Force of the American Society of Civil Engineers and
are likely to survive this treatment. Future study should
the Water Environment Federation (1991) state that in
utilize methods that allow for enumeration of injured cells,
the future, regulators may move toward use of other
especially when working with indicator microorganisms.
organisms as monitoring indicators. Ray (1989) noted
that the ability of some pathogens (Yersinia
LITERATURE CITED
enterocolitica, Listeria monocytogenes, and Aeromonas
hydrophilia) to grow at refrigeration temperature and
the susceptibility of fecal coliforms and E. coli to low
American Public Health Association, American
temperature should be considered in determining their
Water Works Association, and the Water Environ-
suitability as indicator bacteria.
ment Federation (1992) Standard Methods for the
There also is evidence that the standard enumera-
Examination of Water and Wastewater, Nineteenth Edi-
tion method used for total coliforms, fecal coliforms,
tion. Washington, D.C.: American Public Health Asso-
and fecal streptococci may result in erroneously low
ciation.
numbers because of the increased sensitivity of these
Brock, T.D. (1970) Biology of Microorganisms.
bacteria when injured to many of the same compounds
Englewood Cliffs, New Jersey: Prentice-Hall.
that are used in the selective media for their determina-
Colbeck, S.C. (1981) A simulation of the enrichment
tion (Ray 1989). Thus, any future determination of the
of atmospheric pollutants in snow cover runoff. Water
effectiveness of this type of treatment process should
Resources Research, 17: 13831388.
utilize microbiological methods designed to recover
Joint Task Force of the American Society of Civil
stressed organisms.
Engineers and the Water Environment Federation
(1991) Design of Municipal Wastewater Treatment
Plants. Volume II, Chapters 1320. Water Environment
CONCLUSIONS
Federation, Alexandria, Virginia, and the American
Society of Civil Engineers, New York.
The purpose of this research was to examine the
Kraft, A.A. (1992) Psychrotrophic Bacteria in Foods:
impact of the Snowfluent process on bacterial survival.
Disease and Spoilage. Boca Raton, Florida: CRC Press,
Our literature review found that chilling, freezing, fro-
Inc.
zen storage, and warming all have a negative impact
Mackey, B.M. (1984) Lethal and sublethal effects of
on bacteria, but that some species are much more seri-
refrigeration, freezing and freeze-drying on microor-
ously affected than others. Substrate, freezing and thaw-
ganisms. In The Revival of Injured Microbes (M.H.E.
ing rates, holding times, and bacterial age also greatly
Andrew and A.D. Russell, Ed.). Orlando, Florida: Aca-
affect survival.
demic Press, p. 4575.
Our experimental studies specifically examined
MacLeod, R.A., and P.H. Calcott (1976) Cold shock
whether bacteria would survive snowmaking and the
and freezing damage to microbes. In The Survival of
freezethaw processes that occur in snow during win-
Vegetative Microbes, T.R.G. Gray and J.R. Postgate
ter and the spring melt. We found that bacteria, which
(Ed.). Twenty-Sixth Symposium of the Society for
are capable of growing at the temperature of the hu-
General Microbiology. Cambridge, England: Cam-
man body and thus could be pathogens, survived the
bridge University Press, p. 81109.
snowmaking process. Gram-negative coliforms were
Mazur, P. (1966) Physical and chemical basis of in-
the most negatively affected by this process, with losses
jury in single-celled microorganisms subjected to freez-
of two and three orders of magnitude for fecal coliforms
ing and thawing. In Cryobiology (H.T. Merman, Ed.).
and total coliforms, respectively. Fecal streptococci
New York: Academic Press, p. 214315.
were less adversely affected, with a loss of less than
McCarron, J.E. (1965) Survival and distribution of
one order of magnitude (72%). Both gram-positive and
mesophilic bacteria in ice. M.S. thesis, Colorado State
gram-negative bacteria survived the multiple freeze
University, Fort Collins, Colorado.
thaw cycles in the snow columns and replicated during
Ontario Ministry of Environment (1982) Storage and
the melting process.
renovation of sewage effluent by conversion to snow.
Given these findings, those of Sanin et al. (1994)
Interim report, Technical Support Section.
for other types of microorganisms in frozen sludge, and
Rabinowitz, B., T.D. Vassos, W.F. Hyslop, R. Zapf-
those of Ridgway (1984) for other water treatment pro-
Gilje, and D.S. Mavinic (1988) Secondary effluent
cesses, it is possible that helminth eggs and viruses could
disposal through snowmaking. In Proceedings, Joint
also survive this treatment. Clearly, additional study is
CSCE-ASCE National Conference on Environmental
needed on the effect of this treatment process on other
Engineering. Montreal: Canadian Society of Civil En-
types of pathogens and what species or types of bacteria
gineering, p. 736744.
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