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The hazards of incorporating charcoal filters into domestic water systems
14:arer Research Vol. 8. pp. I l I to 113. P e r g a m o n Press 1974.. Printed in G r e a t Britain.
THE HAZARDS OF INCORPORATING CHARCOAL FILTERS INTO DOMESTIC WATER SYSTEMS CRAIG WALLIS,CHARLESH. STAGGand JOSEPH L. MELNICK Department of Virology and Epidemiology. Baylor College of Medicine. Houston. Texas 77025. U.S.A. (Receired 26 July 1973) Abstract--Charcoal filters used in domestic and commercial applications for the removal of objectionable taste and odor support the growth of bacteria to alarmingly high counts. The charcoal beds concentrate both bacteria and organic nutrients that are present in water at low concentration. This results in marked growth of bacteria during the overnight period when the water is stagnant and in their subsequent release into the morning flow.
For a number of years, filters for home use have been sold to improve the quality of drinking water by removing "bad taste and odor." These filters are no more than charcoal columns which absorb chlorine, sulfur and small mol. wt organic compounds, e.g. phenols. Recently, a cigarette manufacturer (Tareyton) promoted the sale of charcoal filters by retailing small units which fit on kitchen taps. It is common knowledge that charcoal or resin (water softener) beds can support bacterial growth (Weber et al., 1970; Stature et al., 1969). During the past 3 yr, we have been evaluating the use of charcoal for filtration-of drinking water and have found that commercially available charcoals efficiently decompose chlorine as well as adsorb sulfur and organic compounds, which are a source of nutrients for bacteria. We also found that charcoal will concentrate bacteria from tap water. Instead of allowing the bacteria present in low concentration in tap water to pass harmlessly into the effluent, the charcoal columns concentrate the bacteria. After overnight storage of the charcoals, the initial effluent the next day contains high concentrations of bacteria. Water conditioners were obtained from Tareyton (manufactured by Universal Water Conditioning Co., Chicago, Illinois), Sears-Roebuck and Co. (manufactured by the Cuno Division, AMF, Meriden, Connecticut), Commercial Filters Division (Carborundum Co., Lebanon, Indiana), and the Filterite Corp. (Timonium, Maryland). All the conditioners contained charcoal enclosed in either a fabric or plastic holder. The filter units were mounted on a cold tap water faucet, and city water was passed through the filters at full pressure (51 lb in--" total pressure). Chlorine levels in tap water were determined with O-tolidine reagent
430nm wavelength. A chlorine standard was made with calcium hypochlorite and chlorine demand-free equipment. Bacterial assays for total colony-forming units (CFU) were conducted according to the membrane filter technique described in "Standard Methods for the Examination of Water and Wastewater" (1970), except that the membrane filters were placed on nutrient agar. Duplicate samples were plated without concentration on membranes. The concentration of chlorine in Houston tap water, as well as the bacterial counts, varied from day to day. The variation in chlorine concentrations is typical of municipal water systems; chlorine levels are dependent on the distance the water must travel from the source of chlorination, the volume used immediately prior to assay for chlorine and various other factors. Chlorine was not detectable in most instances after passing through the charcoal filter, indicating efficient removal by the charcoal unit, whereas the influent water conrained from 0-5 to 0-05 mg 1- ~ chlorine. Bacterial counts ranged from no detectable organisms ( < I CFU 100- ~ ml) to 100 CFU 100- i ml. Experiments were designed to simulate the use of a commercial charcoal filter on a cold water tap to determine whether home water conditioners could concentrate bacteria and then release them under certain conditons. A Tareyton charcoal filter was placed on the cold water tap, and the effluent was monitored for total bacteria and for chlorine. The tap was used 10-20 times a day to simulate typical kitchen use, e.g. drinking, cooking, rinsing hands or dishes, etc., and thus about 5--10 gal d a y - ~ were passed through the charcoal unit. One hundred-millilitre vols. were collected immediately each morning after the water had been stagnant in the unit overnight. These samples and co_ntrol 10(3ml vol. samples which by-passed the charcoal unit III
I12
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Fig. I. Concentration and elution of bacteria from tap water. A Tareyton charcoal filter was installed on the cold water tap and was used daily to simulate home use. Each morning, after the water in the unit had remained stagnant overnight, the first flow of I00 ml (the vol. present in the filter holder) was collected and assayed for total colonyforming units.
