Simulating nutrient cycling and removal through treatment wetlands in arid/semiarid environments

The Constructed Wetlands Algorithm for Nutrient Transformations (CWANT) computer program was designed to mathematically simulate the fate, transformation, and transport of nutrients as they move through ammonium-rich treated secondary wastewater in constructed surface-flow wetland systems. CWANT employs empirically derived mathematical functions to represent a wetland water budget, water temperature, emergent vegetation, and algae dynamics, reactions involving important elements (N, P, CBOD5, and O), and ultimately the water quality of wetland outflow over time. Sensitivity analysis was used to calibrate model parameters. The model was verified with weekly data from the Hemet/San Jacinto Multipurpose Demonstration Wetland, owned and operated by the Eastern Municipal Water District (EMWD), in Riverside County, California, USA. Graphical illustrations showed that, on average, predicted values corresponded to seasonal trends exhibited by the measured data. Overall, the model was determined to slightly overpredict outflow concentrations for most nutrients (mean percent error (MPE) = 1.22% for organic N, 2.1% for NO3−, 8.69% for NH4+, 9.96% for CBOD, and 20.2% for total P). In its current state, CWANT serves as a screening tool to increase understanding of the nutrient transforming mechanisms dominating constructed treatment wetlands.