Hydraulic and Design Parameters in Full-Scale Constructed Wetlands and Treatment Units: Six Case Studies

Abstract

The efficiency of pond and constructed wetland (CW) treatment systems is influenced by the internal hydrodynamics and mixing interactions between water and aquatic vegetation. In order to contribute to current knowledge of how emergent real vegetation affects solute mixing, and on what the shape and size effects are on the mixing characteristics, an understanding and quantification of those physical processes and interactions were made. This paper presents results from tracer tests conducted during 2015–2016 in six full-scale systems in the UK under different flow regimes, operational depths, shapes and sizes, and inlet/outlet configurations. The aim was to quantify the hydraulic performance and mixing characteristics of the treatment units, and to investigate the effect of size and shape on the mixing processes. Relative comparison of outlet configuration, inflow conditions, and internal features between the six different treatment units showed variations in residence times of up to a factor of 3. A key outcome of this study was that the width is a more important dimension for the efficiency of the unit compared to the depth. Results underlined the importance of investigating hydrodynamics and physics of flow in full-size units to enhance treatment efficiency and predictions of water quality models.