Floating Treatment Wetlands Research Articles

Nutrient removal from stormwater in floating treatment wetlands: prediction of kinetic rates, effect of initial concentration and plant performance assessment

Plant dry biomass normalised by water volume predicts nutrient removal kinetics.

Uklanjanje patogenih mikroorganizama u biološkom sistemu sa plutajućim ostrvima

Organic matter is considered one of the main sources of water pollution caused by the discharge of wastewater of different categories directly into rivers. The increased content of organic matter serves as a source of food for water microorganisms and significantly lowers dissolved oxygen of the recipient. Floating treatment wetlands (FTW) are an innovative green technology that removes excess organic matter from water. This paper shows the effectiveness of floating treatment wetlands in removing organic matter from the water of a polluted urban river. Cells with floating islands had BOD reduced by 84-91%, COD in the range of 57-65% and TOC by 16-20%. The highest efficiency in COD and TOC reduction was achieved in Cell I where P. australis was planted, and BOD in Cell II where C. indica was planted. The results of these studies showed that after 6 days of treatment of polluted water, a high reduction of BOD and COD was achieved, as well as a satisfactory reduction of TOC concentration.

Constructed Floating treatment wetlands: can they improve water quality in a northern USA climate?

Constructed floating treatment wetlands (FTWs) are a best management practice (BMP) applied in aquatic environments to improve water quality by mitigating nutrient pollution. We evaluated the efficacy of FTWs in Minnesota, USA as a tool for the removal of excess nutrients in surface water to enhance water quality. We began with a 2015 outdoor mesocosm study to quantify the removal efficiency of total phosphorus (TP), ortho-phosphate-P (PO4-P), nitrate-N, and ammonia-N. The FTWs were each planted with wetland plants Juncus effusus, Eleocharis acicularis, and Glyceria canadensis. A paired controlled TP budget was prepared to identify mesocosm sources and sinks. Mesocosm FTWs showed higher PO4-P reduction efficiencies than the control mesocosms. Mesocosms with FTWs had significantly lower pH and dissolved oxygen (DO) concentrations. Water quality measurements were made along with qualitative observations, such as durability, at two different field scales where FTWs were installed in a pond and lake in 2016. Field deployed FTWs showed measurable changes in several water quality parameters over the study period. Statistically significant reductions were observed in PO4-P, DO, and pH for the pond site but not at the lake site. Though positive results were observed, factors other than FTWs may better explain the field deployed FTW results. Overall, the high FTW spatial coverage (15%) in the mesocosms showed clear PO4-P removal, whereas low FTW spatial coverage (<1%) of the field scale surface water was likely the most limiting factor to achieving optimal water quality at the study sites and rather than individual FTW performance.

Hybrid constructed wetlands integrated with microbial fuel cells and reactive bed filter for wastewater treatment and bioelectricity generation.

The present study aimed to develop a pilot-scale integrated system composed of anaerobic biofilter (AF), a floating treatment wetland (FTW) unit, and a vertical flow constructed wetland coupled with a microbial fuel cell (CW-MFC) and a reactive bed filter (RBF) for simultaneously decentralized urban wastewater treatment and bioelectricity generation. The first treatment stage (AF) had 1450 L and two compartments: a settler and a second one filled with plastic conduits. The two CWs (1000 L each) were vegetated with mixed plant species, the first supported in a buoyant expanded polyethylene foam and the second (CW-MFC) filled with pebbles and gravel, whereas the RBF unit was filled with P adsorbent material (light expanded clay aggregate, or LECA) and sand. In the CW-MFC units, 4 pairs of electrode chambers were placed in different spacing. First, both cathode and anode electrodes were composed of graphite sticks and monitored as open circuit. Later, the cathode electrodes were replaced by granular activated carbon (GAC) and monitored as open and closed circuits. The combined system efficiently reduced COD (> 64.65%), BOD5 (81.95%), N-NH3 (93.17%), TP (86.93%), turbidity (94.3%), and total coliforms (removal of three log units). Concerning bioenergy, highest voltage values were obtained with GAC electrodes, reaching up to 557 mV (open circuit) and considerably lower voltage outputs with closed circuit (23.1 mV). Maximum power densities were obtained with 20 cm (0.325 mW/m2) and 30 cm (0.251 mW/m2). Besides the electrode superficial areas, the HRT and the water level may have influenced the voltage values, impacting DO and COD concentrations in the wastewater.

