The persistence and removal of enteric pathogens in constructed wetlands

Sedimentation is thought to be one of the mechanisms of microbial reduction from wetlands used for wastewater treatment. This study compared the occurrence and survival of enteric indicator microorganisms and pathogens in the water column and sediments of two constructed surface flow wetlands in Arizona. On a volume/wet weight basis the concentration of fecal coliforms and coliphage in the water column and sediment was similar. However, on a volume/dry weight basis the numbers were one to two orders of magnitude higher in the sediment. Giardia cyst and Cryptosporidium oocyst concentrations were one to three orders of magnitude greater in the sediment compared to the water column. The die-off rates of all the bacteria and coliphage were greater in the water column than the sediment. The die-off rates of fecal coliforms in the water and sediment were 0.256 log10 day−1 and 0.151 log10 day−1, respectively. The die-off rates of Salmonella typhimurium in the water and sediment were 0.345 log10 day−1 and 0.312 log10 day−1, respectively. The die-off rates of naturally occurring coliphage in water column and sediment were 0.397 log10 day−1 and 0.107 log10 day−1, respectively, and the die-off rates of and PRD-1 in water and sediment were 0.198 log10 day−1 and 0.054 log10 day−1, respectively. In contrast Giardia die-off in the sediment was greater compared to the water column. The die-off rates of Giardia in water and sediment were 0.029 log10 day−1 and 0.37 log10 day−1, respectively. Coliphage survived the longest of any group of organisms in the sediment and the least in the water column. In contrast Giardia survived best in the water column and least in the sediment.