Losses in the fluorescent tracer used in hydrodynamic modeling of constructed wetlands studied by laser induced fluorescence

Fluorescent tracer trials are performed to obtain useful information for hydrodynamic modeling. Particularly they have been used in constructed wetlands, aimed for residual water treatment, in order to find residence time distribution for particles entering the system and, in general, to know the flux pattern. Nevertheless, it has been reported that some tracers, as Rhodamine WT, exhibit adsorption phenomena over the substrate. This situation has to be considered in the analysis of residence time distribution curves, taking into account advection-dispersion processes which are given by the diffusion modified equation. Laser Induced Fluorescence (LIF) with a Nd:YAG laser (532 nm; 35mW), was used to determine Rhodamine WT accumulated concentration. Through adsorption coefficients obtained experimentally, an advection - dispersion model for solute transport in a subsurface flow constructed wetland was evaluated. Including this phenomenon allows to optimize the model, and another important condition is added in the behavior prediction of these complex ecosystems.