Dispersion in Constructed Channel Wetlands Designed to Treat Aquaculture Effluents in the Semi-Arid Environment of South Texas

Constructed wetlands have been recognized as an ecological alternative in nutrient removal and treating aquaculture effluents. In this study, residence time distribution (RTD) experiments using Rhodamine WT fluorescent dye was evaluated in order to characterize the dispersion in constructed wetland channels, two planted with native South Texas, wetland plants — black mangrove (Avicennia germinans) and Olney's bulrush (Scripus americanus) and two non-vegetated wetland channels. The residence time, τ, of the vegetated and the non-vegetated wetland and its corresponding replicate was shorter than the theoretical residence time, which suggests the presence of dead zones and increased channeling. The results indicated that the presence of the vegetation can improve the system efficiency by retarding the flow of the target compound and reducing short-circuiting. Currently studies using sodium chloride as a tracer to evaluate the RTD at different depths are in process; preliminary results show an increase in RTD with an increase in water depth.