Verification of the implementation of CWM1 in the HYDRUS Wetland Module

Abstract

The Constructed Wetland Model N°1 (CWM1) is a numerical biokinetic model describing microbial transformation and degradation processes in subsurface flow constructed wetlands. In this master thesis the CWM1 implementation in the HYDRUS wetland module was verified using data from previously conducted controlled environment column experiments. These twenty day long batch experiments used synthetic wastewater and three different plant species (Carex rostrata Stokes, Schoenoplectus acutus Muhl. Ex Bigelow and Typha latifolia L.) in addition to unplanted replicates at four different temperatures. The minimum number of adjusted parameters between the sixteen simulated columns was targeted, and it was found that: (1) initial bacterium concentrations, (2) initial adsorbed ammonia nitrogen concentrations, and (3) root oxygen loss rate for each simulation inevitably needed to be set separately. For all other parameters the same values have been used. Some biokinetic parameters had to be adapted during calibration to match measured data. This was required to allow anaerobic, anoxic and aerobic processes to run parallel and explained by the local effect of root zone re-aeration. The simulation results were evaluated by conventional visual and numerical and a new goodness of fit analysis method, deflection analysis. The new method was introduced to compare simulations to measured data with standard deviation. Simulated contaminant concentrations had a very good fit to measured values of NH₄-N and SO₄-S and a reasonable good fit to measured values of COD versus time.