Bioaugmentation-Enhanced Remediation of Crude Oil Polluted Water in Pilot-Scale Floating Treatment Wetlands

Floating treatment wetlands (FTWs) are cost-effective systems for the remediation of polluted water. In FTWs, the metabolic activity of microorganisms associated with plants is fundamental to treatment efficiency. Bioaugmentation, the addition of microorganisms with pollutant-degrading capabilities, appears to be a promising means to enhance the treatment efficiency of FTWs. Here, we quantified the effect of bioaugmentation with a four-membered bacterial consortium on the remediation of water contaminated with crude oil in pilot-scale FTWs planted with Phragmites australis or Typha domingensis. The bacteria had been isolated from the endosphere and rhizosphere of various plants and carry the alkane hydroxylase gene, alkB, involved in aerobic hydrocarbon degradation. During a treatment period of 36 days, FTWs planted with P. australis achieved a reduction in hydrocarbon concentration from 300 mg/L to 16 mg/L with and 56 mg/L without bioaugmentation. In the FTWs planted with T. domingensis, respective hydrocarbon concentrations were 46 mg/L and 84 mg/L. The inoculated bacteria proliferated in the rhizoplane and in the plant interior. Copy numbers of the alkB gene and its mRNA increased over time in plant-associated samples, suggesting increased bacterial hydrocarbon degradation. The results show that bioaugmentation improved the treatment of oil-contaminated water in FTWs by at least a factor of two, indicating that the performance of full-scale systems can be improved at only small costs.

Nitrate-N removal rate variabilities in floating treatment wetland mesocosms with diverse planting and carbon amendment designs

Floating treatment wetlands are an innovative wetland design to passively improve water quality and remove pollutants from reservoirs with limited infrastructure modification or construction as compared to traditional treatment wetlands. However, design recommendations remain limited. Therefore, the objectives of this study were: 1. Determine nitrate-N removal rates in two floating treatment wetland vegetation designs entering a second growing season and 2. Evaluate nitrate-N removal performance in floating treatment wetland designs following the addition of two carbon amendments during the growing season. Three floating treatment wetland mesocosm experiments were conducted during the summer of 2019, where nitrate-N removal was evaluated. Two floating treatment wetland plant designs (Rush species and Diverse species) and three carbon conditions (no amendment, spent coffee grounds, and barley straw) were assessed in replicates of three. Floating treatment wetland vegetation design (Rush versus Diverse) was found to have significant (P < 0.05) effects on nitrate-N removal performance with Diverse floating treatment wetlands removing nitrate-N at more than twice the rate of Rush floating treatment wetlands (491 to 695 mg N m−2 d−1 and 1547 to 1937 mg N m−2 d−1, respectively). However, impacts of nitrate-N removal following carbon amendments were insignificant compared to no amendment Controls. Diverse wetland species should be considered in floating treatment wetland design while alternative methods to add carbon amendments to floating treatment wetland mats should be further explored.

Recent developments and applications of floating treatment wetlands for treating different source waters: a review.

Most water bodies around the world suffer from pollution to varying degrees. Floating treatment wetlands (FTWs) are a simple and efficient ecological treatment technology and have been widely studied and applied as a sustainable solution for different source waters. Based on the analysis of abundant literature in the last ten years, this paper systematically reviews the history and the latest development of FTWs. Meanwhile, the treatment performance and pollutant removal mechanisms of FTWs on the natural water, stormwater, domestic wastewater, industrial wastewater, and agricultural runoff are analyzed. In particular, very interesting information is provided, such as water depth, water surface coverage, the ratio of dissolved to total phosphorous (DRP/TP), the ratio of nitrogen to phosphorous (N/P), BOD/COD ratio, and its effects on the efficiency and removal mechanisms of FTWs. This information will provide useful references and guidance for optimizing the design of FTW and pollutant treatment efficiency of different source waters. This paper also provides an objective review of the limitations of FTWs. Subsequently, the enhancements of FTW technology which are recognized to be effective, including aeration, adding functional fillers or obligate degrading bacteria, and construction of hybrid FTWs, are summarized and recommendations are made for further research.

