Green Roofs for domestic wastewater treatment: Experimental and numerical analysis of nitrogen turnover

The use of Green Roofs (GRs) for domestic wastewater treatment and nitrogen (N) removal is an appealing opportunity to conjugate hydrological, energetic, and water quality benefits. However, the research in this direction has been limited to few experimental studies, while the role of numerical modeling for analysis and design has been overlooked. To advance understating of reactive transport processes in GRs and investigate the use of numerical models, this study presents a comprehensive experimental and numerical investigation of the N turnover in vegetated and non-vegetated GRs exposed to domestic wastewater injection. A Bayesian framework is used to calibrate a mechanistic numerical model against multiple observations from a controlled laboratory experiment. A Global Sensitivity Analysis complements the framework to further enlighten the role of multiple physical processes. Results indicate that GRs have high nitrification capacity, which increases after wastewater application. The total leached N is 94% of the total injected N in a non-vegetated GR, compared to 67% for a vegetated GR. Nitrate leaching is negatively correlated with the root solute uptake capacity of the vegetation, which may reach up to 32% of the total injected N. Maximization of this factor is desirable and can be achieved by selecting appropriate plant species and reducing water stress periods using a proper irrigation schedule.