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Study: Wetlands remove pathogens from water

Duckweed was one of the plants used in the vegetative wetland experiments at the University of Arizona  

By Environmental News Network staff

ATLANTA (CNN) -- Vegetative wetlands can serve as an alternative method for reducing bacterial pathogens such as salmonella in wastewater, according to researchers.

The research was presented Wednesday by Mohammad R. Karim at a meeting of the American Society for Microbiology in Atlanta. A vegetative wetland is a natural system with no added chemicals.

Because more than 30,000 cases of salmonella poisoning are reported each year, it is a major health concern in the United States. Conventional wastewater-treatment technologies depend on disinfection to reduce pathogen populations. The researchers believe wetlands could be an improvement over traditional methods.

Karim and colleagues who conducted the research at the University of Arizona in Tucson examined the survival of E. coli and salmonella typhimurium in six different wetland systems receiving either potable water or secondary sewage.

"Our results suggest that the presence of aquatic plants significantly increases die-off of both bacteria in potable water and secondary sewage, indicating that vegetative wetlands could provide an alternative method for reduction of bacterial pathogens in wastewater," Karim said.

The researchers added E. coli and salmonella typhimurium at a concentration of 1 million cfu/ml to each wetland system. Four wetland systems receiving potable water contained a combination of cattail, iris lily, taro, duckweed and elodea. Two other wetland systems receiving secondary unchlorinated sewage contained water hyacinth and duckweed. Potable water and secondary sewage without the presence of 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," Karim said.

No antibiotic or inhibitory substances were found in these wetland waters.

"Further work on the survival of E. coli in nonsterile, filter sterilized and autoclaved wetland water indicated that the plausible mechanism of bacterial die-off in constructed wetlands is through microbial competition or predation," Karim said.

The results of the University of Arizona research, along with other literature, show promise for improving water quality.

Copyright 1998, Environmental News Network, All Rights Reserved

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