STERILIZATION OF CATION ANGE R Sulfonated Phenol-Formaldehyde Type G. A. CRUICKSHANK A N D D. G. BRAITHWAITE .Yational .4luminczte Corporation, Chicago, I l l . Cation exchange resins of the sulfona tcd phenol-formaldehjde t j pe can be buccessfully sterilized by treatment with O.Z570 formaldehyde applied for a period of 3 hours. I t is suggested that such sterilization be carried out just before regeneration of the exchanger since e-ery trace of the sterilizing agent i s rernoied during the iiormal regeneration cycle.
50 mI. of sterile distilled water were substituted in place of tht chemicals. The flasks were shaken in a uniform manner ar~tl rotated to wash down the resin. They then were allowed to rest undisturbed a t room temperature for 5.5 hours a t nhich time the cheniical solutions and the controls were decanted off and replaced with 50 ml. of sterile distilled water. The flask. were shaken 25 times and bacterial plate counts were made from the supernatant liquid. Included in this series were Hyarnirii~ 1622, a quaternary ammonium compound; Suodex 87, a11 amine salt; Nacconol NR, an anionic detergent; hydrogrli peroxide; and formalin. Results are shown in Table I. Hyamine 1622 and hydrogen peroxide completely sterilized thc contaminated resin when applied in concentration of 1% foJ 5.5. hours. The results with formaldehyde were considerabl~ hrtter; complete sterilization was attained by a concentration oi 0.25%. These three materials, therefore, were tested for possible delet t i rious effect on the resin. Nalcite hIX mas placed in three laboratory percolation units to form beds 30 inches dccp. Thc ICSIII v a s backwashed, allowed to settIe, and the column drained t o bed level. Solutions of 1% of the materials to be tested t h m were introduced from the top of the columns and run through downflo.rv until all the vater present in the beds had been rvplaced with the solutions. Qualitative tests showed the prrsencv of all three chemicals in the effluent. After 3 pints of effluent had been collected, the solutions were allowed to remain in contact with the resin for 2.5 hours. The materials mere still present i n the effluent and there was no evidence ,of breakdown of the resin. After standing for 48 hours at room temperature, hornever, the effluent from the hydrogen peroxide unit was conGierably discolored, indicating a breakdown of the resin. H) xinine 1622 and formaldehyde in 1% concentration shonid n o apparent harmful effect on the rcsin.
HE increased use of exchanger softening plants for treatiiig municipal water supplies has called attention to the necessity of wat,ching for bacterial oontamina,tion of the beds, especially when operating on surface supplies subject to climat'ic variations. Beds of exchangers become contaminated because of the filtering action that occurs when operating as softening units. There has been no evidence that the bacteria normally encountered in n-ater supplies are i o utilize the resinous cation exchange mat>erialit'self as a nutrient. Bacterial growth in the bed appears to be due entirely to suspended organic material filtered from the water supply. Such organic material is capable of supplying the food requirements of a wide variety of microorganisms. Bacterial contamination in installations employing siliceous exchangers or resins of the sulfonated hydrocarbon type can bi. controlled readily by continuous or intermittent chlorination. Most sulfonated phenol-formaldehyde type resins, however, arc oxidized easily by chlorine. Since this oxidation eventually results in decomposition of the exchanger, chlorination can not be recommended for txeatment of installations using this type of rrqin. I n a majority of the cases where bacterial contamiiiatioii is encountered, the complaint will be only periodic and may even be seasonal. A sterilization treatment t h a t could be employed safely when required to maintain the bed in sanitary condition, therefore, would be completely satisfactory for most installations. In addition t,o being noriinjurious to the exchanger, any treatment applied to a mater supply used for human consumption also must be essentially nont'oxic. With t)heaeconditions in mind the writers tested the effect of several chemicals on Xalcite JIX, artificially contaminated with coliform bacteria. This material i s typical of the sulfonated Dheiiol-formaldehyde exchangers.
Bacterial C o u n t pep 111. Concn. of antiseptic, "/o------. 0.2; 0.10
-..
