Simplified hydraulic model of French vertical-flow constructed wetlands

Abstract

Designing vertical-flow constructed wetlands (VFCWs) to treat both rain events and dry weather flow is a complex task due to the stochastic nature of rain events. Dynamic models can help to improve design, but they usually prove difficult to handle for designers. This study focuses on the development of a simplified hydraulic model of French VFCWs using an empirical infiltration coefficient--infiltration capacity parameter (ICP). The model was fitted using 60-second-step data collected on two experimental French VFCW systems and compared with Hydrus 1D software. The model revealed a season-by-season evolution of the ICP that could be explained by the mechanical role of reeds. This simplified model makes it possible to define time-course shifts in ponding time and outlet flows. As ponding time hinders oxygen renewal, thus impacting nitrification and organic matter degradation, ponding time limits can be used to fix a reliable design when treating both dry and rain events.

Numerical modelling of constructed wetlands for wastewater treatment

“…Indeed, a general search for the words constructed wetland model on common databases of scientific papers brings a limitless number of publications on this topic. Among them, a very general distinction can be made: those focusing on the simulation of the hydraulics (Arias et al, 2014;Dittmer et al, 2005;Fan et al, 2008;Galvão et al, 2010;Korkusuz et al, 2007;Kotti et al, 2013),the hydrodynamics and clogging (or any of them individually) (Brovelli et al, 2009b;Giraldi et al, 2009Giraldi et al, , 2010Hua et al, 2013;Knowles et al, 2011;Suliman et al, 2006) and those focusing on the removal of a specific pollutant or a set of pollutants (which generally also include hydraulic and hydrodynamic models of diverse complexity). Among the latter, the most commonly targeted pollutants are organic compounds (Akratos et al, 2008;Henrichs et al, 2007;Liolios et al, 2012;Toscano et al, 2009), nitrogen (Akratos et al, 2009;Henrichs et al, 2009;Mayo and Bigambo, 2005;Mcbride and Tanner, 2000;Meyer et al, 2006;Meyer, 2011;Moutsopoulos et al, 2011;Toscano et al, 2009) sulphur (Lloyd et al, 2004), phosphorous (Hafner and Jewell, 2006), heavy metals and mine drainage (Goulet, 2001;Lee et al, 2006;Mitsch and Wise, 1998), arsenic (Llorens et al, 2013) pesticides (Krone-Davis et al, 2013) and emerging pollutants (Hijosa-Valsero et al, 2011).…”