were monitored daily for total bacterial counts and chlorine. Figure 1 shows the amount of bacteria present in the first 100-ml voi. of water obtained from the charcoal effluent each morning. When the Tareyton unit was first installed, insignificant numbers of bacteria were detected in the effluent. However, the organic nutrient load in the charcoal must have increased daily, because by the sixth day the effluent contained 7,000,000 bacteria 100 -1 ml water. Numerous other experiments gave essentially the-same results. The ability of charcoal to concentrate organics which are used as bacterial nutrients was demonstrated by the following experiment. Sample 100-ml vols. of each of the following were tested: (i) freshly collected tap water, (ii) tap water obtained from the effluent of a freshly installed Tareyton charcoal filter, and (iii) tap water obtained from the same charcoal unit after 600 gal of water had been passed through it during the day it was installed. Each sample was dechlorinated with 1 ppm sodium thiosulfate and filtered through an 0"22 p bacterial membrane to remove any indigenous bacteria present in the water. Each sample then received a mixed population of bacteria that had been isolated from the city water to yield a final concentration of 100 CFU 100-1 ml of tap water. Each day for 3 days, 100ml of each water sample was assayed for bacteria. The results of this test are shown in Fig. 2. (Numerous experiments were conducted, each with essentially the same results.) It is evident that organic compounds were first adsorbed from the water and were later eluted from the charcoal, since bacterial growth occurred only in the sample derived from the charcoal treated with 600 gal of water. In the un-
treated tap water, the bacterial counts decreased linearly. Similar results were obtained with the water from the charcoal effluent of the freshly installed unit, i.e. prior to the passage of 600 gal of water. Experiments conducted with the other charcoal filters yielded essentially the same results as described for the Tareyton filter. The concentration of bacteria by charcoal filters is of signal importance to public health. Persons drinking the first flow of water after overnight storage in the charcoal filters may be affected by the high concentration of bacteria that may be present. In addition, the high concentration of bacteria present in the contaminated charcoal beds may synthesize harmful toxins, The manufacturers recommend that the charcoal filters be changed once every 6 months or whenever the quality of the water decreases (as manifest by bad taste or odor). At such a time, the water conditioner will contain high bacterial counts and perhaps toxins as well. Our experiments have shown that when the charcoal units are functioning as advertised, i.e., when the effluents are free of bad taste, odor and chlorine, the charcoal beds may support the growth of millions of bacteria. A recent article by Geldreich et al. 0972) described the problems of bacterial contamination in municipal water systems. These authors indicate that municipal water systems often contain a myriad of microorganisms which pass the disinfection barrier and pose a potential danger. Bacterial counts may vary from few to thousands per 100ml. Bacteria when present in water in small numbers may be inocuous to man, but
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Fig. 2. Concentration and elution of bacterial nutrients from tap water. Samples of tap water obtained immediately before entering a charcoal filter (labeled "tap water control"), immediately after passing a fresh charcoal filter (labeled "untreated charcoal") and after passing 600 gal of water through the charcoal unit (labeled "water-treated charcoal"). The water was dcchlorinated and filtered through a membrane to remove any bacteria present in the samples. The three samples were then treated with a mixed population of bacteria originally isolated from tap water; each sample received 100 CFU 100- ' ml.
Charcoal filters into domestic water systems " when ingested in large numbers may be capable of causing disease (Geldreich et al., 1972). In the event that a municipal water system became contaminated with pathogenic bacteria, they might pass through the household water system in numbers too small to cause disease. However, if the bacteria were concentrated on a charcoal filter, they could multiply in the water conditioners to a high enough dose to cause illness.
w.R. 8/2--~
I 13 REFERENCES
Geldreich E. E., Nash H. D.. Reasoner D. J. and Taylor R. H. (1972) The necessity of controlling bacterial populations in potable waters" community water supply. J. Am. Wat. 14ks Ass. 64, 596-602. Stature J. M.. Egelhard W. E. and Parsons J. E. (1969) Microbiological study of water-softener resins. Appl. Microbiol. 18, 376-386. Standard Methods for the Examination of Water and Wastewater, 13th edn (1970) Ar~ Publ. Hlth. Ass., New YOrk. Weber W. J., Jr., Hopkins C. B. and Bloom R., Jr. (1970) Physicochemical treatment of wastewater, g. Bat. Pollut. Control Fed. 42, 83-99.