___I_.
~
1. O O
0.80
Controls
EXPEMM ENTAL
- grarna of Saleire MX resin, sodium salt, was placed aseptically in each of a, series of sterile 125-m1. rubber-stoppered Erlenmeyer flasks. To each flask there were added 30 ml. of sterile distilled water; this amount was just sufficient' to cover t'he resin. All flasks then were inoculated with 1 ml. of a 24-hour broth culture of Aerobacter aerogenes (American Type culture collection strain 8308), shaken uniformly 25 times, rotated gently i o wash down the resin from the stopper and sides, and allowed to stand a t room temperaLurc for 18 houm The liquid then was poured off from all flasks and replaced with 50-Inl. amounts of various concentrations of t,he chemicals undw investigation. Control flasks were included in which
Because formaldehyde is. iiipxpensive and appeared to 0ff1.1 certain other advantages over the quaternary ammonium compound, further experiments were carried out to determine the feasibility of its employment as a sterili~irlgagent for ion exrhange I esins. Formaldehyde has thiee outstanding advantagc.6 for this type of use: it has a small moleeulc, thereby enabling highly effirient penetration: i t retains its effectiveness in 1Iic presence of moderate amounts of many kinds of organic materials; and it is not adsorbed or absorbed by the resin to a n ) extent and therefore is not depleted in concentration. Table I indicates that concentrations somewhat lower than 472
March 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
0.25% formaldehyde might be equally effective in a 5.5-hour contact. However, it appeared t o the authors that it would be more desirable to shorten the time of contact necessary t o obtain sterilization rather than to reduce the dosage. With this in mind, the original experiment was modified t o determine the minimum time required t o sterilize the resin completely using a solution of 0.25% formaldehyde. -4series of flasks containing 50 grams of Nalcite MX in 30 ml. of sterile distilled water was inoculated as before with Aerobacter acrogenes. A second series was prepared similarly and inoculated with Escherichia coli (American Type culture collection strain 4657). All flasks were shaken 25 times, rotated to wash down the resin, and allowed to stand a t room temperature for 18 hours. The liquid then was decanted from all flasks and replaced with 50 ml. amounts of 0.25% formaldehyde. The flasks again were shaken 25 times and rotated to wash down the resin. At 0.5hour intervals bacterial plate counts were made from one of the flasks in each series. Since it is known that formaldehyde is bacteriostatic in high dilution, the plating procedure was modified as follows: The formaldehyde solution was drained from the resin by decanting. The flask was refilled with 50 ml. of sterile water, shaken 25 times, and again drained. This process was repeated until the resin had been washed with five separate 50-ml. volumes of sterile water. Plate counts were made from the fifth washing in each case. Controls were included using sterile distilled water in place of the formaldehyde solution. The mechanical manipulation of the controls was the same as for the formaldehyde treated flasks. Results are shown in Table 11.
TABLE 11. EFFECT OF CONTACT TIMEON STERILIZING ACTIONOH‘ 0.25% AQUEOVS FORMALDEHYDE
A . aerogenes E . coli
(48-Hour Plate Counts) Bacterial Count per M1. ____ Contact time, hours 0.5 1 0 1 . 5 2.0 2 . 5 3 . 0 3 . 5 4 . 0 Controls 4200 45 14 7 2 0 0 0 2,900,000 430 69 8 6 0 0 0 0 1,900,000
As a further check on the possibility of simple bacteriostatic action or a delayed growth all negative plates were replaced in the incubator for an additional 8 days. KOgrowth developed. Before applying the laboratory findings to field installations it was necessary to ensure that residual formaldehyde could be removed from the resin. For this purpose two percolation units were set up to form beds 30 inches deep. A 1% formaldehyde solution then was introduced from the top of the columns and passed downflow until all the water present in the beds had been replaced with the solution. The exchanger was kept in contact with the formaldehyde solution for 5.5 hours. At the end of this time both columns were backwashed for 10 minutes. The backwash water a t this time showed a positive test for formaldehyde although taste and odor tests were negative. One column then was washed downflow a t 5 gallons per square foot per minute. The effluent, tested a t 5-minute intervals, showed a positive test for formaldehyde after 15 minutes. This was completely negative at 20 minutes. The test used for detection of formaldehyde was the sodium bisulfite reaction suggested by Feigl ( I ) . It will detect the presence of 0.05 y of formaldehyde. The second column was regenerated, following the backwash, with 6 pounds of salt per cubic foot (loyosolution, 60-minute cycle). The effluent, following regeneration, was entirely free of formaldehyde. This would indicate that the logical time to carry out sterilization is prior t o the regeneration of the exchanger, as every trace of the sterilizing agent is removed during the normal regeneration cycle. Table 111 shows the results obtained in a typical field installation. This unit was of 100-cubic foot capacity, 60 inches in
473
TABLE111. FORMALDEHYDE TREATMENT OF FIELD INSTALLATION
(Water used for backwash, 46,000 per rnl.) Bacterial Plate _ Count _ _ Before After treatment treatment
-
Exchanger T o p of bed, per gram One foot down, per gram T w o feet down, per gram Effluent, per ml.
252,000 115,000 46,000 110,000
~ ~
56 27 12 132
diameter, and 94 inches high. It w a b designed for treating 129 gallons of water per minute. The water supply was from a deep well, with 36 grains hardness, and 1.2 p.p.m. of iron. The procedure used in treating this unit was to backwash at a rate of 6 gallons per square foot per minute for 0.5 hour. The water in the unit was drained off to a point where the bed was just covered and the calculated amount of commercial (407%) formalin necessary to supply a 0.25y0 concentration of formaldehyde was poured in through the manhole. After 3 hours the unit was backwashed for 10 minutes; a t this time there was no odor or taste of formaldehyde in the water. The fact that a few bacteria were found in the mineral after treatment would appear in this case to be due directly to the barkwashing process because the water used for this purpose gave a bacterial count of 46,000 per ml. Although this paper is concerned only with the phenol-formaldehyde type of cation exchange resins, preliminary work by the authors indicates that the formaldehyde treatment described herein may be applied to siliceous exchangers and to resins of the sulfonated hydrocarbon type without injury to the exchanger. LITER 4TURE CITED
(1) Feigl, F., “Spot Tests,” 2nd English edition, pp. 277-8, New York, Nordeman Pub. Co., 1939. RECLIVEDOctober 1, 1948. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 114th Meeting of the A V ~ R I C A Z CHEWICAL S O C I E T Y , St. L O U I S , Mo.
Ion Exchange Resins Being Used to Study the Purification of Pectin at Western Regional Research Laboratories
