Limnetica 39

Urban surface runoff strongly contributes to the degradation of river ecosystems. Innovative and nature-based solutions have been applied to face such environmental problems. In this regard, constructed wetlands – a low-cost green treatment technology – represent a successful example of a solution that results in social and environmental benefits. Floating constructed wetlands (FCW) is a relatively new water treatment technique that consists of emergent macrophytes planted on floating structures. The FCW has been tested for the treatment of wastewater and stormwater runoff. However, few studies assess the system’s capability over short periods of retention time and its performance under hydraulic shock-loading. This research reports the performance of FCW applied to treatment of simulated urban surface runoff. The removal efficiency of total nitrogen (TN) and total phosphorus (TP) was investigated for two macrophyte species: Typha domingensis and Schoenoplectus californicus. Total organic carbon, wet biomass, chlorophyll-a, dissolved oxygen (DO), pH, oxygen reduction potential (ORP), conductivity, temperature and turbidity were also measured. A commercial floating structure without growth medium was employed. The experiment utilized batch mesocosms, first with a seven-day retention time and second, under hydraulic shock-loading with 24, 2, and 4h retention times. Differences between treatments and controls were analysed by PERMANOVA and ANOSIM tests. The results for a seven-day batch indicated that T. domingensis was more efficient than S. californicus (removal efficiency of TP = 47%, TN = 78% and TP = 11%, TN = 30%, respectively). There was a significant difference in nutrient removal for retention times of 24h and 4h for T. domingensis. No significant nutrient removal was noticed for S. californicus when the retention time was less than seven days.