Assessment of Capsicum annuum L. Grown in Controlled and Semi-Controlled Environments Irrigated with Greywater Treated by Floating Wetland Systems

Accumulation of trace elements, including heavy metals, were evaluated in soil and fruits of chilli plants (Capsicum annuum L.) grown under both laboratory-controlled and semi-controlled greenhouse location conditions. Chilli plant biomass growth in different development stages and fruit productivity were evaluated and compared with each other for the impact of growth boundary conditions and water quality effects. Treated synthetic greywaters by different operational design set-ups of floating treatment wetland systems were recycled for watering chillies in both locations. Effluents of each individual group of treatment set-up systems were labelled to feed sets of three replicates of chilli plants in both locations. Results revealed that the treated synthetic greywater (SGW) complied with thresholds for irrigation water, except for high concentrations (HC) of phosphates, total suspended soils, and some trace elements, such as cadmium. Chilli plants grew in both locations with different growth patterns in each development stage. First blooming and high counts of flowers were observed in the laboratory. Higher fruit production was noted for greenhouse plants: 2266 chilli fruits with a total weight of 16.824 kg with an expected market value of GBP 176.22 compared to 858 chilli fruits from the laboratory with a weight of 3.869 kg and an estimated price of GBP 17.61. However, trace element concentrations were detected in chilli fruits with the ranking order of occurrence as: Mg &gt; Ca &gt; Na &gt; Fe &gt; Zn &gt; Al &gt; Mn &gt; Cu &gt; Cd &gt; Cr &gt; Ni &gt; B. The highest concentrations of accumulated Cd (3.82 mg/kg), Cu (0.56 mg/kg), and Na (0.56 mg/kg) were recorded in chilli fruits from the laboratory, while greater accumulations of Ca, Cd, Cu, Mn, and Ni with concentrations of 4.73, 1.30, 0.20, 0.21, and 0.24 mg/kg, respectively, were linked to fruits from the greenhouse. Trace elements in chilli plant soils followed the trend: Mg &gt; Fe &gt; Al &gt; Cr &gt; Mn &gt; Cd &gt; Cu &gt; B. The accumulated concentrations in either chilli fruits or the soil were above the maximum permissible thresholds, indicating the need for water quality improvements.

Performance of hybrid-constructed floating treatment wetlands in purifying urban river water: A field study

Floating treatment wetlands (FTWs) are a new management method for improving urban stormwater runoff. However, most studies have been performed at laboratory, micro, and meso scales. Therefore, it is necessary to evaluate the purification effect of the ecological floating bed in urban water bodies under in situ conditions. The purpose of this study was to compare the treatment potential of two types of hybrid-constructed FTWs for urban river water, and to quantify the effects and concentration radii of dissolved oxygen (DO), water temperature (T), nitrate nitrogen (NO3−-N), ammonia nitrogen (NH4+-N), and total phosphorus (TP) under different rainfall conditions. The difference analysis in the first rainfall stage (p < 0.05) indicated that FTWs with multiple plant species (FTW-A) and FTWs with a single species (FTW-B) had significantly better treatment potential than the blank control for all water quality parameters except T. The second stage study showed that the hybrid system could effectively purify the river water during the rainfall period, and the effect of FTW-A was higher than that of FTW-B. After the initial rainfall, DO decreased, NH4+-N and TP concentrations increased, the removal rate of NH4+-N decreased to 55.88%–58.33%, and the removal rate of TP decreased to 5.00%–10.53%. During continuous rainfall, the removal rate of NH4+-N remained between 16.28% and 63.89%, while the removal rate of TP fluctuated, reaching 26.32%, although the final concentration of TP was not removed during the experimental period. Meanwhile, the hybrid constructed FTW continuously increased the DO concentration; however, denitrification was inhibited, resulting in ineffective removal of nitrate and nitrogen in the water body. Further study on the influence radius of two types of FTWs on DO, T, NO3−-N, NH4+-N, and TP found that the influence radius of FTWs varied with the concentration of each parameter. For the same parameter, the influence radius of FTWs with multiple plant species and FTWs with a single species was RFTW-A ≥ RFTW-B. In this study, the purification effect of hybrid-constructed FTW in urban water was evaluated, which provided guidance and support for the FTW site layout of actual river courses in the future.