THE HAZARDS OF INCORPORATING CHARCOAL FILTERS INTO DOMESTIC WATER SYSTEMS CRAIG WALLIS,CHARLESH. STAGGand JOSEPH L. MELNICK Department of Virology and Epidemiology. Baylor College of Medicine. Houston. Texas 77025. U.S.A. (Receired 26 July 1973) Abstract--Charcoal filters used in domestic and commercial applications for the removal of objectionable taste and odor support the growth of bacteria to alarmingly high counts. The charcoal beds concentrate both bacteria and organic nutrients that are present in water at low concentration. This results in marked growth of bacteria during the overnight period when the water is stagnant and in their subsequent release into the morning flow.
For a number of years, filters for home use have been sold to improve the quality of drinking water by removing "bad taste and odor." These filters are no more than charcoal columns which absorb chlorine, sulfur and small mol. wt organic compounds, e.g. phenols. Recently, a cigarette manufacturer (Tareyton) promoted the sale of charcoal filters by retailing small units which fit on kitchen taps. It is common knowledge that charcoal or resin (water softener) beds can support bacterial growth (Weber et al., 1970; Stature et al., 1969). During the past 3 yr, we have been evaluating the use of charcoal for filtration-of drinking water and have found that commercially available charcoals efficiently decompose chlorine as well as adsorb sulfur and organic compounds, which are a source of nutrients for bacteria. We also found that charcoal will concentrate bacteria from tap water. Instead of allowing the bacteria present in low concentration in tap water to pass harmlessly into the effluent, the charcoal columns concentrate the bacteria. After overnight storage of the charcoals, the initial effluent the next day contains high concentrations of bacteria. Water conditioners were obtained from Tareyton (manufactured by Universal Water Conditioning Co., Chicago, Illinois), Sears-Roebuck and Co. (manufactured by the Cuno Division, AMF, Meriden, Connecticut), Commercial Filters Division (Carborundum Co., Lebanon, Indiana), and the Filterite Corp. (Timonium, Maryland). All the conditioners contained charcoal enclosed in either a fabric or plastic holder. The filter units were mounted on a cold tap water faucet, and city water was passed through the filters at full pressure (51 lb in--" total pressure). Chlorine levels in tap water were determined with O-tolidine reagent
430nm wavelength. A chlorine standard was made with calcium hypochlorite and chlorine demand-free equipment. Bacterial assays for total colony-forming units (CFU) were conducted according to the membrane filter technique described in "Standard Methods for the Examination of Water and Wastewater" (1970), except that the membrane filters were placed on nutrient agar. Duplicate samples were plated without concentration on membranes. The concentration of chlorine in Houston tap water, as well as the bacterial counts, varied from day to day. The variation in chlorine concentrations is typical of municipal water systems; chlorine levels are dependent on the distance the water must travel from the source of chlorination, the volume used immediately prior to assay for chlorine and various other factors. Chlorine was not detectable in most instances after passing through the charcoal filter, indicating efficient removal by the charcoal unit, whereas the influent water conrained from 0-5 to 0-05 mg 1- ~ chlorine. Bacterial counts ranged from no detectable organisms ( < I CFU 100- ~ ml) to 100 CFU 100- i ml. Experiments were designed to simulate the use of a commercial charcoal filter on a cold water tap to determine whether home water conditioners could concentrate bacteria and then release them under certain conditons. A Tareyton charcoal filter was placed on the cold water tap, and the effluent was monitored for total bacteria and for chlorine. The tap was used 10-20 times a day to simulate typical kitchen use, e.g. drinking, cooking, rinsing hands or dishes, etc., and thus about 5--10 gal d a y - ~ were passed through the charcoal unit. One hundred-millilitre vols. were collected immediately each morning after the water had been stagnant in the unit overnight. These samples and co_ntrol 10(3ml vol. samples which by-passed the charcoal unit III
I12
C. WALLIS.C. H. STAGGand J. L. MELNICK 10.000900 i
I00,000
o~ ,o,ooo~ I
o
L000
08
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OAYS
Fig. I. Concentration and elution of bacteria from tap water. A Tareyton charcoal filter was installed on the cold water tap and was used daily to simulate home use. Each morning, after the water in the unit had remained stagnant overnight, the first flow of I00 ml (the vol. present in the filter holder) was collected and assayed for total colonyforming units.
