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 was evaluated. 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 in-/outlet configurations. The aim is 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, demonstrated 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.

Mean residence time of lagoons in shallow vegetated floodplains

“…Therefore, the model here can be used to calculate the mean residence times, which results in 16.52 h and 39.96 h for the Control and Baffled lagoons, respectively. Ioannidou and Pearson (2018), however, calculated the experimental mean residence times of these lagoons were 16.7 h and 52.7 h, respectively, which are 1.01 and 1.32 times greater than that predicted by the model described herein. The discrepancy between the calculated and the experimental mean residence times might be due to the potential presence of dead zones in the experimental lagoon system caused by the presence of secondary eddies, which could further increase the residence times in the whole lagoon system.…”

“…The secondary vortex is reported to increase the residence time of the flow within the deep zone (Jackson et al, 2013). Although shallow operational depths in CW lead to a flow‐through regime, deep operational depths result in dissipated flow detention or ponding velocities (Ioannidou & Pearson, 2018). Consequently, it is worthwhile determining lagoon residence time in terms of flow velocity, as well as the lagoon length to depth ratio at the interface.…”

Seasonal Considerations for Year-Round Operation of On-Farm Wetlands in Temperate Climates: A Review

“…Due to these results, wetlands in Spain were designed with a lower depth, and these systems were shown to have a higher removal efficiency than conventional SSF CWs (Garfi et al, 2012). In SF CWs improved efficiency was seen in wider wetlands compared to deeper wetlands (Ioannidou & Pearson, 2018).…”

Removal of Emerging Pollutants in Horizontal Subsurface Flow and Vertical Flow Pilot-Scale Constructed Wetlands

“…Nowadays, constructed wetlands (CWs) provide a very popular and attractive alternative solution to the wastewater treatment technology, since the construction, operation and maintenance costs are very low [37][38][39][40]. CWs are used in treating various wastewaters, such as municipal [41][42][43][44], agricultural [45,46] and industrial wastewaters [47]. Over the last two decades, CWs have been used in the removal of several EPs [48][49][50].…”