The verification of the Constructed Wetland Model No. 1 implementation in HYDRUS using column experiment data

The Constructed Wetland Model No. 1 (CWM1) is a biokinetic model describing microbial dynamics and transformation and degradation processes in subsurface flow constructed wetlands. The implementation of CWM1 in the HYDRUS program package (©PC Progress s.r.o.) was verified using data from controlled environment column experiments. These 20-day long batch experiments used synthetic wastewater and were run at different temperatures. Columns were either planted with Carex rostrata Stokes, Schoenoplectus acutus Muhl. Ex Bigelow and with Typha latifolia L. or without plants. The minimal adjustment of model parameters between the sixteen setups was targeted and (1) initial bacteria concentrations, (2) initial adsorbed ammonium nitrogen concentrations, and (3) root oxygen loss rates inevitably needed to be set for each columns separately. For all other parameters - including the CWM1 model parameters - identical values have been used. Some biokinetic parameters had to be iteratively adjusted during calibration to allow anaerobic, anoxic and aerobic processes to occur in parallel in order to match measured data. This can be justified by the local effect of root zone re-aeration. The simulation results were evaluated by a new goodness of fit analysis method, deflection analysis. Overall, simulated contaminant concentrations had a very good fit to measured NH4-N and SO4-S concentrations, and a good fit to measured COD concentrations.