A study was conducted to examine the role of aquatic plants used in constructed wetlands on the survival of enteric bacteria and viruses. Four small-scale wetland systems, receiving fresh water and two other wetland systems, receiving secondary unchlorinated sewage were used in this study. Fresh water and secondary sewage without the presence of any aquatic plants were used as controls. Escherichia coli, Salmonella typhimurium, bacteriophage MS-2 and poliovirus were added to the waters collected from the wetlands and controls. The presence of aquatic plants significantly increased the die-off of both bacteria in fresh water and secondary sewage. No significant difference in the die-off of E. coli and S. typhimurium was observed in water from wetlands with different types of plants in freshwater. However, there was a significant difference in the die-off of E. coli in water with aquatic plants when sewage was used. The presence of the plants significantly increased the inactivation of MS-2 and poliovirus. Additional work on the survival of E. coli indicated that the plausible mechanism of bacterial die-off in constructed wetlands is through increased microbial competition or predation.

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