Chemical Engineering Journal 308 (2017) 1120–1132 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Review Constructed Floating Wetlands: A review of research, design, operation and management aspects, and data meta-analysis ⇑ Natalia Pavlineri a,b, Nikolaos Th. Skoulikidis a, Vassilios A. Tsihrintzis b, a Institute of Inland Waters, Hellenic Centre for Marine Research, Greece b Centre for the Assessment of Natural Hazards and Proactive Planning & Laboratory of Reclamation Works and Water Resources Management, Department of Infrastructure and Rural Development, School of Rural and Surveying Engineering, National Technical University of Athens, Zografou 157 80, Athens, Greece highlights graphical abstract Constructed Floating Wetlands. Water and wastewater treatment. Review of research, design, operation and management. article info abstract Article history: This paper summarizes the state-of-the-art on Constructed Floating Wetlands (CFWs). An attempt has Received 26 July 2016 been made here to collect and organize current literature and provide an insight to most topics of the Received in revised form 27 September ongoing scientific conversation on CFWs. Several issues are discussed such as applications, construction 2016 materials, vegetation species, mechanisms for pollutant removal and management strategies. Raw data Accepted 28 September 2016 were extracted from studies and were imposed to statistical analysis in order to reveal correlations Available online 30 September 2016 (Spearman’s r coefficient) between total nitrogen (TN), total phosphorus (TP) and ammonium nitrogen (NH+-N) concentration reduction and several operational or design parameters, e.g., vegetation aerial Keywords: 4 coverage, water depth, initial loading, Hydraulic Loading Rate (HLR) and Hydraulic Retention Time Constructed Floating Wetlands Natural water/wastewater treatment (HRT). TN concentration reduction correlated well with initial loading (r = 0.841; p = 0.000; n = 28) and Total nitrogen removal showed a lower correlation with HRT (r = 0.443; p = 0.013; n = 28), and negative correlations with depth + Total phosphorus removal (r = À0.690; p = 0.000; n = 28) and HLR (r = À0.528; 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 = À0.812; p = 0.000; n = 19 and r = À0.773; p = 0.000; n = 21) and HLR (r = À0.608; p = 0.02; n = 19; and r = À0.558; 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. Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail addresses: [email protected] (N. Pavlineri), [email protected] (N.Th. Skoulikidis), [email protected], [email protected] (V.A. Tsihrintzis). http://dx.doi.org/10.1016/j.cej.2016.09.140 1385-8947/Ó 2016 Elsevier B.V. All rights reserved. N. Pavlineri et al. / Chemical Engineering Journal 308 (2017) 1120–1132 1121 Contents 1. Introduction . ..................................................................................................... 1121 2. Materials and methods . .................................................................................. 1121 2.1. Dataset formation . ........................................................................................ 1121 2.2. Statistical analyses . ........................................................................................ 1123 3. Results and discussion . .................................................................................. 1124 3.1. Applications and design parameters of CFWs ........................................................................ 1124 3.1.1. Applications . ............................................................................. 1124 3.1.2. Design parameters . ............................................................................. 1125 3.2. Pollutant removal . ........................................................................................ 1126 3.2.1. Mechanisms for pollutant removal . .......................................................... 1126 3.2.2. Removal efficiency . ............................................................................. 1127 3.3. Phyto-uptake contribution to overall removal . ..................................................... 1128 3.4. Management strategies. ........................................................................................ 1129 4. Summary and conclusions . .................................................................................. 1130 Appendix A. Supplementary data . .................................................................................. 1131 References . ..................................................................................................... 1131 1. Introduction This paper discusses field and pilot scale applications, as well as laboratory experiments on CFWs, and aims to provide a state-of- Natural floating wetlands occur around the word [1]. Con- the-art overview regarding their technical design characteristics structed Floating Wetlands (CFWs), also called ‘planted floating and their nutrient removal efficiency. The particular objectives system beds’, ‘artificial or vegetated floating islands’ or ‘ecological were to: (1) summarize current research outcomes; (2) discuss in floating beds’, are variants of Constructed Wetlands. Yeh et al. [2] depth and enlighten the vegetation contribution to nutrient summarized the CFW concept and structure, focusing on various removal; and (3) evaluate the various design and operation param- CFW applications, and used the term artificial floating islands eters contributing to nutrient removal rates. Furthermore, a nov- (AFI). Chen et al. [3] comparatively assessed the advantages and elty in this review regarding CFWs is the provision of: (1) disadvantages of CFWs, free-floating wetlands and soil based wet- numerical results regarding CFWs efficiency; (2) correlations lands, and adopted the terminology hydroponic root mats (HRMs). between removal reduction and design aspects; (3) discussion Headley and Tanner [4] discussed the application of CFWs for regarding phyto-uptake contribution in overall removal; and (4) stormwater treatment, and used the term Floating Emergent discussion regarding harvesting and management strategies. Macrophyte Wetlands (FTWs). Moreover, Fonder and Headley [5], in an attempt to describe and categorize this technology, used 2. Materials and methods the technical term ‘Floating Emergent Macrophyte Treatment Wet- lands’ (FEMTWs). In our review, we adopt the term ‘Constructed 2.1. Dataset formation Floating Wetlands’, since it is most widely used in the literature. CFWs consist of emergent vegetation established upon a buoy- A comprehensive literature search was conducted in order to ant infrastructure, floating on surface waters. The upper parts of collect studies regarding CFWs (Table 1). Google Scholar and Sco- the vegetation grow and remain primarily above the water lever, pus were the search engines used for collecting these studies. while the roots extend down in the water column, developing an The main keywords used were: Constructed Floating Wetlands, extensive beneath water-level root system. Thus, the vegetation floating islands, planted platforms and floated treatment wetlands. grows hydroponically, performing direct nutrient uptake from This online search comprises studies conducted up to date. The the water column [4,6]. The development of an extensive and majority of these studies have been discussed and summarized dense root system is crucial for the performance of the system. Bio- in Section 3, Results and discussion. film is attached on the roots and rhizomes, and as physical and bio- Not all the studies presented in Table 1 could be used for further chemical processes take place, the system functions as a natural analysis since some did not present all needed data. A screening filter [7,8]. Fig. 1 presents a vertical section of a CFW. process was employed in order to select for data meta-analysis Fig. 1. Schematic of vertical section of Constructed Floating Wetlands. 1122 N. Pavlineri et al. / Chemical Engineering Journal 308 (2017) 1120–1132 Table 1 Summary of CFWs studies for treatment of various water/wastewater types, presenting author, scale of experiment, type of water/wastewater, plant species, average nutrient removal efficiency, and location. Study Scale Water/WW type Plant species used Average removal rates (%) Location [9] Batch Synthetic Lolium perenne L. Daytona COD: 85; TN: 45.3–57.9; China wastewater NH4: 86.5–92.7 [10] Microcosm Primary treated Cyperus papyrus TN: 90.4; NH4: 89.3; TP: 84.5 Uganda sewage Colocasia esculenta TN: 67.8; NH4: 68.8; TP: 63.8 [11] In situ application River water Equisetum sp., Ipomoea aquatic Forsk COD: 79.3; NH4: 83.6; TP: 87.5 China [12] In situ application Aquaculture effluent Chrysopogon zizanioides,