The aim of this study is the numerical simulation of the nitrogen abatement observed in an experimental installation of twelve mesocosms prepared with gravel, planted with different macrophytes (Carex elata, Juncus effusus, Phragmites australis, Phalaris arundinacea, Typha latifolia, beyond unplanted control tanks) and fed once a week with a water solution of only ammonia and nitrate nitrogen. The mathematical model adopted to simulate the behaviour of the constructed wetland pilot installation is a dynamic multi-component reactive transport model for variably saturated conditions (named FITOVERT) developed by our workgroup. The peculiarity of the experimental conditions made the simulation a severe test for the mathematical model: in fact the model was developed to simulate the standard operation of vertical subsurface flow constructed wetlands, while the test was conducted without any external provision of carbon substrate, with complete lack of soil in the support media, and without any continuous feed flux to the mesocosms. Despite the unusual experimental conditions, the model ended up to obtain accurate simulations of the observed data. The best simulation of the observed nitrogen removal was obtained by the lone nitrification and denitrification processes, driven by the alternated aerobic-anoxic phases deriving from the weekly filling-emptying cycles acted in the mesocosms. Since no carbonaceous substrate was provided in the experiment, the carbon source required for denitrification was provided by the plants, and was the main cause of the different removal performances observed in the different mesocosms. The results of the calibrated simulations allowed us to estimate different endogenous carbon provision for the different plants. The observed evapotranspiration was simulated as well, and was demonstrated to be another cause of the different behaviour of the mesocosms planted with different macrophyte species.
Modelling assessment of carbon supply by different macrophytes for nitrogen removal in pilot vegetated mesocosms
BORIN, MAURIZIO
2011
Abstract
The aim of this study is the numerical simulation of the nitrogen abatement observed in an experimental installation of twelve mesocosms prepared with gravel, planted with different macrophytes (Carex elata, Juncus effusus, Phragmites australis, Phalaris arundinacea, Typha latifolia, beyond unplanted control tanks) and fed once a week with a water solution of only ammonia and nitrate nitrogen. The mathematical model adopted to simulate the behaviour of the constructed wetland pilot installation is a dynamic multi-component reactive transport model for variably saturated conditions (named FITOVERT) developed by our workgroup. The peculiarity of the experimental conditions made the simulation a severe test for the mathematical model: in fact the model was developed to simulate the standard operation of vertical subsurface flow constructed wetlands, while the test was conducted without any external provision of carbon substrate, with complete lack of soil in the support media, and without any continuous feed flux to the mesocosms. Despite the unusual experimental conditions, the model ended up to obtain accurate simulations of the observed data. The best simulation of the observed nitrogen removal was obtained by the lone nitrification and denitrification processes, driven by the alternated aerobic-anoxic phases deriving from the weekly filling-emptying cycles acted in the mesocosms. Since no carbonaceous substrate was provided in the experiment, the carbon source required for denitrification was provided by the plants, and was the main cause of the different removal performances observed in the different mesocosms. The results of the calibrated simulations allowed us to estimate different endogenous carbon provision for the different plants. The observed evapotranspiration was simulated as well, and was demonstrated to be another cause of the different behaviour of the mesocosms planted with different macrophyte species.
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