Constructed Floating Wetlands: A review of research, design, operation and management aspects, and data meta-analysis

Abstract

This paper summarizes the state-of-the-art on Constructed Floating Wetlands (CFWs). An attempt has been made here to collect and organize current literature and provide an insight to most topics of the ongoing scientific conversation on CFWs. Several issues are discussed such as applications, construction materials, vegetation species, mechanisms for pollutant removal and management strategies. Raw data were extracted from studies and were imposed to statistical analysis in order to reveal correlations (Spearman’s r coefficient) between total nitrogen (TN), total phosphorus (TP) and ammonium nitrogen (NH4+-N) concentration reduction and several operational or design parameters, e.g., vegetation aerial coverage, water depth, initial loading, Hydraulic Loading Rate (HLR) and Hydraulic Retention Time (HRT). TN concentration reduction correlated well with initial loading (r=0.841; p=0.000; n=28) and showed a lower correlation with HRT (r=0.443; p=0.013; n=28), and negative correlations with depth (r=−0.690; p=0.000; n=28) and HLR (r=−0.528; p=0.002; n=28). NH4+-N and TP concentration reductions correlated positively with initial loading (r=0.869; p=0.000; n=19 and r=0.840; p=0.000; n=21), and negatively with depth (r=−0.812; p=0.000; n=19 and r=−0.773; p=0.000; n=21) and HLR (r=−0.608; p=0.02; n=19; and r=−0.558; p=0.06; n=21). As the depth factor relates to the percent of root coverage in the water column, the aforementioned negative correlation for TP, TN and NH4+-N with depth could be interpreted as the rhizosphere effect. Multi-linear regression analysis was carried out for TN and TP removal, in an attempt to describe quantitatively TN and TP concentration reduction as function of design and operation parameters. CFWs seem to be an efficient technique for both wastewater treatment and natural water purification; however, further research is needed in order to better interpret system’s behavior and optimize its efficiency.