Investigating degradation metabolites and underlying pathway of azo dye "Reactive Black 5" in bioaugmented floating treatment wetlands.

The direct discharge of azo dyes and/or their metabolites into the environment may exert toxic, mutagenic, and carcinogenic effects on exposed fauna and flora. In this study, we analyzed the metabolites produced during the degradation of an azo dye namely Reactive Black 5 (RB5) in the bacterial-augmented floating treatment wetlands (FTWs), followed by the investigation of their underlying toxicity. To this end, a FTWs system was developed by using a common wetland plant Phragmites australis in the presence of three dye-degrading bacteria (Acinetobacter junii strain NT-15, Pseudomonas indoloxydans strain NT-38, and Rhodococcus sp. strain NT-39). We found that the FTW system effectively degraded RB5 into at least 20 different metabolites with the successful removal of color (95.5%) from the water. The fish toxicity assay revealed the nontoxic characteristics of the metabolites produced after dye degradation. Our study suggests that bacterially aided FTWs could be a suitable option for the successful degradation of azo dyes, and the results presented in this study may help improve the overall textile effluent cleanup processes.

Recent research challenges in constructed wetlands for wastewater treatment: A review

The review paper sis based on the analysis or nearly 700 research papers published during 2019 and the first half of 2020 and indexed by Web of Science under the password “constructed wetlands for wastewater treatment”. Out of this number 132 papers dealing with “new” topics such as new wastewaters treated in constructed wetlands (CW), new filtration materials, role of vegetation, floating treatment wetlands, microbiology of CW, greenhouse gas emissions from CWs, sustainability and secondary benefits of CWs. For the deeper analysis the supporting literature from previous periods has been cited. The analysis indicates increasing popularity and diversification of types and tasks of CWs. This supports the need for further research of processes and design-related properties of CWs. The research in full scale CWs and long-term studies are only rare and in order to upgrade the CWs technology, research must be also carried out in the field under full-scale conditions.

Mechanistic Understanding of Nitrogen Behaviour in Floating Treatment Wetlands: Abatement of Ammonia Flux

Nitrogen behaviour in domestic wastewater was investigated to develop a mechanistic understanding of ammonia dynamics in Floating Treatment Wetlands (FTWs) and to improve design and operation. A critical FTW design (full coverage of the floating mat and maximum plant density) was evaluated to optimize treatment performance of a pilot-scale system in removing ammonia under different operational volumes. A system dynamics approach as a framework was employed for robust understanding of the treatment mechanisms and system performance in removing ammonia. The results revealed that ammonia removal was enhanced in FTWs and the magnitude of removal was controlled by the design examined. Findings suggest that a design code of full coverage of water surface with mat material, high plant density, and low water volume can be considered as a critical design for FTW system to remove ammonia from domestic wastewater. This design promoted nitrification as principal ammonia removal process even when plants were present. The contribution of nitrification to overall ammonia removal was estimated to be between 81 and 85%. Plant uptake contributed to 14-19% of the total N loss. Ammonia loss via volatilization was determined to be negligible in examined system. Kinetics parameters for ammonia removal were between 0.14-0.22 day-1 in FTWs compared to 0.01-0.02 day-1 in controls. Understanding the contribution of removal processes of N could be useful to improve treatment system design, and enhance treatment performance.

The Role of Microbial Biofilm in Removing Ammonia in Floating Treatment Wetlands

Abstract Laboratory experiments were conducted under controlled conditions to quantify the potential of microbial transformation associated with floating matrix of floating treatment wetland (FTW) in ammonia removal and nitrification kinetics. The effect of different design parameters on ammonia removal from synthetic medium was investigated to optimize system performance. Effects of surface area of mat material, range of ammonia concentrations, and aeration on ammonia removal kinetics were studied using microcosm systems. A simple dynamics model of mineral nitrogen transformation was used as a framework for interpreting the experimental results. The results revealed that ammonia removal was enhanced in FTWs, and the magnitude of removal was controlled by the design factors examined. Removal by nitrification was directly proportional to mat surface area. The higher ammonia removal efficiency was caused by a larger surface area, which could support the growth of more microbes. Removal rate constants for treatments were 0.011, 0.015, 0.026, 0.035, and 0.033 day–1 for T1, T2, T3, T4, and T5, respectively. There was also a clear inhibitory effect of NH3 on second-stage nitrification manifested as low production of NO3–. Quantitative index of optimized knit/calibrated knit indicated high inhibition effects of NH3 at high concentration of total ammonia (60 mg N L–1). There was no major effect of oxygen saturation on NHx removal using aerated and nonaerated conditions. Better mechanistic understanding of the fundamental processes operating in FTWs should provide the basis for improving FTW design and efficacy.

