ABSTRACT
The Convection Dispersion Equation (CDE) was used to calculate PRD1 and Br(-) transport parameters in a subsurface flow constructed wetland. Transport parameters from Br(-) displacement were applied into the CDE to estimate a 0.96 day(-1) first order decay coefficient (k). The PRD1 breakthrough curves were also simulated to obtain effective cross-sectional area (Ac), longitudinal dispersion coefficient (D), convective velocity (v), and k. There was practically no difference between Ac and D for both tracers. However, the estimated convective velocity was higher for PRD1 than for Br(-). Further simulations were conducted by taking experimental concentrations from prior research on surface and subsurface flow constructed wetlands. Dispersion number (d) was estimated to be between 0.17 and 0.029 by using PRD1 and Br(-) transport parameters. These parameters were also used to calculate wetland dimensionless removal (K). An analytical solution for the zero moment of the observed breakthrough curves was applied to estimate PRD1 fraction recoveries in the wetland by using d and K. The results of the present study suggest that this analytical solution may be an alternative design tool for pathogen removal estimation in subsurface flow constructed wetlands.
Subject(s)
Coliphages/isolation & purification , Water Pollutants/isolation & purification , Water Purification/methods , Computer Simulation , Models, Theoretical , Water Movements , Water Purification/instrumentation , WetlandsABSTRACT
A tracer study was conducted in a 3-ha surface flow constructed wetland to analyze transport performance of PRD1, an enteric virus model. The convection-dispersion equation (CDE), including a first-order reaction model, adequately simulated transport performance of PRD1 in the wetland under an average hydraulic loading rate of 82 mm/d. Convective velocity (v) and longitudinal dispersion coefficient (D) were estimated by modeling a conservative tracer (bromide) pulse through the wetland. Both PRD1 and bromide were simultaneously added to the entering secondary treated wastewater effluent. The mass of bromide and PRD1 recovered was 76 and 16%, respectively. The PRD1 decay rate was calculated to be 0.3/day. The findings of this study suggest that the CDE model and analytical moment equations represent a suitable option to characterize virus transport performance in surface flow constructed wetlands.
