Occurrence of Pathogenic Free-Living Amoebae and Bacterial Indicators in a Constructed Wetland Treating Domestic Wastewater from a Single Household

Abstract

Constructed wetlands are effective wastewater treatment systems because of their ability to remove large amounts of organic matter and pathogens. The goals of this study were to characterize the presence of pathogenic free-living amoebae and bacterial indicators (total and fecal coliforms), and to ascertain the removal efficiencies of physical and chemical pollutants, in a constructed wetland treating domestic wastewater from a single household. Influent and effluent samples were collected monthly over a ten-month period for biological, physical and chemical analyses. Thirty-two species of free-living amoebae were isolated from the system. The genus Acanthamoeba was the most frequently encountered (59 %) and was removed from the wastewater with the greatest efficiency (80 %). Removal of bacteria was low, the highest removal rates were found in August (4 logarithmic units) and January (3 logarithmic units). The average removal efficiencies of suspended solids, BOD5 and ammoniacal nitrogen were 71.5 %, 50.6 % and 13.1 %, respectively. The relatively low removal efficiencies of the various bacteriological, physical and chemical parameters suggest that the hydraulic retention time was probably insufficient for optimal treatment to occur. The effluent quality was unacceptable for unrestricted irrigation of crops that are eaten uncooked.