Ammonia Removal in Free-Surface Constructed Wetlands Employing Synthetic Floating Islands

Free water surface constructed wetlands (FSCWs) can be used to complement conventional waste water treatment but removal efficiencies are often limited by a high ratio of water volume to biofilm surface area (i.e. high water depth). Floating treatment wetlands (FTWs) consist of floating matrices which can enhance the surface area available for the development of fixed microbial biofilms and provide a platform for plant growth (which can remove pollutants by uptake). In this study the potential of FTWs for ammoniacal nitrogen (AN) removal was evaluated using experimental mesocosms operated under steady-state flow conditions with ten different treatments (two water depths, two levels of FTW mat coverage, two different plant densities and a control, all replicated three times). A simple model was constructed as a framework for understanding N dynamics in each treatment. The model was calibrated using data obtained from one treatment and validated independently for the other treatments. Specifically, we hypothesized that the nitrification and volatilization rate constants are inversely proportional to water depth and proportional to mat surface area. This allowed the relative magnitude of different removal mechanisms to be estimated. The model was able to predict steady-state concentrations of AN and total oxidized nitrogen (TON) across the different treatments well (values for correlation in the regression between measured and predicted steady-state concentrations and RMSE were 0.88 and 0.40 mg N L-1 for AN, and 0.63 and 1.75 mg N L-1 for TON). The results confirm that nitrification is the principal AN removal process, with maximum removal occurring in shallow systems with high matrix cover (i.e. a high ratio of biofilm surface area to water volume). Plant uptake was a relatively minor loss process compared to nitrification. Integrated experimental and model-based approach was found to be a useful tool to improve mechanistic understanding AN dynamics in FSCWs and system performance.

Treatment of university campus wastewaters by anaerobic reactor and multi-stage constructed wetlands

Sustainable and decentralized sanitation is essential for a continental country like Brazil to mitigate its untreated sewage liabilities. This may be directly related to the constructed wetlands (CWs), since these systems are considered clean technology alternatives for the treatment of wastewaters. So, the present research investigated the treatment of university campus wastewaters by a hybrid system composed of: anaerobic reactors (AR) + vertical flow constructed wetlands (VFCW) + floating treatment wetlands (FTW) + horizontal subsurface flow constructed wetlands (HSSFCW). Effluents were treated in batch mode, with a loading time of 1 h, a flow after preliminary treatment of 1.6 m3 h−1 to load the system and hydraulic detention time of 3 days for the AR, and 7 days for each CW unit. CW were planted with 4 different macrophytes: Hymenachne grumosa, Vetiveria zizanoides, Papyrus and Lemna minor sp. The obtained results showed removal rates of 67 % for COD, 53 % for BOD5, 94 % for Total N, 90 % for DOC, 98 % for turbidity and of 5log for E. coli. Almost all the investigated parameters of the treated wastewaters were in accordance the emission limits established by current Brazilian legislation. Moreover, the good performance of the hybrid system brings new reuse possibilities for the treated wastewaters, so that they would be adequate to be reused in orchards, cereals, forages, pastures for livestock and other crops through runoff or by punctual irrigation system.

