 148 75.0
27 39.1 ~o 148 86.4
28 31.3 32 87 63.6
29 62.5 34 87 63.1
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Examples 30-34, the results of which are given in
Table Z, illustrate the removal of trihalomethane
precursors from Delaware River water samples by a
strongly basic, submicro~copic ion exchange resin of
the present invention, in the chloride form.
TABLE 2
Treatment THM Content
Level (~Ig/l) % THM
Example (mg/l) Treated Control Reduction
1 124 136 8.8
31 3 52.6 136 61.3
32 5 25.1 136 81.5
33 7 23.1 136 82.8
34 9 19.1 136 85.9
6~7~
Examples 35-39, the results of which are given in
Table 3, illustrate the removal of trihalomethane
precursors from Delaware River water with a floc of the
present invention formed by mixing the strongl~y basic
S submicroscopic ion exchange resin of Examples 1-29 with
a strongly acidic, submicroscopic ion exchange resin.
TABLE 3
Treal;ment THM Content
Level(~g/l) % THM
Examvle (mg/l)Treated Control Reduction
72 110 34.7
36 100 64 110 41O7
37 62.5 58 ~7 32.8
38 125 62 87 28.4
39 250 52 87 ~l0.5
-- 10 --
Example 40 illustrates the removal of
trihalomethane precurqors from Delaware River water
with a mixture of lO mg/l of ferric sulfate (a krown
coagulant) and 9 mg/l of the strongly basic,
submicroscopic ion exchange resin of the present
invention. Examples 41-45 illustrate, for comparative
purposes, the removal of trihalome.thane precursors from
Delaware River water by ferric sulfate alone. The
results of Examples 40-45 are given in Table 4.
TABLE 4
Treatment THM Content
Level ~ g/l) % THM
Example (m~/l) Treated Control Reduction
10 ~ 9 16 71 77.5
41 10 65 71 8.5
42 20 48 71 32.4
43 30 36 71 49.3
44 40 31 71 56.3
26 71 63.4
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Examples 46-54, the results o~ which are given in
Table 5, illustrate ~or comparative purposes the
removal of trihalomethane precursors from Delaware
River water by conventional treatment with alum, or
aluminum sulPate-16 hydrate.
TABLE 5
Treatment THM Content
Level(~ g/l) ~ THM
Exam~le ~m~!l)Treated Control Reduction
46 10 36 51 29
47 15 34 51 33
48 20 27 51 47
49 30 25 51 51
23 51 55
51 50 34 87 60.9
52 50 25 148 83.2
53 50 49 110 55.1
54 100 41 110 63.1
Examples 55 and 56, the results of which are given
in Table 6, illustrate for comparative purposes the
removal of trihalomethane precursors from Delaware
River water by conventional treatment with activated
charcoal (Pittsburgh RC Pulverized Grade, obtained from
Calgon Corporation).
TABLE 6
Treatment THM Content
Level(~g/l) ~ THM
Example (mg/l)Treated Control Reduction
5079 110 28.5
56 100 42 110 61.9
Examples 57-61, the results of wh.ich are glven in
Table 7, illustrate for comparative purposes the
removal of trihalomethane precursors from Delaware
River water by treatment with soluble cationic polymers
~etz 1175~. These examples are included to compare
the effectiveness of low level treatment with the
insoluble submicroscopic ion exchange re~in~ o~ the
present invention with similar ionic, but soluble9
materials which have been previously used for removal
: lO of anionic material~q from water.
TABLE 7
Treatment THM Content
Level ~ g/1~ ~ THM
Example(mg/1~ Treated_ Control Reduction
lS 57 5 168 176 4.5
58 10 122 176 30.6
59 15 91.9 176 47.7
84.5 176 51.1
61 25 40.4 176 77.0
* Trademark
