Pathogen removal from wastewater by a duckweed pond

Abstract

Duckweed plants (Lemna spp) are increasingly being used to improve the quality of wastewater in many parts of the world. We investigated a duckweed (Lemna gibba L.)-covered pond for its ability to remove Gicrdiq Oyptosporidiurn, enteroviruses, coliphages, and enteric indicator bacteria from unchlorinated secondary effluent. Giardia cysts and Oyptosporidium oocysts were reduced by 98 and 89 percent, respectively; total coliforms by 61 percent; fecal colifoims by 62 percent; and bacteriophages by 40 percent. The results indicate that the larger organisms (parasites) settled to the bottom of the pond, while the removal of bacteriophages by the pond was not as effective. There was a significant correlation between the removal of Giardia cysts and Oyptosporidium oocysts by the pond (p <0.001). Influent turbidity and parasite removal were also significantly correlated (Oyptosporidium and turbidity, p 0.05; and for Giardia and turbidity, p 0.01). However, there appeared to be no correlation between the removal of these parasites and effluent turbidity.