Turbidity reduction induced by Floating Treatment Wetlands (FTW): A flume experiment to assess the impact of flow velocity

The aim of the present study was to investigate the impact of the mean flow velocity on the Floating Treatment Wetland (FTW) roots' network behaviour and associated opportunity for suspended solids entrapment. The objective was to identify the appropriateness of a FTW to reduce turbidity in a retention pond subject to specific flow regimes. A flume experiment with and without FTW was run under three mean flow velocities impacting roots' inclinations and roots' water column occupancy. For initial turbidity of 60–70 FNU, the results indicate that inclusion of a FTW would increase turbidity reduction by up to 37%, 34% and 45% under flow velocity of 0.023 m/s (V1), 0.097 m/s (V2) and 0.181 m/s (V3), respectively, compared to the Control (experiments without FTW). This suggests that even under high flow velocity, inducing the roots to flatten under the mat, the FTW provided an efficient additional particles removal process to settlement, i.e. entrapment of suspended solids into FTW roots' network. For V1, turbidity thresholds for good and very good water quality status (EU guidelines) were reached about 1:00 and 5:30 (h:mm) faster with the inclusion of a FTW. Providing that flow ratio through the FTW roots' network could be promoted in a real retention pond, such as in the present flume experiment, potential turbidity removal efficiency solely induced by a FTW covering 16% of a pond length and 70% of pond width could be extrapolated for various pond sizes. As an example, the inclusion of a 8 m long FTW in a 50 m long pond with inlet turbidity of 60–70 FNU, could improve turbidity removal efficiency by ~32% at low flow velocity (V1) and by ~10% at medium and high flow velocities (V2 and V3).

Pilot-Scale Investigation of Floating Treatment Wetlands as Retrofits to Waste-Stabilization Ponds for Efficient Domestic Wastewater Treatment

This study investigates the efficacy of floating treatment wetlands (FTWs) for retrofitting waste-stabilization ponds (WSPs) operating in cold continental climates, such that in Alberta, Canada. The objective was to determine whether WSPs augmented with FTWs could achieve equal or superior treatment efficiency at shorter hydraulic retention times (HRTs of 25–45 days) than those required in the conventional WSPs (60–365 days). A field study was carried out on treatment of domestic wastewater in a two-stage pilot-scale FTW mesocosm (i.e., FTW treatment train composed of Stage 1 and Stage 2 FTW cells (S1-FTW→S2-FTW), with an overall volume of 84 m3 and 41.85 m3 per cell). An identical system without FTW served as a control (i.e., control treatment train of S1-C→S2-C). Overall, the FTW-augmented WSP system achieved greater treatment of 5-day biochemical oxygen demand (BOD5), total suspended solids (TSS), total nitrogen (TN), ammonium nitrogen (NH4+-N), dissolved reactive phosphorus (DRP), and total phosphorus (TP) than the control. The corresponding removal efficiencies were 91.5% versus 85.0%, 91.3% versus 87.7%, 85.0% versus 75.6%, 93.9% versus 86.1%, 77.6% versus 57.7%, and 75.8% versus 58.7%, with a statistically significant difference (p<0.05) for all except TSS. This difference in performance resulted from the better performance of the Stage 1 FTW cell for BOD5, TN, and NH4+-N removal, and the Stage 2 FTW cell for DRP and TP removal. Simultaneous nitrification-denitrification (SND) occurred in the FTW treatment train, whereas only nitrification occurred in the control treatment train, which resulted in statistically higher TN removal efficiency in the former. Contribution of plant uptake to phosphorus removal was marginal (6.76%) and adsorption-desorption on solid particles was assumed to be the major removal pathway. The FTWs generally decreased the physicochemical parameters, with stronger effects on diurnal variations than seasonal fluctuations. The effect of FTW on daily physicochemical conditions played a key role in superior performance of FTW treatment.

Plant-Microbe Synergism in Floating Treatment Wetlands for the Enhanced Removal of Sodium Dodecyl Sulphate from Water

