Microbial indicator removal in onsite constructed wetlands for wastewater treatment in the southeastern U.S.

Abstract

Seven onsite constructed wetlands for wastewater treatment in the coastal plains of Alabama and North Carolina were studied from September 1997 to July 1998. Each site was examined for its ability to remove a range of fecal contamination indicators from settled wastewater. Indicator organisms include total and fecal coliforms, enterococci, Clostridium perfringens, and somatic and male-specific (F+) coliphages. Four identical domestic wastewater treatment sites in Alabama were evaluated. In these sites the Log10 geometric mean reductions ranged between 0.5 and 2.6 for total and fecal coliforms, 0.1 and 1.5 for enterococci, 1.2 to 2.7 for C. perfringens, -0.3 and 1.2 for somatic coliphages, and -0.2 and 2.2 for F+ coliphages. Three unique designs were examined in North Carolina. Log10 geometric mean reductions ranged between 0.8 to 4.2 for total and fecal coliforms, 0.3 to 2.9 for enterococci, 1.6 to 2.9 for C. perfringens, -0.2 and 2.8 for somatic coliphages, and -0.1 and 1.5 for F+ coliphages. Somatic and F+ coliphage detection was highly variable from month to month.