Two constructed wetlands systems developed for reuse of nitrate-contaminated water in western Phoenix, AZ were analyzed for removal efficacy in this study. Field rates were obtained from the Wetlands of Avondale under variable flow (0–18 mgd) and temperature (13–32°C)
conditions. Laboratory batch tests were also performed using wetland sediment and water from both the Avondale and Tres Rios Wetlands under non-mass transfer limited conditions. Batch tests containing wetland water only demonstrated zero biological denitrification activity, and subsequent
denitrification activity was linked to sediment in the vegetative islands. Per vegetative-island area rates were compared and field rates (0.7–2.6 kg N/acre*day) were approximately an order of magnitude lower than non-mass transfer limited laboratory rates (13.0–20.6 kg
N/acre*day). Removal rates in both the laboratory and the field displayed zero-order kinetics and were similar under varied flow conditions. Temperature increases of approximately 15° C enhanced field rates about 3-fold, however. Turbulent diffusion, or dispersion, in the field
appeared to dominate mass transfer as denitrification rates in the field were comparable under different flow regimes at similar temperatures. Increases in denitrification rates with temperature in the field were comparable to the predicted effect of increased microbial kinetic reaction rates.
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