were monitored daily for total bacterial counts and chlorine. Figure 1 shows the amount of bacteria present in the first 100-ml voi. of water obtained from the charcoal effluent each morning. When the Tareyton unit was first installed, insignificant numbers of bacteria were detected in the effluent. However, the organic nutrient load in the charcoal must have increased daily, because by the sixth day the effluent contained 7,000,000 bacteria 100 -1 ml water. Numerous other experiments gave essentially the-same results. The ability of charcoal to concentrate organics which are used as bacterial nutrients was demonstrated by the following experiment. Sample 100-ml vols. of each of the following were tested: (i) freshly collected tap water, (ii) tap water obtained from the effluent of a freshly installed Tareyton charcoal filter, and (iii) tap water obtained from the same charcoal unit after 600 gal of water had been passed through it during the day it was installed. Each sample was dechlorinated with 1 ppm sodium thiosulfate and filtered through an 0"22 p bacterial membrane to remove any indigenous bacteria present in the water. Each sample then received a mixed population of bacteria that had been isolated from the city water to yield a final concentration of 100 CFU 100-1 ml of tap water. Each day for 3 days, 100ml of each water sample was assayed for bacteria. The results of this test are shown in Fig. 2. (Numerous experiments were conducted, each with essentially the same results.) It is evident that organic compounds were first adsorbed from the water and were later eluted from the charcoal, since bacterial growth occurred only in the sample derived from the charcoal treated with 600 gal of water. In the un-
treated tap water, the bacterial counts decreased linearly. Similar results were obtained with the water from the charcoal effluent of the freshly installed unit, i.e. prior to the passage of 600 gal of water. Experiments conducted with the other charcoal filters yielded essentially the same results as described for the Tareyton filter. The concentration of bacteria by charcoal filters is of signal importance to public health. Persons drinking the first flow of water after overnight storage in the charcoal filters may be affected by the high concentration of bacteria that may be present. In addition, the high concentration of bacteria present in the contaminated charcoal beds may synthesize harmful toxins, The manufacturers recommend that the charcoal filters be changed once every 6 months or whenever the quality of the water decreases (as manifest by bad taste or odor). At such a time, the water conditioner will contain high bacterial counts and perhaps toxins as well. Our experiments have shown that when the charcoal units are functioning as advertised, i.e., when the effluents are free of bad taste, odor and chlorine, the charcoal beds may support the growth of millions of bacteria. A recent article by Geldreich et al. 0972) described the problems of bacterial contamination in municipal water systems. These authors indicate that municipal water systems often contain a myriad of microorganisms which pass the disinfection barrier and pose a potential danger. Bacterial counts may vary from few to thousands per 100ml. Bacteria when present in water in small numbers may be inocuous to man, but
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Fig. 2. Concentration and elution of bacterial nutrients from tap water. Samples of tap water obtained immediately before entering a charcoal filter (labeled "tap water control"), immediately after passing a fresh charcoal filter (labeled "untreated charcoal") and after passing 600 gal of water through the charcoal unit (labeled "water-treated charcoal"). The water was dcchlorinated and filtered through a membrane to remove any bacteria present in the samples. The three samples were then treated with a mixed population of bacteria originally isolated from tap water; each sample received 100 CFU 100- ' ml.
Charcoal filters into domestic water systems " when ingested in large numbers may be capable of causing disease (Geldreich et al., 1972). In the event that a municipal water system became contaminated with pathogenic bacteria, they might pass through the household water system in numbers too small to cause disease. However, if the bacteria were concentrated on a charcoal filter, they could multiply in the water conditioners to a high enough dose to cause illness.
w.R. 8/2--~
I 13 REFERENCES
Geldreich E. E., Nash H. D.. Reasoner D. J. and Taylor R. H. (1972) The necessity of controlling bacterial populations in potable waters" community water supply. J. Am. Wat. 14ks Ass. 64, 596-602. Stature J. M.. Egelhard W. E. and Parsons J. E. (1969) Microbiological study of water-softener resins. Appl. Microbiol. 18, 376-386. Standard Methods for the Examination of Water and Wastewater, 13th edn (1970) Ar~ Publ. Hlth. Ass., New YOrk. Weber W. J., Jr., Hopkins C. B. and Bloom R., Jr. (1970) Physicochemical treatment of wastewater, g. Bat. Pollut. Control Fed. 42, 83-99.