Removal of pathogenic and indicator microorganisms by a constructed wetland receiving untreated domestic wastewater

Wetlands containing floating, emergent and submergent aquatic plants, and o ther water-tolerant species have been found to economically provide a mecha nism of enhancing the quality of domestic wastewater. The use of constructe d wetlands for the removal of indicator bacteria (total and fecal coliforms ), coliphages, protozoan parasites (Giardia and Cryptosporidium) and enteri c viruses was investigated. A pilot scale constructed wetland consisting of two cells, one planted with bulrush and the other unplanted bare sand, wer e used to compare their efficiency in removing pathogens from raw sewage. O verall more than 90 percent of all microorganisms studied were removed by e ither of the two systems with a 1 to 2 day retention time. Removal of all m entioned microorganisms was greater from the surface flow in the unplanted cell than in the planted cell, except for Giardia and Cryptosporidium, alth ough the differences were not statistically significant. Enteric viruses, c oliphages and indicator bacteria were found to penetrate 2 in below the sur face, although concentrations were reduced by greater than 99 percent in bo th cells. Less virus penetration into the sand occurred in the planted wetl and versus the unplanted wetland. Water temperature was found to be the mos t important factor in the removal of enteric bacteria and viruses, while tu rbidity reduction was related to Giardia removal. These results demonstrate that significant reductions of pathogenic microorganisms can occur in cons tructed wetlands receiving untreated domestic wastewater with only a 1-2 da y retention time.