Hydraulic performance of a modified constructed wetland system through a CFD-based approach

Low-cost household technologies, as horizontal subsurface flow constructed wetlands, are important to address water and sanitation needs in the Asia-Pacific region in a more integrated and sustainable manner, and a better understanding of these technologies would benefit their engineering design. Computational Fluid Dynamics (CFD) simulations of a modified constructed wetland system (EvaTAC) were undertaken to determine empirical effects of geometric and flow parameters on the hydraulic performance and the effluent pollutant fraction. The CFD model was validated by comparing the computed residence time distribution (RTD) with experimental results. RTD functions were then used to quantify hydraulic indexes: short-circuiting, mixing, and moment. The EvaTAC is composed of an evapotranspiration and treatment chamber (CEvaT) and a horizontal subsurface flow constructed wetland (HSSF-CW). For the CEvaT, length and the interaction between length and flow rate were the most important factors for the hydraulic efficiency. For the effluent pollutant fraction, the most important factor was flow rate. For the HSSF-CW, the strongest influence on the hydraulic efficiency was the length. Baffles and the interaction between length and baffles also had significant statistical influence on the hydraulic efficiency. Furthermore, the results showed that flow rate, length, and the interaction between flow rate and length influenced the effluent pollutant fraction significantly. Finally, a poor correlation between hydraulic indexes and effluent pollutant fraction was obtained, indicating that the hydraulic indexes are not good predictors of the effluent pollutant fraction. (C) 2016 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. Published by Elsevier B.V. All rights reserved.