Modeling seasonal variation in bacteriophage removal in constructed wetlands using convection–dispersion equation

When livestock manure is applied to drained cropland, viruses in the manure can quickly move through preferential flow paths to tile drains. Contaminated tile drain effluent can then contaminate surface waters. Experiments were conducted to explore the applicability of constructed wetlands in treating tile-drainage. Tub-scale, two-stage, constructed wetlands were spiked with the bacteriophage P22 and the effluent was monitored to quantify removal. The convection–dispersion equation (CDE) was used to estimate convective, dispersive, first-order removal, and retardation parameters. Results showed a mean removal coefficient of 0.065 and 0.285 per day for surface flow (SF) wetlands and 2.67 and 5.36 per day for subsurface flow (SSF) wetlands in winter and summer months, respectively. SSF wetlands were 41 times more effective in winter and 19 times more effective in summer in removing bacteriophage than were SF wetlands. There was greater removal in warm than in cold weather. The P22 bacteriophage was not suitable as a biological tracer for evaluation of the hydraulic properties of the wetlands based on the minimum first-order removal rates of 0.04 per day.