Microbial indicator removal in onsite constructed wetlands for wastewater treatment in the southeastern U.S. E.C. Barrett*, M.D. Sobsey**, C.H. House*** and K.D. White**** * 1308 Aggie Lane, Austin, TX 78757, USA (Research performed at University of North Carolina at Chapel Hill) (Email: ebarrett@texas.net) ** University of North Carolina at Chapel Hill, Department of Environmental Science and Engineering, Chapel Hill, NC 27599-7400, USA *** NC State, Department of Forestry, Raleigh, NC 27695-8008, USA **** University of South Alabama, Department of Civil Engineering, Mobile, AL 36688, USA 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 Log 10 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. Log 10 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. Keywords C. perfringens; coliforms; coliphages; constructed wetlands; enterococci; wastewater Introduction In the U.S. today, 75 to 90 million people are not serviced by municipal sewage treatment systems (Moeller, 1997). These individuals must use onsite wastewater treatment to con- trol nutrient and pathogen contamination of groundwater and surface water. Usually the onsite treatment of choice is a septic tank with a drain field; however, this technology is not appropriate for certain soils and in regions with a high water table. In fact, one quarter of soils in the U.S. are not suitable for drain field use (U.S. EPA, 1980). One inexpensive and attractive alternative to septic systems is the constructed wetland. A broad range of designs for these systems have been studied for removal of indicator bacteria, especially total and fecal coliforms, which are usually reduced by at least 1 log (Kadlec and Knight, 1996). Viral indicator organisms like bacteriophages have been shown to be removed by as much as 34% to 99.9% (Gersberg et al., 1989; Karpiscak et al., 1996). Protozoan organisms like Giardia lamblia have been shown to be removed by as much as 99.9% (Quiñónez et al., 1997). However, there is little research to profile the treatment of constructed wetland onsite wastewater treatment in “real-life” nonmunicipal field situations. In this study, seven constructed wetlands were studied for their ability to remove four bacterial indicator species and two viral indicator species, including total and fecal coliforms, enterococci, C. perfringens, and somatic and male-specific (F+) coliphages. Total and fecal coliforms are the indicator organisms typically used by regulators to assess water quality. They have come under increasing criticism because it is widely accepted that protozoan cysts and viruses are hardier in treatment processes than these Water Science and Technology Vol 44 No 11–12 pp 177–182 © 2001 IWA Publishing and the authors 177 Downloaded from http://iwaponline.com/wst/article-pdf/44/11-12/177/424375/177.pdf by guest