Constructed Floating Wetlands (CFW) for stormwater treatment are increasingly used to treat urban runoff. However, studies of large-scale systems and the long-term evaluation of their treatment efficiency are scarce. This article presents the final results of a two-year study of the pollutant removal performance of a CFW in a stormwater pond capturing runoff from a low-residential catchment in South-East Queensland (Australia) under subtropical conditions. Although the CFW treatment area to catchment ratio was only 0.14%, the results demonstrated a significant removal of both Total Suspended Solids (TSS) and Total Phosphorus (TP) from the stormwater inflows by the CFW. The efficiency ratios for TSS and TP were 81% and 52%, respectively. While the removal rate for total nitrogen was not significant for the CFW evaluated in this study, the ER was still 17%. However, the ERs for nitrate and nitrogen oxide were both 47%. The study results suggest that it may be possible to increase the pollution removal performance of the CFW by upsizing the system and including intermittent re-aeration zones in the surrounding stormwater pond. The results of this research study clearly demonstrate that CFW can be an effective treatment solution for the removal of pollution from urban stormwater runoff.

A main source of surface water pollution in Western Europe stems from combined sewer overflow. One of the few technologies available to reduce this pollution is the retention soil filter. In this research project, we evaluated the cleaning efficiency of retention soil filters measuring the concentration ratio of standard wastewater parameters and bacteria according to factors limiting efficiency, such as long dry phases or phases of long-lasting retention. Furthermore, we conducted an initial investigation on how well retention soil filters reduce certain micropollutants on large-scale plants. There was little precipitation during the 1-year sampling phase, which led to fewer samples than expected. Nevertheless, we could verify how efficiently retention soil filters clean total suspended solids. Our results show that retention soil filters are not only able to eliminate bacteria, but also to retain some of the micropollutants investigated here. As the filters were able to reduce diclofenac, bisphenol A and metoprolol by a median rate of almost 75%, we think that further investigations should be made into the reduction processes in the filter. At this point, a higher accuracy in the results could be achieved by conducting bench-scale experiments.