APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Mar. 1981, p. 646-651
Effects of Activated Carbon and Bacteriostatic Filters on
Microbiological Quality of Drinking Water
R. S. TOBIN,`* D. K. SMITH,2 AND J. A. LINDSAY2
Health Protection Branch, Health and Welfare Canada, Ottawa, Ontario KIA OL2,' and Ontario Research
Foundation, Sheridan Park Research Community, Mississauga, Ontraio L5KIB3,2Canada
Three activated carbon filters for point-of-use water treatment were tested in
laboratory and field studies for chemical removal and microbiological effects on
water. All removed free available chlorine in municipally treated water to below
the limit of detection, but removed only about 50 to 70% of the total available
chlorine and 4 to 33% of the total organic carbon. Standard plate count bacteria
in the effluent increased steadily with time for 3 weeks and remained elevated
over the 8-week period ofthe study. Total coliform bacteria were found to persist
and proliferate on the filters for several days after transient contamination ofthe
influent water. Silver-containing activated carbon filters suppressed total coliform
but not total bacterial growth. Pseudomonas aeruginosa was recovered from the
effluents of all filters at some time during the tests.
Increased awareness among the public of the
health implications of drinking water quality
and the continuing demand for aesthetically
pleasing water have resulted in a rapid prolifer-
ation in the types and numbers of point-of-use
water treatment devices sold (24). A major pro-
portion of all such devices are activated carbon
filters, including those releasing silver to act as
a bacteriostat. Some of these are claimed to
remove taste and odor, sediment, chlorine, tri-
halamethanes, carcinogens, pesticides, and a
number of other perceived problem substances.
Wallis and co-workers (27) were among the first
to demonstrate the tremendous proliferation of
bacteria in such devices, which they considered
to be a potential health hazard. In a later study,
Fiore and Babineau (11) also showed high bac-
terial counts in the effluent after periods of
stagnation, butmaintained that the proliferation
observed was not significantly greater than that
observed in untreated tap water after the same
period. Taylor et al. (24) clearly demonstrated
plate counts from activated carbon filters to be
greater than those from corresponding influent
water, but levels were lower than some previ-
The present study investigates the bacterial
growth on four types of activated carbon filters,
including a silver-releasing bacteriostatic filter.
The growth of total coliform bacteria and of
bacteria of potential health significance on the
filters is shown.
(This paper was presented in part at the An-
nual Meeting of the American Society for Mi-
crobiology, May 1980, in Miami Beach, Fla.).
MATERLALS AND METHODS
Filters. Filter A is a compact in-line filter that is
sold principally for the recreational vehicle, boat, and
vacation home market. The cartridge consists of a
carbon core sandwiched between thin outer and inner
layers of cellulose. It is designed to remove taste, odor,
andsediment. FilterB is a slightly larger unit, intended
for in-line attachment to cold water lines in homes.
The cartridge consists ofa resin-bonded cellulose fiber
filter section at the outlet, an activated carbon core,
and another resin-bonded cellulose network at the
outlet. It is designed to remove objectionable taste and
odor, as well as dirt, rust, and sand. Unit C is a small
unit that attaches to a kitchen faucet. It was tested
with two types of cartridge that are currently availa-
ble. One contained activated carbon, and the other
contained activated carbon plus silver. The silver re-
leased from the latter did not exceed 50,ug/literin the
effluent. Unit C is claimed to reduce chlorine, algae,
suspended particles greater than 8 u, and organic
chemicals such as detergents, pesticides, chloroform,
and polychlorinated biphenyls.
Testing of devices. Two of each of the three
devices were tested in the laboratory on a manifold
system described in detail elsewhere (9). Timers were
adjusted to give an "on" time of 30 s every 0.5 h, and
the flow rates on filters A and B were adjusted by
throttle valves to 7.6 liters/min (high flow rate) and
4.25 liters/min (low flow rate). Control counts were
taken from identically valved lines which were set at
the same flow rates and timing as the filters. The
manifold was operated for 16 h per day and left inac-
tive for 8 h per day. Total volumes processed were
approximately 123 liters per day at the fast flow rate
and 68 liters per day at the slow flow rate. Filter C
units were attached to faucets on the manifold, and
both were adjusted to a flow rate of 475 ml/min to
give a total of 7.6 liters per day. The portion of the
ACTIVATED CARBON FILTERS
scheme for identification ofnonfermentative Gram-neg-
ative bacteria. Health Lab. Sci. 14:83-94.
24. Taylor, R. H., M. J. Allen, and E. E. Geldreich. 1979.
Testing ofhome use carbon filters. J. Am. Water Works
26. U.S. Environmental Protection Agency. 1976. Na-
tional interim primary drhiking water regulations. Re-
port no. EPA-570/9-76-003. U.S. Environmental Pro-
tection Agency, Washington, D.C.
26. U.s. Environmental Protection Agency. 1980. Study
of home drinking water treatment units containing ac-
tivated carbon for organics reduction. Interim Phase 2
report to Criteria and Standards Division,
of Drinking Water. U.S. Environmental Protection
Agency, Washington, D.C.
27. Waflis, C., C. H. Stagg, and J. I Melnick. 1974. The
hazards of incorporating charcoal filters into domestic
water systems. Water Res. 8:111-113.
28. Whitby, J. L., and A. Rampling. 1972. Pseudomonas
aeruginoa contamination in domestic and hospital en-
vironments. Lancet i:15-17.
29. Wilson, M E., R. C. Nelson, L H. Phillips, and R. A.
Boas. 1961. A new source ofPseudomonas aerugiwnosa
in a nursery. J. Am. Med. Assoc. 175:112-114.
VOL. 41, 1981