The Constructed Wetlands Module, built into the HYDRUS-2D software (Langergraber and Simunek, 2005), originally used to simulate wastewater treatment in wetlands, enables simulation of biozone formation and wastewater treatment in STUs. It is a numerical model, which accounts for the main microbial processes that occur in STUs, including growth and lysis of three types of bacterial population, nutrient (N, P and C) assimilation and transformation, and respiration. Column simulations of STUs in CW2D can simulate the biofilm-like growth of microbes at the infiltrative surface. High-resolution visualization of numerical results enables to establish a connection between nutrient stress, microbial behavior and a subsequent nutrient transformation or lack of transformation in STUs, while considering environmental or soil conditions. Results from simulations have shown a relationship between extensive (biofilm-like) microbial growth at the infiltration surface and depletion of P in the underlying STU. The P depletion seems to prevent microbial activities underneath the “biofilm”, as it becomes a limiting nutrient. N concentrations in the STU exceed STE concentrations, a phenomena that has been observed in field experiments as well.
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