permaculture

[Victor Guest <vic@daena.eepo.com.au>]

From: kenn@bogo.co.uk

American Society for Microbiology
20-May-98

                  Wetlands Remove Pathogens from Wastewater

Mohammad Karim Shantz
#429 University of Arizona
Tucson, AZ 85721
520/621-6910

Paper Q-135, Session 203-Q

Salmonella spp. Is one of the major concerns of public health in the U.S.
because of the more than 30,000 reported cases of Salmonella poisoning each
year. Conventional wastewater treatment technologies depend on disinfection to
reduce pathogen population. In this study we examined the survival of E. coli
and Salmonella typhimurium in six different wetland systems receiving either
potable water or secondary sewage which contained different aquatic plants.
Our results suggest that the presence of aquatic plants significantly
increases die-off of both bacteria in potable water and secondary sewage,
indicating that begetative wetland could provide an alternative method for
reduction of bacterial pathogens in wastewater. The experiment was performed
by Mohammad R. Karim and Dr. Edward P. Glenn in Dr. Charles P. Gerba's
laboratory in the Department of Soil, Water and Environmental Science at the
University of Arizona, Tucson. Funding was provided by United States
Geological Survey and the results will be presented at the 98th General
Meeting of the American Society for Microbiology in Atlanta Georgia on May 20,
1998. E. coli and S. typhimurium were added at a concentration of 1,000,000
cfu/ml to six wetland systems. Four wetland systems receiving potable water
contained a combination of Cattail, Iris Lily, Taro, Duckweek and Elodea. Two
other wetland systems receiving secondary unchlorinated sewage contained Water
Hyacinth and Duckweed. Potable water and secondary sewage without the presence
of any aquatic plants were used as controls. Bacterial die-off in potable
water and secondary sewage was significantly higher when aquatic plants were
present in these systems. We examined whether any antibiotic-like substance or
inhibitory substances were released by the plants in the studied wetlands,
which could enhance bacterial die-off. No antibiotic or inhibitory substances
were found in these wetland waters. Further work on the survival of E. coli in
non-sterile, filter sterilized and autoclaved wetland water indicated that the
plausible mechanism of bacterial die-off in constructed wetlands is ! through
microbial competition or predation. Vegetative wetland is a natural system
with no added chemicals in it. These results along with the other published
literature in this area suggest that this natural system might be used for
microbial water quality improvement in the future.