Removal of viruses and pollution indicators in constructed wetlands

Abstract

Tracer studies using Br⁻ and bacteriophage PRD1 in both surface and subsurface flow constructed wetlands were conducted to analyze their hydrodynamic behavior and efficiencies in removing viruses from wastewater. A survival test in situ was also conducted to analyze the persistency of PRD1 in wetland environments. Concurrently, a sampling program for microbial and chemical indicators in the surface flow wetland for a period of 16 months was conducted. The tracer studies revealed a reduction of 99 and 84 percent in the subsurface and surface flow wetland, respectively. Bromide recovery at the outlet of both wetland systems was about 75 percent. The Convective-Dispersion Equation was able to predict the observed PRD1 and Br⁻ breakthrough curves obtained during the tracer study in the surface flow wetland. The monitoring program of pollution indicators showed that biochemical oxygen demand and total suspended solids can be reduced efficiently, reaching the tertiary effluent standard of 10 mg L⁻¹ required by The Arizona Department of Environmental Quality. This sampling program suggested that coliphages may be a better indicator of fecal contamination than total and fecal coliforms in surface flow wetlands.