Excessive use of detergents in wide industrial processes results in unwanted surfactant pollution. Among them, sodium dodecyl sulphate (SDS) has well-known history to be used in pharmaceutical and industrial applications. However, if discharged without treatment, it can cause toxic effects on living organisms especially to the aquatic life. Floating treatment wetlands (FTWs) could be a cost-effective and eco-friendly options for the treatment of wastewater containing SDS. In this study, FTWs mesocosms were established in the presence of hydrocarbons-degrading bacteria. Two plant species (Brachiaria mutica and Leptochloa fusca) were vegetated and a consortium of bacteria (Acinetobacter sp. strain BRSI56, Acinetobacter junii strain TYRH47, and Acinetobacter sp. strain CYRH21) was applied to enhance degradation in a short-time. Results illustrated that FTWs vegetated with both plants successfully removed SDS from water, however, bacterial augmentation further enhanced the removal efficiency. Maximum reduction in SDS concentration (97.5%), chemical oxygen demand (92.0%), biological oxygen demand (94.2%), and turbidity (99.4%) was observed in the water having FTWs vegetated with B. mutica and inoculated with the bacteria. The inoculated bacteria showed more survival in the roots and shoots of B. mutica as compared to L. fusca. This study concludes that FTWs have the potential for the removal of SDS from contaminated water and their remediation efficiency can be enhanced by bacterial augmentation.

Application of floating treatment wetlands for stormwater runoff: A critical review of the recent developments with emphasis on heavy metals and nutrient removal.

Floating treatment wetlands (FTWs) are increasingly gaining popularity due to a set of valuable features like wastewater remediation under varied conditions, ecosystem quality preservation, landscape conservation, and aesthetic benefits. FTW is a phyto-technology in which macrophytes grow on a floating raft with their roots in permanent contact with water and remove pollutants via several physicochemical-biological processes. FTW is highly capable of overcoming technical and operational challenges that come way in stormwater treatment due to the erratic nature of hydrologic and input pollutant loads because this innovative buoyant hydroponic design can move up and down with fluctuating water levels in the stormwater pond and can treat highly variable flows. Plants and biofilms attached to the roots hanging beneath the floating mat play a pivotal role in FTWs. The present review encompasses the concept of FTWs, their structural designs, relevance in stormwater management, and mechanism of plant uptake for pollutant removal. The role of FTWs to remove heavy metals and nutrients is also critically analyzed. Understanding hydraulics and other parameters of FTW is vital to effective design. Hence, the role of vegetation coverage, vegetation type, sorption media, aeration frequency, and intensity, and plant density to enhance system efficiency is also highlighted. Due to their operational flexibility and environmentally friendly working with no additional burden on existing urban land use, FTWs entice broad international interest and offer a coherent solution for stormwater management. MAIN FINDINGS: The review delivers state-of-the-art analysis of the current understanding of hydraulics and other parameters of FTWs, and associated mechanisms to enhance the treatment efficiency of FTWs for nutrients and heavy metals removal.

Plant Nutrient Uptake in Full-Scale Floating Treatment Wetlands in a Florida Stormwater Pond: 2016–2020

Nutrient enrichment of surface waters degrades water quality. Municipalities need effective and economical solutions to remove nutrients from surface waters. From July 2016 to May 2020, full-scale (900 m2, 5% cover) floating treatment wetlands (FTWs) were deployed in Wickham Park pond, a eutrophic water body (0.13 mg/L total phosphorus (P), 0.96 mg/L total nitrogen (N)). The plants in FTWs in close proximity to a SB10000 mixer fixed N and P more efficiently. The rate of N (g/m2/year) fixed within tissues was highest for Juncus effusus (13.5), Agrostis alba (13.2), and Sagittaria lancifolia (12.1). The rate of P (g/m2/year) fixed within plant tissues was similar for all species (3.77, Agrostis alba, Canna spp., Iris hexagona, Juncus effusus, and Sagittaria lancifolia) save Pontederia cordata (2.52) volunteer species (1.41). The N and P removed with plant harvest were similar for non-mixed and mixed FTWs. Notably, the N:P ratio in plant tissues in 2017 (pre-mixer installation) was 11:1; after mixer installation (2018–2020), N:P ratios averaged 2.7:1, indicating increased P fixation within plant tissues. In 2017, 12,828 kg of plant tissues was harvested, removing 334 kg of N and 29.5 kg of P. In 2019, 32,958 kg of plant biomass was harvested from the pond, removing 425 kg of N and 138 kg of P. In 2020, 27,945 kg of biomass was harvested from FTWs, removing 267 kg of N and 95 kg of P. From 2016 to 2020, 73,000 kg of biomass was harvested, removing 1026 kg of N and 262 kg of P from Wickham Park pond. Knowing the total fresh biomass of tissues removed from FTWs at harvest is critical for accuracy in reporting nutrient removal aided by FTWs.